005559   Pati S P;Dash S K;Satpathy S (P G Department of Physics, Sambalpur University, Jyoti Vihar, Burla-768 019) : High frequency positive series resistance in IMPATT devices. Indian J Engng Mater Sci 2001, 8(5), 255-60.

Generalized computer method, which considers drift, diffusion and tunnel currents has been formulated and used to determine the high frequency series resistance (R_s) and its distribution profile along the active layer of a varieties of Avalanche Transit Time (ATT) diode structures. The method is also capable of providing RF properties of the diodes like RF negative resistance (Z_R), band width and mean square noise voltage <60>V²<62>/df and other parameters at various frequencies. The result indicates generation of high value of R_s, Z_R and <60>V²<62>/df for lo-hi-lo and hi-lo double drift region (DDR) diodes as compared to flat profile diodes. A comparison of the series resistance (R_s), microwave properties and noise generation of Si, GaAs and InP DDR diodes has also been made. The R_s distribution profiles for the 3n-lo and lo-hi-lo DDRs are observed to have double spike like profile unlike the normal double peak profiles for flat DDRs.

1 illus, 4 tables, 11 ref

005558   Pathan H M;Sankapal B R;Lokhande C D (Thin Film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur-416 004) : Preparation of CdIn₂S₄ thin films by chemical method. Indian J Engng Mater Sci 2001, 8(5), 271-4.

Semiconducting CdIn₂S₄ thin films have been deposited on amorphous glass subtrates using a chemical method, successive ionic layer adsorption and reaction (SILAR). The influence of preparative parameters on the properties of the films has been studied. The thickness of the film is found to be 0.44 μm. The films have been characterized for structural, optical and electrical transport properties by means of X-ray diffraction, optical absorption, electrical resistivity and thermoelectric power measurements techniques. The films are found to be nanocrystalline with optical bandgap 2.12 eV. The electrical resistivity was of the order of 10⁴ Ω-cm.

5 illus, 2 tables, 14 ref

005557   Patel P G;Deshpande M P;Arora S K;Agarwal M K (Department of Physics, Sardar Patel University, Vallabh Vidyanagar-388 120) : Effect of partial replacement of selenium by sulphur on photoelectrochemical behaviour of WSe2 single crystals. Bull Electrochem 2001, 17(8), 361-6.

Single crystals of tungsten diselenide (WSe2) and tungsten sulphoselenide (WSSe) have been grown by direct vapour transport technique. Using these crystals photoelectrodes were fabricated and their photoelectrochemical behaviour is studied in an appropriate electrolyte. Mott-Schottky plots are constructed from the capacitance measurements being undertaken on these crystals at various potentials from which various parameters are obtained.

3 illus, 5 tables, 24 ref

005556   Nesheva D;Raptis C;Levi Z;Bineva I;Aneva Z (NO, Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria) : Alloying at the interface of ZnSe/CdSe multilayers and ZnSe-CdSe composite films: a Raman study. Asian J Phys 2000, 9(3), 799-808.

Ramana scattering measurements have been carried out on as-deposited and annealed: Polycrystalline multilayers of ZnSe/CdSe having equal ZnSe and CdSe layer thicknesses (2.5, 3.5, 5.0 and 10.0 nm) and ZnSe-CdSe composite films, in which CdSe layers with varying nominal thicknesses (1.0, 2.0, 2.5, 3.5 and 5.0 nm) were sandwiched between twenty times thicker ZnSe layers. Both kinds of samples have been prepared by thermal evaporation in vacuum. The 647.1 nm Kr⁺ laser line and the 482.5 and 514.5 nm Ar⁺ laser lines have been used in these measurements. Two main bands at 212 and 225 cm^-1 have been resolved in the spectra of as-deposited samples excited by the 647.1 nm line. They have been attributed to ILO scattering from "pure" CdSe layers (in multilayers) or "cores" (in composite films) and Zn_xCd_1-xSe interface regions, respectively. Thus, it has been shown that Zn_xCd_1-xSe interface regions are formed during sample preparation and a gradual change in the composition is characteristic for these regions. Annealing of samples enlarges the Zn_xCd_1-xSe interface regions and reduces the CdSe layer thickness or "core" size. This result has been explained assuming diffusion of Cd atoms from CdSe into ZnSe....

4 illus, 17 ref

005555   Nair K P R;Eappen S M (Laser and Spectroscopy Laboratory, Department of Physics, Cochin University of Science and Technology, Cochin-682 022) : Microwave and laser Raman spectroscopy of o-chlorotoluene. Indian J pure appl Phys 2001, 39(11), 750-1.

Microwave spectrum of o-chlorotoluene C₆H₄CH₃Cl shows distinct rotational structures due to four excited vibrational states over and above the ground state spectrum. The vibrational frequency calculated from the relative intensities of the ground and first excited states in the microwave spectra is identified in the laser Raman spectra and is believed to be the first torsional state of the molecule.

^ssc2 illus, 2 tables, 4 ref

005554   Nagels P (NO, Rruca-University Antwerp, B-2020 Antwerpen, Belgium) : Structural characterization of amorphous Ge_xSe_100-x by infrared and Raman spectroscopy. Asian J Phys 2000, 9(3), 693-707.

Films of the amorphous Ge_xSe_100-x system were prepared by plasma-enhanced chemical vapour deposition using the hydrides as precursor gases and by standard thermal evaporation. Bulk glasses were also obtained by quenching the melt. Infrared and Raman spectroscopy was used in order to get some insight into the microstructure of the material. These spectra revealed that all compositions, even the stoichiometric one, are microheterogeneous in structure, indicated by the presence of various discrete molecular units. The IRs and Raman spectra gave evidence for the incorporaton of hydrogen in the plasma deposited films. Thermal annealing experiments showed the rupture of hydrogen bonds at low temperature. A better resemblance between the Raman spectra of the bulk glasses and the PECVD films points to a higher degree of order in the latter ones, compared to the evaporated films. Germanium-rich layers were unstable in air and showed in their IR spectra broad absorption bands of Ge-O vibrations when keeping them in air for a long time.

14 illus, 2 tables, 28 ref

005553   Mytiilineou E;Chao B S;Papadimitriou D (Physics Dept., University of Patras, 265 00 Patra, Greece) : Raman studies of reversible and irreversible photo-induced structural chanes in amorphous Ge₂₅Se_75-xBi_x films. Asian J Phys 2000, 9(3), 737-43.

Raman spectra of sputtered amorphous Ge₂₅Se_75-xBi_x films, with x ranging from 9 to 19, have been studied. When intermediate laser power densities used, reversible effects are observed: the ratio of the 216 cm^-1 to the 197 cm^-1 peak increases. These peaks are associated with the Ge(Se_1/2)₄ tetrahedra. The effect is attributed to reversible structural changes due to photo-induced bond rearrangements that take place during illumination. By further increase of the power density, laser induced crystallisation occurs and sharp peaks characteristic of the crystalline Bi₂Se₃ phase appear.

3 illus, 19 ref

005552   Mukherjee S K (NO, , Lal Bazar, P.O. Dburajpur-731123, Dist. Birbhum) : Some electromagnetic wave equations. Appl Sci Period 2001, 3(1), 33-8.

9 ref

005551   Mukherjee M;Bose P;Bhushan S (School of Studies in Physics, Pt Ravishankar Shukla University, , Raipur-492 010) : Electro-optical studies in chemically deposited Sm/Pr doped (Cd-Pb) S films. Indian J pure appl Phys 2001, 39(12), 804-09.

Results of photoconductivity optical absorption, XRD & SEM studies have been presented for different (Cd-Pb)S films. From the photo-current curves IPC/IDC ratio of the order of 10⁵ is observed for undoped (Cd0.95-P0.05)S film which improves to 10⁶ for the systems prepared with NaF and Samarium/Praseodymium nitrate. Due to annealing of the films at 400°C, dark current decreases to almost zero value along with a decrease in photo-current also but the ratio goes to very high value. From the analysis of decay curves, lifetime of the carriers, mobility and trap-depths are determined. The values of lifetime and mobility are found to increase in presence of impurities. Band-gaps determined from optical absorption and photoconductivity excitation spectral studies show a similar nature in presence of impurities. The direct band-gap is found for mixed films. XRD studies show crystalline nature and according to SEM studies layered growth of films takes place.

4 illus, 5 tables, 14 ref

005550   Misra S C K;Angelucci R (NO, National Physical Laboratory, New Delhi-110 012) : Polyaniline thin film-porous silicon sensors for detection of microoroganisms. Indian J pure appl Phys 2001, 39(11), 726-30.

Quick and simple methods to detect the type of life threatening microbial species are very essential in food and water contaminated with bacteria. Recently, by utilizaing the semiconducting polymeric thin films prepared on silicon macroporous substrates a new technology for detection of micro-organisms has been developed. The advantages of the polymeric devices are the ease of fabrication, the high sensitivity to micro-organisms, the fast response time and the room temperature operations. In this work the current voltage characteristics and the dielectric losses variations of the specifically doped polymeric thin films deposited on silicon macroporous membranes upon exposure to E. Coli were studied. The sensors were prepared by vacuum depositing doped polyaniline in the form of this films on the silicon macroporous structures. The particular doping combination in the polymer makes the sensor specific for detection of E. Colli. Moreover the sensitivity of the to E. Coli is very high and the response time of the sensor is about 5 sec. The total response time is a few tens of seconds. The macroporous silicon substrate allows to obtain a polyaniline thin film with high specific surface area and good crystallinity, as shown by SEM and X-ray investigations, respectively. Both the high surface area and the crystallinity of the polyaniline film deposited on the macroporous silicon substate are believed to be responsible for the excellent properties of the sensor device.

8 illus, 19 ref

005549   mcgreevy R L;Borjesson L (Studsvik Neutron Research Laboratory, Uppsala University, S 611 82 Nykoping, Sweden) : First sharp diffraction peaks. Asian J Phys 2000, 9(3), 513-29.

Some possible origins of first sharp diffraction peaks (FSDP) in the structure factors of liquids and glasses are demonstrated by considering a wide variety of atomic models. The models are then discussed in terms of various proposals for the origin of the FSDP; these are mostly found to be useful qualitative descriptions when applied appropriately, but can be misleading when applied inappropriately. Apparently different proposals often have similar `roots' but are put forward in very different language. It is shown that the FSDP by itself is not an indication of any particular type of intermediate range structural order, but that different possibilities can be assessed by considering other physical information on the system being studied. In general the FSDP can be said to arise from a density fluctuation produced by `competition' between a short range bonding requirement, giving a higher microscopic densit, and a lower macroscopic density. This density fluctuation need only apply to one component in a multicomponent system.

11 illus, 27 ref

005548   Manoj P K;Gopchandran K G;Joseph B;Koshy P; Vaidyan V K (Department of Physics, University of Kerala, Trivandrum-695 581) : Preparation and characterization of indium oxide thin films by chemical spray deposition. Indian J Phys-Pt A 2001, 75(5), 507-10.

Conducting and transparent indium oxide thin films are prepared by chemical spray deposition of aqueous solution of indium chloride. X-ray diffraction and optical transmission are used to characterize these films. The preferential orientation of these films is found to be sensitive to deposition parameters. The preparation conditions are optimized to obtain transparent and highly conducting In2O3 films on the basis of figure of merit.

4 illus, 2 tables, 18 ref

005547   Maniar C P;Raval A H;Joshi M J (Department of Physics, Saurasthra University, Rajkot-360 005) : Growth of antimony single crystals and dislocation etching. Indian J Phys-Pt A 2001, 75(5), 525-9.

Antimony single crystals have been grown by the horizontal Chalmer's technique. The furnace for the growth was designed and fabricated in the laboratory. A specially designed graphite boat was used as a container for the growth. For dislocation studies, the crystals were cleaved at liquid nitrogen temperature in a conventional manner. Optically smooth cleavage surfaces were selected for etching in the etchants consisting of different compositions of malic acid, nitric acid and distilled water. Crystallographically oriented triangular etch pits were obtained at sites of dislocations. The reaction is characterised by kinetic as well as thermodynamic parameters.

8 illus, 1 table, 27 ref

005546   Logothetidis S (Department of Physics, Aristotle University of Thessaloniki, 54006, Thessaloniki, Greece) : Optical properties and new forms of as-grown and post-growth ion irradiated amorphous carbon films. Asian J Phys 2000, 9(3), 643-55.

Amorphous Carbon (a-C) films were developed by sputtering on Si (100) substrates. The film optical properties, structure and C-C bonding depend strongly on the energy E of species bombarding the film during deposition. Several allotropic Carbon forms were detected when species with E=30-230 eV were used. Structural modifications were also detected after post-growth ion beam bombardment (IBB) of the films. Analysis of the film dielectric function provided the composition, electronic structure and bonding configuration. Films deposited with E ≤30 eV exhibit an sp² bonded behaviour, the characteristic D and G Raman bands and low density, and are amorphous with some fullerene-like clusters, while those deposited with 30≤E<60>130 eV exhibit an sp³ bonded behaviour and are condiderably denser. In films deposited with E<62>130 eV the formation of an even denser carbon phase was detected which exhibit a dielectric function diferent than in the sp² and sp³ bonded materials. These films exhibit new Raman peaks and consist of nanocrystals with large d-spacings and unit cell. Post-growth IBB of all type a-C films transform them to diamond, graphite and SiC grains.

9 illus, 25 ref

005545   Lingwal D S;Naithani U C;Semwal B S (Department of Physics, HNB Garhwal Univerity Campus, Pauri, Garhwal-246 001) : Electric field dependent microwave loss in BaTiO₃ and KTaO₃. Indian J pure appl Phys 2001, 39(10), 668-72.

Electric field dependent microwave loss of anharmonic pure BaTiO₃ and KTaO₃ ferroelectric crystals has been calculated in its paraelectric phase from the Silverman-Joseph Hamiltonian augmented with fourth order phonon co-ordinates using double time Green's functions. The loss tangent consists of a contribution, which is quardratic in applied biasing and is a field independent contribution. The variation of tan δ with applied field is noticeable in the vicinity of Curie temperature. In the higher temperature region, the electric field effect ceases and the increase in loss arises mainly due to higher order anharmonic terms. In both cases (BaTiO₃ and KTaO₃) loss tangent increases with the increasing electric field.

2 illus, 1 table, 33 ref

005544   Lingwal D S;Naithani U C;Ashok Kumar;Semwal B S (Department of Physics, HNB Garhwal University, Campus Pauri, Garhwal-246 001) : Field dependent dielectric behaviour of BaTiO₃, SrTiO₃ and KTaO₃ perovskites. Indian J pure appl Phys 2001, 39(10), 673-8.

Electric field dependence of the complex dielectric constant in anharmonic ferroelectric crystals are calculated in its paraelectic phase from the Silverman-Joseph Hamiltonian augmented with fourth order phonon co-ordinates using double time Green's functions technique. The frequency, temperature and electric field dependent dielectric constant of BaTiO₃, SrTiO₃ and KTaO₃ crystals have been discussed. Dielectric constant increases with increase of applied field in BaTiO₃, SrTiO₃ and KTaO₃ cases.

9 illus, 6 tables, 22 ref

005543   Lalmani;Rajou Kumar;Singh R;Singh B (Department of Physics, Engineering College, Srinagar Camp Jammu, Canal Road, Jammu-180 001) : Characteristics of the observed low latitude very low frequency emission periods and whistler-mode group delays at Jammu. Indian J Radio Space Phys 2001, 30(4), 214-16.

First observations on the relationship between whistlers and periodic very low frequency (VLF) emissions observed at low latitude ground station Jammu (geomagn. lat., 22° 26' N;L = 1.17) are presented. The results have been discussed. To explain the results it is proposed that the periodic VLF emissions are generated near the equatorial region at L ″ 1.2 as a result of interaction between trapped energetic particles and one-hop whistlers under cyclotron resonance mechanism and propagated to the ground station Jammu in nonducted mode of whistler propagation.

^ssc1 illus, 1 table, 4 ref

005542   Kumar A (Department of Physics, Indian Institute of Science, Bangalore-560 012) : Critical behaviour of complex fluids and supramolecular length scale. Indian J pure appl Phys 2001, 39(12), 789-94.

Few aspects of complex fluids (electrolyte solutions, polymer solutions, amphiphilic systems, etc.) from the perspective of critical behaviour normally observed in non-interacting, neutral fluids have been presented. A recurring theme in complex fluids is the structuring of these systems and the associated supramolecular (mesoscopic) length scale. The authors adduce evidence to support the claim that, intriguing and poorly understood features emerge in electrolyte solutions and the dilute suspensions of charge-stabilized colloids in liquid solutions. The results are based on investigations near to and away from liquid-liquid critical point using laser light scattering, turbidity, small-angle X-ray scattering (SAXS), visual observations and the excess molar volume measurements.

6 illus, 22 ref

005541   Krishnakumar V;Ramasamy R (Post-graduate Department of Applied Physics, Nehru Memorial College, Puthanampatti-621 007) : Spectral and normal coordinate analysis of 5,6-diamino uracil. Indian J pure appl Phys 2001, 39(12), 829-32.

FTIR spectrum of 5,6-diamino uracil has been recorded in the region 4000-100 cm^-1 and the normal coordinate analysis has been carried out by assuring a Cs point group symmetry. All the normal modes of vibrations are assigned and calculations on the potential energy distribution are performed.

1 illus, 2 tables, 11 ref

005540   Kordas G (NO, Institute of Materials Science, NCSR "Demokritos", GR-15310 Aghia Paraskevi Attikis, Greece) : Unique opportunities for studying the short and medium range order of phosphosilicate glasses by cw-EPR, 1D-ESEEM and HYSCORE. Asian J Phys 2000, 9(3), 621-30.

Phosphosilicate glasses were exposed to ⁶⁰Co γ-ray irradiation for the production of paramagnetic states that were studied by cw-EPR, 1D-ESEEM and HYSCORE spectroscopies. The cw-EPR signal of the 6(Li₂O/Na₂O) 3P₂O₅ 6SiO₂ glasses consisted of a doublet separated by ≈ 47 G. This doublet was assigned to the Qⁿ⁼² -type center (POHC-defect). 1D-ESEEM peaks gave the A_iso (-0.691) [Na] MHz, -1.39 MHz [Li]) and T+ (0.771 MHz [Na], 1.436 MHz (Li]) parameters corresponding to the first phosphorus neighbor. The r(P-O-P)-distance was estimated by the point dipole approximation for T+ to be 2.83 Angstrom and 3.49 Angstrom for Li and Na containing glasses, respectively. HYSCORE spectroscopy revealed the presence of the alkali metal ion in the close proximity of the POHC. The combined information gained by the three EPR techniques and the SCE-HF calculations suggested the existence of the POHC-PPHC-Li complex (Q²-Q²-Li-structure) in the glasses. In the Na₂O P₂O₅ 4SiO₂ glass, an additional doublet was observed separated by ≈ 947 G. The second doublet was attributed to a Qⁿ⁼⁴ - type center (P₂-defect. Theadvanced EPR techniques extend the spatial resolution of the cw-EPR spectroscopy to the medium range order offering a significant tool for the exploration of the amorphous state.

10 illus, 1 table, 12 ref

005539   Kolobov A V (Joint Research Center for Atom Technology, National Institute for Advanced Interdisciplinary Research, 1-1-4 Higa, ) : Reversible photostructural changes: why they occur only in amorphous chalcogenides. Asian J Phys 2000, 9(3), 561-8.

Reversible photostructural change is a phenomenon unique to amorphous chalcogenides. Recent experimental in-situ EXAFS, Raman and ESR studies reveal the microscopic mechanism of this effect involves the formation of dynamic interchain bonds due to unpairing of lone-pair electrons and subsequent bond switching. The important role played by the lone-pair electrons accounts for why this process can only be observed in amorphous chalcogenides.

4 illus, 29 ref

005538   Khanna R K;Nagar A K (Department of Physics, Plasma & Microwave Laboratory, Government College, Ajmer-305 001) : Self-focusing of a Gaussian laser beam in parabolic profile optical fiber having Kerr non-linearity. Indian J pure appl Phys 2001, 39(12), 768-75.

Steady state analysis of self-focusing of Gaussian laser beam propagating in a parabolic index profile silica fiber of cylindrical core has been presented. The Kerr non-linearity acts as perturbation on the geometrically built-in radial inhomogeneity of the dielectric fiber. A paraxial ray approach has been adopted following. Akhmanov and Sodha using WKB approximation. The beam-width parameter at different axial points is studied by varying different parameters. An appreciable decrease in critical beam power for focusing has been reported. It has been found that when the beam power attains this threshold value, the beam propagates in a self-trapped waveguide mode. Above the threshold, the beam gets self-focused when the non-linear effect dominates over the diffraction effect. Below this threshold the beam diverges out forming a diverging lens. The beam intensity at the focusing points has been calculated for the fiber for different media and fiber lasers. The propagation characteristics of laser beam are found to be very sensitive with respect to the delta parameter of the fiber and the self-focusing length is found to decrease with the increase in incident beam power. Results indicate the possibility of a new kind of passive non-linear optical device for manipulating output ligh intensity.

5 illus, 3 tables, 27 ref

005537   Kelires P C (Physics Department, University of Crete, P.O. Box 2208,710 03 Heraclion, Crete, Greece) : Atomic level stresses in amorphous carbon networks. Asian J Phys 2000, 9(3), 631-42.

Atomic level stresses are a valuable tool in probing the local structural characteristics of disordered and amorphous materials. The calculations are based on Monte Carlo simulations within the empirical potential approach. There is a universal relationship between local stress and bonding hybridization, namely, that the most problable stress state for fourfold sites is compression, while threefold sites prefer to be under tension. This relationship not only is valid in the bulk of the material but remains unaltered in the highly inhomogeneous surface and interface regions of the amorphous films. The average intrinsic stress of dense amorphous carbon films can be negligibly small. Still, high average coordination is preserved when compressive conditions locally prevail.

7 illus, 20 ref

005536   Kasap S O (Department of Electrical Engineering, University of Saskatchewan, Saskatoon, S7N 5A9, Canada) : Xerographic measurements for studying localized states in amorphous semiconductors: an overview. Asian J Phys 2000, 9(3), 579-87.

An overview of xerographic measurements as a tool for studying the electrical properties of amorphous semiconductors has been presented. First, the experimental set-up for carrying out xerographic measurements are discussed. Thereafter, the analysis and interpretation of the first cycle residual potential, cycled-up saturated residual potential and dark decay of saturated residual potential are considered and it is shown that such measurements allow deeply localized states in amorphous semiconductors to be probed.

6 illus, 18 ref

005535   Justin Rajesh R;Natarajan T S;Bisht P B (Department of Physics, Indian Institute of Technology Madras, Chennai-600 036) : Computer controlled femtosecond optical delay line for ultrafast optics and spectroscopy. Indian J pure appl Phys 2001, 39(10), 636-9.

Computer controlled optical delay line for experiments in ultrafast laser optics and spectroscopy has been fabricted. Spatial resolution of 0.5 μm and an optical resolution of 16 fs have been obtained from the set up. An ultrafast decay of 50 ps for the relaxation of an organic dye has been recorded using this set up as an example. Fabrication details of this economical and indigenous PC-controlled optical delay line along with the softwere requirement are presented.

5 illus, 1 table, 4 ref

005534   Jha N;Mishra A K;Rafique S M;Singh A N (NO, Rajasthan Vidyapith, Purulia-723 001) : Thermodynamic properties and electrical resistivity of liquid MgZn alloys. Indian J Phys-Pt A 2001, 75(5), 519-23.

Free energy of mixing of MgZn liquid alloy is discussed on the complex formation model. The results for long-wavelength concentration-concentration fluctuations SCC(0), electrical resistivity and thermodynamic activity are presented as a function of concentration. SCC(0) has been further used to obtain the chemical short range order parameter α1. Values of SCC(0) and α1 suggest that segregation-order transformation occurs in the MgZn liquid alloy at around 30 at % of Zn.

3 illus, 1 table, 34 ref

005533   Jai Singh;Shimakawa K (Faculty of Science, Northern Territory University, Darwin, NT 0909, Australia) : Defect formation due to Pairing of holes on covalent bonds in amorphous semiconductors. Asian J Phys 2000, 9(3), 543-50.

Microscopic quantum mechanical model for the mechanism of bond breaking by photo-irradiation is proposed in amorphous semiconductors. It is proposed that the bond breaking occurs as a result of localization of a pair of holes on a covalent bond caused by te strong carrier-lattice interaction. The primary cause of a bond breaking is the optical excitation and not non-radiative recombination.

2 illus, 27 ref

005532   Iakoubovskii K;Adriaenssens G J (Laboratorium voor Halfgeleiderfysica, K.U. Leuven, Celestijnenlaan 200 D, B-3001 Heverlee-Leuven, Belgium) : Stability of some interstitial-related centers in CVD diamond. Asian J Phys 2000, 9(3), 833-9.

Photoluminescence (PL) and transmittance measurements were performed on irradiated CVD films. It is shown that variations in PL with annealing can be due to changes in the non-radiative processes rather than in the concentration of the investigated center. It was found that the intensity of PL from the 3H center increases when the neutral vacany (GRI) anneals out showing that GR1 centers can quench 3H emission. The interstitial-related 3H center was observed in unirradiated films grown at 750°C. A previously undocumented optical center at 2.65 eV is assigned to the distorted TR12 defect. The former shows remarkable temperature stability, being present in films grown at 2100°C.

4 illus, 11 ref

005531   Higazy A A;Khafagy A H;El-Rabie S M;Eid A S (Department of Physics, Faculty of Science, Menoufia University, Shebin El-Koom, Egypt) : Compositional and temperature dependence of elastic constants for Zn(PO3)2. x Nd2O3 glasses. Indian J Phys-Pt A 2001, 75(5), 511-17.

Compositional dependence of the elastic moduli and the attenuation of the longitudinal ultrasonic wave is studied for a series of Nd2O3-ZnO-P2O5 glasses. The density, the ultrasonic wave velocity (longitudinal and shear), the elastic moduli, Poisson's ratio and the ultrasonic attenuation are found to be sensitive to the glass composition. The attenuation of ultrasonic compressional waves in the glasses has been measured over the temperature range from room temperature to 534 K. Twin loss peaks in the attenuation against temperature plots are constant frequency were attributed to a relaxation loss of the standard linear solid type. The properties of the high-temperature relaxation processes are found to be rather sensitive to the glass composition. It is found from this ultrasonic data, that the present glass system can be divided into "three compositional regions". The room temperature ultrasonic measurements are qualitatively interpreted in terms of changes in the coordination number, the interatomic force constant, and the polarizability of the glass network bonds and cations.

8 illus, 1 table, 29 ref

005530   Gurbulak B (Department of Physics, Ataturk University, Faculty of Sciences, 25240 Erzurum, Turkiye) : Optical aborption edge and Urbach tails for Tl_0.995GaPr_0.001Se₂, Tl_0.995 GaPr_0.005Se₂ and TlGaSe₂. Indian J pure appl Phys 2001, 39(10), 647-53.

TlGaSe₂, Tl_0.999GaPr_0.001Se₂ and Tl_0.999GaPr_0.005Se₂ single crystals were grown by the Stockbarger method. The absorption measurements were carried out in these samples in temperature range 10-320 K with a step of 10 K. The phonon energies calculated in TlGaSe₂, Tl_0.999GaPr_0.001Se₂ and Tl_0.995GaPr_0.005Se₂ are 60.0±5, 55.0±5 and 130.0±5 meV respectively. The first defect levels (n=1) have been found as 2.259, 2.235, 2.200 ad 2.149 eV for Tl_0.999GaPr_0.001Se₂ and 2.254, 2.225, 2.189 and 2.149 eV for Tl_0.995GaPr_0.005Se₂ at 10, 100, 200 and 300 K. At 300 K direct band gap of TlGaSe₂ is 2.156 eV, and indirect band gap is 2.075 eV. There are abrupt changes in the Urbach energy peaks for Tl_0.999GaPr_0.001Se₂ at 100 and 200 K, and Tl_0.005GaPr_0.005Se₂ at 200 and 260 K. There is an abrupt change in the σ₀ values for Tl_0.999GaPr_0.001Se₂ and Tl_0.005Se₂ in the temperature range 140-180 K and 220-260 K. These temperatures obtained from the changing of Urbach energy and σ₀ values may be phase transition temperatures.

8 illus, 23 ref

005529   Gupta C S (NO, College of Health Sciences, Ministry of Health, P.O. Box-12, State of Bahrain) : Decay and TL-glow curves of CaS:Er and CaS:Cu phosphors. Indian J Phys-Pt A 2001, 75(5), 535-40.

Phosphorescence decay characteristics of CaS:Er and CaS:Cu are studied at room temperature to gather information about the type of kinetics involved, decay low, the trap distribution, trap depth; and the thermoluminescence studies to determine the role of activators on the trapping states. The trap depths calculated using Randall & Wilkins Equation. Curies Formula also by Urbach Relation for thermoluminescence (TL) found to be in close consonance with that calculated by peeling off the log I - t (decay) curves, justify the validity of the equation p = S exp (-E/kT), which neglects re-trapping. Results reveal that phosphorescence decay follows the hyperbolic relation I = I0t^-b and explained on the basis of superposition theory by assuming the kinetics to be monomolecular.

7 illus, 2 tables, 17 ref

005528   Fornasini P;Rocca F (Dipartimento di Fisica dell'Universita di Trento and Istituto Nazional, , I-38050 Povo (trento) Italy) : X-ray absorption spectroscopy: characterization of thermal and structural disorder. Asian J Phys 2000, 9(3), 569-78.

EXAFS is very sensitive to thermal and structural disorder. Suitable analysis procedures, like the one based on the cumulant expansion, must be implemented to get reliable values of physical parameters. A careful characterization of disorder allows to get original information on the correlation of vibrational motion in crystalline solids. In non-crystalline solids the behaviour of cumulants can monitor the different degrees of static disorder as a function of composition and preparation procedures. Some results recently obtained on both crystalline and amorphous materials are presented.

4 illus, 21 ref

005527   El-Hassan S A (Faculty of Science, Physics Department, Benha University, Benha, Egypt) : Electrical properties of some chalcogenide glassy alloys of the system Se_100-x In_x. Indian J pure appl Phys 2001, 39(10), 661-7.

DC electrical properties of the system Se_100-x In_x (where x = 5, 10, 15 and 20 at. %) have been carried out. I-V characteristics of this system are discussed in terms of Pool-Frenkel and Schottkey effect. The jump distance (d), charge carrier concentration (n) and the trap depth (ϕ) have been deduced for the system. According to Arrhenius Eq. of conductivity, the activation energy of conduction ΔW₁ and Δw₂ for the two arms of conductivity have been found in the range from 0.18 to 1.2 eV. Both of mobility (μ) and diffusion coefficients are calculated for different compositions at different ambient temperatures. The activation energy due to mobility (ΔU) and diffusion (ΔQ) mechanisms have been deduced and their values were ranged from 0.02 to 0.4 eV. The behaviour of ΔW₁, ΔU and ΔQ has the same trend with composition, which indicate that the conduction mechanism is controlled by one type of process. Meyer-Neldel rule has been applid on our results and a confirmation of this rule has been found.

6 illus, 4 tables, 39 ref

005526   Duverger C;Bouazaoui M;Douay M;Ferrari M; Turrell S (NO, Laboratoire de Spectrochimie Infrarouge et Raman, CNRS, UPR 2631L Bat C) : Structural Studies of the photosensitivity of sol-gel derived SiO₂-GeO₂:Eu<. Asian J Phys 2000, 9(3), 731-6.

Raman and Eu³⁺ fluorescence spectroscopies have been used to investigate the effects of UV-laser insolation on sol-gel-derived GeO₂-SiO₂:Eu³⁺ planar waveguides. The Raman data have shown that UV irradiation leads to a structure possessing a larger percentage of smaller rings and to the formation of Ge-OH linkages. Using Eu³⁺ as a probe, luminescence spectroscopic results have shown that this laser insolation results in a densification process, by which the rare-earth ions end up being located in a smaller number of sites with a decreased average distortion. A decrease in the Eu-O covalency has also been observed.

4 illus, 20 ref

005525   Deshamukhya A;Choudhury D K (Department of Physics, Gauhati University, Guwahati-781 014) : Asymptotics and corrections to asymptotics of non-singlet structure function at low x. Indian J Phys-Pt A 2001, 75(5), 573-7.

Uniqueness of t-evolution (t = log (Q²/A²) of non-singlet functions at low x obtained from DGLAP equations. Dependence of asymptotics on boundary conditions are also discussed.

^ssc1 illus, 23 ref

005524   Cristofolini L;Fontana M P (INFM and Department of Physics, University of Parma, Parco Area delle Scienze 7/A, 43100 Parma, Italy) : Vibrational properties and phase transitions in lithium doped fullerides. Asian J Phys 2000, 9(3), 609-20.

Investigations on the structure of the heavily doped fulleride Li₁₂C₆₀, as determined by high resolution XRD, and on the dynamics of both the C₆₀ units and the Li ions, as it emerges from a variety of experimental techniques: ¹³C and ⁷Li NMR, Raman scattering and Quasielastic neutron Scattering. The emerging picture is that Li₁₂C₆₀ at high temperature has the same FCC structure and the same dynamical features as pure C₆₀ with the only difference being the localised Li diffusion within the octahedral void of the C₆₀ structure. As the temperature is lowered, Li diffusion is hindered and a structural transition is induced to a phase of lower than cubic symmetry, which is characterised by the disappearance of the overall C₆₀ librations and the Li diffusion, as well as by a broadening of the localised molecular excitations of C₆₀ detected by QENS.

7 illus, 1 table, 26 ref

005523   Choudhary S N;Prasad K;Choudhary R N P (University Department of Physics, T.M. Bhagalpur University, Bhagalpur-812 007) : Structural and dielectric properties of KTiOPO₄ ceramic. Indian J Engng Mater Sci 2001, 8(5), 289-91.

Ceramic samples of KTiOPO₄ are prepared using chemical method. X-ray diffraction (XRD) technique has been used to check the formation of single phase KTiOPO₄ compound. The cell parameters obtained by XRD analyses are a = 20.125(8) Angstrom, b = 8.433(1) Angstrom and c = 11.492(4) Angstrom in orthorhombic crystal system. The ceramic samples of KTiOPO₄ have been characterized by dielectric studies. The room temperature values of dielectric constant and dielectric loss are found to be 10.32 and 0/12 respectively at 1 kHz.

2 illus, 1 table, 27 ref

005522   Chandola H C;Pandey H C;Yadav D (Department of Physics, Kumaun University, Nainital-263 002) : Flux tube structure of dual QCD and confinement. Indian J Phys-Pt A 2001, 75(5), 561-7.

Study of a dynamical model for analyzing the mechanism of color confinement in QCD has been undertaken and the flux tube structure of the resulting dual gauge theory has been investigated. Using the magnetic symmetry of QCD and the fibre bundle formulation of dual QCD, the topological charges have been shown to lead a unique dual dynamics in QCD, which has its immediate implications in non-perturbative regime. Such dynamics is then shown to derive the magnetic condensation in QCD vacuum by the dynamical breaking of magnetic symmetry which, in strong coupling limit, is shown to impart a unique flux tube structure to the QCD vacuum by generating a state of magnetic (dual) superconductivity. Flux tube energy computation has been used to analyze the QCD vacuum response in different energy sectors and the appearance of the confinement forces at large hadronic distance has been demonstrated. The analysis of the large scale behavior of QCD flux tube solutions has been used to compute the various confinement parameters in terms of different length and mass scales of dual QCD.

26 ref

005521   Bustarret E;Quiroga J M (Laboratoire d'Etudes des Proprietes Electroniques des Solides, CNRS, , BP166X, F-38042 Grenoble 9, France) : Optical properties of non-ideal a-Si:H/ a-SiO₂ multilayers. Asian J Phys 2000, 9(3), 671-9.

Optical absorption and photoluminescence emission by PECVD-deposited amorphous silicon wells separated by SiO₂ barriers were measured and simulated on the basis of a realistic model for the composition depth profile. This profile resulted from a physico-chemical study concluding to the chemical modification of the previous layer by the plasma during the deposition of the following layer. As the thickness of the a-Si:H was reduced below 2 nm, the apparent increase of the extrapolated optical gap was shown to overestimate that of the minimum energy gap so that this increase and the observation of a photoluminescence emission peak around 750 nm at room-temperature could be interpreted without referring to quantum confinement effects.

7 illus, 33 ref

005520   Boolchand P (Department of Electrical, Computer Engineering and Computer Science, University of Cincinnati, Cincinnati, OH 45221-0030, USA) : Maximum in glass transition temperature (T_g) near x = 1/3 in Ge_xSe_1-x glasses. Asian J Phys 2000, 9(3), 709-21.

Result of Raman scattering, Mossbauer spectroscopy and T-modulated Differential Scanning Calorimetry experiments on Ge_xSe_1-x glasses are reviewed. The molecular origin of the maximum in T_g near x=1/3 or mean coordination R^-=2(1+x)=2.67, suggested by these experiments, implies that a nanoscale phase separation of the glass network takes place into Se-rich (A) and Ge-rich (B) molecular clusterrs. Phase separation on a molecular scale initiates at x <62> 0.31, and the B phase becpomes the dominant one for x <62>0.35. In particular, in contrast to α- and β-crystalline GeSe₂, stoichiometric GeSe₂ glass is neither chemically ordered nor a continuous network. In ternary Ge_xAs_ySe_1-x-y glasses at x-y, such nanoscale phase separation is apparently suppressed by chemical alloying As for r^- up to 3.0 and T_gs are found to increase continuously with r^-.

7 illus, 36 ref

005519   Bhuyan H;Mohanty S R;Borthakur T K (Centre of Plasma Physics, , Dispur, Guwahati-781 006) : Analysis of nitrogen ion beam produced in dense plasma focus device using Faraday Cup. Indian J pure appl Phys 2001, 39(11), 698-703.

Nanosecond response Faraday Cup was fabricated and employed to characterize pulsed ion beam of a 2.2 kJ Mather type Dense Plasma Focus Device. The Faraday Cup operating in bias ion collector mode was used to determine the energy spectrum and flux of fast nitrogen ion beam along the electrode axis (0⁰) of the device. It has been possible to register the ion energy up to a lower kinetic energy threshold of <126> 7 keV which is a value much lower than that obtained in any previous works. The correlation of the ion beam intensity with filling gas pressure is also reported.

7 illus, 20 ref

005518   Bansal A K;Singh P J;Sharma K S (Department of Physics, MSJ College, Bharatpur-321 001) : Microwave dielectric measurements in different varieties of rapeseed-mustard seeds in powder form. Indian J pure appl Phys 2001, 39(12), 799-803.

Effect of packing density on dielectric parameters, relaxation time and conductivity of three different varieties of rapeseed-mustard seeds in the form of powders has been studied at x-band (8.93 GHz) microwave frequency. Experimental results on powders of different relative packing fraction (δr) have been used to obtain transformation to 100% solid bulk using correlation formulae of Landau-Lifshitz-Looyenga and Bottcher. In case of seed grains like rapeseed-mustard where it is not possible to define solid bulk exactly, the authors have assumed the finest crushed closely packed assembly of the seed grains as solid bulk for the comparison of these correlation formulae between powder and solid bulk. This assumption works well as there is fair agreement between the calculated values of dielectric parameters and the values obtained experimentally of solid bulk. Appreciable agreement between the experimentally obtained values and the theoretical values obtained by Bottcher's and Landau-Lifshitz-Looyenga's formulae shows large cohesion in the particles of rapeseed-mustard powders under investigation, serving as a continuous medium.

3 tables, 14 ref

005517   Ashok Kumar;Naithani U C;Semwal B S (Department of Physics, Garhwal University, Pauri Campus, Pauri (Garhwal)-246 001) : Sound attenuation in BaxSr1-x TiO3 perovskites. Indian J pure appl Phys 2001, 39(12), 781-8.

Expression is obtained for the sound attenuation constant in anharmonic BaxSr1-xTiO3 ferroelectric crystal, using double-time temperature dependent Green's function technique. The mass and force constant changes due to impurity atoms, are taken into account in the Silverman-Joseph Hamiltonian augmented with higher order anharmonic terms. The defect and anharmonic contributions to the attenuation constant are discussed separately. An anomalous increase in attenuation constant is predicted in the vicinity of Curie temperature. The soft mode is held responsible for this effect. The effect of defect and anharmonicity on stabilization of the soft mode frequency is also studied. With addition of defect (concentration x) in BaxSr1-xTiO3, the soft mode frequency continuously decreases and hence the attenuation constant (α) increases.

2 illus, 2 tables, 31 ref

005516   Anil Kumar;Kalra E;Bose S;Singh A;Bindra S; Haldar S;Gupta R S (Semiconductor Devices Research laboratory, Department of Electronic Sc, South Campus, University of Delhi, New Delhi-110 021) : Analytical model for saturation drain current and substrate current of fully overlapped LDD MOSFET. Indian J pure appl Phys 2001, 39(11), 731-7.

Analytic model for saturation drain current and substrate current of fully overlapped lightly doped drain (FOLD) MOSFET is developed using pseudo-two-dimensional approximation in the channel and drain regions and expression of maximum electric field is obtained. An expression for chennel length modulation factor is also developed and the substrate current is calculated.

4 illus, 14 ref

005515   Anand P P;Singh R;Agarwal V K;Bahadur B (Physics Department, Meerut College, Meerut) : Optical study of some nematic mixtures. Indian J pure appl Phys 2001, 39(11), 752-4.

Optical birefrigence study of four multicomponent nematic mixtures E-80, E-90, E-100 and E-110 (all from E. Merck), were carried out, providing information about their transition temperatures and microscopic order parameter (S).

^ssc3 illus, 8 ref

005514   Alvarez-Garcia J;Morante J R;Perez-Rodriguez A;Romano-Rodriguez A;Calvo-Barrio L;Scheer R;Klenk R;Neisser A (Lab. Enginyeria i Materials Electronics (EME), Unitat Associada CNM-CS, Universitat de Barcelona, C. Marti i Franques 1, 08028 Barcelona, Spain) : Raman scattering from CuInS₂ and Cu(InGa)S₂ thin films. Asian J Phys 2000, 9(3), 809-21.

Reports the spectral characterisation of CulnS₂ and Cu(In_xGa_1-x) S₂ polycrystalline thin films for solar cell devices by Raman scattering. The Raman spectrum from CuInS₂ shows a dominant A₁ Raman mode at about 290 cm^-1, which serves as the main spectral feature of the mode (position, width), sensitive to the structural quality of the films. Besides, films grown under conditions leading to low structural quality (such as Cu deficiency or low temperature of deposition) show additional peaks at 60 cm^-1 and 305 cm^-1in the spectra. Polarisation measuremens performed in epitaxial films show that the 305 cm^-1 mode has the same symmetry as the A₁ peak. The origin of the dominant 305 cm^-1 mode is discussed taking into account the similar behaviour from the better known CuInSe₂ system. On the other hand, the Raman spectrum from the Cu(InGa)S₂ quaternary alloy is characterised by the presence of both A₁ peaks from CuInS₂ and CuGaS₂ crystals, the spectral features of both modes being similar to those from the parent lattices. In-depth measurements performed on polycrystalline samples grown by sequential evaporation of metal precursors and sulphurisation, reveal the formation of an inhomogeneous structure of CuInS₂ and CuGaS₂ regions in the front and rear surface, respectively.

10 illus, 18 ref

005513   Ali S (NO, Shadan College of Engineering and Technology, Peerancheru, Hyderabad-500 008) : Studies on steady plane gas flows. Appl Sci Period 2001, 3(1), 46-53.

Studies flow fields for two dimensional steady gas flows, assuming the Streamlines as confocal conic section and system of co-axial circles. The sonic regions have been identified and the flow parameters are characterised.

4 illus, 5 ref

005512   Ajay Kumar;Baldev Singh;Surinder Singh (Department of Physics, GND University, Amritsar-143 005) : Uranium, radium and radon exhalation studies in some soil samples from Una district, Himachal Pradesh, India using track etching technique. Indian J pure appl Phys 2001, 39(12), 761-4.

LR-115 plastic track detectors have been used for the measurement of radon exhalation rate and radium concentration in soil samples collected from some villages of Una District, Himachal Pradesh, India. Uranium concentration has also been determined in these samples using 'Fission Track Technique'. Uranium concentration in soil sample has been found to vary from 1.07 to 2.47 ppm whereas radium concentration varies from 3.10 to 12.41 Bq/kg. The radon exhalation rate in these samples varies from 126.19 to 506.76 mBqm^-2hr^-1 (3.81 to 15.24 mBqkg^-1hr^-1). A good correlation has been observed between radon exhalation rate and uranium concentration in the soil samples.

1 illus, 1 table, 16 ref

005511   Abdullah A A;Radhi R A;Dakhil Z A (Department of Physics, College of Science, University of Baghdad, Jadiriyah, Baghdad, Iraq) : Elastic magnetic M1 form factor of <. Indian J Phys-Pt A 2001, 75(5), 579-82.

Elastic magnetic M1 electron scattering form factor has been calculated for the ground state J^{π, T = 1/2, 1/2 of 13C using the Cohen-Kurath interaction. The results of a shell-model calculation which uses the 1p-shell and (1p - 2p) - shell model spaces are compared with the available experimental data. Effective one-body transitions are used to reproduce the measured magnetic moment. Meson exchange currents are included which show same q-dependence as the one-body terms with minor contribution. The data are reasonably explained up to q-3.5 fm-1 when the size parameter of the harmonic oscillator potential is reduced from that used to fit the root mean square charge radius.}

^ssc2 illus, 18 ref

003289   Uddin M S;Miah R U;Latif S K A;Islam M N; Zaman M R;Zaman M A;Molla N I (NO, Institute of Nuclear Science and Technology, AERE, Savar, G.P.O. Box-3787, Dhaka, Bangladesh) : Excitation functions of (n,p) and (n,α) reactions on the isotopes of vanadium and cobalt in the neutron energy range of 13.57-14.71 MeV. Indian J pure appl Phys 2001, 39(8), 487-90.

Excitation functions of the reactions ⁵¹V(n,α)⁴⁸Sc, ⁵⁹Co(n,α)⁵⁶Mn and ⁵⁹Co(n,p)⁵⁹Fe have been measured by activation technique using high resolution HPGetector γ-ray spectroscopy. Monoenergetic neutrons were produced via D-T reaction at J-25 neutron generator facility of the Institute of Nuclear Science and Technology, AERE, Savar, Dhaka, Bangladesh. Monitor Reaction ²⁷Al(n,α)²⁴ Na was used to determine neutron flux at different energy position in the range 13.57-14.71 MeV. The measured cross section values along with the literature data have been plotted as a function of neutron energy to get the excitation functions of the reactions. Model calculations using statistical code SINCROS-II was performed to validate the experimental data theoretically.

3 illus, 3 tables, 10 ref