Impedance model of electrolyte-insulator-semiconductor structure with porous silicon semiconductor

We present a generic impedance model for the porous silicon|electrolyte structure that is valid for a range of interfacial layers and bias in these structures. The model is validated using three widely different porous structures: short irregular silicon columns and pores, long cylindrical silicon columns and pores; and branched interconnected silicon microchannels and voids in a mesh structure. The model incorporates appropriate RC or constant phase elements for the different parts of the porous structure, namely, the top of the silicon columns (channels)|electrolyte, the column (channel) walls|electrolyte in the pores/channels, and the electrolyte|semiconductor interface at the base of the pores/channels. This physical model underscores the effects of column/channel depletion and accumulation, either due to applied bias or change of surface charge, to the impedance spectra of the device. The model helps to explain why the porosity needs to be optimized for specific applications and helps as a measurement tool for optimization. (C) 200

Magnetization study of mercurocuprate (Hg,Re)Sr2CuO4+delta

The nominal (Hg1-xRex)Sr2CuO4+delta (x = 0.10 and 0.20) samples were synthesized at similar to 920degreesC in partial vacuum. The compound with x = 0.10 exhibits superconductivity at similar to 54 K while the composition x = 0.20 is non-superconducting down to 5 K. On cooling below 10 K in an applied field of 4 kOe, the former causes a noticeable upturn in the field cooled (FC) magnetization signal. Such a change in magnetic response is also reflected in the magnetic hysteresis loop generated at 9 K. We attribute this effect to a paramagnetic contribution arising from Re in (Hg,Re)-1201 phase

Time response and stability of porous silicon capacitive immunosensors

The time response of affinity sensors made with nanostructured materials is a topic of considerable interest, since affinity sensors made with nanostructured materials provide greater sensitivities than corresponding planar crystalline devices but at the cost of stability and drift. We present a study of the time response of capacitive immunosensors made using porous silicon and ultrathin room temperature anodic oxide. It was found that sensor drift can be substantial but can be reduced by subjecting the capacitive immunosensor in buffer to an anodic bias that is larger than the bias at which sensor capacitance is measured. By measuring sensor response before the addition of the analyte and using it for baseline correction after addition of the analyte, the effect of nonspecific sensor drift can be further reduced. We observed that after the addition of the analyte to the porous silicon immunocapacitor, there is a fast decrease in capacitance (order of tens of seconds) followed by a slow increase (order of tens of minutes), which models well as a sum of exponents with a fast exponential decay followed by a slow exponential rise. Possible processes that can give rise to such a response are perturbations of the double layer for the fast decay and column resistance switching for the slow rise. (c) 200

Magnetization study of (Hg,Cr)Sr2CuO4+delta superconductor

(Hg,Cr)-Sr-1201 type superconductor of nominal composition Hg0.7Cr0.3Sr2CuO4+delta was synthesized by the sealed quartz-tube method. X-ray diffraction analysis of the sample showed it has tetragonal symmetry with lattice parameters a = 3.841(1) Angstrom, and c = 8.664(3) Angstrom. The as-prepared sample is superconducting at 60 K as shown by dc-magnetization and dc-resistivity measurements, The irreversibility line (IL) obtained from the merging point of the zero-field-cooled and the field-cooled magnetization measurements at several applied fields was found to obey the equation H = A(1 - T/T-c)(n) and gave a value of 2.55 for the exponent "n." Using magnetic hysteresis loops the critical current density of superconducting (Hg,Cr)-Sr-1201 was estimated. The irreversibility line and magnetic hysteresis showed reduced pinning properties of (Hg,Cr)-Sr-1201 as compared to HgBa2CuO4+delta

Chemical stabilization of 1201-type Hg-Sr based cuprate superconductors

The 1201-type Ba-free Hg-Sr based cuprate superconductors with nominal compositions of Hg1-xMoxSr2CuO4+delta (x = 0.1 - 0.25) were synthesized and characterized. The 1201-type structure was stabilized by partial substitution of Mo in the Hg site. A typical composition, Hg0.85Mo0.15Sr2CuO4+delta crystallizes in tetragonal structure with a = 3.769 Angstrom and c = 8.801 Angstrom and a superconducting transition of 57 K was measured

Superconductivity in (Hg, Mo)Sr2CuO4+delta system

The 1201-type Hg-Sr-based cuprates with nominal composition of (Hg1-x)Sr2CuO4+delta; x = 0.15, 0.25 and 0.30, were prepared in partial vacuum. XRD data confirms that they are 1201-type structure. The ac-susceptibility measurements of the samples show that for the composition x = 0.15 has a maximum T-c(onset) of similar to66 K. while x = 0.25 exhibits T-c(onset) of similar to50 K. For x = 0.30, the observed T-c(onset) of similar to36 K is at variance with that reported in literature. (C) 2002 Published by Elsevier Science B.V

Phase breaking effects in magnetoconductivity of YBA2CU3O7-DELTA and BI2SR2CACU2O8

We have measured the magnetoconductivity of YBa2Cu3O7-delta and Bi2Sr2CaCu2O8 in the magnetic field of 4T and analysed the data in the fluctuation region in the light of Aronov-Hikami-Larkin (AHL) and Bieri-Maki(BM) theories in their corrected forms and find the BM theory within the clean limit to describe the data more adequetely