Can Atomic Buckling Control a Chemical Reaction? The Case of Dehydrogenation of Phthalocyanine Molecules on GdAu2/Au(111) [component]

unpublished
Our understanding of catalysis, and in particular heterogeneous catalysis, is to a large extent based on the investigation of model systems. Increasing the complexity of the models towards oxide supported nanoparticles, resembling a real disperse metal catalyst, allows one to catch in the model some of the important aspects that cannot be covered by metal or oxide single crystals per se. The main purpose of our studies is to provide conceptual insight into questions concerned with a variety of
more » ... with a variety of topics in catalysis, including support nanoparticle interaction, reactivity at the particle-support interface, strong metal support interaction, reactions in confined space and development of new instrumentation for surface science studies. The talk will address some of those issues. A modified version of HiPIMS, called Deep Oscillation Magnetron Sputtering, with a pulsed reactive gas flow control and tosubstrate reactive gas injection into a high-density plasma in front of the sputtered molybdenum target was used for lowtemperature deposition of Mo-O(-N) films. The depositions were performed using a strongly unbalanced magnetron with a planar molybdenum target of 100 mm diameter in argon-oxygen(-nitrogen) gas mixtures at the total pressure close to 1 Pa. Voltage macropulses, composed of 5 voltage micropulses (pulse-on time of 23 us and pulse-off time of 27 us), with a total length of 250 us and repetition frequency of 400 Hz were used for all depositions with a maximum target power density up to 1150 Wcm-2 during pulses at a deposition-averaged target power density of 10 Wcm-2. The substrate temperatures were less than 120 °C (no external heater) during the depositions of films on floating glass and Si substrates at the distance of 100 mm from the target. A pulsed reactive gas flow control made it possible to produce high-quality MoOx and MoOxNy films with a tunable composition, and optical and electrical properties. The luminous absorption of 4% for 1 um thick non-conductive MoO3 films (the luminous transmittance of 80%) was smoothly changed into 88% for conductive (electrical resistivity decreased by up to 10 orders of magnitude) MoOx or MoOxNy films, keeping hardness of 3-5 GPa and very low macrostress (less than 200 MPa). The contribution deals with thermochromic multilayer VO2-based coatings for smart window applications prepared by reactive magnetron sputtering. First, we show that and how reactive high-power impulse magnetron sputtering with a pulsed O2 flow control allows reproducible preparation of crystalline VO2 of the correct stoichiometry under exceptionally industry-friendly deposition conditions: on soda-lime glass substrates without any substrate bias at a low temperature of around 300 °C [1]. Second, doping of VO2 by W is employed in order to shift the thermochromic transition temperature (68°C for bulk, 57°C for thin film VO2) towards the room temperature (39°C for V0.988W0.012O2, 20°C for V0.982W0.018O2), without concessions in terms of transmittance and its modulation. Third, we employ ZrO2 antireflection layers both below and above the thermochromic V1-xWxO2 layer, and present an optimum design of the resulting ZrO2/V1-xWxO2/ZrO2 coatings [2]. Most importantly, we show that while utilizing a first-order interference on ZrO2 leads to a tradeoff between the luminous transmittance (Tlum) and the modulation of the solar transmittance (dTsol), utilizing a second-order interference allows one to optimize both Tlum and dTsol in parallel. The properties achieved under the aforementioned industry-friendly deposition conditions and at lowered transition temperature include e.g. Tlum=42% and dTsol=12%, or Tlum=59% and dTsol=6% (depending on the V1-xWxO2 thickness). The experimental transmittance values are in agreement with those predicted during the multilayer coating design. [1] A novel electron accelerator, Cornell Brookhaven Energy-Recovery LINAC (ERL) Test Accelerator (CBETA), is developed by collaboration between CLASSE and Brookhaven National Laboratory. Many unique accelerator technologies will be tested in CBETA, including photo-cathode electron injector, 4-turn superconducting RF (SRF) Energy Recover LINAC (ERL), non-scaling Fixed-Field Alternating Gradient (NS-FFAG) optics with 4x energy acceptance. With a total circumference ~80-m, the CBETA consists of an photo-cathode injector and a LINAC SRF cryomodule, a NS-FFAG loop to transport electron beams of four energies (42, 78, 114 and 150 MeV) in single bore beampipe, and two splitter sections where the four energy beams are separately manipulated. CBETA vacuum system is designed to provide adequate level of vacuum and physical aperture for transporting electron beams at four energies, while stay clear of 300+ complex magnets. Furthermore, the vacuum system also accommodate a high density of beam diagnostics tools. Beam path length adjustment is required in the splitter sections. CBETA beampipes are mostly constructed of aluminum alloy (6061-T6), including 80+ metal knife-edge seal flanges made of non-coated aluminum alloy (type 6013-T6). Compact NEG pumps are used due to the space constraints. In this presentation, we report the status of CBETA vacuum system design, chamber fabrications and many stages of beamline installations and operations. Measurements of aluminum alloy outgassing and vacuum simulation, and experiences of using aluminum knife-edge flanges will also be discussed. Nanostructured titanium dioxide (TiO2) has been employed as surface modifiers in medical and dental implants, promoting improvements in biocorrosion resistance of the material and increasing the oxides bioactivity, with promising results in the interaction with living tissue. Although these materials have good mechanical properties, the thin native oxide layer (5-6nm) on their surfaces is not capable of protecting them from long-term corrosion. The surface modification with TiO2 can promote improvement in the biocorrosion resistance of the material and increase the oxides bioactivity, presenting promising results in the interaction with the tissue, since the biocompatibility is determined by chemical processes that occur at the interface between the implant and the proteins of the biological fluids. In this contribution, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to examine the adsorption of 3-mercaptopropionic acid (MPA) on anatase and rutile TiO2 thin films surfaces grown by RF magnetron sputtering. Obtained results showed that by the change of the deposition parameters, it was possible to grow monophasic anatase and rutile films on Ti substrates. AFM results determined the differences in morphology and grain size related to the anatase and rutile phases. Although the similarities of roughness and thickness, the anatase and rutile phases, functionalization was seen to occur only for the rutile phase. Two-dimensional transition metal dichalcogenides (2D-TMDs) are a novel class of materials with many potential applications including electronic and opto-electronic devices, quantum information systems, and catalysis. Properties of these materials are significantly impacted by atomic-scale local morphology and defects within the lattice. Particularly, the formation of electronic resonances that lie within the valence and conduction bands, referred to as in-gap states, result in significantly different optoelectronic than from a pristine lattice. High resolution scanning probe microscopy has the unique capability to resolve both geometric and electronic structure of materials on relevant length scales. Previously [1] using scanning tunneling microscopy/ spectroscopy (STM/STS) in combination with high-resolution NC-AFM imaging we identified and characterized point defects in monolayer tungsten disulfide (WS2) on graphene on silicon carbide. Commonly observed was a negatively charged defect sitting at the chalcogen site with a sharp in-gap resonance just above the valence band. Remarkably, after applying a local electric field (achieved by tunneling with a high current setpoint and bias), this defect can be reproducibly converted to a new type of defect. This new defect shows striking in-gap vibrionic signatures that can be reproducibly fit with a Frank-Condon model resulting in Huang-Rhys (HR) factors of ~5 and a lifetime broadening of 6 meV. Here, using STS we directly observe electron-phonon coupling of a single defect that we have created with an electric field. SPM techniques allow for an unprecedented view of the relationship between atomic structure therefore crucial optoelectronic properties. [1] Schuler, B. et al. Transition-metal (TM) nitrides exhibit an enormous range of useful properties. Cubic TM nitrides have wide single-phase compound fields that can be exploited. Results are presented for vacancy hardening in 3d Group-IV TiNx(001) and Group-V VNx (001); the hardness H (and resistivity) of epitaxial layers increases, while the elastic modulus E and the relaxed lattice constant decrease linearly with decreasing x. In contrast, H(x), E(x), and resistivity(x) for 5d Group-V TaNx(001) remain constant due primarily to the presence of isoelectronic antisites. All Group-IV TM nitrides are very good metallic conductors with room-temperature resistivities of 12-14 micro-ohm-cm. 3d Group-III ScN(001) is a transparent semiconductor with an indirect Γ-X gap of 1.3 eV. Group-IV TM nitrides are superconducting, but not the Group-IV rare-earth nitride CeN. The results are consistent with electron/phonon coupling parameters. Acoustic phonon modes soften monotonically with increasing cation mass; optical mode energies remain approximately constant for the TM nitrides, but are significantly lower for CN due a lower interatomic force constant. While TM nitrides are very hard, they are also brittle, leading to failure by crack formation and propagation. We show several approaches for obtaining TM nitride layers that are both hard and ductile (i.e., tough). IV-VI and V-VI alloys, e.g. Ti1 xWxN and V1 xMoxN, exhibit dramatic delocalization of electron density leading to a more ductile response to shear stress while exhibiting increased hardness under tensile and compressive loading. Vacancy-induced toughening is also observed. Operating turbo-molecular pumps (TMP) in an external magnetic field can induce eddy currents in the fast moving rotor, which leads to an undetected increase of the rotor temperature. The upper limit of the magnetic field for long-term safe operation is of the order of a few mT. It depends not only on the type of the TMP, but also on the direction of the field, the throughput of gas, and on the cooling of the TMP housing. For TMPs with active magnetic bearings, high magnetic fields can also cause a failure of the bearing, with the rotor plunging into the touchdown bearings at full speed. The KATRIN neutrino experiment operates more than 20 TMPs in the vicinity of super-conducting magnets with fields ranging from a few mT up to 18 mT at the location of the pumps. In order to ensure the safe operation of the TMPs, pumping radioactive tritium gas from the beam-line of the experiment, we studied the rotor temperature as a function of the magnetic field and developed an empirical model, describing the rotor temperature over time. Since the fields are far too strong for most of the TMPs, passive magnetic shieldings were installed around the pumps. This talk describes the temperature model, the measurement of the model parameters, the design of the passive shielding, and the experience with the TMPs operated at the beam-line of the KATRIN experiment. KATRIN is supported by the German BMBF project 05A17VK2 and HGF. 2016-A-1902 Performance of III-V//Si triple-junction solar cells fabricated by mechanical stacking and wire bonding Ray-Hua Horng The integration of III-V and Si triple-junction solar cells as photovoltaic devices have been studied in order to achieve high photovoltaic conversion efficiency. However, there exists a large difference in the coefficients of thermal expansion and the lattice parameters of GaAs and Si, which has made it difficult to obtain high-efficiency solar cells grown as epilayers on Si substrates. In this paper, the GaInP/GaAs stacked on Si (GaInP/GaAs//Si) was fabricated via mechanical stacking and wire bonding technologies. Mechanically stacked GaInP/GaAs//Si triple-junction solar cells are prepared via glue bonding. Current-voltage measurements of the sample are made at room temperature. The short-circuit current density of the GaInP/GaAs//Si solar cell is 13.37 mA/cm2, while the open-circuit voltage of the sample is measured to be 2.71 V. After bonding the GaInP/GaAs dual-junction with the Si solar cell, the conversion efficiency is relatively improved by 32.6%, compared to the efficiency of the GaInP/GaAs dualjunction solar cell alone. This study demonstrates the high potential of combining mechanical stacked with wire bonding and ITO films to achieve high conversion efficiency in solar cells with three or more junctions. The synthesis of complex oxide materials in the form of thin films has widely employed the epitaxial growth techniques, but which are limited in the range of compositions that can be accessed because of kinetic phenomena such as surface diffusion and phase separation. Precise control over the functionality of complex oxides arises from microstructural features such as interfaces, defects, lattice deformation, and domain boundaries. In this report, the 100-nm-thick aluminum-gallium oxide (AGO) thin films with bandgaps higher than 5.0 eV were grown on c-plane sapphire substrates using pulsed laser deposition with the oxygen growth pressure ranging from 0.7 to 200 mTorr. The oxygen pressure during the deposition process has a great impact on the lattice deformation in AGO materials as examined by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. Higher oxygen pressure results in the decrease of the AGO (-201) d-spacing. The measured transmittance spectra of AGO films demonstrate that the absorption edge shifts toward higher energy with increasing the oxygen pressure due to the dspacing narrowing of main plane. The AGO films were also utilized as the active layers of metal-semiconductor-metal photodetectors. The presented lattice deformation seems to benefit the enhancement of photocurrent and the reduction of dark current. It is found that the responsivity of lattice-deformed AGO device is over 20 times higher than that with the normal lattice. The separated piezopotential induced by the lattice deformation could contribute to assist the photogenerated carrier recombination more efficiently, resulting in the reduction of decay time. Catalyst synthesis with precise control over the structure of catalytic active sites at the atomic level is of essential importance for the scientific understanding of reaction mechanisms and for rational design of advanced catalysts with high performance. Such precise control is achievable using atomic layer deposition (ALD). ALD is similar to chemical vapor deposition (CVD), except that the deposition is split into a sequence of two self-limiting surface reactions between gaseous precursor molecules and a substrate. The unique self-limiting feature of ALD allows conformal deposition of catalytic materials on a high surface area catalyst support at the atomic level. The deposited catalytic materials can be precisely constructed on the support by varying the number and type of ALD cycles. As an alternative to the wet-chemistry based conventional methods, ALD, facilitated by area-selective deposition, provides a cycle-by-cycle "bottom-up" approach for nanostructuring supported catalysts with near atomic precision. In this presentation, we will discuss synthesis of single-atom catalysts, bimetallic catalysts and nanostructured catalysts using ALD. Such atomic-level catalyst synthesis offered by ALD greatly facilitates our understanding of the structure-activity relations, and provides knowledge for rational catalyst design. Molecular machines are gaining increasing interest and have earned the Chemistry Nobel Prize in 2016. They have the potential to spawn the next technological revolution after microelectronics and optoelectronics. Central issues in molecular machines are energy intake, conversion, output and transmission. Molecular machines promise to convert energy and control mechanical motion at length scales down to the nanometer. This talk will discuss basic issues of the operation of molecular motors, including energy conversion steps, continuous energy supply, the role of thermal energy, intentional start and stop of motion, unidirectionality of motion and transmission of rotation among gear-like molecules. Without intentional control of these aspects, motors create random motion and are largely useless. Some molecular machines cause reciprocal motion, as in muscles and switches, while others cause rotational motion, as in flagellae: we discuss mechanisms and theoretical models of both. Two-dimensional (2D) materials consisting of heavy atoms with particular arrangements may host exotic quantum properties. In this talk, I will present a unique 2D semiconducting binary compound, Sn2Bi atomic layer on Si(111), in which hexagons are formed by bonding Bi with a triangular network of Sn. Due to the unique honeycomb configuration, the heavy elements and the energy-dependent hybridization between Sn and Bi, 2D Sn2Bi not only shows strong spin-orbit coupling effects, but also exhibits high electron-hole asymmetry: nearly free hole bands and dispersionless flat electron band co-exist in the same system. By tuning the Fermi level, it is possible to preserve both nearly free and strongly localized charge carriers in the same 2D material, which provides an ideal platform for the studies of strongly correlated phenomena and possible applications in nanodevices. The increasing use of engineered nanoparticles and metallic nanosized complexes in a variety of applications, from technological to medical areas, raised concerns on their potential toxicity. It is therefore urgent to understand how these nanosized entities interact with biological systems. Due to their small size, the identification and localization within cells is extremely challenging. Various cutting edge techniques are required to detect electron-dense nanoparticles and quantify metals inside the cells. However, few of these techniques are able to peer into cells combining nanometre probe-formation with several other specifications such as, precise elemental quantification, depth profile of the element of interest, and subwavelength fluorescence imaging. This is the prospect of nuclear microscopy techniques using MeV ion beams. Such type of ion probes can be used for whole-cell investigations delivering unique and relevant information for nanotoxicology studies. The main issues are (2): i) visualization of individual and small clusters of nanoparticles; ii) and production of 3D maps of their distribution inside cells. This will help to unravel the internalization efficiency, the mechanisms of action and eventually shed light on the toxicity of nanosized materials to cells (1). An overview of ion probes contribution to nanotoxicology advances will be given concerning visualization and quantification systems, their limitations and pitfalls. The presentation deals with the structure, microstructure, mechanical and tribological properties and oxidation resistance of WNx films with a stoichiometry x=[N]/[W] ranging from 0 to 1.5 prepared by magnetron sputtering. The as-deposited films exhibit high hardness H=22-34 GPa and (1) columnar microstructure and alpha-W phase at x lower or equal to 0.20 or (2) fine-grained microstructure, and a mixture of alpha-W and beta-W2N phase at x between 0.20 and 0.64, beta-W2N phase at x=0.64 and delta-WN phase at x=1.5. It was found that the tribological properties of the films are strongly influenced by (1) the relative humidity RH of ambient air ranging from 5 % (dry nitrogen) to 82 % (moist environment), the coefficient of friction (CoF) decreasing from 0.75 to 0.16 and wear rate k increasing from 0.004 to 2×10E-6 mm3/Nm, respectively, due to the surface hydration at temperature T≈22 °C , (2) the mechanical properties of WNx, where the films with alpha-W phase exhibit low ratio hardness to effective Young's modulus H/E lower to 0.1 and high k up to 5×10E-6 mm3/Nm, the films with beta-W2N and/or delta-WN phase exhibit H/E higher to 0.1 and low k up to 0.01×10E-6 mm3/Nm at T ranging from 22 to 150 °C, and (3) the WO3 surface scale with columnar microstructure created at T increasing from 150 °C to 500 °C acts as an lubricant where CoF decreasing to ≈0.5 due to its low H=4 -5 GPa but k increasing above 6×10E-6 mm3/Nm due to its low H/E=0.05. In the renewable energy category, the solar cells have attracted great attention for alleviating the energy shortage problem. Among the highly anticipated solar cells, the III-V compound solar cells revealed the highest conversion efficiency due to their high carrier mobility and high absorption coefficient. In this study, the AuGeNi/Au nanomesh electrode structure with various intervals were designed on InGaP/InGaAs/Ge triple-junction solar cells to replace the conventional bus-bar electrodes with interval of 125 um The conversion efficiency of the solar cells using nanomesh electrode with the interval of 100 um was 35.25% that was better than that of 30.84% for the solar cells with conventional bus-bar metal electrode. The performance improvement was attributed to that the block ratio of the shadow area and the series resistance of the solar cells using nanomesh electrode structure with interval of 100 um were reduce form 7.50 to 0.66% and 9.1 to 7.9 ohm-cm2, respectively, in comparison with the solar cells with conventional bus-bar metal electrode. To further improve the performance of the solar cells with AuGeNi/Au nanomesh electrode of 100 um, the TiO2 nanorod array with period of 1.00 um was used to replace the standard TiO2/SiO2 antireflection layers. The conversion efficiency was further improved from 35.25% to 37.00%. Consequently, the designed nanomesh electrode and nanostructured antireflection structures were promising candidate for improving conversion efficiency of solar cells. Post-Li-ion batteries: promises and challenges M. Rosa Palacin Current societal challenges in terms of energy storage have prompted to an intensification in the research aiming at unravelling new high energy density battery technologies with the potential of having disruptive effects in the world transition towards a less carbon dependent energy economy through transport electrification and renewable energy integration. Aside from controversial debates on lithium supply, the development of new sustainable battery chemistries based on abundant elements is appealing, especially for large scale stationary applications. Interesting alternatives are to use sodium, magnesium or calcium instead of lithium. While for the Na-ion case fast progresses are expected as a result of chemical similarities with lithium and the cumulated Li-ion battery know how over the years, for Ca and Mg the situation is radically different. On one hand, the possibility to use Ca or Mg metal anodes which would bring a breakthrough in terms of energy density, on the other, development of suitable electrolytes and cathodes with efficient multivalent ion diffusion are bottlenecks to overcome. The presentation will serve to discuss such promises and challenges and describe current state-of-the-art of research in the field. The ALD process can be seen from various perspectives. On the one hand, it allows controlled deposition of thin films on a variety of substrates and in this way enables a modification of a given functionality of a surface or even introduction of a new functionality. On the other hand, it may be seen as a chemical reactor that allows precise dosing of a chemical, allowing for chemical interaction and modification of the substrate. In this talk, some approaches will be discussed that show great promise for establishing ALD as the method-of-choice for innovation in technological fields beyond the microelectronics industry. Rather than growing thin conformal films, the ALD process technology is applied to controllably grow nanoparticles on functional substrates adding value to their chemical or electrochemical properties. In an adapted processing mode, the ALD processing technology also allows infusing metals into polymeric substrates, which leads to novel material blends that cannot easily be obtained in other ways. In either of those cases the chemical or physical properties of the initial substrate are improved or new functionalities added. With some showcases, this talk will discuss approaches towards non-traditional application of ALD to fabricate novel materials with great promise in energy storage, catalysis, personal protection or flexible electronics. "Cavitas sensors" attached to body cavities such as a contact lens type and a mouthguard ("no implantable", "no wearable") are attracted attention for preventive medicine. In this contribution, the soft contact lens (SCL) glucose sensor for tear sugar monitoring and the mouthguard (MG) biosensor with dental materials integrated with Bluetooth low energy (BLE) wireless module would be introduced. The SCL biosensor for tear glucose was fabricated using biocompatible 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer and polydimethyl siloxane (PDMS) as the biosensor material. The biosensor consists of a flexible Pt working electrode and an Ag/AgCl reference/counter electrode, which were formed by ion-beam sputtering. The sensing region was modified with glucose oxidase (GOD). The calibration range of the SCL biosensor was from 0.03-5.0mM. As the result of the sensor application to a rabbit, the basal tear glucose was estimated to 0.11mM. Also, the change of tear glucose induced by the change of blood sugar level was assessed by the oral glucose tolerance test. The MG biosensor with dental materials integrated with BLE wireless module was developed. The biosensor based on the integration of Pt and Ag/AgCl electrodes with an GOD membrane was fabricated on the MG surface of a polyethylene terephthalate glycol (PETG). In artificial saliva, the glucose sensor exhibits high-sensitive detection in a range of 5-1000 µmol/L. The self-detachable cavitas sensors are expected to improve quality of life in view of the aging of society in the near future. The metal-catalyzed coupling of halobenzene derivatives leading to biaryls and larger carbon-based structures is a fundamental reaction in chemical synthesis. Copper is the paradigmatic catalyzer of the Ullmann cross-coupling reaction. Despite this, its role in the reaction is still under debate. Here, we shed light on the mechanistic steps of the debromination, characterizing a prototypical molecule, namely 4,7-dibromobenzo[c]-1,2,5-thiadiazole (2Br-BTD), deposited on a Cu(110) surface. By means of scanning probe techniques and first principle calculations, we demonstrate the oxidative addition of Cu atoms leading to a -C-Cu-Br metal-organic complex. The scission of the strongly bound bromine atoms requires the cooperative action of neighbouring complexes resulting in the formation of Cu coordinated BTD structures. The form of the external potential (FEP) for generating field emission resonance (FER) in a scanning tunneling microscopy (STM) junction is usually assumed to be triangular. We demonstrate that this assumption can be examined using a plot that can characterize FEP. The plot is FER energies versus the corresponding distances between the tip and sample. Through this energydistance relationship, we discover that the FEP is nearly triangular for a blunt STM tip. However, the assumption of a triangular potential form is invalid for a sharp tip. The disparity becomes more severe as the tip is sharper. We demonstrate that the energydistance plot can be exploited to determine the barrier width in field emission and estimate the effective sharpness of an STM tip. Because FERs were observed on Pb islands grown on the Cu(111) surface in this study, determination of the tip sharpness enabled the derivation of the subtle expansion deformation of Pb islands due to electrostatic force in the STM junction. A wide and indirect band gap, high chemical and thermal stability, as well as radiation and electrical hardness, are among the merits that make silicon carbide (SiC), in particular its 4H polytype, an outstanding material for high-voltage and high-power electronics. SiC-based radiation detectors are highly sensitive to defects that introduce deep carrier traps, especially to those with large capture cross section for minority carriers. Among the most recombination-active defects in 4H-SiC we have the carbon vacancy, which may be created by ion and electron bombardment, but due to its low formation energy, it is also present in asgrown material. We report a joint work by means of density functional theory (DFT) calculations and space-charge techniques, including deep-level transient spectroscopy (DLTS) and Laplace-DLTS, to investigate the capture and emission kinetics of electrons involving the Z1/2 electron trap, which was assigned to the carbon vacancy in 4H-SiC. We show how first-principles calculations can be applied to unravel the positions of transition levels in the band gap, as well as the high of capture barriers. A direct comparison between calculations and measurements, allow us to demonstrate the negative-U ordering of the acceptor levels, as well as to assign Laplace-DLTS peaks to electron emissions from carbon vacancies in two symmetry-inequivalent lattice sites. Two crucial criteria for manufacturing biomedical metallic implants are the absence of toxic elements and a low modulus of elasticity. Titanium and its alloys have better mechanical properties, biocompatibility, and corrosion resistance as compared to the most used metallic biomaterials, stainless steel (SS) and cobalt-based alloys [1]. Although Ti alloys are significantly more expensive than SS and Co-Cr alloys, they present better biocompatibility and have elastic modulus values closer to the human bones. An interesting option would be to coat an implant with Ti-based alloy thin films having adequate composition and thickness so that the coating would enhance the material biocompatibility [2]. Since magnesium is a lightweight metal, it is expected that alloying Ti with Mg produces a useful metallic biomaterial [3]. Due to the lack of complete solubility in the Ti-Mg phase diagram, high Mg content Ti-Mg alloys cannot be obtained by conventional melting processes [3], thus non-equilibrium processes, such as magnetron sputtering, have been employed for producing Ti-Mg alloys [4]. In this work, Ti-Mg alloy coatings have been deposited on AISI 316L SS by magnetron sputtering. The structure, morphology, and nanostructure of the coatings have been analyzed by xray diffraction, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy, while the mechanical properties have been evaluated by nanoindentation, scratch, and nanowear tests. Nanostructured silicon (black silicon, BS) was prepared by means of a mask-less plasma process (Reactive Ion Etching) employing CF4 and 10 % of H2 as reaction gases. A full texturing effect was achieved supplying 250W RF power, for a 20 minute process time. These process parameters were previously found as the optimal ones to fabricate silicon surfaces with an ultra-low reflectance. In this work samples obtained with different process time (30 sec-20 min) were studied to investigate in detail the resulting morphological and chemical changes with the aim to identify a growth mechanism of the nanostructures constituting the black silicon. They were characterized via Secondary Electron Microscopy (SEM), 3D mechanical profilometry, X-ray Photoelectron Spectroscopy (XPS), Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Atomic Force Microscopy (AFM) while the plasma phase was investigated using Optical Emission Spectroscopy (OES). In order to discern from the effect of the morphological features, two different experimental procedures were followed to study the effects of the plasma chemistry on the nanostructures growth. The first was to treat the Si surface with the plasma continuously at different exposure times (0.5, 1, 2, 5, 15, 20 minutes). The second was to expose the Si surface to the plasma for a net total time of 20 minutes but cycling between 1 minute of plasma treatment and 1 minute of pumping of the exhaust mixture. In this way the reactive species formed in the plasma phase were removed before the plasma was regenerated. Monolayer transition-metal dichalcogenides (TMDs) are known to be one of the most promising candidates for future nanoelectronic and nanooptoelectronic devices owing to their outstanding electrical and optical properties [1][2][3]. Interest in bringing p-and n-type monolayer semiconducting TMD into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing [4][5][6]. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods, scanning photoelectron micro-spectroscopy (SPEM), and transport measurement. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics.
doi:10.1021/acs.jpcc.8b11412.s001 fatcat:25rl7vaskvc3pmtl7g63mpca4a