There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

We demonstrate that a monolayer graphene membrane is impermeable to standard gases including helium. By applying a pressure difference across the membrane, we measure both the elastic constants and the mass of a single layer of graphene. This pressurized graphene membrane is the world's thinnest balloon and provides a unique separation barrier between 2 distinct regions that is only one atom thick.

/pdf/impermeable-atomic-membranes-from-graphene-sheets-xtis5huy2d.pdf

Impermeable atomic membranes from graphene sheets.

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

We use Raman spectroscopy to study the size, shape and crystallographic orientation of silicon nanocrystals formed by solid phase crystallization of amorphous Si/SiO2 superlattices (SLs) grown by radio-frequency sputtering. The first and second Raman peaks broadening, their relative positions and intensities indicate the presence of nanoscale Si objects with a degree of disorder (grain boundaries) and strain (Si/SiO2 interfaces). Shapes of Si nanocrystals sandwiched between SiO2 layers strongly influence the Si/SiO2 interface roughness, which is inferred from the intensities of folded acoustic phonon scattering. The averaged crystallographic orientation of Si nanocrystals is determined by polarized Raman analysis. The laterally elongated nanocrystals exhibit preferred crystallographic orientation along the SL axis due to orientation-dependent crystallization rates. These results demonstrate that control over Si nanocrystals structural parameters has been achieved and that solid phase crystallization of nanometer-thick amorphous Si films remains one of the most promising techniques for Si-based nanoelectronic device fabrication.

Raman Spectroscopy of Si Nanocrystals in Nanocrystalline Si Superlattices: Size, Shape and Crystallographic Orientation

Here we discuss a novel capacitive-type chemical sensor structure that uses recently discovered porous nanocrystalline silicon (pnc-Si) membranes [1] covered with metal as the capacitor plates while a polymer layer sandwiched between them serves as the sensing layer for solvent vapor detection. Pnc-Si is new ultrathin (15 nm) membrane material with pore sizes ranging from 5 to 50 nm and porosities from < 0.1 to 15 % that is fabricated using standard silicon semiconductor processing techniques. We present a study of pnc-Si membranes as a platform for such a sensor. The degree of swelling and the reversibility of the polymer/pnc-Si membrane system immersed in analyte-containing vapors are observed using optical and electrical techniques.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400012793

Hybrid Polymer/Ultrathin Porous Nanocrystalline Silicon Membranes System for Flow-through Chemical Vapor and Gas Detection

Microcrystalline Si was grown from SiF 4 and H 2 by plasma-enhanced chemical vapor deposition. The films are almost completely crystalline with a crystallite size (determined from Raman spectra) of about 60 A. The optical absorption and the electrical conductivity of these films were studied. With increasing hydrogen content in the films, the dark conductivity decreases strongly and the activation of the conductivity increases. We explain the conductivity qualitatively in terms of a grain boundary model.

Opto-Electronic Properties of μc-Si Grown from SiF4 and H2 by PECVD

Disorder in amorphous semiconductors leads to unusual and interesting optical properties. Using femtosecond time-resolved spectroscopy, we find that the scattering time of carriers in the extended states is subfemtosecond and that the electronic susceptibility is well described by a Drude model. These free carriers recombine non-radiatively in a few picoseconds and the increase in lattice temperature follows the carrier recombination with no measurable delay.

Ultrafast Scattering Times in Amorphous Silicon

The semiconductor industry association roadmap has identified interconnects as a major barrier to progress starting in 2010. Optical interconnects (OI) offer an attractive solution for chip-to-chip communications, however there is no general agreement on how to design them. Eventually, OI may also perform a large amount of intra-chip clocking and signaling, which implies that any chip-to-chip OI system must be designed to be compatible with intra-chip OI, from the points of view of manufacturability, architecture, and device design. We are exploring the use of nanoscale silicon for OI. This paper reports progress toward the demonstration of two basic building blocks of an OI system, namely a Si laser and a Si-based modulator.

Philippe M. Fauchet

Papers

Raman Spectroscopy of Si Nanocrystals in Nanocrystalline Si Superlattices: Size, Shape and Crystallographic Orientation

Hybrid Polymer/Ultrathin Porous Nanocrystalline Silicon Membranes System for Flow-through Chemical Vapor and Gas Detection

Opto-Electronic Properties of μc-Si Grown from SiF4 and H2 by PECVD

Ultrafast Scattering Times in Amorphous Silicon

The Role of Nanoscale Silicon in Optical Interconnects