The low frequency behaviour in high frequency capacitance–voltage characteristics due to contribution of band-to-band tunnelling and generation–recombination in Hg0.75Cd0.25Te MIS capacitors

Hg_1−xCd_xTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions.     

Controlled growth of flower-like,rod-like,and snowflake-like ZnO nanostructures using agarose as biotemplate and its photoluminescence property

Different nanostructures such as flower-like, rod-like, and snowflake-like of ZnO have been synthesized by varying the amount of agarose using sonochemical method. It is found that morphology is governed by amount of agarose as well as ultrasonic treatment. Three amounts of agarose 0.01, 0.1, and 1.00 g are used to investigate its effect on ZnO. X-ray diffraction (XRD) confirmed the formation of single phase with hexagonal structure. Scanning electron microscopy (SEM) showed flower-like, rod-like, and snowflake-like morphology for 1.00, 0.1, and 0.01 g agarose, respectively. UV/Visible absorption study showed blue shift at band-edge absorption in comparison to bulk ZnO. Photoluminescence spectra showed band-edge emission at 399 nm for lowest amount of agarose which quenched on increasing the agarose amount. These findings show a better and more environment friendly procedure for production of ZnO of readily adjustable morphology.     

Growth mechanism and optical property of CdS nanoparticles synthesized using amino-acid histidine as chelating agent under sonochemical process

Using amino-acid histidine as chelating agent, CdS nanoparticles have been synthesized by sonochemical method. It is found that by varying the ultrasonic irradiation time, we can tune the band gap and particle size of CdS nanoparticles. The imidazole ring of histidine captures the Cd ions from the solution, and prevents the growth of the CdS nanoparticles. The deviation in the linear relation in between cube of radius of nanoparticles and ultrasonic irradiation time confirms the growth of CdS nanoparticles occur via two process; one is the diffusion process of the reactants as well as reaction at the surface of the crystallite. CdS nanoparticles synthesized using histidine as organic chelating agent have band edge emission at 481 nm and have greater photoluminescence intensity with blue-shift to higher energy due to typical quantum confinement effect.     

Growth mechanism and optical property of ZnO nanoparticles synthesized by sonochemical method

ZnO nanoparticles have been synthesized by ultrasonic irradiation of an aqueous-alcoholic/aqueous-alcoholic-ethylenediamine (EDA) solutions of zinc nitrate and sodium hydroxide. ZnO nanoparticles possess hexagonal wurtzite structures and they exhibit special photoluminescence properties with a red-shift of 22 nm in UV emission band. It is found that the ultrasonic irradiation time and the solvents both influence the growth mechanism and optical properties of ZnO nanoparticles. The possible growth mechanism of ZnO nanoparticles formation by sonochemical method has been tried to discuss.     

Influence of small DC bias field on the electrical behaviour of Sr- and Mg-doped lanthanum gallate

One of the promising electrolyte materials for solid oxide fuel cells application, Sr- and Mg-doped lanthanum gallate La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM), is synthesized by conventional solid state ceramic route. X-ray Rietveld analysis confirms the formation of main orthorhombic phase at room temperature along with a few minor secondary phases. SEM micrograph reveals the grain and grainboundary morphology of the system. Electrical conductivity of the LSGM sample is measured in the temperature range 573–873 K and in the frequency range 20 Hz–1 MHz at a few small DC bias fields (at 0.0, 0.5, 1.0, 1.5 and 2.0 V). The conductivity spectra show power-law behaviour. Electrical conductivity of the sample is found to be weakly dependent on DC bias field. This is attributed to field-dependent bulk and grainboundary conduction processes. In the present system, under investigated bias field range, the possibility of formation of Schottky barrier is ruled out. The concept of grainboundary channel (pathway) modulation on the application of bias field is proposed.     

Analysis of 99Tc in the radioactive liquid waste after extraction into suitable solvent

⁹⁹Tc is one of the long lived fission product with high fission yield. From radioactive waste management point of view it is very much essential to evaluate the concentration of technetium in the radioactive liquid waste in order to finalise the treatment process to extract/isolate it from the stream which is discharged to the environment. For the estimation of ⁹⁹Tc in the radioactive liquid waste stream, extraction of the stable complex of technetium-tetraphenyl arsonium chloride (TPAC) into chloroform followed by beta counting was studied. Various parameters like pH, time of equilibration, concentration of TPAC in chloroform, use of other solvent for extraction as well as interference of various other radionuclides present in the waste were also studied. The radioactive liquid waste being handled in plant contains high concentrations of salts in the form of sodium nitrate. Hence effect of salt concentration on the percentage extraction was also evaluated. The extraction behavior does not dependent on change in the pH of the solution. Almost 99.5% extraction was observed in the pH range of 1?C13.0. High concentration of salt is affecting the extraction. However, this can be taken care by diluting the radioactive waste. It takes almost 90?min time for maximum extraction. Presence of radionuclides like ¹³⁷Cs, ⁹⁰Sr are not interfering the extraction of ⁹⁹Tc. However, ¹⁰⁶Ru is getting slightly extracted along with ⁹⁹Tc. The error due to ¹⁰⁶Ru can be eliminated by taking gamma spectrum and deducting the activity from the total beta activity to get ⁹⁹Tc activity. Nitrobenzene can be used for extraction of Tc?CTPAC complex in place of chloroform.     

Micro-Raman and photoluminescence study of urchin-like ZnO structure assembled with nanorods synthesized by hydrothermal method

Urchin-like ZnO structures assembled with nanorods have been synthesized by cetyltrimethylammonium bromide-assisted hydrothermal method. The as-obtained products were characterized by powder X-ray diffraction, field-emission scanning electron microscopy for the study of crystal structure and morphology. The ZnO urchin is constructed of well-assembled nanorods of length ~3 μm range and diameter ~20 nm. Micro-Raman study shows characteristic Raman-active mode of hexagonal ZnO at 439 cm⁻¹ and also mode related to defects at ~581 cm⁻¹. The ZnO urchin assembled with nanorods possessed band edge emission at 3.085 eV and defect related visible emission at 2.97, 2.57, and 2.36 eV.     

Comparative studies on conventional and microwave assisted synthesis of benzimidazole and their 2-substituted derivative with the effect of salt form of reactant

Benzimidazole and their derivative were reported to have wide biological activities and were synthesized by using different solvents and ring closing agents. The present work deals with the comparative synthesis of 2-alkyl and aryl substituted benzimidazole derivative in the presence of polyphosphoric acid through microwave and conventional methods and also studied the effect of salt form of reactant for completion of the reaction. The 2-substituted aryl and alkyl benzimidazole derivative were synthesized via microwave and was observed to be more beneficial, in respect of yield (increases up to 10 to 50%) and time (96 to 98% was reduced) than conventional method of synthesis. This study was concluded that the salt form of reactant (o-phenylenediamine dihydrochloride) gave reduced colour impurities, homogenous mixing and reduced time for completion of reaction.     

Luminescence properties of Eu3+ doped CaMoO4 nanoparticles

When Eu(3+) ions occupy Ca(2+) sites of CaMoO(4), which has a body centered tetragonal structure with inversion symmetry, only the magnetic dipole transition ((5)D(0)→(7)F(1)) should be allowed according to Judd-Ofelt theory. Even if there are a few distortions in the Eu(3+) environment, its intensity should be more than that of the electric dipole transition ((5)D(0)→(7)F(2)). We report here the opposite effect experimentally and ascribe this to the polarizability effect of the MoO(4) tetrahedron, which is neighboring to EuO(8) (symmetric environment). The contribution of the energy transfer process from the Mo-O charge transfer band to Eu(3+) and the role of Eu(3+) over the surface of the particle could be distinguished when luminescence decay processes were measured at two different excitations (250 and 398 nm). Further, the luminescence intensities and lifetimes increase significantly with increasing heat-treatment temperature of the doped samples. This is attributed to the reduction of H(2)O from the surface of the particles and a non-radiative process after heat treatment.     

PSPICE circuit simulation of microbolometer infrared detectors with noise sources

In this paper, we present a method of incorporating various types of noise in circuit simulation of a microbolometer infrared detector to analyze the effect of noise on its performance. This ability of simulating electro-thermal performance of microbolometers in circuit simulation platform along with their noise performance allows designing of its suitable readout integrated circuit (ROIC). Being an electro-thermal device, a microbolometer has both the electrical and thermal components interacting with each other. Therefore, the noise sources existing in standard circuit simulators cannot predict the noise of a microbolometer correctly. Disturbances coming from the background radiation, device temperature fluctuations, flicker noise and the Johnson noise etc. contribute in the total noise of a microbolometer element. All these components of noise can be incorporated using the proposed simulation technique. The technique also allows modifying the frequency response of the noise in simulations as per the user defined noise spectrum, making it suitable for any type of microbolometer.