K.G.M. Nair

Effect of irradiation-induced disorder on the optical absorption spectra of CdS thin films

Abstract Optical absorption studies have been carried out on CdS thin-films irradiated with low energy Ar+ ions. The optical band gap was found to reduce with the increase in the irradiation dose. This was accompanied by a progressive reduction in the sharpness of the absorption band edge. These effects have been attributed to the irradiation-induced lattice disorder. Post-irradiation annealing at 773 K resulted in the recovery of the optical band gap and absorption edge sharpness to unirradiated values.

Raman scattering and optical absorption studies of Ar+ implanted CdS thin films

Abstract The effect of argon ion implantation on chemical bath deposited Cadmium sulphide (CdS) thin films is investigated by X-ray diffraction, Raman scattering and optical absorption techniques. The X-ray diffraction pattern of the As-deposited CdS thin films shows the presence of both sphalerite (cubic) and wurtzite (hexagonal) phases. Phase transition from the As-deposited mixed phase to the more stable hexagonal phase along with grain growth is observed on post implantation annealing. Optical absorption studies of the implanted films reveal a reduction in the band gap on implantation and its recovery to As-deposited values on post implantation annealing. A decrease in the intensity of the Raman peak of CdS A 1 (LO) mode is seen on implantation and on post implantation annealing, the intensity is found to increase. A drastic reduction in the full width at half maximum (FWHM) value of the films subjected to post implantation annealing compared to that of As-deposited or implanted films suggests the removal of defects and strain during annealing. The peak position of the Raman mode of CdS remains more or less the same.

Mechanism of bright red emission in Si nanoclusters

A bright photoluminescence around 1.7xa0eV is observed for post-annealed samples of 1xa0MeV Si(2+) implanted in an SiO(2) matrix. A super-linear power dependence of photoluminescence intensity accompanied by pulse shortening under continuous wave laser excitation is recorded without any spectral narrowing. An emission process comprised of an initial non-radiative recombination (time constant ∼280-315xa0ps) of excited carriers in the defect states in SiO(2) matrices to the conduction band minima of nc-Si, followed by a slower process of radiative recombination in the direct band transition for nc-Si along with a non-radiative Auger recombination (time constant ∼2.67xa0ns) is proposed.

Trace metal distribution studies in river water by PIXE

Abstract Proton induced X-ray Emission (PIXE) has been used to measure the trace metals especially heavy metals in Chaliyar river water samples to assess the impact of pollutants from the industrial wastes. Water samples were collected in summer and rainy seasons from three different depths along the course of the river. Measurements were carried out with 2 MeV proton beam using a 3 MV tandem pelletron accelerator at Institute of Physics, Bhubaneswar. Results from the water Samples collected in both the seasons show that the concentrations of certain heavy metals like Hg, Zn and Pb are more than the prescribed limits. This is because of pollution due to industrial wastes, indicating a need for improvement in the industrial waste treatment.

Long-range ferromagnetic ordering at room temperature in Co+ implanted TiO2 nanorods

Long-range ferromagnetic ordering at room temperature is reported for post-annealed TiO2 nanorods doped with Co2+ by an ion implantation technique. The catalyst free anatase TiO2 nanorods are grown normal to the substrate plane. A Curie temperature of ~320?K was recorded for a ~9?at.% Co doped sample. Electronic structural studies confirm the substitutional Co in the Ti lattice site. Microstructural studies show the presence of extended defects, where a minor nonuniformity in doping concentration helps to sustain the intrinsic ferromagnetic ordering in Co doped TiO2 at room temperature. The projected nanorod tip size is found to be smaller than a single magnetic domain, which may lead to an increased signal-to-noise ratio for magnetic recording.

Effect of proton irradiation on the characteristics of GaAs Schottky barrier diodes

Abstract Proton irradiation (80xa0keV) effect on the electrical properties of Au/n-GaAs Schottky barrier diodes (SBDs), fabricated on an epitaxially grown undoped n-GaAs has been studied for a range of particle fluences from 1×10 13 to 1×10 15 particles/cm 2 . Current–voltage ( I–V ), capacitance–voltage ( C–V ) and deep level transient spectroscopy (DLTS) measurements have been carried out to study the change in characteristics of the devices and the defects introduction due to implantations, respectively. Reverse leakage current ( I R ) of the device is the most sensitive parameter to the incident proton irradiation. The I R was increased (1.0×10 −9 to 7.95×10 −5 xa0A) upon irradiation and it strongly depends on the particle fluence. Annealing of irradiated diodes shows reduction in the I R and particularly, enhancement in barrier heights of the diodes. A change of effective free carrier concentration in the material has been observed from the C–V measurements for the irradiated diodes when compared to the unirradiated diode. From DLTS measurements, it was found that the low energy proton irradiation of the SBDs increases the concentration of EL2 defects and the concentration was estimated to be 6.42×10 14 xa0cm −3 .

Raman scattering studies in H+ and He+ implanted n-GaAs

Abstract The liquid encapsulated czochralski (LEC) grown (1xa00xa00) oriented n -GaAs have been implanted with low energy H + and He + for various doses ranging from 10 13 –10 17 cm −2 . Raman spectra of as-grown, H + and He + implanted n-GaAs are recorded and analysed. Full width at half maximum (FWHM) of the LO mode decreases up to a dose of 10 15 cm −2 for H + and 10 13 cm −2 for He + and increases at higher doses. Mode narrowing is accompanied by an increase of the area under the peak, while the area under the peak decreases when the mode broadens. The peak position remains almost the same at low doses but decreases at high doses. These results are explained with carrier concentration reduction at low doses and lattice damage at high doses. Annealing of the high dose implanted n-GaAs reduces the FWHM of the LO mode and increases the area under the peak and the peak frequency, due to the annealing of the implantation induced lattice damage.

Investigations on H+ and He+ implantation effects in n-InP using Raman scattering

Abstract The LEC grown (1xa01xa01) n-InP have been implanted with H + and He + for various doses ranging from 10 12 to 10 16 xa0cm −2 . The Raman spectra of TO and LO modes in as-grown, H + and He + implanted n-InP are recorded and analyzed. FWHM of the LO Raman mode decreases while that of the TO mode remains the same for low doses up to 10 15 xa0cm −2 for H + and 10 14 cm -2 for He + . For higher doses the FWHM of both the modes increase, the increase being larger for TO mode. LO–TO splitting decreases with the increase of dose, for all doses. The ratio between the area under TO and LO modes decrease at low doses but increase for higher doses. These results have been explained with carrier concentration reduction at low doses and lattice damage at high doses. Annealing effects on these Raman mode parameters have also been studied on the as-grown and implanted n-InP, where the thermal annealing anneals partially the implantation induced lattice defects.

PIXE analysis of trace pollutants in Chaliyar river water in Malabar, India

Abstract Analysis of trace elemental concentration in the Chaliyar river water has been carried out using the Proton Induced X-ray Emission (PIXE) spectroscopic technique. Water samples were collected from different locations along the course of the river during summer and rainy seasons. Samples were prepared by a preconcentration method. The PIXE analysis was carried out using 2 MeV protons. The details of the measurements and the results are presented in this paper.

Nitrogen ion beam synthesis of InN in InP(100) at elevated temperature

The InN phase is grown in crystalline InP(100) substrates by 50keV N+ implantation at an elevated temperature of 400°C followed by annealing at 525°C in N2 ambient. Crystallographic structural and Raman scattering studies are performed for the characterization of grown phases. Temperature- and power-dependent photoluminescence studies show direct band-to-band transition peak ∼1.06eV at temperatures ⩽150K. Implantations at an elevated temperature with a low ion beam current and subsequent low temperature annealing step are found responsible for the growth of high-quality InN phase.