Wide Range Of Growth Temperatures Research Articles

Dependence of In 2Se 3 crystal structures grown on GaAs (0 0 1) substrates on growth temperature and VI/III ratio

We have studied the relation between crystal structures and growth condition of molecular beam epitaxy (MBE) grown In 2Se 3 on GaAs (0 0 1) substrates over a wide growth temperature range from 250 to 550 °C and VI/III ratio range from 0.006 to 195. It is confirmed that α-In 2Se 3 crystals were grown at a high VI/III ratio larger than about 1.0 and γ-In 2Se 3 crystals were grown at a low VI/III ratio between about 0.01–0.1 by X-ray diffraction and Raman scattering measurements. It is also found that the γ-In 2Se 3 was even grown at a low temperature of 250 °C. Exciton emissions were clearly observed in the γ-In 2Se 3 films grown at 350 °C. This indicates the grown films have a good crystalline quality.

The effects of buffer growth parameters on heteroepitaxial ZnO films grown by pulsed laser deposition

The effects of buffer layer deposition conditions on subsequent ZnO epitaxy on sapphire (0001) were examined. An initial ZnO buffer layer improves surface roughness for a wide range of buffer layer growth temperatures and pressures. Changes in buffer layer growth pressure and temperature have a moderate effect on the roughness of subsequent film growth. However, the conditions for buffer layer deposition have a large impact on crystallinity of subsequent films. In particular, the out-of-plane X-ray diffraction rocking curve full-width half-maximum decreased as buffer deposition temperature or O 2/O 3 pressure increases. Carrier mobility in the subsequent thick ZnO film was enhanced with increase in buffer layer deposition temperature. Carrier concentration decreased with increasing buffer layer deposition pressure.

Stranski-Krastanow growth of tensile strained Si islands on Ge (001)

Stranski-Krastanow island growth is demonstrated for tensile strained silicon epilayers on Ge (001) substrates over a wide range of growth temperatures. Small, Si-rich islands show sidewall faces near {1,1,10}, whereas larger islands are {113}-terminated truncated pyramids with an aspect ratio near 0.1. In contrast to compressively strained Ge on Si, we find for Si on Ge a significantly thicker wetting layer of >8 ML and coexistence of islands and dislocations.

High electron mobility GaN grown under N-rich conditions by plasma-assisted molecular beam epitaxy

An alternative approach is presented for the plasma-assisted molecular beam epitaxy of high-quality GaN. Under N-rich growth conditions, an unexpected layer-by-layer growth mode was found for a wide range of growth temperatures in the GaN thermal decomposition regime (>750°C). Consequently, superior surface morphologies with roughness of less than 1nm (rms) have been achieved. For lightly Si-doped GaN films, room-temperature electron mobilities exceeding 1100cm2∕Vs were measured, surpassing the commonly insulating nature of GaN grown under N-rich conditions at low temperature.

Spontaneous Chemical Vapor Growth of NiSi Nanowires and Their Metallic Properties

One-dimensional metallic nanostructures offer challenging opportunities to investigate their possible applications as interconnects in electronic circuitry and as field emitters in field emission displays. In particular, metallic silicide nanowires are promising candidates, because their growth can be easily integrated with silicon processing technology. Indeed the synthesis of single-crystalline, transition metal silicide nanowires, such as TaSi2, [6] e-FeSi, and CoSi, has been recently reported using diverse methods. The synthetic methods employed involve relatively high temperature processes, and may not be compatible with the low temperature processes required for their practical applications into electronic and display devices. In contrast, single-crystalline Ni-silicide nanowires, which have been experimentally verified to possess intrinsically low resistivity at low dimensions compared with the others, can be processed at relatively low temperatures, thus can provide practical advantages. For example, Wu et al. reported highly metallic properties of single-crystalline NiSi nanowires fabricated by a solid-state reaction at 550 °C between individual Si nanowires and Ni overshells. Here a simpler and controlled synthesis at low temperatures (∼400 °C) is reported, where single-crystalline NiSi nanowires spontaneously grow by SiH4 chemical vapor deposition (CVD) on Ni thin films predeposited on various substrates, such as SiO2/Si, quartz, and indium tin oxide (ITO) substrates. In fact, the Ni-catalyzed vapor phase thin film deposition has been previously investigated for applications into Si microelectronics and photovoltaics. Specifically, the dimensionality of the Ni-silicides have been reproducibly directed from thin films to single-crystalline nanowires, as well as their phases, by fine-tuning of growth parameters during CVD of a SiH4 gas precursor on predeposited Ni thin films. It is noted that Decker et al. and Kim et al. recently reported similar Ni-silicide nanowire growth by CVD and sputtering, however, the detailed growth mechanism, which is the main focus of this study, is unavailable to date. Here, by providing close observations of the morphological and phase evolution of Ni-silicide nanowires under optimized growth conditions, the spontaneous nanowire growth mechanism is discussed based on one-dimensional nucleation and growth of NiSi at a low supersaturation limit along with one-dimensional Ni diffusion during the chemical vapor reaction. Singlecrystalline NiSi nanowires in this study exhibit typical metallic behaviors, and show promising field-emission properties. It is suggested that our simple method to spontaneously grow NiSi nanowires at low temperatures can provide a practical strategy to fabricate metallic nanostructures based on bottom-up synthetic approaches. Our synthetic approach employs the Ni-catalyzed decomposition of SiH4, [14] which can occur well below the thermal decomposition temperature of SiH4 at above 600 °C. Thermally evaporated Ni thin films of 60–80 nm in thickness are used. During the CVD of SiH4 within the wide range of precursor partial pressures and growth temperatures of 10–100 torr and 250–600 °C, the reaction produces either Ni-silicide thin films or nanowires of various phases. Figure 1 illustrates the evolution of the morphology and the phases of Ni-silicides, grown at 250, 400, and 600 °C at 50 torr of SiH4, with the corresponding scanning electron microscopy (SEM) images, X-ray diffraction (XRD), and element depth profiling by Auger spectrometry. Within the entire growth range, Ni-silicide thin films have been commonly formed on the substrates; however, the surface morphology of the Ni-silicide thin films has been modified from planar sheets to nanowires, as well as phases in Ni-to-Si stoichiometry. The observations from Figure 1 are summarized in the following within the framework of SiH4 vapor–Ni solid reactions, where SiH4 decomposition and solid Ni diffusion are both thermally activated. First, at 250 °C, the catalyzed decomposition of SiH4 and the Ni out-diffusion from the pre-deposited Ni thin films are not sufficient to turn the Ni film into a Ni-silicide thin film during the reaction, and C O M M U N IC A IO N

Effect of Fe/Si Ratio on Epitaxial Growth of Fe3Si on Ge Substrate

The effects of the Fe/Si ratios on molecular beam epitaxy (MBE) of Fe3Si on Ge substrate have been investigated in a wide range of growth temperatures (60-300oC). From XRD measurements, it was found that Fe3Si layers were epitaxially grown on Ge(111) substrates at 60-200oC under the stoichiometric (Fe/Si ratio of Fe:Si=3:1) and non-stoichiometric (Fe/Si ratio of Fe:Si=4:1) conditions. From RBS measurement, it was found that atomic mixing of Fe and Ge at Fe3Si/Ge interfaces began at a growth temperature of 300oC. In the case of MBE under the stoichiometric condition (Fe:Si=3:1), the crystallinity of Fe3Si is significantly improved compared to the non-stoichiometric condition (Fe:Si=4:1). As a result, very low χmin was obtained in a wide temperature (60-200oC) under the stoichiometric condition. From the transmission electron microscopy measurements, it was shown that high-quality DO3-type Fe3Si/Ge structures with atomically flat interfaces were realized at a low temperature (~200oC) under the stoichiometric condition.

Growth and surface passivation of near-surface InGaAs quantum wells on GaAs (1 1 0)

The growth and surface passivation of near-surface InGaAs quantum wells (QWs) on GaAs (1 1 0) substrate have been investigated. Triangular shaped small islands, approximate areal density of 10 7 cm - 2 , are observed on metal organic vapor phase epitaxially grown GaAs single layer and InGaAs multi-quantum wells (MQWs) surfaces in a wide range of growth temperatures. By optimizing the growth conditions, high quality In 0.22 Ga 0.78 As QWs with optical properties comparable to the same structure grown on GaAs (1 0 0) are obtained. Near-surface single QWs are used to study the surface passivation. Epitaxially in situ grown mono-layer thick GaP and InP layers as well as surface phosphorization with tertiarybutylphosphine (TBP) are utilized as passivation methods. Passivation significantly increases photoluminescence (PL) intensity and carrier lifetime of near-surface QWs. The best passivation efficiency is obtained by surface phosphorization with TBP on (1 1 0)-oriented near-surface QW while the ultra-thin InP layer is the best on (1 0 0)-oriented near-surface QW. After 7 months of air exposure, all passivated near-surface QWs still show high PL intensity comparable to deep QW while the PL intensity of unpassivated samples degraded severely. Also, the differences between the optical properties of QWs on GaAs (1 1 0) and (1 0 0) substrates are observed and discussed.

Synthesis solute diffusion growth of bulk GaAs: Effects of growth temperature and stoichiometry

Bulk GaAs crystals were grown by synthesis solute diffusion (SSD) technique in a wide range of growth temperatures between 990 and 1150 °C. Electrical properties of these crystals were studied by means of van der Pauw, admittance spectroscopy, deep levels transient spectroscopy and photoinduced current spectroscopy techniques. It was shown that the main defects determining the properties were the GaAs antisites acceptors and the A center acceptors with the levels, respectively, E v +0.078 eV and E v +0.43 eV. The conductivity of the grown crystals was p-type and showed a pronounced maximum at a level of 10 4–10 5 Ω cm for growth temperatures between 1020 and 1080 °C. If the crystals were additionally compensated either by unintentional Si donors contamination from quartz crucibles or by intentional light Te doping one could get semi-insulating material with the room temperature resistivity higher than 10 6 Ω cm. The Fermi level in such crystals was pinned near E c −0.8 eV, i.e. close to the EL2 donors. Measurements by deep levels transient spectroscopy on n-type doped crystals or by low frequency capacitance–voltage on semi-insulating crystals showed that the density of EL2 in these samples was in the low 10 14 cm −3 and that thus the EL2 donors were not the main compensating agents.

Eurythermalism and the temperature dependence of enzyme activity

The "Equilibrium Model" has provided new tools for describing and investigating enzyme thermal adaptation. It has been shown that the effect of temperature on enzyme activity is not only governed by deltaG(double dagger)(cat) and deltaG(double dagger)(inact) but also by two new intrinsic parameters, deltaH(eq) and T(eq), which describe the enthalpy and midpoint, respectively, of a reversible equilibrium between active and inactive (but not denatured) forms of enzyme. Twenty-one enzymes from organisms with a wide range of growth temperatures were characterized using the Equilibrium Model. Statistical analysis indicates that T(eq) is a better predictor of growth temperature than enzyme stability (deltaG(double dagger)(inact)). As expected from the Equilibrium Model, deltaH(eq) correlates with catalytic temperature tolerance of enzymes and thus can be declared the first intrinsic and quantitative measure of enzyme eurythermalism. Other findings shed light on the evolution of psychrophilic and thermophilic enzymes. The findings suggest that the description of the Equilibrium Model of the effect of temperature on enzyme activity applies to all enzymes regardless of their temperature origins and that its associated parameters, deltaH(eq) and T(eq), are intrinsic and necessary parameters for characterizing the thermal properties of enzymes and their temperature adaptation and evolution.

Low-Temperature Growth of GaAs by Organometallic Vapor Phase Epitaxy Using TEGa and TBAs

GaAs epitaxial layers were grown by organometallic vapor phase epitaxy (OMVPE) using TEGa and TBAs over a wide range of growth temperature (350°C-700°C) and V/III ratio (2-9). GaAs with excellent surface morphology was obtained when the growth temperature was higher than 600°C. The GaAs surface tended to be rough with decreasing growth temperature below 550°C. When the growth temperature was decreased to 400°C, p-type GaAs was obtained with specular surface. The hole concentration increased with decreasing V/III ratio. The hole concentration was as high as 5.5×1017 cm–3 for the sample grown at 400°C with V/III ratio = 2.

The effects of growth temperature and growth phase on the inactivation of Listeria monocytogenes in whole milk subject to high pressure processing

The aim of this study was to explore the effect of a wide range of growth temperatures, growth phases and plating media on the inactivation of Listeria monocytogenes by high pressure processing (HPP). In part one, L. monocytogenes was grown to mid-stationary phase at 4, 15, 25, 35 or 43 °C, inoculated into whole UHT milk at ∼ 10 7 CFU/ml and high pressure processed at 400 MPa at room temperature (20–25 °C). Afterward, the HPP milk was plated on Tryptic Soy Yeast Extract Agar (TSYEA) and Modified Oxford Agar (MOX) to determine the degree of injury. For part two, cells were grown to mid-exponential, late-exponential or mid-stationary phase at 15 or 43 °C and processed in the same way. Time to reach a 5-log reduction was determined and data were analysed by ANOVA. The results from part one showed that both growth temperature and plating medium had a significant effect ( P < 0.001) on the inactivation of stationary phase L. monocytogenes by HPP. Tukey's pairwise comparisons revealed that the effects of all temperatures, except 35 and 43 °C, were significantly different ( P < 0.05). Cells grown at 15 °C were most sensitive to HPP, followed by cells grown at 4, 25 or 35 °C, with cells grown at 43 °C appearing to be the most resistant. Inactivation of cells grown at 4, 15 or 25 °C followed first order kinetics, whereas cells grown at 35 or 43 °C displayed non-linear inactivation kinetics due to tailing. In part two, both growth phase and plating medium had significant effects on the inactivation ( P ≤ 0.001) of L. monocytogenes by HPP. Cells grown at 15 °C to mid-stationary phase were the most pressure-resistant when tested on both media, and were significantly more resistant ( P < 0.05) than cells grown at the same temperature to the other two phases of growth. There was no significant difference between mid- and late-exponential phase cells grown at 15 °C. When cells were grown at 43 °C, mid-exponential phase cells were significantly more sensitive ( P < 0.05) than either late-exponential or mid-stationary phase cells, with no difference between late-exponential or mid-stationary phase cells. It was postulated that membrane composition, stationary phase proteins and/or stress proteins may affect pressure resistance.

GaN materials growth by MOVPE in a new-design reactor using DMHy and NH 3

Thin films of GaN were grown on template substrates of 4-μm-thick GaN layers on sapphire substrates by low-pressure metal organic vapour-phase epitaxy (LP-MOVPE) in a new-design reactor with the shape T. Wide range of growth temperature from 520 to 1100 °C was explored. At low temperature growth between 550 and 690 °C, dimethylhydrazine (DMHy) was used as source of atomic nitrogen while ammonia (NH 3) was used at high temperature growth (1000–1100 °C). At low temperature micro-Raman spectroscopy revealed a significant relaxation of the selection rules for the scattering by the optical phonons in the films grown at lower temperatures. Variation of the intensity ratio for E 2 H and E 1 phonon modes has been attributed to changes in the structural quality of the films grown at different temperatures. At high temperature, the quality of GaN layers were comparable to that of the substrate before growth.

Atomic layer epitaxy of MnAs on GaAs(0 0 1)

Atomic layer epitaxy (ALE) of MnAs on GaAs(0 0 1) has been investigated using bismethylcyclopentadienylmanganese (CH 3C 5H 4) 2Mn and trisdimethylaminoarsine As[N(CH 3) 2] for manganese and arsenic precursors, respectively. The α-MnAs layer of “type B” orientation was successfully grown by an alternative source supply with a wide growth temperature range from 320 to 500 °C. The grown layer showed a smooth surface morphology, reflecting the self-limiting growth. The decreased growth rate was observed below 350 °C, which was caused by the decreased reaction rate of As[N(CH 3) 2] 3 on the growing surface. A clear self-limiting mechanism was realized at higher growth temperatures but the saturation thickness was 9.5×10 −2 nm/cycle, which was attributed to the formation of a stable surface-reconstruction of manganese stabilized surface.

Synonymous codon usage and its potential link with optimal growth temperature in prokaryotes

The relationship between codon usage in prokaryotes and their ability to grow at extreme temperatures has been given much attention over the past years. Previous studies have suggested that the difference in synonymous codon usage between (hyper)thermophiles and mesophiles is a consequence of a selective pressure linked to growth temperature. Here, we performed an updated analysis of the variation in synonymous codon usage with growth temperature; our study includes a large number of species from a wide taxonomic and growth temperature range. The presence of psychrophilic species in our study allowed us to test whether the same selective pressure acts on synonymous codon usage at very low growth temperature. Our results show that the synonymous codon usage for Arg (through the AGG, AGA and CGT codons) is the most discriminating factor between (hyper)thermophilic and non-thermophilic species, thus confirming previous studies. We report the unusual clustering of an Archaeal psychrophile with the thermophilic and hyperthermophilic species on the synonymous codon usage factorial map; the other psychrophiles in our study cluster with the mesophilic species. Our conclusion is that the difference in synonymous codon usage between (hyper)thermophilic and non-thermophilic species cannot be clearly attributed to a selective pressure linked to growth at high temperatures.

Chemical and electrochemical properties of molybdenum oxide thin films prepared by reactive pulsed-laser assisted deposition

Molybdenum oxide (MoO 3) thin films were prepared by pulsed-laser assisted deposition (PLD) over a wide range of growth temperature, 30–500 °C. The chemical composition, crystal structure, and electrochemical properties of PLD MoO 3 thin films were investigated as a function of growth temperature. It was found that the growth temperature, and hence the thermochemical reaction during ablation, strongly influences the structural characteristics and properties of the resulting films. The compositional stability was well maintained up to a temperature on the order of 400 °C, after which point the formation of compositional defects introduces structural disorder and hence the reduced phases. Electrochemical performance evaluation indicated that the PLD MoO 3 films grown at temperatures 300–400 °C display charge–discharge profiles comparable to that of crystalline MoO 3.

Electronic Properties and Performance upon Lithium Intercalation of MoO3 Thin Films Grown by PLD

Over a wide range of growth temperature, 25-500 {degree sign}C, structural and optical characteristics of a series of MoO3 films prepared by PLD technique are studied. It is found that the growth temperature strongly influences the surface morphology, local atomic structure, and optical properties of PLD MoO3 thin films. The compositional stability was found to be well maintained up to a temperature on the order of 400 {degree sign}C, at which point the formation of compositional defects introduces structural disorder and changes in the optical characteristics. The electrochemical features of the insertion of Li ion into the MoO3 host lattice are also considered for various deposition temperature. Performance of Li//MoO3 thin film batteries are evaluated.

Thermal Adaptation of the Small Subunit Ribosomal RNA Gene: A Comparative Study

We carried out a comprehensive survey of small subunit ribosomal RNA sequences from archaeal, bacterial, and eukaryotic lineages in order to understand the general patterns of thermal adaptation in the rRNA genes. Within each lineage, we compared sequences from mesophilic, moderately thermophilic, and hyperthermophilic species. We carried out a more detailed study of the archaea, because of the wide range of growth temperatures within this group. Our results confirmed that there is a clear correlation between the GC content of the paired stem regions of the 16S rRNA genes and the optimal growth temperature, and we show that this correlation cannot be explained simply by phylogenetic relatedness among the thermophilic archaeal species. In addition, we found a significant, positive relationship between rRNA stem length and growth temperature. These correlations are found in both bacterial and archaeal rRNA genes. Finally, we compared rRNA sequences from warm-blooded and cold-blooded vertebrates. We found that, while rRNA sequences from the warm-blooded vertebrates have a higher overall GC content than those from the cold-blooded vertebrates, this difference is not concentrated in the paired regions of the molecule, suggesting that thermal adaptation is not the cause of the nucleotide differences between the vertebrate lineages.

Si (111) substrates as highly effective pseudomasks for selective growth of GaN material and devices by ammonia-molecular-beam epitaxy

The unique property of Si (111) as effective pseudomask substrate for selective growth of GaN by ammonia-molecular-beam epitaxy is reported. The critical nucleation temperature of GaN on Si (111) surface is found to be as low as 700°C, much lower than that on sapphire or AlN surface. As a result, selective growth of GaN is possible by ammonia-molecular-beam epitaxy on Si (111) substrates using a patterned AlN buffer layer. The wide range of growth temperatures (700–900°C) available for selective growth is a critical advantage for control and optimization of the facet characteristics of the selectively grown GaN patterns as required for potential fabrication of site-specific GaN or InGaN quantum dots. The demonstrated ease of selective growth of GaN on silicon has also implications in potential on-chip integration of GaN devices with silicon devices.

Spontaneous growth of Ag and Pb nanopucks on electronic patterns of 2D Pb quantum islands

Two-dimensional ordered Ag and Pb nanopuck arrays have been grown on two different types of Pb quantum islands. Electronic patterns on the surfaces of Pb islands serve as the templates for the growth. Nanopucks of different materials display dissimilar growth behaviors, reflecting the varied interaction strength between adatoms and the substrate. Due to a strong interaction existing between Ag atoms and the substrate, perfectly ordered Ag nanopucks of nearly identical size can be fabricated. The Ag array can sustain a wide growth temperature range from 70Kto150K, while for Pb nanopucks, the similar result can be obtained only below 70K. The stronger interaction also synchronizes the behavior of Ag nanopucks with that of the Pb island substrate, which exhibits a bilayer alternating character.

Metabolic and Genetic Diversity of Mesophilic and Thermophilic Bacteria Isolated from Composted Municipal Sludge on Poly-ε-caprolactones

Thirty mesophilic and thermophilic bacteria were isolated from thermobiotically digested sewage sludge in culture medium supplemented with poly-epsilon-caprolactone (PCL). The ability of each purified isolate to degrade PCL and to produce polymer-degrading extracellular enzymes was assessed. Isolates were characterized based on random amplified polymorphic DNA (RAPD), 16S rDNA sequence-based phylogenetic affiliation and carbohydrate-based nutritional versatility. Mesophilic isolates with ability to degrade PCL were attributed to the genera Acinetobacter, Burkholderia, Pseudomonas, and Staphylococcus. Thermophilic isolates were members of the genus Bacillus. Despite the restricted phylogenetic and genotypic diversity observed for thermophiles, their metabolic versatility and wide range of growth temperatures suggest an important activity of these organisms during the whole composting process.