Russia’s Technological Institute for Superhard and Novel Carbon Materials (TISNCM) which is in Troitsk has been dealing with nano-technologies for a long time. For fifteen years the scientists working here were growing lab-made precious stones willingly bought by nano-technological research centres worldwide. The correspondent of the www.troitsk.ru portal visited the “diamond farm” and talked to Vladimir Blank, General Director of the institute.
What do we need artificial diamonds for? Is it because scientists have not enough natural diamonds? After all, there are still many diamond fields on this planet where diamonds are mined in considerable amounts.
Unlike synthetic diamonds, natural diamonds do not represent a great value for science. Firstly, in nature there are very few gems of absolutely identical physical and other qualities. For example, De Beers which was founded in 1888 in South Africa and now possessing half of the world’s market dealing with mining, processing and sales of this mineral, has a classification dividing diamonds into 15,000 categories. Is it possible in this case to speak about any serial use of these stones for making some type of devices? Certainly, it is not. Each of such stones will generate different data at the output.
Secondly, even the most high-quality natural diamond always has flaws invisible to an eye. And this can be felt at extreme loads, for example, if such stones are used in highly sensitive temperature detectors or in ionizing radiation sensors.
And thirdly, gem-quality diamonds always contain various impurities which considerably worsen their optical properties even if present in small quantities. Nitrogen is a usual impurity: there is 1 atom of this element per 1,000-100,000 atoms of carbon. However, we receive monocrystals, at least 10 times purer.
We are proud that we learned how to grow diamonds with certain concentrations of impurities depending on the requirements of that area of the industry where they will be applied.
Where are they used in particular?
They are traditionally used in the manufacturing industry for polishing modern ultra-high-strength materials, in radio optics and electronics. They are used to make diamond anvils permitting to research the properties of substances and phase transitions in them at ultra-high pressure of up to 2.5 million atmospheres; optical windows for powerful lasers, highly sensitive temperature gauges, as well as detectors of ultra-violet, x-ray and radiation emissions, quick-response heating elements, needles for scanning probe microscopes.
Diamonds have very good prospects for producing a new generation of semiconductors. The silicon transistor changes its characteristics even at a slightly increased temperature or radiation background failing to function properly. And we have created a diamond gauge which is highly accurate in measuring temperature from -200°С to +500°С. The diamond transistor will outperform any silicon transistor one hundred times in measuring a radiation background which is very important for detectors applied at atomic power stations, in nuclear reactors of submarines and space vehicles. The technique developed at our institute makes it possible to grow semi-conductor monocrystals of p-type having a wide range of specific electric resistance from 0.1 to 109 Om·cm. The area of their application is expanding every year.
Dissolving graphite in metal...
In nature diamonds are formed in the earth crust at the depth of tens of kilometers under the pressure of thousands of atmospheres and in a certain chemical environment at temperatures reaching 1500ºC. This process is rather long, but to reproduce it in vitro (moreover, to accelerate it) is rather difficult, though not impossible. As early as in the middle of the 20th century researchers already learned to cope with diamond synthesis perfectly well. Diamonds were produced in special chambers by direct phase transition from graphite, using the energy of a blast wave – trinitrotoluene is more often used for this purpose than other explosives. But such diamond monocrystals (they are also called detonation or explosion diamonds) turn out to be no more than 1 mm in size. Up to now they are used in the industry only as a powder or abrasive material. It appeared impossible to make such crystals “grow in stature” in this way: increasing them in size badly affects their quality. And now the industry demands diamonds at least 5-10 times as large.
This brought to life the “method of temperature gradient” which is now successfully employed by TISNCM.
In this case high pressure chambers are engaged. Their core — the reaction cell — is filled with a catalyst made of a special alloy of iron-based metals. Among the additives to iron there are metals which absorb nitrogen and oxygen impurities. Highly pure graphite is also mixed in as well as a detonation crystal — a nucleating agent of 0.5-0.6 mm in size. Incidentally, nucleating agents are also manufactured at TISNCM.
Pressure in the chamber is brought up to 5.5 hPa and the chamber is heated up to 1300ºС-1500ºС. Then comes the most intriguing part of it all: the reaction cell is designed so that temperature in it is not identical everywhere. Graphite is located in the hottest spot, while the nucleating agent remains in the cold area. The first one starts to be dissolved in metal and its atoms are diffused to the colder area settling on the nucleating agent in the result. And that’s all! The process is computer-controlled and people may go about their daily business.
In 4-5 days there will already be grown a diamond of 1 carat in size and in three or four weeks you will have a stone of 5–6 carats.
Depending on the would-be technical requirements various additives are mixed in the metal catalyst before the process introducing necessary properties to a future crystal.
The institute has 26 installations in which the scientists “cultivate” their products. So far possible maximum weight of each stone is 5-6 carats.
However, recently the institute received its first order for crystals of 10 carats, so some of the “incubators” will have to be modified. As was already mentioned by Vladimir Blank, TISNCM is able to grow several thousands of diamond carats in a year. According to him, so far only 15-20 percent of diamonds are consumed by the domestic market, while the rest are exported. The major buyers are Japan, the United States and Western Europe. All the goods are distributed between institutes and laboratories which are engaged in research in the field of nano-technologies and are used by scientists only. For women of fashion these “jewels” are a bit too expensive, though cheaper than natural ones. The prime cost of a 5-carat crystal is about $400 per carat, while its retail price is $4,000-$10,000 depending on the preset characteristics of the stone.
