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We report on the surface antiferromagnetic (AFM) domain imaging of the prototype antiferromagnet NiO(100) using an electron-microscopy-based laboratory method. Coherently exchange-scattered electrons from the surface AFM lattice are utilized in a low-energy electron microscope to resolve the surface domain structure. Direct comparison with x-ray magnetic linear dichroism photoemission electron microscopy demonstrates a complimentary nature. High surface sensitivity combined with improved spatial resolution of this method enables studying of nanosized magnetic domains in NiO(100) thin films and their thickness-dependent evolution.

Upon exposure of ultrathin vanadium oxide layers on Rh(111) (θV ∼ 0.2 MLE) to the H2 + O2 reaction, we observe the reversible formation of stationary macroscopic stripe patterns caused by lateral redistribution of the vanadium oxide. These patterns are investigated in the 10–6 mbar range at around 750 K, employing LEEM (low energy electron microscopy), microprobe-LEED and microprobe-XPS. The stripe patterns evolve via several stages and structures: essentially, vanadium oxide nanoislands with a (√7 × √7)R19.1° structure are reduced from V+5 to V3+ and condense into a macroscopic (2 × 2) oxide phase upon increasing p(H2). The orientation of the stripe patterns is determined by step bunches, which introduce a diffusional anisotropy. The stationary patterns are discussed within the concept of reactive phase separation.

We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following magnetic saturation, the dominant magnetic states consist of quasi-uniform configurations, where a strong influence from the magnetocrystalline anisotropy is visible. Heating experiments show the stability of the spin configuration of domain walls in confined geometries up to 800 K. The switching temperature for the transition from transverse to vortex walls in ring elements is found to increase with ring width, an effect attributed to structural changes and consequent changes in magnetic anisotropy, which start to occur in the narrower elements at lower temperatures., Comment: 4 pages, 4 figures

The multi-technique approach in the spectroscopic photoemission and low-energy electron microscope (SPELEEM) has proven to be a powerful tool in studies of crystalline, chemical and magnetic structures at surfaces. The energy filtering offered by this instrument enables a variety of complementary analytical characterization methods. Here, we give a summary of the recent studies with the SPELEEM microscope installed at the Nanospectroscopy beamline of the Elettra synchrotron laboratory. The examples cover topics such as surface corrugation in free-standing graphene layers, spin-reorientation transition in thin Fe films on W(110), and stress-induced adsorbate patterns on single crystal surfaces. Moreover, the SPELEEM capabilities of imaging inelastically scattered electrons are demonstrated. [DOI: 10.1380/ejssnt.2011.72]

Free-standing exfoliated monolayer graphene is an ultrathin flexible membrane, which exhibits out-of-plane deformation or corrugation. In this paper, a technique is described to measure the band structure of such free-standing graphene by angle-resolved photoemission. Our results show that photoelectron coherence is limited by the crystal corrugation. However, by combining surface morphology measurements of the graphene roughness with angle-resolved photoemission, energy-dependent quasiparticle lifetime and band-structure measurements can be extracted. Our measurements rely on our development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. Our angle-resolved photoemission spectroscopy measurements show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; we measure the Dirac point to be within 25 meV of ${E}_{F}$. Further, we show that suspended graphene behaves as a marginal Fermi liquid, with a quasiparticle lifetime that scales as ${(E\ensuremath{-}{E}_{F})}^{\ensuremath{-}1}$; comparison with other graphene and graphite data is discussed.

The microscopic structure of the $90\ifmmode^\circ\else\textdegree\fi{}$ in-plane magnetic reorientation transition in Fe(110) films is examined using photoemission x-ray microscopy. At the nanoscale, sharp magnetic boundaries are detected. They are indicative of a first-order transition and are consistent with Fe magnetic anisotropy constants. At the micron scale, the magnetic boundary breaks up into triangular patterns whose characteristic angular dependence is revealed by experiments on conical microwedges. This effect, fully accounted by micromagnetic simulations, opens the possibility to control the sharpness of the transition at the microscopic scale.

We study the depinning of domain walls by pure diffusive spin currents in a nonlocal spin valve structure based on two ferromagnetic permalloy elements with copper as the nonmagnetic spin conduit. The injected spin current is absorbed by the second permalloy structure with a domain wall and from the dependence of the wall depinning field on the spin current density we find an efficiency of 6*10^{-14}T/(A/m^2), which is more than an order of magnitude larger than for conventional current induced domain wall motion. Theoretically we reproduce this high efficiency, which arises from the surface torques exerted by the absorbed spin current that lead to efficient depinning., 11 pages, 3 figures, accepted for publication in Phys. Rev. Lett

Low-energy electron microscopy and microprobe diffraction are used to image and characterize corrugation in SiO(2)-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short-range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction line shape. The effects of both intrinsic and extrinsic corrugation factors are discussed.

Domain wall (DW) depinning and motion in the viscous regime induced by magnetic fields, are investigated in planar perm alloy nanowires in which the Gilbert damping a is tuned in the range 0.008-0.26 by doping with Ho. Real time, spatially resolved magneto-optic Kerr effect measurements yield depinning field distributions and DW mobilities. Depinning occurs at discrete values of the field which are correlated with different metastable DW states and changed by the doping. For 0'

The chemical and structural evolution of supported PtRh alloy nano- and microparticles during oxidation has been studied by means of scanning photoelectron microscopy (SPEM) and low energy electron...

Received 28 July 2009; revised manuscript received 18 September 2009; published 23 November 2009 The connection between magnetization and structure of ultrathin films is studied at room temperature for the case of Fe films on W110 by inserting a 2-monolayer-thick growth-modifying Au layer between film and substrate using spin-polarized low-energy electron microscopy and low-energy electron diffraction. Ferromagnetic order with the easy axis pointing in the 11 ¯ 0 direction appears upon percolation at 1.6 monolayers. Shortly thereafter, the easy axis rotates into the 001 direction. With further increasing thickness the magnetization oscillates between the 001 and the 11 ¯ 0 direction with a maximum deviation from the 001 direction at seven monolayers where the magnetic signal has a maximum. The changes in the magnetization are associated with changes in the structure, strain, and morphology that are deduced from the diffraction patterns and which strongly influence the competition between interface anisotropy, magnetoelastic anisotropy, and dipolar surface anisotropy.

4 pags, 3 figs. -- PACS numbers: 75.75.+a, 75.70.Rf, 87.64.ku, 68.37.Nq, Co islands and films are characterized by x-ray magnetic circular dichroism photoemission electron microscopy. The spatial resolution capabilities of the technique together with atomic growth control permit obtaining perfectly flat triangular islands with a given thickness (3 ML), very close to an abrupt spin-reorientation transition. The magnetic domain configurations are found to depend on island size: while small islands can be magnetized in a single-domain state, larger islands show more complex patterns. Furthermore, the magnetization pattern of the larger islands presents a common chirality. By means of dichroic spectromicroscopy at the CoL absorption edges, an experimental estimate of the ratio of the spin and orbital magnetic moment for three monolayer thick films is obtained. © 2009 The American Physical Society., This research was partly supported by the U.S. Department of Energy under Contracts No. DE-AC04-94AL85000 and No. DE-AC02-05CH11231, by the Spanish Ministry of Education and Science under Project No. MAT2006-13149-C02-02, and by the Comunidad Autónoma de Madrid and the CSIC under Projects No. CCG07-CSIC-MAT-2030 and No. S-0505/MAT/0194

We present an experimental study of the evolution of InAs/GaAs quantum dots partially capped with GaAs, as an annealing process transforms them first into quantum rings and later into holes penetrating the whole cap layer. Shape, composition, and optical emission were monitored as a function of annealing time by means of atomic force microscopy, x-ray photoemission microscopy, and photoluminescence, respectively. Our results show a progressive dissolution of the original dot, with the outdiffused material forming a second wetting layer on the planar region surrounding the dot. For the longest annealing time, in a situation close to thermodynamic equilibrium, no residual dot material is left in the holes, and an In-rich layer covers uniformly the surface. Our findings were examined by taking into account the surface chemical potential previously written for Stranski-Krastanov islands partially covered with a cap layer. We show that the energy gain due to the formation of the second wetting layer is the driving force for the shape and composition evolution, but its analytical expression should be modified, with respect to previous formulations, by taking into account the observed material interdiffusion.

We study the relationship between the damping $(\ensuremath{\alpha})$ and the nonadiabaticity of the spin transport $(\ensuremath{\beta})$ in permalloy nanowires. $\ensuremath{\alpha}$ is engineered by Ho doping, and from the characteristics of the current-induced domain-wall velocity, determined by high-resolution x-ray magnetic circular-dichroism photoemission electron microscopy, $\ensuremath{\beta}$ due to spin relaxation is measured. We find that $\ensuremath{\beta}$ scales with $\ensuremath{\alpha}$ and conclude that the spin relaxation that leads to nonadiabatic spin torque originates from the same underlying mechanism as the angular momentum dissipation that causes viscous damping.

Herein, different concepts for domain wall propagation based on currents and fields that could potentially be used in magnetic data storage devices based on domains and domain walls are reviewed. By direct imaging, we show that vortex and transverse walls can be displaced using currents due to the spin transfer torque effect. For the case of field-induced wall motion, particular attention is paid to the influence of localized fields and local heating on the depinning and propagation of domain walls. Using an Au nanowire adjacent to a permalloy structure with a domain wall, the depinning field of the wall, when current pulses are injected into the Au nanowire, was studied. The current pulse drastically modified the depinning field, which depended on the interplay between the externally applied field direction and polarity of the current, leading subsequently to an Oersted field and heating of the permalloy at the interface with the Au wire. Placing the domain wall at various distances from the Au wire and studying different wall propagation directions, the range of Joule heating and Oersted field was determined; both effects could be separated. Approaches beyond conventional field- and current-induced wall displacement are briefly discussed.

We report measurements of the electronic structure and surface morphology of exfoliated graphene on an insulating substrate using angle-resolved photoemission and low energy electron diffraction. Our results show that although exfoliated graphene is microscopically corrugated, the valence band retains a massless fermionic dispersion, with a Fermi velocity of ~10^6 m/s. We observe a close relationship between the morphology and electronic structure, which suggests that controlling the interaction between graphene and the supporting substrate is essential for graphene device applications., Comment: 10 pages of text, 4 JPEG figures

It is shown that the pulses which develop in the NO+H 2 reaction on an alkali promoted Rh(110) surface reaction can transport alkali metal. This leads to the accumulation of a substantial alkali-metal concentration in the collision area of pulse trains. Realistic simulations revealed that the effect is due to the strong energetic interactions of the alkali metal with coadsorbates, i.e., the attractive interaction with coadsorbed oxygen and the effectively repulsive interaction with coadsorbed nitrogen.

A stress-induced stripe phase of submonolayer Pd on W(110) is observed by low-energy electron microscopy. The temperature dependence of the pattern is explained by the change both in the boundary free energy and elastic relaxation energy due to the increasing boundary width. The stripes are shown to disorder when the correlation length of the condensed phase becomes comparable to its period, while the condensate to lattice-gas transition takes place at a higher temperature, as revealed by low-energy electron diffraction.

We demonstrate for the first time that seeded harmonic generation on electron storage rings can produce coherent optical pulses in the vacuum ultraviolet spectral range. The experiment is performed at Elettra, where coherent pulses are generated at 132 nm, with a duration of about 100 fs. The light source has a repetition rate of 1 kHz and adjustable polarization; it is very bright, with a peak power several orders of magnitude above that of spontaneous synchrotron radiation. Owing to high stability, the source is used in a test photoemission electron microscopy experiment. We anticipate that seeded harmonic generation on storage rings can lead to unprecedented developments in time-resolved femtosecond spectroscopy and microscopy.

The stress-induced lattice changes in a p(1x2) ordered oxygen layer on W(110) are measured by low-energy electron diffraction. We have observed that small oxygen islands show a mismatch with the underlying lattice. Our results indicate that along [1-10] the average mismatch scales inversely with the island size as 1/L for all oxygen coverages up to 0.5 ML, while along [001] it is significant only for the smallest oxygen islands and scales as a higher power of the inverse island size. The behaviour along [1-10] is described by a one-dimensional finite-size Frenkel-Kontorova model. Using this model, together with calculated force constants, we make a quantitative estimate for the change of surface-stress upon oxygen adsorption. The result is consistent with our ab-initio calculations, which give a relative compressive stress of -4.72 N/m along [1-10] and a minute relative tensile stress of 0.15 N/m along [001]. The scaling along [001] is qualitatively explained as an effect induced by the lattice relaxation in the [1-10] direction., 22 pages, 5 figures

By direct imaging we determine spin structure changes in Permalloy wires and disks due to spin transfer torque as well as the critical current densities for different domain wall types. Periodic domain wall transformations from transverse to vortex walls and vice versa are observed, and the transformation mechanism occurs by vortex core displacement perpendicular to the wire. The results imply that the nonadiabaticity parameter $\ensuremath{\beta}$ does not equal the damping $\ensuremath{\alpha}$, in agreement with recent theoretical predictions. The vortex core motion perpendicular to the current is further studied in disks revealing that the displacement in opposite directions can be attributed to different polarities of the vortex core.

Electron-stimulated desorption of bridge-bonded oxygen atoms on the $\mathrm{Ti}{\mathrm{O}}_{2}(110)$ surface at elevated temperature is used to produce an oxygen-deficient $(1\ifmmode\times\else\texttimes\fi{}2)$ reconstruction. Low energy electron diffraction, x-ray photoelectron spectroscopy, and first-principles calculations show that Au adsorbs on this surface with the substrate periodicity in strongly bonded monomer, dimer, and trimer rows with metallic character. In addition, the experimental evidence combined with the theoretical results points to a missing-row type of structure for the initial $(1\ifmmode\times\else\texttimes\fi{}2)$ surface.

The paper is a brief overview of the efforts and achievements at Elettra in development of instrumentation for imaging and spectroscopic analysis using different spectral range of the synchrotron radiation. Selected results will illustrate the potential of these techniques for multi-disciplinary applications.

We have studied the initial stages of the heteroepitaxy of Mg on W(110) in situ, by means of complementary microscopic and spectromicroscopic techniques. In the submonolayer coverage regime the Mg film undergoes a series of structural transitions which are clearly distinguished in the diffraction pattern. Monitoring the Mg $2p$ core-level permits the identification of the different energy shifts associated with each superstructure. During deposition of the second Mg monolayer at moderate temperatures, the growth of single atomic height stripes is observed. The Mg $2p$ core level of the first (interface) and second monolayer are remarkably separated. The density, length, and width of the stripes, stabilized by the anisotropic misfit between the W(110) and Mg(0001) lattices, can be tuned by modifying the growth parameters.

By using X‐Ray Photoemission Electron Microscopy we have obtained two‐dimensional maps of the in‐plane surface composition of InAs/GaAs self‐assembled quantum dots. The chemical analysis reveals a higher In composition on the dot surface, with respect to the surrounding wetting layer, with a concentration increasing from the sides to the center of the dots. Comparison with concentrations found in the core of similar dots suggests strong In segregation on their surface, similarly to the surrounding wetting layer.

Surface compositional maps of self-organized InAs/GaAs quantum dots were obtained with laterally resolved photoemission spectroscopy. We found a surface In concentration of about 0.85 at the center of the islands which decreases to 0.75 on the wetting layer. Comparison with concentration values found in the core of similar dots suggests a strong In segregation on the topmost surface layers of the dots and on the surrounding wetting layer. Furthermore, the morphological properties of the dots such as size and density have been measured with plan-view transmission electron microscopy and low energy electron microscopy.

The impact of Ga preadsorption on the spatial correlation of nanoscale three-dimensional (3D) Ge-islands has been investigated by low-energy electron microscopy and low- energy electron diffraction. Submonolayer Ga adsorption leads to the formation of a 2D chemical nanopattern, since the Ga-terminated (2 x 2) domains exclusively decorate the step edges of the Si(113) substrate. Subsequent Ge growth on such a partially Ga-covered surface results in Ge 3D islands with an increased density as compared to Ge growth on clean Si(113). However, no pronounced alignment of the Ge islands is observed. Completely different results are obtained for Ga saturation coverage, which results in the formation of (112) and (115) facets regularly arranged with a periodicity of about 40 nm. Upon Ge deposition, Ge islands are formed at a high density of about 1.3 x 10(10) cm(-2). These islands are well ordered as they align at the substrate facets. Moreover, the facet array induces a reversal of the Ge islands' shape anisotropy as compared to growth on planar Si(113) substrates.

The interaction of molecular hydrogen with ceria is of important relevance for heterogeneous catalysis related to green chemistry and renewable energy. Here, the complex structural transformations of a well-defined cerium oxide model catalyst are followed in situ and in real time when exposed to a reactive H2 environment. By using electron spectromicroscopy and diffraction with chemical and structural sensitivities, it is demonstrated that the transition from CeO2 to crystalline Ce2O3 occurs through a mixture of transient, coexisting phases on the nanoscale. The findings establish a clear relationship between structure and functionality for hydrogen dissociation over ceria(111), bearing profound implications on the nature of the reduction (Ce4+ Ce3+) and mechanism for H2 scission.

International audience; We report observations of the effect of electrical currents on the propagation and spin structure of vortex walls in NiFe wires. We find that magnetic vortices are nucleated and annihilated due to the spin torque effect. The velocity is found to be directly correlated with these transformations and decreases with increasing number of vortices. The transformations are observed in wide elements, while in narrower structures the propagation of single vortex walls prevails.

We investigated the initial Ge nucleation and Ge island growth on a Si(113) surface using low energy electron microscopy and low energy electron diffraction. The sample temperature was varied systematically between 380 degrees C and 590 degrees C. In this range, a strong temperature dependence of the island shape is observed. With increasing temperature the Ge islands are elongated in the [332] direction. Simultaneously, the average island size increases while their density decreases. From the Arrhenius-like behaviour of the island density, a Ge adatom diffusion barrier height of about 0.53 eV is deduced. (c) 2005 Elsevier B.V. All rights reserved.

The growth and reaction of Fe on a ZnS(1 0 0) substrate are studied in situ and with high lateral resolution using low energy electron microscopy (LEEM), micro low energy electron diffraction ( μLEED), x-ray photoemission electron microscopy (XPEEM), microprobe x-ray photoelectron spectroscopy ( μXPS) and x-ray magnetic circular dichroism PEEM (XMCDPEEM) for complementary structural, chemical, and magnetic characterization. Initially, a two-dimensional (Fe, Zn)S reaction layer forms with thickness that depends on growth temperature. Further growth results in the formation of a variety of three-dimensional crystals, most of them strongly elongated in the form of 'nanowires' of two distinct types, labeled as A and B. Type A nanowires are oriented near the ZnS[1 1 0] direction and are composed of Fe. Type B nanowires are oriented predominantly along directions a few degrees off the ZnS[0 0 1] direction and are identified as Greigite (Fe3S4). Both types of nanowires are magnetic with Curie temperatures above 450 °C. The understanding of the reactive growth mechanism in this system that is provided by these investigations may help to develop growth methods for other elemental and transition metal chalcogenide nanostructures on ZnS and possibly on other II-VI semiconductor surfaces.

We investigate thin films of diindenoperylene deposited on Au(100) single crystals by using real time in situlow energy electron microscopy (LEEM) in synergy with X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. We find evidence for Stranski–Krastanov growth, with island nucleation prevalently at step bunches, and a lower probability of island nucleation at terraces. We also directly observe the effect of the Ehrlich–Schwoebel barrier at the substrate and in the film morphology, in particular inside the islands that show a non-homogeneous thickness due to a rough front growth, because of the additional energy required for the diffusing molecules to surmount a downward step.

The deposition of ceria on a preoxidized W(110) crystal at 870 K has been studied in situ by photoelectron spectroscopy and low-energy electron diffraction. Formation of an epitaxial layer of crystalline cerium tungstate Ce(6)WO(12)(100), with the metals in the Ce(3+) and W(6+) chemical states, has been observed. The interface between the tungsten substrate and the tungstate film consists of WO suboxide. At thicknesses above 0.89 nm, cerium dioxide grows on the surface of Ce(6)WO(12), favoured by the limited diffusion of tungsten from the substrate.

The variation in the surface potential as a function of the ferroelectric polarization of micron scale domains in a thin epitaxial film of Pb(Zr0.48Ti0.52)O-3 is measured using mirror electron microscopy. Domains were written using piezoforce microscopy. The surface potential for each polarization was deduced from the mirror to low energy electron microscopy transition in the local reflectivity curve. The effect of extrinsic screening of the fixed polarization charge at the ferroelectric surface is demonstrated. The results are compared with density functional theory calculations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3523359]

The correlation between the thickness-dependent oxidation rate of ultrathin Al films on W(110) and the quantum-well states (QWS) resulting from electron confinement in the Al film has been explored by combined x-ray photoemission electron microscopy (XPEEM), low energy electron microscopy (LEEM), and first-principles calculations. Hybridization with substrate electronic states is observed to alter the film electronic structure, strongly modifying the electron density decay length in vacuum. The decay length, rather than the density of states at the Fermi energy, is found to dominate the observed reactivity trends.

Low energy electron irradiation of a Ag(111) surface during NO2 adsorption at 300 K induces formation of Ag oxide. Using a spatially confined electron beam, small Ag2O spots could be grown with a sharp, ∼100 nm wide, boundary to the nonirradiated metallic surface. Since the structure size will mainly depend on the sharpness of the irradiating electron beam, this process has the potential of a single step nanostructuring process. Temperature treatment offers an easy way to manipulate the boundary between oxide and metallic silver by steering a chemical front.

One-dimensional Au rows are produced on the TiO2(110) surface by controlled photon-stimulated desorption followed by Au deposition at 750 K. In the resulting (1 × 2) structure, O vacancies are replaced by Au atoms, as demonstrated by combined laterally resolved x-ray spectroscopy and micro-LEED (low-energy electron diffraction) measurements. The experimental results are confirmed by first-principles calculations, which indicate strong Au–Ti bonding and a very stable configuration of the Au rows. The calculations determine the detailed atomic structure of the Au rows, with an inter-row spacing of 13 A and an intra-row Au distance of 2.95 A.

With laterally resolved photoemission spectroscopy, we obtained In and Ga surface concentration maps of InAs/GaAs quantum dots. Our data demonstrate that the dot composition is neither pure InAs nor homogeneous InxGa1-xAs, but presents an In concentration increasing from the borders to the center of the dots. Besides, our observations suggest strong In segregation (x ~ 0.9) on the surface of the dots and of the surrounding wetting layer. Such segregation, well known for two-dimensional InAs/GaAs growth, had not been directly observed so far on the dots, and should be taken into account to model size and composition of GaAs-overgrown structures.

In this paper, a brief overview of the latest developments in synchrotron techniques and their application to magnetic nanostructures will be given. Selected examples will be used to illustrate the use of these techniques for magnetic nanostructures.

Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their current-induced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of N\'eel skyrmions with diameters in the 100-nm range in an ultrathin Pt/Co/MgO trilayer. We find that these skyrmions can be driven at a speed of 100 m/s and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties., Comment: 9 pages, 4 figures + Supplementary Information (12 pages, 9 figures)

Resistive switching in transition metal oxide‐based metal‐insulator‐metal structures relies on the reversible drift of ions under an applied electric field on the nanoscale. In such structures, the formation of conductive filaments is believed to be induced by the electric‐field driven migration of oxygen anions, while the cation sublattice is often considered to be inactive. This simple mechanistic picture of the switching process is incomplete as both oxygen anions and metal cations have been previously identified as mobile species under device operation. Here, spectromicroscopic techniques combined with atomistic simulations to elucidate the diffusion and drift processes that take place in the resistive switching model material SrTiO3 are used. It is demonstrated that the conductive filament in epitaxial SrTiO3 devices is not homogenous but exhibits a complex microstructure. Specifically, the filament consists of a conductive Ti3+‐rich region and insulating Sr‐rich islands. Transmission electron microscopy shows that the Sr‐rich islands emerge above Ruddlesden–Popper type antiphase boundaries. The role of these extended defects is clarified by molecular static and molecular dynamic simulations, which reveal that the Ruddlesden–Popper antiphase boundaries constitute diffusion fast‐paths for Sr cations in the perovskites structure.

In order to unravel the complex interplay between substrate interactions and film configuration, we investigate and characterize graphene on a support with non-three-fold symmetry, the square Ir(100). Below 500 °C, distinct physisorbed and chemisorbed graphene phases coexist on the surface, respectively characterized by flat and buckled morphology. They organize into alternating domains that extend on mesoscopic lengths, relieving the strain due to the different thermal expansion of film and substrate. The chemisorbed phase exhibits exceptionally large one-dimensional ripples with regular nanometer periodicity and can be reversibly transformed into physisorbed graphene in a temperature-controlled process that involves surprisingly few C-Ir bonds. The formation and rupture of these bonds, rather than ripples or strain, are found to profoundly alter the local electronic structure, changing graphene behavior from semimetal to metallic type. The exploitation of such subtle interfacial changes opens new possibilities for tuning the properties of this unique material.