Search

[Display omitted] • The structural stability, electrical properties and optical properties of g-GaN/Al 0.5 Ga 0.5 N heterojunction after surface oxidation are analyzed. • Oxidized surface can be formed spontaneously for adsorption oxidation and substitutional oxidation process does not occur easily. • The increase in work function of heterojunction after oxidation weaken electron emission properties of material surface. • Substitutional oxidation is detrimental to light absorption, whereas adsorption oxidation slightly enhances light absorption. In this paper, the structural stability, charge transfer, band structure, density of states, absorption coefficient and reflectivity of g-GaN/Al 0.5 Ga 0.5 N heterojunction after surface oxidation are investigated. Our results reveal that formation energy of adsorptive oxidation process is negative and the oxidized surface can be formed spontaneously. The substitutional oxidation process is heat-absorbing and structure is unstable, which is not easy to occur. Band structure show that new energy levels are created due to charge transfer between O atom and heterojunction after surface oxidation. The electronic states of O-p orbitals hybridize with those of Ga-s, Ga-p, and Al-p orbitals, while O-s orbitals affect energy levels at low-energy end. Meanwhile, work function of heterojunction increases after oxidation, weakening electron emission properties of material surface. The results of optical properties illustrate that substitutional oxidation is detrimental to light absorption, while adsorption oxidation slightly enhances light absorption, especially when adsorption oxidation occurs in g-GaN layer, which is competitive for improvement of optical properties. This study can be useful for the removal of surface oxides from g-GaN/AlGaN heterojunction. [ABSTRACT FROM AUTHOR]

Issues on the superficial oxidation of mesoporous amorphous silicon and germanium photonic layers generated at oblique angles are reported. Such films were designed to improve the transmittance of optical elements over the mid-IR window (3.6–4.9 μm) by removing the light reflection. These nanostructures were deposited on silicon substrates by e-beam evaporation at room temperature. IR ellipsometry and spectrophotometry studies combined with models based on effective medium approximations predicted the presence of silicon or germanium oxides. Such oxidation was evidenced by combining X-ray photoelectron spectroscopy and advanced (scanning-)transmission electron microscopy studies based on energy-dispersive X-rays and electron energy-loss spectroscopies. Both techniques also allowed to prove the formation of core-shell-type architectures consisting of pure Si or Ge surrounded by oxidized species, even for a Ge layer subsequently capped with a dense MgF 2 coating. The different approaches used for preparing electron transparent specimens (tripod polishing and focused ion-beams) confirmed a fast oxidation of the Ge nanocolumns even for short air exposure periods, and allowed comparing it with the level of oxidation promoted from other pollutant sources. This work sheds light on the spontaneous undesired oxidation in Si or Ge slanted nanorods which can diminish the performances and limit further development of optical devices. Unlabelled Image • Si and Ge porous OAD thin films for optical applications in the infrared. • Optical characterization of the layers grown by ellipsometry and spectrophotometry. • Spontaneous formation of Si and Ge oxidized species predicted by the BEMA model. • Confirmation of the surface oxidation by compositional (S)TEM/EDX and XPS analyses. • Oxidized core-shell type structures evidenced by (S)TEM/EELS analyses at nanoscale. [ABSTRACT FROM AUTHOR]

Surface oxidation, as one of fundamental chemical reactions in metals, greatly affects their properties. Herein, we develop a new quaternary GaInSnZn liquid metal with the melting temperature of 9.7 °C, which is the lowest among all reported Ga-based liquid metals. With high-resolution transmission electron microscopy, we directly observed the oxide layer formed on the surface of the liquid metal. The initially formed oxide layer is revealed to be amorphous and very sensitive to electron beam. Prolonged irradiation results in its structural change from amorphous to crystalline phases. The present finding refreshes the basic understanding of surface oxidization of liquid metals and opens up the possibility of tuning surface structures and morphologies by using electron beam irradiation. • A new GaInSnZn liquid metal with the melting temperature of 9.7 °C was developed. • A thin oxide layer formed on the surface of liquid metal was directly observed. • Amorphous nature of surface oxide layer was confirmed via structural characterization. • The structure of surface oxide layer can be tuned by electron beam irradiation. [ABSTRACT FROM AUTHOR]

Two dimensional molybdenum disulfide (2D-MoS 2) has been recently developed to be used as superb adsorbents for removing heavy metals from water due to its huge sulfur-rich surface area. In this work, single adsorption and co-adsorption performances of H 2 O, Hg2+ and O 2 on MoS 2 surface with and without S-vacancy defects have been theoretically studied to explore the Hg2+ adsorption and surface oxidation through density function theory (DFT) calculations. Moreover, the Hg2+ adsorption and surface oxidation have experimentally studied through atomic force microscopy (AFM) to verify the theoretical calculation results. It has been found that S-vacancy defects make MoS 2 surface more reactive, leading to the much stronger adsorption energy of H 2 O, Hg2+ and O 2 on defective MoS 2 surface. O 2 can only be physically adsorbed on the perfect MoS 2 surface, while it bonds to the unsaturated Mo atoms at the vacancy site on defective MoS 2 surface. Besides, co-adsorption results illustrate that Hg2+ have priority to react with MoS 2 surface than O 2 due to the much stronger binding affinity, and surface oxidation occurs only when there are enough reaction sites for the Hg2+ adsorption and surface oxidation simultaneously. These theoretical co-adsorption results are consistent with the experimental Hg2+ adsorption and surface oxidation results obtained by AFM. These findings in this study are of great significance for the development and utilization of MoS 2 -based nanomaterials as a heavy metal adsorbent. Unlabelled Image • The S-missing vacancy influences both the Hg2+ adsorption and surface oxidation. • MoS 2 has preference for Hg2+ adsorption when there are limited reaction sites. • Oxidation and Hg2+ adsorption both occur when there are redundant reaction sites. [ABSTRACT FROM AUTHOR]

A novel two-step joining method was adopted to achieve the reliable bond of dense Si 3 N 4 (D-Si 3 N 4) with porous Si 3 N 4 (P-Si 3 N 4) components for high temperature applications using Li 2 O-MgO-Al 2 O 3 -SiO 2 -B 2 O 3 glass-ceramic as interlayer. The joining process involved a pre-oxidation of D-Si 3 N 4 in air for a good wettability, followed by a joining process at 1240 °C–1300 °C for 10 min in vacuum. The microstructure evolution, interface structure, fracture characteristics and joining mechanism of the joints were elucidated. The β-spodumene solid solution based glass-ceramic was formed in the seam, which could effectively moderate the thermal expansion mismatch between interlayer and Si 3 N 4 substrates and ensure the high-temperature resistance of joint. Compared with one-step joining , two-step joining method could obtain more reliable D-Si 3 N 4 /glass-ceramic/P-Si 3 N 4 joints. A favorable shear strength of 43 MPa was achieved within 10 min at 1280 °C, which was 15 MPa (~54%) higher than that of the joints by one-step joining method. As a result, good CTE match as well as strong bonding to Si 3 N 4 substrates made the investigated glass-ceramic a suitable candidate for joining Si 3 N 4 ceramics. Unlabelled Image • Porous Si 3 N 4 was firstly joined with dense Si 3 N 4 using Li 2 O-Al 2 O 3 -SiO 2 -B 2 O 3 glass-ceramic interlayer; • Dense Si 3 N 4 was pre-fabricated a oxidation coating for the wettability and compatibility with glass-ceramic interlayer; • β-spodumene based glass-ceramic interlayer contributed to high-temperature resistance and appropriate CTE for the joint; • The room-temperature and high-temperature (850 °C) shear strengths were ~43 MPa and ~54MPa, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 3D view in plasma polymerization is crucial for coating functional materials. • HMDSO yields plasma film-forming species with different sticking probabilities. • Surface oxidation is relevant in plasma polymerization for complex geometries. Hexamethyldisiloxane (HMDSO) low-pressure plasmas are known for their versatility in the deposition of plasma polymer films (PPFs) with different properties and applications. Although they have been studied for decades, the reaction mechanisms of plasma polymer formation leave open questions, particularly when deposition on 3D materials with complex geometries such as cavities and undercuts is considered. In the present study, two configurations named "cavity" and "undercut" have been selected to study the influence of diffusion of film-forming species and surface reactivity in HMDSO plasmas without and with O 2 admixture. A varying spatial chemical composition of the plasma polymer deposit along the penetration depth of the studied configurations indicates different sticking probabilities of the film-forming species. Furthermore, although ion-induced effects are usually only considered for direct plasma exposure, the obtained results and additional etching experiments reveal that the contribution of high-energy particles might still be considered underneath small openings. Finally, the relevance of oxidizing chemical reactions at the surface inside the configurations is clarified when O 2 is added to the plasma. [ABSTRACT FROM AUTHOR]

Galena plays a catalytic role in reducing Fe3+ and creating a Fenton reaction system with H 2 O 2 , leading to a potent oxidation process on the galena surface and the formation of a PbSO 4 layer. [Display omitted] • The synergistic effect of Fe3+ and H 2 O 2 exhibited selective depression of galena. • Galena catalyzed the Fe3+ reduction to create a Fenton reaction system with H 2 O 2. • The galena surface was intensely oxidized by the ⋅OH generated from the Fenton reaction. • The depression of galena was achieved by the formation of a PbSO 4 layer on the surface. Developing an efficient and eco-friendly approach for the separation of chalcopyrite and galena is crucial for maximizing the resource utilization. This study explores the use of galena-assisted Fenton reaction as a method for depressing galena flotation. Various analytical techniques, including micro-flotation tests, contact angle (CA) measurements, Fourier Transform Infrared Spectroscopy (FT-IR) analysis, Scanning Electron Microscope (SEM) observation, X-ray Photoelectron Spectroscopy (XPS) studies, Raman Spectra determinations, electrochemical analysis, and UV–visible spectrophotometer (UV–vis) surveying, were employed to investigate the effectiveness of this approach. The results of the flotation tests reveal that the cooperation of ferric ions and hydrogen peroxide can strongly and selectively depress galena. The CA and FT-IR analyses demonstrate the significant decrease of hydrophobicity and collector adsorption of the galena surface by the synergistic effect of ferric ions and hydrogen peroxide. Further analysis using SEM, XPS, Raman spectra and electrochemical analysis show that galena can reduce ferric ions to ferrous ions, creating a Fenton reaction system upon the addition of hydrogen peroxide. The galena surface is intensely oxidized by the generated hydroxyl radicals, leading to the production of a compact layer of PbSO 4. These findings provide a promising solution for the efficient and environmentally responsible separation of chalcopyrite and galena. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydroxyl radicals in the peracetic acid solution oxidized SiGe selectively over Si. • Hydroxyl radicals increased both SiGe etching rate and SiGe/Si etching selectivity. • The highest etching selectivity of 225 to Si was obtained from Si 0.75 Ge 0.25. • Hydroxyl radicals enhanced selective SiGe etching in vertically-stacked SiGe/Si trench structures. Herein, we investigate the selective oxidation and dissolution behavior of SiGe over Si using mixtures of HF, H 2 O 2 , CH 3 COOH, and CH 3 COOOH (peracetic acid, PAA). We observe a significantly higher dissolution rate for SiGe compared to Si in the PAA solution. This difference can be attributed to more rapid and vigorous oxidation of the SiGe surface compared to that of the Si surface. We introduce a novel method to further enhance the selective dissolution of SiGe by controlling the formation of hydroxyl radicals in the PAA solution. When the formation of hydroxyl radicals is enhanced, the SiGe dissolution rate and selectivity significantly increase from 212 nm/min and 111 to 793 nm/min and 225, respectively. The selective etching of the SiGe layers is also achieved on vertically stacked multilayer SiGe/Si trench structures at an etching factor of 95:1. The increase in the SiGe dissolution rate and selectivity over Si can be attributed to the effective oxidation of the SiGe surface by hydroxyl radicals without causing surface roughening in either SiGe or Si. Based on the results, we propose a mechanism for the selective oxidation and dissolution of SiGe in PAA solution, with and without the enhancement of hydroxyl radicals. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ns-laser ablation of Si in water proceeds via ablative subcritical plasma. • Ablated mass is linear and colloidal extinction is nonlinear vs laser intensity. • At high intensities strong melt expulsion results in saturation of colloidal yield. • Moderately-wet, minorly oxidized Si nanoparticles are strongly bactericidal. Abstract High-productivity regime of nanosecond IR-laser ablative generation of silicon colloidal solutions in water for anti-bacterial applications was found in terms of GW/cm2-level laser intensity and scanning velocity by measuring multi-shot ablative mass loss and extinction coefficients of the colloids as sub-linear and third-power intensity functions, respectively. This advantageous regime implies sub-linear mass loss versus laser intensity at the simultaneous third-power yield of nanoparticles, resulting from the subcritical-density, opaque ablative plasma regulating the sample ablation rate and the related plasma-mediated dissociation (dispergation) of the ablation products. In contrast, at higher intensities, there is a drastic increase in mass loss with the corresponding increased yield of (sub) micrometer-sized particles owing to intense plasma-driven expulsion of micro-scale melt droplets and the corresponding saturation of the extinction coefficient of the colloidal solutions because of their dynamic local "self-limiting" effect during the high-rate ablation. The optimal low-intensity regime for Si nanoparticle production demonstrates the monotonous correlated increase of mass loss and extinction coefficient in terms of increasing laser scanning velocity, indicating the diminished cumulative effects. Surface coatings prepared from the generated Si nanoparticles exhibit minor surface oxidation, as acquired as their elemental composition via energy-dispersive X-ray spectroscopy, making their contact angle for water droplets (≈51°) close to that of bare Si wafer (≈58°) with its nanometer-thick native oxide layer. Owing to good wetting, the nanoparticle-based surface coatings show strong antibacterial response regarding Gram-negative Pseudomonas auereginosa bacteria even despite their minor oxidative passivation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Amorphous As 2 S 3 thin films were prepared by thermal evaporation. • UV light excited Raman spectra at high power density show sharp As 2 O 3 lines. • No As 2 O 3 Raman lines are observed at 515 nm excitation even at much higher power. Abstract Amorphous As 2 S 3 films with surface roughness near 0.5 nm were prepared by thermal evaporation. Raman measurements performed under ultraviolet (UV) laser excitation (325 nm) revealed a series of sharp intense peaks appearing at laser power density P exc above 150 kW/cm2. No such effects were observed at Raman measurements under visible (514.7 or 632.8 nm) light excitation, even for much higher P exc values. The new Raman peaks are identified as arsenolite (As 2 O 3) features. UV light-assisted oxidation of the As 2 S 3 surface is discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Size dependent metal-to-insulator transition in MoO 2 was unveiled by systematic study with various spectroscopic methods. • Electronic transport measurements showed similar metal-to-insulator transition by film thickness. • Surface oxidation in epitaxial thin films would be the main driver to trigger this transition. Abstract Interfaces in transition metal oxides play critical roles for tuning physical properties. In thin film form, multiple interfaces can be created in between a film and a substrate, in between a film and air, and within a thin film. The role of each interface has been rarely studied. In this research, we used MoO 2 as a model system to study the role of the oxidized layer at film-air interface in thickness-driven metal-insulator transition. The oxidized layer at the surface is likely to be the main cause in positive temperature coefficient of resistivity in MoO 2 thin films thinner than about 20 nm. To find the origin of this insulating behavior in electronic transport measurements, we used x-ray diffraction, density functional theory and various spectroscopic methods. We observed the formation of oxidized MoO 2+ x at the film-air interface and its thickness explain the peculiar insulating behavior in the thinner films and even nanoparticles from the literature. [ABSTRACT FROM AUTHOR]

The structural and electrical phase transition in a single core-shell-like VO 2 nanobeam formed by reduction and surface oxidation is systematically investigated. The core-shell-like structures were fabricated by a two-step process through hydrogen-annealing and subsequent oxygen-annealing processes on VO 2 nanobeams that were synthesized on a Si substrate with a 300-nm thick SiO 2 layer. The nanobeam was a roughly rectangular shape elongated along the rutile c -axis with length of approximately 65–110 μm, width of 2–3 μm, and thickness of 200–300 nm. Temperature-dependent Raman and electrical characteristics of the as-grown VO 2 nanobeams and the VO 2 nanobeams treated by annealing under hydrogen and oxygen gases were compared. Specifically, temperature-dependent Raman scattering in the core-shell-like VO 2 nanobeam exhibited a lower transition temperature of the structural phase without the monoclinic M2 phase than those of the as-grown VO 2 nanobeams. With respect to the electrical characteristics, the core-shell-like VO 2 nanobeam exhibited a more gradual change in resistance with non-hysteretic behavior and without abrupt current jumping in contrast to the as-grown VO 2 nanobeams. The shell thickness of the core-shell-like nanobeam was measured to be approximately a few tens of nanometers. These results fit well with the theoretical calculations taking into account the phase coexistence of metal and insulator domains in VO 2 nanobeams. Such different characteristics of the core-shell-like VO 2 nanobeams are understood in terms of their core-shell-like structure with differences in oxygen stoichiometry resulting from the surface oxidation of the hydrogen-annealed VO 2 nanobeams. [ABSTRACT FROM AUTHOR]

Atomically thin monolayer molybdenum disulfides (MoS 2 ) with tunable electronic structure has promising applications in opto-electronic devices and sensors. In this work, unique nano-patterning and surface oxidation of monolayer MoS 2 was achieved based on hydrogen peroxide (H 2 O 2 ) treatment. It was found that the exfoliated monolayer MoS 2 can be uniformly oxidized when exposed to low-concentration H 2 O 2 , forming an intermediate phase composed of MoS x O y . In addition, patterned triangular pits with well-defined edges can be formed under high-concentration H 2 O 2 condition. The band gap of monolayer MoS 2 could be effectively modulated by H 2 O 2 treatment as verified by photoluminescence spectra. This work shows that simple H 2 O 2 treatment can be an alternative approach for both surface functionalization and band gap modulation of MoS 2 flake, and it also provides an alternatively simple way to obtain patterned MoS 2 nanostructures without complicated standard lithography processes. [ABSTRACT FROM AUTHOR]

An oxidized mesoporous carbon (OMC) with fluffy structure was fabricated from the mixture of petroleum asphalt and aluminum isopropoxide, and its structures were characterized by FESEM, TEM, BET, TG, XPS and FT-IR. In addition, bath absorption experiments for malachite green (MG) and lead ion (Pb 2+ ) were carried out to explore the effects of pH, initial concentration, contact time and temperature on its absorption process. Results show that the OMC prepared has a fluffy ultrathin-wall structure with narrow pore size distribution and rich oxygen-containing groups. It exhibits excellent absorption performance for the removal of MG as well as Pb 2+ , as indicated by that its maximum adsorption capacity is 963.1 mg g −1 for MG and 198.6 mg g −1 for Pb 2+ . The absorption experimental data are all fitted well with pseudo-second-order model and Frendlich isotherm, respectively. More importantly, the OMC still maintains relatively high adsorption capacity after five cycles. [ABSTRACT FROM AUTHOR]

High recombination rate of photogenerated electron-hole pairs and relatively narrow photoresponsive range of TiO 2 -based photocatalysts are the remaining challenges for their practical applications. To address such challenges, photocatalysts consisting of AgCl covered Ag nanoparticles (AgCl@Ag), titanate nanotubes (TiNT), and nitrogen-doped reduced graphite oxide (rGO N ) are fabricated through alkaline hydrothermal process, followed by deposition and in situ surface-oxidation of silver nanoparticles. In the synthesized photocatalysts, the titanate nanotubes have average length of about 100 nm with inner diameters of about 5 nm and the size of the formed silver nanoparticles is in the range of 50–100 nm. The synthesized photocatalyst degrades almost all the model organic pollutant Rhodamine B in 35 min and remains 90% of photocatalytic efficiency after 5 degradation cycles under visible light irradiation. Since the oxidant FeCl 3 applied for oxidation of surface Ag to AgCl is difficult to be completely removed due to the high adsorption capacity of TiNT and rGO N , the effect of reside Fe atoms on photocatalytic activity is evaluated and the results reveal that the residue Fe atom only affect the initial photodegradation performance. Nevertheless, the results demonstrate that the formed composite catalyst is a promising candidate for antibiosis and remediation in aquatic environmental contamination. [ABSTRACT FROM AUTHOR]

In this paper we report on the competition in metal surface hardening between the femtosecond shock peening on the one hand, and formation of laser-induced periodic surface structures (LIPSS) and surface oxidation on the other hand. Peening of the stainless steel AISI 316 due to shock loading induced by femtosecond laser ablation was successfully demonstrated. However, for some range of processing parameters, surface erosion due to LIPSS and oxidation seems to dominate over the peening effect. Strategies to increase the peening efficiency are discussed. [ABSTRACT FROM AUTHOR]

Thermally oxidized nickel-based alloys are studied by scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), atomic force microscopy (AFM), scanning kelvin probe force microscopy (SKPFM) and photoelectro-chemical techniques as a function of oxidation time at a fixed temperature of 623 K. By photoelectrochemistry measurements we identify the formation of three oxides NiO, Fe 2 O 3 , Cr 2 O 3 and determine the corresponding gap values. We use these values as parameter for imaging the surface at high bias voltage by STM allowing the spatial localization and identification of both NiO, Fe 2 O 3 oxide phases using STS measurements. Associated to Kelvin probe measurements we show also that STS allow to distinguished NiO from Cr 2 O 3 and confirm that the Cr 2 O 3 is not visible at the surface and localized at the oxide/steel interface. [ABSTRACT FROM AUTHOR]

The spectral emissivities of ZrB 2 -20 vol.% SiC composites with various surface components of ZrB 2 /SiC (ZS1), silica-rich glass (ZS2) and porous zirconia (ZS3) were measured using infrared spectrometer in the wavelength range from 2.5 to 25.0 μm. The relationship between surface oxidation (associated with surface component, thickness of oxide scale, testing temperature as well as roughness) and the radiative properties of ZrB 2 -SiC composites were investigated systematically. Surface component affected the radiative properties of composites significantly. The total emissivity of ZS1 varied from 0.22 to 0.81 accompanied with surface oxidation in the temperature range 300–900 °C. The emissivity of ZS2 was about 1.5 times as that of ZS3 under the same testing conditions. The oxide scale on specimen surface enhanced the radiative properties especially in terms of short-wave range, and the emissivity in the long-wave range gradually increased with the thickness of oxide scale within a certain range. The influence of testing temperature and surface roughness was also investigated. The testing temperature had a little effect on radiative properties, whereas effect of surface roughness could be negligible. [ABSTRACT FROM AUTHOR]

[Display omitted] • Observation of a fast oxidation process of ScAlN when exposed to air. • Identification of the impact of surface oxidation on the properties of ScAlN. • Demonstration of a lattice-matched atomically sharp Sc 0.18 Al 0.82 N/GaN interface. • A type-II band alignment was determined for Sc 0.18 Al 0.82 N/GaN heterojunction. Ferroelectric scandium aluminum nitride (ScAlN), owing to its unique properties and seamless integration with the mainstream GaN technology, has attracted considerable attention as one of the most promising materials for next-generation multifunctional electronics. To date, however, a detailed understanding of the fundamental surface properties and the band alignment of ScAlN/III-nitride heterostructure has remained elusive. In this work, with the use of high-resolution X-ray photoelectron spectroscopy measurements, we demonstrate the existence of a considerable oxidation layer on ScAlN when it is exposed to air, which shows a significant impact on the material characterization and electronic structure evaluation. By excluding the possible impact from the surface oxide layer, the band alignment of Sc 0.18 Al 0.82 N/GaN can be correctly determined. Simulation results further showed that the Sc 0.18 Al 0.82 N barrier layer could offer excellent charge carrier confinement and a high density of two-dimensional electron gas (2DEG) at the heterostructure interface, which is needed for GaN-based high electron mobility transistors (HEMTs) with enhanced performance. This work not only identifies the band alignment between Sc 0.18 Al 0.82 N and GaN for future novel ScAlN/III-nitride device applications but also highlights the importance of considering the prevalent surface oxidation issue in the emerging ferroelectric nitride family. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) with different degree of surface oxidation were used as supports for 5 wt.% Co catalysts. CNTs and Co/CNT catalysts were analyzed by XPS, nitrogen adsorption, TEM and electron diffraction to reveal their structure. High oxidation degree of CNT surface (8.6 at.% of O) and low Co loading led to predominantly amorphous Co species. This resulted in the absence of catalytic activity in both CO and CO 2 hydrogenation in opposite to the catalyst supported on less oxidized CNTs (5.4 at.% of O) where Co species were found to be crystalline. Thermal treatment of inactive catalyst in H 2 and He led to the formation of Co crystal phase which was active in catalysis. Co particle size in catalyst supported on strongly oxidized CNTs was unchanged during CO hydrogenation in opposite to Co supported on less oxidized CNTs. Carbon shell formation on the surface of amorphous Co particles during CO hydrogenation was revealed, which testified CO disproportionation. Qualitative mechanism of CO hydrogenation on small Co particles was proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxidation phenomenon in one laser spot on stainless steel surface is studied. [•] Compositions and morphologies vary from center to edge in one laser spot. [•] Hexagonal Cr2O3 distributes in the edge, while spherical Fe2O3 in the center. [•] Oxidation mechanism is proposed based on thermodynamics and kinetics. [Copyright &y& Elsevier]

[Display omitted] • Surface lattice shrinks but overall particle morphology of UO 2 does not change by Gd. • Doped Gd dramatically reduces the chemical bond of adsorbate O with U. • Three key mechanisms of the enhanced oxidation resistance of Gd-UO 2 are unveiled. • Diffusion of adsorbed O into UO 2 subsurface is thermodynamically infeasible. • Gd retards initiation of surface oxidation and oxide-layer growth of UO 2 particles. An accurate understanding of structural integrity and chemical reactivity of UO 2 disposed in deep underground sites is of importance. Owing to the specific condition of the site location, UO 2 may have substantially different properties from the conventional prediction. In this study, we demonstrate that the oxidation resistivity of UO 2 is considerably modified by gadolinium (Gd), which is the element of neutron absorber and a byproduct of nuclear decay of radioactive U-235. Using density functional theory calculations, we investigate how the oxidation mechanism of UO 2 changes with Gd incorporation in U lattice. Our study indicates that Gd remarkably enhances the thermodynamic stability of pristine UO 2 against surface oxidation via three underlying mechanisms: (i) weakens the chemical bonding of adsorbed oxygen atom (O) with U, (ii) reduces active sites (U) for oxygen adsorption, and (iii) suppresses the subsurface diffusion of adsorbed O delaying the growth of the oxide layers on the UO 2. Electronic and lattice structure analyses for Gd-doped UO 2 indicate that amount of charge transfer from U to O is critically reduced and the lattice of the UO 2 surface is contracted. Our results provide useful information for understanding long-term stability and improving the structural integrity of UO 2 through the chemical doping process. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNTs) with external and internal decoration of Fe2O3 nanoparticles (NPs) were imaged by scanning transmission X-ray microscopy (STXM) with a concurrent identification of the electronic structure. For Fe2O3 outside CNTs, a carbon coating on CNTs was observed while for Fe2O3 inside CNTs, pure CNTs without carbon coating could be clearly identified. Surface oxidation of CNTs with internal decoration of Fe2O3 NPs was also found which showed a heterogeneous distribution. Further experiments suggest that the oxidization of CNTs may favor the internal Fe2O3 decoration of CNTs. [Copyright &y& Elsevier]

Abstract: This paper presents the results of measurements and analysis of the influence of laser marking process parameters on the colour obtained. The study was conducted for AISI 304 multipurpose stainless steel using a commercially available industrial fibre laser. It was determined how various process parameters, such as laser power, pulse repetition rate, scan speed of the material, spacing between successive lines, thickness and temperature of the material, location of the sample relative to the focal plane, size of marked fields and position in the workpiece, affect the repeatability of the colours obtained. For objective assessment of colour changes, an optical spectrometer and the CIE colour difference parameter ΔE ab * were used. Additionally, in order to determine the susceptibility of laser colour marking to the ageing process, two types of tests – UV radiation and a salt spray test – were performed. Based on this analysis, necessary modifications to the laser systems commonly used for monochrome marking are proposed in order to achieve greater repeatability in colour marking. [Copyright &y& Elsevier]

Abstract: Carbon nanotubes (CNTs) were fabricated by the catalytic chemical vapor deposition method and oxidized by HCl, H2SO4, HNO3 and NaOCl solutions for enhancing benzene, toluene, ethylbenzene and p-xylene (BTEX) adsorption in an aqueous solution. The surface nature of CNTs was changed after the H2SO4, HNO3 and NaOCl oxidation, which makes CNTs that adsorb more BTEX. The NaOCl-oxidized CNTs show the greatest enhancement in BTEX adsorption, followed by the HNO3-oxidized CNTs, and then the H2SO4-oxidized CNTs. The adsorption mechanism of BTEX via CNTs is mainly attributed to the π–π electron-donor–acceptor interaction between the aromatic ring of BTEX and the surface carboxylic groups of CNTs. The NaOCl-oxidized CNTs have superior adsorption performance of BTEX as compared to many types of carbon and silica adsorbents reported in the literature. This suggests that the NaOCl-oxidized CNTs are efficient BTEX adsorbents and that they possess good potential applications for BTEX removal in wastewater treatment. [Copyright &y& Elsevier]

The growth of subnanometer silicon overlayers on TiO2 (1 1 0)-(1×2) reconstructed surfaces at room temperature (RT) has been studied by X-ray and ultra-violet photoelectron spectroscopies (XPS and UPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). For Si coverage of 1 monolayer (ML) only Si2+ species were detected on top of a further reduced TiO2 surface. Upon Si coverage, the characteristic (1×2) LEED pattern from the substrate is completely attenuated, indicating absence of long-range order. Therefore, the combination of all the above mentioned techniques, indicates that the Si overlayer consists of a smooth and homogeneous Si oxide layer on a reduced TiO2 surface. [Copyright &y& Elsevier]

The electrochemical oxidation of chalcopyrite (CuFeS2) has been studied at pH 4 using voltammetry, coulometry, X-ray photoelectron spectroscopy (XPS) and both ex situ and in situ atomic force microscopy (AFM). Between 500 and 650 mV an anodic oxidation peak is observed, prior to the onset of the main decomposition reactions. Chalcopyrite electrodes in contact with electrolyte show some release of Cu into solution even without an applied potential. At 500 and 650 mV, the loss of Cu from the surface increases by a factor of 2 and 6, respectively. Oxidation at 500 mV results in the formation of a mixed oxide or hydroxide of iron, coincident with islands (<0.15 μm wide) of reaction products observed on the surface using AFM. The surface coverage of these islands increases with amount of charge passed. Oxidation at 650 mV shows similar processes have occurred, but with a greater island surface coverage and a more deeply altered surface. XPS depth profiling suggests iron oxide or hydroxide is now a major phase in the top ∼40 A˚, with significant sulphate also formed. Observation of islands (alteration products) using in situ AFM under potential control shows that these features are not an artefact of the preparation methods. [Copyright &y& Elsevier]

The determination of the oxygen concentration at the surface is the critical parameter in all models [Surf. Sci. 112 (1981) 168; Nucl. Instrum. Meth. Phys. Res. B 14 (1986) 403; in: A. Benninghoven, B. Hagenhoff, H.W. Werner (Eds.), SIMS, Vol. X, Wiley, New York, 1997, 203 pp.; Phys. Rev. B 50 (1994) 15015; in: A. Benninghoven, P. Bertrand, H.N. Migeon, H.W. Werner (Eds.), SIMS, Vol. XII, Elsevier, Amsterdam, 2000, 151 pp.; J. Appl. Phys. 90 (2001) 4456] that study the large enhancement of the ionisation probability of positive ions by the presence of oxygen at the surface. Different analysis techniques (low energy ion scattering, Rutherford back scattering spectrometry and secondary ion mass spectrometry) are combined in order to clarify the oxygen dependence of the ionisation probability of Si+, αSi+, during O2+ bombardment. A ratio of ion signals is correlated with the surface oxygen content, determined by LEIS, allowing us to study the enhancement of the ionisation probability of Si by oxygen at the surface for energies between 1 and 5 keV per O2+ ion. For a wide range of oxidation conditions the oxygen enhancement can be described by a power law dependence on the oxygen content αSi+∝(CO/CSi)3.24, whereby the power shows no significant energy dependence for the studied energy range. The steep enhancement of the ionisation probability at high oxygen content, which is energy dependent, can be correlated to a change in the surface structure: enhanced shadowing of silicon by oxygen, observed by LEIS. [Copyright &y& Elsevier]

To study the oxygen dependence of ionisation processes during O2+ bombardment, low-energy ion scattering was used as a surface analysis technique since it has very high surface sensitivity. An LEIS instrument was reconfigured to collect secondary ions simultaneously with the compositional analysis based on LEIS. The gradual conversion of the Si surface into an oxidised surface under oxygen bombardment has been studied. A correlation between the Si+ intensity and the oxygen concentration could be established, i.e. I(Si+)∝(CO/CSi)2.9. It was observed that, at the stage where the oxygen concentration no longer increases, the amount of visible (for LEIS) Si atoms decreases further, implying a further structural change. This change coincides with the steep increase in the Si+ ion intensity near complete oxidation and can be interpreted as the main cause for this change in ionisation probability. [Copyright &y& Elsevier]

Surfaces of chalcopyrite CuFeS2, sphalerite ZnS, pyrite FeS2 and galena PbS modified by mechanical activation have been studied by means of infrared (IR) spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS). The different oxidation species were identified on mechanically disordered surfaces of the minerals. The mechanochemical surface oxidation increases with the time of mechanical activation. The sulphides under study are partially covered with oxidised sulphates and carbonate species. They are distinguished by an affinity to the formation of surface compounds. According to the affinity of sulphides for mechanochemical S2−→S6+ surface oxidation the decreasing rate was observed in the following order: FeS2>PbS>CuFeS2>ZnS. The ratio between bivalent and hexavalent form of sulphur depends on the degree of mechanochemical surface oxidation of the sample under study. [Copyright &y& Elsevier]

[Display omitted] • The evaluation of valency states in naturally oxidized Bi, Pb, Sn and Te. • Identification of specific high-mass clusters of Me x O y for molecular speciation. • Semi-quantitative speciation by TOF SIMS analysis of high-mass clusters. Molecular speciation by Time of Flight Secondary Ion Mass Spectrometry (TOF SIMS) was applied to oxidized bismuth, lead, tin, and tellurium. In their pure elemental form, they are basic constituent elements of both topological insulators and topological crystalline insulators, which are very hot topics in the last decade. The range of specific ions masses used to evaluate the valence of investigated oxides has been significantly expanded towards high-mass clusters Me x O y (2 ≤ x ≤ 5). The significant enhancement in the secondary high-mass ion yield by using the Bi cluster ion source reflects the valence of primary ion clusters used in molecular speciation of inorganic species. The results show that chemical composition of clusters differs in three 2, 3, and 4 oxidation states studied. This implies that each oxidation state possesses its own set of the high-mass clusters extracted from oxidized metal surfaces during measurement. Such an approach allows for the first time to perform a semi-quantitatively molecular speciation of oxides exploiting the empirical Plog's model. It describes the secondary ion yield as a function of the metal valency in the oxide. We found that the estimated lattice valence state G 0 is close to the valence state of the metal in stable oxides. [ABSTRACT FROM AUTHOR]

[Display omitted] • The surface of SiC substrate was fabricated a ~ 2 μm thick oxidation coating by heat treatment; • The CLAS glass solder exhibited excellent wettability on the surface-oxidized SiC substrates, with contact angles of 33°; • A glass–ceramic interlayer with a micro-nano structure was formed in the joint seam after the joining process; • The joints showed an excellent mechanical property, with an optimal shear strength of 127 MPa at room temperature. A novel strategy was developed to join SiC ceramics via a two-step method (i.e., SiC surface was modified by pre-oxidation treatment before bonding) using CaO-Li 2 O-Al 2 O 3 -SiO 2 (CLAS) glass as the joining material. The wetting behavior, joint microstructure, bonding strength, fracture characteristics, and joining mechanism were investigated. Due to the formation of the SiO 2 layer on the SiC surface by the pre-oxidation, the wettability of CLAS glass solder on the SiC matrix was significantly improved and the interfacial bonding was also enhanced. The microstructure of the joint revealed that the nanoscale eutectic structure composed of wollastonite and spodumene and the rod-shaped anorthite with micron-size were the main products in the joint seam. Besides, the content and size of anorthite in the joints increased with the increase of the joining temperature. Compared with one-step joining, the two-step method can obtain more reliable SiC/SiC joints due to the strong interfacial bonding. As a result, the optimal shear strength of 127 MPa was achieved at a joining temperature of 1240 °C, which was 119% higher than that obtained by the one-step joining method. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface composition of BaTiO 3 thin films is analyzed by XPS upon atmosphere exposure. • Over time down polarized surfaces are more active for oxidation and more hydrophilic. • High energy component in Ba 3d 5/2 spectra is related to barium peroxide (BaO 2). • O 2 annealing of BaTiO 3 films fosters oxidation of Ba sites and production of BaO 2. • Chemically assisted polarization switching from up to down state is observed. Dissociation and adsorption of water on ferroelectric oxide surfaces play important role in the processes of screening and switching dynamics of ferroelectric polarization, as well as in catalytic processes which can be additionally coupled with light, temperature or vibration stimuli. In this work, we present XPS study of ferroelectric BaTiO 3 thin films and determine the entanglement between surface chemistry, polarization direction and stability, by observing changes upon time exposure to environmental conditions, heating in O 2 atmosphere and irradiation in vacuum. We devote special attention to Ba 3d spectral region and identify two different oxidation states of O atoms in the compounds of Ba. While this second specie was generally attributed to Ba in surface compounds where it has different oxygen coordination than in the bulk, based on the XPS results of oxygen annealed thin films, we demonstrate that this so far neglected component, corresponds to barium peroxide (BaO 2) and identify it as important active specie for the study of screening mechanisms closely related with catalytic activity present in this ferroelectric material. Finally, we report on chemically assisted polarization switching in thin films induced by heating in vacuum or exposure to X-Ray radiation due to the formation of positive surface electric field created by oxygen or electron vacancies, respectively. [ABSTRACT FROM AUTHOR]

The wettability of ceria films has been largely tuned from the hydrophobicity to the quasi-superhydrophilic state and attributed to the significant effect of hydrocarbon adsorption. The removal of surface contamination could activate surface sites of ceria for facilitated water dissociation. [Display omitted] • The wettability of ceria is largely tunable by surface modification. • The hydrophobicity of ceria is mainly contributed by adsorbed hydrocarbon species. • Removal of contamination activates surface sites for facilitated water dissociation. • In-situ annealing in O 2 greatly improves water-splitting performance of ceria powder. The high transmittance, environmentally robust, and unique interaction with water make lanthanide series rare-earth oxides promising for various applications such as next-generation self-cleaning coatings. However, the underlying mechanism of the anomalous hydrophobicity in lanthanide oxides remains controversial due to the lack of molecular-level studies in a well-controlled environment, which greatly limits the possibility to engineer their wettability for broader technical applications. Here, we systematically studied the mechanism that governs the wetting behaviors of ceria films by in-situ X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and water contact angle measurements under the environmentally controlled conditions. It was found that the hydrophobicity of ceria was mainly contributed by the adsorbed hydrocarbon, and the wettability could be enhanced on cleaner ceria surfaces with more degree of hydroxylation. Based on the significant dependence of wetting property on surface contamination, we further developed an in-situ annealing method to significantly improve the water-splitting performance of ceria powders by removing hydrocarbon contamination. These results suggest that the removal of surface contamination by high-grade oxidation is the key factor to facilitate the water dissociation of ceria films, providing new insights into the control of their wetting property and design of high-performance devices based on ceria films. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three different surface oxidation treatments are performed to improve SiV photo-luminescence in nano-diamond films. • The improvement of diamond crystallinity plays an effective role in the PL enhancement of SiV centers. • Air annealing is an efficient approach to optimize the crystalline quality of nano-diamond films. The effect of three different surface oxidation approaches (air annealing, acid oxidation and oxygen plasma) on microstructural evolution and silicon vacancy (SiV) photoluminescence (PL) in the nanocrystalline diamond (NCD) films is investigated. All oxidation methods lead to the bonding of oxygen functional groups at diamond surface. The SiV centers exhibit the PL enhancement of about 105-fold in the air-annealed sample, compared with the as-deposited films. Nevertheless, the PL enhancement is about 7-fold and 2-fold in the acid- and plasma- treated samples, respectively. Combination of Raman spectra, HRTEM imaging with cross-sectional oxygen mapping confirms that such different PL behavior originates from the formed different thick oxidation layers. The air oxidation results in a thicker oxidation layer with improved crystallinity than the other two methods. In addition, when the air-annealed films are re-terminated with hydrogen, the SiV PL emission tends to drop remarkably under the same crystallinity. It indicates that hydrogen termination leads to the PL quenching of SiV centers. Therefore, our work reveals that the direct bonding of oxygen to sp3 carbon or the improvement of diamond crystalline quality plays an effective role in the PL enhancement of SiV centers during the oxidation of hydrogen-terminated NCD particles or films. [ABSTRACT FROM AUTHOR]

• Liquid-gas interface of Bi examined at 550 K via ambient pressure XPS. • Water vapor remained unreactive over the entire pressure range. • Oxygen unreactive up to 10−4 Torr, above this pressure Bi 2 O 3 forms at surface. • Oxygen exposure onset for liquid Bi significantly higher than for solid Bi. Bismuth (Bi) has a fairly low melting point of 544 K making it practical as a liquid metal medium in a number of applications. Under ambient atmospheric conditions the surface of solid Bi oxidizes. While the solid Bi interface has been fairly well characterized with surface science studies upon exposure to oxygen, to date little is known about the molecular level reactivity of the liquid interface. Using ambient pressure X-ray photoelectron spectroscopy the liquid–gas interfacial chemistry of Bi was examined upon exposure to oxygen gas and water vapor at 550 K up to a maximum pressure of 0.5 Torr. Water vapor remained unreactive towards the liquid interface over the entire pressure range. Oxygen remined unreactive up to 10−4 Torr, whereas above this pressure oxidation was observed forming Bi 2 O 3. The oxidation exposure onset was > 5 × 105 Langmuirs, significantly higher than what is required for solid Bi interfaces. [ABSTRACT FROM AUTHOR]

Surface oxidation was easily formed at the edge of WS 2 , thus leading to charge transfer from WS 2 to WO 3. • Size-separation of WS 2 nanosheets was prepared using liquid phase exfoliation. • Surface oxidation defect of WS 2 was formed easily by smaller size. • Size-dependent nonlinear optical Absorption in WS 2 was observed. • Charge transfer at interface is used to explain the tunable nonlinear absorption. Controlling nanosheet size and understanding size-dependent surface oxidation are of quite importance for the nonlinear optical properties of two-dimensional materials. Herein, size-separation of WS 2 nanosheets was prepared successfully using liquid phase exfoliation and a gradient centrifugation method. We confirmed the higher surface oxidation with the decrease of nanosheet size by both high-resolution X-ray photoelectron spectroscopy and Raman spectroscopy. To investigate the effect of size-dependent surface oxidation on nonlinear optical properties in WS 2 , Z-scan technique equipped with 800 nm femtosecond laser was used. We observed the conversion between saturable absorption and reverse saturable absorption in WS 2 dispersions as well as the decrease of saturable absorption in WS 2 films due to the increase of reverse saturable absorption contribution of WO 3. Energy-level model based on type II WS 2 /WO 3 heterostructure was put forth to understand nonlinear optical absorption of the oxidized WS 2. The results show that charge transportation from WS 2 to WO 3 increases the reverse saturable absorption contribution in WO 3 while decreases the saturable absorption in WS 2. The results pave the way to design desirable nonlinear optical devices by controlling size with different level of surface oxidation. [ABSTRACT FROM AUTHOR]

• Atomic structures of mechanically distorted silicon (protrusion and groove) were characterized. • Distorted microstructure plays an important role in nanomanufacturing process of silicon. • Stress-assisted chemical reactions mechanism on mechanically deformed silicon was revealed. • Enhanced oxide layer dominates the strong suppression in mechanochemical reactions of silicon. Ultra-precision of nanomanufacturing process down to subnanometer level is actually to achieve controllable removal of atomic material, however, which would be strongly impacted by the preconditions of manufactured surfaces. Here, the atomic structures, chemical and mechanical properties of mechanically-driven distorted microstructures on silicon formed in pre-treated process were characterized and their roles in atomic attrition dominated by mechanochemical reactions were revealed at atomic scale. Mechanically deformed silicon depending on applied stress physically behaviors protrusion forming and material removal (groove), which play opposite contributions to the mechanochemical reactions, i.e., atomic attrition suppressed on the protrusion surface but facilitated on the groove surface. Analyzing the mechanochemical reactions with the stress-assisted Arrhenius-type kinetics model and the DMT contact mechanics implies that, compared to the limited effect of the amorphous structure, the enhanced oxide layer at the protrusion surface that increases the energy barrier for mechanochemical reactions plays a more important role in the mechanochemical removal process. The results may help gain a profound insight into the mechanochemical removal mechanism of silicon and provide a wider cognition for regulating the mechanochemical reactions widely existing in scientific and engineering applications. [ABSTRACT FROM AUTHOR]

• SiC/SiC was processed by high repetition frequency femtosecond laser. • Surface oxidation is an obvious defect in the laser processing of SiC/SiC. • Causes of the different morphological features can be explained by the simulation. • The width error of microgroove fabricated by femtosecond laser was up to 2 μm. SiC/SiC was processed by high repetition frequency femtosecond laser with a wavelength of 1030 nm. The experimental results were analyzed based on the finite element simulation. In the femtosecond laser ablation experiment of SiC/SiC, the processing morphologies under different laser power, repetition frequency, scanning times and scanning velocity were compared. It was found that surface oxidation is an obvious defect in the high-frequency femtosecond laser processing of SiC/SiC, which needs to be controlled. The oxidation phenomenon became more and more obvious with the increased of laser power, repetition frequency and scanning times, while it decreased with the increased of scanning velocity. The parameters of material and laser processing were input into the heat transfer module of the finite element simulation software. The simulation results could intuitively show the formation of different morphological features from the perspective of the temperature field. Finally, the surface oxidation of SiC/SiC was effectively controlled through rationally optimizing the laser processing parameters, and good morphology was obtained. The comparison between simulation and experimental results can help to understand the ablation mechanism of SiC/SiC by high-frequency femtosecond laser, and provide reference for the efficient and precise manufacture of CMC-SiC materials by pulsed laser. [ABSTRACT FROM AUTHOR]

Various studies have emphasized the importance of surface oxidation of sulfide minerals with regard to xanthate adsorption and their flotation response. However, the correlation between pyrite surface oxidation, xanthate adsorption and its flotation response has not been clearly established. The complexity lies in various intermediate sulfur oxidation products in different solution conditions. Thus, investigation of sulfur oxidation behavior is the key to understand pyrite oxidation. Ion chromatography (IC) and high performance liquid chromatography (HPLC) results showed an increase in the total amounts of occurring sulfur species with increasing slurry pH. Meanwhile, the ratio of S0/sulfur oxyanions was to become lower; X-ray Photoelectron Spectroscopy (XPS) identified the oxidized pyrite surface was rich in SO 4 2− and FeOOH. Both the contact angle results and single mineral flotation data indicated that the more pyrite surface oxidized, the lower hydrophobicity and floatability were. Time-of-flight secondary ion mass spectroscopy (Tof-SIMS) was adopted to analyse xanthate adsorption on the surface of pyrite under conditions of either sufficient oxidation or on freshly polished surface which is assumed little oxidation. A significantly lower intensities of C 4 H 9 O and C 4 H 9 OCSS was found on the intensely oxidized pyrite surface, indicating xanthate adsorption had strong selectivity on FeS 2 rather than FeOOH. The experimental results were further confirmed by theoretical calculation. The self-consistent charge density functional tight binding (SCC-DFTB) calculations indicated that the distances between the xanthate S atoms and surface Fe atoms of FeOOH were larger than the atomic radius of S Fe. Essentially, the different electron configurations of their Fe atoms led to the selective adsorption of xanthate on FeOOH and FeS 2 surfaces in terms of the coordination chemistry theory. This work provides valuable implications for understanding the correlation of surface oxidation, xanthate adsorption and its floatation behavior to mediate pyrite flotation. Unlabelled Image • The increased degree of pyrite surface oxidation has been shown with increasing slurry pH. • XPS investigation indicated the formation of FeOOH and SO 4 2- after sufficient pyrite surface oxidation. • The more pyrite surface oxidized, the lower hydrophobicity and floatability were. • Tof-SIMS measurement confirmed that xanthate adsoprtion had strong selectivity on FeS 2 rather than FeOOH • The different electron configurations of their Fe atoms led to the selective adsorption on the surfaces of FeOOH and FeS 2. [ABSTRACT FROM AUTHOR]