A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K) and 400 W/(m·K), respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon); one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K). Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity.

https://www.mdpi.com/1996-1944/2/4/2467/pdf

Thermal Conductivity of Diamond Composites

Although diamond has the highest known room temperature thermal conductivity, k∼2200W∕mK, highly sp3 amorphous carbon films have k<15W∕mK. We carry out an integrated experimental and simulation study of thermal transport in ultrananocrystalline diamond (UNCD) films. The experiments show that UNCD films with a grain size of 3–5nm have thermal conductivities as high as k=12W∕mK at room temperature, comparable with that of the most conductive amorphous diamond films. This value corresponds to a grain boundary (Kapitza) conductance greater than 3000MW∕m2K, which is ten times larger than that previously seen in any material. Our simulations of both UNCD and individual diamond grain boundaries yield values for the grain boundary conductance consistent with the experimentally obtained value, leading us to conclude that thermal transport in UNCD is controlled by the intrinsic properties of the grain boundaries.

/pdf/thermal-transport-and-grain-boundary-conductance-in-45m5e6yojp.pdf

Thermal transport and grain boundary conductance in ultrananocrystalline diamond thin films

Microstructural and biological properties of nanocrystalline diamond coatings

This paper reviews the research in nanomaterials conducted in our laboratory in the last decade using conventional and synchrotron radiation techniques. While preparative and conventional characterisation techniques are described, emphasis is placed on the analysis of nanomaterials using synchrotron radiation. Materials of primary interests are metal nanoparticles and semiconductor nanowires and naonribbons. Synchrotron techniques based on absorption spectroscopy such as X-ray absorption fine structures (XAFS), which includes X-ray absorption near edge structures (XANES) and extended X-ray absorption fine structures (EXFAS), and de-excitation spectroscopy, including X-ray excited optical luminescence (XEOL), time-resolved X-ray excited optical luminescence (TRXEOL) and X-ray emission spectroscopy (XES) are described. We show that the tunability, brightness, polarisation and time structure of synchrotron radiation are providing unprecedented capabilities for nanomaterials analysis. Synchrotron studies of prototype systems such as gold nanoparticles, 1-D nanowires of group IV materials, C, Si and Ge as well as nanodiamond, and compound semiconductors, ZnS, CdS, ZnO and related materials are used to illustrate the power and unique capabilities of synchrotron spectroscopy in the characterisation of local structure, electronic structure and optical properties of nanomaterials.

http://xrm.phys.northwestern.edu/research/pdf_papers/2008/sham_ijn_2008.pdf

Nanoparticles and nanowires: synchrotron spectroscopy studies

Thermal properties of diamond particle-dispersed Cu composites

Heteroepitaxial nucleation of diamond on Si(100) via double bias-assisted hot filament chemical vapor deposition

Measuring thermal conductivity of CVD diamond and diamond-like films on silicon substrates by holographic interferometry

Nucleation of diamond films by ECR-enhanced microwave plasma chemical vapor deposition

Theoretical study on misoriented diamond nucleations on Si(001) surface

The origin of mis-oriented diamond grains frequently observed in heteroepitaxial diamond films on (001) silicon surfaces was studied. By statistically analyzing the in-plane rotation angles of diamond grains in scanning electron microscopy observations, it was found that the distribution of the grain orientation is not random and two satellite distribution peaks at about 20° and 30° accompany the main distribution peak at zero degree referenced to the direction of substrate. The interface structure corresponding to the main distribution peak at zero degree of oriented diamond growth has been proposed in our previous studies. In this study, our molecular orbital PM3 simulation of a step-by-step diamond nucleation further reveals two other metastable diamond/silicon interfacial structures. The orientations of the corresponding diamond grains are parallel to the (001) silicon surface but with in-plane rotations of 20° and 30° respectively with respect to the direction. We relate these two mis-oriented growths to the two satellite peaks of grain orientation distribution. Based on this study, the possibility in experiment to reduce the formation of mis-oriented configurations and to obtain a perfectly oriented diamond growth is discussed.

C. Sun

Papers

Heteroepitaxial nucleation of diamond on Si(100) via double bias-assisted hot filament chemical vapor deposition

Measuring thermal conductivity of CVD diamond and diamond-like films on silicon substrates by holographic interferometry

Nucleation of diamond films by ECR-enhanced microwave plasma chemical vapor deposition

Theoretical study on misoriented diamond nucleations on Si(001) surface

The origin of mis-oriented diamond grains nucleated directly on (001) silicon surface