Spinel ferrites of composition Ni0.5Zn0.5Fe2O4 were prepared by coprecipitation. Different grain size and grain size distributions were obtained by various heat treatments. Their electrical properties were investigated by impedance spectroscopy in the temperature range 25-200°C and in the frequency range of 5Hz-13MHz. A decrease in resistivity was observed as grain size increased, which can be explained by an increase in the mean free path of electrons. Cole-Cole plots showed two well-resolved semicircles for samples with a narrow grain size distribution. As the width of the distribution increased, the semicircles exhibited a deformation and eventually became unresolved. These results are interpreted on the basis of a distribution of time-constant of the impedance response, associated with the grain size distribution.

The purpose of this research is to improve GaAs yield and enhance the reliability of GaAs MMICs (Monolithic Microwave Integrated Circuits) by first understanding the physical mechanisms of GaAs, Ni,Au-Ge eutectic and Au alloying process. Ohmic ooze has been driving force for this research. Variety of innovative experiments has been designed, so that contact resistance may be guaranteed to be within the permissible range. This resulted into the development of analytical techniques to measure contact resistance to GaAs as a result of alloying process employing Ni,Au-Ge and Au.

Epitaxial growth of dielectric layers on silicon substrates has attracted a great deal of recent interest given their potential applicability in the fabrication of high quality silicon-on-insulator (SOI) structures, high density capacitor devices, and stable buffer layers between silicon and other materials. Cerium dioxide (CeO2) appears to be a particularly attractive candidate, given its high dielectric constant and its compatibility with Si. To date, measurements of the electrical properties of CeO2 films on Si have been largely limited to room temperature. In this study, thin films of CeO2 were prepared by in situ pulsed laser deposition (PLD) on n-type (100) silicon substrates, with varied deposition conditions. Capacitance-voltage measurements (C-V) were used to characterize the response of the Pt/Si/CeO2/Pt MOS capacitor structure. Impedance measurements were performed from room temperature to 350°C. This enabled the independent characterization of the electrical signature of the Pt/Si interface which was found to contribute insignificantly above approximately 150°C. The CeO2 film conductivity was found to be thermally activated with activation energy of ∼0.45 eV, with its magnitude strongly dependent on film microstructure.

Rhodium and iridium are refractory metals which possess intrinsically high electrical conductivity, and their chemical inertness enables their use at relatively high temperatures in microelectronics. However, due to the high Young's modulus of these materials, a residual tensile stress of hundreds of MPa is measured in evaporated thin films. New data is presented, demonstrating control over both the magnitude and the sign of the residual stress in such refractory thin films formed by means of ion-beam-enhanced physical vapor deposition on oxidized Si substrates. The electrical resistivity and stress are determined by controlling the substrate temperature, deposition rate and ion beam parameters. Thicker films are achieved in this manner, including films with near-zero residual stress.

We have induced, measured, and modeled the β - α' martensitic transformation in a Pu-Ga alloy by a resistivity technique on a 2.8-mm diameter disk sample. Our measurements of the resistance by a 4-probe technique were consistent with the expected resistance obtained from a finite element analysis of the 4-point measurement of resistivity in our round disk configuration. Analysis by finite element methods of the postulated configuration of α' particles within model σ grains suggests that a considerable anisotropy in the resistivity may be obtained depending on the arrangement of the α' lens shaped particles within the grains. The resistivity of these grains departs from the series resistance model and can lead to significant errors in the predicted amount of the α' phase present in the microstructure. An underestimation of the amount of α' in the sample by 15%, or more, appears to be possible.

The evolution of deep levels that depend upon annealing temperature is investigated for n-type 4H SiC-Ni Schottky barriers. Several samples, cut from the same wafer, have been left unheated or annealed at 400°C, 700°C and 900°C, in air. Deep level transient spectroscopy (DLTS) has been used to investigate deep levels in all four sets of samples. Electron traps with activation energies EC-ET = 0.19 to 0.5 eV are observed, as well as a hole trap in the sample annealed at 900°C at energy ET-EV = 0.14 eV.

Diamond-Like Carbon (DLC) was gradually converted to the disordered graphite by means of heat-treatment (HT). According to Raman spectroscopy and x-ray diffraction (XRD), the disorder nature of the structure is modified from atomic scale sp2/sp3 disorder to disordered sp2-domain network by the migration of sp3-defects induced by HT at temperatures 200 - 400°C. The structural change increases conductivity and modifies the hopping conduction mechanism at low temperatures. The slight positive thermoelectric power for samples with graphitic domains is suggestive of carrier compensation by the competition of hole and electron carriers that originates from the inhomogeneous charge distribution caused by the difference of Fermi levels among the sp2-domains.

A determination method of the local surface space charge density in thin films on semiconductor surfaces is described. In this method, the displacement current and the tunneling current flow periodically in accordance with the perpendicular vibration of the probe of the scanning tunneling microscopy (STM). The external circuit current is separated into the mean displacement current and the mean tunneling current by using the two-phase lock-in amplifier. The displacement current-probe voltage curve of a p-type silicon with a native oxide layer was measured in a vacuum (>3×10−9 torr). The displacement current-voltage curve has been analyzed taking into account surface space charge. The theoretical displacement current-voltage curve has been fitted to the measurement in order to obtain both the local surface space charge density and the surface potential difference of thin films, and the theory is in good agreement with the measurement in both voltage regions where the majority carriers are accumulated and depleted. We also demonstrate a simple determination method of both the surface space charge density and the surface potential difference of thin films from flat-band conditions in the displacement current-voltage curve.

In the two-junction system of the scanning vibrating probe/ Au dot / vacuum / Si structure, theoretical equations of both the displacement current waveform iD(t) and the mean displacement current ID(VP) due to Coulomb blockade are analyzed by using the orthodox theory. By usingtheoretical iD(t), the single electron motion on a Coulomb island in a period of probe vibration isexplained. Experimental ID(VP) curves due to Coulomb blockade under a constant probe voltage VP clearly show the displacement current staircase and are in good agreement with the theoretical ID(VP) curve. By using this method, the average number of quantized electrons on Au dots is directly measured through the displacement current staircase.

Broadband dielectric spectroscopy has been applied for investigations of the dynamic behavior of liquid crystals (LCs) confined in porous matrices with random pores as well as in parallel cylindrical pores. We observed deep supercooling of LC in random pores. The relaxation times of the process due to the molecular rotation in deeply supercooled state are slower than at the temperatures corresponding to nematic phase by a factor of 106. This slowing down is accompanied by anomalous broadening of the dielectric spectra. For LC confined in cylindrical pores with homeotropic orientation on the pore walls we have investigated the relaxation of the librational mode. The dynamics of this mode is different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependencies of relaxation times of the librational mode needs the involvement of the temperature dependence of orientational order parameter. The investigations of the relaxation in thin LC layers formed on cylindrical pore walls show that the process due to rotation of molecules around their short axis (with single relaxation time for bulk LC) is the process with a distribution of relaxation times in thin layers and this process broadens with decreasing thickness of the layers.

In this study, the quality of thin film diode (TFD) as a switching device for active-matrix liquid-crystal-displays (AM-LCDs) was enhanced by low temperature annealing conditions with high reliability and good electrical properties. Device was composed with Ta as bottom electrode, anodic Ta2O5 as insulator layer and top electrode. Two types of material such as Ti and Cr were evaluated as a top electrode of the TFD device to optimize the symmetry of current-voltage characteristic curve, respectively. The annealing was done at low temperature conditions below 350°C. The low temperature annealing improved the TFD device with nearly perfect symmetry under high electric field.

A study was made of the relationship between the microstructure and electrical properties of the bulk ferroelectric composite materials: (100-x) wt% Ba0.55Sr0.45TiO3-x wt% MgO. The ferroelectric composites (x= 40, 60) were fabricated by dry pressing from two powder precursors: 1) Ba0.55Sr0.45TiO3 (BST) calcined in the solid state with sol-gel MgO (Sg-MgO), and 2) hydrothermal BST and MgO calcined in the solid state. The pellets were sintered at 1250, 1350 and 1450°C. The sintered microstructure, chemistry, and phase with crystallinity was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD), respectively. The density and porosity were determined by the Archimedes technique. Dielectric properties of permittivity and loss tangent were characterized by the parallel plate capacitor method.

Abstract:The films of colossal magnetoresistive La0.67Ca0.33MnO3 (LCMO) and ferroelectric SbSI were grown by pulsed laser deposition method for fabricating their heterostructures. By varying the processing conditions during film growth and controlling subsequently the annealing conditions, the resistivity transport properties of the LCMO films could be greatly modified. Preliminary tests on the ferroelectric field effect transistor (FeFET) based on LCMO-SbSI heterostructure showed that the device behaves like a nonvolatile memory element. The FeFET showed a maximum channel modulation of ∼10% at room temperature, and the switching voltage was less than 2 V.

The lack of surface states within the band gap of the perfect Si(100)2x1:H surface opens the way to scanning tunneling microscopy studies of dopant atom sites in Si(100). In this paper, Boron and Arsenic induced features are studied by ultrahigh vacuum scanning tunneling microscopy. The values of their amplitudes naturally group such that several subsurface layers can be identified. This technique for producing atom-resolved three-dimensional maps of electrically active dopants in silicon may be a useful metric for characterizing dopant profiles in ultra-small electronic device structures.

Local electrochemical impedance mapping and spectroscopy (LEIM/S) have become important tools for the investigation of local electrochemical breakdown events associated with the degradation of organically coated metals in aqueous environments. LEIM/S of organic coated metal substrates has revealed local degradation events that are distributed spatially and temporally. These observations provide support to a number of long-standing theories, as well as provide new insight into the damage process. The local changes in impedance observed at early stages of immersion support the presence of virtual pores, while the metastability of impedance peaks representing the local changes provide evidence of healing via corrosion product formation. Each of these are long-standing theories used to explain global electrochemical impedance measurements. This paper will provide an overview of some of the events observed using LEIM and examine these results in the context of recent analytical and numerical models. Models used to predict the electric field above an equipotential disk electrode support the interpretation of most experimental LEI data as being representative of chemical and physical phenomenon and not a result of measurement artifact. However, certain features may be an artifact of the finite nature of the experimental process. The interpretation of LEIM events in view of current experimental and modeling results will be discussed.

FT-IR spectra from Li(AlxCo1-x)O2 (x=0.1-0.5) are reported. It was found out that there are four peaks located at 556cm−1, 601cm−1, 1438cm−1, 1498cm−1. First two peaks at 556cm−1 and 601cm−1 can be assigned to A2u and Eu vibration modes, respectively. The other two new peaks at 1438cm−1 and 1498cm−1 can not be explained clearly. With the increasing of Al concentration, all peaks position remain unchanged. However a relative change in the intensity of A2u and Eu peaks was observed.

The opportunity of the charge-based deep level transient spectroscopy (Q-DLTS) for study of the structures based on wide bandgap semiconducting and insulating materials such as diamond and Al2O3 was demonstrated. Using our isothermal Q-DLTS method with rate window (tm)scanning we obtained information about concentration, activation energy and capture cross-section of the native and extrinsic electrical active defects - trapping centers (TC) in slightly boron-doped polycrystalline diamond, diamond single-crystal and in the structures Al2O3 film on NiFe and Si substrates. In comparison with widely used capacitance-based deep level transient spectroscopy, Q-DLTS gives one possibility to investigate the structures in which a capacitance does not depend on the charge state of the surface and bulk traps.

Accumulation of electrons and holes in GaAs layers, that contained As clusters and were sandwiched between n- and p-type buffer GaAs layers, was revealed by capacitance-voltage measurements. As a result of majority-carrier accumulation, expansive depletion regions are formed in the adjoining buffer layers. Simulation of the capacitance-voltage characteristics, based on a numerical solution of the Poisson equation, shows that the accumulated charge density is ∼1 × 1012 cm−2, which is comparable with the concentration of As nanoclusters determined by transmission electron microscopy. The levels where the electrons or holes are accumulated lie close but above the GaAs midgap. A strong difference in the emission rates of the accumulated electrons and holes has been revealed.

AC conductivity experiments, or Impedance Spectroscopy, at temperatures between 100 and 400°C, made on 8 mole % Yttria Stabilized Zirconia (8YSZ) with different grain sizes, are presented. The results are analyzed using Effective Media Theories, the Brick Layer Model and percolation theory. The results obtained are satisfactory, only if the measured frequency dependant complex conductivity parameters of the grains are inserted in the equations.

Waspaloy is a nickel base super-alloy used in aircraft engines. When this alloy is placed in service, it is subjected to long term exposure at high temperatures, which can cause the reinforcing gamma prime precipitate population to fluctuate and thus affect its structural integrity. The population fluctuates as a result of coarsening, dissolution or re-precipitation. Samples exposed to 1200° F for times ranging from 0 to 12626 hours were characterized using impedance spectroscopy, microhardness measurements, x-ray diffraction and quantitative stereology. Two important parameters were derived from the impedance measurements: (1) the imaginary admittance peak magnitude (Ymax) and (2) the associated relaxation frequency (fmax). As the distribution, shape and size of the precipitates change with exposure time, these parameters were also found to vary. In addition to the changes in precipitate geometry, lattice constant changes detected by analyzing x-ray diffraction data suggest that there are compositional shifts in the matrix as well as the gamma prime precipitates. Furthermore, the preferred orientation of the precipitates can also be seen to change with exposure time. These changes in composition, size and shape as a function of thermal exposure time are accompanied by changes in the volume fractions of primary and secondary gamma prime particles present. Using effective medium models, it is possible to predict that the measured properties are related to the gamma prime population. The grain boundary carbides do not appear to play any role at the conditions presented.