Marginally twisted WS2 bilayers undergo lattice reconstructions, but it is unclear if the distortion is equally distributed or confined to specific sublayers. Here, we use in situ combined noncontact atomic force microscopy with scanning tunneling spectroscopy to tune the probing depth to extract electronic and atomic lattice information for each sublayer separately. We find a lattice reconstruction unexpectedly confined to the WS2 layer in contact with graphite only, governed by transition metal dichalcogenide-substrate interactions, leading to a peculiar type of a ferroelectric domain wall.

The electron optical phase contrast probed by electron holography at n-n+ GaN doping steps is found to exhibit a giant enhancement, in sharp contrast to the always smaller than expected phase contrast reported for p-n junctions. We unravel the physical origin of the giant enhancement by combining off-axis electron holography data with self-consistent electrostatic potential calculations. The predominant contribution to the phase contrast is shown to arise from the doping dependent screening length of the surface Fermi-level pinning, which is induced by FIB-implanted carbon point defects below the outer amorphous shell. The contribution of the built-in potential is negligible for modulation doping and only relevant for large built-in potentials at e.g. p-n junctions. This work provides a quantitative approach to so-called dead layers at TEM lamellas.

Thermal healing of focused ion beam-implanted defects in GaN is investigated by off-axis electron holography in TEM. The data reveal that healing starts at temperatures as low as about 250 °C. The healing processes result in an irreversible transition from defect-induced Fermi level pinning near the VB toward a midgap pinning induced by the crystalline-amorphous transition interface. Based on the measured pinning levels and the defect charge states, we identify the dominant defect type to be substitutional carbon on nitrogen sites.

Magnetic proximity effects are typically limited to a few nanometers due to the short-range nature of the underlying magnetic interactions. Here, we use off-axis electron holography to reveal an electrostatically induced long-range magnetic proximity effect that extends over a distance of 40 nm at a ferromagnetic/paramagnetic interface in La0.7Sr0.3MnO3. We show that this behavior results from carrier diffusion and drift across the interface, which changes the Mn3+/Mn4+ ratio and hence the local Curie temperature and density of magnetic moments.

Hydrogen exposure and annealing at 400 °C leads to a layer-by-layer etching of the n-doped GaAs(110) cleavage surface removing islands and forming preferentially step edge sections with [001] normal vector. In addition, a large density of negatively charged point defects is formed, leading to a Fermi level pinning in the lower part of the bandgap. Their charge transfer level is in line with that of Ga vacancies only, suggesting that adatoms desorb preferentially due to hydrogen bonding and subsequent Ga–H desorption. The results obtained on cleavage surfaces imply that the morphology of nanowire sidewall facets obtained by hydrogen cleaning is that of an etched surface, but not of the initial growth surface. Likewise, the hydrogen-cleaned etched surface does not reveal the intrinsic electronic properties of the initially grown nanowires.

For the nanoscopic analysis of III/V nanowire surfaces, hydrogen cleaning is a commonly used procedure. While this is reported to achieve clean, atomically flat surfaces, the process and dynamics during the cleaning procedure are rarely examined. Here, we investigate the modifications of GaAs(110) as model system introduced by hydrogen supply at room temperature and under commonly used cleaning conditions at the atomic level by scanning tunneling microscopy and -spectroscopy. Understanding this dynamics is crucial for the interpretation of measurements concerning electronic surface properties as well as conductivity measurements, since the surface-to-volume ratio of nanowires is quite high. Clean, cleaved surfaces of n- and p-doped GaAs differ in their appearance as well as in their electronic behavior. These severe changes are analyzed and interpreted with the help of tunneling current simulations.

We report a comparative study of the bulk electronic structure of two Al-based complex metallic alloys (CMAs), $\ensuremath{\beta}\ensuremath{-}{\mathrm{Al}}_{3}{\mathrm{Mg}}_{2}$ and ${\mathrm{Al}}_{13}{\mathrm{Fe}}_{4}$ using hard x-ray photoemission spectroscopy (HAXPES) interpreted on the basis of density functional theory (DFT) calculations. An experimental confirmation of the role of the Hume-Rothery mechanism for the stability of the $\ensuremath{\beta}\ensuremath{-}{\mathrm{Al}}_{3}{\mathrm{Mg}}_{2}$ phase is established by identification of a shallow pseudogap near ${E}_{F}$ from HAXPES that is corroborated by DFT. An almost parabolic shape of the density of states (DOS), a large $n$(${E}_{F}$), and plasmon loss features that are similar to Al metal show its nearly free-electron-like nature. In the case of ${\mathrm{Al}}_{13}{\mathrm{Fe}}_{4}$ the total DOS exhibits a shallow pseudogap due to Al $s$ -- Fe $d$ hybridization, which results in the DOS at ${E}_{F}$ [$n$(${E}_{F}$)] being large due to Fe $d$ states. However, the Al $s$ states show a deep pseudogap and this is revealed in HAXPES because of the large photoemission cross section of the $s$ states at high photon energies. The overall shape of the valence band is in excellent agreement with DFT for both the CMAs. The larger width of the Al core-level main peak and the plasmon loss peaks as well as the suppression of the intensities of the latter with respect to $\ensuremath{\beta}\ensuremath{-}{\mathrm{Al}}_{3}{\mathrm{Mg}}_{2}$ further underline the importance of $sp\text{\ensuremath{-}}d$ hybridization in ${\mathrm{Al}}_{13}{\mathrm{Fe}}_{4}$.

The initial stages of hydrogen adsorption on GaAs(110) surfaces at room temperature are investigated by atomically resolved scanning tunneling microscopy and spectroscopy. Two effects are found to occur simultaneously: On the one hand a surface phase separation occurs, creating 1x1 reconstructed fully hydrogen-covered areas while leaving the surface in between completely hydrogen free. In the fully hydrogen-covered areas, hydrogen bonds equally to As- and Ga-derived dangling bonds, unbuckling and passivating the surface. On the other hand, hydrogen-induced point defects are formed with increasing density. The dominating defects consist of As vacancy-hydrogen defect complexes, formed by preferential hydrogen etching of As. Using a defect-molecule model the Ga-H bridge bonds and double-occupied Ga dangling bonds are suggested to be at the origin of the observed surface Fermi level pinning 0.25 to 0.3 eV above the valence band edge, identical within error margins for p- and n-doped GaAs(110).

Y. Wang,1,2 M. Schnedler ,1,* Q. Lan,1,3 F. Zheng,3 L. Freter ,1,2 Y. Lu,3 U. Breuer ,4 H. Eisele,5 J.-F. Carlin,6 R. Butté ,6 N. Grandjean,6 R. E. Dunin-Borkowski ,1,3 and Ph. Ebert 1,† 1Peter Grünberg Institut, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany 2Lehrstuhl für Experimentalphysik IV E, RWTH Aachen University, 52056 Aachen, Germany 3Ernst Ruska Centrum, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany 4Zentralinstitut für Engineering, Elektronik und Analytik (ZEA-3), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany 5Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany 6Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Iuliacumite: a novel two-dimensional chemical short range order in a wurtzite single monolayer InAs 1-x Sb x shell on InAs nanowires M. Schnedler, T. Xu, Isabelle Lefebvre, J.-P Nys, S Plissard, P. Caroff, Maxime Berthe, H Eisele, R Dunin-Borkowski, Ph Ebert, et al.

Intrinsic and extrinsic pinning and passivation of m-plane cleavage facets of GaN n-p-n junctions were investigated by cross-sectional scanning tunneling microscopy and spectroscopy. On freshly cleaved and clean p-type GaN(101¯0) surfaces, the Fermi level is found to be extrinsically pinned by defect states, whereas n-type surfaces are intrinsically pinned by the empty surface state. For both types of doping, air exposure reduces the density of pinning states and shifts the pinning levels toward the band edges. These effects are assigned to water adsorption and dissociation, passivating intrinsic and extrinsic gap states. The revealed delicate interplay of intrinsic and extrinsic surface states at GaN(101¯0) surfaces is a critical factor for realizing flatband conditions at sidewall facets of nanowires exhibiting complex doping structures.

A chemical short range order is found in single monolayer InAs1-xSbx shells, which inherit a wurtzite structure from the underlying InAs nanowire, instead of crystallizing in the energetically preferred zincblende structure. The chemical order is characterized by an ordering vector in [0001] and an anti-correlation ordering vector in <11-20> direction and arises from strong Sb-Sb repulsive interactions along the atomic chains in <11-20> direction.

The electron affinity and surface states are of utmost importance for designing the potential landscape within (heterojunction) nanowires and hence for tuning conductivity and carrier lifetimes. Therefore, we determined for stoichiometric nonpolar GaN(10 (1) over bar0) m-plane facets, i.e., the dominating sidewalls of GaN nanowires, the electron affinity to 4.06 +/- 0.07 eV and the energy of the empty Ga-derived surface state in the band gap to 0.99 +/- 0.08 eV belowthe conduction band minimum using scanning tunneling spectroscopy. These values imply that the potential landscape within GaN nanowires is defined by a surface state-induced Fermi-level pinning, creating an upward band bending at the sidewall facets, which provides an electronic passivation.

We observe a composition modulated axial heterostructure in zincblende (ZB) InAs0.90Sb0.10 nanowires initiated by pseudo-periodic twin boundaries using scanning tunneling microscopy. The twin boundaries exhibit four planes with reduced Sb concentration due to a lower Sb incorporation during lateral overgrowth of a 4H wurtzite as compared to a ZB stacking sequence. We anticipate that this leads to compositional band offsets in addition to known structural band offsets present between 4H and ZB polytypes, changing the band alignment from type II to type I.

Resistive switching random access memories (ReRAM) are promising candidates for energy efficient, fast, and non-volatile universal memories that unite the advantages of RAM and hard drives. Unfortunately, the current ReRAM materials are incompatible with optical interconnects and wires. Optical signal transmission is, however, inevitable for next generation memories in order to overcome the capacity-bandwidth trade-off. Thus, we present here a proof-of-concept of a new type of resistive switching realized in III-V semiconductors, which meet all requirements for the implementation of optoelectronic circuits. This resistive switching effect is based on controlling the spatial positions of vacancy-induced deep traps by stimulated migration, opening and closing a conduction channel through a semi-insulating compensated surface layer. The mechanism is widely applicable to opto-electronically usable III-V compound semiconductors.

While nonstoichiometric binary III-V compounds are known to contain group-V antisites, the growth of ternary alloys consisting of two group-V elements might give additional degrees of freedom in the chemical nature of these antisites. Using cross-sectional scanning tunneling microscopy (STM), we investigate low-temperature-grown dilute GaAs1-xPx alloys. High concentrations of negatively charged point defects are found. Combined with transmission electron microscopy and pump-probe transient reflectivity, this study shows that the defects have a behavior similar to the group-V antisites. Further analyses with x-ray diffraction point to the preferential incorporation of arsenic antisites, consistent with ab initio calculations, that yield a formation energy 0.83 eV lower than for phosphorus antisites. Although the negative charge carried by the arsenic antisites in the STM images is shown to be induced by the proximity of the STM tip, the arsenic antisites are not randomly distributed in the alloy, providing insight into the evolution of their charge state during the growth.