Shiv Poojan Patel

Ag doped CdZnS alloy nanostructures are synthesized by means of chemical methods. The stoichiometry and elemental analysis has been carried out with the energy dispersive X-ray (EDAX) and X-ray photoelec-tron spectroscopy (XPS) techniques. X-ray diffraction, transmission electron microscopy and scanning electron microscopy have been employed to determine the particle size, morphology and crystal structure of the alloy nanostructures. The incorporation of Ag ion at the lattice of Zn and Cd alloys shift their binding energy towards higher energy as evidenced from XPS. The XPS measurements have been performed before and after 4 keV Ar + ion sputtering of the samples that gives a new way to interpret the XPS spectra of Ag doped CdZnS nanostructures, which may allow one to further understand the properties of this important material in relation to their full exploitation in optoelectronic devices.

Abstract The effects of 100 MeV O8+ ion beam irradiation on the structural and dielectric behavior of Ba0.90Sr0.10TiO3 ceramics have been analyzed. Ion irradiation does not change the crystalline structure, however the tetragonal distortion increases. The low frequency dielectric dispersion especially at high temperatures increases significantly after ion irradiation. The dielectric relaxation phenomenon has been probed through complex impedance and electric modulus approaches. The observed dielectric relaxation has distributed relaxation times and is a thermally activated process. Ion irradiation enhances the cationic disordering. The contributions of grains and grains boundaries towards impedance have been separated. It is inferred that the grain boundaries become more resistive due to ion irradiation and is associated to oxygen vacancies annihilation. Ion irradiation also decreases the bulk ferroelectric polarization demonstrating that the surface or near surface modifications may tune the bulk properties in polar dielectrics.

Formation of nanorings of ZnS co-sputtered with SiO2 on n-type Si (100) substrates is reported. A subsequent annealing in inert atmosphere at temperature 800° C for 2 hrs was required for development of the crystallinity and the formation of nanorings. The thickness and refractive index of the films estimated by ellipsometry measurements were found to be 180 nm, and 1.59,

ABSTRACT The magnetic properties of Ni doped ZnS thin films fabricated at substrate temperature of 400 °C by means of pulsed laser deposition are presented. The films show crystalline wurtzite structure. Optical absorption and transmission electron microscopic studies indicate that Ni has been appropriately substituted on Zn tetrahedral site. The films show ferromagnetism up to room temperature. The magnetization in the films decreases with increase of Ni concentration. Swift heavy ion (SHI) irradiations have been carried out using 120 MeV Ag ions for the modification of structural and magnetic properties of the films. SHI irradiation suggests the formation columnar ion track inside the films causing decrease in magnetization.

The magnetic properties of Zn1−xCoxS (x=0.025 and 0.05) thin films grown on α-quartz substrates at different temperatures (TS) of 200, 400 and 600°C by means of pulsed laser deposition are presented. The films are crystallized with wurtzite structure. Optical absorption and transmission electron microscopy measurements indicate that Co ions are substituted to Zn on tetrahedral sites. Their magnetic response is

The synthesis of nanocrystalline ZnS thin films by pulsed laser deposition and their modification by swift heavy ions are presented. The irradiations with 150MeV Ni ions at fluences of 1×1011, 1×1012 and 1×1013ions/cm2 have been used for these studies. Irradiation results in structural phase transformation and bandgap modification of these films are investigated by using X-ray diffraction and UV–visible absorption

The nanopatterning of crystalline ZnS thin film surfaces under 80keV Ar+ ions irradiation at incident angles of 0°, 20°, and 40° is presented. Structural and morphological changes have been investigated by means of X-ray diffraction and atomic force microscopy respectively. The surface morphology mainly consists of nanograins of spherical shape in pristine and films irradiated at normal incidence. The irradiation

Low energy particle accelerators have been playing an important role in various fields of science & technology. Among various applications, ion beam processing, ion beam analysis and ion implantation have matured as standard tools. Recently, a 3.0 MV Pelletron Accelerator facility (Model 9SDH-4, NEC, USA) with high current TORVIS ion source (maximum beam current H+ ion ~ 50µA @ 6 MeV, He2+ at ~ 10 µA) and SNICS-II for heavy ions has been commissioned at " National Center for Accelerator Based Research " in the Department of Pure & Applied Physics, Guru Ghasidas Vishwavidalaya, India. The facility has been cleared for trial operation by the Atomic Energy Regulatory Board (AERB), Govt. of India on the basis of safety analysis report. In this paper, we discuss the passive and radiological safety aspects and user defined interlocking schemes implemented in the facility. The details of , X-ray and neutron radiation detected while accelerating the protons at different terminal voltages are presented and the radiological safety aspects implemented are discussed. The radiation doses at different points from high energy beam line for various ions measured are reported which demonstrate the safety aspects and safe operation of this newly acquired research facility being used for pursuing competitive and cutting edge researches in the multidisciplinary areas.

A 3.0 MV high current low energy Pelletron Accelerator facility (Model 9SDH-4, NEC, USA) with TORVIS (ion source for H+ and He2+ beam current H + ion ~ 50µA @ 6 mev, He 2+ at ~ 10 µA) and SNICS-II ion source for heavy ions has been commissioned as " National Centre for Accelerator Based Research " in the Department of Pure & Applied Physics, Guru Ghasidas Vishwavidyalaya, India. The first proton beam accelerated at terminal potential of 0.965 MV has been seen at ion beam analysis chamber in Nov. 2015. After conditioning the facility for about one month, we obtained the lower 10-8 torr vacuum in the beam lines and 3.0 MV terminal voltages at typical chain currents of 120 mA. In addition of system interlocks and passive shielding arrangements as per the AERB guidelines, we have also developed and implemented a PLC based control system to take care of search and secure procedure, ensuring the beam hall and other mandatory gates closure while the beam is on and switching off the machine whenever, the radiation crosses the specified limit. During the period, we faced several maintenance issues and completed the maintenance in-house successfully. This includes, opening of accelerator tank, replacing the OFC link between light link & terminal electronics box inside the Pelletron tank, calibration and routine maintenance of HVAC, compressor and Chiller units. A programmable logic controller (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices. The programming Languages of PLC systems are ladder logic, block diagrams, assembler, or C. The interconnection among PLCs is via the bus provided by PLC manufacturers and they are easy to up-connect to a host computer by computer's I/O ports or a network. The control system uses Siemens hardware & Simatic Wincc flexible runtime SCADA software for user interfacing with the PLC system. The embedded software running on PLC samples the entire digital signal and communicates with SCADA software running on Operator Console (OC) and Display Stations (DSs) on a 100Mbps Local Area Network (LAN). PLC sends the current values of all signals to the OC on the Ethernet link periodically. PLC also sends the alarms and trips generated along with time stamp to the OC as and when they are detected. The OC saves the important signals at regular configurable intervals and sends the user commands to PLC. The configuration of the system is given below: Digital Inputs and Output

The national facility for interdisciplinary research using ion beams based on 3.0 MV Pelletron accelerator (9SDH, NEC) with high current TORVIS (for H, He ions) and SNICS (for heavy ions) ion sources, and two beam lines for ion beam analysis (IBA) and ion implantation/ irradiation have been successfully commissioned at National Centre for Accelerator based Research (NCAR) at the Department of Pure & Applied Physics, Guru Ghasidas Vishwavidyalaya, Bilaspur. After completion of installation as per the procedure, the accelerator conditioning was done over a period of time to achieve desired level of terminal voltage and vacuum in the accelerator tank. A number of test experiments have also been performed to demonstrate the capabilities of the facility commissioned in the beam hall. For example, the PIXE spectra of ZnO, gold on glass and various coins have been recorded. Similarly, the raster scanner for ion implantation has been calibrated and 11.0 MeV gold and 3.0 MeV carbon ions have been successfully implanted on FTO coated glasses and diamond like carbon films respectively. Details of the facilities tested and the demonstrative results are presented.

Ag doped CdZnS alloy nanostructures are synthesized by means of chemical methods. The stoichiometry and elemental analysis has been carried out with the energy dispersive X-ray (EDAX) and X-ray photoelec-tron spectroscopy (XPS) techniques. X-ray diffraction, transmission electron microscopy and scanning electron microscopy have been employed to determine the particle size, morphology and crystal structure of the alloy nanostructures. The incorporation of Ag ion at the lattice of Zn and Cd alloys shift their binding energy towards higher energy as evidenced from XPS. The XPS measurements have been performed before and after 4 keV Ar + ion sputtering of the samples that gives a new way to interpret the XPS spectra of Ag doped CdZnS nanostructures, which may allow one to further understand the properties of this important material in relation to their full exploitation in optoelectronic devices.

Fabrications of ZnS nanocrystalline thin films at different substrate temperatures (T S) of 200, 300 and 400 °C by means of pulsed laser deposition are presented. Thin film deposited at T S of 200 °C is in cubic zinc-blende (ZB) structure while those deposited at T S of 300 and 400 °C are in hexagonal wurtzite (W) phase. The grain size, surface roughness and bandgap of the films increases with increasing T S. The zinc vacancies and interstitials in the films increases while sulfur vacancies decreases with increasing T S. The variation of zinc and sulfur vacancies in ZnS films with T S is responsible for structural phase transition from ZB to W which causes the change in energy bandgap.

The magnetic properties of Ni doped ZnS thin films fabricated at substrate temperature of 400 °C by means of pulsed laser deposition are presented. The films show crystalline wurtzite structure. Optical absorption and transmission electron microscopic studies indicate that Ni has been appropriately substituted on Zn tetrahedral site. The films show ferromagnetism up to room temperature. The magnetization in the films decreases with increase of Ni concentration. Swift heavy ion (SHI) irradiations have been carried out using 120 MeV Ag ions for the modification of structural and magnetic properties of the films. SHI irradiation suggests the formation columnar ion track inside the films causing decrease in magnetization.

The effect of swift heavy ions (SHI) on magnetic ordering in ZnS thin films with Co ions substituted on Zn sites is investigated. The materials have been synthesized by pulsed laser deposition on substrates held at 600 C for obtaining films with wurtzite crystal structure and it showed ferromagnetic ordering up to room temperature with a paramagnetic component. 120 MeV Ag ions have been used at different fluences of 1x1011 ions/cm2 and 1x1012 ions/cm2 for SHI induced modifications. The long range correlation between paramagnetic spins on Co ions was destroyed by irradiation and the material became purely paramagnetic. The effect is ascribed to the formation of cylindrical ion tracks due to the thermal spikes resulting from electron–phonon coupling.

The synthesis of nanocrystalline ZnS thin films by pulsed laser deposition and their modification by swift heavy ions are presented. The irradiation with 150 MeV Ni ions at fluence of 1×1011, 1×1012 and 1×1013 ions/cm2 have been used for these studies. Irradiation results in structural phase transformation and bandgap modification of these films as investigated by using X-ray diffraction and UV-Visible absorption measurements respectively. Since stoichiometry changes induced by irradiation can contribute to the modification of these properties, elastic recoil detection analysis has been performed on pristine and150 MeV Ni ions irradiated ZnS thin films using 120 MeV Ag ion beam. The stoichiometry of the films has been found to be similar for pristine and ion irradiated samples. A structural phase diagram based on thermal and pressure spike has been constructed to explain the structural phase transformation.

The nanopatterning of crystalline ZnS thin films surfaces under 80 keV Ar+ ions irradiation at incident angles of 0˚, 20˚, and 40˚ is presented. Structural and morphological changes have been investigated by means of X-ray diffraction and atomic force microscopy respectively. The surface morphology is mainly consists of nanograins of spherical shape in pristine and films irradiated at normal incidence. The irradiation at oblique angle (20˚ and 40˚) leads to the formation of ripples structures on the surface with a wave vector parallel to the ion beam direction. The existing theories for the ripples formation are invoked to explain the observed surfaces structure.

Fabrication of ZnS thin films having similar stoichiometry at different substrate temperatures (TS) e.g. 200 C, 300 C and 400 C by means of RF magnetron sputtering method is presented. The films grown at TS of 200 C are in cubic zinc-blende phase and textured along (111) plane. The films deposited at TS of 300 C and 400 C are in hexagonal wurtzite phase. The surface roughness and grain size of the films increase with increasing TS. The ultra-violet and visible absorption studies show that the bandgap of films can be tailored by varying TS, taking advantage of the structural transformation.

Zinc sulfide (ZnS) thin films in zinc-blende (ZB) and wurtzite (W) phases have been fabricated by pulsed laser deposition. 150 MeV Ni ion beam irradiation has been carried out at different fluences ranging from 1011 to 1013 ions/cm2 at room temperature for ion induced modifications. Structural phase transformation in ZnS from W to ZB phase is observed after high energy ion irradiation which leads to the decrease in bandgap. Generation of high pressure and temperature by thermal spike during MeV ion irradiation along the ion trajectory in the films is responsible for the structural phase transformation.