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Gruverman, A.
Preferred name
Gruverman, A.
Official Name
Gruverman, A.
Research Output
Now showing 1 - 10 of 12
- PublicationNanoscale observation of photoinduced domain pinning and investigation of imprint behavior in ferroelectric thin films(American Institute of Physics, 2002-09)
; ; ; 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.414Scopus© Citations 92 - PublicationThree-dimensional high-resolution reconstruction of polarization in ferroelectric capacitors by piezoresponse force microscopy(American Institute of Physics, 2004-02)
; ; ; 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)O-3-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 1x1.5 mum(2) 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 90degrees 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.506Scopus© Citations 91 - PublicationNanoelectromechanics of polarization switching in piezoresponse force microscopy(American Institute of Physics, 2005-04)
; ; ; 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 the contact radius (strong indentation) requires the exact field structure. For higher order ferroic switching (e.g., ferroelectroelastic), the domain size is limited by the tip-sample contact area, thus allowing precise control of domain size. (C) 2005 American Institute of Physics.330Scopus© Citations 61 - PublicationInvestigation of the mechanism of polarization switching in ferroelectric capacitors by three- dimensional piezoresponse force microscopyA 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.
334Scopus© Citations 29 - PublicationScanning probe investigation of surface charge and surface potential of GaN-based heterostructures(American Institute of Physics, 2005-03)
; ; ; 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 +/- 0.5x10(10) cm(-2)), and a reduction of 0.3 +/- 0.1 V in the surface potential difference between the N- and Ga-face surfaces.481Scopus© Citations 43 - PublicationPolarization-dependent electron affinity of LiNbO3 surfaces(American Institute of Physics, 2004-09)
; ; ; 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 similar to4.6 eV while that of the positive domains is greater than similar to6.2 eV. 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.428Scopus© Citations 119 - PublicationWeb-like domain structure formation in barium titanate single crystalsThe evolution of ferroelectric domain structure in Remeika-grown BaTiO3 crystals under an inhomogeneous electric field has been investigated using piezoresponse force microscopy. The ac imaging bias was found to affect the metastable polarization state and lead to the formation of a web-like domain structure. It is suggested that this behaviour is due to the existence of subsurface domains arising in single crystals with a layered structure. (C) 2010 American Institute of Physics.
464Scopus© Citations 7 - PublicationPiezoresponse force microscopy for piezoelectric measurements of III-nitride materialsPiezoelectric 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 d(33) 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.
676Scopus© Citations 51 - PublicationSpatial inhomogeneity of imprint and switching behavior in ferroelectric capacitors(American Institute of Physics, 2003-05)
; ; ; 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)O-3-based capacitors on Pt electrodes. Mapping of polarization distribution in the poled capacitors as well as local d(33)-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. (C) 2003 American Institute of Physics.359Scopus© Citations 65 - PublicationPiezoresponse 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.343Scopus© Citations 78