Function Of Surface Preparation Research Articles

Formation of silica-supported platinum nanoparticles as a function of preparation conditions and boron impregnation.

Preparation of supported metal nanoparticles for catalytic applications often relies on an assumption that the initially prepared wet-impregnated support material is covered with approximately a monolayer of adsorbed species that are shaped into the target nanoparticulate material with a desired size distribution by utilizing appropriate post-treatments that often include calcination and reduction schemes. Here, the formation and evolution of surface nanoparticles were investigated for wet-chemistry deposition of platinum from trimethyl(methylcyclopentadienyl)platinum (IV) precursor onto flat silica supports to interrogate the factors influencing the initial stages of nanoparticle formation. The deposition was performed on silicon-based substrates, including hydroxylated silica (SiO2) and boron-impregnated hydroxylated silica (B/SiO2) surfaces. The deposition resulted in the immediate formation of Pt-containing nanoparticles, as confirmed by atomic force microscopy and x-ray photoelectron spectroscopy. The prepared substrates were later reduced at 550 °C under H2 gas environment. This reduction procedure resulted in the formation of metallic Pt particles. The reactivity of the precursor and dispersion of Pt nanoparticles on the OH-terminated silica surface were compared to those on the B-impregnated surface. The size distribution of the resulting nanoparticles as a function of surface preparation was evaluated, and density functional theory calculations were used to explain the differences between the two types of surfaces investigated.

Microshear Bond Strength of Resin Cements to Lithium Disilicate Substrates as a Function of Surface Preparation.

To investigate the effect of hydrofluoric acid (HF) etching, silane solution, and adhesive system application on the microshear bond strength (μSBS) of lithium disilicate glass-ceramic (LD) to three resin cements. Circular bonding areas were delimited on the lithium disilicate surfaces using a perforated adhesive tape. Specimens were assigned to 18 subgroups (n=12) according to surface treatment: NT = no treatment; HF = 4.8% HF for 20 seconds; silane solution: (1) no silane; (2) Monobond Plus, a silane/10-methacryloyloxydecyl dihydrogen phosphate solution for 60 seconds; (3) Monobond Plus+ExciTE F DSC, a dual-cure adhesive; and resin cement: (1) Variolink II, a bisphenol A diglycidyl ether dimethacrylate (bis-GMA)-based, hand-mixed, dual-cure resin cement; (2) Multilink Automix, a bis-GMA-based, auto-mixed, dual-cure resin cement; (3) RelyX Unicem 2, a self-adhesive, auto-mixed, dual-cure resin cement. Tygon tubes (Ø=0.8 mm) were used as cylinder matrices for resin cement application. After 24 hours of water storage, the specimens were submitted to the μSBS test. Mode of failure was evaluated under an optical microscope and classified as adhesive, mixed, cohesive in resin cement, or cohesive in ceramic. Data were statistically analyzed with three-way analysis of variance and Dunnett test (p<0.05). When means were pooled for the factor surface treatment, HF resulted in a significantly higher μSBS than did NT (p<0.0001). Regarding the use of a silane solution, the mean μSBS values obtained with Monobond Plus and Monobond Plus+ExciTE F DSC were not significantly different but were higher than those obtained with no silane (p<0.001). Considering the factor resin cement, Variolink II resulted in a significantly higher mean μSBS than did RelyX Unicem 2 (p<0.03). The mean μSBS for Multilink Automix was not significantly different from those of Variolink II and RelyX Unicem 2. According to Dunnett post hoc test (p<0.05), there was no significant difference in μSBS between the different resin cements for HF-etched and silanized (with or without adhesive application) LD surfaces. LD may benefit from pretreatment of the inner surface with HF and silanization, regardless of the resin cement used.

Soft x-ray photoemission study of the thermal stability of the Al2O3/Ge (100) interface as a function of surface preparation

The high temperature thermal stability of ultra-thin atomic layer deposited Al2O3 on sulphur passivated and hydrofluoric acid (HF) treated germanium surfaces was studied using soft x-ray photoemission spectroscopy. The interface sulphur component was stable up to 500 °C vacuum annealing. The interfacial oxides were completely removed at 600 °C for the sulphur passivated sample, whereas HF treated sample showed traces of residual oxides at the interface. However, this annealing treatment does not show any significant change in Al2O3 stoichiometry. The dielectric-semiconductor band offsets were estimated using photoemission spectroscopy measurements.

The corrosion resistance of Nitinol alloy in simulated physiological solutions: Part 1: The effect of surface preparation

The corrosion behaviour of Nitinol alloy containing nearly equi-atomic composition of nickel and titanium and its constituent metals (nickel and titanium) was investigated in simulated Hanks physiological solution (pH value 7.5) and pH modified simulated Hanks physiological solution (pH values 4.5 and 6.5) and by electrochemical method of anodic potentiodynamic polarization at 37°C. In this chloride-rich medium the corrosion stability of Nitinol is limited by the susceptibility to localized corrosion and is in that sense more similar to nickel than to titanium. The corrosion stability of Nitinol is strongly dependent on the surface preparation—grinding, polishing or chemical etching. Whereas a ground surface is not resistant to localized corrosion, polished and chemically etched surfaces are resistant to this type of corrosion attack. The reasons for this behaviour were investigated through metallurgical, topographical and chemical properties of the surface as a function of surface preparation. For that purpose, scanning electron microscopy combined with chemical analysis, confocal microscopy and X-ray photoelectron spectroscopy were used. The surface roughness decreased in the following order: chemically etched>ground>polished surface. Besides differences in topography, distinct differences in the chemical composition of the outermost surface are observed. Ground, rough surfaces comprised mainly titanium oxides and small amounts of nickel metal. Chemically etched and, especially, polished surfaces are composed of a mixture of titanium, nickel and titanium oxides, as studied by angle resolved X-ray photoelectron spectroscopy. These results emphasize the importance of detailed investigation of the metal surface since small differences in surface preparation may induce large differences in corrosion stability of material when exposed to corrosive environments.

Splice Resistance Measurements on 2G YBCO Coated Conductors

The Oak Ridge National Laboratory has been investigating the electrical splice resistance of second-generation (2G) YBCO coated conductor. The purpose of the experimental investigation is to study the splice resistance of 2G YBCO coated conductor as a function of: a) operating temperature, b) magnetic field strength (B-field), and c) magnetic field orientation (thetas). Understanding the splice resistance with its corresponding variation as a function of surface preparation and operating conditions is essential to the practical implementation of electric utility devices; e.g., motors, generators, transformers, cables, and fault-current limiters, etc. Preliminary test results indicate that the 2G YBCO splice resistance shows a weak temperature dependence and a significantly stronger dependence upon magnetic field strength and magnetic field orientation. Surface preparation conditions are also briefly discussed.

The dependence of the fatigue life of adhesive joints on surface preparation

The fatigue life of epoxy-bonded, single-lap shear joints was investigated as a function of surface preparation both with and without a silane pretreatment, under both dry and wet conditions. The effect of R-ratio was also investigated. The results showed that even in the dry condition, the fatigue life of unsilaned joints was reduced by about an order of magnitude from silaned joints. The fatigue life of the silaned joints was equivalent to that of joints that showed no apparent adhesive failure in the wedge test. Fatiguing the joints while immersed in water had very little effect on both the silaned and unsilaned joints except at low loads where there was an indication that the unsilaned joints performed more poorly than in the dry condition. The unsilaned joints showed very little R-ratio effect, while the silaned joints showed a substantial effect.

Impact of defects on the surface chemistry of ZnO(0001 macro)-O.

Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.

Desorption and Reaction of Water on MgO(100) Studied as a Function of Surface Preparation

Temperature-programmed desorption (TPD) is used in conjunction with X-ray photoelectron spectroscopy (XPS) to probe the surface reactivity of water with MgO surfaces prepared by mechanical polishing/acid etching, vacuum annealing in partial pressures of oxygen, high-temperature annealing in an oxygen ambient, and ion sputtering. The structure and morphology of surfaces prepared by these procedures have been previously characterized on the atomic scale with atomic force microscopy. Surfaces prepared using etching procedures and etch and annealing in partial pressures of oxygen demonstrate an atomically rough surface morphology and broad desorption features indicative of an inhomogeneous surface. Surfaces annealed in an oxygen ambient exhibit atomically flat terraces and sharp desorption features. Ar+ bombardment at 500 eV of atomically flat MgO surfaces results in broad features appearing in the water desorption spectra. These are attributed to surface vacancies created by the sputtering process, which act...

Influence of Some Parameters on Passivation of Zirconium and the Stability of the Anodic Oxide Film

Abstract Passivation of the zirconium surface and stability of anodic oxide film were investigated as a function of surface preparation. The mechanically polished surface appeared to be more reacti...

Combination of scratch-test and acoustic microscopy imaging for the study of coating adhesion

The scratch-test is particularly well suited for the characterization of the adhesion of thin films and acoustic microscopy imaging for the in-depth observation of defects through opaque materials. This work proposes an original combination of these two different techniques for the study of adhesion of thick ductile coatings electrodeposited on a relatively rough substrate, as a function of surface preparation. On the tangential force curve, two distinct transitions have been recorded as a function of displacement along the scratch and correlated with substrate preparation. Interface acoustic images of scratches show pronounced acoustic contrast due to the propagation of delamination around the scratch. This is the only technique capable of imaging such interface defects which are due to the stress induced by the scratch experiment. The delaminated area was measured in these images and could be correlated with coating adhesion. The complementarity of the two methods used is emphasized. The combined approach described in this paper should be useful for the characterization of many other film-substrate systems.

Infrared spectroscopy as a probe of fundamental processes in microelectronics: silicon wafer cleaning and bonding

In this paper, we review our recent infrared studies of the fundamental physical and chemical processes occurring at the interface of bonded silicon wafers, as a function of surface preparation and annealing temperature. We present a brief overview of the practical aspects of silicon-wafer bonding and the techniques used to evaluate the interface integrity, which highlight the need for fundamental studies of the microscopic interface phenomena. Importantly, we show that the interface between two silicon wafers approximates an ideal spectroscopic environment, in that there is a 28-fold enhancement in the sensitivity to the normal component of the interface absorption over any other surface optical geometry. Furthermore, the interface region is almost infinitely stable at room temperature, but can exhibit partial pressures ranging from near vacuum to several atmospheres upon annealing. We present results for two distinct types of wafer bonding: hydrophobic (hydrogen-terminated) and hydrophilic (oxide-terminated), since the origin of the initial attraction between the opposing surfaces is quite different in the two cases. Specifically, we show that ideally hydrogen-terminated Si(111) surfaces come within a few Å, under the influence of a Van der Waals attraction, as evidenced by a pronounced perturbation of the isolated SiH stretch mode. In contrast, the initial attraction between hydrophilic surfaces is via hydrogen bonding, which is mediated by the presence of 2–4 monolayers of water that are trapped at the interface upon room-temperature joining. We demonstrate that vibrational spectroscopy provides unprecedented mechanistic insight into the thermal evolution of the molecular interface, which necessarily has a profound influence on the bonding process. Throughout the paper, emphasis is given to the need for a wide variety of additional (fundamental) studies of the surface phenomena occurring in these novel, technologically important systems.

The effect of tray material and surface condition on the shear bond strength of impression materials

This study compared the adhesive shear bond strength of three selected impression materials with that of thermoplastic and acrylic resin tray materials as a function of surface preparation. Polyether (Impregum), polyvinylsiloxane (Reprosil), and polysulfide (Permlastic) impression materials were evaluated on smooth, rough, and contaminated tray surfaces. Smooth surface samples were formed against glass and served as the control groups. Experimental groups consisted of samples contaminated with artificial saliva and rough surface samples that were abraded with 110 microns of Al203. A total of 126 samples were subdivided into 18 groups of seven specimens each. Each sample consisted of a 1 inch square, 3 mm thick mass of an impression material sandwiched between the prepared surfaces of a pair of resin plates. Each specimen was tested in a universal testing machine for adhesive shear bond strength. Data were analyzed with three-way analysis of variance and Scheffe's test. The results indicated that the thermoplastic resin material had better adhesive properties than the acrylic resin. For both tray materials mean adhesive shear bond strengths for Impregum and Reprosil were significantly greater than those of Permlastic. Tray surface contaminated with saliva decreased the adhesive shear strength at the tray adhesive impression interface.

Influence of interfacial hydrogen and oxygen on the Schottky barrier height of nickel on (111) and (100) diamond surfaces.

In this paper we report on Schottky barrier height measurements of nickel on both diamond (111) and (100) surfaces, as a function of surface preparation. The Schottky barriers of thin (5 \AA{}) nickel films on natural type-IIb (p-type semiconducting) diamond (111) and (100) surfaces were determined with ultraviolet photoemission spectroscopy. Exposing the diamond (111) surfaces to an argon plasma while heated to 350 \ifmmode^\circ\else\textdegree\fi{}C resulted in a change from a negative-electron-affinity surface to a positive-electron-affinity surface. This effect was used as an indication that a hydrogen-free surface had been obtained. Deposition of a monolayer of nickel on the hydrogen-free diamond (111) surface resulted in a Schottky barrier height of 0.5 eV. The nickel caused the surface to exhibit a negative-electron-affinity surface. Nickel deposited on a diamond (111) surface with a negative electron affinity, indicative of a monohydride-terminated surface, resulted in a \ensuremath{\sim}1.0-eV Schottky barrier height. Diamond (100) surfaces were prepared by vacuum annealing to temperatures ranging from 500 \ifmmode^\circ\else\textdegree\fi{}C to 1070 \ifmmode^\circ\else\textdegree\fi{}C. The various anneals resulted in a lowering of the electron affinity by up to \ensuremath{\sim}1 eV, which resulted in a negative electron affinity after the surface had been annealed to \ensuremath{\sim}1000 \ifmmode^\circ\else\textdegree\fi{}C. Oxygen was initially present on the surface but could not be observed after the 1000 \ifmmode^\circ\else\textdegree\fi{}C anneal. The removal of oxygen and the appearance of a negative electron affinity coincided with the appearance of a 2\ifmmode\times\else\texttimes\fi{}1 surface reconstruction. Nickel was deposited after the various anneals, and Schottky barrier heights were found, ranging from 1.5 eV for the 545 \ifmmode^\circ\else\textdegree\fi{}C-annealed surface to 0.7 eV for the 1070 \ifmmode^\circ\else\textdegree\fi{}C-annealed surface. These measurements suggest that for both the (111) and the (100) diamond surfaces the presence of chemisorbed species, such as hydrogen and oxygen, results in an increase in the Schottky barrier height.

The Dependence of Photoetching n ‐ InP on Surface Preparation and Electrolyte Metal Ion Impurities

Photochemical etching of using an Ar+ laser and dilute phosphoric acid was studied as a function of surface preparation. The samples were prepared by chemical polishing with a 1% bromine‐methanol solution and mechanical polishing with alumina powders. The surfaces were characterized using electron microscopy, photoluminescence, and mechanical stylus profiling. Photoetch rate was found to increase with surface roughness. The variation of photoetch rate with polishing powder size and morphology was due to the increased effective surface area associated with rougher surfaces. Samples with similar effective surface areas had similar photoetch rates irrespective of their surface treatment. Samples photoetched in solutions having a copper concentration molar and samples with gold wire bonded to them had photoetch rates 2–5 times larger than those without copper in solution. Both zinc and magnesium in solution did not enhance photoetch rates.

Local roughness and surface states on Si(001): Analysis of vacuum annealings and oxygen adsorption-desorption processes

The clean (001) face of silicon has been studied as a function of surface preparation both prior to and after ultra-high vacuum immersion, using photoemission yield spectroscopy assisted by LEED and AES characterization. It was found that (i) the density of surface defects differs strongly as a function of preparation, (ii) this density can be significantly changed by proper UHV treatments, and (iii) the density of surface states at the Fermi level EF as well as the surface position of EF in the gap depend strongly on the degree of roughness.

Intense source of monochromatic electrons: Photoemission from GaAs

Measurements of intensity and width of the energy distribution for photoemission from negative electron affinity GaAs have been made as a function of surface preparation and temperature. Energy distributions as narrow as 31 meV (full width at half-maximum) have been obtained. The measured currents are compared to those which are currently available by coupling thermionic cathodes with electron monochromators and found to be at least 10 times as intense for distributions of equivalent width.

Characterization of polycrystalline electrodeposited CdSe photoelectrodes using photoluminescence spectroscopy

We have utilized both photoluminescence (PL) and Raman spectroscopy to nondestructively study the surface of polycrystalline electrodeposited CdSe photoelectrodes as a function of surface preparation and aging procedures. The excitation energy dependence of the PL efficiency at 77 K, which depends on surface band bending, is consistent with increased concentration of shallow levels in electrodeposited CdSe compared with single crystal material. No PL was observed for unannealed CdSe films; for annealed, unaged films the spectra at 77 K were qualitatively similar to those of single crystals in that spectral features could be identified with the A exciton at 1.815 eV and with a donor-acceptor-pair band at 1.70 eV exhibiting phonon replicas. The PL and Raman spectra of light-aged electrodes exhibit features which we identify with the formation of a surface layer of CdS and the presence of mixed compounds CdSxSe1−x, which are formed by chemical exchange with the polysulfide electrolyte during light-induced aging. The PL spectra at 4.2 K for the unaged and dark-aged electrodes exhibit sharp lines in the vicinity of 1.81 eV which we identify as due to bound-exciton recombination, but which differ in energy from those exhibited by the light-aged film.

Superconducting Mo&amp;lt;inf&amp;gt;0.75&amp;lt;/inf&amp;gt;Re&amp;lt;inf&amp;gt;0.25&amp;lt;/inf&amp;gt;cavities at X-band

RF properties of superconducting Mo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</inf> Re <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</inf> were studied by performing rf measurements on three TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</inf> mode X-band cavities of the alloy. Cavity surfaces were prepared for testing by means of either electrolytic polishing or uhv anneal. From the temperature-dependent unloaded Q(Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ) of the cavities, the surface resistance of the alloy as a function of temperature, R(T), in the temperature range 4.2K to 1.4K was determined. From the R(T) plots, the residual surface resistance, R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> , and the superconducting energy gap parameter, Δ(0), were obtainable. The highest Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> measured was 1.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> , corresponding to a R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> of 5.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Ω. The average value of the energy gap parameter, Δ(0), was (1.78 ± 0.04)k <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</inf> T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</inf> . Magnetic breakdown fields, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">crf</inf> , were also determined by measuring Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> as a function of peak surface magnetic field. The highest value of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">crf</inf> found for the alloy was 176G. We discuss cavity performance as a function of surface preparation, aging and atmospheric exposure.