Direct Measurement of Periodic Electric Forces in Liquids

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

Dynamic Behavior in Piezoresponse Force Microscopy

Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM) implemented on a beam-deflection atomic force microscope (AFM) is analyzed using a combination of modeling and experimental measurements. The PFM signal comprises contributions from local electrostatic forces acting on the tip, distributed forces acting on the cantilever, and three components of the electromechanical response vector. These interactions result in the bending and torsion of the cantilever, detected as vertical and lateral PFM signals. The relative magnitudes of these contributions depend on geometric parameters of the system, the stiffness and frictional forces of tip-surface junction, and operation frequencies. The dynamic signal formation mechanism in PFM is analyzed and conditions for optimal PFM imaging are formulated. The experimental approach for probing cantilever dynamics using frequency-bias spectroscopy and deconvolution of electromechanical and electrostatic contrast is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques

Probing the role of single defects on the thermodynamics of electric-field induced phase transitions

The kinetics and thermodynamics of first order transitions is 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.Comment: 34 pages,4 figures, high quality figures are available upon request, submitted to Phys. Rev. Let

On completeness of description of an equilibrium canonical ensemble by reduced s-particle distribution function

In this article it is shown that in a classical equilibrium canonical ensemble of molecules with $s$-body interaction full Gibbs distribution can be uniquely expressed in terms of a reduced s-particle distribution function. This means that whenever a number of particles $N$ and a volume $V$ are fixed the reduced $s$-particle distribution function contains as much information about the equilibrium system as the whole canonical Gibbs distribution. The latter is represented as an absolutely convergent power series relative to the reduced $s$-particle distribution function. As an example a linear term of this expansion is calculated. It is also shown that reduced distribution functions of order less than $s$ don't possess such property and, to all appearance, contain not all information about the system under consideration.Comment: This work was reported on the International conference on statistical physics "SigmaPhi2008", Crete, Greece, 14-19 July 200

Experimental observation of parametric X-ray radiation directed along the propagation velocity of relativistic electrons in a tungsten crystal

Parametric X-ray radiation (PXR) due to dynamic diffraction of relativistic electrons is experimentally observed at small angles to the propagation velocity of electrons in a tungsten crystal. The specific features of the experimental method are described, and forward PXR reflections from two crystallographic planes of tungsten are reliably measuredyesBelgorod State Universit

Domain Dynamics in Piezoresponse Force Microscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure

Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is studied using the combination of local hysteresis loop acquisition with simultaneous domain imaging. The analytical theory for PFS signal from domain of arbitrary cross-section is developed and used for the analysis of experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest formation of oblate domain at early stage of the domain nucleation and growth, consistent with efficient screening of depolarization field within the material. The fine structure of the hysteresis loop is shown to be related to the observed jumps in the domain geometry during domain wall propagation (nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.Comment: 17 pages, 3 figures, 2 Appendices, to be submmited to Appl. Phys. Let