Investigation of twin-wall structure at the nanometre scale using atomic force microscopy

Shilo, Doron; Ravichandran, G.; Bhattacharya, Kaushik

doi:10.1038/nmat1151

Cited by 109 publications

(81 citation statements)

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“…It is accepted by now that 90°domain walls trap defects, including dopants and oxygen vacancies, and such defects widen the domain wall. 9,[15][16][17] The variations we have observed are consistent with this mechanism.…”

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confidence: 89%

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Characterization of domain walls in BaTiO3 using simultaneous atomic force and piezo response force microscopy

Franck

Ravichandran

Bhattacharya

2006

Applied Physics Letters

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In this letter a method to simultaneously measure the physical and the polarization thickness of a 90°d omain wall in a ferroelectric perovskite is presented. This method combines accurate atomic force microscopy and piezoresponse force microscopy scans of the same area with little drift and an analysis of the entire scanned area. It is found that the physical thickness is significantly narrower ͑about seven and a half times͒ than the polarization thickness in a 90°domain wall in BaTiO 3 . Evidence of the trapping of defects at such domain walls is also found. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2185640͔ Ferroelectric materials offer great potential for next generation high density storage devices, such as nonvolatile random memory access and high strain actuators in microelectromechanical systems applications due to their inherent high dielectric properties and high strain response. 1-3 Their macroscopic response to mechanical, electrical and optical loads is strongly related to their microstructural domain patterns. 4,5 The formations and kinetics of these domains are governed by the underlying atomistic structure, and their interaction with domain walls and material imperfections. As the size of the devices reduces to micro-and nano-scale, the motion and interaction of twin ͑domain͒ walls significantly influences the overall piezoelectric, optical, and mechanical response of the device. 6 In order to predict and control the phenomenological behavior of twin wall kinetics, their physical and electrical properties need to be accurately determined.Many of the current experimental techniques, including x-ray diffraction and high-resolution transmission electron microscopy ͑TEM͒ are capable of imaging domain walls, but are often unable to provide information about their polarization. 7,8 Also, since these techniques are based on diffraction principles, they only provide averaged information about the physical twin wall thickness. 9 Current far field techniques are limited in their resolution by the wavelength of the light and, although near-field techniques such as NSOM provide useful information, they are still difficult to use.An experimental approach for determining the physical and electrical twin wall thickness in a ferroelectric perovskite material BaTiO 3 by simultaneously using a combination of atomic force microscopy ͑AFM͒ and piezoresponse force microscopy ͑PFM͒ is described here. The recorded AFM and PFM images are quantitatively compared to their respective displacement and polarization fields using the widely used and accepted Devonshire-Ginzburg-Landau ͑DGL͒ phenomenological model. [10][11][12] As has been shown by Shilo, Ravichandran, and Bhattacharya 9 for the case of PbTiO 3 , fitting the measured AFM displacement field to the DGL model by means of a least-squares method produces excellent results with nanometer resolution. Here, this approach is extended to include PFM measurements to determine the polarization domain wall thickness simultaneously along with the physical domain ...

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confidence: 89%

“…7,8 Also, since these techniques are based on diffraction principles, they only provide averaged information about the physical twin wall thickness. 9 Current far field techniques are limited in their resolution by the wavelength of the light and, although near-field techniques such as NSOM provide useful information, they are still difficult to use.…”

mentioning

confidence: 99%

Characterization of domain walls in BaTiO3 using simultaneous atomic force and piezo response force microscopy

Franck

Ravichandran

Bhattacharya

2006

Applied Physics Letters

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“…Recent simultaneous AFM-PFM measurements of emerging 90 domain walls in BaTiO 3 show that the physical width is significantly smaller (over 7 times) than the piezoelectric width consistent with longrange electrostatic interactions [21]. Further, the decoration of the domain wall with defects is consistent with experimental observations of Shilo et al [22] and provides a mechanism for the domain wall to have a memory of its location during annealing. To understand this mechanism, note that the domains that disappear on the application of an electric field will not, in general, reappear at their old locations when the electric field is switched off.…”

Section: Prl 95 247603 (2005) P H Y S I C a L R E V I E W L E T T E supporting

confidence: 76%

Depletion Layers and Domain Walls in Semiconducting Ferroelectric Thin Films

2005

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Commonly used ferroelectric perovskites are also wide-band-gap semiconductors. In such materials, the polarization and the space-charge distribution are intimately coupled, and this Letter studies them simultaneously with no a priori ansatz on either. In particular, we study the structure of domain walls and the depletion layers that form at the metal-ferroelectric interfaces. We find the coupling between polarization and space charges leads to the formation of charge double layers at the 90 domain walls, which, like the depletion layers, are also decorated by defects like oxygen vacancies. In contrast, the 180 domain walls do not interact with the defects or space charges. Implications of these results to domain switching and fatigue in ferroelectric devices are discussed. DOI: 10.1103/PhysRevLett.95.247603 PACS numbers: 77.80.Dj, 73.40.ÿc, 75.60.Ch Ferroelectric perovskites that are widely used as actuators, sensors, and memories have classically been modeled as insulators following the Devonshire-Ginsburg-Landau (DGL) theory [1]. These materials, however, are also wideband-gap semiconductors [2]. Consequently, one has bandbending and depletion layers at electrodes and charge layer formation at domain walls, which in turn affect the polarization distribution. These in turn contribute to fatigue and domain-wall pinning.Recent efforts have sought to augment the DGL theory for these effects [3]. However, they assume a priori the depletion layer and space-charge distribution and calculate the resulting polarization distribution, or vice versa. There have also been ab initio studies of the electronic band structure and atomistic studies of defects [4 -6]. However, they provide limited information at the device scale due to enormous computational effort required to handle realistic length scales and geometries. This Letter provides a comprehensive presentation of a semiconducting ferroelectric at the device scale with no a priori assumptions on the polarization or space charge.We focus on the [001]-polarized tetragonal phase of BaTiO 3 to be specific, though many of our findings are generic. This well-studied material displays both 180 and 90 domain walls. Oxygen vacancies are a common defect and they act as donors [6,7]. We focus on the parallel-plate capacitor geometry (electrode-ferroelectric-electrode), which is the building block of many devices. Our results show the formation of depletion layers and the alteration of the polarization near electrodes, reveal some essential differences between 180 and 90 domain walls, show the redistribution of oxygen vacancies to electrodes and across 90 domain walls during annealing, and provide a concrete mechanism for imprinting a 90 domain wall. These results shed new light on various experimental observations.The state of the semiconducting ferroelectric crystal is determined by the polarization density p, the strain , the space-charge density , and the defect density N d , each of which we treat as field quantities. We assume here that all defects are donors motivated...

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“…25,26 In perovskite oxides, it is known that mobile V O 2 þ ions tend to occupy thermodynamically preferential sites in extended crystal defects, such as DWs, grain boundaries and dislocations. [27][28][29][30][31][32][33][34] Often, these vacancies modify local cation valences and displacements and act as wall-pinning centers. 35 In turn, they contribute to diffusive photovoltaic switching in our multidomain BFO channels, as shown in Figures 5b and d.…”

Section: Resultsmentioning

confidence: 99%

Single ferroelectric-domain photovoltaic switch based on lateral BiFeO3 cells

Sung

Lee

et al. 2013

NPG Asia Mater

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The bistability of ferroelectric polarization states serves as a basis for solid-state memory. This phenomenon can also yield an interesting photovoltaic effect in such a way that the directional photocarrier motion follows the inherent potential gradient imposed by the ferroelectric polarization vectors. Here, we demonstrate a single-domain photovoltaic switch based on lateral BiFeO 3 channels, in which such photovoltaic switching is achieved by a coherent single-domain reversal with a short electrical pulse. We then provide visual evidence for such operations with a series of spatially and spectrally resolved short-circuit photocurrent images. Specifically, we reveal that the sequential photovoltaic current images directly reflect the remanent polarization states of a single-domain channel. We also verify that, in multidomain channels, diffusive switching characteristics are determined not only by the internal polarization vector within the domain but also by oxygen vacancy accumulation at the domain walls. Keywords: ferroelectrics; multiferroics; oxide photonics; photovoltaics INTRODUCTIONHomogeneous light illumination on non-centrosymmetric crystals, such as ferroelectrics, in the intrinsic absorption range can give rise to an interesting photovoltaic effect, dubbed as the bulk photovoltaic effect. 1,2 This effect is distinct from that of typical semiconductor p-n junction photovoltaics and excitonic heterojunction photovoltaics in that the photogenerated carriers can be separated along the inherent polar directions, ensuing the unidirectional photocurrent (I ph ) and photovoltage (V ph ), associated with the spontaneous ferroelectric polarization vector (P s ). Therein, the open-circuit voltage (V oc ) is determined by the magnitude of the remanent polarization of ferroelectrics, and it can be additively as large as a few hundreds of volts, although the short-circuit current (I sc I ph at 0 V) is low due to the insulating character of the system. This phenomenon has been recently revisited with a small band-gap, BiFeO 3 (BFO) ferroelectric, from which a substantially higher photon-to-charge generation efficiency can be achieved in the visible range compared with that of other insulating ferroelectrics. [3][4][5][6][7][8] reported that diodelike rectification follows the polarization-dependent interface bandbending of BFO single-crystal slabs that are electrically switchable, that is, V oc and I sc are defined by the remanent polarization directions. In general, the spatial extent of spontaneous polarization vectors in ferroelectric crystals is typically manifested as domains (typically spanning over a few mm in size) and domain walls (DW, 1-2 nm in

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Investigation of twin-wall structure at the nanometre scale using atomic force microscopy

Cited by 109 publications

References 23 publications

Characterization of domain walls in BaTiO3 using simultaneous atomic force and piezo response force microscopy

Characterization of domain walls in BaTiO3 using simultaneous atomic force and piezo response force microscopy

Depletion Layers and Domain Walls in Semiconducting Ferroelectric Thin Films

Single ferroelectric-domain photovoltaic switch based on lateral BiFeO3 cells

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