Now showing 1 - 10 of 109
  • Publication
    Nanoscale Piezoelectric Properties of Self-Assembled Fmoc-FF Peptide Fibrous Networks
    Fibrous peptide networks, such as the structural framework of self-assembled fluorenylmethyloxycarbonyl diphenylalanine (Fmoc-FF) nanofibrils, have mechanical properties that could successfully mimic natural tissues, making them promising materials for tissue engineering scaffolds. These nanomaterials have been determined to exhibit shear piezoelectricity using piezoresponse force microscopy, as previously reported for FF nanotubes. Structural analyses of Fmoc-FF nanofibrils suggest that the observed piezoelectric response may result from the noncentrosymmetric nature of an underlying β-sheet topology. The observed piezoelectricity of Fmoc-FF fibrous networks is advantageous for a range of biomedical applications where electrical or mechanical stimuli are required.
      497Scopus© Citations 70
  • Publication
    Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals
    Local reactivity on periodically proton exchanged lithium niobate (PPE:LN) surfaces is a promising route for the fabrication of regularly spaced nanostructures. Here, using MgO-doped PPE:LN templates, we investigate the influence of the doping on the nanostructure formation as a function of the proton exchange (PE) depth. The deposition is found to occur preferentially along the boundary between MgO-doped LN and the PE region when the PE depth is at least 1.73 μm, however, for shallower depths, deposition occurs across the entire PE region. The results are found to be consistent with an increased photoconductivity of the MgO-doped LN.
      515Scopus© Citations 12
  • Publication
    Plasmon Enhanced Raman From Ag Nanopatterns Made Using Periodically Poled Lithium Niobate and Periodically Proton Exchanged Template Methods
    We study Ag nanopattern arrays formed using ferroelectric lithography based on two separate approaches, i.e., periodically poled lithium niobate (PPLN) and periodically proton exchanged (PPE) template methods. We demonstrate that such nanoarrays are plasmon active. Raman spectroscopy was applied to study molecular probe 4-aminothiophenol (4-ABT) absorbed onto a silver nanostructured array. The observed Raman spectra show peaks arising from b2 modes, which occur for plasmon enhanced Raman from 4-ABT in place of a1 modes, which occur in normal Raman scattering. We demonstrate that the PPLN and PPE substrates possess different plasmonic properties with PPE creating a stronger SERS signal relative to PPLN substrates.
    Scopus© Citations 50  754
  • Publication
    Direct evidence of mesoscopic dynamic heterogeneities at the surfaces of ergodic ferroelectric relaxors
    (American Physical Society, 2010-02) ; ; ;
    Spatial variability of polarization relaxation kinetics in the relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O-3-0.1PbTiO(3) is studied using time-resolved piezoresponse force microscopy at room temperature. Both the statistical principal component and correlation function analysis and the stretched exponent fits of relaxation curves illustrate the presence of mesoscopic "fast"and "slow" 100-200 nm regions. The spatial distribution of activation energies is reconstructed using a neural-network-based inversion of the relaxation data. The results directly prove the presence of mesoscopic heterogeneities associated with static and dynamic components of the order parameter on the surfaces of ferroelectric relaxors in the ergodic phase.
      524Scopus© Citations 80
  • Publication
    High Resolution Electromechanical Imaging of Ferroelectric Materials in a Liquid Environment by Piezoresponse Force Microscopy
    (American Phyiscal Society, 2006-06) ; ; ;
    High-resolution imaging of ferroelectric materials using piezoresponse force microscopy (PFM) is demonstrated in an aqueous environment. The elimination of both long-range electrostatic forces and capillary interactions results in a localization of the ac field to the tip-surface junction and allows the tip-surface contact area to be controlled. This approach results in spatial resolutions approaching the limit of the intrinsic domain-wall width. Imaging at frequencies corresponding to high-order cantilever resonances minimizes the viscous damping and added mass effects on cantilever dynamics and allows sensitivities comparable to ambient conditions. PFM in liquids will provide novel opportunities for high-resolution studies of ferroelectric materials, imaging of soft polymer materials, and imaging of biological systems in physiological environments on, ultimately, the molecular level.
      707Scopus© Citations 79
  • Publication
    Probing the role of single defects on the thermodynamics of electric-field induced phase transitions
    (American Physical Society, 2008-04) ; ; ;
    The kinetics and thermodynamics of first order transitions are universally controlled by defects that act as nucleation sites and pinning centers. Here we demonstrate that defect-domain interactions during polarization reversal processes in ferroelectric materials result in a pronounced fine structure in electromechanical hysteresis loops. Spatially resolved imaging of a single defect center in multiferroic BiFeO3 thin film is achieved, and the defect size and built-in field are determined self-consistently from the single-point spectroscopic measurements and spatially resolved images. This methodology is universal and can be applied to other reversible bias-induced transitions including electrochemical reactions.
      412Scopus© Citations 86
  • 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.
      647Scopus© Citations 37
  • Publication
    Investigation of the mechanism of polarization switching in ferroelectric capacitors by three- dimensional piezoresponse force microscopy
    A mechanism for the switching behavior of (111)-oriented Pb(Zr,Ti)O3-based 1×1.5 μm2 capacitors has been investigated using three-dimensional piezoresponse force microscopy (3D-PFM). A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM) has been used to map the out-of-plane and the in-plane components of the polarization. The three-dimensional polarization distribution was reconstructed by quantitative analysis of the PFM amplitude images of poled PZT capacitors while taking into account contrast variations in the PFM phase images. The switching behavior of the capacitors was determined by comparison of the static domain patterns in the same capacitors after both positive and negative poling. While 180° degree switching was observed, surprisingly, the switching process was dominated by 90° polarization vector rotation. Furthermore, central regions of the capacitors were characterized by the presence of charged domain boundaries, which could lead to imprint (preference of one polarization state over another.
      341Scopus© Citations 29
  • Publication
    Preparation and characterization of atomically clean, stoichlometric surfaces of AIN(0001)
    In situ exposure of the. (0001) surface of AlN thin films to flowing ammonia at 1120 degreesC and 10(-4) Torr removes oxygen/hydroxide and hydrocarbon species below the detectable limits of x-ray photoelectron spectroscopy and decreases the Al/N ratio from 1.3 to 1.0. The positions of the Al 2p and the N 1s core level peaks acquired from the cleaned surfaces were 75.0 +/- 0.1 eV and 398.2 +/- 0.1 eV, respectively, which were similar to the values determined for the as-loaded samples. The cleaning process left unchanged the (1 X 1) low energy electron diffraction pattern, the step-and-terrace microstructure, and the root mean square roughness values observed for the surfaces of the as-loaded samples; i.e., the surface structure and microstructure were not changed by the high-temperature exposure to ammonia at low pressures. Vacuum annealing under 10(-7) Torr at 1175 degreesC for 15 min removed all detectable hydrocarbons; however, it did not remove the oxygen/hydroxide species. (C) 2005 American Vacuum Society.
      258Scopus© Citations 8
  • Publication
    Biocompatible Gold Nanoparticle Arrays Photodeposited on Periodically Proton Exchanged Lithium Niobate
    Photodeposition of silver nanoparticles onto chemically patterned lithium niobate having alternating lithium niobate and proton exchanged regions has been previously investigated. Here, the spatially defined photodeposition of gold nanoparticles onto periodically proton exchanged lithium niobate is demonstrated. It is shown that the location where the gold nanoparticles form can be tailored by altering the concentration of HAuCl4. This enables the possibility to sequentially deposit gold and silver in different locations to create bimetallic arrays. The cytocompatibility of photodeposited gold, silver, and bimetallic ferroelectric templates to osteoblast-like cells is also investigated. Gold samples provide significantly greater cell biocompatibility than silver samples. These results highlight a potential route for using photodeposited gold on lithium niobate as a template for applications in cellular biosensing.
      514Scopus© Citations 17