Role Of Growth Conditions Research Articles

The Role of Growth Conditions in Modulating Nitrogen Diffusion During Gallium Nitride Crystal Growth by Sodium Flux Method

The Role of Growth Conditions in Modulating Nitrogen Diffusion During Gallium Nitride Crystal Growth by Sodium Flux Method

Effect of preharvest conditions on cut-flower quality.

The cut flower industry has a global reach as flowers are often produced in countries around the equator and transported by plane or ship (reefer) mostly to the global north. Vase-life issues are often regarded as linked to only postharvest conditions while cultivation factors are just as important. Here, we review the main causes for quality reduction in cut flowers with the emphasis on the importance of preharvest conditions. Cut flower quality is characterised by a wide range of features, such as flower number, size, shape, colour (patterns), fragrance, uniformity of blooming, leaf and stem colour, plant shape and developmental stage, and absence of pests and diseases. Postharvest performance involves improving and preserving most of these characteristics for as long as possible. The main causes for cut flower quality loss are reduced water balance or carbohydrate availability, senescence and pest and diseases. Although there is a clear role for genotype, cultivation conditions are just as important to improve vase life. The role of growth conditions has been shown to be essential; irrigation, air humidity, and light quantity and quality can be used to increase quality. For example, xylem architecture is affected by the irrigation scheme, and the relative humidity in the greenhouse affects stomatal function. Both features determine the water balance of the flowering stem. Light quality and period drives photosynthesis, which is directly responsible for accumulation of carbohydrates. The carbohydrate status is important for respiration, and many senescence related processes. High carbohydrates can lead to sugar loss into the vase water, leading to bacterial growth and potential xylem blockage. Finally, inferior hygiene during cultivation and temperature and humidity control during postharvest can lead to pathogen contamination. At the end of the review, we will discuss the future outlook focussing on new phenotyping tools necessary to quantify the complex interactions between cultivation factors and postharvest performance of cut flowers.

Thick epitaxial GaAsBi layers for terahertz components: the role of growth conditions

A series of 1.5 μm-thick epitaxial GaAsBi layers have been grown by molecular beam epitaxy on semi-insulating GaAs(100) substrates at temperatures ranging from 300 to 370°C. Complex studies were carried out with a focus to optimize the technological parameters for application of these layers in photoconductive THz components. The investigation of crystalline structure, layer morphology, optical properties, and characteristics of carrier dynamics was performed. Up to 12% of Bi incorporation has been confirmed by optical and structural analyses of GaAsBi layers grown at relatively low temperatures of about 300°C. The carrier lifetimes of these layers varied from 1 to 3 ps. Thick GaAsBi layers grown at higher than 350°C temperatures exhibited higher crystalline quality and longer carrier lifetimes reaching even tens of picoseconds. The Bi content in high-temperature-grown GaAsBi varied from 3 to 7% Bi.

Role of Growth Conditions on Optical Behavior of Mn Doped ZnTe by Using Chemical Vapor Deposition Route

Role of Growth Conditions on Optical Behavior of Mn Doped ZnTe by Using Chemical Vapor Deposition Route

Role of growth conditions on optical and electrical properties of fiber structured Zn0.90Cd0.1O thin films

Fiber structured Zn0.90Cd0.1O films were obtained on glass substrate using zinc acetate and cadmium acetate solution through chemical spray pyrolysis method. All the deposited films are polycrystalline with hexagonal wurtzite structure. The average crystalline size of the deposited films were estimated through intensity of diffraction peak corresponding (101) plane, which is observed to increase with increase substrate temperature. The films deposited at 673 and 723 K have fibrous structure irrespective of the precursor concentration. The presence of Cd in the deposited films was confirmed by EDAX. The high transparency around 90% in visible region was observed for the sample deposited at 723 K using 0.0125 M concentration. It is seen that the optical energy band gap varies from 2.85 to 3.05 eV as the deposition temperature is changed from 673 to 723 K. The film deposited using 0.05 M concentration had low Urbach energy values compared to other molar concentrations confirming the minimization of defect states in these samples. With increasing deposition temperature the near band edge peak of photoluminescence spectrum shifted towards shorter wavelengths and in the same spectrum the weak green emission may be due to presence of singly ionized oxygen ion. The estimated activation energy of the deposited films was observed to decrease with increasing temperature and precursor concentration.

The roles of growth conditions on the topotactic transformation from TiOF2 nanocubes to 3D hierarchical TiO2 nanoboxes

The roles of growth conditions, such as pH values, reaction temperatures and reaction times, on the morphologies and topotactic transformation processes from TiOF2 to anatase TiO2 has been investigated in this work. The topotactic transformation from TiOF2 to TiO2 can only take place with pH values ranging from 2 to 11. The morphologies of as-prepared samples were greatly dependent on the pH values of precursor solutions. The reaction temperatures can affect the crystalline quality and surface areas of TiO2 nanoboxes. The photocatalytic performances were also discussed.

Large-scale synthesis and the roles of growth conditions on the formation of Zn 2GeO 4 nanorods

Large-scale Zn 2GeO 4 nanorods with a length of about 10 μm have been synthesized via a facile hydrothermal process in the absence of any surfactant. The synthesized nanorods are single crystals with a rhombohedral phase. The dependence on the growth conditions, such as reaction temperature, reaction time, compactness and GeO 2 concentration, of the formation, morphologies and sizes of the Zn 2GeO 4 nanostructures has been investigated. Proper selection and combination of the growth conditions are the key aspects to control the formation, morphologies and sizes of the Zn 2GeO 4 nanostructures. The nucleation and crystalline growth mechanism are proposed to explain the formation and growth of Zn 2GeO 4 nanorods. The photoluminescence spectrum of the Zn 2GeO 4 nanorods exhibits three fluorescence emission peaks centered at 421, 488 and 529 nm when the excitation wavelength is 235 nm.

Residual stress in diamond-like carbon films: Role of growth conditions and ion irradiation

The dependence of the internal residual stress in thin diamond-like carbon films grown by the plasma-enhanced chemical vapor deposition technique on the most important growth parameters, namely, the radio-frequency (RF) power and direct-current (DC) bias voltage, was studied. It was shown that the compressive stress reaches its highest value of 2.7 GPa at the low RF power and DC bias values. Both increase and decrease of these parameters result in stress decrease. The stress increases with increase in the growth temperature from 250 to 350°C. Thermal annealing of up to 350°C does not affect the stress value. Subsequent irradiation of the films by In+ and P+ ions with the energy of 350 and 120 keV, respectively, results in the decrease in the compressive stress followed by its inversion to the tensile one. The stress linearly depends on the effective dose of up to 0.5 DPA with the slope of (8.7 ± 1.3) Gpa/DPA.

Shape variations and anisotropic growth of multiply twinned nanoparticles

Abstract Cyclic multiple twins as nanoobjects that display nearly regular polyhedron shape variety together with strongly anisotropic shape variations due to growth processes are reviewed with regard to their unique shape evolution based on the specific formation modes as well as on the particular structure of twin-related subunits. The review includes (i) the shape variations due to growth by stacking of tetrahedral subunits, (ii) the role of growth conditions in the shape evolution of multiply twinned nanoparticles, and (iii) the modes of twin-based anisotropic growth including branching growth and unidirectional growth. The particular structures are introduced making use of electron microscopy structural characterization of multiply twinned metal nanoparticles as well as some non-metal examples, and instructive models of the various configurations.

Texture development in polycrystalline CrN coatings: the role of growth conditions and a Cr interlayer

The control of the texture of transition-metal nitride coatings by varying the energy of incident ions and the coating thickness and by introducing a highly textured interlayer was demonstrated on polycrystalline CrN coatings grown by reactive magnetron sputtering. Development of the preferred (1 1 1) orientation was observed at moderate ion bombardment as the adatom net flux from the (2 0 0) to (1 1 1)-oriented grains dominated. A reversal of this flux at higher ion energies associated with collisional dissociation of ions at the film surface resulted in the development of a (2 0 0) texture. Coatings composed of grains with mixed (2 0 0) and (2 2 0) orientations were developed under intense ion bombardment due to preferential re-sputtering. The preferred orientation also changes with increasing coating thickness from (2 0 0) towards (1 1 1) through competitive growth. In contrast, a complete (2 0 0)-oriented structure of the CrN layer is formed when it is grown on a Cr interlayer with strong preferred (2 0 0) orientation.

Role of growth conditions on magnetic properties of AlCrN grown by molecular beam epitaxy

AlCrN layers were grown by gas source molecular beam epitaxy with varying amounts of Cr (up to ∼3at.%) under a broad range of Cr cell temperatures and V/III ratio. Magnetic measurements performed in a superconducting quantum interference device magnetometer showed evidence of ferromagnetism up to 350K in single phase material. Magnetization dependence on dopant cell temperature and V/III was used to optimize the growth conditions of the AlCrN layers. The single-phase material was highly insulating (∼1010Ωcm), while the material containing second phases (predominantly Cr2N and AlxCry) was conducting with resistivity of order 1000Ωcm. High resolution x-ray diffraction rocking curves indicated high crystalline quality in the single phase material.

The role of growth conditions on the p-doping of GaN by plasma-assisted molecular beam epitaxy

Mg-doped GaN layers were grown by plasma-assisted molecular beam epitaxy under a range of conditions. The growth temperatures and III/V ratio were altered and the resultant films were analyzed using atomic force microscopy, Hall effect measurements, and secondary ion mass spectroscopy (SIMS). The growth temperatures ranged from 600°C to 700°C. The III/V ratios were varied from N-rich (less than unity) to Ga-rich conditions (greater than unity). AFM showed that N-rich (III/V ratio<1) conditions yielded rough surface morphologies and room temperature Hall measurements show they were not measurably p-type. Ga-rich conditions (III/V ratio>1) yielded smoother morphologies and exhibited p-type conductivity. The trend in morphology with changing III/V ratio is consistent with previous studies of the MBE growth of unintentionally doped GaN. SIMS measurements show that Mg incorporation was negligibly affected by the III/V ratio but exponentially decreased with increasing growth temperature.

High Ge content photodetectors on thin SiGe buffers

PIN SiGe photodetectors (PD) are grown by MBE with Ge contents x=0, 0.10, 0.2, 0.27 and 0.5. For PDs with high Ge content, which are grown beyond the SiGe layer critical thickness, thin (sub 100 nm) strain relaxed, p +(B)-doped SiGe buffers are of special importance. The layer structure of the samples consists of a 5×10 18 cm −3 p +(B)-doped buffer layer as a bottom contact, followed by a 300 nm intrinsic active zone covered with a 3×10 20 cm −3 n ++(Sb)-doped top contact layer. Extremely low temperatures (LT) during the first growth stage of the SiGe buffers are implemented. Process windows for high strain relaxation on different substrates are determined. The role of growth conditions in crystal structure formation is in situ monitored by time resolved reflectivity (TRR) measurements. For comparison, pseudomorphic PDs and that on conventional graded buffers were also realised. Secondary ion mass spectrometry (SIMS), μ-Raman-spectroscopy and energy dispersive X-ray (EDX) analysis are performed to measure Ge content, composition profiles and degree of relaxation. The microstructure is characterised by cross-section transmission electron microscopy (XTEM). By optical microscopy with Nomarski differential interference contrast (NIC) combined with defect etching technique, typical defects in the layers were studied. Electrical measurements are performed to determine the different current components. The DC current–voltage characteristics show a distinct diode ‘s behaviour of the detectors, which are optically characterised in terms of reverse current for different incident wavelengths.

Impurity Effects in the Growth of 4H-SiC Crystals by Physical Vapor Transport

ABSTRACTSiC is an important wide bandgap semiconductor material for high temperature and high power electronic device applications. Purity improvements in the growth environment has resulted in a two-fold benefit during growth: (a) minimized inconsistencies in the background doping resulting in high resistivity (&gt;5000 ohm-cm) wafer yield increase from 10–15% to 70-85%, and (b) decrease in micropipe formation. Growth parameters play an important role in determining the perfection and properties of the SiC crystals, and are extremely critical in the growth of large diameter crystals. Several aspects of growth are vital in obtaining highly perfect, large diameter crystals, such as: (i) optimized furnace design, (ii) high purity growth environment, and (iii) carefully controlled growth conditions. Although significant reduction in micropipe density has been achieved by improvements in the growth process, more stringent device requirements mandate further reduction in the defect density. In-depth understanding of the mechanisms of micropipe formation is essential in order to devise approaches to eliminate them. Experiments have been performed to understand the role of growth conditions and ambient purity on crystal perfection by intentionally introducing arrays of impurity sites on one half of the growth surface. Results clearly suggest that presence of impurities or second phase inclusions during start or during growth can result in the nucleation of micropipes. Insights obtained from these studies were instrumental in the growth of ultra-low micropipe density (less than 2 micropipes cm−2 ) in 1.5 inch diameter boules.

Role of growth conditions and Bi-content on the properties of SrBi 2Ta 2O 9 thin films

Ex-situ and in-situ crystallised films of SrBi 2Ta 2O 9 (SBT) were grown using pulsed laser ablation. Different growth parameters were used for ablation. Both low temperature grown films, followed by annealing and high temperature grown ones were used for comparison. It was found that in-situ crystallised films showed better electrical properties over the annealed films, vis-à-vis the hysteresis loops and dielectric constants. It was also observed that the Bi concentration (which was estimated by EDS analysis) had a marked influence on the ferroelectric properties. With stoichiometric or excess Bi content, growth of in-situ crystallised films resulted in the observation of square hysteresis loops with a P r value of 10 μC/cm 2 and a coercive field of 24 kV/cm, which appears very attractive for NVRAM applications.

Formation of dimeric Fabs in Escherichia coli: effect of hinge size and isotype, presence of interchain disulphide bond, Fab′ expression levels, tail piece sequences and growth conditions

We have made hinge variants of two human Fab′s in order to investigate the factors involved in the formation of dimeric Fab′s in the periplasm of E. coli. Hinges containing one or more copies of the IgG1 hinge with various numbers of spacing residues were tested. Fab′s with hinges based on the γ2, γ3 and γ4 isotypes were also tested. We find that the IgG1 hinge sequence can form approximately 35% F(ab′) 2 in vivo in shake flask experiments, but that only (approximately) 5% F(ab′) 2 can be produced during fermentation. IgM and IgA tail-pieces added to Fab′s did not effect their multimerisation. The possible role of growth conditions upon F(ab′) 2 formation in vivo is discussed.

Role of bacterial growth conditions and adhesion in the bioleaching of chalcopyrite by Thiobacillus ferrooxidans

The role of growth conditions and adhesion of Thiobacillus ferrooxidans on the leaching of chalcopyrite was investigated. Thiobacillus ferrooxidans grown on sulfur, thiosulfate and ferrous ion substrates was used in this comparative study. Growth on sulfur, a solid substrate, requires bacterial adhesion unlike that required in the presence of soluble thiosulfate and ferrous ion in a mineral-salts medium. Solid substrate-grown cells showed higher rates of leaching than those grown in liquid media. An initial lag period noticed during leaching by solution-grown cells was absent when solid substrate-grown cells were used. Such a behavior is attributed to the presence of an inducible proteinaceous cell-surface appendage on the sulfur-grown cells. This appendage aids in bacterial adhesion onto the mineral surfaces. Such an appendage is absent in solution-grown cells, as substantiated by electrophoretic measurements. The importance of bacterial adhesion and the direct mechanism in leaching by Thiobacillus ferrooxidans are demonstrated.

Rough versus dilute interfaces in semiconductor heterostructures: The role of growth conditions

CdTe-CdMnTe interfaces grown by molecular beam epitaxy are studied using excitons confined in quantum wells. For increasing growth temperatures Zeeman splittings indicate an enhanced dilution of Mn ions at the interface while the optical linewidths evidence a decreasing roughness. These results directly illustrate the fact that the two methods are sensitive to different scales of interface broadening.

Towards minimal assumptions for the infimal convolution regularization

We encompass the Moreau-Yosida regularization process by infimal convolution into a general framework. This sheds light on the assumptions required for obtaining the usual properties. In particular the class of lower- T 2 mappings is shown to be a suitable class for performing the usual proximal regularization in open subsets of Hilbert spaces. The role of growth conditions is pointed out.

Aldosterone regulation of Na+ transport and Na+-K+-ATPase in A6 cells: role of growth conditions.

The effects of aldosterone on transepithelial sodium transport (measured by the short-circuit current (SCC) and on Na+-K+-adenosine triphosphatase (ATPase) biogenesis have been studied in A6 kidney cells grown on collagen-coated filters in two different media. In medium A, base-line SCCA was close to zero but transmural electrical resistance (RA) was high. Aldosterone (100 nM, t24h) drastically increased SCCA and RA, but only after a 4-h latent period. In medium B, base-line SCCB and RB were significantly higher than in medium A. Aldosterone significantly enhanced SCCB and to a lesser extent RB after a much shorter latent period (approximately 45 min) than in medium A. In medium A, aldosterone elicited a fourfold increase in the relative rate of synthesis of alpha- and beta-subunits of Na+-K+-ATPase. A twofold increase was already observed within the observed latent period. This time course suggests that de novo synthesis of sodium pumps might be one of the critical factors underlying the increase in sodium transport in this growth medium. In medium B, aldosterone elicited a two- to fourfold increase in the relative rate of synthesis of the alpha- and beta-subunits of Na+-K+-ATPase that paralleled SCCB. Thus de novo synthesis of Na+-K+-ATPase is clearly not a prerequisite for the early mineralocorticoid response (t90 min - t180 min), but still could be part of the late mineralocorticoid response (t3 h - t24 h). In both media, the immunochemical cellular pool of Na+-K+-ATPase was apparently not modulated by aldosterone for up to 48 h of incubation.(ABSTRACT TRUNCATED AT 250 WORDS)