Superparamagnetic iron oxide nanoparticle attachment on array of micro test tubes and microbeakers formed on p-type silicon substrate for biosensor applications

A uniformly distributed array of micro test tubes and microbeakers is formed on a p-type silicon substrate with tunable cross-section and distance of separation by anodic etching of the silicon wafer in N, N-dimethylformamide and hydrofluoric acid, which essentially leads to the formation of macroporous silicon templates. A reasonable control over the dimensions of the structures could be achieved by tailoring the formation parameters, primarily the wafer resistivity. For a micro test tube, the cross-section (i.e., the pore size) as well as the distance of separation between two adjacent test tubes (i.e., inter-pore distance) is typically approximately 1 μm, whereas, for a microbeaker the pore size exceeds 1.5 μm and the inter-pore distance could be less than 100 nm. We successfully synthesized superparamagnetic iron oxide nanoparticles (SPIONs), with average particle size approximately 20 nm and attached them on the porous silicon chip surface as well as on the pore walls. Such SPION-coated arrays of micro test tubes and microbeakers are potential candidates for biosensors because of the biocompatibility of both silicon and SPIONs. As acquisition of data via microarray is an essential attribute of high throughput bio-sensing, the proposed nanostructured array may be a promising step in this direction

Properties of CdS and CdTe thin films deposited by an electrochemical technique

226-230CdS and CdTe films have been deposited onto transparent conducting oxide (TCO) coated glass substrates using an electrochemical technique, where a cadmium foil was used as a sacrificial anode and no external bias being used during film deposition. The films were characterized using X-ray diffraction, scanning electron microscopy and optical absorption measurements. A CdS/CdTe thin film solar cell utilizing this deposition technique has been developed

Synthesis of blue emitting ZnO nanorods exhibiting room temperature ferromagnetism

We report here a facile chemical method to prepare ZnO nanorods with micrometer length in large quantity at 80 degrees C. The as-prepared rods exhibited blue emission and room temperature ferromagnetism simultaneously. The PL of the as-prepared ZnO rods exhibited an overlapped broad emission in the 345-600 nm range. The as-prepared dried rods exhibited a saturation magnetization value of 59.14 x 10(-3) emu g(-1) at room temperature. On heating, though the material retains its morphology, the magnetization value decreased. Since we have observed a reduction in the intensity of the visible emission followed by a disappearance of the ferromagnetic ordering, we attributed the blue emission and the ferromagnetism to the presence of defects related to singly ionized oxygen vacancies and zinc vacancies. (C) 2013 Elsevier B.V. All rights reserved

Tunable charge transport through n-ZnO nanorods on Au coated macroporous p-Si

We report a strategy to synthesize patterned n-ZnO nanorods on Au coated macroporous p-Si. Electric field assisted growth of ZnO under UV exposure results in the formation of well-aligned and relatively defect-free n-ZnO nanorods on the macroporous Si-template. The luminescence characteristics of ZnO exhibit a single Gaussian peak due to band-to-band transition in ZnO. Temperature dependent electrical transport through the n-ZnO/Au/p-Si heterojunction reveals unusual characteristics. Under forward bias, the I-V plots are diode-like with a remarkably low turn-on voltage and significantly high forward bias current. The non-linear forward current decreases appreciably with temperature while the reverse bias current is linear and is almost temperature independent. The Au layer present between the n-ZnO and p-Si significantly modifies the junction and allows tuning the device characteristics from diode-like to ohmic under different biasing conditions

Superparamagnetic iron oxide nanoparticle attachment on array of micro test tubes and microbeakers formed on p-type silicon substrate for biosensor applications

<p>Abstract</p> <p>A uniformly distributed array of micro test tubes and microbeakers is formed on a p-type silicon substrate with tunable cross-section and distance of separation by anodic etching of the silicon wafer in N, N-dimethylformamide and hydrofluoric acid, which essentially leads to the formation of macroporous silicon templates. A reasonable control over the dimensions of the structures could be achieved by tailoring the formation parameters, primarily the wafer resistivity. For a micro test tube, the cross-section (i.e., the pore size) as well as the distance of separation between two adjacent test tubes (i.e., inter-pore distance) is typically approximately 1 &#956;m, whereas, for a microbeaker the pore size exceeds 1.5 &#956;m and the inter-pore distance could be less than 100 nm. We successfully synthesized superparamagnetic iron oxide nanoparticles (SPIONs), with average particle size approximately 20 nm and attached them on the porous silicon chip surface as well as on the pore walls. Such SPION-coated arrays of micro test tubes and microbeakers are potential candidates for biosensors because of the biocompatibility of both silicon and SPIONs. As acquisition of data via microarray is an essential attribute of high throughput bio-sensing, the proposed nanostructured array may be a promising step in this direction.</p

Temperature dependent photoluminescence from porous silicon nanostructures: Quantum confinement and oxide related transitions

Temperature dependent photoluminescence (PL) spectroscopy along with structural investigations of luminescent porous Si enable us to experimentally distinguish between the relative contributions of band-to-band and oxide interface mediated electronic transitions responsible for light emission from these nanostructures. Porous Si samples formed using high current densities (J 80 mA/cm2) have large porosities (P 85%) and consequently smaller (1-6 nm) average crystallite sizes. The PL spectra of these high porosity samples are characterized by multiple peaks. Two dominant peaks—one in the blue regime and one in the yellow/orange regime, along with a very low intensity red/NIR peak, are observed for these samples. The high energy peak position is nearly independent of temperature, whereas the yellow/orange peak red-shifts with increasing temperature. Both the peaks blue shift with ageing and with increasing porosity. The intensity of the blue peak increases whereas the yellow/orange peak decreases with increasing temperature, while the intensity and peak position of the very low intensity red/NIR peak appears to be unaffected by temperature, porosity, and ageing. The low porosity samples (P 60%) on the other hand exhibit a single PL peak whose intensity decreases and exhibits a very small red spectral shift with increase in temperature. From the variation of intensity and PL peak positions, it is established that both quantum confinement of excitons and oxide related interfacial defect states play dominant role in light emission from porous Si and it is possible to qualitatively distinguish and assign their individual contributions