As everyone knows, diamonds have many unique properties--- their hardness, clarity and resistance to corrosion — these features have made them among the most highly prized of natural substances; and they are also very rare.

It is no surprise, therefore, that researchers have sought to reproduce these qualities artificially — that is, to create synthetic diamonds.

Over the past one hundred years, a number of technologies have been developed for generating synthetic diamonds; but, until recently, these diamonds have usually been too full of impurities or too small for widespread practical use.

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A team of researchers at the Geophysical Laboratory of the Carnegie Institution in Washington, D.C. have recently developed a novel, consistent, and rather cheap procedure for changing the properties of large synthetic diamonds. The new technology, called LPHT,  enables large, impure, but high-quality  synthetic, crystal chemical vapor deposition or (SC-CVD) diamonds to be cleansed of their impurities. This study was published online in the Proceedings of the National Academy of Sciences.

Most people, when they think of diamonds, think of them as basically lacking in any color. However it is common for diamonds created in nature as well as synthetic diamonds to have hues, or shades of color, even if invisible to the human eye.

These subtle colours are created by non-carbon atoms, , that become melded into the lattice structure during the diamond's early formation. They change the highly structured bonding of the lattice and as a result, alter the diamond's very properties.

In point of fact, only 1-2% of natural diamonds are classified as devoid of measurable imperfections. Most natural diamonds are stripped of their impurities by heat and pressure before reaching the surface. This process is called plastic deformation.

The classic method of diamond formation is the high-pressure method. High pressure is pressure of more than five gigapascal — and high temperature (1800-2500 degrees centigrade). This mimics the conditions required for diamond formation and prevents the carbon from graphitizing.

But this HPHT method has its problems.

The size of the diamonds that can be made by HPHT is limited by the size of the pressure apparatus — this means that such diamonds are usually pretty small.

In addition, in the annealing process, the outcome depends greatly on the quantity and type of impurities present in the initial sample.

Also, it is an expensive process.

A more recent approach, called single crystal chemical vapor deposition is a low-pressure method for growing lattice structures — like diamonds — from gaseous building blocks.

The  methane is added to a chamber that contains a substrate. This substrate is what the deposited synthetic diamond grows on. The chamber is heated to 900-1500 degrees centigrade by a microwave, then the gaseous molecules break into a plasma and deposit on the substrate.

Result?

A diamond grown like plant, or a pearl in an oyster perhaps!

The rate of growth is very fast: nearly 150 micrometers per hour, and in this way the diamonds can be created on the large side.

The diamonds are often a dark brown, however, because of impurities/imperfections, such as nitrogen, or carbon-hydrogen bonds in the lattice.

A recent study shows the researchers not only found a superior way to remove imperfections from diamonds, but they also gained a clearer understanding of the structural nature of the imperfections.

This new method utilizes high temperatures but low pressure, removing the brown coloring and impurities.

The scientists found that when the diamonds were exposed to various temperatures for different periods of time, imperfections such as vacancies, and nitrogen and hydrogen left over from the initial growth, became mobile and moved out of the lattice, and this in turn, created different hues.

By using methods such as infrared spectroscopy, photoluminescence,and UV visible absorption, they were also able to link certain defects in the crystal with characteristic discolorations. (For example, rosy-pink diamonds are caused by nitrogen vacancy centers, which occur when a nitrogen atom takes the place of a carbon atom adjacent to a vacancy site.)

In addition this new annealing method does not require a high-pressure apparatus, and the process can be done in the same chamber as the CVD growth. "It is striking to see brown CVD diamonds transformed by this cost-efficient method into clear, pink-tinted crystals," co-author Chih-shiue Yan said.

Diamonds are insulators and do not conduct electricity; however, if diamonds are grown with a doping agent under the right conditions, then the gems could become semiconductors.

It may not be likely that next-year's laptops will feature diamond semiconductors in place of silicon, there may be interesting applications.

One rather futuristic possibility mentioned by the Carnegie team is the use of nitrogen-doped rosy-pink diamonds containing nitrogen vacancy centers as semiconductors in quantum computing.

As the advert says 'Diamonds are forever', and quantum computers are considered potentially capable of doing calculations, in hours, or even minutes, that would take traditional computers hundreds, if not millions, of years — so maybe they do go together?

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