In studies using piezoresponse force microscopy, we observe a non-zero lateral piezoresponse at 180$^\circ$ domain walls in out-of-plane polarized, c-axis-oriented tetragonal ferroelectric Pb(Zr$_{0.2}$Ti$_{0.8}$)O$_3$ epitaxial thin films. We attribute these observations to a shear strain effect linked to the sign change of the $d_{33}$ piezoelectric coefficient through the domain wall, in agreement with theoretical predictions. We show that in monoclinically distorted tetragonal BiFeO$_3$ films, this effect is superimposed on the lateral piezoresponse due to actual in-plane polarization, and has to be taken into account in order to correctly interpret the ferroelectric domain configuration.
Piezoresponse force microscopy (PFM) was used to investigate the ferroelectric properties of sol-gel derived LiNbO$_3$ nanoparticles. To determine the degree of ferroelectricity we took large-area images and performed statistical image-analysis. The ferroelectric behavior of single nanoparticles was verified by poling experiments using the PFM tip. Finally we carried out simultaneous measurements of the in-plane and the out-of-plane piezoresponse of the nanoparticles, followed by measurements of the same area after rotation of the sample by 90$^{\circ}$ and 180$^{\circ}$. Such measurements bas…
The interpretation of ferroelectric domain images obtained with piezoresponse force microscopy (PFM) is discussed. The influences of an inherent experimental background on the domain contrast in PFM images (enhancement, nulling, inversion) as well as on the shape and the location of the domain boundaries are described. We present experimental results to evidence our analysis of the influence of the background on the domain contrast in PFM images.
The contrast mechanism for ferroelectric domain imaging via piezoresponse force microscopy (PFM) is investigated. A novel analysis of PFM measurements is presented which takes into account the background caused by the experimental setup. This allows, for the first time, a quantitative, frequency independent analysis of the domain contrast which is in good agreement with the expected values for the piezoelectric deformation of the sample and satisfies the generally required features of PFM imaging.
As a consequence of elasticity, mechanical deformations of crystals occur on a length scale comparable to their thickness. This is exemplified by applying a homogeneous electric field to a multi-domain ferroelectric crystal: as one domain is expanding the adjacent ones are contracting, leading to clamping at the domain boundaries. The piezomechanically driven surface corrugation of micron-sized domain patterns in thick crystals using large-area top electrodes is thus drastically suppressed, barely accessible by means of piezoresponse force microscopy.
We present a quantitative investigation of the impact of tip radius as well as sample type and thickness on the lateral resolution in piezoresponse force microscopy (PFM) investigating bulk single crystals. The observed linear dependence of the width of the domain wall on the tip radius as well as the independence of the lateral resolution on the specific crystal-type are validated by a simple theoretical model. Using a Ti-Pt-coated tip with a nominal radius of 15 nm the so far highest lateral resolution in bulk crystals of only 17 nm was obtained.
In piezoresponse force microscopy a lateral signal at the domain boundaries is occasionally observed. In recent years, a couple of experiments have been reported and varying explanations for the origin of this lateral signal have been proposed. Additionally, elaborated theoretical modeling for this particular issue has been carried out. Here we present experimental data obtained on different crystallographic cuts of $\rm LiNbO_3$, $\rm BaTiO_3$, and $\rm KTiOPO_4$ single crystals. We could thereby rule out some of the explanations proposed so far, introduce another possible mechanism, and quan…
Piezoresponse force microscopy (PFM) is a powerful tool for probing nanometer-scale ferroelectric and piezoelectric properties. Hysteretic switching of the phase and amplitude of the PFM response are believed to be the hallmark of ferroelectric and piezoelectric behavior respectively. However, the application of PFM is limited by the fact that similar hysteretic effects may also arise from mechanisms not related to ferroelectricity or piezoelectricity. In this paper we report our studies on regular glass slides that show ferroelectric-like signal without being ferroelectric and frequently used…
Coupling between electrical and mechanical phenomena is a near-universal characteristic of inorganic and biological systems alike, with examples ranging from ferroelectric perovskites to electromotor proteins in cellular membranes. Understanding electromechanical functionality in materials such as ferroelectric nanocrystals, thin films, relaxor ferroelectrics, and biosystems requires probing these properties on the nanometer level of individual grain, domain, or protein fibril. In the last decade, Piezoresponse Force Microscopy (PFM) was established a powerful tool for nanoscale imaging, spect…
Given that a ferroelectric domain is generally a three dimensional entity, the determination of its area as well as its depth is mandatory for full characterization. Piezoresponse force microscopy (PFM) is known for its ability to map the lateral dimensions of ferroelectric domains with high accuracy. However, no depth profile information has been readily available so far. Here, we have used ferroelectric domains of known depth profile to determine the dependence of the PFM response on the depth of the domain, and thus effectively the depth resolution of PFM detection.
Piezoresponse Force Spectroscopy (PFS) has emerged as a powerful technique for probing highly localized switching behavior and the role of microstructure and defects on switching. The application of a dc bias to a scanning probe microscope tip in contact with a ferroelectric surface results in the nucleation and growth of a ferroelectric domain below the tip, resulting in changes in local electromechanical response. Resulting hysteresis loops contains information on local ferroelectric switching behavior. The signal in PFS is the convolution of the volume of the nascent domain and the probing …
The interplay between electrochemical surface charges and bulk ferroelectricity in thin films gives rise to a continuum of coupled ferro-ionic states. These states are exquisitely sensitive to chemical and electric conditions at the surfaces, applied voltage, and oxygen pressure. Using the analytical approach combining the Ginzburg-Landau-Devonshire description of the ferroelectricity with Langmuir adsorption isotherm for the ions at the film surface, we have studied the temperature-, time- and field- dependent polarization changes and electromechanical response of the ferro-ionic states. The …
Electromechanical hysteresis loop formation in piezoresponse force microscopy of thin ferroelectric films is studied with special emphasis on the effects of tip size and film thickness, as well as dependence on the tip voltage frequency. Here, we use a combination of Landau-Ginzburg-Devonshire (LGD) theory for the description of the local polarization reversal with decoupling approximation for the calculation of the local piezoresponse loops shape, coercive voltages and amplitude. LGD approach enables addressing both thermodynamics and kinetics of hysteresis loop formation. In contrast to the …
The extrinsic size effect in Piezoresponse Force Microscopy of ferroelectric and piezoelectric thin films on non-polar dielectric substrate is analyzed. Analytical expressions for effective piezoresponse, object transfer function components, and Rayleigh two-point resolution are obtained. These results can be broadly applied for effective piezoelectric response calculations in thin piezoelectric and ferroelectric films as well as surface polar layers e.g. in organic materials and bio-polymers. In particular, the effective piezoresponse strongly decreases with film thickness whereas the sharpne…
Piezoresponse Force Microscopy contrast in transversally isotropic material corresponding to the case of c+ - c- domains in tetragonal ferroelectrics is analyzed using Green's function theory by Felten et al. [J. Appl. Phys. 96, 563 (2004)]. A simplified expression for PFM signal as a linear combination of relevant piezoelectric constant are obtained. This analysis is extended to piezoelectric material of arbitrary symmetry with weak elastic and dielectric anisotropies. This result provides a framework for interpretation of PFM signals for systems with unknown or poorly known local elastic and…
Piezoresponse Force Spectroscopy (PFS) has emerged as a powerful tool for probing polarization dynamics on the nanoscale. Application of a dc bias to a nanoscale probe in contact with a ferroelectric surface results in the nucleation and growth of a ferroelectric domain below the probe apex. The latter affects local electromechanical response detected by the probe. Resulting hysteresis loop contains information on local ferroelectric switching. The self-consistent analysis of the PFS data requires (a) deriving the thermodynamic parameters of domain nucleation and (b) establishing the relations…
We report the first investigation of the piezoelectric response on a nanoscale in the poled ferroelectric crystals with engineered configuration of domains. Piezoresponse force microscopy of tetragonal 0.63PMN-0.37PT relaxor-based ferroelectric crystals reviled that the d33 piezoelectric coefficient is significantly reduced within the distance of about 1 um from the uncharged engineered domain wall. This finding is essential for understanding the mechanisms of the giant piezoresponse in relaxor-based crystals and for designing new piezoelectric materials.
Piezoresponse force microscopy (PFM) has been extensively utilized as a versatile and an indispensable tool to understand and analyze nanoscale ferro- /piezoelectric properties by detecting the local electromechanical response on a sample surface. However, it has been discovered that the electromechanical response not only originates from piezoelectricity but also from other factors such as the electrostatic effect. In this study, we explore the dependence of off-field PFM hysteresis loops on the surface-potential-induced electrostatic effect in a prototypical ferroelectric thin film by applyi…
Correlated domain and crystallographic orientation mapping in uniaxial ferroelectric polycrystals by interferometric vector piezoresponse force microscopy
The contributory mechanisms associated with high piezoelectric response in piezoelectric ceramics have been examined by in-situ electric field dependent high energy synchro x-ray diffraction study. A comparative study of electric field induced lattice strain and the propensity for non-180o domain switching on two closeby compositions of a high performance piezoelectric alloy (1-x)PbTiO3-(x)BiScO3, one within the morphotropic phase boundary (MPB) region exhibiting d33 of 425 pC/N and another just outside the MPB region exhibiting d33 of 260 pC/N, unravelled that, inspite of the MPB specimen exh…
Nanoscale polarization switching in ferroelectric materials by Piezoresponse Force Microscopy (PFM) in weak and strong indentation limits is analyzed using exact solutions for electrostatic and coupled electroelastic fields below the tip. It is proposed that the tip-induced domain switching can be mapped on the Landau theory of phase transitions with the domain size as an order parameter. For a point charge interacting with a ferroelectric surface, switching of both first and second order is possible depending on the charge-surface separation. For a realistic tip shape, the domain nucleation p…
Hafnium oxide (HfO2)-based ferroelectrics offer remarkable promise for memory and logic devices in view of their compatibility with traditional silicon CMOS technology, high switchable polarization, good endurance and thickness scalability. These factors have led to steep rise in research on this class of materials over the past number of years. At the same time, only a few reports on the direct sensing of nanoscale ferroelectric properties exist, with many questions remaining regarding the emergence of ferroelectricity in these materials. While piezoresponse force microscopy (PFM) is ideally …
The local hysteresis loop obtained by switching spectroscopy piezoresponse force microscopy (SS-PFM) is usually regarded as a typical signature of ferroelectric switching. However, such hysteresis loops were also observed in a broad variety of non-ferroelectric materials in the past several years, which casts doubts on the viewpoint that the local hysteresis loops in SS-PFM originate from ferroelectricity. Therefore, it is crucial to explore the mechanism of local hysteresis loops obtained in SS-PFM testing. Here we proposed that non-ferroelectric materials can also exhibit amplitude butterfly…
To achieve quantitative interpretation of Piezoresponse Force Microscopy (PFM), including resolution limits, tip bias- and strain-induced phenomena and spectroscopy, analytical representations for tip-induced electroelastic fields inside the material are derived for the cases of weak and strong indentation. In the weak indentation case, electrostatic field distribution is calculated using image charge model. In the strong indentation case, the solution of the coupled electroelastic problem for piezoelectric indentation is used to obtain the electric field and strain distribution in the ferroel…
Electromechanical hysteresis loop measurements in Piezoresponse Force Microscopy (Piezoresponse Force Spectroscopy) have emerged as a powerful technique for probing ferroelectric switching behavior on the nanoscale. Interpretation of PFS data requires the relationship between the domain parameters and PFM signal to be established. Here, we analyze the switching process using a modified point charge model for the electric field of the tip. The charge value and position are selected so that its electric field isopotential surface reproduces the tip with definite radius of curvature. Using linear…
Signal formation mechanism of Piezoresponse Force Microscopy of piezoelectric surface layers and thin films on stiff and elastically matched substrates is analyzed and thickness dependence of effective piezoelectric response, object transfer function components and Rayleigh two-point resolution are derived. Obtained exact series and simple Pade approximations can be applied for the effective piezoresponse analytical calculations in the case of films capped on different substrates. The effective piezoresponse is thickness dependent for piezoelectric films on substrates with low dielectric permi…
We present a full analysis of the contrast mechanisms for the detection of ferroelectric domains on all faces of bulk single crystals using scanning force microscopy exemplified on hexagonally poled lithium niobate. The domain contrast can be attributed to three different mechanisms: i) the thickness change of the sample due to an out-of-plane piezoelectric response (standard piezoresponse force microscopy), ii) the lateral displacement of the sample surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample interaction at the domain boundaries caused by surface charges on…
Piezoresponse Force Microscopy (PFM), as a powerful nanoscale characterization technique, has been extensively utilized to elucidate diverse underlying physics of ferroelectricity. However, the intensive study of conventional PFM has revealed a growing number of concerns and limitations which are largely challenging its validity and application. Herein, we developed a new advanced PFM technique, named Heterodyne Megasonic Piezoresponse Force Microscopy (HM-PFM), which uniquely uses 106 to 108 Hz high-frequency excitation and heterodyne method to measure the piezoelectric strain at nanoscale. W…
Combination of local heating and biasing at the tip-surface junction in temperature-assisted piezoresponse force microscopy (tPFM) opens the pathway for probing local temperature induced phase transitions in ferroics, exploring the temperature dependence of polarization dynamics in ferroelectrics, and potentially discovering coupled phenomena driven by strong temperature- and electric field gradients. Here, we analyze the signal formation mechanism in tPFM and explore the interplay between thermal- and bias-induced switching in model ferroelectric materials. We further explore the contribution…
Ferroelectrics are technologically important, with wide application in micromechanical systems, nonlinear optics, and information storage. Recent discoveries of exotic polarisation textures in these materials, which can strongly influence their properties, have brought to the forefront questions about the nature of their domain walls -- long believed to be primarily Ising, with locally null polarisation. Here, combining three complementary techniques -- second harmonic generation microscopy, piezoresponse force microscopy, and transmission electron microscopy - to cover all the relevant length…
Ferroelectric domain imaging with piezoresponse force microscopy (PFM) relies on the converse piezoelectric effect: a voltage applied to the sample leads to mechanical deformations. In case of PFM one electrode is realized by the tip, therefore generating a strongly inhomogeneous electric field distribution inside the sample which reaches values up to $10^8 $V/m directly underneath the apex of the tip. Although often assumed, this high electric field does not lead to an enhancement of the piezoelectric deformation of the sample. On the contrary, internal clamping of the material reduces the ob…
Recently, a layered ferroelectric CuInP2Se6 was shown to exhibit domain walls with locally enhanced piezoresponse - a striking departure from the observations of nominally zero piezoresponse in most ferroelectrics. Although it was proposed that such "bright" domain walls are phase-boundaries between ferri- and antiferroelectrically ordered regions of the materials, the physical mechanisms behind the existence and response of these boundaries remain to be understood. Here, using Landau-Ginzburg-Devonshire phenomenology combined with four sub-lattices model, we describe quantitatively the bright…
In purely c-axis oriented PbZr$_{0.2}$Ti$_{0.8}$O$_3$ ferroelectric thin films, a lateral piezoresponse force microscopy signal is observed at the position of 180°domain walls, where the out-of-plane oriented polarization is reversed. Using electric force microscopy measurements we exclude electrostatic effects as the origin of this signal. Moreover, our mechanical simulations of the tip/cantilever system show that the small tilt of the surface at the domain wall below the tip does not satisfactorily explain the observed signal either. We thus attribute this lateral piezoresponse at domain wal…
Rapid emergence of the multimodal imaging in scanning probe, electron, and optical microscopies have brought forth the challenge of understanding the information contained in these complex data sets, targeting both the intrinsic correlations between different channels and further exploring the underpinning causal physical mechanisms. Here, we develop such analysis framework for the Piezoresponse Force Microscopy. We argue that under certain conditions, we can bootstrap experimental observations with the prior knowledge of materials structure to get information on certain non-observed propertie…
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 pa…
Piezoresponse force microscopy (PFM) has been used extensively for exploring nanoscale ferro/piezoelectric phenomena over the past two decades. The imaging mechanism of PFM is based on the detection of the electromechanical (EM) response induced by the inverse piezoelectric effect through the cantilever dynamics of an atomic force microscopy. However, several non-piezoelectric effects can induce additional contributions to the EM response, which often lead to a misinterpretation of the measured PFM response. This review aims to summarize the non-piezoelectric origins of the EM response that im…
2D Ferroelectric materials are promising for designing low-dimensional memory devices. Here, we explore strain tunable ferroelectric properties of group-IV monochalcogenides MX (M=Ge, Sn; X=S, Se) and their potential application in lateral field tunnel junction devices. We find that these monolayers have in-plane ferroelectricity, with their ferroelectric parameters being on par with other known 2D ferroelectric materials. Amongst SnSe, SnS, GeSe, and GeS, we find that GeS has the best ferroelectric parameters for device applications, which can be improved further by applying uniaxial tensile …
We investigated the ferroelectric properties of strontium titanate (STO) thin films deposited on SrTiO3 (001) substrate with SrRuO3 electrodes. The STO layer was grown coherently on the SrTiO3 substrate without in-plane lattice relaxation, but its out-of-plane lattice constant increased with a decrease in the oxygen pressure during deposition. Using piezoresponse force microscopy and P-V measurements, we showed that our tetragonal STO films possess room-temperature ferroelectricity. We discuss the possible origins of the observed ferroelectricity.
Trimerization-polarization domains in ferroelectric hexagonal YMnO$_3$ were resolved in all three spatial dimensions by piezoresponse force microscopy. Their topology is dominated by electrostatic effects with a range of 100 unit cells and reflects the unusual electrostatic origin of the spontaneous polarization. The response of the domains to locally applied electric fields explains difficulties in transferring YMnO$_3$ into a single-domain state. Our results demonstrate that the wealth of non-displacive mechanisms driving ferroelectricity that emerged from the research on multiferroics are a…
The contrast mechanism for the visualization of ferroelectric domain boundaries with lateral force microscopy is generally assumed to be caused by mechanical deformation of the sample due to the converse piezoelectric effect. We show, however, that electrostatic interactions between the charged tip and the electric fields arising from the surface polarization charges dominate the contrast mechanism. This explanation is sustained by quantitative analysis of the measured forces as well as by comparative measurements on different materials.
Piezoresponse Force Microscopy (PFM) has emerged as a primary tool for imaging, domain engineering, and switching spectroscopy on ferroelectric materials. Quantitative interpretation of PFM data including measurements of the intrinsic width of the domain walls, geometric parameters of the domain below the tip in local hysteresis loop measurements, as well as interpretation of switching and coercive biases in terms of materials properties and switching mechanisms, requires reliable knowledge on electrostatic field structure produced by the tip. Using linear imaging theory, we develop a theoreti…
SrTiO3 ceramics are investigated by piezoresponse force microscopy. Piezoelectric contrast is observed on polished surfaces in both vertical and lateral regimes and depends on the grain orientation varying in both sign (polarization direction) and amplitude. The observed contrast is attested to the surface piezoelectricity due to flexoelectric effect (strain gradient-induced polarization) caused by the surface relaxation. The estimated flexoelectric coefficient is approximately one order of magnitude smaller as compared to those recently measured in SrTiO3 single crystals. The observed enhance…
Ferroelectric nanostructures can be formed by local switching of domains using techniques such as piezo-force microscopy (PFM). Understanding lateral size effects is important to determine the minimum feature size for writing ferroelectric nanostructures. To understand these lateral size effects, we use the time-dependent-Ginzburg-Landau equations to simulate localized switching of domains for a PFM type and parallel-plate capacitor configurations. Our investigations indicate that fringing electric fields lead to switching via 90 deg domain wedge nucleation for thicker films while at smaller t…
The screening efficiency of a metal-ferroelectric interface plays a critical role in determining the polarization stability and hence the functional properties of ferroelectric thin films. Imperfect screening leads to strong depolarization fields that reduce the spontaneous polarization or drive the formation of ferroelectric domains. We demonstrate that by modifying the screening at the metal-ferroelectric interface through insertion of ultrathin dielectric spacers, the strength of the depolarization field can be tuned and thus used to control the formation of nanoscale domains. Using piezore…
We report on extensive domain wall motion in ferroelectric nanocapacitor arrays investigated by piezoresponse force microscopy. Under a much longer or higher bias voltage pulse, compared to typical switching pulse conditions, domain walls start to propagate into the neighbouring capacitors initiating a significant cross-talk. The propagation paths and the propagated area into the neighbouring capacitors were always the same under repeated runs. The experimental and the simulated results show that the observed cross-talk is related to the capacitor parameters combined with local defects. The re…
We report polarized neutron scattering and piezoresponse force microscopy studies of millimeter-sized single crystals of multiferroic BiFeO$_3$. The crystals, grown below the Curie temperature, consist of a single ferroelectric domain. Two unique electric polarization directions, as well as the populations of equivalent spiral magnetic domains, can be switched reversibly by an electric field. A ferroelectric monodomain with a single-$q$ single-helicity spin spiral can be obtained. This level of control, so far unachievable in thin films, makes single-crystal BiFeO$_3$ a promising object for mu…
Piezoresponse Force Spectroscopy (PFS) is a powerful method widely used for measuring the nanoscale ferroelectric responses of the materials. However, it is found that certain non-ferroelectric materials can also generate similar responses from the PFS measurements due to many other factors, hence, it is believed that PFS alone is not sufficient to differentiate the ferroelectric and non-ferroelectric materials. On the other hands, this work shows that there are distinct differences in contact resonance frequency variation during the PFS measurements for ferroelectric and non-ferroelectric mat…
Domain structures of 320 nm thin epitaxial films of ferroelectric PbTiO3 grown by MOCVD technique in identical conditions on SmScO3 and TbScO3 perovskite sub- strates have been investigated by Raman spectroscopy and piezoresponse force microscopy techniques. Phonon frequency shifts and typical domain structure motifs are discussed. The results reveal strikingly different domain structure architecture: domain structures of the PbTiO3 film grown on SmScO3 have dominantly a-domain orientation while strongly preferential c-domain orientation was found in the PbTiO3 film grown on the TbScO3 substra…
SrTiO$_{3}$ is known to be an incipient ferroelectric. It is thought that ferroelectric stability in SrTiO$_{3}$ is suppressed by a delicate competition with quantum fluctuation and antiferrodistortion. The ferroelectric phase can, however, be stabilized by doping, isotope manipulation and strain engineering etc. Till date ferroelectricity in SrTiO$_{3}$ thin films was observed to exist up to room temperature -- that was when the films were grown on specially engineered substrates using complex growth techniques. It was possible to write and erase ferroelectric domains on the specially enginee…
Electric Scanning Probe Microscopies are used to characterize the surface behavior of ferroelectric materials. The effects of local charge density on the chemistry and physics of ferroelectric surfaces are investigated. The kinetics and thermodynamics parameters of adsorption are assessed by variable temperature Scanning Surface Potential Microscopy. Contrast formation mechanism of Piezoresponse Force Microscopy (PFM) is analyzed in detail, and the contributions of electroelastic constants of the material to response amplitude are determined. The effect of experimental conditions including ind…
Finite size effects in ferroelectric thin films have been probed in a series of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down to 28 A (7 unit cells). The evolution of the film tetragonality c/a, studied using high resolution x-ray diffraction measurements, shows first a decrease of c/a with decreasing film thickness followed by a recovery of c/a at small thicknesses. This recovery is accompanied by a change from a monodomain to a polydomain configuration of the polarization, as directly demonstrate…
Freestanding BaTiO3 nanodots exhibit domain structures characterized by distinct quadrants of ferroelastic 90° domains in transmission electron microscopy (TEM) observations. These differ significantly from flux-closure domain patterns in the same systems imaged by piezoresponse force microscopy. Based upon a series of phase field simulations of BaTiO3 nanodots, we suggest that the TEM patterns result from a radial electric field arising from electron beam charging of the nanodot. For sufficiently large charging, this converts flux-closure domain patterns to quadrant patterns with radial net p…
Domains walls and topological defects in ferroelectric materials have emerged as a powerful new paradigm for functional electronic devices including memory and logic. Similarly, wall interactions and dynamics underpin a broad range of mesoscale phenomena ranging from giant electromechanical responses to memory effects. Exploring the functionalities of individual domain walls, their interactions, and controlled modifications of the domain structures is crucial for applications and fundamental physical studies. However, the dynamic nature of these features severely limits studies of their local …
By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), piezoresponse force microscopy (PFM) and first-principles calculations, we have studied the low-energy band structure, atomic structure and charge polarization on the surface of a topological semimetal candidate TaNiTe5. Dirac-like surface states were observed on the (010) surface by ARPES, consistent with the first-principles calculations. On the other hand, PFM reveals a switchable ferroelectric-like polarization on the same surface. We propose that the noncentrosymmetric surface reconstructi…
Interest in epitaxial ferroelectric nanoislands was growing rapidly in recent years driven by their potential for devices, especially ultradense memories. Recent advances in the "bottom- up" (self-assembly) nanometer scale techniques have opened up the opportunities of fabricating high-quality epitaxial ferroelectric nanoislands with extremely small thickness and lateral size on the order of 1 nm and 20 nm, respectively. On the other hand, recent emergence of powerful probes, such as piezoresponse force microscopy (PFM), has enabled imaging of a local domain structure with sub-10 nm resolution…
