Microwave Chemical Vapor Deposition Research Articles

Etching Kinetics of Nanodiamond Seeds in the Early Stages of CVD Diamond Growth.

We present an experimental study on the etching of detonation nanodiamond (DND) seeds during typical microwave chemical vapor deposition (MWCVD) conditions leading to ultra-thin diamond film formation, which is fundamental for many technological applications. The temporal evolution of the surface density of seeds on the Si(100) substrate has been assessed by scanning electron microscopy (SEM). The resulting kinetics have been explained in the framework of a model based on the effect of the particle size, according to the Young-Laplace equation, on both chemical potential of carbon atoms in DND and activation energy of the reaction with atomic hydrogen. The model describes the experimental kinetics of seeds' disappearance by assuming that nanodiamond particles with a size smaller than a "critical radius," r*, are etched away while those greater than r* can grow. Finally, the model allows to estimate the rate coefficients for growth and etching from the experimental kinetics.

Nongrowth regime in microwave chemical vapor deposition reactor due to formation of plasma nonhomogeneity

AbstractA new form of microwave discharge with a filament inside plasma volume was investigated in a microwave plasma‐assisted chemical vapor deposition (CVD) reactor. The threshold values of methane content in a hydrogen–methane gas mixture, gas pressure, and microwave power for discharge transition to the new form were found. The parameters' range of existence of the new form of discharge was investigated in three types of CVD reactors. Measurements of the electron density, gas temperature, and spatial distributions of the plasma optical emission lines intensity were carried out for both forms of the discharge. The reasons for the transition of the discharge to a new form and the possibility of using the new discharge form in the microwave plasma‐assisted (MPA) CVD reactor are discussed.

Hydrogen plasma characteristics in a microwave chemical vapor deposition chamber

Hydrogen plasma characteristics in a microwave chemical vapor deposition chamber

Efficient Preparation of a Magnetic Helical Carbon Nanomotor for Targeted Anticancer Drug Delivery.

The applications of nanomotors in the biomedical field have been attracting extensive attention. However, it remains a challenge to fabricate nanomotors in a facile way and effectively load drugs for active targeted therapy. In this work, we combine the microwave heating method and chemical vapor deposition (CVD) to fabricate magnetic helical nanomotors efficiently. The microwave heating method can accelerate intermolecular movement, which converts kinetic energy into heat energy and shortens the preparation time of the catalyst used for carbon nanocoil (CNC) synthesis by 15 times. Fe3O4 nanoparticles are in situ nucleated on the CNC surface by the microwave heating method to fabricate magnetically driven CNC/Fe3O4 nanomotors. In addition, we achieved precise control of the magnetically driven CNC/Fe3O4 nanomotors through remote manipulation of magnetic fields. Anticancer drug doxorubicin (DOX) is then efficiently loaded onto the nanomotors via π-π stacking interactions. Finally, the drug-loaded CNC/Fe3O4@DOX nanomotor can accurately accomplish cell targeting under external magnetic field control. Under short-time irradiation of near-infrared light, DOX can be quickly released onto target cells to effectively kill the cells. More importantly, CNC/Fe3O4@DOX nanomotors allow for single-cell or cell-cluster-targeted anticancer drug delivery, providing a dexterous platform to potentially perform many medically relevant tasks in vivo. The efficient preparation method and application in drug delivery are beneficial for future industrial production and provide inspiration for advanced micro/nanorobotic systems using the CNC as a carrier for a wide range of biomedical applications.

Synthesis of h-BN/diamond heterojunctions and its electrical characteristics

Conductive channel on the surface of hydrogen terminated diamond with two-dimensional h-BN passivation exhibits high hole mobility. However, the current h-BN passivated diamond mainly uses the method of mechanical peeling, which cannot achieve a large-size conductive channel and is difficult to meet the actual application requirements. In this study, the effect of classical transfer h-BN on the conductive channel on the surface of hydrogen terminated diamond is studied. High-quality single crystal diamond is epitaxially grown by microwave chemical vapor deposition (MPCVD) and the hydrogen terminated diamond is obtained by surface hydrogenation treatment. H-BN/H-diamond heterojunctions with different layers of h-BN are prepared by wetting transfer, and the characteristics of channel carrier transport are systematically studied. The results show that the channel conductivity is significantly enhanced after h-BN transfer, and with the increase of h-BN thickness, the enhancement effect of channel conductivity tends to be stable. The transfer of multilayer h-BN can increase the carrier density on the surface of hydrogen terminated diamond by nearly 2 times, and the square resistance is reduced to 50%. The current results show that the h-BN/H-diamond heterojunction may have a transfer doping effect, resulting in a significant increase in carrier density. With the increase of the channel carrier density, the channel mobility on the surface of the h-BN passivated diamond remains stable. The H-BN absorbs on the surface of the diamond, so that the negative charge originally on the surface of the hydrogen termination moves to the surface of h-BN, and the distance of action increases, weakening the coupling of the negative charge of the hole with the negative charge of the dielectric layer in the conductive channel of the hydrogen terminated diamond, which makes the mobility stable.

Replacement of Waveguides by a Resonant Cavity in a Microwave CVD Reactor

There are several configurations of a microwave chemical vapor deposition (MWCVD) reactor. The common characteristic of this reactor is the presence of waveguides. We describe a method that replaces the waveguide, responsible for conducting electromagnetic waves, with a resonant cavity (RC) coupled to a low-pressure chamber. Using RCs over waveguides can help produce dense plasma, which can be used in dissociation processes as the reagents are forced to move within a cavity until they reach the reaction chamber. Based on the excellent performance of the system, it was possible to deposit silicon oxide (SiO2), with the aid of the argon gas mixture, oxygen, and tetraethylorthosilicate (TEOS), on a silicon substrate at room temperature. The film formed was analyzed using an interferometer and FTIR, concluding on the satisfactory quality of the film.

Dielectric Spectroscopy of Hydrogen-Treated Hexagonal Boron Nitride Ceramics

Hexagonal boron nitride (h-BN) is a critical material for 2D electronic devices and has attracted considerable attention owing to its structural similarity to graphene. However, it is a dielectric and modifying its electrical properties is a challenge. Hydrogenation has been calculated as a potential method, although is rarely experimentally measured. Here, dielectric spectroscopy of hot-pressed h-BN after various hydrogen treatments has been investigated. Untreated h-BN showed a frequency independent dielectric constant (4.2±0.2) and an immeasurably low dielectric loss factor, demonstrating the ideal dielectric nature of h-BN across the 103 to 1010 Hz range. However, hydrogen plasma (H+) treatment in a microwave chemical vapour deposition (CVD) reactor amplified the complex permittivity dramatically, introducing Havriliak-Negami (HN) type dispersion (es ≈ 20 ± 2, e∞ ≈ 4.2 ± 0.2) and a percolating long range conductivity (∼ 0.32 mS/m). Annealing in molecular hydrogen (H2) at similar CVD temperatures showed minimal impact, implying that H2 diffusion is not the cause. Oxygen plasma treatment, however, removes the percolating conductivity but the Debye mechanism remains. This leads to the conclusion that the electrical conductivity of h-BN ceramics can be modified through hydrogenation, using atomic hydrogen. The potential as a tunable wide-band gap semiconductor is highlighted however for insulating dielectric substrate applications, microwave CVD may destroy these desirable properties.

Nitrogen-Terminated Polycrystalline Diamond Surfaces by Microwave Chemical Vapor Deposition: Thermal Stability, Chemical States, and Electronic Structure

In this work, we investigate the interaction of microwave (MW) N2 plasma with polycrystalline diamond surfaces. Optical emission spectroscopy (OES) was used to identify different species present in...

Cobalt Phosphide Ultrathin and Freestanding Sheets Prepared through Microwave Chemical Vapor Deposition: A Highly Efficient Oxygen Evolution Reaction Catalyst

AbstractThe oxygen evolution reaction (OER) is the prime barrier for many appealing energy conversion and storage technologies, including water electrolysis, metal–air batteries, and fuel cells. Therefore, developing a cost‐effective, efficient, and robust OER catalyst is still a challenge. Herein, we report a fast, low‐cost, and gram‐scale approach to overcome the synthesis of freestanding, ultrathin (ca. 1.3 nm), and mesoporous CoP sheets through the microwave‐assisted growth of a cobalt‐layered double hydroxide (Co‐LDH) precursor coupled with chemical vapor deposition. The present 2D nanostructure not only guarantees a rich surface of active sites, but also promotes the charge and mass transfers due to the ultrathin and mesoporous features that allow it to efficiently perform the OER. It was found that the surface of the CoP sheets was oxidized in situ under the catalytic conditions, suggesting that Co3O4/CoP is effectively the active form of the catalyst, thereby modulating the electronic structure of Co atoms (active centers). This was embodied by the lowering of the Co‐LDH's required overpotential to achieve 10 mA cm−2 (η10) from 296 to 265 mV and the Tafel slope decrease from 75 to 63 mV dec−1 upon phosphorization. Such performances of CoP nanosheets are remarkably superior to those of commercial RuO2 and compare favorably to the best values reported for noble‐metal‐free OER electrocatalysts.

Low Loss Microwave Ceramic and other Microwave Dielectric Materials for Beam Physics Applications

Introduction. Relativistic, high intensity and small emittance electron bunches are the basis of a future linear collider and free electron laser projects. Drive beam generation in a wakefield structure employing for power extraction and acceleration low loss dielectrics like microwave ceramics, fused silica and Chemical Vapor Deposition (CVD) diamond were considered.Objective. We report here our experimental testing of a ceramic material with extremely low loss tangent at GHz frequency ranges allowing the realization of high efficiency wakefield acceleration. We also present Barium Strontium Titanium oxides (BST) ferroelectric material, which is a critical tuning element of the 400 MHz superconducting radiofrequency (RF) tuner developed and tested by the CERN/Euclid Techlabs collaboration. The materials discussed here also include quartz and CVD diamonds that are capable of supporting the high RF electric fields generated by electron beams or pulsed high power microwaves. These materials have been optimized or specially designed for accelerator applications.Materials and methods. The ceramic materials for accelerators, commonly used for the dielectric based accelerating structures, have to withstand high gradient accelerating fields, and prevent potential charging by electron beams. Correspondingly, the ceramic materials, fused silica and CVD diamond were tested with high power wakefield accelerating structures at Argonne Wakefield Accelerator of Argonne National Laboratory. Some of the presented here ceramic materials were tested at X-band 11.4 GHz magnicon high power source.Results. Low loss microwave ceramics, fused silica, and CVD diamonds have been considered as materials for dielectric based accelerating structures to study of the physical limitations encountered driving > 100 MV/m at microwave and ~ GV/m at THz frequencies in a dielectric based wakefield accelerator. Various ceramic compositions were high power and electron beam tested at X-band 11.4 GHz magnicon power source and Argonne Wakefield Accelerator correspondingly. Special attention was paid to the CVD diamond cylindrical Ka-band 35 GHz wakefield structure development. Finally, the dielectric based structure tuning was demonstrated by varying the permittivity of the BST ferroelectric layer by temperature changes and by applying an external direct current electric field across the ferroelectric. This allows us to control the effective dielectric constant of the composite system and therefore, to control the structure frequency during operation. The same type of ferroelectric material was used for the Ferroelectric Fast Reactive tuner (FE-FRT) development. In a world first, CERN has tested the prototype FE-FRT with a superconducting cavity, and frequency tuning has been successfully demonstrated.Conclusion. Recent results on the development and experimental testing of advanced dielectric materials for accelerator applications are presented. Low loss microwave ceramics, quartz and CVD diamond are considered. We presented our experimental results on wakefield generation in microwave frequency ranges with the dielectric based accelerating structures. Special attention was paid to the experimental results on high power testing at X-band of the externally powered dielectric based components. Finally, we present here first experimental demonstration of ferroelectric tunable microwave ceramic for accelerator application, which includes both tunable dielectric wakefield accelerating structure and ferroelectric based fast high power tuner for superconducting cavities. The experimental results presented here are critical for the advanced dielectric wakefield accelerating structures and other components development intended for the future linear collider projects.

Bias effects on wear and corrosion behavior of amorphous hydrogenated carbon films with zirconia interlayer

This paper describes bias voltage effects during the deposition of amorphous hydrogenated carbon (a-C:H) on an interlayer of zirconia doped with silicon. The a-C:H film was synthesized using a microwave chemical vapor deposition (MPCVD) system. The interlayer was deposited via R.F. sputtering. The a-C:H and the interlayer were deposited on Ti6Al4V titanium alloy, AISI 316 L stainless steel, and silicon wafer. A mixture of methane and hydrogen (CH4 + H2) as a feed gas was needed to grow the a-C:H film. The interlayer was grown using a ZrO2 target stabilized with yttrium (8%) and placed silicon cubes in the greatest erosion zone. The chemical compositions of the a-C:H and the interlayer were determined using energy dispersive X-ray spectroscopy, and the chemical structure was analyzed using Raman spectroscopy on the a-C:H and X-ray diffraction on ZrO2 interlayer. The morphology, surface, and cross section were studied with atomic force microscopy and field emission scanning electron microscopy. The effect of bias voltage variation on the microstructure, mechanical properties, wear, corrosion resistance, and coefficient of friction was studied. The behavior under different normal loads and sliding speeds in the wear test was analyzed. Wear mechanism transitions, wear rate variations, and coefficients were recorded for each bias value applied. The best performance against wear and corrosion was achieved for the film deposited with a bias voltage of −300 V, due the wear rate is reduced as well as the current density compared to lower negative bias voltage values.

DFT studies of refractive index of boron-doped diamond

The density functional theory is one of the optimal solutions in calculation of optical properties of materials on the quantum scale. In this paper, we have investigated refractive index of a boron-doped diamond structure with the usage of Atomistic Toolkit software from Synopsys. During this study, various methods and pseudopotentials were checked to obtain an optimal performance-accuracy method for calculation of such materials. Leading method used in calculation was used meta-GGA with Fritz-Haber Institute pseudopotential. Full Text: PDF ReferencesW. Kohn and L. J. Sham, "Self-Consistent Equations Including Exchange and Correlation Effects", Phys. Rev., vol. 140, no. 4A, pp. A1133–A1138 (1965). CrossRef J. P. Perdew, K. Burke, and M. Ernzerhof, "Generalized Gradient Approximation Made Simple", Phys. Rev. Lett., vol. 77, no. 18, pp. 3865–3868 (1996). CrossRef Y. Yan, J. Gong, and Z. Zong, "Superconductivity of p-type diamond (001) and (111) thin films: Ab initio calculations", Thin Solid Films, vol. 518, no. 17, pp. 4989–4996 (2010). CrossRef M. P. Desjarlais, "Density functional calculations of the reflectivity of shocked xenon with ionization based gap corrections", Contributions to Plasma Physics, vol. 45, no. 3–4, pp. 300–304 (2005). CrossRef L. G. Ferreira, M. Marques, and L. K. Teles, "Approximation to density functional theory for the calculation of band gaps of semiconductors", Physical Review B, vol. 78, no. 12, (2008). CrossRef J. M. Soler et al., "The SIESTA method for ab initio order- N materials simulation", Journal of Physics: Condensed Matter, vol. 14, no. 11, pp. 2745–2779 (2002). CrossRef L. Kleinman and D. M. Bylander, "Efficacious Form for Model Pseudopotentials", Phys. Rev. Lett., vol. 48, no. 20, pp. 1425–1428 (1982). CrossRef Synopsys QuantumWise, Atomistix Toolkit version 2017.12.F. Tran and P. Blaha, "Accurate Band Gaps of Semiconductors and Insulators with a Semilocal Exchange-Correlation Potential", Phys. Rev. Lett., vol. 102, no. 22, p. 226401 (2009). CrossRef D. R. Lide, Ed., CRC Handbook of Chemistry and Physics, 83rd Edition, Boca Raton, Fla.: CRC Press, 2002.N. Troullier and J. L. Martins, "Efficient pseudopotentials for plane-wave calculations", Phys. Rev. B, vol. 43, no. 3, pp. 1993–2006 (1991). CrossRef W. A. Harrison, Solid state theory. McGraw-Hill, 1970.M. Sobaszek et al., "Optical and electrical properties of ultrathin transparent nanocrystalline boron-doped diamond electrodes", Optical Materials, vol. 42, pp. 24–34 (2015). CrossRef M. Ficek et al., "Optical and electrical properties of boron doped diamond thin conductive films deposited on fused silica glass substrates", Applied Surface Science, vol. 387, pp. 846–856 (2016). CrossRef R. Maezono, A. Ma, M. D. Towler, and R. J. Needs, "Equation of State and Raman Frequency of Diamond from Quantum Monte Carlo Simulations", Phys. Rev. Lett., vol. 98, no. 2, p. 025701 (2007). CrossRef R. Bogdanowicz et al., "Opto-Electrochemical Sensing Device Based on Long-Period Grating Coated with Boron-Doped Diamond Thin Film", J. Opt. Soc. Korea, JOSK, vol. 19, no. 6, pp. 705–710, (2015). CrossRef M. Ficek et al., "Linear antenna microwave chemical vapour deposition of diamond films on long-period fiber gratings for bio-sensing applications", Opt. Mater. Express, OME, vol. 7, no. 11, pp. 3952–3962 (2017). CrossRef M. Ficek, R. Bogdanowicz, and J. Ryl, "Nanocrystalline CVD Diamond Coatings on Fused Silica Optical Fibres: Optical Properties Study", Acta Physica Polonica A, vol. 127, no. 3, pp. 868–873 (2015). CrossRef P. J. Stephens, F. J. Devlin, C. F. Chabalowski, and M. J. Frisch, "Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields", J. Phys. Chem., vol. 98, no. 45, pp. 11623–11627 (1994). CrossRef P. Rivero, W. Shelton, and V. Meunier, "Surface properties of hydrogenated diamond in the presence of adsorbates: A hybrid functional DFT study", Carbon, vol. 110, pp. 469–479 (2016). CrossRef

Graphene sheets produced by carbon nanotubes unzipping and their performance as supercapacitor

Carbon nanotubes (CNTs) are well known by their unique properties, such as high electrical conductivity and chemical stability, which can improve charge transfer, facilitating double layer charging in supercapacitor devices. In this work we report on a simple method to unzip CNTs, producing graphene sheets. The amount of hydrogen atoms in the nanotubes synthesis by micro-wave chemical vapor deposition is a critical parameter for unzipping process. High crystalline quality graphene sheets are obtained by this method because of the sp2 bonds sensibility to hydrogen ions reactivity. Unzipped CNTs provided higher capacitance values without an increase in pseudocapacitance. The resulting structure presented an increase in double-layer charging, suggesting a material with good electron transfer rate. This new synthesis method is promising for obtainment of graphene sheets from carbon nanotubes. Besides, unzipped carbon nanotubes presented themselves to be a good alternative for supercapacitors electrodes material.

Linear antenna microwave chemical vapour deposition of diamond films on long-period fiber gratings for bio-sensing applications

The growth processes of nanocrystalline diamond (NCD) thin films on fused silica optical fibers with UV-induced long-period gratings (LPGs) were investigated with regard to biosensing applications. The films were deposited using a linear antenna microwave plasma enhanced chemical vapor deposition system, which allows for the growth of diamond at temperatures below 350°C. The films exhibited a high refractive index n = 2.32, as estimated at λ = 550 nm. The biosensing applications of NCD-coated LPG were considered in relation to bovine serum albumin (BSA) as an external medium. In response to BSA binding and the subsequent formation of a thin bio-layer on the NCD surface, the LPG resonances slightly split and shifted towards lower wavelengths.

Ultrathin Nanocrystalline Diamond Films with Silicon Vacancy Color Centers via Seeding by 2 nm Detonation Nanodiamonds

Color centers in diamonds have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of nanocrystalline diamond (NCD) films as thin as 5-6 nm with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4-6 nm detonation nanodiamonds (DNDs), we prepared and employed hydrogenated 2 nm DNDs (zeta potential = +36 mV) to form extremely dense (∼1.3 × 1013 cm-2), thin (2 ± 1 nm), and smooth (RMS roughness < 0.8 nm) nucleation layers on an Si/SiOx substrate, which enabled the CVD growth of such ultrathin NCD films in two different and complementary microwave (MW) CVD systems: (i) focused MW plasma with an ellipsoidal cavity resonator and (ii) pulsed MW plasma with a linear antenna arrangement. Analytical ultracentrifuge, infrared and Raman spectroscopies, atomic force microscopy, and scanning electron microscopy are used for detailed characterization of the 2 nm H-DNDs and the nucleation layer as well as the ultrathin NCD films. We also demonstrate on/off switching of the SiV center PL in the NCD films thinner than 10 nm, which is achieved by changing their surface chemistry.

Heteroepitaxial diamond growth on 4H-SiC using microwave plasma chemical vapor deposition.

Deposition of heteroepitaxial diamond via microwave chemical vapor deposition has been performed on a 4H-SiC substrate using bias enhanced nucleation followed by a growth step. In future work, the diamond film will serve as a protective layer for an alpha particle sensor designed to function in an electrorefiner during pyroprocessing of spent fuel. The diamond deposition on the 4H-SiC substrate was carried out using a methane-hydrogen gas mixture with varying gas flow rates. The nucleation step was conducted for 30 minutes and provided sufficient nucleation sites to grow a diamond film on various locations on the substrate. The resulting diamond film was characterized using Raman spectroscopy exhibiting the strong Raman peak at 1332 cm−1. Scanning electron microscopy was used to observe the surface morphology and the average grain size of the diamond film was observed to be on the order of ∼2–3 μm.

The nanostructure and microstructure of SiC surface layers deposited by MWCVD and ECRCVD

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) – layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

Impact of chemical vapour deposition plasma inhomogeneity on the spatial variation of sp2 carbon in boron doped diamond electrodes

The impact of plasma inhomogeneity on the sp2 content of thin film (∼micron) boron doped diamond (BDD) electrodes, grown using microwave chemical vapour deposition (MW-CVD) under different methane (CH4) concentrations (1% and 5%), is investigated. The sp2surface content (critical for interpreting electrochemical data) is comparatively assessed using a variety of electrochemical measurements: capacitance; solvent window analysis and quinone surface coverage. For all growths, distinctive regions containing appreciably differing amounts of sp2 carbon are identified, across the wafer. For example, on the 1% CH4 wafer, some areas exhibit electrochemical signatures indicative of high quality, minimal sp2 content BDD, whereas others show regions comprising significant sp2 carbon. Note Raman microscopy was unable to identify these variations. On the 5% CH4 wafer, no region was found to contain minimal levels of sp2 carbon. Changes in sp2 content across the BDD films indicates spatial variations in parameters such as temperature, methane and atomic hydrogen concentrations during growth, in this case linked directly to the use of a commonly employed multi-moded (overmoded) chamber for MW-CVD BDD synthesis, operated under low power density conditions. Varying sp2 levels can have significant impact on the resulting electrochemical behaviour of the BDD.

Fabrication of Nanotwinned Surface on a Nickel Alloy Using a Developed Diamond Panel with Tips Array

In this study, nanotwinned surface is fabricated on a Nickel alloy by means of a developed diamond panel with tips array. The diamond panel has an area of 10×10 mm2, and is grown using microwave chemical vapor deposition. The diamond tips are submicron in radius and formed on a silicon substrate with an array full of uniformed inverted pyramid pits. The nanotwinned surface is produced under the pressure of 1 MPa exerted by the diamond panel with tips array. Nanotwins are confirmed using transmission electron microscopy. The nanotwinned surface is generated by indention of diamond panel at room temperature using mechanical force, neither material removal nor chemical reagents. This is different from previous reports, in which high temperature, high pressure, chemical reagents or vacuum conditions are employed usually.

Preparation of nano-diamond films on GaN with a Si buffer layer

Gallium nitride (GaN) has been widely used in electronic and optoelectronic devices because of its unique electrical properties. However, its low thermal conductivity and the high thermal boundary resistance at the interface between GaN and substrates such as Si and Al2O3preventefficient heat dissipation from the heated regions, which limits the further development of GaN-based high power devices. Diamond, with the highest thermal conductivity, has been considered to be one of the most promising heat sink materials. However, it is hard to prepare a diamond film on a GaN substrate because there is a high thermal expansion coefficient difference and also a large lattice mismatch between them. An approach to prepare a nano-diamond film on a GaN substrate by incorporating a Si buffer layer has been proposed. A GaN substrate decomposes significantly from 560 to 680°C when exposed to ahydrogen plasma for 5 min and no adhesive nano-diamond film can be directly grown on it. This decomposition is significantly suppressed by the presence of a Si buffer layer and a nano-diamond film about 2 μm thick can be deposited on a GaN substrate by microwave chemical vapor deposition using CH4 as the carbon source. With an optimum Si layer of 10 nm, the adhesive force between the nano-diamond film and the GaN substrate reaches 10N, which is ascribed to the complete conversion of the Si layer to a silicon carbidetransition layer during the deposition.