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 introduction of photonic crystal fibers (PCFs) has enabled researchers to redefine the concept of optical fibers and extend their functionality beyond the realm of traditional optical transportation. The regular lattice of holes that characterizes PCFs gives rise to unique waveguiding properties, along with fascinating effects such as photonic bandgap (PBG) guidance, “endlessly single-mode” guidance and supercontinuum generation.1 Until recently, however, the periodic nature of PCFs has been used only to enhance the fibers’ longitudinal waveguiding characteristics. We have introduced another application of PCFs: the manipulation of light propagating transversely across the fiber.2 In other words we exploit the fact that the fiber’s cross-sectional profile is essentially a two-dimensional (2D) photonic crystal (PC). Figure 1(a) illustrates such a geometry, with a scanning electron micrograph of a typical microstructure. The light enters the PCF from the side, interacts with the periodic microstructure and emerges on the far side as it would in a planar PC.3 By studying its transmission and reflection characteristics both experimentally and through modeling, we have demonstrated that such a transverse fiber can indeed behave as a 2D PC. For instance, light emerges at a series of angles to form diffraction spots [Fig. 1(b)], and the transmission of certain wavelengths is suppressed by the PBG. The existence of this transverse PCF geometry leads to the possibility that a range of planar-device concepts can be designed into the fiber microstructure. In this context, the simple yet flexible fabrication of PCFs gives the transverse fiber an advantage in many respects over the variety of existing PCs. These include: smooth walls which suppress scattering; a potentially arbitrary microstructure which adds flexibility to device concepts; and tunability.

https://researchbank.swinburne.edu.au/file/de6ff2d7-499e-4483-a730-28aa316f5e3e/1/PDF (Published version).pdf

Photonic structures: lateral thinking with photonic crystal fibers

A new class of porous membrane has been fabricated that is unique in its combination of nanoscale thickness (<50 nm) with macroscopic, yet robust, millimeter-scale lateral dimensions and tunable pore size in the range of ˜5nm to ˜100nm. The membrane material is porous nanocrystalline Si (pnc-Si)1, and is being scaled-up to commercial volumes by a startup company, SiMPore, Inc. Standard commercial separation membranes with pores in this size regime are polymeric materials (poly ether sulphone, cellulose, etc.), microns in thickness, leading to pore morphologies that resemble long narrow tubes or tortuous-path 3-D matrices. As pnc-Si membrane thickness approaches the pore diameters, a simplified structure of holes in a thin sheet results, greatly enhancing both diffusive and forced flow transport through the membrane, as predicted by classical transport theories2. Pnc-Si has confirmed these theoretical predictions, demonstrating record-breaking transport rates, in addition to precise size-separation of nanoparticles, viruses, proteins, and nucleic acids. Applications for this highly precise silicon-based membrane range from highly efficient separations and purification of biomolecules, complexes, and nanoparticles, to substrates for microscopy to cell culture and co-culture. SiMPore is focused on navigating this application space with the goal of quickly introducing products that will allow the company to become self-sustaining and profitable though direct sales or partnerships with market leaders. Key product development drivers include potential competitive performance advantages and perceived value to a particular market, the IP landscape, development costs of the membrane and the device package/interface, and alignment with existing in-house capabilities.

Porous ultrathin silicon membranes for purification of nanoscale materials

The optical constants of molten silicon are not as well known as those of solid silicon. We are aware of one cw ellipsometric measurement of the dielectric function ∈ for molten Si around the visible1 and 1-ns time-resolved ellipsometric measurement of ∈ at 633 nm during pulsed excimer laser irradiation.2 With shorter pulses, there should be no problem associated with surface contamination, and it may even be possible to measure ∈ during superheating.

Optical constants of liquid silicon after picosecond laser illumination

/pdf/front-matter-volume-7888-jygfeypmc7.pdf

Front Matter: Volume 7888

Since the discovery of high-temperature superconductors (HTS), there have been intensive investigations of their transient response under ultrashort laser-pulse excitation. Recently, using the femtosecond pump-probe technique, Han et al.[1] observed a very fast (several picoseconds) optical response on YBa2Cu3Ox (YBCO) in the superconducting state under weak excitation and attributed it to the generation and recombination of quasi- particles. As the ambient temperature drops below the superconductor’s critical temperature (Tc), the transient reflectivity signal abruptly changes both its sign and temporal behavior—this striking behavior appears to be correlated to the onset of superconductivity. However, the physical significance of such an ultrafast response is still not clear, since the position of the Fermi level (EF) and the density of states near EF are not well known. Independently, a series of transient photovoltage measurements have also been performed on YBCO. Recent experimental work [2] demonstrated that for ultra-thin films the relative magnitude of the nonthermal component was enhanced and could be as fast as tens of picoseconds. The fact that the electrical response is at least one order of magnitude slower than the optical response suggests that more in-depth studies are necessary in order to find the ultimate speed of optoelectronic devices made of HTS.

Philippe M. Fauchet

Papers

Photonic structures: lateral thinking with photonic crystal fibers

Porous ultrathin silicon membranes for purification of nanoscale materials

Optical constants of liquid silicon after picosecond laser illumination

Front Matter: Volume 7888

Ultrafast Optical and Optoelectronic Response of Y-Ba-Cu-O