X-ray Diffraction Peak Width Research Articles

Growth and structural characterization of single-crystal (001) oriented MoV superlattices

Dual target magnetron sputtering has been used to grow single-crysal MoV superlattice structures (SLS) with modulation wavelengths λ ranging from 0.6 to 17.7 nm on (001) oriented MgO substrates held at temperatures T s between 600 and 900°C. High resolution cross-sectional transmission electron microscopy (HRXTEM) images and comparisions between experimental and calculated X-ray diffraction (XRD) spectra show that SLS with an interface sharpness of ±1 monolayer (±0.15 nm) could be grown for λ ⩽ 4.9 nm and T s ⩽ 700°C whereas interdiffusion broadened the interfaces for higher T s values. This interface sharpness was also verified by growing SLS with λ = 0.6 nm (one unit cell of Mo and one of V) which exhibited strong superlattice satellites in both XRD and selected area electron diffraction (SAED), and contrast from the individual layers was also observed in HRXTEM images. For λ > 4.9 nm, HRXTEM images showed non-uniform layers and the XRD peak width (FWHM) increased by 250%.

Growth of single-crystal metastable (GaAs)1−x(Si2)x alloys on GaAs and (GaAs)1−x(Si2)x/GaAs strained-layer superlattices

Epitaxial zinc blende structure metastable (GaAs)1−x(Si2)x alloys have been grown with 0<x<0.3 on As-stabilized GaAs(100) substrates by a hybrid sputter deposition/evaporation technique. The films, typically 2–3 μm thick, were deposited at 570 °C with growth rates between 0.7 and 1 μm h−1. Alloys with 0<x<0.12 were defect-free as judged by plan-view and cross-sectional transmission electron microscopy (TEM and XTEM) with x-ray diffraction peak widths approximately the same as that of the substrate, 30 arcsec 2θ. XTEM lattice images showed smooth abrupt interfaces. (GaAs)1−x(Si2)x alloys with x>0.12 exhibited increasing evidence of interfacial defects associated with lattice strain when grown on GaAs. However, defect-free alloys with x up to 0.3 were obtained using (GaAs)1−x(Si2)x/GaAs strained-layer superlattice buffer layers to provide a better lattice match.

Growth of In xGa 1− xAs on GaAs (001) by molecular beam epitaxy

As a precursor to investigating the growth of In x Ga 1− x As on Si, a series of 2.8 ± 0.2 μ m thick films of various compositions ( x = 0, 0.13, 0.56 and 1.0) have been deposited by molecular beam epitaxy onto (001) GaAs on-axis substrates, using a minimized As 4 flux and a range of growth temperatures. In addition, a series of layers were grown at a fixed temperature of 350°C over the whole composition range. It was found that the electrical and structural characteristics of InAs and In 0.56Ga 0.44As were very similar, in both cases the layers were n-type, and growth below 330° produced a rapid deterioration of crystalline quality with the associated dislocations/defects being electrically active. In addition, the characteristics of GaAs and In 0.13Ga 0.87As were also found to be very similar. Both were doped with Si to make them conduct and showed a transition to insulating behaviour on reducing the growth temperature below ∼ 480±10°C; above this temperature good mobilities were obtained. Increasing the growth temperature for all the In containing alloys produced a gradual increase in surface roughness up to the point at which In accumulation on the surface occurred (∼410°C for InAs, ∼510°C for In 0.56Ga 0.44As and ∼550°C for In 0.13Ga 0.87As). Growth at 350°C showed a rapid deterioration in crystalline quality as x approached 0.5, as can be illustrated by a pronounced maximum in the X-ray diffraction peak width.

Material properties of InP-on-Si grown by low-pressure organometallic vapor-phase epitaxy

Undoped InP epilayers have been grown directly on (100) Si substrates by low-pressure organometallic vapor-phase epitaxy. The surface morphology, x-ray diffraction peak width, and ion backscattering yield each improve substantially with InP thickness (0.1–3 μm). X-ray and photoluminescence (PL) measurements demonstrate that the InP heteroepilayers are under biaxial tensile strain in the surface parallel direction. The carrier concentration profile shows that the carrier distribution in the InP layer is very uniform, while an apparent reduction in concentration occurs at the InP/n-type Si interface. The 77-K PL spectrum reveals a strong near-band-edge emission with a full width at half maximum of 14 meV. Post-growth thermal annealing at 780 °C was confirmed to be effective in improving the overall quality of InP-on-Si. The results presented are superior to those reported previously for InP/Si heteroepitaxy.

Measurement of the miscut angle of crystal surfaces vicinal to major crystal planes by x-ray diffractometry at glancing incidence

The width of an x-ray diffraction peak is a sensitive function of the angle of incidence when the angle of incidence is less than 1°. Measurements of x-ray diffraction peak widths taken at a glancing angle of incidence can be interpreted to yield information on miscut angles of crystal surfaces relative to major crystal planes. Miscut angles of a few arcminutes can be measured. A high-resolution multiple crystal x-ray diffractometer is necessary to achieve the accuracy of peak width measurement required. The technique is applicable to any crystal. As an example, we discuss the case of a (100) InP surface measured using the highly asymmetric (311) diffraction.

Growth, structure, and physical properties of single-phase metastable fcc Cu1−xCrx solid solutions

Single-phase fcc-structure metastable Cu1−xCrx alloys have been grown with Cr concentrations of up to 23 at. %. The films, which were typically 1.5–3 μm thick, were deposited by rf co-sputter deposition onto glass and oxidized-Si substrates at temperature between 55 and 180 °C. The average grain size of alloys grown at 90 °C was ∼100 nm. The lattice parameter of Cu1−xCrx was found to increase linearly with x resulting in an effective fcc Cr radius, in solution, of 0.1332 nm. ∼7% larger than the elemental bcc Cr bonding radius. The room-temperature resistivity of these alloys also increased linearly with x at a rate of 2.8 μΩ cm per at. % Cr. This high differential resistivity was due, in addition to simple alloys scattering, to scattering of conduction electrons into virtual bound states associated with the Cr atoms. Cu0.9Cr0.1 alloys were found to be stable for 24-h anneals at temperatures up to ∼300 °C. From an analysis of x-ray diffraction peak positions and widths as a function of both growth and annealing temperatures, we conclude that the reaction path for the phase transition from the metastable to the equilibrium state involves first the precipitation of coherent fcc Cr particles followed by a transformation to bcc Cr as phase separation continues. The oxidation rate of Cu0.9Cr0.1 was found to be much less that that of pure Cu. At an annealing temperature of 250 °C, the oxide thickness tox on Cu0.9Cr0.1 saturated at J25 nm after 1 h while tox on Cu continued to increase parabolically with time from ∼60 nm at 1 h to 140 nm at 4 h.

Electronic and structural studies of carbon/carbon composites

Room temperature Raman microprobe, (00 l) x-ray diffraction and electrical resistivity measurements have been performed on carbon/carbon composites made from mesophase pitch which were heat treated (T HT) at 2680°C, 2820°C and 3015°C. Results of these measurements indicate that both the ex-pitch carbon fiber and mesophase pitch matrix constituents of the composites were highly graphitic, exhibiting in-plane crystallite dimensions (L a) greater than 1000 Å for this range of T HT values. The c-axis crystallite dimensions (L c) were determined by analysis of x-ray diffraction peak widths to be ∼ 150 A ̊ . CuCl 2 was successfully reacted with T HT = 3020°C composites forming a stage 3 intercalation compound in both the fibers and the matrix, as determined by their Raman spectra.

Characterization of GaAs grown by metalorganic chemical vapor deposition on Si-on-insulator

Epitaxial GaAs layers were grown by metalorganic chemical vapor deposition on Si-on-insulator structures formed by high dose oxygen implantation. The quality of the GaAs films was examined as a function of layer thickness (0.01–4 μm). The surface morphology, ion backscattering yield, x-ray diffraction peak width, and Si implant activation efficiency all improve substantially with GaAs thickness. At a film thickness of 4 μm many of these properties are comparable to bulk GaAs, but some cracking of the epitaxial film is evident. Cross-sectional transmission electron microscopy reveals an average defect density of ∼108 cm−2 in the GaAs layer, which is similar to the density in GaAs films grown directly on Si.

MO-CVD GaAs Grown by Direct Deposition on Si

ABSTRACTGaAs layers were grown directly on misoriented (2° off (100)→[011]) Si substrates by Metalorganic Chemical Vapor Deposition. The threading dislocation density at the surface of 4 μm thick layers was typically 108cm−2, as determined by both preferential etching and transmission electron microscopy. Rapid thermal annealing (900°C, 10s) improved the crystalline quality of the GaAs near the heterointerface while allowing no detectable Si diffusion into this layer. Two deep electron traps were observed in the undoped GaAs, but were present at a low concentration (∼ 1013 cm−3 ). The (400) x-ray diffraction peak width from the GaAs was significantly reduced with increasing GaAs layer thickness, indicating improved material quality. This is supported by Si implant activation data, which shows higher net donor activity in thicker layers.

シリコンの高圧焼結

High pressure hot-pressing of pure silicon was examined as one of the fundamental studies on hot-pressing of the non-oxide ceramics, which are expected as new high temperature structural materials. Three kinds of silicon powders with different average particle size were used as starting materials and hot-pressed under various high pressure-temperature conditions. When the coarse powders were used, the relative densities of hot-pressed compacts were higher than those fabricated from the submicron fine powders at lower temperatures. The densification proceeded with increasing temperature and applied pressure, but no time dependence of densification was found. The results of the Vickers microhardness measurement of the hotpressed compacts showed the maximum and minimum values depending upon the hot-pressing time in a short run. This results was explained by considering the distribution state of strain within the grains and the strength of self-bonding between the grains. The interpretation could be supported by the results of the line width of X-ray diffraction peaks and also the microstructures of hot-pressed bodies.

Crystal growth of Co ferrite on fine acicular γ-Fe 2O 3 particles

Highly coercive magnetic powder was obtained by growing cobalt ferrite on the surface of γ-Fe 2O 3 particles in highly alkaline suspensions containing cobalt and ferrous ions in a Co/Fe molar ratio = 1 2 . The mechanism of the growth and the structure of cobalt ferrite on γ-Fe 2O 3 were studied by X-ray diffraction and electron diffraction techniques. Results show that crystals of cobalt ferrite CoFe 2O 4 with a spinel type crystal structure of lattice constant 8.415 Å grew epitaxially on γ-Fe 2O 3. The acicular direction of the epitaxially grown Co-γ-Fe 2O 3 as well as γ-Fe 2O 3 was in the [ 1 01] direction. It was found that from the lattice constant value and the half width of X-ray diffraction peaks, the lattice constant epitaxially grown Co γ-Fe 2O 3 may be attributed to two kinds of crystals, viz., seed γ-Fe 2O 3 ( a = 8.35 ∼ 8.37 A ̊ ) which was partly reduced to Fe 3O 4, and surface layer CoFe 2O 4 ( a = 8.415 A ̊ ). The crystal growth in the interface between the seed crystals and the growth layer was affected by the crystal structure of the seed crystals. The lattice constant of CoFe 2O 4 which was located in the vicinity of the interface was almost equal to that of the seed crystals.