Changes In Chemical State Research Articles

Control of the chemical state change of sulfur in solid compound targets during high-resolution PIXE measurements

A high-energy-resolution wavelength-dispersive (WD) X-ray spectrometer in the Johansson geometry, which allowed energy resolution below the natural linewidth of the Kα lines was employed in measurements of the proton-induced Kα X-ray emission spectra for six typical sulfur compounds (CdS, Na2SO3, Na2 S2O5, NaHSO3, (NH4)2SO4, and Na2SO4) to investigate the chemical state change during 2.4-MeV proton irradiation with a current density of 7.5 nA/mm2. We found that the chemical state change of each compound depended on the various factors affecting the surface temperature increase, such as target thickness, mounting method, and existence of active cooling during the measurement. The chemical state of sulfur on the target surface of S4+ compounds was gradually changed into S6+ without exception through irradiation under poor cooling conditions. Sulfur compounds of the S0 and S6+ states with closed shell structures were proven to be chemically stable against proton bombardment, as expected. However, (NH4)2SO4 was found to be most sensitive to proton irradiation among the sulfur compounds, and S0, one of the reaction products, became a major element at doses higher than 3 × 108 Gy. If thick targets were mounted by using a carbon adhesive tape, chemical state change could be observed in some cases even with lowtemperature cooling down to −80 °C, however, the chemical state change seemed to be remarkably suppressed by using very thin targets mounted with a silver paste even without active cooling. In conclusion, the chemical states of sulfur compounds could be preserved without significant change for an accumulated dose of about 3 × 107 Gy, equivalent to a typical high-resolution PIXE scanning period, by adopting a proper target preparation scheme to discharge proton-induced thermal energy effectively from the irradiated target surface.

A study on the characteristics of TiOxNy thin films with various nitrogen flow rate by PECVD method

TiOxNy thin films were deposited on Si(100) substrates at 500 °C using RF PECVD system. Titanium isopropoxide was used as precursor with different nitrogen flow rate to control nitrogen contents in the films. Changes of chemical states of constituent elements in the deposited films were examined by X-ray photoelectron spectroscopy (XPS) analysis. The data showed that the nitrogen content ratio was increased with increasing nitrogen flow rate, also the binding energy shift toward high energy side. The characteristics of film growth orientation and structure as well as morphology were also analyzed by X-ray diffraction (XRD), transmission electron diffraction (TED), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The film growth orientation, structure, and morphology were changed by increasing nitrogen flow rate. Nano-indentation experiments showed strong dependency on the composition of nitrogen and nano-structure in the hardness range of between 8 and 16 GPa.

Matrix effect-free depth profiling of multilayered Si/Ti with laser-SNMS

In order to reveal matrix effect at surface and interfacial regions, we have measured the depth profiles of multilayered Si/Ti by secondary ion mass spectrometry (SIMS) and resonance-enhanced multiphoton ionization sputtered neutral mass spectrometry (REMPI-SNMS) using Ar+ beam as primary ion beam. Titanium profile of SIMS was strongly influenced with matrix effect in comparison to silicon one. Especially in the Si/Ti interfacial regions, the Ti+ yield of SIMS was enhanced, whereas the Ti neutral yield of SNMS was proportional to the actual Ti in-depth concentration profile. By means of the XPS measurement, we confirmed the existence of the TiSi2 at these regions. Useful yield of Ti+ sputtered from a TiSi2 sample was about five times larger than that sputtered from a Ti sample which is caused by the difference of chemical state in Ti and TiSi2 bulk. This difference could be interpretable by using the electron tunneling model. On the other hand, useful yield of Ti neutral sputtered from Ti sample was same as that from TiSi2 one. In conclusion, the distribution of the fraction of secondary ion species relating with Ti, such as Ti+, TiO+, TiSi+, etc., was only varied with the change of chemical state in the sample, which caused the matrix effect for the SIMS measurement. We consider the results of both SIMS and SNMS measurements give us the significant knowledge about the mechanism of the matrix effect for depth profile measurement.

Phase and structural evolution of sol–gel synthesized ZrO2/Si thin films under heat treatment

ZrO2/Si thin films were fabricated using a sol–gel technique, and the chemical state change and structural evolution from sol to gel to Zr oxide by heat treatment were investigated. The precursor sol was synthesized using a Zr-acetylacetonate (Zr-acac) precursor, spin-coated, dried on Si(100) substrates, and then annealed at 300–700 °C in air. With increased annealing temperature of the sol–gel-derived layer, Zr-acac decomposed into Zr-acetate, an amorphous ZrO2 phase formed, and crystallization into a tetragonal phase occurred. In addition, the ZrO2 layer became denser and the interfacial layer between ZrO2 and Si thickened, whereas the surface morphology was nearly unaffected and remained smooth with root-mean-square values < 4.5 A.

CORROSION RESISTANCE OF DECORATIVE CHROMIUM FILMS OBTAINED FROM TRIVALENT CHROMIUM SOLUTIONS

In this work, the resistance to corrosion of chromium films obtained from trivalent chromium solutions of different compositions and the influence of solution compounds on the coatings electrochemical behavior and the microstructure were studied. The chromium coatings were obtained from trivalent solutions in a chloride-based bath with different complexing agents adding also sodium hypophosphite and aluminum chloride. UV-vis spectroscopy was carried out on all solutions before and after plating to observe changes in the chromium complexes chemical state due to the plating process. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) were performed to examine the coatings surface morphology and composition; respectively. The coulometric method was used for measuring coating thickness. Electrochemical impedance spectroscopy (EIS) was done using 3% NaCl as electrolyte and using a three-electrode cell with a standard calomel electrode (SCE) as reference. Bright chromium films were obtained from all baths however, differences were observed concerning morphology, thickness and corrosion resistance depending on the composition of the forming solution.

Thermal desorption of mercury from gold-loaded granule activated carbon and its effect on gold elution

The thermal desorption technique has been explored experimentally to remove mercury from the gold-loaded granule activated carbon (GAC) co-adsorbed during heap leaching of gold ores bearing mercury. The effects of treatment temperature, retention time and flow rate of steam used as purge gas on residual mercury levels were investigated. Characterization techniques such as N2 adsorption–desorption, X-ray powder diffraction and X-ray photoelectron spectroscopy, were employed to understand how thermal treatment affects the gold elution in a caustic cyanide-free eluant from the treated GAC. The results showed that mercury desorption was strongly affected by the treatment temperature and steam flow rate. Treatment for 3h at 550°C under steam atmosphere with 0.4m3/h flow rate was allowed to remove more than 99.78% mercury and the content of residual mercury in the treated GAC was decreased to 0.035g/kg, likely reaching the thresh level of mercury extraction during gold elution in a caustic cyanide eluant. Meanwhile, activated carbon was partially regenerated, with only 4.06% weight loss of carbon, mainly due to microporosity recovery. However, it was observed that the thermal process would have heavily influenced elution of gold from the treated activated carbon in a caustic eluant without sodium cyanide. This phenomenon has been attributed primarily to the change of chemical state of gold species and accumulation of highly dispersed gold species and even formation of more stable gold nano-particles caused by a combination of promotion of high temperature and steam oxidation. The elution of gold from the treated sample could be improved through introduction of NaCN into the caustic eluant. However only 83.84% of gold was eluted, probably because the elution time was insufficient.

XPS studies on surface reduction of tungsten oxide nanowire film by Ar+ bombardment

WO3 nanowire film was bombarded by Ar ion beam in the analysis chamber of an X-ray photoelectron spectroscopy (XPS) system to produce uniform tungsten cone arrays. The WO3 nanowire film itself served as an etching mask during the Ar+ bombardment. The changes of surface chemical states and electronic structures during bombardment were monitored by in situ XPS. The morphological evolution with different Ar+ bombardment time was observed by ex situ scanning electron microscopy (SEM). At the start of Ar+ bombardment partial W6+ in WO3 was reduced to W5+ immediately, subsequently to W4+ and then to Wx+ (intermediate chemical state between W4+ and W0), finally to W0. Multiple oxidation states of tungsten coexisted until finally only W0 left. SEM images showed that the nanowires were broken and then fused together to be divided into clusters with a certain orientation after long-time high-energy ion beam bombardment. The mechanism of the ion-induced reduction during bombardment and the reason of the orientated cone arrays formation were discussed respectively.

Oxidative dehydrogenation of cyclohexene on size selected subnanometer cobalt clusters: improved catalytic performance via evolution of cluster-assembled nanostructures

The catalytic activity of oxide-supported metal nanoclusters strongly depends on their size and support. In this study, the origin of morphology transformation and chemical state changes during the oxidative dehydrogenation of cyclohexene was investigated in terms of metal-support interactions. Model catalyst systems were prepared by deposition of size selected subnanometer Co(27±4) clusters on various metal oxide supports (Al(2)O(3), ZnO and TiO(2) and MgO). The oxidation state and reactivity of the supported cobalt clusters were investigated by temperature programmed reaction (TPRx) and in situ grazing incidence X-ray absorption (GIXAS) during oxidative dehydrogenation of cyclohexene, while the sintering resistance monitored with grazing incidence small angle X-ray scattering (GISAXS). The activity and selectivity of cobalt clusters shows strong dependence on the support. GIXAS reveals that metal-support interaction plays a key role in the reaction. The most pronounced support effect is observed for MgO, where during the course of the reaction in its activity, composition and size dynamically evolving nanoassembly is formed from subnanometer cobalt clusters.

Dechlorination of Environmental Contaminants Using a Hybrid Nanocatalyst: Palladium Nanoparticles Supported on Hierarchical Carbon Nanostructures

This paper demonstrates the effectiveness of a new type of hybrid nanocatalyst material that combines the high surface area of nanoparticles and nanotubes with the structural robustness and ease of handling larger supports. The hybrid material is made by fabricating palladium nanoparticles on two types of carbon supports: as-received microcellular foam (Foam) and foam with carbon nanotubes anchored on the pore walls (CNT/Foam). Catalytic reductive dechlorination of carbon tetrachloride with these materials has been investigated using gas chromatography. It is seen that while both palladium-functionalized carbon supports are highly effective in the degradation of carbon tetrachloride, the rate of degradation is significantly increased with palladium on CNT/Foam. However, there is scope to increase this rate further if the wettability of these structures can be enhanced in the future. Microstructural and spectroscopic analyses of the fresh and used catalysts have been compared which indicates that there is no change in density or surface chemical states of the catalyst after prolonged use in dechlorination test. This implies that these materials can be used repeatedly and hence provide a simple, powerful, and cost-effective approach for dechlorination of water.

In situ study of oxidation states and structure of 4 nm CoPt bimetallic nanoparticles during CO oxidation using X-ray spectroscopies in comparison with reaction turnover frequency

In situ near edge X-ray absorption fine structure (NEXAFS) spectroscopy and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) were performed to monitor the oxidation state and structure of 4nm CoPt nanoparticles during the reaction of CO with O2 – a model oxidation reaction. In addition, reversible changes in the oxidation state of cobalt as a function of cycling CO and O2 pressure (in the range of millitorr to 60Torr) were quantified and compared. Turnover frequency reaction data was also obtained for the CoPt nanoparticles and correlated with the oxidation states and structures observed spectroscopically. These findings indicate that separated from the effect of partial pressure of the reactant gases, chemical state and structure changes of the CoPt nanoparticles during CO oxidation are important factors in determining the rate of the reaction.

Formation and electrochemical behavior of Al and O plasma-implanted biodegradable Mg-Y-RE alloy

Mg-Y-RE alloy is potentially useful in biodegradable implants but the fast degradation rate in the physiological environment restrains actual applications. In order to enhance the corrosion resistance, aluminum and oxygen ion implantation is employed to modify the surface of the Mg-Y-RE alloy. X-ray photoelectron spectroscopy (XPS) is conducted to obtain elemental depth profiles and determine chemical state changes. Electrochemical impedance spectroscopy and potentiodynamic polarization are employed to investigate the electrochemical behavior in simulated body fluids (SBF). After polarization, the corroded surface is further studied by scanning electron microscopy (SEM). The results indicate Al and O ion implantation produces an Al 2O 3-containing protection layer which improves the corrosion resistance of Mg-Y-RE alloy. After the surface treatment, localized corrosion becomes the dominant corrosion mechanism instead of general corrosion.

57Fe Mössbauer spectroscopic analysis of deep-sea pelagic chert: Effect of secondary alteration with respect to paleo-redox evaluation

Chemical states of iron in the pre-Jurassic pelagic deep-sea cherts are used as one of redox indicators of lost deep-oceans, e.g. the Permian–Triassic boundary case. Primarily red hematite-bearing cherts were often altered secondarily into greenish gray cherts. We examined the pattern of secondary change in chemical state of iron, associated with color change, in the Middle Triassic chert beds at Hisuikyo in central Japan by 57Fe Mössbauer spectroscopy. Three sets of chert bed with the lateral color change from red to greenish gray were analyzed. The analyses confirmed that the red cherts contain hematite, paramagnetic Fe 3+, and paramagnetic Fe 2+, whereas the greenish gray cherts contain paramagnetic Fe 3+ and paramagnetic Fe 2+ without hematite. The greenish gray parts contain larger amounts of paramagnetic Fe 2+ component of amorphous siderite-like mineral, in contrast to the red parts have lesser amounts. These results confirmed that the primary hematite has changed into paramagnetic Fe 2+-bearing minerals, in accordance with the color change, by the secondary alteration. Further comparison with the pyrite-bearing primary black to dark-gray cherts was discussed with respect to the evaluation for primary redox change in the past oceans.

Behavior of Ru surfaces after ozonated water treatment

In order for the development of cleaning technology of extreme ultra violet lithography photomask, the behavior of Ru surfaces after treatment with ozonated deionized water (DIO 3) solution was studied using Ru and ruthenium oxide particles and 2 nm-thick Ru capping layers. No significant changes in crystalline structures or chemical states of the Ru surfaces, nor any similarities with the structures or states of ruthenium oxide, were observed after DIO 3 treatment. Oxidation of ruthenium to form RuO 2 or RuO 3 was not observed. Adsorption of H 2O molecules on the Ru layer increased the surface roughness, but the desorption of H 2O molecules recovered it. Local chemisorption of H 2O molecules on the Ru surface may be the reason why rougher Ru surfaces were observed after DIO 3 cleaning.

The trapping of N2 molecules and the reduction in its bonding length in Ge(001) due to N2+ ion implantation

To find the cause of N2 → N + N dissociation in Ge(001) at low temperature, the N2+ ion implantation process was carried out on a Ge(001) substrate, followed by rapid thermal annealing (RTA). After N2+ ion implantation, the presence of N2 molecules and the chemical states of GeNx were determined using near-edge x-ray absorption of fine structure (NEXAFS) and high-resolution x-ray photoelectron spectroscopy with synchrotron radiation, respectively. Rapid thermal annealing was performed at 600 °C, after which a change in chemical state from the chemically meta-stable state of GeNx to the stable state of Ge3N4 was observed. In addition, the intensity of the N2 vibration mode peak in NEXAFS was decreased, although it did not completely disappear. To explain the N2 →N + N dissociation at the low temperature, a first-principle calculation for N2 bonding length was performed in both vacuum and Ge(001) states. We confirmed that implantation resulted in the trapping of N2 molecules in Ge(001), and their bonding length was changed from 1.117 to 1.205 Å at a difference energy of 2.529 eV. It was assumed that the relaxed change in the N2 bonding length originated from the dissociation of N2 molecules at low temperature.

Microstructural analysis and XPS investigation of nodular oxides formed on Zircaloy-4

In order to study nodular oxidation behavior under LOCA conditions, Zircaloy-4 cladding tubes were oxidized in high-temperature steam ambience and the growth evolution and microstructural properties of the oxides formed on the Zircaloy-4 surfaces were then investigated. Optical metallography showed different growth behaviors of uniform black oxide and localized whitish nodular oxide. The changes in composition and chemical states of the oxides formed on the Zircaloy-4 surface were investigated using X-ray photoelectron spectroscopy (XPS). Anion-deficient and non-stoichiometric ZrO was the main species in initial black uniform oxide surface, while stoichiometric ZrO 2 was the main oxide species in the whitish nodular oxide. A stoichiometric composition in the nodular oxide resulted in a decrease in plasticity of the oxide layers. Unlike black uniform oxide, XPS spectrum from the nodular oxide showed clear Sn photopeak, which indicates that Sn species were observed in the nodular oxide only. As a result, it is concluded that the decreased plasticity and localized Sn additives may be the causes of nodular oxide initiation under LOCA conditions.

EFFECTS OF ARGON+ ION BOMBARDMENT ON A PLATINUM/ZIRCONIUM DIOXIDE/IRIDIUM RESISTIVE SWITCHING MEMORY CELL

We have fabricated Pt/ZrO2/Ir memory cells with pristine and Ar+ ion bombarded ZrO2 films, which show unipolar resistive switching behaviors. Ar+ ion bombardment induces change in surface morphology and chemical states of ZrO2 films. We have found that forming voltage significantly decreases in a Pt/ZrO2/Ir memory cell whose Ar+ ion bombarded ZrO2 film shows oxygen vacancy like defects and the largest root-mean-square (RMS) roughness. It seems that forming process may be more easily induced in an Ar+ ion bombarded ZrO2 film with higher RMS roughness mainly due to locally enhanced electric field in a region with oxygen vacancy like defects.

Thermal Effect on Structure of Silver in Ion-Exchanged Soda-Lime Glasses and Aluminum-Doped Zinc Oxide Films

Heat treatment is commonly used during device processing in order to achieve specific functionalities of the devices. How a series of heat treatment applies to accomplish this goal can be found in the literature. However, specific properties of the devices after the treatment are more emphasized than the details of the structural modifications in the industrial applications. In this paper, it is intended to illustrate the fundamental changes in the structure due to heat treatment which result in the desired physical properties of the devices. Two study cases, Ag ion-exchanged soda-lime glasses and aluminum doped ZnO (AZO) films, were illustrated. The changes in chemical states, the structural modification during and after heat treatment are explored. By understanding how the metallic Ag formed and accumulated during annealing, an optimum heat treatment to grow the proper size and density of silver quantum dots in the films are possible. Post annealing effect on the AZO films shows that the crystallinity, the peak positions shifts, and grain sizes were changed after annealing. Both illustrated cases indicate thermally induced changes in chemical state, the stress release, and rearrangement of atoms in materials during and after annealing.

Evolution of Structure and Chemistry of Bimetallic Nanoparticle Catalysts under Reaction Conditions

Three series of bimetallic nanoparticle catalysts (Rh(x)Pd(1-x), Rh(x)Pt(1-x), and Pd(x)Pt(1-x), x = 0.2, 0.5, 0.8) were synthesized using one-step colloidal chemistry. X-ray photoelectron spectroscopy (XPS) depth profiles using different X-ray energies and scanning transmission electron microscopy showed that the as-synthesized Rh(x)Pd(1-x) and Pd(x)Pt(1-x) nanoparticles have a core-shell structure whereas the Rh(x)Pt(1-x) alloys are more homogeneous in structure. The evolution of their structures and chemistry under oxidizing and reducing conditions was studied with ambient-pressure XPS (AP-XPS) in the Torr pressure range. The Rh(x)Pd(1-x) and Rh(x)Pt(1-x) nanoparticles undergo reversible changes of surface composition and chemical state when the reactant gases change from oxidizing (NO or O(2) at 300 degrees C) to reducing (H(2) or CO at 300 degrees C) or catalytic (mixture of NO and CO at 300 degrees C). In contrast, no significant change in the distribution of the Pd and Pt atoms in the Pd(x)Pt(1-x) nanoparticles was observed. The difference in restructuring behavior under these reaction conditions in the three series of bimetallic nanoparticle catalysts is correlated with the surface free energy of the metals and the heat of formation of the metallic oxides. The observation of structural evolution of bimetallic nanoparticles under different reaction conditions suggests the importance of in situ studies of surface structures of nanoparticle catalysts.

Evaluation of Resonance Characteristics Change of Silicon Resonators Due to Surface Treatment

Mechanical resonators are applicable to sensors owing to their vibration characteristics. When a mechanical resonator is used as a sensor, the Q factor of resonance is a very important characteristic for achieving a high sensitivity of the resonator. Several trials have been reported to improve the Q factor by surface treatment. However, how the physical or chemical state of the resonator surface affects the Q factor has not yet been clarified. In this study, we examined the effect of the surface state on the Q factor. From experiments for examining surface-treated samples, we found that the Q factor increases with reactive ion etching (RIE) with CF4 gas, and decreases with Ar or O2 gas. To evaluate the effect of the surface state on the Q factor, the surface free energy and chemical bond state changes of the resonator surface were measured. From the result of the experiments, it was proved that lower surface free energies result in larger Q factors.

Electrical Characteristics and Doping Mechanism of DNA Molecules Doped with Iodine Solutions

This study examined the electrical characteristics of deoxyribonucleic acid (DNA) molecules doped with iodine solution and their chemical state changes before and after doping. The experiments were progressed in each lambda (A), poly(dA)-poly(dT) and poly(dG)-poly(dC) DNA under the same conditions. The authors prepared 20 nm gap Au/Ti electrodes fabricated by e-beam lithography. DNA solutions were dropped on the nano gap of the electrodes and DNA films were formed by drying in a vacuum. DNA films were doped with an iodine solution dissolved in methanol. The authors measured the electrical conductivity of DNA molecules as the number of iodine doping times in 10(-2) torr vacuum. As increase of the iodine solution doping number, the electrical conductivity of three sorts of DNA molecules was remarkably improved respectively. X-ray photoelectron spectroscopy (XPS) was performed to inspect the electrical conduction mechanism that holes on DNA nitrogen region were generated by transferring electrons to iodine molecules.