In situ growth of epitaxial cerium tungstate (100) thin films

The deposition of ceria on a preoxidized W(110) crystal at 870 K has been studied in situ by photoelectron spectroscopy and low-energy electron diffraction. Formation of an epitaxial layer of crystalline cerium tungstate Ce(6)WO(12)(100), with the metals in the Ce(3+) and W(6+) chemical states, has been observed. The interface between the tungsten substrate and the tungstate film consists of WO suboxide. At thicknesses above 0.89 nm, cerium dioxide grows on the surface of Ce(6)WO(12), favoured by the limited diffusion of tungsten from the substrate.     

Time‐of‐flight secondary ion mass spectroscopic characterization of the nitrogen profile of shallow gate oxynitride thermally grown on a silicon substrate

Silicon oxynitride has been used as a shallow gate oxide material for microelectronics and its thickness has been reduced over the years to only a few tens of angstroms due to device size scaling. The nitride distribution and density characteristic in the gate oxide thus becomes imperative for the devices. The shallow depth profiling capability using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) has huge potential for the nitrogen characterization of the shallow gate oxide film. In this article, both positive and negative spectra of TOF‐SIMS on silicon oxynitride have been extensively studied and it was found that the silicon nitride clusters Si_xN^? (x = 1–4) are able to represent the nitrogen profiles because their ion yields are high enough, especially for the low‐level nitride doping in the oxide, which is formed by the annealing of nitric oxide on SiO₂/Si. The gate oxide thickness measured by the TOF‐SIMS profiling method using ¹⁸O or CsO profile calibration was found to correlate very well with transmission electron microscope measurement. The nitrogen concentration in the gate oxide measured using the TOF‐SIMS method was consistent with the results obtained using the dynamic SIMS method, which is currently applied to relatively thicker oxynitride films. Copyright © 2012 John Wiley & Sons, Ltd.     

The distribution of hydroxyl ions at the surface of anodic alumina

Barrier‐type anodic films 3–15 nm thick have been formed on electropolished 99.999% aluminium. Variable‐angle XPS has been used to identify a significant proportion of hydroxyl ions at the surface of the relatively compact alumina films. The location of an oxygen‐rich region at the outer surface of the oxide has been confirmed by medium‐energy ion scattering (MEIS). Combining the information from these two techniques leads to the conclusion that a hydroxyl‐containing surface region is responsible for this oxygen‐rich surface layer, MEIS revealing an approximately linear relationship between the total oxide thickness and the thickness of the hydroxyl‐rich surface region. From consideration of the mechanisms of amorphous alumina formation by ionic transport, with incorporation of electrolyte‐derived species into the thickening film, the generation of the hydroxyl‐rich outermost region is considered to result from the formation of gel‐like material at the film/electrolyte interface. Copyright © 2003 John Wiley & Sons, Ltd.     

Solution Layer Deposition: A Technique for the Growth of Ultra‐Pure Manganese Oxides on Silica at Room Temperature

With the ever increasing miniaturization in microelectronic devices, new deposition techniques are required to form high‐purity metal oxide layers. Herein, we report a liquid route to specifically produce thin and conformal amorphous manganese oxide layers on silicon substrate, which can be transformed into a manganese silicate layer. The undesired insertion of carbon into the functional layers is avoided through a solution metal–organic chemistry approach named Solution Layer Deposition (SLD). The growth of a pure manganese oxide film by SLD takes place through the decoordination of ligands from a metal–organic complex in mild conditions, and coordination of the resulting metal atoms on a silica surface. The mechanism of this chemical liquid route has been elucidated by solid‐state ²⁹Si MAS NMR, XPS, SIMS, and HRTEM.     

Lifetimes of organic photovoltaics: photooxidative degradation of a model compound

A poly phenylene vinylene (PPV‐type) oligomer used in organic photovoltaics was designed to facilitate the interpretation of mass spectral data. A film of the oligomer was subjected to various degrees of illumination (1000 W m^?2, AM1.5) in air resulting in photooxidation of the material. The surface chemistry was monitored by TOF‐SIMS and XPS. The experiment described accelerated photooxidation without any contributions from interface processes. The photooxidative degradation mechanisms are described starting from the intact molecule through presumably, intermediate photooxidation products to small photooxidation products. The processes are described with various degrees of specificity and with varying degrees of detail. Copyright © 2006 John Wiley & Sons, Ltd.     

In‐depth diffusion of oxygen into LDPE exposed to an Ar–O2 atmospheric post‐discharge: a complementary approach between AR‐XPS and Tof‐SIMS techniques

The in‐depth oxygen diffusion into a low density polyethylene film is performed in the post‐discharge of an atmospheric plasma torch, supplied in argon as carrier gas and with or without oxygen as reactive gas. The chemical and structural properties of the polymer surface and bulk are studied in terms of plasma parameters (treatment time, power, and reactive gas flow rate). A good correlation between XPS and Fourier transform infrared spectroscopy analyses is demonstrated. The penetration depth of oxygen into the bulk of the polymer is investigated by angle resolved‐XPS and time‐of‐flight SIMS. It is shown that, depending on the plasma conditions, oxygen could penetrate up to 20–40 nm into the low density polyethylene during the atmospheric plasma treatment. Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular adsorption and the chemistry of plasma-deposited thin organic films: Deposition of oligomers of ethylene glycol

Weakly ionized, radio-frequency, glow-discharge plasmas formed from methyl ether or the vapors of a series of dimethyl oligo(ethylene glycol) precursors (general formula: H-(CH₂OCH₂)_n-H;n=1 to 4) were used to deposit organic thin films on polytetrafluoroethylene. X-ray photoelecton spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) of the thin films were used to infer the importance of adsorption of molecular species from the plasma onto the surface of the growing, organic film during deposition. Films were prepared by plasma deposition of each precursor at similar deposition conditions (i.e., equal plasma power (W), precursor flow rate (F), and deposition duration), and at conditions such that the specific energy (energy/mass) of the discharge (assumed to be constrained byW/FM, whereM=molecular weight of the precursor) was constant. At constantW/FM conditions, two levels of plasma power (and, hence, twoFM levels) and three substrate temperatures were examined. By controlling the energy of the discharge (W/FM) and the substrate temperature, these experiments enabled the study of effects of the size and the vapor pressure of the precursor on the film chemistry. The atomic % of oxygen in the film surface, estimated by XPS, and the intensity of theC-O peak in the XPS C_ls spectra of the films, were used as indicators of the degree of incorporation of precursor moieties into the plasma-deposited films. Analysis of films by SIMS suggested that these two measures obtained from XPS were good indicators of the degree of retention in the deposited films of functional groups from the precursors. The XPS and SIMS data suggest that adsorption of intact precursor molecules or fragments of precursor molecules during deposition can have a significant effect on film chemistry. Plasma deposition of low vapor pressure precursors provides a convenient way of producing thin films with predictable chemistry and a high level of retention of functional groups from the precursor.     

The effect of glow discharge sputtering on the analysis of metal oxide films

The potential of radiofrequency glow discharge optical emission spectrometry (rf-GD-OES) for the quantification and the solid-state speciation of metal oxide films has been investigated in this work. Two types of oxide coatings, an iron oxide film deposited on silicon and a chromate conversion coating (CCC), were studied at 700 Pa of pressure and 30 W of forward power. The metal to oxygen ratios in the quantitative depth profiles (Fe/O and Cr/O, respectively) were used to evaluate the oxidation states of iron and chromium in the oxide films, demonstrating the capability of GD-OES technique for depth-resolved solid-state speciation. Furthermore, the effect of glow discharge sputtering on the samples surface in terms of modifications in the surface morphology and species transformations, were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The iron and chromium oxidation states were carefully studied by XPS at the original samples surface and at the bottom of GD craters, and a systematic reduction of metal elements was observed after rf-GD-OES analysis. In the case of thin oxide films, preferential sputtering can be considered as a critical factor since oxygen atoms can be preferentially sputtered, leaving a metal-enriched surface and, therefore, promoting the reduction of metal elements. In the present study preferential sputtering was found to be sample dependent, changing the proportion of the metal reduction in the oxide film with its composition. Additionally, alternative sputter-depth-profiling techniques such as secondary ion mass spectrometry (SIMS), femtosecond laser ablation (fs-LA), and XPS ion gun were used for the analysis of the CCC in order to evaluate the reduction of Cr⁶⁺ to Cr³⁺ depending on the sputtering mechanism.     

Surface characterization of WO(3)/ZrO(2) catalysts

A series of WO(3)/ZrO(2) catalysts with tungsten (W) loadings ranging from 0.5 to 11.4 wt% was prepared by incipient wetness impregnation on a preformed ZrO(2) support. The oxidic catalysts were characterized using XRD, Raman spectroscopy, XPS, ISS, and IR spectroscopy. XRD and Raman results showed that the ZrO(2) support was predominantly present in the monoclinic form. XPS and Raman measurements indicated the formation of increasing amounts of W interaction species for catalysts with W loadings up to 8.8 wt% WO(3). In addition to the W interaction species, bulk WO(3) was also observed for catalysts with W loadings > or = 3.0 wt% WO(3). Comparison of the XPS results with coverage measurements by ISS and CO adsorption suggests that the W surface phase is in the form of two-dimensional polymeric patches for catalysts with W loadings 3.0 < or = wt% WO(3) < or = 4.5. For catalysts with W loadings >4.5 wt% WO(3), the results indicated an additional build-up of a bilayer (or multilayer) polymeric W species. Analysis of the hydroxyl region of ZrO(2) by IR spectroscopy showed that initial additions of W occur on the high frequency hydroxyl group. A schematic for the structure of the catalysts has been proposed based on the above observations.     

Layer‐by‐layer deposition of nitrilotris(methylene)triphosphonic acid and Zr(IV): an XPS,ToF‐SIMS,ellipsometry, and AFM study

Layer‐by‐layer assemblies consisting of alternating layers of nitrilotris(methylene)triphosphonic acid (NTMP), a polyfunctional corrosion inhibitor, and zirconium(IV) were prepared on alumina. In particular, a nine‐layer (NTMP/Zr(IV))₄NTMP stack could be constructed at room temperature, which showed a steady increase in film thickness throughout its growth by spectroscopic ellipsometry up to a final thickness of 1.79 ± 0.04 nm. At higher temperature (70 °C), even a two‐layer NTMP/Zr(IV) assembly could not be prepared because of etching of the alumina substrate by the heated Zr(IV) solution. XPS characterization of the layer‐by‐layer assembly showed a saw tooth pattern in the nitrogen, phosphorus, and zirconium signals, where the modest increases and decreases in these signals corresponded to the expected deposition and perhaps removal of NTMP and Zr(IV). Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) confirmed the attachment of the NTMP molecule to the surface through PO^?, PO₂^?, PO₃^?, and CN^? signals. Increasing attenuation of the Al signal from the substrate after deposition of each layer was observed by both XPS and ToF‐SIMS. Essentially complete etching of the alumina by the heated Zr(IV) solution was confirmed by spectroscopic ellipsometry, XPS, and ToF‐SIMS. Atomic force microscopy revealed that all the films were smooth with R_q roughness values less than 0.5 nm. Copyright © 2015 John Wiley & Sons, Ltd.     

Combinatorial study of WInZnO films deposited by rf magnetron co-sputtering

The compositional dependence of co-sputtered tungsten indium zinc oxide (WInZnO) film properties was first investigated by means of a combinatorial technique. Indium zinc oxide (IZO) and WO₃ targets were used with different target power. W composition ratio [W/(In+Zn+W)] was varied between 3 and 30 at% and film thickness was reduced as the sample position moved toward WO₃ target. Furthermore, the optical bandgap energy increased gradually, which might be affected by the reduction in film thickness. All the WInZnO films showed an amorphous phase regardless of the W/(In+Zn+W) ratio. As the W/(In+Zn+W) ratio in WInZnO films increased, the carrier concentration was restricted, causing the increase in electrical resistivity. W cations worked as oxygen binders in determining the electronic properties, resulting in suppressing the formation of oxygen vacancies. Consequentially, W metal cations were effectively incorporated into the WInZnO films as a suppressor against the oxygen vacancies and the carrier generation by employing the combinatorial technique.     

X-Ray Analysis of Multi-Films for Electrochromic Device Application

Multilayer films based on tungsten oxide (WO₃), ITO (indium tin oxide) and CdS were deposited mainly by reactive dc magnetron sputtering onto glass substrates for electrochromic application. The thin films were analyzed by means of XPS (X-ray photoelectron spectroscopy), GIXD (grazing incidence X-ray diffraction) and XRD (X-ray diffraction). XRD and XPS results confirmed that the films were WO₃, CdS and ITO, respectively. The surface and interface of the CdS/ITO bi-layered film was studied by GIXD in different incidence angles. Detailed results about the amorphous characterization of the films during room temperature growth and post annealing are given.     

Acetone‐Induced Graphene Oxide Film Formation at the Water–Air Interface

Graphene oxide (GO) is an amphiphilic soft material, which can accumulate at the water–air interface. However, GO sheets diffuse slowly in the aqueous phase because of their large size. It is still challenging to form high quality GO films in a controllable and simple way. In this study, we showed that GO sheets can quickly migrate to the water–air interface and form thin films when a suitable amount of acetone is directly mixed with a GO aqueous dispersion. The film formation rate and surface coverage of GO sheets depend on the volume of acetone added, GO dispersion concentration, and formation time. Among several organic solvents, acetone has its advantage for GO film formation owing to its three properties: a nonsolvent to GO aqueous dispersions, miscible with a GO aqueous dispersion, and fast evaporation. Furthermore, we have found that the film formation also is governed by the size of GO sheets and their oxygen content. Although smaller GO sheets could migrate to the water–air interface faster, the overlapping of small GO sheets and the increase in contact resistance is not desirable. A higher oxygen content in GO sheets could also result in smaller GO sheets. Multilayer GO films can be obtained through layer‐by‐layer dip‐coating. These findings open opportunities in developing simple scalable GO film fabrication processes.     

Multitechnique characterization of thin films of immiscible polymer systems: PS–b‐PMMA diblock copolymers and PS–PMMA symmetric blends

Immiscible polymer systems are known to form various kinds of phase‐separated structures capable of producing self‐assembled patterns at the surface. In this study, different surface characterization methods were utilized to study the surface morphology and composition produced after annealing thin polymer films. Two different SIMS techniques—static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and dynamic nano‐SIMS—were used, complemented by x‐ray photoelectron spectrometry (XPS) and atomic force microscopy (AFM). Thin films (spin‐coated onto silicon wafers) of polystyrene (PS)–poly(methyl methacrylate) (PMMA) symmetric blends and diblock copolymers of similar molecular weight were investigated. Surface enrichment by PS was found on all as‐cast samples. The samples were annealed at 160 °C for different time periods, after which the blend and the copolymer films exhibited opposite behaviour as seen by ToF‐SIMS and XPS. The annealed blend surface presented an increase in the PMMA concentration whereas that of copolymers showed a decrease in PMMA concentration compared with the as‐cast sample. For blends, the nano‐SIMS as well as AFM images revealed the formation of phase‐separated domains at the surface. The composition information obtained from ToF‐SIMS and XPS, as well as the surface mapping by nano‐SIMS and AFM, allowed us to conclude that PS formed phase separated droplet‐like domains on a thin PMMA matrix on annealing. The three‐dimensional nano‐SIMS images showed that the PS droplets were supported inside a rim of PMMA and that these droplets continued from the surface like columnar rods into the film until the substrate interface. In the case of annealed copolymer samples, the AFM images revealed topographical features resembling droplet‐like domains on the surface but there was no phase difference between the domains and the matrix. In the case of copolymers, owing to the covalent bonding between the blocks, complete phase separation was not possible. The three‐dimensional nano‐SIMS images showed domain structures in the form of striations inside the film, which were not continuous until the substrate interface. Information from the different techniques was required to gain an accurate view of the surface composition and topographical changes that have occurred under the annealing conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

ToF‐SIMS studies of the oxidation of Fe by D2O vapour: comparison with XPS

The oxidation of iron (Fe) by water (D₂O) vapour at low pressures and room temperature was investigated using time‐of‐flight (ToF) SIMS. The results supported those found previously using XPS and the QUASES^? program in that a duplex oxide structure was found containing a thin outer surface hydroxide (Fe(OD)₂) layer over an inner oxide (FeO) layer. The extraordinary depth resolution of the ToF‐SIMS profiles assisted in identifying the two phases; this resolution was achieved by compensation for surface roughness. A substantial concentration of deuterium was found in the subsurface oxide layer. This observation confirmed previous assessments that the formation of FeO was from the reaction of Fe(OD)₂ with outward‐diffusing Fe, leaving deuterium as a reaction product. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigation of the synthesis and internal structure of protective oxide layers on high-purity chromium with SIMS scanning techniques

The major problem affecting the application of chromium in high temperature processes is the ongoing spallation of the protective oxide layer formed during hot-gas oxidation. This results in a continuous material erosion. To gain a deeper insight in the spallation and oxidation process, a high-purity powder-metallurgically produced chromium sample was submitted to a two-stage hot gas oxidation process. The formed oxide layers were investigated by 3D SIMS and scanning SIMS. The formation of the protective oxide layer is carried by the diffusion of chromium from the bulk through the already existing oxide layer and the reaction of the diffused chromium with the oxygen from the gaseous phase. In parallel to the growing of the oxide layer, an accumulation of impurities at the interface oxide layer – bulk can be observed. The enrichment of trace elements at the interface level (for the investigated sample Cl and N) can be explained by the low solubility of these elements in chromium oxide and therefore their inability to diffuse through the already formed protective layer. Received: 24 June 1996 / Revised: 22 January 1997 / Accepted: 26 January 1997     

Low‐density polyethylene films doped with europium(III) complex: their properties and applications

Light‐converting polyethylene film containing europium(III) complex with phenanthroline was manufactured under an extrusion process. The film was characterized first by means of time‐of‐flight secondary‐ion‐mass spectrometry (TOF‐SIMS), ultraviolet‐visible‐infrared (UV‐vis‐IR) spectroscopy, then a study of excitation and luminescence spectra, quantum yield and lifetime of luminescence. The quantum yield of luminescence was measured as 5±2%, and the lifetime of luminescence was determined about 470 μsec. TOF‐SIMS surface mapping showed the uniform distribution of europium(III) over the film. Visualization of strong picosecond UV laser beams through the use of the developed film has been demonstrated. Copyright © 2004 John Wiley & Sons, Ltd.     

一种新的WO3纳米管的制备方法

一维纳米材料因可用来构造高性能纳米器件的结构单元而成为纳米材料研究的热点．目前的研究重点集中在材料的制备和结构性能表征方面,已发展了多种制备方法,主要有模板法、V-L-S法、L-L-S法和V-S法等,其中阳极氧化铝(AAO)模板法是制备一维材料的好方法．AAO模板的制备工艺已相当成熟,     

Effects of oxygen plasma treatment on the surface of bisphenol A polycarbonate: a study using SIMS,principal component analysis,ellipsometry, XPS and AFM nanoindentation

The effects of oxygen plasma treatment and the subsequent air exposure on the surface composition and properties of bisphenol A polycarbonate (BPA‐PC) were analysed by X‐ray photoelectron spectroscopy (XPS), ellipsometry, static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) with principal component analysis (PCA) and nanoindentation using an atomic force microscope (AFM). PCA showed systematic changes in the film chemistry after short treatment times (0.1 s), with the main sites of attack being the carbonate and aromatic ring structure. On the basis of this multitechnique analysis, it was unambiguously determined that extended oxygen plasma treatment times resulted in the formation of low‐molecular‐weight material (LMWM) within the first 50 nm on the surface, and not in a cross‐linked skin as has been proposed by other researchers. The study shows that controlled surface modification of BPA‐PC polymers is possible, allowing surface oxygen incorporation without degradation of the polymer structure. This result is relevant for improved adhesion of coatings applied to BPA‐PC polymers. Copyright © 2006 John Wiley & Sons, Ltd.     

Mechanism of anodic oxidation of tungsten in neutral sulphate-fluoride solutions

The anodic oxidation of tungsten has been studied in 1 M Na₂SO₄ solutions containing 0–0.25 M NaF. Steady-state currents measured in the passivation and passivity ranges increase significantly with increasing fluoride concentration, indicating enhanced dissolution of the oxide film. The electrochemical impedance response is dominated by the processes in the barrier layer and at its interface with the electrolyte. The presence of a pseudo-inductive loop in the impedance spectra at intermediate frequencies indicates point defect interaction during film growth and dissolution processes. A kinetic model including the recombination reaction between oppositely charged point defects at the film/solution interface as well as a kinetic scheme for tungsten dissolution through the film mediated by cation vacancies is proposed. It is found to reproduce satisfactorily the steady-state currents and the impedance spectra in the potential range 0.2–2 V. Such a model for the conduction mechanism in the barrier layer is believed to be an essential part of a modelling approach to the formation of a nanoporous overlayer on tungsten in fluoride-containing solutions.