Comparative hall measurements on wet- and dry-oxidized 4H-SiC MOSFETs

Hall measurements have been used to compare the properties of 4H-SiC inversion-mode MOSFETs with “wet” and “dry” gate oxides. While the field-effect mobilities were approximately 3–5 cm²/Vs, the Hall mobilities in 4H-SiC MOSFETs in the wet and dry oxide samples were approximately 70–80 cm²/Vs. The dry-oxidized metal oxide semiconductor field effect transistors (MOSFETs) had a higher transconductance, improved threshold voltage, improved subthreshold slope, and a higher inversion carrier concentration compared to the wet-oxidized MOSFETs. The difference in characteristics between the wet- and the dry-oxidized MOSFETs is attributed to the larger fixed oxide charge in the dry oxide sample and a higher interface trap density in the wet oxide sample.     

Structural,dielectric, impedance and ferroelectric properties of lead-free Bi(Fe0.85Dy0.15)O3 ceramic

Nowadays, several research groups are extensively trying to develop by synthesizing and characterizing single/co-doped single-phase bismuth ferrite (BFO) in order to get a highly efficient eco-friendly multifunctional devices. In this process, this report is an attempt to provide the detailed studies of structural, dielectric, impedance and ferroelectric properties of Bi(Fe_0.85Dy_0.15)O₃ ceramic fabricated via the solid-state reaction method. Analysis of X-ray diffraction (XRD) data confirms a single phase of orthorhombic symmetry. The average crystallite (particle) size is found to be in the order of?~?41 nm. The field emission scanning electron microscopy (FE-SEM) spectrum shows a homogeneous grain distribution of the sample. The elemental composition examined by means of energy dispersive X-ray spectroscopy (EDXS) shows the existence of constituent elements of the sample. The electrical measurements and analysis, carried out using a computer-controlled phase sensitive multimeter (PSM) in a frequency range of 1 kHz–1 MHz at different sets of temperature (25–325 °C), provide many interesting features to explain further conduction mechanism. The dielectric analysis exhibits high value of dielectric constant (?_r) and small value of dielectric loss (tanδ). Due to the effect of electronic and space charge polarization, the ?_r value falls with an increasing frequency. The frequency–temperature dependence of impedance and electrical modulus analysis reveals the presence of semiconductor nature and non-Debye type of relaxation process in the sample. The analysis of ac-conductivity (σ_ac) with respect to frequency and temperature obeys the universal Jonscher’s power law. The electric polarization study shows an enhancement in ferroelectric property of the material. Hence, based on the significant enhancement in electrical and ferroelectric properties of the Bi(Fe_0.85Dy_0.15)O₃ material, the material may be considered for some applications.

     

Optical and microstructural investigations of porous silicon

Raman scattering and photoluminescence (PL) measurements on (100) oriented n-type crystalline silicon (c-Si) and porous silicon (PS) samples were carried out. PS samples were prepared by anodic etching of c-Si under the illumination of light for different etching times of 30, 60 and 90 min. Raman scattering from the optical phonon in PS showed the redshift of the phonon frequency, broadening and increased asymmetry of the Raman mode on increasing the etching time. Using the phonon confinement model, the average diameter of Si nanocrystallites has been estimated as 2.9, 2.6 and 2.3 nm for 30, 60 and 90 min samples, respectively. Similar size of Si crystallites has been confirmed from the high resolution transmission electron microscopy (HRTEM). Using 2TO phonon mode intensity, we conjectured that the disordered Si region around the pores present in 30 min PS dissolved on etching for 90 min. The photoluminescence (PL) from PS increased in intensity and blue shifted with etching time from 2.1–2.3 eV. Blue shifting of PL is consistent with quantum confinement of electron in Si nanocrystallites and their sizes are estimated as 2.4, 2.3 and 2.1 nm for 30, 60 and 90 min PS, respectively which are smaller than the Raman estimated sizes due to temperature effect. Unambiguous dominance of quantum confinement effect is reported in these PS samples.     

Role of the stimulated-emission rate in the photostability of solid-state dye lasers

The lasing and photostability characteristics of Rhodamine 6G and Pyrromethene 567 dyes dispersed in polymeric host materials have been investigated as a function of the intensities of incident pump and signal beams in a longitudinally pumped dye laser in an oscillator-amplifier configuration. A substantial reduction in the rate of photodegradation was observed under lasing conditions and with increasing signal intensity in a dye amplifier, establishing that the service lives of these materials improve with an increase in the rate of stimulated emission. We observed approximately 62% amplifier efficiency at 2 Hz operation and 10% reduction in amplifier efficiency at 10 Hz operation after exposure of 72,000 pulses by use of a Pyrromethene disk.     

Mechanochemically assisted room temperature solid state metathesis reaction for the synthesis of MMoO4 (M = Ca, Sr and Ba)

This communication reports a novel mechanochemically assisted room temperature solid state metathesis reaction for the synthesis of submicron-size alkaline-earth molybdates crystallizing in a tetragonal Scheelite structure. The solids were characterized by powder XRD, FTIR, TGA, DTA, SEM, EDAX and TEM to ascertain their composition, phase homogeneity and morphology.     

Spectral characteristics of a binary dye-mixture laser

We have investigated laser action in a binary mixture of dyes, Rh-6G and DCM, resulting in tunable laser emission over an extended frequency region. The two dyes absorb the same pump radiation but fluoresce over frequency ranges that are shifted with respect to each other, thereby resulting in extended tunability. Following a time-dependent analysis of a rate-equation model that describe the operation of such a laser, theoretical estimates for optimum dye concentrations and the corresponding extension of the laser tuning range have been obtained.     

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa₂Cu₃O_7?δ (YBCO) thin films have been deposited on bare and La_0.67Sr_0.33MnO₃ (LSMO) modified single crystal SrTiO₃ (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.     

EXSHOF: An artificial intelligence approach to high-order filter synthesis

A two-tier expert-system-based synthesis of high-order filters is developed. Expert-system techniques have been used for choosing a particular biquad structure and for selection of the high-order filter structure as well. The data inputs will be either filter specifications or transfer functions and the output will be a detailed filter circuit with all its element values. EXSHOF ( pert System based ynthesis of igh rder ilter) is totally menu-driven and highly interactive. It assumes little knowledge of computers or filters from the user. The complete package is implemented in Turbo PASCAL and Turbo PROLOG languages.     

A theoretical and empirical investigation of multi‐item on‐line auctions

In this paper we explore and analyze the structure of Internet auctions from an analytical and an empirical perspective. Such web‐based auctions are rapidly emerging as a mercantile process of choice in the electronic marketplace. We observe current Internet auctions for one‐time products, such as rapidly aging hardware, and analyze them within the framework of the existing auction theory. While traditional auction theory focuses on single‐item auctions, we observe that a majority of on‐line auctions are multi‐item auctions. A significant contribution of this work is the theoretical derivation of the structure of the winning bids in multi‐item progressive on‐line auctions. Additionally, for comparative purposes, we explore the structural characteristics of alternative multi‐item auction mechanisms proposed in the auction theory. We derive hypotheses based on our analytical results and compare two different types of auction mechanisms. We test the traditional auction theory assumption regarding the homogeneity of bidders and present the first ever empirically derived classification and performance‐comparison of on‐line bidders. We test our hypotheses using real‐world empirical data obtained by tracking a premier web‐based auction site. Statistical analysis of the data indicates that firms may gain by choosing alternative auction mechanisms. We also provide directions for further exploration of this emerging but important dimension of electronic commerce. This revised version was published online in July 2006 with corrections to the Cover Date.