JP2001526996A - Diamond or gemstone marking with multiple grooves - Google Patents

Abstract

(57) Abstract: A method and apparatus for forming a mark on the surface of a diamond or gemstone are disclosed. The mark consists of a plurality of grooves (10) that do not adversely affect the clarity value of the diamond or gemstone and exhibits a high diffraction effect under certain lighting and magnification conditions. An apparatus and a method for observing such marks are also disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for marking diamond or other gemstone surfaces. The mark may be any mark, but the invention is not exclusively concerned with marking information marks, especially on diamonds. Diamond is, for example, an industrial diamond such as a wire-drawing die, but the present invention is particularly important when marking diamonds, which are gemstones. When a mark is applied to a polished facet of a gemstone that does not reduce the value of clarity, the mark cannot be identified with the naked eye or cannot be identified using a 10-fold loupe (used by jewelers). It is to attach.

The mark is used to uniquely identify the gemstone by its serial number as a brand or as a quality mark, but should not affect the value or appearance of the gemstone and should be darkened (blackened). ) Exposure of appearance is not preferred.

[0003] In WO 97/03846, the properties of the marks are described in detail. The marks are formed by irradiating a diamond gemstone with laser radiation in the ultraviolet region using a projection mask. wear.

[0004] It is usually desirable to produce marks with good resolution and visibility when viewed under appropriate loupe and lighting conditions, which marks the value and appearance of diamond or other gemstones. It does not hurt.

[0005] invention According to a first aspect of the present invention, the surface of the diamond or gemstone, a method of forming a mark consisting of one or more alphanumeric characters or the like, a diamond or gemstone Providing a plurality of grooves in the surface of the mark, wherein the mark is not readable by the naked eye, but is readable under predetermined magnification conditions, and the grooves are visible under predetermined illumination conditions. Bring effect.

Further, according to a first aspect of the present invention, there is provided an apparatus for performing the above method. The invention also extends to diamonds or gemstones marked by the method described above.

According to a second aspect of the present invention, there is provided a method of forming a mark on a surface of a diamond or a gemstone, the method comprising the step of forming a plurality of grooves on the surface of the diamond. Provides a visible diffraction effect under certain lighting conditions without adversely affecting the clarity value of the diamond or gemstone.

[0008] Further, according to a second aspect of the present invention, there is provided an apparatus for performing the above method. The invention also extends to diamonds or gemstones marked by the method described above.

The greater the depth of the groove, the better the visibility of the mark when observed. The groove should have an appropriate depth so that the mark has considerable visibility under appropriate viewing conditions, but if too deep it will adversely affect the clarity value of the diamond or other gemstone Effect. In one preferred embodiment, each groove is
Depth not less than about 10 nm and / or not more than about 50 nm without showing any signs of darkening. In a specific embodiment, it is about 30 nm.

The grooves are in the form of parallel lines, and the plurality of intersecting grooves form a cross-hatched pattern depending on the desired effect.

[0011] The marking is performed using any suitable means, such as etching with an excimer laser or plasma etching, but preferably the marking is performed using an ion beam, and more preferably on the diamond surface with a focused ion beam. Written directly. By limiting the dose, it is possible to avoid sputtering of carbon atoms, which causes a direct removal of the material. As a result, it is possible to control the mark depth and good resolution. Typically, gallium ions are utilized, but alternatively, other suitable ion beams may be utilized.

Each incident ion displaces a large number of carbon atoms from its site, creating voids and voids in the diamond crystal. As the amount of damage (crystal lattice irregularity) increases, the diamond sp ³ bonds tend to be replaced by pseudo-graphite sp ² bonds. The bond is attacked by a chemical etch, causing the irregular layer to be removed. By limiting the dose, when given a sufficient dose, the incident ions cause disorder to change the diamond to a pseudo-graphite or other non-diamond structure, which has a strong structure such as molten potassium nitrate. The oxidizing agent is washed at a temperature of about 380 to 550 ° C. for a time of several minutes to several hours.

[0013] The use of potassium nitrate is more effective in removing disordered diamond than other known methods, and thus can produce constant depth marks with relatively low doses of ions. It turned out to be.

[0014] Other suitable oxidizing agents include molten compounds such as alkali metal salts and compounds in the form of XnYm, wherein the X group is Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , a cs ⁺ or other cations, Y ^{groups _{OH -, NO 3 -, O}} 2 2-, O 2-, CO 3 2 - a, or other anions, are integers n and m maintain charge balance Used to cause Mixtures of such compounds can also be used. Air or other oxygen-containing gases are also present.

[0015] Alternatively, the irregular layer of diamond is removed using an acid or potassium nitrate dissolved in the acid. However, acid fumes are eliminated, for example, by the use of molten potassium nitrate. In addition, it eliminates the need to treat spent acid, thus providing safe, environmental and economic benefits.

There is a need to minimize the depth of the disorder applied by the ion beam to the diamond surface. The depth of the disorder is determined by the spread of the ions. For 50 keV gallium, the spread is about 30 nm. The minimum dose is about 10 ¹³ / cm ² , preferably about 10 ¹⁴ / cm ^{2 to} 10 ¹⁵ / cm ² , but a good mark can be made with a suitable medium dose, The preferred maximum dose is about 1
0 ¹⁶ / cm ² or up to about 10 ¹⁷ / cm ² . However, the dose depends on the ions utilized and the energy of the ions (measured in keV). The ion beam dose is the total number of incident ions per unit area of the sample surface during marking. The beam current is about 0.5 nA, and the beam energy is about 10 keV or about 30 keV or more, and / or about 100 keV or about 50 keV or less.

When the mark depth is plotted against the beam dose for a series of different beam energies, the mark depth increases with increasing beam energy. Mark characteristics are optimized by selecting from dose / energy combinations that result in the desired depth of the mark.

The area to be marked and / or the surrounding area is coated with a conductive layer, for example gold, prior to the formation of the mark, and the electrical connections are made before marking with an ion beam to prevent charging. It is formed. The thickness of the gold or other coating varies with the depth of the mark due to the beam energy and is selected to optimize the mark produced. However, it is preferable to irradiate the area to be marked with a low energy source of electrons (eg, about 1-100 eV) from an electron flood gun, eg, during marking while preventing charging. .

When a focused ion beam is used to form a plurality of grooves, the method of the present invention does not require masking, and places the ion beam at the location where the grooves are required to be formed. There is precision that can be applied directly to the surface. However, with other methods, the method of forming the grooves is not very accurate, and it is necessary to mask the area between the grooves to avoid marking.

According to a third aspect of the present invention, there is provided an apparatus for observing a mark formed on a diamond using the method according to the first or second aspect of the present invention, comprising: An irradiation unit for irradiating the mark with directional light at an angle corresponding to the diffraction angle of the band light, an observation unit for observing the mark, and an apparatus including an enlargement unit for enlarging an observation image of the mark. provide. Further, the present invention extends to an observation method for observing a mark corresponding to the above-described device.

Preferably, the mark is observed against a dark background, ie, the illumination light is preferably substantially prevented from reflecting off the rough and appearing directly behind or near the mark. In order to achieve the above, the angle and direction of the illumination light provided (and the orientation and spacing of the lines) must be chosen to ensure that the light does not follow unnecessary paths. Will be apparent to those skilled in the art.

A typical magnification range required for observing a mark is 10 to 50 times.

The distance between the plurality of grooves and the directional light determines the color of the mark that appears when observed. In a general diffraction grating, there is a relationship of dsin θ = ± nλ, where d is the distance between the grooves, θ is the angle of the incident light, and λ
Is the wavelength of the diffracted light, and n is an integer. n is preferably 1.

Therefore, when a mark is formed on a diamond, d and n are determined, and the wavelength of the diffracted light, that is, the color of the mark that appears when observed, is changed by changing the angle of the incident light. Therefore, if it is desired to display the mark in blue when observed, the angle of the incident light, that is, using the above equation, θ so that λ is about 450 nm
Is set. Similarly, if one wishes to represent the mark in red, θ is set so that λ is about 620 nm.

In one embodiment of the device according to the third aspect of the present invention, the illuminating means comprises a light source and a transparent screen arranged in the path of the incident light, said screen comprising two formed inside. Having openings, each opening is usually formed on either side of the central position,
Two angular directional lights are produced. The distance between the openings determines the angle of the incident light source. However, it is believed that the directional light source is provided by means known in the art, for example, two separate light sources. Conventionally known microscopes are equipped with illumination means having a circular ring-shaped source with optical fibers illuminated by a remote tungsten light valve. The illumination means of the present invention is obtained by masking off two, but not all, diametrically opposed sections of the illuminator.

Preferred Embodiments The practice of the present invention will be described with reference to the following examples and the accompanying drawings. Referring to FIG. 1 of the drawings, a mark in the form of an alphanumeric character is constituted by a plurality of equally-spaced, parallel, elongated grooves 10, each of which is separated by a distance d. Each groove 10 usually has a square or rectangular cross section as shown in FIG. Alternatively, a sinusoidal profile is preferred to reduce unnecessary high order diffraction.

[0027]An example  A specific method for forming each groove will be described below.

The diamond gemstone is mounted in a suitable holder and placed in a vacuum chamber equipped with a focused ion beam source sold by FEI or Micrion.
During exposure, the area to be marked is illuminated, for example, using an electron flood gun sold by Micrion, which gives a low energy of 1 to 100 eV, as an electron source, so that the diamond is not charged.

For example, utilizing a focused ion beam in a raster scan or similar beam scan, an electric field deflection (alternatively a diamond moves, but this is not very practical) and any control of the ion beam Suitable software,
A series of closely spaced parallel lines are "written" into the diamond facet.

The sample is removed from the vacuum chamber, placed in a stainless steel crucible, and covered with a strong oxidizing agent such as molten potassium nitrate for about one or two hours.
The sample is then cooled and removed from the potassium nitrate prior to washing with water and ethanol, thereby removing the diamond surface portions that have been disordered by the ion beam and a series of intimate without darkening. About 30 grooves at regular intervals
To a depth of about 35 nm.

When inspected before cleaning, for example, when observed with a reflected light microscope, the exposed areas can be identified as pseudo-graphite appearance. Such marks are unacceptable for diamond grades in that they substantially reduce the clarity value of the diamond. However, if the cleaning is performed using a strong oxidizing agent, there is no contrast between the mark and the surrounding area with a microscope, and the mark cannot be easily observed. The mark is only visible when illuminated, for example, by two directional light sources, at an angle corresponding to the angle of the diffracted light of a particular wavelength of blue, for example, where the mark appears blue. Such marks are acceptable for diamond grades in that they do not adversely affect the clarity value of the diamond.

The closely spaced grooves are preferably formed in “non-identifiable outlines” such as alphanumeric characters, as shown in FIG. 1 of the drawings.

Referring to FIG. 3 of the drawings, a method and apparatus for observing marks made by the above-described method will be described by the following example.

A diamond 104 with a mark is formed on the observation surface 10 of the conventionally known microscope 102.
Set to 0. The diamond 104 is illuminated by two directional light sources 106 having an angle θ with respect to the vertical axis Y. As described above, θ is selected, for example, to be represented as blue or red if desired. Thus, if one wants to represent the mark in blue, d is about 1200 nm and θ is selected to satisfy the following equation: dsin θ = (about) 450 nm where n is 1 and 450 nm is blue light. Is the wavelength of the diffracted light at X in FIG. In this case, θ is 22 °.

The directional light source is usually provided with a ring-shaped illuminator, where two, but not all, of the illuminators are masked off. However, any suitable light source is utilized to produce the same effect.

The present invention has been described purely by the above examples, and variations are possible within the spirit of the invention and extend to equivalents of the described features. Furthermore, the invention resides in the individual features described, is implied in the present application or example, and is implied by the drawings, combinations of such features, and generalizations of such features or combinations.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic view of a mark type formed using the method and apparatus of the first and second aspects of the present invention.

FIG. 2 is a further enlarged sectional view taken along the line AA of FIG. 1;

FIG. 3 is a schematic view of an embodiment of the device according to the third aspect of the present invention.

[Procedure amendment]

[Submission date] July 4, 2000 (200.7.4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

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[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for marking diamond or other gemstone surfaces, wherein the mark comprises one or more uniform marks . The mark may be any mark, but the present invention is not exclusively concerned with making an information mark especially on a diamond, and the mark may be alphanumeric characters or the like. Diamond is, for example, an industrial diamond, such as a wire-drawing die, although the present invention provides a method for marking gemstone diamonds.
Of particular importance, specifically, polished facets of gemstones that do not degrade the value of clarity are marked with invisible eyes or use a 10x loupe (used by jewelers) when marked. This is because it is impossible to identify even if it is marked.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

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[0004] It is usually desirable to produce marks with good resolution and visibility when viewed under appropriate loupe and lighting conditions, which marks the value and appearance of diamond or other gemstones. It does not hurt. Overcome least one of the drawbacks of the prior art, or by improved, that it produces a useful alternative is an object of the m invention.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

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The invention
According to a first aspect of the present invention, there is provided a method for forming a mark comprising one or more unified marks on a surface of a diamond or gemstone, the method comprising: Providing a method comprising forming a groove, wherein the groove defines a mark or feature , wherein the mark is indistinguishable to the naked eye, but the groove is visible under certain lighting and magnification conditions. Brings diffraction effect.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

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According to a second aspect of the present invention, there is provided a method of forming a mark on a surface of a diamond or a gemstone, the method comprising the step of forming a plurality of grooves on the surface of the diamond. Provides a visible diffraction effect under certain lighting and magnification conditions without adversely affecting the clarity value of the diamond or gemstone.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0009

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[0009] The mark can not be identified with the naked eye, however, by the this providing grooves, in certain lighting conditions, resulting in a diffraction effect with visibility. The deeper the groove, the better the visibility of the mark when observed. The groove should have an appropriate depth so that the mark has considerable visibility under appropriate viewing conditions, but if too deep it will adversely affect the clarity value of the diamond or other gemstone Effect. In one preferred embodiment, each groove is about 10 nm or more and / or about 50 nm or less in depth without showing any signs of darkening. In a specific embodiment, it is about 30 nm.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

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According to a third aspect of the invention, a mark on a surface of a diamond or gemstone, which is illuminated and comprises a plurality of grooves, which, when enlarged, provides a visible diffraction effect. An apparatus corresponding to a diffraction angle of light of a specific wavelength or wavelength band, and having substantially the same angle with respect to the normal to the surface , but substantially observing with respect to the normal to the surface. There is provided an apparatus comprising two illuminating means for illuminating the mark with each light beam, which is the opposite method, and observing and enlarging means for observing the mark and enlarging an observation image of the mark . Further, the present invention extends to an observation method for observing a mark corresponding to the above-described device.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

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The directional light source is usually provided with a ring-shaped illuminator, where two, but not all, of the illuminators are masked off. However, any suitable light source is utilized to produce the same effect. Throughout the description and claims, unless otherwise required herein , the terms "comprising" and "comprising" are the same, not an exclusive or exhaustive meaning, It is to be construed to be inclusive, that is to say " inclusive and not limiting ."

[Procedure amendment 9]

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FIG.

FIG. 2

FIG. 3

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Claims (61)

[Claims] 1. A method for forming a mark comprising one or more alphanumeric characters or the like on a surface of a diamond or gemstone, wherein a plurality of grooves are formed on the surface of the diamond or gemstone. The mark is not readable by the naked eye, the groove provides a visible diffraction effect under predetermined lighting conditions,
A method wherein the mark is readable under predetermined magnification conditions. 2. The method of claim 1, wherein said grooves are formed by a focused ion beam. 3. The method of claim 2, wherein the crystal lattice on the surface of the diamond or gemstone is disordered by the focused ion beam and removed by a strong oxidizing agent. 4. The method according to claim 3, wherein said strong oxidizing agent is molten potassium nitrate. 5. The strong oxidizing agent is a compound of the form XnYm, wherein:
The X groups are Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ or other cations or mixtures thereof, and the Y groups are OH ⁻ , NO ^{3 —} , O ₂ ^{2 −} , O ^{2 —} , CO 2 ₃ is a ^2- or other anion, or mixtures thereof, the method of claim 3, wherein the integer n and m are to be used so as to maintain charge balance. 6. The method according to claim 1, wherein the grooves are substantially equally spaced and are formed as parallel, elongated grooves. 7. The method of claim 6, wherein an intersecting set of grooves is formed to provide a shading effect. 8. The method according to claim 2, wherein the focused ion beam has a beam energy of 50 keV or less. 9. The method according to claim 2, wherein the focused ion beam has a beam current of about 0.5 nA. 10. The dose of ions generated by said focused ion beam is about 10 ¹³ / cm²To 10¹⁷/ cm²The method according to any one of claims 2 to 9, wherein
Method. 11. The method of claim 10, wherein said dose is between about 10 ¹⁴ / cm ^{2 and} 10 ¹⁶ / cm ² . 12. The method according to claim 2, wherein the surface area of the diamond or gemstone on which the mark is to be formed is irradiated with a low-energy source of electrons in order to eliminate charges. . 13. The method according to claim 1, wherein the diamond is a gemstone diamond. 14. An apparatus for forming a mark comprising one or more alphanumeric characters or the like on a surface of a diamond or gemstone, wherein a plurality of grooves are formed on the surface of the diamond or other gemstone. A device comprising means for forming, wherein said mark is not readable by the naked eye, said groove provides a visible diffraction effect under predetermined lighting conditions and is readable under predetermined magnification conditions. 15. The means for forming the plurality of grooves includes: means for irradiating a portion of the diamond or gemstone; and irradiating a crystal lattice of the diamond or gemstone portion by irradiation, The apparatus of claim 14, further comprising means for producing a disordered layer and removing said disordered layer. 16. The apparatus of claim 15, wherein said means for irradiating a portion of said diamond comprises a focused ion beam. 17. The method according to claim 1, wherein the disordered layer is removed by a strong oxidizing agent.
17. The device according to 5 or 16. 18. The apparatus of claim 17, wherein said strong oxidizing agent is molten potassium nitrate. 19. The strong oxidizing agent is a compound of the form XnYm, wherein the X group is Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ or another cation or a mixture thereof; The Y group is OH ⁻ , NO ^{3 −} , O ₂ ^{2 −} , O ^{2 −} , CO ₃ ^{2 −} or other anions or mixtures thereof, wherein the integers n and m are used to maintain charge balance. Item 18. The device according to Item 17. 20. The apparatus according to claim 15, wherein the focused ion beam has a beam energy of 50 keV or less. 21. The apparatus according to claim 15, wherein the focused ion beam has a beam current of about 0.5 nA. 22. The ion dose generated by the focused ion beam is about 10 ¹³ / cm²To 10¹⁷/ cm²22. The method according to claim 15, wherein
On-board equipment. 23. The apparatus of claim 22, wherein the dose is between about 10 ¹⁴ / cm ^{2 and} 10 ¹⁶ / cm ² . 24. The method according to claim 14, further comprising irradiating the surface area of the diamond to be marked with a low energy source of electrons in order to eliminate charging. apparatus 25. The apparatus according to claim 24, wherein said irradiating means is an electronic flood gun. 26. A method according to claim 1, wherein the mark does not adversely affect the clarity value of the diamond.
The device according to any one of the preceding claims. 27. A diamond or gemstone having a mark formed by the method according to any one of claims 1 to 13. 28. A method of forming a mark on a surface of a diamond or gemstone, the method comprising forming a plurality of grooves in the diamond or gemstone, wherein the grooves are formed of a clarity of the diamond or gemstone. A method that produces a visible diffraction hardening under defined lighting conditions without adversely affecting the value. 29. The method of claim 28, wherein the mark is in the form of one or more alphanumeric characters or the like. 30. The method according to claim 28, wherein the groove is formed by a focused ion beam. 31. The method according to claim 29, wherein the crystal lattice of the surface region of the diamond or gemstone is disordered by the focused ion beam and removed by a strong oxidizing agent. 32. The method of claim 31, wherein said strong oxidizing agent is molten potassium nitrate. 33. The strong oxidizing agent is a compound of the form XnYm, wherein the X group is Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ or other cations or mixtures thereof; The Y group is OH ⁻ , NO ^{3 −} , O ₂ ^{2 −} , O ^{2 −} , CO ₃ ^{2 −} or other anions or mixtures thereof, wherein the integers n and m are used to maintain charge balance. Item 31. The method according to Item 31, 34. The method of claim 28, wherein the grooves are substantially equally spaced and are formed as parallel, elongated grooves. 35. The method of claim 34, wherein an intersecting set of two or more grooves is formed to provide a shading effect. 36. The method according to claim 29, wherein the focused ion beam has a beam energy of 50 keV or less. 37. The method of claim 29, wherein the focused ion beam has a beam current of about 0.5 nA. 38. The ion dose generated by the focused ion beam is about 10 ¹³ / cm²To 10¹⁷/ cm²38. The method according to claim 29, wherein
The method described. 39. The method of claim 38, wherein said dose is between about 10 ¹⁴ / cm ^{2 and} 10 ¹⁶ / cm ² . 40. The surface area of diamond or gemstone to form a mark is irradiated with a low energy source of electrons to eliminate charge.
40. The method according to any one of 8 to 39. 41. A diamond having a mark formed by the method according to claim 28. 42. An apparatus for forming a mark on the surface of a diamond or gemstone, comprising: means for forming a plurality of grooves on the surface of the diamond;
An apparatus wherein the grooves provide a diffractive effect that is visible under predetermined lighting conditions without adversely affecting the value of the clarity of the diamond. 43. The means for forming the plurality of grooves includes: means for irradiating the diamond or gemstone portion; and irradiating the crystal lattice of the diamond or gemstone portion with irregularity, 43. An apparatus as claimed in claim 42, wherein a disordered layer is created and comprising means for removing said disordered layer. 44. The apparatus of claim 43, wherein said means for irradiating said diamond or gemstone portion comprises a focused ion beam. 45. The disordered layer is removed by a strong oxidizing agent.
45. The apparatus according to 3 or 44. 46. The apparatus of claim 45, wherein said strong oxidizing agent is molten potassium nitrate. 47. The strong oxidizing agent is a compound of the form XnYm, wherein the X group is Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ or other cation or a mixture thereof; The Y group is OH ⁻ , NO ^{3 −} , O ₂ ^{2 −} , O ^{2 −} , CO ₃ ^{2 −} or other anions or mixtures thereof, wherein the integers n and m are used to maintain charge balance. Item 46. The method according to Item 45. 48. The apparatus according to claim 44, wherein the focused ion beam has a beam energy of 50 keV or less. 49. The apparatus according to claim 44, wherein the focused ion beam has a beam current of about 0.5 nA. 50. The dose of ions generated by said focused ion beam is about 10 ¹³ / cm²To 10¹⁷/ cm²50. Any one of claims 44 to 49.
On-board equipment. 51. The apparatus of claim 50, wherein said dose is between about 10 ¹⁴ / cm ^{2 and} 10 ¹⁶ / cm ² . 52. The surface area of a diamond or gemstone to form a mark is irradiated with a low energy source of electrons to eliminate charge.
The device according to any one of items 2 to 51. 53. The apparatus according to claim 52, wherein said irradiating means is an electronic flood gun. 54. An apparatus for observing a mark of a plurality of grooves on a surface of a diamond or gemstone, which, when illuminated under magnification, provides a significant diffraction effect, comprising a predetermined wavelength or wavelength band. A device that illuminates with directional light at an angle corresponding to the diffraction angle of the light, an observation unit that observes the mark, and an enlargement unit that enlarges an observation image of the mark. 55. The apparatus of claim 54, wherein the angle and direction of the illumination light is provided such that the mark is observable against a relatively dark background. 56. A method of observing a mark on a surface of a diamond or gemstone, the mark comprising a plurality of grooves that provide a diffraction effect when illuminated,
A method comprising: illuminating the mark with directional light at an angle corresponding to a diffraction angle of light of a predetermined wavelength or wavelength band; observing the mark; and enlarging an observation image of the mark. . 57. The method of claim 56, wherein the angle and direction of the illuminating light is selected to cause the mark to be viewed against a relatively dark background. 58. A method of forming a mark on a diamond or gemstone substantially as described herein with reference to the accompanying drawings. 59. An apparatus for forming a mark on a diamond or gemstone substantially as described herein with reference to the accompanying drawings. 60. An apparatus for observing marks formed on the surface of a diamond or gemstone substantially as described herein with reference to the accompanying drawings. 61. A method of observing a mark formed on a diamond or gemstone substantially as described herein with reference to the accompanying drawings.