Electron Diffraction Studies Research Articles

Electron diffraction studies of beam-sensitive samples using hybrid-pixel detectors

Electron diffraction studies of beam-sensitive samples using hybrid-pixel detectors

Hydrothermal Synthesis of Cu0.66‐xZn0.34+xSe Materials and Investigation of Their Structural, Optical, and Magnetic Properties

AbstractIn the current paper, we have prepared Cu0.66‐xZn0.34+xSe materials by varying the concentration of copper and zinc (x=0, 0.085, 0.17, 0.255, 0.34) with the help of a facile one‐step hydrothermal method. The X‐ray diffraction study reveals that the as‐prepared nanomaterials show the polycrystalline property. The crystallinity increases with the variation of Zn concentration, and the average crystallite size was calculated in the 39 to 55 nm range. The morphological analysis shows the uniform and agglomerated particles having an average size of around 596 nm. High‐resolution transmission electron microscopy and selected area electron diffraction study reveal the crystalline phases of the prepared sample. The energy‐dispersive X‐ray analysis confirmed the presence of constituent elements in the sample. The sample shows a high optical bandgap in the range of 3.6 eV to 4.09 eV, which was calculated from absorbance spectra. Photoluminescence measurements of the samples were carried out with 532 nm laser excitation, where the defect‐related emission peaks in the 540–850 nm range are observed. A change in the bandgap and optical emission is observed for different compositions. The magnetic properties analysis through the vibrating sample magnetometer reveals that the prepared sample exhibits ferromagnetic behaviour at room temperature, which can be used in magnetic storage applications. The tuning of the optical properties of the samples by varying the copper and zinc concentrations will be useful for various photonic devices.

Temperature dependence of incommensurate modulation in Ca0.28Ba0.72Nb2O6

We present an electron microscopy and diffraction study of a CaxBa1−xNb2O6 ceramic with x=0.28 (CBN28), a ferroelectric material with a partially filled tetragonal tungsten-bronze structure. The microstructure has strong similarities to that of SrxBa1−xNb2O6, with an average orthorhombic symmetry and an intimate intermixture of merohedral twin variants at a length scale of tens of nanometers. Superstructure spots in diffraction patterns are displaced by a one-dimensional incommensurate modulation, characterized by a propagation vector δδ0. Heating experiments show that δ is strongly coupled to ferroelectric polarization, decreasing as 180° ferroelectric domains become more finely spaced and needle-like as the Curie temperature TC is approached during heating and increasing once more above TC. No change in symmetry is observed at TC, consistent with a transition from ferroelectric to antiferroelectric (or ferrielectric) relaxor properties. The superstructure spots and incommensurate modulation disappear ∼250°C above TC, consistent with polar regions in the material becoming fully transient.

Scanning precession electron diffraction study of carbide precipitation sequence in low alloy martensitic Cr-Mo-V tool steel

Precipitation of carbides after tempering of a medium carbon low alloyed Cr-Mo-V tool steel at 600°C was studied with scanning precession electron diffraction (SPED) in a transmission electron microscope (TEM). The precipitation sequence was evaluated by mapping the carbide distribution on carbon extraction replicas prepared from samples tempered for different durations of up to 24 h. The SPED results were supplemented by equilibrium calculations and energy dispersive x-ray spectroscopy (EDX) measurements in a TEM. It was found that ε-Fe2C precipitates within martensite laths during quenching via auto-tempering. During reheating to tempering temperature ε-Fe2C was dissolved and replaced by cementite, θ-M3C, which predominately form on martensite boundaries. It was further found that the small carbides in the early stage of tempering have predominantly a cubic MC structure, even if the V/Mo-ratio of the studied steel was only 0.12, and it is known from literature that V and Mo form cubic MC or hexagonal M2C carbides, respectively. Later during tempering more stable carbides, such as M7C3 and M23C6, also form, and it was concluded that the M7C3 form both by separate nucleation and precipitation on the cementite/matrix interface. The latter phenomenon was seen as particles with a core of cementite and a shell of M7C3 after 24 h of tempering.

Thermal annealing induced linear/nonlinear properties of Ag2S/As2Se3 heterojunction films for optoelectronic applications

The present study reports the annealing induced structural as well as optical properties of Ag2S/As2Se3 heterostructure film at different annealing temperatures. The trigonal AgAsSe2 phase formation was confirmed from the X-ray diffraction (XRD) and selective area electron diffraction (SAED) study. The bandgap of as-prepared Ag2S/As2Se3 film decreased on annealing. The reduction in bandgap increased the static refractive index with annealing. The Urbach energy increased from 422±3 meV to 464±2 meV whereas the optical density and extinction coefficient increased by annealing due to the formation of AgS–AsSe solid solution. The dispersion energy increased and consequently increased the oscillator wavelength and oscillator strength upon annealing. The carrier concentration and optical conductivity increased whereas the optical electronegativity decreased with annealing. The 3rd order nonlinear susceptibility (χ(3)) increased from 2.804x10−11 esu (as-prepared Ag2S/As2Se3) to 5.132 x10−11 esu upon annealing at 200 °C. The n2 value increased upon annealing which increased the nonlinear absorption coefficient but decreased the figure-of-merit. The contact angle value decreased (93°–47.6°) that shows the transformation of hydrophobicity to hydrophilic nature which is good for sensor applications like biological sensor. The surface roughness decreased upon annealing. The change in optical parameters upon annealing makes them the appropriate candidate for optoelectronics, dielectric and nonlinear optical applications such as memory devices, optical switch, etc.

Structural modulation and spin glassiness upon oxidation in oxygen storage material LnFeMnO4+x for Ln = Y, Lu, and Yb

The mixed valence multiferroic LnFe2+Fe3+O4 (where Ln = Y, Lu, and Yb) can reversibly uptake oxygen into its lattice, which is evidenced by a crystallographic phase transition along with the appearance of structural modulations. In this study, we show that the Mn-substituted version of this multiferroic can also be readily oxidized to LnFe3+Mn3+O4.5 revealing similar oxygen storage behavior. Through neutron, electron, and synchrotron x-ray diffraction studies, we observe a structural modulation that we attribute to a displacement wave in the fully oxidized compound. This wave exhibits commensurability with a wavevector q = (−2/7, 1/7, 0). Bond valence summation analysis of plausible interstitial oxygen positions suggests that oxygen insertion likely occurs at the middle of the Fe/Mn–O bipyramid layers. The structural modulation of LnFeMnO4.5 is two-dimensional, propagates along the ab-plane, and is highly symmetric as 12 identical modulation vectors are observed in the diffraction patterns. The nature of the lanthanide, Ln3+, does not seem to influence such modulations since we observe identical satellite reflections for all three samples of Ln = Y, Lu, and Yb. Both LnFeMnO4 and LnFeMnO4.5 display spin glassy behavior with 2D short-range magnetic ordering being observed in LnFeMnO4. Analysis of the neutron diffraction data reveals a correlation length of ∼10 nm. Upon oxidation to LnFeMnO4.5, the short-range magnetic order is significantly suppressed.

WITHDRAWN: Precession electron diffraction study on the microtexture of the zirconium oxide film in aqueous solutions

The oxide film formed on zirconium alloy (Zr-0.45 Sn-0.38 Nb-0.30 Fe-0.05 Cu-0.015 Si-0.13 O, wt. %) respectively corroded for 300 days in 360 °C/18.6 MPa pure water and lithiated water was characterized using precession electron diffraction (PED). The results revealed that the grain morphology (columnar and equiaxed) and the grain crystallography orientation (angular deviation of {112¯}m-ZrO2 from the oxide growth direction) gradually changed periodically with the distance of metal/oxide (O/M) interface. In lithiated water sample, the proportion of oxide grains deviated from the {112¯}m-ZrO2 texture by 50-60° is higher than that in pure water, resulting in an early corrosion transition. This is attributed to that Li+ ions were unfavorable for the formation of well-oriented and coarse columnar grains. In the pure water, a small amount of hexagonal ZrO (h-ZrO) suboxide was found at the O/M interface where just go trough a high-rate corrosion transition, while in the lithiated water, a continuous h-ZrO suboxide layer was formed at the O/M interface where experiences a low-rate corrosion just before transition. This suggests that the present of suboxide layer greatly correlates to the instantaneous oxidation rate. Electron energy loss spectroscopy (EELS) further found that the presence of h-ZrO affected the oxygen level in the nearby substrate metal.

Direct Observation of Intragrain Defect Elimination in FAPbI3 Perovskite Solar Cells by Two-Dimensional PEA2PbI4

Two-dimensional perovskites have widely been used to improve the efficiency and stability of perovskite solar cells and are generally believed to passivate defects at the grain boundaries of three-dimensional perovskites. Herein, we studied introducing various combinations of two-dimensional phenyl ethylammonium lead iodide (PEA2PbI4) and methylammonium chloride (MACl) to the formamidinium lead iodide (FAPbI3) precursor solution. Ultralow dose selected area electron diffraction studies prove that the high density of intragrain planar defects in FAPbI3 can be strongly reduced by adding PEA2PbI4 and fully eliminated by adding further MACl. Although PEA+ is too large to incorporate into FAPbI3, PEA2PbI4 not only improves crystallization but also suppresses intragrain defect formation. As a result, a longer charge carrier lifetime, higher photoluminescence quantum yield, lower Urbach energy, and current–voltage hysteresis are achieved, resulting in a champion PCE of 23.69%, with an improvement of humidity stability.

Ligand-Mediated Control of the Surface Oxidation States of Copper Nanoparticles Produced by Laser Ablation

We report on studies that demonstrate how the chemical composition of the surface of copper nanoparticles (CuNPs) - in terms of percentage copper(I/II) oxides - can be varied by the presence of N-donor ligands during their formation via laser ablation. Changing the chemical composition thus allows systematic tuning of the surface plasmon resonance (SPR) transition. The trialed ligands include pyridines, tetrazoles, and alkylated tetrazoles. CuNPs formed in the presence of pyridines, and alkylated tetrazoles exhibit a SPR transition only slightly blue shifted with respect to CuNPs formed in the absence of any ligand. On the other hand, the presence of tetrazoles results in CuNPs characterized by a significant blue shift of the order of 50-70 nm. By comparing these data also with the SPR of CuNPs formed in the presence of carboxylic acids and hydrazine, this work demonstrates that the blue shift in the SPR is due to tetrazolate anions providing a reducing environment to the nascent CuNPs, thus preventing the formation of copper(II) oxides. This conclusion is further supported by the fact that both AFM and TEM data indicate only small variations in the size of the nanoparticles, which is not enough to justify a 50-70 nm blue-shift of the SPR transition. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies further confirm the absence of Cu(II)-containing CuNPs when prepared in the presence of tetrazolate anions.

Exploring the effects of graphene and temperature in reducing electron beam damage: A TEM and electron diffraction-based quantitative study on Lead Phthalocyanine (PbPc) crystals

High-resolution transmission electron microscopy (TEM) of organic crystals, such as Lead Phthalocyanine (PbPc), is very challenging since these materials are prone to electron beam damage leading to the breakdown of the crystal structure during investigation. Quantification of the damage is imperative to enable high-resolution imaging of PbPc crystals with minimum structural changes. In this work, we performed a detailed electron diffraction study to quantitatively measure degradation of PbPc crystals upon electron beam irradiation. Our study is based on the quantification of the fading intensity of the spots in the electron diffraction patterns. At various incident dose rates (e/Å2/s) and acceleration voltages, we experimentally extracted the decay rate (1/s), which directly correlates with the rate of beam damage. In this manner, a value for the critical dose (e/Å2) could be determined, which can be used as a measure to quantify beam damage. Using the same methodology, we explored the influence of cryogenic temperatures, graphene TEM substrates, and graphene encapsulation in prolonging the lifetime of the PbPc crystal structure during TEM investigation. The knowledge obtained by diffraction experiments is then translated to real space high-resolution TEM imaging of PbPc.

Formation of Large-Area Twisted Bilayer Graphene on Ni(111) Film via Ambient Pressure Chemical Vapor Deposition

Due to the destruction of the intrinsic symmetry between the layers, twisted bilayer graphene has the advantages of available interlayer coupling, tunable electronic bandgap, and diverse phonon dispersion features, which offers a unique platform for the advanced electronic devices. The segregation growth of large-area twisted bilayer graphene on Ni(111) film by ambient pressure chemical vapor deposition (APCVD) methods is presented in this paper. The growth kinetics include two main aspects of the catalytic reaction of methane on the Ni surface and the carbon segregation from the Ni bulk. The large-area twisted bilayer graphene (TBG) can be fabricated by controlling carbon segregation for the continuous second layer graphene that is rotated relative to the first layer graphene. Low energy electron diffraction (LEED) studies reveal a dominant twist angle of about 22.7°. The analysis shows that the dominant twist angle is closely related to the stable energy structure of TBG with the smallest moiré periodicity. Besides, the other twist angles of TBG are also formed in vicinity of the dominant angle, confirmed by microscopic observations with selected area electron diffraction (SAED). The work in this paper provides a convenient route for the synthesis of TBG on Ni(111) substrate, which can promote the application of twisted graphene in future photoelectric and spintronic devices.

An Electrochemical Study of the Corrosion Behaviour of T91 Steel in Molten Nitrates

A study of the corrosion behaviour of T91 steel in molten 60 wt% NaNO3-40%KNO3 has been carried out at 300, 400 and 500 °C during 1000 h. Employed techniques included potentiodynamic polarization tests, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements. Experiments were complemented by detailed scanning electronic measurements and X-ray diffraction studies. Polarization curves revealed the existence of a passive layer formed onto the steel, composed mainly of Cr2O3, FeCr2O4, NaCrO4 and K2Fe2O4. Corrosion current density values increased, whereas the polarization resistance value decreased more than one order of magnitude as the testing temperature increased. EIS tests indicated a charge transfer controlled corrosion process, regardless of the testing temperature, and that the double electrochemical layer resistance decreased with the temperature.

Morphology, electrical and linear and nonlinear optical properties of Pb0.85Sn0.15Se thin film

The ternary PbSnSe chalcogenide thin film compounds are promising materials for infrared imaging and semiconducting devices due to their large transparency in infrared regions in this study, we will look to present some physical properties of the ternary Pb0.85Sn0.15Se compound, in order to be able to use it in the optoelectronic application. A thin film of stoichiometric composition Pb0.85 Sn0.15 Se was prepared by thermal evaporation process at a vacuum pressure of 103 Pa. The X-ray and electron diffraction studies revealed that the deposited films are crystalline in nature and belong to a Cubic structure as depicted from the JCPS cards. The surface morphology of the films was examined using the scanning electron microscope. The optical transmission and reflection spectra of the deposited film have been measured in the wavelength spectral range of 200–2500 nm. Therefore, the optical band gap energy and refractive index were evaluated. The dispersion of the refractive index was adequately described using the suggested Wemple – DiDomenico single-oscillator model, whereby the corresponding dispersion parameters, high-frequency dielectric constants besides evaluating the non-linear refractive index, and nonlinear optical susceptibility were evaluated. Further analysis of the refractive index based on the Fan model was also conducted to calculate the carrier concentration to the effective mass ratio. The variation of the conductivity versus temperature was performed and present in the temperature range 293–623 K where the activation energy was calculate.

Synthesis, spectroscopic elucidation, in vitro antimicrobial, cytotoxic and CT-DNA binding evaluation of heterobimetallic complexes of Ni(II) with main group/transition metal dichlorides

Heterobimetallic complexes of Nickel (II) have been synthesized and characterized of the type [Ni(L)2(M)2R4Cl2], where L = 2,6-diaminopyridine (C5H7N3), M = Sn, Si, Ti and Zr and R = Ph, Me, C5H5 etc. The monometallic complexes of nickel have been synthesized by using 2,6-diaminopyridine in the presence of NiCl2·6H2O dissolved in methanol to form complexes of the type [Ni(L)2]Cl2. To synthesize heterobimetallic complexes, these synthesized complexes were further processed with main group metal or transition metal dichlorides in a 1:2 molar ratio in MeOH. Elemental analyses, molecular weight calculations, electronic, infrared, magnetic susceptibility, conductivity measurements, mass spectra, 1HNMR , 13CNMR , and powder X-ray diffraction studies have been used to evaluate these synthesized compounds. Using a monometallic complex, the heterobimetallic complexes were synthesized, and an octahedral geometry was perceived for these heterobimetallic complexes. The antimicrobial potency of the synthesized complexes has been evaluated against four different bacterial and three fungal strain at different concentrations. The cytotoxicity activity of these resulting complexes against MCF-7, HeLa and HaCaT cell lines using MTT assay has been scrutinized. Also, the interaction of the reported complexes with calf thymus DNA (CT-DNA) by different techniques revealed that the complexes could bind to CT-DNA by intercalative mode. The binding of the reported complexes to CT-DNA has been investigated using UV–vis and fluorescence spectra. The results indicated a much lower binding affinity of monometallic complex than that of the heterobimetallic complexes.

Novel copper-sawdust nanocomposite preparation and evaluation

A readily available and reasonably priced lignocellulosic material that comes from nature is sawdust or wood shaving. It is a waste product of both industry and agriculture that is widely distributed and has disposal issues. The management of waste (such as sawdust) and research into transforming it into various compounds for specialized purposes and objectives have recently drawn a lot of interest. Therefore, the primary objective of this investigation can be summed up as showcasing sawdust as a type of intriguing bio-waste and turning it into wealth for a variety of applications. Copper-Sawdust nanocomposites have been produced into powder and rectangular slabs using the chemical reduction method.The nanocomposite was investigated with Transmission Electron Microscopy which revealed a spherical shape with particle sizes ranging between 3 and 14 nm. Electron diffraction studies confirmed the planes (111), (200), and (220) as well as the presence of metal copper.X-ray Diffraction studies confirmed the Miller indices for the characteristic high-intensity peaks in the range 35°- 65° as (111), (200), and (220) with corresponding Crystallite sizes as 14.4 nm, 14.7 nm, and 11.9 nm respectively. The crystallite size was comparable to the actual size of the Nanocomposite confirming the precision of the results. The average lattice constant is 4.23Å. The research also confirms that the copper nanoparticle was crystalline with Face Centered Cubic (FCC) structure similar to the bulk Copper. The Electron diffraction and the X-ray diffraction also confirmed similar planes. The current study indicates that Copper nanocomposite may find use in several industrial domains making it extremely beneficial to the scientific community.

Impact of the lanthanide size on the polymorphism and electrical properties of Ln5.4MoO11.1 (Ln = Nd, Sm and Gd)

Mixed proton-electronic conductors are of great interest for high temperature electrochemical devices, such as hydrogen separation membranes. In this contribution, ceramics with composition Ln5.4MoO11.1 (Ln = Nd, Sm and Gd) were prepared by a freeze-drying precursor method. The resulting powders were sintered at 1500 °C and cooled down at different rates to investigate the different polymorphic forms: quenching (rapid cooling), 5 and 0.5 °C min−1. The ceramics were characterized by different techniques: X-ray diffraction, scanning and transmission electron microscopies and X-ray photoelectron and impedance spectroscopies. X-ray diffraction studies confirmed that all materials are single phase regardless of the cooling rate used. Those cooled by quenching present a simple cubic fluorite structure. At lower rates, 5 and 0.5 °C min−1, the cubic symmetry is stabilized as the size of the lanthanide decreases. However, electron diffraction studies indicated the formation of domains with superstructure ordering. Furthermore, XPS analysis showed the presence of mixed Mo6+ and Mo5+ for all compositions, which explains the electronic conduction in an oxidizing atmosphere. All materials are stable in reducing atmosphere and the ionic and electronic conductivities show opposite trends as the ionic radii of the lanthanide element becomes smaller, where the former decreases and the latter increases.

Defect equilibrium and charge transport in R0.25Sr0.75FeO3−δ (R = La, Nd, Y, Ho): The effect of cation type

The perovskite-type oxides of R0.25Sr0.75FeO3−δ series for R = La, Nd, Y, Ho were subjected to X-ray and electron diffraction studies, thermogravimetric and dilatometric measurements. Coulometric titration and four-probe DC techniques were used to obtain data on oxygen content and electrical conductivity of the oxides in the range of oxygen partial pressure from 10−19 to 0.5 atm at 750–950 °C. A decrease in the size of R-cation in R0.25Sr0.75FeO3−δ was found to result in a decrease in the oxygen content in the oxides, thermal expansion, and electrical conductivity. In case of Y and Ho, an extra factor, in addition to the cation radius, affecting the oxide properties, is argued to be the limited oxygen coordination, which promotes local ordering in the respective oxides. This statement was confirmed by electron diffraction study, which detected incommensurate diffuse scattering as the evidence of partial local ordering of cations in the A sublattice in combination with the ordering of oxygen vacancies. This partial local ordering affects strongly functional properties of Y and Ho containing oxides. In particular, oxygen-ion conductivity at 950 °C decreases from 0.328 ± 0.005 to 0.055 ± 0.003 S/cm in response to the substitution of La in R0.25Sr0.75FeO3−δ by Y.

Enhanced visible light induced dye degradation and antibacterial activities of ZnO/NiO nanocomposite synthesized using Clitoria ternatea flower extract

In this study, ZnO/NiO Nanocomposites (NCs) were prepared using a rapid, simple and eco-friendly green synthesis method using medicinal flower extract of Clitoria ternatea and their visible light assisted dye degradation and antibacterial properties were investigated. The synthesised ZnO/NiO NCs were characterised by ultraviolet–visible (UV–Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), High resolution transmission electron microscopy (TEM) and Selected area electron diffraction (SAED) studies. XRD results revealed that ZnO/NiO NCs exhibit hexagonal wurtzite and cubic crystal structure with an average crystallite size of 18 nm. HRTEM images revealed roughly spherical and hexagonal morphology with an average particle size of 23 nm. The antibacterial activity of ZnO/NiO NCs examined against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria using well diffusion method indicated significant antibacterial activity. The photocatalytic activity of the ZnO/NiO NCs showed 83.4 % and 84.4 % of dye degradation efficiency, respectively against Bromophenol Blue (BPB) and Crystal Violet (CV) dye for 150 min under sun light irradiation. The result shows that the ZnO/NiO NCs investigated in this study exhibited a strong potential agent and was successful in the removal of dye from wastewater.

Optical, Structural, Morphological, Antibacterial, and Photodegradation Characteristics of BaxMg0.8−xFe2O4(x = 0.2, 0.4, and 0.6) Nanocrystalline Powders Synthesized by Combustion Method

Herein, a series of barium‐doped magnesium ferrites [BaxMg0.8−xFe2O4(x = 0.2, 0.4, and 0.6)] with metal nitrates and egg white solution are prepared to show how simultaneous substitution of divalent cations affects the structural, morphological, antibacterial, and photocatalytic capabilities of ferrites. A cubic spinel and hexagonal structures are discovered through a wide particle size dispersion in the sample. The infrared (IR) spectra of the octahedral and tetrahedral sites exhibit two prominent absorption bands about 576 and 450 cm−1. With increasing Ba2+doping, the optical band gaps decreased from 6 to 5.6 eV. The elemental analysis of Ba, Mg, Fe, and O is confirmed using energy dispersive X‐ray spectroscopy (EDX) analysis. High‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies reveal the formation of spherical nanoparticles along with some hexagonal structures. For antibacterial studies, BaxMg0.8−xFe2O4nanoparticles are tested against Gram‐positive and Gram‐negative bacteria. The photodegradation test of the produced nanoparticles for the degradation of Congo red and methylene blue dyes is examined under ultraviolet (UV) light irradiation.

Controlled Synthesis of Tellurium Nanowires.

One-dimensional tellurium nanostructures can exhibit distinct electronic properties from those seen in bulk Te. The electronic properties of nanostructured Te are highly dependent on their morphology, and thus controlled synthesis processes are required. Here, highly crystalline tellurium nanowires were produced via physical vapour deposition. We used growth temperature, heating rate, flow of the carrier gas, and growth time to control the degree of supersaturation in the region where Te nanostructures are grown. The latter leads to a control in the nucleation and morphology of Te nanostructures. We observed that Te nanowires grow via the vapour-solid mechanism where a Te particle acts as a seed. Transmission electron microscopy (TEM) and electron diffraction studies revealed that Te nanowires have a trigonal crystal structure and grow along the (0001) direction. Their diameter can be tuned from 26 to 200 nm with lengths from 8.5 to 22 μm, where the highest aspect ratio of 327 was obtained for wires measuring 26 nm in diameter and 8.5 μm in length. We investigated the use of bismuth as an additive to reduce the formation of tellurium oxides, and we discuss the effect of other growth parameters.