Dilip Kumar De

Preparation and characterization of indium tin oxide films produced by the d.c. sputtering technique

Abstract Indium tin oxide (ITO) films were produced using the d.c. sputtering technique. The thermal stability and electrical, galvonomagnetic, thermoelectric and optical properties of these films were critically studied. It was found that films comparable with those produced using r.f., magnetron or evaporation techniques can be obtained by means of this method which is believed to be a cost-effective and simple technique for the production of device grade ITO films.

Observation of the cubic‐field splitting of an excited S=2 manifold in a cubic copper tetramer

EPR measurements on single crystals of Cu4OCl6(triphenylphosphine oxide)4 at liquid helium temperatures in the frequency ranges 14–17 and 34–35 GHz were fitted to a simple cubic S=2 spin Hamiltonian with g=2.10±0.01 and a zero‐field splitting of (0.53±0.01) cm−1. From the decrease in intensity of the S=2 spectrum on cooling below 4.2 K and the absence of an S=1 spectrum, the S=2 manifold was deduced to lie (14±1) cm−1 above a nonmagnetic ground state. The EPR results are used as a test of the various theories developed to explain the magnetic susceptibility of copper tetramers.

Characterization of CdS film prepared by hot wall technique

Abstract Cadmium sulphide films were deposited by hot wall technique at a system pressure of ≈10−6 Torr onto corning 7059 glass slides. Electrical conductivity, temperature coefficient of resistivity and Hall mobility were measured simultaneously for undoped and doped films. Thermoelectric power (TEP) and optical transmission were also measured for the above films. Information regarding carrier concentration, refractive index and band gap was computed from the above data. Mobilities of the films indicated a temperature dependence, μ=4.07 × 104T−1.53 and 8.69 × 103T−0.89 cm2/Vs for undoped and doped films, respectively.

Jahn‐Teller EPR spectra of Cu2+ in MgSiF6⋅6H2O

The 34 GHz EPR spectrum of Cu2+ in MgSiF6⋅6H2O showed a ‘‘static’’ Jahn–Teller effect at 4.2 K with two inequivalent Jahn–Teller sites per unit cell. The six axially symmetric sets of Cu2+ lines had their z axes parallel to the three tetragonal axes of two cubes, which were rotated by approximately 40° with respect to each other about a common [111] axis, which is the crystal c axis. The measured spin‐Hamiltonian parameters at 4.2 K for each set of lines were g∥=2.47±0.01, g⊥=2.10±0.01, and ‖A∥‖=(110±3)×10−4 cm−1. There was a gradual decrease in the anisotropy of the spectrum on warming the crystal, with a single, nearly isotropic line being observed above 220 K. At 270 K the spectrum had axial symmetry about the c axis with g′∥ =2.23±0.01 and g⊥ =2.25±0.01. The temperature evolution of the spectrum was interpreted in terms of a Boltzmann distribution over inequivalent distorted Jahn–Teller configurations, with one potential well lowered by an amount Δ≊105 cm−1 below the other two.

Thermoelectric power of aluminum films

The thermoelectric power (TEP) of aluminum film was measured in the thickness range of 300–1600 A. From the size effect of electron diffusion term, the energy dependence of the mean free path of conduction electrons (U) and the Fermi surface area (V) were calculated to be U=0.957 and V=1.322. The phonon‐drag part of TEP also exhibited a size effect from which the mean free path of the dominant phonon mode was estimated to be 400 A. The effect of grain boundary scattering on thermoelectric power was also studied.

White light tunable emissions from ZnS: Eu3+ nanophosphors over 330–465 nm excitation range for white LED applications

(ZnS: Eu3+ -CMC) nanophosphors of cubic (zinc blende) structure were synthesized using a precipitation technique with doping concentrations of Eu3+ ions 1 mol% and 5 mol%. The crystal sizes were 2.56 nmand 2.91 nmrespectively. Annealing at 300 °Cin a sulfur-rich atmosphere altered the crystal size to 4.35 nmand 3.65 nmrespectively and the band gap from 4.2 eV to 3.76 eV and 3.81 eV respectively. The as-synthesized samples gave pure orange-red emission when excited at wavelengths of 394 nmand 465 nm. After thermal annealing of the samples, a broad emission band in the blue-green region assigned to defect related states emerged or were enhanced. Also enhanced were the emission lines of Eu3+ ions in the orange-red region. A combination of these two transitions gave white light of different shades (recorded on the CIE 1931 chromaticity diagram) from cool white through day-light to warm white light, depending on Eu3+ concentration and the excitation wavelengths (UV-330 to blue 465 nm), thus showing great potential of these nano-phosphors in the generation of high quality white light.

EPR measurement of Cu2+–Fe2+ exchange in FeSiF6 ⋅ 6H2O at 4.2 K

Six inequivalent Cu2+ EPR spectra were observed at 4.2 K in single crystals of FeSiF6 ⋅ 6H20. The estimated parameters gz∼2.38 and θ∼40°, where θ is the angle between the ionic z axis and the c axis, differ from those measured in crystals of similar structure. These differences have been explained in terms of an isotropic Cu2+–Fe2+ exchange Hamiltonian JS1 ⋅ S2, with J=+(0.030±0.003) cm−1, which gives a contribution gex∼−5.05 J sin2 θ, where θ is the angle between the external magnetic field and the z axis. Perpendicular to the c axis, an independent estimate of +0.034 cm−1 for J was made from the low‐field displacement of a satellite spectrum.

High‐Q magnetostatic surface wave planar yttrium iron garnet resonator

Experimental results on the magnetostatic surface wave resonance characteristics of planar yttrium iron garnet resonators are given. Single‐mode resonance with wide tunability range and high Q have been achieved. Q as high as 3500 and insertion loss as low as 13 dB with off‐resonance rejection as high as 15 dB have been achieved at 6 GHz. A microwave oscillator built with the resonators and a laboratory‐made hybrid amplifier provided oscillations in the range 3–5.3 GHz with phase noise of −105 dBc/Hz at 10 KHz offset from the carrier frequency.

Electron Paramagnetic Resonance Study of Copper(II)Fluosilicate Hexahydrate

An electron paramagnetic resonance study was performed on single crystals of copper fluosilicate hexahydrate. EPR signals correspond to three tetragonally distorted pctahedral Cu(II) ions (A site) with g values: g11 = 2.390, gJ. .= 2.093, and ·one regular octahedral Cu(II) ion (B site) with g = 2.093. The spectra are thus quite different from those observed earlier by Bleaney and Ingram in Cu(II):ZnSiF6 • 6H20. Fluosilicate hexahydrates of divalent metals belong to a series of crystals wellsuited for X-ray, magnetic susceptibility and anisotropy, electron paramagnetic resonance, optical, and other studies (J-4). Observations of an isotropic EPR signal at 90 K and above and anisotropic EPR signals at 20 K by Bleaney and Ingram (J) in Cu:ZnSiF6 • 6H20 provided the first experimental evidence of the Jahn-Teller effect. A determination of crystal structures of this series by Ray eta/. (2, 3) has revealed that copper(II) fluosilicate hexahydrate (3), contrary to earlier belief, is not isomorphous with zinc fluosilicate hexahydrate. The structure is still rhombohedral (space group R3) with a cell four times as large as that supposed earlier. The unit cell, which has dimensions a = b = 18.18 A and c = 9.857 A, contains three magnetically nonequivalent tetragonally distorted Cu(II) · 6H20 octahedra (Cu-0(1) = 1.97 A, Cu-0(2) = 1.97 A, Cu-0(3) = 2.367 A) designated as the A sites; and one regular Cu(II) · 6H20 octahedron (Cu-0 = 2.074 A) designated as the B site. It was therefore considered of interest to study EPR in single crystals of copper fluosilicate hexahydrate with the object of unravelling the nature of the ligand fields in a crystal where two types of Cu(II) complexes coexist.

Electron paramagnetic resonance in CuTiF6⋅4H2O

Electron paramagnetic resonance in single crystals of CuTiF6⋅4H2O was studied between 77 and 485 K in the frequency ranges 23–25 and 34–36 GHz. The monoclinic lattice has two magnetically distinct Cu2+ sites, but (except at 4.2 K) only one resonance line was observed at all orientations. Assuming tetragonal symmetry at each Cu2+ site, the observed g values were used to determine the single ion parameters g∥ = 2.403±0.005 and g⊥ = 2.082±0.002 at 77 K. Linewidth data in the ac plane were explained in terms of the exchange narrowing of the line broadened by the dipolar and unresolved hyperfine interactions.