Infrared studies of the phase transitions of alkylammonium halides, RNH3X, and bis-(alkylammonium) tetrahalogenometallates(II), (RNH3)2MX4, (R = alkyl, M = metal, X = Cl or Br)

Internal vibration modes of bis-(alkylammonium) tetrachlorometallates(II) and the corresponding alkylammonium chlorides have been studied through their phase transitions using infrared spectroscopy. The studies show that the vibrational states of alkylammonium ions change markedly through the phase transitions. Spectra of the analogous tetrabromometallates and alkylammonium bromides also confirm this behaviour. There is appreciable motion of the alkylammonium ions in the high-temperature phases; thus, CH3NH+3 ions are essentially undistorted in these phases. The low-temperature, ordered phases show evidence of stronger hydrogen bonding of the cations and for the presence of C—N torsional modes.

Spin State Selective Excitation of Single Quantum Transitions Using Multiple Quantum Spectroscopy- an Aid to Analyse Complex Proton NMR spectra of Oriented Molecules

NMR spectra of molecules oriented in liquid-crystalline matrix provide information on the structure and orientation of the molecules. Thermotropic liquid crystals used as an orienting media result in the spectra of spins that are generally strongly coupled. The number of allowed transitions increases rapidly with the increase in the number of interacting spins. Furthermore, the number of single quantum transitions required for analysis is highly redundant. In the present study, we have demonstrated that it is possible to separate the subspectra of a homonuclear dipolar coupled spin system on the basis of the spin states of the coupled heteronuclei by multiple quantum (MQ)−single quantum (SQ) correlation experiments. This significantly reduces the number of redundant transitions, thereby simplifying the analysis of the complex spectrum. The methodology has been demonstrated on the doubly 13C labeled acetonitrile aligned in the liquid-crystal matrix and has been applied to analyze the complex spectrum of an oriented six spin system.

Measurement of Electron Spin Lifetime and Optical Orientation Efficiency in Germanium Using Electrical Detection of Radio Frequency Modulated Spin Polarization

We propose and demonstrate a technique for electrical detection of polarized spins in semiconductors in zero applied magnetic fields. Spin polarization is generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by a sensitive radio-frequency coil. Using a calibrated pickup coil and amplification electronics, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of 4.8% could be determined for Ge at 1342 nm excitation wavelength. In the presence of a small external magnetic field, the signal decayed according to the Hanle effect, from which a spin lifetime of 4.6 +/- 1.0 ns for electrons in bulk Ge at 127 K was extracted.

Electron paramagnetic resonance study of porous silicon

Electron paramagnetic resonance studies under ambient conditions of boron‐doped porous silicon show anisotropic Zeeman (g) and hyperfine (A) tensors, signaling localization of the charge carriers due to quantum confinement.

Time-dependent transitions with time-space noncommutativity and its implications in quantum optics

We study the time-dependent transitions of a quantum-forced harmonic oscillator in noncommutative R(1,1) perturbatively to linear order in the noncommutativity theta. We show that the Poisson distribution gets modified, and that the vacuum state evolves into a `squeezed' state rather than a coherent state. The time evolutions of uncertainties in position and momentum in vacuum are also studied and imply interesting consequences for modeling nonlinear phenomena in quantum optics.

Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 degrees C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires. (C) 2011 Elsevier B.V. All rights reserved.