Search

Valence band spectra of a polycrystalline Pt3Co alloy were measured with photon energies near Co L 3 absorption edge. On the absorption edge, Co L 3 M 4 , 5 M 4 , 5 Auger signals are superimposed on the valence band spectra. Prior to the absorption maximum, the Auger signals display constant binding energy corresponding to radiationless Raman Auger process. After the absorption maximum, normal Auger process occurs, showing characteristics of constant kinetic energy. The transition of Auger process in Pt3Co is carefully discussed, which is deviating to that in Co metal and other 3d transition metals. Our analysis of resonant Auger spectra confirmed the strong delocalization of Co 3d band in Pt3Co alloy.

Oxygen vacancies and their correlation with the electronic structure are crucial to understanding the functionality of TiO2 nanocrystals in material design applications. Here, we report spectroscopic investigations of the electronic structure of anatase TiO2 nanocrystals by employing hard and soft X-ray absorption spectroscopy measurements along with the corresponding model calculations. We show that the oxygen vacancies significantly transform the Ti local symmetry by modulating the covalency of titanium-oxygen bonds. Our results suggest that the altered Ti local symmetry is similar to the C3v, which implies that the Ti exists in two local symmetries (D2d and C3v) at the surface. The findings also indicate that the Ti distortion is a short-range order effect and presumably confined up to the second nearest neighbors. Such distortions modulate the electronic structure and provide a promising approach to structural design of the TiO2 nanocrystals.

Formamidinium lead triiodide (FAPbI3) perovskite solar cells (PSCs) are mainly fabricated by sequentially coating lead iodide and formamidinium iodide, or by coating a solution in which all components are dissolved in one solvent (one-pot process). The PSCs produced by both processes exhibited similar efficiencies; however, their long-term stabilities were notably different. We concluded that the major reason for this behaviour is the stabilization of the α-FAPbI3 phase by isopropylammonium cations produced by the chemical reaction between isopropyl alcohol, used as solvent, and methylammonium chloride, added during the process. On this basis, we fabricated PSCs by adding isopropylammonium chloride to the perovskite precursor solution for the one-pot process and achieved a certified power conversion efficiency of 23.9%. Long-term operational current density–voltage measurements (one sweep every 84 min under 1-Sun irradiation in nitrogen atmosphere) showed that the as-fabricated device with an initial efficiency of approximately 20% recorded an efficiency of about 23% after 1,000 h that gradually degraded to about 22% after an additional 1,000 h. The operational stability of formamidinium lead triiodide solar cells varies with the fabrication method of the perovskite layer. Now Park et al. find that isopropylammonium stabilizes the perovskite structure and leads to solar cells with 2,000-h stability under constant illumination.

The relationship between nanoscale friction and the surrounding environment has long been a critical issue in the field of nanotribology. Here, we utilized ambient pressure–atomic force microscopy ...

SrTiO3, an ABO3-type perovskite structure, has been a popular choice of substrate for many important heterostructures, e.g., ferroelectric thin films and superlattices. As numerous exotic physical phenomena are closely related to delicate electron/ion exchanges at the interfacial layer between the substrate and overlayer, precise characterization of surface/interfacial properties has become the center of many research studies. In most cases of SrTiO3 research, Nb-doping is applied on the SrTiO3 surface in order to characterize electrical properties with a negligible effect of contact potential between SrTiO3 and overlayer. On the other hand, the presence of doping can possibly interfere with a correct interpretation of the surface defect states, which become critical to apprehend the electrical properties of heterostructures. In this report, the undoped SrTiO3 (001) surface is investigated utilizing ambient-pressure XPS (AP-XPS) and low energy electron diffraction (LEED). We identified the complete chemical/structural/electronic states of O and Sr vacancies on the undoped SrTiO3 surface from ultra-high vacuum (UHV

The adsorption structures and reaction mechanism of tetrahydrofuran on a Ge(100) surface were investigated through high-resolution photoemission spectroscopy (HRPES) and density functional theory (DFT) calculations. On the basis of our analysis of the HRPES spectra, two adsorption species consisting of a major Ge–(CH2)4–O–Ge structure formed via a ring-opening reaction and a minor molecularly adsorbed structure formed via O dative bonding were identified. Our DFT results provided not only the optimized adsorption structures and their corresponding adsorption energies but also the level of the transition state for the pathway from the molecularly adsorbed species to the major adsorption structure. The results confirmed that the adsorption of tetrahydrofuran on the Ge(100) surface is under both kinetic and thermodynamic controls. Our discovery of the ring-opening reaction is an unprecedented result in the field of Ge(100) surface chemistry.

Objective To examine the biomechanical stress distribution at the upper instrumented vertebra (UIV) according to unicortical- and bicortical purchase model by finite element analysis (FEA). Methods A T8 to Sacrum with implant finite element model was developed and validated. The pedicle screws were unicortically or bicortically inserted from T10 to L5, and each model was compared and the von Mises (VM) yield stress of T10 was calculated. According to the motion (flexion, extension, lateral bending, and axial rotation) of spine, boundary condition values were set as 15°, 15°, 10°, 4°. Results Although the 2 stress values did not show a significant difference between the unicortical- and bicortical purchase models in the flexion and extension, bicortical purchase model showed a larger stress distribution. However, the asymmetric behavior was significantly greater in the case of lateral bending (0.802 MPa vs. 0.489 MPa) and the rotation (5.545 MPa vs. 4.905 MPa). The greater stress was observed on the spinal body surface abutting the implanted screw. Although the maximum stress was observed around the implanted screw in the bicortical purchase model under axial loading, the VM stress of both models was not significantly different. Conclusion Bicortical purchase model showed a larger stress distribution than the unicortical model, especially in the case of lateral bending and the rotation behavior. Our biomechanical simulation by FEA indicates that bicortical fixation at UIV can be a risk factor for early UIV compression fracture after adult spinal deformity surgery.

We thank UNIST Central Research Facilities (UCRF) and Y. K. Kim for the cross-sectional high-resolution TEM images. This work was supported by Samsung Electronics (Samsung-SKKU Graphene/2D Center), the research fund (NRF-2017R1E1A1A01074493 and NRF-2019R1A4A1027934), the IBS (IBS-R-019-D1) and a grant (CASE-2013M3A6A5073173) from the Centre for Advanced Soft Electronics under the Global Frontier Research Program via the National Research Foundation of the Ministry of Science and ICT, South Korea. The NEXAFS experiments performed at the 4D, 6D and 10A2 beamlines of the Pohang Accelerator Laboratory (PAL) were supported in part by the Ministry of Science and ICT, POSTECH and UNIST. M.C. acknowledges support from Leverhulme Trust Research Grant RPG-2019-227. S.R., A.A. and M.C. acknowledge the European Union Horizon 2020 research and innovation programme for grant number 785219 and 881603 (Graphene Flagship). A.A. is supported by Project MECHANIC (PCI2018-093120) funded by Ministerio de Ciencia, Innovación y Universidades. The Catalan Institute of Nanoscience and Nanotechnology is funded by the CERCA Programme/Generalitat de Catalunya and supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (grant number SEV-2017-0706).

An ambient-pressure photoemission spectroscopy beamline has been constructed and has recently begun regular user service at Pohang Accelerator Laboratory. This beamline is a soft X-ray beamline with undulator (U6.8) insertion device and will be a platform for operando surface science., Beamline 8A (BL 8A) is an undulator-based soft X-ray beamline at Pohang Accelerator Laboratory. This beamline is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), soft X-ray absorption spectroscopy (soft-XAS) and scanning photoemission microscopy (SPEM) experiments. BL 8A has two branches, 8A1 SPEM and 8A2 AP-XPS, that share a plane undulator, the first mirror (M1) and the monochromator. The photon beam is switched between the two branches by changing the refocusing mirrors after the monochromator. The acceptance angle of M1 is kept glancing at 1.2°, and Pt is coated onto the mirrors to achieve high reflectance, which ensures a wide photon energy range (100–2000 eV) with high resolution at a photon flux of ∼1013 photons s−1. In this article, the main properties and performance of the beamline are reported, together with selected experiments performed on the new beamline and experimental system.

Here, we demonstrate that the density of oxygen vacancies generated by the doped transition metal (TM) ions at the surface of ZnO nanoparticles (TM-doped ZnO NPs; TM = Cr or Co) determines the photocatalytic degradation (PCD) activity for organic pollutants; to this end, we employ multimodal microscopy and spectroscopy that encompass material probing at multiple length scales, ranging from the atomic to mesoscale. Following the doping treatment of pristine ZnO NPs as a post-synthetic process, Cr ion doping leads to a significant enhancement of the PCD activity of the ZnO NPs, whereas Co ion doping results in a negative effect. Atomic-scale observations and site-specific spectroscopy confirm that these two TM ions substitute for Zn, in different valence states (Cr3+ and Co2+, respectively), without inducing a phase change of the host ZnO matrix (wurtzite structure). Cr-doped ZnO NPs have the highest density of oxygen vacancies originating from charge mismatch, which contributes to a notably enhanced PCD effect on the tested pollutants, whereas the other two samples (pristine and Co-doped ones) have similar amounts of oxygen vacancies. Our multimodal and multiscale spectroscopic probing provides a clear insight into the significant role of charge mismatch, induced by the substitution of the host cation by the doped cation, in controlling the oxygen vacancies. This can serve as a practical guideline for atomically precise control of oxygen vacancies toward the development of high-performance metal oxide photocatalysts.

Bimetallic platinum–cobalt (Pt–Co) catalysts have highly enhanced performance for the oxygen reduction reaction (ORR), where this peculiar surface alloy structure contributes to efficient energy co...

Programmable optoelectronic devices calls for the reversible control of photo-carrier recombination process by in-gap states in emergent oxide semiconductors. However, previous approaches to produce oxygen vacancies as a source of in-gap states in oxide semiconductors have hampered the reversible formation of oxygen vacancies and their related phenomena. Here, a new strategy to manipulate the two-dimensional photoconductivity from perovskite stannates is demonstrated by exploiting spatially-selective photochemical reaction under ultraviolet illumination at room temperature. Remarkably, the ideal trap-free photocurrent of air-illuminated BaSnO3 (∼ 200 pA) is reversibly switched into three orders of magnitude higher photocurrent of vacuum-illuminated BaSnO3 (∼ 335 nA) with persistent photoconductivity depending on ambient oxygen pressure under illumination. Multiple theoretical and experimental characterizations elucidate that ultraviolet illumination of BaSnO3 under low oxygen pressure induces surface oxygen vacancies as a result of surface photolysis combined with the low oxygen-diffusion coefficient of BaSnO3 ; the concentrated oxygen vacancies are likely to induce a two-step transition of photocurrent response by changing the characteristics of in-gap states from shallow level to deep level. These original results suggest a novel strategy that uses light-matter interaction in a reversible and spatially-confined way to manipulate functionalities related to surface defect states, for the emerging applications using newly discovered oxide semiconductors. This article is protected by copyright. All rights reserved.

X-ray absorption spectroscopy at Mn K- and L-edges, and at O K-edge, combined with the x-ray diffraction and magnetization measurements are performed to study the electron structure of La0.7Ca0.3Mn1-xScxO3 (x = 0.0; 0.03, and 0.05) perovskites. Substitution of manganese by scandium decreases Curie temperature, Tc, and increases lattice parameters because of the different electron configuration and radii of trivalent manganese and scandium ions. The Tc decrease is explained by the change of level of hybridization of O 2p and Mn 3d states. This is manifested by the parallel shift of O K-edge, change of intensity of 2p3/2 and 2p1/2 spectrum lines and TC with x increase. Fourier transform of the EXAFS spectra shows a change of local crystal structure caused by the larger Sc3+ than the Mn3+ ions.

We report a method that uses van der Waals interactions to transfer continuous, high-quality graphene films from Ge(110) to a different substrate held by hexagonal boron nitride carriers in a clean, dry environment. The transferred films are uniform and continuous with low defect density and few charge puddles. The transfer is effective because of the weak interfacial adhesion energy between graphene and Ge. Based on the minimum strain energy required for the isolation of film, the upper limit of the interfacial adhesion energy is estimated to be 23 meV per carbon atom, which makes graphene/Ge(110) the first as-grown graphene film that has a substrate adhesion energy lower than that of typical van der Waals interactions between layered materials. Our results suggest that graphene on Ge can serve as an ideal material platform to be integrated with other material systems by a clean assembly process.

Open in a separate window π-Conjugated molecule-bridged silicon quantum dot (Si QD) clusters were first synthesized by Sonogashira cross-coupling reaction between 4-ethynylstyryl and octyl co-capped Si QDs (4-Es/Oct Si QDs) and 2,5-dibromo-3-hexylthiophene. The formation of Si QD clusters was confirmed by field emission transmission electron microscopy. The electronic coupling between the QDs in the Si QD cluster is significantly enhanced as compared with that for 4-Es/Oct Si QDs, which is verified from the red shift in ultraviolet–visible absorption and photoluminescence spectra of the Si QD cluster with the possibility of exciton transport, the increased charging effect found in the core-level photoemission spectra, the shift to lower binding energy of the valence band photoemission spectrum, and more decisively, the increase in electrical conductance of the Si QD cluster thin film. To investigate the physical origin of the temperature dependence of the electrical conductance, we have merged the microscopic viewpoint, Marcus theory, on the electron transfer (W) between the adjacent QDs, with macroscopic concepts, such as the conductance (G), mobility (μ), and diffusion coefficient (D). The effective reorganizational energies of charge transfer between the neighboring Si QDs in 4-Es/Oct Si QD and Si QD cluster thin films are estimated to be 170 and 140 meV, respectively, while the ratio of the effective electronic coupling of the latter to that of the former is determined to be 7.3:1.

While organic–inorganic hybrid perovskite solar cells are emerging as promising candidates for next-generation solar cells with fascinating power conversion efficiency, the instability of perovskites remains a significant bottleneck for their commercialization. An atomic scale understanding of the degradation of hybrid perovskites, however, is only in its beginning stages because of the difficulty in preparing well-defined surface conditions for characterization. Using atomic force microscopy at ultra-high vacuum and room temperature, we report the first direct observation of the degradation process of a cleaved methylammonium lead bromide, MAPbBr3 (MA: CH3NH3+), single crystal. Upon in situ cleavage, atomic force microscopy images show large flat terraces with monolayer height steps, which correspond to the surface of cubic MAPbBr3 with methylammonium ligand termination. While this surface can be prepared via the cleavage process and is energetically stable, we observe that after several weeks under dark and vacuum conditions it degrades and produces clusters surrounded by pits. Guided by density functional theory calculations, we propose a degradation pathway that initiates even at low humidity levels and leads to the formation of surface PbBr2 species. We finally identify the electronic structure of the MA-bromine-terminated flat surface and find that it is correlated with a strong field-induced degradation of the MAPbBr3 only at positive sample bias voltages.

The coverage and temperature dependence of ZIRLO cladding with H2O adsorption are studied using synchrotron-based high-resolution photoemission spectroscopy (HRPES). Based on the analytical results of the Zr 3d, O 1 s, C 1 s, and Sn 3d HRPES profiles prior to H2O adsorption, we determine the surface compositions of O2−, hydroxyl OH−, chemisorbed H2O, zirconium carbide, adventitious carbon, Sn metal, and SnO2 in ZIRLO. When ZIRLO is exposed to H2O molecules, the relative proportion of zirconium metal decreases, whereas that of the total zirconium oxides increases, suggesting the reaction between H2O and the zirconium metal in ZIRLO. On annealing a sample with 1000 L H2O on ZIRLO at 300 °C, Zr2O3 and ZrO2 decompose, and oxygen diffuses into the bulk, thereby reducing the oxidation states of zirconium on the surface. Moreover, at this temperature, the excess H2O molecules on ZIRLO are thoroughly desorbed and tin element is diffused into the bulk in ZIRLO.

The surface morphology and electronic structure of hexagonal graphene onion rings (HGORs), a modified graphene structure, were investigated to confirm the possibility as an efficient catalyst when compared to graphene. After confirming the formation of HGORs with a smaller width (~4.2 μm) from scanning electron microscopy (SEM) and optical microscopy images, we compared the catalytic activities of HGORs and graphene by measuring the rate of oxidation of thiophenol using high-resolution photoemission spectroscopy (HRPES). In addition, we also assessed in 4-chlorophenol degradation and the OH radical formation with a benzoic acid to confirm the possibility for photocatalytic activities of HGORs. As a result, we confirmed that HGORs, which has an increased active site due to its three-dimensional structure formed by the reaction of graphene with hydrogen, can act as an effective catalyst. In addition, we could also realize the possibility of optical applicability by observing the 0.13 eV of band gap opening of HGORs.

Herein, graphite is proposed as a reliable Ca2+‐intercalation anode in tetraglyme (G4). When charged (reduced), graphite accommodates solvated Ca2+‐ions (Ca‐G4) and delivers a reversible capacity of 62 mAh g−1 that signifies the formation of a ternary intercalation compound, Ca‐G4·C72. Mass/volume changes during Ca‐G4 intercalation and the evolution of in operando X‐ray diffraction studies both suggest that Ca‐G4 intercalation results in the formation of an intermediate phase between stage‐III and stage‐II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca‐G4 has a planar structure with Ca2+ surrounded by G4, which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g−1 at 1.0 A g−1 s vs 62 mAh g−1 at 0.05 A g−1) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca2+‐shuttling calcium‐ion batteries with a graphite anode, a full‐cell is constructed by coupling with an organic cathode and its electrochemical performance is presented., Graphite can intercalate/deintercalate Ca2+ ions with excellent cyclability and rate capability. Calcium ion batteries, which consist of a graphite anode and a perylene‐3,4,9,10‐tetracarboxylic dianhydride cathode in Ca(TFSI)2/G4, can operate in a rocking‐chair mode and deliver a reversible capacity of ≈80 mAh g−1 with good stability.

Ionic liquids and gels have attracted attention for a variety of energy storage applications, as well as for high-performance electrolytes for batteries and supercapacitors. Although the electronic structure of ionic electrolytes in these applications is of practical importance for device design and improved performance, the understanding of the electronic structure of ionic liquids and gels is still at an early stage. Here we report soft X-ray spectroscopic measurements of the surface electronic structure of a representative ammonia-based ionic gel (DEME-TFSI with PS-PMMA-PS copolymer). We observe that, near the outermost surface, the area of the anion peak (1s N– core level in TFSI) is relatively larger than that of the cation peak (N+ in DEME). This spontaneous ionic polarization of the electrolyte surface, which is absent for the pure ionic liquid without copolymer, can be directly tuned by the copolymer content in the ionic gel, and further results in a modulation in work function. These results shed...

Utilizing ambient pressure x-ray photoelectron spectroscopy, the surface segregation and the oxidation dynamics of platinum (Pt)-3d transition metal (M) alloys, Pt3M (M = Ti, V), are investigated. Under oxygen-rich conditions, i.e., P(CO)/P(O2) = 0.1, Pt3V surface forms Pt skin layer while Pt3Ti shows the presence of both Ti and Pt atoms. As temperature increases to 450 K, V atoms make surface segregation to form oxide while Ti atoms start to form various Ti oxides (Ti2O3 and TiOx) on the surface. When CO oxidation occurs at 600 K, the oxidation continues on both surfaces of Pt3M (M = Ti, V), showing the enhancement of TiOx for Pt3Ti and V2O5 and VOx for Pt3V. Also, during CO oxidation, a sign of pure metallic Pt state is found at Pt 4f spectra in both surfaces, suggesting the redistribution of electrons from the transition metals during the oxide formation.

The local electronic and crystal structures of self-doped Pr1-xMnO3+δ (x = 0.0 and 0.2) perovskites are studied by x-ray absorption spectroscopy at Mn K-, Mn L- and O K-edges. The Mn K-edge shifts towards higher energy with increasing x indicating the increase in average manganese valence, which, in turn, leads to an increase in magnetization. The Mn L-edge spectra display a splitting into L3(2p3/2) and L2(2p1/2) peaks which is caused by core hole spin-orbit coupling. The intensities of 2p3/2 and 2p1/2 peaks increase with x, which correlates with the increase in magnetization and results from the change in hybridization between O 2p and Mn 3d orbitals. Altering x do not affect the O K-pre-edge spectra indicating no changes in Fermi level. Difference in relation of magnetic properties to electron structure in self-doped manganites and oxides doped in A- and B-positions of perovskites ABO3 cell is underlined. The Fourier transform of EXAFS spectra shows the decrease in oxygen and praseodymium contents and the formation of trivalent manganese anti-site defects in praseodymium position with increasing x.

Colloidal 4-ethynylstyryl and octyl cocapping silicon quantum dot (4-Es/Oct Si QD) and its spin-coated film were synthesized and fabricated at three different curing temperatures, 150, 250, and 350 °C under argon for 4 h. Thermal cross-linking of 4-ethynylstyryl-terminated 4-Es/Oct Si QD during the curing process was confirmed by differential scanning calorimetry for the 4-Es/Oct Si QD powder and by Fourier transform infrared spectroscopy for the Si QD thin films. The effect of thermal cross-linking of 4-ethynylstyryl capping groups on the electronic coupling between Si QDs in Si QD solids of thin film states was investigated by monitoring optical and electrical properties of the Si QD thin films at different curing temperatures. The valence-band spectra of 4-Es/Oct Si QD thin films obtain from high-resolution photoemission spectroscopy at 130 eV showed the shift to lower binding energy as curing temperature increases from 150 to 350 °C. The optical bandgap values estimated from the extinction-coefficient...

The correlation between the defect structures of hydrothermally grown TiO2 nanorods (TNR) and their photocatalytic activity has been investigated by using various surface spectroscopic analysis techniques including scanning transmission X-ray microscopy (STXM) and high-resolution photoemission spectroscopy (HRPES). Defect states related to Ti3+ and oxygen vacancies in TNR were observed when the growth time was over 90 min (i.e., those over 500 nm in height), and these TNR samples showed photocatalytic oxidation activity with respect to the molecules 2-mercaptoethanol (2-ME) or 2-aminothiophenol (2-ATP), also confirmed by HRPES. The presence of defect structures on the TNR influences on the electronic states of titanium and oxygen, and thus can improve the catalytic oxidation reactions.

Defect engineered Fe3O4 nanoparticles (NPs) with magnetic properties can act as efficient photocatalysts in spite of no intrinsically photocatalytic property of bare Fe3O4. The purpose of this study is to confirm the possibility whether the modified Fe3O4 NPs can be an efficient photocatalyst by engineering the surface defects without compromising the magnetic properties of Fe3O4 NPs. Herein, we report a facile method to introduce surface defects on Fe3O4 and Cr@Fe3O4 NPs without degrading their magnetic properties via simple pH treatments at moderate temperatures. Our results showed that Cr@Fe3O4 NPs fabricated under basic conditions, denoted as Cr@Fe3O4-B NPs, showed a clear electronic structural evidence for surface defects on Fe3O4. The presence of defects on Fe3O4 induced an alternative approach to solar activation via ligand-to-metal charge transfer to drive selective photocatalytic degradation of phenolic compound without losing its magnetic property. It is highly desirable to seek a strategy for achieving the recovery of catalysts using a magnet, while minimizing the loss of catalyst and the cost for a complicate recovery process.

Introduction of defect structures into Fe-doped TiO2 nanoparticles (Fe@TiO2 NPs) has been shown to endow NPs with improved photocatalytic properties. However, current strategies for the preparation of defect-containing NPs require high temperature or complicated treatments, which can induce unwanted phase transition. In this paper, we report a facile method to introduce surface oxygen vacancies into anatase-type Fe@TiO2 NPs without altering the crystalline phase via simple pH treatments at moderate temperatures. Furthermore, we present the effects of pH on the formation of surface oxygen vacancies. The optimized treatment under basic conditions is revealed to promote the formation of oxygen vacancies on the surface of anatase Fe@TiO2 NPs and effectively reduces the particle size by more than 25%, thereby causing a significant enhancement in the photocatalytic activities of the NPs (e.g. ~3.5 times better in photocatalytic degradation rate of 4-CP as compared to acid-treated Fe@TiO2). Comprehensive structural and chemical characterizations reveal that the point defects are predominantly formed on the surface of anatase NPs, and their population can be maximized by use of basic pH conditions. Our results pave a way toward the facile and efficient engineering of surface defect structures on catalytic metal oxide NPs for the design of high-performance photocatalysts.

The correlation between the structural phase transition (SPT) and oxygen vacancy in SrRuO3 (SRO) thin films was investigated by in situ X-ray diffraction (XRD) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In situ XRD shows that the SPT occurs from a monoclinic SRO phase to a tetragonal SRO phase near ∼200 °C, regardless of the pressure environment. On the other hand, significant core level shifts in both the Ru and Sr photoemission spectra are found under ultrahigh vacuum, but not under the oxygen pressure environment. The directions and behavior of the core level shift of Ru and Sr are attributed to the formation of oxygen vacancy across the SPT temperature of SRO. The analysis of in situ XRD and AP-XPS results provides an evidence for the formation of metastable surface oxide possibly due to the migration of internal oxygen atoms across the SPT temperature, indicating the close relationship between oxygen vacancy and SPT in SRO thin films.

The presence of excess lead iodide in halide perovskites has been key for surpassing 20% photon-to-power conversion efficiency. To achieve even higher power conversion efficiencies, it is important to understand the role of remnant lead iodide in these perovskites. To that end, we explored the mechanism facilitating this effect by identifying the impact of excess lead iodide within the perovskite film on charge diffusion length, using electron-beam-induced current measurements, and on film formation properties, from grazing-incidence wide-angle X-ray scattering and high-resolution transmission electron microscopy. Based on our results, we propose that excess lead iodide in the perovskite precursors can reduce the halide vacancy concentration and lead to formation of azimuthal angle-oriented cubic α-perovskite crystals in-between 0° and 90°. We further identify a higher perovskite carrier concentration inside the nanostructured titanium dioxide layer than in the capping layer. These effects are consistent with enhanced lead iodide-rich perovskite solar cell performance and illustrate the role of lead iodide., Excess lead iodide in the mixed halide perovskites solar cells leads to high device performance but its origin remains elusive. Here Park et al. unveil the underlying microscopic mechanism to be promoting the oriented growth of the perovskites crystals and reducing the defect concentration.

Through Bi deposition on the single-crystalline $\mathrm{Mo}{\mathrm{S}}_{2}$ surface, we find that the density of the sulfur vacancy is a critical parameter for the growth of the crystalline Bi overlayer or cluster at room temperature. Also, the $\mathrm{Mo}{\mathrm{S}}_{2}$ band structure is significantly modified near \ensuremath{\Gamma} due to the orbital hybridization with an adsorbed Bi monolayer. Our experimental observations and analysis in combination with density functional theory calculation suggest the importance of controlling the sulfur vacancy concentration in realizing an exotic quantum phase based on the van der Waals interface of Bi and $\mathrm{Mo}{\mathrm{S}}_{2}$.

We present a new method for transferring chemical vapor deposition (CVD)-grown graphene onto the surfaces of organic materials directly. Raman and near edge X-ray absorption fine structure measurements prove that high-quality and single layer graphene/organic thin films can be obtained with minimized impurity introduction. In-situ synchrotron radiation photoemission spectroscopy combined with ultraviolet photoelectron spectroscopy experiments demonstrate that the inserted graphene can not only act as a buffer layer to reduce the interfacial chemical reactions between the deposited Al and organic materials, but also tune the metal/organic interface electronic structure significantly. This new graphene transfer technique may have a great potential in the application of engineering the metal–organic interface properties, which is one of the key technologies for the optimal design and fabrication of organic electronic and optoelectronic devices.

The capacities of graphene oxide (GO) and reduced graphene oxide (rGO) films grown on silicon substrate to cause the aniline to azobenzene oxidation reaction were compared by using Raman spectroscopy, high-resolution photoemission spectroscopy (HRPES), and work function measurements as well as scanning electron microscopy (SEM). The oxygen carriers’ existence on GO film, which includes a lot of oxygen carriers, can facilitate the aniline to azobenzene oxidation reaction with slightly partial conversion of aniline to nitrobenzene, as determined by the Raman shifts and core-level spectra resulting from exposure to aniline. The work function of the GO film was found to change dramatically in comparison with rGO film, indicating that aniline exposed to a GO film produced n-type doping characteristics by electron charge transfer from GO to aniline. These results indicate that the oxygen carriers on a GO film oxidize aniline to azobenzene and show that GO film prefers to act as a reaction reagent rather than rGO.

In order to compare the catalytic activities of reduced graphene oxide (rGO), graphene oxide (GO), and graphene, we conducted oxidation of 2-aminothiophenol (2-ATP) and reduction of nitrobenzene (NB) in their presence by using high-resolution photoemission spectroscopy (HRPES). In addition, we determined conversion rates of CO to CO2 in the presence of these catalysts by performing a residual gas analyzer (RGA) under a UHV condition, Orange II and methylene blue degradations UV-vis spectrophotometry, and electrochemistry (EC) measurements in an aqueous solution, as well as by obtaining cyclic voltammograms and determining the change of the condition of electrodes before and after the oxidation of 2-ATP. We found that we can successively fabricate GO (oxidation) and graphene (reduction) from rGO by controlling the oxidation or reduction procedure time and then clearly comparing the critical properties among them as we perform various oxidation and reduction activities.

We studied the structural characteristics of poly imides (PI) chains according to the film thickness and the temperature treatment using the angle resolved near edge X-ray adsorption fine structure (AR-NEXAFS). The molecular directional angle a of the twisted nematic (TN) and the in-plane switching (IPS) mode alignment film (AF) decrease the tilt angle as increasing the film thickness. These films also shows the temperature dependence of C=C * according to the annealing conditions. In case TN mode sample lost its angular dependency after annealing 230 °C for 2400 sec on the hot plate, but IPS mode sample maintained its angular dependency after same annealing condition with TN mode sample.

The modification of the electronic properties of a coverage-dependent graphene layer by nitrogen ions irradiation was investigated using core-level photoemission spectroscopy (CLPES). Here we describe preparation of monolayer and multilayer epitaxial graphene (EG) functionalized by nitrogen ions irradiation with 100 eV to minimize the damage of graphene layer as we annealed up to 1300 K to track the surface property changes using CLPES. As a result, on the monolayer EG, we found that pyridinic nitrogen mainly existed on the surface. On the multilayer EG, we observed the formation of graphitic nitrogen remaining as a major species confirmed using N 1s core-level spectra. Through a work function change (ΔΦ) measurement, both systems indicated p-type doping properties with 4.71 (monolayer EG) and 4.87 eV (multilayer EG) of work function values after N2 ion irradiation. Interestingly, we observed that monolayer EG maintained its p-type doping character, whereas multilayer EG changed the doping character from ...

Westudiedtheeffectsofsubstratetemperature(Ts)onthesurfaceroughness,resistivity(ρ),mobility(μ),chargecarrierconcentrations (n), transmission and optical bandgap (Eg) of amorphous In-Ga-Zn-O thin films (∼250 nm thickness) deposited by radio-frequency magnetron sputtering. As Ts increased from RT to 300 ◦ C, n increased (2.6 × 10 19 → 5.0 × 10 19 /cm 3 ), ρ decreased (7.0 × 10 −3 → 4.7 × 10 −3 � −cm), and Eg (3.9 → 3.7 eV) along with the average transmission (89 → 82%) in the visible region decreased. Investigation of the O 1s core level and the Ga 3d ,I n 4d ,a nd Zn 3d shallow-core levels spectra obtained by high-resolution X-ray photoelectron spectroscopy revealed that as Ts increased, an O 1s component representing the oxygen vacancies increased in amount and that the intensity ratio of In/Ga increased but that of Zn/Ga decreased. The analysis suggests that the increase of oxygen vacancies could explain the increase of charge carrier concentration and that the compositional change could explain the change of Eg.

High-resolution photoemission spectroscopy using synchrotron radiation was employed to understand the bonding state of N incorporated into a reduced TiO2(110)-1×1 surface. N-doping into TiO2(110) was accomplished both by dosing NH3 at elevated temperatures (800 K) and by using a NHx+ ion implantation method onto TiO2(110) at room temperature. Our results indicate that the N-doped TiO2(110) obtained after final annealing to 900 K contains N species incorporated into the subsurface region of TiO2substitutionally replacing the lattice O2–. Interestingly, we find that some of the N species are found to have a direct N–H bond (NH species). The valence band indicates that the band-gap state related to the Ti 3d state is enhanced with increasing subsurface N species, which explains an attractive interaction between N species and defects with a charge in the Ti 3d state, such as reduced Ti3+ species and oxygen vacancies.

The ring formation and electronic properties of furan adsorbed on graphene layers grown on 6H-SiC (0001) has been investigated using atomic force microscopy (AFM), near edge X-ray absorption fine structure (NEXAFS) spectra for the C K-edge, and core level photoemission spectroscopy (CLPES). Moreover, we observed that furan molecules adsorbed on graphene could be used for chemical functionalization via the lone pair electrons of the oxygen group, allowing chemical doping. We also found that furan spontaneously form rings with one of three different bonding configurations and the electronic properties of the ring formed by furan on graphene can be described using by AFM, NEXAFS and CLPES, respectively.

The Chemical Doping of epitaxial graphene (EG) due to p-tert-butylcalix[4]arene was investigated using high resolution photoemission spectroscopy (HRPES). The measured work function changes verified that increased adsorption of the p-tert-butylcalix[4]arene on EG showed p-type doping characteristics due to charge transfer from the graphene to the p-tert-butylcalix[4]arene through the hydroxyl group. A single oxygen bonding feature associated with the O 1s peak was clearly observed in the core-level spectra, indicating the presence of one equivalent adsorption state.

Electronic band structures of viologen-doped graphene have been investigated. Pristine graphene film, synthesized by chemical vapor deposition (CVD), showed numerous oxygen-related functional groups, and was annealed to remove oxygen content. Two species of viologen, di-cationic and mono-cationic, were observed in the viologen-doped graphene. The work function of the CVD graphene was dramatically decreased by 1.1 eV after viologen doping. Viologen, therefore, is a strong n-type dopant for graphene, and this report shows the first direct evidence of changing the work function of viologen-doped graphene by cutting-off the kinetic energy of secondary electrons.

Background/Objectives: The purpose of this study was to propose a method to maintain the objectivity and validity of measuring image sharpness by changes of ETL using MTF in MRI quantitatively and provide fundamental data for future evaluation and management of magnetic resource imaging quality.Methods/Statistical analysis: We conducted phantom test using ACR MRI phantom. ImageJ and OriginPro programs were used for MTF measurement. For MTF measurement using edge method, after achieving ESF by using ImageJ, LSF was calculated by differentiation in OriginPro. Finally, MTF value was obtained through conversion. Image sharpness was defined based on 50% of MTF value.Findings: Results of sharpness measurement by ETL increase revealed that MTF 50% was decreased when ETL was increased. Sharpness comparison between 1ch head coil and 8ch brain coil at 1.5T showed that it was higher for 1ch head coil, although the difference between the two was not statistically significant. However, sharpness of 1ch head coil at 3.0T MRI was found to be significantly higher than that of 8ch brain coil at 3.0T MRI.Improvements/Applications: This study confirms the theoretical concept that MTF measured by ACR standard phantom can be used as a quantitative evaluation method for spatial resolution in the magnetic resonance medical image quality management. It can be considered a meaningful objective evaluation method.

We studied adsorption of pyridine on Si(1 0 0) at room temperature using high resolution photoemission spectroscopy (PES) and near edge X-ray adsorption fine structure (NEXAFS) in the partial electron yield (PEY) mode. The Si 2p, C 1s, N 1s spectra of pyridine on Si(1 0 0) showed that pyridine is chemisorbed on Si(1 0 0)-2 × 1 through the formation of the tetra-σ-bonded structure with the N atom and three C atoms. NEXAFS was conducted to characterize the adsorption geometry of pyridine on Si(1 0 0). The π* orbital of C C bond showed a good angle dependence in C K-edge NEXAFS spectra, and we were able to estimate the adsorption angle between chemisorbed pyridine of C C bond and the Si(1 0 0) surface using an analytical solution of NEXAFS intensity. We find the coexistence of two different tight bridges with the adsorption angles 42 ± 2° and 45 ± 2° with almost equal abundance.

Pentacene films on Si(1 0 0)-(2 × 1) surface at 300 K were investigated using near edge X-ray absorption fine structure (NEXAFS) at the carbon K-edge. NEXAFS spectra show that pentacene molecules are chemisorbed on the Si(1 0 0)-(2 × 1) surface for monolayer with flat-laying and predominantly physisorbed on the Si(1 0 0)-(2 × 1) surface for multilayer films with an upright molecular orientation. Absorption angle of pentacene molecules were measured through π ∗ transition. The angles between the double bond and the silicon surface were 35–55°, 65° and 76° at monolayer, 24 and 48 nm pentacene deposited on the Si(1 0 0) surface, respectively. We observed that the intermediate flat-laying phase is favored for monolayer coverage, while the films of molecules standing perpendicular to the Si(1 0 0) surface are favored for multilayer coverage.

Highly luminescent graphene oxide (GO)-phosphor hybrid thin films with a maximum quantum yield of 9.6% were synthesized via a simple chemical method. An intense luminescence emission peak at 537 nm and a broad emission peak at 400 nm were observed from the GO-phosphor hybrid films. The maximum quantum yield of the emissions from the hybrid films was found to be 9.6%, which is 48 times higher than that of pristine GO films. The GO-phosphor hybrids were prepared via spin-coating and subsequent postannealing of the films, resulting in scrolling of the GO sheets. The resulting GO nanoscrolls exhibited a length of ∼2 μm with nanoscale interior cavities. Transmission electron microscopy and selected-area electron diffraction analyses revealed that the lattice structure of the tubular scrolls is similar to that of carbon nanotubes. While pristine GO films are p-type, in the GO-phosphor hybrids, the Fermi level shifted upward and fell between the HOMO-LUMO gap due to phosphor attachment via C-N bonding. The highly luminescent GO-phosphor hybrids will find important applications in graphene-based optoelectronic devices.

The initial stage of the thermal nitridation on Si (1 0 0)-2 × 1 surface with the low-energy nitrogen ion (200 eV) implantation was studied by photoemission spectroscopy (PES). The formation of nitride was shown the different characteristics depending on the annealing temperature. The disordered surface at room temperature was changed to 2 × 1 periodicity with the low-energy electron diffraction (LEED) as increasing the nitridation temperature. By decomposition of Si 2p spectrum, we can identify the three subnitrides (Si1+, Si2+, and Si3+). By changing the take-off angle of the Si 2p, we can increase surface sensitivity and estimate that Si1+, Si2+ and Si3+ are the interface states.

Vacuum thermal oxidation methods, which are based on the concept of selective oxidations of chromium at low oxygen partial pressures, have been used for practical fabrication of protective oxide films on stainless steels. This passive oxide films was characterized to investigate the chemical composition by surface-sensitive photoelectron spectroscopy (PES). PES revealed that the 10 A thickness of Cr 2 O 3 layer was formed in 450 °C and oxygen partial pressure of 1×10 −9 Torr, and a top layer was mixed with metallic chromium and oxygen exited Cr 2 O 3 at the initial stage of oxidation. Photoemission electron microscope (PEEM) and the synchrotron radiation, which were tuned at the core level energy of iron and chromium components, were used to obtain the real time image acquisition of the initial forming phenomena with annealing process.