The electrodeposition of metal onto a low energy electrode surface like graphite or H-terminated silicon produces mesoscopic metal particles that are broadly distributed in diameter Broad size distributions are observed even in cases where the nucleation of metal is temporally controlled For this reason, electrodeposition has been infrequently used as a means for obtaining metal nanostuctures The central problem is the diffusional “cross-talk” that exists between neighboring metal nanostructures on the electrode surface Evidence for this diffusional interparticle coupling is encoded into particle size and position distributions obtained from experimental data and from Brownian Dynamics computer simulations of nanostructure growth Diffusional cross-talk between nanostructures can be turned off using either of two growth strategies described in this paper These methods permit the size-selective electrodeposition of metal nanoparticles and nanowires that are narrowly distributed in diameter

Mesoscopic Metal Particles and Wires by Electrodeposition

Bioresorbable silicon electronics technology offers unprecedented opportunities to deploy advanced implantable monitoring systems that eliminate risks, cost and discomfort associated with surgical extraction. Applications include postoperative monitoring and transient physiologic recording after percutaneous or minimally invasive placement of vascular, cardiac, orthopaedic, neural or other devices. We present an embodiment of these materials in both passive and actively addressed arrays of bioresorbable silicon electrodes with multiplexing capabilities, which record in vivo electrophysiological signals from the cortical surface and the subgaleal space. The devices detect normal physiologic and epileptiform activity, both in acute and chronic recordings. Comparative studies show sensor performance comparable to standard clinical systems and reduced tissue reactivity relative to conventional clinical electrocorticography (ECoG) electrodes. This technology offers general applicability in neural interfaces, with additional potential utility in treatment of disorders where transient monitoring and modulation of physiologic function, implant integrity and tissue recovery or regeneration are required.

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Bioresorbable silicon electronics for transient spatiotemporal mapping of electrical activity from the cerebral cortex

The term "calibration" in accelerometry research has come to mean the conversion of counts into other established measurement units. In this article, two types of calibration research are described. Unit calibration (or interinstrument variability) is described as a reliability issue, whereas value calibration is described as more of a validity issue. Principles for design of accelerometry-based validation studies are described to provide a guide for future calibration research. The population must be representative of the intended population in terms of demographics and size, monitors must be representative of the population of monitors that would be available, and activities in the protocol must be representative of the types of activities performed by the intended population. It is also important to employ appropriate analytical strategies in this type of research. A case study employing the appropriate design principles is included to demonstrate how results can vary depending on the type of analyses that are used. Direct comparisons are made between a mixed model regression approach and an approach based on receiver operator characteristic curves.

Principles of design and analyses for the calibration of accelerometry-based activity monitors

Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.

/pdf/single-crystalline-mesoporous-silicon-nanowires-54a12ety7i.pdf

Single crystalline mesoporous silicon nanowires.

Several of the multiple applications of titanium dioxide nanomaterials are directly related to the introduction or generation of charge carriers in the oxide. Thus, electrochemistry plays a central role in the understanding of the factors that must be controlled for the optimization of the material for each application. Herein, the main conceptual tools needed to address the study of the electrochemical properties of TiO(2) nanostructured electrodes are reviewed, as well as the electrochemical methods to prepare and modify them. Particular attention is paid to the dark electrochemical response of these nanomaterials and its direct connection with the TiO(2) electronic structure, interfacial area and grain boundary density. The physical bases for the generation of currents under illumination are also presented. Emphasis is placed on the fact that the kinetics of charge-carrier transfer to solution determines the sign and value of the photocurrent. Furthermore, methods for extracting kinetic information from open-circuit potential and photocurrent measurements are briefly presented. Some aspects of the combination of electrochemical and spectroscopic measurements are also dealt with. Finally, some of the applications of TiO(2) nanostructured samples derived from their electrochemical properties are concisely reviewed. Particular attention is paid to photocatalytic processes and, to a lesser extent, to photosynthetic reactions as well as to applications related to energy from the aspects of both saving (electrochromic layers) and accumulation (batteries). The use of TiO(2) nanomaterials in solar cells is not covered, as a number of reviews have been published addressing this issue.

The Electrochemistry of Nanostructured Titanium Dioxide Electrodes

The general concepts governing the electrochemical deposition of metal films onto semiconductors are discussed Deposition onto semiconductor surfaces is complicated due to the band structure of the semiconductor, which affects both the thermodynamics and the kinetics of metal deposition processes The influence of the potential distribution at the semiconductor/solution interface on the charge transfer mechanisms involved in deposition of metals is discussed Models for electrochemical nucleation and growth are described and the influence of the unique physical properties of semiconductors is analysed Finally, we present recent results for electrochemical deposition of gold, copper and platinum onto n-type silicon

https://iopscience.iop.org/article/10.1088/0022-3727/31/16/001/pdf

Electrochemical deposition of metals onto silicon

The formation of porous GaAs in HF solutions

In semiconductor electrochemistry there is considerable confusion concerning the potential distribution at the semiconductor/solution interface under weak depletion and accumulation conditions. The...

The potential distribution at the semiconductor/solution interface

Determination of the band bending in a semiconductor in contact with a solution is not straightforward since the potential is partitioned between the space charge layer in the semiconductor and the Helmholtz layer on the solution side of the interface. In deep depletion, a change in the applied potential usually appears across the space charge layer, however, under conditions of weak depletion or accumulation, the applied potential is partitioned between the two double layers and the band bending is usually unknown. In this article we show how microwave reflectivity measurements can be used to determine the potential distribution at the semiconductor/solution interface.

Characterization of silicon surfaces in HF solution using microwave reflectivity

Microwave reflectivity can be used to probe the electrical properties of the semiconductor/solution interface by measuring the reflectivity response to a modulation in the band bending. We use a multiphase stratified media model to calculate the microwave reflectivity for a semiconductor in contact with a solution. The reflectivity change produced by such systems is related to the frequency of the microwave source, the thickness of the semiconductor, the thickness of the space charge layer of the semiconductor, the dielectric constants, and conductivities of the various media. The sensitivity factor of this model is compared to experimental results for silicon surfaces.

Arun Natarajan

Papers

Electrochemical deposition of metals onto silicon

The formation of porous GaAs in HF solutions

The potential distribution at the semiconductor/solution interface

Characterization of silicon surfaces in HF solution using microwave reflectivity

Theory of potential modulated microwave reflectivity at semiconductor surfaces