Optimum Substrate Temperature Research Articles

Deposition and characterization of AZO thin films on flexible glass substrates using DC magnetron sputtering technique

Al-doped zinc oxide (AZO) thin films were deposited onto flexible ultra-thin glass substrates by using a direct current (DC) magnetron sputtering process. The effects of sputtering power, working pressure and substrate temperature on the morphology and optoelectronic performances of AZO films were investigated. The optimal sputtering power, working pressure and substrate temperature for AZO film were determined to be 100W, 0.9Pa and 150℃, respectively. Further increasing or decreasing the sputtering power, working pressure and substrate temperature degrades the quality of AZO films. XRD patterns show all as-sputtered AZO thin films are preferred to grow along <0002> direction. Moreover, the largest grain size, which depicts the best microstructure of AZO films, matches with the smallest stress value. It can be seen from SEM images that the surface is smooth and dense. The smallest value of the resistivity is 1.784×10−3Ωcm and the average transmittance of all AZO films in the visible range is about 80%. The X-ray photoelectron spectroscopy spectra show that the amount of Al element in the AZO film is very small.

Biaxial stress and optoelectronic properties of Al-doped ZnO thin films deposited on flexible substrates by radio frequency magnetron sputtering.

Transparent conductive Al-doped ZnO (AZO) thin films were deposited on polyethylene terephthalate (PET) and polycarbonate (PC) substrates using radio frequency (RF) magnetron sputtering. The biaxial stress was measured with a double beam shadow moiré interferometer, and x-ray diffraction (XRD) was used to investigate the crystal orientation of ZnO. The substrate temperature was varied from room temperature to 150°C in steps of 25°C. The experimental results showed that the residual and shearing stresses increased with the increase in substrate temperature. The residual stress can be separated into principle and shearing stresses by Mohr's circle rule, and the shearing stress (tensile stress) was different from the compressive stress of the residual stress. However, the optimal substrate temperatures for PET and PC were 75°C and 100°C, and the shearing stresses were 424.82 and 543.68 MPa, respectively. AZO/PET and AZO/PC thin films cracked at substrate temperatures of 75°C and 100°C, respectively. AZO/PET thin film at a substrate temperature of 100°C had a resistivity low to the order of 10-3 Ω-cm.

Effects of annealing on elemental composition and quality of CZTSSe thin films obtained by spray pyrolysis

The spray pyrolysis was used for the deposition of Cu2ZnSn(S, Se)4 (CZTSSe) kesterite thin films. The basic spray pyrolysis solution was prepared from two precursor solutions containing thiourea and cooled to a temperature near 1°C, which leads to minimizing the number of insoluble hydrates of copper chloride. The optimal substrate temperature was 350°C and the distance from the sprayer nozzle 30 cm. The as-deposited Cu2ZnSnS4 layers were annealed in S2 atmosphere for the compensation of the sulfur deficiency and with the addition of Sn in order to avoid tin loss. Cu2ZnSn(S, Se)4 thin films were obtained after the annealing of as-deposited films in the (S2 + Se2) atmosphere. The surface morphology and composition of obtained thin films were investigated using the energy dispersive X-ray (EDX) microanalysis and Raman spectroscopy measurements. The structural characterization by the grazing incidence X-ray diffraction (GIXRD) showed the presence of Cu2–xS phases in all of the annealed thin films. For the Se/(S + Se) ratio of the thin films annealed in the (S + Se) atmosphere was established from EDX measurements and analysis of GIXRD data, the results are in satisfactory agreement.

Purification and characterization of alginate lyase from locally isolated marinePseudomonas stutzeriMSEA04

An alginate lyase with high specific enzyme activity was purified from Pseudomonas stutzeri MSEA04, isolated from marine brown algae. The alginate lyase was purified by precipitation with ammonium sulphate, acetone and ethanol individually. 70% ethanol fraction showed maximum specific activity (133.3 U/mg). This fraction was re-purified by anion exchange chromatography DEAE- Cellulose A-52. The loaded protein was separated into 3 peaks. The second protein peak was the major one which contained 48.2% of the total protein recovered and 79.4% of the total recovered activity. The collected fractions of this peak were subjected to further purification by re-chromatography on Sephadex G-100. Alginate lyase activity was fractionated in the Sephadex column into one major peak, and the specific activity of this fraction reached 116 U/mg. The optimal substrate concentration, pH and temperature for alginate lyase activity were 8 mg/ml, pH 7.5 and 37 °C, respectively. While, Km and Vmax values were 1.07 mg alginate/ ml and 128.2 U/mg protein, respectively. The enzyme was partially stable below 50 °C, and the activity of the enzyme was strongly enhanced by K(+), and strongly inhibited by Ba(+2), Cd(+2), Fe(+2) and Zn(+2). The purified enzyme yielded a single band on SDS-PAGE with molecular weight (40.0 kDa).

Optoelectronic properties and Seebeck coefficient in SnSe thin films

SnSe thin films of thickness 180 nm have been deposited on glass substrates by reactive evaporation at an optimized substrate temperature of 523 ± 5 K and pressure of 10−5 mbar. The as-prepared SnSe thin films are characterized for their structural, optical and electrical properties by various experimental techniques. The p-type conductivity, near-optimum direct band gap, high absorption coefficient and good photosensitivity of the SnSe thin film indicate its suitability for photovoltaic applications. The optical constants, loss factor, quality factor and optical conductivity of the films are evaluated. The results of Hall and thermoelectric power measurements are correlated to determine the density of states, Fermi energy and effective mass of carriers and are obtained as 2.8 × 1017 cm−3, 0.03 eV and 0.05m0 respectively. The high Seebeck coefficient ≈ 7863 μV/K, reasonably good power factor ≈ 7.2 × 10−4 W/(m·K2) and thermoelectric figure of merit ≈ 1.2 observed at 42 K suggests that, on further work, the prepared SnSe thin films can also be considered as a possible candidate for cryogenic thermoelectric applications.

Improving the activity of heparinase I by the directed evolution, its enzymatic properties and optimal conditions for heparin degrading by recombinant cells

Heparinase I can degrade heparin and heparin sulfate to produce low molecular weight heparins (LMWHs) that are widely used as an anticoagulant and antithrombotic drug. In this study, directed evolution was used to improve the activity of heparinase I. The clone E. coli-heparinase-I133/P316 with two amino acid substitutions was screened and identified. This clone produced 366U/L of heparinase I, which was 57.8% higher than that from the control clone (232U/L). The optimal temperature of heparinase-I133/P316 was lower than that of the original heparinase I. The mutated enzyme and original one presented almost the same varying trend as an function of pH, and their optimal pH was near 7.5. Ca2+ at 1mM could significantly increase the activity of heparinase-I133/P316. Cu2+, Ni2+, Mg2+, Mn2+ and Zn2+ at 1mM were found to inhibit its activity, and Ba2+ and Fe2+ at 1mM almost had no obvious effect on its activity. The optimal substrate concentration, temperature, pH, shaker speed and cell concentration for heparin degradation by E. coli-heparinase-I133/P316 were 125μg/mL, 40°C, 7.5, 400rpm and 40mg/mL, respectively. After reaction for 6h, degradable products are basically concentrated in a small molecular weight region. This study provides a new insight into the high production of heparinase I and the preparation of LMWHs by E. coli-heparinase-I133/P316 cells.

Optimization of Growth Parameters for Diamond Films Grown by MPCVD Using Response Surface Methodology

Diamond films were synthesized by microwave plasma chemical vapor deposition under different deposition parameters. Response surface methodology was adopted to guide the optimization of synthesis parameters including the substrate temperature (716–884 \({^{\circ}{\rm C})}\), gas pressure (4.32–7.68 kPa), and volume concentration of methane to hydrogen (1.3–4.7 %) for deposition of the films. A 5-level-3-factor central composite design was employed to evaluate effects of the deposition parameters on the response (growth rate and pure index). The significant level of both the main effects and the interaction is investigated by analysis of variance. With its assistance, the growth quality of the obtained samples was improved dramatically. The structure, surface morphology and growth rate of films were characterized by X-ray diffractometer and scanning electron microscopy. The diamond phase content of films was investigated using Raman spectroscopy and X-ray photoelectron spectroscopy. The optimum substrate temperature, gas pressure, and volume concentration of methane to hydrogen were found to be 837 \({^{\circ}}\)C, 6.95 kPa and 2 %, respectively. Under this experimental condition, the growth rate and pure index of diamond films were 0.378 \({\mu}\)m/h and 4.092, which are quite good correlation with value (0.383 \({\mu}\)m/h and 4.182) predicted by the model. The diamond phase content of the films is 89.5 %.

Effect of substrate temperature on the plasma texturing process of c‐Si wafers for black silicon solar cells

We report on a study of the effect of the substrate temperature on the formation of black silicon on c‐Si wafers and consequently on the reduction of the wafer surface diffuse reflectance. We observed that lower substrate temperatures enhance the texturing processes producing completely black silicon surfaces. The optimized substrate temperature (2.5 °C) used during the plasma process has resulted in the formation of well‐defined pyramid‐like structures as is done by wet processes. Moreover, the textured c‐Si wafers have very low diffuse reflectance values, as low as 3%, which are much lower than those values obtained using wet texturing processes based on KOH and NaOH solutions (which are in the range of 12–14%).

Effect of Argon/Oxygen Flow Rate Ratios on DC Magnetron Sputtered Nano Crystalline Zirconium Titanate Thin Films

High transmitting, non absorbent, nano crystalline zirconium titanate (ZT) thin films suitable for anti reflection coatings (ARC) were deposited on to glass substrates by direct current (DC) magnetron reactive sputtering technique, under distinct Argon to Oxygen (Ar/O2) gas flow rate ratios of 31/1, 30/2, 29/3 and 28/4, with a net gas flow (Ar + O2) of 32sccm, at an optimum substrate temperature of 250°C. The influence of the gas mixture ratio on the film properties has been investigated by employing x-ray diffraction (XRD), ultra violet visible (UV–vis) spectroscopy, atomic force microscopy (AFM), energy dispersive x-ray analysis (EDX) and four point probe methods. The films showed a predominant peak at 30.85° with (111) orientation. The crystallite size reduced from 22.94 nm to 13.5 nm and the surface roughness increased from 11.53 nm to 50.58 nm with increase in oxygen content respectively. The films deposited at 31/1 and 30/2 showed almost similar chemical composition. Increased oxygen content results an increase in electrical resistivity from 3.59 × 103 to 2.1 × 106 Ωm. The film deposited at Ar/O2 of 28/4 exhibited higher average optical transmittance of 91%, but its refractive index is higher than that of what is required for ARC. The films deposited at 31/1 and 30/2 of Ar/O2 possess higher transmittance (low absorbance) apart from suitable refractive index. Thus, these films are preferable candidates for ARC.

Low-temperature preparation of ZnO thin film by atmospheric mist chemistry vapor deposition for flexible organic solar cells

A low-temperature method for the large-scale growth of ZnO thin films on flexible substrates was realized using a mist chemistry vapor deposition setup. We prepared and analyzed ZnO thin films grown on flexible PET/ITO in the temperatures range of 125–250 °C. The growth of ZnO crystallites was qualitatively investigated with respect to nucleation and substrate temperature. We observed a mixed phase in the ZnO thin films prepared at 125 and 150 °C. We conclude that the optimal substrate temperature for optimal ZnO thin films growth is between 150–200 °C. Our results show that the photovoltaic performance of an organic solar cell (OSC) is strongly dependent on both composition and morphology. To demonstrate its application on flexible organic optoelectronic devices, a large OSC with as-grown ZnO thin film as cathode buffer layer was successfully prepared.

Optimized substrate temperature range for improved physical properties in spray pyrolysis deposited Tin Selenide thin films

Tin diselenide (SnSe2) thin films have been deposited on glass substrate using the spray pyrolysis technique by varying substrate temperatures (Tsub) from 250 °C to 400 °C. These films were characterized for structural, morphological, electrical and thermoelectric properties by using X-ray Diffraction, Field Emission Scanning Electron Microscopy (FESEM), four probe resistivity/conductivity and thermoelectric measurement respectively. X-Ray Diffraction patterns revealed that substrate temperature plays a critical role in phase formation and a single phase SnSe2 film were formed at a critical temperature range 275–375 °C. FESEM study of single phase film at 300 °C shows uneven and irregular shape grains throughout the film and the EDX shows the stoichiometric ratio of deposit. The variations of the micro-structural parameters, such as crystallite size (D), dislocation density (δ), and micro-strain (ε), were investigated for all films. The results showed that the crystallite sizes increase with an increase in substrate temperature, whereas the dislocation density and micro-strain decreases with increasing substrate temperature. The resistivity (ρ) of SnSe2 film was found to be decreasing with increasing temperature and also with substrate temperature. The predefined substrate temperature range (275–375 °C) was further narrowed down using 4-probe resistivity measurement. It shows that, although 275–375 °C is enough formation of single phase SnSe2, but there is a small temperature range 325–375 °C where one will get low resistive sample, which influence the flow of charge carrier. Low electrical resistance or inversely high electrical conductivity is one of the prime requirements of thermoelectric samples. The 4-probe resistivity measurement of single phase thin films shows that the lowest electrical resistance obtained for substrate temperature of 350 °C. Thermoelectric measurement confirms that the coated films were n-type semiconductor materials and the thermo-emf increases with an increase in substrate temperature. Among all the films the film with substrate temperature of 350 °C shows enhanced behaviour to be used in industrial applications.

Low pressure MOVPE growth and characterization of ZnTe homoepitaxial layers

AbstractThe growth rate and photoluminescence (PL) spectrum of ZnTe homoepitaxial layer grown at a reactor pressure of 500 Torr by metalorganic vapor phase epitaxy have been clarified as a function of substrate temperature. An optimum substrate temperature for obtaining ZnTe layers with better PL property is determined by taking into account the growth rate behavior. Furthermore, the growth rate, PL spectrum, surface roughness and surface morphology of ZnTe layer have also been investigated by varying reactor pressure. With increasing reactor pressure, both the PL property and surface roughness of ZnTe layer are improved and subsequently become degraded, according as the growth rate increases monotonically and then shows saturated tendency. Change in the surface morphology of ZnTe layer with the increase of reactor pressure resembles that with the decrease of substrate temperature, probably due to the change from mass‐transport regime to surface kinetics one. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effect of substrate temperature on the structure and magnetic properties of CoPt/AlN multilayer films

The effect of substrate temperature on the structure and magnetic properties of CoPt/AlN multilayer films has been investigated. The crystallinity of CoPt has been improved with increasing substrate temperature from room temperature to 400 °C. After post-annealing process, L10 CoPt structure transformation has also been promoted. However, since the easy magnetic axis of L10 CoPt is in [001] orientation, the promotion of L10 CoPt transformation causes the change of easy magnetic axis in (111) textured CoPt layers, which impairs the perpendicular magnetic anisotropy. The optimum substrate temperature should be room temperature to obtain the strongest perpendicular magnetic anisotropy according to the results of the present work.

Spray pyrolytically grown NiAlOx cermets for solar thermal selective absorbers: spectral properties and thermal stability

After deposition of NiAlOx thin films on stainless-steel substrates by the spray pyrolysis technique, various properties of the films were investigated using Fourier transform infrared spectroscopy, UV–visible reflectance spectrophotometry, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical quantities were determined using reflectance spectra in the relevant spectrum region. At first the optimal substrate temperature was selected and then different nickel to aluminium ratios were examined to find the efficient solar absorber. The SEM revealed changes in morphology due to different molar ratios. The XRD of the selected sample showed a mixture of nickel and nickel oxide phases with the strong presence of substrate peaks and without the presence of alumina phase while in the EDX test the peaks corresponding to O, Al and Ni appeared. Long-term thermal stability study was performed by means of performance criterion concept.

Characterization of polyphenol oxidase in two cocoa (Theobroma cacao L.) cultivars produced in the south of Bahia, Brazil

The reactions leading to the formation of precursors of chocolate flavor are performed by endogenous enzymes present in the cocoa seed. Polyphenol oxidase (PPO) presence and activity during fermentation of cocoa beans is responsible for the development of flavor precursors and is also implicated in the reduction of bitterness and astringency. However, the reliability of cocoa enzyme activities is complicated due to variations in different genotypes, geographical origins and methods of fermentation. In addition, there is still a lack of systematic studies comparing different cocoa cultivars. So, the present study was designed to characterize the activity of PPO in the pulp and seeds of two cocoa cultivars, PH 16 and TSH 1188. The PPO activity was determined spectrophotometrically and characterized as the optimal substrate concentration, pH and temperature and the results were correlated with the conditions during the fermentation process. The results showed the specificity and differences between the two cocoa cultivars and between the pulp and seeds of each cultivar. It is suggested that specific criteria must be adopted for each cultivar, based on the optimal PPO parameters, to prolong the period of maximum PPO activity during fermentation, contributing to the improvement of the quality of cocoa beans.

Structural, morphological, optical and gas sensing properties of nanocrystalline ceria thin films

Ceria thin films are deposited with varying oxygen pressures (1- 225 m torr) and at an optimized substrate temperature of 1023K on quartz substrates by pulsed laser deposition technique. X-ray diffraction studies indicated that the prepared thin films are polycrystalline in nature. The prepared thin films contain nano crystals of size in the range of 20-31nm. Crystallite size, strain and dislocation densities of the ceria thin films have been calculated. To know the preferred orientation of the films texture coefficient has been calculated. The characteristic Raman peak appeared at 463 cm-1 is associated with F2g active mode confirm the cubic fluorite structure of ceria. Surface morphology of the thin films carried out by atomic force microscopy. The optical properties of the thin films are investigated by using UV-Vis spectroscopy technique in the wavelength range 200-800nm.The optical band gap, refractive index and absorption coefficient are calculated. Gas sensing characterization of ceria thin films have been carried out by chemiresistive method for various concentrations of acetone vapour and operating temperatures.

Perpendicularly magnetized (001)-textured D22 MnGa films grown on an (Mg0.2Ti0.8)O buffer with thermally oxidized Si substrates

We report the growth of (001)-textured polycrystalline D022 MnGa films with perpendicular magnetic anisotropy (PMA) on thermally oxidized Si substrates using an (Mg0.2Ti0.8)O (MTO) buffer layer. The ordered D022 MnGa film grown at the optimum substrate temperature of 530 °C on the MTO buffer layer shows PMA with magnetization of 80 kA/m, PMA energy density of 0.28 MJ/m3, and coercivity of 2.3 T. The scanning transmission electron microscope analysis confirms the formation of a highly (001)-textured structure and the elementally sharp interfaces between the MTO layer and the MnGa layer. The achieved D022 MnGa PMA films on an amorphous substrate will provide the possible pathway of integration of a Mn-based PMA film into Si-based substrates.

Selenium Flux Effect on Cu(In,Ga)Se2 Thin Films Grown by a 3‐stage Co‐evaporation Process

AbstractAn investigation into the effects of Se flux on absorber thin film growth at each step of a 3‐stage co‐evaporation process was conducted to further optimize the performance of CIGS solar cells. In ‘step I’ forming an In‐Ga‐Se precursor thin film during the 3‐stage process, Se flux affected the preferred orientation of the CIGS crystal structure, but not the film morphology. In ‘step II’, no correlation was found between Se flux and the crystal structure, although excessively high Se flux employed throughout the 3‐stage process degraded the solar cell performance. A CIGS thin film, with a (220/204) crystal orientation, minor physical surface defects and ∼20 nm thick MoSe2 at CIGS/Mo interface, was obtained by fine control of Se flux conditions (high Se flux at ‘step I’ and low Se flux at ‘step II’) at optimum substrate temperatures. The solar cell fabricated using the aforementioned CIGS thin film showed the highest conversion efficiency of 20.02 %.

Effects of substrate temperature on performance of calcium‐doped zinc oxide TFTs

In this reported work, high-performance fully transparent bottom-gate-type calcium-doped zinc oxide thin-film transistors (Ca–ZnO TFTs) have been successfully fabricated on glass substrate. The effects of substrate temperature during active layer deposition on the electrical properties of Ca–ZnO TFTs were investigated and an optimum condition (substrate temperature: 100°C) was achieved. The optimised thin-film transistors (TFTs) exhibit excellent electrical properties, with an off-state current (Ioff) of 1.31 × 10−12 A, an Ion/Ioff current ratio of 3.015 × 108, a saturation mobility (μsat) of 25 cm2/Vs and a threshold voltage (Vt) of 4.24 V. The variation trend of Vt, the Ion/Ioff current ratio and μsat against substrate temperatures is analysed in detail. The experimental results suggest that the performance of Ca–ZnO TFTs can be improved effectively by optimum substrate temperature.

Large-Scale Molecular Packing and Morphology-Dependent High Performance Organic Field-Effect Transistor by Symmetrical Naphthalene Diimide Appended with Methyl Cyclohexane

The influence of structural ordering of methyl cyclohexane appended naphthalene diimide (NMeCy2) thin films and their correlation with enhanced device performances are presented here. The vacuum-deposited thin-film microstructure and morphology of NMeCy2 have been investigated using thin-film X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM) and were comparable with the bulk-phase crystalline structure and packing of NMeCy2. The organic field-effect transistor (OFET) fabricated on a glass substrate consists of a bilayer polymer dielectric poly(methyl methacrylate) (PMMA) over poly(vinyl alcohol) (PVA) and an inorganic high-k dielectric Al2O3 as the third layer. NMeCy2 thermally deposited at an optimized substrate temperature (Tsub) of 60 °C displayed excellent molecular packing over a large area that resulted in the improved field-effect performance with electron mobility (μe) value of 0.6 cm2 V–1 s–1 and current on/off ratio (Ion/off) of 106 via modifications in dielectric configuration. Furthermore, the device afforded an unprecedented threshold voltage (VTh) of 5.23 V with this material. We have been successful in developing a facile, reliable, and cheap method to tune the dielectric features which can culminate in improved field-effect transport properties.