Now showing 1 - 10 of 108
  • Publication
    Direct measurement of periodic electric forces in liquids
    (American Institute of Physics, 2008-01-07) ; ; ;
    The electric forces acting on an atomic force microscope tip in solution have been measured using a microelectrochemical cell formed by two periodically biased electrodes. The forces were measured as a function of lift height and bias amplitude and frequency, providing insight into electrostatic interactions in liquids. Real-space mapping of the vertical and lateral components of electrostatic forces acting on the tip from the deflection and torsion of the cantilever is demonstrated. This method enables direct probing of electrostatic and convective forces involved in electrophoretic and dielectroforetic self-assembly and electrical tweezer operation in liquid environments.
      351Scopus© Citations 8
  • Publication
    Domain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopy
    (American Institute of Physics, 2005-01) ; ; ;
    The kinetics of sidewise domain growth in an inhomogeneous electric field has been investigated in stoichiometric LiNbO3 single crystals by measuring the lateral domain size as a function of the voltage pulse magnitude and duration using piezoresponse force microscopy. The domain size increases linearly with the voltage magnitude suggesting that the domain size is kinetically limited in a wide range of pulse magnitudes and durations. In spite of that, the written domains exhibit strong retention behavior. It is suggested that the switching behavior can be described by the universal scaling curve. Domain kinetics can be described as an activation process by calculating the field distribution using the charged sphere model under the assumption of an exponential field dependence of the wall velocity. The activation energy is found to be a function of the external field.
    Scopus© Citations 203  478
  • Publication
    Piezoelectricity in collagen type II fibrils measured by scanning probe microscopy
    (American Institute of Physics, 2014-08-11) ; ; ; ;
    The converse piezoelectric effect in collagen type II fibrils, the main collagen constituent in cartilage, was investigated using piezoresponse force microscopy. The fibrils exhibited shear piezoelectric behavior similar to that previously reported in collagen type I fibrils and followed the same cantilever-fibril angle dependence present for type I. A uniform polarization directed from the amine to carboxyl termini, as seen for collagen type I, was observed in all type II fibrils studied. The shear piezoelectric coefficient, d 15, however, for type II was roughly 28–32% of the value measured for type I fibrils. Possible explanations for the reduced piezoelectric coefficient of type II collagen are provided.
    Scopus© Citations 20  567
  • Publication
    Nanomechanics of Cells and Biomaterials Studied by Atomic Force Microscopy
    The behavior and mechanical properties of cells are strongly dependent on the biochemical and biomechanical properties of their microenvironment. Thus, understanding the mechanical properties of cells, extracellular matrices, and biomaterials is key to understanding cell function and to develop new materials with tailored mechanical properties for tissue engineering and regenerative medicine applications. Atomic force microscopy (AFM) has emerged as an indispensable technique for measuring the mechanical properties of biomaterials and cells with high spatial resolution and force sensitivity within physiologically relevant environments and timescales in the kPa to GPa elastic modulus range. The growing interest in this field of bionanomechanics has been accompanied by an expanding array of models to describe the complexity of indentation of hierarchical biological samples. Furthermore, the integration of AFM with optical microscopy techniques has further opened the door to a wide range of mechanotransduction studies. In recent years, new multidimensional and multiharmonic AFM approaches for mapping mechanical properties have been developed, which allow the rapid determination of, for example, cell elasticity. This Progress Report provides an introduction and practical guide to making AFM-based nanomechanical measurements of cells and surfaces for tissue engineering applications. Atomic force microscopy is an indispensable tool for nanomechanical measurements of cells, cell microenvironments, and biomaterials. The mechanical properties of cells and their function are influenced by the elasticity of the extracellular matrix. Thus, understanding the nanomechanical properties is key for tissue engineering applications.
      597Scopus© Citations 36
  • Publication
    Electric Field-Induced Chemical Surface-Enhanced Raman Spectroscopy from Aligned Peptide Nanotube–Graphene Oxide Templates for Universal Trace Detection of Biomolecules
    Semiconductor-graphene oxide-based surface-enhanced Raman spectroscopy substrates represent a new frontier in the field of surface-enhanced Raman spectroscopy (SERS). However, the application of graphene oxide has had limited success because of the poor Raman enhancement factors that are achievable in comparison to noble metals. In this work, we report chemical SERS enhancement enabled by the application of an electric field (10-25 V/mm) to aligned semiconducting peptide nanotube-graphene oxide composite structures during Raman measurements. The technique enables nanomolar detection sensitivity of glucose and nucleobases with up to 10-fold signal enhancement compared to metal-based substrates, which, to our knowledge, is higher than that previously reported for semiconductor-based SERS substrates. The increased Raman scattering is assigned to enhanced charge-transfer resonance enabled by work function lowering of the peptide nanotubes. These results provide insight into how semiconductor organic peptide nanotubes interact with graphene oxide, which may facilitate chemical biosensing, electronic devices, and energy-harvesting applications.
    Scopus© Citations 34  797
  • Publication
    Piezoresponse force microscopy for polarity imaging of GaN
    (American Institute of Physics, 2002-06) ; ; ;
    The polarity distribution of GaN based lateral polarity heterostructures is investigated by piezoresponse force microscopy (PFM). Simultaneous imaging of surface morphology, as well as the phase and magnitude of the piezoelectric response, is performed by PFM on a GaN film with patterned polarities on a c-Al2O3 substrate. We demonstrate that the polarity distribution of GaN based lateral polarity heterostructures can be deduced from the phase image of the piezoresponse with nanometer scale spatial resolution.
    Scopus© Citations 78  338
  • Publication
    Individual switching of film-based nanoscale epitaxial ferroelectric capacitors
    We have investigated the individual switching of nanoscale capacitors by piezoresponse force microscopy. Nanoscale epitaxial ferroelectric capacitors with terabyte per inch square equivalent density were fabricated by the deposition of top electrodes onto a pulsed laser deposited lead zirconate titanate thin film by electron beam evaporation through ultrathin anodic aluminum oxide membrane stencil masks. Using bias pulses, the nanoscale capacitors were uniformly switched and proved to be individually addressable. These film-based nanoscale capacitors might be a feasible alternative for high-density mass storage memory applications with near terabyte per inch square density due to the absence of any cross-talk effects. (C) 2010 American Institute of Physics. [doi:10.1063/1.3474960]
    Scopus© Citations 18  421
  • Publication
    Nanoscale characterization of β-phase HxLi1−xNbO3 layers by piezoresponse force microscopy
    We investigate a non-destructive approach for the characterization of proton exchanged layers in LiNbO3 with sub-micrometric resolution by means of piezoresponse force microscopy (PFM). Through systematic analyses, we identify a clear correlation between optical measurements on the extraordinary refractive index and PFM measurements on the piezoelectric d 33 coefficient. Furthermore, we quantify the reduction of the latter induced by proton exchange as 83 ± 2% and 68 ± 3% of the LiNbO3 value, for undoped and 5 mol. % MgO-doped substrates, respectively.
      435Scopus© Citations 8
  • Publication
    Imaging mechanism of piezoresponse force microscopy in capacitor structures
    (American Institute of Physics, 2008-04-18) ; ; ;
    The image formation mechanism in piezoresponse force microscopy (PFM) of capacitor structures is analyzed. We demonstrate that the spatial resolution is a bilinear function of film and top electrode thicknesses and derive the corresponding analytical expressions. For many perovskites, the opposite contributions of d(31) and d(33) components can result in anomalous domain wall profiles. This analysis establishes the applicability limits of PFM for polarization dynamics studies in capacitors and applies them to other structural probes, including focused x-ray studies of capacitor structures. (c) 2008 American Institute of Physics.
      330Scopus© Citations 56
  • Publication
    Breaking the limits of structural and mechanical imaging of the heterogeneous structure of coal macerals
    The correlation between local mechanical (elasto-plastic) and structural (composition) properties of coal presents significant fundamental and practical interest for coal processing and for the development of rheological models of coal to coke transformations. Here, we explore the relationship between the local structural, chemical composition, and mechanical properties of coal using a combination of confocal micro-Raman imaging and band excitation atomic force acoustic microscopy for a bituminous coal. This allows high resolution imaging (10s of nm) of mechanical properties of the heterogeneous (banded) architecture of coal and correlating them to the optical gap, average crystallite size, the bond-bending disorder of sp2 aromatic double bonds, and the defect density. This methodology allows the structural and mechanical properties of coal components (lithotypes, microlithotypes, and macerals) to be understood, and related to local chemical structure, potentially allowing for knowledge-based modeling and optimization of coal utilization processes.
      454Scopus© Citations 17