Surface Oxide Thickness Research Articles

Exploring the relationship between deposition method, microstructure, and performance of Nb/Si-based superconducting coplanar waveguide resonators

Superconducting quantum circuits (SQC) are one of the most promising hardware platforms for quantum computing, yet their performance is currently limited by the presence of various structural defects inside the circuit's structure. Despite impressive progress in the past decade, a precise understanding of the origin of these defects from various fabrication processes and their impact on coherence is still lacking. In this study, we performed a comprehensive investigation on the microstructure, superconductivity, and resonator quality factor of Nb films deposited by high-power impulse magnetron sputtering (HiPIMS) and direct current (DC) magnetron sputtering. A suite of characterization techniques, including electron microscopy with spectroscopy, secondary ion mass spectrometry, magneto-optical microscopy, and pump-probe reflectivity spectroscopy is used. We reveal that niobium (Nb) resonators fabricated using HiPIMS exhibit a smaller average grain size, thicker surface oxide with larger thickness variations (rougher surface), and a thicker amorphous Nb/Si interface layer compared to samples deposited by DC sputtering. We identified that the amorphous Nb oxides (mainly located at the Nb surface and along the grain boundaries) and Nb-Si amorphous layers (at the Nb/Si interface) are major and potential sources of two-level system (TLS), while off-stochiometric oxides and suboxides of Nb close to the surface, crystalline defects (i.e., dislocations at grain boundary, point defects introduced during deposition) are main contributors of non-TLS sources. Our findings clarify the relationship between different defects and coherence loss mechanisms, highlighting the importance of material microstructure control on performance optimization in SQC.

Probing the Electrode-Liquid Interface Using Operando total-Reflection X-Ray Absorption Spectroscopy

Traditional operando methods to study electrochemical (EC) processes, although successful, are based on EC measurements, lacking in direct sensitivity of chemical and structural changes. A fundamental understanding of the underlying mechanism occurring during an EC reaction could allow to improve performances and properties of applied material systems. EC processes are localized at the electrode-electrolyte interfacial regions, but several surface sensitive experimental techniques are often limited to ex situ conditions, owing to the need of a Ultra High Vacuum (UHV) environment, e.g., Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Low Energy Electron Diffraction (LEED), etc.1 On the contrary, synchrotron-based hard x-rays provide an intense and highly energetic source that can penetrate the electrolyte without undergoing significant attenuation. Furthermore, the x-ray beam can be focused on a flat metal surface adopting a grazing incidence geometry, increasing surface sensitivity up to a few nanometers in subcritical condition. The latter case is achieved when the incident angle is set below the critical angle for total external reflection (TER), characterized by the occurrence of an evanescent wave confined at the surface. As a result, x-ray photon-in photon-out techniques can be used to probe the electrode-liquid interface in working conditions.2,3 In this contribution, we performed operando Grazing Incidence X-ray Absorption Spectroscopy (GI-XAS) in total external reflection (TER) mode4 (Fig. 1) at P64 (DESY, Hamburg), using our EC setup designed for multimodal studies with hard x-ray scattering and spectroscopy techniques3. XAS can provide unique information about the local chemical and structural environment of absorbing atoms during electrochemical polarization. The electro-oxidation of polycrystalline gold, relevant for the understanding of electrolysis, and the surface passive film development and breakdown of Ni-Cr-Mo corrosion resistant alloys, have been investigated. Despite the presence of the electrolyte and the PEEK walls of the EC cell, 1-3 nm thick surface oxides film can be detected in TER mode using energies down to 8 keV. Advantages and challenges of this method will be discussed showing experimental results. Figure 1 Left: Schematic of our EC cell showing sample geometry for GI-XAS in TER mode, the incidence angle q is always lower than the critical angle. Right: GI-XAS in TER mode from a Ni 59 alloy sample at the Ni k-edge at increasing EC polarization in 1M NaCl and pH 12. Maurice, V. Progress in corrosion science at atomic and nanometric scales. Progress in Materials Science 40 (2018).Timoshenko, J. & Roldan Cuenya, B. In Situ / Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy. Chem. Rev. 121, 882–961 (2021).Långberg, M. Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses. npj Materials Degradation, 3(1): p. 22. (2019).D. Gajdek. Structural Changes in Monolayer Cobalt Oxides under Ambient Pressure CO and O 2 Studied by In Situ Grazing-Incidence X-ray Absorption Fine Structure Spectroscopy, J. Phys. Chem. C, vol. 126, n. 7, pagg. 3411–3418 (2022) Figure 1

Surface Controlled Silicon Nanoparticles Production and Their Effects on High Capacity and High Cyclability of All-Solid-State Lithium-Ion Batteries

Si nanoparticle is expected as anode for high density Lithium-ion batteries as as it facilitates high capacity and high cyclability simultaneously owing to its structural robustness to suppress fracture during cycled (de)lithiation reactions. Direct TEM observation has revealed that the particle size of 150 nm is the threshold for facture and the particles smaller than 150 nm are anticipated to contribute to the structural stability during cycles. However, the surface of silicon nanoparticle is oxidized spontaneously and the specific surface area increases significantly with decreasing the particle size. Accordingly, the specific oxygen content of the Si active material becomes inevitably high for smaller nanoparticles. High oxygen content in Si anode decreases the initial efficiency and capacityas a result of irreversible silicate formation. Therefore, smaller nanoparticle with a limited amount of oxidation would be ideal and necessary to attain high capacity and high cyclability. However, there is few report on the approach to suppress oxidation of smaller silicon nanoparticles and discuss the effect of size and oxygen content separately. Also, no general understanding of the effect of the particle size and oxygen for the case of all-solid-state batteries (ASSBs). In this work, we have produced Si nanoparticles with differently controlled size and oxygen content by plasma flash evaporation (PFE) from low-cost powder feedstock, and the effect of characteristic oxide surface structure on the battery performance of ASSBs with Argyrodite electrolyte has been identified.We have successfully produced the nanoparticles as small as 20 nm and reduced the oxygen content x in SiOx representation from the standard amount of 0.24 to 0.049. As a result, the initial discharged capacity can be improved by 110% while attaining similar cyclabilities. When we compare the nanoparticles with different sizes ranging from 20 nm to 165 nm and having small oxygen content x < 0.05, although the initial discharged capacities are almost the same for these particles, only the particle with 165 nm shows rapid capacity decay in 10 cycles, whereas the 20 nm and 84 nm particles tend to maintain the capacity similarly. This confirms that the particles smaller than 100 nm are effective to maintain high capacity also in ASSBs under a low 0.1 C-rate condition. Furthermore, XPS analysis revealed that the surface of the particles with less oxidation is composed of suboxide Si-O bond oxide preferentially and the amount of Si-O4 bond is less than the conventional particles covered by the oxide shell, with which the Si-O bond ratio is described by the conventional random bond model. No apparent dependence of the capacity with the amount of Si-O4 bond. However, the surface oxide shell thickness estimated by the Si-O bond amount and the total oxygen content has shown a clear linear correlation with the charged capacity, irrespective of the particle size. This suggests that the surface oxide thickness affects significantly the amount of the lithiation reaction and is ideally as thin as possible to attain high capacity, especially for the case of ASSBs.

Influence of pre-treatments on adhesion, barrier and mechanical properties of epoxy coatings: A comparison between steel, AA7075 and AA2024

In this work five independent pre-treatments – mechanical polishing, alkaline and acid etching, sol-gel primer, and anodizing – were applied on mild steel and aluminum (AA7075 and AA2024) substrates before the deposition of epoxy coatings. The results demonstrate that efficient adhesion can be achieved by simple methodologies and widely available chemicals as an alternative to toxic conversion layers or highly energetic processes. All the treatments provided higher adhesion (up to 75%, 61% and 14% on AA7075, AA2024 and steel, respectively) and better anti-corrosion performance (increase of impedance values at low frequency up to four orders of magnitude) than the polished reference. The anodizing of aluminum alloys yielded good anti-corrosion performance, but slightly lower mechanical properties compared to sol-gel primer and alkaline etching. The hydroxyls density was found to play a major role in strong adhesion prevailing over surface roughness, contact area, oxide thickness and hydrophobicity. Despite the efficient performance of hydrogen bonds from acid and alkaline etching on aluminum, these connections do not yield sufficiently stable bonds that make an impermeable barrier of epoxy coatings on steel. Covalent bonds (Me-O-Si) represent the key to achieve a significant improvement in mechanical and chemical resistance against the ingress of water and polymer chain relaxation. This makes the sol-gel primer a simple, economical, and environmentally alternative towards efficient bonding at a molecular level.

Pockels Effect at the Interface between Water and Ti Electrode

The Pockels coefficient of interfacial water between bulk water and a Ti electrode was estimated from the electroreflectance spectra (ΔR/R) to be r13≈−150 pm/V as the maximum value of magnitude, which is comparable in magnitude to the largest coefficient for electrode interfacial water, i.e., 200 pm/V for interfacial water on a transparent oxide electrode. This Pockels signal increased by a factor of about ±3 by applying a DC bias voltage of ±1 V. The reflectance (R) of the Ti electrode had a dip structure in the UV region (3.5–4.5 eV) due to the interference of a 14 nm thick surface oxide film, and the ΔR/R spectra in aqueous electrolyte solution showed a large reflectance change in the UV region with a dispersive shape due to the contribution of the TiO2 film. The reproducibility of the electroreflectance experiment was high, suggesting that the surface oxide film contributes to the large Pockels effect of interfacial water and the robustness of the electrode.

Resistivity size effect in epitaxial VNi2 layers

Epitaxial VNi2 layers are deposited onto MgO(001) and their resistivity ρ measured as a function of layer thickness d = 10.5–138 nm to quantify the resistivity size effect. The layers exhibit resistivity minima at both stoichiometric V:Ni = 1:2 composition and 700 °C growth temperature, which is attributed to electron scattering at V–Ni antisite defects and is described using the ordering parameter within the framework by Rossiter. A cube-on-cube epitaxy of the fcc parent structure on MgO(001) leads to two possible layer orientations for orthorhombic VNi2(010) and VNi2(103), resulting in considerable atomic disorder at domain boundaries, consistent with relatively small x-ray coherence lengths of 8 and 14 nm in-plane and along the growth direction of a 33.5 nm thick layer. In situ ρ vs d measurements yield a bulk resistivity of ρo = 46 ± 2 μ Ω cm and a benchmark quantity of ρoλ = (138 ± 5) × 10−16 Ω m2, where λ is the bulk electron mean free path. Air exposure causes a minor resistivity increase due to 2 ± 1 nm thick surface oxide that perturbs the surface potential. Resistivities at 77 K are Δρ = 16 ± 3 μ Ω cm below those at room temperature. This Δρ is thickness independent and is close to the previously predicted 13.9 μ Ω cm bulk resistivity for VNi2 along [100]. However, the measured bulk resistivity is well above this prediction, which is attributed to electron scattering at domain boundaries/atomic disorder. Consequently, the theoretically predicted superior directional conduction cannot be experimentally confirmed in this study. The overall results indicate that VNi2 is only a promising compound for narrow interconnects if a synthesis scheme can be developed that results in a strong atomic order, a negligible domain boundary density, and a [100] crystalline orientation along the transport direction.

Engineering of niobium surfaces through accelerated neutral atom beam technology for quantum applications

A major roadblock to scalable quantum computing is phase decoherence and energy relaxation caused by qubits interacting with defect-related two-level systems (TLSs). Native oxides present on the surfaces of superconducting metals used in quantum devices are acknowledged to be a source of TLS that decrease qubit coherence times. Reducing microwave loss by “surface engineering” (i.e., replacing the uncontrolled native oxide of superconducting metals with a thin, stable surface with predictable characteristics) can be a key enabler for pushing performance forward with devices of higher intrinsic quality factor. In this work, we present a novel approach to replace the native oxide of niobium (typically formed in an uncontrolled fashion when its pristine surface is exposed to air) with an engineered oxide, using a room-temperature process that leverages accelerated neutral atom beam (ANAB) technology at 300 mm wafer scale. This ANAB is composed of a mixture of argon and oxygen, with tunable energy per atom, which is rastered across the wafer surface. The ANAB-engineered Nb-oxide thickness was found to vary from 2 to 6 nm depending on ANAB process parameters. The modeling of variable-energy x-ray photoelectron spectroscopy data confirms the thickness and compositional control of Nb surface oxide by the ANAB process. These results correlate well with those from transmission electron microscopy and x-ray reflectometry. Since ANAB is broadly applicable to material surfaces, the present study indicates its promise for modification of the surfaces of superconducting quantum circuits to achieve longer coherence times.

The effect of elastic and plastic strain on surface and intergranular oxidation of alloy 600 in simulated PWR primary water

The effects of deformation and stress on the surface and grain boundary oxidation of Alloy 600, exposed to primary water of Pressurized Water Reactors (PWRs), were investigated by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Scanning Electron Microscopy (SEM). It was found that tensile straining prior to oxidation does not modify the surface oxide thickness while the intergranular oxide depth increases when the strain reaches a critical value of 15%. The oxide growth rates at surface and grain boundaries are enhanced under stress. The effect of stress is more significant when the specimen is under elastic strain than plastically deformed.

Machine-Guided Design of Oxidation-Resistant Superconductors for Quantum Information Applications

Decoherence in superconducting qubits has long been attributed to two-level systems arising from the surfaces and interfaces present in real devices. A recent significant step in reducing decoherence was the replacement of superconducting niobium by superconducting tantalum, resulting in a tripling of transmon qubit lifetimes (T1). The identity, thickness, and quality of the native surface oxide, is thought to play a major role, as tantalum only has one oxide whereas niobium has several. Here we report the development of a thermodynamic metric to rank materials based on their potential to form a well-defined, thin, surface oxide. We first computed this metric for known binary and ternary metal alloys using data available from the Materials Project and experimentally validated the strengths and limits of this metric through the preparation and controlled oxidation of eight known metal alloys. Then we trained a convolutional neural network to predict the value of this metric from atomic composition and atomic properties. This allowed us to compute the metric for materials that are not present in the Materials Project, including a large selection of known superconductors, and, when combined with Tc, allowed us to identify new candidate superconductors for quantum information science and engineering (QISE) applications. We tested the oxidation resistance of a pair of these predictions experimentally. Our results are expected to lay the foundation for the tailored and rapid selection of improved superconductors for QISE.

Effect of Amino Acids on the Corrosion and Metal Release from Copper and Stainless Steel

Copper (Cu) and stainless steel 316 L are widely used for biomedical applications, such as intrauterine devices and orthopedic/dental implants. Amino acids are abundantly present in biological environments. We investigated the influence of select amino acids on the corrosion of Cu under naturally aerated and deaerated conditions using a phosphate-free buffer. Amino acids increased the corrosion of Cu under both aeration conditions at pH 7.4. Cu release was also significantly (up to 18-fold) increased in the presence of amino acids, investigated at pH 7.4 and 37 °C for 24 h under naturally aerated conditions. Speciation modelling predicted a generally increased solubility of Cu in the presence of amino acids at pH 7.4. 316 L, investigated for metal release under similar conditions for comparison, released about 1,000-fold lower amounts of metals than did Cu and remained passive with no change in surface oxide composition or thickness. However, amino acids also increased the chromium release (up to 52-fold), significantly for lysine, and the iron release for cysteine, while nickel and molybdenum release remained unaffected. This was not predicted by solution speciation modelling. The surface analysis confirmed the adsorption of amino acids on 316 L and, to a lower extent, Cu coupons.

Impact of surface oxide on hydrogen permeability of chromium membranes

Hydrogen permeation through pure and oxidised bulk chromium membranes was measured by the classical gas technique to get insight into oxide as a hydrogen permeation barrier (HPB). An additional palladium-coated reference chromium membrane was tested to avoid the influence of native Cr oxide. Key parameters for Cr permeability: P0 = 3.23 × 10−7 mol H2/s/m/Pa0.5 and Ea = 0.68 eV and Cr diffusivity D0 = 9.0 × 10−5 m2/s and Ea = 0.59 eV. In the sample preparation stage, a thin ∼2 nm thick oxide was formed. Additional oxidation in pure oxygen at 400 °C increased the thickness from 20 to 50 nm. At this temperature, its efficiency as HPB was evaluated by comparing permeation rates to the reference chromium membrane. The highest permeation reduction factor of ∼3900 corresponded to only a ∼28 nm thick Cr oxide layer. Surface morphology and oxide thickness were investigated by SEM, while the thickness and type of chromium oxide by XPS.

Effect of processing gas on spatter generation and oxidation of TiAl6V4 alloy in laser powder bed fusion process

The atmosphere is a vital factor influencing powder degradation during laser powder bed fusion. Particularly, its purity, density, and thermal conductivity, can strongly affect spatter generation, thermal history, and oxidation. It is critical to understand the atmosphere-spatter properties relationship to enhance powder recyclability and overall process sustainability. Herein, the effect of processing gases, among pure Ar, (Ar+He), and He, on spatter generation and oxidation during TiAl6V4 processing is investigated. To evaluate their influence on impurity pickup and morphology of spatters, bulk chemical analysis and scanning electron microscopy were conducted. The nature and thickness of surface oxides on spatters were comprehensively examined using surface analysis tools including X-ray photoelectron spectroscopy, Auger electron spectroscopy, and nano secondary ion mass spectroscopy. The bulk chemical analysis showed a 70% increase in oxygen content and a 3-fold increase in nitrogen content from virgin to spatter collected in standard argon atmosphere. The increase of impurities was substantially lower for the spatters generated in He and the mixture of (Ar+He). The surface analysis showed that the spatter surface was covered with a uniform Ti- and Al-rich oxide layer along with Al-based oxide particulates. Finally, this study discusses the nature of oxide on TiAl6V4 spatters.

An effective laser surface treatment method to reduce biofilm coverage of multiple bacterial species associated with medical device infection

Device associated infection (DAI) is recognized as a worldwide health challenge in total joint replacement (TJR). Bacteria exhibit very strong antibiotic tolerance when they attach to a device and form a biofilm and thus DAI is difficult to treat. In this study, a one-step, clean (no chemicals or additional materials involved) and effective surface engineering approach via laser surface treatment (LST) to tackle the DAI challenge is reported. Commercially pure (CP) Ti were laser-treated in open air using continuous wave (CW) fibre laser. The laser-treated CP Ti was tested against five bacterial species including Gram positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram negative (Pseudomonas aeruginosa, Escherichia coli and Proteus mirabilis). Live/Dead staining and image analysis results indicated that LST can significantly reduce biofilm coverage of the five tested bacterial species on the CP Ti surfaces. Overall biofilm coverage as a percentage of the surface reduced after laser treatment averaging from 4.24 % to 17.4 %. This meant that relative to the untreated surface, biofilm coverage was reduced after laser treatment, ranging from 84.9 % to 95.6 % across the five species. Furthermore, cytotoxicity results (using MTT assay) showed that the laser-treated CP Ti is non-toxic across both L929 fibroblast and RAW macrophage cell lines. Surface properties after LST were investigated using WLI and AFM (measuring micro-/nano-surface roughness and topography) as well as ToF-SIMS (measuring surface chemistry and oxide thickness), respectively. The cross-sectional microstructure at the surface was imaged using SEM and analysed by XRD, whilst the surface wettability was measured using sessile drop method. To summarise, the reduction of biofilm coverage can be attributed to the favourable changes in surface roughness and topography together with the increased concentration of oxides at the topmost surface after LST.

The exceptional oxidation of Ti6Al4V alloy with a pre-deposited silver layer

For the first time, we discovered the exceptional oxidation phenomenon on Ti6Al4V alloy. A thin layer of silver was pre-deposited via PVD on a Ti6Al4V alloy surface before ceramic conversion treatment (CCT) based on thermal oxidation in air at 620 °C. The pre-deposited silver particles accelerated the oxidation of the Ti6Al4V alloy by up to 50 times, and also helped to produce a thick compact surface oxide layer with a larger surface area compared to a non-silver pre-treated surface. However, silver had a less profound effect on the oxidation of other titanium alloys that didn’t contain vanadium, additionally the silver particles tended to agglomerate on their surfaces, particularly for commercially pure titanium (CPTi). Systematic work examining the impact of vanadium found that vanadium together with silver played a critical role in activating oxygen and promoting its diffusion in the oxide layer, thus dramatically accelerating the oxidation of the vanadium-containing titanium alloys with a pre-deposited Ag layer in CCT. SEM/EDX, TEM, XRD and XPS analyses on the surface phase constituents and microstructure helped to explicate the rapid oxidation mechanism of pre-deposited silver on Ti6Al4V surfaces, and thus provide a new insight into modifying the titanium alloys surface efficiently.

Composition and electronic structure of porous silicon nanoparticles after oxidation under air- or freeze-drying conditions

A controlled change in the composition and electronic structure of porous silicon nanoparticles by variation the drying conditions is proposed. Two types of nanopowders were obtained from mechanically milled porous silicon films with subsequent air- or freeze-drying processing. Obtained nanoparticles surface morphology and structure were investigated. Silicon atoms local surrounding specificity and electronic structure probing of studied powders were performed with the use of synchrotron ultrasoft X-ray absorption near edge structure spectroscopy technique. Noticeable changes in surface composition and structure are observed. The air-dried porous silicon nanoparticles were characterized by the presence of a thick surface oxide layer, while the presence of unoxidized silicon atoms at a depth of less than 3 nm was demonstrated for the lyophilized ones.

Effect of anodization on friction behavior of β‑titanium orthodontic archwires.

To evaluate the effects of anodization on the friction behavior of beta-titanium (β-Ti) orthodontic archwires in conventional or self-ligating brackets in vitro. β‑Ti archwires (0.018 × 0.025inch) pre- and postanodization were tested in combination with 0.022-inch stainless steel conventional and self-ligating brackets. The surface composition and oxide thickness of the β‑Ti archwires pre- and postanodization were measured using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). Detailed surface topography and roughness were assessed using atomic force microscopy (AFM). Surface topographies of the β‑Ti archwires pre- and postanodization were examined using scanning electron microscopy (SEM). Friction was measured using auniversal testing machine; the data were statistically analyzed. Postanodization, the identified titanium oxide layer on the surface of the β‑Ti archwires increased in thickness from10 to 100 nm; at the same time, the values for surface roughness were significantly reduced by half (p < 0.001). The archwire surfaces post anodization were harder and had fewer scratches after the friction test. Anodization significantly reduced 23.77% of the static (p < 0.01) and 25.61% of the kinetic (p < 0.001) friction of the β‑Ti archwires in conventional brackets, while it significantly reduced 85.71% of the static and 84.38% of the kinetic friction (p < 0.01) in self-ligating brackets. Anodization reduced the β‑Ti archwire friction, which was particularly more effective in combination with self-ligating brackets. The friction reduction via anodization could be attributed to the increased thickness, surface hardness, and decreased surface roughness of the titanium oxide layer.

Thermal atomic layer etching of germanium-rich SiGe using an oxidation and “conversion-etch” mechanism

The thermal atomic layer etching (ALE) of germanium-rich SiGe was demonstrated using an oxidation and “conversion-etch” mechanism with oxygen (O2) or ozone (O3), hydrofluoric acid (HF), and trimethylaluminum [TMA, Al(CH3)3] as the reactants. The crystalline germanium-rich SiGe film was prepared using physical vapor deposition and had a composition of Si0.15Ge0.85. In situ spectroscopic ellipsometry was employed to monitor the thickness of both the SiGe film and the surface oxide layer on the SiGe film during thermal ALE. Using a reactant sequence of O2-HF-TMA, the etch rate of the SiGe film increased progressively with temperatures from 225 to 290 °C. At 290 °C, the SiGe film thickness decreased linearly at a rate of 0.57 Å/cycle with a surface oxide thickness of 18–19 Å. This etch rate was obtained using reactant pressures of 25, 0.2, and 0.4 Torr and doses of 1.5, 1.0, and 1.0 s for O2, HF, and TMA, respectively. The TMA and HF reactions were self-limiting and the O2 reaction was reasonably self-limiting at 290 °C. Using an O3-HF-TMA reaction sequence, the SiGe ALE etch rate was 0.42 Å/cycle at 290 °C. This etch rate was obtained using reactant pressures of 15, 0.2, and 0.4 Torr and dose times of 0.5, 1.0, and 1.0 s for O3, HF, and TMA, respectively. The O3, TMA, and HF reactions were all self-limiting at 290 °C. Atomic force microscopy images revealed that thermal ALE with the O2-HF-TMA or O3-HF-TMA reaction sequences did not roughen the surface of the SiGe film. The SiGe film was etched selectively compared with Si or Si3N4 at 290 °C using an O2-HF-TMA reaction sequence. The etch rate for the SiGe film was &amp;gt;10 times faster than Si(100) or Si3N4 that was prepared using low-pressure chemical vapor deposition. This selectivity for the SiGe film will be useful to fabricate Si nanowires and nanosheets using SiGe as the sacrificial layer.

Investigation of oxygen penetration during UV nanosecond laser annealing of silicon at high energy densities

In this work, we present a comprehensive investigation of impurities contamination in silicon during UV Nanosecond Laser Annealing at high energy density. By investigating in detail the impact of the annealing ambient and of the surface preparation prior to UV-NLA (including the variation of the surface oxide thickness), we show that the observed oxygen penetration originates from the surface oxide layer. It is proposed that, at high energy UV-NLA, the prolonged contact of SiO2 with high temperature liquid Si induces a partial degradation of the SiO2/Si interface, leading to bond breaking and subsequent injection of O atoms into the substrate. A degradation involving less than 5% of the O atoms contained in the 1st SiO2 mono-layer is sufficient to account for the measured amount of in-diffused O in all of the analysed samples.

The role of surface oxide thickness and structure on the corrosion and nickel elution behavior of nitinol biomedical implants.

Biocompatibility is an important factor for metallic medical device implants, and corrosion resistance of implantable alloys is one aspect of biocompatibility. Corrosion behavior of nitinol is strongly dependent upon the nature of the surface oxide, which forms during processing. The surface oxide is comprised of a mixture of titanium and nickel oxides, and subsequent thermal exposure (e.g., during shape setting) and surface removal (e.g., electropolishing, mechanical polishing, etching, etc.) influence its structure. Corrosion behavior is often assessed through testing methods such as cyclic potentiodynamic polarization (e.g., ASTM F2129) and nickel ion release. Studies have suggested that a correlation exists between oxide thickness and nickel ion release, with thicker oxides eluting more nickel. It is hypothesized that the composition of the surface oxide, and not only its thickness, influences the corrosion performance of nitinol. To investigate this, nitinol wire samples were processed to produce surface oxides with different structures both in terms of thickness and composition. These samples were tested per ASTM F2129 and nickel ion release testing.

Temperature dependence of nickel ion release from nitinol medical devices.

Nitinol exhibits unique (thermo)mechanical properties that make it central to the design of many medical devices. However, nitinol nominally contains 50 atomic percent nickel, which if released in sufficient quantities, can lead to adverse health effects. While nickel release from nitinol devices is typically characterized using in vitro immersion tests, these evaluations require lengthy time periods. We have explored elevated temperature as a potential method to expedite this testing. Nickel release was characterized in nitinol materials with surface oxide thickness ranging from 12 to 1564 nm at four different temperatures from 310 to 360 K. We found that for three of the materials with relatively thin oxide layers, ≤ 87 nm nickel release exhibited Arrhenius behavior over the entire temperature range with activation energies of 80 to 85 kJ/mol. Conversely, the fourth ''black-oxide'' material, with a much thicker, complex oxide layer, was not well characterized by an Arrhenius relationship. Power law release profiles were observed in all four materials; however, the exponent from the thin oxide materials was approximately 1/4 compared with 3/4 for the black-oxide material. To illustrate the potential benefit of using elevated temperature to abbreviate nickel release testing, we demonstrated that a > 50 day 310 K release profile could be accurately recovered by testing for less than 1 week at 340 K. However, because the materials explored in this study were limited, additional testing and mechanistic insight are needed to establish a protective temperature scaling that can be applied to all nitinol medical device components.