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Two-dimensional (2D) allotropes of tellurium (Te), recently coined as tellurene, are currently an emerging topic of materials research due to the theoretically predicted exotic properties of Te in its ultrathin form and at the single atomic layer limit. However, a prerequisite for the production of such new and single elemental 2D materials is the development of simple and robust fabrication methods. In the present work, we report three different 2D superstructures of Te on Au(111) surfaces by following an alternative experimental deposition approach. We have investigated the superstructures using low-temperature scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy (AES), and field emission AES. Three superstructures (13 × 13, 8 × 4, and √11 × √11) of 2D Te are observed in our experiments, and the formation of these superstructures is accompanied by the lifting of the characteristic 23 × √3 surface reconstruction of the Au(111) surface. Scanning tunneling spectroscopy reveals a strong dependence of the local electronic properties on the structural arrangement of the Te atoms on the Au(111) support, and we observe superstructure-dependent electronic resonances around the Fermi level and below the Au(111) conduction band. In addition to the appearance of the new electronic resonances, the emergence of band gaps with a p-type charge character has been evidenced for two out of three Te superstructures (13 × 13 and √11 × √11) on the Au(111) support.

We successfully identified native point defects that occur in Bi 2 Te 3 crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown Bi 2 Te 3 crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects. In particular, scanning tunneling spectroscopy reveals the dependence on not only the local atomic environment but also on the growth kinetics and the resulting sample doping from n-type toward intrinsic crystals with the Fermi level positioned inside the energy gap. Our results establish a bias-dependent STM signature of the Bi 2 Te 3 native defects and shed light on the link between the native defects and the electronic properties of Bi 2 Te 3 , which is relevant for the synthesis of topological insulator materials and the related functional properties.

The free-standing Au 20 cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The "magic" Au 20 has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au 20 clusters are obtained. We demonstrate that individual size-selected Au 20 on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au 20 n agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Scanning tunneling microscopy and spectroscopy experiments under ultrahigh vacuum and low-temperature conditions have been performed on water-intercalated graphene on Pt(111). We find that the confined water layer, with a thickness around 0.35 nm, induces a strong hole doping in graphene, i.e., the Dirac point locates at round 0.64 eV above the Fermi level. This can be explained by the presence of a single "puckered bilayer" of ice-Ih, which has not been experimentally found on bare Pt(111), being confined in between graphene and Pt(111) surface. Moreover, the water intercalation makes graphene highly decoupled from the substrate, allowing us to reveal the intrinsic graphene phonons and double Rydberg series of even and odd symmetry image-potential states. Our work not only demonstrates that the electronic properties of graphene can be tuned by the confined water layer between graphene and the substrate, but also provides a generally applicable method to study the intrinsic properties of graphene as well as of other supported two-dimensional materials.

Magnetic nanoparticles embedded oxide semiconductors are interesting candidates for spintronics in view of combining ferromagnetic (FM) and semiconducting properties. In this work, Co-ZnO and Co-V 2 O 3 nanocomposite thin films are synthesized by Co ion implantation in crystalline thin films. Magnetic orders vary with the implantation fluence in Co-ZnO, where superparamagnetic (SPM) order appears in the low-fluence films (2  ×  10 16 and 4  ×  10 16 ions cm -2 ) and FM order co-exists with the SPM phase in high-fluence films (1  ×  10 17 ions cm -2 ). Exchange bias (EB) appears in the high-fluence films, with an EB field of about 100 Oe at 2 K and a blocking temperature of around 100 K. On the other hand, Co-V 2 O 3 thin films with an implantation fluence of 3.5  ×  10 16 ions cm -2 exhibit a clear antiferromagnetic (AFM) coupling at low temperatures without the EB effect. The different magnetic behavior of the Co-implanted films with different Co content leads us to conclude that the observed EB effect in the Co-ZnO films results from the FM/AFM coupling between sizable Co nanoparticles and their CoO/Co 3 O 4 surroundings in the (Zn,Co)O matrix. On the other hand, the absence of EB effect in Co-V 2 O 3 appears to be due to the small size of the FM Co nanoparticles in spite of an AFM magnetic order. Detailed studies of magnetic orders and EB effect in magnetic nanocomposite semiconductors can pave the way for their application in spintronics.

The key steps of a transfer of two-dimensional (2D) materials are the delamination of the as-grown material from a growth substrate and the lamination of the 2D material on a target substrate. In state-of-the-art transfer experiments, these steps remain very challenging, and transfer variations often result in unreliable 2D material properties. Here, it is demonstrated that interfacial water can insert between graphene and its growth substrate despite the hydrophobic behavior of graphene. It is understood that interfacial water is essential for an electrochemistry-based graphene delamination from a Pt surface. Additionally, the lamination of graphene to a target wafer is hindered by intercalation effects, which can even result in graphene delamination from the target wafer. For circumvention of these issues, a direct, support-free graphene transfer process is demonstrated, which relies on the formation of interfacial water between graphene and its growth surface, while avoiding water intercalation between graphene and the target wafer by using hydrophobic silane layers on the target wafer. The proposed direct graphene transfer also avoids polymer contamination (no temporary support layer) and eliminates the need for etching of the catalyst metal. Therefore, recycling of the growth template becomes feasible. The proposed transfer process might even open the door for the suggested atomic-scale interlocking-toy-brick-based stacking of different 2D materials, which will enable a more reliable fabrication of van der Waals heterostructure-based devices and applications.

We investigated the topological insulator (TI) Bi 2 Te 3 in four different environments (ambient, ultra-high vacuum (UHV), nitrogen gas and organic solvent environment) using scanning probe microscopy (SPM) techniques. Upon prolonged exposure to ambient conditions and organic solvent environments the cleaved surface of the pristine Bi 2 Te 3 is observed to be strongly modified during SPM measurements, while imaging of freshly cleaved Bi 2 Te 3 in UHV and nitrogen gas shows considerably less changes of the Bi 2 Te 3 surface. We conclude that the reduced surface stability upon exposure to ambient conditions is triggered by adsorption of molecular species from ambient, including H 2 O, CO 2 , etc which is verified by Auger electron spectroscopy. Our findings of the drastic impact of exposure to ambient on the Bi 2 Te 3 surface are crucial for further in-depth studies of the intrinsic properties of the TI Bi 2 Te 3 and for potential applications that include room temperature TI based devices operated under ambient conditions.

We report on the adsorption of Te adatoms on Au(1 1 1), which are identified and investigated relying on scanning tunnelling microscopy, Auger electron spectroscopy, and density functional theory. The Te adatoms lift the 23  ×  √3 surface reconstruction of the Au(1 1 1) support and their organization is similar to that of previously reported chalcogen adatoms on Au(1 1 1), which are also known to lift the herringbone reconstruction and can adopt a (√3  ×  √3)R30° structure. The adatoms show strong interaction with the Au(1 1 1) surface, resulting in scattering and confinement of the Au surface state (SS) electrons near the Fermi level. More remarkably, scanning tunnelling spectroscopy reveals the existence of an electronic resonance at high voltages well above the Fermi level. This resonance can be interpreted as a bound state that is split off from the bottom of the Au(1 1 1) bulk conduction band. A similar split-off state may exist for other types of adatoms on metallic surfaces that exhibit a surface band gap.

The combination of lithography and ion implantation is demonstrated to be a suitable method to prepare lateral multilayers. A laterally, compositionally, and magnetically modulated microscale pattern consisting of alternating Co (1.6 µm wide) and Co-CoO (2.4 µm wide) lines has been obtained by oxygen ion implantation into a lithographically masked Au-sandwiched Co thin film. Magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an effective positive giant magnetoresistance (GMR) behavior at room temperature. Conversely, anisotropic magnetoresistance and GMR contributions are distinguished at low temperature (i.e., 10 K) since the O-implanted areas become exchange coupled. This planar GMR is principally ascribed to the spatial modulation of coercivity in a spring-magnet-type configuration, which results in 180° Néel extrinsic domain walls at the Co/Co-CoO interfaces. The versatility, in terms of pattern size, morphology, and composition adjustment, of this method offers a unique route to fabricate planar systems for, among others, spintronic research and applications., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Stacking faults are known as defective structures in crystalline materials that typically lower the structural quality of the material. Here, we show that a particular type of defect, that is, stacking fault tetrahedra (SFTs), exhibits pronounced quantized electronic behaviour, revealing a potential synthetic route to decoupled nanoparticles in metal films. We report on the electronic properties of SFTs that exist in Au(111) films, as evidenced by scanning tunnelling microscopy and confirmed by transmission electron microscopy. We find that the SFTs reveal a remarkable decoupling from their metal surroundings, leading to pronounced energy level quantization effects within the SFTs. The electronic behaviour of the SFTs can be described well by the particle-in-a-box model. Our findings demonstrate that controlled preparation of SFTs may offer an alternative way to achieve well-decoupled nanoparticles of high crystalline quality in metal thin films without the need of thin insulating layers.

Topological insulators (TIs) are renowned for their exotic topological surface states (TSSs) that reside in the top atomic layers, and hence, detailed knowledge of the surface top atomic layers is of utmost importance. Here we present the remarkable morphology changes of Bi2Te3 surfaces, which have been freshly cleaved in air, upon subsequent systematic annealing in ultrahigh vacuum and the resulting effects on the local and area-averaging electronic properties of the surface states, which are investigated by combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and Auger electron spectroscopy (AES) experiments with density functional theory (DFT) calculations. Our findings demonstrate that the annealing induces the formation of a Bi bilayer atop the Bi2Te3 surface. The adlayer results in n-type doping, and the atomic defects act as scattering centers of the TSS electrons. We also investigated the annealing-induced Bi bilayer surface on Bi2Te3 via voltage-dependent quasi-particle-interference (QPI) mapping of the surface local density of states and via comparison with the calculated constant-energy contours and QPI patterns. We observed closed hexagonal patterns in the Fourier transform of real-space QPI maps with secondary outer spikes. DFT calculations attribute these complex QPI patterns to the appearance of a "second" cone due to the surface charge transfer between the Bi bilayer and the Bi2Te3. Annealing in ultrahigh vacuum offers a facile route for tuning of the topological properties and may yield similar results for other topological materials.

We probe the electron-phonon coupling for in situ engineered porphyrin-based magnetic molecular layers supported on weakly reactive surfaces. Using high-resolution scanning tunneling microscopy and spectroscopy at 4.5 K we show that the electronic and magnetic properties of the engineered molecules are the result of interplay between many-body spin-flip excitations and electron-phonon interactions.

Atomic-level substitutional doping can significantly tune the electronic properties of graphene. Using low-temperature scanning tunneling microscopy and spectroscopy, the atomic-scale crystalline structure of graphene grown on polycrystalline Cu, the distribution of nitrogen dopants and their effect on the electronic properties of graphene were investigated. Both the graphene sheet growth and nitrogen doping were performed using microwave plasma-enhanced chemical vapor deposition. The results indicated that the nitrogen dopants preferentially sit at the grain boundaries of the graphene sheets and confirmed that plasma treatment is a potential method to incorporate foreign atoms into the graphene lattice to tailor the graphene's electronic properties.

The interplay between magnetocrystalline anisotropy and exchange bias is investigated in CoO/Co bilayer films, which are grown epitaxially on MgO (0 0 1), by magnetization reversal measurements based on the anisotropic magnetoresistance (AMR) effect. While an asymmetric magnetization reversal survives after training for cooling field (CF) along the hard axis, the magnetization reversal becomes symmetric and is dominated in both branches of the hysteresis loop by domain wall motion before and after training for CF along the easy axis. When performing an in-plane hysteresis loop perpendicular to the CF, the hysteresis loop along the easy axis becomes asymmetric: magnetization rotation dominates in the ascending branch, while there is a larger contribution of domain wall motion in the descending branch. Furthermore, the azimuthal angular dependence of the AMR shows two minima after performing a perpendicular hysteresis loop, instead of only one minimum after training. Relying on the extended Fulcomer and Charap model, these effects can be related to an increased deviation of the average uncompensated antiferromagnetic magnetization from the CF direction. This model provides a consistent interpretation of training and asymmetry of the magnetization reversal for epitaxial films with pronounced magnetocrystalline anisotropy as well as for the previously investigated polycrystalline films.

Small soluble species of amyloid-beta (Aβ) formed during early peptide aggregation stages are responsible for several neurotoxic mechanisms relevant to the pathology of Alzheimer's disease (AD), although their interaction with the neuronal membrane is not completely understood. This study quantifies the changes in the neuronal membrane elasticity induced by treatment with the two most common Aβ isoforms found in AD brains: Aβ40 and Aβ42. Using quantitative atomic force microscopy (AFM), we measured for the first time the static elastic modulus of living primary hippocampal neurons treated with pre-aggregated Aβ40 and Aβ42 soluble species. Our AFM results demonstrate changes in the elasticity of young, mature and aged neurons treated for a short time with the two Aβ species pre-aggregated for 2 hours. Neurons aging under stress conditions, showing aging hallmarks, are the most susceptible to amyloid binding and show the largest decrease in membrane stiffness upon Aβ treatment. Membrane stiffness defines the way in which cells respond to mechanical forces in their environment and has been shown to be important for processes such as gene expression, ion-channel gating and neurotransmitter vesicle transport. Thus, one can expect that changes in neuronal membrane elasticity might directly induce functional changes related to neurodegeneration.

Membranes and their size-selective filtering properties are universal in nature and their behavior is exploited to design artificial membranes suited for, e.g., molecule or nanoparticle filtering and separation. Exploring and understanding penetration and transmission mechanisms of nanoparticles in thin-film systems may provide new opportunities for size selective deposition or embedding of the nanoparticles. Here, we demonstrate an unexpected finding that the sieving of metal nanoparticles through atomically thin nonporous alkali halide films on a metal support is size dependent and that this sieving effect can be tuned via the film thickness. Specifically, relying on scanning tunneling microscopy and spectroscopy techniques, combined with density functional theory calculations, we find that defect-free NaCl films on a Au(111) support act as size-dependent membranes for deposited Au nanoclusters. The observed sieving ability is found to originate from a driving force toward the metal support and from the dynamics of both the nanoparticles and the alkali halide films.

We report on the observation of complex superlattices at the surface of the topological insulator Bi2Te3. Scanning tunneling microscopy reveals the existence of two different periodic structures in addition to the Bi2Te3 atomic lattice, which is found to strongly affect the local electronic structure. These three different periodicities are interpreted to result from a single small in-plane rotation of the topmost quintuple layer only. Density functional theory calculations support the observed increase in the DOS near the Fermi level, and exclude the possibility that strain is at the origin of the observed Moiré pattern. Exploration of Moiré superlattices formed by the quintuple layers of topological insulators holds great potential for further tuning of the properties of topological insulators.

Nanoparticles of different materials are already in use for many applications. In some applications, these nanoparticles need to be deposited on a substrate in a fast and reproducible way. We have developed a new direct liquid injection system for nanoparticle deposition by chemical vapor deposition using a liquid nanoparticle precursor. The system was designed to deposit nanoparticles in a controlled and reproducible way by using two direct liquid injectors to deliver nanoparticles to the system. The nanoparticle solution is first evaporated and then the nanoparticles flow onto a substrate inside the vacuum chamber. To allow injection and evaporation of the liquid, a direct liquid injection and vaporization system are mounted on top of the process chamber. The deposition of the nanoparticles is controlled by parameters such as deposition temperature, partial pressure of the gases, and flow rate of the nanoparticle suspension. The concentration of the deposited nanoparticles can be varied simply by changing the flow rate and deposition time. We demonstrate the capabilities of this system using gold nanoparticles. The selected suspension flow rates were varied between 0.25 and 1 g/min. AFM analysis of the deposited samples showed that the aggregation of gold nanoparticles is well controlled by the flow and deposition parameters.

Co-rich ZnCoO nanoparticles embedded in wurtzite Zn0.7Co0.3O thin films are grown by pulsed laser deposition on a Si substrate. Local superconductivity with an onset Tc at 5.9 K is demonstrated in the hybrid system. The unexpected superconductivity probably results from Co3+ in the Co-rich ZnCoO nanoparticles or from the interface between the Co-rich nanoparticles and the Zn0.7Co0.3O matrix.

We demonstrate the effective confinement of surface electrons in the pores of molecular networks formed by dehydrobenzo[12]annulene (DBA) molecules with butoxy groups (DBA-OC4) on Au(111). Investigation of the network formation starting from single molecules reveals a considerable interaction of the molecules with the substrate, which is at the origin of the observed confinement.

During the last 20 years, using scanning tunneling microscopy (STM) and atomic force microscopy, scientists have successfully achieved vertical and lateral repositioning of individual atoms on and in different types of surfaces. Such atom manipulation allows the bottom-up assembly of novel nanostructures that can otherwise not be fabricated. It is therefore surprising that controlled repositioning of virtual atoms, i.e., atomic vacancies, across atomic lattices has not yet been achieved experimentally. Here we use STM at liquid helium temperature (4.5 K) to create individual Cl vacancies and subsequently to laterally manipulate them across the surface of ultrathin sodium chloride films. This allows monitoring the interactions between two neighboring vacancies with different separations. Our findings are corroborated by density functional theory calculations and STM image simulations. The lateral manipulation of atomic vacancies opens up a new playground for the investigation of fundamental physical properties of vacancy nanostructures of any size and shape and their coupling with the supporting substrate, and of the interaction of various deposits with charged vacancies.

Ultrafine ZnO nanocrystals with a thickness down to 0.25 nm are grown by a metalorganic chemical vapor deposition method. Electronic band structures and native point defects of ZnO nanocrystals are studied by a combination of scanning tunneling microscopy/spectroscopy and first-principles density functional theory calculations. Below a critical thickness of ∼1 nm ZnO adopts a graphitic-like structure and exhibits a wide band gap similar to its wurtzite counterpart. The hexagonal wurtzite structure, with a well-developed band gap evident from scanning tunneling spectroscopy, is established for a thickness starting from ∼1.4 nm. With further increase of the thickness to 2 nm, VO-VZn defect pairs are easily produced in ZnO nanocrystals due to the self-compensation effect in highly doped semiconductors.

Scanning tunneling microscopy (STM) experiments combined with density functional theory (DFT) calculations reveal that deposited Cr atoms replace either Na or Cl ions, forming substituting dopants in ultrathin NaCl/Au(111) films. The Cr dopants exchange electrons with the support thus changing the electronic properties of the film and in particular the work function. The Cr atoms spontaneously aggregate near the edges of the bilayer (2L) NaCl islands, forming a new phase in the insulator with a remarkably dense population of Cr dopants. The spectra of differential conductance yield evidence that, compared to the undoped or Cr-poor 2L NaCl films on Au(111), the Cr-rich region shows different interface states, shifted image-potential states, and a reduced work function. This demonstrates the potential of doping ultrathin films to modify their adsorption properties in a desired manner.

Enhancing the transport contribution of surface states in topological insulators is vital if they are to be incorporated into practical devices. Such efforts have been limited by the defect behaviour of Bi2Te3 (Se3) topological materials, where the subtle bulk carrier from intrinsic defects is dominant over the surface electrons. Compensating such defect carriers is unexpectedly achieved in (Cu0.1Bi0.9)2Te3.06 crystals. Here we report the suppression of the bulk conductance of the material by four orders of magnitude by intense ageing. The weak antilocalization analysis, Shubnikov-de Haas oscillations and scanning tunnelling spectroscopy corroborate the transport of the topological surface states. Scanning tunnelling microscopy reveals that Cu atoms are initially inside the quintuple layers and migrate to the layer gaps to form Cu clusters during the ageing. In combination with first-principles calculations, an atomic tunnelling-clustering picture across a diffusion barrier of 0.57 eV is proposed.

We report on in situ chemical reactions between an organic trimesic acid (TMA) ligand and a Co atom center. By varying the substrate temperature, we are able to explore the Co-TMA interactions and create novel magnetic complexes that preserve the chemical structure of the ligands. Using scanning tunneling microscopy and spectroscopy combined with density functional theory calculations, we elucidate the structure and the properties of the newly synthesized complex at atomic or molecular size level. Hybridization between the atomic orbitals of the Co and the π orbitals of the ligand results in a delocalized spin distribution onto the TMA. The here demonstrated possibility to conveniently magnetize such versatile molecules opens up new potential applications for TMAs in molecular spintronics.

Preformed Co clusters with an average diameter of 2.5 nm are produced in the gas phase and are deposited under controlled ultra-high vacuum conditions onto a thin insulating NaCl film on Au(111). Relying on a combined experimental and theoretical investigation, we demonstrate visualization of the three-dimensional atomic structure of the Co clusters by high-resolution scanning tunneling microscopy (STM) using a Cl functionalized STM tip that can be obtained on the NaCl surface. More generally, use of a functionalized STM tip may allow for systematic atomic structure determination with STM of nanoparticles that are deposited on metal surfaces.

Nowadays molecular nanoporous networks have numerous uses in surface nanopatterning applications and in studies of host-guest interactions. Trimesic acid (TMA), a benzene derivative with three carboxylic groups, is a marvelous building block for forming 2D H-bonded porous networks. Here, we report a low-temperature study of the nanoporous "chicken-wire" superstructure formed by TMA molecules adsorbed on a Au(111) surface. Distinct preferential orientations of the porous networks on Au(111) lead to the formation of peculiar TMA polymorphs that are stabilized only at the boundary between rotational molecular domains. Scanning tunneling microscopy (STM) and spectroscopy are used to investigate the electronic properties of both the molecular building blocks and the pores. Sub-molecular-resolution imaging and spatially resolved electronic spectroscopy reveal a remarkable change in the appearance of the molecules in the STM images at energies in the range of the lowest unoccupied molecular orbital, accompanied by highly extended molecular wave functions into the pores. The electronic structure of the pores reflects a weak confinement of surface electrons by the TMA network. Our experimental observations are corroborated by density-functional-theory-based calculations of the nanoporous structure adsorbed on Au(111).

We introduce the use of ferromagnetic resonance (FMR) to actuate mechanical resonances in as grown arrays of carbon nanotubes (CNTs) loaded with Ni particles (Ni-CNTs). This contactless method is closely related to the magnetic resonance force microscopy technique and provides spatial selectivity of actuation along the array. The Ni-CNT arrays are grown by chemical vapor deposition and are composed of homogeneous CNTs with uniform length (~600 nm) and almost equal diameter (~20 nm), which are loaded with Ni catalyst particles at their tips due to the tip growth mode. The vibrations of the Ni-CNTs are actuated by relying on the driving force that appears due to the FMR excited at about 2 GHz in the Ni particles (diameter ~100 nm). The Ni-CNT oscillations (frequency ~40 MHz) are detected mechanically by atomic force microscopy. The acquired oscillation images of the Ni-CNT uniform array reveal clear maxima in the spatial distribution of the oscillation amplitudes. We attribute these maxima to the "sensitive slices", i.e., the spatial regions of the Ni-CNT array where the FMR condition is met. Similar to magnetic resonance imaging, the sensitive slice is determined by the magnetic field gradient and moves along the Ni-CNT array as the applied magnetic field is ramped. Our excitation method does not require the presence of any additional microfabricated electrodes or coils near the CNTs and is particularly advantageous in cases where the traditional electrical actuation methods are not effective or cannot be implemented. The remote actuation can be effectively implemented also for arrays of other magnetic nanomechanical resonators.

Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions.

We investigated the growth and the electronic properties of crystalline NaCl layers on Au(111) surfaces by means of cryogenic scanning tunneling microscopy and spectroscopy under ultra-high vacuum conditions. Deposition of NaCl on Au(111) at room temperature yields bilayer NaCl islands, which can be transformed into trilayer NaCl islands by post-annealing. Upon NaCl adsorption, the Au(111) Shockley surface state becomes an interface state (IS) at the NaCl/Au(111) interface. Using Fourier-transform images of maps of the local density of states, the energy versus wave vector dispersions of the IS and the Au(111) bulk states are determined. The dispersion of both states is found to depend strongly on the thickness of the adsorbed NaCl layer.

A promising method for the production of few-layer graphene (FLG) is microwave plasma-enhanced chemical vapour deposition (MW PECVD). However, the growth mechanism of PECVD-synthesized FLG is not completely understood. The aim of this work was to investigate the initial stages of the growth process of FLG deposited by MW PECVD on several substrates (quartz, silicon, platinum). The deposited thin films were characterized by angle-resolved x-ray photoelectron spectroscopy (ARXPS), electron backscattered diffraction (EBSD), scanning electron microscopy (SEM) and x-ray diffraction (XRD). It was found that the initial stages of the deposition were different for the three chosen substrate materials. However, the fully grown FLG layers were similar for all substrates.

The supramolecular organization of a new polychlorotriphenyl (PTM) radical bearing three long alkyl chains has been studied by scanning tunneling microscopy (STM) at the liquid-solid interface. This radical hierarchically self-assembles on graphite forming head-to-head dimers that organize in rows following an interesting spin-containing two-leg molecular ladder topology, in which the alkyl chains determine the space between the radical rows and act as diamagnetic barriers. In addition, these double-rows also self-assemble three-dimensionally, leading to a multilayer organization which is still influenced by the HOPG substrate symmetry. The observed nanostructures are sustained by different intermolecular interactions such as Cl...Cl, Cl...Ph, pi-pi, van der Waals, and CH...pi interactions. Theoretical calculations were used to model the observed assemblies, and the results were in complete agreement with the experimental data. Remarkably, atomic force microscopy (AFM) studies confirmed that this tendency to form double rows composed by the PTM magnetic heads surrounded by the alkyl chains is maintained after the complete evaporation of the solvent. The electrochemical and magnetic properties of these PTM nanostructures were also demonstrated.

The deposition of n-octylphosphonic acid on aluminum oxide was studied. The substrate was pretreated in order to achieve a root-mean-square roughness of <1 nm, a hydroxyl fraction of 30%, and a thickness of approximately 170 nm. It was proven using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) that, rather than a monolayer, an organic multilayer was formed. The growth mechanism was identified as a Stranski-Krastanov one. It was also shown that the use of AFM, probing the surface topography, is essential for a reliable quantification and interpretation of data obtained with XPS.

The training effect and asymmetry in exchange-coupled polycrystalline CoO/Co bilayers with in-plane magnetization has been investigated. This system is selected for its large training effect and initial asymmetry of the magnetic hysteresis after field cooling, which is removed after training. Applying an in-plane magnetic field perpendicular to the cooling field largely restores the untrained state with its pronounced asymmetry. The possibility to reinduce the asymmetry strongly depends on the magnitude of the perpendicular field, providing the key to identify the physical origin of training and removal of the asymmetry. These effects result from misalignment between the ferromagnetic magnetization and the uncompensated magnetization of the granular antiferromagnet.

Phosphorylation of Tau protein and binding to microtubules is complex in neurons and was therefore studied in the less complicated model of humanized yeast. Human Tau was readily phosphorylated at pathological epitopes, but in opposite directions regulated by kinases Mds1 and Pho85, orthologues of glycogen synthase kinase-3beta and cdk5, respectively (1). We isolated recombinant Tau-4R and mutant Tau-P301L from wild type, Delta mds1 and Delta pho85 yeast strains and measured binding to Taxol-stabilized mammalian microtubules in relation to their phosphorylation patterns. Tau-4R isolated from yeast lacking mds1 was less phosphorylated and bound more to microtubules than Tau-4R isolated from wild type yeast. Paradoxically, phosphorylation of Tau-4R isolated from kinase Pho85-deficient yeast was dramatically increased resulting in very poor binding to microtubules. Dephosphorylation promoted binding to microtubules to uniform high levels, excluding other modifications. Isolated hyperphosphorylated, conformationally altered Tau-4R completely failed to bind microtubules. In parallel to Tau-4R, we expressed, isolated, and analyzed mutant Tau-P301L. Total dephosphorylated Tau-4R and Tau-P301L bound to microtubules very similarly. Surprisingly, Tau-P301L isolated from all yeast strains bound to microtubules more extensively than Tau-4R. Atomic force microscopy demonstrated, however, that the high apparent binding of Tau-P301L was due to aggregation on the microtubules, causing their deformation and bundling. Our data explain the pathological presence of granular Tau aggregates in neuronal processes in tauopathies.

We performed a detailed study of the training effect in exchange biased CoO/Co bilayers. High-resolution measurements of the anisotropic magnetoresistance (AMR) display an asymmetry in the first magnetization reversal process and training in the subsequent reversal processes. Surprisingly, the AMR measurements as well as magnetization measurements reveal that it is possible to partially reinduce the untrained state by performing a hysteresis measurement with an in-plane external field perpendicular to the cooling field. Indeed, the next hysteresis loop obtained in a field parallel to the cooling field resembles the initial asymmetric hysteresis loop, but with a reduced amount of spin rotation occurring at the first coercive field. This implies that the antiferromagnetic domains, which are created during the first reversal after cooling, can be partially erased.

Protein tau-3R/4R isoform ratio and phosphorylation regulates binding to microtubules and, when disturbed by aging or mutations, results in diverse tauopathies and in neurodegeneration. The underlying mechanisms were studied here in three transgenic mouse strains with identical genetic background, all expressing the tau-4R/2N isoform driven specifically in neurons by the thy1 gene promoter. Two strains, expressing human tau-4R/2N or mutant tau-4R/2N-P301L at similar, moderate levels, developed very different phenotypes. Tau-4R/2N mice became motor-impaired already around age 6-8 weeks, accompanied by axonopathy (dilatations, spheroids), but no tau aggregates, and surviving normally. In contrast, tau-P301L mice developed neurofibrillary tangles from age 6 months, without axonal dilatations and, despite only minor motor problems, all succumbing before the age of 13 months. The third strain, obtained by tau knock-out/knock-in (tau-KOKI), expressed normal levels of wild-type human tau-4R/2N replacing all mouse tau isoforms. Tau-KOKI mice survived normally with minor motor problems late in life and without any obvious pathology. Biochemically, a fraction of neuronal tau in aging tau-P301L mice was hyperphosphorylated concomitant with conformational changes and aggregation, but overall, tau-4R/2N was actually more phosphorylated than tau-P301L. Significantly, tau with changed conformation and with hyperphosphorylation colocalized in the same neurons in aging tau-P301L mice. Taken together, we conclude that excessive binding of tau-4R/2N as opposed to reduced binding of tau-P301L to microtubules is responsible for the development of axonopathy and tauopathy, respectively, in tau-4R/2N and tau-P301L mice and that the conformational change of tau-P301L is a major determinant in triggering the tauopathy.

We measured the intrinsic domain wall resistance (DWR) of 180 degrees Ne el walls in a polycrystalline Co thin film deposited on top of a patterned antiferromagnetic CoO template. After field cooling through the CoO blocking temperature, exchange bias induces a spatially modulated coercivity of the Co film, resulting in a periodic domain pattern with 180 degrees Ne el walls. The intrinsic DWR is determined unambiguously by using rotating magnetic fields that result in a reversible creation and annihilation of the Ne el walls. In contrast with earlier reports, the DWR is positive and in agreement with models based on the giant magnetoresistance mechanism. A reliable, quantitative determination of the DWR requires careful numerical evaluation of the anisotropic magnetoresistance effect.