Showing papers by "Ralph G. Nuzzo published in 2002"
TL;DR: A new soft-lithographic method for micropatterning polymeric resists, Decal Transfer Microlithography (DTM), is described, which offers useful new capabilities for the design and fabrication of advanced planar and 3D microfluidic assemblies and microreactors.
Abstract: A new soft-lithographic method for micropatterning polymeric resists, Decal Transfer Microlithography (DTM), is described. This technique is based on the transfer of elastomeric decal patterns via the engineered adhesion and release properties of a compliant poly(dimethylsiloxane) (PDMS) patterning tool. An important feature of the DTM method is the exceptionally broad spectrum of design rules that it embraces. This procedure is capable of transferring micron to submicron-sized features with high fidelity over large substrate areas and potentially simplifies to a significant degree the requirements for effecting multiple levels of registration. The DTM method offers some potential advantages over other soft-lithographic patterning methods in that it is amenable to transferring resist patterns with both open and closed forms, negative and positive image contrasts, and does so for a wide variety of aspect ratios and a significant range of pattern pitches that can be accommodated without degradation due to mechanical distortions of the pattern transfer tool. The most significant advance embodied in the DTM method, however, is that it offers useful new capabilities for the design and fabrication of advanced planar and 3D microfluidic assemblies and microreactors.
196 citations
TL;DR: In this article, a solution-based procedure that affects the bulk recrystallization of Au and Au/Cu alloy thin films was described, and the films were sequentially treated with piranha solution (3:1 concentrated H2SO4/30% H2O2).
Abstract: We describe a solution-based procedure that affects the bulk recrystallization of Au and Au/Cu alloy thin films. Nanocrystalline Au or Au/Cu films of 1800−2000 A in thickness were deposited on glass substrates by DC-plasma-source sputtering. A 5 A thick Ti layer was used to promote the adhesion of these films to the substrate. The films were sequentially treated with piranha solution (3:1 concentrated H2SO4/30% H2O2), followed by immersion in 3:1:16 HCl/HNO3/H2O. Atomic force microscopy (AFM) revealed that this treatment results in a coalescence of the fine-scale metal grains into larger, often irregular shaped domains. Commercially acquired films grown by thermal evaporation behaved in a similar manner but displayed more extensive grain growth. X-ray diffraction (XRD) rocking angle measurements made of the Au(222) peak show a reduction in the fwhm of approximately 50−80% in the treated Au films, indicating that the oxidative treatment induces a significant bulk recrystallization of the metal. The dynamic...
43 citations
Princeton University1, Cornell University2, Columbia University3, Texas A&M University4, North Carolina State University5, California Institute of Technology6, Rensselaer Polytechnic Institute7, University of Tennessee8, University of California, Davis9, University of Illinois at Urbana–Champaign10, Georgia Institute of Technology11, University of Michigan12, University of Notre Dame13, Massachusetts Institute of Technology14, Stanford University15, Newcastle University16, University of Valencia17, University of California, Los Angeles18, Lawrence Livermore National Laboratory19, University of Houston20, Michigan State University21, University of North Carolina at Chapel Hill22, University of Texas at Austin23, University of Chicago24, National Renewable Energy Laboratory25, University of Arkansas26, Oak Ridge National Laboratory27, United States Naval Research Laboratory28, National Institute of Standards and Technology29, Ohio State University30, University of California, Berkeley31
TL;DR: The second of a series of workshops planned in this topical area was held at NSF headquarters in Arlington, Virginia, in January 1998, and was designed to address the core of the field, describing how it has developed in the US and worldwide in the past decade, and how the members of the community saw the central thrusts of research and education in solid state chemistry proceeding in the next several years as discussed by the authors.
26 citations
TL;DR: These experiments highlighted the importance of the surface chemistry of PDMS, especially as it pertains to its ability to support stable electroosmotic flow within the separation device, and channel priming at high pH provides a necessary, but by itself insufficient means by which this instability can be minimized.
Abstract: This article describes the successful electrophoretic separation of simple carbohydrates in a polymeric microfluidic chip. The device fabricated in poly(dimethylsiloxane) (PDMS) is found to be stable in high-pH solutions. This allows sugars to be separated electrophoretically at pH values at or above their pK(a) using indirect fluorescence detection. Signal-to-noise values greater than 10:1 were obtained using a mercury arc lamp excitation source and a fluorescein-containing mobile phase for the detection of sugars at concentrations as low as 5 mM. The results obtained compare favorably with published results for the same system using a traditional fused-silica capillary. Analysis of the data revealed a significant experimental sensitivity of the migration times measured in these PDMS devices, an aging effect that leads to considerable systematic drift over the course of a series of replicate measurements. These experiments highlighted the importance of the surface chemistry of PDMS, especially as it pertains to its ability to support stable electroosmotic flow within the separation device. Channel priming at high pH provides a necessary, but by itself insufficient, means by which this instability can be minimized.
25 citations
TL;DR: Time-resolved FTIR studies that enable the direct measurement of the rate constants for the electric-field-induced orientation and thermal relaxation reveal that the dynamic transitions of the two film structures are significantly different.
Abstract: The orientation and dynamics of two 40-nm thick films of 4-n-pentyl-4'-cyanobiphenyl (5CB), a nematic liquid crystal, have been studied using step-scan Fourier transform infrared spectroscopy (FTIR). The films are confined in nanocavities bounded by an interdigitated electrode array (IDA) patterned on a zinc selenide (ZnSe) substrate. The effects of the ZnSe surface morphology (specifically, two variations of nanometer-scale corrugations obtained by mechanical polishing) on the initial ordering and reorientation dynamics of the electric-field-induced Freedericksz transition are presented here. The interaction of the 5CB with ZnSe surfaces bearing a spicular corrugation induces a homeotropic (surface normal) alignment of the film confined in the cavity. Alternately, when ZnSe is polished to generate fine grooves along the surface, a planar alignment is promoted in the liquid crystalline film. Time-resolved FTIR studies that enable the direct measurement of the rate constants for the electric-field-induced orientation and thermal relaxation reveal that the dynamic transitions of the two film structures are significantly different. These measurements quantitatively demonstrate the strong effects of surface morphology on the anchoring, order, and dynamics of liquid crystalline thin films.
13 citations
TL;DR: A split-channel microfluidic device that can be used to compensate for changes in electroosmotic flow is described, using a model adopted from the literature to precisely account for the drift that characterizes electrophoretic separations made in a polymer chip.
Abstract: Organic polymers offer many advantages as materials for the construction of microfluidic devices but suffer frequently from the limitation that the electrodynamic flow they support can exhibit considerable instability This article describes a split-channel microfluidic device that can be used to compensate for changes in electroosmotic flow The design of the separation system divides an analyte plug after injection between two separation channels of differing length The two channels are later recombined for single point detection, eliminating the need for a scanning optical detection system The utility of this simple design lies in the fact that the migration time of any analyte can be referenced to its twin in the parallel separation channel This eliminates the need for a separate electroosmotic marker and allows mobilities measured in multiple devices to be compared quantitatively Using a model adopted from the literature, the data from the split channel system can be
used to precisely account for the drift that characterizes electrophoretic separations made in a polymer chip The relative standard deviations of the analyte mobilities measured for replicate runs on multiple devices were reduced from values as high as 20% to ca 1% RSD This internal standardization procedure also appears to address other sources of drift in the electroosmotic flow (EOF) supported by the polymer microchannel, eliminating the need for careful monitoring of either the temperature or reservoir pH between separation runs
11 citations
2 citations