Temperature dependent structural and optical properties of nanocrystallineCdO thin films deposited by sol–gel process

Nanocrystallites of cadmium oxide (CdO) thin films were deposited by sol–gel dip coating technique on glass and Si substrates. XRD and TEM diffraction patterns confirmed the nanocrystalline cubic CdO phase formation. TEM micrograph of the film revealed the manifestation of nano CdO phase with average particle size lying in the range 1.6–9.3 nm. UV–Vis spectrophotometric measurement showed high transparency (nearly 75% in the wavelength range 500–800 nm) of the film with a direct allowed bandgap lying in the range 2.86–3.69 eV. Particle size has also been calculated from the shift of bandgap with that of bulk value for the films for which the particles sizes are comparable to Bohr exitonic radius. The particle size increases with the increase in annealing temperature and also the intensity of XRD peaks increases which implies that better crystallinity takes place at higher temperature.This revised version was published online in August 2005 with a corrected issue number.     

Stress in polycrystalline GaN films prepared by r.f sputtering

Undoped, Be-doped and Si-doped polycrystalline GaN films were deposited by R.F. sputtering onto fused silica substrates. The films were deposited at various deposition temperatures ranging from 300 K to 623 K and characterized by optical measurements while the microstructural information was obtained from SEM and XRD studies. The compositional study for the GaN film was carried out using SIMS. Residual stresses in these films were evaluated from the band tail of the absorption spectra as well as from direct measurements of hardness by commercially available depth sensing indentometer. It was observed that undoped GaN films had the highest hardness followed by that for Be-doped and Si-doped films. The values of hardness obtained form the above optical measurement tallied quite well with those obtained from direct indentation measurement.     

Electrical and optical properties of vacuum deposited MnPc thin films

Sandwich and planar structures were fabricated using manganese phthalocyanine (MnPc) as active layer and gold (Au) as electrodes by thermal evaporation method. The permittivity ε of MnPc was determined from the dependence of capacitance on film thickness. J-V characteristics of Au/MnPc/Au structure at room temperature were performed. Thermally generated hole concentration p₀, hole mobility μ_p, total trap concentration N_t and depth of the trap level were estimated. The activation energies of MnPc films were determined from the Arrhenius plots of ln σ versus 1000/T. The absorption and reflectance spectra of MnPc thin film deposited at room temperature were recorded in the spectral range 300–900 nm. The optical band gap of MnPc thin film was determined from the α² versus hν graph. The optical constants n and k were found. The real and imaginary parts of the optical dielectric constant ε₁ and ε₂ were calculated.     

Electrical properties of hybrid phthalocyanines thin films using gold and lead electrodes

The electrical properties of mixed copper phthalocyanine (CuPc) and nickel phthalocyanine (NiPc) thin films devices with gold and lead electrodes have been investigated. The two phthalocyanines were co-evaporated and deposited on to a pre-cleaned glass substrate by thermal evaporation technique at room temperature. By the co-sublimation technique an integrated phthalocyanine sample was prepared. At low voltages the film showed an ohmic conduction whereas at higher voltage levels the conduction mechanisms were dominated by space charged limited conduction (SCLC). The value of mobility of holes were calculated as μ= 3.1×10^-8 m² V^-1 s^-1 which is lower for the mixed phthalocyanines whereas the trap concentrations N_t(e) = 8.06 ×10²⁵ m^-3 have increased in the SCLC region. Further the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident.     

Supersymmetric quantum mechanics on non-commutative space

We construct a supersymmetric quantum mechanics in terms of two real supercharges on non-commutative space in arbitrary dimensions. We obtain the exact eigenspectra of the two- and three-dimensional non-commutative superoscillators. We further show that a reduction in the phase space occurs for a critical surface in the space of parameters. At this critical surface, the energy spectrum of the bosonic sector is infinitely degenerate, while the degeneracy in the spectrum of the fermionic sector gets enhanced by a factor of two for each pair of reduced canonical coordinates. For the two-dimensional non-commutative “inverted superoscillator”, we find exact eigenspectra with a well-defined ground state for certain regions in the parameter space, which have no smooth limit to the ordinary commutative space.Received: 24 February 2005, Revised: 21 April 2005, Published online: 22 June 2005PACS: 03.65.-w, 03.65.Fd, 11.30.Pb, 11.10.Nx     

Proposed search for an electric-dipole moment using laser-cooled 171Yb atoms

We propose an experiment to search for a permanent atomic electric-dipole moment (EDM) using laser-cooled 171Yb atoms launched in an atomic fountain. A uniform B field sets the quantization axis, and the Ramsey separated-oscillatory-fields method is used to measure the Zeeman precession frequency of the atoms. Laser beams of appropriate polarization are used for preparation and detection in a given magnetic sublevel. The signature of an EDM is a shift in the Ramsey resonance correlated with application of a large E field. The precision is expected to be at least 20 times better than current limits because the use of a cold atomic beam allows application of E field 10 times larger than in a vapor cell, and the interaction time with the E field is 200 times larger compared to a thermal beam. The leading source of systematic error in beam experiments, the ×/c motional magnetic field, is reduced considerably because of the near-perfect reversal of velocity between up and down trajectories through the E-field region.     

Comparative studies of the magnetic dipole and electric quadrupole hyperfine constants for the ground and low lying excited states of 25Mg+

We have employed the relativistic coupled cluster theory to calculate the magnetic dipole and electric quadrupole hyperfine constants for the ground and low lying excited states of singly ionized magnesium. Comparison with experimental and the other theoretical results are done and predictions are also made for a few low lying excited states which could be of interest. We have made comparative studies of the important many body effects contributing to the hyperfine constants for the different states of the ion.     

A superdense star model as charged analogue of Schwarzschild’s interior solution

A charged analogue of Schwarzschilds interior solution has been derived by considering the non-gravitational energy density to be constant along with a special choice of electric intensity. The charged fluid sphere so obtained is seen to be more general than that of P.S. Florides and joins smoothly with the Reissner-Nordström metric at the pressure-free interface. Also the new charged fluid sphere is capable of representing a superdense star with surface density of 2×10¹⁴ g cm^–3 which can occupy maximum mass 1.502408 times the solar mass. In the process of deriving the solution, the authors have also come across A. L. Mehras gaseous charged fluid model which is found to be unphysical as it has negative pressure at least at the center of the model.This revised version was published online in April 2005. The publishing date was inserted.     

Acceleration of the universe with a simple trigonometric potential

In this paper, we investigate the quintessence model with a minimally coupled scalar field in the context of recent supernovae observations. By choosing a particular form of the deceleration parameter q, which gives an early deceleration and late time acceleration for the dust dominated model, we show that this sign flip in q can be obtained by a simple trigonometric potential. The early matter dominated model expands with q = 1/2 as desired and enters a negative q phase quite late during the evolution.     

A Short-Range Force

We consider a successful Kerr–Newman formulation of elementary particles and deduce a mass independent but spin-dependent short-range force and point out that exactly such an inexplicable force has been experimentally detected.