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

Visible photoluminescence (PL) from thermally oxidized porous silicon (PSi) has been investigated in terms of polarization memory (PM). The PSi samples were prepared by anodization of (100)p+-Si wafers in a HF/ethanol solution, followed by thermal oxidation at 700–1000 °C. These oxidized PSi samples show significantly anisotropic PM which depends largely on the polarization direction of the excitation light with respect to their crystallographic axes. In addition, the anisotropic PM from samples oxidized at 800 and 900 °C shows an anomalous emission-energy dependence. It is also observed that thermal oxidation at 1000 °C results in a significant decrease in the degree of PM, although it increases with increasing oxidation temperatures for ⩽900 °C. These experimental results suggest that the PL from oxidized PSi cannot be explained as a simple extension of the PL from as-anodized PSi and should be attributed to several different origins.

http://repository.hyogo-u.ac.jp/dspace/bitstream/10132/1795/1/koyama_AIP_APL2000.pdf

Anisotropic polarization memory in thermally oxidized porous silicon

We have fabricated erbium-doped porous silicon (PSi) devices and demonstrated stable room-temperature electroluminescence (EL) at 1.54 μm under both forward and reverse bias conditions. Erbium was infiltrated into the nanostructured matrix of PSi (≤ 1019 cm—3) by cathodic electrochemical migration of the ions followed by high temperature annealing (950–1100 °C). The devices exhibit an exponential EL dependence in both bias conditions as a function of driving current and voltage. External quantum efficiencies of 0.01% have been obtained. The EL intensity in reverse bias and the transport properties of the devices show large temperature dependences. From the differences in temperature, electrical, and EL characteristics in forward and reverse biases, we believe that different excitation mechanisms are responsible for the EL.

1.54 μm Electroluminescence from Erbium‐Doped Porous Silicon Composites for Photonic Applications

Electrical tuning of high refractive index-contrast photonic bandgap (PBG) structures is required for a majority of PBG applications, particularly for integrated optics. When the host material is a semiconductor with poor electro-optical properties, tuning can be achieved by infiltrating the structure with an active optical material. In this paper we analyze the switching of electro-optic material in such structures, and suggest design rules to help achieve electrical tuning. In particular, a design concept that eliminates the electric field screening effects is proposed. The developed rules and concepts are demonstrated by the electrical tuning of liquid crystals inside two-dimensional porous silicon PBG structures. This approach can be generalized to different combinations of semiconductor PBG structures and active optical materials

Philippe M. Fauchet

Papers

Anisotropic polarization memory in thermally oxidized porous silicon

1.54 μm Electroluminescence from Erbium‐Doped Porous Silicon Composites for Photonic Applications

Electrically Tunable Silicon 2-D Photonic Bandgap Structures

Confocal imaging of porous silicon with a scanning laser macroscope/microscope

Strongly nonlinear luminescence in oxidized porous silicon films