Showing papers by "Sergei V. Kalinin published in 2005"

Domain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopy

Abstract: 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.

Dynamic Behavior in Piezoresponse Force Microscopy

Abstract: 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.

Electromechanical imaging of biological systems with sub-10nm resolution

Abstract: Electromechanical imaging of tooth dentin and enamel has been performed with sub-10nm resolution using piezoresponse force microscopy. Characteristic piezoelectric domain size and local protein fiber ordering in dentin have been determined. The shape of a single protein fibril in enamel is visualized in real space and local hysteresis loops are measured. Because of the ubiquitous presence of piezoelectricity in biological systems, this approach is expected to find broad application in high-resolution studies of a wide range of biomaterials.

Electromechanical Imaging of Biological Systems with Sub-10 nm Resolution

Abstract: Electromechanical imaging of tooth dentin and enamel has been performed with sub-10 nm resolution using piezoresponse force microscopy. Characteristic piezoelectric domain size and local protein fiber ordering in dentin have been determined. The shape of a single collagen fibril in enamel is visualized in real space and local hysteresis loops are measured. Because of the ubiquitous presence of piezoelectricity in biological systems, this approach is expected to find broad application in high-resolution studies of a wide range of biomaterials.

Nanoelectromechanics of piezoelectric indentation and applications to scanning probe microscopies of ferroelectric materials

Abstract: Nanoelectromechanics of piezoelectric indentation, including the structure of coupled electroelastic fields and stiffness relations, is analysed for flat, spherical, and conical indenter geometries. Exact solutions in elementary functions for electroelastic fields inside the material are obtained using the recently established correspondence principle between the elastic and the piezoelectric problems. The stiffness relations fully describe the indentation process and relate indentation depth, indentation force and bias to the relevant material properties and indenter parameters. This extends the results of Hertzian mechanics to piezoelectric materials. The stiffness relations are utilized for quantitative understanding of the electromechanical scanning probe microscopies (SPM) of ferroelectric and piezoelectric materials, including piezoresponse force microscopy, atomic force acoustic microscopy, scanning near-field acoustic microscopy, and heterodyne ultrasonic-electrostatic force microscopy. The structure of the electroelastic field yields a quantitative measure of signal generation volume in electromechanical SPMs and also provides a quantitative basis for the analysis of tip-induced polarisation switching and local hysteresis loop measurements.

Local Phenomena in Oxides by Advanced Scanning Probe Microscopy

Abstract: In the last two decades, scanning probe microscopies (SPMs) have become the primary tool for addressing structure and electronic, mechanical, optical, and transport phenomena on the nanometer and atomic scales. Here, we summarize basic principles of SPM as applied for oxide materials characterization and present recent advances in high-resolution imaging and local property measurements. The use of advanced SPM techniques for solutions of material related problems is illustrated on the examples of grain boundary transport in polycrystalline oxides and ferroelectric domain imaging and manipulation. Future prospects for SPM applications in materials science are discussed.

Nanoelectromechanics of polarization switching in piezoresponse force microscopy

Abstract: Nanoscale polarization switching in ferroelectric materials by piezoresponse force microscopy in weak and strong indentation limits is analyzed using exact solutions for coupled electroelastic fields under the tip. Tip-induced domain switching is mapped on the Landau theory of phase transitions, with domain size as an order parameter. For a point charge interacting with a ferroelectric surface, switching by both first and the second order processes is possible, depending on the charge–surface separation. For a realistic tip, the domain nucleation process is first order in charge magnitude and polarization switching occurs only above a certain critical tip bias. In pure ferroelectric or ferroelastic switching, the late stages of the switching process can be described using a point charge model and arbitrarily large domains can be created. However, description of domain nucleation and the early stages of growth process when the domain size is comparable with the tip curvature radius (weak indentation) or th...

Electronic Transport Imaging in a Multiwire SnO2 ChemFET Device

Abstract: The electronic transport and the sensing performance of an individual SnO2 crossed nanowires device in a three-terminal field effect configuration were investigated using a combination of macroscopic transport measurements and Scanning Surface Potential Microscopy (SSPM). The structure of the device was determined using both Scanning Electron- and Atomic Force Microscopy data. The SSPM images of two crossed 1D nanostructures, simulating a prototypical nanowire network sensors, exhibit large dc potential drops at the crossed-wire junction and at the contacts, identifying them as the primary electroactive elements in the circuit. The gas sensitivity of this device was comparable to those of sensors formed by individual homogeneous nanostructures of similar dimensions. Under ambient conditions, the DC transport measurements were found to be strongly affected by field-induced surface charges on the nanostructure and the gate oxide. These charges result in a memory effect in transport measurements and charge dynamics which are visualized by SSPM. Finally, scanning probe microscopy is used to measure the current-voltage characteristics of individual active circuit elements, paving the way to a detailed understanding of chemical functionality at the level of an individual electroactive element in an individual nanowire.

Electronic transport imaging in a multiwire SnO2 chemical field-effect transistor device

Abstract: The electronic transport and the sensing performance of an individual SnO2 crossed-nanowires device in a three-terminal field-effect transistor configuration were investigated using a combination of macroscopic transport measurements and scanning surface-potential microscopy (SSPM). The structure of the device was determined using both scanning electron- and atomic force microscopy data. The SSPM images of two crossed one-dimensional nanostructures, simulating a prototypical nanowire network sensors, exhibit large dc potential drops at the crossed-wire junction and at the contacts, identifying them as the primary electroactive elements in the circuit. The gas sensitivity of this device was comparable to those of sensors formed by individual homogeneous nanostructures of similar dimensions. Under ambient conditions, the dc transport measurements were found to be strongly affected by field-induced surface charges on the nanostructure and the gate oxide. These charges result in a memory effect in transport m...

Real space imaging of the microscopic origins of the ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12

Abstract: The origins of an ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12 (CCTO) were studied using the combination of impedance spectroscopy, electron microscopy, and scanning probe microscopy (SPM) Impedance spectra indicate that the transport properties in the 01Hz–1MHz frequency range are dominated by a single parallel resistive-capacitive (RC) element with a characteristic relaxation frequency of 16Hz dc potential distributions measurements by SPM illustrate that significant potential drops occur at the grain boundaries, which thus can be unambiguously identified as the dominant RC element High frequency ac amplitude and phase distributions illustrate very weak grain boundary contrast in SPM, indicative of strong capacitive coupling across the interfaces These results demonstrate that the ultrahigh dielectric constant reported for polycrystalline CCTO materials is related to grain-boundary behavior

Simultaneous elastic and electromechanical imaging by scanning probe microscopy: Theory and applications to ferroelectric and biological materials

Abstract: An approach for combined imaging of elastic and electromechanical properties of materials, referred to as piezoacoustic scanning probe microscopy (PA-SPM), is presented. Applicability of this technique for elastic and electromechanical imaging with nanoscale resolution in such dissimilar materials as ferroelectrics and biological tissues is demonstrated. The PA-SPM signal formation is analyzed based on the theory of nanoelectromechanics of piezoelectric indentation and signal sensitivity to materials properties and imaging conditions. It is shown that simultaneous measurements of local indentation stiffness and indentation piezocoefficient provide the most complete description of the local electroelastic properties for transversally isotropic materials, thus making piezoacoustic SPM a comprehensive imaging and analysis tool. The contrast formation mechanism in the low frequency regime is described in terms of tip-surface contact mechanics. Signal generation volumes for electromechanical and elastic signal...

Scanning probe microscopy apparatus and techniques

Abstract: Scanning probe techniques based on the measurement of impedance spectroscopy using a conductive an SPM tip is provided and applied to the study of local transport properties, especially at a grain boundary. The contributions of the grain boundaries and tip-surface interaction can be distinguished based on the analysis of the equivalent circuit. The technique is applicable for both the spatially resolved study of transport mechanisms of polycrystalline semiconductors and the tip-surface contact quality. A piezoresponse force microscopy technique yields quantitative information about local non-linear dielectric properties and higher order electromechanical coupled of ferroelectrics.

Observation of Ferroelectricity in a Confined Crystallite Using Electron Backscattered Diffraction and Piezoresponse Force Microscopy

Abstract: LaBGeO5 is a model transparent ferroelectric glass-ceramic (TFGC) material, developed as an inexpensive alternative to single-crystal nonlinear optical materials. The optical activity of the TFGC originates from the ferroelectric phase which remains under a hydrostatic pressure exerted by the surrounding glass matrix. A combination of two techniques, electron-backscattered diffraction (EBSD) and piezoresponse force microscopy (PFM), is employed to monitor the development of the ferroelectric phase. A method is proposed to theoretically construct PFM amplitude maps from EBSD orientation maps. The theoretical vertical piezoresponse map is compared with the experimental piezoresponse map from PFM. A good correlation between the theoretical and experimental maps is observed.

Imaging Bio-electro-mechanics with Scanning Probe Microscopy: Unveiling Nature's Nanoscale Form and Function

Abstract: Since the discovery in the late eighteenth century of electrically induced mechanical response in muscle tissue, coupling between electrical and mechanical phenomena has been shown to be a ubiquitous feature of biological systems. Here, we measure the local electromechanical properties of biological samples using piezoresponse force microscopy (PFM). This technique is combined with atomic force acoustic microscopy (AFAM) for simultaneous mapping the topography, structure, and electro-mechanical behavior of biological systems down to nanometer scales. We demonstrate the capability of these scanning probe microscopy (SPM) techniques to visualize as of yet unseen spatial variations in the composition and structure of calcified tissues, such as antlers, with 5 nm spatial resolution as well as local mechanical properties variation in a butterfly wing.

Local origins of sensor activity in 1D oxide nanostructures: from spectromicroscopy to device

Abstract: We have tested a range of imaging techniques to address local transport behavior in the working metal oxide nanostructure sensor. In particular, we were using scanning surface potential microscopy (SSPM) to dc potential distributions in an operating device. We also have successfully implemented of synchrotron radiation based photoelectron emission spectro-microscopy (PEEM) to explore submicron lateral compositional and electronic (work function) inhomogeneousity in individual nanowire sensor. These results open new avenue to visualize the adsorption / desorption phenomena on individual nanostructure both in real time and at nano- and mesoscopic level

Surface Defect-mediated Reactivity of Au/TiO2(110)

Abstract: Metal clusters supported by transition metal oxides, as exemplified by the Au/TiO2 system, have found broad applications as catalytic and sensor materials. The unusual properties of these systems originate from the specific interactions of metal clusters mediated by an oxide substrate, including local reduction below the cluster. In this work, we present recent results on the local interactions between one-dimensional defects on a TiO2 surface and their reactivity with oxygen and Au nano-clusters studied by a combination of Scanning Tunneling Microscopy and Spectroscopy (STM/S). High-resolution STM images, interpreted with first-principles theory, show that the observed one-dimensional strands have partially reduced Ti atoms coordinated above three-coordinated, surface oxygen atoms. When strands are exposed to 5 x 10-7 Torr O2 at 300 K, oxygen is adsorbed and randomly nucleated on and along the strands. The results indicate the presence of exposed Ti that act as an active site for oxygen adsorption even at room temperature. Gold nano-particles of diameters 5 nm and less have also been deposited on the sub-stoichiometric rows of TiOx and characterized by STM. Like point defects and step edges on TiO2(110), the strands serve as nucleation sites for gold nano-clusters. The 1D defects of the surface are interpreted in terms of a surface crystallographic shear type structure, in contrast to the proposed Ti2O3 added row model by Onish and Iwasawa [Phys. Rev. Lett. 76, (1996) 791]. The implications of this behavior and specific interaction between gold clusters, defects and gas molecules for catalytic activity of the Au/TiO2 system are discussed.

Recent Developments in Electromechanical Probing on the Nanoscale: Vector and Spectroscopic Imaging, Resolution, and Molecular Orientation Mapping

Abstract: Strong coupling between electrical and mechanical phenomena and the presence of switchable polarization have enabled applications of ferroelectric materials for nonvolatile memories (FeRAM), data storage, and ferroelectric lithography. Understanding the local functionality of inorganic ferroelectrics including crystallographic orientation, piezoresponse, elasticity, and mechanisms for polarization switching, requires probing material structure and properties on the level of a single ferroelectric grain or domain. Here, I present recent studies on electromechanical, mechanical, and spectroscopic characterization of ferroelectric materials by Scanning Probe Microscopy. Three-dimensional electromechanical imaging, referred to as Vector Piezoresponse Force Microscopy, is presented. Nanoelectromechanics of PFM, including the structure of coupled electroelastic fields and tip-surface contact mechanics, is analyzed. This establishes a complete continuum mechanics description of the PFM and Atomic Force Acoustic Microscopy imaging mechanisms. Mechanism for local polarization switching is analyzed. The hysteresis loop shape is shown to be determined by the formation of the transient domain below the tip, the size of which increases with the tip bias. Spectroscopic imaging that allows relevant characteristics of switching process, such as imprint bias, pinning strength, remanent and saturation response, is introduced. Finally, resolution in PFM and vector PFM imaging of local crystallographic and molecular orientation and disorder is introduced.