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Notes: An inhomogeneous laminar conductor model developed earlier has been applied to glasses in the system Na2O-GeO2. Detailed modulus spectra have been measured for glasses containing 10–20 mol % Na2O. The experimental data are in satisfactory agreement with the theoretical values as obtained by this model.

Notes: Composite materials containing conducting polypyrrole and insulating poly (vinyl methyl ether) (PVME) have been synthesized by oxidative polymerization of pyrrole in ethanol using FeCl3 oxidant in the presence of PVME. The ac conductivity measurements have been carried out in the frequency range of 100 Hz to 10 MHz and in the temperature range of 110 to 350 K. The frequency dependent conductivity has been explained on the basis of a small polaron tunnelling mechanism. © 1997 American Institute of Physics.

Notes: Highly conductive phosphorus-doped n-type hydrogenated microcrystalline silicon (μc-Si:H) films have been prepared by the usual (13.56 MHz) radio-frequency glow discharge of silane (SiH4), phosphine (PH3), and hydrogen (H2) in an ultrahigh-vacuum deposition system. The highest conductivity of the films obtained in this study is 100 S cm−1 after optimizing the hydrogen dilution ratio, chamber pressure, substrate temperature, and doping concentration of phosphorus. The formation of microcrystallinity in the material has been studied by transmission electron microscopy, x-ray-diffraction studies, and Raman spectroscopy. The volume fraction of microcrystallinity in these amorphous-microcrystalline mixed-phase materials has been estimated from Raman spectra. Sizes of the crystallites and volume fraction of microcrystallinity vary with hydrogen dilution, chamber pressure, and substrate temperature. The variations in the properties with deposition parameters have been explained in terms of the growth kinetics. The n-type μc-Si:H thin film, thus developed, has been applied in the first cell of a double-junction amorphous silicon solar cell. The prepared p-i-n–p-i-n stacked cell employing the n-type μc-Si:H film has exhibited appreciable improvement in open-circuit voltage, fill factor, and efficiency compared to the one with amorphous n layer in the inner n–p contact. Degradation of the cells prepared with and without μc-n layer has been studied. © 1995 American Institute of Physics.

Notes: A collective laser light scattering diagnostic ALTAIR (a french acronym for local analysis of anomalous transport using infrared light), using a CO2 laser beam (λ=10.6 μm) has been realized to measure plasma density fluctuations in the TORE SUPRA tokamak. This article describes in detail the optical setup, the signal processing, acquisition, and control systems required for this experiment. As the density fluctuations propagating in tokamaks have small wave numbers and require small scattering angles, such scattering experiments are considered as having no resolution along the beam. However, taking advantage of the pitch angle variation of the magnetic field lines around the magnetic axis along a vertical chord, it has been possible to obtain partial spatial localization of the scattering volume by rotating the direction of the analyzed wave vector in a horizontal plane. Heterodyne detection is used to determine the fluctuations propagation direction. The experiment has been tested on acoustic waves and the first results obtained on TORE SUPRA indeed show the existence of a spatial resolution.

Notes: An electronic hardware has been developed for the real time determination of the position of the plasma column in the SINP tokamak. The method is based on the Fourier integration of the poloidal magnetic field using cos θ and sin θ coils. The spurious pickups in these coils due to time varying magnetic fields have been explained by a model as being due to eddy currents in the vacuum vessel and the conducting shell. These pickups have been compensated in the hardware by simulating the effects of the eddy currents by linear networks. This diagnostic provides outputs proportional to the horizontal and vertical displacements of the plasma column at three toroidal locations simultaneously. An output proportional to the plasma current is also available. Performance evaluation shows that for both plasma current and displacements, the hardware outputs are in good agreement with the values computed by software. © 1998 American Institute of Physics.

Notes: Plasma diamagnetism has been measured in the SINP tokamak by a toroidal flux loop placed inside the vacuum vessel. The flux due to the strong toroidal field has been compensated for by a coplaner annular loop which encircles but does not contain the plasma column. The influence of the eddy currents in the vacuum vessel and the conducting shell in these loops has been calculated analytically by a circuit model using the theory of linear networks and compensated accordingly. This method has been shown to yield an almost exact compensation for toroidal flux (∼0.01%) as well as pickups from other fields. Typical results with plasma shots have been presented. © 2001 American Institute of Physics.

Notes: Temperature- and field-dependent electroluminescence and quantum efficiency have been investigated in tris-(8-hydroxy) quinoline aluminum (Alq3) light-emitting diodes over the temperature range from 10 to 300 K. At lower applied voltage, two peaks have been observed in the quantum efficiency with temperature. The two peaks are attributed to the deep trap levels (high-temperature regime) and shallow trap levels (low-temperature regime) in Alq3. With increasing voltage, the high-temperature peak shifts toward lower temperature but no significant shift of the low-temperature peak is observed. At voltage around 10 V, superposition of two peaks causes the apparent saturation in the low-temperature regime of the quantum efficiency. © 2001 American Institute of Physics.

Notes: The microstructural dependence of electrical properties of (Ba, Sr)TiO3(BST) thin films were studied from the viewpoint of dc and ac electrical properties. The films were grown using a pulsed laser deposition technique in a temperature range of 300 to 600 °C, inducing changes in grain size, structure, and morphology. Consequently, two different types of films were realized, of which type I, was polycrystalline, multigrained, while type II was [100] oriented possessing a densely packed fibrous microstructure. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. The results revealed a contribution from both electronic and ionic conduction. In the case of type I films, two trapping levels were identified with energies around 0.5 and 2.73 eV, which possibly originate from oxygen vacancies VO¨ and Ti3+ centers, respectively. These levels act as shallow and deep traps and are reflected in the current–voltage characteristics of the BST thin films. The activation energy associated with oxygen vacancy motion in this case was obtained as 1.28 eV. On the contrary, type II films showed no evidence of deep trap energy levels, while the identified activation energy associated with shallow traps was obtained as 0.38 eV. The activation energy obtained for oxygen vacancy motion in type II films was around 1.02 eV. The dc measurement results were further elucidated through ac impedance analysis, which revealed a grain boundary dominated response in type I in comparison to type II films where grain response is highlighted. A comparison of the mean relaxation time of the two films revealed three orders of magnitude higher relaxation time in the case of type I films. Due to smaller grain size in type I films the grains were considered to be completely depleted giving rise to only grain boundary response for the bulk of the film. The activation energy obtained from conductivity plots agree very well with that of dc measurements giving values 1.3 and 1.07 eV for type I and type II films, respectively. Since oxygen vacancy transport have been identified as the origin of resistance degradation in BST thin films, type I films with their higher value of activation energy for oxygen ion mobility explains the improvement in breakdown characteristics under constant high dc field stress. The role of microstructure in controlling the rate of degradation is found useful in this instance to enhance the film properties under high electric field stresses. © 2000 American Institute of Physics.

Notes: MnBi crystallizes in a NiAs-type hexagonal crystal structure, exhibits a high uniaxial anisotropy, and is potentially useful as a permanent magnet material. We have examined the effect of partial substitution of Bi with rare earth elements on the magnetic properties of MnBi. MnBi1−xRx (R=Nd, Dy) were prepared by mechanically alloying powders of the constituent elements at liquid nitrogen temperature followed by heat treatment. X-ray diffraction and magnetic measurements were performed on powder samples to characterize the samples. We found that in MnBi1−xNdx, coercivity (at room temperature) increases from 0.7 kOe to 6.6 kOe for x=0.0 and 0.3, respectively. In MnBi1−xDyx the coercivity increases from 0.7 kOe to 7.9 kOe for x=0.0 and 0.3. The increase in coercivity may be in part due to the increase in the crystal field anisotropy as Nd or Dy is introduced and in part due to the finer particle size. A magnet made from MnBi shows coercivity of ∼17 kOe. A very fine particle size is considered to be the reason for this high coercivity. © 2000 American Institute of Physics.

Notes: The effect of using bilayer Ni/Al-1%Cu or Co/Al-1%Cu metallization stacks with regard to hillock formation is investigated in this study and compared to hillock suppression capabilities of Al-1%Si and Al-1%Cu single layer films and Ti/Al-1%Cu bilayer metallization stacks. Various heat treatments during and immediately after depositions were used to study the resistances of different metallization stack specimens to hillock formation. The densities and sizes of hillocks were characterized using scanning electron microscopy and atomic force microscopy, while interfacial reactions between the transition metal layer and Al-1%Cu in the metallization stack were examined using glancing angle x-ray diffraction. Resistivities of the bilayer metallization stacks were characterized using conventional four-point probe measurements. Our studies indicate that metallization processes involving bilayer metallization stacks of nickel and cobalt with Al-1%Cu are more robust compared to those involving titanium with Al-1%Cu. The mechanism of hillock formation is analyzed in light of intermetallic compound formation and stress-strain considerations. © 1999 American Institute of Physics.