US3819377A - Method of imaging and imaging material - Google Patents

Abstract

In an imaging material, which normally produces upon imaging and development an image of one normal polarity (positive or negative), the trapping level is selectively controlled to produce, upon imaging and development, an image of the opposite polarity. This may be achieved, for instance, by adding a trap former to the imaging material, to produce, after selective activation of the trap former, for instance, by energy, the desired differential of the trapping levels in the image and nonimage areas. Also imaging materials comprising a trap former.

Description

United States Patent 1191 Klose et'al.

[ June 25, 1974 METHOD OF IMAGING AND IMAGING MATERIAL 1 [75] Inventors: Peter M. Klose, Troy; Stanford R.

- Ovshinsky, Bloomfield Hills, both of 21 Appl. No.: 171,104

52 Us. 01. 96/48 R, 96/27 E, 96/48 HD, a 96/59, 96/64 151 1m. (:1. G03c 5/24,.0030 5/04, 603C 5/50 [58] Field of Search 96/88, 48 R, 48 HD, 64,

[56] References Cited UNITED'STATES PATENTS 3,305,359 2/1967 Delmont 96/33 Kaspaul 96/48 R Somg et al. 96/64 Primary Examiner-Ronald H. Smith Assistant Examiner-Richard L. Schilling [5 7] ABSTRACT In an imaging material, which normally produces upon imaging and development an image of one normal polarity (positive or negative), the trapping level is selectively controlled to produce, uponimaging and development, an image of the opposite polarity. This may be achieved, for instance, by adding a trap former to the imaging material, to produce, after selective activation of the trap former, for instance, by energy, the desired differential of the trapping levels in the image and non-image areas.

Also imaging materials comprising a trap former.

36 Claims, 8 Drawing Figures l o o o o o o o 0 o o oo o ooo o o o o o o o 0 6 6 0 o. ooooooooooo o o o o o o .o

030 ooooo-o'o METHOD OF IMAGING AND IMAGING MATERIAL The present invention relates to a new method for recording information and for producing images and to new imaging materials.

The silver halide imaging system is a negative working system. In those areas of the image which are struck by light, a dark precipitate of silver is formed upon development. In order to produce positive images either copies must be made from the negative or the original image must be reversed in the development by the inclusion of a bleaching step, a reversal exposure step and a second development step. Both methods are cumbersome and time consuming. Positive copies may also be produced in the silver halide system by diffusion techniques though also this adds to the cost of the system and usually extends the access time.

The various known non-silver halide imaging systems, which are based on a great variety of chemical reactions. produceeither negative or positive images as is inherent in the particular physical or chemical reaction involved in the system and in the material used in the system. Generally the systems which are not based on the silver halide chemistry, cannot be adapted to a reversal development. It is therefore not possible with these systems to reverse the polarity of the image. The user of a given system has no choice of the polarity of the images which he obtains.

, Imaging systems are selected for a given imaging task on the basis of image quality, performance features, cost and other considerations and often a system, which otherwise would fit all the desired requirements, is not acceptable because it produces images of the wrong polarity. Often'it is also desirable, once a system has been adopted, to produce by one and the same system images of both polarities, i.e., both positive and negative images as may be needed or desired, without adding'costly and time-consuming copying or duplicating steps or reversal steps in the development. As stated, the various commerically used non-silver halide imaging systems do not provide for such choice of polarity. There is therefore a need for an imaging method, which permits change of the polarity of the image produced by a given system without requiring expensive or time-consuming additional steps and without being limited to the silverhalide system. The present invention provides such a new method for producing images of a polarity which is opposite to that normally produced by a given material or system.

In accordance with the invention, an imaging material, which is capable of producing upon exposure to imaging energy alatent image and of producing upon development an actual image of a first or normal polarity, is provided with a trap former to produce, after imaging and development, an image of a polarity which is opposite to the polarity normally produced. Stated more generally, the new method of the invention permits, by selective control of the trapping levels in the imaging material, to produce images of the polarity which is opposite to the one normally produced by a given system.

The term polarity as usedhereinis designating the character or contrast of the image viz. whether the image is positive or negative. It is understood that an image is positive, if the gradient of contrast is under the conditions of detection in the same direction as it was in the imaging energy. Accordingly, in a negative image, the gradient of contrast of the image is opposite to that of the imaging energy.

The new method of the invention is generally applicable to all those imaging materials which are capable of forming a latent image, when they are selectively subjected to imaging energy, and in which the latent image can be developed by suitable developing means to form an actual image, which may be visually detected or which may be detected by other means such as read-out equipment using physical phenomena such as electromagnetic radiation, electrical energy, mechanical means or the like. The formation of the latent image and the development of the actual image may be effected as successive steps or both the imaging and development may be carried out simultaneously in a single step by applying the imaging energy and the means causing development at the same time.

Depending on the nature of the imaging material and the manner in which the contrast in the image is generated, it is also desirable, that the development conditions are such or can be modified to be such that in the development a change takes place in the areas, which have not been subjected to the imaging energy, resulting in a substantial .change of detectable characteristics in these areas. The invention applies to imaging systems, which normally are negative working as well as to systems which are normally positive working.

Using imaging energy, for instance light or other actinic radiation or any other suitable energy as the imaging energy, photons or other energy quanta may be absorbed by the imaging material itself or they may be absorbed by another constituent of the imaging material such as an activator or a senstizer, which transfers the absorbed photon energy to the imaging material. In either case material being in a different energy state is formed inthe areas which have been subjected to the imaging energy. Material is formed by the effects of the imaging energy, which results in a higher or lower energy in the areas, which have been subjected to the imaging energy as compared with the areas which have not been subjected to the imaging energy. These different energy states of material may be in the form of carriers such as electrons or positive or hole carriers, or of free radicals, or the different state may be represented by the fact that an electron is raised by the absorbed photon or other energy to a higher level. Carriers may be represented by broken bonds generated by the breaking of molecular chains or rings and the like such asof chains of selenium atoms. The different energy states may also be represented by ions such as ionized atoms or ionized atom groups or they may be represented by a chemical derivative of a compound which is in a state of higher reactivity than the material surrounding it. In the case of organic compounds, the different state may be represented by a broken chain or by the dangling bond generated by the omission of an atom or of an atom group or by a free radical. Carriers or free radicals or any other material being in a different energy state or having an increased or decreased reactivity may be formed by any desired mechanism as a result of absorption of imaging energy. The foregoing described different or changed energy states may be provided in the imaging material itself or it may be provided in any activator and/or sensitizer or in any other material being present in the imaging layer.

The various forrns of energy states, of radicals, carriers or activated material which forms the latent image and which, by one or another mechanism initiate and bring about a physical or chemical change in the imaging material for producing a change in the detectable characteristics of the imaging material upon development will be referred to herein as energy carriers." It is to be understood, that the term, energy carriers" is broader than the term carrier as it is normally used and that the term energy carriers" includes the materials of different energy states listed hereinbefore including any other energy state which is capable of forming a latent image and causing or preventing the formation of material having changed detectable characteristics to form an actual image upon development.

In the course of the development of one type of the imaged materials useful in the method of the present invention, in normal, conventional operation the energy carriers forming the latent image initiate and make possible a physical or chemical change, as the case may be, to produce a new state of the material having different detectable characteristics from the detectable characteristics of the original imaging material.

Energy carriers can be trapped. Trapping may be the loss or reduction of mobility of the energy carriers, making them incapable of moving to the site where they can exert their effect on the physical or chemical change in the image areas. Trapping may also be the linking up of the energy carrier with another material, which supplies a missing electron, or an energy carrier may take up an otherwise available electron to replace a missing electron thereby changing the energy of the energy carrier making the energy carrier so modified incapable of initiating or causing the physical or chemical change. Similar situations may occur in the case of free radicals. The free radicals may link up with another free radical thereby forming a neutral compound of lower reactivity, making it incapable of initiating or causing the change of detectable characteristics in the imaged areas. Or the free radical may link up with another activated material to form a neutral compound of lower reactivity, which does not initiate the desired change in the imaged areas. Likewise compounds being of higher energy and more reactive may react with another material to form a compound of lower reactivity which is incapable of initiating the changes in the imaged areas. All these and any similar event, which reduces the available energy of an energy carrier, are called herein trapping."

In accordance with the present invention, trapping levels are introduced, preferably to the point that no energy carriers are available for initiation of a physical or chemical change in the areas in which no detectable change is desired. Trapping levels may be increased in various manner, for instance by control of the temperature, by the provision of electrons, for instance, in form of an electric current, or by chemical means. In accordance with the present invention, trapping levels are preferably increased by providing the imaging material with another material which is capable of forming traps for the energy carriers or which is capable of trapping the energy carriers, for instance, in a manner as set out hereinbefore or by any other desired mechanism. The materials added in this manner to the imaging material are usually trap precursors or materials which directly form traps upon the absorption of energy. All these materials are called herein trap formers. The invention provides for the introduction of trapping levels, trap precursors or trap formers of the kind as will be described hereinafter, and which in the state, in which they are introduced to the imaging material, possess only little or no trapping ability. They acquire their capacity of forming a trap only after they have been subjected to energy contained in the imaging energy or to energy which is applied imagewise in a separate step for the purpose of activating the trap former. The activation of the trap former is therefore usually imagewise the same as the formation of the energy carriers generated by the application of the imaging energy. The trap formers are therefore made available in their active or trapping state usually where the imaging energy has been applied. Furthermore, for reasons to be explained hereinafter the trap former is usually applied in a sufficient quantity, such that a substantial excess of traps will be formed over those needed for trapping the energy carriers generated by the imaging energy in the imaged areas.

To produce an image of opposite polarity, it is not only necessary to trap the energy carriers in the areas having received the imaging energy, so as to suppress or prevent the taking place of the physical or chemical change which leads to the formation of the change in detectable characteristics in the imaged areas, but it is also required to generate energy carriers in the areas of the image, which have not received the imaging energy, so as to produce a physical or chemical change in these areas for the production of a change of detectable characteristics in the areas which have not received energy. This can be readily achieved by the application of suitable development conditions. However, development is not imagewise and encompasses all areas, the areas which have not received the imaging energy as well as the areas which have received the imaging energy. Consequently, merely selecting the development conditions which produce energy carriers for the initiation of a physical or a chemical change is non-selective and not imagewise. The changes in detectable characteristics resulting therefrom would extend therefore all over the layer of the imaging material. No image would be produced in this manner.

As stated above, in the preferred embodiment of the method of the invention, the trap former is employed in excess such that a substantially larger number of traps is formed in the imaging step than is needed for trapping the energy carriers formed by the imaging energy. In this manner, an excess of traps is available in the areas which have received imaging energy. When, in the course of development, energy carriers are generated by the development conditions, these energy carriers are trapped in the available excess of traps as soon as they are generated. Therefore, in the areas which have received imaging energy, no energy carriers are and no or only very few energy carriers become available during development, which could initiate or cause a physical or chemical change in the imaging material. Therefore no change in detectable characteristics takes place in the areas which have been subjected to the imaging energy.

On the other hand, in the areas which have not received imaging energy, the trap former is not activated, no traps are formed and the energy carriers generated in these areas remain free and untrapped and can initiate or cause, by the mechanism, normal for the particular imaging material, the physical or chemical change, thus producing a substantial change in the detectable characteristics in the areas which have not received imaging energy. As can be readily seen, in this manner an imaging material which would normally become nonreflective or non-transparent in the areas which have received the maximum imaging energy, and which normally remains reflective or transparent in the areas which have not received imaging energy (negative polarity) reverses its polarity. By the provision of the selectively introduced trapping levels in accordance with the invention, the areas, which have received maximum imaging energy, remain reflective or transparent and the areas which have not received imaging energy become non-reflective or non-transparent. Accordingly, the material has become positive working merely by the selective control and change of the trapping levels.

Of course, for best operability of the method, it is desirable to select a trap former, which does not become activated under the conditions employed for development and the conditions necessary for the generation of the energy carriers in the areas which have not received imaging energy. Or, in other words, the development conditions should be selected, such that generation of energy carriers occurs under these conditions, while the trap former is not activated to form traps under these same conditions. This may, for instance, be achieved by using different energy forms or radiant energy of different wave lengths for imaging and development, as will be exemplified hereinafter.

The selectivity of the'method of the invention in producing images of a polarity which is opposite to normal may also be achieved in another manner. With certain imaging materials, the number of energy carriers which can be generated in a given areas is limited. Accordingly, in the imaging step sufficient imaging energy may be applied, to generate the maximum possible number of energy carriers. At the same time, the increased amount of imaging energy generates traps in sufficient numbers for trapping essentially all the generated energy carriers. 'As before, no energy carriers have been generated in the areas which have not received imaging energy. Therefore, in the development step, energy carriers can be generated in sufficient number in the areas which have not received imaging energy, while no energy carriers are generated by the development conditions in those areas, which have received imaging energy, because the energy carriers precursors responding to the development energy have been exhausted in these areas. In this manner, sufficient energy carriers are available in the areas which have not received the imaging energy, to bring about the physical or chemical change for producing the change in detectable characteristics in these areas. Essentially no energy carriers are generated by the development energy in the areas which have received imaging energy, and essentially no change in the detectable characteristics takes place in these areas. Thus also in this case, the images of opposite polarity are produced.

The method has been described hereinbefore in connection with .a black and white system producing merely reflective or transparent and nonreflective or hereinbefore as separate, successive steps. The method of the invention may also be operated in such manner, that the imaging is effected at development conditions so that imaging and development proceed at the same time.

The generation of the energy carriers may be catalyzed by the presence of catalysts or activators in the imaging materials. Sensitizers may be present, which absorb the employed imaging energy and transfer it to the catalyst or activator materialand/or to the imaging material in a form, in which the imaging layer responds with the formation of energy carriers.

In a similar'manner, catalysts or activators and/or sensitizers may be present in the imaging material which are capable of absorbing imagewise energy and transferring it to the trap former in a form best suited for effective activation of the trap former to form the traps. Generally, it is preferred, that the catalysts, activators, and/or sensitizers favoring the generation of the energy carriers and of the latent images are not the same as'those added for the favoring of the formation of the traps. If different materials are used for these distinct purposes, it is possible to adjust the quantity and kind of these materials to each of these purposes, though sometimes, it is possible to use the same materials for the catalysis of the generation of traps and of the generation of energy carriers. An important consideration'in this respect is, to select and add to the imaging material such catalysts or activators or other materials, which catalyze or favor the generation of the energy carriers under the selected development conditions and which preferably also favor and promote the physical or chemical process leading to the change of the detectable characteristics in the areas, which have not been subjected to imaging energy.

I-Iereinbefore an embodiment of the method of the invention has been described, wherein a trap former is combined with an imaging material to produce images of a polarity which is opposite to that which is normal with the same imaging material. Accordingly, using the imaging material without the trap former, one will obtain images of normal polarity. The method of the invention may' also be modified in such manner, that one and the same material is capable of producing images of either polarity as may be described or needed.

For this embodiment of the invention, one employs an imaging material in combination with a trap former as described before. Preferably, one selects a trap former which is activated by imaging energy of a different kind or of a different wavelength than is required for the generation of the carriers. At the same time one may use different development conditions for produc ing images of either one of the polarities.

To produce images of the normal polarity imaging energy is used, which does not activate the trap formers but which is capable of generating carriers in the areas subjected to the imaging energy. For development one non-transparent areas. The new method is capable of selects the normal developing conditions at which substantially no energy carriers are generated and no physical or chemical changes takes place in the areas which have not received imaging energy. In the case that images of the opposite polarity are desired from the same imaging material imaging energy of a kind or wavelength is used which activates the trap former. In this case development conditions are selected such that energy carriers are generated in the areas which have not received imaging energy to produce a physical or chemical change in these areas resulting in a change of the detectable characteristics.

Thus merely by varying the nature of the imaging energy and the development conditions either a positive or a negative image may be produced at will from one and the same material. With some imaging materialtrap former combinations, it is also possible to merely vary the intensity or time of energy application to either activate the trap formers or not activate them as may be desired for producing either a positive or a negative image from a given imaging material.

Other objects, advantages, and features of the invention will become apparent to those skilled in the art from the following description and claims of the invention and from the attached drawings in which:

FIG. 1 is a schematical, fragmentary sectional representation of a conventional imaging structure being selectively subjected to imaging energy through an opening in a mask and showing the latent image of energy carriers formed by the imaging energy.

FIG. 2 is similar to FIG. 1, showing the structure after development, with the mask removed.

FIG. 3 is a schematical, fragmentary, sectional representation of an imaging structure of the invention containing a trap former and being selectively subjected to energy through an opening in the mask and showing energy carriers formed by the imaging energy trapped.

FIG. 4 is similar to FIG. 3 showing the structure with the mask removed at the beginning of the development step.

FIG. 5 is similar to FIG. 4, showing the structure after completion of the development.

FIG. 6 is an imaging structure of the invention containing a trap former or trap precursor in form of a layer adjoining to a layer of an imaging material.

FIG. 7 is similar to FIG. 6, showing the structure of FIG. 6 being exposed through a mask.

FIG. 8 is similar to FIG. 7, showing the structure of FIG. 7, with the mask removed, as it is developed by heat.

Referring to the drawings, the imaging structure shown in FIG. 1 generally at 10 comprises a substrate 12 and deposited thereon a layer 14 of conventional imaging material. The imaging material in layer 14 may be any desired imaging material which is capable of forming, upon selective exposure to imaging energy, a latent image of energy carriers which upon development produces an actual image in the layer 14. Upon layer 14 is placed a mask 16, having opaque areas 18 and transparent area 20. Imaging energy 22, such as light, is applied through the transparent areas 20 of the mask onto layer 14 of imaging material. The imaging energy 22 generates in the area of layer 14 underlying the transparent area 20 of the mask energy carriers 24, represented in the drawings by small dots. These carriers form in the layer 14 a latent image corresponding to the outline of transparent area 20 of mask 16.

After completion of the exposure of layer 14 to the imaging energy, the mask is removed and the structure 10 subjected to suitable selected development conditions. The energy carriers 24 forming the latent image initiate thereby a physical or chemical change to take place in the layer 14 of imaging material to produce in the area 26 a change in the detectable characteristics as indicated by the large dots 28 in FIG. 2. The areas 30 of layer 14 which were covered by opaque portions 18 of mask 16 during exposure to the imaging energy 22 and in which no energy carriers 24 were generated remain, during development, unaltered and no substantial change of detectable characteristics takes place in area 30. If, for instance, layer 14 was transparent or reflective in the original unexposed structure, and if area 26 has become, during development, opaque or nonreflective, the image represented in FIG. 2 and being the result of the exposure of the original structure, is a negative image. This means, that the imaging material of the structure 10 is negatively working.

In FIG. 3 is shown an imaging structure 36 which comprises substrate 38, extended thereon a layer 40 of imaging material and placed thereon an imaging mask 42 having opaque areas 44 and transparent area 46. The layer 40 of imaging material comprises the same, negatively working imaging material as was used in layer 14 of FIG. 1, however in layer 40 there is admixed to the imaging material a trap former (not shown) as described hereinbefore. The trap former, as contained in layer 40 is inert and has as such no effect on the imaging material. When imaging energy 48, for instance light or other electromagnetic radiation, strikes the layer 40 through the transparent area 46 of mask 42, energy carriers 50 are generated as described before in connection with FIG. 1. At the same time, the imaging energy 48 comprises a component which selectively activates the trap former admixed with the imaging material, generating traps 52 for the carriers. The energy carriers 50 are, as before, represented in the drawings by small dots, the traps 52 are represented by circles. As the energy carriers 50 and the traps 52 are formed, the carriers 50 are trapped in the traps 52. This is indicated in the drawings by placing the small dots representing a carrier inside the ring representing the trap. The trap former is used in such concentration and selected for its ability to be activated by a component of the imaging energy 48 and in such manner than an excess of the number traps 52 over the number carriers 50 is generated at a given exposure time. This is indicated in FIG. 3 by the representation of rings 54, which do not contain a dot, i.e., these are available or empty traps.

After removal of mask 42, the structure 36 is subjected to development conditions. The development conditions are selected such that energy carriers 56 are generated in layer 40 (FIG. 4). The carriers 56 form under these conditions in the areas 58, which have not received imaging energy 48 as well as in area 60, which has received imaging energy 48, and which already contains the trap-energy carrier combination 50-52 and the empty traps 54. As the energy carriers 56 are formed by the development conditions in area 60, the energy carriers are trapped in traps 54. In areas 58, containing no traps, the energy carriers 56 are not trapped and initiate under the development conditions a physical or chemical change in the material producing material 62 of altered detectable characteristics in areas 58 (FIG. 5). The imaging material in area 60 of layer 40, has, because of the trapping of the generated energy carriers 56, not undergone any physical or chemical change, so that the detectable characteristics of the imaging material in area 60 are essentially unchanged and identical to those of the original material. If the layer 40 in its original state, prior to exposure, was transparent or reflective, and the imaging material in area 58 has become by the development opaque or non-reflective, a positive image has been produced.

This means, the structure 36 is positive working. The basic imaging material used therein is originally negative working as demonstrated in FIGS. 1 and 2. The addition of the trap former has therefore resulted in a reversal of the polarity.

When the negative image was produced according to FIGS. 1 and 2, development conditions were selected such, that substantially no energy carriers were generated in areas 30, i.e., in the areas which have not received imaging energy. In other words, development in this instance is carried out under normal conditions as they have been established for the particular material.

When the positive image was produced according to FIGS. 3 to 5, using the same basic imaging material as was used in accordance with FIGS. 1 and 2 with the addition of the trap former, the development conditions were modified in such manner that energy carriers were generated in areas 58, i.e., in the areas which have not received imaging energy. The manner, in which the development conditions may be changed in order to produce energy carriers in the dark areas 58 depends on the nature of the development system. In the case of heat development, generally slight to modest increase of the development temperature, and/or increase of the development time produce the desired effeet. In the case of development by radiant energy, increase of the intensity, change of wave length and/or increase of the length of the development may produce the desired effect. The use of additives or other means may produce'the desired effect. If chemical developers are used, increase of the development temperature and/or extension of the development-time and/or the use of a different development agent or adjustment of the development medium, for example of the pH, change of buffering, or the use of additives or other means can be used to produce the desired effect. In other methods of development, corresponding changes may be made as is appropriate for the particular imaging materials used.

The embodiment of the method of the invention, wherein a negative working imaging material may be used to produce either negative or positive images, as illustrated in FIGS. 1 to 5, will be exemplified by way ofan elemento-organic imaging material. In US. Pat. application Ser. No. 163,891 filed July 19, 1971 by Yew C. Chang, Stanford R. Ovshinsky and Werner W. Buechner are disclosed new elemento-organic imaging materials, which can be readily adapted for the purposes of the present invention permitting the production of positive and negative images from the same imaging material solely by the selective control of trapping levels. Special reference is herewith made to said application Ser. No. 163,891 and the disclosure thereof is herewith made part of the present application.

In one embodiment of the method disclosed and claimed in said Application Ser. No. 163,891 an imaging layer containing an elementoorganic imaging compound is selectivelysubjected to imaging energy to produce upon heat development an image as a result of a chemical reaction in which theinorganic element, for instance tellurium or a metal is precipitated in its elementary form as the image former. This embodiment of the method works negative, i.e., this type of elementoorganic imaging material is a negatively working imaging material.

Using as an example the compound (I) the following results will be obtained, if the compound is used in layer 16 of FIG. 1 and layer 40 of FIG. 3 as the imaging material, respectively.

For normal operation the compound (I) was incorporated in a binder of for instance, cyano ethylated starch together with acetophenone as a catalyst and acetone as a solvent in a manner as is described in said application Ser. No. 163,891. The mixture was applied in form of a thin layer onto a glass substrate and was air dried to result in structure 10 of FIG. 1. After exposure to the radiation generated by a xenon electronic flashgun and through a mask of transparent and non-transparent areas, and after a heat development, a negative duplicate of the image represented by the mask was obtained.

The experiment was repeated using the same materials except that dimethylformamide was substituted as the solvent for the acetone. The mixture was spread out in form of a thin layer on a glass substrate as described before, except that the film was only partially dried, leaving a considerable residue of dimethylformamide in the layer to represent the structure 40 in F IG. 3. After exposure to radiation through a mask as described before and after heat development at essentially the same temperature, a positive duplicate of the image represented by the mask was obtained in the manner illustrated in and described in connection with FIGS. 3 to 5. This shows, that the compound (1) representing an imaging material which normally produces negative images, can produce positive images by the addition of a trap former. The only essential difference between the first and the second experiment was, that the layer 40 used in the second experiment contained during the exposure by the same energy source a relatively small amount of dimethyl formamide which served as the trap former. Upon exposure to the radiation traps were selectively formed and the energy carriers formed in the illuminated areas by the radiation were trapped.

When the second experiment was repeated, using dimethyl formamide as the solvent but removing prior to exposure substantially all of the dimethyl formamide, a negative image was obtained as described in the first experiment.

The temperature used for development in all three experiments was essentially the same. It would be expected that a higher temperature should be necessary for the generation of energy carriers or radicals by thermal means in the areas which have not been exposed to the radiation. It is believed that the dimethyl formamide which was present in the non-illuminated areas, served as a plasticizer thereby facilitating not only the generation of energy carriers or radicals by thermal means but also facilitating thermal nucleation by giving greater mobility to the generated energy carriers and to the molecules of compound (1) and/or to the various reaction products and intermediaries occurring in the reaction leading from the compound (I) to the precipitation of crystallites of tellurium. Thus, in effect, the presence of the excess of dimethyl formamide in the areas which have not been subjected to the radiation has the same effect as would otherwise have the increase of the development temperature. This effect is offset in the illuminated areas by the presence of a sufficiently large excess of traps, which immediately trap the energy carriers or radicals as they are formed during the heat development and therefore prevent thermal nucleation and formation of a tellurium precipitate in the illuminated areas.

The need for an excess of traps in the illuminated areas was demonstrated by another experiment, wherein an intermediary substantially lower content of dimethyl formamide was used under conditions similar to those in the second experiment. The reduction of the amount of dimethyl formamide and thus of the traps caused the precipitation of tellurium in both the illumi nated and non-illuminated areas so that no distinct image was formed, even though the development temperature was essentially the same as used in the first three experiments.

The method of the invention may be operated in similar manners with any of the other elemento-organic imaging materials taught and claimed in said application Ser. No. l63,89l.

The method of the invention may also be used to produce negative images with an imaging material which normally produces positive images. This embodiment of the method will be demonstrated and exemplified by way of an inorganic imaging system.

A structure was prepared as shown at 10 in FIG. 1 of the drawing using as the layer 14 an amorphous material which consisted of about 95 atomic percent selenium and about atomic percent sulfur. The layer was about 0.5 micron thick. When the structure was imaged and heat developed as described in conjunction with FIGS. 1 and 2 using the conditions nonnally applied for this type of material an image was obtained which consisted of crystalline material in area 26 and of essentially amorphous material in areas 30 (FIG. 2). The imaging proceeds by a mechanism in which carriers are generated, which form nucleation centers serving as the sites for crystallization in a manner as generally described in conjunction with FIGS. 1 and 2. The crystalline material in area 26 scatters light more efficiently than the amorphous material in area 30, so that the image upon reflection viewing is positive.

ln an example demonstrating the reversal of the polarity of the just described selenium-containing imaging system by the use of trapping levels, a structure was prepared as shown generally at 70 in FIG. 6. The structure comprises a substrate, for instance, of glass or plastic such as Mylar, a thin layer 74 of copper extended on the substrate 72 and a layer of the above described selenium composition comprising about 95 atomic percent selenium and about 5 atomic percent sulfur. The layer 74 of copper, serving as the trap precursor, may be for instance from 0.01 to 0.1 micron thick and the layer of the selenium composition may be about 0.5 micron thick. As shown in FIG. 7, a mask 78, having opaque areas 80 and transparent areas 82 was placed onto structure 70 in contact with the layer 76 of the selenium composition. The structure 70 was thereafter exposed to a 60 joule flash of an electronic xenon flashgun as indicated in FIG. 7 by arrows 84. Carriers 86, generated, for instance, as hole-electron pairs by the breaking of bonds in selenium chains or rings, are formed primarily at the interface of layers 74 and 76. The carriers 86 are indicated as before by small dots in the drawings. At the same time, certain energy components of the flashgun activated by the copper layer 74 to form directly or indirectly, as will be explained hereinafter, traps 88 primarily at the interface between layers 74 and 76. Traps 88 trapped the carriers 86 as indicated in FIG. 7 by placing the dots 86 representing the carriers into the partial circle 88 representing traps. Under the imaging conditions, a great excess of traps 90 is formed, which traps 90 are empty and do not contain any carriers. These empty traps 90 may be formed at and stay primarily at the interface between layer 74 and 76, or they may under the effect of the flash energy, migrate into the interior of layer 76 as shown.

The mask was thereafter removed and structure 70 was heated by heat source 92 and heat radiation 94 to about 120 C. for about 1 minute. The selenium composition crystallized in areas 96 to form the characteristic selenium crystals 98, while essentially no crystallization occured in illuminated area 100. A negative image of highly reflective areas 96 and'of a substantially amorphous surface in area 100 of low reflectivity was formed. Areas 96 had not received the imaging energy of the flashgun. The crystallization in the nonilluminated areas is thermally initiated and proceeds by this mechanism. Thermally generated carriers form nucleation centers serving as the growth sites for the crystallites. in the illuminated area, the carriers 86 formed by the radiant energy are trapped in traps 88 and any thermally generated carriers 91 are trapped in the empty traps 90.

As stated hereinbefore, it is also possible that the strong illumination 84 has exhausted all thermally excitable carriers by light excitation, placing them into the traps already in the illumination step. In this instance, no more carriers can be thermally generated in the illuminated area during the heat development, because the material has been exhausted of thermally excitable carriers.

Metallic copper, as it was laid down in layer 74, is not believed to be in itself the trap former. The metallic copper may form at the interface with the selenium and sulfur containing layer the respective selenide and/or sulfide molecules which may serve as the trap formers. When the layer is exposed to the imaging energy, the copper selenide and/or sulfur molecules become activated forming the traps, which may be represented by, for instance, copper ions. Additional quantities of copper selenide and/or sulfides may form under the effect of the imaging energy to form instantaneously additional quantities of traps. Therefore the deposited copper may be merely a trap precursor. It is, however, also possible that the copper is the trap former by the fact, that under the effect of the illumination copper diffuses into the layer of the selenium composition to directly form the traps. The copper layer itself may also directly serve as the traps after it has been activated. It may trap the carriers which are in the case of selenium holeelectron pairs and which may attach themselves to the copper layer thus becoming unable to move to the crystallization sites. Thus, the copper layer selectively provides directly or indirectly suitable trapping levels to keep the carriers trapped for sufficiently long times to prevent them from forming nucleation centers and crystallization sites. The invention is not limited in any way to any particular theory of the trap formation.

lt is also possible to admix the copper to the selenium composition instead of depositing it as a separate layer.

take place, as has been described above.

Other trap formers or trap precursors such as arsenic may be used, which may likewise be deposited as an intermediary layer in contact with the layer of selenium imaging material or which'may be admixed to the selenium material in the layer. If desired, a silver catalyst layer may be deposited between the copper layer 74 and the layer76 of the selenium composition. The silver exerts in this case a catalytic effect, without inhibiting or preventing the effect of the copper layer as to its ability of selectively controlling trapping levels.

If silver is admixed to the selenium imaging material in small percentages of up to about 6 to 10 atomic percent depending on the composition of selenium layer, it acts as a catalyst, promoting the crystallization and making possible lower illumination levels and shorter development times without reversal of the polarity of the image. If silver is admixed to the selenium composition in higher percentages of, for instance, 10 to or more atomic percent, it acts as a trap former or trap precursor, making possible reversal of the polarity of the image and the forming of negative images in accordance with the method of the invention as described hereinbefore in connection with the use of copper.

It is important in the method of the invention, that the imaging energy contain a component which is capable of activating the trap formers and that it is applied in'such way and at such energy level and in such amount, that the carriers responsible for crystal growth are predominantly trapped in the illuminated areas. It is furthermore important, that the traps are deep enough so as to prevent that the energy employed in the development step such as heat, raise the carriers out of the traps.

The first requirement is demonstrated by an experiment, in which the structure described in connection with FIG. 6 and comprising the copper layer and the selenium composition was exposed to light of about 1,000 foot candles from an incandescent lamp at about 120C. with a development of seconds. Under these conditions a positive image was obtained instead of the negative image described in connection with FIG. 7. Thus under these light conditions, the trap former (coper or copper derivatives) was not activated to form traps or the traps formed under these conditions are not deep enough to hold the carriers under development conditions. More nuclei were formed in the illuminated area than in the non-illuminated areas, and crystallization proceeded much more rapidly in the illuminated areas than in the non-illuminated areas.

The second requirement is demonstrated by an experiment in which a structure as described in FIG. l was used in which the layer 14 consisted of a composition of 75 atomic parts selenium and 25 atomic parts silver, Le, a composition high in silver content as vmentioned hereinbefore. The structure was subjected to the light of an incandescent light source providing about 1,000 foot candles illumination, while it was simultaneously heated. When the heating was effected at I provides sufficient energy, which permits the carriers to leave the traps allowing them to contribute to the growth of the crystallites in the usual way by light-- enhanced crystal growth. At the lower development temperature of C. the heat energy is not sufficient to raise the carriers from the traps. The carriers remain trapped and the negative imaging process proceeds in the manner as described in connection with FIGS. 6 to 8. At some temperature intermediary between 100 and C. no contrast and no image is obtained with the selenium composition used for this experiment. With other imaging systems, the trapping levels differ and usually, the traps are deep enough so that the development energy does not free the energy carriers. The foregoing experiments show, that it is sometimes possible to obtain with an imaging material containing a trap former an image of normal or of reversed polarity, solely by varying the developing energy.

Hereinbefore has been demonstrated, that trapping levels can be controlled and changed in such manner, that an image of reversed polarity is obtained by varying among others the intensity and/or the nature of the imaging energy and/or by varying the intensity of the development energy. Trapping levelsand thereby the polarity of the image can also be controlled and varied by a pre-treatment given to the imaging material prior to the application of the imaging energy. The following examples demonstrate the effect of a thermal pretreatment of an inorganic imaging material comprising a selenium composition.

Four samples I to IV of a structure as shown in FIG. 3 were prepared, wherein the substrate 38 was glass and the layer 40 of imaging material was a 0.5 micron thick layer of a composition of 94 atomic parts selenium, 5 atomic parts sulfur and 1 atomic part arsenic. The arsenic serves as the trap former as explained hereinabove.

Each of the samples I to IV was exposed at room temperature to a 2 millisecond flash from a 60 joule electronic xenon flashgun. All samples were developed identically in the dark at a temperature of C., so that exposure and development of all samples were the same. However, each of the samples I to IV was given a different pre-treatment prior to the exposure to the flash of the flashgun. Sample I received no thermal pretreatment. Upon flashing and development as stated above, a negative image was obtained as expected in accordance with the teaching of the present invention. Sample II was preheated by placing it for 10 seconds onto a hotplate heated to 130C. After flashing and development as described above, a negative image was obtainedas in Sample I. This shows, that the short time of preheating (a certain time is required to bring the sample to the preheat temperature) did not change the trapping levels. No change in the polarity was effected by the very short preheating treatment.

Sample III was placed on the aforementioned hotplate for 20 seconds. After flashing and development in the above described manner, a positive image was obtained. The thermal pre-treatment of somewhat longer time initiated thermal nucleation and generation of crystallization sites, thereby changing the trapping levels and causing the crystallization to proceed in normal manner, i.e., the effect of the trap formers is eliminated and no essential trapping of carriers occurs.

Sampel IV was placed on the aforementioned hotplate for 30 seconds. After flashing and development in the above described manner, a negative image was obtained. Sample lV therefore produced a reversed image as expected in accordance with the teaching of the invention. Trapping levels are high and traps generated by the arsenic are effective in trapping the carriers genereated by the light and by thermal energy in the illuminated areas.

With other imaging materials, trapping levels may be readily controlled in a similar manner, for instance by subjecting the material to a brief pre-exposure to specific energy forms, such as electromagnetic radiation of a certain wavelength and intensity for an optimum length of time and so forth. In similar manner, a brief pre-treatment with chemicals such as in vapor form or in liquid or in dissolved form may readily affect trappping levels in a given imaging material. In this manner it is possible to make a choice with these imaging materials of whether a positive or a negative image is produced. This may be simply achieved by giving the material a short pre-exposure or briefly contacting the material with a chemical material without the need for altering the exposure and/or development conditions. Of course, with other imaging materials the choice of the polarity of the produced image may be determined by varying the exposure and/or development conditions as has been set out and demonstrated hereinbefore.

The trapping levels may also be controlled by purely physical means without the addition of a trap former. So, for instance, may the polarity of an image in a selenium composition or other imaging material be controlled by the selective application of an electric current which may have the effect of trapping carriers or of generating carriers, so that in effect a reversal of the polarity of the image from its normal polarity may also be effected in this manner.

The operation of the method of the invention has been demonstrated hereinbefore by way of example with elemento-organic imaging materials and with selenium-type imaging materials. The method may be used in similar manner with any other suitable imaging material in which in the imaging process a latent image is formed by energy carriers, which is thereafter developed by suitable development means. Suitable imaging materials include the so-called memory materials which under the effect of imaging energy and development energy produce a physical change in structure to produce a change in detectable characteristics. These materials which may be inorganic or organic are described and their application is taught, for instance, in US. Patent 3,530,441 issued on Sept. 22, 1970, to S. R. Ovshinsky and in copending application Ser. No. 143,781 filed on May 17, 1971 by Robert W. Hallman and Stanford R. Ovshinsky. Special reference is herewith made to this patent and to this application and the disclosure thereof is herewith incorporated into the present application. Examples of suitable memory materials, useful in the present invention include besides the materials mentioned in the said patent and patent application various other selenium-containing compositions including a large variety of metal selenides, such as cadmium selenides. Other materials useful in the method of the present invention include various sulfides such as cadmium sulfide, arsenic trisulfide and arsenic pentasulfide. Generally preferred are those memory materials which have an energy gap of at least about 1 eV.

Other suitable imaging materials which may be used in the method of the invention are the hereinbefore described elemento-organic imaging materials as well as any other suitable organic or inorganic imaging materials, in which the image forming mechanism involves the formation of energy carriers which are capable of being trapped in accordance with the method of the invention.

A wide variety of trap formers may be used in the practice of the invention. Generally one will select the trap former most suited to provide upon activation the most effective traps. As has been set out hereinbefore, the energy carriers may have a variety of forms. The traps become effective by either lowering the mobility of the energy carrier or by deactivating them, for instance, by releasing the excess absorbed energy or by absorbing the excess absorbed energy. This may be achieved by electrical neutralization with the release of the energy, for instance, in form of heat, by attachment of carriers to reduce their mobility, by chemical reaction to form a more stable and less reactive compound and so forth. In each of these instances one will select a trap former which is most adapted to achieve the trapping event in the most effective manner. Of course, as explained hereinbefore, the trap former should also be capable of being selectively activated to form the desired active traps in the desired areas. As stated, the term trap former as used herein includes also materials which do not directly form the traps upon activation by the energy, but which by one mechanism or another provide at least one constituent which eventually is part of the trapping mechanism. These materials include the hereinbefore mentioned trap precursors and it is understood that these materials fall under the meaning of the term trap former.

The method of the invention has been described hereinbefore as requiring a trap former, which upon activation by energy produces traps. The invention includes also the opposite situation, where an active material is added to the imaging material, which is capable of serving as the active traps. When layers of imaging material containing these active traps are selectively subjected to imaging energy, the traps in the areas receiving the energy are deactivated and become ineffective as traps.

The method of the invention is predicated on the concept of controlling in an imaging material the trapping levels. Oftentimes, two different energy forms are used, one for imaging and one for development. The trapping levels are not only determined by the ability of an imaging material of trapping the energy carriers generated in the imaging step by the imaging energy, but it is also desirable that an excess of traps is available for trapping the energy carriers generated by the development energy. This means also, that the trap should be sufficiently deep to prevent that the trapped energy carriers are released under the effect of the development energy. On the other hand the traps should not be too deep so as to prevent that the imaging energy can put the carriers into the trap. In reference to the above recited effects generated by the presence of the traps, this means that the new state of the matter achieved by the trapping of the energy carriers or the deenergized form of the energy carriers is either irreversible or requires for its reversal a higher level of energy than is provided by the development energy. Or, in other words, the development energy should be of a lower in- 17 tensityor energy level, than is required for the lifting of the carrier from the trap.

So, for instance in the case, that the trapping is represented by a chemical reaction the bond fonnation requires a certain amount of energy to form a less reactive compound. The energy required therefore may be provided by the imaging energy, for instance, by an absorbed photon. Usually, a certain higher energy being 'at a levelhigher than is supplied by the development Any desired imagingenergymay be used as has been established to be most beneficial for a given imaging required for the activation of the trap former is present in the imaging energy oris supplied ina separate imaging. step in sufficientamount. Preferred is generally electromagnetic radiation including actinic radiation, i.e., such radiation which-is capable ofinitiating a photographic effect inan imaging material. Other imaging energy including chemical energy,,heat', electric'currents, and sometimes mechanicalenergy may be used provided'they canbe applied-selectively and imagewise to the imaging material: The development energy useful in the methodof. the invention will generally be the same as that used for the particular selected imaging material for normal operation, though sometimes, as explained hereinbefore, the use of a different type of energy or the use of different levels of the samedevelopment energy may be beneficial. Development energy may include chemical energy, i.e., the energy provided inform of the reactivity of a chemical compound with the imaging material. Further included areheat, electro'magnetic energy, particle energy, electricalenergy,

mechanical energy and so forth. Generally preferred is heat because heat can be readily controlled as .to its temperature and to the length of application to produce the greatest benefits in accordance with the method of the invention-Heat is generally also inexpensive and available from inexpensive equipment, providing rapid access to the finished image.

The method of the invention is useful for producing any kind of a record of retrievable information including images. Examples are photographic images produced in the camera, duplicates of images produced by projection or by contact printing as well as any other type of images including those produced by laser energy. The record of information produced by the methodof the invention may be detected by visual inspection or "by read-out meansor read-out equipment using any desired manner and means of read-out most suitable for a given imaging material.

Hereinbefore, the methodof the invention has been described in an embodiment, in which at least some energy carriers are generated by the imaging energy, which are thereafter trappedimagewise by the activated traps. It is also possible, to use imaging energy,

which merely consistsv of a form of energy, which activates the trap former in the areas, subjected to the imaging energy, and which does not generate'energy car-. riers in these areas. Also inthis case, the empty trapsformed in the areas having received the imagingenergy will trap any energy carriers formedby the development energy in these areas. Here againit is possible to use one and the same imaging material containing a trap former to produce at will images of either polarity merely by selectingfor the imaging a type of energy (such as selected wavelengths in. case cse of electro magnetic radiation) which will either activate the energy carriers for normal operation or which will activate the trap formers for reversed operationin accordance with the invention.

Numerous'other modifications may be made tovarious forms of the invention described hereinwithout de parting from the spirit and scope of the invention.

We claim:

1. A methodfor producing a recordof retrievable information comprising:

the step of providing a layer comprising an imaging material which normally, uponselective imagewise exposure to imaging energy anduponsubjection to development conditions generates carriers and produces an-image of one polarity, and incontactwith the imaging materialatrap formerv whichis capable of forming traps for thecarriers inthe imaging material,

the step of selectively subjecting saidlayer comprising the imaging material andsaid trap former imagewiseto imaging energy for controlling image wise the trapping level in said imaging material to trap the carriers in the area subjected tothe imaging energy, and v the step of subjecting the imaged layer of imaging material to development conditions,

thereby producing in said layer comprising the imaging material an image which has the oppositepolarity of said one normal polarity.

2. The method of claim 1, in which said imaging ma.- terial is one which is capable of producing upon the selective imagewise exposure to imaging energy a latent image comprising energy carriers, and in which. said. trapping level in said imaging material is substantially increased, thereby trapping in those areas of the layer, whichhave received the imaging energy, the energy carriers generated by said imaging energy.

3. The method of claim 2, in which additionalenergy carriers are generated, when the layer of imaging material is subjected to development conditions, and

wherein the trapping level is increased. sufficiently to.

trap also the energy carriers generated by the development conditions in the areas which have receivedimaging energy, while the trapping levelin the areas which have not received imaging energy is maintained. at a low level such that the energy carriers. generated in these areas by the development conditions aresubstantially not trapped, thereby contributing during development to the formation of a detectable change in the areas which have not received imaging energy.

4. The method of claim 2, in which additional energy is non-imagewise applied to said layer to generate in said layer additional energy carriers, which are capable of selectively initiating under development conditions the change of at least one detectable characteristic in the areas of the layer which have not received imaging energy.

5. The method of claim 4, in which said additional energy is applied in a separate step.

6. The method of claim 5, in which said additional energy is applied subsequent to the imagewise application of the imaging energy.

7. The method of claim 1, in which said layer of said imaging material is selectively and imagewise subjected to electromagnetic radiation.

8. The method of claim 1, in which the step of controlling the trapping level includes the imagewise application to said layer of energy, which is capable of controlling said trapping level.

9. The method of claim 8, in which said energy controlling the trapping level and said imaging energy are applied simultaneously.

10. The method of claim 1, in which said layer of said imaging material is selectively and imagewise subjected to actinic radiation.

11. The method of claim 1, in which said imaged layer is subjected to heat energy, thereby producing a change of detectable characteristics in the areas of the layer which have not received said imaging energy.

12. The method of claim 11, in which the heat is applied at a temperature which is higher than the temperature required for development when an image of said normal one polarity is produced without the step of controlling said trapping level.

13. A method for producing a record of retrievable information comprising:

the step of 'providing' a layer comprising an imaging material which normally, upon selective imagewise exposure to imaging energy is capable of forming a latent image of energy carriers and which normally, upon subjection to development conditions, produces an image of one polarity,

the step of providing in contact with said imaging material a trap former which is capable of forming, upon the application of energy, traps for said energy carriers,

the step of selectively subjecting selected areas of said layer comprising the imaging material to imaging energy and to energy which activates said trap former to form traps in said selected areas,

the step of subjecting the imaged layer of imaging materials to development conditions,

thereby producing in said layer comprising the imaging material an image which has the opposite polarity of said one normal polarity.

14. The method of claim 13, in which the layer comprising the imaging material is selectively and imagewise subjected to imaging energy, which comprises a component which is capable of activating said trap former to form imagewise traps in said layer.

15. The method of claim 13, in which an excess of traps is formed, thereby trapping in said selected areas which have received said imaging energy the energy carriers which are generated in these areas by the imaging energy and the energy carriers which are generated in these areas under the development conditions.

16. The method of claim 13, in which said trap former is admixed to said imaging material.

17. The method of claim 13, in which a layer of imaging material is provided, which comprises an elementoorganic imaging material.

18. The method of claim 13, in which said energy capable of activating said trap former is selectively applied imagewise in a separate step.

19. The method of claim 18, in which a trap former is provided which is an organic material.

20. The method of claim 13, in which said development conditions comprise the application of heat to said layer comprising an imaging material.

21. The method of claim 20, in which said heat is applied simultaneously with the application of said imaging energy.

22. A method for producing a record of retrievable information, which method comprises:

the step of providing a structure comprising a layer of a memory material, which is capable of generating, upon the application of energy, carriers, which cause a physical change in structure of said memory material between at least two conditions, and in contact with said memory material a trap former which is capable, upon the application of energy, to form traps for said carriers,

the step of selectively applying to selected areas of said layer of memory material and to said trap former imaging energy of such intensity and pulse lengththat said trap formers become activated to fonn traps, whereby the carriers generated in said selected areas are trapped in said traps, and

the step of applying development energy to said structure, thereby causing a physical change in structure in those areas of said layer of memory material, which have not been subjected to said imaging energy, and producing essentially no physical change in structure in those areas of the layer of memory material, which have been subjected to said imaging energy.

23. The method of claim 22, in which a memory material is provided in said layer in which the energy gap difference between said conditions is at least about 1 electron volt.

24. The method of claim 22, in which one of said conditions of said memory material is an amorphous state and the other of said conditions is a crystalline state.

25. The method of claim 22, in which a memory material is provided in said layer, which comprises selenium.

26. The method of claim 22, in which a memory material is provided in said layer, which comprises selenium and sulfur.

27. The method of claim 22, in which a memory material is provided in said layer, which comprises a metal selenide.

28. The method of claim 22, in which a memory material is provided in said layer, which comprises a metal sulfide.

29. The method of claim 22, in which heat is applied as the development energy.

30. The method of claim 22, in which heat is applied simultaneously with the application of the imaging energy.

31. The method of claim 22, in which electromagnetic radiation is imagewise applied as the imaging energy.

32. The method of claim 22, in which the trap fonner is admixed to the memory material.

vided as said trap former.

36. The method of claim 22, in which silver in an amount exceeding about 10 atomic percent is admixed to the memory material thereby serving as the trap former.

Claims (35)

1. 2. The method of claim 1, in which said imaging material is one which is capable of producing upon the selective imagewise exposure to imaging energy a latent image comprising energy carriers, and in which said trapping level in said imaging material is substantially increased, thereby trapping in those areas of the layer, which have received the imaging energy, the energy carriers generated by said imaging energy.
2. 3. The method of claim 2, in which additional energy carriers are generated, when the layer of imaging material is subjected to development conditions, and wherein the trapping level is increased sufficiently to trap also the energy carriers generated by the development conditions in the areas which have received imaging energy, while the trapping level in the areas which have not received imaging energy is maintained at a low level such that the energy carriers generated in these areas by the development conditions are substantially not trapped, thereby contributing during development to the formation of a detectable change in the areas which have not received imaging energy.
3. 4. The method of claim 2, in which additional energy is non-imagewise applied to said layer to generate in said layer additional energy carriers, which are capable of selectively initiating under development conditions the change of at least one detectable characteristic in the areas of the layer which have Not received imaging energy.
4. 5. The method of claim 4, in which said additional energy is applied in a separate step.
5. 6. The method of claim 5, in which said additional energy is applied subsequent to the imagewise application of the imaging energy.
6. 7. The method of claim 1, in which said layer of said imaging material is selectively and imagewise subjected to electromagnetic radiation.
7. 8. The method of claim 1, in which the step of controlling the trapping level includes the imagewise application to said layer of energy, which is capable of controlling said trapping level.
8. 9. The method of claim 8, in which said energy controlling the trapping level and said imaging energy are applied simultaneously.
9. 10. The method of claim 1, in which said layer of said imaging material is selectively and imagewise subjected to actinic radiation.
10. 11. The method of claim 1, in which said imaged layer is subjected to heat energy, thereby producing a change of detectable characteristics in the areas of the layer which have not received said imaging energy.
11. 12. The method of claim 11, in which the heat is applied at a temperature which is higher than the temperature required for development when an image of said normal one polarity is produced without the step of controlling said trapping level.
12. 13. A method for producing a record of retrievable information comprising: the step of providing a layer comprising an imaging material which normally, upon selective imagewise exposure to imaging energy is capable of forming a latent image of energy carriers and which normally, upon subjection to development conditions, produces an image of one polarity, the step of providing in contact with said imaging material a trap former which is capable of forming, upon the application of energy, traps for said energy carriers, the step of selectively subjecting selected areas of said layer comprising the imaging material to imaging energy and to energy which activates said trap former to form traps in said selected areas, the step of subjecting the imaged layer of imaging materials to development conditions, thereby producing in said layer comprising the imaging material an image which has the opposite polarity of said one normal polarity.
13. 14. The method of claim 13, in which the layer comprising the imaging material is selectively and imagewise subjected to imaging energy, which comprises a component which is capable of activating said trap former to form imagewise traps in said layer.
14. 15. The method of claim 13, in which an excess of traps is formed, thereby trapping in said selected areas which have received said imaging energy the energy carriers which are generated in these areas by the imaging energy and the energy carriers which are generated in these areas under the development conditions.
15. 16. The method of claim 13, in which said trap former is admixed to said imaging material.
16. 17. The method of claim 13, in which a layer of imaging material is provided, which comprises an elemento-organic imaging material.
17. 18. The method of claim 13, in which said energy capable of activating said trap former is selectively applied imagewise in a separate step.
18. 19. The method of claim 18, in which a trap former is provided which is an organic material.
19. 20. The method of claim 13, in which said development conditions comprise the application of heat to said layer comprising an imaging material.
20. 21. The method of claim 20, in which said heat is applied simultaneously with the application of said imaging energy.
21. 22. A method for producing a record of retrievable information, which method comprises: the step of providing a structure comprising a layer of a memory material, which is capable of generating, upon the application of energy, carriers, which cause a physical change in structure of said memory material between at least two conditions, and in contact with said memory material a trap former which is capable, upon the application of energy, to form traps for said carriers, the step of selectively applying to selected areas of said layer of memory material and to said trap former imaging energy of such intensity and pulse length that said trap formers become activated to form traps, whereby the carriers generated in said selected areas are trapped in said traps, and the step of applying development energy to said structure, thereby causing a physical change in structure in those areas of said layer of memory material, which have not been subjected to said imaging energy, and producing essentially no physical change in structure in those areas of the layer of memory material, which have been subjected to said imaging energy.
22. 23. The method of claim 22, in which a memory material is provided in said layer in which the energy gap difference between said conditions is at least about 1 electron volt.
23. 24. The method of claim 22, in which one of said conditions of said memory material is an amorphous state and the other of said conditions is a crystalline state.
24. 25. The method of claim 22, in which a memory material is provided in said layer, which comprises selenium.
25. 26. The method of claim 22, in which a memory material is provided in said layer, which comprises selenium and sulfur.
26. 27. The method of claim 22, in which a memory material is provided in said layer, which comprises a metal selenide.
27. 28. The method of claim 22, in which a memory material is provided in said layer, which comprises a metal sulfide.
28. 29. The method of claim 22, in which heat is applied as the development energy.
29. 30. The method of claim 22, in which heat is applied simultaneously with the application of the imaging energy.
30. 31. The method of claim 22, in which electromagnetic radiation is imagewise applied as the imaging energy.
31. 32. The method of claim 22, in which the trap former is admixed to the memory material.
32. 33. The method of claim 22, in which the trap former is provided as a separate layer in contact with said memory material in said layer.
33. 34. The method of claim 22, in which copper is provided as said trap former.
34. 35. The method of claim 22, in which arsenic is provided as said trap former.
35. 36. The method of claim 22, in which silver in an amount exceeding about 10 atomic percent is admixed to the memory material thereby serving as the trap former.

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