Carbon has all kinds of uses between its different forms, and some of them you might not realize. For example, diamond has the best known thermal conductivity at roughly 2200 watts per meter-Kelvin (Wm-1K-1), which would make it very useful in electronics, but the high cost of the material and its being an electrical insulator prevent it from being used to cool our devices. Luckily researchers at multiple universities have been working together over the years to create a material that is far more viable for this application.
Currently most modern processors are made from silicon, which has an adequate thermal conductance of around 150 Wm-1K-1, and when combined with other cooling methods it gets the job done, but as the demand for more powerful devices increases, so does the need for better cooling. This is where the work at the Universities of Texas at Dallas, Illinois at Urbana-Champaign, and of Houston comes into play as they have successfully synthesized a material with a thermal conductivity bested only by diamond. It was in 2013 when researchers at Boston College and the Naval Research Laboratory predicted boron arsenide could compete with diamond as a heat spreader, then in 2015 researchers at the University of Houston made a small, imperfect sample of it. Now the researchers from the three universities listed earlier have successfully created a sample of boron arsenide 4 mm x 2 mm x 1 mm with a thermal conductivity of 1000 Wm-1K-1. It took 14 days to grow the crystal in this experiment, but by increasing this time, it could have become even larger. That smaller sample from 2015 was under 500 microns and had a thermal conductivity around 200 Wm-1K-1.
Key to both growing the crystal this size and improving its thermal conductivity was the method used to grow it; chemical vapor transport. The way this works is one side of a chamber is hot while the other is cold and the raw materials are placed at the hot end. Another chemical then transports the boron and arsenic to the cold side, where they combine to form the boron arsenide crystals. It was only by tuning this process that it reached 1000 Wm-1K-1.
While diamond does still beat boron arsenide for thermal conductivity, both boron and arsenic are cheaper materials and as boron arsenide is a semiconductor, it can be used with computer chips. Just as important as successfully making boron arsenide though is how it directly challenges a theory concerning thermal conductivity, which could lead other researchers to design and synthesize other materials with high thermal conductivities. For now though, the next step is to work on improving the synthesis process for large-scale applications.
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