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

Dark and photoconductivities, drift mobilities and diffusion lengths of α-Si, Ge:H, F alloys are reported. Structural inhomogeneity of un-alloyed Ge and alloys with high Ge concentration has been observed with X-ray diffraction and Raman scattering.

Transport properties of α-Si, Ge:H alloys prepared from SiF4, GeF4 and H2 in R.F. or D.C. Glow discharges

We report the deposition and comprehensive evaluation of a hydrogenated, fluorinated amorphous silicon‐germanium alloy with an optical gap of 1.28 eV. This low‐gap alloy of the a‐Si, Ge system possesses a small midgap defect density (6.5×1016 cm−3), and useful electron (σph/σd=23) and hole (LD=0.13 μm) transport properties. The alloy was grown by radio‐frequency plasma‐enhanced decomposition of SiF4, GeF4, and H2 in a reactor built to ultrahigh‐vacuum specifications.

Optical and electronic properties of an amorphous silicon‐germanium alloy with a 1.28 eV optical gap

In modulators that rely on changing refractive index, switching energy is primarily dependent upon the volume of the active optical mode. Photonic crystal microcavities can exhibit extremely small mode volumes on the order of a single cubic wavelength with Q values above 106. In order to be useful for integration, however, they must be embedded in oxide, which in practice reduces Q well below 103, significantly increasing switching energy. In this work we show that it is possible to create a fully oxide-clad microcavity with theoretical Q on the order of 105. We further show that by using MOS charge depletion this microcavity can be the basis for a modulator with a switching energy as low as 1 fJ/bit.

Ultra-low power modulators using MOS depletion in a high-Q SiO₂-clad silicon 2-D photonic crystal resonator.

These proceedings collect papers on lasers Topics include: design requirements for high power lasers, modular optics, free-electron laser photoelectric injectors, liquid crystal optics for laser systems, nonlinear optical properties, and abrasion-resistant porous silica antireflective coatings

Laser optics for intracavity and extracavity applications

Publisher Summary This chapter discusses the photoluminescence and electroluminescent devices of porous silicon. Radiative recombination of an electron with a hole across the bandgap of semiconductors produces luminescence. The emitted photons have energy equal to the bandgap energy and a momentum that is negligible. Thus, the electron and the hole must be located at the same point in the Brillouin zone, which is the case in direct gap semiconductors, such as GaAs. Under these conditions, the radiative recombination rate is large and the radiative lifetime is short (typically of the order of a few nanoseconds for a dipole-allowed transition). Silicon (Si) is an indirect gap semiconductor, in which electrons and holes are found at different locations in the Brillouin zone. Therefore, recombination by emission of a single photon is not possible. Photon emission is possible only if another particle, such as a phonon, capable of carrying a large momentum is involved. In this case, both energy and momentum can be conserved in the radiative transition.

Philippe M. Fauchet

Papers

Transport properties of α-Si, Ge:H alloys prepared from SiF4, GeF4 and H2 in R.F. or D.C. Glow discharges

Optical and electronic properties of an amorphous silicon‐germanium alloy with a 1.28 eV optical gap

Ultra-low power modulators using MOS depletion in a high-Q SiO₂-clad silicon 2-D photonic crystal resonator.

Laser optics for intracavity and extracavity applications

Chapter 6 Porous Silicon: Photoluminescence and Electroluminescent Devices