J.A. Schaefer

Technische Universität Ilmenau | TUI · Institute of Physics

The scientific interest in two-dimensional topological insulators (2D TIs) is currently shifting from a more fundamental perspective to the exploration and design of novel functionalities. Key concepts for the use of 2D TIs in spintronics are based on the topological protection and spin-momentum locking of their helical edge states. In this study w...

We study the temperature dependence of the metallic-like bands of Si(553)-Au by angular-resolved photoemission spectroscopy (ARPES). First, we define a protocol for dealing with the short-term stability due to surface contamination and the effect of photo-voltage. After that, we extract the changes in the band-filling and Fermi-velocity. We conclud...

We study the effects of Rashba splitting on two-leg ladders with weakly screened Coulomb interactions. Past research has shown that in this class of systems the two backscattering channels with the largest amplitude favor ordering of canonically conjugated collective fields which effectively renders the system gapless. Here we show that the band-de...

The scientific interest in two-dimensional topological insulators (2D TIs) is currently shifting from a more fundamental perspective to the exploration and design of novel functionalities. Key concepts for the use of 2D TIs in spintronics are based on the topological protection and spin-momentum locking of their helical edge states. In this study w...

Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele’s original suggestion, one approach is to synthesize monolayers of heavy atoms with hone...

The impact of compositional disorder on manybody couplings is a subject of prime focus in many materials systems. In this paper, we report photoemission measurements of Mo 1-x Re x (110)-(1x1)H alloy surfaces to probe the relationship between the surface Fermi contours and recently observed giant Kohn anomalies in the surface phonon dispersion rela...

Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele's original suggestion, one approach is to synthesize monolayers of heavy atoms with hone...

Quantum spin Hall insulators are two-dimensional materials that host conducting helical electron states strictly confined to the one-dimensional boundaries. These edge channels are protected by time-reversal symmetry against single-particle backscattering, opening new avenues for spin-based electronics and computation. However, the effect of the in...

We report on the electronic structure of α-Sn films in the very low thickness regime grown on InSb(111)A. High-resolution low photon energy angle-resolved photoemission spectroscopy allows for the direct observation of the linearly dispersing two-dimensional (2D) topological surface state (TSS) that exists between the second valence band and the co...

We report on the electronic structure of $\alpha$-Sn films in the very low thickness regime grown on InSb(111)A. High-resolution low photon energies angle-resolved photoemission (ARPES) allows for the direct observation of the linearly dispersing 2D topological surface states (TSSs) that exist between the second valence band and the conduction band...

The diamond and zinc-blende semiconductors are well-known and have been widely studied for decades. Yet, their electronic structure still surprises with unexpected topological properties of the valence bands. In this joint theoretical and experimental investigation, we demonstrate for the benchmark compounds InSb and GaAs that the electronic struct...

In search for a new generation of spintronics hardware, material candidates for room temperature quantum spin Hall effect (QSHE) have become a contemporary focus of investigation. Inspired by the original proposal for QSHE in graphene, several heterostructures have been synthesized, aiming at a hexagonal monolayer of heavier group IV elements promo...

Topological quantum matter is characterized by non-trivial global invariants of the bulk which induce gapless electronic states at its boundaries. A case in point are two-dimensional topological insulators (2D-TI) which host one-dimensional (1D) conducting helical edge states protected by time-reversal symmetry (TRS) against single-particle backsca...

Au adsorption on high-index Si surfaces is known to form quasi-one-dimensional surface reconstructions with interesting physical properties such as Rashba-split bands and ordered arrays of local magnetic moments. Here we report on a novel family of Au-induced chain systems, hosted on Ge(hhk) substrates. Our study includes Ge(553), Ge(557), and Ge(3...

The quantum spin Hall effect (QSHE) has formed the seed for contemporary research on topological quantum states of matter. Since its discovery in HgTe/CdTe quantum wells and InAs/GaSb heterostructures, all such systems have so far been suffering from extremely low operating temperatures, rendering any technological application out of reach. We form...

The quantum spin Hall effect (QSHE) has formed the seed for contemporary research on topological quantum states of matter. Since its discovery in HgTe/CdTe quantum wells and AlGaAs/GaAs heterostructures, all such systems have so far been suffering from extremely low operating temperatures, rendering any technological application out of reach. We fo...

In search for a new generation of spintronics hardware, material candidates for room temperature quantum spin Hall effect (QSHE) have become a contemporary focus of investigation. Inspired by the original proposal for QSHE in graphene, several heterostructures have been synthesized, aiming at a hexagonal monolayer of heavier group IV elements in or...

We propose a quantitative and reversible method for tuning the charge localization of Au-stabilized stepped Si surfaces by site-specific hydrogenation. This is demonstrated for Si(553)-Au as a model system by combining density functional theory simulations and reflectance anisotropy spectroscopy experiments. We find that controlled H passivation is...

Due to their large bulk band gap, bismuthene, antimonene, and arsenene on a SiC substrate offer intriguing new opportunities for room-temperature quantum spin Hall (QSH) applications. Although edge states have been observed in the local density of states (LDOS) of bismuthene/SiC, there has been no experimental evidence until now that they are spin-...

The triangular lattice of localised electrons is the canonical example for a geometrically frustrated spin arrangement. In conjunction with strong local Coulomb interactions, it leads to a competition of antiferromagnetic order and spin liquid behaviour. However, when longer-ranged Coulomb interactions become relevant, charge order might emerge and...

We report on the electronic structure of the elemental topological semimetal $\alpha$-Sn on InSb(001). High-resolution angle-resolved photoemission data allow to observe the topological surface state (TSS) that is degenerate with the bulk band structure and show that the former is unaffected by different surface reconstructions. An unintentional $p...

Interacting electrons confined to only one spatial dimension display a wide range of unusual many-body quantum phenomena, ranging from Peierls instabilities to the breakdown of the canonical Fermi liquid paradigm to even unusual spin phenomena. The underlying physics is not only of tremendous fundamental interest, but may also have bearing on devic...

We use scanning tunneling microscopy to investigate the interactions between atomic chains, of two different types, formed by the adsorption of submonolayer Au onto a stepped Si surface. The first chain consists of a double row of Au atoms. The second is a single row of Si dangling bonds at the edges of the steps. The two chains are interspersed an...

Adsorption of Au on Si(553) results in the self-assembly of highly ordered step arrays of one-dimensional (1D) Au atomic wires along the step direction. Charge transfer from the terrace to the step edge causes every third Si atom at the step edge to exhibit a partially filled dangling bond hosting a single fully spin-polarized electron which forms...

Making a large-gap topological insulator Although of interest to basic research, topological insulators (TIs) have not yet lived up to their technological potential. This is partly because their protected surface-edge state usually lives within a narrow energy gap, with its exotic transport properties overwhelmed by the ordinary bulk material. Reis...

Preparation of SiC(0001) substrates is of high relevance to graphene growth. Yet, if only a smooth surface could be achieved, heteroepitaxy of many other two-dimensional materials comes into reach. Here we report a novel approach to hydrogen etching of SiC, based on stepwise ultrapure H exposure with slow substrate cooling rates. For the first time...

High-index surfaces of silicon with adsorbed gold can reconstruct to form highly ordered linear step arrays. These steps take the form of a narrow strip of graphitic silicon. In some cases-specifically, for Si(553)-Au and Si(557)-Au-a large fraction of the silicon atoms at the exposed edge of this strip are known to be spin-polarized and charge-ord...

Using inelastic electron scattering in combination with dielectric theory simulations on differently prepared graphene layers on silicon carbide, we demonstrate that the coupling between the 2D plasmon of graphene and the surface optical phonon of the substrate cannot be quenched by modification of the interface via intercalation. The intercalation...

Two-dimensional (2D) atom lattices provide model setups for Coulomb correlations inducing competing ground states, partly with topological character. Hexagonal SiC(0001) is an intriguing wide-gap substrate, spectroscopically separated from the overlayer and hence reduced screening. We report the first study of an artificial high-Z atom lattice on S...

We have used photoemission spectroscopy in order to investigate the electronic states and chemical bonding related to Au induced atomic chains on the Ge(001) surface. Angle-resolved photoemission reveals two types of dispersions around the Fermi level whose intensities strongly depend on the incident photon energy. Around h. = 100 eV, the band stru...

DOI:https://doi.org/10.1103/PhysRevLett.112.239903

We report on the epitaxial fabrication and electronic properties of a topological phase in strained α-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density functional and GW slab-layer calculations. Angle-resolved photoemission including spin detection p...

Stabilization of the Si(553) surface by Au adsorption results in two different atomically defined chain types, one of Au atoms and one of Si. At low temperature these chains develop two- and threefold periodicity, respectively, previously attributed to Peierls instabilities. Here we report evidence from scanning tunneling microscopy that rules out...

We report a detailed experimental and theoretical study of the electronic structure of Mo1−xRex random alloys. We have measured electronic band dispersions for clean and hydrogen-covered Mo1−xRex(110) with x = 0–0.25 using angle-resolved photoemission spectroscopy. Our results suggest that the bulk and most surface electronic bands shift relative t...

Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about 'melted' phases, known a...

The one-electron spectral function is the key quantity to extract detailed information on the complex spin pattern in a frustrated magnetic system. This is demonstrated here by a detailed comparison of theory, which combines a priori density-functional (LDA) with cluster many-body (LDA + DCA) calculations, with high-precision angle-resolved photoel...

Atomic nanowires on the Au/Ge(001) surface are investigated for their structural and electronic properties using scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). STM reveals two distinct symmetries: a c(8 × 2) describing the basic repeating distances, while the fine structure on top of the wires causes an a...

With modern microelectronics moving towards smaller and smaller length scales on the (sub-) nm scale, quantum effects (apart from band structure and band gaps) have begun to play an increasingly important role. This especially concerns dimensional confinement to 2D (high electron mobility transistors and integer/fractional quantum Hall effect physi...

This article reports on a newly developed reciprocating microtribometer for evaluating the tribological performance of materials and coatings in vacuum and controllable atmospheres on the micro- and milli-Newton scale. The microtribometer consists of a piezo driving table, an elastic force sensor and two laser interferometers to precisely detect no...

The p(2×1)/c(4×2) and the c(4×2) reconstruction of the Ge(001) surface have been studied by polarized Raman spectroscopy at 300 and 40 K, respectively. Raman spectra show several well-defined surface phonon modes related to the atomic structure of the Ge surface. Four modes are detected in the range between 5.70 and 28.15 meV. Their eigenenergies a...

The one-dimensional reconstruction of Au/Ge(001) was investigated by means of autocorrelation functions from surface x-ray diffraction (SXRD) and scanning tunneling microscopy (STM). Interatomic distances found in the SXRD-Patterson map are substantiated by results from STM. The Au coverage, recently determined to be 3/4 of a monolayer of gold, tog...

Strontium segregation as function of electrochemical environment is measured for La0.6Sr0.4Co0.2Fe0.8O3 − δ using X-ray absorption spectroscopy. Gaseous Cr is used as a tracer to distinguish the bulk Sr from the segregated SrO at the surface via formation of SrCrO4. From the SrCrO4 to Cr2O3 ratio, the impact of cathodic and anodic overpotentials on...

The Sn-induced $\sqrt3 \times \sqrt3$ surface reconstruction on Si(111) has been investigated by material-specific many-body calculations and by angle-resolved photoelectron spectroscopy (ARPES). This triangular surface system in the low adatom coverage regime is governed by rather localized dangling bond orbitals with enhanced electronic correlati...

The one-dimensional (1D) model system Au/Ge(001), consisting of linear chains of single atoms on a surface, is scrutinized for lattice instabilities predicted in the Peierls paradigm. By scanning tunneling microscopy and electron diffraction we reveal a second-order phase transition at 585 K. It leads to charge ordering with transversal and vertica...

This article reports on the tribological performance of a WC/C multilayer coating with a periodicity WC/C=15/5nm deposited on bearing steel substrates. These substrates were initially polished to achieve different RMS roughness values ranging from 15 to 900nm. Tribological tests were performed using a precision reciprocating microtribometer under a...

An advanced two-step cleaning process of the Ge(001) surface for nanoscience requirements is presented. First, wet-chemical etching with a variant of the Piranha solution (H(2)SO(4), H(2)O(2), H(2)O) is used to remove contaminants as well as the native oxide layer. Second, passivation of the surface is achieved by a rapid thermal oxidation step, le...

Atom assemblies on surfaces represent the ultimate lower size limit for electronic circuits, and their conduction properties are governed by quantum phenomena. A fundamental prediction for a line of atoms confining the electrons to one dimension is the Tomonaga-Luttinger liquid. Yet, astonishingly, this has not been observed in surface systems so f...

Nanocrystalline diamond films (NCD) are strong candidates for applications in a wide variety of fields. An important concern in all these applications is to understand the properties of variously prepared NCD surfaces. This contribution is focussed on the surface science study of hydrogen and oxygen containing NCD films using X-ray photoelectron sp...

The interaction of ethene with silicon (111) surfaces at different process temperatures (580°C, 680°C, 780°C) was monitored in situ by spectroscopic ellipsometry. It is shown that spectroscopic ellipsometry is a reliable method to monitor the carbonization process of silicon surfaces. Different SiC formation stages (incubation time, (√3×√3)R30° rec...

Nanotribological improvements concerning adhesion and friction can be obtained by chemical modification of the sample surface. Due to adsorption a thin water film is always present. However, the thickness of the fim can be reduced or temporarily suppressed by hydrofluoric (HF) acid etching, leading to hydrophobic surface conditions for the case of...

Thin tungsten carbide films of different compositions were prepared by DC magnetron sputtering of tungsten and carbon and subsequent annealing in different environments. The onset of carbide formation was around 800°C. Annealing in a pure hydrogen ambient generally results in carbon depletion in the layers with the formation of a dominant W2C phase...

This article reports on the use of high-resolution electron energy loss spectroscopy (HREELS) for the investigation of as-grown (hydrogen-terminated) and oxidized nanocrystalline diamond films (NCD) using chemical, physical, and electrochemical approaches. The results indicate that the nature and number of oxygen-related chemical groups generated o...

Interactions of gaseous Cr contaminants with the perovskite material LSCF (La0.6Sr0.4Co0.2Fe0.8O3) commonly used as cathode for Solid Oxide Fuel Cells (SOFC) were investigated by means of X-ray absorption Spectroscopy (XAS) and Raman Spectroscopy. The setup consisted of a model cell with a GDC (Gd0.1Ce0.9O2) electrolyte pellet with a LSCF cathode o...

We report on strong coupling of the charge carrier plasmon $\omega_{PL}$ in graphene with the surface optical phonon $\omega_{SO}$ of the underlying SiC(0001) substrate with low electron concentration ($n=1.2\times 10^{15}$ $cm^{-3}$) in the long wavelength limit ($q_\parallel \rightarrow 0$). Energy dependent energy-loss spectra give for the first...

From topographic inspection of the (√3×√3)-Pt/Si(111) surface by scanning tunneling microscopy, key structural elements are identified. A characteristic triangular building block in each (√3×√3) unit cell, composed of charge maxima at approximately the bulk Pt-Pt distance bond, is observed. The orientation of the trimers is incompatible with the Si...

The properties of Ga-face and N-face GaN surfaces were studied by X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS), atomic force microscopy (AFM), reflection high energy electron diffraction (RHEED) as well as high resolution electron energy loss spectroscopy (HREELS). The Ga-face GaN was grown on 6H-SiC(0001) and the N-face GaN directly...

GaN(0001)-2×2 surfaces were investigated by angleresolved ultraviolet photoelectron spectroscopy (ARUPS) as well as X-ray photoelectron spectroscopy (XPS). Contamination-and metal-free GaN thin films with a 2×2 reconstruction and a rms roughness below 1 nm were grown on 6H-SiC(0001) by plasma assisted molecular beam epitaxy (PAMBE). The valence ban...

A quasianalytical modeling approach for graphene metal-oxide-semiconductor field-effect transistors (MOSFETs) with gapless large-area graphene channels is presented. The model allows the calculation of the I-V characteristics, the small-signal behavior, and the cutoff frequency of graphene MOSFETs. It applies a correct formulation of the density of...

The valence band offset (VBO) at a InN/In0.3Ga0.7N(0001) as well as HfO2/InN(0001) heterojunction is investigated by X-ray photoelectron spectroscopy using monochromated AlKα radiation. The InN and In0.3Ga0.7N films were grown using plasma-assisted molecular beam epitaxy, whereas HfO2 layers were deposited by plasma-assisted electron beam evaporati...

Angle-resolved photoemission with polarized synchrotron radiation is measured from a ferromagnetic single-crystal Ni(110) surface. Polarization dependence and dispersion with k∥ of spectral structures along the high-symmetry lines Γ-K-X of the bulk Brillouin zone is discussed. An ab initio calculation within the one-step theory of photoemission rev...

Investigations of the impact of Cr2O3 overlayers on the oxygen self diffusion in two SOFC materials were conducted to gain insight into the Cr poisoning mechanism at the cathode side of solid oxide fuel cells (SOFCs) with stainless steel interconnects. High density Y0.15Zr0.85O2 (YSZ) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) sintered pellets were covered...

We investigated the surface chemistry and valence band (VB) structure of as-grown thin InN(0001)-2 × 2 films as well as their change upon the exposure to oxygen and water. The InN films were grown by plasma-assisted molecular beam epitaxy (PAMBE) and in situ characterized by reflection high electron energy diffraction (RHEED) and photoelectron spec...

Atomic nanowires formed by Au on Ge(001) are scrutinized for the band topology of the conduction electron system by k-resolved photoemission. Two metallic electron pockets are observed. Their Fermi surface sheets form straight lines without undulations perpendicular to the chains within experimental uncertainty. The electrons hence emerge as strict...

In the recently discovered self-organized Au atomic nanowires on Ge(001) a power-law behavior in the density of states (DOS) has been discovered by low-temperature scanning tunneling spectroscopy (STS). We present temperature dependent STS data in a temperature range from T = 5K to T = 50K that show energy and temperature dependence as expected for...

Many insects, such as flies, ants, and bugs, and some animals, such as tree frogs, have proven able to run up and down on smooth vertical surfaces using their specialized pads via a wet adhesive mechanism. Although many meniscus adhesion models were proposed to reveal the origin of the interfacial force, few studies have investigated the dynamic co...

The geometry, stability, and electronic properties of Au-induced quantum wire structures on Ge(001) surfaces with c(8×2) and p(4×2) translational symmetry are investigated using total-energy and electronic-structure calculations based on density-functional theory in local and semilocal approximations for exchange and correlation. About 150 candidat...

Using high resolution electron energy loss spectroscopy (HREELS) in conjunction with low energy electron diffraction (LEED) and X-ray induced photoelectron spectroscopy (XPS), we have studied surface reconstructions from Si-rich to C-rich surfaces up to graphene formation. It is shown that the coupling between the longitudinal optical phonons and t...

We studied InN (0001) grown by plasma assisted molecular beam epitaxy (PAMBE) with high-resolution electron energy-loss spectroscopy (HREELS) after vacuum transfer thus avoiding any further surface preparation. We were able to detect for the first time besides the Fuchs-Kliewer surface phonon ω0 two plasmarons ω– and ω+, which originate from the co...

We performed an in-situ analysis of the interaction of water with clean 2×2 reconstructed GaN(0001) surfaces grown by plasma assisted molecular beam epitaxy. The as-grown surfaces were exposed to molecular water by backfilling. Photoemission spectra reveal an extremely high reactivity and dissociative adsorption with an oxygen sticking coefficient...

Ultrathin layers of N-face GaN(000) on c-plane sapphire have been grown via plasma assisted molecular beam epitaxy (PAMBE) and investigated in-situ via reflection of high energy electron diffraction (RHEED), Xray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Our studies of the electronic interface between substrate and adsorba...

Due to increasing costs of synthetic polymers or plastics, which are directly correlated with the oil and gas prices, natural polymers with similar properties are becoming more and more interesting. One such product is a commercially available wood-based compound Arboform® composed largely of lignin and cellulose. From these two materials, lignin i...

It has been shown that few-layer graphene films can be grown by atmospheric chemical vapor deposition using deposited Ni thin films on SiO(2)/Si substrates. In this paper we report the correlation between the thickness variations of the graphene film with the grain size of the Ni film. Further investigations were carried out to increase the grain s...

Atomic structures of quasi-one-dimensional (1D) character can be grown on semiconductor substrates by metal adsorption. Significant progress concerning study of their 1D character has been achieved recently by condensing noble metal atoms on the Ge(001) surface. In particular, Pt and Au yield high quality reconstructions with low defect densities....

Unique electronic properties of self-organized Au atom chains on Ge(001) in novel c(8 x 2) long-range order are revealed by scanning tunneling microscopy. Along the nanowires an exceptionally narrow conduction path exists which is virtually decoupled from the substrate. It is laterally confined to the ultimate limit of single atom dimension, and is...

A Reply to the Comment by Arie van Houselt et al.

Nanocrystalline diamond (NCD) films are of great importance for many applications. They can be implemented as transparent protective coatings or for the use in electronic devices, sensor systems, and bioelectronic systems. In many applications the surface properties dictate the eventual performance of the device and, therefore, need to be thoroughl...

The transfer film on steel spheres formed in reciprocating sliding against nanocomposite coatings based on nanocrystalline WC1-x in amorphous carbon matrix is characterized and correlated with the tribological properties measured by a precision microtribometer. With the presence of transfer film, a coefficient of friction approximately 0.13 and a d...

Indium-tin-oxynitride (ITON) films have been fabricated by rf sputtering from an indium-tin-oxide target in nitrogen plasma. The influence of postdeposition annealing up to 800 degrees C is analyzed by electrical, optical, and surface characterization of the films in comparison to indium-tin-oxide (ITO) films fabricated in argon plasma. High-temper...

We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition(CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can significantly improve th...

High indium content ([In>]25%) AlInN/GaN multi quantum well structures grown by metal organic vapor phase epitaxy were analyzed by X-ray diffraction, X-ray reflection, and photoluminescence measurements. The samples, which exhibit an excellent crystalline quality and smooth interfaces, are found to show broad luminescence below the GaN-bandgap whic...

The surface properties of thin InN(0001) films grown by plasma assisted molecular beam epitaxy (PAMBE) were characterised. Two stable surface reconstructions (a (2 × 2) and a (√3 × √3) R30°) are identified which develop depending on the used preparation conditions. The structural, compositional and electronic surface properties were analysed in-sit...

X-ray and UV-induced photoelectron spectroscopy (XPS and UPS) and scanning electron microscopy (SEM) have been performed to characterise the pyrolysis of cellulose and lignin and their interaction with methanol. Clean highly oriented pyrolitic graphite (HOPG) was also analysed as a reference material. Asymmetric C1s core level fits and valence band...

The quasiparticle dynamics of electrons in a magnetically ordered state is investigated by high-resolution angle-resolved photoemission of Ni(110) at 10 K. The self-energy is extracted for high binding energies reaching up to 500 meV, using a Gutzwiller calculation as a reference frame for correlated quasiparticles. Significant deviations exist in...

Molecular beam epitaxy was used to deposit single crystal thin film Fe _1-x Ga _x samples on ZnSe buffer layers grown on (001) and (110) single crystal GaAs substrates. The crystal quality of the GaAs surface and each deposited layer was monitored in situ by reflection high energy electron diffraction. The magnetic properties of...

In this paper, in order to weaken the corrosion property of ionic liquids and use it as vacuum lubricant, we coated the ionic liquids with some other liquid and tested their friction and corrosion properties using microtribometer and scanning electron microscope (SEM). The result is gratifying. Compared to the pure ionic liquid, most of the coated...

Gallium nitride thin films were grown on silicon carbide (0001) by plasma-assisted molecular beam epitaxy (PAMBE). The samples were cooled down in nitrogen plasma and characterized in situ by reflection high energy electron diffraction (RHEED), photoelectron spectroscopy (XPS/UPS), and atomic force microscopy (AFM) revealing stoichiometric and smoo...

A setup based on a laser interferometer has been developed to measure the shear response of thin polytetrafluoroethylenethe-like fluorocarbon (FC) films. By using a smooth Si sphere in a ball-on-flat configuration, the shear force was determined for FC films on Si for a thickness of 300, 600 and 1200nm, respectively. Results indicate that the shear...

Combining total-energy calculations, electronic-structure studies, and scanning tunneling microscopy (STM), we demonstrate that the observed one-dimensional nanowires are composed of Pt-induced Ge structures instead of Pt chains. Pt-Ge bonds are favored versus Pt-Pt ones. The novel tetramer-dimer-chain model explains STM features and the differenti...

GaN-based lateral polarity heterostructures (LPH) were grown on sapphire substrates using molecular beam epitaxy. The LPH samples consist of periodical N-face (000-1) (grown directly on Al2O3) and Ga-face (0001) (grown on a AlN bufferlayer) GaN stripes. The GaN-based LPH have been characterized using surface sensitive techniques. The GaN-based LPH...

Endothelial cells cover the inner surface of blood vessels and form the interface between the blood and the tissues. Endothelial cells are involved in regulating barrier function, which is maintained by the interendothelial cell contacts. These interendothelial cell contacts are established by the interaction of different molecules. The maintenance...

Different thin fluorocarbon (FC) films were deposited on Si(111) using plasma polymerisation and then exposed to X-ray radiation. Changes in the chemical composition of the deposited fluorocarbon films as a function of irradiation time were investigated in situ using X-ray photoelectron spectroscopy. The evaluation of the C1s and F1s core level ind...

The structural, chemical and electron transport properties of In2O3/InN heterostructures and oxidized InN epilayers are reported. It is shown that the accumulation of electrons at the InN surface can be manipulated by the formation of a thin surface oxide layer. The epitaxial In2O3/InN heterojunctions show an increase in the electron concentration...

This paper reports on the analysis of vibrational modes of atmospheric adsorbates on the 6H–SiC(0 0 0 1) surface by means of high resolution electron energy loss spectroscopy (HREELS). Three vibrational O–Si–O modes on silicon carbide were registered for the first time with high accuracy. Furthermore, a strong dependence of the energy of the antisy...

In this work metalorganic chemical vapor phase epitaxy (MOVPE) growth and characterization of AlInN in the whole compositional range and the impact on the development of field effects transistors (FET) structures will be presented. Due to the large difference in the lattice parameters of the binaries AlN and InN the growth of AlInN with high indium...