Composite stamps composed of two layerssa stiff layer supported by a flexible layersextend the capabilities of soft lithography to the generation of 50-100-nm features. The preparation of these stamps was adapted from a procedure originally developed by Schmid et al. (Macromolecules 2000, 33, 3042) for microcontact printing. This paper demonstrates how pattern transfer using other soft lithographic techniquessmicromolding in capillaries, microtransfer molding, and phase-shifting lithographyscan be improved using two-layer stamps relative to stamps made of Sylgard 184 poly(dimethylsiloxane).

The adsorption of n-alkanethiols onto polycrystalline thin films of palladium containing a strong (111) texture produces well-organized, self-assembled monolayers. The organization of the alkane chains in the monolayer and the nature of the bonding between the palladium and the thiol were studied by contact angle measurements, optical ellipsometry, reflection absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). The XPS data reveals that a compound palladium-sulfide interphase is present at the surface of the palladium film. The RAIR spectra, ellipsometry data, and wetting properties show that the palladium-sulfide phase is terminated with an organized, methyl-terminated monolayer of alkanethiolates. The local molecular environment of the alkane chains transitions from a conformationally disordered, liquidlike state to a mostly all-trans, crystalline-like structure with increasing chain length (n = 8-26). The intensities and dichroism of the methylene and methyl stretching modes support a model for the average orientation of an ensemble of all-trans-conformer chains with a tilt angle of approximately 14-18 degrees with respect to the surface normal and a twist angle of the CCC plane relative to the tilt plane of approximately 45 degrees. The SAMs are stable in air, although the sulfur present at the surface oxidizes in air over a period of 2-5 days at room temperature. The differences in chain organization between SAMs formed by microcontact printing and by solution deposition are also examined by RAIRS and XPS.

The deposition of a thin, metal film onto an array of spherical silica colloids, followed by dissolution of the colloidal template, produces metallic half-shells with nanometer-scale dimensions. Half-shells of gold, platinum, and palladium were fabricated, with diameters of the particles ranging from 100 to 500 nm, and shell thicknesses of 8−15 nm. The half-shells have three useful properties because of their geometries: (i) a high ratio of surface area to volume, (ii) a large length of edge relative to size, and (iii) an entropic resistance to assembling into close-packed structures. The surface properties of these half-shells can be modified with self-assembled monolayers (SAMs), formed by adsorption of alkanethiols. The surfaces composed of aggregated gold half-shells are superhydrophobic; the measured contact angle of water on a surface of unmodified gold half-shells was ∼151°and on a surface of gold half-shells functionalized with a hexadecanethiolate SAM was ∼163°. Aggregates of half-shells were patterned using template-assisted self-assembly. This paper describes a versatile and experimentally simple technique for fabricating hollow metallic hemispheres (which we call "half-shells") with diameters of 100-500 nm and thicknesses of 8-15 nm. The method uses monolayers or multilayers of spherical silica colloids on glass substrates as templates on which the half-shells are formed. The silica exposed at the surface of the array is coated with a thin film of metal by physical vapor deposition. Subsequent dissolution of the colloidal template releases the half-shells into a suspension. This work provides a route to another class of nanostructures useful for bottom-up assembly. 1 The semiconductor industry has developed a number of techniques, including molecular beam epitaxy (MBE), physical vapor deposition (PVD), and chemical vapor deposition (CVD), for depositing thin solid films. 2 These techniques provide control over the composition and thickness of a deposited film with precision on the order of Å. Natelson et al. used MBE and selective chemical etching to fabricate narrow trenches with critical dimensions of 3 nm on the cleaved edge of an alternating stack of AlGaAs/GaAs thin films. 3 Electron-beam and thermal evaporation sources can deposit a wide array of materials, including metals, semiconductors, alloys, and refractory compounds. 2 The combination of these methods for the deposition of thin films with the use of sacrificial structures as templates to guide the formation of particles provides a method of synthesizing nanoparticles of materials that are difficult to synthesize using other procedures.The use of templates in the formation of nanofeatured structures is common: examples include mesoporous silica and zeolites, 4 nanotubules and rods, 5 colloidal crystals and inverse opals, 6 core/shell particles, 7 and others. 8 Evaporation of metal into the spaces between crystallized arrays of spheres has been used to form tetrahedral nanoparticles with useful optical properties. 9 Evaporation of ...

▪ Abstract  Nanostructures are fabricated using either conventional or unconventional tools—that is, by techniques that are highly developed and widely used or by techniques that are relatively new and still being developed. This chapter reviews techniques of unconventional nanofabrication, and focuses on experimentally simple and inexpensive approaches to pattern features with dimensions <100 nm. The techniques discussed include soft lithography, scanning probe lithography, and edge lithography. The chapter includes recent advances in fabricating nanostructures using each set of techniques, together with demonstrated advantages, limitations, and applications for each.