X-ray Photoelectron Spectroscopy Characterization Research Articles

XPS analysis of molecular contamination and sp2 amorphous carbon on oxidized (100) diamond

Abstract The efficacy of oxygen (O) surface terminations on diamond is an important factor for the performance and stability for diamond-based quantum sensors and electronics. Given the wide breadth of O-termination techniques, it can be difficult to discern which method would yield the highest and most consistent O coverage. Furthermore, the interpretation of surface characterization techniques is complicated by surface morphology and purity, which if not accounted for will yield inconsistent determination of the oxygen coverage. We present a comprehensive approach to consistently prepare and analyze oxygen termination of surfaces on (100) single-crystalline diamond. We report on X-ray Photoelectron Spectroscopy (XPS) characterization of diamond surfaces treated with six oxidation methods that include various wet chemical oxidation techniques, photochemical oxidation with UV illumination, and steam oxidation using atomic layer deposition (ALD). Our analysis entails a rigorous XPS peak-fitting procedure for measuring the functionalization of O-terminated diamond. The findings herein have provided molecular-level insights on oxidized surfaces in (100) diamond, including the demonstration of clear correlation between the measured oxygen atomic percentage and the presence of molecular contaminants containing nitrogen, silicon, and sulfur. We also provide a comparison of the sp2 carbon content with the O(1s) atomic percentage and discern a correlation with the diamond samples treated with dry oxidation which eventually tapers off at a max O(1s) atomic percentage value of 7.09 ± 0.40%. Given these results, we conclude that the dry oxidation methods yield some of the highest oxygen amounts, with the ALD water vapor technique proving to be the cleanest technique out of all the oxidation methods explored in this work.

Impact of the Surface Microenvironment on the Redox Properties of a Co-Based Molecular Cathode for Selective Aqueous Electrochemical CO2-to-CO Reduction.

Electrode-confined molecular catalysts are promising systems to enable the efficient conversion of CO2 to useful products. Here, we describe the development of an original molecular cathode for CO2 reduction to CO based on the noncovalent integration of a tetraazamacrocyclic Co complex to a carbon nanotube-based matrix. Aqueous electrochemical characterization of the modified electrode allowed for clear observation of a change of redox behavior of the Co center as surface concentration was tuned, highlighting the impact of the catalyst microenvironment on its redox properties. The molecular cathode enabled efficient CO2-to-CO conversion in fully aqueous conditions, giving rise to a turnover number (TONCO) of up to 20 × 103 after 2 h of constant electrolysis at a mild overpotential (η = 450 mV) and with a faradaic efficiency for CO of about 95%. Post operando measurements using electrochemical techniques, inductively coupled plasma, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy characterization of the films demonstrated that the catalysis remained of molecular nature, making this Co-based electrode a new promising alternative for molecular electrocatalytic conversion of CO2-to-CO in fully aqueous media.

Combustion characteristics and nitrogen conversion mechanism in ammonia/coal Co-firing process

The coupled combustion of coal with the carbon-free fuel NH3 is an effective technology for reducing CO2 emissions. Based on elemental analysis, proximate analysis, Fourier Transform infrared spectroscopy (FTIR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), and X-ray photoelectron spectroscopy (XPS) characterizations, a coal macromolecular model was constructed. The combustion characteristics of coal/NH3 co-firing were investigated by reactive force field molecular dynamics simulations (ReaxFF MD). The transformation mechanism of elemental N was elucidated. The influence of temperature, oxygen concentration, and NH3 co-firing ratio (CR) on products was investigated. The results showed that during the non-isothermal combustion phase, the coal macromolecules decomposed more rapidly when the heating rate was low. In the isothermal phase, high temperatures promoted secondary reactions. The production of inorganic gases increased with increasing temperature. As the molar fraction of NH3 increased, the production of CO2 and CO was effectively reduced. There were three main pathways for NO formation. As NH3 decomposed to form NH2, NH2 was subsequently converted to NH, and NH reacted with O2 to form NO. The NH2 could also react with O radicals to form HNO, which was then converted to NO. Besides, both thermal NOx and prompt NOx were generated since the N2 was involved in the reaction. In addition, the production of NOx increased significantly at oxygen concentrations greater than 1.4.

Effects of dissolved organic matter from sludge pyrolysis biochar on the triclosan removal from contaminated soil

When sludge biochar (SC) prepared from sewage sludge was used to remove triclosan (TCS) from both aqueous solution and soil, the adsorption capacity increased with increasing pyrolysis temperature, while the degradation rate showed a different pattern, namely, SC-500 > SC-800 > SC-600 > SC-700. TCS degradation rate achieved nearly 100 % at 2 h with SC-500 used as a Fenton catalyst. Aromaticity of dissolved organic matter (DOM) was positively correlated with the degradation of TCS and adding homologous DOM solution shortened the equilibrium time of TCS degradation, while removing DOM from SC prolonged, compared to the original SC. The results of X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectrometer (EPR) characterization indicated that SC-500 performed a stronger catalytic degradation ability due to the relatively high Fe2+ content to produce more ∙OH and SC-derived DOM act as an electron shuttle to promote other reactive oxidative species generation through two free radical pathways in the activation of H2O2 by Fe2+, which in turn promoted the degradation of TCS.

Constructing Cu9S5@CuSe heterostructures under microwave irradiation for rechargeable magnesium batteries

Copper chalcogenides are believed as the prospective cathode materials for rechargeable magnesium batteries. However, their practical application is seriously restricted by slow diffusion and reaction kinetics due to the large charge/radius ratio of divalent Mg2+ ions. Herein, a simple two-step microwave-assisted synthesis method is rationally developed to construct Cu9S5@CuSe heterostructures as the capable cathode materials for rechargeable magnesium batteries. Two-dimensional CuSe nanosheets are vertically grown on the surface of single-crystal Cu9S5 substrate through selenation reaction under microwave irradiation to form the mixed-dimensional heterostructures. Electrochemical measurements reveal that the as-synthesized Cu9S5@CuSe heterostructures show high reversible capacity of 240 mAh/g and good long-term cyclic stability with approximate 0.013 % capacity decay per cycle at 500 mA g−1 within 1000 cycles. Furthermore, the obviously enhanced rate capability can be achieved in comparison with that of single-crystal Cu9S5 substrate and CuSe nanoparticles. Ex-situ X-ray photoelectron spectroscopy and X-ray diffraction characterizations reveal favourable electrochemical conversion reaction over the Cu9S5@CuSe heterostructure cathode. The superior electrochemical properties are attributed to the optimized diffusion kinetics within the unique heterostructure. This research offers a valuable strategy to develop high-performance cathode materials with favourable kinetics for magnesium batteries.

Fabrication of carbonized derivatives from a novel azo polymer as a precursor for the layered adsorption of iodine and bromine

A nitrogen-rich polymer (AZO-TPA) was synthesized and employed as a precursor for calcined carbonized derivatives. After this polymer was activated with KOH, it was doped separately with melamine and urea, both of which are rich in carbon and nitrogen, and nine distinct carbonized derivatives were obtained through carbonization at various temperatures. Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) characterization revealed that the carbonized structures were rich in nitrogen functional groups, including pyridinic-N, pyrrolic-N, and N+–O- (nitrogen oxides), and possess additional active sites such as –OH and CO groups. The adsorption of bromine, iodine, and the fractional adsorption of bromine/iodine were investigated via the prepared carbonized derivatives. The results indicated that the polymer was successfully doped with urea and yielded carbonized derivatives at 600 °C (AZO-TPAU-600) which exhibited favorable adsorption capacity, particularly after KOH activation and urea doping (iodine vapor: 2782 mg g−1; bromine/iodine: 1854 and 867.55 mg g−1). In addition, the AZO-TPA-600 exhibited high selectivity for bromine adsorption in I2–Br2/cyclohexane solution, and the carbonized derivatives loaded with iodine/bromine could be efficiently desorbed via organic solvents, the adsorption capacity remains above 75 % even after 4 cycles. Finally, the adsorption mechanism was explained in detail.

The activation of PMS for PFOA degradation by adjustable metal stripping Fe/Co/N@BC catalysts: Degradation performance with single-line oxygen and high-valent metal oxides as the main active substances

In this study, a modified biochar (P-Fe/Co/N@BC) catalyst was prepared with wood chips as raw material by hydrothermal method for the activation of peroxymonosulfate (PMS) and degradation of perfluorooctanoic acid (PFOA). Scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) characterization methods were used to demonstrate the presence of FeNx, CoNx, Fe-Co and CO active sites, which contribute to the improvement of the PMS activation capacity for single-line oxygen (1O2). Electron paramagnetic resonance spectroscopy (EPR), reactive oxygen species (ROS) scavenging experiments and methyl phenyl sulfoxide (PMSO) conversion experiments were performed to clarify the main mechanisms of PFOA degradation by reactive species. Further, 1O2, sulfate radical (SO4−), hydroxyl radical (OH), high-valent metal oxides (Fe(IV) and Co(IV)) were jointly involved in the degradation of PFOA, and nonradical were the main activation pathway of PMS. In particular, Fe3+ decomposed from Fe(IV) in the presence of Fe0 and Co2+ decomposed from Co(IV) are able to enhance iron cycling and cobalt cycling, respectively. Meanwhile, Co0 accelerates the conversion of Co3+ to Co2+. The findings suggested that the removal rate of the P-Fe/Co/N@BC-PMS system (99 %) was much higher than that of the P-Fe-N-C/PMS (68.9 %) over 180 min. It emphasized that the incorporation of PTFE (polytetrafluoroethylene) can regulate metal leaching significantly and improve the cycling stability of the catalysts. This study aimed to prepare efficient and stable modified biochar catalysts to activate PMS, which provided an effective solution to the problem of metal ion leaching from metal-modified biochar materials.

A self-cleaning photocatalytic membrane loaded with Bi2O2CO3/In(OH)3 S-scheme heterojunction composites for removing tetracycline from aqueous solutions

Bi2O2CO3/In(OH)3 (BON) photocatalysts were synthesized by a one-pot method and loaded onto polyvinylidene fluoride (PVDF) membranes to obtain a Bi2O2CO3/In(OH)3/PVDF (BON-M) catalytic membrane system. The catalytic membranes demonstrated complete degradation of tetracycline within 40 min under visible light. They demonstrated robust photocatalytic activity across a broad pH range (5–11) and in the presence of coexisting ions. The membranes demonstrated excellent self-cleaning performance. Following exposure to light, the irreversible contamination decreased from 27.1 % to 4.7 % and the membrane’s permeability was almost completely restored. Moreover, the charge transfer mechanism at the S-scheme heterojunction interface of BON was demonstrated by Density functional theory and in-situ X-ray Photoelectron Spectroscopy characterisation, and the active sites involved in tetracycline’s degradation were identified. Meanwhile, the mechanism of the “anemone effect” of BON-M was demonstrated in conjunction with Electron paramagnetic resonance, and the intrinsic Some factors enhancing the membranes’ photocatalytic activity are specified.

Facile Synthesis of Fe-Doped, Algae Residue-Derived Carbon Aerogels for Electrochemical Dopamine Biosensors.

An abnormal level of dopamine (DA), a kind of neurotransmitter, correlates with a series of diseases, including Parkinson's disease, Willis-Ekbom disease, attention deficit hyperactivity disorder, and schizophrenia. Hence, it is imperative to achieve a precise, rapid detection method in clinical medicine. In this study, we synthesized nanocomposite carbon aerogels (CAs) doped with iron and iron carbide, based on algae residue-derived biomass materials, using Fe(NO3)3 as the iron source. The modified glassy carbon electrode (GCE) for DA detection, denoted as CAs-Fe/GCE, was prepared through surface modification with this composite material. X-ray photoelectron spectroscopy and X-ray diffraction characterization confirmed the successful doping of iron into the as-prepared CAs. Additionally, the electrochemical behavior of DA on the modified electrode surface was investigated and the results demonstrate that the addition of the CAs-Fe promoted the electron transfer rate, thereby enhancing their sensing performance. The fabricated electrochemical DA biosensor exhibits an accurate detection of DA in the concentration within the range of 0.01~200 µM, with a detection limit of 0.0033 µM. Furthermore, the proposed biosensor is validated in real samples, showing its high applicability for the detection of DA in beverages.

One-Step Decoration of Subnanometer MoOx Clusters on Bi11VO19 Nanotubes for Visible-Light-Driven Water Oxidation.

For the sluggish reaction kinetics due to a four-electron transfer process, water oxidation is always a major obstacle to solar splitting of water to hydrogen. It remains a tough challenge to develop efficient nonnoble-metal photocatalysts for water oxidation. Herein, we decorate the host photocatalyst of Bi11VO19 nanotubes with the coatalyst of subnanometer MoOx clusters (denoted as Bi11VO19/MoOx hetero-nanotubes) via a one-step cation-exchange solvothermal reaction using Na2V6O16 nanowires as the hard template. It is observed that the morphology and microstructure of Bi11VO19/MoOx hetero-nanotubes vary with the dosage of Mo source and polyvinylpyrrolidone, as well as with the solvent composition. The optimized Bi11VO19/MoOx hetero-nanotubes significantly enhance the photooxidation of water to oxygen with visible light, delivering an oxygen production rate of 790 μmol g-1 h-1, which is 12 times that of bare Bi11VO19 nanotubes. In situ X-ray photoelectron spectroscopy and (photo)electrochemical characterization suggest that the enhanced photoactivity may be caused by the decorated cocatalyst of MoOx clusters, which extracts electrons from Bi11VO19 nanotubes, leaving an abundance of holes for water photooxidation. This work demonstrates a potential strategy to develop photocatalysts for energy conversion by constructing Bi11VO19-based nanostructures.

MoSe2 with Ultra-Fine Pt Decoration for Efficient Photodegradation

Transition metal dichalcogenides are widely studied for their photocatalytic ability due to the adjustable bandgap, high carrier mobility and possibility of foreign-element doping. In this work, multilayer molybdenum diselenide (MoSe2) was decorated with ultra-fine Pt nanoparticles through the mild hydrothermal method. MoSe2-Pt nanocomposites were synthesized and showed good structural and chemical stabilities. The incorporation of Pt nanoparticles provides plenty of active sites for MoSe2. The dominant Pt particle sizes are 1.8 nm, 1.8 nm, and 1.9 nm for the three synthesized samples, respectively. The mean crystal sizes of Pt (111) were calculated from X-ray diffraction patterns and we found that they were in accordance with the particle sizes. Both the particle sizes and mean crystal sizes are related to the synthesis conditions. X-ray photoelectron spectroscopy (XPS) characterizations revealed the formation of Se–Pt bonding. The relative contents of Pt–Se bonding were also calculated from XPS results, and they show the same trends as the optical absorption properties. Combining the XPS and optical absorption results, the effects of Se–Pt bonding during the photo-related process could be further confirmed. By degrading methylene blue (MB) under visible light, the synthesized nanocomposites proved promising for application in real-case degradation of organic pollutants. The sample synthesized with a moderate content of MoSe2 exhibited the best photodegradation efficiency, which could be explained by the maximum Pt-Se contents. Based on the experimental findings, we proposed a possible photodegradation mechanism.

Strong nonlinear-polarization in ZnMgO epitaxial thin-films with Li incorporation

The second-order nonlinear-polarization originated from the interaction between thin-film materials with second-order nonlinear susceptibility (χ (2)) and high-power laser is essential for integrated optics and photonics. In this work, strong second-order nonlinear-polarization was found in a-axis oriented Zn1-x Mg x O (ZnMgO) epitaxial thin-films with Li incorporation, which were deposited by radio-frequency magnetron sputtering. Mg incorporation (x > 0.3) causes a sharp fall in the matrix element χ 33 of χ (2) tensor, although it widens optical bandgap (E opt). In contrast, moderate Li incorporation significantly improves χ 33 and resistance to high-power laser pulses with a little influence on E opt. In particular, a Zn0.67Mg0.33O:Li [Li/(Zn + Mg + Li) = 0.07] thin-film shows a |χ 33| of 36.1 pm V−1 under a peak power density (E p) of 81.2 GW cm−2, a resistance to laser pulses with E p of up to 124.9 GW cm−2, and an E opt of 3.95 eV. Compared to that of ZnO, these parameters increase by 37.8%, 53.4%, and 18.6%, respectively. Specially, the Zn0.67Mg0.33O:Li shows higher radiation resistance than a Mg-doped LiNbO3 crystal with a comparable E opt. First-principle calculations reveal the Li occupation at octahedral interstitial sites of wurtzite ZnO enhances radiation resistance by improving structural stability. X-ray photoelectron spectroscopy characterizations suggest moderate Li incorporation increases χ 33 via enhancing electronic polarization. These findings uncover the close relationship between the octahedra interstitial defects in wurtzite ZnMgO and its nonlinear-polarization behavior under the optical frequency electric field of high-power laser.

Selective Adsorbent Design with Multifunctional Surfaces: Innovating Solutions for Heterogeneous Catalysis in Water.

Heterogeneous catalytic systems with water as the solvent often have the disadvantage of cross-contamination, while concerns about the purification and workup of the aqueous phase after reactions are rare in the lab or industry. In this context, designing and developing the functional selective solid adsorbent and revealing the adsorption mechanism can provide a new strategy and guidelines for constructing supported heterogeneous catalysts to address these issues. Herein, we report the stable composite adsorbent (Fe/ATP@PPy: magnetic Fe3O4/attapulgite with the polypyrrole shell) that features an integrated multifunctional surface, which can effectively tune the selective adsorption processes for Cu2+, Co2+, and Ni2+ ions and nitrobenzene via the cooperative chemisorption/physisorption in an aqueous system. The adsorption experiments showed that Fe/ATP@PPy displayed significantly higher adsorption selectivity for Ni2+ than Cu2+ and Co2+ ions, especially which exhibited an approximate 100.00% removal for both Ni2+ ions and nitrobenzene in the mixture system with a low concentration. Furthermore, combined tracking adsorption of Ni2+ ions and X-ray photoelectron spectroscopy characterization confirmed that the effective adsorption occurs via ion transfer coordination; the pathway was further validated at the molecular level through theoretical modeling. In addition, the selective adsorption mechanism was proposed based on the adsorption experiment, characterization, and the corresponding density functional theory calculation.

Effect mechanism of phosphorous-containing additives on carbon structure evolution and biochar stability enhancement

The regulation of the pyrolysis process is a key step in increasing the carbon sequestration capacity of biochar. The effect of K3PO4 addition on the yield, chemical composition, characteristic functional groups, macromolecular skeleton, graphite crystallites, and stability of biochar was studied in this paper using two-dimensional infrared correlation spectroscopy (2D-PCIS), X-ray photoelectron spectroscopy, Raman spectrum, and other characterization methods combined with thermal/chemical oxidation analysis. It is discovered that adding K3PO4 may effectively minimize the graphitization temperature range and increase biochar's yield, aromaticity, H/C ratio, and proportion of refractory/recalcitrant organic carbon. The 2D-PCIS and Raman analysis revealed that K3PO4 mostly promoted the dehydrogenation and polycondensation process of the aromatic rings in the char precursor, transforming the amorphous carbon structure of biochar into an ordered turbostratic microcrystalline structure. K3PO4 enhanced biochar stability mostly at medium-high temperatures (350 ~ 750℃) by stimulating the transformation of unstable structures of biochar to stable carbon-containing structures or by inhibiting the interaction of its active sites with oxidants through the mineralization process. A 20% phosphorus addition increased biochar's refractory index (R50) by roughly 11%, and it also boosted biochar's oxidation resistance (H2O2 or K2CrO4) efficiency, reducing carbon oxidation loss by up to 7.31%. However, at higher temperatures (> 750 ℃), the doping of phosphorus atoms into the carbon skeleton degraded the biochar structure's stability. The results of this study suggest that using exogenous phosphorus-containing additives is an efficient way to improve the stability of biochar.Graphical abstract

Interphase design enabling stable cycling of all-solid-state lithium metal batteries by in-situ X-ray photoelectron spectroscopy lithium metal sputtering

Interface compatibility is one of the key issues for all-solid-state lithium metal batteries (ASSLMBs). The interface problems include the formation of lithiophobic phases (e.g., Li2CO3) on the surface of the solid electrolytes to worsen the solid-solid interface contact and the continuous parasitic reactions between the highly reactive lithium metal and the electrolyte during cycling. In this work, the in-situ XPS (X-ray Photoelectron Spectroscopy) characterization is used to study the interface between lithium metal and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte using different modification strategies. An ultra-thin composite modification layer of 6 nm Au-6 nm LiF is deposited on the LAGP, which is called C-LAGP. The Li|C-LAGP|Li symmetric cell can be stably cycled for more than 800 h at room temperature at the current density of 0.1 mA cm−2, and the critical current density can reach 1 mA cm−2. The LiFePO4|C-LAGP|Li solid-state battery delivers good cycling stability and high reversible capacity at room temperature. All these good electrochemical performances are resulted from the well-constructed interfacial structure at the solid electrolyte/Li contact. This work provides new ideas and characterization methods for the design of artificial modification layers to solve the interface issues for all-solid-state lithium metal batteries.

Oxygen vacancy-rich CoMoO4/Carbon nitride S-scheme heterojunction for boosted photocatalytic H2 production: Microstructure regulation and charge transfer mechanism

Developing highly efficient S-scheme photocatalysts is a subject of immense interest for harnessing solar energy towards sustainable hydrogen production. Herein, a novel S-scheme heterojunction of oxygen vacancy-rich CoMoO4/CN (CMO/CN) photocatalyst was rationally constructed through loading CoMoO4 nanorods on carbon nitride (CN) nanosheets via a direct one-pot calcination method. The CMO/CN S-scheme heterojunction exhibited enhanced surface area, fine CN dispersion, rich oxygen vacancies, and accelerated charge separation/transfer efficiency, which were conducive to improving photocatalytic H2 evolution performance. Of note, the optimal 3 %CMO/CN sample displayed the highest H2 production rate of 8.35 mmol g−1 h−1, which is 4.6 folds that of pristine CN. In situ irradiated X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) characterizations confirmed the S-scheme charge transfer path between CN and CMO, which greatly promoted spatial charge separation. Density functional theory (DFT) calculations together with contact angle tests revealed the reduced activation energies for H2O dissociation and enhanced hydrophilicity of the CMO/CN. The CMO/CN photocatalysts also presented high stability and fine reusability. This work may provide insights into the combination of defect engineering and heterojunction designing for high-efficiency solar-to-chemical energy conversion.

Hypersensitized electrochemical sensing of Hg(II) based on phase engineering of Co doped MoSe2 nanosheets: Insight in dynamic phase change induced by the chemical interaction between Se and Hg(II)

Transition metal dichalcogenides (TMDs) are regarded as promising nanomaterials for electrochemical detection to heavy metal ions due to their variable performance. However, their detection performances are still limited by inferior conductivities and adsorption ability. In this work, the defects and phase engineering strategy are proposed to utilize cobalt (Co) doped MoSe2 nanosheet for electrochemical detection of Hg ion (Hg(II)). Through Co doping, we successfully achieved the phase transition of MoSe2 from the 2 H phase of semiconductor to the 1 T phase of conductor. Moreover, the 1 T MoSe2 is demonstrated to show a better adsorption and catalytic ability for Hg(II) detection than that of 2 H MoSe2. As a result, the MoSe2 containing atomic ratio of Co is 10% (named CM10) owning suitable content of 1 T phase has a superior sensitivity of 52.17 μA μM−1 and a low LOD of 3.96 nM for Hg(II). More importantly, combining with the characterization of X-ray photoelectron spectroscopy (XPS) and density-functional theory (DFT) calculation, it is found that the Hg(II) adsorption will also lead to the phase change of MoSe2, and the change state in the samples after the adsorption of Hg(II) will be more accurate to be responsible for the improvement of catalytic ability.

XPS and ARXPS for Characterizing Multilayers of Silanes on Gold Surfaces

X-ray photoelectron spectroscopy (XPS) and angle-resolved XPS (ARXPS) characterization of surface layers resulting from the functionalization of polymers such as polyvinylchloride (PVC) modified with 3(mercaptopropyl)-trimethoxysilane (MPTMS) and (3-aminopropyl) triethoxysilane (APTES) is challenging due to the overlap in signals, deriving both from the substrate and the functionalized layers. In this work, a freshly cleaved, ideally flat gold surface was used as carbon-free model substrate functionalized with MPTMS and subsequently grafted with APTES. Avoiding the overlap of signals from carbon atoms present in the substrate, the signals in the C1s, O1s, Si2p, S2p and N1s high-resolution spectra could be assigned to the MPTMS/APTES functionalized layer only and the curve-fitting parameters could be determined. Quantitative analysis was in very good agreement with the expected stoichiometry of the functionalized layer, confirming the adopted curve-fitting procedure. In addition, it was found that one molecule of APTES grafted two MPTMS via silane groups. ARXPS allowed for determining the thickness of the functionalized layers: MPTMS thickness was found to be 0.5 (0.2) nm, whereas MPTMS + APTES thickness 1.0 (0.2) nm was in good agreement with Avogadro model calculations. This approach can be considered a powerful tool for characterizing functionalized surfaces of more complex systems by XPS.

Structural, chemical, and metal-oxide-semiconductor characteristics of RF magnetron sputtered thulium oxide passivation layer on 4H-silicon carbide substrate

Thulium oxide (Tm2O3) passivation layer (PL) deposited on 4H-silicon carbide (SiC) that was subjected to postdeposition annealing at 700 °C in forming gas-oxygen-forming gas ambient was reported for the first time in this work. X-ray photoelectron spectroscopy characterization revealed the success of annealing process in minimizing the concentration of oxygen vacancies and also curbed the presence of TmO suboxide bonding in the annealed Tm2O3 PL. In addition, XPS characterization has also disclosed the incorporation of nitrogen ions into the Tm2O3 lattice through the annealing process in which grazing incidence X-ray diffraction has also revealed the shift of detected peaks with regards to Tm2O3 phases to small diffraction angles. Although X-ray reflectivity measurements have disclosed the formation of thicker SiO2 interfacial layer (IL) for the annealed Tm2O3 PL, the acquisition of a higher dielectric constant (k) by the annealed PL when compared to as-deposited PL has suggested that the formation of SiO2 IL has minimal effect toward the k value of annealed PL. Metal-oxide-semiconductor characteristics of the annealed Tm2O3 PL on 4H-SiC was systematically reported in this letter.

Outside-to-inside: Efficacy comparation of Mn bulk and surface-doped TiO2{201} in E-fueled solar flow battery system

The all-in-one E-fueled solar flow battery system that can be recharged with liquid fuel is a new type of power system. It can continuously convert solar energy into liquid fuel without relying on external power supply equipments. However, the interface between the photoanode and the electrolyte often exhibits unsteady behavior, resulting in poor performance of the system. In this work, the {201} facets are selected and the impact of two doping treatment strategies for TiO2 {201} photoanode on the performance of the E-fueled solar flow battery system is systematically studied through the I-t curve, linear sweep voltammetry, Mott-Schottky plot. The results show that the un-biased photocharging current of bulk-doped TiO2 can reach 2.7 mA·cm−2 in the battery system test, only relying on the self-built electric field at the interface, and the energy conversion efficiency approaches 2.67 %. In addition, the performance is analyzed by the combination of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and other characterizations, with the aim of distinguishing the effects of bulk- and surface-doped Mn and accurately revealing the mechanism of their influences from the outside to the inside. Finally, the optimization rules of the un-biased light charging mode of the system are explored.