Native Oxide Research Articles

Sub-Nanometer Depth Profiling of Native Metal Oxide Layers Within Single Fixed-Angle X-Ray Photoelectron Spectra.

Many metals form nanometer-thin self-passivating oxide layers upon exposure to the atmosphere, which affects a wide range of interfacial properties and shapes the way how metals interact with their environment. Such native oxide layers are commonly analyzed by X-ray photoelectron spectroscopy (XPS), which provides a depth-resolved chemical state and compositional analysis either by ion etching or modeling of the electron escape depths. The latter is commonly used to calculate the average thickness of a native oxide layer. However, the measurement of concentration profiles at the oxide-metal interface remains challenging. Here, a simple and accessible approach for the depth profiling of ultrathin oxide layers within single fixed-angle XPS spectra is proposed. Instead of using only one peak in the spectrum, as is usually the case, all peaks within the energy range of a standard lab device are utilized, thus resembling energy-resolved XPS without the need for a synchrotron. New models that allow the calculation of depth-resolved concentration profiles at the oxide-metal interface are derived and tested, which are also valid for angular- and energy-resolved XPS. The proposed method not only improves the accuracy of earlier approaches but also paves the way for a more holistic understanding of the XPS spectrum.

An efficient sensor based on anodic activation of graphene oxide for sensitive and selective determination of dopamine in blood serum

A native graphene oxide (NGO) prepared by Hummers modified method was used as the template materials for the fabrication of electrochemically oxidative graphene oxide (OGO) onto a glassy carbon electrode (GCE). The fabrication of OGO-GCE persuaded via anodic reversible potentiodynamic of NGO base surface materials that increases the concentration of oxygen functionalities. The development of a new aldehyde/alcoholic functional group on OGO-GCE characterized by XPS analysis is a marked signal for oxygen richness surface which provoked on the cost of sp2 hybridized function. The EIS data underline that OGO-GCE promote the electron transfer kinetics much more than NGO-GCE by 9 times as estimated by the rate constant calculation. The XPS and EIS data highlight the influence of anodic treatment on increasing the interlayer spacing distance between the resultant OGO. Differential pulse voltammetry (DPV) results were evident for a promising efficiency of OGO-GCE on the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA). In addition, the selectivity of the proposed sensor for DA quantification in the presence of high concentrations of AA and UA was achieved successfully with a detection limit (DL3s) approach to 12 nM. The analytical performance of OGO-GCE on serum blood revealed its potential application for trace DA quantification.

Early stages of liquid-metal corrosion on pre-oxidized surfaces of austenitic stainless steel 316L exposed to static Pb-Bi eutectic at 400 °C

The effect of pre-oxidation in air at 300–500 °C on the initiation and development of liquid metal corrosion attack on 316L austenitic steel in static lead-bismuth eutectic (LBE) with ∼10−10 – 10−9 mass% dissolved oxygen at 400 °C for 1200 h is investigated. General dissolution with preferential attack along twin boundaries was observed on polished surfaces with native oxide films. Fe/Cr-based oxide films pre-formed in air at 300 and 400 °C protect surfaces against dissolution. Localized corrosion was observed on surfaces pre-oxidized at 500 °C. Thermal oxide degradation rate depends on its composition rather than thickness.

Gallium phosphide conformal film growth on in-situ tri-TBP dry-cleaned InGaP/GaAs using atomic hydrogen ALD

Nearly stoichiometric (high P/Ga ratio and low oxygen content) ∼ 20 nm GaP epi-layers were conformally deposited on the side-walls of InGaP layers using an atomic H ALD process with triethyl gallium (TEGa) and tri-tertiary butyl phosphine (tri-TBP). The key for uniform nucleation is an in-situ tri-TBP dry-clean in 40 mTorr Ar and 160 mTorr H2 without acidic wet-clean to generate a particle-free and damage-free InGaP surface which induces local epitaxy growth of homogeneous GaP thin films. The in-situ tri-TBP dry-clean removed the native oxide of InGaP, surface particles, and the residual impurities simultaneously. It is hypothesized that the key to the process is in-situ formation of PHx(C4H9)y surface adsorbates from atomic H and tri-TBP surface reactions. In-situ AES, cross-sectional STEM image, ex-situ XPS, AFM, and EDS confirmed the formation of high-quality GaP thin films on InGaP/GaAs with a high-quality interface and smooth surface morphology.

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Rapid preparation of sintered Ag nanoparticles pastes for high-power electronic packaging

This study developed a low-temperature pressureless sintered Ag nanoparticles (AgNPs) paste with high thermal conductivity (TC), which can be produced on a large scale through rapid pre-treatment. Commercially available unmodified AgNPs were coated with polyvinylpyrrolidone (PVP), and subsequently, citric acid (CA) was used to remove the native oxide layer from the AgNPs surface and improve sintering activity. Compared to the treatment strategy of CA activation followed by PVP coating, applying PVP coating prior to CA activation could prevent their spontaneous bonding that will significantly promote the formation of large grains and strong sintering necks, reducing the interface scattering and leading to an ultra-high TC (≥200 W/mK), thereby meeting the packaging requirements of high-power electronic applications.

Full liquid phase sintering of binder jetting printed magnesium alloy

Migration and diffusion of materials play a critical role in densifying magnesium alloy parts made by binder jetting technology, which is closely related to the sintering temperature. However, the native oxide film of the magnesium alloy forms a barrier between particles, hindering the migration and diffusion processes and making it challenging to manufacture parts with the desired properties. To overcome this issue, this study employs a full liquid sintering method to achieve densification by breaking the oxide film at high temperature, allowing particles to diffuse and migrate. The density, microstructure, grain growth, phase change, cross-sectional morphology and mechanical properties of the manufactured samples at different sintering temperatures were investigated. The results showed that the density and mechanical properties of the samples first increases and then decreases with increasing temperature. The best properties are obtained at 620 °C where the density, the compressive strength and the tensile strength reach 93.16 %, 181.92 MPa and 91.20 MPa respectively. Further, the grain size grows from 38.03 μm at 600 °C to 45.09 μm at 640 °C, a size increase of 18.56 %. Additionally, the material phase composition is consistent at different temperatures, but the α-Mg peak shows a small shift to the left as the temperature increases. The sample morphology shrinks and swells significantly at sintering temperatures above 630 °C, where grain coarsening and larger holes appear in the microstructure, resulting in reduced properties. In summary, the full liquid phase sintering method offers significant advantages in optimizing the sintering process for binder jetting of magnesium alloys.

Augmentation of Liquid Metal Particle Mechanics via Non‐Native Oxide Nanoshells

AbstractRoom‐temperature liquid metal particles based on gallium have become significantly important for developing next‐generation soft electronics. Eutectic gallium‐indium (EGaIn) alloys can be fabricated into core‐shell particles discretely encapsulated by a passivating oxide. Application of mechanical stimuli results in rupturing the molten core through the oxide shell, merging EGaIn particles to form conductive pathways. Generally, the mechanical properties of EGaIn are largely defined by the native oxide which imparts viscoelastic properties to the fluid. In this work, the practical implications of EGaIn deformation and fracture behavior with the native oxide and a non‐native inorganic silica shell are demonstrated. To augment the mechanical properties of EGaIn, silica nanoshells are introduced as a chemically inert coating to enable brittle fracture of particles. In situ single‐particle nanoindentation characterization reveals the environmental and geometrical considerations for particle deformation and fracture. Silica‐coated EGaIn particles reach stiffness values at least an order of magnitude higher than that of native EGaIn particles. The thickness of the silica shell can be tailored to further modify the mechanical behavior of EGaIn, enabling potential pressure‐sensitive conductivity. These results provide additional pathways to understand the design and implementation of functionalized EGaIn particles for future applications in mechanoresponsive electronics, plasmonics, and therapeutics.

A practical guide to interpreting low energy ion scattering (LEIS) spectra

Low-Energy Ion Scattering (LEIS) spectrometry is extraordinarily sensitive and specific to the outermost atomic layers of materials. It is a powerful tool for surface science. Here, we present a practical guide on LEIS spectral interpretation that is based on actual LEIS spectra of a variety of materials. While this article covers some of the theory of LEIS, it is not an exhaustive description of this aspect of the technique. Rather, it is intended for the broad community of scientists who, while not necessarily active users of LEIS instruments, need LEIS in their research, perhaps obtaining LEIS spectra by collaboration or encountering it in the scientific literature. The spectra/experimental results we present reflect both basic and advanced features of LEIS. We believe this guide is quite comprehensive. Most of the spectra shown herein were obtained on a modern high sensitivity (HS)-LEIS instrument. The analyser of this instrument defines and fixes a scattering angle of 145°. However, these results are representative of other widely used geometries. The features of these spectra are quite general. Key concepts covered in this work include surface peaks, elements that promote reionization, double and multiple scattering/collisions, quantification with reference materials, the effect of contamination, differences between particulate and crystalline materials/surfaces, direct scattering from the second atomic layer of a material, and the use and effects of different primary ions, e.g., He+, Ne+, and Ar+. The LEIS spectra shown and discussed in this work come from different materials, including as-received, clean, and oxidized Cu, silicone rubber, Ca evaporated onto SiO2, Al, graphene on Cu, Fe, Rh, FeRh, CaF2, native silicon oxide (SiO2) on silicon, BeO, B2O3, Bi2Se3, Teflon (polytetrafluoroethylene), LiF, SrTiO3, an alloy with five elements (Cr, Mn, Fe, Co and Ni), and Au. Many of these materials are of substantial technological interest.

Sensitive Aluminum SPR Sensors Prepared by Thermal Evaporation Deposition.

We used straightforward thermal evaporation deposition to form thin Al films on fused silica slides as surface plasmon resonance (SPR) sensors in the blue visible region. Compared to other studies, we achieved high-quality Al SPR sensors with a low vacuum level at 7 × 10-4 Pa and a low deposition rate between 1.47 and 3.41 nm/s. These Al films have an atomic-level surface roughness. With our recipe, the requirements for deposition conditions are relaxed, and the operation time is reduced remarkably. The experimental sensitivity of the bulk refractive index measurements using 405 nm probing light is as high as 149.9°/RIU. Compared with other studies, our blue visible Al SPR completes the Al SPR working frequency range from deep UV to near-infrared which is much broader than the working range of Au SPR sensors. The cost of Al material is cheap, and the deposition instrument is also economic and operation easy. Considering the compatibility with most of the nanofabrication procedures and stability from the native oxide layer, Al SPR sensors have a huge potential to replace Au SPR sensors as the new golden standard of SPR sensing technology.

Electron-enhanced atomic layer deposition of Ru thin films using Ru(DMBD)(CO)3 and effect of forming gas anneal

Ruthenium (Ru) thin films were deposited utilizing electron-enhanced atomic layer deposition (EE-ALD). Sequential exposures of Ru(DMBD)(CO)3 (DMBD = 2,3-dimethylbutadiene) and low-energy electrons at ∼125 eV were used to grow the Ru films at temperatures ≤160 °C. The electrons were obtained from a hollow cathode plasma electron source that provided an electron current of ∼200 mA over a surface area of ∼4 cm2. Low-energy electrons can desorb surface ligands derived from Ru(DMBD)(CO)3, such as CO, through electron-stimulated desorption. The desorbed surface ligands leave chemically reactive sites for subsequent Ru(DMBD)(CO)3 precursor absorption. Ru EE-ALD film growth was monitored utilizing in situ spectroscopic ellipsometry (SE). The electron exposures resulted in rapid Ru film nucleation and growth. Under saturation conditions at 160 °C, the growth rate for Ru EE-ALD was 0.2 Å/cycle. The electron efficiency factor for Ru EE-ALD was ∼21 500 electrons/deposited Ru atom. There was no film growth without electron exposures. Ru growth was observed on various substrates including silicon with native oxide and titanium. Ru growth was also obtained on insulating substrates such as 400 nm thick thermal SiO2 substrates. XPS analysis measured <1 at. % oxygen in the deposited Ru films. XRD, x-ray reflectivity, and SE were used to characterize the Ru films before and after forming gas anneal (FGA). FGA successfully removed carbon impurities from the as-deposited Ru films. The resistivity of the Ru EE-ALD films after FGA was determined to be as low as 17 μΩ cm for a film thickness of 6.7 nm. SE measurements of the imaginary part of the pseudodielectric function, 〈ɛ2〉, were utilized to characterize the as-deposited Ru films and the high purity Ru films after FGA. The low resistivity of the Ru films after FGA was consistent with a prominent Drude absorption in the ⟨ε2⟩ spectrum at ≤1 eV. Various reactive background gases such as H2, NH3, and H2O were utilized during EE-ALD to attempt to remove the carbon from the as-deposited Ru EE-ALD films.

In Situ Ellipsometry and EIS Study of Potentiostatic Synthesis of Pseudocapacitive MnOx

This work discusses the one-step potentiostatic growth of manganese oxide on stainless steel for pseudocapacitor electrodes. The electrode material was studied through in situ ellipsometry and electrochemical impedance spectroscopy, in order to correlate its microstructure with the capacitive response. Ellipsometry results show the formation of three layers during the potentiostatic synthesis of manganese oxide on stainless steel: the thickening of the native oxide of the substrate, and the growth of two distinct layers of manganese oxide. The inner layer is slightly more compact (>n) and more resistive (<k) than the outer one. The electrochemical characterization of modified electrodes showed that the increase in the growth potential (from 0.7 to 1.0 VSCE) leads to the formation of manganese oxide films with higher specific capacitance (from 64 to 330 F g−1 at 2 A g−1). This effect is due to an increase in the area of the active material and to a decrease in the thickness of the inner layer of the manganese oxide film. However, higher growth potentials also lead to an increase in film resistivity due to the increase in the density and thickness of the outer layer, which hinders the diffusion of ions through the film as evidenced by EIS.

Analysis of Hydrogen Distribution and Diffusion in Pre-Strained SUS316L through Scanning Kelvin Probe Force Microscopy and Thermal Desorption Spectroscopy

Austenitic stainless steels (γ-SS) play an important role in the storage of high-pressure hydrogen. However, hydrogen embrittlement (HE) can significantly degrade the mechanical properties of γ-SS. Measuring the distribution of hydrogen in γ-SS is a vital way to learn about HE. In this paper, scanning Kelvin probe force microscopy (SKPFM) and thermal desorption spectroscopy (TDS) have been utilized to analyze the distribution and diffusion of hydrogen in pre-strained SUS316L. Additionally, the McNabb–Foster model is employed to calculate hydrogen in the lattice and phase boundaries along the sample’s thickness direction. The results demonstrate that the combination of SKPFM and TDS is an effective approach for studying hydrogen distribution and diffusion in metals. It was observed that hydrogen segregation occurs at the boundary between the martensitic (α′) and austenite (γ) phases. The inhibitory effect of the oxide film on hydrogen diffusion is more significant at lower temperatures. However, it should be noted that the McNabb–Foster model exhibits relatively high accuracy in predicting hydrogen desorption at higher temperatures while disregarding the influence of the native oxide film.

A novel method for extracting metals from asteroids using non-aqueous deep eutectic solvents

Extra-terrestrial mining and metal processing are vital for access to strategic metals for space exploration. This study demonstrates for the first time the catalytic dissolution of metals from meteorite proxies of metal-rich asteroids using a deep eutectic solvent (DES). DESs are of particular interest for extra-terrestrial mining as they can be designed to have relatively low vapour pressures and could potentially be made from organic waste products created in extra-terrestrial settlements. Three types of meteorites were investigated: two chondrites (H3, H5) and one iron (IAB-MG) meteorite. Chondrite samples were composed of silicates (olivine, pyroxene) with metal-rich phases occurring as native metal alloys, sulphides and oxides. Metallic Fe–Ni and troilite (FeS) are the most abundant metal-bearing phases in all three samples, particularly in the iron-rich meteorite. The samples were subjected to chemical micro-etching experiments with iodine and iron(III) chloride as oxidising agents in a DES formed from the mixture of choline chloride and ethylene glycol. Micro-etching experiments demonstrated that Fe–Ni rich phases are effectively leached out in this system, while other mineral phases remain unreactive.

Vibratory polishing effects on passivity of 304L stainless steel surfaces

ABSTRACT Surface spectroscopy analysis and electrochemistry were applied to study the effects of surface preparation by vibratory polishing on the passivity of stainless steel 304L surfaces. Compared to grinding by traditional mechanical polishing, vibratory polishing promotes the enrichment of Cr(III) oxide and hydroxide species in the duplex chemical structure of the surface native oxide film by enhancing selective Fe oxidation and dissolution. As a result, spontaneous passivity, tested in aggressive sulphuric acid electrolyte, is enhanced. However, in the absence of enrichment in Mo(IV) and Mo(VI) species in the passive film, the Cr enrichment does not enhance passivity upon anodic polarisation nor increase the resistance to Cl-induced passivity breakdown and initiation of localised corrosion in accelerated testing conditions. The results provide comprehensive insight into the mechanisms underlying the passivity enhancement of stainless steel by surface engineering.

Transport kinetics of protium and deuterium in titanium: Experiments and modeling

We conducted absorption experiments on Ti using hydrogen isotopes, protium and deuterium, to gain insights into the kinetics of hydrogen atoms, particularly across the Ti surface. Rather than relying on various surface pretreatments, we identified the initial temperature of Ti in vacuum as the determining factor in achieving a high absorption rate and content. Specifically, we found that the initial Ti temperatures of approximately 900 and 980 °C are optimal for protium and deuterium, respectively, likely due to sufficient removal of the native surface oxide on Ti. The dependence of the absorption rate and amount of hydrogen isotopes on the temperature during absorption was partially explained by the phase transformation and exothermicity of the hydrogenation reaction. Moreover, this dependence strongly indicated the existence of a tunneling transport process. Additionally, we developed a kinetic model for hydrogen isotope transport in Ti to conduct numerical simulations. The absorption curves, calculated using the developed model, closely matched a series of experimental curves obtained at different temperatures. These curves were from an identical set of equations and kinetic parameters for both protium and deuterium. Our numerical kinetic model has the potential to serve as a valuable simulation tool for various applications, such as the design of high-performance hydrogen storage systems and maintenance strategies against hydrogen embrittlement of structural materials.

(Invited) Al-Al Waferbonding Process Development for Heterogeneous Integration

This paper presents a surface-activated Al-Al wafer bonding process for patterned 200 mm wafers that removes the native oxide in an argon plasma and enables high bond quality with accurate alignment at temperatures below 300 °C. The study focuses on various factors that influence the final Al-Al bond in terms of contact resistance and shear strength. In addition to temperature, force and time during the actual bonding process, these include steps during the wafer fabrication that affect the Al bonding pads and the wafer bow. Furthermore, the impact of a post-bond cleaning process on the final bond result is analyzed. This work shows a low temperature Al-Al bonding process with high yield >90%, excellent bond strength >150 MPa and contact resistances in the mΩ range.

Surface Activated Si-Si Wafer Bonding Using Different Ion Species

Surface activated bonding on wafer level is enabled by an advanced direct wafer bonding system for irradiation with different ion species. In this process, the native oxide of 200 mm Si wafers is sputter-removed and an amorphous layer is generated. After ion treatment, the wafers are bonded in ultra-high vacuum at room temperature. The impact of Ar, Kr and Xe ion irradiation on the amorphous layer thickness was investigated with the goal of optimizing the bonding process for establishing interfaces with electronic functionality. This was i.a. motivated by the fact, that the presence of an amorphous layer reduces the electrical conductivity across the wafer interface.

An Amorphous Native Oxide Shell for High Bias-Stress Stability Nanowire Synaptic Transistor.

The inhomogeneous native oxide shells on the surfaces of III-V group semiconductors typically yield inferior and unstable electrical properties metrics, challenging the development of next-generation integrated circuits. Herein, the native GaOx shells are profitably utilized by a simple in-situ thermal annealing process to achieve high-performance GaSb nanowires (NWs) field-effect-transistors (FETs) with excellent bias-stress stability and synaptic behaviors. By an optimal annealing time of 5min, the as-constructed GaSb NW FET demonstrates excellent stability with a minimal shift of transfer curve (ΔVth ≈ 0.54V) under a 60min gate bias, which is far more stable than that of pristine GaSb NW FET (ΔVth ≈ 8.2V). When the high bias-stress stability NW FET is used as the chargeable-dielectric free synaptic transistor, the typical synaptic behaviors, such as short-term plasticity, long-term plasticity, spike-time-dependent plasticity, and reliable learning stability are demonstrated successfully through the voltage tests. The mobile oxygen ion in the native GaOx shell strongly offsets the trapping states and leads to enhanced bias-stress stability and charge retention capability for synaptic behaviors. This work provides a new way of utilizing the native oxide shell to realize stable FET for chargeable-dielectric free neuromorphic computing systems.

Precisely constructing hybrid nanogap arrays via wet-transfer of dielectric metasurfaces onto a plasmonic mirror.

We propose a new method for fabricating hybrid metasurfaces by combining Mie and plasmonic resonances. Our approach involves obtaining an ultrasmooth gold film and separately structuring monocrystalline silicon (c-Si) nanoantenna arrays, which are then wet-transferred and finally immobilized onto the gold film. The experimental and simulation analysis reveals the importance of the native oxide layer of Si and demonstrates fascinating dispersion curves with nanogap resonances and bound states in the continuum. The localized field enhancements in the nanogap cavities result from the coupling between multipolar Mie resonances and their mirror images in the gold film. This effective method improves our understanding of hybrid modes and offers opportunities for developing active metasurfaces, such as depositing c-Si nanoantenna arrays onto stretchable polydimethylsiloxane substrates or electro-optic and piezoelectric sensitive lithium niobate films for potential applications in MEMS, LiDAR, and beyond.