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Elastic Properties of Fullerites and Diamond-Like Phases
摘要： Diamond-like structures, that include sp2 and sp3 hybridized carbon atoms, are of considerable interest nowadays. In the present work, various carbon auxetic structures are studied by the combination of molecular dynamics (MD) and analytical approach. Two fullerites based on the fullerene C60 and fullerene-like molecule C48 are investigated as well as diamond-like structures based on other fullerene-like molecules (called fulleranes), carbon nanotubes (called tubulanes) and graphene sheets. MD is used to find the equilibrium states of the structures and calculate compliance and stiffness coefficients for stable configurations. Analytical methods are used to calculate the engineering elastic coefficients (Young’s modulus, Poisson’s ratio, shear modulus and bulk modulus), and to study their transformation under rotation of the coordinate system. All the considered structures are partial auxetics with the negative value of Poisson’s ratio for properly chosen tensile directions. It is shown that some of these structures, in a particular tension direction, have a very high Young’s modulus, that is, 1852 GPa for tubulane TA6.
关键词： carbon diamond-like phases,elastic properties,fullerites,molecular dynamics,auxetics
更新于2025-09-04 15:30:14
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Prospects of Impact Avalanche Transit-Time Diode Based on Chemical-Vapor-Deposited Diamond Substrate
摘要： We propose a chemical-vapor-deposited (CVD) diamond-based double-drift-region (DDR) impact avalanche transit-time diode (IMPATT) for use in microwave applications. CVD diamond is taken as the base substrate material. Simulations were carried out to perform direct-current (DC), small-signal, and noise analyses on the IMPATT. The results are in agreement with experimental reports. The IMPATT based on CVD diamond offers better performance compared with other materials reported to date at 26 GHz to 40 GHz. In the near future, this device could represent the best alternative for designers and semiconductor industry, due to its numerous advantages including higher DC-to-radiofrequency (RF) conversion efficiency (27.81%), highest power density (6.206 9 109 W m?2), minimum noise measure value (?98.22 dBm), and best optimized conductance–susceptance profile with lower quality factor (0.0215).
关键词： conversion efficiency,power density,impact ionization,DDR IMPATT,CVD diamond,noise measure
更新于2025-09-04 15:30:14
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Binding of hydrogen to phosphorus dopant in phosphorus-doped diamond surfaces: A density functional theory study
摘要： Although phosphorus is an n-type donor in diamond, H impurities can bind to and passivate P. Here, H binding to a P dopant in both diamond (0 0 1) and (1 1 1) surfaces is investigated by density functional theory. The energy calculations reveal the most stable P–H complex structures for each P-doped position. P–H binding energies are the lowest for the second P doped C layer among those for four investigated P-doped C layers. H migration from on-surface to P in the second C layer is exothermic, with an energy barrier of zero, whereas that from on-surface to P below the second C layer is endothermic, with an energy barrier greater than 0.95–7.09 eV. Thus, both of binding energy and migration calculations imply that P–H complex is more likely to form when P is doped in the second C layer than when P is doped below the second C layer. Moreover, H migration energy barrier from on-surface to P below the second C layer in the (1 1 1) surface is at least 0.85 eV greater than that in the (0 0 1) surface, which indicates that P–H complex is less likely to form in (1 1 1) surface than in (0 0 1) surface.
关键词： P–H complex,Hydrogen,Density functional theory,P-doped diamond
更新于2025-09-04 15:30:14
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Microwave cavity perturbation of nitrogen doped nano-crystalline diamond films
摘要： Non-contact and non-destructive electrical conductivity measurements of nitrogen doped nano-crystalline diamond films have been demonstrated using a microwave cavity perturbation system. The conductivity of the films was controlled by simply varying the CH4 gas concentration during microwave plasma assisted chemical vapour deposition, thereby promoting the formation of sp2 carbon at the grain boundaries. The presence of sp2 carbon is verified through Raman spectroscopy, x-ray photoelectron spectroscopy and electron energy loss spectroscopy, while scanning electron microscopy confirms an increasing surface area for sp2 to form. The microwave cavity perturbation results show that the measured cavity quality factor varies with CH4 concentration. The extraction of conductivity is achieved through a depolarisation model, which must be considered when the sample is smaller than the cavity and through both electric and magnetic field perturbations. The microwave measurements are comparable to contacting and damaging measurements when the film conductivity is greater than the substrate, thus demonstrating an invaluable method for determining conductivity without the need for depositing any electrodes on the film.
关键词： non-contact,microwave dielectric spectroscopy,nano-crystalline diamond,electrical conductivity
更新于2025-09-04 15:30:14
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High-speed synthesis of heavily boron-doped diamond films by in-liquid microwave plasma CVD
摘要： In-liquid microwave plasma CVD (IL-MPCVD) processes allow rapid growth of diamond from mixtures of alcohols. Here, we report the first synthesis of polycrystalline boron-doped diamond (BDD) by an In-liquid microwave plasma CVD (IL-MPCVD) process from a mixture of alcohols and boron trioxide (B2O3). We simultaneously achieved high growth rates (up to 287 μm/h) and high boron concentrations (up to 7 × 1021 cm?3). We examined the growth mechanism and show that water generated by dissolution of B2O3 in the alcohol is key to rapid growth of BDD. Even with the same C:H:O ratio, diamond growth rate and nucleation density drastically decreased by addition of water. Water has an strong etching effect, which enables shifts diamond to grow in carbon rich conditions. Our results indicate that the C:H:O composition is not the only factor affecting diamond growth in IL-MPCVD processes but rather the actual substances used are also important. Finally, we evaluated the as-grown BDD film as a diamond electrode. Despite the high growth rate, oOur IL-MPCVD-grown BDD showed electrochemical properties comparable to those of BDD grown by the conventional CVD process in terms of its potential window (3.2 V) and peak separation (85 mV) in 1 mM K3[Fe(CN)6]. Owing to the high growth rate, IL-MPCVD is an effective technique for synthesizing BDD.
关键词： electrodes,chemical vapor deposition,diamond film,electrochemical,plasma CVD
更新于2025-09-04 15:30:14
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Investigations on electrical and thermal transport properties of Cu2SnSe3 with unusual coexisting nanophases
摘要： The ternary diamond-like compound Cu2SnSe3 is a potential thermoelectric material. Its Cu-Se conducting network leaves Sn as a likely doping site to optimize the carrier concentration without much deterioration to the carrier mobility. Thus, the precise determination on the intricate phase structures of Cu2SnSe3 is critical. Here, we first use the atomically resolved scanning transmission electron microscopy and reveal an unusual phase coexistence (monoclinic and orthorhombic phases) in Ag-doped Cu2SnSe3. Owing to coexisting phases and the orderedisorder transition in the orthorhombic phase, the Ag-doped Cu2SnSe3 shows an unusual three-stage behavior in its temperature-dependent electrical transport properties and achieves record high power factors in this system. The observed three-stage behavior due to the phase coexistence is supported by the first principle calculations, Hall measurements, and optical diffuse reflectance measurements. To fully understand the band structures and the coherent interface between these coexisting phases, a band contact model is proposed that could well explain the three-stage electrical transport behavior. Moreover, the phase coexistence is observed at the nanoscale regime, thus providing a high density of phase boundaries. Such coexisting nanophases play an important role in lowering the lattice thermal conductivity. As a result, the ZT value obtained in Cu2Sn0.93Ag0.07Se3 is double that of undoped Cu2SnSe3.
关键词： Diamond-like compound,Phase coexistence,Thermoelectric,Cu2SnSe3
更新于2025-09-04 15:30:14
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CVD Diamond Interaction with Fe at Elevated Temperatures
摘要： Chemical vapor deposition (CVD) diamond is a prospective thin film material for cutting tools applications due to the extreme combination of hardness, chemical inertness, and thermal conductivity. However, the CVD diamond cutting ability of ferrous materials is strongly limited due to its extreme affinity to iron, cobalt, or nickel. The diamond–iron interaction and the diffusion behavior in this system are not well studied and are believed to be similar to the graphite–iron mechanism. In this article, we focus on the medium-temperature working range of 400–800 ?C of a CVD diamond–Fe system and show that for these temperatures etching of diamond by Fe is not as strong as is generally accepted. The starting point of the diamond graphitization in contact with iron was found around 400 ?C. Our results show that CVD diamond is applicable for the cutting of ferrous materials under medium-temperature conditions.
关键词： Fe–C interaction,CVD diamond,diffusion
更新于2025-09-04 15:30:14
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Isotopic effects on phonons and excitons in diamond studied by deep-ultraviolet continuous-wave photoluminescence spectroscopy
摘要： Photoluminescence (PL) spectroscopy is performed for natural-abundance (N.A.C) and isotopically purified (13C) synthetic diamond using a deep-ultraviolet continuous-wave laser. Because the excitation source creates low-density low-temperature excitons even under a moderate excitation power, the PL spectra show suppressed collisional and thermal broadening with a high signal-to-noise ratio. Our approach can accurately resolve the isotopic effects. The experimentally determined effects for phonons and excitons in diamond are ΔETA = ?2.5 meV, ΔETO = ?4.9 meV, ΔELO = ?5.7 meV, and ΔEex = 14.5 meV.
关键词： diamond,photoluminescence spectroscopy,isotopic effects,excitons,phonons
更新于2025-09-04 15:30:14
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Deposition and Patterning of Polycrystalline Diamond Films Using Traditional Photolithography and Reactive Ion Etching
摘要： Given the exceptional characteristics of diamond films, they have become increasingly popular in the fields of medicine, microelectronics, and detector electronics. However, despite all the advantages, there are many technological problems that complicate their widespread application and impose limitations on diamond use in technological processes. In this study, we proposed a new technique for obtaining a complex topology of polycrystalline diamond coatings by selective seeding of the substrate by nucleation centers and subsequent surface treatment with reactive ion etching to reduce the number of parasitic particles. As a result, diamond films were obtained with a high particle concentration in the film region and high repeatability of the pattern. Moreover, parasitic particles influenced neutralization in areas where film coverage was not needed. The effect of the diamond nanoparticle concentration in a photoresist and the effect of reactive ion etching on the formation of a continuous film and the removal of parasitic nucleation centers were examined. The relative simplicity, low power consumption, and high efficiency of this method make it attractive for both industrial and scientific applications.
关键词： pattern,diamond,parasitic particles,deposition,photolithography,reactive ion etching,films,selective,CVD
更新于2025-09-04 15:30:14
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Ohmic graphite-metal contacts on oxygen-terminated lightly boron-doped CVD monocrystalline diamond
摘要： A process to obtain ohmic contacts on oxygen-terminated lightly boron-doped CVD monocrystalline diamond films was developed. Samples were contacted by Ti/Au metallic pads in the transmission line model (TLM) configuration. The electric contacts were placed onto a mesa structure produced on the CVD boron-doped layer. One of the samples was additionally implanted with helium ions at 10 keV in order to induce the formation of a graphitic layer underneath the diamond surface before contacting so as to improve electrical conduction. The electrical performance of both devices was characterized by the TLM method and compared. As a result, the sample with metallic electrodes exhibited a small and non-linear electrical conduction, while the graphitic/metallic contacts showed an ohmic behaviour with an estimated specific contact resistance as low as 3.3 × 10-4 Ω.cm2 for a doping level of a few 1017 cm-3. This approach opens the way to more efficient ohmic contacts on intrinsic or low-doped diamond that are crucial for the development of electronic devices and detectors.
关键词： oxygen terminations,graphitization,Ohmic graphite-metal contacts,lightly boron-doped CVD diamond film,ion implantation
更新于2025-09-04 15:30:14