Showing papers by "Mahesh Kumar published in 2015"

Binary group III-nitride based heterostructures: band offsets and transport properties

Abstract: In the last few years, there has been remarkable progress in the development of group III-nitride based materials because of their potential application in fabricating various optoelectronic devices such as light emitting diodes, laser diodes, tandem solar cells and field effect transistors. In order to realize these devices, growth of device quality heterostructures are required. One of the most interesting properties of a semiconductor heterostructure interface is its Schottky barrier height, which is a measure of the mismatch of the energy levels for the majority carriers across the heterojunction interface. Recently, the growth of non-polar III-nitrides has been an important subject due to its potential improvement on the efficiency of III-nitride-based opto-electronic devices. It is well known that the c-axis oriented optoelectronic devices are strongly affected by the intrinsic spontaneous and piezoelectric polarization fields, which results in the low electron-hole recombination efficiency. One of the useful approaches for eliminating the piezoelectric polarization effects is to fabricate nitride-based devices along non-polar and semi-polar directions. Heterostructures grown on these orientations are receiving a lot of focus due to enhanced behaviour. In the present review article discussion has been carried out on the growth of III-nitride binary alloys and properties of GaN/Si, InN/Si, polar InN/GaN, and nonpolar InN/GaN heterostructures followed by studies on band offsets of III-nitride semiconductor heterostructures using the x-ray photoelectron spectroscopy technique. Current transport mechanisms of these heterostructures are also discussed.

Growth of residual stress-free ZnO films on SiO2/Si substrate at room temperature for MEMS devices

Abstract: ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2”-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 to 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ∼3.275 eV to ∼3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications.

Schottky-contacted vertically self-aligned ZnO nanorods for hydrogen gas nanosensor applications

Abstract: Vertically well aligned ZnO nanorods (NRs) were grown on Si(100) substrate using RF magnetron sputtering technique. Scanning electron microscopy images confirms uniform distribution of NRs on 2 in. wafer with average diameter, height and density being ∼75 nm, ∼850 nm, and ∼1.5 × 1010 cm−2, respectively. X-ray diffraction reveals that the ZnO NRs are grown along c-axis direction with wurtzite crystal structure. Cathodoluminescence spectroscopy, which shows a single strong peak around 3.24 eV with full width half maxima 130 meV, indicates the high crystalline and optical quality of ZnO and very low defect density. Vertically aligned nanosensors were fabricated by depositing gold circular Schottky contacts on ZnO NRs. Resistance responses of nanosensors were observed in the range from 50 to 150 °C in 1% and 5% hydrogen in argon environment, which is below and above the explosive limit (4%) of hydrogen in air. The nanosensor's sensitivity increases from 11% to 67% with temperature from 50 to 150 °C and also s...

Observation of Room Temperature Ferromagnetism in InN Nanostructures.

Abstract: The room temperature ferromagnetic behavior of InN nanostructures grown by molecular beam epitaxy (MBE) is explored by means of magnetization measurements. The saturation magnetization and remanent magnetization are found to be strongly dependent on the size of the nanostructures. This suggests that the ferromagnetism is essentially confined to the surface of the nanostructures due to the possible defects. Raman spectroscopy shows the existence of indium vacancies which could be the source of ferromagnetic ordering in InN nanostructures.

Radiation Induced Response of ${\rm Ba}_{0.5}{\rm Sr}_{0.5}{\rm TiO}_3$ Based Tunable Capacitors Under Gamma Irradiation

Abstract: ${\rm Ba}_{0.5}{\rm Sr}_{0.5}{\rm TiO}_3$ (BST) thin films were deposited on sapphire substrate by RF magnetron sputtering techniques and interdigital capacitor (IDC) structures were fabricated using photolithography. Gamma irradiation induced changes of the BST based tunable capacitor have been investigated under various doses from 0 kGy to 600 kGy. Structural and surface morphological studies have been carried out for un-irradiated and irradiated film and revealed that the grain sizes and crystallinity are strongly depended on gamma irradiation doses. The leakage current is increased with increasing gamma irradiation doses due to creation of charge carriers and large numbers of defect in close proximity, provided path for charge carriers. The capacitance of the IDC devices decreased with increasing gamma dose up to 50 kGy and thereafter capacitance gradually increased with radiation doses and reached higher than the un-irradiated device at 600 kGy for 1 MHz frequency. The observed tunability ( $\sim 25\% $ ) of the un-irradiated device was found nearly constant with gamma irradiation doses. This study shows that gamma ray induced defects play important role to the electrical properties of the devices and the BST based devices are highly resistant to gamma radiation, which reflects possible use in space and nuclear applications.

Production of powder from kinnow juice using spray drying technology

Abstract: Experiments to produce powder from kinnow juice were carried out at three blends of maltodextrin with kinnow juice (35:65, 37.5:62.5, 40:60) and another blend of maltodextrin, sucrose and kinnow juice (40:10:50) using spray drying technique. These studies were conducted at three feed temperatures viz. 23°C, 26°C and 29°C to minimize heat loss in the blend and at three inlet temperatures i.e. 143°C, 146.5°C and 150°C which were near to glass transition temperature of maltodextrin (DE-20). The powder responses analysed were powder recovery, moisture content, dispersibility and colour. The powder recoveries were best at 40:60 blend (36.45%), inlet temperature of 146.5°C (36.34%) and feed temperature of 26°C (36.69%). For the blend of maltodextrin and sucrose with juice (40:10:50), powder recovery was 37.66%. The moisture content and dispersibility were found best at 40:60 blend as 5.55% and 87.13%, respectively. For the blend of maltodextrin and sucrose with juice, the moisture content was 4.60% while dispersibiity was 86.07%. The inlet temperature had significant effect on measure of psychometric lightness or darkness, psychrometric yellowness or blueness, colour change and chroma. Feed temperature had non-significant effect on colour parameters while blend proportions had significant effect on psychrometric redness or greenness and hue angle.

CLONING OF HUMAN ERYTHROPOIETIN GENE IN pVAX1 VECTOR FOR PRODUCTIONOF r-DNA epo

Abstract: The epo.hu gene is already cloned in pTarget vector. In the present study we have released the epo.hu gene insert from the pTarget.epo.hu using plasmid isolation, RE digestion and ligated with pVAX1 vector. Prepared the competent cell to transformation of ligated product in E.coli DH5α. Make the L.B Agar plate and the large number of colonies (approximately 25) were picked from the overnight grown transformants. The individual colonies were inoculated in fresh ampicillin (50 μg/ml) containing LB broth and allowed to grow for large scale production for further experiments. This can be used for expression and immunological studies.

Screening of phytochemical and antimicrobial activity of leaves extract of euphorbia milli

Abstract: Plants contain many bioactive compounds, which are primary or secondary metabolites and have ability to cure diseases with no side effects. Present study explores the phytochemical properties of Euphorbia milli plant leaves extracted in petroleum ether, ethyl ether, chloroform, ethyl alcohol, and aqueous. Antimicrobial activities against Staphylococcus aureus, Klebsilla pneumonia, Escherichia coli, and Pseudomonas aeruginosa in the extracts were evaluated by well diffusion method. The Minimum inhibitory concentration (MIC) of different extracts ranged between 50 to 250 µl. Qualitative phytochemical analysis revealed presence of alkaloids, flavonoids, glycosides, reducing sugars, saponins, and terpenoids. Ethanol extract showed highest activity against all the pathogens, with the maximum zone of inhibition (25.5±0.35 mm) demonstrated against Staph. aureus. The results indicated that Euphorbia milli may be used for the treatment of various ailments of skin diseases, the treatment of warts, cancer and hepatitis.

Identification of novel starch synthase genes using de novo assembly and heat-induced expression and activity in developing wheat ( Triticum aestivum L.)

Abstract: Terminal heat stress (HS) reduces quantity and quality of grains. Wheat is highly sensitive to HS and there is a wide diversity among different genotypes for HS-tolerance. The enzymes associated with starch biosynthesis are severely affected by HS, especially starch synthases (SS). Different isoforms of SS have been reported from cereals viz. rice, maize, etc.; however, limited information is available in the wheat. In this study, we investigated the effect of HS on contrasting wheat (Triticum aestivum L.) cultivars — HD2985 (thermotolerant) and HD2329 (thermosusceptible) at grain-filling stage. Here we report the identification and cloning of three putative SS genes from wheat. The putative SS has been characterized in silico with other SS reported from different plant and non-plant sources in order to investigate potential functional and evolutionary relationships between SSs. The correlation between HS and SS activity and other biochemical parameters associated with thermotolerance in two cultivars was also studied. Three putative SS genes (transcript_7326, transcript_24546 and transcript_38472) were cloned from HD2985 cultivar under HS by data mining generated from whole transcriptome analysis. The sequences were in silico characterized and submitted in NCBI GenBank (accession nos. KM206143, KM206144 and KJ854903). Glucosyltransferase domain was observed in all the three sequences. Based on ClustalW alignment, SSs were classified into four distinct families. Expression analysis and SS activity assay showed significantly higher transcript level and SS activity during mealy-ripe stage than at milky-ripe stage in HS-treated HD2985, compared to HD2329 cultivar. Both the cultivars showed decrease in starch content under HS and the overall content was higher in HD2985, compared to HD2329. Similarly, guaiacol peroxidase, catalase, free amino acid and total antioxidant capacity were higher during mealy-ripe stage in HD2985. HS during milky-ripe had more severe impact on the overall physiochemical properties of wheat grain and thus needed to be targeted using different approaches in order to enhance the quality and yield of wheat under HS.