In this work we present first cycle charge/discharge performance of synthetic graphite and petroleum coke and the influence of the binder used for the preparation of the electrodes on the irreversible capacity losses and an investigation of LiMn2O4/graphite and LiMn2O4/petroleum coke cells in respect to the cathode to anode electrode mass balance using three-electrode cells. The irreversible capacity of synthetic graphite electrodes varies from about 85 to 215 mAh/g depending on the binder material. Li-ion cells assembled after the optimization of the cathode/anode material mass ratio r showed first discharge capacities of about 100 and 102 mAh/g, for LiMn2O4/graphite and LiMn2O4/petroleum coke respectively.

The aim of this work is to examine the performance and in particular the irreversible capacity of synthetic graphites. Our analysis is based on the evaluation and study of the differential capacity (dx/dV), computed by numerical differentiation of the galvanostatic curve. The dx/dV curve shows a series of peaks that correspond to potential plateaus. The area under each peak results in the charge related to the particular process, and by peak de-convolution analysis we can determine the charge consumed by or released from each process. This approach enables us to identify the processes involved (formation of SEI, solvated Li co-intercalation, cell self discharge, etc.).

TlBiSe2 epitaxial thin films were grown on NaCl substrates by electron beam evaporation under different growth conditions. The as-grown films were characterised by infrared reflectance measurements and transmission electron microscopy observations. It is determined that the interfacial region of such films under certain supersaturation conditions presents a new fcc cubic phase sub-layer which grows with the substrate lattice parameter to a considerable thickness. The occurrence of this phase has a dependence on the deposition rate which is evident particularly when low substrate temperatures are employed in the growth process. A plausible explanation is offered for the observed cubic phase in terms of a pressure induced structural modification. Finally, it is shown that the complimentary nature of the two methods allows a complete structural and electrical characterisation of thin film structures.

In this work we have examined different types of synthetic graphites (SFG and KS types) that have different morphology and particle sizes. In our analysis we examined the incremental capacity (dC/dV), which shows a series of peaks that correspond to potential plateaus. This approach enable us to identify the processes involved (formation of SEI, Li + intercalation or de-intercalation, etc.). Our analysis was mainly concentrated on the first lithiation, in an attempt to specify the origin of the capacity loss related to each type of synthetic graphite.

Lithiated spinel manganese dioxide was synthesised from electrochemical MnO2 and Li2CO3 with deficiency or excess lithium (LixMnxO4, 0.8 < x < 1.3) for use in Li/LixMn2O4 and Li-ion cells. Micron-sized Li1.05Mn2O4 prepared at 730 degrees C showed high Li utilization, excellent cyclability and good rate capability with an initial discharge capacity of 123 mA h/g and 10% discharge capacity reduction after 20 cycles. Different types of commercial carbonaceous materials were also investigated with respect to their electrochemical performance vs. Li. Unoptimised Li-ion cells, using Li1.05Mn2O4 prepared at 730 degrees C as the cathode material, EC-DMC-LiPF6 electrolyte and carbon fibres, showed promising performance characteristics. (C) 1998 Elsevier Science S.A. All rights reserved.

The characterization and optimization of synthesized spinel LixMn2O4 cathode material with respect to its lithium utilization, cyclability and rate capability by controlling the synthesis conditions and the particle size of the prepared material is reported. Lithiated spinel manganese dioxide was prepared from EMD and Li containing compounds at different synthesis temperatures (450-850 degrees C) and with deficiency or excess lithium (LixMn2O4, 0.8<x<1.3). The prepared material was single phase LiMn2O4 within the range 1.1<x<1.25 while at temperatures below 730 degrees C Mn2O3 was present. Li1.05Mn2O4 prepared at 730 degrees C and ground to micron sized particles in a vibrating ball mill, showed a high initial discharge capacity (123mAh/g), excellent capacity retention (similar to 11% discharge capacity reduction after 100 cycles) and small capacity reduction for relatively high current rates (similar to 5% from C/8 to 1C).

Silicon was implanted with 2 MeV O+ ions with doses covering the range from 1 x 10(17) to 2 x 10(18) O+ cm(-2), at an implantation temperature of 700 degrees C. Subsequently, samples were capped and annealed at 1300 degrees C. Infrared reflectance spectroscopy has been used in order to characterize the as-implanted and annealed samples. The optical modeling of the multilayer structures and the data reduction procedure are given in detail. The thickness, chemical composition, crystallinity, interface macroscopic roughness, and refractive index profiles are quantified. It is shown that infrared reflectance spectroscopy is a quick, nondestructive, analytical, and precise method for characterizing high energy separation by implantation of oxygen (SIMOX) structures. Cross correlation with H+ beam Rutherford backscattering/channeling, secondary ion mass spectroscopy, and cross-sectional transmission electron microscopy results, gives good agreement. The formation of oxide in the high energy region follows the same basic rules as in the standard SIMOX case. No anomalous oxygen diffusion was observed during annealing and a buried layer formed during annealing even for the lowest dose. It is found that the microstructure of the annealed samples is strongly dependent on the implantation conditions such as beam current density and that even for the highest dose of 2 x 10(18) O+ cm(-2), a continuous stoichiometric silicon dioxide layer has not formed after annealing.

Polycrystalline semiconducting FeSi2 thin films were grown on (100) Si substrates of high resistivity by electron beam evaporation of amorphous Si/Fe ultrathin multilayers in an ultrahigh vacuum system, followed by conventional vacuum furnace (CF) or rapid thermal annealing (RTA). Infrared reflectance and transmittance measurements were employed for optical characterization of the samples at room temperature. The results indicate a direct transition at about 0.85 eV, an indirect transition at about 0.79 eV, and exponential band tail states within the band gap. The quality of the silicide is improved by increasing the annealing temperature from 600 to 800 °C in the RTA process, while the opposite is observed in the CF annealed samples. Transport measurements were performed on a typical β-FeSi2 layer of high quality grown by CF at low temperature. The measured mobility is about 97 cm2/V s and the hole concentration is about 1×1017 cm−3. The mobility is a factor of 10 higher and the hole concentration a factor of 100 lower than the corresponding published data, indicating a significantly improved quality of β-FeSi2 layers. Temperature-dependent measurements indicate that carrier transport is dominated by impurity conduction.

High quality β-FeSi2 thin films were grown on Si〈100〉 substrates by UHV electron beam evaporation of α-Si/Fe multilayers and annealed by conventional vacuum furnace and rapid thermal techniques. Infrared spectroscopy (reflectance and transmittance) and electrical measurements were employed to characterize the films. Hall measurements performed on the thin films yielded exceptionally high free carrier mobilities, up to 112 cm2/Vs.

The damage produced by 200 keV Ge + ion implantation in 6H-SiC (from Cree Research) has been studied by fast Fourier transform infrared (IR) reflectance spectroscopy. A new, recently developed at the spectroscopy laboratory of AUTh, non-destructive optical method, based on the normalized atomic vibrational damping of the ‘reststrahlen band’, has been applied to determine damage depth profiles of SiC for damage over three orders of magnitude, up to amorphisation. For the amorphized state IR results show an up to 30% reduction of heteronuclear SiC bonds. No new broad SiSi or CC vibrational bands were observed.

A generalized matrix method is presented for calculating the optical reflectance and transmittance of an arbitrary thin-solid-film multilayer structure on very thick substrates with rough surfaces and interfaces. We show that the effect of roughness and the influence of incoherently reflected light on the back side of a thick layer can be accounted for with a more general transfer matrix that enables the inclusion of modified complex Fresnel coefficients. Coherent, partially coherent, and incoherent multiply reflected light inside the multilayer structure is treated in the same way. We demonstrate the method by applying it to simulated and experimental reflectance spectra of thin epitaxial Si overlayers on very thick SiO(2) substrates and on a separation by ion implantation of oxygen structure with a SiO(2) buried layer exhibiting substantial roughness on both of its interfaces (Si/SiO(2) and SiO(2)/Si).

TlBiSe2 bulk single crystals are grown with an unusually large spread in carrier concentration for the family of compounds of the general type TlAB2 (A: Bi, Sb; B: Te, Se, S) of almost one order of magnitude. This is achieved by varying the growth and annealing conditions. By employing electrical and IR reflectivity measurements the dispersion of the free carrier properties is determined such as the mobility mu, the mean free path 1, the ocnductivity sigma, and the susceptibility effective mass m(s)* in an attempt to probe the band structure of the material but also to lay down the groundwork for the characterization of epitaxial thin films of this material. It is found that TlBiSe2 can be characterized as a narrow gap semiconductor with a non-parabolic conduction band. In addition evidence of a second higher lying conduction band is presented.

The characterization of semiconductive TlBiSe2 thin films by the use of electron microscopy and infrared spectroscopy is presented. It was determined that the deposition conditions profoundly influence the microstructure and surface quality of the as-grown films, consequently affecting their electronic properties such as the free-carrier mobility, the amount of band edge tailing and the value of the optical energy gap. The results show that these two techniques are a very useful combination in material characterization.

TlBiSe2 thin films were fabricated by electron-beam evaporation and the influence of the deposition rate on the growth was investigated by transmission electron microscopy (TEM) and IR reflectivity measurements in the plasma edge reflectance region. It was determined that depending on the deposition rate two types of films are produced with significantly different microstructural, optical and electrical transport properties. In particular, incoherent grain boundaries present in the films fabricated with high deposition rates drastically reduce the reflectivity in the NaCl substrate reststrahlen region. This is attributed to a large increase in the free carrier scattering frequency γp, a consequence of which is the reduction of the free carrier mobility μ and of the conductivity in these films by as much as 4 and 14 times respectively, compared with thin films fabricated by low deposition rates.

TlBiSe2 thin films grown with very high deposition rates exhibit a weak reflectance in the far infrared as compared to films grown at lower rates. This behavior is ascribed to a reduction in the free carrier mobility or equivalently, to a large increase in the free carrier scattering frequency of the former. By utilizing this increased transperancy of the films fabricated with high rates the only ir active optical phonon of this material was identified. The analysis of the absorption coefficient in the mid infrared showed that the fundamental absorption in TlBiSe2 takes place by direct transitions, the magnitude of the optical energy gap ranging from 0.45 to 0.47 eV.