@article{gruverman_wu_fan_vrejoiu_alexe_harrison_scott_2008, title={Vortex ferroelectric domains}, volume={20}, number={34}, journal={Journal of Physics. Condensed Matter}, author={Gruverman, A. and Wu, D. and Fan, H. J. and Vrejoiu, I. and Alexe, M. and Harrison, R. J. and Scott, J. F.}, year={2008} }
 @article{yang_lichtenwalner_morris_menzel_nauenheim_gruverman_krim_kingon_2007, title={A new test facility for efficient evaluation of MEMS contact materials}, volume={17}, ISSN={["1361-6439"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-51649090154&partnerID=MN8TOARS}, DOI={10.1088/0960-1317/17/9/006}, abstractNote={A novel test facility for the efficient evaluation of microelectromechanical system (MEMS) switches and the development of alternative contact materials is described. The facility utilizes the upper cantilever from commercial MEMS contact switches, and tests these against alternative bottom contact materials within a modified atomic force microscope (AFM). The test closely approximates the real switch, but can accommodate a wider range of test conditions and contact materials. The facility allows alternative contact materials to be easily and quickly incorporated, and therefore evaluated by measuring the number of cycles to failure. The evolution of the wear surfaces of the switch contact materials under test can also be easily examined. In order to demonstrate the facility, the evolution of the contact resistance and wear of a commercial RF MEMS cantilever with Au contacts was monitored under accelerated test conditions, comparing the behavior of Au bottom contacts to an alternative Au–Ni alloy contact material. The Au–Ni (20 at.%) alloy displayed reduced wear rates and improved switch cycle lifetimes compared to pure Au, while retaining acceptable values of contact resistance.}, number={9}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Yang, Z. and Lichtenwalner, D. and Morris, A. and Menzel, S. and Nauenheim, C. and Gruverman, A. and Krim, J. and Kingon, A. I.}, year={2007}, month={Sep}, pages={1788–1795} }
 @article{gruverman_wu_rodriguez_kalinin_habelitz_2007, title={High-resolution imaging of proteins in human teeth by scanning probe microscopy}, volume={352}, ISSN={["0006-291X"]}, DOI={10.1016/j.bbrc.2006.10.182}, abstractNote={High-resolution studies of dental tissues are of considerable interest for biomedical engineering and clinical applications. In this paper, we demonstrate the application of piezoresponse force microscopy (PFM) to nanoscale imaging of internal structure of human teeth by monitoring the local mechanical response to an electrical bias applied via a conductive tip. It is shown that PFM is capable of detecting dissimilar components of dental tissues, namely, proteins and calcified matrix, which have resembling morphology but different piezoelectric properties. It is demonstrated that collagen fibrils revealed in chemically treated intertubular dentin exhibit high piezoelectric activity and can be visualized in PFM with spatial resolution of 10 nm. Evidence of the presence of protein inclusions of 100-200 nm wide and several micrometers long in tooth enamel has been obtained. Furthermore, it is found that the peritubular dentin and intertubular dentin exhibit different piezoelectric behavior suggesting different concentration of collagen fibrils. The obtained results demonstrate a high potential of PFM in providing an additional insight into the structure of dental tissues. It is suggested that the PFM approach can be used to study the structure of a wide range of biological materials by monitoring their electromechanical behavior at the nanoscale.}, number={1}, journal={BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS}, author={Gruverman, A. and Wu, D. and Rodriguez, B. J. and Kalinin, S. V. and Habelitz, S.}, year={2007}, month={Jan}, pages={142–146} }
 @article{habelitz_rodriguez_marshall_marshall_kalinin_gruverman_2007, title={Peritubular dentin lacks piezoelectricity}, volume={86}, ISSN={["1544-0591"]}, DOI={10.1177/154405910708600920}, abstractNote={ Dentin is a mesenchymal tissue, and, as such, is based on a collagenous matrix that is reinforced by apatite mineral. Collagen fibrils show piezoelectricity, a phenomenon that is used by piezoresponse force microscopy (PFM) to obtain high-resolution images. We applied PFM to image human dentin with 10-nm resolution, and to test the hypothesis that zones of piezoactivity, indicating the presence of collagen fibrils, can be distinguished in dentin. Piezoelectricity was observed by PFM in the dentin intertubular matrix, while the peritubular dentin remained without response. High-resolution imaging of chemically treated intertubular dentin attributed the piezoelectric effect to individual collagen fibrils that differed in the signal strength, depending on the fibril orientation. This study supports the hypothesis that peritubular dentin is a non-collagenous tissue and is thus an exception among mineralized tissues that derive from the mesenchyme. }, number={9}, journal={JOURNAL OF DENTAL RESEARCH}, author={Habelitz, S. and Rodriguez, B. J. and Marshall, S. J. and Marshall, G. W. and Kalinin, S. V. and Gruverman, A.}, year={2007}, month={Sep}, pages={908–911} }
 @article{watanabe_funakubo_osada_uchida_okada_rodriguez_gruverman_2007, title={Probing intrinsic polarization properties in bismuth-layered ferroelectric films}, volume={90}, number={11}, journal={Applied Physics Letters}, author={Watanabe, T. and Funakubo, H. and Osada, M. and Uchida, H. and Okada, I. and Rodriguez, B. J. and Gruverman, A.}, year={2007} }
 @misc{cross_tsukada_horii_gruverman_kingon_2007, title={Semiconductor device and its manufacture method, and measurement fixture for the semiconductor device}, volume={7,241,656}, number={2007 Jul. 10}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Cross, J. S. and Tsukada, M. and Horii, Y. and Gruverman, A. and Kingon, A.}, year={2007} }
 @misc{cross_tsukada_horii_gruverman_kingon_2007, title={Semiconductor device having die attachment and die pad for applying tensile or compressive stress to the IC chip}, volume={7,239,026}, number={2007 Jul. 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Cross, J. S. and Tsukada, M. and Horii, Y. and Gruverman, A. and Kingon, A.}, year={2007} }
 @misc{kalinin_baddorf_lee_shin_gruverman_karapetian_kachanov_2007, title={Ultrahigh density ferroelectric storage and lithography by high order ferroic switching}, volume={7,292,768}, number={2007 Nov. 6}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kalinin, S. V. and Baddorf, A. P. and Lee, H. N. and Shin, J. and Gruverman, A. L. and Karapetian, E. and Kachanov, M.}, year={2007} }
 @article{kalinin_rodriguez_shin_jesse_grichko_thundat_baddorf_gruverman_2006, title={Bioelectromechanical imaging by scanning probe microscopy: Galvani's experiment at the nanoscale}, volume={106}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2005.10.005}, abstractNote={Since the discovery in the late 18th century of electrically induced mechanical response in muscle tissue, coupling between electrical and mechanical phenomena has been shown to be a near-universal feature of biological systems. Here, we employ scanning probe microscopy (SPM) to measure the sub-Angstrom mechanical response of a biological system induced by an electric bias applied to a conductive SPM tip. Visualization of the spiral shape and orientation of protein fibrils with 5 nm spatial resolution in a human tooth and chitin molecular bundle orientation in a butterfly wing is demonstrated. In particular, the applicability of SPM-based techniques for the determination of molecular orientation is discussed.}, number={4-5}, journal={ULTRAMICROSCOPY}, author={Kalinin, SV and Rodriguez, BJ and Shin, J and Jesse, S and Grichko, V and Thundat, T and Baddorf, AP and Gruverman, A}, year={2006}, month={Mar}, pages={334–340} }
 @article{rodriguez_kalinin_shin_jesse_grichko_thundat_baddorf_gruverman_2006, title={Electromechanical imaging of biomaterials by scanning probe microscopy}, volume={153}, ISSN={["1095-8657"]}, DOI={10.1016/j.jsb.2005.10.008}, abstractNote={The majority of calcified and connective tissues possess complex hierarchical structure spanning the length scales from nanometers to millimeters. Understanding the biological functionality of these materials requires reliable methods for structural imaging on the nanoscale. Here, we demonstrate an approach for electromechanical imaging of the structure of biological samples on the length scales from tens of microns to nanometers using piezoresponse force microscopy (PFM), which utilizes the intrinsic piezoelectricity of biopolymers such as proteins and polysaccharides as the basis for high-resolution imaging. Nanostructural imaging of a variety of protein-based materials, including tooth, antler, and cartilage, is demonstrated. Visualization of protein fibrils with sub-10 nm spatial resolution in a human tooth is achieved. Given the near-ubiquitous presence of piezoelectricity in biological systems, PFM is suggested as a versatile tool for micro- and nanostructural imaging in both connective and calcified tissues.}, number={2}, journal={JOURNAL OF STRUCTURAL BIOLOGY}, author={Rodriguez, BJ and Kalinin, SV and Shin, J and Jesse, S and Grichko, V and Thundat, T and Baddorf, AP and Gruverman, A}, year={2006}, month={Feb}, pages={151–159} }
 @article{hanson_rodriguez_nemanich_gruverman_2006, title={Fabrication of metallic nanowires on a ferroelectric template via photochemical reaction}, volume={17}, ISSN={["0957-4484"]}, DOI={10.1088/0957-4484/17/19/028}, abstractNote={Fabrication of silver nanowires on a domain-patterned lithium niobate template by inducing a photochemical reaction in an aqueous solution is reported. Silver deposition occurs preferentially along the domain boundaries which separate antiparallel domains. The nanowires can reach lengths of hundreds of micrometres, and their location can be controlled by generating domain patterns of a desired configuration while their width depends on deposition conditions, such as temperature, solution concentration and ultraviolet (UV) light exposure time. The selective deposition process is explained by a combination of the inhomogeneous distribution of the electric field in the vicinity of the domain wall and the polarization screening mechanism of the template material. Controllable and selective deposition of metal species onto nanoscale domain-patterned ferroelectric templates may provide an alternative bottom-up route to lithographic fabrication methods.}, number={19}, journal={NANOTECHNOLOGY}, author={Hanson, J. N. and Rodriguez, B. J. and Nemanich, R. J. and Gruverman, A.}, year={2006}, month={Oct}, pages={4946–4949} }
 @article{kim_hanson_gruverman_kingon_streiffer_2006, title={Ferroelectric behavior in nominally relaxor lead lanthanum zirconate titanate thin films prepared by chemical solution deposition on copper foil}, volume={88}, number={26}, journal={Applied Physics Letters}, author={Kim, T. and Hanson, J. N. and Gruverman, A. and Kingon, A. I. and Streiffer, S. K.}, year={2006} }
 @article{gruverman_kholkin_2006, title={Introduction to the special issue on nanoscale ferroelectrics}, volume={53}, number={12}, journal={IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control}, author={Gruverman, A. and Kholkin, A.}, year={2006}, pages={2206–2207} }
 @misc{gruverman_kholkin_2006, title={Nanoscale ferroelectrics: processing, characterization and future trends}, volume={69}, number={8}, journal={Reports on Progress in Physics}, author={Gruverman, A. and Kholkin, A.}, year={2006}, pages={2443–2474} }
 @article{gruverman_kalinin_2006, title={Piezoresponse force microscopy and recent advances in nanoscale studies of ferroelectrics}, volume={41}, ISSN={["1573-4803"]}, DOI={10.1007/s10853-005-5946-0}, number={1}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Gruverman, A and Kalinin, SV}, year={2006}, month={Jan}, pages={107–116} }
 @misc{cross_tsukada_horii_gruverman_kingon_2006, title={Semiconductor device having a stress layer for applying tensile of compressive stress to the ferroelectric film}, volume={7,075,135}, number={2006 Jul. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Cross, J. S. and Tsukada, M. and Horii, Y. and Gruverman, A. and Kingon, A.}, year={2006} }
 @article{dawber_gruverman_scott_2006, title={Skyrmion model of nano-domain nucleation in ferroelectrics and ferromagnets}, volume={18}, ISSN={["1361-648X"]}, DOI={10.1088/0953-8984/18/5/L03}, abstractNote={A skyrmion model of nano-domain ejection from large domain walls in ferroelectrics is presented, together with data on lead germanate Pb5Ge3O11 and comparison data on ferromagnetic iron garnet. Notable is the occurrence of a short-wavelength transverse wall instability (wiggles) prior to the nano-domain emission. This nonlinear, defect-free model is qualitatively different from all known models of ferroelectric nucleation and propagation; nucleation in ferroelectrics has almost always been viewed as inhomogeneous, initiated at static impurity or defect sites that are fixed in space; the present model is also inhomogeneous but involves nucleation at existing domain walls, which are dynamic and not fixed in space. This defect-free ferroelectric nucleation model contrasts with the frequently invoked mechanism in thin-film switching of nucleation at electrode–dielectric interfaces and thus has significant implications for the ultimate switching speed in thin-film memory devices.}, number={5}, journal={JOURNAL OF PHYSICS-CONDENSED MATTER}, author={Dawber, M and Gruverman, A and Scott, JF}, year={2006}, month={Feb}, pages={L71–L79} }
 @article{balke_lupascu_blair_gruverman_2006, title={Thickness profiles through fatigued bulk ceramic lead zirconate titanate}, volume={100}, number={11}, journal={Journal of Applied Physics}, author={Balke, N. and Lupascu, D. C. and Blair, T. and Gruverman, A.}, year={2006} }
 @article{kalinin_rodriguez_jesse_shin_baddorf_gupta_jain_williams_gruverman_2006, title={Vector piezoresponse force microscopy}, volume={12}, ISSN={["1431-9276"]}, DOI={10.1017/S1431927606060156}, abstractNote={A novel approach for nanoscale imaging and characterization of the orientation dependence of electromechanical properties—vector piezoresponse force microscopy (Vector PFM)—is described. The relationship between local electromechanical response, polarization, piezoelectric constants, and crystallographic orientation is analyzed in detail. The image formation mechanism in vector PFM is discussed. Conditions for complete three-dimensional (3D) reconstruction of the electromechanical response vector and evaluation of the piezoelectric constants from PFM data are set forth. The developed approach can be applied to crystallographic orientation imaging in piezoelectric materials with a spatial resolution below 10 nm. Several approaches for data representation in 2D-PFM and 3D-PFM are presented. The potential of vector PFM for molecular orientation imaging in macroscopically disordered piezoelectric polymers and biological systems is discussed.}, number={3}, journal={MICROSCOPY AND MICROANALYSIS}, author={Kalinin, Sergei V. and Rodriguez, Brian J. and Jesse, Stephen and Shin, Junsoo and Baddorf, Arthur P. and Gupta, Pradyumna and Jain, Himanshu and Williams, David B. and Gruverman, Alexei}, year={2006}, month={Jun}, pages={206–220} }
 @article{dehoff_rodriguez_kingon_nemanich_gruverman_cross_2005, title={Atomic force microscopy-based experimental setup for studying domain switching dynamics in ferroelectric capacitors}, volume={76}, ISSN={["1089-7623"]}, DOI={10.1063/1.1850652}, abstractNote={This article describes an experimental setup for combined measurements of domain switching dynamics and switching currents in micrometer scale ferroelectric capacitors. The setup is based on a commercial atomic force microscope (AFM) that is equipped with a piezoresponse mode for domain imaging and with a wide bandwidth current amplifier for switching current recording. The setup allows combined domain/current measurements in capacitors as small as 1μm2 with switching times resolved down to 10ns. The incorporation of switching current measurement capability into piezoresponse AFM makes detailed analysis of switching behavior in ferroelectric memory devices possible.}, number={2}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Dehoff, C and Rodriguez, BJ and Kingon, AI and Nemanich, RJ and Gruverman, A and Cross, JS}, year={2005}, month={Feb} }
 @article{gruverman_rodriguez_dehoff_waldrep_kingon_nemanich_cross_2005, title={Direct studies of domain switching dynamics in thin film ferroelectric capacitors}, volume={87}, ISSN={["1077-3118"]}, DOI={10.1063/1.2010605}, abstractNote={An experimental approach for direct studies of the polarization reversal mechanism in thin film ferroelectric capacitors based on piezoresponse force microscopy (PFM) in conjunction with pulse switching capabilities is presented. Instant domain configurations developing in a 3×3μm2 capacitor at different stages of the polarization reversal process have been registered using step-by-step switching and subsequent PFM imaging. The developed approach allows direct comparison of experimentally measured microscopic switching behavior with parameters used by phenomenological switching models. It has been found that in the low field regime (just above the threshold value) used in the present study, the mechanism of polarization reversal changes during the switching cycle from the initial nucleation-dominated process to the lateral domain expansion at the later stages. The classical nucleation model of Kolmogorov–Avrami–Ishibashi (KAI) provides reasonable approximation for the nucleation-dominated stage of switching but is inapplicable to the slow switching stage. It has been suggested that the switching dynamics can be approximated by averaging the KAI model over a broad distribution of switching times.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Rodriguez, BJ and Dehoff, C and Waldrep, JD and Kingon, AI and Nemanich, RJ and Cross, JS}, year={2005}, month={Aug} }
 @article{rodriguez_nemanich_kingon_gruverman_kalinin_terabe_liu_kitamura_2005, title={Domain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopy}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1845594}, abstractNote={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.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Rodriguez, BJ and Nemanich, RJ and Kingon, A and Gruverman, A and Kalinin, SV and Terabe, K and Liu, XY and Kitamura, K}, year={2005}, month={Jan} }
 @article{kalinin_rodriguez_jesse_thundat_gruverman_2005, title={Electromechanical imaging of biological systems with sub-10 nm resolution}, volume={87}, number={5}, journal={Applied Physics Letters}, author={Kalinin, S. V. and Rodriguez, B. J. and Jesse, S. and Thundat, T. and Gruverman, A.}, year={2005} }
 @article{rodriguez_gruverman_kingon_nemanich_cross_2005, title={Investigation of the mechanism of polarization switching in ferroelectric capacitors by three- dimensional piezoresponse force microscopy}, volume={80}, ISSN={["1432-0630"]}, DOI={10.1007/s00339-004-2925-2}, abstractNote={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).}, number={1}, journal={APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ and Cross, JS}, year={2005}, month={Jan}, pages={99–103} }
 @article{kalinin_gruverman_rodriguez_shin_baddorf_karapetian_kachanov_2005, title={Nanoelectromechanics of polarization switching in piezoresponse force microscopy}, volume={97}, number={7}, journal={Journal of Applied Physics}, author={Kalinin, S. V. and Gruverman, A. and Rodriguez, B. J. and Shin, J. and Baddorf, A. P. and Karapetian, E. and Kachanov, M.}, year={2005} }
 @article{nagarajan_aggarwal_gruverman_ramesh_waser_2005, title={Nanoscale polarization relaxation in a polycrystalline ferroelectric thin film: Role of local environments}, volume={86}, number={26}, journal={Applied Physics Letters}, author={Nagarajan, V. and Aggarwal, S. and Gruverman, A. and Ramesh, R. and Waser, R.}, year={2005} }
 @article{yang_rodriguez_gruverman_nemanich_2005, title={Photo electron emission microscopy of polarity-patterned materials}, volume={17}, ISSN={["1361-648X"]}, DOI={10.1088/0953-8984/17/16/012}, abstractNote={This study presents variable photon energy photo electron emission microscopy (PEEM) of polarity-patterned epitaxial GaN films, and ferroelectric LiNbO3 (LNO) single crystals and PbZrTiO3 (PZT) thin films. The photo electrons were excited with spontaneous emission from the tunable UV free electron laser (FEL) at Duke University. We report PEEM observation of polarity contrast and measurement of the photothreshold of each polar region of the materials. For a cleaned GaN film with laterally patterned Ga- and N-face polarities, we found a higher photoelectric yield from the N-face regions compared with the Ga-face regions. Through the photon energy dependent contrast in the PEEM images of the surfaces, we can deduce that the threshold of the N-face region is less than ∼4.9 eV while that of the Ga-face regions is greater than 6.3 eV. In both LNO and PZT, bright emission was detected from the negatively poled domains, indicating that the emission threshold of the negative domain is lower than that of the positive domain. For LNO, the measured photothreshold was ∼4.6 eV at the negative domain and ∼6.2 eV at the positive domain, while for PZT, the threshold of the negative domain was less than 4.3 eV. Moreover, PEEM observation of the PZT surface at elevated temperatures displayed that the domain contrast disappeared near the Curie temperature of ∼300 °C. The PEEM polarity contrast of the polar materials is discussed in terms of internal screening from free carriers and defects and the external screening due to adsorbed ions.}, number={16}, journal={JOURNAL OF PHYSICS-CONDENSED MATTER}, author={Yang, WC and Rodriguez, BJ and Gruverman, A and Nemanich, RJ}, year={2005}, month={Apr}, pages={S1415–S1426} }
 @article{rodriguez_yang_nemanich_gruverman_2005, title={Scanning probe investigation of surface charge and surface potential of GaN-based heterostructures}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1869535}, abstractNote={Scanning Kelvin probe microscopy (SKPM) and electrostatic force microscopy (EFM) have been employed to measure the surface potentials and the surface charge densities of the Ga- and the N-face of a GaN lateral polarity heterostructure (LPH). The surface was subjected to an HCl surface treatment to address the role of adsorbed charge on polarization screening. It has been found that while the Ga-face surface appears to be unaffected by the surface treatment, the N-face surface exhibited an increase in adsorbed screening charge density (1.6±0.5×1010cm−2), and a reduction of 0.3±0.1V in the surface potential difference between the N- and Ga-face surfaces.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={Rodriguez, BJ and Yang, WC and Nemanich, RJ and Gruverman, A}, year={2005}, month={Mar} }
 @article{shin_rodriguez_baddorf_thundat_karapetian_kachanov_gruverman_kalinin_2005, title={Simultaneous elastic and electromechanical imaging by scanning probe microscopy: Theory and applications to ferroelectric and biological materials}, volume={23}, number={5}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Shin, J. and Rodriguez, B. J. and Baddorf, A. P. and Thundat, T. and Karapetian, E. and Kachanov, M. and Gruverman, A. and Kalinin, S. V.}, year={2005}, pages={2102–2108} }
 @article{gruverman_cao_bhaskar_dey_2004, title={Investigation of Pb(Zr,Ti)O-3/GaN heterostructures by scanning probe microscopy}, volume={84}, ISSN={["1077-3118"]}, DOI={10.1063/1.1765740}, abstractNote={Piezoresponse force microscopy (PFM) technique has been utilized to study the evolution of domain structure with varying Pb(Zr,Ti)O3(PZT) thickness on GaN substrate. Sol-gel PZT films were deposited on the GaN∕sapphire substrate with PZT thickness of 100, 200, and 300nm. The films exhibit ferroelectric properties that vary as a function of the film thickness. This is explained by the mechanical stress at the PZT∕GaN interface. The thicker film (300nm) is characterized by the presence of a number of oppositely polarized domains and a relatively high value of the effective piezoelectric constant. The laminar domain structure, consisting of 90° and 180° domains, has been revealed in the thinner (200nm) PZT film. Both films show clear ferroelectric switching behavior, which is in contrast to the thinnest film (100nm), where no switching has been observed due to mostly in-plane polarization orientation. The observed results indicate the utility of the PFM technique for characterization of the electronic properties of the PZT∕GaN heterostructures.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Cao, W and Bhaskar, S and Dey, SK}, year={2004}, month={Jun}, pages={5153–5155} }
 @article{yang_rodriguez_gruverman_nemanich_2004, title={Polarization-dependent electron affinity of LiNbO3 surfaces}, volume={85}, ISSN={["1077-3118"]}, DOI={10.1063/1.1790604}, abstractNote={Polar surfaces of a ferroelectric LiNbO3 crystal with periodically poled domains are explored using UV-photoelectron emission microscopy (PEEM). Compared with the positive domains (domains with positive surface polarization charges), a higher photoelectric yield is found from the negative domains (domains with negative surface polarization charges), indicating a lower photothreshold and a corresponding lower electron affinity. The photon-energy-dependent contrast in the PEEM images of the surfaces indicates that the photothreshold of the negative domains is ∼4.6eV while that of the positive domains is greater than ∼6.2eV. We propose that the threshold difference between the opposite domains can be attributed to a variation of the electron affinity due to opposite surface dipoles induced by surface adsorbates.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Yang, WC and Rodriguez, BJ and Gruverman, A and Nemanich, RJ}, year={2004}, month={Sep}, pages={2316–2318} }
 @article{kalinin_gruverman_bonnell_2004, title={Quantitative analysis of nanoscale switching in SrBi2Ta2O9 thin films by piezoresponse force microscopy}, volume={85}, ISSN={["1077-3118"]}, DOI={10.1063/1.1775881}, abstractNote={Local switching properties in SrBi2Ta2O9 thin films have been studied by spatially resolved piezoresponse force microscopy (PFM) and spectroscopy. Variations in PFM contrast of individual grains due to their random crystallographic orientation are consistent with the grain switching behavior examined via vertical and lateral hysteresis loops. Theoretical description of vertical hysteresis loop shape obtained in the point-charge approximation is shown to be in good agreement with the experimental data. Dependence of the hysteresis loop parameters on the grain crystallographic orientation is analyzed. It has been found that grain deviation from the ideal (010) orientation when the polar axis is normal to the film plane results in the decrease of the PFM signal and increase of the coercive voltage in agreement with theoretical predictions.}, number={5}, journal={APPLIED PHYSICS LETTERS}, author={Kalinin, SV and Gruverman, A and Bonnell, DA}, year={2004}, month={Aug}, pages={795–797} }
 @article{rodriguez_gruverman_kingon_nemanich_cross_2004, title={Three-dimensional high-resolution reconstruction of polarization in ferroelectric capacitors by piezoresponse force microscopy}, volume={95}, ISSN={["1089-7550"]}, DOI={10.1063/1.1638889}, abstractNote={A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM, respectively) has been used to map the out-of-plane and in-plane polarization distribution, respectively, of (111)-oriented Pb(Zr,Ti)O3-based (PZT) ferroelectric patterned and reactively-ion-etched capacitors. While VPFM and LPFM have previously been used to determine the orientation of the polarization vector in ferroelectric crystals and thin films, this is the first time the technique has been applied to determine the three-dimensional polarization distribution in thin-film capacitors and, as such, is of importance to the implementation of nonvolatile ferroelectric random access memory. Sequential VPFM and LPFM imaging have been performed in poled 1×1.5 μm2 PZT capacitors. Subsequent quantitative analysis of the obtained piezoresponse images allowed the three-dimensional reconstruction of the domain arrangement in the PZT layers of the capacitors. It has been found that the poled capacitors, which appear as uniformly polarized in VPFM, are in fact in a polydomain state as is detected by LPFM and contain 90° domain walls. Despite the polycrystallinity of the PZT layer, regions larger than the average PZT grain size are found to have the same polarization orientation. This technique has potential for clarifying the switching behavior and imprint mechanism in micro- and nanoscale ferroelectric capacitors.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ and Cross, JS}, year={2004}, month={Feb}, pages={1958–1962} }
 @article{gruverman_rodriguez_kingon_nemanich_tagantsev_cross_tsukada_2003, title={Mechanical stress effect on imprint behavior of integrated ferroelectric capacitors}, volume={83}, ISSN={["0003-6951"]}, DOI={10.1063/1.1593830}, abstractNote={Stress-induced changes in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3 (PZT)-based capacitors have been studied using piezoresponse force microscopy. Visualization of polarization distribution and d33-loop measurements in individual 1×1.5-μm2 capacitors before and after stress application, generated by substrate bending, provided direct experimental evidence of stress-induced switching. Mechanical stress caused elastic switching in capacitors with the direction of the resulting polarization determined by the sign of the applied stress. In addition, stress application turned capacitors into a heavily imprinted state characterized by strongly shifted hysteresis loops and almost complete backswitching after application of the poling voltage. It is suggested that substrate bending generated a strain gradient in the PZT layer, which produced asymmetric lattice distortion with preferential polarization direction and triggered polarization switching due to the flexoelectric effect.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Rodriguez, BJ and Kingon, AI and Nemanich, RJ and Tagantsev, AK and Cross, JS and Tsukada, M}, year={2003}, month={Jul}, pages={728–730} }
 @article{kelman_mcintyre_gruverman_hendrix_bilodeau_roeder_2003, title={Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr0.35Ti0.65)O-3 thin films}, volume={94}, ISSN={["1089-7550"]}, DOI={10.1063/1.1610773}, abstractNote={The structural and electrical properties of Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 Å have been investigated. These (001)/(100)-textured films were grown by metalorganic chemical vapor deposition on (111)-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high temperature anneal, a large fraction of the grains contain several ferroelastic domains. Wafer curvature measurements in combination with x-ray diffraction stress measurements in the Ir bottom electrode showed that the as-deposited PZT films are, within experimental error, stress free at room temperature. Landau–Ginbzurg–Devonshire formalism was used to explain the origin of the rhombohedral phase as a result of substrate constraint on single domain PZT grains. Annealing was found to affect the relative volume fractions of the rhombohedral and tetragonal phases and the electrical properties of PZT films. Intermediate temperature anneals increased the volume fraction of the rhombohedral phase and the coercive field extracted from the polarization-electric field hysteresis loops. After a high temperature anneal (650 °C) the majority of the grains transformed into a polydomain state, decreasing the volume fraction of the rhombohedral phase and the coercive field. If the high temperature anneal was performed after deposition of the top electrode, the coercive field became independent of the PZT thickness.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Kelman, MB and McIntyre, PC and Gruverman, A and Hendrix, BC and Bilodeau, SM and Roeder, JF}, year={2003}, month={Oct}, pages={5210–5219} }
 @article{gruverman_rodriguez_kingon_nemanich_cross_tsukada_2003, title={Spatial inhomogeneity of imprint and switching behavior in ferroelectric capacitors}, volume={82}, ISSN={["0003-6951"]}, DOI={10.1063/1.1570942}, abstractNote={Piezoresponse force microscopy has been used to perform nanoscale characterization of the spatial variations in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3-based capacitors on Pt electrodes. Mapping of polarization distribution in the poled capacitors as well as local d33–V loop measurements revealed a significant difference in imprint and switching behavior between the peripheral and inner parts of the capacitors. It has been found that the inner regions of the capacitors are negatively imprinted (with the preferential direction of the normal component of polarization upward) and tend to switch back after application of the positive poling voltage. On the other hand, switchable regions at the edge of the integrated capacitors generally exhibit more symmetric hysteresis behavior. Application of an ac switching voltage, contrary to what was expected, resulted in an increase of the negatively imprinted regions. The observed effect has been explained by incomplete or asymmetric switching due to the mechanical stress conditions existing in the central parts of the capacitors.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Rodriguez, BJ and Kingon, AI and Nemanich, RJ and Cross, JS and Tsukada, M}, year={2003}, month={May}, pages={3071–3073} }
 @article{kim_gopalan_gruverman_2002, title={Coercive fields in ferroelectrics: A case study in lithium niobate and lithium tantalate}, volume={80}, ISSN={["0003-6951"]}, DOI={10.1063/1.1470247}, abstractNote={The experimentally measured coercive electric fields for domain reversal in ferroelectrics are typically many orders of magnitude lower than the estimates from phenomenological free-energy theory. This letter specifically investigates the influence of polarization gradients at pre-existing 180° domain walls in ferroelectrics on coercive fields for domain wall motion. It is shown that the ratio of theoretical coercive field without and with a preexisting domain wall is directly proportional to the ratio xo/a, where a is the lattice parameter and 2xo is the polarization wall width. This factor is 7.5–45 for a 20–120 nm wall width, the latter width determined here as the experimental upper limit for polarization wall width in lithium tantalate.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Kim, S and Gopalan, V and Gruverman, A}, year={2002}, month={Apr}, pages={2740–2742} }
 @misc{gruverman_2002, title={Ferroelectric film property measuring device, measuring method therefor and measuring method for semiconductor memory units}, volume={6,466,039}, number={2002 Oct. 15}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gruverman, A.}, year={2002} }
 @article{terabe_takekawa_nakamura_kitamura_higuchi_gotoh_gruverman_2002, title={Imaging and engineering the nanoscale-domain structure of a Sr0.61Ba0.39Nb2O6 crystal using a scanning force microscope}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1506945}, abstractNote={We have investigated the ferroelectric domain structure formed in a Sr0.61Ba0.39Nb2O6 single crystal by cooling the crystal through the Curie point. Imaging the etched surface structure using a scanning force microscope (SFM) in both the topographic mode and the piezoresponse mode revealed that a multidomain structure of nanoscale islandlike domains was formed. The islandlike domains could be inverted by applying an appropriate voltage using a conductive SFM tip. Furthermore, a nanoscale periodically inverted-domain structure was artificially fabricated using the crystal which underwent poling treatment.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={Terabe, K and Takekawa, S and Nakamura, M and Kitamura, K and Higuchi, S and Gotoh, Y and Gruverman, A}, year={2002}, month={Sep}, pages={2044–2046} }
 @article{gruverman_rodriguez_nemanich_kingon_2002, title={Nanoscale observation of photoinduced domain pinning and investigation of imprint behavior in ferroelectric thin films}, volume={92}, ISSN={["1089-7550"]}, DOI={10.1063/1.1497698}, abstractNote={Piezoresponse force microscopy has been used to investigate the nanoscale mechanism of imprint behavior of ferroelectric PbTiO3 thin films by studying the photoinduced changes in the hysteresis loops of individual grains. Illumination of the film with UV light resulted in a voltage shift opposite to that observed in ferroelectric thin film capacitors. This effect is attributed to the generation of an electric field within the surface dielectric layer as a result of the interaction between photoinduced charges and polarization charges. Application of a small nonswitching bias to the film with simultaneous UV illumination resulted in domain pinning in the grains where the polarization direction coincided with the direction of the applied field, in agreement with the proposed model. Domain pinning was also observed in grains with polydomain structure suggesting that charge entrapment at the existing domain boundaries in the bulk of the film contributes to the suppression of switchable polarization. However, a symmetric character of hysteresis loops observed in such grains implies that charge entrapment in the bulk of the film does not cause the voltage shift. It has been suggested that a thin high-dielectric interfacial layer can improve the imprint behavior of ferroelectric capacitors.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Gruverman, A and Rodriguez, BJ and Nemanich, RJ and Kingon, AI}, year={2002}, month={Sep}, pages={2734–2739} }
 @article{rodriguez_gruverman_kingon_nemanich_2002, title={Piezoresponse force microscopy for piezoelectric measurements of III-nitride materials}, volume={246}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)01749-9}, abstractNote={Piezoelectric constants and polarity distributions of epitaxial AlN and GaN thin films are investigated by piezoresponse force microscopy (PFM). The magnitude of the effective longitudinal piezoelectric constant d33 is determined to be 3±1 and 2±1 pm/V for wurtzite AlN and GaN/AlN layers grown by organo-metallic vapor phase epitaxy on SiC substrates, respectively. 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. We also present images of AlN/Si samples with regions of opposite piezoresponse phase, which indicate the presence of antiphase domains. We discuss the potential application of this technique for determination of the orientation of bulk crystals.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ}, year={2002}, month={Dec}, pages={252–258} }
 @article{rodriguez_gruverman_kingon_nemanich_ambacher_2002, title={Piezoresponse force microscopy for polarity imaging of GaN}, volume={80}, ISSN={["1077-3118"]}, DOI={10.1063/1.1483117}, abstractNote={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.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ and Ambacher, O}, year={2002}, month={Jun}, pages={4166–4168} }
 @article{gruverman_kholkin_kingon_tokumoto_2001, title={Asymmetric nanoscale switching in ferroelectric thin films by scanning force microscopy}, volume={78}, ISSN={["1077-3118"]}, DOI={10.1063/1.1366644}, abstractNote={Scanning force microscopy (SFM) has been used to perform nanoscale studies of the switching behavior of Pb(Zr, Ti)O3 thin films via the direct observation of their domain structures. The study revealed a significant asymmetry of a switching pattern which is a function of the voltage polarity and original domain structure of individual grains. The phenomenon of asymmetric switching is attributed (1) to the presence of an internal built-in electric field at the bottom interface and (2) to the mechanical stress exerted by the SFM tip. The former effect results in incomplete 180° switching, while the latter effect leads to a 90° rotation of the polarization vector. The resulting shear stress deformation of the grain underneath the tip combined with the applied field effect propels polarization reversal in the adjacent grains.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Kholkin, A and Kingon, A and Tokumoto, H}, year={2001}, month={Apr}, pages={2751–2753} }
 @article{gruverman_tokumoto_2001, title={On the imaging mechanism of ferroelectric domains in scanning force microscopy}, volume={1}, ISSN={["1530-6984"]}, DOI={10.1021/nl005522r}, abstractNote={Scanning force microscopy (SFM) studies of the domain structure in ferroelectric thin films on a nonmetal substrate allowed direct assessment of the electrostatic mechanism contribution to the domain contrast in the SFM contact mode. It has been shown that the polarization charges of the ferroelectric film are effectively compensated. This result suggests secondary effect of the electrostatic tip-sample interaction on domain imaging mechanism in ferroelectric thin films in contact SFM compared to the major contribution of the piezoelectric effect.}, number={2}, journal={NANO LETTERS}, author={Gruverman, A and Tokumoto, H}, year={2001}, month={Feb}, pages={93–95} }
 @article{gruverman_tanaka_2001, title={Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale}, volume={89}, number={3}, journal={Journal of Applied Physics}, author={Gruverman, A. and Tanaka, M.}, year={2001}, pages={1836–1843} }
 @article{kholkin_gruverman_wu_avdeev_vilarinho_salvado_baptista_2001, title={Seeding effect on micro- and domain structure of sol-gel-derived PZT thin films}, volume={50}, ISSN={["1873-4979"]}, DOI={10.1016/S0167-577X(01)00228-2}, abstractNote={Abstract Current trend to miniaturization requires precise control of micro- and domain structure of ferroelectric materials at the nanoscale level. This is essential for future applications of ferroelectric thin films in non-volatile memories, microactuators and pyroelectric arrays. In this work, the seeding effect on the nanoscale properties of ferroelectric Pb(Zr,Ti)O 3 (PZT) thin films is investigated using scanning force microscopy (SFM) capable of simultaneously resolving topographic and domain features on the surface of the films. It is shown that the addition of 5 mol% seeds (fine PZT powder) into the sol–gel precursor solution completely modifies the film's microstructure leading to the improved morphology of the grains, reduced roughness and smaller microporosity. At the same time, significant imprint and instability of the written domain pattern is reduced due to the smaller influence of the bottom electrode interface.}, number={4}, journal={MATERIALS LETTERS}, author={Kholkin, AL and Gruverman, A and Wu, A and Avdeev, M and Vilarinho, PM and Salvado, IMM and Baptista, JL}, year={2001}, month={Sep}, pages={219–224} }
 @article{auciello_gruverman_tokumoto_prakash_aggarwal_ramesh_1998, title={Nanoscale scanning force imaging of polarization phenomena in ferroelectric thin films}, volume={23}, number={1}, journal={MRS Bulletin}, author={Auciello, O. and Gruverman, A. and Tokumoto, H. and Prakash, S. A. and Aggarwal, S. and Ramesh, R.}, year={1998}, pages={33–42} }