DE1159405B - Process for the synthetic production of electrically conductive diamonds - Google Patents

Description

The invention relates to a method for the synthetic production of electrically conductive Diamonds in a diamond growing process.

The term "electrically conductive diamond" refers to a diamond crystal in which in In a similar way to metals, an electric current is transmitted with the help of mobile electrons will. This term is not intended to include the conduction of electricity running through the diamond crystal interconnected inclusions of foreign substances, for example metals, arise. In the description is also used in connection with the diamonds synthetically produced according to the invention the term "semiconducting" is used.

Although diamond and graphite are two allotropic modifications of the same element, namely carbon, they have different electrical properties. While carbon conducts electricity, will Diamond generally regarded as an insulator, although some artificial at very high temperatures Diamonds have a low electrical conductivity. Some diamonds were also found which are electrically conductive, but it seems that their electrical conductivity is caused by foreign matter inclusions and these diamonds only conduct electricity because of these inclusions. There were too found natural diamonds that do not conduct electricity due to inclusions. These Diamonds have a distinctive blue color because of their rarity and their unpredictability Properties have only found widespread commercial use examined for study purposes.

Since diamond has high strength and high resistance to high temperatures, Both a conductive and a semiconducting diamond are desirable. One is particularly desirable semiconducting diamond, as it has high strength, durability and, above all, proportional is free from high temperature effects which are detrimental to semiconductor materials such as silicon and germanium are.

According to the invention, the diamond-catalyst combination used in a diamond growing process an activator made of boron or aluminum is added, which is an electrically conductive Diamond crystal generated.

Attempts have often been made to make natural diamonds electrically conductive with the aid of the processes customary in the field of semiconductors, in which atoms of an activator material, for example of gallium or indium, are converted into another material. Process for synthetic production
electrically conductive diamond

Applicant:

General Electric Company,
Schenectady, NY (V. St. A.)

Representative: Dipl.-Ing. M. Licht, patent attorney,
Munich 2, Sendlinger Str. 55

Claimed priority:
V. St. v. America, June 16, 1960 (No. 36 595)

Robert Henry Wentorf Jr., Schenectady, NY,
and Harold Paul Bovenkerk, Royal Oak, Mich.

(V. St. A.),
have been named as inventors

both materials are at high temperatures. About these in general Processes called "inoculation" include, for example, irradiation, impregnation, diffusion, Injection. However, not all materials are suitable for this process, since the introduction of the atoms depends on the different energy levels of the electrons, the size and distance of the atoms, etc. With the exception of irradiation with natural diamonds, these procedures gave no positive results Results. For example, attempts have been made in natural diamonds in a known manner Incorporate diffusion or impregnation elements such as boron, aluminum and nitrogen. It happened however, that no atoms of these substances could be introduced into the diamond crystal, since none Changes in properties were observed. However, it has now been found that diamond can be made electrically conductive if in the course of a diamond growing process, i.e. during the conversion of non-diamond-shaped carbon to diamond, an incorporation of foreign atoms is carried out. One method for synthesizing diamonds is, for example, in US Pat British Patent 830,743 and is that carbonaceous material and a Metal catalyst can be subjected to very high pressures and temperatures. An apparatus for

309 769/358

Generating the required high pressures and high temperatures is for example in the British Patent 830 210 indicated.

The following is an example of a conversion of carbonaceous material to diamond, the apparatus described in the last-mentioned British patent was carried out.

various other carbonaceous substances are used, for example amorphous carbon, coal, Coke, charcoal. Carbon-containing organic or inorganic compounds can also be used.

5, for example coal, tar, pitch, wood, paper, lithium carbide, naphthalene.

The activator material can be in elemental form or as a compound as a powder or in the form of Solids are used. The solids can

can be designed as disks, cylinders or any other geometric shape. For example, boron can be used in the form of a compound such as B ₄ C, B ₂ O ₃ , BN, NaB ₄ O ₇ , B _ip H ₁₄ , NiB, and LiBH ₄ , and so on. Aluminum can also be in metallic or

The carbon-catalyst-activator combination can be built up in a number of ways, but the end results do not result in any

example 1

The load was in the form of each other
alternating thin cylinders made from commercially available spectroscopically pure graphite and from
Nickel with a purity of 99.6% placed in a reaction vessel and heated by direct resistance 15 non-metallic form or in the form of heating. The reaction vessel has a bond, for example as Al ₄ C ₃ . Pressure of about 90,000 atmospheres combined
subjected to a temperature of about 1600 ° C. These conditions were held for about 3 minutes. After removing from the 20 significant differences. In the examples are apparatus, several arrangements could be obtained from the reaction vessel diamond. The amount of boron added is not critical, since

In similar examples, less than a thousand carats of diamonds have been extracted with this apparatus on a graphite basis. 0.1 to over 20 percent by weight in all cases electrically conductive. These diamonds had resulted in a black, water-white 25 electrically conductive diamond. Aluminum was made in or a range from dark green to light yellow
Colour. It turned out that these diamonds
no electrical conductors or semiconductors are there
any existing electrical conductivity only
seems to be coming from the impurities.

If the procedure described in Example 1 is used and in addition to graphite and nickel one a small amount of activator material in the reaction vessel brought and subjected to the required pressures and temperatures, then arise Diamonds that are electrically conductive and semiconducting. With the expression activator material will be here denotes boron, aluminum and / or compounds of these elements that decompose or otherwise react and in this way pass into the elementary state. Formed by adding boron Diamonds that are light blue to dark purple in color. It is now noteworthy that those natural diamonds that are in the restricted

Circumferences are electrically conductive, also colored light blue 45 with a thickness of 2.5 mm used. The nickel and graphite disks were alternated. It is an important feature that the atoms of these are layered within a tube. There activator elements during the growth or BiI- were used fifteen catalyst disks and fourteen generation of diamonds from carbonaceous material graphite disks. Penetrate the diamond crystal lattice at the intermediate surfaces. There is therefore 5 ° between the nickel and graphite discs, any method that has such a can be used
Causes diamond formation. When the invention
So there are no other pressures and procedures
Temperatures required than the pressures and temperatures suitable for diamond growth. Each 55 of 1450 ° C and a pressure of 68 000 Atmonach the type of catalyst used can be exposed to spheres. The ge from the reaction vessel

added in an amount based on graphite of less than 0.5 to more than 25 percent by weight. Will however, if more boron is added, then in general not only diamonds with a larger one are obtained Conductivity, but also with a darker color, i.e. i.e., the color shifts more from light blue after dark purple. An increase in the amount of aluminum also has an increased conductivity and brighter ones or more colorless diamonds.

In the following examples, the invention is described in more detail on the basis of specific results.

Example 2

A reaction vessel was made using nickel as a catalyst and by spectroscopically loaded with pure graphite as a carbonaceous material. Nickel was in the form of discs with a Thickness of 0.5 mm and graphite in the form of discs

powdered boron in the ratio of about 1 weight percent boron to about 500 weight percent Graphite arranged. The reaction vessel was kept at temperature for approximately 60 minutes

For example, pressures from about 50,000 atmospheres and temperatures from about 1200 ° C are used will. Metals of Group VIII of the Periodic Table, chromium, Manganese and tantalum, alloys of these metals, metals containing these metals and compounds which decompose or otherwise react to yield these metals.

p g

mined diamonds were colored blue and electrically conductive.

Example 3

The arrangement described in Example 2 was used. The catalyst disk consisted of an alloy of 5% titanium, 65% iron and 30% nickel. The interfaces between the catalytic

The carbon-containing material is preferably made of graphite and graphite disks with boron powder used because it is very pure and dusty. The reaction vessel turned approximately 90 minutes is and can be easily converted. ten for a temperature of 1220 ° C and one In addition to graphite, it can of course also be exposed to pressure of 66,000 atmospheres. The GE-

5 6

mined diamonds had a blue color and font 830 210 described press used and

were electrically conductive. a pressure of about 75,000 atmospheres and

_B. .J ₄ subjected to a temperature of approximately 1450 ° C

^p fen. After these conditions for a few minutes

The arrangement described in Example 2 was maintained, the temperatures were

used. As a catalyst, a steel with temperature and pressure was reduced and then from the

low carbon content used. The intermediate reaction vessel removes the formed diamonds.

areas between the catalyst and the graphite These diamonds were blue in color and showed

were sprinkled with boron powder. The reaction vessel has good electrical conductivity.

was kept at a temperature of io for about 10 minutes

of 142O ⁰ C and a pressure of 76,000Atmo- Example 7

Spheres exposed. The diamonds obtained The treatment of Example 6 was repeated,

were blue and electrically conductive. but there was about 1 mg of boron powder on that

g. . , j Dusted outside of the nickel tube. The diamonds obtained from the P ^{1 1} S reaction vessel had a

It became the arrangement blue color described in Example 2 and were electrically conductive, used. The catalytic converter disks passed

made of tantalum. A powder mixture of iron and boron Example 8 (2 percent by weight boron, based on iron) was

on the interfaces between tantalum and graphite ao In the reaction shown in the drawing

scattered. The assembly took about 10 minutes. A nickel-iron alloy was used for the tube 55.

long a temperature of 1420 ° C and a pressure tion (Invar) used. The tube 55 contained one

exposed to 76,000 atmospheres. The cylinders obtained from spectroscopically pure graphite. On the

Diamonds were blue in color and were electrically conductive. Outside of the tube 55 was about 1 mg Bortrisch conductive. 25 powder dusted on. The reaction vessel was un-

In the following examples 6 to 15 and 18, a pressure of 66,000 atmospheres is applied for about 60 minutes.

another reaction vessel is used, in which spheres and a temperature of 1250 ° C below-

the load is heated indirectly. One of the throws. The ones removed from the reaction vessel

The like reaction vessel is shown in the drawing. The diamonds were blue in color and were electrified and denoted by the reference number 50. The 30 trisch conductive.

The reaction vessel consists, for example, of Example 9

Pyrophyllite cylinder 51 with a wall thickness of un- ^p

about 4 mm and an outside diameter of approx.

about 19 mm. Concentric inside the cylinder was the inside of the vessel consisting of Invar

51 is a heating tube 52 made of graphite, the 35 tube 55 with about 1 mg of B ₄ C powder (fine sieve

has an outer diameter of about 11mm (i.e. 240 meshes per centimeter). The pipe

and rests on the cylinder 51. Within the Heizroh- was then spectroscopic with powdery graphite

Res 52 is a cylinder 53 made of aluminum oxide, the pischer purity filled. The reaction vessel became

an outside diameter of about 9.3 mm has a pressure of about 45 minutes

and rests on the heating tube 52. Inside the cylinder 40 70 000 atmospheres and a temperature of

53 is a tube 55 made of a for the dia- 1280 ° C subjected. The diamonds won

coat-making suitable metal catalyst, which had a blue color and were electrically conductive, Graphite suitable for diamond production 54

is filled and has a wall thickness of 0.5mm. Example 10 Instead of the graphite 54, 45 can of course also be used

other reaction substances and instead of the tube 55, the tube 55 made of Invar in the

other catalysts can be used. The reaction vessel shown at the bottom drawing was with

and the upper end of the graphite heating tube 52 sits a mixture of B ₄ C and graphite powder (5 parts

because a stopper 56 or 56 'made of aluminum oxide, weight percent B ₄ C, based on graphite) is filled. That

The graphite and catalyst between the two 50 reaction vessels was held for about 40 minutes

Sides of the vessel 50 holds. At the ends of the ge a pressure of 70,000 atmospheres and one

Fäßes 50 are suitable cover plates 57 and 57 'exposed to a temperature of 1250 ° C. The ones from the

attached, via which the flow to the heating tube 52 was removed from the reaction vessel, diamonds had one

is directed. The alumina cylinder 53 should be blue in color and be electrically conductive, must be pre-fired so that it is relatively soft. 55

In this reaction vessel, the filling is heated indirectly. that is, the current flows through the graphite tube

and not through the filling isolated from the heating pipe. _{The reaction vessel R} shown in the drawing. ■ λ f. Was charged with a composed of Invar tube 55 and ο ei play 60 of a pure graphite from spectroscopy including the opening of the stationary cylinder 54 shown in the drawing is used. The cylinder 54 of the reaction vessel was a nickel product with 2.9 percent by weight boron (based on the tube, which was a 2 g cylinder made of graphite weight) impregnated. As a result, it contained spectroscopically pure graphite. About 65% of the boron was added mechanically to the outside of the graphite cylinder during the production of the graphite. The assembly was dusted with 1 mg of boron powder before the graphite cylinder was inserted into the nickel tube for about 30 minutes at a pressure. The arrangement- 64,000 atmospheres and a temperature of voltage was then subjected to one in the British patent- 1,240 ° C. The one from the reaction vessel

7 8

The diamonds obtained were colored blue and showed a thickness of 2.5 mm made of spectroscopically pure th an electrical conductivity. Graphite and fifteen catalyst disks with one. · ₁₁₀ thickness of 0.5 now from commercially available _rei-NEM Example 12 j _{E sen to} g _eo RDnet. The graphite and iron discs 5 g of borax were dissolved in 500 ml of water. In 5 benches were alternately placed on top of one another, the solution was immersed in a graphite cylinder 54, the solution being heated between each graphite disk and the associated one, the cylinder being removed and an aluminum foil being dried at the same time as the catalyst disk. The cylinder was then covered within a thickness of 0.025 mm. The Reak-Invar existing tube 55 is arranged. The reaction vessel was subjected to a pressure of 75,000 atmospheres and a temperature of about 1450 ° C. for about 60 minutes. The diamonds obtained had been subjected to a door of 1250 ° C. The obtained slides were light color and were electrically conductive. The Beim assistants had a blue color and were electrically game 16 is representative of a variety of Beileitend play in which using Alumi T ₅ · ι ₁ ο 15 nium ranging from 75000 to 80000 atmospheres ueibpici id _{and 1400 Electrically} conductive diamonds _{up to 1500} o c

The nickel tube 55 shown in the drawing could be manufactured, with a mixture of boron powder (140 mesh per

Centimeter) and spectroscopically pure graphite example 17

powder filled. Based on the graphite, 20

2 percent by weight boron powder used. The React- The reaction vessel used in the previous example was placed in an alternating pressure vessel for about 30 minutes of 78,000 atmospheres and a temperature disks made of spectroscopically pure graphite and door of 1500 ° C. The obtained slide from an iron-aluminum alloy with one on The shells were blue in color and had an electrical content of 8 iron-related aluminum Conductivity. weight percent filled. The panes were the same

In the following examples, the conductive thicknesses were the same as the discs used in Example 16. Diamonds by adding aluminum with the The reaction vessel was a pressure of reaction vessels described obtained. 80000 atmospheres and a temperature of

30 1500 ° C exposed. The recovered diamonds Example 14 were light in color and electric

conductive.

The pipe 55 shown in the drawing consisted of Example 18

commercially available iron with a purity of

over 99.5%. The pipe had an outside diameter of 35 In the indirect heater shown in the drawing of 7.8 mm and a wall thickness of 0.38 mm. th reaction vessel, the tube 55 from commercial-A spectroscopically pure graphite rod was made with ordinary pure nickel. Inside this A commercially available aluminum foil with a thick tube became a thin-walled tube made from commercially available 0.025 mm wrapped about five times. Those arranged with ordinary pure aluminum, its GeAluminium Coiled graphite rod became about 3 weight iron pipe in the 4 ° weight with respect to nickel pushed and made the percentage in the reaction vessel. Inside the aluminum tube arranges. The reaction vessel was under a pressure of a rod made of spectroscopically pure graphite 68 000 atmospheres and a temperature of arranged. The arrangement then became one Exposed to 1350 ° C. The diamonds formed had pressures of approximately 77,000 atmospheres and one a lighter color than those produced only with iron 45 exposed to temperatures of about 1450 ° C. the Diamonds and showed electrical conductivity. mined diamonds were electrically conductive and

were slightly lighter in color than those with just nickel Example 15 Diamonds Made Alone.

It is pointed out again that in

The tube 55 was made of commercially available iron 50 of the present invention, the term "electrical, with a purity of over 99.5 vol. It had a conductive effect due to the enclosed outside diameter of approximately 7.8 mm and a foreign matter, such as catalyst metal, etc., wall thickness of 0.38 mm. An electrical conduction brought about by spectroscopy relates. For example, a rod made of pure graphite was covered with a cubic diamond crystal of poor quality commercially available aluminum foil of approximately 55 mm. The graphite rod, which was wrapped with alumi- des crystal on the other side of the crystal, was ken in the iron tube and connected to one another. The is now inserted and placed in the reaction vessel. Crystal placed between two electrodes, so the reaction vessel was held at a pressure of -75,000 atmospheres and a temperature of 60 through the inclusions alone. Power conduction can also occur if exposed to 1450 ° C. The extracted diamonds were present on the surface of impurities, were brightly colored and showed electrical conductivity. excluded the invention and it turned out-

Example 16 provided that the power line with the according to the

65 discovery of synthetically produced diamonds by im

Movable charge carriers take place in a crystal lattice used in Examples 1 to 5. Reaction vessel for direct heating of the filling The diamonds obtained in each example

suitable, about fourteen discs were carefully looked through, and the-

selected those diamonds that were characterized by extraordinary clarity and also hundreds of times Magnification showed no impurities pointing to extensive inclusions between close the crystal faces. These diamonds were then concentrated with a hot one Solution of sulfuric acid and potassium nitrate treated to remove impurities on the surface dissolve and leach out any inclusions connected to the surface. When cleaning aqua regia was also used.

The diamonds so treated were then placed between the conductors of a volt-ohm-milliampere meter for resistivity measurement. Several measurements were made on different crystal faces of each crystal and there were only minor changes in resistivity for the same crystal. The specific resistance at room temperature for diamonds seeded with boron was 10 ⁴ ao to ΙΟ ⁷ Ω cm and for diamonds seeded with aluminum was approximately 10 ⁵ to 2 ⁷ Ω cm. The following table shows the change in electrical resistance as a function of temperature for these diamonds.

Electrical resistance

depending on the temperature

for electrically conductive diamonds

Temperature, ° C

25th

50

420

-210

Relative resistance

With aluminum
Inoculated with boron

0.3

3 x 10 ~ ^a
2-10 ²

1.5 ■ ΙΟ " ¹
1.5 x 10-3
3 -10 ²

35

40

The following tests were carried out on the selected and cleaned diamond crystals to investigate the semiconductor. A single crystal was placed in a tough, small diameter tube and a silver wire probe was passed to the crystal from each end of the tube. The silver probes were connected to a volt-ohm-milliampere meter to measure the resistance of the crystal. The tube was immersed in liquid nitrogen for measurement at these temperatures. After the temperature had settled, the apparatus was heated in an oven to a maximum temperature of approximately 450 ° C. In all cases the electrical resistance decreased with increasing temperature and fluctuated from 100 · ΙΟ ⁶ Ω at the temperature of liquid nitrogen to about 200 Ω at 250 ° C.

The semiconductor could also be determined by measuring the thermal force as follows. If nickel is used as a catalyst in diamond production, it can be assumed as a hypothesis that the electrical conduction comes about through the nickel inclusions. One on the one described Kind of cleaned diamond crystal was then brought together with an iron electrode, so that a Thermocouple solder joint was created. Now if the nickel were responsible for the electrical conduction, then the voltage characteristic of a nickel-iron thermocouple should be able to be observed. In the present case, however, the thermocouple-voltage characteristic curve observed was not the same of iron-nickel. This experiment was repeated several times with different metal reference electrodes repeated, but in all cases there is a different voltage characteristic from the metals assumed revealed.

It was found that the electrically conductive diamonds in the above examples are similar to the p-type semiconductors. This resulted from the sign of the thermopower, that is, from the direction of the stress gradient that resulted when they were exposed to a temperature gradient. Between silver metal probes showed at an average temperature of about 200 ° C, the vaccinated with boron diamond thermal forces from 10 to 100 microvolts per ⁰ C and seeded with aluminum diamonds thermal forces of 20 to 80Mikrovolt per ^'0 C.

The crystal lattice of diamond is commonly referred to as a diamond cubic lattice. The bonding scheme is tetrahedral, with four closest neighbors attached to each atom by valence bonding forces. The diamond cubic lattice is an example of a loosely packed lattice as distinct from a tightly packed lattice. The distance d between the closest neighboring atoms of a diamond crystal is 1.45 A. Since a boron atom is only slightly larger than this distance, it is assumed that the diamond crystal lattice accepts a boron atom. Like the foreign atoms in the semiconductors, the boron atom is then an impurity or a foreign atom in the crystal lattice.

Contaminants can sit in interstitial spaces or on correct lattice spaces. In the first case the atoms are arranged between the lattice atoms, and in the second case they replace lattice atoms. The box atom, which contains three electrons, seeks a fourth electron from the surrounding carbon atoms to get a shell occupied by eight electrons. This is how it arises a defect and therefore a p-type crystal.

Diamonds inoculated with boron according to the invention are light blue to dark purple in color, which is comparable to the color of natural electrically conductive diamonds. Will be different other substances added in the diamond manufacturing process as impurities in the crystal structure can be seen, then the result is diamonds with a green to yellow color. It is hence it can be assumed that the boron atoms built into the carbon crystal lattice form lattice building blocks and do not represent inclusions. The electrical conductivity of such a diamond is therefore on the Crystal structure and not due to added inclusions. The characteristic blue color is thus achieved by a change in the crystal structure or electronic structure.

The present process can also be used for the synthetic production of colored diamonds, blue diamonds are made in a color range from light blue to dark purple can. The invention can thus also be used as a method for coloring diamonds. It it has already been stated that the color of diamonds produced with the catalysts described depending on the temperatures and pressures used

309 769 58

varies between brown, green, yellow, white and black and the various shades of them. At high pressures and temperatures, you get clearer and more transparent diamonds, and through The addition of boron can produce diamonds with a light blue to a deep purple color will. In general, colors, the combinations, are obtained at lower temperatures and pressures of blue and the above-mentioned colors, with individual crystals partly a blue Color and partly a green color and other combination colors. Aluminum can can be used to create shiny white diamonds and to change the shades of color. By adding aluminum or aluminum compounds or aluminum alloys to the catalyst material lighter or clearer colors can be achieved.

Claims (1)

Claim. Process for the synthetic production of electrically conductive diamonds, in which non-diamond-shaped carbonaceous material and a catalyst consisting of a metal of group VIII of the Periodic Table, manganese, chromium or tantalum or one of these elements for converting the carbonaceous material into diamond, pressures of are exposed to over approximately 50,000 atmospheres and temperatures of at least approximately 1200 ° C, characterized in that the reaction mixture consisting of non-diamond-shaped carbonaceous material and catalyst is added boron or aluminum or a compound which yields one of these elements under the reaction conditions. 1 sheet of drawings © 309 769/358 12.63