Native Oxide Surface Research Articles

Fabrication of a tantalum-clad tungsten target for LANSCE

Development of a solid state bonding technique suitable to clad tungsten targets with tantalum was completed to improve operation of the Los Alamos Neutron Science Centers spallation target. Significant deterioration of conventional bare tungsten targets has historically resulted in transfer of tungsten into the cooling system through corrosion resulting in increased radioactivity outside the target and reduction of delivered neutron flux. The fabrication method chosen to join the tantalum cladding to the tungsten was hot isostatic pressing (HIP) given the geometry constraints of a cylindrical assembly and previous success demonstrated at KENS. Nominal HIP parameters of 1500°C, 200MPa, and 3h were selected based upon previous work. Development of the process included significant surface engineering controls and characterization given tantalums propensity for oxide and carbide formation at high temperatures. In addition to rigorous acid cleaning implemented at each step of the fabrication process, a three layer tantalum foil gettering system was devised such that any free oxygen and carbon impurities contained in the argon gas within the HIP vessel was mitigated to the extent possible before coming into contact with the tantalum cladding. The result of the numerous controls and refined techniques was negligible coarsening of the native Ta2O5 surface oxide, no measureable oxygen diffusion into the tantalum bulk, and no detectable carburization despite use of argon containing up to 5ppm oxygen and up to 40ppm total CO, CO2, or organic contaminants. Post bond characterization of the interface revealed continuous bonding with a few microns of species interdiffusion.

Templated patterning of graphene oxide using self-assembled monolayers

A cost-effective and efficient route for graphene oxide (GO) patterning through site-selective deposition of GO onto a photopatterned self-assembled monolayer (SAM) of octadecylphosphonic acid on the surface of native oxide of titanium was demonstrated. In this process, SAMs on titanium oxide was first patterned via ultraviolet light exposure through a mask, subsequent drop-casting of GO aqueous dispersion on the substrate resulted in the site-selective deposition of GO on the hydrophilic areas. The formation of GO patterns is evidenced by Raman mapping. Atomic force microscopy studies indicate that the thickness of patterned GO can be controlled by adjusting the concentration of the GO dispersion. Scanning electron microscopy, and inverted fluorescence microscopy of large area GO patterns demonstrate this process is scalable and that the fluorescent property of nanoscale GO sheets is still reserved after deposition.

Characterization of enhancement-mode AlGaN/GaN high electron mobility transistor using N2O plasma oxidation technology

In this study, an enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) using N2O plasma oxidation process has been performed. Before the gate metal deposition, the AlGaN barrier layer was treated by 135 W N2O plasma for 240 s. The surface native oxide of AlGaN was removed and a 4 nm high quality Ga2O3/Al2O3 compound insulator was simultaneously formed. The threshold voltage of conventional depletion-mode (D-mode) GaN HEMT was −3.6 V and this value can be shifted to +0.17 after N2O plasma oxidation treatment beneath the gate metal. This 4 nm Ga2O3/Al2O3 compound insulator oxidized by N2O can suppress the polarization charge density for E-mode operation of gate terminal and the gate leakage was also reduced simultaneously.

The effect of de-ionized water rinsing after immersion in hydrofluoric acid on the electrical conductivity of silicon nanomembranes

Electrical conductivity of 28 and 220-nm thick silicon membranes was measured by the van der Pauw method in dry air (relative humidity < 5%) at room temperature (around 20 °C). Immediately after hydrofluoric acid immersion the conductivity increases several orders of magnitude because of surface-induced band bending; it then drops and reaches the level of samples with a native oxide surface in several weeks due to the surface's re-oxidation. The oxidation rate is found to increase with the de-ionized water rinsing time, which is confirmed by X-ray photo electron spectroscopy measurements.

Arrays of Au Nanoparticles on Si Formed by Nanoindentation and a Simple Thermal/Wipe-Off Technique

This study demonstrates a novel technique for the fabrication of ordered arrays of Au rich nanoparticles on a Si substrate. Si substrates, with their native oxides intact, are pre-patterned using nanoindentation to create regions on the surface that readily alloy at higher temperatures with a thin thermally evaporated Au layer. Larger Au rich particles are observed to form at the indentation sites after high temperature annealing in an inert atmosphere. After mechanical wiping, the Au rich particles lying within the indentation sites remain while almost all the particles on the native oxide surface are readily removed. Using PECVD techniques, multi-prong Si nanowires are shown to grow from the remaining arrays of Au rich particles.

Novel Size and Surface Oxide Effects in Silicon Nanowires as Lithium Battery Anodes

With its high specific capacity, silicon is a promising anode material for high-energy lithium-ion batteries, but volume expansion and fracture during lithium reaction have prevented implementation. Si nanostructures have shown resistance to fracture during cycling, but the critical effects of nanostructure size and native surface oxide on volume expansion and cycling performance are not understood. Here, we use an ex situ transmission electron microscopy technique to observe the same Si nanowires before and after lithiation and have discovered the impacts of size and surface oxide on volume expansion. For nanowires with native SiO(2), the surface oxide can suppress the volume expansion during lithiation for nanowires with diameters <∼50 nm. Finite element modeling shows that the oxide layer can induce compressive hydrostatic stress that could act to limit the extent of lithiation. The understanding developed herein of how volume expansion and extent of lithiation can depend on nanomaterial structure is important for the improvement of Si-based anodes.

In-assisted desorption of native GaAs surface oxides

We demonstrate In-assisted desorption of native GaAs surface oxides at substrate temperatures of 480–550 °C. The oxides are removed through production of volatile Ga and In suboxides, Ga2O, and In2O. Compared to a Ga-assisted desorption process, excess In is easily removed at low substrate temperature, favouring a clean, smooth surface. The feasibility of using In-assisted desorption for the regrowth of high quality quantum dot structures is shown.

Influence of Fluorine on the Conductivity and Oxidation of Silicon Nanomembranes after Hydrofluoric Acid Treatment

After immersion in hydrofluoric acid, the sheet resistance of a 220-nm-thick silicon nanomembrane, measured in dry air by van der Pauw method, drops around two orders of magnitude initially, then increases and reaches the level of a sample with a native oxide surface in about one month. The surface component and oxidation rate are also characterized by x-ray photo electronic spectroscopy measurement. Fluorine is found to play a significant role in improving conductivity and has no apparent influence on the oxidation rate after hydrofluoric acid treatment.

Corrosion Behavior of Super-Hydrophobic Surface on Fe&lt;sub&gt;3&lt;/sub&gt;Al in Seawater

Self-assembled monolayer of n-tetradecanoic acid (CH3(CH2)14COOH) are formed on the native oxide surfaces of Fe3Al. The structure of the monolayer is probed with contact angle measurement and SEM. The results (indicate) that the structure of the adsorbed film like lotus structure and the contact angle are larger than 150° for seawater. Moreover, the corrosion behavior of bare Fe3Al and Fe3Al with super-hydrophobic surface, with two different surface microstructure, in seawater(pH=8.02), has been investigated using electrochemical impedance spectroscopy (EIS) and weight loss measurements. Both methods reveal that corrosion rate of Fe3Al with Super-hydrophobic surface sample decreases dramatically because of its special microstructure. These results indicate that the super-hydrophobic surface formed on the Fe3Al can improve corrosion resistance of Fe3Al in seawater significantly.

Aging mechanism of the native oxide on silicon (100) following atmospheric oxygen plasma cleaning

Silicon native oxide surfaces were cleaned with a radio frequency, atmospheric pressure helium and oxygen plasma and with an RCA standard clean-1. Both processes create a hydrophilic state with water contact angles of &amp;lt;5° and 16.2° ± 1.7°, respectively. During subsequent storage in a chamber purged with boil off from a liquid nitrogen tank, the water contact angle increased over time at a rate dependent on the cleaning method used. Internal reflection infrared spectroscopy revealed that the change in water contact angle was due to the adsorption of organic molecules with an average hydrocarbon chain length of 10 ± 2. The rate of the adsorption process decreased with the fraction of hydrogen-bonded hydroxyl groups on the surface relative to those groups that were isolated. On Si (100) surfaces that were cleaned by RCA standard clean-1 and then the plasma, 95.8% of the silanol groups were hydrogen bonded. The first-order rate constant for adsorption of the organic contaminant on this surface was 0.182 ± 0.008 h−1.

Effect of HF & H 2SO 4 pretreatment on interfacial adhesion energy of Cu–Cu direct bonds

Effects of HF & H 2SO 4 pretreatment conditions on the interfacial bonding strength of Cu–Cu direct bonds were systematically investigated. The evaluated interfacial adhesion energies for 3 μm-thick Cu bonding layers were 0.58, 0.46, and 4.90 J/m 2 for different HF & H 2SO 4 pretreatment times of 0, 15, and 30 s, respectively, with bonding temperature of 350 °C, which is ascribed to the effective removal of native surface oxide at optimum wet cleaning conditions before Cu–Cu bonding.

Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied in 0.6 M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 h of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl 2O 4) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition.

Charge referencing issues in XPS of insulators as evidenced in the case of Al‐Si‐N thin films

AbstractAccurate charge referencing in XPS of insulating specimens is a delicate issue. This difficulty is illustrated in the case of Al‐Si‐N composite thin films deposited by reactive magnetron sputtering with variable composition from pure aluminum nitride to pure silicon nitride. The samples were mounted with Au‐coated metallic clamps. Argon sputter cleaning was required to remove a surface native oxide before analysis. For charge referencing implanted argon atoms from the sputter gas and a small amount of gold re‐deposited from the metallic clamps onto the specimen surface during sputter cleaning were evaluated. For the argon atoms, a surprisingly large chemical shift (∼1 eV) and a significant peak broadening (0.6 eV) of the Ar 2p3/2 photoelectron line were found with varying the Si content of the films. This could be related to chemical and structural changes of the Al‐Si‐N films. Hence implanted argon could not be used for charge referencing of Al‐Si‐N samples. In contrast to the implanted argon, the Au 4f7/2 line width of the gold re‐deposited onto the sample surface did not depend on the Si content of Al‐Si‐N films. A constant energy shift (∼1.2 eV) of the Au 4f7/2 line as compared with bulk gold was, however, found, which was related to the size of gold particles formed on the insulating films. Therefore gold could be reliably used to study chemical shifts of sample‐relevant species in Al‐Si‐N films, but the absolute binding energies of Al 2p, Si 2p and N 1s photoelectrons could not be determined. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Effect of surface oxidation on the nm-scale wear behavior of a metallic glass

Metallic glasses are good candidates for applications in micromechanical systems. With size reduction of mechanical components into the micrometer and submicrometer range, the native surface oxide layer starts playing an important role in contact mechanical applications of metallic glasses. We use atomic force microscopy to investigate the wear behavior of the Ni62Nb38 metallic glass with a native oxide layer and with an oxide grown after annealing in air. After the annealing, the wear rate is found to have significantly decreased. Also the dependency of the specific wear on the velocity is found to be linear in the case of the as spun sample while it follows a power law in the case of the sample annealed in air. We discuss these results in relation to the friction behavior and properties of the surface oxide layer obtained on the same alloy.

Controlled Oxide Removal and Surface Morphology on InSb(100) Using Gas Phase HF/H2O

The native oxide removal, surface termination, composition, and morphology of InSb(100) surfaces etched in gas phase HF/H2O mixtures at a total pressure of 100 Torr and 29 °C were investigated usin...

ToF‐SIMS imaging of surface self‐organized fractal patterns of bacteria

AbstractTime‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) imaging has been shown to be a useful tool to study cell adhesion onto a surface. The purpose of this work was that of investigating by means of ToF‐SIMS imaging the influence of different salt environments on the adhesion and self organization of Staphylococcus epidermidis ATCC 12228 onto a nonleaching surface (native silicon oxide). Chemical maps show that the different media influence the distribution of bacteria and that their different surface organization in different media is accompanied by characteristic distributions of alkali ions and organic fragments related to the bacteria. This could help in understanding the mechanisms involved in self organization of bacteria, that are thought to be related with the ability of bacteria to modify, by means of ionic fluxes through the cell membrane, the electrostatic interactions that, in turn, appear to rule their self organization in fractal patterns. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Ga束流低温辅助清理GaAs衬底表面氧化物的研究

Ga束流低温辅助清理GaAs衬底表面氧化物的研究

The Effects of Native Oxide Surface Layer on the Electrochemical Performance of Si Nanoparticle-Based Electrodes

This study controllably reduces the silicon dioxide (SiO2) layer on Si nanoparticles and evaluates its effect on the performance of Si nanoparticle-based electrodes in Li-ion batteries. Various thicknesses of this native oxide are present on Si nanoparticles generated by chemical vapor deposition (CVD) due to the process conditions and exposure to oxygen during storage. This layer can be effectively reduced by hydrofluoric acid (HF) etching, which results in improved electrochemical performance over as-received samples. As-received Si sample has a higher first-cycle capacity loss than that of the etched Si samples, when the capacity loss is normalized to the surface area of the Si particles. Spectroscopic analysis reveals that when the Si electrode is held at a low potential, the oxide layer can be converted to a more stable silicate form due to the irreversible consumption of lithium species in the cell. The thick SiO2 surface layer also isolates the Si core from lithium-ion alloying; therefore, the as-received Si nanoparticles deliver a lower specific capacity than their etched counterpart. Incomplete lithiation of the as-received Si particles is confirmed by transmission electron microscopy, which shows that nanocrystalline Si domains remain after cycling. The surface insulating effects of SiO2 also cause high impedance in the Si electrode.

Pre-treatment of Zn surfaces for droplet corrosion studies

In this work, the significance of pre-treatment techniques to prepare stable and reproducible surfaces for corrosion and coatings studies on zinc-based materials is presented. The stability and consistency of Zn surface films were investigated using chemical and physical pre-treatment methods, whereas the effectiveness of pre-treatments was assessed by water contact angle measurements using droplet profiles. Morphology and composition of pre-treated Zn surfaces were investigated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Chemical etchants, such as HNO 3 (acidic) and NaOH (alkaline), were found to be aggressive towards the Zn metal surface and responsible for the formation of various oxides of inhomogeneous thickness. Air plasma pre-treatment proved to be effective in removal of hydrocarbon contaminants, leaving the surface highly hydrophilic irrespective of the fact that the thickness and roughness of native surface oxides remained unchanged. Zn surfaces pre-treated with organic solvents were found to be hydrophobic in nature in contrast to Zn surfaces pre-treated with abrasives like SiC paper, which were found to be relatively hydrophobic. Further, SEM-EDS analysis showed contamination of these surfaces with SiC. As expected the last surface pre-treatment step exerts a large influence over the final characteristics of the surface film when a number of pre-treatments are applied sequentially to the same surface. This work demonstrates that Zn surfaces pre-treated with diamond particles of sizes 9, 6, 3 and 1 μm show a moderate hydrophobic character. SEM-EDS analysis showed that surface films prepared via diamond polishing are uncontaminated. Additionally, surface film thickness was estimated using Auger signals produced during X-ray Photoelectron Spectroscopy (XPS). Surface depth profiling through depth sputtering revealed that the surface film is composed of ZnO and had a thickness of 1.98 nm. Specifically, the objective of this study is to lay the groundwork for future research on Zn corrosion in which consistent and reproducible surfaces are paramount to produce meaningful results. However, this work may also find more general utility in showing how different surface pre-treatments affect surface reactivity and in turn could impact adhesion to Zn or other metal surfaces.

Reduction of 3T3 fibroblast adhesion on SS316L by methyl-terminated SAMs

Inhibiting the non-specific adhesion of cells and proteins to biomaterials such as stents, catheters and guide wires is an important interfacial issue that needs to be addressed in order to reduce surface-related implant complications. Medical grade stainless steel 316L was used as a model system to address this issue. To alter the interfacial property of the implant, self-assembled monolayers of long chain phosphonic acids with –CH 3, –COOH, and –OH tail groups were formed on the native oxide surface of medical grade stainless steel 316 L. The effect of varying the tail groups on 3T3 fibroblast adhesion was investigated. The methyl-terminated phosphonic acid significantly prevented cell adhesion however presentation of hydrophilic tail groups at the interface did not significantly reduce cell adhesion when compared to the control stainless steel 316L.