Surface Oxide Thickness Research Articles

Atomic oxygen treatment effects on magnetron sputtered Zr–Ti binary films

Atomic oxygen (AO) exposure effects on magnetron sputtered Zr–Ti films have been performed by ground simulation instrument under different doses up to 1×1021ions/cm2. XRD, Raman spectrum, FE-SEM, XPS depth profile, and nano-indentation characterizations were applied to study the structural and mechanical properties upon AO treatments. The as-received films show crystallization and morphology variation with substrate temperature. Upon AO treatment, preferred oxidation and erosion of Zr on the top surface and invariant oxide thickness was revealed. Moreover, films with different structure was verified to have different erosion resistance, i.e. those with poor crystallization presented best AO resistance while (0002) textured films shown the worst. With the micro modification upon AO, macro properties of sheet resistance, hardness and modulus evolved.

An Investigation into the Effect of a Post-electroplating Electrochemical Oxidation Treatment on Tin Whisker Formation

Since the ‘cracked oxide theory’ was proposed by Tu in 1994,1 there has only been a limited number of studies that have sought to investigate the effect of the Sn oxide on whisker growth. The current study has used electrochemical oxidation to produce oxide films, which has enabled the effect of the surface oxide thickness on whisker growth to be established. The effect of oxide thickness on whisker growth has been investigated for tin electrodeposits on both Cu and brass substrates. The influence of applied oxidation potential on the thickness of the Sn oxide film has been investigated using x-ray photoelectron spectroscopy (XPS) for potassium bicarbonate–carbonate and borate buffer electrolyte solutions. Whisker growth from electrochemically oxidised Sn-Cu deposits on Cu and Sn deposits on brass has been investigated and compared with samples left to develop a native air-formed oxide. XPS studies show that the thickness of the electrochemically formed Sn oxide film is dependent on the applied oxidation potential and the total charge passed. Subsequent whisker growth studies demonstrate that electrochemically oxidised Sn-Cu deposits on Cu and Sn deposits on brass are significantly less susceptible to whisker growth than those having a native oxide film. For Sn deposits on brass, the electrochemically formed Sn oxide greatly reduces Zn oxide formation at the surface of the tin deposit, which results in whisker mitigation. For Sn-Cu deposits on Cu, the reduction in whisker growth must simply derive from the increased thickness of the Sn oxide, i.e. the Sn oxide film has an important role in stemming the development of whiskers.

Surface oxidation behavior of Ti–6Al–4V manufactured by Electron Beam Melting (EBM®)

Additive manufacturing is an emerging manufacturing technology that enables production of patient specific implants, today primarily out of titanium. For optimal functionality and proper integration between the titanium implant and the body tissues surface properties, such as surface oxide thickness is of particular importance, as it is primarily the surface of the material which interacts with the body. Hence, in this study the surface oxidation behavior of titanium parts manufactured by Electron Beam Melting (EBM®) is investigated using the surface sensitive techniques ToF-SIMS and AES. Oxide thicknesses comparable to those found on conventionally machined surfaces are found by both analysis techniques. However, a build height dependency is discovered for different locations of the EBM® manufactured parts due to the presence of trapped moisture in the machine and temperature gradients in the build.

Coexistence and competition of surface diffusion and geometric shielding in the growth of 1D bismuth nanostructures and their ohmic contact

We study the physical-vapor-deposition of 1D bismuth nanostructures. Bi nanowire elongating along [012] and/or [110] direction as well as anisotropic Bi nano-columns are physical-vapor-deposited successfully. The coexistence and competition of surface diffusion and geometric shielding are critical to their formation as well as growth mode transition among them. Since physical-vapor-deposition is a vacuum process, we make use of it to fabricate the ohmic contact to prevent the damage to the bismuth nanostructures brought by the etching to their thick surface oxide layer.

(Morris Cohen Graduate Student Award of the Corrosion Division) Stainless Steel in Biological Environments – Relation Between Material, Surface Chemistry and Toxicity

Stainless steels are commonly used in a variety of essential applications in our daily-life, for instance as biomaterials and in food contact applications. Even though the corrosion resistance of such grades is high, or very high, alloy components will be released to different extent in contact with biological media of varying composition, acidity and metal complexation capacity, a process that may induce adverse toxicological effects. Research activities have focused to quantitatively determine, and kinetically and mechanistically assess the metal release process in relation to material and surface properties of stainless steels of different grade as massive sheet and as powders in contact with biological systems of relevance for human exposure. Surface-protein interactions have been addressed from a combined surface chemistry, corrosion and material science and toxicological approach. Generated findings clearly show that both bulk and surface oxide properties such as phase, structure, morphology, chemical and electrochemical stability, largely influence the metal release process, biointerfacial interactions, bioavailability of released metals, and subsequent toxicity. For example, the cooling-rate dependent surface oxide speciation (surface oxide thickness, composition, phase and phase distribution, crystallinity etc.) of stainless steel particles strongly determines whether the dominant mechanism of metal release in complexing biological environments is corrosion-controlled or ligand-induced chemical dissolution. Research findings are of vital importance for risk assessments of stainless steel and alloys, to understand adsorption phenomena on stainless steel, metal release and corrosion processes, and the influence of surface oxide speciation on metal release, corrosion, and toxicity.

Solution-based functionalization of gallium nitride nanowires for protein sensor development

A solution-based functionalization method for the specific and selective attachment of the streptavidin (SA) protein to gallium nitride (GaN) nanowires (NWs) is presented. By exploiting streptavidin's strong affinity for its ligand biotin, SA immobilization on GaN NWs was achieved by exposing the GaN NW surface to a 3-aminopropyltriethoxysilane (APTES) solution followed by reaction with biotin. Functionalization of the NWs with APTES was facilitated by the presence of an ≈1nm thick surface oxide layer, which formed on the NWs after exposure to air and oxygen plasma. Biotinylation was accomplished by reacting the APTES-functionalized NWs with sulfo-N-hydroxysuccinimide-biotin at slightly alkaline pH. It was determined that the biotinylated GaN NW surface was specific towards the binding of SA and demonstrated no affinity towards a control protein, bovine serum albumin (BSA). There was however, evidence of non-specific, electrostatic binding of both the SA protein and the BSA protein to the APTES-coated NWs, revealing the importance of the biotinylation step. Successful SA immobilization on the biotinylated GaN NW surface was verified using fluorescence microscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The functionalized GaN NWs demonstrate potential as biosensing platforms for the selective detection of proteins.

Stimulated oxygen impurity gettering under ultra-shallow junction formation in silicon

Ultra-shallow junctions were formed by low-energy As ion implantation followed by furnace annealing. It was found that a significant amount of oxygen is redistributed from the silicon bulk to the As-implanted region. Using a marker layer created by implantation of 18O isotope, it is confirmed that a large number of interstitial oxygen atoms are transferred from the bulk of Si wafer to the surface during dopant activation annealing, which leads to an increase of the surface oxide thickness. Estimation of the oxygen diffusivity in silicon during the 950 °C anneal, yields a value close to 1 × 10−10 cm2 s−1 which is more than an order of magnitude larger than the literature value which is close to 7 × 10−12 cm2 s−1.

Electrochemical reduction of carbon dioxide III. The role of oxide layer thickness on the performance of Sn electrode in a full electrochemical cell

A full electrochemical cell was employed to investigate the role of the surface oxide thickness on the activity of Sn-based electrodes for the electrochemical conversion of CO2. The current density showed a negligible dependence on the thickness of the surface SnOx layer of Sn nanoparticles (100 nm), while the selectivity towards the formation of CO and formate exhibited a strong relationship with the initial SnOx thickness. Electrodes with a native SnOx layer of ∼3.5 nm exhibited the highest Faradaic efficiency (64%) towards formate formation at -1.2 V. The Faradaic efficiency towards CO production reached a maximum (35%) for the electrode with an oxide thickness of 7.0 nm, formed by annealing the Sn nanoparticles at 180 °C for 6 hours. The electrodes with a native SnOx layer displayed the highest overall selectivity towards CO2 reduction. The decrease of the selectivity towards CO2 reduction with increasing the thickness of the SnOx layer can be attributed to the enhancement of hydrogen evolution on the Sn clusters with a low-coordination number derived from the reduction of SnOx. The Faradaic efficiency towards hydrogen production was observed to increase with increasing the thickness of the SnOx layer. Our results suggest the importance of the underlying surface structure on the selectivity and activity of the Sn electrode for CO2 reduction and provide an insight into the development of efficient catalysts.

Liquid-Sn-driven lateral growth of poly-GeSn on insulator assisted by surface oxide layer

Effects of surface oxide layers on liquid-Sn-driven GeSn crystallization on insulators at various temperatures (<475 °C) are investigated. An amorphous Ge in neighborhood of patterned-Sn (<3.5 μm) becomes to polycrystalline Ge1−xSnx (x ≈ 0.025 − 0.14) after annealing at 150–475 °C, which is independent of the surface oxide thickness. Interestingly, a 50-μm-length lateral growth of polycrystalline Ge0.99Sn0.01 layers achieved by combination of thickening of the surface-oxide treated by NH4OH and annealing above melting temperature of Sn (231.9 °C). The growth length is 15 times longer than without the treatment. The advanced process promises to achieve group-IV-based optic and electronic devices on flexible substrates and Si platforms.

Synthesis of iron-oxide nanowires using industrial-grade iron substrates

A method for synthesis of large quantities of iron oxide nanowires using low purity substrates is presented. One cm thick commercially available iron plates of purity 98 at.% were supplied from a steel company. The plates prepared by hot rolling contained several μm thick surface oxide films formed during industrial processing. Plates were cut to small samples and exposed to highly dissociated oxygen plasma and heated to elevated temperatures. The evolution of surface morphology on plasma treated samples was monitored by scanning electron microscopy. Nanowires of typical diameter about 20 nm and length of several μm grew on the substrate surface in a narrow temperature range and best results were obtained at about 1200 K. Higher temperature caused shortening and widening the nanowires. The results clearly show possibility for cheap manufacturing of iron oxide nanowires suitable for application in photovoltaics.

Effects of surface oxide layer on nanocavity formation and silver gettering in hydrogen ion implanted silicon

We have made an investigation of the surface oxide effects on nanocavity formation in hydrogen implanted silicon and the influence of resultant nanocavities on diffusion and gettering of implanted silver atoms. A wafer with a 200-nm SiO2 surface layer was implanted with 22.5 keV H ions to a dose of 1 × 1017 cm−2, yielding the concentration peak of implanted H ions at ∼140 nm below the SiO2/Si interface. Subsequently, two sets of Si samples were prepared, depending on whether the oxide layer was etched off before (Group-A) or after (Group-B) post-H-implantation annealing. As evidenced by transmission electron microscopy, Group-A samples exhibited an array of large-sized nanocavities in hexagon-like shape, extending from the surface to the depth ∼140 nm, whereas a narrow band of sphere-shaped nanocavities of small size was present around 140 nm below the surface in Group-B samples. These Si samples with pre-existing nanocavities were further implanted with Ag ions in the surface region (∼40 nm projected range) and post-Ag-implantation annealing was conducted in the temperature range between 600 and 900 °C. Measurements based on Rutherford backscattering spectroscopy revealed much different behaviors for Ag redistribution and defect accumulation in these two sets of samples. Compared to the case for Group-B Si, Group-A Si exhibited a lower concentration of residual defects and a slower kinetics in Ag diffusion as well. We discuss the role of thick surface oxide in point defect generation and recombination, and the consequence on nanocavity formation and defect retention in Si. The properties of nanocavities, e.g., their depth distribution, size, and even shape, are believed to be responsible for the observed disparities between these samples, including an interesting contrast of surface vs. bulk diffusion phenomena for implanted Ag atoms.

Characterization and comparison of materials produced by Electron Beam Melting (EBM) of two different Ti–6Al–4V powder fractions

Electron Beam Melting (EBM) has been recognized as a revolutionary technique to produce mass-customized parts to near-net-shape from various metallic materials. The technique produces parts with unique geometries from a powder stock material and uses an electron beam to melt the powder layer-by-layer to fully solid structures. In this study we have investigated the use of two different Ti–6Al–4V powders of different size fractions in the EBM process; a larger 45–100μm powder, and a smaller 25–45μm powder. We have also investigated the effects of two build layer thicknesses, 70μm and 50μm, respectively. We hypothesize that the smaller powder has the potential to improve surface resolution of parts produced in the EBM process. The EBM as-built parts were investigated regarding surface and bulk chemistry, surface oxide thickness, macro- and microstructure, surface appearance and mechanical properties. We conclude from the results that both powders and both build layer thicknesses are feasible to use in the EBM process. The investigated material properties were not significantly affected by powder size or layer thickness within the studied range of process parameters. However, the surface appearance was found to be different for the samples made with the different powder sizes.

Voltage-controlled cellular viability of preosteoblasts on polarized cpTi with varying surface oxide thickness

Cathodic voltage shifts of metallic biomaterials were recently shown to induce cell apoptosis in-vitro. The details of the reduction-based physico-chemical phenomena have not yet been fully elucidated. This study shows how surface oxide thickness of commercially pure titanium affects the voltage viability range, and whether anodic oxidation can extend this range. Cell viability, cytoskeletal organization, and cellular adhesion on bare and anodized Ti, at −500, −400mV(Ag/AgCl) and open circuit potential were assessed. Surfaces were characterized using contact angle measurement and atomic force microscopy, and the observed cellular response was related to the changes in electrochemical currents, and impedance of the samples. Results show that anodization at 9V in phosphate buffer saline generates a compact surface oxide with comparable surface roughness and energy to the starting bare surface. The anodized surface extends the viability range at 24h from −400mV(Ag/AgCl) by about −100mV, which corresponds to an increase in impedance of the surface from 58kΩcm2 to 29MΩcm2 at −400mV(Ag/AgCl) and results in low average current densities below 0.1μAcm−2. The results demonstrate that the voltage range for cell viability under cathodic polarization is expanded due to anodization of the surface oxide and lowering of cathodic currents.

Nano-size protein at the surface of a Ti–Zr–Ni quasi-crystalline alloy: Fibronectin adsorption on metallic nano-composites

Surface characterisation of alloys before and after their interaction with proteins allows a more rational design of biomaterials. In this work, fibronectin adsorption on a Ti-based quasicrystals-forming alloy was studied by X-ray photoelectron spectroscopy (XPS) and compared to those obtained on pure titanium substrates (cp Ti). Different fibronectin (Fn) solution concentrations were tested in interaction with the quasi-crystalline/amorphous Ti45Zr38Ni17 composite. N 1s, C 1s, Ti 2p, Zr 3d and Ni 2p core level spectra were systematically recorded. The results indicate that fibronectin is chemically adsorbed on Ti45Zr38Ni17 as well as on cp Ti. The alloy surface composition and oxide thickness are not significantly changed in presence of the adsorbed protein. Data on the elemental distribution in the alloy surface obtained by XPS were completed by depth profiling with Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Surface saturation is clearly reached for Fn solution concentrations of 100–150μgmL−1 for both surfaces. On the plateau, the equivalent protein thickness is 6nm for Ti45Zr38Ni17 and 8nm for cp Ti, both corresponding to one fibronectin monolayer. These results are in accordance with previous observations on osteoblasts adhesion, confirming the biocompatibility of Ti45Zr38Ni17. However, quasicrystals do not seem to influence the alloy surface reactivity.

Surface oxide analysis of lead‐free solder particles

PurposeThe composition and thickness of surface oxide of solder particles is extremely important to the quality of interconnect and reliability of packaged system. The purpose of this paper is to develop an observable measurement to research the issue.Design/methodology/approachAES (Auger electron spectroscopy), XPS (X‐ray photoelectron spectroscopy), TEM (transmission electron microscopy) and STEM (scanning transmission electron microscopy) were employed to examine the oxide layer on microscale solder powders. Conventional techniques and FIB (Focus Ion Beam) were employed for the TEM sample preparation. High angle annular dark field (HAADF) pattern was applied to distinguish the oxide layer and the solder matrix by the contrast of average atomic number. The results were confirmed by AES and XPS measurement.FindingsThe solder powders were exposed to air (70% relative humidity) at 150°C for 0, 120 and 240 h for the accelerated growth of oxide. The surface oxide thickness was 6 nm and 50 nm measured by TEM for 0 h and 120 h samples, respectively. It was found that the increase in surface oxide thickness of solder particles is proportional to the rooting of time. The elemental distribution along the oxide was quantified by line scanning using STEM and the atomic ratio of Sn to O in the oxide layer nearer to the outer, the middle, and the inner (adjacent to the solder matrix) was found to be 1:2, 2:3 and 1:1, respectively. The result was validated using XPS which gave Sn to O ratio of 1:2 at 5 nm depth of surface oxide.Originality/valueThis is the first time FIB technology has been used to prepare TEM specimens for solder particles and TEM pictures shown of their surface oxide layer. Though requiring more care in sample preparation, the measurements by TEM and STEM are believed to be more direct and precise.

Influence of Material Properties on Major Tribological Factors at a Nanoscale Sliding Electric Contact of Probe Devices

Precise processes or devices utilizing scanning nanoprobes, e.g., probe-based nanolithography and probe-based data storage, are state-of-the-art technologies that can handle nm-sized tiny patterns. To transfer these technologies from the research and development stage to practical implementation, a significant improvement in the wear resistance of the probe tip is required for reliable and long-term operation of the system. On the other hand, to remove the unevenness of the size of drawn patterns or recorded bits, the electric contact resistance at the nanoscale sliding contact area of the probe tip must be stable even when the scanning speed of the probe increases to achieve higher throughput. To solve these dilemmatic problems, tribological investigation of the probe tip is very important.In this study, the influence of the material properties on the relations among electric contact resistance, friction force, and wear durability of nanoprobe tips was examined in detail to clarify the tribological phenomena that occur at the nanoscale contact area of the probe tips. From the results, the authors discussed the key material properties that are dominant for the abovementioned three tribological factors. In conclusion, management of the surface oxide thickness of metal electrodes was the key among all the three factors.

Thermal Treatment Optimization of Electrodeposited Hydroxyapatite Coatings on Ti6Al4V Substrate

AbstractThermal behavior of electrodeposited hydroxyapatite (HAP) coating on a titanium alloy (Ti6Al4V) is investigated in order to optimize the heat treatment conditions for this prosthetic material. The synthesized coatings are annealed in air atmosphere at 400, 600, 800, and 1000 °C, and then characterized by X‐ray diffraction (XRD) and selected area electron diffraction (SAED) for structure and phases analysis. Scanning and transmission electron microscopy associated to energy dispersive X‐ray microanalysis (SEM‐EDXS and STEM) are used for morphology and composition analysis. The results show that when the electrodeposited coating is annealed at temperatures greater than 600 °C, a well‐crystallized HAP is obtained with a notable change of its morphology. However, at these temperatures the surface of Ti6Al4V alloy (uncoated zones of the implant) is deteriorated by the formation of a thick surface oxide layer. Therefore, we limit the heat treatment temperature for the electrodeposited coatings on a Ti6Al4V alloy at 550 °C. At this optimized temperature it is demonstrated that the link between the coating and the substrate is improved and the crystallinity of the coating is controlled which make it well bioactive.

Low Surface Recombination Velocity on (100) Silicon by Electrochemically Grown Silicon Dioxide Annealed at Low Temperature

This letter investigates silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layers that are electrochemically grown in nitric acid (HNO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) at room temperature. It examines the dependence of surface recombination velocity (SRV), oxide charge, interface states, and oxide thickness on the concentration of HNO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . The results show that an SRV of less than 40 cm/s can be attained after SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is annealed at 400°C in oxygen first and then forming gas. This SRV is similar to that attained by the best thermal oxides. Photoconductance and capacitance-voltage measurements indicate that the low SRV is caused by a large positive charge rather than a low interface state density. The SRV is found to degrade due to a decrease in charge and an increase in interface states, where the rate depends on the HNO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> concentration in which the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer was grown.

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.

Secondary ion mass spectrometry characterization of anomalous behavior for low dose ion implanted phosphorus in silicon

Significant changes over time have been observed in surface and near surface phosphorus concentration for low dose phosphorus implants measured using secondary ion mass spectrometry (SIMS) with cesium bombardment. These variations in concentration affect the ability to make reproducible dose measurements. Phosphorus measurements have been documented for samples from wafers kept at ambient conditions and also for those stored in a range of other conditions including heat, high humidity, low humidity, and liquid nitrogen. An initial study of wafers ion implanted over a range of doses showed that the change in the surface phosphorus concentration was most apparent for the lowest phosphorus dose (1×1012 atoms/cm2) and that heating the sample resulted in the most significant change (increase in almost three orders of magnitude) in apparent surface P concentration. Only the specimens stored at liquid nitrogen temperature showed no change in P surface concentration. SIMS analysis conditions were optimized and a second set of analyses were performed on wafers that included different wafer processing (thicker surface oxide, preamorphization, and anneal) in an effort to reduce the change in surface phosphorus. Significant improvement in P dose reproducibility was noted for the wafer that had been implanted through a 5 nm oxide and stored in dry conditions.