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Crystalline nanoporous molecular networks are assembled on the Ag(111) surface, where the pores confine electrons originating from the surface state of the metal. Depending on the pore sizes and their coupling, an antibonding level is shifted upwards by 0.1 to 0.3 eV as measured by scanning tunneling microscopy. On molecular sites, a down-shifted bonding state is observed, which is occupied under equilibrium conditions. Low-temperature force spectroscopy reveals energy dissipation peaks and jumps of frequency shifts at bias voltages, which are related to the confined states. The dissipation maps show delocalization on the supra-molecular assembly and a weak distance-dependence of the dissipation peaks. These observations indicate that two-dimensional arrays of coupled quantum dots are formed, which are quantitatively characterized by their quantum capacitances and resonant tunneling rates. Our work provides a method for studying the capacitive and dissipative response of quantum materials with nanomechanical oscillators., 24 pages, 4 figures

Solution-synthesized graphene nanoribbons (GNRs) facilitate various interesting structures and functionalities, like nonplanarity and thermolabile functional groups, that are not or not easily accessible by on-surface synthesis. Here, we show the successful high-vacuum electrospray deposition (HVESD) of well-elongated solution-synthesized GNRs on surfaces maintained in ultrahigh vacuum. We compare three distinct GNRs, a twisted nonplanar fjord-edged GNR, a methoxy-functionalized "cove"-type (or also called gulf) GNR, and a longer "cove"-type GNR both equipped with alkyl chains on Au(111). Nc-AFM measurements at room temperature with submolecular imaging combined with Raman spectroscopy allow us to characterize individual GNRs and confirm their chemical integrity. The fjord-GNR and methoxy-GNR are additionally deposited on nonmetallic HOPG and SiO

Substituting heteroatoms and non-benzenoid carbons into nanographene structure offers an unique opportunity for atomic engineering of electronic properties. Here we show the bottom-up synthesis of graphene nanoribbons (GNRs) with embedded fused BN-doped rubicene components on a Au(111) surface using on-surface chemistry. Structural and electronic properties of the BN-GNRs are characterized by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) with CO-terminated tips supported by numerical calculations. The periodic incorporation of BN heteroatoms in the GNR leads to an increase of the electronic band gap as compared to its undoped counterpart. This opens avenues for the rational design of semiconducting GNRs with optoelectronic properties., Comment: 18 pages, 4 figures

Molecular self-assembly plays a very important role in various aspects of technology as well as in biological systems. Governed by covalent, hydrogen or van der Waals interactions–self-assembly of alike molecules results in a large variety of complex patterns even in two dimensions (2D). Prediction of pattern formation for 2D molecular networks is extremely important, though very challenging, and so far, relied on computationally involved approaches such as density functional theory, classical molecular dynamics, Monte Carlo, or machine learning. Such methods, however, do not guarantee that all possible patterns will be considered and often rely on intuition. Here, we introduce a much simpler, though rigorous, hierarchical geometric model founded on the mean-field theory of 2D polygonal tessellations to predict extended network patterns based on molecular-level information. Based on graph theory, this approach yields pattern classification and pattern prediction within well-defined ranges. When applied to existing experimental data, our model provides a different view of self-assembled molecular patterns, leading to interesting predictions on admissible patterns and potential additional phases. While developed for hydrogen-bonded systems, an extension to covalently bonded graphene-derived materials or 3D structures such as fullerenes is possible, significantly opening the range of potential future applications.

On-surface synthesis is a powerful method for the fabrication of π-conjugated nanomaterials. Herein, we demonstrate chemoselective Sonogashira coupling between (trimethylsilyl)ethynyl and chlorophenyl groups in silylethynyl- and chloro-substituted partially fluorinated phenylene ethynylenes (SiCPFPEs) on Ag(111). The desilylative Sonogashira coupling occurred with high chemoselectivity up to 75 %, while the competing Ullmann and desilylative Glaser homocoupling reactions were suppressed. A combination of bond-resolved scanning tunneling microscopy/atomic force microscopy (STM/AFM) and DFT calculations revealed that the oligomers were obtained by the formation of intermolecular silylene tethers (-Me2 Si-) through CH3 -Si bond activation at 130 °C and subsequent elimination of the tethers at an elevated temperature of 200 °C.

The production of ammonia (NH 3 ) with low-pressure, radiofrequency plasmas is studied in this paper in a wide range of experimental conditions using tungsten as a catalyst. The relative position of the tungsten foil in the pyrex tube was observed to dramatically impact ammonia formation. By positioning the catalyst in the middle of the tube, the concentration of NH 3 peaked at 120 W with ≈20 mol %, while it decreased by more than a factor of 2 at 300 W. When the foil was placed close to the end of the tube, the production of NH 3 was rather stable beyond 120 W. These results provide clear evidence of the surface's role in the local enhancement of the NH 3 formation rates. In the plasma volume, at some distance from the foil, the decomposition of NH 3 is the major occurring process and the decomposition rate increases with the power primarily due to a higher electron density. The optimum production of NH 3 was found to be at 45 mol % N 2 and 120 W, and the position of the maximum was observed to slightly decrease to

Nitrogen-doped Kagome graphene (N-KG) has been theoretically predicted as a candidate for the emergence of a topological band gap as well as unconventional superconductivity. However, its physical realization still remains very elusive. Here, we report on a substrate-assisted reaction on Ag(111) for the synthesis of two-dimensional graphene sheets possessing a long-range honeycomb Kagome lattice. Low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) with a CO-terminated tip supported by density functional theory (DFT) are employed to scrutinize the structural and electronic properties of the N-KG down to the atomic scale. We demonstrate its semiconducting character due to the nitrogen doping as well as the emergence of Kagome flat bands near the Fermi level which would open new routes towards the design of graphene-based topological materials.

Dendritic polyphenylenes (PPs) can serve as precursors of nanographenes (NGs) if their structures represent 2D projections without overlapping benzene rings. Here, we report the synthesis of two giant dendritic PPs fulfilling this criteria with 366 and 546 carbon atoms by applying a "layer-by-layer" extension strategy. Although our initial attempts on their cyclodehydrogenation toward the corresponding NGs in solution were unsuccessful, we achieved their deposition on metal substrates under ultrahigh vacuum through the electrospray technique. Scanning probe microscopy imaging provides valuable information on the possible thermally induced partial planarization of such giant dendritic PPs on a metal surface.

Sepsis is a life-threatening condition mostly caused by a bacterial infection resulting in inflammatory reaction and organ dysfunction if not treated effectively. Rapid identification of the causing bacterial pathogen already in the early stage of bacteremia is therefore vital. Current technologies still rely on time-consuming procedures including bacterial culturing up to 72 h. Our approach is based on ultra-rapid and highly sensitive nanomechanical sensor arrays. In measurements we observe two clearly distinguishable distributions consisting of samples with bacteria and without bacteria respectively. Compressive surface stress indicates the presence of bacteria. For this proof-of-concept, we extracted total RNA from EDTA whole blood samples from patients with blood-culture-confirmed bacteremia, which is the reference standard in diagnostics. We determined the presence or absence of bacterial RNA in the sample through 16S-rRNA hybridization and species-specific probes using nanomechanical sensor arrays. Via both probes, we identified two clinically highly-relevant bacterial species i.e., Escherichia coli and Staphylococcus aureus down to an equivalent of 20 CFU per milliliter EDTA whole blood. The dynamic range of three orders of magnitude covers most clinical cases. We correctly identified all patient samples regarding the presence or absence of bacteria. We envision our technology as an important contribution to early and sensitive sepsis diagnosis directly from blood without requirement for cultivation. This would be a game changer in diagnostics, as no commercial PCR or POCT device currently exists who can do this.

AIM(S): The aim of the study was to fabricate a nanospike surface on a titanium alloy surface using a newly established method of low-energy helium ion bombardment. Various methods to achieve nanospike formation on titanium have been introduced recently, and their antibacterial properties have been mainly investigated with respect to Escherichia coli and Staphylococcus aureus. Oral pathogens such as Porphyromonas gingivalis play an important role in the development of peri-implantitis. For that reason, the antibacterial properties of the novel, nanostructured titanium surface against P. gingivalis were assessed, and a possible effect on the viability of gingival fibroblasts was evaluated. MATERIALS AND METHODS: Helium sputtering was employed for developing titanium surfaces with nanospikes of 500 nm (ND) in height; commercially available smooth-machined (MD) and sandblasted and acid-etched titanium disks (SLA) were used as controls. Surface structure characterization was performed through scanning electron microscopy (SEM) and atomic force microscopy (AFM). Following incubation with P. gingivalis, antibacterial properties were determined via conventional culturing and SEM. Additionally, the viability of human gingival fibroblasts (HGFs) was tested through MTT assay, and cell morphology was assessed through SEM. RESULTS: SEM images confirmed the successful establishment of a nanospike surface with required heights, albeit with heterogeneity. AFM images of the 500 nm nanospike surface revealed that the roughness is dominated by large-scale hills and valleys. For frame sizes of 5 × 5 μm and smaller, the average roughness is dominated by the height of the titanium spikes. ND successfully induces dysmorphisms within P. gingivalis cultures following the incubation period, while conventional culturing reveals a 17% and 20% reduction for ND compared to MD and SLA, respectively. Moreover, the nanospike surfaces did not affect the viability of human growth fibroblasts despite their sharp surface. CONCLUSION(S): This study successfully developed a novel titanium-nanospike-based structuration technique for titanium surfaces. In addition, the nanospikes did not hinder gingival fibroblast viability. Enhanced antimicrobial effects for such a novel nanospike-based resurfacing technique can be achieved through further optimizations for nanospike spacing and height parameters. ispartof: NANOMATERIALS vol:12 issue:7 ispartof: location:Switzerland status: published

We present an experimental investigation of the ion flux–energy distribution functions (IFEDFs) obtained across grounded grids in an asymmetric capacitively coupled RF source using a helium discharge. The powered electrode in the RF source is DC-grounded via a λ/4 filter, which lifts its DC potential to zero. Grids of different dimensions (hole width, thickness, and geometric transparency) were used to confine the plasma, while the IFEDF of the ion beam departing the grid and reaching the reactor walls was studied using a retarding field energy analyser. The IFEDF obtained was double-peaked, indicating the presence of fast ions arriving from the plasma source, and cold ions generated upon charge exchange collisions between the fast ions and neutrals. The flux, as well as the peak energies of the two ion groups, depended significantly on the process parameters: RF power, He pressure, the distance between grids and walls, and the dimensions of the grids. The results indicate that confining plasma with grids can reduce the ion flux at the walls by over 60%, significantly lowering the wall sputtering rate. This was confirmed with a dedicated long-exposure plasma discharge with a gridded plasma reactor, wherein less than 1 nm of Cu deposition was found on the DC-grounded powered electrode, and the surface reflectivity was preserved to pristine values. In contrast, a similar experiment in a gridless reactor resulted in Cu deposition of 35 nm with a drastic drop in surface reflectivity. These studies are of great importance for the application of similar RF plasma sources with in-situ cleaning of diagnostic mirrors in fusion devices, as well as in a variety of plasma processing applications.

Friction force microscopy experiments on moiré superstructures of graphene-coated platinum surfaces demonstrate that in addition to atomic stick–slip dynamics, a new dominant energy dissipation route emerges. The underlying mechanism, revealed by atomistic molecular dynamics simulations, is related to moiré ridge elastic deformations and subsequent relaxation due to the action of the pushing tip. The measured frictional velocity dependence displays two distinct regimes: (i) at low velocities, the friction force is small and nearly constant; and (ii) above some threshold, friction increases logarithmically with velocity. The threshold velocity, separating the two frictional regimes, decreases with increasing normal load and moiré superstructure period. Based on the measurements and simulation results, a phenomenological model is derived, allowing us to calculate friction under a wide range of room temperature experimental conditions (sliding velocities of 1–104 nm/s and a broad range of normal loads) and providing excellent agreement with experimental observations.

The atomic buckling in 2D “Xenes” (such as silicene) fosters a plethora of exotic electronic properties such as a quantum spin Hall effect and could be engineered by external strain. Quantifying the buckling magnitude with subangstrom precision is, however, challenging, since epitaxially grown 2D layers exhibit complex restructurings coexisting on the surface. Here, we characterize using low-temperature (5 K) atomic force microscopy (AFM) with CO-terminated tips assisted by density functional theory (DFT) the structure and local symmetry of each prototypical silicene phase on Ag(111) as well as extended defects. Using force spectroscopy, we directly quantify the atomic buckling of these phases within 0.1-Å precision, obtaining corrugations in the 0.8- to 1.1-Å range. The derived band structures further confirm the absence of Dirac cones in any of the silicene phases due to the strong Ag-Si hybridization. Our method paves the way for future atomic-scale analysis of the interplay between structural and electronic properties in other emerging 2D Xenes.

Kelvin probe force microscopy is a scanning probe method for imaging the surface potential by atomic force microscopy. The surface potential is one of the most important surface properties and is correlated to e.g. the work function, surface dipoles, localized surface charges and structural properties. It gives detailed information on the electrical properties and can be combined with optical and electrical excitation mechanisms providing additional properties like surface band bending and charge carrier mobilities. We will introduce the main concept and will briefly describe the major methods of operation. Based on the analysis of a Si superjunction device, structures dopant profiling and the concept of surface photovoltage measurements will be introduced. The influence of local charge accumulation on these devices will be presented and the effect on the measured contact potential values will be discussed.

On-surface chemical reaction has become a very powerful technique to synthesize nanostructures by linking small molecules in the bottom-up approach. Given the fact that most reactants are simultaneously activated at certain temperatures, a sequential reaction in a controlled way has remained challenging. Here, we present an on-surface synthesis of multi-block co-oligomers from trifluoromethyl (CF3 ) substituted porphyrin metal complexes. The oligomerization on Au(111) is demonstrated with a combination of bond-resolved scanning probe microscopy and density functional theory (DFT) calculations. Even after the first oligomerization of single monomer unit, the termini of the oligomer keep the CF3 group, which can be used as a reactant for further coupling in a sequential order. Consequently, copper, cobalt, and palladium complexes of bisanthracene-fused porphyrin oligomers were linked with each other in a designed order.

Objectives: The transgingival part of titanium implants is either machined or polished. Cell-surface interactions as a result of nano-modified surfaces could help gingival fibroblast adhesion and support antibacterial properties by means of the physico-mechanical aspects of the surfaces. The aim of the present study was to determine how a nanocavity titanium surface affects the viability and adhesion of human gingival fibroblasts (HGF-1). Additionally, its properties against Porphyromonas gingivalis were tested. Material and Methods: Two different specimens were evaluated: commercially available machined titanium discs (MD) and nanostructured discs (ND). To obtain ND, machined titanium discs with a diameter of 15 mm were etched with a 1:1 mixture of 98% H2SO4 and 30% H2O2 (piranha etching) for 5 h at room temperature. Surface topography characterization was performed via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Samples were exposed to HGF-1 to assess the effect on cell viability and adhesion, which were compared between the two groups by means of MTT assay, immunofluorescence and flow cytometry. After incubation with P. gingivalis, antibacterial properties of MD and ND were determined by conventional culturing, live/dead staining and SEM. Results: The present study successfully created a nanostructured surface on commercially available machined titanium discs. The etching process created cavities with a 10–20 nm edge-to-edge diameter. MD and ND show similar adhesion forces equal to about 10–30 nN. The achieved nanostructuration reduced the cell alignment along machining structures and did not negatively affect the proliferation of gingival fibroblasts when compared to MD. No differences in the expression levels of both actin and vinculin proteins, after incubation on MD or ND, were observed. However, the novel ND surface failed to show antibacterial effects against P. gingivalis. Conclusion: Antibacterial effects against P. gingivalis cannot be achieved with nanocavities within a range of 10–20 nm and based on the piranha etching procedure. The proliferation of HGF-1 and the expression levels and localization of the structural proteins actin and vinculin were not influenced by the surface nanostructuration. Further studies on the strength of the gingival cell adhesion should be performed in the future. Clinical relevance: Since osseointegration is well investigated, mucointegration is an important part of future research and developments. Little is known about how nanostructures on the machined transgingival part of an implant could possibly influence the surrounding tissue. Targeting titanium surfaces with improved antimicrobial properties requires extensive preclinical basic research to gain clinical relevance.

The fusion reactor ITER will use nitrogen gas to spread the power loads on the tungsten (W) divertor, which extracts heat and ash produced by the fusion reaction. However, once ionised in the fusion plasma, the nitrogen ions and radicals will form stable compounds with the fusion fuel i.e. hydrogen isotopes deuterium (D) and tritium (T). As a result, ammonia isotopologues (e.g., ND 2 T) will be formed. As a polar molecule, ammonia will stick on the reactor walls, imposing concerns on the tritium safety limit for ITER 1 . Hence, it is crucial to investigate the conditions at which ammonia is produced and identify strategies to destroy/process it.

Background: Topological superconductivity emerging in one- or two-dimensional hybrid materials is predicted as a key ingredient for quantum computing. However, not only the design of complex heterostructures is primordial for future applications but also the characterization of their electronic and structural properties at the atomic scale using the most advanced scanning probe microscopy techniques with functionalized tips.Results: We report on the topographic signatures observed by scanning tunneling microscopy (STM) of carbon monoxide (CO) molecules, iron (Fe) atoms and sodium chloride (NaCl) islands deposited on superconducting Pb(111). For the CO adsorption a comparison with the Pb(110) substrate is demonstrated. We show a general propensity of these adsorbates to diffuse at low temperature under gentle scanning conditions.Conclusion: Our findings provide new insights into high-resolution probe microscopy imaging with terminated tips, decoupling atoms and molecules by NaCl islands or tip-induced lateral manipulation of iron atoms on top of the prototypical Pb(111) superconducting surface.

Properties of metal oxides, such as optical absorption, can be influenced through the sensitization with molecular species that absorb visible light. Molecular/solid interfaces of this kind are particularly suited for the development and design of emerging hybrid technologies such as dye-sensitized solar cells. A key optimization parameter for such devices is the choice of the compounds in order to control the direction and the intensity of charge transfer across the interface. Here, the deposition of two different molecular dyes, porphyrin and coumarin, as single-layered islands on a NiO(001) single crystal surface have been studied by means of non-contact atomic force microscopy at room temperature. Comparison of both island types reveals different adsorption and packing of each dye, as well as an opposite charge-transfer direction, which has been quantified by Kelvin probe force microscopy measurements.

Plasma catalysis has drawn attention in the past few decades as a possible alternative to the Haber-Bosch process for ammonia production. In particular, radio frequency plasma assisted catalysis has the advantage of its adaptability to the industrial scale. However, in the past years, very few experimental studies have focused on the synthesis of ammonia from nitrogen/hydrogen radio frequency plasma. As a consequence, to date, there has been little agreement about the complex mechanisms underlying the radio frequency plasma-catalyst interactions. Gaining such an understanding is therefore essential for exploiting the potential of radio frequency plasma catalysis for ammonia production. In this study, we present results of ammonia formation from a nitrogen/hydrogen radio frequency plasma both without and with a tungsten catalyst for different initial nitrogen ratios. High yields of ammonia up to 32% at 25/75% of nitrogen/hydrogen were obtained using a combination of radio frequency low pressure plasma and a W surface as a catalyst. Furthermore, based on chemical analysis of the catalytic surface composition, a formation pathway of ammonia via the Eley-Rideal mechanism between adsorbed nitrogen and hydrogen from the gas phase is presented.

Maintaining clean conditions for samples during all steps of preparation and investigation is important for scanning probe studies at the atomic or molecular level. For large or fragile organic molecules, where sublimation cannot be used, high-vacuum electrospray deposition is a good alternative. However, because this method requires the introduction into vacuum of the molecules from solution, clean conditions are more difficult to be maintained. Additionally, because the presence of solvent on the surface cannot be fully eliminated, one has to take care of its possible influence. Here, we compare the high-vacuum electrospray deposition method to thermal evaporation for the preparation of C60 on different surfaces and compare, for sub-monolayer coverages, the influence of the deposition method on the formation of molecular assemblies. Whereas the island location is the main difference for metal surfaces, we observe for alkali halide and metal oxide substrates that the high-vacuum electrospray method can yield single isolated molecules accompanied by surface modifications.

A novel reconstruction of a two-dimensional layer of KBr on an Ir(111) surface is observed by high-resolution noncontact atomic force microscopy and verified by density functional theory (DFT). The observed KBr structure is oriented along the main directions of the Ir(111) surface, but forms a characteristic double-line pattern. Comprehensive calculations by DFT, taking into account the observed periodicities, resulted in a new low-energy reconstruction. However, it is fully relaxed into a common cubic structure when a monolayer of graphene is located between substrate and KBr. By using Kelvin probe force microscopy, the work functions of the reconstructed and the cubic configuration of KBr were measured and indicate, in accordance with the DFT calculations, a difference of nearly 900 meV. The difference is due to the strong interaction and local charge displacement of the K+/Br− ions and the Ir(111) surface, which are reduced by the decoupling effect of graphene, thus yielding different electrical and mechanical properties of the top KBr layer.

Controlling friction on the nanometer scale is one of nowadays’ challenges for scientists and engineers. Since the first observation of atomic friction reported by Mate et al. for a tungsten tip sliding on graphite, a lot of progress has been made in the understanding of this phenomenon on the atomic scale. An accurate description of the motion of a sharp tip elastically driven on a crystal surface by a microcantilever was first given by Tomanek et al., who based their interpretation on the Prandtl–Tomlinson model. The lateral (friction) force acting on the tip can be estimated by measuring the angle of torsion of the cantilever. The tip sticks to a given equilibrium position on the surface lattice until the driving force becomes high enough to cause a slip into the closest equilibrium position along the pull direction. The resulting stick-slip motion corresponds to a sawtooth-shaped time evolution of the lateral force with the atomic periodicity of the surface lattice. However, this scenario is observed only if a precise condition is fulfilled. The lateral stiffness of the driving spring must be lower than the curvature of the tip-surface interaction potential. If this is not the case, the tip slides on the surface without abrupt jumps, and a “superlubric” scenario is observed.

The intercalation of graphene is an effective approach to modify the electronic properties of two-dimensional heterostructures for attractive phenomena and applications. In this work, we characterize the growth and surface properties of ionic KBr layers altered by graphene using ultra-high vacuum atomic force microscopy at room temperature. We observed a strong rippling of the KBr islands on Ir(111), which is induced by a specific layer reconstruction but disappears when graphene is introduced in between. The latter causes a consistent change in both the work function and the frictional forces measured by Kelvin probe force microscopy and frictional force microscopy, respectively. Systematic density functional theory calculations of the different systems show that the change in work function is induced by the formation of a surface dipole moment while the friction force is dominated by adhesion forces.

Future prospects of scanning probe microscopy are discussed. Arrays of cantilevers can be used for ultrasensitive bio-sensors or be used as a mechanical storage medium. The role of scanning probe microscopy in fields of nanoscience, nanotechnology but also quantum information will be elaborated.

In this chapter, some other members of the scanning probe microscopy family are briefly described. All probe microscopes are based upon probing tips, but some tips are rather different from standard STM tips. Methods such as scanning near-field optical microscopy (SNOM), scanning ion conductance microscopy (SICM) or photoemission microscopy with scanning aperture (PEMSA), are based on tips with apertures, where light, ions or electrons can pass through. The scanning near-field acoustic microscope (SNAM) is the acoustic analogue of the SNOM. Other methods essentially depend on a standard STM feedback and measure outcoming radiation, as in the case of STM with inverse photoemission (STMiP), or measure the influence of incoming light on the tunneling current, as in the case of laser STM (LSTM), or measure the temperature of the tip, as in the case of scanning thermal microscopy (SThM), or perform measurements in an electrolyte, as in the case of electrochemical STM (ECSTM). In scanning noise microscopy (SNM), the noise of the tunneling current is measured at a compensated thermovoltage. In scanning capacitance microscopy (SCM), the capacitance between probing tip and sample is measured. In scanning potentiometry microscopy (SPotM), the electrical potential, which depends on the resistivity of the sample, is measured. In scanning spreading resistance microscopy (SSRM), the spreading resistance is monitored. Finally, scanning tunneling atom probe (STAP) is an example of the combination of STM with a time-of-flight mass spectrometer, where the mass of single ions from the probing tip can be analyzed.

This chapter is related to the field of magnetic force microcopy (MFM), where the probing tip is covered with a magnetic layer and the magnetic domain structure of the sample can be characterized with high lateral resolution. In addition, other scanning probe methods mapping the magnetic field at a microscopic scale and techniques providing access to atomic scale magnetism are reviewed.

We present a combined experimental and numerical investigation of the plasma properties in an asymmetric capacitively coupled radio frequency plasma source using argon discharge. Besides driving the system in the conventional way, which results in a high negative self-bias voltage V DC due to the asymmetric configuration, we also connect a ‘quarter-wavelength filter’ to the powered electrode, which lifts its DC potential to zero. At the powered side of the plasma, we employ electrodes with conducting and insulating surfaces, as well as electrodes combining both in different proportions (‘hybrid electrodes’). Measurements are carried out for the plasma potential, the electron density and temperature in the bulk plasma, as well as for the flux-energy distribution of the ions at the grounded surface of the system. The nature of the surface of the powered electrode as well as the presence of the quarter-wavelength filter are found to highly influence the plasma potential, V p ‾ . For the electrode with a conducting surface V p ‾ ∼ 20 V and ∼150 V are found in the absence and the presence of the filter, respectively. For the electrode with an insulating surface, the self-bias voltage builds up directly at the plasma interface, thus the filter has no effect and a plasma potential of ∼20 V is found. For the electrodes with different conducting/insulating proportions of their surface, V p ‾ ranges between the above values. Particle-in-Cell/Monte Carlo Collisions calculations for identical conditions with hybrid electrodes predict double-peaked ion energy distribution at the powered electrode with peaks corresponding to e V p ‾ and e ( V p ‾ − V DC ) along with a lowering of the plasma potential (whencompared to wholly conducting electrode), a trend that is observed experimentally. These studies are of great importance for the application of similar plasma sources with in-situ cleaning of mirrors in fusion devices and the results can be extended to a variety of plasma processing applications.

Maintaining clean conditions for samples during all steps of preparation and investigation is important for scanning probe studies at the atomic or molecular level. For large or fragile organic molecules, where sublimation cannot be used, high-vacuum electrospray deposition is a good alternative. However, because this method requires the introduction into vacuum of the molecules from solution, clean conditions are more difficult to be maintained. Additionally, because the presence of solvent on the surface cannot be fully eliminated, one has to take care of its possible influence. Here, we compare the high-vacuum electrospray deposition method to thermal evaporation for the preparation of C60 on different surfaces and compare, for sub-monolayer coverages, the influence of the deposition method on the formation of molecular assemblies. Whereas the island location is the main difference for metal surfaces, we observe for alkali halide and metal oxide substrates that the high-vacuum electrospray method can yield single isolated molecules accompanied by surface modifications.

A trifunctional, partially fluorinated anthracene-substituted triptycene monomer was spread at an air/water interface into a monolayer, which was transformed into a long-range-ordered 2D polymer by irradiation with a standard UV lamp. The polymer was analyzed by Brewster angle microscopy, scanning tunneling microscopy measurements, and non-contact atomic force microscopy, which confirmed the generation of a network structure with lattice parameters that are virtually identical to a structural model network based on X-ray diffractometry of a closely related 2D polymer. The nc-AFM images highlight the long-range order over areas of at least 300×300 nm2 . As required for a 2D polymer, the pore sizes are monodisperse, except for the regions where the network is somewhat stretched because it spans over protrusions. Together with a previous report on the nature of the cross-links in this network, the structural information provided herein leaves no doubt that a 2D polymer has been synthesized under ambient conditions at an air/water interface.

On-surface chemical reaction has become a very powerful technique to conjugate small precursor molecules and several reactions have been proposed with the aim to fabricate functional nanostructures on surfaces. Here we present an unforeseen adsorption mode of 9,10-bis-((trimethylsilyl)ethynyl)anthracene on a Cu(111)surface and the resulting one-shot desilylative homocoupling of of the adsorbate by annealing at 400 K. With a combination of high-resolution atomic force microscopy and density functional theory calculations, we found that the triple bonds and silicon atoms of the monomer chemically interact with the copper surface. After the oligomerization, we discovered that the anthracene units are linked to each other via buta-1,3-diynediyl fragments while keeping the surface clean. Furthermore, the force measurement revealed the chemical nature at the center of anthracene unit.

Investigation of the local sample elasticity is of high importance in many scientific domains. In 2014, Herruzo et al. published a new method based on frequency-modulation atomic force microscopy to locally determine the elasticity of samples (Nat. Commun. 2014, 5, 3126). This method gives evidence for the linearity of the relation between the frequency shift of the cantilever first flexural mode Δf1 and the square of the frequency shift of the second flexural mode Δf22. In the present work, we showed that a similar linear relation exists when measuring in contact mode with a certain load FN and propose a new method for determining the elastic modulus of samples from this relation. The measurements were performed in non-dry air at ambient temperature on three different polymers (polystyrene, polypropylene and linear low-density polyethylene) and a self-assembled monolayer of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) on a silicon oxide substrate perforated with circular holes prepared by polymer blend lithography. For all samples the relation was evidenced by recording Δf1, Δf2 and FN as a function of the Z-displacement curves of the piezoelectric scanner. The occurence of a plastic deformation followed by an elastic deformation is shown and explained. The necessary load FN for measuring in the elastic domain was assessed for each sample, used for mapping the frequency shifts Δf1 and Δf2 and for determining the elastic modulus from Δf22/Δf1. The method was used to give an estimate of the Young’s modulus of the FDTS thin film.

This work aims at investigating the role of tungsten and boron surfaces on ammonia production with N2–H2 radiofrequency plasmas at 3 Pa. The experiments combine the analysis of the reaction products and surface chemical environment using mass spectrometry and x-ray photoelectron spectroscopy (XPS). We show that NH3 is formed upon discharges of N2 or H2 after having exposed a tungsten (W) foil to H2 or N2, respectively. A higher amount of ammonia is formed for the N2-then-H2 case, which we explain by the larger number of Eley–Rideal reaction channels for the formation of NH x (s) and the lower surface diffusion barrier for adsorbed hydrogen, calculated using the density functional theory (DFT). As a result, H(s) combines with N(s) or NH x (s) through Langmuir–Hinshelwood at a faster rate than N(s) combines with another N(s). The amount of NH3 formed with N2–H2 discharges after conditioning the tungsten foil with H2, N2 or O2 was also investigated. We observed that this pre-conditioning plays no major role on the amount of NH3 detected with the residual gas analyser, albeit a small decrease was observed after H2 contamination. With DFT, the adsorption energies of H on WO3 and W are found to be similar, while the adsorption of N on WO3 is significantly weaker. The similar NH3 concentrations obtained with a clean and oxidized tungsten surface thus suggest that the adsorption of N does not limit the formation rate of ammonia. The production of NH3 on boron was evaluated as well. The boron surface reduced the amount of detected ammonia almost by half. On the one side, a significant amount of H2 was removed from the surface during the Ar cleaning that followed, which suggests a strong retention of hydrogen. On the other side, the XPS data reveals that nitrogen forms strong bonds with boron and impurities on the surface, regardless on whether hydrogen is previously present on the surface or in the plasma volume. The presence of hydrogen in the plasma volume, simultaneously with nitrogen or after nitrogen exposure, is nevertheless necessary for the formation of NH(s) and NH2(s). No NH3(s) was however detected with XPS. The increased retention of both hydrogen and nitrogen on the boron surface may thus hinder the formation of NH3.

In ITER, several first mirrors (FMs) are expected to be DC-grounded with the water cooling lines being implemented as a quarter wavelength ($lambda$/4) RF-filter. DC-grounding of the FMs can significantly increase the plasma potential V p, which could trigger an increased wall sputtering and associated re-deposition on the FMs during plasma cleaning. To understand the scope of this impact, helium discharges were excited with DC-grounded FMs in an ITER-sized mock-up of a first mirror unit (FMU) using wall materials with different sputtering energy thresholds (E th). Additionally, a part of the FM was electrically isolated from the RF to study its impact on the erosion/re-deposition properties on the surface. The E th of the wall materials, as well as its native oxide layers, had a significant influence on the re-deposition observed on the FMs. With high E th where walls were unsputtered, both the DC-grounded and electrically isolated parts of the FM were free of deposits. However, with low E th where the walls were sputtered, there was a net wall re-deposition on the DC-grounded parts of the FM, while electrically isolated parts were still relatively clean. Further, to study the impact of floating wall components, Cu walls in the FMU were isolated from the ground. Here the walls developed a floating potential V f and the ion energy at the walls was lowered to e(V p - V f). The floating walls, in this case, were relatively unsputtered and the FMs experienced a net cleaning with total reflectivity of the mirror preserved at pristine mirror levels. This work shows that electrically isolating the FM as well as the wall surface minimizes wall re-deposition in presence of $lambda$/4 filter and therefore are promising techniques for effective FM cleaning in ITER.

This paper presents the measurement of the bidirectional reflectance distribution function of tungsten (W) samples and the resulting reflection models in the nuclear fusion device WEST (tokamak). For this, an experimental gonio-spectrophotometer was developed to fully characterize the material’s optical and thermal-radiative properties of metallic samples with different roughnesses. Ray-tracing photonic simulation was then carried out to predict the photon behavior in a fully metallic environment as a function of reflectance measurement. Low emissivity (0.1 at 4 μm) and highly specular reflectance (fitting with a Gaussian distribution around the specular direction with a small width lower than 10°) are found for W samples. These measurements have been used as input for the photonic simulation, and the resulting synthetic image reproduced the reflection features well on the upper divertor, detected in WEST infrared experimental images.