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Nanostructured surfaces exhibit remarkable chemical, physical and microbiological properties and have therefore various technical and industrial applications. The ultrashort laser pulse irradiation (wavelength λ = 355 nm, pulse duration Δtp = 12 ps, repetition rate f = 100 kHz) of copper samples with appropriate laser parameters results in the formation of a micro- and nanostructured surfaces. The influence of these hierarchically textured surfaces on the secondary electron yield (SEY) was studied especially with regard to their morphological and geometrical properties. Specific SEY changes are caused by both, the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures; that can be either compact flower head-like nanostructures, non-compact filament-shaped nanostructures, molten and resolidified spherical structures, or minor modified surfaces. The measured SEY as a function of the primary electron energy is correlated with the surface topography that forms upon laser irradiation. The SEY decreases with increasing accumulated laser fluence and ablated volume, respectively. Especially flower-head-like nanostructures can be produced at high laser power (P ≥ 400 mW) and low scanning velocity (v ≤ 10 mm/s) and represent a surface with strongly reduced SEY maximum as low as 0.7.

The influence of microgeometries on the Secondary Electron Yield (SEY) of surfaces is investigated. Laser written structures of different aspect ratio (height to width) on a copper surface tuned the SEY of the surface and reduced its value to less than unity. The aspect ratio of microstructures was methodically controlled by varying the laser parameters. The results obtained corroborate a recent theoretical model of SEY reduction as a function of the aspect ratio of microstructures. Nanostructures - which are formed inside the microstructures during the interaction with the laser beam - provided further reduction in SEY comparable to that obtained in the simulation of structures which were coated with an absorptive layer suppressing secondary electron emission.

The formation of a fissured copper surface by picosecond pulsed laser irradiation is combined with functional coatings consisting of Ti and amorphous carbon layers or a Ti–Zr–V compound film to fabricate surfaces with the maximum of the secondary electron yield being as low as 0.4. By structural and spectroscopic analysis of the formed surfaces it is demonstrated that both coatings enclose the nanostructures generated by redeposition of metal structures from the laser-induced plasma plume, keeping the initial topography intact. This allows an efficient elimination of secondary electron emission by combining the benefits from structural surface modification and adaption of electronic surface properties to efficiently dissipate the energy of impinging electrons. Thermal activation tests of the Ti–Zr–V nonevaporable getter films revealed that for films on nanostructured substrates, which have a much higher effective surface, a slight diminution of surface activation occurs at 160 and 200 °C, while this effect is completely compensated when heating up to 250 °C indicating promising pumping capabilities. Both examples highlight the benefits from combining 3D substrate patterning with classical 2D deposition technologies.

Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu[Formula: see text]O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence ([Formula: see text] J/cm[Formula: see text]), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10-4 C/mm[Formula: see text]. Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between processing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.

Cost-effective thick film manufacturing offers a wide material portfolio for sensor solutions. Low Temperature Cofired Ceramic (LTCC) technology as thick film based multilayer manufacturing process enables the design of complex fluid reactors used in versatile application scenarios. The technology meets the requirements for the design of 3-dimensional electrode arrays, which are essential for impedance monitoring in 3D cell cultures. Since the miniaturization of gold electrodes is limited, electrode functionalization is necessary for achieving high spatial resolution in sensor arrays. Coating of thick film gold electrodes with electropolymerized poly-3,4-ethylenedioxythiophene can significantly decrease the impedance. This work optimizes the coating process applying design of experiments. Electrode topography, chemical composition and electrochemical properties of coated and uncoated electrodes are compared and scaling effects are discussed based on fit parameters obtained from impedance spectroscopy. In addition to a reduction of impedance by two orders of magnitude, poly-3,4-ethylenedioxythiophene coating induces a reduction of size effects and a significant decrease of the variation. The scaling-down capability of electrodes achieves herewith dimensions of several tens of μm. The results evince an approach for sensor array integration with high spatial resolution providing increased measurement certainty for impedance monitoring in ceramic fluid systems and 3-dimensional bioreactors.

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In2O3), is often challenged by the presence of a distinct surface electron accumulation layer. We investigated the material properties and electrical transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the preparation of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evaporation and (reactive) sputtering in an (O and) Ar atmosphere, with oxygen plasma interface treatments, we identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chemical properties of the contact layers and the interface region toward In2O3, to analyze charge transfer and plasma oxidation processes as well as to evaluate the precision and limits of different methodologies to determine heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissolution of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In2O3 electron concentration of ∼1018 cm-3. A reactive sputter process in an Ar and O atmosphere is required to fabricate rectifying contacts that are composed of platinum oxide (PtOx). Combining oxygen plasma interface oxidation of the semiconductor surface with reactive sputtering of PtOx layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 106. An additional oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.

Electrochemical quartz crystal microbalance (EQCM) with damping monitoring is applied for real-time analysis of solid-electrolyte interphase (SEI) formation in diphenyl octyl phosphate (DPOP) and vinylene carbonate (VC) modified electrolytes. Fast SEI formation is observed for the DPOP containing electrolyte, whereas slow growth is detected in VC-modified and reference electrolytes. QCM measurements in a dry state show considerable reduction of the mass quantity for DPOP and reference samples and minor mass decrease for the SEI layer formed in the presence of VC. The results indicate that VC enhances SEI stability, whereas the addition of DPOP or no additive results in incorporation of loosely attached species, leadubg to SEI instability. Resonance frequency damping, Δw, and dissipation factor, D, are used for analyzing mechanical properties of the SEI layers. The apparent increase of Δw and D during SEI formation in presence of DPOP suggests a pronounced viscoelasticity of the layer. QCM results are compared with surface morphology and chemical composition, revealing excellent agreement of the applied characterization approaches.

Energy-resolved secondary electron spectroscopy has been performed on air-exposed standard Cu samples and modified Cu surfaces that are tested and possibly applied to efficiently suppress electron cloud formation in the high-luminosity upgrade of the Large Hadron Collider at CERN. The Cu samples comprise pristine oxygen-free, carbon-coated and laser-structured surfaces, which were characterized prior to and after electron irradiation and rare-gas ion bombardment. Secondary-electron and reflected-electron yields measured with low charge dose of the samples exhibit a universal dependence on the energy of the primary impinging electrons. State-of-the-art models can successfully be used to describe the spectroscopic data. The supplied spectral dependence of electron emission and integrated electron yield as well as the derived parametrization can serve as a basis for forthcoming simulations of electron cloud formation and multipacting.

${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ is an $n$-type transparent semiconducting oxide possessing a surface electron accumulation layer (SEAL) like several other relevant semiconductors, such as InAs, InN, ${\mathrm{SnO}}_{2}$, and ZnO. Even though the SEAL is within the core of the application of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ in conductometric gas sensors, a consistent set of transport properties of this two-dimensional electron gas (2DEG) is missing in the present literature. To this end, we investigate high-quality single-crystalline as well as textured doped and undoped ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$(111) films grown by plasma-assisted molecular beam epitaxy to extract transport properties of the SEAL by means of Hall effect measurements at room temperature while controlling the oxygen adsorbate coverage via illumination. The resulting sheet electron concentration and mobility of the SEAL are $\ensuremath{\approx}1.5\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and $\ensuremath{\approx}150\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}/\mathrm{Vs}$, respectively, both of which are strongly reduced by oxygen-related surface adsorbates from the ambient air. Our transport measurements further demonstrate a systematic reduction of the SEAL by doping ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ with the deep compensating bulk acceptors Ni or Mg. This finding is supported by x-ray photoelectron spectroscopy (XPS) measurements of the surface band bending and SEAL electron emission. Quantitative analyses of these XPS results using self-consistent, coupled Schr\"odinger-Poisson calculations indicate the simultaneous formation of compensating bulk donor defects (likely oxygen vacancies), which almost completely compensate the bulk acceptors. Finally, an enhancement of the thermopower by reduced dimensionality is demonstrated in ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$: Seebeck coefficient measurements of the surface 2DEG with partially reduced sheet electron concentrations between $3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ and $7\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ (corresponding average volume electron concentration between $1\ifmmode\times\else\texttimes\fi{}{10}^{19}$ and $2.3\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$) indicate a value enhanced by $\ensuremath{\approx}80%$ compared to that of bulk Sn-doped ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ with comparable volume electron concentration.

Electron cloud ($e$-cloud) mitigation is an essential requirement for proton circular accelerators in order to guarantee beam stability at a high intensity and limit the heat load on cryogenic sections. Laser-engineered surface structuring is considered a credible process to reduce the secondary electron yield (SEY) of the surfaces facing the beam, thus suppressing the $e$-cloud phenomenon within the high luminosity upgrade of the LHC collider at CERN (HL-LHC). In this study, the SEY of Cu samples with different oxidation states, obtained either through laser treatment in air or in different gas atmospheres or via thermal annealing, has been measured at room and cryogenic temperatures and correlated with the surface composition measured by x-ray photoelectron spectroscopy. It was observed that samples treated in nitrogen display the lowest and more stable SEY values, correlated with the lower surface oxidation. In addition, the surface oxide layer of air-treated samples charges upon electron exposure at a low temperature, leading to fluctuations in the SEY.

The interaction of n-type GaN(0001) surfaces with potassium and water is investigated using photoelectron spectroscopy, with special focus on adsorbate–substrate charge-transfer processes and water dissociation. Potassium atoms adsorb at the surface, forming a distinct surface dipole layer. For very low K coverage, the attached ionized K adsorbates result in a drop of the work function and the released electrons induce a reduction of the initial upward band bending. After stabilization of both quantities in the sub-monolayer regime, a reverse effect is observed for higher K coverage up to one monolayer (ML), exceeding the upward band bending of the clean surface. If the K-covered surface is exposed to water, hydroxyl groups are formed, whereas during long K and H2O coadsorption, a potassium hydroxide film grows. In both cases, a further reduction of the work function and an abrupt change in the surface depletion layer is recorded. For the coadsorption, initially an electron accumulation layer forms at the...

This paper describes the deposition of superconductive Nb-N thin films in a metal-organic plasma-enhanced atomic layer deposition process using (tert-butylimido)-tris (diethylamino)-niobium and hydrogen plasma as precursors. In extension of our previous work, which investigated the possibility to deposit superconducting Nb-N, we systematically investigated the influence of different plasma parameters on superconducting and morphological properties of the niobium nitride thin film formed during the process. An initial increase of the duration of the plasma dose led to higher transitions temperatures and critical current densities, the optimum being a plasma dose time of 50 s. By decreasing plasma pressure, the resistivity at room temperature decreased, while the transition temperature increased. In addition, Nb-N thin films were deposited onto several substrates such as silicon, thermally grown silica, magnesium oxide (MgO), and r-plane sapphire. ${\rm{T}}_{{\rm{C}}}$ values from 6.2 K up to 14 K were achieved independently of the substrate materials. However, films deposited on MgO showed lower ${\rm{T}}_{{\rm{C}}}$ values. X-ray photoelectron spectroscopy measurement revealed the presence of niobium nitride but also of niobium oxide and oxy-nitride components in the films as well as the existence of a high amount of incorporated carbon impurities. X-ray diffraction measurements revealed two significant reflexes, which could be attributed to niobium nitride only. No crystalline niobium oxide or niobium oxynitride was detected. Thus, the films consisted of a matrix of polycrystalline Nb-N and amorphous or microcrystalline grains of different niobium oxide and oxynitride phases. Due to the fact that the deposited material showed superconductivity especially for ultrathin layers with thicknesses in the nanometer range, these films may be suitable for superconducting nanowire single photon detectors.

Gallium oxide nanowires were grown on different substrates using a corona plasma assisted vapor phase epitaxy process and gold catalyst. It is shown that the silicon carbide pseudo substrate in combination with the plasma excitation of the gas phase supports the growth of the gallium oxide nanowires. Analyzing the orientation of the nanowires with respect to the growth surface, it is concluded that the nanowires growth proceed along the fast growth direction of gallium oxide.

The vacuum/liquid interface of ionic liquid/metal salt binary mixtures was investigated under ultra-high vacuum conditions using photoelectron spectroscopy. In this study we compare two ionic liquids 1- B utyl-1- m ethyl- p yrrolidinium-bis( t ri f luoromethylsulfonyl)-imide, [BMP][Tf 2 N] and 1- P ropyl-3- m ethyl- im idazolium- bis( t ri f luoromethyl-sulfonyl)-imide [PMIm][Tf 2 N] – in combination with two fluoride salts – TaF 5 and NbF 5 – at different concentrations. The results show a clearly different behavior for samples, which were in contact with ambient conditions and those being kept in inert conditions. Under inert atmosphere, the experimental results suggest rather equal anion and cation concentration of the IL constituents in the near surface region. At ambient conditions and high MF 5 (M = Ta, Nb) concentration, a strong deviation from the expected stoichiometry in the near surface region was observed, obviously caused by chemical reactions of the IL/salt system with the atmospheric environment. It is expected, that these reactions have also impact on the quality of electrodeposited metal films from these solutions.

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In

The surface resistance of copper samples with an amorphous carbon (a-C) coating or with laser surface structuring, the surface treatments of choice for electron cloud suppression in critical cryogenic sectors of the high-luminosity upgrade of the Large Hadron Collider (HL-LHC), has been measured for the first time at a cryogenic temperature using the quadrupole resonator at CERN. Three different frequencies of relevance for evaluating beam impedance effects, namely, 400, 800, and 1200 MHz, have been investigated. No significant increase in surface resistance is observed for the a-C coating, compared to plain copper. In the case of laser structuring, the surface resistance depends on the direction of the surface currents relative to the laser-engraved groove pattern. The increase is minimal for parallel patterns, but in the perpendicular case the surface resistance increases considerably. Radio frequency (rf) heating from wake losses would then also increase in the HL-LHC case; however, the reduction in the power deposited onto the cold surfaces thanks to electron cloud suppression would still outweigh this effect.

Amorphous carbon thin films were prepared by direct current hollow cathode sputter deposition in Ar discharge with the injection of small amounts of H2 and/or N2. The influence of these additives on the film properties with particular focus on the application as a coating for electron cloud mitigation in particle accelerators is characterized by optical spectroscopy, X-ray photoelectron spectroscopy, and secondary electron yield (SEY) measurements. The SEY maximum increased from initially 0.98 with pure Ar in the gas discharge up to 1.38 at 0.5% H2 while the addition of 1% of pure N2 enabled to reduce it to 0.88. The simultaneous addition of N2 to the H2 containing discharge allowed an average SEY maximum reduction of 20%. The optical bandgap revealed a correlation between the increase/decrease of the bandgap and the SEY increment/reduction for H2/N2 addition. The surface composition changes and the resulting modification of the sp2/sp3 ratio correlate with the changes in SEY and optical properties. The obtained results highlight the potential of intentionally injected N2 to counteract the detrimental effect of the inevitable H2 partial pressure in the coating systems during the production of amorphous carbon thin films for anti-multipacting applications in particle accelerators.

Controlling the surface formation of the group-V face of (1 1 1)-oriented III-V semiconductors is crucial for subsequent successful growth of III-V nanowires for electronic and optoelectronic applications. With a view to preparing GaP/Si(1 1 1) virtual substrates, we investigate the atomic structure of the MOVPE (metalorganic vapor phase epitaxy)-prepared GaP(1 1 1)B surface (phosphorus face). We find that upon high-temperature annealing in the H2-based MOVPE process ambience, the surface is phosphorus-depleted, as evidenced by X-ray photoemission spectroscopy (XPS). However, a combination of density functional theory calculations and scanning tunneling microscopy (STM) suggests the formation of a partially H-terminated phosphorus surface, where the STM contrast is due to electrons tunneling from non-terminated dangling bonds of the phosphorus face. Atomic force microscopy (AFM) reveals that a high proportion of the surface is covered by islands, which are confirmed as Ga-rich by Auger electron spectroscopy (AES). We conclude that the STM images of the samples after high-temperature annealing only reflect the flat regions of the partially H-terminated phosphorus face, whereas an increasing coverage with Ga-rich islands, as detected by AFM and AES, forms upon annealing and underlies the higher proportion of Ga in the XPS measurements.

Single crystalline and textured In2O3 thin films with (1 1 1) surface orientation, grown by plasma-assisted molecular beam epitaxy, were used as a model system to study the role of bulk and surface electron accumulation layer conductance for ozone sensing. Both conductance contributions, which add to the total film conductance, were systematically varied. The resulting ozone sensitivity was determined by total conductance measurements in synthetic air with defined ozone concentration using UV irradiation instead of heating to regenerate the In2O3 surface. Depletion of the surface electron accumulation by an oxygen plasma treatment, confirmed by X-ray photoelectron spectroscopy, rendered the films ozone insensitive. The ozone response of films with an accumulation layer was increased by thickness reduction or by designing the bulk of the film semi-insulating using deep acceptor doping by Mg. Our results of using electron accumulation layers for gas sensing and bulk doping by deep acceptors to increase sensitivity can be generalized to other gas sensing materials. The use of single crystalline films allows selecting the most sensitive crystallographic surface orientation and may have further advantages over polycrystalline films, such as increased stability and sensing speed.

authoren The interaction of defect-rich nanocrystalline indium oxide films, which have previously shown to exhibit excellent ozone sensing properties, with O3, O2, and H2O molecules is investigated using ultra-violet and X-ray photoelectron spectroscopy. The investigated samples are grown by metalorganic chemical vapor deposition at low temperatures resulting in high oxygen deficiency and high defect density. The ozone-induced surface oxidation and UV-induced photoreduction mechanisms of the ozone sensor active material are evaluated with respect to surface stoichiometry and electronic properties including adsorbate features, band bending and surface dipole formation. A strong interaction with ozone and water is found, whereas the interaction with O2 is relatively weak. In all cases the interaction results in the same negatively charged oxygen adsorbate species, which can either be removed by UV light or by annealing resulting in the capability of these films to be used in reversible adsorption induced oxidation and UV/thermal reduction cycles.

We report the design of a low-temperature liquid metal battery (LMB). Li and Ga as the negative and positive electrode, respectively, are used in combination with a room temperature ionic liquid as an electrolyte. 1 mol/L lithium bis(trifluoromethylsulfonyl)imide (Li[TFSI]) in 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide ([BMP][TFSI]) is chosen as electrolyte. The battery operates at 220 °C which is a relatively low temperature for a LMB and shows good electrochemical performance at low current density. The cells were cycled for more than 600 h and achieved a round-trip Coulombic efficiency close to 100% and an average voltage efficiency of 66% resulting in an overall energy efficiency of 65%. At higher current densities, however, the system showed up to 75% irreversible capacity loss after three cycles. To understand the origin of this strong deterioration, we characterized the surface and the bulk properties of the Ga cathode using X-ray Photoelectron Spectroscopy. Especially at higher current densities a decomposition of the electrolyte was found. The chemical changes that occurred and the elemental distribution at the Ga cathode are analyzed based on XPS measurements at different stages of the battery charge/discharge cycling.

Besides interesting applications in drug delivery, photoresponsive molecules have great potential to serve as an efficient basis for postfunctionalization photopatterning of polymer surfaces. To the best of our knowledge, only UV light sources have been exploited as a photoinducer for creating patterned templates with or without hydrogels. In this work, we present a practically facile method for grafting visible light responsive donor-acceptor stenhouse adducts (DASAs) on amino-functionalized polycarbonate surfaces. DASA grafted surfaces have shown excellent lithographic performance using visible light. The functionalized surfaces exhibit significant changes of their physical properties after being illuminated with visible light. By using suitable masks, well-defined patterns can be replicated with high precision and resolution. Since the DASA ligand synthesis and surface functionalization is not cumbersome, this method may serve as a facile protocol for obtaining photopatterned polymer surfaces for various applications.

Boron-doped multi-walled carbon nanotubes were synthesized upon decomposition of ethyl alcohol and boric acid via chemical vapor deposition. The boron-doped nanotubes were treated with hydrochloric acid and were characterized by means of scanning electron and transmission electron microscopy in conjunction with energy-dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. The electrochemistry of ferrocyanide/ferricyanide on boron-doped nanotubes was studied in temperature range of 283.15–303.15 K. The findings exhibit an improvement of films’ current response and kinetics of electron transfer with the rise in temperature. The kinetics for electron transfer enhances and the redox process occurs slightly more spontaneously upon acid treatment.

Neurobiological concepts based on state-of-the art technology have so far lacked the complexity of actual high-level neurobiological systems. Two key advances are needed to improve our understanding of such systems: in vitro 3D-neuronal cell culture and 3D MEA systems for measuring such 3D-cultures. These requirements call for smart multilayer and packaging technology. The material Green Tape TM from DuPont Nemours is chosen for the presented works, because its compatibility and those of available metallisation with cell cultures is already proven. An LTCC multilayer circuit with gold electrodes is the base of the 3D MEA. The layout of the 3D MEA is designed to fit the MEA2100-System for in vitro recording from Multi Channel Systems and enable thus a comparable data processing to established 2D MEAs Slots. The surface topography of the thick film electrodes and the surface state is investigated with laser scanning microscopy, SEM, XPS and measurements of the wetting angle of contact. The impedance of the screen printed electrodes is discussed taking these data into account. Their impedance amounts to 24 kΩ and are falls thus below the impedance of commercially available electroplated gold electrodes of 30 kΩ. First promising results have been achieved using 3D MEAs for 2D culture of human pluripotent stem cell derived neural cells.

We studied structure and charge transport properties of thin films of donor-acceptor block copolymers, poly(3-hexylthiophene-block-perylene bisimide acrylate), using a combination of X-ray scattering, AFM and vertical charge transport measurements in diode devices. Block copolymer self-assembly and crystallization of the individual components are interrelated and different structural states of the films could be prepared by varying preparation conditions and thermal history. Generally the well-defined microphase structures found previously in bulk could also be prepared in thin films, in addition alignment induced by interfacial interactions was observed. Microphase separated block copolymers sustain ambipolar charge transport, but the exact values of electron and hole mobilities depend strongly on orientation and connectivity of the microdomains as well as the molecular order within the domains.

The adsorption of hydrogen at nonpolar $\mathrm{GaN}(1\overline{1}00)$ surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of ${\mathrm{H}}_{2}$ and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the $\mathrm{GaN}(1\overline{1}00)$ surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga--N surface dimer buckling. The signatures of the Ga--H and N--H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean $\mathrm{GaN}(1\overline{1}00)$ surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion.

We report the room-temperature anisotropic dielectric functions (DFs), refractive indices, and absorption coefficients as well as birefringence and dichroism of wurtzite GaN in the spectral range between 0.6 eV and 6 eV. They have been determined by combined spectroscopic ellipsometry, optical retardation, and transmission measurements on a series of m- and c-plane bulk substrates prepared from crystals grown by hydride vapor phase epitaxy. The accuracy of the derived DFs is estimated by investigation of the role of mosaicity-related crystal imperfections, self-consistency test based on a Kramers-Kronig analysis, and examination of the influence of kind of overlayer. We also briefly discuss optical properties of a highly defective near-surface layer of GaN crystals introduced by their mechanical polishing.

In this work we investigate the interaction of potassium and water with 2×2 reconstructed InN(0001) surfaces prepared by plasma-assisted molecular beam epitaxy. The influence of adsorbate-substrate-interaction on surface properties is characterized in-situ by photoelectron spectroscopy. Potassium exposure leads to a strong reduction in the work function Φ to 1.6 eV revealing a charge transfer from the adsorbate to the InN surface. In parallel, a reduction of the surface downward band bending by 0.2 eV and hence a reduced electron accumulation density is observed. While interaction of water with clean InN(0001)-2×2 surfaces induces only minor changes in the surface band bending, water adsorption at potassium covered InN(0001) leads to a reversal of the K-induced reduction in surface band bending and a slight increase of Φ to 2.4 eV. These results show that surrounding water modifies the interaction of potassium with InN(0001) surfaces. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Under general working conditions, organic solar cells are exposed to a multitude of degradative stresses, including light, oxygen, temperature and humidity. We selectively exposed the layer stacks of three different material systems, P3HT, PCDTBT and AnE-PVcc in bulk heterojunction with fullerene, to different combinations of stresses, starting from one single stress and then iteratively adding a new stress to the combination. This allowed us to determine how harshly different polymers get affected by individual stress factors. P3HT based devices show an overall higher stability compared to PCDTBT or AnE-PVcc. All of the devices are affected the most by combined influences of light, oxygen, humidity and temperature, and they cease functioning within a couple of hours of exposure. A thermodynamically driven formation of a thin PCBM layer at the anode is observed with the prolonged storage, which causes an increase in the current densities for the large reverse voltages. We explain this phenomenon by tunneling from the fullerene HOMO to the LUMO, as a result of a large gradient in the electric potential over this layer. The increase of open circuit voltage of the pre-annealed P3HT devices upon UV photolysis was investigated, and attributed to the UV irradiation facilitated destruction of the face-on P3HT layer grown on the surface of the active layer. The effect of the sequence in which the annealing step is performed with respect to evaporation and degradation on the performance upon degradation is discussed.

To meet various application requirements, it is important to enable an improvement of a-C structure and properties, such as hardness, adhesion, and wear resistance. In this study, we used the Raman spectroscopy to investigate the a-C thin films structure dependence on the different deposition parameters. The effect of nitrogen, argon, and hydrogen gas flow rate was analyzed to determine the influence on the film properties. The change in the gas type, combination, and flow had a significant influence on the D and G bands of the a-C Raman spectra. The addition of N2into the chamber promoted the sp2creation, while with adding hydrogen the layer contained more sp3bonds. The depositions of a-C thin films were carried out in pulsed arc discharge vacuum installation. Micro-Raman measurements of the deposited materials were performed using an ISA Dilor-Jobin Yvon-Spex Labram confocal system with 632.8 nm radiation from a He-Ne laser using a back-scattering geometry.

Commercial titanium was treated in ambient atmosphere using pulsed Nd:YAG ( λ = 1064 nm ) laser irradiation. Repeated laser treatments induce a removal of surface contaminants as well as the formation of a nanostructured top layer exhibiting a large effective surface and nanometer roughness. The laser induced oxidation leads to the presence of a surface layer with strongly improved, hydrothermally stable adhesion when joined to a one-component, hot-curing epoxy-based adhesive. Changes in the material properties have been characterized with respect to the topography, the chemical composition and the crystal structure using SEM, cross-beam FIB, XPS and XRD analyses in order to correlate the adhesion behavior with the structural and chemical characteristics of the surface.

We investigated the impact of SF6 plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma conditions as well as annealing in nitrogen atmosphere at 425 °C. The electrical properties are characterized by Hall-effect measurements while electron spectroscopy and X-ray measurements are used to investigate changes in the surface chemical composition and in the layer structure, respectively. It is demonstrated that plasma treatments strongly affect the 2DEG properties of the heterostructure due to altering of the surface potential accompanied by the formation of a thin fluorinated amorphous film. Increasing the DC bias voltage for the plasma treatment leads to an additional degradation of the mobility caused by incorporation of fluorine into the heterostructure interface. Furthermore, the thin GaN cap layer is etched by plasma treatments with higher bias potential, which increases the carrier density at the interface (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The valence band offset (VBO) at the interface between indium nitride (InN) and selected oxide materials (Al2O3, TiO2, In2O3 and HfO2) is determined using X-ray photoelectron spectroscopy (XPS). For exact VBO determination, InN samples with oxide cap layers of varying thickness are investigated. The VBO values are extrapolated by linear regression of the thickness dependent energetic distances ΔE between the valence band maxima (VBM) at the oxide and InN surface and their corresponding heterointerface. The determined VBO values are (2.7 ± 0.2) eV for Al2O3/InN, (1.8 ± 0.2) eV for TiO2/InN, (1.5 ± 0.2) eV for In2O3/InN, (1.3 ± 0.2) eV for e-beam evaporated HfO2 on InN, and (2.0 ± 0.2) eV for atomic layer deposited HfO2 on InN. In some cases the oxide deposition process leads to an oxidation of the InN film at the oxide/InN interface (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The surface electronic properties and adsorption behaviour of as-grown and oxidized N-polar InN films are characterized by photoelectron spectroscopy (XPS, UPS). The epitaxial growth of the InN layers was performed by plasma-assisted molecular beam epitaxy on GaN/6H-SiC(000-1). After growth and in situ characterization the InN surfaces were exposed to molecular oxygen to evaluate the adsorption behaviour of O2 on N-polar InN and to study its impact on the surface electronic properties of the III-nitride material. The results are compared with studies on In-polar InN on GaN/sapphire templates. The as-grown N-polar InN surface exhibits a pronounced surface state at a binding energy of ∼1.6 eV. The valence band minimum lies about 0.8–1.0 eV below the surface Fermi level. Additionally, the XPS core level binding energies for InN(000-1) are reduced compared to InN(0001) films, indicating different surface band bending for clean N-polar and In-polar InN, respectively. The interaction of molecular oxygen with the InN(000-1) surface leads to a downward band bending by 0.1 eV compared to the initial state. Additional adsorption of species from the residual gas of the UHV chamber increases the surface downward band bending. Furthermore two pronounced oxygen related states with an energy distance of ∼5 eV could be detected in the valence band region. The adsorbed oxygen results in an additional component in the N1s core level spectra, which is interpreted as formation of NOx bonds.

Epitaxial graphene was grown on Si-face 4H-SiC. A SiC pretreatment with a carbon cap¬ping technique was used as well as slow heating rates and a temperature of 1800 °C under atmos¬pheric argon pressure. The surface morphology was investigated by atomic force microscopy and Raman spectroscopy was performed for samples with different graphitization times.

Radiation induced degradation effects are studied for a model ionic liquid (IL)--[EMIm]Tf(2)N--in order to distinguish in which way the results of X-ray based material analysis methods can be falsified by the radiation supplied by typical X-ray sources itself. Photoelectron spectroscopy is commonly used for determining the electronic structure of ionic liquids. Degradation effects, which often occur e.g. in organic materials during X-ray or electron irradiation, are potentially critical for the interpretation of data obtained from ionic liquids. The changes of the chemical composition as well as the radiation-induced desorption of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm]Tf(2)N) fragments are analysed by X-ray photoelectron spectroscopy (XPS) as well as quadrupole mass spectroscopy (QMS) upon exposure to monochromated or non-monochromated AlKα X-rays from typical laboratory sources. During the irradiation of [EMIm]Tf(2)N, an increasing carbon concentration is observed in both cases and especially the [Tf(2)N](-) ion is strongly altered. This observation is supported by the results from the QMS analysis which revealed a variety of different IL fragments that are desorbed during X-ray irradiation. It is shown that the decomposition rate is directly linked to the photon flux on the sample and hence has to be considered when planning an XPS experiment. However, for typical experiments on this particular IL the measurements suggest that the changes are on a larger time scale as typically required for spectra acquisition, in particular if monochromated X-ray sources are used.

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 spectroscopy (UPS, XPS). The oxygen and water exposure was directly performed on the as-grown, contamination-free InN surfaces at room temperature and leads to changes in the chemical surface states as well as the electronic properties. For 2 × 2 reconstructed InN surfaces one observes directly after growth a surface state at the Fermi-edge which decreases continuously with oxygen and water exposure. Furthermore, two oxygen related electronic states develop in the VB at binding energies at around 5 and 10 eV. For water exposure a third weak state around 8 eV is additionally observed. The impact of oxygen and water on the work function Φ as well as the variation of surface band bending was investigated. In both cases for initially 2 × 2 reconstructed surfaces a reduction in the downward band bending is found, while Φ increases in the case of oxygen exposure but in the case of interaction with water a reduced work function is observed. The oxygen uptake rates reveal a higher reactivity of water with InN surfaces compared to oxygen. Furthermore, during oxidation and water exposure different chemical oxygen bonds are formed, but a direct assignment to In–O or N–O bonds is difficult due to changes in the In3d and N1s XPS core level peak shape.

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 of 0.3 and a saturation coverage of approximately 1 ML. Core level spectra of the O1s state show three individual oxygen components with different temporal behavior. Furthermore, the initial reconstruction quickly vanishes and surface states in the valence band of the as-grown surface are removed during the exposure of the first few Langmuirs. For higher exposures, two oxygen-related states appear. The initial upward band bending of 0.4 eV for the as-grown surface is effectively reduced during oxidation resulting in flat band conditions. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)