Using atomic layer deposition (ALD), we show that Pt nanoparticles can be deposited on the inner surfaces of carbon aerogels (CA). The resultant Pt-loaded materials exhibit high catalytic activity for the oxidation of CO even at loading levels as low as approximately 0.05 mg Pt/cm2. We observe a conversion efficiency of nearly 100% in the 150-250 degrees C temperatures range, and the total conversion rate seems to be limited only by the thermal stability of the CA support in ambient oxygen. The ALD approach described here is universal in nature, and can be applied to the design of new catalytic materials for a variety of applications, including fuel cells, hydrogen storage, pollution control, green chemistry, and liquid fuel production.

Following the work of John [1] and Yablonovitch, [2] the study of photonic crystals (PCs) has become an important area of research for applications in optoelectronics and electromagnetics, as well as chemical and biological sensors. Formation of a complete photonic bandgap (PBG) requires a three-dimensional (3D) periodic structure exhibiting high refractiveindex contrast. PCs based on infiltration of self-assembled opals are promising structures, [3±5] and a full PBG at infrared wavelengths has been produced in a silicon PC. [6,7] Also, transparent materials with indexes ranging from~1.4 (SiO 2 ) to 3.8 (Sb 2 S 3 ) have been used to form inverse opals with pseudophotonic bandgaps (PPBGs) and potentially full PBGs in the visible-wavelength range.[8±12] Two-dimensional (2D) and 3DPC structures are being extensively modeled, and these studies show that changes in the structures, such as shifting the distribution of dielectric material, can significantly improve PBG properties. The importance of the precise placement of the dielectric material is demonstrated by the inverted ªshellº structure, where the opal is infiltrated with a conformal shell-like coating, leaving small air pockets in the face-centered cubic (fcc) interstitial sites. For example, in a silicon inverse shell opal, the width of the PBG can be increased from 4.25 % to 8.6 %. [13] Similarly, the PBG width can also be increased to 9.6 % by formation of a non-close-packed structure. [14] Thus, the performance of these structures critically depends on precisely and accurately placed high-dielectric material, and the fabrication of these optimized structures will require a highly controllable infiltration method. Similarly, even for 2D and 3D photonic crystals not based on the opal architecture, highly controllable deposition methods will be imperative for maximizing desired photonic effects in real structures. Atomic layer deposition (ALD) allows formation of low porosity, conformal films with submonolayer control.[15] These features make ALD ideal for infiltration, and we have successfully used the technique to create ZnS/Mn inverse opals. [16,17] A similar layer-by-layer method has also been demonstrated to increase the mechanical stability and oxide-filling fraction of a SiO 2 opal using SiCl 4 and H 2 O precursors. [18] In this paper, we extend the ALD studies to TiO 2 , which has long been a candidate material for use in PCs because its refractive index (n) can exceed 2.8 and 2.65 (k = 500 nm) for the rutile and anatase phases, respectively. [3,19±21] Unfortunately, the growth methods used to date have resulted in infiltration filling fractions of, at most, 50 % of the available pore volume. In addition, these opals were infiltrated either by solution precipitation or by nanoparticle co-sedimentation, neither of which offers much precision in placement of the high-dielectric material. Infiltration by ALD holds promise for attaining inverse shell opals that exhibit filling fractions very close to the optimum 90 % of the pore volume. For this study, ...

A novel approach is presented for the large-scale fabrication of ordered TiO 2 nanobowl arrays. The process starts with a self-assembled monolayer of polystyrene spheres, which is used as a template for atomic layer deposition of a TiO 2 layer. After ion-milling, toluene-etching, and annealing of the TiO 2 -coated spheres, ordered arrays of nanostructured TiO 2 nanobowls have been fabricated. The nanobowls exhibit smooth interior and exterior surfaces and uniform sizes and thickness. The nanobowl arrays have been demonstrated to be useful for selecting spheres smaller than the inner diameter of the bowls. This approach can be extended to a wide range of coating materials and substrates (ceramics, metals, polymers, glasses) with controlled wall thickness and size.Monolayer self-assembly (MSA) of polystyrene (PS) submicron spheres on a flat substrate 1,2 is an effective and economical technique for fabricating patterns on a relatively large scale.3,4 The catalyst pattern created by MSA has been applied for growing aligned and spatial-distribution controlled carbon nanotubes 5 and oxide nanorods. 6 Atomic layer deposition (ALD), in which film growth is a cyclic, multistep process of alternating surface-limited chemical reactions, has been demonstrated to be a powerful technique for fabrication of high-quality and multifunctional thin films on various substrates. 7,8 A diversity of nanostructures can be synthesized using ALD owing to its wide operation temperature and precursor adaptability. For example, by controlling the thickness of the uniformly deposited films, a templateassisted ALD process has been applied to the fabrication of inverse opal structures 9,10 and quasi-one-dimensional (1D) nanostructures. 11,12 In this paper, we present a process that utilizes MSA and ALD for fabricating arrays of TiO 2 nanobowls. The TiO 2 nanobowls exhibit smooth surfaces and uniform size and thickness. The nanobowls may be used as ultra small containers for holding fluid of nanoscale volume, and are also demonstrated to be useful for the size selection of submicron spheres. The approach presented could be extended to a wide range of coating materials and substrates with controlled wall thickness and size.The experimental procedures are schematically illustrated in Figure 1. First, a monolayer of highly ordered PS spheres (505 nm in diameter) was self-assembled onto a sapphire substrate (5 mm × 5 mm) using a technique we reported previously 6 (Figure 1a). The substrate was placed at the center of an ALD chamber, which was kept at 80°C during the entire growth process. Then, pulses of TiCl 4 vapor and H 2 O vapor were introduced sequentially into the chamber under a vacuum of 4.5 × 10 -3 Torr. The pulse duration was 4 s for each precursor, and the pulses were separated by a N 2 purging gas for 10 s. A TiO 2 layer was slowly grown on the surfaces of the PS spheres and the substrate (Figure 1b). The growth was terminated after 200 pulse cycles, which produced a uniform amorphous TiO 2 layer ∼20 nm in thickness. The estima...