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Competitive metal-coordination of hexaaminotriphenylene on Cu(111) by intrinsic copper versus extrinsic nickel adatoms
摘要： The interplay between self-assembly and surface chemistry of 2,3,6,7,10,11-hexaaminotriphenylene (HATP) on Cu(111) was complementarily studied by high-resolution Scanning-Tunneling-Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS) under ultra-high vacuum conditions. To shed light on competitive metal-coordination, comparative experiments were carried out on pristine and nickel-covered Cu(111). Directly after room temperature deposition of HATP onto pristine Cu(111) self-assembled aggregates were observed by STM, while XPS indicated non-deprotonated amino groups. Annealing up to 200 °C activated the progressive single deprotonation of all amino groups as indicated by chemical shifts of both N 1s and C 1s core levels in the XP spectra. This enabled the formation of topologically diverse π-d conjugated coordination networks with intrinsic copper adatoms. The basic motif of these networks was a metal-organic trimer, where three HATP molecules were coordinated by Cu3 clusters, as corroborated by accompanying Density Functional Theory (DFT) simulations. Additional deposition of more reactive nickel atoms resulted in both chemical and structural changes with deprotonation and formation of bis(diimino)-Ni bonded networks already at room temperature. Even though fused hexagonal metal-coordinated pores were observed, extended honeycomb networks remained elusive, as tentatively explained by a restricted reversibility of these metal-organic bonds.
关键词： Scanning Tunneling Microscopy,Cu(111),metal-coordination,hexaaminotriphenylene,X-ray Photoelectron Spectroscopy
更新于2025-09-10 09:29:36
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Landscape of s-triazine molecule on Si(100) by a theoretical x-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectra study
摘要： The chemisorbed structure for an aromatic molecule on a silicon surface plays an important part in promoting the development of organic semiconductor material science. The carbon K-shell x-ray photoelectron spectroscopy (XPS) and the x-ray absorption near-edge structure (XANES) spectra of the interfacial structure of an s-triazine molecule adsorbed on Si(100) surface have been performed by the ?rst principles, and the landscape of the s-triazine molecule on Si(100) surface has been described in detail. Both the XPS and XANES spectra have shown their dependence on different structures for the pristine s-triazine molecule and its several possible adsorbed con?gurations. By comparison with the XPS spectra, the XANES spectra display the strongest structural dependency of all of the studied systems and thus could be well applied to identify the chemisorbed s-triazine derivatives. The exploration of spectral components originated from non-equivalent carbons in disparate local environments has also been implemented for both the XPS and XANES spectra of s-triazine adsorbed con?gurations.
关键词： silicon surface,x-ray absorption near-edge structure (XANES),x-ray photoelectron spectroscopy (XPS),s-triazine
更新于2025-09-09 09:28:46
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High-Temperature Cs <sub/>x</sub> C <sub/>58</sub> Fullerides
摘要： Cs doped non-IPR fullerides have been grown by co-depositing C58 cations and Cs atoms on HOPG. The C58 cages, as building blocks of the material, form a predominantly covalently stabilized scaffold, C58–C58, which is doped by Cs atoms thermally diffusing across the bulk. The heating of the solid CsxC58 sample is accompanied by sublimation of Cs, C58, and C60 species from the topmost layers of the sample. However, the major part (>94%) of the material survives the heating procedure and constitutes a doped high-temperature carbon solid, HT-CsxC58. The new non-IPR material exhibits surprisingly high thermal stability. It survives a heating flash up to 1100 K at which the classic IPR-CsxC60 phase does not exist anymore. However, the thermally treated HT-CsxC58 phase exhibits a considerably depleted Cs content (x < 2) and a significantly modified carbon scaffold. The apparent stability of the scaffold results from covalent C–C bonds interlinking adjacent carbon cages. Cs atoms in the HT-CsxC58 phase contribute to this stability only as minority species, forming comparably weak ionic bonds with C58–C58 oligomers. However, this interaction facilitates the formation of structural defects (new non-IPR sites) in carbon cages. The surface topography of the HT-CsxC58 as monitored by SPEM, AFM, and SEM is governed by islands standing out by their elevated Cs/C ratio.
关键词： X-ray photoelectron spectroscopy,fullerenes,desorption,isolated pentagon rule,cesium doping
更新于2025-09-09 09:28:46
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Engineering the Palladium–WSe <sub/>2</sub> Interface Chemistry for Field Effect Transistors with High Performance Hole Contacts
摘要： Palladium has been widely employed as a hole contact to WSe2 and has enabled, at times, the highest WSe2 transistor performance. However, there are orders of magnitude variation across the literature in Pd–WSe2 contact resistance and ION/IOFF ratios with no true understanding of how to consistently achieve high–performance contacts. In this work, WSe2 transistors with impressive ION/IOFF ratios of 106 and Pd–WSe2 Schottky diodes with near–zero variability are demonstrated utilizing Ohmic–like Pd contacts through deliberate control of the interface chemistry. The increased concentration of a PdSex intermetallic is correlated with an Ohmic band alignment and concomitant defect passivation, which further reduces the contact resistance, variability, and barrier height inhomogeneity. The lowest contact resistance occurs when a 60 minute post metallization anneal at 400 °C in forming gas (FG) is performed. X-ray photoelectron spectroscopy indicates this FG anneal produces 3× the concentration of PdSex and an Ohmic band alignment, in contrast to that detected after annealing in ultra–high vacuum, during which a 0.2 eV hole Schottky barrier forms. Raman spectroscopy and scanning transmission electron microscopy highlight the necessity of the fabrication step to achieve high–performance contacts as no PdSex forms and WSe2 is unperturbed by room temperature Pd deposition. However, at least one WSe2 layer is consumed by the necessary interface reactions that form PdSex requiring strategic exploitation of a sacrificial WSe2 layer during device fabrication. The interface chemistry and structural properties are correlated with Pd–WSe2 diode and transistor performance and the recommended processing steps are provided to enable reliable high–performance contact formation.
关键词： annealing,palladium,WSe2,interface chemistry,X-ray photoelectron spectroscopy,transistor,metal contact
更新于2025-09-09 09:28:46
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Band alignment of BiOCl/ZnO core shell nanosheets by X-ray photoelectron spectroscopy measurements
摘要： To improve optoelectronic properties of bismuth oxyhalides, hybrid BiOX photocatalytic materials have draw a great attention, because of the separation of photogenerated electron-hole pairs. The band offset and band alignments are considered as the key parameters to elaborate carrier transport properties in heterojunction. In this paper, to determine the band alignment of BiOCl and ZnO heterostructure, BiOCl/ZnO core shell nanosheets with different thickness of shell layer were synthesized. The valence band offset (VBO or DEV) of BiOCl/ZnO heterostructure was determined using X-ray Photoelectron Spectroscopy measurements. The DEV value of 0.294 § 0.10 eV was calculated by using the Zn 2p3/2, Bi 4f5/2 binding energies as references. Taking the band gaps of 3.37 eV and 3.4 eV for ZnO and BiOCl samples into consideration, respectively, we obtained the type-II band alignment of BiOCl/ZnO heterostructure with a conduction band offset (CBO or DEc) of 0.324 § 0.10 eV.
关键词： X-ray photoelectron spectroscopy (XPS),band offset,BiOCl,ZnO,atomic layer deposition (ALD)
更新于2025-09-09 09:28:46
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Persistent hydrophilicity for Titanium oxide (TiO2) thin films by Silicon oxide (SiO2) over nanolayers
摘要： SiO2 thin layers in thicknesses (1, 5, 10, 18 nm) on TiO2 thin layer in thickness 79 nm deposited by reactive RF sputtering technique. The deposited films were heat treated at temperatures (200, 400, 500, 600°C). The surface properties of thin films by atomic force microscopy (AFM), surface chemical composition by X-ray photoelectron spectroscopy (XPS) and self-cleaning effect in bi layers, were studied. In addition, enhanced hydrophilicity property in the films under the effect of annealed temperature and persistence without UV light illumination were evaluated.
关键词： Nanolayers,X-ray photoelectron spectroscopy (XPS),hydrophilicity,annealed temperature
更新于2025-09-09 09:28:46
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Quantitative determination of a model organic/insulator/metal interface structure
摘要： By combining X-ray photoelectron spectroscopy, X-ray standing waves and scanning tunneling microscopy, we investigate the geometric and electronic structure of a prototypical organic/insulator/metal interface, namely cobalt porphine on monolayer hexagonal boron nitride (h-BN) on Cu(111). Specifically, we determine the adsorption height of the organic molecule and show that the original planar molecular conformation is preserved in contrast to the adsorption on Cu(111). In addition, we highlight the electronic decoupling provided by the h-BN spacer layer and find that the h-BN–metal separation is not significantly modified by the molecular adsorption. Finally, we find indication of a temperature dependence of the adsorption height, which might be a signature of strongly-anisotropic thermal vibrations of the weakly bonded molecules.
关键词： hexagonal boron nitride,X-ray standing waves,X-ray photoelectron spectroscopy,cobalt porphine,Cu(111),scanning tunneling microscopy,organic/insulator/metal interface
更新于2025-09-04 15:30:14
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Depth-resolved electronic structure measurements by hard X-ray photoemission combined with X-ray total reflection: Direct probing of surface band bending of polar GaN
摘要： We have developed high-throughput depth-resolved electronic structure measurements using hard X-ray photoelectron spectroscopy (HAXPES) combined with X-ray total reflection (TR). By utilizing a steep change of the X-ray attenuation length around the TR condition, we controlled the effective inelastic mean-free-path of photoelectrons from >2 to >12 nm in HAXPES. We applied this method to probe the surface band bending of n-type polar GaN and found the different band bending behaviors in the Ga- and N-polar surfaces. This result is related to the surface contaminations and crystal quality near the surfaces of polar GaN.
关键词： hard X-ray photoelectron spectroscopy,surface band bending,depth-resolved electronic structure,polar GaN,X-ray total reflection
更新于2025-09-04 15:30:14
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A glassy carbon electrode modified with TiO2(200)-rGO hybrid nanosheets for aptamer based impedimetric determination of the prostate specific antigen
摘要： TiO2(200)-rGO hybrid nanosheets were synthesized starting from TiO2, rGO and NaOH solid powders via a scalable hydrothermal process. The weight ratio of TiO2-GO was found to be crucial on the crystal growth and biosensor properties of the final hybrid nanosheets. They were characterized by means of SEM, FESEM-EDX, XRD, XPS, Raman and FTIR spectroscopies in order to verify the formation of very thin TiO2 anatase nanosheets with an orientation of the anatase crystal structure towards the (200) plane. The free active sites of TiO2 structure and the large surface of the 2D graphene structure strongly facilitate charge transport confirmed by BET-BJH analyses. Compared to pure AuNPs, rGO and TiO2, the hybrid nanosheet modified electrode represents the most sensitive aptasensing platform for the determination of PSA. The detection was based on that the variation of electron transfer resistance (Rct) at the modified electrode surface in a solution containing 3.0 mmol L?1 [Fe(CN)6]3?/4- as a redox probe and 0.1 mol L?1 KCl as supporting electrolyte. The detection limit of the sensor is 1 pg mL?1, and the sensor can be operated up to 30 days. It was applied to the analysis of PSA levels in spiked serum samples obtained from patients with prostate cancer. Data compare well with those obtained by an immunoradiometric assay.
关键词： X-ray photoelectron spectroscopy,Effective surface area,Electrochemical impedance spectroscopy,Aptasensor,Voltammetry,Work function
更新于2025-09-04 15:30:14
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Deposition of Amorphous Carbon Thin Films by RF Magnetron Sputtering using Woodceramics as Target
摘要： Woodceramics, a substance based on woody materials carbonized at elevated temperatures after impregnating with phenolic resin, have been developed as a new kind of porous carbonaceous material. To expand the industrial application, we attempted to produce amorphous carbon films were RF magnetron sputtering using woodceramics as its target. As a result, typical amorphous carbon films were successfully produced using woodceramics, and the films were characterized by X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. The films produced were composed of carbon turbostratic structure or amorphous whose electron configurations consisted of sp2 and sp3. The ratio of sp3 bonding in the films were about 53% just after the sputtering, but the number increased to about 82% after etching the material using argon ions. Fundamental mechanical properties such as hardness and friction coefficient were also measured and taken into account.
关键词： magnetron sputtering,Raman spectroscopy,X-ray photoelectron spectroscopy,amorphous carbon film,woodceramics
更新于2025-09-04 15:30:14