Carpick, Robert W

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Now showing 1 - 10 of 36
  • Publication
    A Course in Micro- and Nanoscale Mechanics
    (2003-01-01) Carpick, Robert W
    At small scales, mechanics enters a new regime where the role of surfaces, interfaces, defects, material property variations, and quantum effects play more dominant roles. A new course in nanoscale mechanics for engineering students was recently taught at the University of Wisconsin - Madison. This course provided an introduction to nanoscale engineering with a direct focus on the critical role that mechanics needs to play in this developing area. The limits of continuum mechanics were presented as well as newly developed mechanics theories and experiments tailored to study and describe micro- and nano-scale phenomena. Numerous demonstrations and experiments were used throughout the course, including synthesis and fabrication techniques for creating nanostructured materials, bubble raft models to demonstrate size scale effects in thin film structures, and a laboratory project to construct a nanofilter device. A primary focus of this paper is the laboratory content of this course, which includes an integrated series of laboratory modules utilizing atomic force microscopy, self-assembled monolayer deposition, and microfluidic technology.
  • Publication
    Measurement of interfacial shear (friction) with an ultrahigh vacuum atomic force microscope
    (1996-03-01) Carpick, Robert W; Agraït, N.; Ogletree, D. F; Salmeron, Miguel
    We have studied the variation of frictional force with externally applied load for a Pt-coated atomic force microscope tip in contact with the surface of mica cleaved in ultrahigh vacuum. At low loads, the frictional force varies with load in almost exact proportion to the area of contact as predicted by the Johnson-Kendall-Roberts (JKR) theory [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Sec. London Ser. A 324, 301 (1971)] of elastic adhesive contacts. The friction-load relation for a deliberately modified tip shape was proportional to an extended JKR model that predicts the area-load relation for nonparabolic tips, The tip shape was determined experimentally with a tip imaging technique and was consistent with the predicted friction behavior. This demonstrates that the frictional force is proportional to the area of contact between the tip and sample. Using the JKR/extended JKR model, interfacial surface energies and shear strengths can be estimated.
  • Publication
    Lateral force calibration in atomic force microscopy: A new lateral force calibration method and general guidelines for optimization
    (2006-05-22) Cannara, Rachel J; Eglin, Michael; Carpick, Robert W
    Proper force calibration is a critical step in atomic and lateral force microscopies (AFM/LFM). The recently published torsional Sader method [C. P. Green et al., Rev. Sci. Instrum. 75, 1988 (2004)] facilitates the calculation of torsional spring constants of rectangular AFM cantilevers by eliminating the need to obtain information or make assumptions regarding the cantilever's material properties and thickness, both of which are difficult to measure. Complete force calibration of the lateral signal in LFM requires measurement of the lateral signal deflection sensitivity as well. In this article, we introduce a complete lateral force calibration procedure that employs the torsional Sader method and does not require making contact between the tip and any sample. In this method, a colloidal sphere is attached to a "test" cantilever of the same width, but different length and material as the "target" cantilever of interest. The lateral signal sensitivity is calibrated by loading the colloidal sphere laterally against a vertical sidewall. The signal sensitivity for the target cantilever is then corrected for the tip length, total signal strength, and in-plane bending of the cantilevers. We discuss the advantages and disadvantages of this approach in comparison with the other established lateral force calibration techniques, and make a direct comparison with the "wedge" calibration method. The methods agree to within 5%. The propagation of errors is explicitly considered for both methods and the sources of disagreement discussed. Finally, we show that the lateral signal sensitivity is substantially reduced when the laser spot is not centered on the detector.
  • Publication
    Synthesis and characterization of smooth ultrananocrystalline diamond films via low pressure bias-enhanced nucleation and growth
    (2008-04-02) Chen, Y. C; Zhong, X. Y; Konicek, A. R; Grierson, D. S; Tai, N. H; Lin, I. N; Kabius, Bernd; Hiller, Jon M; Sumant, A. V; Carpick, Robert W; Auciello, Orlando
    This letter describes the fundamental process underlying the synthesis of ultrananocrystalline diamond (UNCD) films, using a new low-pressure, heat-assisted bias-enhanced nucleation (BEN)/bias enhanced growth (BEG) technique, involving H2/CH4 gas chemistry. This growth process yields UNCD films similar to those produced by the Ar-rich/CH4 chemistries, with pure diamond nanograins (3–5 nm), but smoother surfaces (~6 nm rms) and higher growth rate (~1 µm/h). Synchrotron-based x-Ray absorption spectroscopy, atomic force microscopy, and transmission electron microscopy studies on the BEN-BEG UNCD films provided information critical to understanding the nucleation and growth mechanisms, and growth condition-nanostructure-property relationships.
  • Publication
    A variable temperature ultrahigh vacuum atomic force microscope
    (1995-11-01) Dai, Q.; Vollmer, R.; Carpick, Robert W; Ogletree, D. F; Salmeron, Miguel
    A new atomic force microscope (AFM) that operates in ultrahigh vacuum (UHV) is described. The sample is held fixed with spring clamps while the AMF cantilever and deflection sensor are scanned above it. Thus, the sample is easily coupled to a liquid nitrogen cooled thermal reservoir which allows AFM operation from ≈ 100 K to room temperature. AFM operation above room temperature is also possible. The microscope head is capable of coarse x-y positioning over millimeter distances so that AFM images can be taken virtually anywhere upon a macroscopic sample. The optical beam deflection scheme is used for detection, allowing simultaneous normal and lateral force measurements. The sample can be transferred from the AFM stage to a low energy electron diffraction/Auger electron spectrometer stage for surface analysis. Atomic lattice resolution AFM images taken in UHV are presented at 110, 296, and 430 K.
  • Publication
    Cantilever tilt compensation for variable-load atomic force microscopy
    (2005-04-20) Canara, Rachel J; Brukman, Matthew J; Carpick, Robert W
    In atomic force microscopy (AFM), typically the cantilever's long axis forms an angle with respect to the plane of the sample's surface. This has consequences for contact mode experiments because the tip end of the cantilever, which is constrained to move along the surface, displaces longitudinally when the applied load varies. As a result, the AFM tip makes contact with a different point on the surface at each load. These different positions lie along the projection of the lever's long axis onto the surface. When not constrained by static friction, the amount of tip-displacement is, to first order, proportional to the load and is shown to be substantial for typical AFM and cantilever geometries. The predictions are confirmed experimentally to within 15% or better. Thus, care should be taken when performing load-dependent contact mode experiments, such as friction versus load, elasticity versus load, or force versus displacement measurements, particularly for heterogeneous or topographically-varying samples. We present a simple method to reliably and precisely compensate for in-plane tip displacement that depends only on the range of vertical motion used to vary the load. This compensation method should be employed in any load-varying AFM experiment that requires the tip to scan the same line or to remain at the same point at each load. ©2005 American Institute of Physics
  • Publication
    Lateral stiffness: A new nanomechanical measurement for the determination of shear strengths with friction force microscopy
    (1997-03-24) Carpick, Robert W; Ogletree, D. F; Salmeron, Miguel
    We present a technique to measure the lateral stiffness of the nanometer-sized contact formed between a friction force microscope tip and a sample surface. Since the lateral stiffness of an elastic contact is proportional to the contact radius, this measurement can be used to study the relationship between friction, load, and contact area. As an example, we measure the lateral stiffness of the contact between a silicon nitride tip and muscovite mica in a humid atmosphere (55% relative humidity) as a function of load. Comparison with friction measurements confirms that friction is proportional to contact area and allows determination of the shear strength.
  • Publication
    Material Anisotropy Revealed by Phase Contrast in Intermittent Contact Atomic Force Microscopy
    (2002-05-17) Marcus, Matthew S; Carpick, Robert W; Sasaki, Darryl Y; Eriksson, Mark A
    Phase contrast in intermittent-contact atomic force microscopy (AFM) reveals in-plane structural and mechanical properties of polymer monolayers. This is surprising, because measurements of nanoscale in-plane properties typically require contact mode microscopies. Our measurements are possible because the tip oscillates not just perpendicular but also parallel to the sample surface along the long axis of the cantilever. This lateral tip displacement is virtually universal in AFM, implying that any oscillating-tip AFM technique is sensitive to in-plane material properties.
  • Publication
    Temperature dependence of mechanical stiffness and dissipation in ultrananocrystalline diamond
    (2009-05-28) Adiga, Vivekananda P; Sumant, A V; Suresh, S; Gudeman, C; Auciello, O; Carpick, R W; Carlisle, J A
    Ultrananocrystalline diamond (UNCD) films are promising for radio frequency micro electro mechanical systems (RF-MEMS) resonators due to the extraordinary physical properties of diamond, such as high Young’s modulus, quality factor, and stable surface chemistry. UNCD films used for this study are grown on 150 mm silicon wafers using hot filament chemical vapor deposition (HFCVD) at 680°C. UNCD fixed free (cantilever) resonator structures designed for the resonant frequencies in the kHz range have been fabricated using conventional microfabrication techniques and are wet released. Resonant excitation and ring down measurements in the temperature range of 138 K to 300 K were conducted under ultra high vacuum (UHV) conditions in a custom built UHV AFM stage to determine the temperature dependence of Young’s Modulus and dissipation (quality factor) in these UNCD cantilever structures. We measured a temperature coefficient of frequency (TCF) of 121 and 133 ppm/K for the cantilevers of 350 ìm and 400 ìm length respectively. Young’s modulus of the cantilevers increased by about 3.1% as the temperature was reduced from 300 K to 138 K. This is the first such measurement for UNCD and suggests that the nanostructure plays a significant role in modifying the thermo-mechanical response of the material. The quality factor of these resonators showed a moderate increase as the cantilevers were cooled from 300 K to 138 K. The results suggest that surface and bulk defects significantly contribute to the observed dissipation in UNCD resonators.
  • Publication
    Ultra Thin AlN Piezoelectric Nano-Actuators
    (2009-06-01) Sinha, Nipun; Wabiszewski, Graham E; Carpick, Robert W; Mahameed, Rashed; Piazza, Gianluca; Felmetsger, Valery V; Tanner, Shawn M
    This paper reports the first implementation of ultra thin (100 nm) Aluminum Nitride (AlN) piezoelectric layers for the fabrication of vertically deflecting nano-actuators. An average piezoelectric coefficient (d31~ 1.9 pC/N) that is comparable to its microscale counterpart has been demonstrated in nanoscale thin AlN films. Vertical deflections as large as 40 nm have been obtained in 18 μm long and 350 nm thick cantilever beams under bimorph actuation with 2 V. Furthermore, in-plane stress and stress gradients have been simultaneously controlled. Leakage current lower than 2 nA/cm2 at 1 V has been recorded and an average relative dielectric constant of approximately 9.2 (as in thicker films) has been measured. These material characteristics and preliminary actuation results make the AlN nano-films ideal candidates for the realization of nanoelectromechanical switches for low power logic applications.