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.

The term 'photonics' describes a technology whereby data transmission and processing occurs largely or entirely by means of photons. Photonic crystals are microstructured materials in which the dielectric constant is periodically modulated on a length scale comparable to the desired wavelength of operation. Multiple interference between waves scattered from each unit cell of the structure may open a 'photonic bandgap'--a range of frequencies, analogous to the electronic bandgap of a semiconductor, within which no propagating electromagnetic modes exist. Numerous device principles that exploit this property have been identified. Considerable progress has now been made in constructing two-dimensional structures using conventional lithography, but the fabrication of three-dimensional photonic crystal structures for the visible spectrum remains a considerable challenge. Here we describe a technique--three-dimensional holographic lithography--that is well suited to the production of three-dimensional structures with sub-micrometre periodicity. With this technique we have made microperiodic polymeric structures, and we have used these as templates to create complementary structures with higher refractive-index contrast.

Fabrication of photonic crystals for the visible spectrum by holographic lithography

Review of the proton exchange membranes for fuel cell applications

Hollow tubular structures of molecular dimensions may offer a variety of applications in chemistry, biochemistry and materials science. Concentric carbon nanotubes have attracted a great deal of attention, while the three-dimensional tubular pore structures of molecular sieves have long been exploited industrially. Nanoscale tubes based on organic materials have also been reported previously. Here we report the design, synthesis and characterization of a new class of organic nanotubes based on rationally designed cyclic polypeptides. When protonated, these compounds crystallize into tubular structures hundreds of nanometres long, with internal diameters of 7-8 A. Support for the proposed tubular structures is provided by electron microscopy, electron diffraction, Fourier-transform infrared spectroscopy and molecular modelling. These tubes are open-ended, with uniform shape and internal diameter. We anticipate that they may have possible applications in inclusion chemistry, catalysis, molecular electronics and molecular separation technology.

Self-assembling organic nanotubes based on a cyclic peptide architecture

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

: We have recently described a template method for the synthesis of organic microtubules. This method entails the use of the pores in a microporous membrane as templates for tubule formation. The key to the tubule-formation process in the presence of molecular anchors on the pore walls, These anchors insure that the tubule-forming materials deposits as a thin skin which lines the pore wall. We describe in this paper an electrochemical template method for the synthesis of metal (Au) microtubles. We also present a general paradigm for the formation of molecular anchors on the pore walls of alumina template membranes. We believe that this paradigm should allow for the synthesis of microtubles composed of any desired material.

https://apps.dtic.mil/sti/pdfs/ADA232827.pdf

Template synthesis of metal microtubules

: Arrays containing greater than 10(exp 9) 2000A-diameter CdSe or graded CdSe/CdTe cylinders have been electrochemically synthesized within the pores of Anopore(tm) membranes. The alumina template suppresses the 'cauliflower' morphology that is typically observed in electrodeposited CdSe and CdTe films, although X-ray diffraction reveals the materials to be of poor crystallinity. The Anopore membrane template can be removed by treatment with aqueous 1M NaOH, resulting in an array of free-standing CdSe or CdSe/CdTe wires. Current-voltage data show that the Ni/CdSe array is rectifying, with a rectification ratio of 1000 at + or - 2 V.... Nanoparticles, Nanosemiconductors.

Electrochemical Fabrication of Cadmium Chalcogenide Microdiode Arrays

Microtubules are an interesting type of microstructure that resemble miniature drinking straws. Such tubular microstructures are found in nature. In addition, we and others have been investigating strategies for making synthetic analogs. We are especially interested in the idea of making metal microtubules. Four procedures for preparing metal microtubules are described in this paper. The general approach, called template-synthesis, entails using the pores in a microporous membrane as templates for forming the tubules. Microporous anodic aluminum oxide membranes and nuclear track-etch membranes are used as the template membranes. Gold and silver microtubules are made with outer diameters as small as 200 nm. These microstructures are characterized by scanning electron microscopy.

/pdf/template-synthesis-of-metal-microtubule-ensembles-utilizing-26lrlcx45q.pdf

Template synthesis of metal microtubule ensembles utilizing chemical, electrochemical, and vacuum deposition techniques

A new interfacial polymerization method for forming metal/ conductive polymer Schottky barriers

: A procedure for preparing microhole array electrodes is described. These electrodes are based on a microporous alumina filtration membrane. This membrane (Anopore) contains linear 200 nm diameter pores. These pores define the holes in the microhole array. The microelectrodes at the bottoms of the holes are formed by simply coating the back of the membrane with gold. This procedure yields an electrode with a high density of uniform microholes. Furthermore, this microhole array electrode combines very deep microholes with the smallest microhole diameters (200 nm) to be reported in the literature to date. Cyclic voltammetry was used to characterize these electrodes.

Charles J. Brumlik

Papers

Template synthesis of metal microtubules

Electrochemical Fabrication of Cadmium Chalcogenide Microdiode Arrays

Template synthesis of metal microtubule ensembles utilizing chemical, electrochemical, and vacuum deposition techniques

A new interfacial polymerization method for forming metal/ conductive polymer Schottky barriers

Microhole array electrodes based on microporous alumina membranes