Communications film, resulting in terraces of bilayer steps. The regions of arachidic acid in the mixed LB film can be removed by washing in ethanol to leave behind islands of cadmium arachidate molecules. ExperimentalLangmuir-Blodgett films of arachidic acidicadmium arachidate were prepared using a constant-perimeter barrier trough (purpose-built) located in a Class 10000 microelectronics clean room. The subphase was ultrapure water obtained from a commercial reverse osmosisideionizationiUV sterilization system. The arachidic acid (eicosanoic acid) was obtained from Sigma (99 % purity). For salt formation, CdCIp (BDH, Analar Grade) was added to the suhphase to give an overall concentration of 2.5 x lo4 M. The pH was adjusted to 5.7i0.1 by the addition of HCI (BDH, Aristar Grade) or ammonia solution (BDH, Aristar Grade). Transfer of the floating monolayers onto hydrophilic silicon wafers ((100) orientation) was undertaken at a suhphase temperature of 19i1 "C and a deposition pressure of 30 mN m-'. The dipping speed was 2 mm m i d . Transfer ratios for all the monolayers deposited were 1.0oi0.05.A Digital Instruments Nanoscope Ill atomic force microscope was used to examine the topographical nature of the arachidic acidicadmium arachidate LB film surface following dipping and after washing in ethanol (to remove the free acid). All of the high resolution AFM images were acquired in air at room temperature using the contact mode and a 1 pm x 1 pm piezoelectric scan head. A 200 pm narrow-legged silicon nitride cantilever with a small spring-constant ( k = 0.06 Nm-') was used to minimize film damage due to high contact forces. The lower resolution images were acquired in air using the tapping mode in conjunction with a 10 ym x 10 Fm piezoelectric scan head. This technique employs a stiff silicon cantilever oscillating at a large amplitude near its resonance frequency (several hundred kilohertz) which is detected by an optical beam system. AFM images are presented as unfiltered data in gray-scale and were found to be stable and unchanged over long periods of observation.

The sharpness of tips used in scanning tunneling microscopy (STM) is one factor which affects the resolution of the STM image. In this paper, we report on a direct-current (dc) drop-off electrochemical etching procedure used to sharpen tips for STM. The shape of the tip is dependent on the meniscus which surrounds the wire at the air–electrolyte interface. The sharpness of the tip is related to the tensile strength of the wire and how quickly the electrochemical reaction can be stopped once the wire breaks. We have found that the cutoff time of the etch circuit has a significant effect on the radius of curvature and cone angle of the etched tip; i.e., the faster the cutoff time, the sharper the tip. We have constructed an etching circuit with a minimum cut-off time of 500 ns which uses two fast metal–oxide semiconductor field effect transistors (MOSFET) and a high-speed comparator. The radius of curvature of the tips can be varied from approximately 20 to greater than 300 nm by increasing the cutoff time of the circuit.

No abstract

With a scanning tunneling microscope (STM) operating in vacuum, we have studied the lithographic patterning of self-assembling organosilane monolayer resist films. Where the organic group is benzyl chloride, the resist layer can be patterned with electrons down to 4 eV in energy. The patterned films have been used as templates for the electroless plating of thin Ni films. Linewidths down to ∼20 nm have been observed in scanning electron micrographs of the plated films. Still smaller features are observed in STM images of the exposed organosilane films.

The surface morphology of a surface-bound colloidal Pd(II) catalyst and its effect on the particle size of an electroless Ni deposit is examined. The deposited catalyst is found to have a broad distribution of particle sizes with the largest particles reaching approximately 50 nm in diameter. Catalyst surface coverages as low as 20% are found to be sufficient to initiate complete and homogenous metallization. The distribution of particle sizes for the electroless metal deposit, found to be a function of plating time, is broad with the maximum Ni particle size exceeding 120 nm. Results indicate controlling the size of the bound catalyst is the principal determining factor in controlling the particle size of the electroless deposit. Modification of the surface by depleting the concentration of surface functional groups capable of binding catalyst is used to shift the size distribution of bound catalyst to smaller values. A resulting three-to fourfold reduction in the particle size of the electroless deposit is demonstrated.

We show that microtubule polymers can be immobilized selectively on lithographically patterned silane surfaces while retaining their native properties. Silane films were chemisorbed on polished silicon wafers or glass coverslips and patterned using a deep UV lithographic process developed at the Naval Research Laboratory. Hydrocarbon and fluorocarbon alkyl silanes, as well as amino and thiol terminal alkyl silanes, were investigated as substrates for microtubule adhesion with retention of biological activity. Microtubules were found to adhere strongly to amine terminal silanes while retaining the ability to act as substrates for the molecular motor protein kinesin. Aminosilane patterns with linewidths varying from 1 to 50 microns were produced lithographically and used to produce patterns of selectively adhered microtubules. Microtubules were partially aligned on the patterned lines by performing the immobilization in a fluid flow field. Patterns were imaged with atomic force microscopy and differential interference contrast microscopy. Motility assays were carried out using kinesin-coated beads and observed with differential interference contrast microscopy. Kinesin bead movement on the patterned microtubules was comparable to movement on microtubule control surfaces.

High-resolution lithographic performance of polymethyl methacrylate (PMMA) of molecular weights (MWs) of 50, 100, 496, and 950 K is compared. A chain scission model is used to analyze the behavior of the four molecular weight resists. The chain scission model is combined with an empirical dissolution model to successfully describe the edge profile of a bar pattern. Isolated linewidth data for the 100 and 496 K resists both fit a Monte Carlo code generated linespread function that was convolved with a Gaussian of standard deviation 9 nm. The width was comparable to that in the 950 K resist, but a factor of 3 narrower than that found for the 50 K resist. The higher molecular weight, 496 and 950 K resists showed more developer induced swelling than the lower molecular weight resists. In fact, the developer induced swelling limited the ability to develop 40 nm gratings in the 496 and 950 K resists. Reduction in developer strength produced some improvement. Etching of the supporting resist structure in the gratings was also observed, particularly in the 50 and 100 K resists. The 50 K MW resist exhibited the worst grating contrast upon development. Grating enhanced etching relative to 10 μm bar areas exposed with comparable area dose was observed. A 40 nm period grating was defined in the 100 K resist.

The ability to fabricate spatially well-defined, patterned, metal films on various substrates is critically important for numerous microelectronics applications. For example, fabrication of metal contacts and conductors is required in microwave circuits, printed wiring board (PWB) circuitry, local and global chip interconnects, and other aspects of electronics packaging technology. 1 Metal patterns are routinely used to define the opaque regions of reticles and masks for optical and X-ray lithography. Thin metal films have also been used as protective layers for pattern transfer in integrated circuit (IC) lithography due to the extremely high etching resistance of metals and/or oxides derived from elements such as titanium, 2 tungsten, 3 zirconium, 4 and nickel. 5 Many processes exist for metal pattern fabrication. Metal deposition techniques include sputtering, evaporation, chemical vapor deposition, electrolytic deposition, and electroless (EL) deposition. Of these, EL deposition 6 is particularly attractive in manufacturing because it offers the ability to metallize nonplanar, insulating substrates with low-temperature processes using simple materials and equipment at low cost. Approaches for producing lithographic patterns of metals are of two general classes: subtractive and additive. The traditional lift-off method is an example of a subtractive process wherein metal is initially homogeneously deposited over an exposed and developed photoresist; the remaining resist must then be stripped to remove metal from the regions where it is not required. Additive metallization is a simpler and less wasteful approach having distinct advantages in ease of processing and cost. A typical example of this approach involves initial deposition of a thin, homogeneous metal layer (by any of the above-mentioned techniques) onto a substrate, followed by lithographic patterning of a resist to block selected regions of the underlying metal film. The exposed metal underlayer serves as either an electrode for electrolytic 7 up-plating or as a catalytic region for EL metal deposition. 8 However, even with these approaches, the initial thin metal layer can lead to significant problems in the ultimate device structures, and subtractive steps must again be used to remove the buried metal. We therefore sought to develop an alternative process utilizing photolithography and molecular self-assembly together to spatially control the binding of a Pd EL catalyst to a substrate and initiate EL metal deposition in a fully additive manner.We have previously shown that self-assembled (SA) films of organosilanes containing ligand functional groups such as phosphines, pyridines, or alkylamines are useful for binding Pd catalysts to surfaces and that the bound catalysts initiate EL deposition. 9-12 These films are formed by chemisorption of alkoxysilane or chlorosilane precursors (typically of formula R n SiX 4Ϫn , where R contains the ligating group, X ϭ Cl, OCH 3 , or OC 2 H 5 , and n ϭ 1-3) to hydroxyl groups on the surface of various substrates...