X-ray Photoelectron Spectroscopy Investigation Research Articles

Pentafluorophenyl Isocyanate as an Effective Electrolyte Additive for Improved Performance of Silicon-Based Lithium-Ion Full Cells.

Due to its high specific and volumetric capacity and relatively low operation potential, silicon (Si) has attracted much attention to be utilized as a high-capacity anode material for lithium-ion batteries (LIBs) with increased energy density. However, the application of Si within commercial LIBs is still hindered by its poor cycling stability related to the huge volume changes of Si upon lithiation/delithiation, followed by continuous electrolyte decomposition and active lithium loss at the anode side. In this work, we present the application of pentafluorophenyl isocyanate (PFPI) as an effective electrolyte additive for lithium-ion full cells, containing a pure, magnetron-sputtered Si anode and a LiNi1/3Mn1/3Co1/3O2 (NMC-111) cathode. The performance of the Si/NMC-111 full cells is significantly improved in terms of capacity retention and Coulombic efficiency by the addition of 2 wt % PFPI to the baseline electrolyte and is compared to the well-known additives vinylene carbonate and fluoroethylene carbonate. Furthermore, it is revealed that the additive is able to reduce the active lithium losses by forming an effective solid-electrolyte interphase (SEI) on the Si anode. X-ray photoelectron spectroscopy investigations unveil that PFPI is a main part of the SEI layer, leading to less active lithium immobilized within the interphase. Overall, our results pave the path for a broad range of different isocyanate compounds, which have not been studied for Si-based anodes in lithium-ion full cells so far. These compounds can be easily adjusted by modifying the chemical structure and/or functional groups incorporated within the molecule, to specifically tailor the SEI layer for Si-based anodes in LIBs.

EIS and XPS Investigation on SEI Layer Formation during First Discharge on Graphite Electrode with a Vinylene Carbonate Doped Imidazolium Based Ionic Liquid Electrolyte

Adding organic carbonates (e.g., vinylene carbonates, VC) into ionic liquid based electrolyte generally improves the electrochemical performances of graphite electrode (Cgr) in lithium ion batteries. In this study, step-by-step electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) were performed during the first reduction cycle to follow the formation of the solid electrolyte interphase (SEI) in lithium/graphite (Li/Cgr) cell using (1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) [C1C6Im][NTf2] doped with vinylene carbonate (VC). The EIS spectra evolution, recorded at different cutoff voltages, indicated a two-step SEI thin film formation. These results were supported by XPS measurement at the same cutoff voltage. Hence, we pointed out that the first film results from the VC decomposition at 0.8 V to form an organic layer constituted of lithium alkylcarbonates. This film was developed up to 0.2 V. From 0.8 to 0.2 V, we detected a slight decomposition of IL ...

Surface properties of magnesium improved by Sr ion implantation

Strontium (Sr) ion implantation was conducted to improve the surface properties of pure magnesium through a metal vapor vacuum arc (MEVVA) ion implantation. The x-ray photoelectron spectroscopy investigation demonstrated a Sr-implanted layer of approximately 30 nm in thickness formed on the pure Mg surface and Sr element content as a function of the depth in modified layer was similar to a Gaussian distribution. The atomic force microscopy analysis indicated that the roughness value of the pure Mg apparently decreased and the surface became smoother subsequently to Sr ion implantation. Besides, the nanoindentation measurements demonstrated that the elastic modulus and hardness value of the Sr-implanted Mg were both higher than those of pure Mg. Furthermore, compared with untreated Mg, the Sr-implanted Mg exhibited a more positive corrosion potential and a lower corrosion current density in electrochemical tests, and fewer corrosion damage after 12 h immersion tests in SBF. The results suggested that the corrosion resistance and mechanical properties of pure Mg could be improved through Sr ion implantation.

Equilibrium, kinetic and mechanism studies of Cu(II) and Cd(II) ions adsorption by modified chitosan beads

In this study, the Cu(II) and Cd(II) ions removal behavior of crosslinked chitosan beads grafted poly(methacrylamide) (abbreviated as crosslinked chitosan-g-PMAm) from single metal ion solutions was investigated. The modified chitosan beads presented a remarkable improvement in acid resistance. The batch experiments demonstrated that pH of solution played a significant role in adsorption. It was found that the adsorption of Cu(II) and Cd(II) were optimum at pH 4 and pH 5, respectively. The maximum adsorption capacities for Cu(II) and Cd(II) based on Langmuir equation were 140.9 mg g−1 and 178.6 mg g−1, respectively. Pseudo-second order gave a better fit for adsorption data with respect to linearity coefficients than pseudo-first order suggesting that chemisorption or electron transfer is the dominant mechanism of the metal ions onto crosslinked chitosan-g-PMAm. In addition, X-ray photoelectron spectroscopy (XPS) investigations revealed that adsorption of both metal ions took place on the surfaces of crosslinked chitosan-g-PMAm by chelation through CNH2, CO and CO groups. Overall, the modified chitosan has proved a promising adsorbent for removal of metal ions.

XPS investigations on the corrosion mechanism of V(IV) conversion coatings on hot-dip galvanized steel

The corrosion mechanisms of a vanadyl oxalate (VOC2O4) conversion coating on hot-dip galvanized (HDG) steel were clarified as using VOC2O4 as an alternative to chromate has not yet been examined. X-ray photoelectron spectroscopy (XPS) was utilized extensively for studying the elemental composition and doping level of coatings. Scanning Kelvin probe (SKP) technique was used to investigate the change in surface potential of HDG. Corrosion behavior of the conversion coating was investigated using electrochemical impedance spectroscopy (EIS) measurements. With 10 s of dipping, V(IV) (tetravalent vanadium) was present in coating layers at a level of 80 at% to total V while V(III) (trivalent vanadium) at a level of 20 at%. During exposure in the desiccator, partial V(III) translation to V(IV) increased V(IV) concentration to 83 at%, due to oxidation by the ambient oxygen. V(IV) has a cathodic inhibition in the corrosion of HDG. An enhanced corrosion performance of the coating was achieved by the increase in V(IV) concentration in coating layers over exposure time. Nevertheless, during neutral salt spray (NSS) V(IV) vanished and only V(III) retained a certain amount that played a major role in the corrosion inhibition of HDG.

Synthesis and Evaluation of Iridium Oxide Nanoparticle Catalysts Supported on Nitrogen-Doped Reduced Graphene Oxides

Recently, progress toward sustainable societies with renewable energies is a critical issue to overcome environmental and social problems, for example, global warming and depletion of fossil fuels. To utilize effectively renewable energies such as solar and wind energy, conversion of renewable energies to hydrogen via water electrolysis is one of the most attractive approaches for energy storage. However, for the practical application of water electrolysis systems, its activity, durability, and catalysts cost are insufficient due to high over-potential and low kinetics of electrode reactions, especially, oxygen evolution reaction (OER) at the anode [1,2] for polymer electrolyte water electrolyzer (PEWE). As anode catalysts, iridium oxide (IrO2) particles have been used because of its high activity and durability for OER. However, iridium is one of the platinum group metals and reducing loading amount of iridium is required to reduce catalyst cost. Recently, we have successfully synthesized novel catalysts, IrO2 nanoparticle catalysts supported on nanocarbon materials with improved specific surface area, surface area per weight, of anode catalysts for PEWE. In this study, we focus on modification of IrO2 catalysts by doping of hetero atom (N) on supporting materials and characterization its electronic state condition and catalytic activity for OER. Novel catalyst of IrO2 nanoparticles supported on nitrogen-doped reduced graphene oxide (N-rGO) was prepared by hydrothermal synthesis. Graphene oxide (GO) prepared by modified Hummers method [3] was mixed with urea and hydrothermally treated at 180 ˚C for 12 h to synthesize N-rGO. For the synthesis of IrO2 / N-rGO catalysts, mixture of H2IrCl6 complex and N-rGO dispersed in ethanol/water mixture solution was stirred at 80 ˚C for 6 h in a flask to attach iridium oxide colloid to N-rGO and heated at 150 ˚C for 4 h in a hydrothermal autoclave to form IrO2 nanoparticles. The IrO2 / N-rGO catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersed X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. The OER activity of the IrO2/ N-rGO was examined in sulfuric acid solution using rotating disk electrode system. Figure 1 shows TEM image of synthesized IrO2 / N-rGO catalysts. The IrO2 nanoparticles with an average particle size of 1.2 nm are uniformly dispersed on surface of the N-rGO substrate. The loading amount of the IrO2 nanoparticles and doping weight of nitrogen atom of the IrO2 / N-rGO catalysts are approximately 9 and 7 wt%, respectively, which was estimated from EDX measurements. Figure 2 shows the results of XPS investigation on GO, N-rGO, and IrO2 / N-rGO. The XPS data reveal nitrogen doping on GO by hydrothermal synthesis of GO with urea. After the reaction between Ir complexes and N-rGO, Ir 4f peak appeared on the spectrum and intensity of O 1s was decreased due to reduction of GO during the hydrothermal reaction. Deconvolution analysis of the N 1s peak of N-rGO indicates doped nitrogen has three different types, pyridinic, pyrrolic, and graphitic type. The binding energy of the Ir 4f peak was shifted to a lower energy state. In addition, XRD pattern of the IrO2 / N-rGO catalyst suggests that the interlayer distance of graphene sheets decreased during hydrothermal reaction because of reduction of GO. The XRD data suppot the results of the XPS measurement.Figure 3 shows linear sweep voltammogram of the IrO2 / N-rGO catalyst obtained in 0.5 M H2SO4 solution. Electrochemical measurement reveals high activity of the IrO2 / N-rGO catalyst for OER, onset potential of the reaction is ca. 1.43 V and mass activity at 1.60 V is ca. 1000 A g-1. The overvoltage of the IrO2 / N-rGO catalysts is 70 mV lower than that of conventional IrO2 powder catalysts. High activity of the IrO2 / N-rGO catalyst indicates that the IrO2 / N-rGO catalyst is a promising candidate of anode material for PEWE. Acknowledgements This work was supported by JSPS KAKENHI Grant number 17K05969. Reference[1] M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen Energy 38 (2013) 4901.[2] E. Antolini, ACS Catal. 4 (2014) 1426.[3] W. S. Hummers, R. E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. Figure 1

XPS investigation of new solid forms of 5-fluorouracil with piperazine

The present study reports the results obtained by X-ray photoelectron spectroscopy (XPS) for new solid forms of antineoplastic agent 5-fluorouracil with anthelmintic piperazine obtained by liquid assisted ball milling and slurry crystallization methods as co-crystal and salt, respectively. The interest for these new solid forms of 5-fluorouracil with another drug consists in obtaining new compounds with potential pharmaceutical and biomedical applications. The XPS results bring additional deciding information on the atomic environments in the newly obtained solid forms of 5-fluorouracil with piperazine beside the earlier reported X-ray diffraction and infrared spectroscopy data. The deconvolution of N 1s core level spectra allows to distinguish unequivocally the protonated (salt) from hydrogen-bonded (co-crystal) nitrogen species based on the N 1s binding energy associated with the protonation of nitrogen atoms. The N 1s component around 402 eV observed only for the solid form obtained following the slurry route proves in this case the formation of a salt on basis of positively charged nitrogen resulted by protonation of secondary amine groups. Moreover, for the solid form obtained following the ball milling route, one notices a large negative shift of N 1s binding energy that supports the development of a co-crystal.

Probing molecular orientations in thin films by x-ray photoelectron spectroscopy

A great number of functional organic molecules in active thin-film layers of optoelectronic devices have highly asymmetric structures, such as plate-like, rod-like, etc. This makes molecular orientation an important aspect in thin-films as it can significantly affect both the optical and electrical performance of optoelectronic devices. With a combination of in-situ ultra violet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS) investigations for organic molecules having a broad range of structural properties, we discovered a rigid connection of core levels and frontier highest occupied molecular orbital levels at organic interfaces. This finding opens up opportunities of using X-ray photoemission spectroscopy as an alternative tool to UPS for providing an easy and unambiguous data interpretation in probing molecular orientations.

Toward Enhancing Solar Cell Performance: An Effective and "Green" Additive.

Performance of bulk heterojunction polymer solar cells (PSCs) highly relies on the morphology of the photoactive layer involving conjugated polymers and fullerene derivatives as donors and acceptors, respectively. Herein, butylamine was found to be able to optimize the morphology of the donor/acceptor (D/A) film composed of a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Compared to the commonly used alkane dithiols and halogenated additives with high boiling points, butylamine has a much lower boiling point between 77 and 79 °C, and it is also much "greener". A specific interaction between butylamine and PCBM was demonstrated to account for the morphology improvement. Essentially, butylamine can selectively dissolve PCBM in the P3HT:PCBM blend and facilitate the diffusion of PCBM in the film fabrication processes. Atomic force microscopy and X-ray photoelectron spectroscopy investigations confirmed the formation of the P3HT-enriched top surface and the abundance of PCBM at the bottom side, i.e., the formation of vertical phase segregation, as a consequence of the specific PCBM-butylamine interaction. The D/A film with inhomogeneously distributed D and A components in the vertical film direction, with more P3HT at the hole extraction side and more PCBM at the electron extraction side, enables more efficient charge extraction in the D/A film, reflected by the largely enhanced fill factor. The power conversion efficiency of devices reached 4.03 and 4.61%, respectively, depending on the thickness of the D/A film, and these are among the best values reported for P3HT:PCBM-based devices. As compared to the devices fabricated without the introduction of butylamine under otherwise the same processing conditions, they represented 19.6 and 21.6% improvement in the efficiency, respectively. The discovery of butylamine as a new, effective additive in enhancing the performance of PSCs strongly suggests that the differential affinity of additives toward donors and acceptors likely plays a more important role in morphology optimization than their boiling point, different from what was reported previously. The finding provides useful information for realizing large-area PSC fabrication, where a "greener" additive is always preferred.

Self-Assembly of Metal Oxide Nanoparticles in Liquid Metal toward Nucleation Control for Graphene Single-Crystal Arrays

Summary We have achieved the spontaneous assembly of alumina nanoparticles on a liquid metal surface and further synthesized a very-large-scale graphene single-crystal array. The effective electrical field established as a result of the electrical charge of the alumina nanoparticles in the liquid metal ensures the ordered self-assembly of the alumina islands and lays the foundation for precise spatial control of graphene nucleation, leading to the formation of graphene single-crystal arrays. In addition, controlling the density of the alumina in the liquid metal can precisely tune the periodicity of the arrays. This simple strategy, which is unlike the usual solid/aqueous solution system, opens up new territory for nanoparticle assembly. Focusing on the origin of the nanoparticle interaction that drives the self-assembly of ordered structure in the liquid metal system is a promising avenue for triggering more interesting applications.

Non-destructive determination of ultra-thin GaN cap layer thickness in AlGaN/GaN HEMT structure by angle resolved x-ray photoelectron spectroscopy (ARXPS)

Angle resolved X-ray photoelectron spectroscopy (ARXPS) and secondary ion mass spectrometry (SIMS) investigations have been carried out to characterize the GaN cap layer in AlGaN/GaN HEMT structure. The paper discusses the qualitative (presence or absence of a cap layer) and quantitative (cap layer thickness) characterization of cap layer in HEMT structure non-destructively using ARXPS measurements in conjunction with the theoretical modeling. Further the relative sensitive factor (RSF=σGaσAl) for Ga to Al ratio was estimated to be 0.963 and was used in the quantification of GaN cap layer thickness. Our results show that Al/Ga intensity ratio varies with the emission angle in the presence of GaN cap layer and otherwise remains constant. Also, the modeling of this intensity ratio gives its thickness. The finding of ARXPS was also substantiated by SIMS depth profiling studies.

Structural Changes of Highly Active Pd/MeOx (Me = Fe, Co, Ni) during Catalytic Methane Combustion

Fe2O3, Co3O4 and NiO nanoparticles were prepared via a citrate method and further functionalized with Pd by impregnation. The pure oxides as well as Pd/Fe2O3, Pd/Co3O4, and Pd/NiO (1, 5 and 10 wt % Pd) were employed for catalytic methane combustion under methane lean (1 vol %)/oxygen rich (18 vol %, balanced with nitrogen) conditions. Already, the pure metal oxides showed a high catalytic activity leading to complete conversion temperature of T100 ≤ 500 °C. H2-TPR (Temperature-programmed reduction) experiments revealed that Pd-functionalized metal oxides exhibited enhanced redox activity compared to the pure oxides leading to improved catalytic combustion activity at lower temperatures. At a loading of 1 wt % Pd, 1Pd/Co3O4 (T100 = 360 °C) outperforms 1Pd/Fe2O3 (T100 = 410 °C) as well as 1Pd/NiO (T100 = 380 °C). At a loading of 10 wt % Pd, T100 could only be slightly reduced in all cases. 1Pd/Co3O4 and 1Pd/NiO show reasonable stability over 70 h on stream at T100. XPS (X-ray photoelectron spectroscopy) and STEM (Scanning transmission electron microscopy) investigations revealed strong interactions between Pd and NiO as well as Co3O4, respectively, leading to dynamic transformations and reoxidation of Pd due to solid state reactions, which leads to the high long-term stability.

S and B microalloying of biodegradable Fe-30Mn-1C - Effects on microstructure, tensile properties, in vitro degradation and cytotoxicity

Austenitic Fe-Mn-C-based alloys are considered as promising candidates for biodegradable vascular implants due to their high strength, ductility and mechanical integrity during degradation.The present study demonstrates that microalloying with S and B is an effective method to further enhance the degradation rate and the mechanical properties of a Fe-30Mn-1C twinning-induced plasticity (TWIP) alloy without deteriorating the biocompatibility. For studying the microstructural changes due to S or B addition, the alloys were analysed by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX), wavelength dispersive X-ray analysis (WDX) and electron backscatter diffraction (EBSD). Thereby precipitates of (Fe0.3Mn0.7)S and (Fe,Mn)23(C3B3) types were detected in the austenitic matrix. These precipitates have a distinct influence not only on the mechanical properties under tensile load but also on the occurring corrosion mechanism. This was displayed by potentiodynamic polarization measurements and immersion tests in simulated body fluid (SBF) and associated SEM as well as X-ray photoelectron spectroscopy (XPS) investigations. In vitro cytotoxicity analyses with L929 fibroblast cells indicated that microalloying with S and B does not affect the cytocompatibility.Thus, the novel alloy modifications show a high potential for future application as biodegradable implant material.

UV-laser cleaning and surface characterization of an aerospace carbon fibre reinforced polymer

In the recent aerospace generations, composite materials have shown that they can fulfil the increasing demand for structural efficiency. In this context adhesive bonding could be used to max out the material properties of carbon fibre reinforced polymers (CFRP). However, investigations have shown that residues of release agents on the CFRP surface can cause adhesion problems. Thus, a reliable surface cleaning procedure for removing residues prior to bonding is necessary.Analytical surface investigations of an Aerospace CFRP material revealed the thickness and morphology of the predominant adhesion-weakening contamination. The optical absorptions of the epoxy material and the release agent characterised by UV–vis measurements were considered to develop a cleaning model based on a ns-pulsed ultra-violet laser with 266nm wavelength. This removal mechanism leads to chipping and peeling of the release agent layer and could be supported with light microscopy, scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) investigations. Single lap shear tests of the CFRP samples in the pristine and contaminated state, pre-treated with UV-laser as well as with the reference process (grinding) show that the laser pre-treated samples lead to the highest joint strength in the study. The failure mode changed from adhesion failure in the pristine state to a failure in the fibre-resin interface after laser treatment. Comparing a laser parameter with the focus on a smooth cleaning process and a laser parameter that lead to a surface with exposed carbon fibres, the surfaces treated with the smooth laser parameter showed the higher joint strength. The measured joint strength was 100% higher than with grinding, which underlines the high potential of laser technology for CFRP surface pre-treatment.

Spectroscopic evidence and molecular simulation investigation of the bonding interaction between lysine and montmorillonite: Implications for the distribution of soil organic nitrogen

Abstract Clay minerals, widespread in natural soil environment, play important roles in the distribution of organics and their utilization by plants and microorganisms. Interface interactions of clay minerals and amino acids are essential for soil and life sciences. The bonding interaction between montmorillonite and lysine was studied systematically and comprehensively in this paper. The montmorillonite-lysine complexes were characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier-transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and molecular simulation investigation. The results of XRD showed that interlayer spacing of montmorillonite increased or decreased with different amounts of lysine indicating two different bonding interactions. Amino acids adsorbed onto montmorillonite through the bonding interaction of electrostatic attraction between negatively charged surface of montmorillonite and NH3+ at the end of lysine on interlayer adsorption aspect as confirmed by XPS and ATR-FTIR spectroscopy. For edge adsorption aspect, the adsorption was through the bonding interaction between COO– group and > AlOH2+/>SiOH2+ groups. Electron localization function calculations for O, Si and Al atoms further demonstrated the bonding interaction of NH3+ groups and the Si O– groups intuitively. These findings give more understandings on the adsorption and distribution of amino acids in different sites of clay minerals.

X-ray photoelectron spectroscopy investigations of band offsets in Ga0.02Zn0.98O/ZnO heterojunction for UV photodetectors

Here, we report the valence and conduction band offset measurements in pure ZnO and the Ga0.02Zn0.98O/ZnO heterojunction by X-Ray photoelectron spectroscopy studies for UV photodetector applications. For detailed investigations on the band offsets and UV photodetection behavior of Ga0.02Zn0.98O/ZnO heterostructures, thin films of pristine ZnO, Ga-doped ZnO (Ga0.02Zn0.98O), and heterostructures of Ga-doped ZnO with ZnO (Ga0.02Zn0.98O/ZnO) were deposited using a pulsed laser deposition technique. The deposited thin films were characterized by X-ray diffraction, atomic force microscopy, and UV-Vis spectroscopy. X-ray photoelectron spectroscopy studies were carried out on all the thin films for the investigation of valence and conduction band offsets. The valence band was found to be shifted by 0.28 eV, while the conduction band has a shifting of −0.272 eV in the Ga0.02Zn0.98O/ZnO heterojunction as compared to pristine ZnO thin films. All the three samples were analyzed for photoconduction behavior under UVA light of the intensity of 3.3 mW/cm2, and it was observed that the photoresponse of pristine ZnO (19.75%) was found to increase with 2 wt. % doping of Ga (22.62%) and heterostructured thin films (29.10%). The mechanism of UV photodetection in the deposited samples has been discussed in detail, and the interaction of chemisorbed oxygen on the ZnO surface with holes generated by UV light exposure has been the observed mechanism for the change in electrical conductivity responsible for UV photoresponse on the present deposited ZnO films.

Low temperature preparation of oxygen-deficient tin dioxide nanocrystals and a role of oxygen vacancy in photocatalytic activity improvement

The introduction of oxygen vacancies (Vos) into tin dioxide crystal structure has been found as an effective method to improve its photocatalytic performance. Herein, oxygen-deficient tin dioxide (SnO2−x) nanocrystals were successfully prepared via a facile, one-step hydrothermal method at the temperature lower than those reported previously. The effect of hydrothermal temperature on phase composition and Vos content was also firstly investigated. Due to its high oxygen vacancy concentration, the SnO2−x prepared at 80 °C provides the best photocatalytic degradation of methyl orange under UV–visible light. Scavenger trapping and nitroblue tetrazolium experiments also show that the Vos act as electron trapped sites and molecular oxygen adsorption sites, therefore increasing the production of active O2− radical which is the main species governing the photocatalytic activity of SnO2−x nanocrystals. Raman spectroscopy, X-ray photoelectron spectroscopy, photoluminescence measurement and electron spin resonance investigation clearly indicate that increasing the hydrothermal temperature results in the coexistence of SnO2−x and Sn3O4 phases and the reduction of Vos concentration which are detrimental to the photocatalytic performance. Density functional theory calculations also reveal that the presence of Vos is responsible for the upshift of valence band maximum and an extended conduction band minimum, hence a valence band width broadening and band gap narrowing which consequently enhance the photocatalytic performance of the oxygen-deficient SnO2−x.

Band Offset Enhancement of a-Al2O3/Tensile-Ge for High Mobility Nanoscale pMOS Devices

The band alignment properties of amorphous Al2O3 on strain-engineered biaxial tensile-strained epitaxial Ge, grown in situ by molecular beam epitaxy on InxGa1–xAs virtual substrates, are presented. X-ray photoelectron spectroscopy investigation demonstrated an increase in the valence band offset of the Al2O3/strained Ge system with increasing tensile strain. For Ge strain-states of 1.14%, 1.6%, and 1.94%, the corresponding valence band offsets were found to be 4.43 ± 0.1 eV, 3.95 ± 0.1 eV, and 4.55 ± 0.1 eV, respectively, demonstrating a ~0.8 eV increase as compared with Ge grown on GaAs. The observed enhancement in the valence band discontinuity between tensile-strained Ge and Al2O3 offers a unique and novel path for the simultaneous improvement of hole mobility (via strain) and hole confinement (via a larger valence band offset) in future low-power and high-performance Ge-based nanoscale pMOS devices.

Separation of Nickelocene‐Filled Single‐Walled Carbon Nanotubes by Conductivity Type and Diameter

We have performed the separation of nickelocene‐filled single‐walled carbon nanotubes (SWCNTs) with a mean diameter of 1.7 nm by conductivity type and diameter using density gradient ultracentrifugation. The separated nanotube fractions were characterized by optical absorption spectroscopy (OAS), X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The OAS investigation of the separated samples showed the absence of optical absorption bands of semiconducting tubes in metallic sample and vice versa, which proved a high purity of the nanotube fractions. The XPS investigation of the separated samples showed different positions, spectral widths and asymmetry of the C 1s core level spectra. The multifrequency Raman spectroscopy investigation of the separated samples allowed performing an analysis of the diameter range of nanotubes. The demonstrated successful separation of the filled SWCNTs by conductivity type and diameter enables demanding applications of ultra pure SWCNTs with tailored properties.

Fabrication and Characterization of Surfaces Modified with Carboxymethylthio Ligands for Chelate-Assisted Trapping of Copper.

The metal ion chelating property was conferred onto silicon (Si) and gold (Au) surfaces by direct electrografting of the 4-[(carboxymethyl)thio]benzenediazonium cation (4-CMTBD). Infrared spectroscopic ellipsometry showed the presence of characteristic phenyl and carbonyl vibrational bands on the functionalized surfaces as a proof of existence of surface-bound organic units of 4-[(carboxymethyl)thio]benzene, (4-CMTB). The loss of diazonium group (N≡N+) upon electrografting of 4-CMTBD was investigated using IR spectroscopy. A Faradaic efficiency of about 18.8-20.0% was realized in mass deposition experiments for grafting 4-CMTB on the Au surface using an electrochemical quartz crystal microbalance technique. Raman spectroscopy performed on the Si-(4-CMTB) surface after treatment with copper (Cu) ion solution provided evidence of metal ion chelation based on an observed v(Cu-O) peak at about 487 cm-1 and a v(Cu-S) signal at about 267 cm-1. The binding of Cu ions by the chelating ligands also caused a red shift of about 10 cm-1 in the Raman spectrum of the Si-(4-CMTB)-Cu surface within the spectral region, characteristic of the v(C-O) signal. X-ray photoelectron spectroscopy investigations showed indications of the Cu(II) ion species chelated by the surface-bound carboxymethylthio ligands. The functionalized surface, Si-(4-CMTB), constitutes an alternative metal ion chelating surface that may potentially be developed for applications in trace-level trapping of Cu ions.