L. K. Malhotra

Studies of ambient dependent electrical behavior of nanocrystalline SnO2 thin films using impedance spectroscopy

Impedance spectroscopy has been used to investigate the properties of sol-gel derived ultrafine grained tin oxide thin films subjected to various ambients and temperatures. The impedance measurements have been carried out in the frequency range 250 kHz–10u2002mHz and Cole–Cole plots drawn. Equivalent circuit models have been suggested and fitting of the experimentally obtained data done on the basis of the approach of “universal dielectric behavior” introduced by Jonscher. The films have shown strong interaction with water vapor in the atmosphere at room temperature (300 K) as reflected from the changes in the values of resistive and capacitive components in the equivalent circuits at different humidity levels. The conduction mechanism appears to be due to the transfer of protons through the physisorbed layer of water molecules. A low frequency spur has been observed in the impedance diagram at medium and high humidity levels and attributed to the migration of adsorbed ions towards the electrode sample contac...

Size dependence of core and valence binding energies in Pd nanoparticles: Interplay of quantum confinement and coordination reduction

An analysis is given of the electronic structure of Pd nanoparticles synthesized by inert gas evaporation technique. A study of the effect of size on various core and valence electrons in Pd nanoparticles reveals a varied dependence of binding energy of electrons in different electronic levels. The shift in the Pd x-ray photoelectron spectroscopy 4d valence band centroid is more than the core level shift. The results of the present study provide a direct evidence of interplay of quantum confinement (a size effect) and coordination reduction (a surface effect).

Faster H recovery in Pd nanoparticle layer based Gd switchable mirrors: Size-induced geometric and electronic effects

An investigation of the effect of the nanoparticle size in the Pd overlayer on the hydrogen-induced changes in the Gd switchable mirrors is reported in the present study. Deposition of a 10nm thick Pd overlayer consisting of nanoparticles of 9nm size results in a large increase in optical and electrical contrast and a substantial decrease in response and recovery time in Gd switchable mirrors. This study shows that a uniformly-deposited nanoparticle catalytic layer is important for improving H recovery. These results have been explained in terms of the size-induced increase in surface area, lattice contraction, and shift of Pd d-band centroid. The results of the present study, specifically the observation of decrease in recovery time has important implications for hydrogen sensor, storage, and switching applications.

Plasma‐processed positive and negative resist behavior of obliquely deposited amorphous P–Se films

Thin films of amorphous phosphorus decaselenide (P4Se10) have been explored for lithographic applications. Depending on the substrate temperature during plasma etching in CF4 gas, either positive or negative resist behavior is observed. The effects of substrate temperature and exposure time on etching characteristics are discussed. Contrast values of 2.5 and 2.9 for positive and negative resist, respectively, have been obtained.

Infrared and x‐ray photoelectron spectroscopic study of photostructural changes in amorphous P‐Ge‐Se thin films

The structure of thin films of P40−xGexSe60 glasses deposited at various angles of incidence and the photostructural changes occurring therein on illumination with UV light have been studied by far‐infrared (IR) spectroscopy and x‐ray photoelectron spectroscopy (XPS). IR spectra reveal the absorption bands due to P=Se, P‐Se‐P, Ge‐Se, and ‐Se‐Se‐ group vibrations. The coexistence of various types of structural units (SePSe3/2, PSe3/2, GeSe4/2, ‐Se‐Se‐) in these films is supported by XPS and IR results. The photostructural changes are a consequence of the changes in the relative concentration of these structural units. Annealing of the films also causes a change in the concentration of these structural units, which in turn gives rise to a partial reversibility of the photoeffects. It has been established that the magnitude of the photostructural changes is maximum for the composition (P20Ge20Se60) having maximum concentration of fourfold coordinated units.

EPR studies on amorphous Ge‐Al and Ge‐Cu films

Electron paramagnetic resonance in amorphous germanium (a‐Ge) alloy films containing varying concentrations of Al and Cu has been studied. The concentration of free spins (dangling bonds) is found to decrease rapidly on alloying to less than 5×1017/cm3 for about 8 at.% Al and 10 at.% Cu concentrations. The g factor and line shape remain unaffected on alloying. The linewidth, however, shows minor changes.

Synthesis and luminescence properties of alumina encapsulated InN nanorods.

The present study reports a two-step procedure to synthesize InN nanorods inside the pores of an anodic alumina membrane. In the first step, pores of the membrane are filled with indium via electrodeposition. The second step involves nitridation of the as-deposited nanorods by room temperature plasma annealing. X-ray diffraction studies reveal that as-deposited nanorods consist of In, In2O3 and In(OH)3 phases which get converted to mixed hexagonal and cubic phase InN on plasma annealing. Cross sectional scanning electron microscope study reveals nanorod diameter and length to be 150 nm and 1 microm respectively. X-ray mapping results establish that uniform distribution of nitrogen throughout the length of nanorod has been achieved as a result of plasma annealing. Observation of photoluminescence peaks at 1.4 and 1.6 eV corresponding, to the absorption edges of cubic and hexagonal phases of InN show that room temperature photoemission is due to band to band recombination. The use of alumina as a template for nanorod growth prevents post-deposition agglomeration and provides mechanical strength. Possibility of total internal reflection at the InN-Al2O3 interface makes these structures ideally suitable to reduce the emitted light intensity losses.

Chapter 228 Switchable Metal Hydride Films

Publisher Summary This chapter summarizes various studies carried out on different generations of rare earth metal switchable mirrors based on polycrystalline, epitaxial layers, rare earth–Mg alloys, rare earth–Mg multilayers structures, and nanoparticles. In case of polycrystalline and epitaxial rare earth metals, switching behavior measured in terms of optical and electrical contrast, switching and recovery times and transparency and color neutrality of the trihydride state is explained in terms of intrinsic effects such as crystal structure change, phase modification, lattice contraction/expansion, and lateral and longitudinal H diffusion during hydrogenation and dehydrogenation. Moreover, a large scope for fabricating a variety of devices based on hydrogen induced structural, optical, and electrical changes and the possibility of new physics required to explain the intriguing phenomenon accompanying the switchable mirror effect – provided the necessary impetus for applied and basic research in this area. More work needs to be carried out to understand R metal–palladium (Pd) interface. Use of Pd nanoparticles has been shown to improve the switching properties and it may be possible to modify Pd layers by other means. It may also be possible to use chemical methods for growing rare earth layer.

Negative resist behavior of obliquely deposited Ge-Sb-Se thin films

The photon and electron‐beam induced changes in the selective solubility of Ge–Se–Sb films have been investigated to show that these films can be used as a negative resist. The formation of Sb2Se3 on the top of the film surface after exposure, as confirmed by x‐ray diffraction and x‐ray photoelectron spectroscopy studies, gives rise to a negative tone behavior. The addition of 10 at.u2009% of Sb in the GeSe3 films saturates the change in the chemical solubility after photo‐ and electron‐beam exposures. The chemical solubility difference can be increased by increasing the angle of deposition and is maximum at 80°. Contrast (γ) and sensitivity (s) values of 2.85 and ∼1020 photons/cm2, respectively, for photons, and 4.2 and 6×10−5 C/cm2 for electrons have been obtained.

Photon and electron beam induced chemical solubility changes in amorphous P-Ge-Se thin films

The structural changes brought in by photon and electron beam exposure of P–Ge–Se thin films lead to large changes in the chemical solubility and, hence, have been exploited for resist applications. The chemical solubility difference can be increased by increasing the angle of deposition and is maximum at 80°. As‐deposited films show a positive resist behavior, while by depositing a very thin Ag overlayer, a negative resist behavior can be obtained. Contrast and sensitivity (S) values of 2.5 and ∼1020 photons/cm2, respectively, for photons and 5 and 4×10−4C/cm2 for electrons have been obtained.