CA1280312C - Emulsions and photographic elements containing ruffled silver halide grains - Google Patents

Abstract

EMULSIONS AND PHOTOGRAPHIC ELEMENTS CONTAINING
RUFFLED SILVER HALIDE GRAINS
Abstract of the Disclosure Silver halide photographic emulsions comprised of radiation sensitive silver grains of a cubic crystal lattice structure having ruffled faces and photographic elements including these emulsions are disclosed.

Description

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EMULSIONS AND PHOTOGRAPHIC ELEM~NTS CONTAINING
RUFFLED SILV~R HALIDE GRAINS
E~ld of the Invention This invention relates to photography. More 5 specifically, this invention is directed to photographic emulsions containing silver halide grains and to photographic elements containing these emulsions.
Brief Description of the Drawings Figure l is an isometric view of a regular cubic silver halide grain;
Figure 2 is a schematic diagram of the atomic arrangement at a silver bromide cubic crystal face;
Figure 3 is an isometric view of a regular octahedral silver halide grain;
Figure 4 is a schematic diagram of the atomic arrangement at a æilver bromide octahedral crystal face;
Figure 5 is an isometric view of a regular rhombic dodecahedron;
Figure 6 is a schematic diagram of the atomic arrangement at a silver bromide rhombic dodecahedral crystal face;
Figure 7 is an isometric view of a regular cubic silver halide grain, a regular octahedral silver halide grain, and intermediate cubo-octahedral silver halide grains.
Figures 8 and 9 are plan views of pyramidal protrusions from a base plane;
Figure 10 is an isometric view of a regular {33~} tri~octahedral silver halide grain;
Figure 11 is a schematic diagram of the atomic arrangement at a {331} silver bromide trisoctahedral crystal face;
Figure 12 is an isometric view of a regular {210} tetrahexahçdral silver halide grain;

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Figure 13 i~ a schematic diagra~ of the atomic arrangement at a silver bromide {210}
tetrahexahedral crystal face;
Figure 14 is an isometric view of a regular {211~ icositetrahedral silver halide grain;
Figure 15 is a schematic diagram o the atomic arrangement at a silver bromide {211}
icositetrahedral crystal face;
~ igure 16 is an isometric view of a regular {321} hexoctahedral silver halide grain;
Figure 17 is a schematic diagram of the atomic arrangemeIlt at a silver bromide {321}
hexoctahedral crystal face; and Figures 18, 19, 20, 21A, 21B, 21C, 21D, 22, 23A, 23B, 23C, 24A, 24B, 24C, 24D, 25, 26A, 26B, 26C, 26D, 26E, 27, 28, 2~A, 29B, 30A, 30B, 31A, 31B, 32, 33A, and 33B, are electron micrographs of silver halide emulsion grains.
Baçk~round of the Invention Silver halide photography has been practiced for more than a century. The radiation sensitive silver halide compositions initially employed for imaging were termed emulsions, since it was not originally appreciated that a solid phase was present. The term ~photographic emulsion" has remained in use, although it has long been known that the radiation sensitive component is present in the form of dispersed microcrystals, typically referred to as grains.
Over the years silver halide grains have been the subject of intense investigation. Although high iodide silver halide grains, those containing at least 90 mole pcrcent iodide, based on silver, are known and have been suggested for photographic applications, in practice photographic emulsions almost always contain silver halide grains comprised of bromide, chloride, or mixtures vf chloride and bromide optionally c~ .., ' .
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containing minor amounts of iodide. Up to about 40 mole percent iodide, based on silver, can be accommodated in a silver bromide crystal structure without observation of a separate silver iodide phase. However, in practice silver halide emulsions rarely contain more than about 15 mole percent iodide, wi~h iodide well below 10 mole percent being most common. All silver halide grains, except rarely employed high iodide silver halide grains, hereinafter excluded from consideration except as expressly noted, exhibit cubic crystal lattice structures.
It has been recognized for many years that the ratio of silver halide grain surface area to grain volume is not constant. Finer silver halide grains exhibit higher grain surface area in relation to graln volume, more commonly referred to indirectly in terms of coating coverages - e.g., grams of silver per square meter. An increased ratio of silver halide grain surface area to grain volume, hereinafter referred to as the grain surface area ratio, can be advantageous in improving photographic performance dependent on surface effects, such as interaction with processing agents as well as interactions with adsorbed addenda, such as spectral sensitizing dyes.
~owever, extremely fine grain emulsions, ~uch as Lippmann emulsions, which have the highest surface area ratios, are not commonly employed for forming latent images in'silver halide emulsions, since they exhibit low photographic speeds. Within the range of silver halide grain sizes normally encountered in photographic elements the maximum speed obtained at optimum sensitization increases linearly with increasing grain size. Thus, radiation sensitive emulsions have often represented a compromise between meeting photographic speed objectives dictating larger grain sizes and satisfying other performance criteria benefiting by increasing grain surface area ratios and .1a ~
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therefore favoring finer silver halide grains.
A variety of regular and irregular grain shapes have been observed in silver halide photo-graphic emulsions. While grains can show corner and edge rounding attributable to a lower activation energy for silver halide solubilization at these locations, in general silver halide grains are polyhedral, being bounded by distinct crystal faces.
Silver halide favor3 the formation of crystallographic faces of either the cubic or octahedral form. Silver chloride strongly favors the formation of cubic crystal faces. Silver bromide also favors the formation of cubic crystal faces, but favors the formation of octahedral crystal faces in the presence of an excess of bromide ions. Iodide ions in the crystal structure tend to increase the grain preference for cry~tal faces of the octahedral form. A discussion of the factors which cause one crystallographic form to be favored over another is offered by James, The _heory of ~k~ Photographic Process, 4th Ed., Macmillan, New York, 1977, pp. ~8 through 100.
Regular silver halide grains bounded by cubic crystal faces are cubic in appearance when examined by electron microscopy. A regular cubic grain 1 is shown in Figure 1. The cubic grain is bounded by six identical crystal faces. In the photographic literature theæe`crystal faces are usually referred to as {100} crystal faces, referring to the Miller index employed for designating crystal faces. While the {100} crystal face designation is most commonly employed in connection with silver halide grains, these same crystal faces are sometimes also referred to as {200} crystal faces, the diffcrence in designation resulting from a difference in the definition of the basic unit of the crystal structure. Although the cubic crystal shape is 1~303~2 readily visually identified in regular grains, in irregular grain~ cubic crystal faces are not always square. In grains of more complex shape~ the presence of cubic crystal faces can be verified by a combination of visual in~pection and the 90~ angle o~
intersection formed by adjacent cubic crystal ~ace~.
The practical importance of the cubic crystal faces is that they present a unique surface arrangement of silver and halide ions, which in turn 10 influences the grain surface reactions and adsorptions typically encountered in photographic applications.
This unique æurface arrangement of ions as theoreti-cally hypothesized is schematically illustrated by Figure 2, wherein the smaller spheres 2 represent silver ions while the larger spheres 3 designate bromine ions. Although on an enlarged scale, the relative size and position of the silver and bromide ions is accurately represented. When chloride ions are substituted for bromide ions, ths relative 20 arrangement would remain the same, although the chloride ion~ are smaller than the bromide ions. It can be seen that a plurality of parallel rows, indicated by lines 4, are present, each formed by alternating æilver and bromine ions. In Figure 2 a 25 portion of the next tier of ions lying below the surface tier is shown to illustrate their relationship to the surface tier of ions.
In another form re~ular silver hallde grains when observed by electron microscopy are octahedral in 30 appearance. A regular octahedral grain 5 is shown in Figure 3. The octahedral grain is bounded by eight identical crystal faces. These erystal faces are referred to as octahedral or {111} crystal faces.
Although the octahedral crystal shape is readily 35 visually identified in regular grains, in grains of more complex shapes the presence of octahedral crystal faces can be verified by a combination of visual ,~, ~213~3~

inspection and the 109.5 angle of intersection formed by adjacent octahedral crystal faces.
Ignoring possible ion adsorptions, octahedral crystal faces differ from cubic crystal face~ in that the surface tier of ions can be theoretically hypothesized to consist entirely of ~i1ver ions or halide ions. Figure 4 is a schematic illustration of a {111} crystal face, analogous to Figure 2, wherein the smaller spheres 2 represent silver ions 10 while the larger spheres 3 designate bromine ions.
Although silver ions are shown at the surface in every available lattice position, it has been suggested that having silver ions in only every other available lattice position in the surface tier of atoms would be 15 more compatible with surface charge neutrality.
Instead of a surface tier of silver ions, the surface tier of ions could alternatively be bromide ions. The tier of ions immediately below the surface silver ions consists of bromide ions.
In comparing Figures 1 and 2 with Figures 3 and 4 it is important to bear in mind that both the cubic and octahedral grains have exactly the same cubic crystal lattice structure and thus exactly the same internal relationship of silver and halide ions.
The ~wo grains differ only in their surface crystal faces. Note that in the cubic crystal face of Figure 2 each surface silver ion lies immediately adjacent five halide ions, whereas in Figure 4 the silver ions at the octahedral crystal faces each lie immediately adjacent only three halide ions.
Five remaining achievable crystallographic forms for cubic crystal lattice materials are not favored by silver halide. In a few instances silver halide grains having faces of the rhombic dodecahedral form have been observed. Crystal faces of the rhombic dodecahedral form in silver chloride and silver chlorobromide emulsions are reported by Claes et al J~
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3~L2 U.S. Patent 3,817,756. Wyrsch, Papers from the 1~78 International Congress of Photographic Science, Rochester, N.Y., II-13, p. 122, reported rhombic dodecahedral silver chloride emulsions prepared by a triple jet precipitation procedure in the presence of divalent cadmium ions and ammonia. Berry, "Surface Structure and Reactivity of AgBr Dodecahedra", Photographic Science and Engineering, Vol. 19, No.3, May/June 1975, pp. 171 and 172, illustrates silver bromide grains having crystallographic faces of the rhombic dodecahedral crystallographic form.
A regular rhombic dodecahedral grain 7 is shown in Figure 5. The rhombic dodecahedral grain is bounded by twelve identical crystal faces. These crystal faces are referred to as rhombic dodecahedral or {110} (or, less commonly in reference to silver halide grains, {220}) crystal faces. Although the rhombic dodecahedral crystal shape is readily visually identified in regular grains, in grains of more complex shapes the presence of rhombic dodecahedral crystal faces can be verified by a combination of visual inspection and measurement of the angle of intersection of adjacent rhombic dodecahedral crystal faces.
Rhombic dodecahedral crystal faces can be theoretically hypothesized to consist of alternate rows of silver ions and halide ions. Figure 6 is a schematic illust:ration analogous to Figures 2 and 4, wherein it can be seen that the surface tier of ions is formed by repeating pairs of silver and bromide ion parallel rows, indicated by lines 8a and 8b, respectively. In Figure 6 a portion of the next tier of ions lying below the surface tier is shown to illustrate their relationship to the surface tier of ions. Note that each surface silver ion lies immediately adjacent four halide ions.

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There are four additional crystallographic forms which can be exhibited by cubic crystal lattice structures, but which have never been reported previously for silver halide. These are the S hexoctahedral, tetrahexahedral, trisoctahedral, and icositetrahedral crystal forms.
The seven possible crystallographic forms for cubic crystal lattice structure materials are named for the polyhedrons that are produced by a regular crystal structure bounded entirely by faces of a sin~le crystallographic form. For example, regular silver halide grains bounded entirely by crystallo-graphic faces of the cubic form are cubes; bounded entirely by crystallographic faces of the octahedral form are octahedra; etc.
In addition to regular grains of a polyhedral shape produced by being bounded entirely by crystal faces of the same crystallographic form, it is not uncommon to observe regular silver halide grains bounded by both cubic and octahedral crystal faces.
Such grains are referred to as being cubo-octahedral.
This is illustrated in Figure 7, wherein cubo-octa-hedral grains 9 and 10 are shown along with cubic grain 1 and octahedral grain 5. The cubo-octahedral grains have fourteen crystal ~aces, six cubic crystal faces and eight octahedral crystal faces, and for that reason they are sometimes alternatively referred to as tetradecahedral grains. Analogous combinations of cubic and/ox octahedral crystal faces and rhombic dodecahedral crystal faces are possible, a rare example of grains having cubic, octahedral, and rhombic dodecahedral crystal faces being provided by Berry, cited above in connection with rhombic dodecahedral grains.
Further diversity in silver halide grain shape can be attributed to irregularities in the grains, such as twin planes or screw dislocations.

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' ' ' ~86~3~2 _g_ Irregular grains of distinctive shapes, often observed in minor proportions, such as tabular silver bromide grains having octahedral crystal faces, have been the subject of many silver halide crystallographic studies. Klein et al, "Formation of Twins of AgBr and AgCl Crystals in Photographic Emulsions", ~koto-~raphische Korres~ndenz, Vol. 99, No. 7, pp. 9g 102 (1963) describes a variety of singly and doubly twinned silver halide crystals having cubic and 10 octahedral crystal faces. Klein et al is of interest in illustrating the variety of shapes which twinned silver halide grains can assume while still exhibiting only cubic or octahedral crystal faces.
Recently dramatic photographic improvements 15 have been obtained with thin as well as high aspect ratio tabular grain emulsions, as illustrated by Wilgus et al U.S. Patent 4,434,226; Kofron et al U.S.
Patent 4,439,520; Daubendiek et al U.S. Patent 4,414,310; Abbott et al U.S. Patents 4,425,425 and ~0 i426; Wey U.S. Patent 4,399,215; Solberg et al U.S.
Patent 4,433,048; Dickerson U.S. Patent 4,414,304;
Mignot U.S. Patent 4,386,156, Mignot Research Disclosure, Vol. 232, August 1983, Item 23210; Jones et al U.S. Patent 4,478,929; Maskasky U.S. Patent 4,400,463; and Wey et al U.S. Patent 4,414,306.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire P010 7DD, England. While ;thin and high aspect ratio tabular grain emulsions exhibit high surface area ratios, their major faces are of the same cubic or octahedral crystallographic forms exhibited by silver halide grains of other shapes.
There has been some investigation of silver halide grains of composite shapes produced by depositing silver halide either of the same or a d;fferent composit;on onto a host silver halide grain.

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~28~3~2 Core-shell silver halide emulsions constitute the most common examples of silver halide grains of a composite structure. Core-shell emulsions are illustrated by Porter et al U.S. Patents 3,20S,313 and 3,317,322, Berriman U.S. Patent 3,367,778, and Evans U.S. Patent 3,761,276, and, in tabular form, by Evans et al U.S. Patent 4,504,570.
Turning to composite silver halide gxains in which the additionally deposited silver halide does not form a shell around the host silver halide grains, Koitabashi et al U.S. Patent 4,349,622 discloses epitaxially depositing on silver halide grains containing from 15 to 40 mole percent iodide silver halide which contains less than 10 mole percent iodide.
Hammerstein et al U.S. Patent 3,804,629 discloæes that the stability of silver halide emulsion layers against the deleterious effect of dust, particularly metal dust, is improved by adding to physically ripened and washed emulsion before chemical ripening a silver chloride emulsion or by precipitat ing silver chloride onto the physically ripened and washed silver halide emulsion. Hammerstein et al discloses that silver chloride so deposited will form hillocks on previously formed silver bromide grains.
Berry and Skillma~, "Surface Structures and Epitaxial Growth on AgBr Microcrystals", Journal of ~liç~ Phvsics, Vol. 35, No. 7, July 196~, pp.
2165-2169, discloses the growth of silver chloride on silver bromide. Octahedra of silver bromide form growths all over their surface and are more reactive than cubes. ~ubes react primarily at the corners and along the edges. Twinned tabular crystals form growths randomly distributed over their major crystal faces, with some preference for growths near their edges being observed. In addition, linear arrange-ments of growths can be produced after the emulsion coatings have been bent, indicating the influence of ' ' .

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slip bands.
Maskasky U~S. Patent 4,435,501 teaches high aspect ratio tabular grain emulsions having one or more silver salts deposited at selected surface sites. Maskasky U.S. Patent 4,463,087 is essentially cumulative, but additionally discloses deposition at the ed~es and corners of nontabular silver halide host grains. ~ach patent teaches the use of adsorbed site directors to locate æilver salts at selected sites on the host grains.
A. P. H. Trivelli and S. E. Sheppard, ~h~
Silver Bromide Grain ~ PhotQgraphic Emulsions, Van Nostrand, Chapters VI and VIII, 1921, is cited for historical interest. Magnifications of 2500X and lower temper the value of these observations. Much higher resolutions of grain features are obtainable with modern electron microscopy.
W. Reinders, "Studies of Photohalide Crystals", Kolloid-Zeitschrift, Vol. 9, pp. 10-14 (1911); W. Reinders, "Study of Photohalides III
Absorption of Dyes, Proteins and Other Organic Compounds in Crystalline Silver Chloride", Zeitschrift fur Phvsikalische Chemie, Vol. 77, pp. 677-699 (1911);
Hirata et al, "5rystal Habit of Photographic Emulsion Grains~, J. Photog. Soc. of Japan, Vol. 36, pp.
359-363 (1973); Locker U~S. Patent 4,183,756, and Locker et al U.S. Patent 4,225,666 illustrate teachings of modifying silver halide grain shapes through the presence of various materials present during silver halide grain formation.
Wulff et al U.S. Patent 1,696,830 and ~eki et al Japanese Kokai S8[1983]-54333 describe the precipitation of silver halide in the presence of benzimidazole compounds.
Halwig U.S. Patent 3,519,426 and Oppenheimer et al, "Role of Cationic Surfactants in Recrystalliza-tion of Aqueous Silver Bromide Dispersions", Smith J~
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Particle rowth and Suspension., Academic Press, London, ~973, pp. 159-178, disclose additions of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene to ~ilver chloride and silver bromide emulsions, respectively, F. C. Phillips, An Introduction to Crvstallo~raphv, 4th Ed., John Wiley & Sonæ, 1971, i8 relied upon as authority for the basic precepts and terminology of crystallography herein presented.
Summarv of the Invention In one aspect this invention is directed to a radiation sensitive emulsion comprised of silver halide grains of a cubic crystal lattice structure having faces ruffled by protrusions which are silver halide crystal lattice eætensions from a base plane of a first crystallographic form. Silver halide adjacent the base plane, that is, beneath the base plane and in the protrusions, favor the formation of surfaces of the first crystallographic form, and the protrusions present surfaces of a second crystallographic form.
In another aspect thi~ invention is directed to a photographic element containing at least one emulsion of the type previously described.
The invention makes available to the art silver halide grains presenting surfaces that are increased in area and which are of a crystallographic form differing from that favored by the silver halide forming the grain surfaces. Each of these surface features offers ~ts distinct advantages.
First, a high grain surface area ratio is realized. Whereas the art has resorted to making grains finer in order to increase their surface area ratio, this invention allows the grain surface area ratio to be increased independently of grain size.
Further, the surface area ratio can be increased independently of overall grain shape. Specifically, an increase in grain surface area ratio by ruffled major crystal ~aces as contemplated by thiæ invelltion .~ it .~....

~28~3~2 is equally applicable to otherwise regular or irregular cubic or octahedral grains.
Still ~urther, the novel ruffling approach of this invention and other known approaches for increasing grain surface area ratios, epecifically reducing grain size or providing irregular grain shapes, are compatible and can be used in combination to produce additive increases in grain surface area ratios.
Thin or high aspect ratio tabular grain emulsions can be increased in their grain surface area ratios by providing ruffled major grain faces as contemplated by this invention. This results in emulsions of higher grain surface area ratios than have heretofore been realized for corresponding grain sizes.
At the same time, the invention permits increased grain surface area ratios without resorting to a tabular grain shape. The invention offers particular advantages when applied to regular and other non-tabular grain shapes.
The second distinctive silver halide grain surface feature of the invention is that the ruffled grain faces render accessible varied and new choices of crystallographic forms at grain faces for modifying photographic characteristics. As an example, whereas silver chloride strongly favors the cubic crystal form, this invention permits silver chloride grain faces to be achieved of other crystallographic forms compatible with a cubic crystal lattice struG~ure. As a second example, whereas thin and high aspect ratio tabular grain emulsions are most easily generated with octahedral crystal faces, this invention allows tabular grain faces to be realized of other crystallographic forms compatible with a cubic crystal lattice structure.

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8 ~ 3 The invention offers the advantage of allowing both high grain surface area ratios and grain faces of differing crystallographic forms to be concurrently realized. This combination permlts emulsions of unique and diverse photographic properties to be realized.
These and other features and advantages of the invention can be better appreciated by considera-tion of the description of the preferred embodiments 10 and the drawings.
_escription of Preferred _mbodiments The present invention relates to silver halide photographic emulsions comprised of ~adiation sensitive silver grains of a cubic cry~tal lattice structure having ruffled faces and to photographic elements including these emulsions.
By reason of being ruffled these grain faces present a larger surface area than a corresponding planar grain face. Considering a regular polyhedron 20 bounded by planar faces, such as the cube 1 in Figure 1 or the octahedron 5 in Figure 3, it is apparent that the planar faces each present the minimum surface area consistent with the size of the polyhedron.
It has been discovered quite unexpectedly that the grain surface area ratio of silver halide grains of a cubic crystal lattice structure can be greatly increased without significantly altering the overall shape or size of the grains. This is achieved merely by ruffling the surfaces presented by the grains. The degree to which the grain surface area ratio is increased is a matter of choice that ., , ,. . .

3~2 can be vAried from slight increases to increase~ that more than double the grain surface area ratio. The grain faces employed in the practice of this invention are preferably ruffled to an extent 5 sufficient to provide a 50 percent incre~se ln the grslns surface area ratio. This is well above the incldental increases in grain ~urface srea heretofore realized by r~ndom non-uniformities of cry~t~l faces and unsought increases in graln surface area r~tios 10 realized by producing composite ~ilver halide grains. The silver hslide emulsions of this invention most preferably exhiblt ruffled grsin faces which increa3e grain surface area ratios by st least 100 percent and optimally at least 200 percent ag 15 compsred to grains of liXe size and shap~, but lacking ruffled faces.
The silver halide grains having rufEled faces are formed ~tarting with any conventional emulsion containing silver halide grains of a cubic 20 crygtal lgttice structure presenting faces of a crystallographic form favored by the silver halide.
For silver hallde grsins which are predomln~ntly ~ilver chloride (greater than 50 mole percent chloride, bssed on silver) and especially grRins 25 which are at lea~t 90 mole percent chloride ~he favored crystallographic form is cubic, and the grain faces to be ruffled are therefore cubic (i.e., {lO0}) crystal faces. For other silver halides, silver bromide, sllver bromoiod~de, sllver chloro-30 ~rom~de, and silver chlorobromoiodides, the favored crystallo~raphic form and therefore the gra1n faces csn be either cubic or, when formed in the pre~ence of an excess of bromide ions, octahedral (i.e., { 111 } ) .
The ~rsin faces of the favored cry~tallo-graphic form for the silver halide employed pre~ent planar surface3 and serve as deposition ~ite~ for , ~

~28~31;2 sdd$tionsl ~ilver h~lide forming the ruffles~ It i8 therefore apparent that the planar surface~ of the crystsllogr~phic form f~vored by the silver halide of the host grains form a bsse plane for the ruffles 5 The ruffles take the form of protrusions fro~ the base plane which ~re extensions of the silver h~lide cubic crystal lattice structure of the underlying ho3t grain. The silver halide within the ruEfles ad~acent the base plane is of a composition thst 10 favorq the same crystallogrsphic form as the ~ilver halide of the host grains forming the base plane.
The silver halide ad~acent the base plsne ln the host grain and in the protrusions can be identicsl in composition or different, the cho$ce of lS silver hslide in each location being clrcumscribed only by the requirement of forming a cubic cryqtal lattice structure and the requirement that silver halide in each location favor ~ common crystallo-graphic form corresponding to that of the base 20 plsne. Thus, the protrusions sd~acent the base plane csn be formed, for example, of silver halide which is predominantly silver chloride, ~s defined above, depo~ited on a predominantly silver chloride base plsne; silver bromide deposited on a silver bromide 25 or bromoiodide base plane; ~ilver bromoiodide deposited on a silver bromide or bromoiodide base plsne; or silver chlorobromide optiona~ly containing iodide deposited on a silver chlorobromide base plane optionally also containing iodide. Predominantly 30 sllver chloride can be deposited on a ~100~
silver bromide or bromoiodide base pl~ne. However,-protrusions which ~re predominantly silver chloride deposited on a ~ silver bromide or bromo-iodide bs~e pl~ne hsve no spplicability to this 35 invention for reasons presented below. The portion of the protrusions which does not lie ~d~R~ent the bs~e plane - e.g., the surfaces of the protrusivns c~n ~X8~2 be of any known photographically useful silver halide composition independently of the silver halide composition of the host grain ad~acent the base plane, slnce once the protrusions are formed their 5 surface modification in any desired manner i~ a matter o~ choice.
The protrusions h~ve been observed to take in most instances the form of pyrami~ and, occa~ion-811y, the form of ridges. For convenience the 10 discussion whlch follows is directed specifically to the protru~ions in thelr pyramidal form, but extension to protrusions in the $orm of ridges i5 apparent. Aside from incidental rounding thst can occur at edges and corners of silver halide ~rains, 15 each protru~ion i5 a pyramid having its bsse in common with the ba3e plane pre~ented by the under-lying ho~t grain.
Each pyramid presenks a number of surface faces (all faces other than the base) which are of a 20 cry~tallographic form differing from thQt of the ba~e plane. The number of ~urface faces that a pyramid presents is determined by the cry~tallGgraphic form of the bs~e plane and the crystQllographic form of the pyramidal ~urface faces. The combin~tion~ are 25 set forth below in Table I.
Table I
Pyramidal Surface Face~
PYrsmidsl Faces Favored Host Grain Face~
{100} { 11~ }
{1~0} - 3 {111} 4 ~110} 4 3 {hhQ} 8 3 {hkO} 4 6 {hQQ} 4 {hkL} 8 6 ~ X 8 Looking at Figure 1 it can be seen th~t corner3 of the cube 1 are each formed by three {100} crystal face~. The pyr&mids of {100) crystal faces formed on a {111} base plane cre 5 similar in shape to the corners o the cube. Thi~
schematically shown ln Figure 8, which ia a plan view of a pyramid 11 havin~ three ~100} crys~al face~
118, llb, and llc on a {111} base plane 12.
Similarly, looking st Figure 3 it c~n be 10 geen that corners of the octahedron 5 are e~ch formed by four {1~1} crystal face~. The pyramids of {111} crystal faces formed on ~ {100} base plane are aimilar in shape to the corner~ of the octahedron. Thia is schematically shown in Figure 9, 15 which i~ a pl~n view of A pyr~mid 13 having four {111~ cry3tal faces 13a, 13b, 13c, and 13d on 8 {100~ base plane 14.
Turning to pyramids with rhombic dodec~he-dral faces, it can been seen in Figure 5 that the 20 regular rhombic dodecahe~ron 7 has eight corners e~ch formed by the intersection of three crystal faces an~
~ix corners formed by the inter~ection of four crystAl face~. When a pyramid presenting rh~mbic dodecahedral or {110~ crystal faces is located on 25 a {100} b~se plsne, it presents four ~urf~ce f~ces, thus appearing in plPn similarly ~s shown in Figure 9; but when a {1113 base plane is presented, a pyramid with tllO) crystal face~
presents three surface faces, thus appearing in plan 30 ~imilarly ag shown in Figure 8.
It ~hould be pointed out that ~lthough three surf~ce face pyramlds formed by ~100} crystal faces on a {lll~ base plane snd three ~ur~ce f~ce pyramids formed by {110} cry~tal face~ on a 35 {111; base pl~ne appear ~imilar in plan vie~, they are distinguishable. Similarly four surf~ce face pyramida formed by {111} cry~tal faces on a ~8~3~2 {lOO} ba~e plsne ~nd four ~urface face pyramids formed by {110~ crystal face~ on a {100} bs~e plsne sre distinguishable. One way of identifying the cry~t~llographic form of the ~urface Eace~ of the 5 pyramids i~ to mea~ure the ~ngle of inter~ection of a surface f~ce with the base pl~ne of the ho~t gr~in.
Another basi~ for di~tinguiQhing the cry~tsl faces of the pyrsmids is by noting the angles of inter~ections of the pyramid surface face~. A compar~on of either 10 of these mea~ured ~ngles of intersection with the theoretic~lly po~sible interaection angle~ and a further knowledge of the cryatallographic form of the base plane~ presented by the host grains snd the number of ~urface f~ces pre~ented by the pyrsmids, 15 allow~ positive identification of the cryatallo-graphic form of the pyramidal surfsce face~.
In cry~tallography measur2ment of relative angl2s of ad~acent cryatal faces is employed for crystal face identification. Such techniques sre 20 described, for example, by Phillip~, cited ~bove.
These technique~ can be combined with techniques for the microscopic sxamination of ~ilver halide grains to identify positively either or both pyramidsl and host grain base plsne cry~tal face~. Technique~ for 25 preparing electron micrographs of ~ilver halide grains are gener~lly well known in the art, as illustrated by B.M. Spinell and C.F~ Octer~ "Phot~-graphic Materi~l~", The EncYclopedia of Microscopy snd Microtechnique, P. Gray, ed., Van Nostrand, N.Y., 30 1973, pp.427-434, note psrticularly the section dealing with c~rbon replica electron micro3copy at pages 429 and 430. Employing technique~ well known in elec~ron micro~copy, csrbon replic~ of ~ilver halide ~rains are fir~t prepsred. The earbon 35 replicss reproduce the grain ~h~pe while avoiding ~hape altering silver print-out that 13 known to re~ult from employing the ~ilver h~lide graina 8~ 3~L2 without c~rbon shells. Electron~ rather than light are employed for ima~ing to permlt higher ranges of magnification to be reslized th~n when llght i~
employed. By tllting the ssmple being viewed 5 relative to the electron beam a selected ~r~in can be oriented so thst the line of ~ight is substsnti~lly psrallel to both of two sd~acent crystal f~ces, seen 8S edges. When the grain faces are par~llel to the imaginK electron beam, the two corresponding edges of 10 the grain which they define will appear ~h~rper than when the faces ~re merely clo~e to being parallel.
Once the de~ired grain orientation with two inter-secting crystal face~ each presenting a psrsllel edge to the electron beam is obtained, the angle of 15 intersection can be messured from an electron micrQgrsph of the oriented Rrain. In thi~ way the relstive angle pre~ented by any two inter~ect~ng crystsl f~ce~ can be measured. By narrowing the rsnge ~f possibilitie~ through visu~l clues, such as 20 host grsin shspe, angles of intersection for possible cry3tal forms can be calculsted and compared to me~sured inter~ection ~ngle values. In many, if not mo~t, instances vi~ual inspection of ho~t grain3 by electron micrDscopy allows posltive identlfication of 25 the base planes 90 ~hat further investigation can be limited to the pyrsmidal surface face~.
Referring to the mutually perpendlcular x, y, and z axes of a cublc crystal lattice, it is well recognized in the art thst cubic crystal face~ are 30 parallel to two of the axes and inter~ect the third, thus the {100} M~ller index assignment; sctahe-dral crystal faces inter~ect each of the three ~xes st an e~u~l interval, thus the {111} Miller index a~signment; and rhombic dodecahedral crystal faces 35 intersect two of the three axe~ at an equal interval and are parallel to the third axis, thus the ~110} Miller index ~s~ignment. For a given . .

3~:

definition of the b~sic crystsl unit, there iR one and only one Miller index ~signment for each of cubic, octahedrRl, and rhombic dodecahedr~l crystal faces.
TriRoctahedral, tetrahexshedrAl, icoRltetr~-hedral, and hexoctahedr~l cry~tal faces can have differing Miller index values and are therefore identified in Table I generically ag {hhQ}, {hkO}, {hQQ}, snd {hkQ~ cry~tal faces, 10 respectively, where h, k, and Q ~re independently in each occurrence unlike integers 8reater than zero, h is 8reater than Q, and k, when present, is le~s than h and grester than Q. Although there is no theoretical lim~t on the maximum value~ of the 15 integer h, crystal face~ having a value of h of 5 or le~s are more easily generated. Subsequent discu~sion is for convenience directed to faces in which h is 5 or less. Relationship~ for faces ln which h iR greater thsn 5 are entirely ana10gou~.
Considering value~ of h up to 5, tri~octahe-dr~l cry~tal faces c8n h~ve any one of the followin~
Miller indices: {2?1}, l331}, {441}, {551}, {33~}, {552}, {443}, {553}, or {554}. Fi~ure 10 is an isometric 25 view of a tri~octahedron 15 bounded by fAces of the {331~ crystallographic form. The point or coign 16 is formed by three intersecting crystal face~ 16a, 16b, and 16c and i~ one of eight identical coigns~
The point or coign 17 is formed by eight ~ntersecting 30 crystal faces 16a, 16c, 17a, 17b, 17c, 17d, 17e, and 17f and is one o~ six identical coigns. Referring to Table I, it ig apparent that a pyramid having eight surface faces ~uch as tho~e defining colgn 17 i5 present when the surface fsce~ of the pyramid are 35 trisoctahedral or {hh~l crystal faces on a cubie or ~100} base plane pre~ented by the ho~t grain.
If, on the other hand, the host grain presents an .

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octahedral or {111} base plsne, a pyrsmid having three surface fsce~ such as those def~nin~ coign 16 i9 present when the surface fsces of the pyrRmid ~re tri~oct~hedrsl. For trisoct~hedrsl crystal fQces of 5 differing Miller indices the geometric~l rel~tlon-ships sre the s~me, but the ~ngles of ~urf~ce fflce intersections, with e~ch other ~nd with the ba~e plane, differ.
The {331} tri~octshedral cry~tal faces 10 present a unique srrangement of surf~ce ~ilver snd halide ions th~t differ~ from that pre~ented ~y all other possible cryst~l facPs for cubic cry~t~l lattice ~tructure silver halide~. This unique surf~ce arrangement of ion~ ~s theoretically 15 hypothesized is ~chemstic~lly illustrated by Figure 11, wherein a {331} trisoct~hedrsl crystal f~ce i5 shown formed by silver ions 2 and bromide ion~ 3.
Comparing Figure 11 with Figures 2, 4, ~nd 6, it is sppsrent that the surfsce positioning of silver ~nd 20 bromide ions in esch figure i~ di~tinctive. The {331} trisoctahedral cryst~l face presents sn ordered, but more varied arrsngement o$ surfsce silver and bromide ions than is pre~ented at the cubic, octahedral, or rhombic dodecahedr~l silver 25 bromide cryst~l faces. This i3 a result of the tiering thst occurs st the ~331) tri~octahedrsl cryst~l face~ Trisoctahedrsl crystal fsce~ with differin~ Miller indices ~l~o exhib1t tiering. The differing Miller indices result in ~n~logous, but 30 nevertheless unique surfsce srr~ngement~ of 3ilver snd h~lide ions.
~ on~idering vslue~ of h up to 5, tetrahexa-hedral cry~tal fRces can have sny one of the following Miller indices: {210}, {310}, 35 {320}, {410}, ~430}, {~10}, {520}, {530}, or {540}. Figure 12 is an isometric view of a tetrshexahedron 18 bounded by 3~2 -~3-faces of the ~210} cryst~llographic form. The point or coign 19 is formed by four intersectin~
crystal f~ces l~a, l9b, l9c, and l~d ~nd is one of six identical eoigns. The coign 20 ls formed by ~ix 5 inter~ecting crystal faces 19~, l9e, 20~, ZOb, 20c, ~nd 20d and 19 one of eight identical colgns.
Referring to T~ble I, lt is apparent th~t a pyramid having four surf~ce face~ such 8s tho~e defining coign 1~ is present when the surface faces of the 10 pyrsmid ~re tetrahexahedral or ~hkO} cryst~l faces on a cubic or {100} base plsne presented by the host grain. If, on the other hand, the host ~rain presents Qn octflhedral or {111} ba~e pl~ne, 8 pyramid having six surface faces such as those 15 defining coign 20 i~ present when the ~urfac~ faces of the pyramid are tetrahexahedr~l. For tetrahexahe-dral cry9t81 fQces of differing Miller indices the geometrical relationships are the same, but the sngles of ~urface fsce intersections 9 with each other 20 and with the base plane, differ.
The {210~ tetrahexahedr~l crystal face~
present 8 unique arran8ement of 3urf~ce silver and halide ions that differs from th~t presented by all other pos~ible cry~al face~ for cubic ~ry~tal 25 lattice structure silver halides. Thi~ unique surf~ce ~rran~ement of ions as theoretically hypothe~ized is schematically illustratsd by Figure 13, wherein a t210~ tetrahexahedral crystal f~ce is shown formed by silver ions 2 and bromide ion~ 3.
30 Comparing Figure 13 with Figures 2, 4, 6, and 11, $t is apparent that the ~urface positioning of silver and bromide ions in each figure i~ distinctive. The i210~ tetrshexahedral crystal face present~ an ordered, but more vflried ~rran8ement of ~urface 35 silver snd bromide ion~ than is presented at the cubic, octahedralJ or rhombic dodecahedr~l silver bromide crystal faces. Thi~ i3 a re~ult of the .

- . ~

~2 ~ 3 ~2 tierin~ that occurs 3t the {210} tetrahexQhedral crystal fAce. Tetrahexahedral crystQl fQces with differing Miller indices also exhibit tierin~. The differing Miller indices re~ult in Qnslogou~, but 5 nevertheless unique surfsce arrangementa o~ sllver snd halide lons.
Considerin~ value~ of h up to 5, ~co~itetra-hedral crystal fQces csn h~ve any one of the following Mill~r indices: {211}, {311~, lo {322~, {411}, ~433~, l511}, ~522}, 1533}, or {544}. Figure 14 is an isomPtric view of ~ ico~itetr~hedron 21 bounded by faces of the ~211} crystallographic form. The point or coign 22 ia formed by four intersectin~
15 crystal faces 22a, 22b, 22c, and 22d and i~ one of 9iX ~ dentical coigns. The coi~n 23 is formed by three intersecting crystal faces 22~, 23al ~nd 23b and i9 one of eight identical coigns. Referring to Table I~ it ig app rent that a pyramid having four 20 surfsce face3 ~uch a~ those defining colgn 22 i~
present when the surf~ce fsce~ of the pyramid are ico~itetr~hedral or {hkO} crystsl f~ces on a cubic or ~100~ b~e plane presented by the host grain. If, on the other hand, the ho~t grsin 25 presents ~n octahedral or ~111} base plsne, a pyr~mid hAving three urfsce f~ces ~uch as tho~e defining coign 23 i9 present when the surface faces of the pyrsmid are icositetrahedral. For icositetr~-hedrsl crystal fsces of differing Miller indices the 30 geometric~l relationships are the ~ame, but the an~les ~f surface fsce intersections, with each other and with the bsse plane, differ.
The {211} icositetrshedrsl cry~tal faces present a unique arr~ngement of ~urface ~ilver and 35 halide ions thst differs from that presented by all other po~ible cryst~l f~ces for cubic cry~t~l lattice structure silver hslide~. This unique 3~Z

~urface srrangement of ion~ a3 theoretically hypothesized is schematically illustrated by Figure 15, wherein a t211) icositetrahedral crystAl face is shown formed by silver lons 2 and bromide ions 3.
5 Comparing Flgure 15 with Figure~ 2, 4, 6, 11, ~nd 13, it is appsrent that the surface positioning of silver ~nd bromide ions in each figure ig di~tinctive. The {211} icositetrahedral crystal face present~ an ordered, but more varied arr~ngement of ~urface 10 silver and bromide ions than i~ presented at the cubic, octahedral, or rhombic dodecahedral silver bromide crystsl faces. This is a re~ult of the tiering that occurs at the {211} icositetrahedral crystal face. Ico~itetrahedral crystal faces with lS differing Miller indices also exhibit tiering. The differing Miller indices result in snalogous, but nevertheless un$que surfece arrangements of silver snd halide ions.
Considerin~ values of h up to 5, hexoctahe-20 dral crystal fsces can have any one of the following Miller indices: {321}, {421}, {431}, {432}, {521}, {531}, ~532}, {541}, {$42~, or ~543}. Figure 16 i~ an isometric view of a hexoctahedron 24 bounded by face~
25 of the {321} cry~tallogrsphic ~orm. The coign 25 i9 formed by eight intersecting crystal f~ces 25e, 25b, 25c, 25d, 25e, 25f, 25g, snd 25h and is one of six identical coigns. The point or coign 26 i8 formed by six intersecting crystal faces 25g, 25h, 30 26a, 26b, 26c, hnd 26d and i9 one of six identical coigns. The coign 27 i5 formed by four intersecting crystal faces 25a, 25h, 26a, snd 27a. Referring to Table I it is apparent that a pyr~m~d having eight surface face~ such ~g those defining coign 25 i~
35 present when the surface faces of the pyramid ~re hexoctshedral or {hk~} crystal face~ on a cubic or {100} base plane pre~ented by the host grain ' .
~- .

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If, on the other hand, the ho~t grain presents an octahedral or {111~ base plane, a pyremid having six Aurface faces such a tho~e defining coign 26 is present when the surface faces of the pyramld are 5 hexoctahedral. Although excluded from the present invention because of their rarity snd therefore l~ck of practical importance, if the base plane were of a rhombic dodecahedrAl or ~110~ cryst~llographic form, the pyram~ds thereon would have ~urface face~
10 corresponding to those forming coign 27. For hexoctahedral crystal fsces of differing Miller indices the geometrical relstionships are the same, but the angles of ~urface face intersections, with each other and with the base plane, differ.
The ~321} hexoct~hedral crystal faces present a unique arrangement of surface silver and halide ions that differs from that presented by all other possible crystal faces for cubic crystRl lattice structure silver halides. This unique 20 surface arr~ngement o~ ions as theore~ic~lly hypothe~ized i9 schematically lllustrQted by Figure 17, wherein a {321} hexoctahedral crystal face ls shown formed by silver ions 2 and bromide ions 3.
Comparing Figure 17 with Fi~ures 2, 4, 6, 11, 13, and 25 15, it is apparent that the surface po~itioning of silver and bromide ions in each figure i3 distinc-tive. The {321~ hexoctahedral crystal f~ce presents an ordered, but more ~aried arrangement of surf~ce silver snd bromide ions than is presented at 30 the cub1c, octahedral, or rhombic dodecahedr~l silver bromide crystal faces. This i3 ~ result of the oblique tiering that occurs at the ~321}
hexoct~hedral crystal face. Icositetrshedral cry~tal f~ces with differing Miller indices ~lso exhibit 35 oblique tiering. The differing Miller indice~ re~ult in an~loeous, but nevertheles unique surf~ce ~rrsngements of silver and halide ions.

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An intere3ting point to note i~ that it i~
the collective ba e areas occupied rather th~n the ~ize or number of pyramid~ of any particular form that control~ the surfsce area they present. The 5 re~son for this i~ that ~ur~ce fsce are~ i~ in R
fixed ratio to the base ares for ~11 pyramid~ of the ssme form. For example, 8 population o~ ~ hundred pyramlds of a given form and a second populstion of a thousand smaller pyramids of the same form exhibit 10 the same rstio of collective base area to collective surf~ce area - i.e., if the collective base area~ for the two pyramid populations are equal, their collective surface sresa sre al~o equal. Hence, the degree to which ruffling can increase the surface 15 area of the host grain~ i~ a function of the pyramidal coverage of the bs~e plane~ and the form of the pyramid~ 8g opposed to their ~ize or number.
Thu~, the invention i~ not restricted to ruf~led grain~ having sny psrticular size or number of 20 pyramid~.
Having made this observstion, however, it i~
~lso pointed out that the ~urf~ce ares ratio (as opposed to the ~urface area) pre~ented by ruffled ~ilver halide grain~ is directly influenced by the 25 size of the pyramids. A hundred pyramids providing the ~ame ~urface area a~ a thousand smaller pyramid~
of the same form nevertheless have 8 much larger collective volume and therefore require more silver hfllide to form. This 19 one reason to favor ~maller 30 pyrsmid~ over l~rger pyramid~. It i9 accordingly preferred to employ pyramids having average ba~e areas le~s than 10 and most preferably les~ than 10 3 times the average area~ of the bas~ plane~ on which they are locsted.
When it is desired to maximize the surface srea ratio provided by the pyramids, it is, of cour~e, obvious to ~elect pyramid~ which themse~ve~

~za~3~

exhibit a maximum surfsce area r~tio, ~lthough the smount of silver hslide contained in relatively small pyramids is virtually negligible. A second factor to consider is whether the pyramidal base define~ a 5 polygonal figure that can be close packed. Al~
pyramids of the 3sme form on a given base plane ~re identic~lly oriented. Looking at Figure 9 it can be seen thst the bsse plAne 14 csn in theory be entirely covered with pyramids of the form of pyrsmid 13, lo whether or not the pyr~mids are of the same or different sizes. On the other hand, given the restr~int that ~11 pyrsmid~ of like form on the same bs~e plane must be identicslly oriented, it is clesr from Figure 8 that the base plane 12 cannot be 15 entirely covered by pyramida identicsl in form to pyramid 11, although the vac~ncies between ad~scent pyr~mids can be reduced where pyramids of different size~ ~re present.
The presence of ruffle3 formed by pyramidal 20 crystel faces differing in their crys~allogr~phic form from thst of the baae planes presented by the host ~rains h~s been confirmed by observ~tions ~nd me2surements, 8~ described in the Exsmples below.
Since the ba~e plsne represents the favored crystal-25 logr~phic form for the silver hslide being depositedthereon, the formstion of crystsl faces of 8 differing cryatallographic form is a depsrture from what normslly would be obtained. In addition, the formation of pyrsmidal cry~tal faces i~ highly 30 unexpected, and, beyond thi~, obtaining pyramidsl cry~tal faces of crystallographic forms which h~ve rarely or never before been observed for ~llver hslide is sn exceptionsl deperture from the pB~t knowledge of the art~
While it is not intended to limit the invention by any p~rticular theory, 8 digcus~ion of po3sible mechanism~ for cry~tal face formatlon i~

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~ 9_ offered. Con~iderlng ~n emul~ion conta1ning host grain~ bounded by face~ of a favored crystallographic form for the ~ilver h~lide ad~acent the grain ~urface, depositing additional silver halide which 5 f~vors the ~ame cryst~llogr~phic form result~ in ~ubstanti~lly uniform shelling of the grains with the resulting shelled grain, though larger in size, still exhibiting crystal faces of the same crystallographic form ag the ho~t grain~
~urnlng to Figure 7, it is known in emulsion precipitation that grsin~ of octahedral crystRl face~
can be changed in 3hape to cubic cryst~l faces and vice ver~a by changing precipitAtion conditions as the grain~ are being grown~ Thu~, the octshedral 15 grain 5 bounded by {111} crystal faces can be grown to form succes~ively the tetr~decahedron 9, the tetradec~hedron 10, and the cube 1 merely by changing the precipitation conditions to favor the formstion of ~100} crystal faces. (In practice the cube 20 and tetradecahedr~ are usually somewhat larger in relation to the oct~hedron than shown.) By comparing tetradecahedra 9 and 10 it can be readily appreciated that the cubic crystAl faces are becoming larger becau~e silver halide is more rapidly depositing on 25 what remsins of the octahedral cry~tal faces. From this the observation follows that the ma~or crystal faces of ~ilver halide 8rains sre tho~e oE 8 cry~tallographic form onto which silver ~nd halide ions precipitate most slowly. Once only faces of 30 this le~ reactive crystallographic form remain, 1n the in~tance above the llOQl face~ of cubic gr~in 1, silver and halide ions depo~it i~otropically on the~e ~urface~.
The succe~ful formation of cry~t~l faces of 35 a differing crystsllogrsphic form from th~t f~vored by the silver halide bein8 depo3ited depend~ on identifying grsin growth condition~ that retsrd the o~z r~te of silver snd hali.de lon deposition onto faces of the desi.red differing crystRllographic form. Msny ex~mples can be found in the art of growing host grains presentLnp, cubic or octahedral face3 to form 05 gr~ins in whLch some or ~11 of the Esces ~re of the other crystallogrsphlc form--i.e., octahedrsl or cubic. A1.thou~h rhombic dodecAhedral ~ilver halide grains are rsre, similar erowth conversions in grain shape are equally applicable to this cry~tallographic ~orm. By observlng samples taken st intermediete sts~es ot` p,rsin growth it has been confirmed that growth p~tterns analogous to the conversion of an octshedral. grain to a cubic grsin, described above by refsrence to Fl~ure 7, can and do occur~
Surprlsingly, however, there i5 snother growth pattern po3sible, snd it is this latter growth pattern th~t gl.ve~ rlse to the present inventlon.
Referring again to Figure /, it csn be seen thst in growing the oct~hedral graln 5 to form the cubic grain 1, the {100~ crystal faces or~gin~te at the coigns of the octshedron snd increase progressively in area unt.ll the eubic form is complete. Comparing Fi~,ure 7 with Figures 8 snd 9, it is immediately apparent that formation of pyrsmidal surfaces does not occu~ selectiYely st the coigns or even edges oE
the host grsins, but occurs on the fsces of the grains.
Berry snd Skillman, discussed sbove, grew sl.lver chloride ag di~crete depo its on the {lll}
maJor surfaces of tabular sllver bromide grains. The ~ao3~'~

failure of the silver chlor~de to simply shell the silver bromide gra$ns can be explained by the fact that silver chloride strongly favors ~lrfacçs of a ~100 } crys tal lographic fsrm and was therefore 5 lncom~atible with continulng ~ crystal ~ce growth under the conditions of precipitation employed~ Unlike Berry snd Skillman the present invention employs silver halide to ruffle the host crystal faces that favors a orystallographic form 10 corregponding to that of the crystal faces presented by the host grains.
It is believed that this i~ made possible by cresting conditions which 310w the rate of silver and halide ion deposition for at least one other 15 crystallogrsphic form below the rate of silver snd hslide ion deposition for the crystallographic form exhibited by the host grain. Deposition of silver halide on~o the host grain crystal faces under these created conditions causes to be formed over the faces 20 of the host grains pyrsmids bounded by surface faces of the slower growing crystallographic form. M~ximum ruffling is achieved when substantially all of the host grain surfsces are ~ust covered by the pyramidal protrusions. If deposition is continued thereafter, 25 the grains revert eventually to an unruffled form, but are bounded by faces of a crystallographic form corresponding to that of the interim pyramidal surface faces.
Failure of the art to observe ruffled grain 30 faces or ~ny grain faces of the trisoctahedral, tetrahexahedral, icositetrahedrsl, or hexoctahedrsl crystallographic forms and rarely for the art to observe grain faces of the rhombic dodecahedral cryatallographic form over decades of ~ilver halide 35 crystallographic studies suggests that there i~ not an extensive rsnge of conditions that favor ~he ruffling of the normally observed {100} and ..

~ ~3C33~Z

{111~ Bra$n faces. It has been discovered that growth modifiers c~n be employed to produce ruffled grain faces. The growth modifiers which have been identified are organic compounds. They are believed 5 to be effective by rea30n of showing an adsorption ~, preference for the pyramidal crystal face forme~ by rea~on of it~ unique ~rraneement of silver snd halide n ions. The growth modifier thereby slows the rate of halide ~nd silver ion deposition onto the pyramidal 10 cry~tal face relative to the rate of ~ilver and halide ion deposition onto the original host grain crystsl faces. Thus crystal faces of the cry~tallo-grsphic form presented by the pyr~mid ~urface faces per~ist and predominate while differing cry~tal face~
15 originally pre~ented by the host Brsin~ are quickly diminished or obliterated by further ~ilver halide deposition. Growth modifiers that have been empirically proven to be effective in producing ruffled grain faces as well as the combination~ of 20 host grsin and pyramidal crystal faces which they hsve produced are described in the exAmples, below.
These growth modifiers are effective under the conditions of their use in the examples. From empirical screening of a variety of csndidate growth 25 modifiers under differin8 conditions of silver halide precipitation it ha~ been concluded that multiple parameter~ must be satisfied to achieve ruffled grain face~, including not only the proper choice of a growth modifier, but ~190 proper choice of other 30 precipitation p~rameter~ identified in the example~.
Fsilure~ to achieve ruffled grain faces with compounds shown to be effective as growth modifier~
for producing ruffled grain faces have been observed when accompsnying conditions for ~ilver halide 35 precipitation have been varied. However, it i~ -sppr~ciated that having demonstrsted success in the preparations of silver halide emulsions containing ~2al~)3~Lz 8rains with ruffled grain faces, routine empiric~l studie~ sy~tematicfllly varying parameter~ are likely to le~d to additional useful prep~ration technique Once silver halide grsin growth condition~
5 are satisfied th~t ~electively retard ~ilver hallde depo~ition at pyramid~l crystal f~ces, continued grain growth u~ually results in ruffling of ~11 the grains present in the silver halide precipit~tion reaction vessel. It doe~ not follow, however, that lO all of the radiation sensitive silver h&lide grains in the emulsion3 of the pre~ent invention must have ruffled faces. For exsmple, ~llver halide grain~
having ruffled faces can be blended with any other conventional ~ilver halide gr~in population to 15 produce the final emulsion. Wh~le silver halide emul~ion~ containing any identifiable ruffled gr~in surfsce are considered within the scope of this invention, in most applications the grains h~ving at least one identifiable ruffled face account for st 20 least 10 percent of the total grain population snd usually these grains will account for greater than 50 percent of the total gr~in population.
The host grain emulsions presenting cubic and/or octahedral cry~t~l faces from which the 25 emulsion~ of this invention are produced ~nd any emul~ions ~acking ruffled grain faces blended into ruffled grain emulsion Rccording to this invention can be cho~en from among a vsriety of conventionsl emulsions. Generally the techniques for producing 30 surface latent image forming grain~, internal l&tent image forming grains, internally fogged grains, surfsce fogged grains, and blend~ of differing grains described in Research Disclo~ure, Vol. 176, December 1978, Item 17643, Section I, can be applied to the 35 prepar~tion of emulsions according to this invention.
It i~ specific&lly contemplsted to employ thin and high aspect rstio tabular grain silver ~2~3~

-3~-halld~, ~mul.slon~ ~s host ~rain emulsions. Such emulslons are illustrated by Wilgus et al U.S. Patent 4,43~t,226; Koron et al U.S. Patent 4,439,520;
Dsubendi.~k et al U.S. Patent 4,414,310; Abbott et Al 05 U.S. Patents 4,4~5,425 and '426; Wey U.S. P~tent 4,3~9,215; Solber~ et al U.S. Patent 4,433,048;
Dickerson U.S. Patent 4,414,304; Mignot U.S. Patent 4,386,156, Ml.~not Research Disclosure, Vol. 232, Augu~t 1983, Item 23210; Jones et al U.S. Patent 4,478,929; Evan~ et Ql U.S. Patent 3,761,276;
MaskssXy U.S. Patent 4,400,463; Wey et al U.S. Patent 4,41~,306; and Maskssky 4,435,501, cited above.
As herein defined hi.gh aspect ratio tabular grain emulsions are tho~e comprised of a dispersing medium and si.lver ha~.lde grains, wherein st least 50 percent o~ the total pro3ected area o~ the ilver hsl.lde grA1.ns is prov.Lded by tabular silver halide grAlns hsvLng a th5.ckne~s of less than 0.3 ~m, a diAmeter of At lea~t 0.6 ~m, and an average aspect rat,lo ot` greate~ th~n 8:1. In ~ome application~, such ~s :Ln recordlng radiation within a portion of th~ spectrum that the ~ilver hAlide i~ capable of absorbi.n~, at lea~t 50 percent of the total pro~ected area of the tota]. pro~ected area of the silver halide grAI.ns ls provlded by tabulAr silver halide grains havi.ng a thi.ckness of less than 0.5 ~m, a diameter of st least 0.6 ~m, and an average aspect ratio of p,rester than 8:1. Pre~erred high a~pect ratio tabulAr grain emulsions are those in which the average asp~ct ratio is at least 12:1 ~nd optim&lly At least 20:1. It i~ 9lgo preferred to incre~se the pro~ct~d area ~eferred to above from 50 percent to 70 percP,nt and opti.mally to 90 percent. Silver-brom:i.odide e~ulsi.ons are generally preferred for camera speed imaging appllcation~ while silver bromi.de and sll.vQr bromoiodi.de emulsions are preferred for radi.ographic imaging.

3~Z

A~ hereln defined thin tabular grain emul~ions are tho~e comprised of a dispersing medium and silver halide grains, wherein at lea~t 50 percent of the total pro~ected area of the silver hslide 5 grains is provided by tabular silver halide grs~ns having a thicknes~ of less than 0.2 ~m und an aversge a3pect rstio of greater than S:l. The preferences noted above for high a~pect ratio emulsions apply also to thin tabular grain emul-10 sions. Emulsions which ~ati3fy both definitions arepreferred for most photographic applications.
Apart from the novel grain ~tructures identified above, the radiation sen3itive ~ilver halide emulsion~ and the photographic elements in 15 which they are incorporated of this inventlon csn tske any convenient conventional form~ The emulsions csn be wsshed as described in Research Disclosure, Item 17643, cited above, Section II.
The radiation sensitive ~ilver halide grains 20 of the emulsions can be surface chemically sen~i-tized. Noble metal ~e.~, gold), middle chalcogen (e.g., ~ulfur, selenium, or tellurium), and reduction sensitizers, employed individually or in combination are specifically contemplated. Typical chemical 25 sensitizers are listed in Research Disclosure, Item 7643, ci~ed above, Section III.
The silver halide emulsions can be Rpectral-ly sensitized with dyes from a variety of cl~3ses, including the polymethine dye class, which includes 30 the cyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-, tetra-, and polynuclear cyanine~ and merocyanines), oxonols, hemioxonols) styryls, merostyryls, and ~treptocyanines. Illu-~tra-tiYe ~pectral ~ensitizing dyes are disclosed in 35 Research Di~closure, Item 17643, cited above, Section IV.

z The silver halide emul~ion~ a~ well a5 other layer~ of the photogr~phic element~ o~ thi~ invention can contain ~ vehioles hydrophilic: colloids, employed alone or in comblnation with other polymer~c 5 materidls (e~g., l~tice~). Suitable hydrophilic material~ include both naturally occurr$ng sub~tances ~uch as protein~, protein derivatives, cellulo~e derivative~ - e.g., cellulose ester~, gel~tin - e.g., alkali treated gelatin (cattle9 bone, or hide 10 gelatin) or acid treated gelatin (pi8~kin gelatin), gelatin derivatives - e.g., acetylated gelatin, phthalated gelstin, and the like~ poly~accharides such a~ ~extran, gum arabic, 2ein, ca~ein~ pectin, eollsgen derivatives, collodion, agar-agar, srrow-l5 root, and slbumin~ The vehicle~ can be hsrdened by conventional procedure~. Further detail~ of the vehicles and hardeners ~re provided in ~esesrch Disclo~ure, Item 17643, cited above, Section~ IX and X.
The ~ilver hslide photogrsphic element3 of thl~ invention can contain other addenda conventional in the photographic art. U~eful sddenda are de~cribed, for example, in Re~e~rch Di~clo~ure, Item 17643, clted above. Other conventional u~e~ul 25 addenda include antifoggant3 and ~tab~lizer~,couplers (~uch ~ dye forming couplers, ma~king coupler~ and DIR couplers) DIR compounds, anti-~tain sgents, ima~e dye stabilizers, absorblng material3 ~uch a~ filter dyes and UV absorber~, light ~catter-30 ing materlsl~, anti~tatic agent~, coating sid3, ~ndpla~tici2ers and lubricant~.
The photographic element~ of the present invention can be ~imple black-and-white or monochrome element~ compr~ing a ~upport bearing ~ lsyer of the 3S silver halide emul~ion, or they c~n be multilayer and~or multicolor element~. The photographic element~ produce image~ ranging from low contra~t to :, 3~ 2 very high contr~st, ~uch A9 those employed for producing half tone images in graphic arts. They can be designe~ for processing with separate ~olutions or for in-cflmera processing. In the latter in~tance the 5 photographic elements can include conventional image transfer features, such a-~ those illustrated by Re~earch Di~closure, Item 17643, cited above, Section XXIII. Multicolor elements contain dye image forming units sen~itive to each of the three primary regions lo of the spectrum. Each unit can be comprised of a single emul~ion layer or of multiple emul~ion layers sensitive to a given region of the spectrum. The layers of the element, including the lsyers of the image f~rminB units, can be arranged ln various 15 order~ ~g known 1n the art. In an alternative format, the emulsion or emulsions can be disposed a~
one or more se~mented layer~, e.g., as by the use of microves~els or microcells, as described in Whitmore U.S. Patent 4,387,154.
A preferred multicolor photographic element according to thi~ invention containing incorporated dye image providing materials comprises a support bearing at least one blue senqitive silver halide emul~ion layer having associated therewith a yellow 25 dye forming coupler, at least one green ~en~itive ~ilver hslide emul~ion layer having as~ociated therewith a msgenta dye formin~ coupler, and at least one red sensitive silver halide emulsion layer having Associated therewith a cyan dye forming coupler, at 30 lesst one of the ~ilver halide mul~ion layer~
containing grains having ruffled faces as previou~ly described.
The element~ of the present invention c~n contain addltional layers conventional in photo-35 graphic elements, such ~s overcoat layer3, ~pacerlayer~, filter layers, antihalation layers, ~nd scavenger layer~. The support can be any suitable ~8~ 3 ~Z

support u~ed with photographic elements. Typical support~ include polymerlc films, paper (including polymer-coated p~per), glass, and metal ~upports.
Detsil3 regsrding supports and other lQyers of the 5 photogr~phic elements of this invention are contained in Re~earch Di~closure, Item 17643, cited sbove, Section XVII.
The photogrsphic elements can be im~gewise exposed with various forms of energy, which encompass 10 the ultraviolet, visible, and infrared regions of the electromagnetic spectrum as well a3 electron beam and beta rsdi~tion, gamms ray, X rsy~ alpha psrticle, neutron radiation, and other form~ of corpuscular and wave-like radiant energy in either noncoherent 15 (rsndom phase) form~ or coherent (in pha~e) forms, as produced by laser~. When the photographic elements are intended to be expo~ed by X rflys, they c~n include features found in conventional radiographic elements, ~uch AS those illustrated by Re~earch 20 Di~closure, Vol. 184, August 1979, Item 18431.
Processing of the imagew1se exposed photographic elements can be accompli~hed in any convenient conventional manner. Processing proced-ures, developing agents, and development modifiers 25 are illuqtrAted by Re~earch Disclosurel Item 17643, cited above, Sections XIX, XX, ~nd XXI, respect~vely.
The emulsions of this invention can be ~ubstituted for conventional emulsions to sstisfy known photographic application~. In addition, the 30 emul~ion~ of this invention can lead to further photogrsphic advaQtages. In general the further photographic advantages can be attrlbuted one or a combinatlon of ~a) the incre~sed surf~ce area r~tios which the ruffled grsins make possible, (b) the 35 varied crystal faces presented by the ruffled grains, and (c) the high affinity between the ruffled gra~n faces and ~dsorbed compounds.
, ~8~3~

For exsmple, the pre~ent lnvention ~llows increa3es in photvgraphic ~peed to be realized. In con~idering a photographic Rpplication in which the emulsion~ are expo3ed imagewise to light in the mlnus 5 blue portion of the ~pectrum (i.e., the 8reen and/or red portion of the spectrum) and thereby require spectral sensitization, it i~ gener~ accepted in the art that it is the amount of ~pectral sensitizing dye which csn be adsorbed to the surf~ces of grain~
10 of a cho~en size which limit~ the maximum minus blue ~peed that can be resllzed. Note that decrea~ing aversge ~rain ~ize to increase the ~urface area ratio of the grains and therefore the amount of sensitizing dye per unit volume of silver halide is ineffective 15 to increase ~peed. It instead lowers photographic speed. The present invention by incre~ing the ~urface area ratio of the grains without reducing average grain size allows an increase in photographic speed to be realized.
In considering the minus blue speed gain the angle which the light ~trike~ the ~pectral ~ensitiz-ing dye adsorbed to the grain crystal fsce~ i~ an important consideration. Photon capture is mo~t efficient when the transition moment dipole (~ee 25 Zbinden, Infrared SPectroscopY- of HiKh Polymer~, Academic Press, New York, 1964, p. 215) of the ~pectral ~ensitizing dye absor~ed to the cry~tal face presented by the ~ilver halide grain~ is sub~t~ntial-ly normal to the direction of expo~ing radi~tion.
30 When the grains sre randomly oriented in the emul~ion, as i~ typical for emul~ion~ containing predominsntly nontabular grains (e.g., regular cubic or octahedral grain~) or tabular grain3 of low ~spect ratios (e.g., le~ than S:l), ruffling of the grain 35 faces does not change the average angle of incidence of expoQing radiation with the transition moment dipole of the ad~orbed spectrsl ~en~itizing dye~ In ~z~

thi~ instance speed increases reeliz~ble ~hould be approxim~te in proportion to the increa~e in the surface are~ ratio.
In conventional thin and high aspect ratio 5 tabular 8r~in emutsion~ the grains Qre typlcally oriented with their ma~or faces normal to the direction of unscattered exposing radiation. For most spectral sens$tizing dyes the transition moment dipole is psrallel to the crystal fsce to whlch it is 10 absorbed; therefore, 8 normal orientation of the silver h~lide crystal faces with respect to the direction of exposing r~diation also normally orients the transition moment dipole of the spectral sensit~zing dye. ThuQ, the graln faces are already l5 oriented optimally for dye absorpt~on of unscattered light. In thi3 instsnce increasing the grain ~urf~ce area by ruffling increases the amount of spectral sensitizing dye which can be ~dsorbed to the grain surfaces before encountering desensitization, but the 20 speed gain which flows from this increase in grain 3urface area is diminished by the less efficient orientation of the transition moment dipvle of the ~dsorbed spectrsl sensitizing dye~ Where, however, the exposing radi~tion has undergone ~lgnificant 25 scattering prior to reaching a spectrally ~ensitized ruffled thin or high aspect ratio tabular grain emulsion layer, the angulsr orientation of the dye transition moment ~ipoles i5 reduced if not eliml-nated ~n significance. Thus, n optimum location for 30 a spectrally sensitized ruffl~d thin or high aspect r~tio tabular grain emulsion in a photographic element is nesrer the support ~nd beneath overlying light scsttering layers. For examplel in a multl-color photographic element such ~n emul3ion is most 35 efficient as the slower green snd/or red recording layers norm~lly loc~ted nesrest the photographic support .

~zao3~

If de~ired, the photogrsphic ~peed of ~he~e recording layers csn be increased by employing reflective msterisl~, either tn the emulsion laysr or layer~ or in underlylng lsyer~. The reflective 5 materials in the ~ilver halide emulsion layers c~n include pigments o~ high refr~ctive index, 8S
illustrated by M~rri~ge U.K. P~tent 504,283 and Yutzy et al U.K. Patent 760,775 or reflecting undercoat layers containing silver halide, a~ illustr~ted by 10 Ru~gell U.S. Pstent 3,140,179.
Although the above di~cus~ion i~ directed ~pecifically to the u~e of minus blue ~b~orbing ~pectr~l sensitizing dyes, it can be apprecisted that ~imil~r con~iderstion~ ~pply to sdsorbed ~pectrsl 15 ~ensitizers, regardless of the region of the ~pectrum in which they sb~orb~ The combinstion of emul~ion~
having r~ndomly oriented ruffled grsins of a ~ilver h~llde composition cap~ble of sb~orbing blue light (e.g., ~ilver bromide and silver bromoiodide) and a 20 blue ab~orbing spectrsl 3en~itizing dye i ~pe~ifically recognized as being a photographically advantsgeou~ form of the pre~ent invention.
In the foregoing discus~ion only the increase in the gr~in surfPce area r~tio i~ nece~qsry 25 to account the pho~ographic advantage. However, photogr~phic advantage~ can al~o be ~ttributed to improved interactions of ad~orbed sddenda snd the ruffled silver h~lide grains surf~ces. For example, when a growth modifier is present adsorbed to the 30 ruffled face~ of the grRin~ and h~s ~ known phot~-gr~phic utility that is enhanced by ad~orption to a gr~in surfsce, either becsu~e of the more intim~te ~soci~tion with the gr~in ~urf~ce or becau~e of the reduced mobility of the growth modifier, improved 35 photographic performsnce can be expected. The re~son for thi~ i~ that for the growth modif~er to produce a pyr~mid~l crystal face it mu~t exhibit an adsorption . ' .

~8~3~2 preference for that crystallographic form th~t is greater than that exhibited for sny other possible silver halide crystallographic form.
Thi~ can be appreciated, for example, by 5 con~iderlng growth in the pre~ence of An ~dsorbed growth modifier of a ~ilver hal$de grain havlng both cubic snd hexoctahedral crystsl faces. If the growth modifier shows ~n adsorption preference for the hexoctahedrsl crystQl faces over the cubic crystal 10 faces, deposition of ~ilver and halide ion3 onto the hexoct~hedral cry~tal faces is retarded to a greater extent than along the cubic cry~tal f~ces, and grsin growth results in the eliminati~n of the cubic ~rystal facea in favor of hexoctahedral crystal 15 fAces. From the foregoing it is ~pparent that growth modifiers which produce hexoctahedral cry~t~l faces are more tightly adsorbed to these grain surfsces than to other silver halide grain surfaces during 8rain growth, and this enhanced ad~orption carrie~
20 over to the completed emulsion.
To provide an exemplary photographic application, Locker U.S. Patent 3,989,527 describe~
improving the speed of a photographic element by employin~ an emulsion contain~ng radiation ~en~itive 25 ~ilver halide grains having a spectral sensitizing dye adsorbed to the grain surface~ in combination with ~ilver halide grain~ free of spectral ~ensitiz-inB dye having an average diflmeter chosen to maximize light ~cattering, typically in the 0.15 to 0.8 ~m 30 rsnge. Upon imagewise exposure radiation ~triking the undyed grains ig scattered rather than being ab~orbed. This re~ults in an increa3ed ~mount of exposing radiation 3triking the radiation ~ensitive imaging grsins having a spectral sensitl~ing dye 35 adsorbed to their ~urfAces.
A dissdvantage encGuntered with thi~
approach has been that spectral sen~itizing dyes can ~ao3~Lz -~3-mi~rate in the emulsion, so that to some extent the initi~lly undyed grains sdsorb spectrsl sen~itizing dye which has migrated from the initially spectrally sen3itized grsins. To the extent thst the initi~lly 5 spectrslly sensitized gr~ins were optim~lly sen~i-tized, dye migration away from their surfaces reduces sensitizstion. At the ssme time, ad~orptlon of dye on the gr~ins intended to scatter imaging radiation reduces their scsttering efficiency.
In the examples below it is to be noted that spectral sensitizing dye~ have been identified as 8 growth modifiers useful in forming ruffled silver halide grains. When radiation ~ensitive silver halide gr~ins having ruffled faces snd a growth 15 modifier ~pectral sensitizing dye Rdsorbed to the ruffled faces are 3ubstituted for the spectr~llg sensitized silver hslide grAins employed by Locker, the disadvantageous migr~tion of dye from the ruffled grain faces to the silver halide grains intended to 20 scatter light is reduced or eliminated. Thus, an improve~ent in photographic efficiency can be re~lized.
To illustrste ano~her advantageous photo-gr~phic application, the layer ~tructure of ~
25 multicolor photographic element which introduces dye ima8e providing materisls, such as couplers, during processing can be simplified. An emul~ion intended to record green exposures can be prepsred using a growth modifier that is a green spectral sen~itizing 30 dye while an emulsion intended to record red exposurPs can be prepsred using a growth modifier that is a red spectral sensitizing dye. ~ince the growth modifiers are tightly adsorbed to the grains snd non-wandering, instead of coating the green and 35 red emulsions in separate color forming layer units, as is convention~l practice, the two emulsions can be blended and coated as a single color forming layer ~803~L;2 -4~
unt. The blue recording l~yer c~n take any conventional form, and a convention~l yello~ filter layer can be employed to protect the blended green and red recording emul~ions from blue light expo-5 sure. Except for blending the gre~n and redrecording emul~ions in a single lsyer or group of layers dlfferin8 in ~peed in ~ ~ingle color forming layer unit, the ~tructure and process~n8 of the photo~raphic element lg unaltered. If silver 10 chloride emulsions are employed, the approach descri~ed above can be extended to blending in a single color forming layer unit blue, green, and red recording emul~ions, and the yellow filter layer can be eliminated. The advantage in either case i~ a 15 reduction in the number of emul~ion l~yer~ required as compared to ~ corresponding conventional multi-color photogr~phic element.
In more genersl applications, the ~ub~titu-tion of an emul~ion sccording to the invention 20 containing a growth modifier ~pectral ~en~itiz~ng dye should produce a more invarisnt emulsion in term~ of spectral properties th~n a corre~ponding emulsion containing silver halide grain~ lacking ruffled faces. Where the growth modifier is capable of 25 inhibiting fog, ~uch as 2-merc~ptoimidA~ole or sny of the tetrsaz~indenes ~hown to be effective growth modifiers in the example~, more effective fog inhibitinn at lower concentrations may be expected.
It is recognized that ~ varlety of photo-30 graphic effect~, such 8~ photographlc ~en~itivity, minimum background dPnsity levels, latent im~ge ~tability, nucleation, developability, image tone, absorption, and reflectivity, ~re influenced by grain ~urfsce intersctions with other components~ By 35 employing components, ~uch ~ peptizer~, ~ilver halide solvents, sensitizers or desensitizers, supersensiti~er~, halogen acceptors, dyes, ~ntifog-, ~LZ803~Z

~ants, stabilizers, latent image keeping agents, nucle~ting sgents, tone modifiers, development sccelerstDrs or inhibitors, development re~trsiners, developing ~gents, snd other addends that ~re 5 uniquely m~tched to the ruffled gr~ln f~ces, distinct sdvant~ges in photogrsphic perform~nce over that which can be realized with silver halide gralns of differing crystsl fsces sre po~sible.
ExsmPles The invention csn be better ~ppreci~ted by reference to the following ~pecific examples. In esch of the examples ~11 solutions, unless otherwise indicated, are squeous solutions. Dilute nitric acid or dilute ~odium hydroxide wa~ employed for pH
15 ~d~ustment, as required.
ExamPle 1 Emulsion Exsmple 1 illu3trate~ the prepsr~-tion of a ruffled tsbular gr~in silver bromoiodide emulsion uslng as growth modifier Compound I, 20 5-carbe~hoxy-4-hydroxy-1,3,3a,7-tetraazsindene, which is known to be useful as sn antifoggsnt snd ~tabilizer.
To a reaction vessel supplied with ~ stirrer W8S added 0 05 mole of a thin and high aspect ratio 25 tsbular ~rain silver bromolodide emulsion (6 mole I) of me~n gr~in size 5.3 ~m, thickne~s 0.07 ~m, and containing sbout 40 g/Ag mole gelatin, herein-sfter designated Host Gr~in Emulsion 1 Water wa~
sdded to make the total weigh$ 50 g. To the emulsion 30 at 40C W8S sdded 6.0 millimole/initlal Ag mole of Compound I dissolved in lmL of methanol 9 lmL of wster, snd 3 drops of trlethylsmine. The emulsion W89 then held for 15 min. at 40C. The pH wa~
ad~u3ted to 6.0 st 40C. The temper~ture wss raised 35 to 60C, and the pAg adJusted to 8.5 a~ 60C with KBr and maintsined ~t th~t vslue during the preeipita-tion. A 2.OM solution of AgN03 was introduced at a .~8~3~Z

constant rste over a period of 38 min while a ~olution that wa~ 1.88M in KBr and 0.12M in KI wa~
added a~ needed to hold the pA~ constant. A tot~l of O.015 mole Ag was added.
A cRrbon replica electron micrograph oP the resulting emulsion grains i~ shown in Figure 18. The ruffle~ were ~mall, closely po~tioned, and uniformly distributed over the faces of the tabular gratn~.
Example 2 Emul~ion Exsmple 2 illu~trates the prepara-tion of ~ ruffled tabul~r-grain silver bromoiodide emul~ion u~ing as a growth modifier, Compound II, which is known to be useful as a blue spectral ~en~itizing dye.
I._rCH_i' '~--s Compound II
Emulsion Example 2 wa~ prepared as de~cribed for Example 1, except that the growth modifier wa~ 6.0 millimole/Ag mole of Compound II, di~olved in 3mL
methanol, 2mL water, and 2 drops of triethyl~mine.
25 The precipit~tion w~s c~rried out for 37.0 min, con~uming 0.015 mole Ag.
An electron micrograph of the re~ulting emulsion is ~hown in Figure 19. U~ing the above preparation condition~, but ~ubstituting sn AgBr 30 regular octahedral grain host emulsion for t~bul~r grain ho~t emulsion, Compound II wa~ determined to ~e a growth modifier which produce~ pyramidal crystal fAce~ of the {211} icositetrahedral form. The ruffle~ were ~imilar to those of Example 1.
35 ExamPle 3 Emul~ion Exsmple 3 illu~trates the prepara-tion of a ruffled tabulsr grain pure bromide emul~ion :

~ ~, . . .

u~in~ ~s ~ growth modifier Compound III, anhydro-5-chloro-9-ethyl-5'-phenyl-3,3'-di-(3-sulfopropyl)ox~-carbocyanine hydroxide, triQthyl~mine ~lt, which i~
known to be useful as ~ green ~pectr~l sensltizing 5 dye.
To a reaction ves~el supplied with a ~tirrer was ~dded 0.05 mole of ~ thin and high aspect ratlo tabulAr gr~n AgBr emulsion of mean grain size 5.6 ~m ~nd thickness 0.10 ~m cont~ining about 20 g/Ag 10 mole gelatin, hereinafter desi~na~ed Host Gr~in Emulsion 2. Water was ~dded to make the total weight 50 g. To the emulsion ~t 40C was ~dded 5.0 millimole/initial Ag mole of Compound III di~solved in 2mL met~anol. The emulsion was then held for 15 15 min at 40C. The pH w~s ad~usted to 6.0 at 40C.
The temperature w~ lowered to 30C, ~nd the pAg ~d~usted to 7.6 at 30C with KBr and maintained at that level during ~he precipitation. A 2.OM ~olution of AgN03 wa~ introduced at a constant rate over a 20 period of lO min while a 2.OM solution of KBr w~
added a~ needed to hold the pAg constant. A totsl of 0.020 mole Ag was added.
An electron micrograph of the resulting emulsion grains ig 3hown in Figure ~0. The ruffles 25 were larger th~n in the previous exsmples, closely arranged, and uniformly distributed over the face3 of the tabular grains. Us1n~ ~imilar conditions, but on sn AgBr regulsr octshedr~l host grslns, ~ompound III
was determined to be ~ {100} growth modif1er~
30 ExamPle 4 The four psrts of Example 4 ~how the effects of varying the pAg and temperature of precipitation on the propertie~ of the resulting ruffles. The ho~t w~s a tabular grain AgBr emulsion, and the growth 35 modifier Compound IV, ~nhydro-9-ethyl~5>5'-diphenyl 3,3'-dl(3-sulfob~tyl)oxacarbocy~nine hydroxide, monosod$um salt, which i~ known to be u3eful as a green spectral sensitizing dye.

~ 3 ~'~

To ~ re~ction vessel supplied with 8 stirrer w~ added 0.05 mole of HoQt Gr~in Emul~ion 2. W~ter wss added to make the total weight 50 g. To the emulsion ~t 40C wa~ added 5~0 millimole/initl~l Ag S mole o~ Compound IV dissolved in 9mL methanol. The emulsion w~s then held for 15 mln at 40C. The pH
wa5 sd~u~ted to 6.0 at 40C. Under the pAg ~nd tempersture conditions shown in Table II, 0.02 mole of A 2.OM AgN03 solution was introduced ~t a lO con~tant rate over a period of lQ minutes while ~
2.OM solution of KBr wss ~dded a needed to hold the pAg constant.
TABLE II
Example 4 PreciPitation ~ondition~
Figure Example No ~B~ T( DC) 4A 21A 7.6 60 4B 21B 7.6 40 4C 21C 7.6 30 20 4D 21D 5.2 40 Figures 21A, B, C ~nd D show electron micrographs of the rPsulting grsins. ~xample 4A
produced growths of large flat triangle~. Example 4B
produced a growth of ~ome flat trisngles and some 25 pyr~mids 3msller than in 4A. Exsmple 4C produced fairly uniform pyramids. Example 4D produced unlform closely arranged, smsll pyrsm~ds. ExAmination indicated the growths to h~ve ~100} (cubic) crystsl face~. Compound IV w~s determined to be 30 {100} growth modifier by depositing AgBr onto ~n regular octahedr~l gr~in host emul~ion at pAg 7.6, 40C in the presence of thi~ compound; AgBr eube~
re~ulted.
ExamPle 5 Emulsion Exsmple 5 illustr~te~ the prep~ra-tion of ~ ruffled tabul~r grain silver bromide emul3ion u~ing a~ a growth modifier Compound V~

~ Z 8~ 3 5-~3-ethyl-2-benz~thiazolinylidene)-3-~-sulfoethyl-rhodanin~, which is known to be useful as 8 blue spectral sensitlzing dye.
To a re~ction vessel supplied wlth R stirrer 5 W8~ added 0.04 mole of Host Grain Emulsion 2 W~ter was added to make the total weight 40 g. To the emulsion ~t 40C was added 4 millimole/initi~l Ag mole of Compound Y di~solved in 7mL of N,N-dimethyl-formamide, 3mL water, and 2 drops of triethylamine.
10 The emulsion waa then held for 15 min at 40~C. The pH was sd~usted to 6.0 at 40C. The temperature was raised to 60C, and the pAg ~d~usted to 8.5 at 60C
with KBr and maintsined at that vAlue during the precipitstion. A 2.OM solution of AgN03 wa~
15 introduced at a constant rate over ~ period of 20 min while a 2M solution of KBr was added as needed to hold the pAg constant. A total of O.02 mole Ag was added.
An electron micrograph of ~he resulting 20 emulsion grains is shown in Figure 22. The gr~in faces were uniformly covered with clo~ely ~rranged, ~harp, small pyramidal ruffles. This was consistent with the {211} icositetrahedral crystal face~
expected from investigstion of the same growth 25 modifier employ$ng a nontabular host grain emulsion.
ExsmPle 6 Example 6 illustrates the preparatlon of ruffled tabular graln silver bromoiodide emulsions using Compound V (Example 5) ~s the growth modifier.
30 Example 6A is a control ~howing that no ruffles are formed if the growth modifier is ~dded following, rather than preceding, the silver halide precipita-tion on the hc~t emul~ion. The ho~t emul~ion ~0.05 mole for e~ch exper~ment) and precipitation con~i-35 tion~ were a~ described in Example 1, except that thegrowth modifier was Compound V ~nd the addition rate of the AgN03 solution was half that used in Example ~Z8~3~
~50-1, (pr2cipitstion time about 74 min, 0.015 mole Ag added). The detsils of the three experiments sre shown in Table III.
T~BLE III
ExamPle 6 Precipitstion~
Cpd. V
Figure mmole/
Example No Ag mole_ Comments 6A 23A 3.0Control - Cpd. V added after preclpit~tion 6B 23B 3.0Invention 6C 23C 4.5Invention Figures 23A, B, and C show electron micrographs of the resulting grain~. In Example 6A, 15 addition of the growth modifier after the precipita-tion re~ulted in no growth of ruffle3 on the host emulsion gr~ins. Example 6B, with the same amount of growth modifier ~dded prior to the precipitation, produced uniform, closely arr~n~ed, ~mall ruffles.
20 Example 6C, with a higher level of growth modifier, produced a similfir result, but with sllghtly better defined ruffle~ (pyr~mids).
Mea~urement wa~ made of the interfacial angle of a ruffle on an electron microgr~ph of 25 Example 6C in order to determine the crystallographic form. The angle between the face vectors was found to be 35~. The theoretical ~ngle between [211 vectors i~ 33.6. The form wa~ therefore ~211~
icositetrahedral. This is con~istent with other 30 observations of {211} icositetrahedra being formed startin~ with nontabul~r host grains ~nd employing Compound V a~ a growth modifier.
ExamPle 7 Example 7 again illu~trste~ the prepsratlon 35 of ruffled tabular grsin silver bromoiodide emul~ions u~ing Compound V (Exsmple 5) as the growth modifier, but 3howR the dependence o~ the result on the lev21 of growth modifier added.

The ho~t emulsion (0.05 mole for each experiment) and the precipitation conditions were a~
described in Example 6. The deta~ls of the experi-ment~ are shown in Table IV.
TABLE IV
ExamPle 7 PreciPltations Cpd. V
Figure mmole/
ExsmPle No A~ mole 7B 24B 0.75 7C 24C 1.5 7D 24D 3.0 Figure~ 24A, B, C, and D sre electron 15 micrographs of the resulting emulsion grsin3.
Example 7A, without Krowth modifier, and 7B, with 0.75 millimole/Ag mole, showed no ruffles. At 1.5 millimole, relatively large truncated pyramids appeared, as -qhown in Figure 24C. At 3.0 millimole~
20 Example 7D produced uniform, closely arrsnged, sm~ll ruffle~. The pyr~midal crystal f~ces were consistent with the l211) cry~tal face~ expected from using Compound V as a growth modifier in the previou~
examples.
25 ExamPle 8 Emulsion Example 8 illu~trstes the prepara-tion of a ruffled tabular grain qilver bromide emulsion using aa growth modifier Compound XIII, anhydro-3,9-diethyl-5,5',6'-trimethoxy-3'-(3-30 sulfopropy~)thiacarbocyanine hydroxide, which i~ ared spectral sensiti7.ing dye.
To a reaction ve~el supplied with a stlrrer was added 0.05 mole of Host Grain Emulsion 2. Water was added to m~ke the total volume 50mL. To the 35 emul~on at 40C was added 5 mill~mole/initial ~g mole of Compound XIII dissolved in 3mL of N,N-di-methylformamide. The pH was ad~usted to 6.0 at ~8~2 40C. The pAg w~ ~d~usted to 7.6 at 40~C ~nd msintain~d at that v~lue dur~ng the precipitation. A
2.0 M solution of AgN03 w~ introduced at a con~tent rate over a period of 10 min while a 2.0 M
5 ~olution of KBr wa9 sdded ag needed to hold the pAg con~tant. A totsl of 0.02 mole Ag wa~ sdded.
Figure 25 i9 sn electron microgr&ph o~ the resulting emulsion grains. Closely arr~nged ruffles are uniformly distributed over the faces of the 10 tabular grAins.
ExamPle 9 The emulsions of Example 9 illustrate the preparstion of ruffled silver bromide tabular grains by phy~ical ripening in the presence of a fine grain 15 silver bromide emulsion and a growth modifier.
ExamPle ~A
To a resction vessel supplied with 8 ~tirrer wa~ added O.OlS mole of a freshly prepared fine grain silver bromide emulsion of mean Brain si~e 0.02 ~m, 20 containing 167 g/Ag mole ~elatin and having R weight of 65 g. To the emulsion at 40~C was added 0.18 millimole (6 millimole/A~ mole of ho~t emul~ion~ of Compound VII, 4-hydroxy-6-methyl-1,2,3a~7-tetraaza-indene, a known antifoggant and stabilizer, dissolved 25 in 2.SmL water and 2 drop~ of triethylamine. Host Grain Emulsion 2 in the amount of 0.03 mol~, m~d~ up to 25 g, wa~ then added. The pH was ad~usted ~o 6.0 at 40C, and the pAg to 9.3 at 40C. The mixture was then hested at 60C ror 4 hr.
Figure 26A ~ an electron micrograph showing the fairly uniform, clo~ely ~rranged ruffle3 which resulted. The ruffle~ were m~de up of pyramidal crystal faces of the {110~ (rhombic dodecahedrat) crystallDgraphic form.
35 ExamPle 9B
Emulsion ~xample 9B was prepared a~
de~cribed for Exsmple 9A, but with ~rowth modifier ~L~8~33~2 Compound VIII, 4-hydroxy-6-methyl-2-methylthio-1,3,3a,7-tetraazaindene, a known antifoggant ~nd st~bilizer, dissolved in 2mL water and 2 drops of triethylamlne.
S Flgure 26B i5 an electron microgr~ph showing the relatively large and closely arran~ed ruf~les which resulted. The ruffles were made up of pyramidal crystal f~ces of the ~211~ icositetra-hedral crystsllographic form.
10 ExamPle 9C
Emulsion Example 9~ was prepared as described for Example 9A, but with Compound V a~
growth modifier, dissolved in 6mL N,N-dimethylform-amide, 2mL water, and 2 drop~ triethylamine.
Figure 26C is an electron microgrAph showing the uniform closely arranged ruffles which resulted.
The pyramidal crystal faces were consistent wlth the {211} crystal faces expected from usin~ Compound V a~ a growth modifier in the previous examples.
20 ExamPle 9D
Emulsion Example 9D W8S prepared as described for Example 9A, using Compound IX, 5-imino-3-thiourazole, as a growth modifier, dissolved in 2mL N,N-dimethylformamide.
Figure 26D is an electron microgr~ph showing the resulting uniform, closely srranged ruffle~ which resulted. The ruffles were made up of pyramidsl crystAl f~ces of the {110} (rhombic dodecahedral) crystallographic form.
30 ExamPle 9E
To a re~ction vessel ~upplied with a ~tirrer was sdded 0.0667 mole of Host Grain Emulsion 2. This was m1xed with 0.033 mole of a O.OS ~m silver bromide emui~ion, containing 56 g/Ag mole gel~tin and 35 which hsd been precipitated in the presence of 10 millimole/Ag mole of Compound X, 4-hydroxy-6-methyl-1,3,3a,7-tetraszaindene, sodium salt, a known 3~L2 antifoggant and 3tabilizer. The emulsion mixture was made up to 100 g with wster. The pH w~s ad~usted to 6.2 at 40C~ and the pAg to 9.3 at 40C. The mixture WA9 then heated at 60C for 4 hr.
Figure 26E is an electron microgr~ph ~howing the rather large ruEfles whlch resulted. The ruffles were made up of pyramidal cry~tal fsce~ of the {331} tri~octahedral cry~tallographic form.
ExamPlP 1 0 Emul~ion Example 10 illustrate~ the preparstion of a ruffled octahedral silver bromide emul~ion using Compound I as a growth modifier.
To a reaction vessel ~upplied with a ~tirrer was added 0.05 mole of an octahedral regular grain 15 silver bromide emul~ion of mean grain 3ize 1.35 ~m containing 40 g/Ag mole gelatin. Water was added to mske the total wei~ht S0 g. To the emulsion at 40C
w~s added 6.0 millimole/initial Ag mole of Compound I
dl~301ved in 2mL of 1:1 water-methanol. The emul~ion 20 was then held for lS min at 40C. The pH was ad~u~ted to 6.0 at 40C. The temperature was rsised to 60C snd the pAg ad~usted to 8.5 at 60C with KBr and msintained at that value during the precipita-tion. A 2.SM ~olution of AgNO3 was introduced at a 25 constant rete over a period of 40 min while a 2.5M
solution of KBr was added as needed to hold the pAg con~tant~ A total of 0.02 mole Ag was added.
An electron micro~raph of the ruffled grain~
of the resulting emulsion is ~hown in F~gure 27.
30 ExamPle 11 Emulsion Example 11 illustrates ~he preparation of a ruffled octahedral ~ilver bromide emulsion using Compound VII as R growth modifier.
New faces formed indicate that in ~ddition to forming 35 ruffle~ growth of the host 8r~ins into rhombic dodecahedral form has commenced.

~Z~3~3~2 To ~ reaction ve~sel ~upplied with a stirrer was added 0.05 mole of an octahedral regulsr grain silver bromide emulsion of mean grain ~ize 0.8 ~m and containing about 10 g/Ag mole gel~tin. Water wa~
5 added to mske the total weight 50 g. To the emul~ion at 40~C was added 6.0 millimole/initial Ag mole of Compound VII dissolved in 3mL methanol and 3 drop~
triethylsmine. The emul~ion wa~ then held for 15 min at 40C. The temperature was rai3ed to 50C and the 10 pH ad~usted to 6.0 at 50C. The pAg was ad~usted to 8.8 at 50C with KBr and maintained at that value during the precipitation. A 2.OM solution of AgN03 was introduced at a constant rate over a period of 70 min while a 2.OM ~olution of KBr w~s added A~ needed 15 to hold the pAg con3tant. A total of 0.014 mole Ag was added.
An eleotron micrograph of the resultlng emulsion ~rsins is shown in Figure 28. The octahe-dral face~ of the host grsin~ appeared to be 20 uniformly ruffled. In addition, new faces h~ve begun to form along the edges between the octahedral faces, indicating that the crystals are growing ~nto ~110~ rhombic dodecahedrs.
ExamPle 12 Emulsion Example 12 ~llu~trate~ the preparation of a ruffled octahedral silver bromide emulsion using Compound X as growth modifier. A~ the precipitation continued, the form~tion of trisoctshe-dra became evident.
The ho~t emul~ion and procedure wa9 the same as in Example 10. The growth modifier w~s 6.0 millimole/Ag mole of Compound X dissolved $n 3mL of water. For Example 12A the precipitation time wag lS
min, using 0.0075 mole Ag. For Example 12B the 35 precipitation tlme was 30 mln, using 0.015 mole Ag.
Figures 29A and 29B ~re eleotron micrographs showing the resulting emulsion grains of Example~ 12A

~Z~)3~2 and 12B, re~pectively~ In Example 12A uniform ruffle~ formed over the octahedral faces, while new tri30ctshedral faces formed along the edges bPtween the original fsces. In Ex~mple 12B the proces~ of il 5 forming {331} tri~octahedra is slmont complete.
Exsmple 13 Emulsion Example 13 illustrates the D
formation of octahedral silver bromide emul~ions which have their surfsce area incre~ed by ruffles in 10 the form of un$form ridge~.
The ho~t emul~ion and procedure wa5 the ~ame as in Example 10. The growth modifier w~ 2.0 millimole/initial Ag mole of Compound XI, a known green spectral sen~itizing dye, di~olved in 3mL
15 methanol 9 2mL wster and 3 drops of triethylamine.
The precipitation ~olutions were 2.OM rather than 2.5M AgN03 and KBr.

~S\ H ~-- --CH2 H2_i ~ =CH C ~S-~
+
(CH~3S03 Na Compound XI
For Example 13A the precipitation time was 200 min, u~ing 0.04 mole Ag. For Exsmple 13B the time was 350 min, u~ing O.07 mole Ag.
Figure~ 30A and 30B are electron micrographs of the resulting emulsion grains produced by Examples 30 13A and 13B, re~pectively. The face~ ~re uniformly covered with ridge~ running in a direction perpen-dicular to the (110) Ag row3 of the lattlce.
Tri~octahedr~l face~ have begun to form. In Example 13B the ridge~ remain evident 9 while the macro habit 35 has become ~331~ tri~octahedrsl.
Example 14 Ex~mple 14 illustrate~ the preparation of ruffled cubic ~ilver bromide grain~ u~ing Compound . ~ .

~2 80 3~2 XII, 2-mercaptoimidazole as a grow~h modifier.
Continued growth result~ in icositetrahedral grains.
To a resction ve~sel supplied with a ~tirrer wa~ added 0.05 mole of ~ cubic regular grain silver 5 bromide emulsion of mean grsin size 0.8~m, containing about 10 g/Ag mole gel~tin. Water w~
sdded to make the total weight 50 g. To the emul31On at 40C wa~ added 3.0 millimole/A~ mole of Compound XII dissolved in 3mL methanol. The emulsion W8S then 10 held for 15 min ~t 40C. The pH was ad~u~ted to 6.0 at 40C. The temperature was raised to 60C, and the pAg ad~u3ted to 8.5 at 60C with KBr and maintained at that v~lue during the precipit~tion. A 2.5M
solution of AgN03 was ~dded at ~ constant rate over 15 a period of 25 min while a 2.5M solution of KBr was Added 83 needed to hold the pAg constsnt. A total of 0.0125 mole Ag was added to form Example 14A. For Example 14B the precipitation was continued Eor a total of 175 min, using a total of 0.0875 mole Ag.
20 An additional 3 millimole/initial Ag mole of Compound XII was added after 100 min of precipitation time.
Figures 31A and 31B are electron micrcgraphs of the resultlng emulsion grains produced by Example3 14A and 14B, re~pectively. Figure 31A show~ a 25 pattern of growths covering the crystal faces.
Figure 31B illustretes the format~on of {533}
icositetrahedral grains with continued precipit~tion.
ExamPle 15 Example 15 illu~trate~ the preparstion of ~
30 ruffled cubic silver bromide emulsion using Compound VIII under ammoniacal precipit~tion conditions.
To a reaction vessel supplied ~ith ~ 3tlrrer was added 0.05 mole of a cubic regul~r grain silver bromide emul~ion of mean grain slze 0.~ ~m, 35 contsin~ng about 10 g/Ag mole gelatin. An addikion~l 10 g/Ag mole of de~onized bone gelatin was ~dded, and the whole made up to about 51 g with wster. To the 9~8S~3~;2 emulsion at 40C W8S added 6.0 millimole/initial Ag mole of C~mpound VIII di~solved in 3mL of water and 3 drops of triethylamine. The emul~ion Wfl~ then held for 15 min st 40C. Just before the ~tart of 5 precipitstion, l.0 mL of a 3.4M ~olution of (NH4)2S04, 1.75 mL of conc. NH40H and 0.5 mL
of 8 O. SOM solution of KBr were sdded. The pAg w~s found to be 9.1 at 40C, and was maintained ~t that value during the precipitAtion. A 2~5M solutlon of 10 AgN03 waa introduced at a constant rate over a period of 100 min while a 2.5M ~olution of KBr W8S
added QS needed to hold the pAg constAnt. A total of 0.05 mole Ag was sdded.
Figure 32 i~ an electron microgr~ph of the 15 resulting emulsion grains. The cube~ sre somewhat rounded with the cubic face~ covered with uniform ruffles .
ExamPle 16 This example illu~trates an increase in 20 photographic speed which can be realized with ruffled grains sccording to the present invention.
Example Emul~ion 16A
A reaction ves~el equipped with a stirrer was charged ~ith 0.05 mole of an octahedral silv2r 25 bromoiodide emul~ion containing 6 mole % silver iodide, of mesn grain size 0.3 ~m and cont~ining about 20 g/Ag mole gelatin. Water was added to make the total weight 50 g. The emul~ion wa~ heated to 40C. A ~olution was prepared ~.625 millimole of 30 growth modifier Compound V, a blue spectral sen~itiz-ing dye, in a solvent con3isting of 12 m~ water and 10 drop~ of triethylamine m~de up to 50 mL with N,N-dimethylformamide. A 15 mL portion ~f thi~
~olution containing 3.75 millimole/inltial Ag mole of 35 Compound V w~s sdded to the emul~ion, which W8~ then held for 15 minute~ at 40C. The pH was ad~u~ted to 6.0 at 40C. The temperaturP was ra~ed to 60C, and ~ Z 8 ~ 3 the pAg adjusted to 8.5 at 60G with KBr and maintained at that value during the precipitation. A
2.0 M solution of AgN03 was introduced at a constant state over a period of 67 minutes, while a solution which was 1.88 M in KBr and 0.12 M in KI was added as needed to keep the pAg constant. A total of 0.013 mole Ag was added. The resulting emulsion was then centrifuged and resuspended in 40 mL of a 3% deioniæed bone gelatin solution.
Figure 33A is an electron micrograph of the resulting ruffled grain octahedral emulsion.
Control Emulsion 16B
Control Emulsion 16B was prepared as described for Example Emulsion 16A, but without the growth modifier (Compound V) being present during the precipitation. Following precipitation 1.25 millimole of Compound V was added, a typical amount of sensitizing dye for an emulsion of this gra;n size.
Figure 33B is an electron micrograph showing the resulting regular octahedral grains. No ruffling of the grain surfaces is identlfiable.
Control Emulsion 16C
A portion of Control Emulsion 16B was modified after precipitation and before coating by increasing the total content of Compound V to 3.75 millimolejAg mole, which equaled its concentration in Example Emulsion 16A.
Each of:~the emulsions was coated on a cellulose acetate support at 1.18 g/m2 silver and 4.20 g/m2 gelatin. Samples of the coatings were exposed for l/2 second through a graduated tablet to a 365 nm filtered mercury light source to provide a measure o~ intrinsic speed, and to a Wratten 47 filtered tungsten light source to provide blue speed.
Eastman lBTM Sensitometers were used. The exposed samples were developed for 6 minutes at 20C in Kodak RapidTM X-ray Developer. The difference A~

., . . .,.. ~ . .

3~

between blue speed and 365 nm speed waq taken as the messure of the relative degree of spectral sen~itiz~-tion for each of the three coating~ and is tabulaked in in Table V.
TABLE V
Example 16 Sensitometric Result~
Blue SPeed - 365 nm SPeed ~ Relstive EmulsionSPeed Comments 10 16B0 Control, 1.25 mmole Cpd. V/Ag mole 16C+25 Control, 3~75 mmole Cpd. V/Ag mole 16A+SB Example, 3.75 mmole Cpd~ V/Ag mole The d~ta show that Ex~mple Emulsion 16A had a slgnificantly greater blue ~peed relative to its 365 15 nm speed than did the control unruffled Control Emul~ions 16B snd 16C with a normal spectral ~ensitization or with an equal amount of sensitizing dye equal to that of the ruffled grain Example Emul~ion 16A, re~pectivlely.
20 ComParative ExamPle 17 The purpo~e of thi~ comparatlve example is to report the result of ~dding 6-nitrobenzimidazole to a reaction vessel prior to the precipitation o~
silver bromide, a~ ~uggested by Wulff et al U.S.
25 Patent 1,6~6,830.
A reaction vessel equipp~d with e stirrer wa~ charged with 0.75 g of deioni~ed bone gelatin msde up to 50 g with water. 6-Nitroben2imidazole, 16.2 mg (O.3 weight % based on the Ag u~ed), 30 disgolved in lmL of methanol, W8~ added, followed by 0.055 mole of KBr. At 70C 0.05 mole of a 2M
301ution of AgN03 was added at a uniform r~te over a perlod of 25 min. The grain-~ formed were relative-ly thick tablets showing ~ cry~tal faces.
35 There w~s no indic~tion of ruffled cry~tal faces of the invention.

~ Z~ 3~Z

Compsrative ExamPle 18 The purpose of this compsrative example is to report the result of employing 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, ~odium salt during 5 gr~in precipitation, ~g suggested by Smith P~rticle Growth and SusPension, cited above.
TD 100 mL of 8 3~ bone gel~tin solution were added slmultaneou~ly 10 m~ of 1.96 M ~gNO3 and lOmL
of l g6 M KBr at 50C with stirring over a period of lO about 20 sec. The AgBr dispersion wa~ aged for 1 min at 50C, then diluted to 500 mL. The disper~ion wa~
ad~usted to pBr 3 with KBr.
Samples 18a, 18b.
To 80mL of lX10 M KBr containing 0~4 15 mmole/Q of 4-hydroxy-6-methyl-1,3,3a,7-tetr~aza-in~ene, ~odium salt snd 0.6 mmole/Q of l-dodecyl-quinolinium bromide waq added 20 mL of the above dispersion, which was then stirred ~t 23C. Samples were removed after 15 min (Sample 18a~ and 60 min 20 ~Sample 18b).
Samples 18c, 18d Samples 18c and 18d were prepsred similarly a~ Samples 18~ and 18b, re~pectively, except that 0.8 mmole/Q of 4-hydroxy-6-methyl-1,3,3a,7-tetra~za-25 indene and ~.6 mmole/Q of l-dodecylquinolinium bromide were u~ed.
Examination of the grain~ of each of the sample~ revealed rounded cubic gralns. No ruffled crystal faces were ob~erved.
The invention has been described ~n detail with particular reference to preferred embodiments thereof, it will be understood that variation~ and modifications can be effected within the ~pirit-and scope of the invention.

Claims (26)

1. A radiation sensitive emulsion comprised of silver halide grains of a cubic crystal lattice structure having faces ruffled by protrusions which are silver halide crystal lattice extensions from a base plane of a first crystallographic form, silver halide adjacent said base plane, beneath said base plane and in said protrusions, favoring the formation of surfaces of the first crystallographic form, and said protrusions presenting surfaces of a second crystallographic form.

2. A radiation sensitive emulsion according to claim 1 wherein said ruffles present a total surface area at least 50 percent greater than that presented by the base planes on which they are located.

3. A radiation sensitive emulsion according to claim 1 in which said first crystallographic form is a cubic crystallographic form.

4. A radiation sensitive emulsion according to claim 1 in which said first crystallographic form is an octahedral crystallographic form.

5. A radiation sensitive emulsion according to claim 1 in which silver halide adjacent said base plane, beneath said base plane and in said protru-sions, consists essentially of silver bromide optionally additionally containing a minor proportion of iodide.

6. A radiation sensitive emulsion according to claim 1 in which tabular silver halide grains having at least one ruffled major crystal face and a thickness of less than 0.2 µm have an average aspect ratio of greater than 5:1 and account for at least 50 percent of the total projected area of all silver halide grains having at least one ruffled major crystal face.

7. A radiation sensitive emulsion according to claim 1 in which tabular silver halide grains having at least one ruffled major crystal face, a thickness of less than 0.5 µm, and a diameter of at least 0.6 µm have an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of all silver halide grains having at least one ruffled major crystal face.

8. A radiation sensitive emulsion according to claim 1 in which said protrusions include those which are in the form of ridges or pyramids.

9. A radiation sensitive emulsion according to claim 1 in which a growth modifier is adsorbed to said ruffled faces of said silver halide grains.

10. A radiation sensitive emulsion according to claim 9 in which said growth modifier is chosen from the class consisting of 5-carbethoxy-4-hydroxy-1,3,3a,7-tetrazaindene; 3-carboxymethyl-5-(2-pyrrolino-1-cyclopenten-1-ylmethylene)rhodanine;
anhydro-5-chloro-9-ethyl-5'-phenyl-3,3'-di-(3-sulfo-propyl)oxacarbocyanine hydroxide, triethylamine salt;
anhydro-9-ethyl-5,5'-diphenyl-3,3'-di-(3-sulfobutyl)-oxacarbocyanine hydroxide, monosodium salt; 5-(3-ethyl-2-benzothiazolinylidene)-3-.beta.-sulfoethyl-rhodanine; 4-hydroxy-6-methyl-1,2,3a,7-tetraazain-dene; 4-hydroxy-6-methyl-2-methylthio-1,3,3a,7-tetra-azaindene; 5-imino-3-thiourazole; 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene; 3-carboxymethyl-5-{[3-(3-sulfopropyl)-2-thiazolidinylidene]ethyli-dene}rhodanine, sodium salt; 2-mercaptoimidazole;
and anhydro-3,9-diethyl-5,5',6'-trimethoxy-3'-(3-sulfopropyl)thiacarbocyanine hydroxide.

11. A radiation sensitive emulsion comprised of silver halide grains of a cubic crystal lattice structure having ruffled faces characterized in that said faces are ruffled by pyramidal protrusions which are silver halide crystal lattice extensions from a base plane of a first crystallographic form, silver halide adjacent said base plane, beneath said base plane and in said protrusions, favoring the formation of surfaces of the first crystallographic form and consisting essentially of silver bromide optionally containing a minor proportion of iodide, and said pyramidal protrusions presenting surfaces of a second crystallographic form.

12. A radiation sensitive emulsion according to claim 11 in which said pyramidal protrusions exhibit a surface area which is at least 100 percent greater than their base ares.

13. A radiation sensitive emulsion according to claim 11 in which said base plane is of a {111} crystallographic form.

14. A radiation sensitive emulsion according to claim 11 in which tabular silver halide grains having at least one ruffled major crystal face and a thickness of less than 0.2 µm have an average aspect ratio of greater than 5:1 and account for at least 50 percent of the total projected area of all silver halide grains having at least one ruffled major crystal face.

15. A radiation sensitive emulsion according to claim 14 in which tabular silver halide grains having at least one ruffled major crystal face, a thickness of less than 0.2 µm, and a diameter of at least 0.6 µm have an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of all silver halide grains having at least one ruffled major crystal face.

16. A radiation sensitive emulsion according to claim 11 in which at least a portion of said protrusions have pyramidal crystal faces of the {hh?}, {hk0}, {h??}, or {hk?}
crystallographic form, where h, k, and ? are independently in each occurrence unlike integers greater than zero, h is 5 or less and greater than ? and k, when present, is less than h and greater than ?.

17. A radiation sensitive emulsion according to claim 16 in which at least a portion of said protrusions have pyramidal crystal faces of the icositetrahedral form.

18. A radiation sensitive emulsion according to claim 17 in which a growth modifier is adsorbed to said icositetrahedral pyramidal crystal faces chosen from the group consisting of 3-carboxy-methyl-5-(2-pyrrolino-l-cyolopenten-1-ylmethylene)-rhodanine; 5-(3-ethyl-2-benzothiazolinylidene)-3-.beta.-sulfoethylrhodanine; 4-hydroxy-6-methyl-2-methyl-thio-1,3,3a,7-tetraazaindene; and 2-mercaptoimidazole.

19. A radiation sensitive emulsion according to claim 16 in which at least a portion of said protrusions have pyramidal crystal faces of the trisoctahedral form.

20. A radiation sensitive emulsion according to claim 19 in which a 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene growth modifier is adsorbed to said trisoctahedral pyramidal crystal faces.

21. A radiation sensitive emulsion according to claim 16 in which at least a portion of said protrusions have pyramidal crystal faces of the rhombic dodecahedral form.

22. A radiation sensitive emulsion according to claim 21 in which a growth modifier is adsorbed to said rhombic dodecahedral pyramidal crystal faces chosen from the group consisting of 4-hydroxy-6-methyl-1,2,3a,7-tetraazaindene and 5-imino-3-thiourazole.

23. A radiation sensitive emulsion according to claim 16 in which at least a portion of said protrusions have pyramidal crystal faces of the cubic form.

24. A radiation sensitive emulsion according to claim 23 in which a growth modifier is adsorbed to said cubic pyramidal crystal faces chosen from the group consisting of anhydro-5-chloro-9-ethyl-5'-phenyl-3,3'-di-(3-sulfopropyl)oxacarbocyanine hydroxide, triethylamine salt and anhydro-9-ethyl-5,5'-diphenyl-3,3'-di(3-sulfobutyl)oxacarbocyanine hydroxide, monosodium salt.

25. A photographic element containing an emulsion according to claim 1.

26. A photographic element containing an emulsion according to claim 11.