A highly ordered metal nanohole array (platinum and gold) was fabricated by a two-step replication of the honeycomb structure of anodic porous alumina. Preparation of the negative porous structure of porous alumina followed by the formation of the positive structure with metal resulted in a honeycomb metallic structure. The metal hole array of the film has a uniform, closely packed honeycomb structure approximately 70 nanometers in diameter and from 1 to 3 micrometers thick. Because of its textured surface, the metal hole array of gold showed a notable color change compared with bulk gold.

https://science.sciencemag.org/content/sci/268/5216/1466.full.pdf

Ordered Metal Nanohole Arrays Made by a Two-Step Replication of Honeycomb Structures of Anodic Alumina

Materials with nanoscopic dimensions not only have potential technological applications in areas such as device technology and drug delivery but also are of fundamental interest in that the properties of a material can change in this regime of transition between the bulk and molecular scales. In this article, a relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed. This method entails synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes used contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. This "template" method has been used to prepare polymers, metals, semiconductors, and other materials on a nanoscopic scale.

https://science.sciencemag.org/content/sci/266/5193/1961.full.pdf

Nanomaterials: a membrane-based synthetic approach.

This paper reviews a relatively new method for preparing nanomaterials:  membrane-based synthesis. This method entails the synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes employed contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. These nanocylinders may be either hollow (a tubule) or solid (a fibril or nanowire). We call this approach the “template” method because the pores in the nanoporous membranes are used as templates for forming the desired material. This template method is a very general approach; it has been used to prepare nanotubules and fibrils of polymers, metals, semiconductors, carbons, and other materials.

Membrane-Based Synthesis of Nanomaterials

The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.

https://science.sciencemag.org/content/sci/267/5204/1629.full.pdf

Self-Assembled Metal Colloid Monolayers: An Approach to SERS Substrates.

A highly ordered gold nanodot array was fabricated by vacuum evaporation using an anodic porous alumina membrane with through-holes of nanometer scale as a mask. This technique resulted in an orderly arrangement of Au dots with a diameter of approximately 40 nm over a large area on a Si substrate.

https://iopscience.iop.org/article/10.1143/JJAP.35.L126/pdf

Fabrication of gold nanodot array using anodic porous alumina as an evaporation mask

Long, nanometer-size metallic wires can be synthesized by injection of the conducting melt into nanochannel insulating plates. Large-area arrays of parallel wires 200 nanometers in diameter and 50 micrometers long with a packing density of 5 x 108 per square centimeter have been fabricated in this way. When charged, the ends of the wires generate strong, short-range electric fields. The nanowire electric fields have been imaged at high spatial resolution with a scanning force microscope.

https://science.sciencemag.org/content/sci/263/5148/800.full.pdf

Nanowire Array Composites

The epitaxial growth of an insulator, BaF 2 , and semiconductors of the II-VI and the IV-VI families on Si substrates were carried out. In-situ XPS analyses during the growth of the first monolayers were used to study the surface chemical reactions involved. The results point to a common ingredient in these growths: that the Ba atoms are involved in forming interfacial compounds that would facilitate the heteroepitaxies. In the case of BaF 2 /Si, a BaSi 2 compound has been identified previously. In the case of PbTe and CdTe, the heteroepitaxies on Si are made possible with the BaSi 2 buffer. As a result, the impinging semiconductor molecules are broken up, and the metallic elements are ejected from the BaSi 2 surface. A new surface chemical, BaTe, is thereby formed. These surface Ba compounds appear to be the dominant factors as the crystal orientations of the BaF 2 , CdTe, and PbTe layers are independent of those of the Si substrates.

The Role of Barium in the Heteroepitaxial Growth of Insulator and Semiconductors on Silicon

: Raman scattering measurements have been performed on semiconductor- insulator nanocomposites in which the semiconducting phase occupies a significant (30%) volume fraction. The composites have been synthesized by high pressure injection of the conducting melt into the nanochannels of commercially available insulating matrices. The optical phonon spectra of GaSb- and Te-SiO, composites exhibit shifts, broadenings, and asymmetries when compared to those of the semiconducting bulk. These are interpreted in terms of strains and phonon confinement in the microcrystalline semiconducting phase. X-ray diffraction measurements allow us to correlate the effects of crystallite size and strains on the optical modes of the composites.

Raman and X-Ray Scattering from Defense Semiconductor-Dielectric Nanocomposites

Raman scattering measurements have been performed on semiconductor-insulator nanocomposites in which the semiconducting phase occupies a significant (30%) volume fraction. The composites have been synthesized by high pressure injection of the conducting melt into the nanochannels of commercially available insulating matrices. The optical phonon spectra of GaSb- and Te-SiO2 composites exhibit shifts, broadenings, and asymmetries when compared to those of the semiconducting bulk. These are interpreted in terms of strains and phonon confinement in the microcrystalline semiconducting phase. X-ray diffraction measurements allow us to correlate the effects of crystallite size and strains on the optical modes of the composites.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400449742

Raman and X-Ray Scattering from Dense Semiconductor-Dielectric Nanocomposites

The authors report on the Raman scattering spectra and fundamental absorption edge of dense semiconductor-insulator nanocomposites. These were synthesized by injection of the semiconducting melt into the channels of dielectric matrices. The Raman spectra exhibit shifts, broadenings, and asymmetries consistent with phonon confinement in nanometre-size shifts, broadenings, and asymmetries consistent with phonon confinement in nanometre-size semiconductor crystallites. Nanoscale networks of small effective mass semiconductors show evidence for electron confinement as manifested by a blue shift of the fundamental absorption edge.

C. A. Huber

Papers

Nanowire Array Composites

The Role of Barium in the Heteroepitaxial Growth of Insulator and Semiconductors on Silicon

Raman and X-Ray Scattering from Defense Semiconductor-Dielectric Nanocomposites

Raman and X-Ray Scattering from Dense Semiconductor-Dielectric Nanocomposites

Synthesis and optical properties of dense semiconductor-dielectric nanocomposites