Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics最新文献

The authors report a method for rapidly prototyping attonewton-sensitivity cantilevers with custom-fabricated tips and illustrate the method by preparing tips consisting of a magnetic nanorod overhanging the leading edge of the cantilevers. Micron-long nickel nanorods with widths of 120-220 nm were fabricated on silicon chips by electron beam lithography, deposition, and lift-off. Each silicon chip, with its integral nanomagnet, was attached serially to a custom-fabricated attonewton-sensitivity cantilever using focused ion beam manipulation. The magnetic nanorod tips were prepared with and without an alumina capping layer, and the minimum detectable force and tip magnetic moment of the resulting cantilevers was characterized by cantilever magnetometry. The results indicate that this serial but high-yield approach is an effective way to rapidly prepare and characterize magnetic tips for the proposed single-electron-spin and single-proton magnetic resonance imaging experiments. The approach also represents a versatile route for affixing essentially any vacuum-compatible sample to the leading edge of an attonewton-sensitivity cantilever.

This manuscript details a general method for patterning coplanar alkylsilane monolayers using deep-ultraviolet photolithography that has broad application for high fidelity patterning of cells of varying phenotype in long-term cultures. A polyethylene glycol monolayer was formed on a silica substrate and then patterned using 193 nm light from an ArF excimer laser. The regions of photoablation were then rederivatized with (3-trimethoxysilyl propyl) diethyltriamine (DETA), yielding high contrast cytophilic islands that promoted cell adhesion and growth. Rat hippocampal neurons, motoneurons, and myoblasts were then cultured in a defined, serum-free medium on the patterned surfaces for periods in excess of 40 days. This approach has been shown to be useful as a general method for the long-term culture of multiple cell types in highly defined spatial patterns and can be used for supporting complex cocultures for creating in vitro models for biological systems.

Corner cube retroreflectors are objects with three mutually perpendicular reflective surfaces that return light directly to its source and are therefore extremely bright and easy to detect. In this work, we have fabricated suspended corner cube retroreflectors, 5 microns in size, consisting of a transparent epoxy core and three surfaces coated with gold as ultra-bright labels for use in a rapid, low-labor diagnostic platform. The authors have demonstrated that individual cubes are easily imaged using low-cost, low numerical aperture objectives in suspension and that they remain suspended over long periods of time. Moreover, we have demonstrated that the gold outer surfaces can be decorated with proteins, and that individual cubes can be bound to magnetic sample preparation particles bearing antibodies which recognize these proteins. The bound cubes can be imaged and tracked as they move through solution in response to an external magnetic field, and we have, as such, demonstrated the principle of the new biosensing approach.

Soft-polymer based microparticles are currently being applied in many biomedical applications, ranging from bioimaging and bioassays to drug delivery carriers. As one class of soft-polymers, hydrogels are materials, which can be used for delivering drug cargoes and can be fabricated in controlled sizes. Among the various hydrogel-forming polymers, poly(ethylene glycol) (PEG) based hydrogel systems are widely used due to their negligible toxicity and limited immunogenic recognition. Physical and chemical properties of particles (i.e., particle size, shape, surface charge, and hydrophobicity) are known to play an important role in cell-particle recognition and response. To understand the role of physicochemical properties of PEG-based hydrogel structures on cells, it is important to have geometrically precise and uniform hydrogel structures. To fabricate geometrically uniform structures, we have employed electron beam lithography (EBL) and ultra-violet optical lithography (UVL) using PEG or PEG diacrylate polymers. These hydrogel structures have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy, and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirming control of chemistry, size, and shape.

A membrane that allows selective transport of molecular species requires precise engineering on the nanoscale. Membrane permeability can be tuned by controlling the physical structure and surface chemistry of the pores. Here, a combination of electron beam and optical lithography, along with cryogenic deep reactive ion etching, has been used to fabricate silicon membranes that are physically robust, have uniform pore sizes, and are directly integrated into a microfluidic network. Additional reductions in pore size were achieved using plasma enhanced chemical vapor deposition and atomic layer deposition of silicon dioxide to coat membrane surfaces. Cross sectioning of the membranes using focused ion beam milling was used to determine the physical shape of the membrane pores before and after coating. Functional characterization of the membranes was performed by using quantitative fluorescence microscopy to document the transport of molecular species across the membrane.

The ability to orient biologically active proteins on surfaces is a major challenge in the design, construction, and successful deployment of many medical technologies. As methods to orient biomolecules are developed, it is also essential to develop techniques that can an accurately determine the orientation and structure of these materials. In this study, two model protein and peptide systems are presented to highlight the strengths of three surface analysis techniques for characterizing protein films: time-of-flight secondary ion mass spectrometry (ToF-SIMS), sum-frequency generation (SFG) vibrational spectroscopy, and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. First, the orientation of Protein G B1, a rigid 6 kDa domain covalently attached to a maleimide-functionalized self-assembled monolayer, was examined using ToF-SIMS. Although the thickness of the Protein G layer was similar to the ToF-SIMS sampling depth, orientation of Protein G was successfully determined by analyzing the C₂H₅S⁺ intensity, a secondary ion derived from a methionine residue located at one end of the protein. Next, the secondary structure of a 13-mer leucine-lysine peptide (LK3₁₀) adsorbed onto hydrophilic quartz and hydrophobic fluorocarbon surfaces was examined. SFG spectra indicated that the peptide's lysine side chains were ordered on the quartz surface, while the peptide's leucine side chains were ordered on the fluorocarbon surface. NEXAFS results provided complementary information about the structure of the LK3₁₀ film and the orientations of amide bonds within the LK3₁₀ peptide.

A complete form of the van der Waals dispersion interaction between an infinitely long anisotropic semiconducting/insulating thin cylinder and an anisotropic half space is derived for all separations between the cylinder and the half space. The derivation proceeds from the theory of dispersion interactions between two anisotropic infinite half spaces as formulated in Phys. Rev. A 71, 042102 (2005). The approach is valid in the retarded as well as nonretarded regimes of the interaction and is coupled with the recently evaluated ab initio dielectric response functions of various semiconducting/insulating single wall carbon nanotubes, enables the authors to evaluate the strength of the van der Waals dispersion interaction for all orientation angles and separations between a thin cylindrical nanotube and the half space. The possibility of repulsive and/or nonmonotonic dispersion interactions is examined in detail.

Direct thermal-UV nanoimprinting of an organometallic hybrid film has been demonstrated to fabricate nanoscale features into a novel organic-inorganic solution containing selected metals. The film can be patterned at low temperature and pressure, and requires only a short processing time. When analyzed by energy dispersion X-ray spectroscopy, the authors observe both organic and metal content in the final patterned features. They have also observed that film thermal stability increases after UV and oxygen plasma treatments, which may lead to devices that perform well across a wide spectrum of temperatures.