The fabrication and characterization of a glass containing a regular parallel array of submicrometer channels or capillaries are described. The capillaries are arranged in a two-dimensional hexagonal close packing configuration with channel diameters as small as 33 nanometers and packing densities as high as 3 x 10(10) channels per square centimeter. The high-temperature stability of the nanochannel glass array is well suited as a host or template for the formation of quantum confined semiconductor structures or as a mask for massively parallel patterned lithographic applications.

The preparation of thin metallic membranes containing uniform, patterned voids with diameters as small as 40 nanometers and packing densities greater than 3 x 1 O9 voids per square centimeter is described. These membranes, made of platinum, gold, tungsten, and molybdenum, have been fabricated by thin-film deposition with nanochannel glass wafers as substrates. The membranes are well suited for use as masks in substrate patterning applications such as ion implantation, reactive ion etching, and materials deposition. Results are presented on their use in the parallel patterning of silicon by direct materials deposition with features in the 100-nanometer size regime.T h e scientific and technological interest in materials engineered on a nanometer scale is widespread, impacting research and development in many disciplines. These materials have found use in electronic and optical devices ( I ), filtration (2), and biomedical applications (3, 4). In addition, these materials provide an opportunity to study quantum effectylot observed in bulk materials.In this report we describe the fabrication and patterning applications of nanochannel glass replica membranes. These membranes, prepared thus far from refractory and noble metals, are thin films that contain uniform. nanometer-scale voids, the sizes, positions, geometric patterns, and packing densities of which may be controlled to a high degree. In addition, the thicknesses of the membranes. and thus the asvect ratios of the voids, may also be controlled. These properties make nanochannel glass revlica mem--branes somewhat different than polymeric track-etch membranes and porous alumina membranes, which have been used in replication studies (5), as hosts for the fabrication of other materials (3, 6), and as electrochemically switchable filters (7). Currently, we have prepared tungsten, molybdenum, platinum, and gold membranes with void diameters as small as 40 nm at packing densities greater than 3 x lo9 voids per square centimeter. The aspect ratios of the voids present in these membranes have ranged from 0.06 to approximately 2, reflecting our primary interest in low-aspectratio masks for patterning applications.The processes used in the preparation of these membranes, however, are not limited to the materials nor the asDect ratios listed above. In principle, membranes with larger aspect ratios may be prepared, and other materials that can be deposited by physical vapor deposition may be used, provided the resulting membranes possess the necessary robust character and chemical stability to withstand the processing conditions en-

Quantum-confined nanocrystallites of GaAs are fabricated in porous Vycor glass and the bound electronic nonlinear refractive index, the two-photon absorption coefficient, and the refraction from carriers generated by two-photon absorption are simultaneously determined using the Z-scan method and compared to those of bulk GaAs. The measured nonlinear refractive index is an order of magnitude larger than that of bulk GaAs at 1060 nm.

We demonstrate the ability to fabricate large-scale patterned two-dimensional arrays of identical nanometer size metallic wires with high aspect ratios and packing densities of greater than 3 X 10' elements/cm2. The arrays are made by electrodeposition into nanochannel glass templates. Scanning electron microscopy and tunneling electron microscopy have been used to characterize the nanostructures. Magnetic characterizations of the ferromagnetic wire arrays using a superconducting quantum interference device magnetometer and a magnetic force microscope reveal one-dimensional characteristics with preferred magnetization direction perpendicular to the array film plane and enhanced coercivities compared to the bulk values. Preliminary results on fabrication of nanometer size metallic tubes are also presented. InfroductionNanostructured materials exhibit a host of interesting new phenomena directly related to their reduced dimensionality. They provide a means of studying quantum size effects, excitons, and electron-electron interactions.1'2 Magnetic nanostructures such as nanometer scale particles and wires tend to be single-domain with large coercive fields and high remanent magnetizations.3'4 The abil-

We use a near-field scanning optical microscope to study optical transmission through a two-dimensional triangular photonic crystal. Spatial variations in the intensity of light coupled through the sample depend on the photon energy and the numerical aperture of the collection optics. We discuss the relationship between the observed dependence and the local structure of the optical modes in the crystal. Features in the data arising from modes with Fourier components inside and outside the first Brillouin zone can be distinguished by this technique. ͓S0163-1829͑97͒09816-0͔With the invention of photonic devices, the ability to frequency select and direct light on microscopic length scales is rapidly becoming a reality. One device that has recently attracted much interest is a periodic dielectric structure called a photonic crystal. 1 Spatial periodicity in this device leads, for instance, to coupling of the electromagnetic field modes of neighboring dielectric waveguides. This results in a nontrivial dispersion relation between the energy and wave vector of the allowed modes, i.e., a photonic band structure. Photonic crystals can be designed to transmit or reflect light in a specific range of frequencies, 1 and their properties are tunable by, for example, modification of their periodicity or index of refraction. Defect structures could be designed to introduce impurity bands not only in selected energy ranges, but also in spatial positions. The first demonstration of bandstructure effects in photonic crystals was in the mm-wave regime. 2 Since this proof of principle, much research effort has concentrated on making structures for visible and nearinfrared light. 1 Recently, photonic band-structure effects in the near-infrared and visible have been measured 3 in twodimensional ͑2D͒ photonic crystals made from nanochannel glass ͑NCG͒ arrays. 4 Photonic crystals have been studied by measuring bulk optical properties such as attenuation and transmission, and band-structure calculations have been used to model and predict these properties. 1 A more detailed understanding can be obtained by studying the microscopic properties such as the local density of photon states and electromagnetic mode structure. Here we demonstrate the use of a transmissionmode near-field scanning optical microscope ͑NSOM͒ to measure directly the spatial variations of light coupled through the sample. The resulting optical intensity distributions depend in part on the local mode structure in the photonic crystal.For a photonic device to be useful at optical frequencies, its lattice spacing must be of the same order as the optical wavelength ͑͒. Measuring optical properties within a unit cell therefore requires resolution higher than that provided by conventional, far-field, diffraction-limited techniques. In near-field scanning optical microscopy ͑also NSOM͒, optical resolution can be better than /10, 5 limited not by but rather by the size of the subwavelength aperture used as a probe. In the study of photonic materials, NSOM has been used to me...

For a complete experimental and theoretical explanation of the magnetic processes in an interacting collection of submicron magnetic particles, a fundamental understanding of the magnetic properties of individual single-domain particles must first be achieved. We have prepared elongated Ni columns ranging in diameter from 0.15 to 1.0 m by electroplating into specially prepared Al 2 O 3 and glass channeled pore membranes. We have also prepared controlled arrays of Ni columns using e-beam lithography, subsequently electroplating into the written patterns. Using transmission electron microscopy, we have characterized the shape, size, morphology, and crystal structure of the columns. Magnetic force microscopy has been used to determine the switching field H s versus the applied field angle of the columns. Although the switching field data can be fit to the functional form for nucleation by curling in an infinite cylinder, the observed weak dependence of H s on column diameter is inconsistent with that expected for curling, particularly for columns of diameter Ͼ0.3 m.

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Nanochannel glasses, containing regular hexagonal closed packed arrays of parallel air cylinders with periods varying from 0.25 to 0.19 μm, are shown to display photonic band-gap behavior throughout the visible that is consistent with previously published theory. Immersing the glasses in liquids of various refractive indices allowed observation of the buildup of the bands as a function of cylinder dielectric constant.