Monolayer Of Sulfur Research Articles

XXVI Международный симпозиум Нанофизика и наноэлектроника", Нижний Новгород, 14-17 марта 2022 г. Влияние химической пассивации поверхности GaAs(001) на анизотропию и ориентацию образующихся на ней нанокластеров золота и их плазмонов

A principal role of chemical passivation of GaAs surface in the formation of oriented anisotropic on-surface nanoclusters of gold is discussed. The gold nanoclusters are fabricated by thermal annealing of the gold film deposited onto GaAs(001) surface passivated preliminary by an atomic monolayer of nitrogen or sulphur. These atoms forming a crystal lattice are bonded chemically to gallium atoms of the crystal surface to prevent chemical interaction of Au with GaAs. Annealing Au on passivated GaAs(001) surface results in formation of arrays of anisotropic (elongated) nanolusters of chemically pure Au oriented preferably in crystal direction. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and the optical techniques of reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Within an optical model of plasmon polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons polarized in Au nanoclusters predominantly in direction on GaAs(001) surface.

Ultrathin covalent and cuprophilic interaction-assembled copper-sulfur monolayer in organic metal chalcogenide for oriented photoconductivity.

We report the thinnest copper sulfur atomic monolayer in an organic copper chalcogenide [Cu(CMP)]n (CMP = 5-chloro-2-mercaptopyridine). The layer features a new type of copper sulfur structure woven by both covalent bond and cuprophilic interaction and shows an intriguing oriented photoconductivity.

Composite Electroforming As Novel and Innovative Synthesis Method of Additive-Free Cathodes for Li-S Batteries

The increasing requirements for high power and energy storage systems have led to the implementation of a considerable number of electrode materials. Several crucial parameters such as energy, power density, rate capability and cyclability can be significantly influenced by modifying, in addition to the active materials chemistry, the manufacturing process of the electrode in the metal matrix. The novel electrodes for Li-S batteries proposed in the present work are intended to make a significant contribution to overcoming the concept-related disadvantages of the state-of-the-art conventional coating processes. Their basic development and suitability were investigated by our research group in various projects [1-4].The recently self-developed composite electroforming [5] is a very promising electrodes production process. It is significantly improving the existing conventional coating technology in terms of reduced technological steps, low costs and better electrochemical performance. The aforementioned manufacturing process consists on electroforming the metal matrix, which operates as a current collector foil, in a one-step process. Simultaneously, the active material is incorporated into the metal matrix by means of composite plating [6]. In contrast to the state-of-the-art approach using non-conducting binders such as PVDF and non-binding conductive agents such as carbon black, conductivity and mechanical stability can be synergistically optimized.In the present work, composite electroformed foils, composed of Ni matrix and sulfur loaded on Al alloy carrier particles AlSi10Mg, are used as cathodes for Li-S batteries. The synthesis procedure consists on the selective etching of the Al particles which are used as dispersoids in the composite electroforming process. BET results proved that after etching, the specific area is remarkably increased. Afterwards, the etched Al alloy particles are cemented with cobalt nanocrystallites, as these act as ideal electrocatalysts for the sulfur half cell [7].In a way to optimize the composite electroformed cathodes, which should ideally consist of a dense monolayer of sulfur loaded carrier particles without Ni overgrowth, several parameters can be evaluated. In the present work, parameters such as particle concentration in the electrolyte, current density, nickel concentration, pH value, temperature and convection are kept constant. Only the current and thus the corresponding time to achieve the desired composite thickness are varied. Moreover, the experimental conditions were extended to the application of pulse and pulse reverse plating.Therefore, in order to evaluate the parameter-structure relationships and to assess the efficacy of the presented approach, a broad range of morphological testing by SEM of all the composite electroformed cathodes was carried out. Furthermore, the electrochemical behavior of the novel cathodes that were galvanostatically cycled at slow and moderate rates was investigated and will be presented.[1] C. Erhardt, Ş. Sörgel, S. Meinhard, T. Sörgel, J. Power Sources, 296 (2015) 70-77.[2] T. Sörgel, ZVO report, 1 (2019) 46.[3] S. Meinhard, O. Kesten, K. Jäger, I. Hägele, T. Sörgel, Galvanotechnik, 8 (2020) 1164-1169.[4] A. K. Jäger, S. Meinhard, O. Kesten, I. Hägele, T. Sörgel, WoMag, 4 (2020) 25-26.[5] T. Sörgel, S. Meinhard, Ş. Sörgel, Film Composite Material, EP 3114721 B1, 2015.[6] T. Sörgel, J. Meyer, WOMag, 9 (2013) 24–33.[7] Ş. Sörgel, O. Kesten, A. Wengel, T. Sörgel, Energy Storage Mater. 2018, 10, 223-232.

Electronic and optical properties of sulfur vacancy-defect monolayer PtS2: A first-principles study

In this work, Density Functional Theory (DFT) simulations are performed to study the sulfur vacancy in monolayer PtS2. The structural, electronic, and optical properties of monolayer PtS2 with sulfur vacancy have been investigated. The sulfur vacancy slightly affects the structure near the vacancy and the remaining atoms show inward relaxation. The formation energies of a single sulfur vacancy are 1.65–1.73 eV in S-rich conditions and 0.69–0.77 eV in the Pt-rich environment. The sulfur vacancy induced three defect bands in the bandgap. It is found that when the concentration of Vs increases, then the gap between the highest occupied and lowest unoccupied state decreases. The sulfur vacancy increases the in-plane static dielectric constant and causes extra ε2//peaks which appear in the range of 0.5–1.8 eV, i.e., infrared absorption. Finally, we show that an O atom, O2 molecule, and three hydrogens can cause the partial passivation of sulfur vacancy. Though the three schemes cannot remove all the defective states of the gap, the bandgaps of the defective PtS2 monolayer became similar to the perfect one. We suggest that the proposed passivation methods may further facilitate their practical applications.

Identification of an AgS2 Complex on Ag(110)

Adsorbed sulfur has been investigated on the Ag(110) surface at two different coverages, 0.02 and 0.25 monolayers. At the lower coverage, only sulfur adatoms are present. At the higher coverage, there are additional bright features which we identify as linear, independent AgS2 complexes. This identification is based upon density functional theory (DFT) and its comparison with experimental observations including bias dependence and separation between complexes. DFT also predicts the absence of AgS2 complexes at low coverage, and the development of AgS2 complexes around a coverage of 0.25 monolayers of sulfur, as is experimentally observed. To our knowledge, this is the first example of an isolated linear sulfur-metal-sulfur complex.

Wafer-Scale Sulfur Vacancy-Rich Monolayer MoS2 for Massive Hydrogen Production.

As one of the promising low-cost and high-efficiency catalysts for the electrochemical hydrogen evolution reaction (HER), it is well-known that there are both tiny exposed catalytic active edge sites and large-area inert basal planes in two-dimensional MoS2 structures. For enhancing its HER activity, extensive work has been done to activate the inert basal plane of MoS2. In this article, wafer-scale (2 in.) continuous monolayer MoS2 films with substantial in situ generated sulfur vacancies are fabricated by employing the laser molecular beam epitaxy process benefitting from ultrahigh vacuum growth condition and high substrate temperature. The intrinsic sulfur vacancies throughout the wafer-scale basal plane present an ideal electrocatalytic platform for massive hydrogen production. The fabricated vacancy-rich monolayer MoS2 can achieve a current density of -10 mA/cm2 at an overpotential of -256 mV. The wafer-scale fabrications of sulfur vacancy-rich monolayer MoS2 provide great leaps forward in the practical application of MoS2 for massive hydrogen production.

The Electronic Properties of O-Doped Pure and Sulfur Vacancy-Defect Monolayer WS₂: A First-Principles Study.

Based on the density functional theory (DFT), the electronic properties of O-doped pure and sulfur vacancy-defect monolayer WS2 are investigated by using the first-principles method. For the O-doped pure monolayer WS2, four sizes (2 × 2 × 1, 3 × 3 × 1, 4 × 4 × 1 and 5 × 5 × 1) of supercell are discussed to probe the effects of O doping concentration on the electronic structure. For the 2 × 2 × 1 supercell with 12.5% O doping concentration, the band gap of O-doped pure WS2 is reduced by 8.9% displaying an indirect band gap. The band gaps in 3 × 3 × 1 and 4 × 4 × 1 supercells are both opened to some extent, respectively, for 5.55% and 3.13% O doping concentrations, while the band gap in 5 × 5 × 1 supercell with 2.0% O doping concentration is quite close to that of the pure monolayer WS2. Then, two typical point defects, including sulfur single-vacancy (VS) and sulfur divacancy (V2S), are introduced to probe the influences of O doping on the electronic properties of WS2 monolayers. The observations from DFT calculations show that O doping can broaden the band gap of monolayer WS2 with VS defect to a certain degree, but weaken the band gap of monolayer WS2 with V2S defect. Doping O element into either pure or sulfur vacancy-defect monolayer WS2 cannot change their band gaps significantly, however, it still can be regarded as a potential method to slightly tune the electronic properties of monolayer WS2.

NaHS Induces Complete Nondestructive Ligand Displacement from Aggregated Gold Nanoparticles

Ligand displacement from gold is important for a series of gold nanoparticle (AuNP) applications. Complete nondestructive removal of organothiols from aggregated AuNPs is challenging due to the strong Au–S binding, the steric hindrance imposed by ligand overlayer on AuNPs, and the narrow junctions between the neighboring AuNPs. Presented herein is finding that monohydrogen sulfide (HS–), an anionic thiol, induces complete and nondestructive removal of ligands from aggregated AuNPs. The model ligands include aliphatic (ethanethiol(ET)) and aromatic monothiols, methylbenzenethiol (MBT), organodithiol (benzenedithiol (BDT)), thioamides (mercaptobenzimidazole (MBI) and thioguanine (TG)), and nonspecific ligand adenine. The threshold HS– concentration to induce complete ligand displacement varies from 105 μM for MBI and TG to 60 mM for BDT. Unlike using HS–, complete ligand displacement does not occur when mercaptoethanol, the smallest water-soluble organothiol, is used as the incoming ligand. Mechanistically, HS– binding leads to the formation of sulfur monolayer on AuNPs that is characterized with S–S bonds and S–Au bonds, but with no detectable S–H spectral features. The empirical HS– saturation packing density and Langmuir binding constant on AuNPs are 960 ± 60 pmol/cm2 and (5.5 ± 0.8) × 106 M–1, respectively. The successful identification of an effective ligand capable of inducing complete and nondestructive removal of ligands from AuNPs should pave the way for using AuNP for capture-and-release enrichment of biomolecules that have high affinity to AuNP surfaces.

Enhanced Negative Photoconductivity in InAs Nanowire Phototransistors Surface‐Modified with Molecular Monolayers

AbstractNegative photoconductivity (NPC) mechanisms are widely investigated for high‐performance InAs nanowire (NW) phototransistors, where these mechanisms are usually attributed to severe carrier scattering centers, light‐assisted hot electron trapping in the surface oxide, and/or defects induced photogating layer. However, further insights into their photodetecting mechanisms, as well as corresponding performance enhancement of these NW phototransistors, are still very limited. This work reports the NPC behavior in surface‐modified InAs NW phototransistors based on photoexcitation induced majority electron trapping in the bonded sulfur monolayer under optical illumination. In order to enhance hot electron trapping ability of the bonded sulfur layer, aromatic thiolate (ArS−)‐based molecular monolayer with strong electron‐withdrawing group is employed using simple wet chemistry for the surface modification of InAs NW phototransistors. The magnitude of the photoexcitation induced hot electron trapping is increased by the stronger electron‐withdrawing ability of the ArS−‐based molecular monolayer, enabling the hot electrons to be trapped and released more efficiently, resulting in NW phototransistors with good sensitivity, fast photoresponse, and long‐term stability to low intensity visible light. These results confirm the potential of InAs NW phototransistors surface‐passivated with molecular monolayers in the application and realization of high‐sensitive and long‐term stable room temperature nanoscale photodetectors.

Coverage evolution of the unoccupied Density of States in sulfur superstructures on Ru(0001)

Sulfur adsorbed on Ru(0001) presents a large number of ordered structures. This characteristic makes S/Ru(0001) the ideal system to investigate the effect of different periodicities on the electronic properties of interfaces. We have performed scanning tunneling microscopy/spectroscopy experiments and density functional theory calculations showing that a sulfur adlayer generates interface states inside the Γ directional gap of Ru(0001) and that the position of such states varies monotonically with sulfur coverage. This is the result of the interplay between band folding effects arising from the new periodicity of the system and electron localization on the sulfur monolayer. As a consequence, by varying the amount of sulfur in S/Ru(0001) one can control the electronic properties of these interfacial materials.

Cross-sectional measurement of grain boundary segregation using WDS

A new method is proposed for the quantification of grain boundary segregation using Wavelength Dispersive Spectroscopy (WDS) in a Scanning Electron Microscope (SEM). Analyses are undertaken on a simple metallographically polished section of material. The method is demonstrated for the model system of sulphur segregation to nickel grain boundaries. Quantification was carried out from sulphur concentration profiles acquired across 11 grain boundaries of a nickel specimen containing 5.4wtppm of sulphur in the bulk and equilibrated at 550°C. The average sulphur grain boundary concentration determined is µ=35.2ngcm−2=6.6×1014 atoms cm−2≈0.5 monolayer, which is in good agreement with a previous quantification obtained from SIMS (Secondary Ion Mass Spectrometry) on the same material. However this is lower by a factor of two than the quantification obtained using “surface” techniques on fractured specimens of the same material. With the conditions of analysis used in this study, the limit of detection of the method developed is found to be better than 10% of a sulphur monolayer.

Determination of free electron density in sequentially doped InxGa1-xAs by Raman spectroscopy.

The advent and exponential growth of mobile computing has spurred greater emphasis on the adoption of III-V compound semiconductors in device architectures. The introduction of high charge carrier densities within InxGa1-xAs and the development of metrologies to quantitate the extent of doping have thus emerged as an urgent imperative. As an amphoteric dopant, Si begins to occupy anionic sites at high concentrations, thereby limiting the maximum carrier density that can be obtained upon Si doping of III-V semiconductors. Here, we present Raman results on sequentially doped In0.53Ga0.47As wherein sulfur monolayer doping is used to introduce additional carrier density to Si-doped samples. The sequential doping of Si and S allows for high carrier concentrations of up to 1.3 × 10(19) cm(-3) to be achieved without damaging the III-V lattice. The coupling of the plasmon in the doped samples to the longitudinal optic phonons allows Raman spectroscopy to serve as an excellent probe of the extent of dopant activation, charge carrier density, and the surface depletion region. In particular, the energy position of a high-frequency coupled mode (HFCM) that is detected above 400 cm(-1) is used to extract the free electron density in these samples. The extracted free electron densities are well correlated with measured sheet resistance values and the carrier densities deduced from Hall measurements.

Wet-transfer of CVD-grown graphene onto sulfur-protected W(110)

Abstract Graphene, grown by chemical vapor deposition, is transferred onto W(110) surface with a protective sulfur layer. Sulfur was adsorbed on the W(110) surface in ultrahigh vacuum (UHV) by reaction with H2S at 1 × 10− 8 Torr at 800 °C. Low-energy electron diffraction and scanning tunneling microscopy (STM) measurements show that an ordered sulfur adsorbate layer is formed on W(110) with a 1 × 5 superstructure. The monolayer of sulfur subsequently protects the W(110) surface from oxidation during wet-transfer of CVD-grown graphene. After the graphene transfer, the sample is re-introduced to UHV and characterized by STM, Auger electron spectroscopy, x-ray and ultraviolet photoemission spectroscopy. The adsorbed sulfur layer prevents carbide formation, by reaction of graphene with tungsten, to annealing temperatures of at least ~ 750 °C in vacuum. Finally, photoemission measurements of the graphene/S/W(110) interface indicates p-type doping of graphene due to charge transfer at the interface as a consequence of the high work function of the W(110)-S substrate.

Kinetics of oxygen interstitial injection and lattice exchange in rutile TiO2

The existence of a facile surface pathway for generation of O interstitials (Oi) in rutile that can facilitate annihilation of O undesirable vacancies has been demonstrated recently. Through isotopic self-diffusion experiments, the present work determines a value of approximately 1.8 eV for the activation energy of Oi injection from TiO2 (110). The mean path length for Oi diffusion decreases by nearly an order of magnitude upon adsorption of 0.1 monolayer of sulfur. Sulfur apparently inhibits the surface annihilation rate of Ti interstitials, lowering their bulk concentration and the corresponding catalytic effect they seem to exert upon Oi exchange with the lattice.

Activation of H2 oxidation at sulphur-exposed Ni surfaces under low temperature SOFC conditions

Ni-YSZ (yttria-stabilized zirconia) cermets are known to be very good anodes in solid oxide fuel cells (SOFCs), which are typically operated at 700-1000 °C. However, they are expected to be increasingly degraded as the operating temperature is lowered in the presence of H2S (5-10 ppm) in the H2 fuel stream. However, at 500 to 600 °C, a temperature range rarely examined for sulphur poisoning, but of great interest for next generation SOFCs, we report that H2S-exposed Ni-YSZ anodes are catalytic towards the H2 oxidation reaction, rather than poisoned. By analogy with bulk Ni3S2/YSZ anodes, shown previously to enhance H2 oxidation kinetics, it is proposed that a thin layer of Ni sulphide, akin to Ni3S2, is forming, at least at the triple point boundary (TPB) region under our conditions. To explain why Ni3S2/YSZ is so active, it is shown from density functional theory (DFT) calculations that the O(2-) anions at the Ni3S2/YSZ TPB are more reactive towards hydrogen oxidation than is O(2-) at the Ni/YSZ TPB. This is accounted for primarily by structural transformations of Ni3S2 during H2 oxidation, rather than by the electronic properties of this interface. To understand why a thin layer of Ni3S2 could form when a single monolayer of sulphur on the Ni surface is the predicted surface phase under our conditions, it is possible that the reaction of H2 with O(2-), forming water, prevents sulphur from re-equilibrating to H2S. This may then promote Ni sulphide formation, at least in the TPB region.

Ultra-fast sulphur grain boundary segregation during hot deformation of nickel

Sulphur grain boundary segregation during hot-compression of nickel (5.4wt.ppmS) is monitored using Auger electron spectroscopy and wavelength dispersive X-ray spectroscopy. The deformation conditions (temperature/deformation rate) investigated are: 550°C/0, 550°C/3×10−5s−1, 550°C/3×10−4s−1 and 450°C/3×10−5s−1. It is shown that plastic deformation accelerates the kinetics of sulphur grain boundary segregation by a factor of ∼103 to a few 105, depending on the deformation conditions. Very high levels of segregation (∼0.8 monolayer of sulphur) are obtained after very low deformation (∼5%). In addition a linear dependence of the segregation level with time and deformation is demonstrated. The segregation kinetics during plastic deformation is proportional to the deformation rate and almost independent of temperature. Several metallurgical mechanisms are discussed and confronted with the experimental results: dislocations dragging, pipe diffusion, dislocation collection/diffusion and acceleration by excess vacancies. It appears that the models developed in this work on the basis of the two latter mechanisms (dislocation collection/diffusion and acceleration by excess vacancies) predict the experimental data correctly.

Analysis of sulfur-induced selectivity changes for anhydrous methanol dehydrogenation on Ni(100) surfaces

The absorption of sulfur on the Ni(100) surface has been reported to influence its product selectivity for methanol dehydrogenation. While dehydrogenation on the clean Ni(100) surface primarily produces a mixture of carbon monoxide and hydrogen, preadsorption of 0.25–0.33 monolayers of sulfur shifts the selectivity to mainly formaldehyde and hydrogen. Density functional theory calculations of clean and sulfur-modified Ni(100) surfaces demonstrate that sulfur destabilizes methanol dehydrogenation reaction intermediates in a manner consistent with this shift in selectivity. Microkinetic modeling of the reaction system further indicates that these changes alter the reaction selectivities from CO to CH2O production in the steady state. The reaction selectivities of metal alloy surfaces, which also have heterogeneous surface morphologies, are hypothesized to be influenced in a similar manner as these S/Ni(100) surfaces.

A study of capping layers for sulfur monolayer doping on III-V junctions

Recently, high dosage doping on Si multi-gate field effect transistors and III–V planar structures using a self-limiting monolayer doping technique was reported to overcome challenges in scaling nano-sized transistors. The stoichiometry or composition of the capping layer was found to affect the diffusion efficiency of this process. In this work, we study the effect of a capping layer in sulfur monolayer doping on III–V junctions. Various capping temperatures and growth methods were compared. Based on the theoretical and experimental results, we suggest an optimized scheme consisting of a bi-layer capping structure. From Hall measurements and secondary ion mass spectrometry, a SiNx/BeO bi-layer capping, compared to single layer cap, exhibited the best results with a surface sheet resistance of 232 Ω/sq, junction depth of 11 nm, dopant profile abruptness of 3.5 nm/dec, electrically active S concentration of 4.9 × 1019/cm3 (=1.34 × 1013/cm2), and 3 times higher activation efficiency without significant transient-enhanced dopant diffusion.

Influence of Sulfur Poisoning on CO Adsorption on Pd(100)

Investigations of CO adsorption on sulfur covered Pd(100) surface were conducted in order to obtain insight into the deleterious effects of sulfur on this system. First-principles density functional theory calculations indicate that CO is markedly destabilized when it shares surface atoms with neighboring sulfur. Based on the analysis of the electronic properties, the decrease in binding is attributed to localized S–Pd bonding plus the interaction between CO and S. The internal C–O stretching frequency was blue shifted relative to that on the clean surface as a result of the weakening of the C–Pd bonds. The poisoning effect is predicted to diminish for distant sites. Kinetic Monte Carlo simulations (with adsorbate lateral interactions included) revealed that the introduction of S creates competition for adsorption sites. At a finite temperature, CO adsorption is essentially nullified when the surface is covered by a quarter of monolayer of sulfur in agreement with experiments. Aside from reduction of possible adsorption sites, sulfur severely inhibits the mobility of CO as well.

聚苯乙烯单层空心微球掺硫层不均匀结构研究

聚苯乙烯单层空心微球掺硫层不均匀结构研究