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

The density dependence of the initial scattering rate of free carriers within nearly monoenergetic distributions is studied both experimentally and theoretically in bulk GaAs. The net decay rate of the population at the centre of such athermal distributions due to carrier-carrier scattering within the distribution is found to increase slowly, as the density of carriers to the power 0.3+or-0.1. The calculated result, which is quite insensitive to the approximation used to treat the screening of the Coulomb interaction, indicates that this carrier-carrier scattering rate increases significantly with the mean energy of the athermal distribution.

Carrier-carrier scattering within athermal distributions

The physics of highly excited semiconductors has recently been the subject of many studies, especially in connection with the problem of pulsed laser annealing. Careful experiments [1–3] have now been performed with the temporal resolution required to demonstrate that one single picosecond or femtosecond pulse can produce melting at the surface of silicon. Since the carrier relaxation time is very short ( 1020 cm−3) and hot (Te > 2000°K) plasma close to but below the melting phase transition in Si and GaAs.

Ultrafast Spectroscopy of Very Dense and Hot Electron-Hole Plasmas in Crystalline and Amorphized Semiconductors

The Raman spectrum of semiconductors is sensitive to changes in the structural, mechanical and electrical properties. We report results obtained with the Raman microprobe after laser processing or damage of semiconductor thin films. The spatial resolution in our experiments has allowed the observation of unsuspected modifications.

Raman Microscopy Of Semiconductor Films

Optical properties of size restricted Cu 2 O obtained through aqueous and non aqueous preparations are compared with those of commercially available bulk crystals. One method of synthesis involved using polyvinyl alcohol as a restraining agent in an aqueous preparation to produce nanocrystals having diameters with a mean of 11 nm and a standard deviation of 6 nm. Low-temperature spectroscopie studies indicate size restriction effects are manifest by a decrease in exciton luminescence and a 3.0 to 9.0 meV blue shift in 0,0 transition. No noticeable changes in the dynamics were observed for the nanocrystals, indicating no alteration or relaxation of the selection rules for the direct forbidden transition.

Philippe M. Fauchet

Papers

Carrier-carrier scattering within athermal distributions

Ultrafast Spectroscopy of Very Dense and Hot Electron-Hole Plasmas in Crystalline and Amorphized Semiconductors

Raman Microscopy Of Semiconductor Films

Optical Properties of Cuprous Oxide Nanocrystals

Silicon Photonics for Biology