Fouran Singh

Modifying the nanocrystalline characteristics—structure, size, and surface states of copper oxide thin films by high-energy heavy-ion irradiation

In the present study, x-ray diffraction, Raman spectroscopy, spectroscopic ellipsometry, photoluminescence, and x-ray photoelectron spectroscopy techniques were used to study the effect of 120 MeV 107Ag9+ ion irradiation on nanocrystalline Cu2O thin films grown by the activated reactive evaporation technique. The influence of dense electronic excitations during ion irradiation on the structural and optical properties of the Cu2O thin films was studied. Experimental results demonstrate that the phase and the size of nanocrystallites in the Cu2O thin films as well as associated surface states can be tailored by controlling ion fluence. The Cu2O higher symmetry cubic phase is observed to be quite stable under a higher temperature and irradiation-induced thermal spikes, which accompanies ion irradiation.

On the origin of photoluminescence in indium oxide octahedron structures

A sixfold decrease in photoluminescence signal intensity at 590nm with increase in deposition time from 3to12h has been observed in single crystalline indium oxide octahedron structures grown by vapor-phase evaporation method. Electron paramagnetic resonance and energy dispersive x-ray analysis confirm that the concentration of oxygen vacancies increases with deposition time. These results are contrary to the previous reports where oxygen vacancies were shown to be responsible for photoluminescence in indium oxide structures. Our results indicate that indium interstitials and their associated complex defects other than oxygen vacancies are responsible for the photoluminescence in In2O3 microstructures.

Synthesis of elongated Au nanoparticles in silica matrix by ion irradiation

The present work reports the synthesis of elongated Au nanoparticles (NPs) parallel to each other, embedded in silica matrix. Au NPs in silica, prepared using rf magnetron sputtering, were irradiated by 120MeV Au ions at different fluences to induce elongation. Optical absorption study of irradiated film showed a clear splitting of surface plasmon bands corresponding to transverse and longitudinal modes. Transmission electron microscopy investigations of pristine and irradiated samples revealed an elongation (aspect ratio of ∼3.5) in Au NPs occurred as a result of irradiation. The results are discussed in the framework of thermal spike model.

Photoluminescence studies of ZnO/porous silicon nanocomposites

This paper reports on the intense broadband photoluminescence (PL) emission from the ZnO/porous silicon nanocomposite films. The porous silicon (PS) samples were formed by electrochemical anodization on p-type (1 0 0) silicon wafer and ZnO thin films are deposited by the sol–gel spin coating technique in the pores of PS. The average pore size of PS samples is 30 nm. The glancing angle x-ray diffraction pattern of as-deposited and annealed films shows that the quality of (0 0 2) oriented ZnO nanocrystallites improves with annealing at moderate temperature and are polycrystalline in nature. The average crystallize size was found to be 40 nm. The surface topography of the ZnO/PS nanocomposite films has been studied using atomic force microscopy. The mechanism and interpretation of broadband PL from 400 to 900 nm of the nanocomposites are discussed using oxygen-bonding and native defects models for PS and ZnO, respectively. These nanocomposite films could be used as a source of broadband luminescence across most of the visible spectrum.

Effect of substrate temperature on the physical properties of copper nitride films by r.f. reactive sputtering

Abstract Deposition of copper nitride films are of significant interest because of their low thermal stability and semiconducting characteristics resulting in emerging applications in optical memories and laser writing. Copper nitride films are deposited by 13.56 MHz r.f. reactive sputtering (in the nitrogen plasma environment), keeping the substrates at 30°C (no deliberate heating of the substrate), 75°C and 150°C. Crystalline phases of the films are identified by grazing angle X-ray diffraction (GAXRD) technique. With an increase in substrate temperature, the film orients strongly towards the (100) plane of the Cu 3 N phase. Surface morphology of the films studied by atomic force microscopy (AFM) indicates an increase in grain size and a decrease in surface roughness in the films with increasing substrate temperature. Agglomeration effect of grains are observed at the substrate temperature corresponding to 75°C. The bandgap of the films are found by UV-VIS absorption spectroscopy varying from 1.3 to 1.76 eV. Stoichiometry of the films is determined by heavy ion elastic recoil detection analysis (ERDA) technique with a Δ E – E detector telescope. This study provides insight into the importance of substrate temperature on the characteristics of copper nitride films.

White light emission from chemically synthesized ZnO–porous silicon nanocomposite

White light emission across the extended visible region of the electromagnetic spectrum from the ZnO‐porous silicon (PS) nanocomposite is reported. Nanocrystallites of ZnO were grown inside the spongy structures of PS by the chemical route of sol‐gel spin coating. The property of the material arises from versatile interactions among the host structures of PS and ZnO. The origin of the observed extended white light emission from 1.4 to 3.3eV is discussed by developing a flat band energy diagram. (Some figures in this article are in colour only in the electronic version)

Thermoluminescence and photoluminescence characteristics of nanocrystalline LiNaSO4?:?Eu phosphor

Europium doped LiNaSO4 in its nanocrystalline form has been prepared and its thermoluminescence (TL) properties are studied. The TL glow curve of the phosphor has been found to have a simple structure with a single peak at 432?K. Though the highly sensitive, commercially available TL phosphor LiF?:?Mg, Cu, P (TLD-700H) is about 1.5 times more sensitive than the nanocrystalline material, the sensitivity of the concerned nanomaterial is much higher (~10 times) than the other standard phosphor TLD-100 (LiF?:?Mg, Ti). Compared to the conventional LiNaSO4?:?Eu phosphor (prepared through a melting procedure and having particle size of 125??m), the nano-sized phosphor has a lesser TL sensitivity. However, this reduction in TL sensitivity on decreasing the particle size from micrometres to nanometres gives a better understanding of the TL phenomenon. The order of TL kinetics for the concerned nanomaterial is also found to be different from that of the conventional material. Photoluminescence studies that have been performed on these materials throw light on the reasons for such a change in the order of kinetics. Further, fading and reusability of the concerned nanomaterial has also been studied and it has been found that the phosphor is quite suitable for radiation dosimetry.

Engineering of nanocrystalline cadmium sulfide thin films by using swift heavy ions

Swift heavy ion (SHI) irradiation experiments have been performed on as-deposited nanocrystalline cadmium sulfide (CdS) thin films by using 100 MeV Au8+ ions with 5 × 1012 ions cm−2. In addition, the as-deposited films were annealed at 300 °C in air for 1 h. Structural, optical and electrical properties of pristine (as-deposited), annealed and irradiated thin films were carried out by using x-ray diffraction (XRD), energy dispersive spectra, scanning electron microscopy, atomic force microscopy, UV-VIS spectroscopy and Arrhenius plots for resistivity and thermoemf, respectively. XRD shows the intrinsic peak of (0 0 2) for the hexagonal phase of CdS. After annealing and SHI irradiation this peak was enhanced drastically and dramatically, showing the dominant orientation in this plane. The grain growth observed in these two post-deposition processes was different. This resulted in a decrease in resistivity of the annealed and the irradiated samples by one and two orders from the pristine sample, respectively.

Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films

Origin of the Raman mode in nanocrystalline zinc oxide in the vicinity of A1 (LO) phonon mode induced by energetic heavy ions is reported. The evolution of this mode in the irradiated films is ascribed to the effect of disorder and the high density of lattice defects induced by irradiation. The presence of such defects is confirmed by the reduction in the intensity of E2 (high) mode and band bending of the near band edge absorption. A softening of the evolved Raman mode with increasing in ion fluence is also observed. This softening cannot be attributed to spatial confinement of phonons, as the sizes of the crystallites are large. Therefore, it is explained in terms of the combined effects of phonon localization by lattice defects and the structural strain in the lattice induced by electronic energy loss transferred by energetic heavy ions.

Size effect on electronic sputtering of LiF thin films

Electronic sputtering in polycrystalline LiF thin film by 120MeV Ag25+ is investigated. The sputter yields of Li and F for the different thicknesses (10–265nm) of films are measured with online elastic recoil detection analysis technique. A reduction in sputter yield, from ∼2.3×106 to 2.2×104 atoms/ion, is observed with increase in the film thickness. The trend in the experimental results can be explained in terms of size effect in thin film following inelastic thermal spike model. The confinement of energy in the film having smaller grains and lower thickness results in higher temperature causing higher sputtering yield.