X-ray Photospectroscopy Research Articles

Improvement of initial activation of a Ti–Cr alloy by surface modification with potassium (K)

The alkaline treatment of the surface of a Ti–Cr hydrogen storage alloy was made by sticking potassium (K) metal onto the alloy block surface or by milling the alloy powder with K metal blocks instead of the use of KOH solution. This dry surface treatment was found effective to reduce the work function of electrons of the alloy surface and to ease the rate of hydrogen dissociation, resulting in an accelerated activation rate. The K atoms were found distributed in the surface oxide layer; however, X-ray photo spectroscopy (XPS) analyses in the vicinity of Fermi level suggest rather the induction of a metallic feature of the surface modified by K atoms.

Layer-by-Layer Self-Assembled Pyrrole-Based Donor−Acceptor Chromophores as Electro-Optic Materials

The synthesis of the heterocycle-based diethanolaminomethyl-functionalized derivative 1-(pyridin-4-yl)-2-[(N-methylpyrrol-2-yl)-5-methylenediethanolamine]ethene (2) from (1-pyridin-4-yl)-2-(N-methyl-pyrrol-2-yl)ethene (1) and their methylpyridinium dyes 1-(N-methylpyridinio)-2-[(N-methylpyrrol-2-yl)-5-methylenediethanolamine]ethene iodide (3) and 1-(N-methylpyridinio)-2-[(N-methylpyrrol-2-yl)-5-methylenediethanolamine]ethene iodide (4) is described. NLO-active chromophore monolayers SA-1 and SA-2 were obtained by reaction of p-iodomethylphenyldiiodochlorosilane (5)-functionalized substrates and dye precursors 1 and 2, respectively. A χ(2) value of ∼120 pm/V is observed for SA-2. The new diethanolaminomethyl-functionalized chromophore 2 is also a suitable building block for the layer-by-layer formation of intrinsically acentric, highly transparent nonlinear optical/electro-optic multilayers (SAS = self-assembled superlattice). The organic SAS films are characterized by a combination of physicochemical methods including synchrotron specular X-ray reflectivity, angle-dependent polarized second-harmonic generation, optical (absorption and photoluminescence) spectroscopy, X-ray photospectroscopy, atomic force microscopy, and advancing contact angle measurements.

Ion Beam Synthesis and Optical Properties of Zn and Zno Nanocrystals in Sio2 and Caf2 Substrates

AbstractIon implantation was used to inject zinc ions into crystalline CaF2 and amorphous SiO2 substrates. Zn or ZnO nanoparticles were formed after annealing in a reducing (4% H2 + 96%Ar) or an oxidizing (10%O2 + 90% Ar ) atmosphere, respectively. When the sample was annealed in a reducing atmosphere, the absorption band at ∼ 5.3 eV for zinc implanted into SiO2 was attributed to zinc metal colloids. The absorption peak observed in the 4.3 – 4.7 eV region was due to the formation of ZnO nanocrystals, after the sample was annealed in an oxidizing environment. Both X-ray diffraction (XRD) and X-ray photospectroscopy (XPS) were used to confirm ZnO nanocrystal formation. For zinc implanted into CaF2, the as-formed ZnO nanocrystals were aligned with their [002] axes parallel to the [111] axis of the CaF2. Photoluminescence (PL) spectra showed UV and green emission from the zinc-implanted silica samples annealed under an oxygen atmosphere; however, no green emission was observed for ZnO formed in a CaF2 substrate. An additional emission was observed at ∼ 420 nm which might be due to F centers in CaF2 created by ion beam damage.

Zn-Al based alloys as Pb-free solders for die attach

The present study examines the potential of Zn-Al based alloys for replacing Pb-containing solders used in the die-attaching process. Four alloys (Zn-6wt.%Al, Zn-6wt.%Al-1wt.%Ga, Zn-3wt.%Al-3wt.%Mg, and Zn-4wt.%Al-3wt.%Ga-3wt.%Mg) were cast and characterized in terms of microstructure and mechanical behavior. Based on the criteria of thermodynamics (phase diagram extrapolations) and mechanical behavior (flow curves), it was possible to select the Zn-Al-Ga alloy as best meeting the requirements concerning melting range necessary for die attach and mechanical properties. A wire with 0.76-mm thickness was produced successfully by extrusion. However, the alloy, in the form of wires, is subject to substantial embrittlement after extruding to a degree that further handling becomes impossible. The reason for the embrittlement was investigated using x-ray techniques (x-ray diffraction and x-ray photo spectroscopy (XPS)) and transmission electron microscopy. The temperature dependence of the Ga solubility in the hexagonal close-packed (hcp) Zn-rich phase in combination with the affinity of Ga to the surface of the Al-rich and Zn-rich phases is held responsible for the embrittlement. A remedy for the embrittlement could be a reduction of the solubility at high temperatures in the Zn-rich phase. This will be attempted by adding small fractions of further alloying elements in future work.

Predicting Growth Rates of SiC Epitaxial Layers Grown by Hot-Wall Chemical Vapor Deposition

The growth of device quality epitaxial layers requires precise control of the thickness and doping uniformity. By using simulations a better understanding of the growth process can be achieved and process optimization may be possible. The present work uses an extensive chemistry model, to accurately predict growth rates of epitaxial layers grown by chemical vapor deposition. Simulations are made in three dimensions to accurately model the horizontal reactor used in the experiments. Experimental results show four main growth zones, which are characterized by different morphological defects. Certain defects can be attributed to either silicon rich or carbon rich deposition, which is confirmed by X-ray photospectroscopy measurements. Different cases are studied, changing the total pressure in the growth chamber.

Surface Passivation of AlGaN terminated and GaN Terminated HEMT Structures Studied by XPS

ABSTRACTSamples of both AlGaN and GaN terminated HEMT structures were studied using x-ray photo spectroscopy (XPS). It was found that the XPS spectra of both AlGaN and native oxide surfaces were shifted by a surface charge of 0.5 to 1.0 eV. The samples were then oxidized using an UV-ozone treatment for 25 minutes at room temperature. The ozone oxide XPS spectra of the AlGaN terminated surface was found to have the same 0.5 to 1.0 eV shift while the ozone oxide XPS spectra of the GaN terminated surface was found to have a 5.0 eV shift, indicating that the native GaN oxide is more insulating. Processed HEMT devices using both surface terminations were given the same UV-ozone treatment followed by a 10nm MBE grown Sc2O3 film for passivation. The GaN terminated HEMT structures showed on average a 10% increase in channel current (from gate-lag measurements, pulse mode) over the AlGaN terminated HEMT structures.

Characterization of a New Potassium Titanate, KTiO2(OH) Synthesized via Hydrothermal Method

A new potassium titanate, KTiO2(OH), synthesized by hydrothermal oxidation of Ti metal powder in KOH solution was characterized. The X-ray photospectroscopy revealed that titanium contained in this compound consists of only Ti4+, and FT-IR spectrum supported the existence of hydroxyl group in the structure. It was found that the titanate has a hexagonal tunnel structure with the space group P6122 and lattice parameters a = 9.8889 Å and c = 28.6711 Å, by crystal structure analysis with the use of powder XRD pattern. This agrees with the results of electron diffraction and morphology observed by SEM. The heating of KTiO2(OH) above 528 °C led to dehydration and phase transformation to give K2Ti2O5.

Si–N linkage in ultrabright, ultrasmall Si nanoparticles

Ultrabright ultrasmall (∼1 nm) blue luminescent Si29 nanoparticles are chlorinated by reaction with Cl2 gas. A Si–N linkage is formed by the reaction of the chlorinated particles with the functional amine group in butylamine. Fourier transform infrared spectroscopy and x-ray photospectroscopy measurements confirm the N linkage and the presence of the butyl group, while emission, excitation, and autocorrelation femtosecond optical spectroscopy show that, after the linkage formation, the particles with the ultrabright blue luminescent remain, but with a redshift of 40 nm.

An amorphous hydrocarbon diamond-like polymer as a precursor for diamond growth

A diamond-like polymer, poly(phenylcarbyne), was synthesized by reductive condensation of α,α,α-tricholorotoluene monomer with an ultrasonically-generated NaK alloy emulsion in tetrahydrofuran under an inert atmosphere. The polymer consists of a randomly constructed rigid network of tetrahedral polycarbyne units in which each carbyne carbon forms three CC bonds to the network and one to a substituent structure of the polymer, which was analyzed by nuclear magnetic resonance (NMR), X-ray photospectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The polymer is easily soluble in organic solvents to form a solution which can be applied to various substrates and forms films with a large area. By a simple heat-treatment process, this amorphous polymer can transform into diamond crystals at relatively low temperature (600°C), and the structure of the diamond crystals was confirmed by micro-Raman spectroscopy. The correlation of thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), FTIR and Raman spectra of polymers provides important information on the process of phase transformation.

Interface structure and mechanical properties of Al 2O 3–20vol%SiCw ceramic matrix composite

Al 2O 3–20vol%SiCw composites with as-received and acid-leached whiskers were fabricated by a hot-pressing technique. The microstructure, mechanical properties, fracture behavior and toughening mechanisms of the composites were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution electron microscopy (HREM), X-ray photo spectroscopy (XPS), energy dispersive analysis of X-ray (EDAX) techniques and three-point bending tests. The results show that whisker surface acid-leached treatment obviously reduces the oxygen content of SiC whisker and makes the whisker surface smooth, resulting in composites with higher fracture toughness.

Microstructural assessment of laser nitrided Ti-6Al-4V alloy

A microstructural study of the phases developed during the laser nitriding of a Ti-6Al-4V alloy by, using a CL5 continuous CO2 laser with a spinning beam and concentration of 80% nitrogen, was undertaken. The vertical sections, perpendicular to the melt track were examined by optical microscopy and scanning electron microscopy (SEM), while specimens for X-ray diffractometry (XRD), X-ray photospectroscopy (XPS) and transmission electron microscopy/selected area electron diffraction (TEM/SAED), were taken parallel to the melt track. In this way the variation in microstructure as a function of depth from the laser treated surface, was studied. This supplemented XRD and XPS investigations undertaken previously. Two zones were identified. Zone 1, within 50 μm of the surface, contained well defined dendrites of fcc TiN0.8, plus hcp TiN0.3 and hcp α′Ti. Zone 2, below 50 μm, consisted of needles of hcp α′Ti. From a consideration of the hardness profiles in Zone 2, it is suggested that at the top of the zone, the α′ phase is, in fact, a solid solution containing 3–4% N, which decreased to <1% N at the bottom of the zone. The TEM/SAED study permitted the three phases fcc TiN0.8, hcp TiN0.3 and hcp α′Ti to be identified through a combination of morphology and SAED patterns. This also showed that the fccTiN0.8 contained fringes, which were considered to be stacking fault fringes and allowed this phase to be readily recognized in the TEM. The presence of stacking faults may be associated with the high nitrogen concentration of 80% used for the laser nitriding in this work.

Cell culture tests for assessing the tolerance of soft tissue to variously modified titanium surfaces.

The aim of our research project was to achieve an improvement in the integration of enossal dental implants in the region of peri-implantary soft tissue. Improvement in the adhesion of the gingiva of the surface of enossal implants was to be achieved by modification of the titanium surface. The effect of different modifications on the biocompatibility of the modified titanium surfaces was tested: sulfur dioxide plasma treatment of titanium; acetylene plasma treatment of titanium followed by sulfur dioxide plasma etching; plasma nitration of titanium; replacement of titanium by glycidoxypropyltrimethoxy silane; coating titanium with poly[(ethene-co-vinyl acetate)-graft-vinyl chloride] and coating titanium with fibronectin. Determination of the chemical composition of the surface was carried out using X-ray photospectroscopy. The adsorption of fibronectin at the surface of the titanium was tested using an Enzyme Linked Immunosorbent Assay. In selected in vitro tests with human gingival fibroblasts, cell morphology was assessed using scanning electron microscopy and light microscopy. Cell proliferation and protein synthesis, as well as the activity of mitochondrial dehydrogenases were evaluated. By means of centrifugation and by determining initial cell adhesion, the adhesion of gingival fibroblasts was investigated. According to the kind of modification made to the titanium surfaces, it was possible to observe differences in the cellular behavior of gingiva fibroblasts on the differently modified surfaces of the implants. Coating the titanium using fibronectin produced optimization of cell growth and improvement in the adhesion of gingiva fibroblasts to the implant surface. In contrast, modification of the titanium with poly[(ethene-co-vinyl acetate)-graft-vinyl chloride] generally resulted in a deterioration of the biocompatibility of the surface. A marked correlation between the cellular compatibility of the modified titanium and the surface modification made did not become apparent. One reason for this is the large number of parameters determining the interaction between implant and tissue.

The friction behavior of Ni −-, SiO −2- and mica sodium silicate-based solid lubrication composites

The friction behavior of Ni −-, SiO − 2- and mica sodium silicate-based lubricant composites, which included BN, WS 2 and graphite as lubricants, were examined. A ring-on-disk apparatus, in which a solid lubricant composite disk was held against a rotating stainless ring, was used as the test configuration. The tests were run with a load from 62 to 250 N in temperatures from 20 to 800°C in the laboratory environment. The wear surface was characterized by scanning electron microscope and X-ray photo spectroscopy. The major findings were that both mica sodium silicate- and SiO − 2-based composites failed at above 500°C due to severe wear and surface damage; in contrast, Ni −-based composite showed a stable friction coefficient and low wear from 20 to 800°C.

Electrochemical and X-ray photospectroscopy studies of polytetrafluoroethylene and polyvinylidene fluoride in Li/C batteries

The stability of polytetrafluorethylene (PTFE) and polyvinylidene fluoride (PVDF) used as the anode binders in lithium-ion batteries was studied by electrochemical and X-ray photospectroscopy (XPS) measurements. The characteristic discharge/charge curves for PTFE and PVDF were obtained. It is shown that the behavior of PTFE and PVDF exhibits much discrepancy when they are attacked by high active lithium ion in electrochemical cells. PTFE reacts with lithium easily and decomposes during the first discharge process, which is indicated by a long plateau appearing around 1.2 V in the first discharge curve of Li/Ni(PTFE) cell. XPS results show that PTFE decomposes after one discharge/charge cycle. PVDF is rather stable due to a possible surface passivation process.

Recent studies on the correlation between surface chemistry, morphology, three-dimensional structures and performance of Li and Li-C intercalation anodes in several important electrolyte systems

This paper reviews some advances in the comparative study of lithium and graphite electrodes in a large matrix of solvents, salts and additives. The major purpose of this work was to support R&D of lithium metal and Li-ion batteries by understanding the correlation between the anode's performance, its morphology and three-dimensional structure upon cycling, interfacial electronic properties and the surface chemistry. The emphasis was on the use of the most sophisticated novel spectroscopic tools in conjunction with standard electrochemical techniques. These included in situ and ex situ Fourier-transform infrared spectroscopy (FT-IR) and X-ray difraction (XRD), impedance spectroscopy and atomic force microscopies (EIS and AFM, respectively), X-ray photospectroscopy (XPS), energy dispersive analysis of X-rays (ED AX) and electrochemical quartz crystal microbalance (EQCM). Major achievements included: (i) analysis ofthe surface reactions which are taking place on both the lithium and the carbon electrodes which form surface films that control the electrochemical behaviour in many electrolyte systems of interest; (ii) successful and useful application of AFM and EQCM in order to study the surface film formation and Li-deposition processes; (iii) understanding the correlation between the reversibility and stability of graphite electrodes in Li-intercalation processes and their surface chemistry, and (iv) finding an interesting correlation between the three-dimensional structure of graphite electrodes, the diffusion coefficient of Li + and their voltammetric behaviour in Li-intercalation processes.

Reaction kinetics of fluorite in flow systems and surface chemistry

The kinetic experiments of fluorite in water-HCl solution in an open-flow system at the temperatures ≤100℃ reveal that the variation of flow rate (U) can change the reaction rate orders from 0 to 2 or higher. In the far from equilibrium systems, the dissolution rates of fluorite in aqueous solutions have a zero order.The reaction rates are controlled by pH values of input solutions. In fact, the reaction rates are related to the concentrations of the active sites occupied by H+ on fluorite surface [SOH]. X-ray photospectroscopy observations on fluorite surface before and after reaction indicate that surface chemical processes control the reaction rates: Cl- cations attach on and enter into surface of fluorite besides H+ when fluorites react with HCl solutions, which affect the reaction rates.

PROTECTIVE PROPERTIES OF OFF-STOICHIOMETRIC SiNx FILMS FOR MAGNETO-OPTICAL DISKS

Chemical bonding state and protective properties of nitrogen defective off-stoichiometric silicon nitride (SiNx) films for magneto-optical disks were investigated with X-ray photo spectroscopy. Both refractive index and extinction coefficient increase with decreasing gas flow ratio of N2 to Ar. Changes in the optical constants of SiNx with decreasing nitrogen content are caused by (1) an increase of Si clusters and (2) a change on tetrahedral sites of Si from Si-N4 to Si substitutional Si-N4-xSix. An aging test (80°C, 90%RH) was carried out for a magneto-optical disk with SiNx protective layers. C/N ratio and reflectivity remained constant up to 1000 hours. The SiNx film is sufficient for use as a protective layer in magneto-optical disks.

The surface of particles in Tamagawa estuary and Tokyo Bay and their influence on the distribution of trace elements.

The surface and bulk chemical composition of suspended particles (SP) from the Tamagawa estuary and Tokyo Bay have been studied. X-ray photospectroscopy (XPS) was used for the surface analyses. By comparison with bulk analysis, it was found that there was a surface layer enriched in organic matter and manganese, and that such the particles were coexisting. Silica may also be adsorbed onto the surface, but is depleted relative to the bulk nevertheless. The organic matter in the surface is considered to be humic acids from its chemical composition, and becomes the dominant substance on the surface with increasing depth and distance offshore, overwhelming silicates and oxides. The effect of such particles on dissolved trace metals was investigated by comparing their concentration gradients with the coverage of humic acid, silicates and oxides in the surface. The concentration gradients of dissolved Ni, Cu and Zn correlate better with the surface areas of Al, Fe and Mn than with that of organic matter, suggesting the former are more effective adsorbers of metals than the latter.

Low dose monitors — the movements and causes

A previous paper [Nucl. Instr. and Meth. B55 (1991) 178] has demonstrated that the correct equipment specification and process procedures enable the reliable direct probing of low dose sheet resistance monitors. Utilizing this, we are able to characterize the instability of low dose monitors to process and ambient conditions. Several experiments are conducted to determine the origin of the movements. These movements were found to be either “short term”, or “long term”. The former is a result of the interaction of the wafer and its processing prior to measurement. While the latter is a slow change after processing. The correct specification of the wafers, wafer processing, and the condition of the four point probe tips enable the low dose measurement to be performed. The value of the initial result, “short term movement”, is shown to be directly the consequence of wet chemistry and the ambient anneal condition. While the stability of the wafer after measurement, “long term movement”, is found to be the electrical degradation of the surface of the silicon. A key factor in this stability problem is the exposure of the wafer to air, especially to moisture in the atmosphere. X-ray photo spectroscopy (XPS), and time of flight secondary ion mass Spectrometry (TOP SIMS) results give an insight to the complexity of the surface condition. These range from oxide growth, surface chemistry, and hydrogen injection.

Carbonlithium anodes for lithium secondary batteries

For the development of a superior anode for practical lithium secondary batteries, the carbonlithium composite anode has been studied. As a carbon material, the carbon fiber M46 was mainly studied in this study. This material was proved to be highly reversible in comparison with other carbon materials. It is shown that lithium ions and/or solvated lithium ions intercalate into the fiber by using the X-ray diffraction (XRD) method and X-ray photospectroscopy (XPS) measurement. Coupled with the Cr 3O 8 cathode, a coin-type cell was constructed. Over 170 cycles were possible when the M46 carbonlithium composite anode was used, whereas with the bare lithium metal anode only 80 cycles were observed. From the observation of scanning electron micrographs (SEM), it is shown that the carbon fiber prevents the formation of dendritic lithium metal.