Hydrothermal growth of boron nitride microcrystals

Boron nitride (BN) crystals with size of several micrometers have been successfully synthesized by hydrothermal method. The reactants used in our experiments were boric acid (H₃BO₃), sodium azide (NaN₃) and white phosphor (P). The samples were characterized by X‐ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), selective area electron diffraction (SAED). It is found that the existence of Cl^‐ in the reaction mixture has much effect on the synthesis of BN. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detection of boron and carbon in flux grown single crystals of hexagonal ferrites using electron energy loss spectroscopy

A method of detecting boron and carbon in the lattice of the flux grown single crystals of hexagonal ferrites using Electron Energy Loss Spectroscopy is given. Our results have led us to conclude that these elements are present as a solid solution and not as inclusions.     

Molecular beam epitaxial growth of hexagonal boron nitride on Ni(1 1 1) substrate

We demonstrate hexagonal boron nitride (h-BN) epitaxial growth on Ni(1 1 1) substrate by molecular beam epitaxy (MBE) at 890 °C. Elemental boron evaporated by an electron-beam gun and active nitrogen generated by a radio-frequency (RF) plasma source were used as the group-III and -V sources, respectively. Reflection high-energy electron diffraction revealed a streaky (1×1) pattern, indicative of an atomically flat surface in the ongoing growth. Correspondingly, atomic force microscopy images exhibit atomically smooth surface of the resulting h-BN film. X-ray diffraction characterization confirmed the crystallinity of the epitaxial film to be h-BN, and its X-ray rocking curve has a full-width at half-maximum of 0.61°, which is the narrowest ever reported for h-BN thin film. The epitaxial alignments between the h-BN film and the Ni substrate were determined to be [0 0 0 1]_h−BN∥[1 1 1]_Ni, [1 1 2¯ 0]_h−BN∥[1¯ 1 0]_Ni, and [1 1¯ 0 0]_h−BN∥[1¯ 1¯ 2]_Ni.     

Flow of space-charge-limited currents in cubic boron nitride

Current-voltage characteristics of polycrystal cubic nitride samples are studied at various temperatures. The samples were undoped crystals obtained by the method of direct phase transformation of pyrolytic graphite-like boron nitride and crystals doped with sulfur to obtain n-type conductivity. The current-voltage characteristics consist of three different parts: linear and quadratic segments and the region of dramatic increase in the current, which indicates the existence of space-charge-limited currents. The activation energy, E_t, and concentration of the trapping centers, N_t, are determined. The experimental data obtained allowed us to calculate, for the first time, the mobility and concentration of free carrier in the conduction band. Possible mechanisms giving rise to a dramatic increase in are made the current on the current-voltage characteristics are discussed.     

The effect of local centers on conduction and luminescence of boron nitride

Energetic and kinetic characteristics of charge carrier trapping and recombination centres in graphite-like boron nitride produced by gas-phase deposition are discussed. Local levels in X-ray excited PBN are studied using the method of thermally activated spectroscopy of luminescence and conduction, and their position in the band gap is determined from the temperature dependences of the diffusive current and depolarization current. Acceptor and donor level models for different PBN are developed. Their influence on conduction and on luminescence is determined. The scheme of hole-electron transitions by luminescence is suggested. The carbon influence on the nature of the defects creating local levels is discussed.     

Synthesis and optical properties of purified translucent,orthorhombic boron nitride films

Large-area (>1 cm²) freestanding translucent orthorhombic boron nitride (oBN) films have been synthesized by magnetron sputtering at a low radio-frequency power of 120 W. The structural characterizations were performed by means of X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It is demonstrated that oBN is a direct band gap semiconductor (E_g∼3.43 eV). Excited by ultraviolet laser (wavelength at 325 nm), the oBN films emit strong white light, which can be seen by the naked eyes in the dark. In the photoluminescence spectrum, besides the ultraviolet near-band-edge radiative recombination emission, there are three visible emission bands (centered at 400, 538, and 700 nm) arising from the defect-related deep-level centers of oBN, which are mixed to form the white light emission. The hardness and elastic modulus of oBN films are 11.5 and 94 GPa, respectively, examined by nanoindentation measurements.     

Transmission electron microscopy study of hexagonal GaN film grown on GaAs (0 0 1) substrate by using AlAs nucleation layer

Hexagonal gallium nitride (h-GaN) films have been grown on AlAs nucleation layer by using radio frequency (RF) plasma source-assisted molecular beam epitaxy on GaAs (0 0 1) substrate. Transmission electron microscopy (TEM) techniques are used to characterize such h-GaN epilayers. TEM results show that (0 0 0 1) atom planes of h-GaN are parallel to (0 0 1) atom planes of the GaAs substrate. Defects, such as stacking faults and dislocations, have also been observed.     

New schemes for recording electron diffraction patterns of hexagonal and monoclinic crystals

Some new schemes for recording electron diffraction patterns of hexagonal crystals rotating around the axes lying in the (hk0) plane of the reciprocal lattice and monoclinic crystals rotating around the a and b axes of the direct lattice and the a* axis of the reciprocal lattice have been developed. Formulas for interpreting electron diffraction patterns are reported. The electron diffraction patterns obtained based on these schemes were used to solve the 2H and 3R polytypes of CdInGaS₄ crystals and the 3R polytype of Zn_1.5In₃Se₆ crystal with the parameters a = 4.046 and c = 59.292 Å, sp. gr. R3m.     

Structural characteristics of the boron nitride sphalerite modification synthesized in a shock wave

Crystallography Reports - The real structure of ultradispersed powders of sphalerite boron nitride synthesized under shock compression has been studied by X-ray diffraction. The lattice microstrain...     

Influence of the nitrogen flow rate on the order and structure of PECVD boron nitride thin films

Three sets of boron nitride (BN) thin films are deposited with different N₂/B₂H₆ flow ratios (r = 4, 10 and 25) by plasma enhanced chemical vapor deposition (PECVD). The variations of physical properties in different deposition sets are analyzed by optical (XPS, FTIR, UV–visible spectroscopies), mechanical and electrical measurements. The films are considered to be deposited in a turbostratic phase (t-BN). Evolution of bonding configurations with increasing r is discussed. Relatively higher nitrogen flow rate in the source gas mixture results in lower deposition rates, whereas more ordered films, which tend to reach a unique virtual crystal of band gap 5.93 eV, are formed. Anisotropy in the film structure and film inhomogeneity along the PECVD electrode radial direction are investigated.     

Growth of hexagonal and cubic InN nanowires using MOCVD with different growth temperatures

We have performed a detailed investigation of the metal-organic chemical vapor deposition (MOCVD) growth and characterization of InN nanowires formed on Si(1 1 1) substrates under nitrogen rich conditions. The growth of InN nanowires has been demonstrated by using an ion beam sputtered (∼10 nm) Au seeding layer prior to the initiation of growth. We tried to vary the growth temperature and pressure in order to obtain an optimum growth condition for InN nanowires. The InN nanowires were grown on the Au+In solid solution droplets caused by annealing in a nitrogen ambient at 700 °C. By applying this technique, we have achieved the formation of InN nanowires that are relatively free of dislocations and stacking faults. Scanning electron microscopy (SEM) showed wires with diameters of 90–200 nm and lengths varying between 3 and 5 μm. Hexagonal and cubic structure is verified by high resolution X-ray diffraction (HR-XRD) spectrum. Raman measurements show that these wurtzite InN nanowires have sharp peaks E₂ (high) at 491 cm⁻¹ and A₁ (LO) at 591 cm⁻¹.     

Low-voltage scanning electron microscopy of multilayer polymer systems

The possibilities of low-voltage scanning electron microscopy for visualization of specific features of the microstructure in internal layers of multilayer polymer films are demonstrated by the example of “chitosan–polyelectrolyte complex–alginic acid” composite. The process of electron beam interaction with a sample at low electron energies is considered. The key parameters of low-voltage electron microscopy, which make it possible to increase the resolution of SEM images of polymer systems, are discussed.     

High-resolution transmission electron microscopy for crystallographic study of nanomaterials

The potential of high-resolution transmission electron microscopy (including the quantitative computer processing of images and computer simulation) in a local analysis of nanomaterials is discussed. A number of examples of the application of fast Fourier transform and simulated high-resolution electronmicroscopy images in the identification of nanophases and the crystallographic study of nanocrystals and nanoparticles are considered. The role that B.K. Vainshtein played in the development of a unified approach for determination of the structure of materials using short-wave diffraction is indicated.     

Study of magnetic metal periodic structures by X-Ray and electron microscopy methods

Complex studies of magnetic periodic metallic systems based on Dy/Gd layers have been carried out by X-ray diffraction, resonance X-ray reflectometry, transmission electronic microscopy, and energydispersve microanalysis. The application of these methods and joint analysis of their results provide an effective approach to study of the structure and determination of the parameters of individual layers and interfaces and their structural quality with a high degree of reliability.     

Investigation of structural defects in polycrystalline silicon by electron microscopy

Thermostability of polycrystalline films and their structure changes have been investigated in dependence on the fast electron irradiation. It was shown that the type of the radiation defects depends on the irradiation. temperature. The temperature of the recrystallization process is shown to decrease from 1300°C in the case without irradiation down to 1000°C in the case of recrystallization when irradiating.