Transmission Electron Micro Research Articles

Step bunching and correlated SiGe nanostructures on Si(113)

We have studied the step bunching properties of Si and SiGe layers on vicinal Si(113) substrates and the self-organized formation and spatial correlation of SiGe wire and island structures induced by such surface steps. The parameters for MBE growth have been varied systematically in order to investigate the self-assembling and self-ordering mechanisms appearing in growth of strained SiGe layers on vicinal surfaces. The nanostructures are analyzed by atomic force microscopy (AFM), transmission electron microscopy (TEM) and micro Raman spectroscopy. Si(113) substrates have a low surface energy which is comparable to Si(001) but show a much stronger tendency for bunching of steps on vicinal surfaces. The Si(113) surface reveals step bunches which are mainly multiples of a 4-atomic step unit. Periodic arrays of SiGe wires form by strain-mediated self-organization during deposition of a SiGe/Si multilayer. The correlation of wires in different layers is inclined with respect to the growth direction. This is well described by a model calculation assuming the Si surface steps to locate at the maxima of local strain. Ge islands nucleate preferentially at the step edges of vicinal Si(113) substrates and form ordered rows of islands. No Ge islands but wire-like Ge accumulations are observed at the step edges of the step bunched SiGe/Si multilayer buffers.

Metal-Organic Chemical Vapor Deposition of Zn-In-Sn-O and Ga-In-Sn-O Transparent Conducting Oxide Thin Films

AbstractThe metal-organic chemical vapor deposition (MOCVD) technique has been successfully applied for growth of Sn-doped transparent, conducting Zn-In-O and Ga-In-O films using Sn(acac)2, In(dpm)3, Ga(dpm)3, and Zn(dpm)2, as volatile precursors. The 25 °C electrical conductivity of the as-grown films is as high as 1030 S/cm (n-type, carrier density N = 4.5 × 1020 cm−3, mobility µ = 14.3 cm2/V•s) for the Zn-In-O series and 700 S/cm (n-type, N = 8.1 × 1019 cm−3, µ = 55.2 cm2/V•s) for the Ga-In-O series. After Sn-doping, the Zn-In-O series exhibits 25 'C electrical conductivities as high as 2290 S/cm with a higher carrier mobility, while the Ga-InO series exhibits higher electrical conductivity (3280 S/cm at 25 °C) and much higher carrier density, but with diminished mobility. All films show broader optical transparency windows than that of commercial ITO films. Reductive annealing, carried out at 400-425 °C in a flowing gas mixture of H2(4%) and N2, results in increased carrier density and mobility as high as 64.6 cm2/V•s for films without Sn doping, but lowered carrier density for the Sn-doped films. X-ray diffraction, transmission electron microscopy, micro diffraction, and high-resolution X-ray analysis show that all films with good conductivity have cubic, homogeneously doped In2O3-like crystal structures.

A novel UHV-REM as applied to observation of reconstruction of Pt(100) surface

Direct observation of surface reconstruction under reflection electron micros-copy(REM) provides an intimate insight into basic processes on the surface, leading to more comprehensive understanding of surface physics in atomic scale. For this purpose we have developed a special UHV-specimen chamber, which allows various types of attachments, e.g., evaporator, ion gun, cooling facility, gas inlet and STM if necessary, to be mounted. This chamber was mounted in a 200kV transmission electron micro scope(TEM), Hitachi H-700H, to construct a novel UHV-REM for surface study.Fig.l shows a schematic diagram of the UHV-TEM constructed in the present work. The specimen chamber is evacuated with turbomolecular pump and Ti sublimation pump to the vacuum pressure of ~10-9 Torr. Some additional ports for, evaporator, gas-inlet, etc. are also attached around the specimen stage. Feedthrough metal bellows for driving system allows specimen holder to be translated in X- and Y-directions and to be tilted against electron beam without deterioration of vacuum pressure.

Ion-beam-assisted deposition of Al 2O 3 thin films

The density, composition and microstructure of Al 2O 3 films grown by the ion-beam-assisted deposition (IBAD) technique were studied. This technique involves direct evaporation of Al 2O 3 by electron (e) beam while simultaneously bombarding with 300–500 eV O 2 + ions. The arrival rates of ions and atoms were adjusted by varying the ion current and deposition rate respec- tively. The composition and density of the films were determined by a combination of Rutherford backscattering spectroscopy, thickness profilometry and cross-section transmission electron microscopy, while the microstructure was studied by plan-view transmission electron micro- scopy. The hydrogen content of the films was also analyzed using the proton recoil detection technique. IBAD of Al 2O 3 resulted in an amorphous phase with substrate at room temperature and a crystalline η phase at a substrate temperature of about 600 °C. The IBAD films at 600 °C had bulk-like densities (about 3.7–3.9cm -3) and they were free from pores. The stoichiometry of these films was about the same as the bulk stoichiometry. The IBAD film at 600 °C contained a very small quantity of hydrogen atoms (about 1.48×10 21cm -3) as compared with a regular e-beam-deposited film (about 4.4×10 22cm -3).

Crystal structure refinement and electron microscopy of arsenopyrite

Arsenopyrite crystals from Hakansboda (Sweden) have been studied by single crystal X-ray diffraction and analytical transmission electron microscopy. The material contains an excess of sulfur and some cobalt. Microprobe analyses gave a mean value of Feo.87Coo,13Aso.88S1.12' All crystals examined were twinned; the volume ratio of the twinned in- dividuals was taken into account. The structure was refined from 834 independent diffractometer data in the monoclinic space group C2dd and final R = 0.049 and Rw = 0.025 were obtained. The refined occupation numbers of As and S are in good agreement with the microprobe analysis. Fe-S distances range from 2.239 to 2.257, Fe-As distances from 2.336 to 2.375, the As - S distance is 2.346 A, where S and As stands for (As, S) with predominant S and As, respectively. A transmission electron micro- scopestudy revealed antiphase domains and microtwins. Lamellar exsolu- tion was observed in Co-rich specimens. These submicroscopic defects are interpreted on the base of group-subgroup relationships which relate the marcasite to the arsenopyrite structure.

A (110) CS structure in reduced rutile crystals

Abstract Abstract Rutile crystals, grown in vacuum-deposited amorphous films by electron beam heating, have been investigated by high-resolution transmission electron micro scopy with the aid of computer image simulation. A new type of ordered (110) CS structure with 1/2 [0I1] shear has been found in reduced TinO2n−1 crystals with n = 2.

Substructure Measurements by Statistical Fluctuations in X-Ray Diffraction Intensity

AbstractThe substructures of a bet a-quenched and a recrystallized form of high-purity uranium were measured by a method based on statistical fluctuations in X-ray diffraction intensity. For these measurements, Warren's statistical equation for determining grain size was modified to make the equation applicable to materials with high absorption coefficients or moderate-to-large grain size ( > 20 microns) or both, since many metals fall into this category, and to allow for defocusing of the X-ray beam which occurs as a natural consequence of the experiment.The beta-quenched uranium was found to have numerous subgrains with a range of misorientation angles that was smaller and larger than the limits of the X-ray measurements (Ω = 10−4 to 10−2 steradians). The presence of the large subgrains was corroborated by optical microscopy. The presence of very small subgrains was corroborated by transmission electron microscopy which showed 0.1- to 1-micron subgrains relatively free of dislocations bounded by dense dislocation networks, and by micro Laue diffraction patterns (30-micron beam diameter) which showed partial rings similar to a powder pattern.The recrystallized uranium had no misorientation within the grains greater than 5.5 × 10−3 steradians. In contrast to the beta-quenched case, no subgrains were found either by transmission electron microscopy (TEM) or micro Laue diffraction patterns. The TEM micrographs showed a uniform distribution of dislocation networks. Since no other substructural elements were observed, the dislocations are believed to be the cause of the misorientation within the grains for solid angles of less than 5 × 10−3 steradiflns.These preliminary experiments show that the statistical method may be used in conjunction with transmission electron microscopy and micro Laue diffraction for the study of substructure. The statistical method gives quantitative data on “bulk” specimens that can be given a meaningful interpretation with the aid of the other techniques.