Some aspects of the thermal conductivity of isotopically enriched diamond single crystals

Insight into Interfacial Heat Transfer of β-Ga2O3/Diamond Heterostructures via the Machine Learning Potential

β-Ga2O3 is an ultrawide-band gap semiconductor with excellent potential for high-power and ultraviolet optoelectronic device applications. Low thermal conductivity is one of the major obstacles to enable the full performance of β-Ga2O3-based devices. A promising solution for this problem is to integrate β-Ga2O3 with a diamond heat sink. However, the thermal properties of the β-Ga2O3/diamond heterostructures after the interfacial bonding have not been studied extensively, which are influenced by the crystal orientations and interfacial atoms for the β-Ga2O3 and diamond interfaces. In this work, molecular dynamics simulations based on machine learning potential have been adopted to investigate the crystal-orientation-dependent and interfacial-atom-dependent thermal boundary resistance (TBR) of the β-Ga2O3/diamond heterostructure after interfacial bonding. The differences in TBR at different interfaces are explained in detail through the explorations of thermal conductivity value, thermal conductivity spectra, vibration density of states, and interfacial structures. Based on the above explorations, a further understanding of the influence of different crystal orientations and interfacial atoms on the β-Ga2O3/diamond heterostructure was achieved. Finally, insightful optimization strategies have been proposed in the study, which could pave the way for better thermal design and management of β-Ga2O3/diamond heterostructures according to guidance in the selection of the crystal orientations and interfacial atoms of the β-Ga2O3 and diamond interfaces.

A Critical Review of Thermal Boundary Conductance across Wide and Ultrawide Bandgap Semiconductor Interfaces

The emergence of wide and ultrawide bandgap semiconductors has revolutionized the advancement of next-generation power, radio frequency, and opto- electronics, paving the way for chargers, renewable energy inverters, 5G base stations, satellite communications, radars, and light-emitting diodes. However, the thermal boundary resistance at semiconductor interfaces accounts for a large portion of the near-junction thermal resistance, impeding heat dissipation and becoming a bottleneck in the devices' development. Over the past two decades, many new ultrahigh thermal conductivity materials have emerged as potential substrates, and numerous novel growth, integration, and characterization techniques have emerged to improve the TBC, holding great promise for efficient cooling. At the same time, numerous simulation methods have been developed to advance the understanding and prediction of TBC. Despite these advancements, the existing literature reports are widely dispersed, presenting varying TBC results even on the same heterostructure, and there is a large gap between experiments and simulations. Herein, we comprehensively review the various experimental and simulation works that reported TBCs of wide and ultrawide bandgap semiconductor heterostructures, aiming to build a structure-property relationship between TBCs and interfacial nanostructures and to further boost the TBCs. The advantages and disadvantages of various experimental and theoretical methods are summarized. Future directions for experimental and theoretical research are proposed.

Hyperbolic-Metamaterials-Based SPR Temperature Sensor Enhanced by a Nanodiamond-PDMS Hybrid for High Sensitivity and Fast Response

A high-performance surface plasmon resonance (SPR) fiber sensor is proposed with hyperbolic metamaterials (HMMs), nanodiamonds (NDs), and polydimethylsiloxane (PDMS) to enhance the temperature sensitivity and response time. The HMM with tunable dispersion can break through the structural limitations of the optical fiber to improve the refractive index (RI) sensitivity, while NDs and PDMS with large thermo-optic coefficients enable to induce significant RI change under varied thermal fields. The ternary composite endows the sensor with a high temperature sensitivity of -9.021 nm/°C, which is 28.6 times higher than that of the conventional gold film-based SPR sensor. Furthermore, NDs with high thermal conductivity (2200 W/mK) effectively expedite the thermal response of PDMS, which reduces the response time from 80 to 6 s. It is believed that the proposed sensors with high sensitivity, fast response time, and compact size have great potential for applications in industrial production, healthcare, environmental monitoring, etc.

Electrical Characteristics of Diamond MOSFET with 2DHG on a Heteroepitaxial Diamond Substrate

In this work, hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field-effect-transistors (MOSFETs) on a heteroepitaxial diamond substrate with an Al₂O₃ dielectric and a passivation layer were characterized. The full-width at half maximum value of the diamond (004) X-ray rocking curve was 205.9 arcsec. The maximum output current density and transconductance of the MOSFET were 172 mA/mm and 10.4 mS/mm, respectively. The effect of a low-temperature annealing process on electrical properties was also investigated. After the annealing process in N₂ atmosphere, the threshold voltage (V_th) and flat-band voltage (V_FB) shifts to negative direction due to loss of negative charges. After annealing at 423 K for 3 min, the maximum value of hole field effective mobility (μ_eff) increases by 27% at V_th − V_GS = 2 V. The results, which are not inferior to those based on homoepitaxial diamond, promote the application of heteroepitaxial diamond in the field of electronic devices.

Revisiting the thermal conductivity of Si, Ge and diamond from first principles: roles of atomic mass and interatomic potential

The thermal conductivity (κ) of nonmetals is determined by the constituent atoms, the crystal structure and interatomic potentials. Although the group-IV elemental solids Si, Ge and diamond have been studied extensively, a detailed understanding of the connection between the fundamental features of their energy landscapes and their thermal transport properties is still lacking. Here, starting from first principles, we analyze those factors, including the atomic mass (m) and the second- (harmonic) and third-order (anharmonic) interatomic force constants (IFCs). Both the second- and third-order IFCs of Si and Ge are very similar, and thus Si and Ge represent ideal systems to understand how the atomic mass alone affectsκ. Although the group velocity (v) decreases with increasing atomic mass (v-1∝m), the phonon lifetime (τ) follows the opposite trend (τ∝m). Since the contribution toκfrom each phonon mode is approximately proportionalv²τ,κis lower for the heavier element, namely Ge. Although the extremely high thermal conductivity of diamond is often attributed to weak anharmonic scattering, the anharmonic component of the interatomic potential is not much weaker than those of Si and Ge, which seems to be overlooked in the literature. In fact, the absolute magnitude of the third-order IFCs is much larger in diamond, and the ratios of the third-order IFCs with respect to the second-order ones are comparable to those of Si and Ge. We also explain the experimentally measuredκof high-quality diamonds (Inyushikinet al2018Phys. Rev. B97144305) by introducing boundary scattering into the picture, and obtain good agreement between calculations and measurements.

Molecular dynamics simulation of phonon thermal transport in nanotwinned diamond with a new optimized Tersoff potential

The inaccuracy of the most widely used potentials in calculating the phonon transport of sp³ carbon materials hinders the use of molecular dynamics simulations for revealing the underlying mechanism of phonon transport in diamond and related materials. Here, we introduce an optimized Tersoff potential by optimizing the parameters to fit the experimentally determined phonon dispersion in diamond along the high-symmetry directions. Molecular dynamics simulations are performed using this new potential to investigate the phonon thermal transport in flawless and nanotwinned diamond. The simulation results show that while the phonon lifetimes of nanotwinned diamond are slightly lower than those of the flawless one, the phonon group velocities of nanotwinned diamond are obviously lower than those of diamond. The present results indicate that the twin boundaries in diamond are ineffective in scattering the phonons and the lower thermal conductivity of the nanotwinned diamond mainly originates from the lower group velocities due to its reduced structural rigidity.

Isotope Effect in Thermal Conductivity of Polycrystalline CVD-Diamond: Experiment and Theory

We measured the thermal conductivity κ(T) of polycrystalline diamond with natural (natC) and isotopically enriched (12C content up to 99.96 at.%) compositions over a broad temperature T range, from 5 to 410 K. The high quality polycrystalline diamond wafers were produced by microwave plasma chemical vapor deposition in CH4-H2 mixtures. The thermal conductivity of 12C diamond along the wafer, as precisely determined using a steady-state longitudinal heat flow method, exceeds much that of the natC sample at T>60 K. The enriched sample demonstrates the value of κ(298K)=25.1±0.5 W cm−1 K−1 that is higher than the ever reported conductivity of natural and synthetic single crystalline diamonds with natural isotopic composition. A phenomenological theoretical model based on the full version of Callaway theory of thermal conductivity is developed which provides a good approximation of the experimental data. The role of different resistive scattering processes, including due to minor isotope 13C atoms, defects, and grain boundaries, is estimated from the data analysis. The model predicts about a 37% increase of thermal conductivity for impurity and dislocation free polycrystalline chemical vapor deposition (CVD)-diamond with the 12C-enriched isotopic composition at room temperature.

Ultrahigh Thermal Conductivity of θ-Phase Tantalum Nitride

Extracting long-lasting performance from electronic devices and improving their reliability through effective heat management requires good thermal conductors. Taking both three- and four-phonon scattering as well as electron-phonon and isotope scattering into account, we predict that semimetallic θ-phase tantalum nitride (θ-TaN) has an ultrahigh thermal conductivity (κ), of 995 and 820  W m^{-1} K^{-1} at room temperature along the a and c axes, respectively. Phonons are found to be the main heat carriers, and the high κ hinges on a particular combination of factors: weak electron-phonon scattering, low isotopic mass disorder, and a large frequency gap between acoustic and optical phonon modes that, together with acoustic bunching, impedes three-phonon processes. On the other hand, four-phonon scattering is found to be significant. This study provides new insight into heat conduction in semimetallic solids and extends the search for high-κ materials into the realms of semimetals and noncubic crystal structures.

Crystalline Interlayers for Reducing the Effective Thermal Boundary Resistance in GaN-on-Diamond

Integrating diamond with GaN high electron mobility transistors (HEMTs) improves thermal management, ultimately increasing the reliability and performance of high-power high-frequency radio frequency amplifiers. Conventionally, an amorphous interlayer is used before growing polycrystalline diamond onto GaN in these devices. This layer contributes significantly to the effective thermal boundary resistance (TBR_eff) between the GaN HEMT and the diamond, reducing the benefit of the diamond heat spreader. Replacing the amorphous interlayer with a higher thermal conductivity crystalline material would reduce TBR_eff and help to enable the full potential of GaN-on-diamond devices. In this work, a crystalline Al_0.32Ga_0.68N interlayer has been integrated into a GaN/AlGaN HEMT device epitaxy. Two samples were studied, one with diamond grown directly on the AlGaN interlayer and another incorporating a thin crystalline SiC layer between AlGaN and diamond. The TBR_eff, measured using transient thermoreflectance, was improved for the sample with SiC (30 ± 5 m² K GW^-1) compared to the sample without (107 ± 44 m² K GW^-1). The reduced TBR_eff is thought to arise from improved adhesion between SiC and the diamond compared to the diamond directly on AlGaN because of an increased propensity for carbide bond formation between SiC and the diamond. The stronger carbide bonds aid transmission of phonons across the interface, improving heat transport.

Effect of Deep-Defects Excitation on Mechanical Energy Dissipation of Single-Crystal Diamond

The ultrawide band gap of diamond distinguishes it from other semiconductors, in that all known defects have deep energy levels that are less active at room temperature. Here, we present the effect of deep defects on the mechanical energy dissipation of single-crystal diamond experimentally and theoretically up to 973 K. Energy dissipation is found to increase with temperature and exhibits local maxima due to the interaction between phonons and deep defects activated at specific temperatures. A two-level model with deep energies is proposed to explain well the energy dissipation at elevated temperatures. It is evident that the removal of boron impurities can substantially increase the quality factor of room-temperature diamond mechanical resonators. The deep energy nature of the defects bestows single-crystal diamond with outstanding low intrinsic energy dissipation in mechanical resonators at room temperature or above.

Thermal conductivity of one-dimensional organic nanowires: effect of mass difference phonon scattering

We report the thermal conductivity of π-stacked metallophthalocyanine nanowires using the thermal bridge method. In the temperature range of 20-300 K, the thermal conductivity of copper phthalocyanine nanowires (CuPc NWs) and iron phthalocyanine nanowires (FePc NWs) increases with temperature and reaches a peak value at around T = 40 K, then decreases at a higher temperature following T ^-1 behavior. For three FePc NWs, the peak values are 7.1 ± 1.21, 8.3 ± 1.33, and 7.6 ± 1.42 Wm^-1 K^-1, respectively. The peak thermal conductivity is 6.6 ± 0.67 and 6.6 ± 0.51 Wm^-1 K^-1 for the two CuPc nanowires. The thermal conductivity of FePc NWs is slightly larger than that of CuPc NWs, which is believed to result from the different mass of metal atoms in the phthalocyanine centers, indicating a phonon mass-difference scattering effect. Meanwhile, the thermal contact conductance of the FePc-Pt interface is measured, which will benefit from a better understanding of the thermal transport across dissimilar interfaces.

Thermal conductivity of hexagonal BC2P – a first-principles study

In this work, we report a high thermal conductivity (k) of 162 W m⁻¹ K⁻¹ and 52 W m⁻¹ K⁻¹ at room temperature, along the directions perpendicular and parallel to the c-axis, respectively, of bulk hexagonal BC₂P (h-BC₂P), using first-principles calculations.

A lower bound to the thermal diffusivity of insulators

It has been known for decades that thermal conductivity of insulating crystals becomes proportional to the inverse of temperature when the latter is comparable to, or higher than, the Debye temperature. This behavior has been understood as resulting from Umklapp scattering among phonons. We put under scrutiny the magnitude of the thermal diffusion constant in this regime and find that it does not fall below a threshold set by the square of sound velocity times the Planckian time ([Formula: see text]). The conclusion, based on scrutinizing the ratio in cubic crystals with high thermal resistivity, appears to hold even in glasses where Umklapp events are not conceivable. Explaining this boundary, reminiscent of a recently-noticed limit for charge transport in metals, is a challenge to theory.

Development of ultrafast capabilities for X-ray free-electron lasers at the linac coherent light source

The ability to produce ultrashort, high-brightness X-ray pulses is revolutionizing the field of ultrafast X-ray spectroscopy. Free-electron laser (FEL) facilities are driving this revolution, but unique aspects of the FEL process make the required characterization and use of the pulses challenging. In this paper, we describe a number of developments in the generation of ultrashort X-ray FEL pulses, and the concomitant progress in the experimental capabilities necessary for their characterization and use at the Linac Coherent Light Source. This includes the development of sub-femtosecond hard and soft X-ray pulses, along with ultrafast characterization techniques for these pulses. We also describe improved techniques for optical cross-correlation as needed to address the persistent challenge of external optical laser synchronization with these ultrashort X-ray pulses. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

High Thermal Conductivity in Boron Arsenide: From Prediction to Reality

Modern first-principles calculations predict that the thermal conductivity of boron arsenide is second only to that of diamond, the best thermal conductor, which may be of benefit for waste heat management in electronic devices. With the optimization of single-crystal growth methods, large-size and high-quality boron arsenide single crystals have been grown and thermal conductivity measurements have verified the related predictions. Benefiting from the increased size and improved qualities, additional properties have been characterized. Important factors related to boron arsenide, remaining challenges, and the future outlook are addressed in this minireview.

Giant thermal conductivity in diamane and the influence of horizontal reflection symmetry on phonon scattering

Diamane, a chemically derived two-dimensional material, shows many superior physical and chemical properties similar to diamond thin films. Through the Peierls-Boltzmann transport equation, we reveal giant thermal conductivity in diamane with a stacking order of both AB and AA (respectively, abbreviated as D-AB and D-AA, hereafter) which are both comparable to that of diamond. Like in graphene, the phonon transport falls into the hydrodynamic regime even at room temperature, and the major contribution to the total thermal conductivity comes from the out-of-plane acoustic phonon modes (>40%). In addition, the thermal conductivity shows a dependence on the stacking order, namely, the thermal conductivity of D-AA, ∼2240 W m-1 K-1 at 300 K, is around 15% larger than that of D-AB, which is due to the strong restriction on the phonon scattering phase space induced by the horizontal reflection symmetry in D-AA. Such a kind of restriction, not limited to single atomic plane systems, is a general feature in two-dimensional materials with a horizontal reflection symmetry.

Design and numerical simulations of W-diamond transmission target for distributed x-ray sources

Distributed x-ray sources enable novel designs of x-ray imaging systems. However, the x-ray power of such sources is limited by the focal spot power density of the fixed anode. To further improve x-ray output, we have designed and evaluated a diamond-W transmission target for multi-pixel x-ray sources. The target features a thin layer of tungsten deposited on a diamond substrate. The thickness of tungsten layer was optimized for maximum fluence through Monte Carlo simulations. Finite element thermal simulations were performed to evaluate focal spot temperature in the target under different power loadings and dwell duration. The results showed that the optimal thickness of the tungsten layer in the W-diamond transmission target is linearly proportional to the electron energy. A 5-6 μm tungsten thickness is suitable for the kVps ranges from 60 kVp to 140 kVp. A W-diamond transmission target produces up to 20% more x-ray fluence than a traditional W reflection target in the beam center depending on the kVp settings. The x-ray spectrum of the transmission target shows less characteristic x-rays than that of reflection target. The thermal performance of W-diamond targets for peak power is significantly better than that of reflection targets. The maximum focal spot power densities of W-diamond transmission and W reflection targets are both strongly dependent on the dwell duration. For longer pulse durations, the W-diamond target allows as much as a four-fold increase in power and an eight-fold increase in power density in comparison to a traditional W reflection target for the same temperature spikes. The stability of the W-diamond bond needs to be tested experimentally. Nevertheless, the W-diamond transmission target is an appealing target that can significantly simplify the design and improve the performance of distributed x-ray sources.

Fermi Surface Nesting and Phonon Frequency Gap Drive Anomalous Thermal Transport

The lattice thermal conductivity, k_{L}, of typical metallic and nonmetallic crystals decreases rapidly with increasing temperature because phonons interact more strongly with other phonons than they do with electrons. Using first principles calculations, we show that k_{L} can become nearly independent of temperature in metals that have nested Fermi surfaces and large frequency gaps between acoustic and optic phonons. Then, the interactions between phonons and electrons become much stronger than the mutual interactions between phonons, giving the fundamentally different k_{L} behavior. This striking trend is revealed here in the group V transition metal carbides, vanadium carbide, niobium carbide, and tantalum carbide, and it should also occur in several other metal compounds. This work gives insights into the physics of heat conduction in solids and identifies a new heat flow regime driven by the interplay between Fermi surfaces and phonon dispersions.

Thermal Mode Spectroscopy for Thermal Diffusivity of Millimeter-Size Solids

Heat conduction possesses (thermal) modes in analogy with acoustics even without oscillation. Here, we establish thermal mode spectroscopy to measure the thermal diffusivity of small specimens. Local heating with a light pulse excites such modes that show antinodes at the heating point, and photothermal detection at another antinode spot allows measuring relaxation behavior of the desired mode selectively: The relaxation time yields thermal diffusivity. The Ritz method is proposed for arbitrary geometry specimens. This method is applicable even to a diamond crystal with ∼1  mm dimensions.

Defect-Engineered Heat Transport in Graphene: A Route to High Efficient Thermal Rectification

Low-dimensional materials such as graphene provide an ideal platform to probe the correlation between thermal transport and lattice defects, which could be engineered at the molecular level. In this work, we perform molecular dynamics simulations and non-contact optothermal Raman measurements to study this correlation. We find that oxygen plasma treatment could reduce the thermal conductivity of graphene significantly even at extremely low defect concentration (∼83% reduction for ∼0.1% defects), which could be attributed mainly to the creation of carbonyl pair defects. Other types of defects such as hydroxyl, epoxy groups and nano-holes demonstrate much weaker effects on the reduction where the sp² nature of graphene is better preserved. With the capability of selectively functionalizing graphene, we propose an asymmetric junction between graphene and defective graphene with a high thermal rectification ratio of ∼46%, as demonstrated by our molecular dynamics simulation results. Our findings provide fundamental insights into the physics of thermal transport in defective graphene, and two-dimensional materials in general, which could help on the future design of functional applications such as optothermal and electrothermal devices.

Thermal conductivity of group-IV semiconductors from a kinetic-collective model

The thermal conductivity of group-IV semiconductors (silicon, germanium, diamond and grey tin) with several isotopic compositions has been calculated from a kinetic-collective model. From this approach, significantly different to Callaway-like models in its physical interpretation, the thermal conductivity expression accounts for a transition from a kinetic (individual phonon transport) to a collective (hydrodynamic phonon transport) behaviour of the phonon field. Within the model, we confirm the theoretical proportionality between the phonon-phonon relaxation times of the group-IV semiconductors. This proportionality depends on some materials properties and it allows us to predict the thermal conductivity of the whole group of materials without the need to fit each material individually. The predictions on thermal conductivities are in good agreement with experimental data over a wide temperature range.

First-principles determination of ultrahigh thermal conductivity of boron arsenide: a competitor for diamond?

We have calculated the thermal conductivities (κ) of cubic III-V boron compounds using a predictive first principles approach. Boron arsenide is found to have a remarkable room temperature κ over 2000 W m(-1) K(-1); this is comparable to those in diamond and graphite, which are the highest bulk values known. We trace this behavior in boron arsenide to an interplay of certain basic vibrational properties that lie outside of the conventional guidelines in searching for high κ materials, and to relatively weak phonon-isotope scattering. We also find that cubic boron nitride and boron antimonide will have high κ with isotopic purification. This work provides new insight into the nature of thermal transport at a quantitative level and predicts a new ultrahigh κ material of potential interest for passive cooling applications.

Thermal rectification in mass-graded nanotubes: a model approach in the framework of reverse non-equilibrium molecular dynamics simulations

The thermal rectification in nanotubes with a mass gradient is studied by reverse non-equilibrium molecular dynamics simulations. We predict a preferred heat flow from light to heavy atoms which differs from the preferential direction in one-dimensional monoatomic systems. This behavior of nanotubes is explained by anharmonicities caused by transverse motions which are stronger at the low-mass end. The present simulations show an enhanced rectification with increasing tube length, diameter and mass gradient. Implications of the present findings for applied topics are mentioned concisely.

Diamond at 800 GPa

A new compression technique, which enables the study of solids into the TPa regime, is described and used to ramp (or quasi-isentropically) compress diamond to a peak pressure of 1400 GPa. Diamond stress versus density data are reported to 800 GPa and suggest that the diamond phase is stable and has significant material strength up to at least this stress level. Data presented here are the highest ramp compression pressures by more than a factor of 5 and the highest-pressure solid equation-of-state data ever reported.

The effect of Al/Si ratio on the transport properties of the layered intermetallic compound CaAl(2)Si(2)

We report the results of the electrical resistivity and Seebeck coefficient as well as thermal conductivity measurements on the stoichiometric CaAl(2)Si(2) and non-stoichiometric CaAl(1.75)Si(2.25), CaAl(1.9)Si(2.1), CaAl(2.1)Si(1.9), and CaAl(2.25)Si(1.75) compounds in the temperature range 10-300 K. It has been found that the magnitude of electrical resistivity decreases for the non-stoichiometric samples, attributed to the shift of Fermi energy from the dip of the density of states as a consequence of the changed Si/Al content. In addition, a systematic change in the magnitude of Seebeck coefficient as a function of Al/Si concentration has been observed. The results have been associated with the effect of hole/electron doping on the Fermi level density of states. A detailed analysis of the electrical resistivity and Seebeck coefficient suggests the presence of two types of charge carrier and the temperature dependent changes in their mobility. From the thermal conductivity results, we correlated the extent of disorder and Al/Si ratio with various thermal scattering mechanisms in the investigated temperature range.

Isotope effect on the thermal conductivity of boron nitride nanotubes

We have measured the temperature-dependent thermal conductivity kappa(T) of individual multiwall boron nitride nanotubes using a microfabricated test fixture that allows direct transmission electron microscopy characterization of the tube being measured. kappa(T) is exceptionally sensitive to isotopic substitution, with a 50% enhancement in kappa(T) resulting for boron nitride nanotubes with 99.5% 11B. For isotopically pure boron nitride nanotubes, kappa rivals that of carbon nanotubes of similar diameter.

''The Identity of 14N and 13C Contamination Dependence on the Heat Conductivity of Diamond Monocrystals''

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Thermal and optical applications of thin film diamond

Virtually all recent reviews of the market potential for chemical vapour deposited (CVD) diamond have featured the thermal management of electronic semiconductor devices as an imminent application for this new material. There is an existing market for natural diamond substrates (‘heat sinks’) in sub-millimetre sizes, and their thermal performance has been extensively studied, CVD diamond heat sinks in millimetre and larger sizes are already in use, but there are constraints to their applicability arising from thermal and mechanical factors. Their advantages and limitations are discussed. The first ‘optical’ applications of CVD diamond films were as X-ray transmissive components (lithography masks and windows for soft X-ray detectors), but with improvements in the technology of CVD diamond growth a larger market for wide-band infrared transmissive windows is now developing. This results from the availability of large area (greater than 1000 mm 2 ) CVD diamond plates of adequate thickness and with transparency achieved through control of diamond grain size and orientation.

The thermal conductivity of CVD diamond films

The thermal conductivity of chemical vapour deposition diamond films is controlled by the microstructure, impurity content and carbon double bonds in the films. In high conductivity films, dislocation scattering is dominant at low temperatures, while phonon-phonon scattering limits the conductivity at room temperature. In lower quality films, hydrogen and metal impurities as well as carbon double bonds constrain the conductivity up to room temperature. Significant anisotropies and gradients in the thermal conductivity exist in some films because of their micro structure.