Reflections In Electron Diffraction Patterns Research Articles

Epitaxial Growth of InN by Halogen Transport Method

InN was epitaxially grown on (0001) α-Al2O3 substrates by the halogen transport method. Surface treatment of the substrate by a H2+Br2 gas (passed over In) just before the growth was essential for obtaining the epitaxial layers of InN. Arrays of extra spots were observed in the reflection electron-diffraction patterns of thin InN films. The extra spot arrays could be explained from the viewpoint that the crystal film was composed of twins. In these twin structures, the twinning planes were (7̄ 12 5̄ 0) and (1̄ 1̄ 20 9̄ 0). These extra spots ultimately disappeared with prolonged growth time. This result shows that as the growth proceeds, crystallites having a predominant orientation overwhelm other crystallites.

Epitaxial growth of aluminum-doped zinc oxide films on (11–.0) oriented sapphire substrates

ZnO:AI films were deposited on (11–0) oriented sapphire substrates heated up to 400°C with an RF power ranging from 25 to 170 W by RF magnetron sputtering from a ZnO target mixed with AI 2 O 3 of 2 wt%. Films deposited on substrates heated to a temperature in the range 50-350°C were (0001) oriented single crystals but those grown at 400°C consisted of crystallites with the (0001) and (101) orientation. The epitaxial relationships between ZnO:AI films and the substrates were determined by using the reflective electron diffraction patterns from the films and the back-reflection Laue patterns from the substrates. From these measurements, it was found that there were two types of epitaxial relationships between the (0001) ZnO:AI films and the (1120) sapphire substrates. One was [1010]ZnO:AI ll[00111]sapphire and the other [2110]ZnO:AI ‖[0001]sapphire.

Direct observation of atomic images of ultrathin diamond and diamond-like films

Atomic images of ultrathin diamond and diamond-like films grown on tungsten tips have been directly observed by field ion microscopy (FIM). The atomic image of diamond exhibits a triangular topography. It suggests that the diamond crystal is preferentially grown along the [111] direction during the initial growth-stage. FI images of diamond-like films show an amorphous random network of carbon atoms with some atomic arrangement of diamond crystals along the [111] direction too. It is found that there exists a strong reflection electron diffraction (RED) pattern of tungsten carbide (WC) from the tip used for FIM imaging of the diamond film.

Imaging of the crotoxin crystal in vitreous ice at 3.9 Å resolution

The crotoxin complex is a 24,500 dalton neurotoxic protein isolated from the venom of the Brazilian rattlesnake Crotalus durissus terrificus. The crotoxin complex crystallizes as thin crystals suitable for high resolution 3-D reconstruction by electron crystallographic analysis. High resolution imaging of an untilted crotoxin complex crystal embedded in glucose has been reported. Presented here is high resolution (3.9 Å) imaging of an untilted crotoxin complex crystal embedded in vitreous ice.Several technical problems are involved in the collection of high resolution electron crystallographic data for 3-D reconstruction. First, the specimen should be as flat as possible on the grid since bending due to specimen preparation or due to beam-induced movement may cause smeared reflections in electron diffraction patterns or optical diffractograms, a phenomenon that is particularly noticeable in highly tilted specimens.

A simple method of depositing oxygen-free titanium silicide films using vacuum evaporation

Abstract A novel technique for depositing oxygen-free low resistivity titanium silicide films with a controllable amount of excess silicon has been developed and is reported in this paper. This method employs electron beam evaporation of titanium and silicon in an ultrahigh vacuum environment to deposit alternate layers of metal and silicon in an appropriate ratio. The composite structure thus formed is finally covered with a relatively thick layer of evaporated silicon to eliminate the possibility of contamination of titanium during annealing. Heating in an inert ambient above 600°C results in a low resistivity titanium silicide layer. Auger analysis reveals the absence of oxygen contamination. Detailed analysis of the annealed layer from its reflection electron diffraction pattern indicates possible phase changes with varying annealing temperature.

Effect of Group V/III Flux Ratio on Lightly Si‐Doped AlxGa1 − xAs Grown by Molecular Beam Epitaxy

Optical and electrical properties of lightly Si‐doped layers grown by molecular beam epitaxy under various V/III flux ratios (1 to 4) and at various substrate temperatures (720°–780°C) have been studied by low temperature (≈4 K) photoluminescence and Hall measurements. Bound exciton (BE) peak intensity and Hall mobility increase with decreasing flux ratio and increasing substrate temperature. An excess reduction in the flux ratio causes the condensation of group III metals on epilayers. An optimum flux ratio was found to be 2.3 for the highest substrate temperature investigated here, 780°C. The peak intensity of the defect complex has been shown to be correlated with the growth conditions. It is suggested that the defect complex includes defects dominant under excess arsenic population. Reflection electron diffraction patterns from the growing layers have been related to the growth conditions and the qualities of the epitaxial layers. A sample with the highest BE peak intensity and smooth surface has been grown with a metal‐rich structure present on the surface. A structure has reproducibly been observed at intermediate amounts of group V/III composition on the surface between those for the and the arsenic‐stabilized structures. Growth conditions which result in surfaces with a structure are found to cause surface roughening on the epilayers.

Glass formation of several semiconductors and alloys by laser irradiation

Several samples of semiconductors (InSb and InSbTe) and alloys (FeBC, FeNiPBC and AlSi) were irradiated by a high-power CW CO 2 laser and pulsed YAG laser beams. The surface morphology of the samples was examined by a scanning electron-microscope (SEM). The reflection electron diffraction patterns were recorded by using a transmission electron microscope (TEM). The critical cooling rate for glass formation of different samples has been determined. Characteristics of the glass formation process are discussed.

H.V.E.M. study of ordering and disordering in Cu3Au

Abstract Cu3Au has been irradiated with 600 kV electrons, and the rate of ordering and disordering determined between 140 and 400 K. The degree of order has been measured from the ratio of the intensities of the superlattice and fundamental reflections in electron diffraction patterns, these ratios having been calibrated under appropriate conditions using specimens of a known degree of order. At all irradiation temperatures a steady-state degree of order is developed. The results have been interpreted in terms of a model due to Zee and Wilkes (1980) with minor modifications. It has been found on this basis that the energy of migration of the defect responsible for ordering during irradiation is ∼0–62 eV, and this same value can be used to match the limited earlier data from neutron-damage studies.

Corrosion of Copper and Brass: Non-Stoichiometric Mixed-Valence Oxides

During the course of studies of the corrosive effects of specific dissolved ions on copper and brass, persistent indications were found that the initial corrosion products did not conform to the simple cuprous and cupric oxides. Visual examination showed corrosion to be highly inhomogeneous, ranging from red to black or blue-black, with the red product commonly in sweeping, feather- like patches or spots. Reflection electron diffraction patterns did not show a simple correspondence: black = CuO and red = CU2O. Many black samples gave diffraction patterns for the red copper oxide, CU2O, although some had CuO patterns. Many of the CU2O patterns contained extra peaks, and preferred orientation was especially common in the brass samples (Figures 1 and 2, Table 1).

On `spike' diffuse reflections in electron diffraction patterns of diamonds

The commonest natural diamonds (classification type Ia) contain platelet defects on {100}, usually with mean diameters in the 20 to 100 nm range, which generate disorder diffuse X-ray reflections in the form of (100) spikes through reciprocal-lattice points. Corresponding spikes in electron diffraction patterns of diamonds, recorded with 100 and 120 kV electrons, have been investigated. It has been established that (100) spikes appear most strongly in electron diffraction patterns of diamonds very rich in platelets, and are absent in the case of platelet-free diamonds (types IIa and IIb). Spikes from diamonds containing relatively large platelets are sharper than those from diamonds containing very small platelets. Multiple scattering of electrons prevents measurement of the dependence of spike intensity upon diffraction order as can be done in the X-ray case. Some experiments with spike electron reflections have been performed that are impossible in the X-ray case. It has been shown that when the crystal volume sampled by the electron beam contains only one platelet, then the spike distribution reduces to a pattern containing only spikes normal to the platelet concerned. Also, dark-field weak-beam microscopy has been applied, by selecting one spike only in the diffraction pattern, to identify orientations of small platelets through the imaging of only those platelets normal to the spike selected.

Mechanically induced phase transformations in CdS, CdSe and ZnS

The chalcogenides of zinc and cadmium usually crystallize in either the sphalerite cubic or wurtzite hexagonal modification, except in rare cases where very high pressure leads to the rocksalt structure. Most of the compounds in question have a phase transition from hexagonal to cubic at some characteristic temperature, and which phase a particular compound assumes, depends on such factors as the temperature of crystallization and the nature of the bonding [1]. The incorporation of impurity ions can also be important [2]. It has long been known that the luminescence efficiency of hexagonal ZnS phosphor powders decreases on grinding and ball milling, and at t he same time the proportion of the cubic phase detected in X-ray powder photographs increases [3 -5 ] . However, as far as we are aware there is no published account of the structure of mechanically polished layers on large single crystals of II-VI compounds, although such layers can have profound effects on the apparent electrical and optical properties of a material. For example polished layers may introduce difficulties in experiments in which measurements of carrier diffusion lengths are made on angle lapped devices [6]. For some time past we have been carrying out a programme of work concerned with the preparation of photovoltaic cells and light emitting diodes on single crystals of hexagonal II-VI compounds. Devices are usually fabricated on dice of millimetre dimensions cut from large single crystals of CdS, CdSe and ZnS grown in this laboratory. Photovoltaic devices are prepared in CdS [7] and CdSe, and light emitting diodes on ZnS [8]. Sawing with the diamond wheel leaves dice with severely work-damaged surfaces. If attempts are made at this stage to remove the work-damaged layer by chemical etching, the result is a rough surface with numerous large hillocks, steps and kink sites. Devices prepared on such surfaces invariably have poor photosensitivity or low luminescence efficiency. In order to prepare more efficient devices with greater reproducibility, it is necessary to polish the sawn faces mechanically to produce physically flat surfaces before the chemical etch is administered. The purpose of the etch is to remove the damaged layer completely so that its effects are eliminated. Recently, however, we have made a brief study of the properties of the work damaged layers. The results are reported here. When a crystal of CdSe with the wurtzite structure was polished by hand, or on a lapping wheel, using alumina powder with a particle size of 1/am or less, the resulting surface, regardless of the orientation of the underlying crystal, gave rise to the reflection electron diffraction (RED) pattern shown in Fig. 1. The diffraction rings in this pattern indicate that the surface layer on this sample was entirely polycrystalline. The radii of the first three rings increase in the sequence X/3, x/8, x/l l, and are indexed as the (1 11), (220) and (311) reflections of the cubic sphalerite phase of CdSe. Similar cubic polycrystatline surface layers were produced on single crystals of CdS

Reflection electron diffraction patterns from Si layers epitaxially grown on BP-Si substrates

BP(100) was epitaxially grown on a Si(100) substrate by the thermal reaction of B 2H 6 and PH 3 in hydrogen. A BP(100)- c(2 x 2) surface structure was observed for a BP thickness of 400–6000 Ȧ. There was characteristic twinning in an early growth stage (less than 400 ȧ;) of the BP. On the BP-Si substrate with a BP(100)-c(2 x 2) surface structure, Si was epitaxially grown by the thermal decomposition of SiH 4 in hydrogen. A Si layer with high crystalline perfection without any extra spots on the reflection electron diffraction patterns was obtained.

P-CuGa1-xInxS2/n-ZnSe Heterojunction by LPE Method from In Solution

p-CuGa1-xInxS2/n-ZnSe heterojunction was made by the LPE method from the In solution of solute CuGaS2 and solvent In, though a p-CuGaS2/n-ZnSe heterojunction was not obtained. The reflection electron diffraction pattern from the interface indicates an epitaxial growth. The measurements of EPMA have shown that Zn and Se decrease monotonically, and Cu, Ga and S increase monotonically, from the substrate to the over-growth layer. Indium from the solvent showed a monotonic increase from the substrate to the over-growth layer. The maximum temperature Tm of 650°C and cooling rate of 0.5°C/min were taken. The epitaxial layer is represented by the formula CuGa1-xInxS2, where x was 0.16 for Tm of 650°C. It is suggested that a complete series of solid solutions (CuGa1-xInxS2)1-y-(2ZnSe)y alloys is formed. The thickness of the mixedcrystal layer was 4.9 µm.

Morphology of poly-p-phenylene formed during the polymerization of benzene by molybdenum pentachloride or ferric chloride

Abstract The morphology of poly-p-phenylene(PPh) formed during the polymerization of benzene by molybdenum pentaehloride(MoCl5) or ferric chloride(FeCl3) has been studied. It has been found that well-developed fibrillar structures are formed during the polymerization by MoCl5. Electron diffraction confirms that the molecular axes of PPh are oriented parallel to the fibril axis. These fibrillar structures suggest that the nascent PPh possesses a predominantly para structure. It is thought that the fibrillar structures result from simultaneous polymerization and crystallization. The reflections in electron diffraction patterns can be indexed by assuming a monoclinic unit cell with dimensions a = 7.78 Å, b = 5.62 Å, c = 4.26 Å, (fiber axis), and β = 79%. It can be assumed that the most likely space group is P21a. Aggregates of many crystalline fragments with an indefinite shape were formed during the polymerization by FeCl3. They give electron or x-ray diffraction pattern having broad Debye rings. It is thought that subsequent reaction of the polymer with benzene to form polyphenyl side chains or polynuclear structures occurs much more frequently during the polymerization by FeCl3. These side reactions may prevent the formation of the fibrillar structures with higher crystallinity.

酸性くえん酸浴による光沢Ｆｅ‐Ｍｏ合金めっきと電着過程の２，３の性質について

Crack-free iron-molybdenum alloy coating having a micro-vickers hardness of a bout 450 and a light black hue has been electroplated onto mild steel substrates at cathodic current densities of 1-1.5A/dm2 and at 35°C. The optimum electrolyte composition was found to be 0.26mol/l Na3C6H5O7, 0.12mol/l Na2MoO4, and 0.14mol/l of FeSO4 at pH 4.0 adjusted with dilute H2SO4. The alloy composition exactly corresponds to Fe3Mo. Transmission and reflection electron diffraction patterns of the alloy showed an amorphous structure but the surface was found to be crystallized. Three kinds of the alloy plating baths in which sodium or potassium concentration is kept constant at two different levels have been prepared for the analysis of the current-potential characteristics. In addition, the catholyte pH was directly measured by using an antimony microelectrode. It was found that the electrodeposition involves a cycle of electrolytic reduction-reoxidation by the sodium, potassium and molybdenum ions. It was also revealed that sodium and potassium atoms form a layer on the electrode to protect the electrode surface from the reoxidation of electrolytically formed lower oxide of molybdenum. This provides a good explanations for the previously reported characteristics of the induced molybdenum codposition.

Preparation and Some Properties of CuInSe2 on ZnSe Heterojunction Grown by LPE

CuInSe2 has been grown on ZnSe by LPE from the Bi solution. The value of lattice mismatch is 2.06%. The reflection electron diffraction pattern showed an epitaxial growth. Optimum growth condition was the following: maximum temperature of 600°C, cooling rate of 0.5°C/min, thickness of the over-growth layer of 6 µm and thickness of mixed crystal layer of 4.5 µm. The flatness of overgrowth surface was dependent on the substrate orientation and the quality was in order of (111)Se, (100), (111)zn and (110). Hall measurements on over-growth layer were carried out after the heat-treatment in Se and Zn atmosphere for 10 minutes at 600°C. The p·CuInSe2–n·ZnSe and n·CuInSe2–n·ZnSe heterodiodes were measured for their I–V, C–V characteristics and photoresponse. Especially, the n-n heterodiode showed a high photosensitivity.

Diffraction effects from inclined grain boundaries in polycrystalline thin foils

Using thin-film gold bicrystals with the boundary plane parallel to the foil surface, it has been shown(l,2) that networks of grain boundary dislocations can act as diffraction gratings and give rise to subsidiary reflections close to the matrix reflections in electron diffraction patterns. Recently several groups of workers(3-5) have shown that inclined boundaries in polycrystalline specimens also produce extra reflections which may be due to the periodic nature of the boundaries. In general grain boundaries in polycrystalline specimens will be steeply inclined to the foil surface and additional reflections due to wave matching at the boundary(6) will also be present. The diffraction technique has the potential for providing detailed information on the structure of inclined boundaries (see, for example (5)), especially for the case where the image contains no useful information. In order to provide a firm basis for this technique, the geometry of the diffraction effects expected from inclined boundaries and the influence of these effects on the appearance of images will be examined.

A transmission electron microscopy study of molybdenum irradiated with helium ions

Abstract The paper describes the application of transmission electron microscopy to investigate the structure developed in the surface layers of molybdenum samples during irradiations with helium ions in the range 18 to 60 keV. Specimen temperatures were varied over a wide range from 20° C to above 1000°C and both dynamic and post-irradiation analytical techniques were utilised to provide information on the separate contributions of interstitials, vacancies and the helium gas to the formation of the damage structures. The interstitials formed dislocation loops, with subsequent growth to a dislocation network, while the combination of vacancies and gas resulted in a very high density (≈10 19 cm −3 ) of small helium bubbles over a wide temperature range (20–700°C). The helium bubbles were frequently found to be aligned in a body-centred-cubic lattice which produced extra reflections in electron diffraction patterns. Measured [110] bubble lattice spacings varied between 32 A and 50 A but showed no significant temperature dependence up to 700°C. At high helium doses (≈5 × 10 17 ions cm −2 ) blisters were clearly seen, together with the small bubbles, thus indicating the rapid growth of blisters rather than the slow coalescence and growth of the bubbles. At high temperatures larger helium bubbles were present. The insensitivity of the bubble parameters to vacancy mobility, the role of interstitials in creating surface stresses, and other aspects, are discussed particularly in relation to mechanisms of blistering. Although no definite conclusions are reached, it is clear that TEM evidence is important and that any proposed mechanism of blister formation must take this evidence into account.

Epitaxial growth of al thin films on mica and investigation of film structure

The temperature dependence of the structure of the aluminium thin film was studied. Reflection and transmission electron diffraction (RED and TED, respectively) patterns show that the changes of the polar orientation (texture) and the azimuthal orientation (due to epitaxy) arise in the film as the temperature of substrate surface is increased. The simultaneous presence of spot patterns at RED and arc or ring patterns at TED in a certain temperature range is explained by the preferred orientation of the film grains in the azimuthal direction and the nearly perfect orientation in the polar direction. The particular changes of the azimuthal orientation became at the temperature of the largest desorption of water molecules from mica so that we deduce that the presence of water molecules is necessary for the particular degree of the azimuthal orientation at lower temperature. At a higher temperature (≈500°C) of the substrate surface the well-oriented films were prepared with the same diffraction patterns as single crystal with orientation (111)Al// //(001)M and (110)Al//(010)M (double positioning is present in the films).

Optical waveguiding properties of sputtered LiNbO3 single crystalthin films on LiTaO3 substrates

Optical waveguiding layers of LiNbO3 on LiTaO3 substrates were obtained by rf sputtering. The LiNbO3 layer was determined to be a single crystal over the whole deposited legion by reflection electron diffraction patterns. Propagation of TE0 and TM0 modes were observed for an as-sputtered film, and TE0, TEi, TM0 modes for a film annealed at 1100°C for 10 minutes. The layer's effective thickness and refractive index (n0) of 2500 A and 2.318 at 6328 A respectively, were calculated from the coupling conditions. The losses were 16 dB/cm for the as-sputtered film and 8 dB/cm for the annealed film.