Vacancy in 6H—Silicon Carbide Studied by Slow Positron Beam

The defect changes in 6H-SiC after annealing and 10MeV electron irradiation have been studied by using a variable-energy positron beam.It was found that after annealing,the defect concentration in n-type 6H-SiC decreased due to recombination with interstitials.When the sample was annealed at 1400℃ for 30 min in vacuum,a 20-nm thickness Si layer was found on the top of the SiC substrate,this is a direct proof of the Si atoms diffusing to surface when annealed at high temperature stages.After 10MeV electron irradiation,for n-type 6H-SiC,the S parameter increased from 0.4739 to 0.4822,and the relative positron-trapping rate was about 27.878 times of the origin sample,this shows that there are some defects created in n-type 6H-SiC.For p-type 6H-SiC,it is very unclear,this may be because of the opposite charge of vacancy defects.     

Gas-Phase Synthesis of Silicon-Rich Silicon Nitride Nanoparticles for High Performance Lithium–Ion Batteries

The practical application of silicon-based anodes is severely hindered by continuous capacity fade during cycling. A very promising way to stabilize silicon in lithium–ion battery (LIB) anodes is the utilization of nanostructured silicon-rich silicon nitride (SiN_x), a conversion-type anode material. Here, SiN_x with structure sizes in the sub-micrometer range have been synthesized in a hot-wall reactor by pyrolysis of monosilane and ammonia. This work focusses on understanding process parameter–particle property correlations. Further, a model for the growth of SiN_x nanoparticles in this hot–wall–reactor design is proposed. This synthesis concept is of specific interest regarding simplicity, flexibility, and scalability: A way utilizing any mixtures of precursor gases to build multi-functional nanoparticles that can be directly used for LIBs instead of focusing on modification of nanostructures after they have been formed. Lab-scale production rates as high as 30 g h⁻¹ can be easily achieved and further scaled. SiN_0.7 nanoparticles provide a first cycle coulombic efficiency of 54%, a specific discharge capacity of 1367 mAh g⁻¹, and a capacity retention over 80% after 300 cycles at 0.5 C (j = 0.68 mA cm⁻²). These results imply that silicon-rich silicon nitrides are promising candidates for high-performance LIBs with very high durability.     

Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature

Hydrogen-free silicon nitride （SiNx） films were deposited at room temperature by microwave electron cyclotron resonance （MW-ECR） plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm.     

Mechanism of Formation of Carbon–Vacancy Structures in Silicon Carbide during Its Growth by Atomic Substitution

Physics of the Solid State - The mechanism of formation of carbon-vacancy structures in silicon carbide SiC from silicon vacancies that inevitably form during synthesizing SiC from Si by atomic...     

Relaxation Processes and Coherent Spin Manipulations for Triplet Si–C Divacancies in Silicon Carbide Enriched Tenfold in the 13C Isotope

JETP Letters - Coherent spin manipulations of ensembles of color centers in the form of neutral VSi–VC divacancies with the spin $$S = 1$$ in hexagonal silicon carbide 6H–SiC enriched...     

Strained and Piezoelectric Characteristics of Nitride Quantum Dots

The deformation potential and piezoelectric field in nitride GaN/AIN quantum dots （QDs） are investigated in the framework of effective mass approximation （EMA） and finite element method （FEM）. The strained fields and piezoelectric characteristics are studied by using FEM for GaN/AIN QDs （GaN embedded in AIN） in the shape of truncated hexagonal pyramids. We presented the calculated results of the electronic states, wave functions, QD strain field distribution and piezoelectric effects in the QDs. Effects of spontaneous and piezoelectric polarization are taken into account in the calculation. The theoretical results are dependent on QD shapes and sizes. Some of them make the GaN/AIN QDs interesting candidates in optoelectronic applications.     

Study on Laser Heat Treatment of Cemented Carbide

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Photoluminescence Properties of Silicon Nanowires and Carbon Nanotube—Silicon Nanowire Composite Arrays

Composite arrays of multi-wall carbon nanotubes(MWNTs)and silicon nanowires(SiNWs) are fabricated by means of the chemical vapour deposition method in porous anodic aluminium oxide(AAO) templates.The results of the scanning electron microscopy.high-resolution transmission electron microscopy.and transmission electron microscopy have shown that SiNWs are successful nested or filled in the hollow cavities of synthesized MWNT arrays in AAO templates to form MWNT-SiNW composite arrays.The photoluminescence(PL) intensity degradation and a blueshift of PL peak position,usually created from the chemical instability of the SiNW surfaces,are decreased and eliminated clearly in the composite arrays.The composite arrays of MWNTs-SiNWs exhibit more enhanced intensity and stability of PL performance than the SiNW arrays deposited in AAO templates.     

Development of Silicon Multi-strip Detector

Position sensitive detector is very important for nuclear physics experiment. There several techniques can be used to fabricate position sensitive detector, for example, Si-surface barrier method, diffusion method, ion implantation and planar process etc. Among all the techniques mentioned above planar process is the best one. We have developed batch of position sensitive detector -- silicon multi-strip detector by using planar process.     

A New Method for Preparation of Nanocrystalline Molybdenum Nitride

Nanocrystalline molybdenum nitride （γ-Mo2N） with the cubic structure is prepared by the direct-current arc discharge method in N2 gas, using metal Mo or W rod as a cathode. The x-ray diffraction （XRD） and transmission electron microscopy （TEM） are used to characterize the product. It is found that the conversion of Mo to γ-Mo2N and affinity of Mo to N2 are determined by the nitrogen pressure. Moreover, we compare the effect of Mo and W rod as a cathode for preparing γ-Mo2N. The average size of γ-Mo2N particles is about 5 nm. The rapid quenching mechanism can be used to explain the formation of nanocrystalline γ-Mo2N.     

Study on Laser Welded Strength of Cemented Carbide

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First-Principles Study on the Elastic Properties of Platinum Nitride

Elastic properties of platinum nitride （PtN） are studied by first-principles calculations with the fully relativistic full potential linearized augmented plane-wave （LAPW） method, the plane-wave ultrasoft pseudopotential （PWPP） and the projector-augmented wave （PAW） methods. The results reveal that： （1） the scalar relativistic scheme is sufficient to treat the valence electronic structure, i.e. the spin-orbit effect has little effect on the bulk modulus value of platinum nitride; （2） the all-electron full potential method is no more accurate than the pseudopotential and PAW-based methods when calculating the lattice constant and bulk modulus properties of the platinum nitride; （3） platinum nitride in zinc-blende structure is unstable and its crystal structure is still an open problem.     

A New Method to Prepare Boron Nitride Thin Films

We report a new method to prepare boron nitride (BN) thin films on Si (100) substrates in an Ar-N2-BCl3-H2 gas system by magnetron arc enhanced plasma chemical vapour deposition. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize the films. The FTIR spectra show that the deposited boron nitride films experienced a transition from pure h-BN phase to a cubic-containing phase with the variation of arc current ranging from IOA to 18A. The BN film with 42% c-BN was obtained without substrate bias voltage. In the gas system of Ar-N2-BCl3-H2, h-BN can be preferentially etched by chlorine. The chemical etching effect of chlorine allows the formation of c-BN without substrate bias voltage, which may develop a new perspective for the deposition of high quality c-BN film with low stress.     

Quantum Computation on a Silicon Chip

We propose a potential quantum-computer hardware-architecture model on a silicon chip in which the basic cell gate is the atom-photon controlled phase flip gate. This gate can be implemented through a single-photon pulses scattering by a toroidal microcavity trapping a neutral atom, and it does not require very strict strong-coupling regime and can work beyond the Lamb-Dicke limit with high fidelity and success probability under practical noise environments. Especially, good and bad losses of the toroidal cavity are discussed in detail. Finally, a possibly simple experiment based on current experimental technology is proposed to demonstrate our scheme.     

“In vivo” STM studies of the growth of Germanium and Silicon on Silicon

A scanning tunneling microscope (STM) capable of imaging during crystal growth from the vapour is described. This method (MBSTM) opens the possibility to follow the growth process of semiconductor molecular beam epitaxy (MBE) in vivo. The ability of the microscope to access the evolution of specific features during growth is demonstrated by images of the Si homoepitaxy. The transition from initial multilayer to layer-by-layer growth was imaged in Si(1 1 1) homoepitaxy. In Si/Si(1 0 0) homoepitaxy the fractional coverage of non-equivalent terraces was studied as function of coverage and a theoretically predicted transient growth mode was observed. In Ge on Si(1 1 1) heteroepitaxy the nucleation of 3D Ge islands was observed. When 3D islands occurred on the surface an etching of the 2D Stranski-Krastanov layer was observed.     

Growth Feature of Cubic Boron Nitride on c-BN Crystal Substrates

Cubic boron nitride （c-BN） films were deposited on highly-oriented （111） bulk c-BN crystal by using the rf magnetron sputtering method. The growth films are characterized by micro-Raman spectroscopy （μ-RS） and scanning electron microscopy （SEM）, The results show that the high crystallization electron transparent c-BN films in thickness of about 10μm are obtained, Island and step growth models are clearly shown.