Observations and analyses of microstructural defects for chemical vapour deposited β-SiC by transmission electron microscopy

A transparent silicon carbide was grown by a cold-wall chemical vapour deposition (CVD) system using CH₃SiCl₃ and hydrogen gas mixtures on to a graphite substrate. Transmission electron microscopy was used to observe microstructural defects of CVD -SiC, usingg.b = 0,±1/3 and theg.R _F = integer criterion, quantitative information on defects can be obtained. Theb was identified as 1/6 [11¯2] for Shockley partial dislocations andR _F as 1/3[¯111], 1/3 [1¯11], 1/3 [11¯1] for stacking faults. Twin planes were identified as (11¯1), (¯11¯1) in this study. Stacking faults and twins always existed on {111}. Subgrains were surrounded by dislocation networks and full of microtwins. Other defects, such as dislocation loops and dislocation dipoles, were also observed.     

Etch pits in flux-grown corundum

Procedures have been developed for chemically polishing and etching {0001}, {10¯11}, {10¯12}, {11¯20}, and {1¯100} planes in crystals of ruby and sapphire grown from a PbF₂ flux. The shape and the orientation of the etch pits were found to be characteristic for each plane and the density of the pits was 10² to 10⁴/cm². Similar pits were produced in flame-fusion material, but the density was 10⁶ to 10⁸/cm². Ruby and sapphire crystals grown by the same process behaved similarly. There is evidence that etch pits reveal dislocations which emerge normally to the basal or to the prismatic planes, since similar patterns of pits were produced after the removal of successive layers of material parallel to these planes, and a correlation was found between the pit patterns on opposite {0001} faces. Inconclusive evidence on this point was obtained for the rhombohedral planes.     

Microstructure of Epitaxial La0.7Ca0.3MnO3 Thin Films Deposited by Direct Current Magnetron Sputtering on LaAlO3 Substrate

Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been used to study the microstructural properties of La_0.7Ca_0.3MnO₃ films on (001) LaAlO₃ substrates prepared by direct current magnetron sputtering technique. The as-grown thin films with different thickness are perfectly coherent with the substrates. The film suffers a tetragonal deformation in the area near the interface between the film and the substrate. With increasing thickness, the film is partially relaxed. It was found that La_0.7Ca_0.3MnO₃ films consist of two types of oriented domains described as: (1) (110)_f [001]_f||(001)_s[100]_s and (1¹10)_f [001]_f||(001)_s[100]_s and (2) (110)_f [001]_f||(001)_s[010]_s and (1¹10)_f [001]_f//(001)_s[010]_s. Upon annealing, the film is relaxed by the formation of mis¯t dislocations. Other than mis¯t dislocations, two types of threading dislocations with Burgers vector of <100> and <110> were also identified.     

Grazing incidence reciprocal space mapping of partially relaxed SiGe films

Epitaxially grown lattice mismatched semiconductor structures are increasingly important for microelectronic and optoelectronic applications. Recently, a great deal of research has been carried out on strain relaxation mechanisms in lattice mismatched epitaxial films. Here, we describe triple-axis x-ray diffraction measurements that were performed to study strain relaxation mechanisms and dislocation formation in Si_1–x Ge _x alloys grown on (0 0 1) Si substrates. At low growth temperature (T_g 600°C) and small lattice mismatch (>2%), two different mechanisms of strain relaxation are observed, depending on the growth temperature and the magnitude of the strain. At Higher growth temperatures or larger lattice mismatch, strain relaxation occurs initially by surface roughening. Subsequently, 60° misfit dislocations nucleate in regions of high strain. At smaller lattice mismatch or lower growth temperature, the surface of the film does not roughen and the 60° misfit dislocations are formed primarily by Frank–Read multiplication. Triple-axis x-ray diffraction reciprocal space maps taken at grazing incidence on very thin epitaxial films can easily distinguish between these two mechanisms. Here, the lattice planes perpendicular to the interface are measured, whereas conventional diffractometry looks either at the planes parallel to the wafer surface or at planes having components both parallel and perpendicular to the surface. In the grazing incidence geometry, thickness broadening of the x-ray peak is eliminated, since the film is essentially infinitely thick parallel to the surface.     

Analysis of the effects of substrate temperature,concentration of tin chloride and nature of dopants on the structural and electrical properties of sprayed SnO2 films

The correlations between structural and electrical properties of sprayed SnO₂ films have been investigated as a function of substrate temperature (380–560 °C), concentration of tin precursor (0.02–0.8 M SnCl₄) and the nature of the doping agent (chlorine, fluorine, antimony). High-resolution transmission electron microscopy has shown that chlorine or fluorine incorporation promotes the same type of defects, which are <0 1 1> twins. These latter behave as neutral defects, the density of which limits the carrier mobility of degenerated fluorine- or chlorine-doped films to around 20 cm² V^–1 s^–1. The situation is totally different with antimony. Below the solubility limit in the SnO₂ lattice (3%–4% Sb/Sn), Sn⁴⁺ are substituted by Sb⁵⁺, creating two conduction electrons per site and acting as point-charged defects which lower carrier mobility. Above this limit, the Sb³⁺ and Sb⁵⁺ forms coexist and are associated with an extremely large concentration of structural defects, especially twins induced by the Sb³⁺ species. These ions enter two-dimensional arrangements on both sides of the twins, making them planar charged defects.     

Structural,optical and electrical studies on nanocrystalline tin oxide (SnO<Subscript>2</Subscript>) thin films by electron beam evaporation technique

Nanocrystalline tin oxide (SnO₂) thin films were coated using electron beam evaporation technique on glass substrates. To study the gleaming out look of the structure and surface morphological changes, the films were annealed in the temperature 350–550 °C for 1 h. The annealed films were subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) studies. The XRD patterns of SnO₂ thin films as-deposited and annealed at 350 °C illustrate that the films were amorphous, and beyond 350 °C and thereafter they became polycrystalline with tetragonal structure. The crystallite size of the annealed films, obtained through the XRD analysis, increased with the increasing annealing temperature, and it was found to be from 3.6 to 12 nm. The photoluminescence (PL) studies on these films were also carried out. The origin of luminescence was assigned to the defects of the nanocrystalline SnO₂ films. The Optical studies (UV-VIS) were performed and the optical band gab energy (Eg) calculations, the dependence of absorption coefficient on the photon energy at short wavelengths, were found to be increasing from 3.65 to 3.91 eV is also investigated.     

XRD and SEM studies of reactively deposited tin oxide thin films

Stoichiometric polycrystalline tin oxide thin films were deposited by the reactive evaporation of tin and the SnO₂ formation was found to be strongly dependent on the deposition parameters. The preferred orientation of the SnO₂ films deposited on different substrates was varying due to the dislocation defects arising during the thin film formation. The X-ray diffraction (XRD) studies identified a tetragonal structure while the scanning electron microscopic (SEM) studies revealed a polycrystalline surface for the SnO₂ films reactively deposited.     

Synthesis and properties of epitaxial SnO2 films deposited on MgO (100) by MOCVD

Epitaxial tin oxide (SnO₂) thin films have been prepared on MgO (100) substrates at 500-600 °C by metalorganic chemical vapor deposition method. Structural and optical properties of the films have been investigated in detail. The obtained films were pure SnO₂ with the tetragonal rutile structure. An in-plane orientation relationship of SnO₂ (110) [010]//MgO (200) [110] between the film and substrate was determined. Two variant structure of SnO₂ were analyzed. The structure of the film deposited at 600 °C was investigated by high-resolution transmission electron microscopy, and an epitaxial structure was observed. The absolute average transmittance of the SnO₂ film at 600 °C in the visible range exceeded 90%. The optical band gap of the film was about 3.93 eV.     

Microstructural investigation and SnO nanodefects in spray-pyrolyzed SnO2 thin films

Spray pyrolysis is one of the most cost-effective methods to prepare SnO₂ films due to its ability to deposit large uniform area, low fabrication cost, simplicity and low deposition temperature. Conventionally, scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) are routinely used to investigate microstructure and crystal structure of the SnO₂ films. In the present study, the SnO₂ films were deposited by spray pyrolysis at 300, 400 and 500 °C and the microstructure of the 500 °C film was further examined by using transmission electron microscopy (TEM) and convergent beam electron diffraction (CBED). It was found that large grain-size vertically-aligned columnar SnO₂ grains were formed after a few layers of small grain-size randomly oriented SnO₂ grains. Moreover, CBED showed the presence of SnO nanodefects that had not been reported before and could not be detected by SEM or XRD.     

Effect of oxygen partial pressure on the microstructural and physical properties on nanocrystalline tin oxide films grown by plasma oxidation after thermal deposition from pure Sn targets

In this work, microstructural and physical properties were studied in the tin oxide films deposited by thermal evaporation of Sn films on stainless steel substrates followed by in situ D.C. plasma oxidation at 200 °C substrate temperature. The surface properties were studied by scanning electron microscopy, X-ray diffraction, atomic force microscopy and four-point probe electrical resistivity. The typical calculated grain size of the films deposited by thermal evaporation was between 28 nm and 66 nm and the texture structure was found to be dependent on the thermal deposition pressure. A cassiterite structure of SnO₂ was produced by D.C. plasma oxidation with the main diffraction peaks of the (101), (200), (211), (310) and (221) planes at the 25% and 50% O₂ partial pressure conditions. However, at 12.5% O₂ partial pressure oxidation conditions, amorphous tin oxide structure and crystalline SnO phases were detected. Increasing thermal deposition pressure resulted in preferential texture formation at (211) and (310) planes. The surface structure investigation of the produced films by SEM and AFM studies showed large SnO₂ islands with approximately 1.0 μm and 1.5 μm sized nodules, and they are called as grape-like structures. The grape-like grains possess nano grains, which are between 20 nm and 30 nm in diameter calculated by Scherer's formula. The grape-like grains were seen to be separated by large cavities and the size of these cavities and nano grains was seen to be larger when the O₂ partial pressure is increased. The four-point probe resistivity of the films, grown at different oxidation temperatures, decreased with the increase in oxygen partial pressure. The values of resistivity for SnO₂ phase were measured as low as 10⁻⁵ Ω-cm and observed to decrease with increasing thermal deposition pressure and oxygen partial pressure.     

Fast response detection of H2S by CuO-doped SnO2 films prepared by electrodeposition and oxidization at low temperature

Fast response detection of H₂S by CuO-doped SnO₂ films prepared was prepared by a simple two-step process: electrodeposition from aqueous solutions of SnCl₂ and CuCl₂, and oxidization at 600 °C. The phase constitution and morphology of the CuO-doped SnO₂ films were characterized by X-ray diffraction and scanning electron microscopy. In all cases, a polycrystalline porous film of SnO₂ was the product, with the CuO deposited on the individual SnO₂ particles. Two types of CuO-doped SnO₂ films with different microstructures were obtained via control of oxidation time: nanosized CuO dotted island doped SnO₂ and ultra-uniform, porous, and thin CuO film coated SnO₂. The sensor response of the CuO doped SnO₂ films to H₂S gas at 50–300 ppm was investigated within the temperature range of 25–125 °C. Both of the CuO-doped SnO₂ films show fast response and recovery properties. The response time of the ultra-uniform, porous, and thin CuO coated SnO₂ to H₂S gas at 50 ppm was 34 s at 100 °C, and its corresponding recovery time was about 1/3 of the response time.     

Structure of heterosystems formed by a SnO<Subscript>2</Subscript> film and island metal (Ag,Au, or Pd) condensate

We have studied the phase composition and microstructure of thin tin(IV) oxide films surfacemodified with silver, gold, and palladium nanoislands. Using high-energy electron diffraction, we have shown for the first time that the thermal oxidation of the Sn films leads to the formation of nanocrystalline multiphase SnO₂ films in which the major phase is orthorhombic. Also present are (in order of decreasing content) tetragonal and cubic phases. Blocks of SnO₂(O) subgrains with 〈101〉 texture contain dislocations and stacking faults, which are interpreted as layers of the tetragonal phase. It has been shown that vacuum condensation makes it possible to modify the surface of SnO₂ films with noble metals and obtain homogeneous nanoisland coatings characterized by a unimodal, uniform island size distribution.     

Structural,Optical and Photoluminescence Study of Nanocrystalline SnO2 Thin Films Deposited by Spray Pyrolysis

Undoped SnO₂ thin films prepared by spray pyrolysis method reveal polycrystalline nature with prominent peaks along (110), (101) and (211) planes. All the films are nanocrystalline with particle size lying in the range of 3·14–8·6 nm calculated by DS formula. Orientation along plane (200) decreases continuously as molar concentration of SnO₂ increases. Dislocation density along plane (110) also decreases as molar concentration increases except 0·4 M SnO₂ thin film. Scanning electron microscopy image of the films contain jelly structures along with agglomerated clusters of particles. SnO₂ synthesized successfully, which confirms by Fourier transform infra-red spectroscopy. The optical transmittance spectra of 0·2 M SnO₂ thin film shows transmittance about 50–60% transmission in visible and near infrared region with a sharp cut off in the ultraviolet region. The transmission decreases in visible and near infrared region as molar concentration increases. Broad UV emission at 398 nm is observed in photoluminescence spectra of the films along with a blue emission, when excited at 250 nm wavelength. Emission intensity randomly changed as SnO₂ molar concentration increases. When excited at 320 nm, one UV and two visible peaks appeared at 385, 460 and 485 nm, respectively.     

Epitaxial growth of CdS on ionic substrates

Transmission electron microscopy has been used to study the structure of films of CdS evaporatedin vacua in the 10^–5 torr range on to (100) cleavage faces and cut and polished (110) and (111) faces of NaCl, and also on to (111) cleavage faces of BaF₂, (111) substrate faces were found to produce wurtzite structure (hexagonal) films with great structural perfection over wider ranges of epitaxial growth temperature than (100) substrate faces. The (100) and (110) substrates produced sphalerite structure (cubic) films. Electron beam evaporation and generally clean growth conditions were found to produce good quality films at low substrate temperatures. The films were in general free of any included grains and the diffraction patterns free of satellite spots. 111 or 10¯10 streaking was present in the diffraction patterns, however, except in the case of films grown on BaF₂ above 170° C, and on NaCl (111) above 250° C. These films were also free of planar defects and only contained of the order of 10¹⁰ dislocations per cm².     

HRTEM study of [001] low-angle tilt grain boundaries in fiber-textured BaTiO3 thin films

Low-angle tilt grain boundaries in [001] fiber-textured BaTiO₃ thin films were investigated by high-resolution transmission electron microscopy. Extensive observation revealed a very high density of low-angle tilt grain boundaries in the film. The low-angle tilt grain boundaries can be described as periodical arrays of dislocations on {100} and {110} boundary planes. The boundaries with (100) plane on {100} planes are composed of perfect dislocations with Burgers vectors b = a < 100 > (a = lattice constant of BaTiO₃: 0.3992 nm), while the boundaries with (110) plane on {110} planes are composed of the dissociated dislocations with Burgers vectors a/2 < 110 >. It was thus found that the difference in the boundary plane leads to different dislocation structures along the low-angle grain boundaries.     

Structural and optoelectronic properties of indium doped SnO2 thin films deposited by sol gel technique

Indium doped tin oxide (SnO₂:In) thin films were deposited on glass substrates by sol–gel dip coating technique. X-ray diffraction pattern of SnO₂:In thin films annealed at 500 °C showed tetragonal phase with preferred orientation in T (110) plane. The grain size of tin oxide (SnO₂) in SnO₂:In thin films are found to be 6 nm which makes them suitable for gas sensing applications. AFM studies showed an inhibition of grain growth with increase in indium concentration. The rms roughness value of SnO₂:In thin films are found to 1 % of film thickness which makes them suitable for optoelectronic applications. The film surface revealed a kurtosis values below 3 indicating relatively flat surface which make them favorable for the production of high-quality transparent conducting electrodes for organic light-emitting diodes and flexible displays. X-ray photoelectron spectroscopy gives Sn 3d, In 3d and O 1s spectra on SnO₂:In thin film which revealed the presence of oxygen vacancies in the SnO₂:In thin film. These SnO₂:In films acquire n-type conductivity for 0–3 mol% indium doping concentration and p type for 5 and 7 mol% indium doping concentration in SnO₂ films. An average transmittance of >80 % (in ultra-violet–Vis region) was observed for all the SnO₂:In films he In doped SnO₂ thin films demonstrated the tailoring of band gap values. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in indium doping concentration which may be due structural defects or luminescent centers, such as nanocrystals and defects in the SnO₂.     

Etude optique,par microscopie electronique des dislocations dans l'oxysulfure de lanthane II. Dislocations dans un plan pyramidal

Observation of the deformation of thin lanthanum oxysulphide specimens inside the transmission electron microscope has revealed the intimate connection between defects and structure. A pyramidal glide system was identified, from slip propagation and slip steps next the 〈101&#x0304;0〉 directions, screw dislocations with a Burgers vector $\text{1}\text{3}$ [1&#x0304;1&#x0304;23] and pyramidal dislocation loops. With this type of crystal, the glide plane {101&#x0304;1}, is parallel to the faces of the OLa₄ tetraedron.     

Self-construction of SnO2 cubes based on aggration of nanorods

The SnO₂ cubes with the rutile structure have been successfully synthesized without using any catalyst. Their morphology and microstructure were studied by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and elected area electron diffraction (SAED). It is revealed that the SnO₂ nanocubes exhibit high crystalline quality. The size of the nanocubes ranges from 100 nm to 300 nm. The side surfaces of nanocubes are {110} planes, while their cube axes are [001] direction. The growth mechanism of SnO₂ nanocubes was discussed and we suggested vapor-solid process should dominate the growth. These SnO₂ nanostructures represent an important example of spontaneous organization.     

Characterization of asymmetric rhombohedral twin in epitaxial α-Cr2O3 thin films by X-ray and electron diffraction

Epitaxial chromium oxide (α-Cr₂O₃) films grown by atomic layer deposition at 375 °C from CrO₂Cl₂ and CH₃OH on (1 1¯ 0 2) oriented α-Al₂O₃ have been studied by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and X-ray reflection (XRR). The thickness of the films ranged from 10 to 310 nm, and the average growth rate was 0.1 nm per deposition cycle. According to the XRD analysis, the orientation relationship in thinner films was (1 1¯ 0 2)[1 1 0]Cr₂O₃ || (1 1¯ 0 2)[1 1 0]Al₂O₃. Confirmed by the RHEED and XRD analyses, (1¯ 1 0 2) became the preferred growth plane at the thicknesses above 40 nm. This change has been interpreted as the appearance of an asymmetric rhombohedral twin with the orientation relationship between the layers (1¯ 1 0 2)[1 1 0]top || (1 1¯ 0 2)[1 1 0]bottom and (1¯ 1 0 2)[1 1¯ 1]top || (1 1¯ 0 2)[1¯ 1 1]bottom. The match of the anion and cation sublattices of both layers was characterized in terms of the structural model of the twin interface.     

Stacking faults in chromium,iron and vanadium mixed carbides of the type M7C3

Carbides found in white cast-iron containing 2.88% carbon, 15.22% chromium and 3.08% vanadium have the stoichiometric formula Cr_2.8V_0.7Fe_3.4C₃. They belong to the type M₇C₃ and are isomorphic with the chromium carbide Cr₇C₃. A modification of the approximate structure, given by Westgren, was considered in which carbon atoms were assumed to be situated right at the centre of gravity of perfectly symmetrical right-angled prisms. The great number of crystal defects that the carbides always contain were studied by electron microscopy and electron diffraction. They are stacking faults having as their fault planes one of the three equivalent planes (1 0 ¯1 0), (1 ¯1 0 0) or (0 1 ¯1 0), and as their fault vectorsR=a/2 orb/2 or (a+b)/2. A detailed examination of the diffraction patterns which contain streaks or extra reflections indicates that, in strongly faulted carbides, the stacking faults are ordered. A simple model which views the structure of M₇C₃ as a stacking sequence of right-angled prisms containing carbon atoms is proposed. Using this model, the order of the stacking faults can be easily interpreted. It suggests that the stacking fault energy is very weak, hence the frequent occurrence of the stacking faults in the carbides.