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Now showing items 17 - 32 of 5260

  • Self-heating in piezoresistive cantilevers RID A-4835-2010

    Doll, Joseph C.   Corbin, Elise A.   King, William P.   Pruitt, Beth L.  

    We report experiments and models of self-heating in piezoresistive microcantilevers that show how cantilever measurement resolution depends on the thermal properties of the surrounding fluid. The predicted cantilever temperature rise from a finite difference model is compared with detailed temperature measurements on fabricated devices. Increasing the fluid thermal conductivity allows for lower temperature operation for a given power dissipation, leading to lower force and displacement noise. The force noise in air is 76% greater than in water for the same increase in piezoresistor temperature. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3595485]
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  • DEVICE FOR CALORIMETRIC MEASUREMENT

    In one aspect, provided herein is a single crystal silicon microcalorimeter, for example useful for high temperature operation and long-term stability of calorimetric measurements. Microcalorimeters described herein include microcalorimeter embodiments having a suspended structure and comprising single crystal silicon. Also provided herein are methods for making calorimetric measurements, for example, on small quantities of materials or for determining the energy content of combustible material having an unknown composition.
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  • Natural advection from a microcantilever heat source RID B-1123-2009

    Kasper, Matthew J.   Natrajan, Vinay K.   Privorotskaya, Natalya L.   Christensen, Kenneth T.   King, William P.  

    Fluid motion induced by a microcantilever heat source immersed in water is assessed by microscopic particle image velocimetry. Large fluid velocity is observed near the heated cantilever and its magnitude increases with cantilever temperature. Neither Brownian nor thermophoretic motion of the tracer particles can account for these large velocities. Rather, this fluid motion is consistent with buoyancy-driven advection. The observation of natural advection due to a microscopic heat source is important for electronics cooling, performance of thermal sensors, and the thermal processing of small biological samples.
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  • Heterogeneity of spiral wear patterns produced by local heating on amorphous polymers

    Rice, Reginald H.   Gnecco, Enrico   King, William P.   Szoszkiewicz, Robert  

    We report on spiral wear patterns produced at constant angular velocity by hot tip atomic force microscopy (HT-AFM) on surfaces of two common amorphous polymers: polystyrene (PS) and polymethylmethacrylate (PMMA). Topography of these patterns is obtained with regular AFM cantilevers. Topography cross-sections taken from a center of each spiral at a given azimuthal angle Theta relate changes of surface corrugation h(corr) with tangential velocity v of a thermal cantilever. Polymer wear is characterized by a power law h(corr)(v) = alpha(v/v(max))(-beta), which yields a pre-factor alpha and an exponent beta. Below the glass transition temperature T-g, alpha is polymer specific and beta varies weakly between similar conditions and samples. Variations of beta are hypothesized to reflect polymer relaxation processes, which are expected to vary only weakly between amorphous polymers. At and above T-g, alpha approaches initial thermal tip indentation depth within a polymer, beta plummets, and a power law relation of h(corr) with v diverges. These results are explained by heterogeneous wear around T-g due to a local nature of glass transition. At all studied temperatures, additional wear heterogeneities are found as due to position on the polymer and Theta. Variations of alpha and beta with position on the polymer are found to be only marginally larger then uncertainties of the thermal tip-polymer interface temperature. Variations of alpha and beta with Theta are found to be largely influenced by buckling of thermal cantilevers traveling in a spiral pattern. (C) 2013 Elsevier B.V. All rights reserved.
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  • Local Nanoscale Heating Modulates Single-Asperity Friction RID B-6490-2009

    Greiner, Christian   Felts, Jonathan R.   Dai, Zhenting   King, William P.   Carpick, Robert W.  

    We demonstrate measurement and control of single-asperity friction by using cantilever probes featuring an in situ solid-state heater. The heater temperature was varied between 25 and 650 degrees C (tip temperatures from 25 2 to 120 +/- 20 degrees C). Heating caused friction to increase by a factor of 4 in air at similar to 30% relative humidity, but in dry nitrogen friction decreased by similar to 40%. Higher velocity reduced friction in ambient with no effect in dry nitrogen. These trends are attributed to thermally assisted formation of capillary bridges between the tip and substrate in air, and thermally assisted sliding in dry nitrogen. Real-time friction measurements while modulating the Lip temperature revealed an energy barrier for capillary condensation of 0.40 +/- 0.04 eV but with slower kinetics compared to isothermal measurements that we attribute to the distinct thermal environment that occurs when heating in real Lime. Controlling the presence of this nanoscale capillary and the associated control of friction and adhesion offers new opportunities for tip-based nanomanufacturing.
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  • Silicon microcantilever hotplates with high temperature uniformity

    Privorotskaya, Natalya L.   King, William P.  

    This paper presents microcantilevers with integrated heater-thermometers that are engineered to have regions of highly uniform temperature. The cantilevers are fabricated from doped single crystal silicon. Four cantilever designs are considered, where the regions of doping and the cantilever dimensions are selected to achieve the highest temperature uniformity over a region 100 mu m x 100 mu m at the cantilever free end. The cantilever electrical, thermal, and mechanical properties were characterized using laser vibrometry and Raman spectroscopy. The temperature uniformity achieved is 2-4%, varying slightly over the temperature range 25-200 degrees C and varying between the cantilever designs. The cantilevers are of size suitable for operation in AFM or as cantilever sensors. (C) 2009 Elsevier B.V. All rights reserved.
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  • Cadherin-Mediated Cell-Cell Contact Regulates Keratinocyte Differentiation

    Charest, Joseph L.   Jennings, Jean M.   King, William P.   Kowalczyk, Andrew P.  

    Cell-extracellular matrix (ECM) and cell-cell interactions regulate keratinocyte cell fate and differentiation. In the present analysis, we examined the differentiation of primary human keratinocytes cultured on micropatterned substrates that varied the extent of cell-cell contact while maintaining constant cell-ECM areas. Bowtie-shaped micropatterned areas (75-1600 mu m(2)) were engineered to either permit or prevent cell-cell contact for pairs of adherent keratinocytes. Cell pairs with direct cell-cell contact exhibited enhanced expression of the differentiation markers involucrin and keratin 10 compared to cells with no cell-cell contact. In contrast, available cell-spreading area, as regulated by pattern size, did not alter keratinocyte involucrin expression. Disruption of E-cadherin binding by either antibody blocking or expression of a dominant-negative receptor diminished the ability of micropattern-regulated cell-cell contact to modulate involucrin expression. These results demonstrate that cadherin-mediated cell-cell contact regulates early keratinocyte differentiation independently from changes in cell shape.
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  • Nanometer-scale flow of molten polyethylene from a heated atomic force microscope tip

    Felts, Jonathan R.   Somnath, Suhas   Ewoldt, Randy H.   King, William P.  

    We investigate the nanometer-scale flow of molten polyethylene from a heated atomic force microscope (AFM) cantilever tip during thermal dip-pen nanolithography (tDPN). Polymer nanostructures were written for cantilever tip temperatures and substrate temperatures controlled over the range 100-260 degrees C and while the tip was either moving with speed 0.5-2.0 mu m s(-1) or stationary and heated for 0.1-100 s. We find that polymer flow depends on surface capillary forces and not on shear between tip and substrate. The polymer mass flow rate is sensitive to the temperature-dependent polymer viscosity. The polymer flow is governed by thermal Marangoni forces and non-equilibrium wetting dynamics caused by a solidification front within the feature.
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  • Heat transfer enhancement of internal laminar flows using additively manufactured static mixers

    Kwon, Beomjin   Liebenberg, Leon   Jacobi, Anthony M.   King, William P.  

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  • Electrical noise characteristics of a doped silicon microcantilever heater-thermometer

    Corbin, Elise A.   King, William P.  

    We measure the electrical noise characteristics of doped silicon microcantilevers during cantilever self-heating over the temperature range 296-781 K. The dominant noise source is 1/f below about 10 kHz, while at higher frequency, the dominant noise source is Johnson noise. The 1/f noise matches the Hooge model. The noise floor is about 10 nV/Hz(1/2) and depends upon temperature, matching the theoretical Johnson noise. The Johnson noise-limited temperature resolution is about 1 mu K/Hz(1/2). (C) 2011 American Institute of Physics. [doi:10.1063/1.3673279]
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  • Microcantilever hotplates: Design, fabrication, and characterization

    Lee, Jungchul   King, William P.  

    This paper describes design, fabrication, and characterization of microhotplates based on microcantilevers. Six different hotplate cantilever designs are proposed to investigate heating response time and temperature uniformity. Devices were fabricated and their electrical, thermal, and mechanical characteristics were measured. The cantilevers have electrical resistance in the 1 k Omega range, consume 1-100 mW power, have a heating and cooling time constant < 1 ms, and maximum operation temperature > 1000 degrees C. The temperature uniformity was characterized and is excellent for all of the devices. These cantilevers are targeted for use where both microhotplates and microcantilevers would be useful sensing platforms. (c) 2006 Elsevier B.V. All rights reserved.
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  • Thermal conduction between a heated microcantilever and a surrounding air environment

    Kim, Kyoung Joon   King, William P.  

    This paper investigates transient heat conduction between a heated microcantilever and its air environment. Continuum finite element simulations allow detailed analysis of heat flow within and from the resistively heated microcantilever. Heat generation of 8 mW excites the cantilever with heating that is either steady, pulse, sinusoidal, or pulse duty cycle. The time-averaged heat conduction from the cantilever leg to the nearby air is typically two to six times greater than the heat conduction from the heater to the air. The cooling time constant increases as the pulse heating time increases; for heating times of 1-1000 mu s, the cooling time ranges 4.6-70 mu s. The effective heat transfer coefficients around the heater and around the leg are considerably large; on the order of 1 kW/m(2) K. This study of heat transfer between a microcantilever and its surrounding air environment will aid the design and operation of microcantilever heaters. (C) 2008 Elsevier Ltd. All rights reserved.
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  • Micromechanical devices with controllable stiffness fabricated from regular 3D porous materials

    Pikul, James H.   Dai, Zhenting   Yu, Xindi   Zhang, Huigang   Kim, Taewan   Braun, Paul V.   King, William P.  

    Hierarchical pore structures can dramatically change the mechanical properties of materials, but current methods for creating porous materials make the mechanical properties difficult to engineer. Here we present template based techniques for making three-dimensional (3D) regular macroporous microcantilevers with Young's moduli that can vary from 2.0 to 44.3 GPa. The Young's moduli can be tuned by controlling the porosity and the deformation mode, which is dependent on the pore structure. The template technique allows 3D spatial control of the ordered porous structure and the ability to use a broad set of materials, demonstrated with nickel and alumina microcantilevers.
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  • Conformal ZnO nanocomposite coatings on micro-patterned surfaces for superhydrophobicity

    Steele, Adam   Bayer, Ilker   Moran, Stephen   Cannon, Andrew   King, William P.   Loth, Eric  

    A conformal coating process is presented to transform surfaces with inherent micro-morphology into superhydrophobic surfaces with hierarchical surface structure using wet chemical spray casting. Nanocomposite coatings composed of zinc oxide nanoparticles and organosilane quaternary nitrogen compound are dispersed in solution for application. The coating is applied to a micro-patterned polydimethylsiloxane substrate with a regular array of cylindrical microposts as well as a surface with random micro-structure for the purpose of demonstrating improved non-wettability and a superhydrophobic state for water droplets. Coating surface morphology is investigated with an environmental scanning electron microscope and surface wettability performance is characterized by static and dynamic contact angle measurements. (C) 2010 Elsevier B.V. All rights reserved.
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  • Microcantilever actuation via periodic internal heating

    Lee, Jungchul   King, William P.  

    This paper reports electrothermal actuation of silicon microcantilevers having integrated resistive heaters. Periodic electrical excitation induced periodic resistive heating in the cantilever, while the cantilever deflection was monitored with a photodetector. Excitation was either at the cantilever resonant frequency, f(0), f(0)/2, or f(0)/3. When the time averaged maximum cantilever temperature was 174 degrees C, the cantilever out-of-plane actuation amplitude was 484 nm near the cantilever resonance frequency of 24.9 kHz. This actuation was sufficiently large to operate the cantilever in intermittent contact mode and scan a calibration grating of height of 20 nm. (c) 2007 American Institute of Physics.
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  • Ultrananocrystalline diamond tip integrated onto a heated atomic force microscope cantilever

    Kim, Hoe Joon   Moldovan, Nicolaie   Felts, Jonathan R.   Somnath, Suhas   Dai, Zhenting   Jacobs, Tevis D. B.   Carpick, Robert W.   Carlisle, John A.   King, William P.  

    We report a wear-resistant ultrananocrystalline (UNCD) diamond tip integrated onto a heated atomic force microscope (AFM) cantilever and UNCD tips integrated into arrays of heated AFM cantilevers. The UNCD tips are batch-fabricated and have apex radii of approximately 10 nm and heights up to 7 mu m. The solid-state heater can reach temperatures above 600 degrees C and is also a resistive temperature sensor. The tips were shown to be wear resistant throughout 1.2 m of scanning on a single-crystal silicon grating at a force of 200 nN and a speed of 10 mu m s(-1). Under the same conditions, a silicon tip was completely blunted. We demonstrate the use of these heated cantilevers for thermal imaging in both contact mode and intermittent contact mode, with a vertical imaging resolution of 1.9 nm. The potential application to nanolithography was also demonstrated, as the tip wrote hundreds of polyethylene nanostructures.
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