Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.

Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers

The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, nanotube positioning by patterning, and nanotube self-assembly for orientation. The mechanisms of nanotube growth and self-orientation are elucidated. The well-ordered nanotubes can be used as electron field emission arrays. Scaling up of the synthesis process should be entirely compatible with the existing semiconductor processes, and should allow the development of nanotube devices integrated into silicon technology.

https://science.sciencemag.org/content/sci/283/5401/512.full.pdf

Self-Oriented Regular Arrays of Carbon Nanotubes and Their Field Emission Properties

A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

The structural and luminescence properties of porous silicon

The present invention relates to a structure comprising a biological membrane and a porous or perforated substrate, a biological membrane, a substrate, a high throughput screen, methods for production of the structure membrane and substrate, and a method for screening a large number of test compounds in a short period. More particularly it relates to a structure comprising a biological membrane adhered to a porous or perforated substrate, a biological membrane capable of adhering with high resistance seals to a substrate such as perforated glass and the ability to form sheets having predominantly an ion channel or transporter of interest, a high throughput screen for determining the effect of test compounds on ion channel or transporter activity, methods for manufacture of the structure, membrane and substrate, and a method for monitoring ion channel or transporter activity in a membrane.

High throughput screen

/pdf/micro-total-analysis-systems-1-introduction-theory-and-27f7corp18.pdf

Micro Total Analysis Systems. 1. Introduction, Theory, and Technology

Recent reports describing photoluminescence in porous silicon have heightened the level of interest in it as a unique electronic material, and have created a need for a more complete understanding of the mechanism of porous silicon formation. The various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon. Because the specific surface dissolution chemistry is critical for a complete understanding of pore formation, some of the more prominent dissolution reactions are also reviewed and their relative importance to pore generation and morphology is discussed. Some aspects of the recently reported quantum effects are also reviewed. Because the mechanism of porous silicon formation involves a wide range of interdisciplinary fields, a considerable number of analogies and examples to related phenomena ...

Porous silicon formation mechanisms

This paper presents the design, fabrication and testing of a hollow microneedle array with integrated, fluidic microchannels. The microneedles are machined from single crystal silicon to a shank height of 250–350 μm with 300 μm center-to-center spacing. The needle size, density and shape are controlled by independent processing steps. Piercing of the protective stratum corenum layer of the skin by the microneedles, providing access to the living epithelial layers underneath, is successfully demonstrated. Filling of the integrated microchannels by capillary action with both non-biological fluids (glycerol, ethanol, surrogate interstitial fluid (ISF) and water) as well as biological fluids (ISF and whole blood) is demonstrated. The ability to extract interstitial fluid from human skin is successfully achieved and verified by the in situ measurement of glucose concentration. The microchip presented here represents the first step towards the realization of a transdermal, ISF extraction and analysis microsystem.

Microneedle array for transdermal biological fluid extraction and in situ analysis

Porous Silicon Formation and Electropolishing of Silicon by Anodic Polarization in HF Solution

A physical model is presented which quantitatively describes the threshold voltage instability, commonly known as drift, in n-channel Si3N4-gate and as well as Al2O3-gate pH ISFETs. The origin of the so-called drift is postulated to be associated with the relatively slow chemical modification of the gate insulator surface as a result of exposure to the electrolyte. The chemical modification of the surface is assumed to result from a transport-limited reaction whose rate is modeled by a hopping and/or trap-limited transport mechanism known as dispersive transport. The change in the chemical composition of the insulator surface leads to a decrease in the overall insulator capacitance with time, which gives rise to a monotonic temporal increase in the threshold voltage.

A physical model for drift in pH ISFETs

A method is described to control the thickness of single-crystal silicon membranes, fabricated by wet anisotropic etching. The technique of an electrochemical etch-stop on an epitaxial layer is used to yield better thickness control over the silicon membranes (+or-0.2 mu m s.d.) and hence improve the reproducibility of piezoresistive pressure sensors. The output characteristics of such sensors are compared with previously fabricated pressure sensors not utilizing accurate control over membrane thickness. The benefits of the etch-stop approach become apparent when reductions in the pressure-sensitivity variations are considered. Without etch-stop, the sensitivity on one wafer varied by a factor of two from one sensor to the other. With etch-stop, the pressure sensitivity of devices fabricated on the same wafer can be controlled to within +or-4% s.d. >

Rosemary L. Smith

Papers

Porous silicon formation mechanisms

Microneedle array for transdermal biological fluid extraction and in situ analysis

Porous Silicon Formation and Electropolishing of Silicon by Anodic Polarization in HF Solution

A physical model for drift in pH ISFETs

Study of electrochemical etch-stop for high-precision thickness control of silicon membranes