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Abstract: Benzene bilayer islands were observed by STM to be structurally similar on both Cu(111) and Cu(110) surfaces. The local electronic structure of the bilayers was studied using tunneling spectroscopy of Stark-shifted image potential states. On both Cu substrates, the n =1 bilayer state was locally shifted away from the Fermi level when compared to the n =1 monolayer state. The Stark-shift due to the electric field of the STM tip was observed to be greater for the n =1 bilayer state than the n =1 monolayer state on Cu(111). [Copyright &y& Elsevier]

Abstract: The chemisorption of benzoate on a Cu(110) crystal at room temperature was studied using low temperature scanning tunneling microscopy. STM images, obtained at 5K for low benzoate coverage, show isolated surface species that consist of a single Cu adatom stabilizing two benzoate molecules in a flat orientation. These species are discussed in relation to other known metal-organic surface compounds. At higher coverage the overlayer, called the α-phase, was also observed at 5K and found to contain features attributable to two Cu adatoms associated with two pairs of non-equivalent benzoate species. The observed topographic features are used to suggest refinements of the structural model of the ordered α-phase overlayer. [Copyright &y& Elsevier]

Abstract: Two large and complex adsorbed organic molecules, coronene (C24H12) and C60, have been used to produce Si dimer vacancy defects on Si(001) by thermal decomposition. Studies by STM show that the aligned structural arrangement of the dimer vacancy defects produced is independent of the chemical structure of the organic molecules. This indicates that the chemistry of the thermally decomposed carbon species produced by decomposition of the organic molecule controls the organization of the Si dimer vacancy defects. It is found that ∼1 C atom is responsible for each dimer vacancy defect for both molecules in accordance with earlier studies of C2H2 decomposition on Si(001). [Copyright &y& Elsevier]

Adsorption of H2O on the TiO2(1 1 0)–(1 × 2) surface was studied in ultrahigh vacuum (UHV) using the scanning tunneling microscope (STM). At 300 K H2O adsorbs preferentially on the crosslinks of the TiO2(1 1 0)–(1 × 2) surface. Cooling down the surface to 110 K during H2O exposure results in adsorption on the crosslinks and other surface sites, presumably the 5-fold coordinated Ti-atoms. The reaction products, observed as bright protrusions at positive sample bias, are attributed to hydroxyl groups due to H2O dissociation. In addition, it was found that the UV-induced line-defects on the TiO2(1 1 0)–(1 × 2) surface do not interact with H2O as seen by STM. [Copyright &y& Elsevier]

The effect of UV radiation (1.6 eV⩽hν⩽5.6 eV) on the rutile surface was studied in ultrahigh vacuum (UHV) using the scanning tunneling microscope (STM). It was found that the TiO2(1 1 0)-(1×1) surface remains unaffected by UV irradiation. However, line defects along the 〈0 0 1〉 direction were formed on the TiO2(1 1 0)-(1×2) surface, the cross-section for the defect formation being 10−23.5±0.2 cm2 photon−1 (hν⩾3.0 eV). The defects are attributed to collective oxygen removal by UV light. It was also found that the defects were stable in UHV (up to 48 h), and their formation was not temperature dependent. [Copyright &y& Elsevier]

Despite multiple efforts, there exist many unsolved fundamental problems related with detection and analysis of internal polarization structure and related phase transitions in ferroelectric domain walls. Their solution can be very important for the progress in domain wall nanoelectronics and related applications in advanced memories and other information technologies. Here, we theoretically study the features of phase transitions in the domain walls, which are potentially detectable by the scanning probe capacitance microwave microscopy. The finite element modelling based on the Landau-Ginzburg-Devonshire theory is performed for the capacitance changes related with the domain wall motion in a multiaxial ferroelectric BaTiO3. [ABSTRACT FROM AUTHOR]

Characterizing the novel properties of layered van der Waals materials is key for their application in functional devices. A better understanding of this type of material requires correlative imaging of diverse nanoscale material properties. Within this class of materials, CuInP2S6 (CIPS) has received a significant degree of interest due to its ionically mediated room temperature ferroelectricity. Moreover, it is possible to form stable self-assembled heterostructures of ferroelectric CuInP2S6 (CIPS) and non-ferroelectric (i.e., lacking Cu) In4/3P2S6 (IPS) phases, by controlling the targeted composition and kinetics of synthesis. In this work, we present a correlative nanometric imaging study of the phononic modes and piezoelectricity of the phase-separated thin heteroepitaxial CIPS/IPS flakes. We show that it is possible to isolate the different phononic modes of the two phases by spatially correlating them with their distinct ferroelectric behavior. The coupling of our experimental data with unsupervised learning statistical methods enables unraveling specific Raman peaks that are characteristic of each chemical phase (CIPS and IPS) present in the composite sample, discarding the less significant ones. [ABSTRACT FROM AUTHOR]

Ferroelectric surfaces involve a complex interplay between polarization and dielectric properties, internal and external surface charge screening, and ionic and electrochemical effects. There is currently no good way to simultaneously capture all the required information at appropriate length scales. To this end, we present an advanced scanning probe microscopy approach for simultaneously mapping surface potential, dielectric, and piezoelectric properties on the nanoscale. For quantitatively mapping electromechancial properties, we utilize interferometric displacement sensing piezoresponse force microscopy, which measures the effective piezoelectric coefficient free of background artifacts such as the cantilever body electrostatics. The dielectric and surface electrochemical properties are captured during G-mode electrostatic force microscopy/Kelvin probe force microscopy operated in the lift mode. We show the capabilities of this approach on the chemically phase separated composite sample consisting of a van der Waals layered ferroelectric CuInP2S6 phase and a non-polar In4/3P2S6 phase. Finally, we demonstrate domain structure evolution during thermally stimulated phase transition. [ABSTRACT FROM AUTHOR]

Self-poling of ferroelectric films, i.e., a preferred, uniform direction of the ferroelectric polarization in as-grown samples is often observed yet poorly understood despite its importance for device applications. The multiferroic perovskite BiFeO3, which crystallizes in two distinct structural polymorphs depending on applied epitaxial strain, is well known to exhibit self-poling. This study investigates the effect of self-poling on the monoclinic domain configuration and the switching properties of the two polymorphs of BiFeO3 ( R′ and T′) in thin films grown on LaAlO3 substrates with slightly different La0.3Sr0.7MnO3 buffer layers. This study shows that the polarization state formed during the growth acts as 'imprint' on the polarization and that switching the polarization away from this self-poled direction can only be done at the expense of the sample's monoclinic domain configuration. The observed reduction of the monoclinic domain size is largely reversible; hence, the domain size is restored when the polarization is switched back to its original orientation. This is a direct consequence of the growth taking place in the polar phase (below Tc). Switching the polarization away from the preferred configuration, in which defects and domain patterns synergistically minimize the system's energy, leads to a domain state with smaller (and more highly strained and distorted) monoclinic domains. [ABSTRACT FROM AUTHOR]

A new paradigm of domain wall nanoelectronics has emergedrecently,in which the domain wall in a ferroic is itself an active device element.The ability to spatially modulate the ferroic order parameter withina single domain wall allows the physical properties to be tailoredat will and hence opens vastly unexplored device possibilities. Here,we demonstrate via ambient and ultrahigh-vacuum (UHV) scanning probemicroscopy (SPM) measurements in bismuth ferrite that the conductivityof the domain walls can be modulated by up to 500% in the spatialdimension as a function of domain wall curvature. Landau–Ginzburg–Devonshirecalculations reveal the conduction is a result of carriers or vacanciesmigrating to neutralize the charge at the formed interface. Phase-fieldmodeling indicates that anisotropic potential distributions can occureven for initially uncharged walls, from polarization dynamics mediatedby elastic effects. These results are the first proof of concept formodulation of charge as a function of domain wall geometry by a proximalprobe, thereby expanding potential applications for oxide ferroicsin future nanoscale electronics. [ABSTRACT FROM AUTHOR]

Many interesting materials phenomena such as the emergence of high-Tc superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor–insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO3 through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p–n junction can be created, erased and inverted in this material. A ‘dome-like’ feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of ∼1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO3. [ABSTRACT FROM AUTHOR]

Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO3. The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features. [ABSTRACT FROM AUTHOR]