Scanning Tunneling Microscopy and Spectroscopy (STM/STS) are used for obtaining nano-scale information on morphological and electronic properties of the surface of diamond-like amorphous hydrogenated carbon (a-C:H) filns. The films are prepared by rf plasma decomposition of methane CH4.A two phase model of a-C:H is suggested - sp3 bonded matrix in which sp2 clusters are embedded. A novel method of mapping graphite-like clusters over a-C:H surface is proposed. Tunneling I/V characteristics with a gap acquired on indium tin oxide (ITO) deposited on a-C:H indicate location of sp2 regions at the surface of a-C:H below an ITO overlayer

Mercuric iodide (HgI2) is a semiconductor that has shown great promise for use in roomtemperature high-resolution x-ray and gamma-ray spectrometers. Its widespread usage has been limited, however, by low yield and long-term reliability problems. The processing of this material is still in its infancy compared to silicon, so research efforts continue to pursue the root causes of device failures. Two likely sources of performance limitations are impurities and poor contacts. Significant efforts have been expended in developing and using various purification schemes. However, quantitative chemical analyses have shown that several metallic impurities still exist at the high ppb level. In addition, it has not yet been definitively determined which impurities are most problematic and at what level they have a detrimental effect. Leakage currents and currentvoltage measurements have been used to study the movement of mobile impurity-related defect centers in the bulk mercuric iodide. In particular, this method has been used to quantify the drift of metallic impurities, such as Ag and Cu, which are known to or believed to degrade HgI2 detectors. Four-point-probe sheet resistance measurements have been used to study the stability of contacts and the formation of reaction layers. In particular, such measurements have revealed that the Pd contacts currently used for the highest quality detectors are not as stable as previously thought, as the films of Pd react with the HgI2 to form the amalgam PdHg.

The chemical structure of a series of aluminum substituted sodium trisilicate glasses is determined by x-ray photoelectron spectroscopy. It reveals a significant change of the chemical structure around the sodium cations and oxygen anions with the addition of aluminum. A microscopic model is developed to understand the composition dependence of the dielectric constant of these glasses in terms of the changes of chemical structure.

As sodium and potassium are removed from silica xerogels through leaching, the dielectric properties of gels are significantly altered. Work has been done to relate the magnitude of the change in alkali ion content to the change in dielectric properties. Gels were prepared through a colloidal processing method and leached in ammonium nitrate, nitric acid, and water to reduce, to different degrees, the content of sodium and potassium ions. Atomic absorption (AA) was used to determine the actual sodium and potassium content of each gel after its capacitance and dielectric loss were measured as a function of frequency. All electrical measurements were carried out at room temperature and constant humidity. At least three samples for each leaching treatment were evaluated. Data obtained shows a definite relationship between the sodium and potassium content measured by AA and the dielectric constant.

The exposure of molybdenum disilicide to combustion products at 1370° and 1600°C for 1 and 60 hours led to the formation of a silica surface film. The thickness of this protective layer, ranging from 4.4–18.2 μm, increased with temperature and exposure time. However, the dielectric constant (3.16) of the thin film was independent of ac field frequency, exposure time, and temperature, according to complex impedance analysis in the frequency range of 500 Hz to 1 MHz. MoSi2 specimens with a silica coating on one side resembled, in impedance spectroscopy terms, a resistor of low resistivity (MoSi2, 10−4 Ω·cm) in series with a parallel RC circuit of high resistivity (SiO2, 3.0×1010 Ω·cm). From this analysis, a calibration curve was generated for converting measured capacitance to silica film thickness. Relaxation time (on the order of 0.1 sec) and relaxation frequency (on the order of 1–10 Hz) were also derived, with the aid of semicircular regression of the complex impedance curves.

Polymeric materials such as polyimides are used in a multitude of microelectronic applications including interlevel dielectrics for insulation. Polyimide films have shown a difference between the through-plane and in-plane refractive index measurements.(1,2,3) This anisotropy in optical properties has been attributed to in-plane orientation of polymer chains and implies anisotropy in electrical properties. Thus, it is necessary to measure the electrical properties in both the in-plane and through-plane directions to accurately design three-dimensional electronic packages. The purpose of this research is to develop an in-situ technique to measure the in-plane permittivity of these spin-coated polymer films. Using capacitance measurements obtained from interdigitated electrodes, through-plane permittivity measurements, and ANSYS finite element analysis software, the in-plane permittivity of a given material can be determined. Several polyimide systems including Du Pont PI-2611 (BPDA-PPD), Du Pont PI-2540 (PMDA-ODA), and Probimide 293 (BTDA-DAPI) from OCG Microelectronics, as well as Cyclotene 3022 (BCB) from Dow Chemical were investigated. Anisotropy in the permittivity was observed in the three polyimide films, but not in the BCB film. Results were compared with predictions using refractive index measurements and a modified form of Maxwell's equation.

AC impedance spectroscopy and chronopotentiometry have been used to study solid state ionic conductors. Results obtained using three electrodes are compared to those using a two electrode configuration. The uncompensated resistance was shown to depend strongly on the geometric placement of the electrodes. The optimal configuration is similar to the Luggin capillary arrangement in the liquid phase. The effect of non-negligible geometric capacitance on interpretation of results is discussed.

The effect of electrode surface unevenness on electrode impedance was examined at rectangular groove electrodes by numerically solving the Laplace equation. CPE behavior appeared for the double-layer charging at considerably large groove electrodes in the absence of outer solution layer at high frequencies. This behavior originated from the current concentration to the upper portions of the groove. In the presence of an outer solution layer, the current concentration was greatly weakened by the series connection of solution resistance, resulting in the disappearance of CPE behavior. The real part of the impedance at high frequencies was not additive in the presence of exposed electrode surfaces outside the groove. The origin of no impedance additivity was discussed based on equipotential-amplitude data.

A technique for the measurement of quartz supported electrode oscillation frequency with special reference to transient electrochemical experiments was prepared. Due to changes in solution viscosity and density and in surface roughness during potential step experiments, the error in calculation of mass changes from frequency responses can reach 3–5 %. Initial deviation of electron numbers from unity by 30–60% during pulse electroreduction of dicyanoargentate shows that this process is not a simple faradaic reaction.

A fuel electrode consisting of particles of Ni and mixed conductor, Nd-doped ceria (NDC) has been developed. The electrode resistance decreased with decreasing the oxygen partial pressure lower than 10−11 atm, where the electronic conduction is predominant for NDC. This decrease in the resistance could be attributed to an increase in the triple phase boundary caused by an increase in electronic conductivity of NDC.

The chemical compatibility of (La0.6Sr0.4)MnO3 (LSM), (La0.6Sr0.4)CoO3 (LSC), (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF), and (La1.7Sr0.3)CuO4 (LSU) as cathode materials with the oxygen conductor (La0.9Sr0.l)(Ga0.8Mg0.2)O3-δ (LSGM) was studied. The interfacial resistance between the cathode materials and LSGM was measured using AC impedance spectroscopy. The same studies were done with yttria-stabilized zirconia (YSZ) electrolyte. The results showed that no new compounds formed between LSGM and the cathode materials LSM, LSC, and LSCF up to at least 1200°C; however, a solid solution formed between the materials. With YSZ, only LSM did not form new compounds, and no solid solutions formed. The interfacial resistance was much lower between all the cathode materials and LSGM than YSZ. The lowest interfacial resistances were for LSC/LSGM and LSCF/LSGM, which are suggested for medium temperature solid oxide fuel cells.

Observations have been made by impedance spectroscopy of various microstructure-induced blocking effects in cubic zirconias and composites. Correlations have been established between shape parameters of the microstructure defects and specific parameters of the electric response, such as the blocking factor and frequency factor, in the medium frequency range.

Appropriate diagrams show the continuity and changes in the regimes of the microstructure evolutions.

Thin films of 4% Y2O3 doped CeO2/Pd film/(001)LaA103 with a very low pinhole density were successfully prepared using electron-beam deposition technique. The microstructure of the films was characterized by x-ray diffraction and the electrical properties were studied as a function of temperature with AC impedance spectroscopy. A brick layer model was adopted to correlate the electrical properties to the microstructure of the films, which can be simplified as either a series or a parallel equivalent circuit associated with either a fine grain or a columnar grain structure, respectively. The conductivities of the films fell between the conductivities derived from the two circuit models, suggesting that the films are of a mixed fine grain and columnar grain structure. The measured dielectric constants of the films were found smaller than that of the bulk.

Earth scientists study electrical properties of Earth materials to understand mechanisms of transport and deformation under conditions existing in the Earth's interior, and for comparison with direct determinations of the conductivity – depth structure of the Earth. We have performed impedance spectroscopic studies of natural and artificial (hot-pressed and sintered) rocks composed of (Mg9Fe1)2SiO4 olivine, a major constituent of the Earth's upper mantle between 40 and 400 km depth. The studies were performed over the frequency range 105 to 10−4 Hz at 1 bar total pressure and temperatures of 800 – 1400 °C under controlled oxygen atmospheres. Complex impedance plane analysis of the results shows depressed impedance arcs corresponding to grain interior and grain boundary transport in series, analogous to the behavior of zirconia and other materials. Distinct grain boundary phases that might cause the resistive grain boundary behavior are not observed. The exponent of the oxygen pressure dependence of the grain boundary conductivity ranges from 0.02 to −0.08, which is very different than the 1/5.5 to 1/7 dependence of the polaronic grain interior mechanism. However, lack of constraints on the composition of the intergranular material limit interpretation of these exponents in terms of mechanism. Key issues for application to the Earth's interior are determination of the mechanism and pressure dependence of the grain boundary transport.

Microwave magnetic properties of Gd substituted yttrium iron garnets are known to depend on their microstructural characteristics such as porosity and grain size. Surface coating of the garnet powders through a gelation of Si and Mn organic solution was conducted to inhibit the grain boundary movement during sintering with considerable densification. High density and uniform microstructure were obtained after sintering at 1400°C in O2 atmosphere. Grain growth kinetics were studied with variation in sintering time as a function of grain size. An activation energy of 102.9 kcal/mol was obtained for grain growth of the sol-gel coated sample. Grain boundary region was investigated by using TEM and EDS. A very thin grain boundary layer was observed with Si segregation in the region. Electrical resistivity at 100 Hz was 1.46×109 Ωcm for the sol-gel coated sample sintered at 1400°C for 3hrs in O2. Above results were discussed and compared with those obtained by the conventional batch mixing of additives.

Simplified varistor systems of bismuth- and cobalt-doped zinc oxide are studied. A prior study has shown that the distributions of bismuth segregation at the grain boundaries in such samples can be controlled by varying microstructure and heat treatment. Current-voltage and deep level transient spectroscopy measurements were done to evaluate the corresponding electrical properties. Low leakage and α values of ˜30 were attained, despite the nominal, twocomponent doping of these simplified varistors. Moreover, these samples show the signature defects that are found in many multi-dopant, commercial devices: two shallow bulk traps at ˜0.14 eV and ˜0.24 eV and one prominent interfacial trap at ˜1 eV.

Composition dependence of electrical conductivity of ceramic composite was analyzed using a ZnO(n-type semiconductor)-CuO(p-type semiconductor) composite as a model. The contributions from grain and grain boundaries to the total conductivity of the composite were determined. New equivalent circuits were proposed which represented the distribution and connection of n and p grains and the total electrical conductivity was analyzed using the proposed circuits. Dominant equivalent circuit changed with composition and the total conductivity was determined by the exponential fractional change of two equivalent circuits. Effect of grain size on the grain boundary and total conductivity were also examined.

The widely used Bruggeman symmetric and asymmetric media equations and the Clausius-Mossetti approximation are presented, and the idealized microstructures characterizing these media are examined.

The percolation equations for the conductivity (σm) and complex dielectric constant (ɛm = ɛrm + iɛim) for ideal perfect conductor–conductor and conductor–perfect insulator continuum media (and lattices) are then introduced. The parameters characterizing the microstructure in the percolation equations are a critical volume fraction or percolation threshold (φc) and two exponents (t&s). The equations characterizing the crossover region, which occurs whenever the ratio of the conductivities of the two components is finite, or dielectric measurements are made, are also introduced. A general effective media equation, which has the same parameters as the percolation equations is noted, and its success in obtaining φc, when the ratio of the conductivities is finite, examined.

The microstructures that allow φc to have values between a few percent and over 60%, as well as the occurrence of non–universal values of t, will also be discussed.

The microstructure of granular superconductors are discussed and the difference between granular and random composites is noted. The model where a granular (and a random) superconductor, close to the percolation threshold, is considered to be made up of large granular clusters, linked by tunnelling junctions or weak links, is introduced. This model is illustrated using recent experimental measurements on nanostructured granular Aℓ–Ge. The measurements clearly show that the coupling junctions between clusters can,depending on the volume fraction of superconductor, be of either a Josephson or quasi–particle nature, or a combination of both. The differences between a granular and adirty superconductor and the upper critical field of granular superconductors is then discussed and it is shown that the diameter of the grains can be estimated from the upper critical field. Random Aℓ–Ge, which has a rather different microstructure, is also discussed.

The addition of Y2BaCuO5 (211) particles to large grain Yba2Cu3O7−δ (Y123) has significantly improved the critical current (Jc) in this material. Here a systematic quantitative analysis on the effect of the measured 211 present in large grains of Y123 has been performed, after the process of melt texturing, both on a microscopic and a nanoscopic scale with a systematic variation of the initial volume percent of 211 addition. From the correlation between critical current measurements and quantitative microscopy of both (001) and (110) sections, a maximum value of weighted Jc is observed corresponding to a measured Y123 volume percent of 20%. Although an increasing addition of 211 is effective in producing efficient flux pinning sites in the Y123 matrix, percolation paths in the Y123 matrix become limited for supercurrent. Accounting for the loss of liquid phase, we estimate an optimum initial volume of 211 for highest Jc to be 40%. Further correlation between the Jc and the true flux pinning force (Fp) shows a maximum pinning force for an initial 211 addition of 40%. However the pinning efficiency of the superconducting Y123 matrix is found to improve with an increasing 211 addition. Hence an optimum amount of 211 addition is essential for obtaining the best possible electrical characteristics in the superconducting composite.