X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by X-ray absorption near edge structure spectra and X-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t2g and eg levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.

Red-shift law of intense laser-induced electro-absorption in solids

A theoretical study on the red-shift of laser-induced electro-absorption is presented. It is found that laser-induced red-shift scales with the cube root of the pump laser intensity in the optical tunneling regime and has an obvious deviation from this scale in the multi-photon regime. Our results show that in the optical tunneling regime, the laser-induced red shift has the same law as that in the direct current （DC） approximation. Though the scales are the same in the optical tunneling regime, the physical pictures in the two cases are quite different. The electro-absorption in the DC case is a tunneling-assisted transition process, while the laser-induced electro-absorption is a mixed multi-photon process.

Non-parabolic effect for femtosecond laser-induced ultrafast electro-absorption in solids

A theoretical study for femtosecond laser-induced ultrafast electro-absorption of bulk solids is presented.Our numerical results show that,in the case of low intensity of the pump laser where the interaction between the pump laser and solids is in the multi-photon regime,the energy band of solids can be approximately taken as a parabolic band and electro-absorption spectrums from the parabolic band and real band are nearly the same.While,in the case of high intensity where the interaction is in the tunneling regime,spectrums from the parabolic band and real band are quite different.The physical mechanism for the difference in the tunneling regime is found.We find that the non-parabolic parts of the real energy band and Bragger scattering of electrons near the first Brillouin zone boundaries,which are neglected in previous studies,strongly influence the electro-absorption spectrum in the tunneling regime.These two physical processes cause the difference of spectrums.Our theoretical results are in accordance with the experiment result.

Sulfur speciation transformation during bioleaching of pyrite-containing sphalerite concentrate by thermophile Sulfolobus metallicus at 65 °C

Sulfur speciation transformation during bioleaching of pyrite-containing sphalerite concentrate by thermophile Sulfolobus metallicus （S. metallicus） at 65 ℃ was investigated by X-ray diffraction （XRD）, diffuse reflectance Fourier transform infrared spectroscopy （FT-IR） and sulfur K-edge X-ray absorption near edge structure spectroscopy （XANES）. The results show that the presence of S. metallicus effectively enhances the dissolution of the mineral. The yield of zinc increases from 0.5 g/L in sterile control to 2.7 g/L in bioleaching. The pyrite in the concentrate facilitates zinc dissolution in the early stage, but has hindrance role in the late stage for the formation of jarosite. Sulfur speciation analyses show that jarosite and elemental sulfur are main products in bioleaching process, and the accumulation ofjarosite is mainly responsible for the decline of leaching efficiency.

Quasiparticle Band Structures of Defects in Anatase TiO2 Bulk

Quasiparticle band structures of the defective anatase TiO2 bulk with O vacancy, Ti interstitial and H interstitial are investigated by the GW method within many-body Green＇s function theory. The computed direct band gap of the perfect anatase bulk is 4.3 eV, far larger than the experimental optical absorption edge （3.2 eV）. We found that this can be ascribed to the inherent defects in anatase which drag the conduction band （CB） edge down. The occupied band-gap states induced by these defects locate close to the CB edge, exclud- ing the possible contribution of these bulk defects to the deep band-gap state below CB as observed in experiments.

MULTIPLE-SCATTERING STUDIES OF ADSORPTION STRUCTURE OF C_2D_2/Si(111)7×7

The multiple scattering cluster (MSC) method has been employed to perform a theoretical analysis on carbon is near edge X-ray absorption fine structure of the deuteron acetylene (C2 D2) adsorbed on Si(111)7× 7 at room temperature. From the MSC study. it is confirmed that the (22D2 molecule is bonded to a pair of adjacent Si adatom and Si restatom with C-Si bond length about 0.18nm. The carbon-deuteron bond is bent away front the surface and the CCD bond angle is about 120°. The molecule plane tilt slightly away from the surface normal. Compared with C2D2 in gas phase, the C-C bond and C-D bond are elongated by about 0.03nm and 0.02nm respectively when acetylene was adsorbed on the subtrate. Keyowrds: adsorption of deuteron acetylene on Si(111)7×7. near edge X- ray absorption fine structure. multiple scattering cluster method

Molybdenite as a Rhenium Carrier:First Results of a Spectroscopic Approach Using Synchrotron Radiation

The chemical and physical properties of rhenium render it a highly demanded metal for advanced applications in important industrial fields. This very scarce element occurs mainly in ores of porphyry copper-molybdenum deposits associated with the mineral molybdenite, MoS2, but it has also been found in granite pegmatites and quartz veins as well as in volcanic gases. Molybdenite is a typical polytype mineral which crystal structure is based on the stacking of [S-Mo-S] with molybdenum in prismatic coordination by sulphide anions;however, it is not yet clearly established if rhenium ions replace Mo4+ cations in a disordered way or else, if such replacement gives rise to dispersed nanodomains of a rhenium-rich phase. As a contribution to clarify this question, an X-ray absorption spectroscopy (XANES) study using synchrotron radiation was performed at the Re L3-edge of rhenium-containing molybdenite samples. Obtained results are described and discussed supporting the generally accepted structural perspective that rhenium is mainly carried by molybdenite through the isomorphous replacement of Mo, rather than by the formation of dispersed Re-specific nanophase(s).

ASb(SO_(4))_(2)(A=Rb,Cs):Two short-wave UV antimony sulfates exhibiting large birefringence

Herein,two antimony sulfates,named RbSb(SO_(4))_(2)(1)and CsSb(SO_(4))_(2)(2),have been successfully synthesized with the introduction of Sb^(3+)cation with stereochemically active lone pairs(SCALP)into sulfates by the conventional hydrothermal method.Both two compounds endow short ultraviolet(UV)absorption edges(281 nm and 278 nm,respectively)and large birefringence(0.171@546 nm and 0.174@546 nm,respectively),which means that they are promising short-wave UV optical materials.Interestingly,though both of the two compounds exhibit similar 1D chained structures,and possess the same functional moieties including SbO4 seesaws and SO4 tetrahedral groups,they exhibit significantly opposite macroscopic symmetries,i.e.,compound 1 crystallizes in a centrosymmetric(CS)manner(P2_(1)/n)and compound 2 in a noncentrosymmetric(NCS)manner(P2_(1)2_(1)2_(1)),due to the size of cations[r(Rb+)=1.56 A˚,r(Cs+)=1.67 A˚]affects the orientation of SCALP of the adjacent Sb^(3+).

Two UV organic-inorganic hybrid antimony-based materials with superior optical performance derived from cation-anion synergetic interactions

Finding suitable strategies to effectively enhance the optical properties of materials are the goal being pursued by researchers.Herein,cation-anion synergetic interactions strategy was proposed to develop two novel organic-inorganic hybrid antimony-based optical materials,(C_(3)H_(5)N_(2))Sb F_(2)SO_(4)(I)and(C_(5)H_(6)N)Sb F_(2)SO_(4)(Ⅱ),which were obtained by introducing Sb^(3+)cation containing stereochemically active lone-pair(SCALP)and organicπ-conjugated cations into sulphate system.The synergistic interactions of the organicπ-conjugated cations,the inorganic[SbO_(2)F_(2)]^(3-)seesaw anions and the[SO_(4)]^(2-)distorted tetrahedra anions make their ultraviolet(UV)absorption edges approach 297 and 283 nm,respectively,and raise their birefringence up to 0.193@546 nm and 0.179@546 nm,respectively.Interestingly,although the two compounds have the same stoichiometric ratio and similar one-dimensional(1D)chain structure,they show opposite macroscopic symmetry,where the NCS compound(Ⅱ)exhibits a large secondharmonic generation(SHG)response(1.6 times that of KH_(2)PO_(4)).The two reported compounds are found to be promising UV optical materials in the experimental tests.

Optical bandgap energy of CH3NH3PbI3 perovskite studied by photoconductivity and reflectance spectroscopy

Organic-inorganic hybrid perovskite materials have been receiving considerable attention due to their promising applications in many optoelectronic fields. However, the optical bandgap of CH3NH3PbI3 perovskite is still disputed. In order to comprehend the intrinsic characteristics of these materials, we study the near-band-edge optical responses of the solution-processed CH3NH3PbI3 perovskite crystals by photoconductivity and reflectance spectroscopy at room temperature. All these spectra of the CH3NH3PbI3 polycrystals show only one significant absorption edge at 1.58 eV. However, we observe an extra absorption edge at 1.47 eV in CH3NH3PbI3 single crystal. We establish a simple kinetic model of charge annihilation processes to explain why the low-energy structure of the photoconductivity and diffuse reflectance spectra of CH3NH3PbI3 polyerystals disappear, which provides another possibility for understanding the difference in absorption edge. It is noteworthy that this low-energy absorption edge of CH3NH3PbI3 single crystal has, to the best of our knowledge, seldom been reported on organic-inorganic hybrid perovskites. Therefore, the CH3NH3PbI3 single crystal exhibits a relatively wide absorption which makes it a promising candidate for photoelectric applications.

Sulfur speciation and bioaccumulation in camphor tree leaves as atmospheric sulfur indicator analyzed by synchrotron radiation XRF and XANES

Analyzing and understanding the effects of ambient pollution on plants is getting more and more attention as a topic of environmental biology.A method based on synchrotron radiation X-ray fluorescence and X-ray absorption near edge structure spectroscopy was established to analyze the sulfur concentration and speciation in mature camphor tree leaves （CTLs）,which were sampled from 5 local fields in Shanghai,China.Annual SO2 concentration,SO42-concentration in atmospheric particulate,SO42-and sulfur concentration in soil were also analyzed to explore the relationship between ambient sulfur sources and the sulfur nutrient cycling in CTLs.Total sulfur concentration in mature camphor tree leaves was 766-1704 mg/kg.The mainly detected sulfur states and their corresponding compounds were ＋6 （sulfate,include inorganic sulfate and organic sulfate）,＋5.2 （sulfonate）,＋2.2 （suloxides）,＋0.6 （thiols and thiothers）,＋0.2 （organic sulfides）.Total sulfur concentration was strongly correlated with sulfate proportion with a linear correlation coefficient up to 0.977,which suggested that sulfur accumulated in CTLs as sulfate form.Reduced sulfur compounds （organic sulfides,thiols,thioethers,sulfoxide and sulfonate） assimilation was sufficed to meet the nutrient requirement for growth at a balanced level around 526 mg/kg.The sulfate accumulation mainly caused by atmospheric sulfur pollution such as SO2 and airborne sulfate particulate instead of soil contamination.From urban to suburb place,sulfate in mature CTLs decreased as the atmospheric sulfur pollution reduced,but a dramatic increase presented near the seashore,where the marine sulfate emission and maritime activity pollution were significant.The sulfur concentration and speciation in mature CTLs effectively represented the long-term biological accumulation of atmospheric sulfur pollution in local environment.

Preparation and optical properties of solid solution semiconductor (Zn_xCd_(1-x)S) doped silica glasses

Semiconductor(Zn\-\%x\%Cd 1-x S) doped silica glasses were prepared by Sol_Gel process and \%in situ\% growth technique. The structure of the materials was characterized by X_ray diffraction technique, the particle size of semiconductor crystallites from X_ray patterns was estimated less than 10 nm. From absorption spectra, it is obtained that the absorption edges shifted to short wavelength diraction when Zn contents increased, and the absorption edge can be adjusted from 2.46 eV to 2.96 eV by controlling Zn contents. The third_order nonlinear optical susceptibility was studied at 532 nm with 8 ns pulse laser by degenerate four wave mixing (DFWM) technique.

Amorphous nickel-iron oxides/carbon nanohybrids for an efficient and durable oxygen evolution reaction

Highly efficient and durable water oxidation electrocatalysts are critically important in a wide range of clean energy technologies,including water electrolyzers and rechargeable metal-air batteries.Here,we report a novel sonochemical approach to synthesize amorphous nickel-iron oxides/carbon nanohybrids with tunable compositions for the oxygen evolution reaction （OER）.The sonochemically synthesized amorphous electrocatalysts with optimal composition exhibit a low overpotential of 290 mV at 10 mA＆#183;cm-2 and a Tafel slope of 31 mV＆#183;decade-1 in a 0.1 M KOH electrolyte,outperforming the benchmark RuO2 catalyst.Meanwhile,these nanohybrids are also highly stable and remain amorphous even after prolonged cycling.In addition to amorphism,sonochemistry endows as-prepared nickel-iron oxides/carbon nanohybrids with a simultaneously formed carbon scaffold and internal Ni（0）,which can enhance the stability and activity for the OER.This work demonstrates that sonochemistry is a unique method for synthesizing amorphous metal oxides toward an efficient and durable OER.

Total electron yield mode for XANES measurements in the energy region of 2.1-6.0 keV

The total electron yield （TEY） mode has been developed successfully for XANES measurements at Beamline 4BTA of BSRF （Beijing Synchrotron Radiation Facility）. Its performance was studied by measuring sulphur K-edge XANES of three CdS samples （mixed with graphite powder as an electric conductor） with different concentration： 75%, 50~ and 25%. The data are collected in TEY mode and fluorescence yield （FY） mode respectively for comparison. The results demonstrate that the TEY spectra of three samples agree well with each other after the background is subtracted and normalized. The measured XANES spectra by TEY mode without bias and with 100V bias are almost identical to one another, but the signal-to-noise ratio of spectra measured without bias is better than that with 100V bias. The consistency of the self-absorption corrected FY spectra and TEY spectra are within 10% for the three samples.

Synchrotron radiation studies of the orientation of thin silicon phthalocyanine dichloride film on HOPG substrate

Thin silicon phthalocyanine dichloride films on HOPG were prepared and the sample was heated in the vacuum with laser. The thickness of the thin sample on HOPG was checked by X-ray photoemission spectroscopy. The orientation of the molecules in respect to the substrate plane was investigated by measuring the silicon K-edge near edge X-ray absorption fine structure （NEXAFS）. In the NEXAFS spectra of the thin sample, two clear peaks which were assigned to Is → σ^＊Si-N and 1s→ σ^＊Si-Cl appeared around 1847.2 eV and 1843.1 eV respectively. The intensities of the resonance peaks showed strong polarization dependence. A quantitative analysis of the polarization dependence revealed that the Si-N bond tended to lie down while the Si-Cl bond was out of the molecular plane.

β-Nickel hydroxide cathode material for nano-suspension redox flow batteries

As part of an effort to build a prototype flow battery system using a nano-suspension containing β-Ni（OH）2 nanoparticles as the cathode material, nano-sized β-Ni（OH）2 particles with well-controlled particle size and morphology were synthesized via the one-step precipitation of a NiCl2 precursor. The composition and morphology of the nanoparticles were characterized by scanning electronic microscopy （SEM） and X-ray diffraction （XRD）. The XRD patterns confirmed that β-Ni（OH）2 was successfully synthesized, while SEM results showed that the particle sizes range from 70 to 150 nm. To ensure that Ni（OH）2 could be employed in the nano-suspension flow battery, the electrochemical performance of the synthesized 13-Ni（OH）2 was initially tested in pouch cells through charge/discharge cycling. The phase transformations occurring during charge/discharge were investigated using in-situ X-ray absorption spectroscopy to obtain the shift in the oxidation state of Ni （X-ray adsorption near edge structure, XANES） and the distances between Ni and surrounding atoms in charged and discharged states （extended X-ray absorption fine structure, EXAFS）. XANES results indicated that the electrode in the discharged state was a mixture of phases because the edge position did not shift back completely. XAFS results further proved that the discharge capacity was provided by β-NiOOH and the ratio between β-Ni（OH）2 and γ-NiOOH in the electrode in the discharged state was 71：29. Preliminary nano-suspension tests in a lab-scale cell were conducted to understand the behavior of the nano-suspension during charge/discharge cycling and to optimize the operating conditions.