Investigation of polycrystalline silicon layers by electron microscopy and x-ray diffraction

The structure of polycrystalline Si layers deposited by pyrolysis of silane in a hydrogen ambient has been investigated by replica electron microscopy and X-ray diffraction. When the gas flow ratio (SiH₄/H₂) is 3·64 × 10⁻⁴ the temperature region below 900°C is a surface reaction control region and the activation energy of the chemical surface reaction rate is 1·6 eV. The temperature range above 900°C is a mass transfer region and the deposition rate is about 500 Å/min. The grains become larger and the texture of the surface of the poly Si layers becomes coarser with the deposition temperature. Some phase change was found to occur around 900°C by replica electron microscopy. The X-ray diffraction experiments show that there exist three preferred orientations of (220), (111) and (311) in the poly Si layers. The decrease of the relative intensity of the (311) orientation might have a relation to the phase change around 900°C.     

Local lattice parameter determination of a silicon (001) layer grown on a sapphire (1102) substrate using convergent-beam electron diffraction

All the six lattice parameters (a, b, c, alpha, beta and gamma) of a Si (001) layer grown on a sapphire (1102) substrate were determined by convergent-beam electron diffraction with no assumption of crystal lattice symmetry. A lattice compression in the Si (001) plane and an elongation in the [001] direction were revealed. An anisotropic lattice compression in the (001) plane was clearly detected for the first time. That is, the lattice compression in the Si [100] direction, which is parallel to the sapphire [1101] direction, was larger than that of the Si [010] direction, which is parallel to the sapphire [1120] direction. It was also revealed that the lattice parameters of the Si-layer depend on the distance from the interface. Anisotropy of carrier mobility was reasonably explained in terms of the anisotropy of the lattice parameters determined.     

Structural characterization of ultra-thin (0 0 1) silicon films bonded onto (0 0 1) silicon wafers:: a transmission electron microscopy study

Ultra-thin (0 0 1) silicon films (thickness less than 25 nm) directly bonded onto (0 0 1) silicon wafers have been investigated by transmission electron microscopy. Twist interfacial dislocations accommodate the twist between the two crystals, whereas tilt interfacial dislocations accommodate the tilt resulting from the residual vicinality of the initial surfaces. In low-twist angle grain boundaries, twist interfacial dislocations are dissociated and no precipitates are detected. In high-twist angle grain boundaries, there is no dissociation and a high density of silicon oxide precipitates is observed at the interface. Tilt interfacial dislocations are pinned by these precipitates, they are more mobile than precipitates. Without precipitates, their lines are straighter than those with precipitates, and this is especially when the bonded wafers are annealed at a high temperature. When no precipitates are present, tilt interfacial dislocations are associated by pairs, and we demonstrate that each tilt interfacial dislocations introduce a diatomic interfacial step at the interface.     

Infrared spectroscopy and transmission electron microscopy of polycrystalline silicon carbide

The polycrystalline structure of silicon carbide was investigated by infrared spectroscopy and transmission electron microscopy (TEM). The films were obtained by annealing in the temperature range 950–1250°C of amorphous silicon carbide films deposited on a silicon substrate by PECVD. The broad absorption band at around 750 cm⁻¹ in the infrared spectrum of amorphous material after annealing at high temperature changes from a Gaussian to a Lorentzian shape, corresponding to the transition from an amorphous to a polycrystalline phase. The SiC peak becomes sharper with increasing the annealing temperature, this effect being related to the growth of crystalline grains. TEM microscopy indicates that the crystallisation occurs homogeneously in the films and the diffraction pattern shows that the film crystallises into cubic 3C–SiC. The distribution of polycrystalline grains as determined by TEM evidences an increase of the grain size with increasing the annealing temperature. A correlation between infrared peak width and mean grain radius has been found.     

High-resolution transmission electron microscopy observation of the cross-sectional structure of reconstructed silicon (5,5,12) surface

The cross-sectional reconstructed structure of Si (5,5,12) surface was, for the first time, observed using ultrahigh vacuum high-resolution transmission electron microscopy (UHV-HRTEM) profile view method. In the high-index region, two units of the (337) surface combine with one units of the (225) surface to complete one unit cell of (5,5,12) surface. The (337) unit at one side of the (225) unit is distinctly different from that at another side of (225) unit. The observed HRTEM images do not agree with the previous structural models of the (5,5,12) surface. We propose a new structure model of this surface using a TEM image simulation. Our model is agreement with the previously reported scanning tunnelling microscope images.     

X-ray diffraction and high resolution transmission electron microscopy of 3C-SiC/AlN/6H-SiC(0001)

The structure and crystal quality of epitaxial films of SiC/AlN/6H-SiC(0001) prepared by chemical vapor deposition were evaluated by high resolution transmission electron microscopy (HRTEM) and x-ray diffraction techniques. Cross-sectional HRTEM revealed an abrupt AlN layer-6H-SiC substrate junction, but the transition between the AlN and SiC layers was much rougher, leading to the formation of a highly disordered SiC region adjacent to the interface. The AlN layer was relatively defect free, while the SiC layer contained many microtwins and stacking faults originating at the top SiC/AlN interface. The SiC layer was the 3C-polytype, as determined by double crystal x-ray rocking curves. The SiC layers were under in-plane compressive stress, with calculated defect density between 2–4×10⁷ defects/cm⁻².     

Lattice parameter determination of a composition controlled Si1-x Gex layer on a Si (001) substrate using convergent-beam electron diffraction

The six lattice parameters (a, b, c, alpha, beta and gamma) of Si(1-x)Ge(x), which was grown epitaxially on a Si (001) substrate with a varying Ge concentration, were determined by convergent-beam electron diffraction (CBED) without any assumption of crystal lattice symmetry. It was revealed that the lattice parameter c of Si(1-x)Ge(x) varies linearly with the Ge concentration and that the lattice symmetry is lowered from cubic to tetragonal, excluding an artifact due to the thinning of the specimen. The effect of strain relaxation that is caused by thinning specimens is discussed. Ge concentrations of examined specimen areas are evaluated using the obtained lattice parameters.     

Characterization of Co25Ag75 and (Co90Al10)28Ag72 granular films by electron diffraction,high-resolution transmission electron microscopy and electron spectroscopic imaging

Series of sputter-deposited Co25Ag75 and (Co90Al10)28Ag72 giant-magnetoresistance granular films were characterized by electron diffraction, high-resolution transmission electron microscopy and electron spectroscopic imaging. Crystalline particles of fcc silver and hcp cobalt were detected in both thin-film systems before annealing. Annealing of (Co90Al10)28Ag72 films at 773 and 823 K yielded mixtures of fcc and hcp cobalt clusters and notably enlarged silver particles. In addition, crystallites of bcc Ag3Al were detected in the sample annealed at 823 K. The mesoscopic structure of the as-deposited films was investigated by dark-field imaging showing columnar growth-domains for silver. The columns were preserved during thermal treatment up to 773 K, whereas annealing at 823 K destroyed these domains.     

Heat- and electron-beam-induced transport of gold particles into silicon oxide and silicon studied by in situ high-resolution transmission electron microscopy

In this study, we describe the transport of gold (Au) nanoparticles from the surface into crystalline silicon (Si) covered by silicon oxide (SiO(2)) as revealed by in situ high-resolution transmission electron microscopy. Complete crystalline Au nanoparticles sink through the SiO(2) layer into the Si substrate when high-dose electron irradiation is applied and temperature is raised above 150 degrees C. Above temperatures of 250 degrees C, the Au nanoparticles finally dissolve into fragments accompanied by crystallization of the amorphized Si substrate around these fragments. The transport process is explained by a wetting process followed by Stokes motion. Modelling this process yields boundaries for the interface energies involved.     

Detection and evaluation of current filaments in MIS sandwich systems by applying mirror electron microscopy (MEM) and scanning electron microscopy (SEM)

Conducting channels form at weak points of an insulating layer by applying a voltage to MIS sandwich systems produced by vacuum evaporation. Local variations of the surface potential caused by the current filaments can be detected by applying MEM and SEM. An evaluation of the filament current is possible by a quantitative contrast interpretation of the corresponding image structures observed in the MEM     

Energy-filtered electron diffraction and high-resolution electron microscopy on short-range ordered structure in GaAs(0.5)Sb(0.5)

Characteristic intensity distribution of diffuse scattering in III-V alloy semiconductor GaAs(0.5)Sb(0.5) epitaxially grown was observed by the energy-filtered electron diffraction method with [110] incidence. The diffuse scattering situates at the one-third positions between the fundamental reflections extending parallel to the q002 direction in the reciprocal space. A high-resolution electron microscope image shows weak contrast modulation corresponding to the diffuse scattering. The image processed with the Fourier transform by selecting the diffuse scattering and a fundamental reflection shows small regions consisting of bright dots being elongated along the (111) planes and aligning on the (002) planes, which are considered to result from the ordering of As and Sb during the growth process. The effect of including the fundamental reflection for imaging the ordered regions in the image processing method is also discussed. Finally, based on the results obtained by energy-filtered electron diffraction and high-resolution electron microscopy, a simple structure model for the short-range ordered structure in GaAs(0.5)Sb0.5 is proposed.     

Transmission electron microscopy observations of low-temperature ion implanted (100) silicon

Phosphorus implantations have been performed at room temperature and near 77°K on (100) silicon wafers. It is shown that this low-temperature process is able to produce after furnace annealing doped layers completely free from the usual residual damage (mainly dislocation loops) that is observed in room temperature implanted and furnace annealed silicon.     

Nanoscale characterization of the silicon dioxide-silicon carbide interface using elemental mapping by energy-filtered transmission electron microscopy

Energy-filtered transmission electron microscopy (EFTEM) was used to study 6H-SiC/SiO₂ interfaces produced by thermal oxidation as a function of the oxidation conditions. Elemental maps of C and Si were used to calculate C-to-Si concentration profiles across the interfaces. Enhanced C/Si concentrations (up to ∼ 35%) were observed at distinct regions in samples oxidized at 1100°C for 4 h in a wet ambient. The data from a number of randomly selected regions indicate that re-oxidation at 950°C for 3 h significantly reduced, but did not eliminate, the amount of excess interfacial carbon.     

Anisotropy of the spatial distribution of In(Ga)As quantum dots in In(Ga)As-GaAs multilayer heterostructures studied by X-ray and synchrotron diffraction and transmission electron microscopy

High-resolution X-ray and synchrotron (crystal truncation rods) diffraction methods and transmission electron microscopy have been employed to study MBE-grown multilayer In(Ga)As-GaAs heterostructures with arrays of vertically coupled In(Ga)As quantum dots (QDs) in a GaAs matrix. Additional (vertical and lateral) spatial ordering of QDs in perfect crystalline structures, giving rise to undulations of the crystalline planes and quasi-periodic elastic strain, was shown to be essentially anisotropic with respect to crystallographic directions of the [110] type. The anisotropy of the QD formational system of can be accounted for by assuming that the spatial ordering of the QDs and the corrugation of the crystal planes are the initial stages of relaxation of the elastic strain introduced into the system by the QDs. The anisotropic relief of the crystal planes (corrugated growth surface) results from the formation of a system of spatially ordered quantum quasi-wires uniformly filled with QDs. In a multilayer heterostructure with high crystal perfection, the anisotropic relief of the crystal planes is inherited by overlying layers and its amplitude decreases gradually with increasing distance from the source of elastic strain—the superstructure containing In(Ga)As QDs in the given case.     

Growth of silicon nanowires on H-terminated Si {111} surface templates studied by transmission electron microscopy

We have studied the growth of silicon nanowires (SiNWs) by means of transmission electron microscopy. SiNWs are grown from nanocatalysts via the Vapor-Liquid-Solid (VLS) mechanism using silane (SiH4) gas as a source gas. The nanocatalysts are prepared on a hydrogen (H)-terminated Si surface. We have examined the formation mechanism of nanocatalysts on H-terminated surface and have observed several structural variants of SiNWs. According to the study we have suggested that many structural variations of SiNWs are possible, which modify the structural properties of SiNWs to great extents.     

High-resolution transmission electron microscopy study of Ca(3)Co(4)O(9)

The crystal structure of Ca(3)Co(4)O(9) was investigated using high-resolution transmission electron microscopy (HRTEM) and the image-simulation method. The c(*) was 10.8A and the b parameters were 4.56A for the Ca(2)CoO(3) block and 2.82A for the CoO(2) sheet. The [110] zone axis HRTEM images confirmed that Ca(3)Co(4)O(9) has a modulated layered structure with modulation. For the first time, the atomic positions of the Ca and Co atoms in the Ca(2)CoO(3) block were identified, corresponding to three rows of dark spots in the [110] direction. The observed HRTEM images for Ca(2)CoO(3) agreed well with the calculated images based on the structural model obtained by the Rietveld refinement method.     

Critical thickness determination of InxGa1-xAs/GaAs strained-layer system by transmission electron microscopy

The critical thicknesses of In_xGa_1-xAs/GaAs and GaAs/In_xGa_1-xAs/GaAs strained-layer systems were determined by transmission electron microscopy using the lift-off technique. The onset of misfit dislocation generation has been observed for the first time and the geometries of the misfit dislocations in both uncapped and capped layers correspond to the predicted models. A comparison is given between the predicted and experimental critical thicknesses.     

First observation of SiO2/Si(100) interfaces by spherical aberration-corrected high-resolution transmission electron microscopy

SiO2/Si(100) interfaces were for the first time observed by a spherical aberration-corrected high-resolution transmission electron microscope in a cross-sectional mode. As the Fresnel fringes were not contrasted at the interfaces, the interfacial structures were clearly observed without the need for artificial image contrast. Atomic steps and defects on the Si(100) surfaces were accurately identified. Also, image simulations with the target imaging performance revealed oxygen atomic columns between silicon-silicon bonds. The present instrument is of potential use for semiconductor science and technology, even for the analysis of oxygen atoms at interfaces.     

一株来自金雕的霉形体的形态研究

本文利用航向电镜观察了一株来自金雕的形体在培养过程中的各种形态。结果表明该霉形体的形态极其多变，主要有丝状分枝体、原质小体、较大型体和巨大型体。它们在固体培养和液体培养等条件下的形态变化各有特点和规律。同时还进一步证实，除原质小体外的细胞均有直接的分裂连续增殖，而原质小体由丝状分枝体和较大型体产生，经转主为其它形态后再增殖。     

Electronic structure of single-layer superlattices (GeC)<Subscript>1</Subscript>(SiC)<Subscript>1</Subscript>, (SnC)<Subscript>1</Subscript>(SiC)<Subscript>1</Subscript>, and (SnC)<Subscript>1</Subscript>(GeC)<Subscript>1</Subscript>

The crystal and electronic structures of GeC, SiC, and SnC crystals and superlattices based on them, GeC/SiC, SnC/SiC, and SnC/GeC, are modeled within density functional theory. The equilibrium lattice constants are obtained, the band spectra and densities of states are calculated, and the specific features of the formation of the valence band and chemical bonding in these crystals and superlattices are studied.