Properties Of Single Crystal Diamond Research Articles

Terahertz optoelectronic properties of synthetic single crystal diamond

A systematic investigation is undertaken for studying the optoelectronic properties of single crystal diamond (SCD) grown by microwave plasma chemical vapor deposition (MPCVD). It is indicated that, without intentional doping and surface treatment during the sample growth, the terahertz (THz) optical conduction in SCD is mainly affected by surface H-terminations, -OH-, O- and N-based functional groups. By using THz time-domain spectroscopy (TDS), we measure the transmittance, the complex dielectric constant and optical conductivity σ(ω) of SCD. We find that SCD does not show typical semiconductor characteristics in THz regime, where σ(ω) cannot be described rightly by the conventional Drude formula. Via fitting the real and imaginary parts of σ(ω) to the Drude-Smith formula, the ratio of the average carrier density to the effective electron mass γ = ne/m*, the electronic relaxation time τ and the electronic backscattering or localization factor can be determined optically. The temperature dependence of these parameters is examined. From the temperature dependence of γ, a metallic to semiconductor transition is observed at about T = 10 K. The temperature dependence of τ is mainly induced by electron coupling with acoustic-phonons and there is a significant effect of photon-induced electron backscattering or localization in SCD. This work demonstrates that THz TDS is a powerful technique in studying SCD which contains H-, N- and O-based bonds and has low electron density and high dc resistivity. The results obtained from this study can benefit us to gain an in-depth understanding of SCD and may provide new guidance for the application of SCD as electronic, optical and optoelectronic materials.

Epitaxial lateral growth of single-crystal diamond under high pressure by a plate-to-plate MPCVD

The epitaxial lateral growth of single-crystal diamond (SCD) using a plate-to-plate microwave plasma chemical vapor deposition (MPCVD) reactor under high pressure is investigated. The radicals’ distribution in H2/CH4 plasma as a function of pressure was locally detected by optical emission spectroscopy (OES). Raman spectroscopy and optical microscope were employed to analyze the properties of SCD deposited in different pressure. The OES results show that radicals’ distribution along the substrate direction is symmetrical under 20 kPa pressure. The symmetrical distribution of radicals at 20 kPa is in favor of epitaxial lateral growth SCD around the seed and without polycrystalline diamond (PCD) rim. When the pressure is increased to 21.5 kPa, the optical emission spectra center of plasma shifts close to the microwave reflector where is far away from the microwave source. The contact state between the diamond seed and the plasma is deteriorated and the PCD rim occurs in the plasma uncovered area. While the epitaxial lateral growth pattern occurs in the plasma covered area and the lateral growth rate of this region improves with the increase of pressure. A higher growth rate does not result in good quality; meanwhile, the diamond growth step spacing and direction become inconsistent in the transition zone as a function of pressure increasing. Finally, the overall effective lateral expansion area does not increase with the improvement of pressure. Therefore, the uniform and symmetrical distributed plasma is more conducive to the epitaxial lateral growth of SCD, and the effective expansion growth SCD can be realized at 20 kPa.

Precision micro-mechanical components in single crystal diamond by deep reactive ion etching

The outstanding material properties of single crystal diamond have been at the origin of the long-standing interest in its exploitation for engineering of high-performance micro- and nanosystems. In particular, the extreme mechanical hardness, the highest elastic modulus of any bulk material, low density, and the promise for low friction have spurred interest most notably for micro-mechanical and MEMS applications. While reactive ion etching of diamond has been reported previously, precision structuring of freestanding micro-mechanical components in single crystal diamond by deep reactive ion etching has hitherto remained elusive, related to limitations in the etch processes, such as the need of thick hard masks, micromasking effects, and limited etch rates. In this work, we report on an optimized reactive ion etching process of single crystal diamond overcoming several of these shortcomings at the same time, and present a robust and reliable method to produce fully released micro-mechanical components in single crystal diamond. Using an optimized Al/SiO2 hard mask and a high-intensity oxygen plasma etch process, we obtain etch rates exceeding 30 µm/h and hard mask selectivity better than 1:50. We demonstrate fully freestanding micro-mechanical components for mechanical watches made of pure single crystal diamond. The components with a thickness of 150 µm are defined by lithography and deep reactive ion etching, and exhibit sidewall angles of 82°–93° with surface roughness better than 200 nm rms, demonstrating the potential of this powerful technique for precision microstructuring of single crystal diamond.

Measuring the distribution of the charge carrier concentration in delta-doped layers based on diamond

Properties of single crystal diamond with four delta-doped layers are studied. The goal of this research is to measure the charge carrier concentration profile. Admittance spectroscopy was used as the principal method to measure the properties of samples at different temperatures and applied biases. The measurements showed that only the first (shallow located) δ-layer was confidently registered, especially at elevated temperatures (350–450 K). In addition, the concentration profiles included a weak response from the second delta layer, significantly shifted from its true location. A general conclusion is made concerning the observed charge carrier distribution. Further study is needed to determine the responses from the deeper delta-doped layers.

Complex refractive index variation in proton-damaged diamond

An accurate control of the optical properties of single crystal diamond during microfabrication processes such as ion implantation plays a crucial role in the engineering of integrated photonic devices. In this work we present a systematic study of the variation of both real and imaginary parts of the refractive index of single crystal diamond, when damaged with 2 and 3 MeV protons at low-medium fluences (range: 10(15) - 10(17) cm(-2)). After implanting in 125 × 125 μm(2) areas with a scanning ion microbeam, the variation of optical pathlength of the implanted regions was measured with laser interferometric microscopy, while their optical transmission was studied using a spectrometric set-up with micrometric spatial resolution. On the basis of a model taking into account the strongly non-uniform damage profile in the bulk sample, the variation of the complex refractive index as a function of damage density was evaluated.

Mechanical Properties of Single Crystal Diamond Estimated by Molecular Dynamics Simulation with the Second-Generation REBO Potential

ABSTRACTWe investigated the effects of tensile direction and periodic boundary condition (PBC) on the mechanical properties of single crystal diamond (SCD) under tensile loading, using MD simulations with the second-generation reactive empirical bond order (REBO) potential. We found that when the Poisson’s ratio is assumed to be constant under the canonical (NVT) ensemble and the PBC is applied to all directions of X, Y, and Z, each qualitative relation between a mechanical property such as tensile strength or Young’s modulus and the tensile direction is in agreement with both the results calculated by the first principle and by the cleavage energy method. In addition, we found that when the PBC is applied only to the Y direction under the NVT ensemble, each qualitative relation between a mechanical property and the tensile directions is in agreement with the MD results using the Tersoff potential.Our results indicate that the second-generation REBO potential is also useful for MD simulations on the tension of diamond.

An investigation of combined size, rate and thermal effects on the material properties of single crystal diamond

The ability to predict the properties of material specimens with different sizes under various loading rates and temperatures is essential to evaluating the integrity and durability of NEMS/MEMS devices under extreme loading conditions. To better understand the rate, thermal and crystal orientation effects on size-dependent material responses, Molecular Dynamics (MD) simulations are performed with the use of Single Crystal Diamond (SCD) of various sizes under uniaxial tensile loading. In the MD simulations, the responses of SCD blocks of different sizes under <100> and <110> tensions at different loading rates and temperatures are studied. By combining the available experimental and simulation data, a hyper-surface is formulated to predict the combined size, rate and thermal effects on the strength of pristine diamond.

Modification of the electrical and optical Properties of Single Crystal Diamond with Focused MeV Ion Beams

AbstractIn this paper an overview is given on recent results obtained in the framework of an Italian/Croatian collaboration aimed to explore the potential of techniques based on focused MeV ion beams to locally modify the structural, electrical and optical features of diamond.Experiments were carried out using light (H, He, C) ion beams with energies of the order of MeV, focused to micrometer-size spot and raster scanned onto the surface of monocrystalline (IIa or Ib) diamond samples. Different energies, ion species and fluences were used, in conjunction with variable thickness masks and post annealing processes, to define three-dimensional structures in diamond, whose electrical/optical/structural properties have been suitably characterized. Finite element numerical methods have been employed in the modeling of the material modification and in device design.

Elastic properties of single crystal diamond made by CVD

Brillouin light scattering has been used to investigate the elastic properties of high quality homoepitaxial diamond layers about 1 mm thick that have been elaborated by microwave plasma assisted chemical vapour deposition. Taking advantage of the detection of different acoustic modes, a complete elastic characterization of the crystal has been achieved. Three single crystal elastic constants, namely, c 11, ( c 11 − c 12) / 2 and c 44 have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes travelling parallel to the film surface. These determinations are in agreement with the frequency of the observed surface modes and of the bulk waves propagating at different angles from a normal single crystal film plane and consistent with the properties of natural diamond. By adding a low amount of nitrogen ranging from 2 to 50 ppm in the gas phase, the growth rates were increased from 6 to 33 μm/h whereas the mechanical properties of the resulting layers remained close to those of natural diamond.

A Numerical Study of the Size and Rate Effects on the Mechanical Response of Single Crystal Diamond and UNCD Films

To better understand the mechanical response of ultrananocrystalline diamond (UNCD) and its grain boundary mechanism, a numerical study is performed of the specimen size and rate effects on the mechanical properties of single crystal diamond and UNCD films under uniaxial and shear loading paths, respectively. To compare with the UNCD films, single crystal diamond blocks of various sizes under tensile loading in the 100 hi direction and shear loading with the {100} 110 hi slip at different rates are first investigated via the molecular dynamics (MD) simulation. A combined kinetic Monte Carlo (KMC) and MD procedure is then developed for large-scale atomistic simulation of the mechanical response of UNCD films. In this numerical procedure, two single crystal diamond films, that are formed by the KMC method based on the mechanisms of UNCD growth from carbon dimers on the hydrogen-free (001) surface, are compressed along the [001] direction with two growth surfaces contacting each other at an elevated temperature in the MD simulation to create a polycrystalline UNCD film with certain grain boundary. The mechanical response of the resulting UNCD film is investigated by applying displacement-controlled shear loading in the MD simulation, and is compared with that of single crystal diamond. The preliminary results presented in this article provide a better understanding of the size and rate effects on the material properties of diamond and the role played by the grain boundary on influencing the mechanical response of UNCD films.

The Current And Future Status Of Diamond in Electronics

ABSTRACTBoth passive and active electronic applications of CVD diamond have been proposed since the earliest stages of its development, largely based on an extrapolation of the superlative properties of single crystal diamond. Consequently, CVD diamond research has striven hard to match up to this expectation and significant advances have been made.CVD diamond compares favourably with natural or high pressure synthetic single crystal material for passive electronic applications. The development of CVD diamond deposition technology for thermal management has led producers to address issues such as production cost, yield and quality. CVD polycrystalline diamond is becoming a commodity material and commercial applications in thermal management are emerging. Many of these developments are expected to feed into active electronic applications and will act as a springboard for diamond into commercial technology.The active electronic applications for diamond are more demanding in terms of materials and process technologies. For example, doping, structure delineation and contact schemes have been widely demonstrated and prototype devices are showing potential benefits in sensors, detectors, photonics and cold cathodes. The current and future status of diamond electronics is reviewed.

Lapping and frictional properties of diamond, and characteristics of diamond cutting tool

Properties of single crystal diamond on the lapping, the friction and the cutting test (by diamond tool) have been studied with a special reference to the crystallographic orientation of diamond. By a novel apparatus newly designed, the orientation of diamond is identified in terms of X-ray diffraction technique, and other experiments were also conducted with the apparatus as setting the diamond oriented. In the lapping and frictional tests, the forces, the temperatures and the wears are measured. In the cutting tests, the friction between chip and tool rake face is calculated. The diamond reveals its highly anisotropic characteristics in the all tests. On the lapping test of diamond, it is clear that the force ratio, the temperature and coefficient of friction become lowest values in the <100> direction of the {110} plane rather than the other. On the cutting aluminum alloy by diamond cutting tool, the minimum of the cutting force and coefficient of the friction revealed on the rake face which is identified with {110} plane, and its direction on the plane is <100> direction, as same as the case of lapping and frictional examinations.