This article presents an overview of the essential aspects in the fabrication of silicon and some silicon/germanium nanostructures by metal-assisted chemical etching. First, the basic process and mechanism of metal-assisted chemical etching is introduced. Then, the various influences of the noble metal, the etchant, temperature, illumination, and intrinsic properties of the silicon substrate (e.g., orientation, doping type, doping level) are presented. The anisotropic and the isotropic etching behaviors of silicon under various conditions are presented. Template-based metal-assisted chemical etching methods are introduced, including templates based on nanosphere lithography, anodic aluminum oxide masks, interference lithography, and block-copolymer masks. The metal-assisted chemical etching of other semiconductors is also introduced. A brief introduction to the application of Si nanostructures obtained by metal-assisted chemical etching is given, demonstrating the promising potential applications of metal-assisted chemical etching. Finally, some open questions in the understanding of metal-assisted chemical etching are compiled.

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Metal-Assisted Chemical Etching of Silicon: A Review

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

Nanotechnology is providing new solutions and opportunities to ensure sustainable energy and environments for the future. Materials of nanofiberous morphology are attractive to solve numerous energy and environmental issues. Nanofibers can be effectively produced by electrospinning, which is a simple and low cost technique. In addition, electrospinning allows the production of nanofibers from various materials e.g. organics and inorganics in different configurations and assemblies. This is highly beneficial for energy devices, where inorganic materials especially metal oxides can be synthesized and electrospun, improving conducting and ceramic properties. Excitonic solar cells fabricated with aligned nanofiberous metal oxide electrodes provide higher solar–electric energy conversion efficiency, whereas fuel cells made with nanofiberous electrodes enable uniform dispersion of catalysts, and thus increase electrocatalytic activity to obtain higher chemical–electric energy conversion efficiency. The nanofibers used in filtration membranes for environmental remediation, minimize the pressure drop and provide better efficiency than conventional fiber mats. The large surface area-to-volume ratio of nanofiber membranes allows greater surface adsorption of contaminants from air and water, and increases the life-time of the filtration media. This review highlights the potential and application of electrospun nanofiberous materials for solving critical energy and environmental issues.

Electrospun nanofibers in energy and environmental applications

Several hundred thousands of tons of ZnO are used by per year, e.g. as an additive to concrete or to rubber. In the field of optoelectronics, ZnO holds promises as a material for a blue/UV optoelectronics, alternatively to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits, which are transparent in the visible or for semiconductor spintronics. The main problem is presently, however, a high, reproducible and stable p-doping. We review in this contribution partly critically the material growth, fundamental properties of ZnO and of ZnO-based nanostructures, doping as well as present and future applications, with emphasis on the electronic and optical properties including stimulated emission. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO : From basics towards applications

Hydrothermal technology for nanotechnology

ZnO films with orientations of (001), (110), and (100) were fabricated on silicon by different substrate biases at low temperature. Dynamic cathodoluminescence (CL) dependence on electron bombardment revealed unstable Zn-N bonding if N2 was used as a predecessor. CL under various accelerated voltages showed the possible energies of Zn-N. N-related photoluminescence (PL) at low temperature confirmed that nitrogen was released after annealing. These N-doping behaviors agreed to the theoretical calculation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400113181

Controlled Growth of ZnO films on Si Substrate and N-doping Behavior

We have demonstrated that gas pressure (pG) is a key parameter for fabricating stoichiometric LiNbO3 thin films during laser ablation. To theoretically describe the influence of pG, a cylindroid rigid-wall model was presented. It was shown that there exist two critical pressures related to Li and Nb: pLi and pNb(pLi<pNb). They separate pG into three intervals. When pG<pLi, pG has little influence on film stoichiometry and the obtained films contain fixed Li deficiency. When pLi⩽pG⩽pNb, pG plays an important role in forming stoichiometric films. When pG⩾pNb, the change of pG does not affect film stoichiometry, but the film growth because of greatly reduced energies of the species that reach the substrate. The presented theory was in good agreement with experiments. This model provides a useful way for growing multicomponent films by pulsed laser deposition.

Cylindroid rigid-wall simulation of the influence of gas pressure in pulsed laser deposition of LiNbO3 films

Via electroless metal deposition and industrial plasma technology, we have successfully synthesized unique composite silicon nanowire structures with diamondlike carbon (DLC) sheaths acting as inorganic passivation layers. We have also discussed their growth mechanism in terms of a self-organization process. The thickness of the DLC sheaths were quantified with Raman spectroscopy. The Raman analytical result is in good agreement with direct microstructure observations.

Si nanowires sheathed with thin diamondlike carbon films

Infrared photoluminescence from Ge+-implanted SiO2 film

The structure and optical properties of poly {[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene]-alt-[2,5-diphenylene-1,3,4-oxadiazole vinylene]} (MEH-OPPV) are studied by examining and analyzing the photoluminescence, absorption, and Fourier transform infrared spectra of the MEH-OPPV films annealed at different temperatures It is revealed that MEH-OPPV is of high thermal stability due to aryl-substituted oxadiazole groups introduced in the polymer backbone, which increases the conformational disorder to result in short conjugation lengths in MEH-OPPV Because the interchain distance and the conjugation length are restricted by the large dihedral angle between the adjacent monomer units, the relaxation of the polymer chains cannot change the electron structures during thermal annealing As a result, the optical properties of MEH-OPPV in the film are nearly unaffected by thermal annealing

Gg G. Siu

Papers

Controlled Growth of ZnO films on Si Substrate and N-doping Behavior

Cylindroid rigid-wall simulation of the influence of gas pressure in pulsed laser deposition of LiNbO3 films

Si nanowires sheathed with thin diamondlike carbon films

Infrared photoluminescence from Ge+-implanted SiO2 film

Stable optical emission from annealed poly (p-phenylene vinylene) derivative films containing oxadiazole