Native Oxide Growth Research Articles

Corrosion Enhancement of PM Processed Magnesium by Turning Native Oxide on Mg Powders into Carbonates

In addition to its use as a lightweight material, pure magnesium is a promising candidate for prospective bioimplants considering its excellent biocompatible properties. Regardless of what Mg application is used, the ultimate goal is to improve magnesium's mechanical properties and degradation behaviour. Because of the high affinity for oxygen native oxide layer of gas-atomized powders is naturally formed in contact with the atmosphere. S/TEM investigation of the native oxide of the Mg powder particles revealed a nonhomogeneous nano-crystalline MgO layer. MgO is relatively soluble in water and does not provide sufficient corrosion protection. Among various surface treatment methods, conversion of the non-protective magnesium oxide to carbonate products is possible depending on the environmental conditions. This work used a simple experimental method using CO2 and water vapour to achieve surface carbonation of Mg powders. Two carbonated samples and pure magnesium were prepared by direct extrusion. The samples after carbonation retained good mechanical properties and the layer of carbonates had a significant impact on corrosion resistance. 1 day carbonation resulted in transformation of native oxide into amorphous layer and reduction of corrosion rate. Longer carbonation (10 days) revealed layer growth and transformation of native oxide to crystalline nesquehonite structure.

Band-offsets scaling of low-index Ge/native-oxide heterostructures

We investigate, through XPS and AFM, the pseudo layer-by-layer growth of Ge native oxide across Ge(001), (110) and (111) surfaces in ambient environment. More significantly, our study reveals a universal set of valence and conduction band offset (VBO and CBO) values observed for Ge(001), Ge(110), and Ge(111) surfaces as a function of Ge-oxide concentration. We find that the band offsets appear to be the same across these low-index Ge surfaces i.e., for Ge-oxide/Ge heterostructures with the same Ge-oxide overlayer concentration or thickness. In contrast, different oxidation rates for Ge(001), Ge(110), and Ge(111) surfaces were observed, where the oxidation rate is fastest for Ge(001), compared to Ge(110) and Ge(111). This can be attributed to the different number of unsatisfied Ge dangling bonds (2 vs 1) associated to the respective ideal Ge surface in forming Ge-oxide. Thus, at any given oxidation time, the oxide concentration or thickness for each type of low index Ge surface will be different. This in turn will lead to different band offset value observed for each type of Ge surface. More significantly, we show that while oxidation rates can differ from different Ge surface-types, the band offset values can be estimated simply based on the Ge-oxide concentration regardless of Ge surface type.

Impact of sample storage type on adventitious carbon and native oxide growth: X-ray photoelectron spectroscopy study

The type and degree of contamination on surfaces intended for X-ray photoelectron spectroscopy (XPS) studies is considered decisive for meaningful and reliable analysis as in many cases in-situ cleaning methods are not applicable or otherwise undesired. We report on the effects of sample storage environment on predominantly carbon- and oxygen-containing species accumulating on the surfaces of fourteen types of thin film samples spanning group IVB-VIB transition metals (TMs), TM nitrides, and TM diborides. All specimens were deposited by magnetron sputtering and stored for six months in different common sample storage environments such as openly on a shelf in the office or XPS lab, or within a polypropylene wafer carrier, polystyrene box, cellulose/polyester wipers or sealed polyethylene bag. Self-consistent modelling of C 1s, O 1s, B 1s, N 1s, and metal core level spectra allowed to identify the types and quantities of surface contaminants, metal oxidation states, and thicknesses of native oxides, as well as to address influence from storage ambient type and volume, direct sample contact to other surfaces, or material release from containers. The results reveal significant differences between the various storage types and, hence, provide guidance for all sorts of studies including even those that employ Ar+ ion etch prior to analyses, as also in such cases the amount and type of surface contaminants may impact the outcome.

Fast imaging of laser ablation of cerium: Dependence of plasma plume dynamics and structure on native oxide growth

We have imaged the evolution of plasma following nanosecond pulsed laser ablation of cerium in air with sub-10 ns resolution. We find the ablated plasma plume expansion and shape to be strongly dependent on the time after mechanical polishing of the sample surface. After an initial shock front common to both new and aged samples (velocities up to 16 km s−1), we observe a second front that is relatively localized to the surface vicinity of newly polished samples, but in the case of older samples it moves outward at velocities of up to 4 km s−1. We attribute this behavior to the formation and growth of a native oxide layer on the order of hours after polishing. These results demonstrate that plasma imaging can be used to diagnose the presence of, and evaluate the extent of, thin surface oxides or other compounds that form soon after exposure to some atmosphere. These findings also highlight the need to explicitly consider the presence of such overlayers when modeling laser/metal interaction, when making measurements of vapor phase chemistry, and when analyzing the composition, phase, and morphology of solid particulates formed after the ablation of reactive metals.

Stabilization of unstable and metastable InP native oxide thin films by interface effects

III-V semiconductor - oxide interfaces have attracted huge interest due to their substantial potential in electronic applications. However, due to the extreme complexity of the modeling of the interfaces, there are only few ab initio studies of these interfaces.Several model interfaces of native InPO4 oxides are designed in this study. It is shown that energies of the (quasi-)coherent interfaces are much smaller than energies of the incoherent interfaces. Furthermore, it is pointed out that the interface energy can stabilize oxide structures not found in bulk form. Relatively small strain energy and configurational match imply a small interface energy.It is estimated that the gap state density of the In-terminated quasi-coherent interfaces is small or zero. However, partial oxidation of the substrate P atoms, which can be induced, e.g., by non-stoichiometry of the oxide, causes distinct gap states. This is a mechanism to explain Fermi level pinning of the III-V – oxide interfaces. Non-stoichiometric compositions are also investigated. Experimental results on InP native oxide growth are discussed. The models can be used to study various properties of the interfaces and more complex models including, e.g., dislocations or non-planar surfaces can be based on the models.

Intertrack surface losses in miniature coplanar waveguide on silicon-on-insulator

Attenuation has been studied in different-sized coplanar waveguides (CPW) patterned onto silicon-on-insulator (SOI) for three different surfaces between the CPW tracks: a silicon dioxide/silicon interface, a hydrogen-terminated silicon surface, and a native oxide. For large-gap CPW (signal track width = 100 µm, gap width = 63.5 µm), selective removal of the silicon dioxide from between the metal tracks reduces losses from 0.79 dB mm−1 to 0.69 dB mm−1 at 50 GHz. The subsequent growth of a native oxide on the silicon surface between the tracks results in losses equal to 0.67 dB mm−1. For small-gap CPW ( = 2 µm, = 2.5 µm), losses are reduced from 5.6 dB mm−1 to 3.4 dB mm−1 at 50 GHz by selectively removing the silicon oxide between the metal tracks. However, when a native oxide is allowed to grow on the silicon surface between the tracks, the losses increase significantly to 5.8 dB mm−1. When the native oxide is removed, the losses decrease to those observed following removal of the silicon dioxide. The measurements suggest that the contribution of the intertrack surface losses is the result of free-carrier losses due to a surface inversion layer. The surface-associated losses are proportionally larger as the CPW dimensions shrink—as predicted by modelling. We suggest that technologies employing miniature CPW should take this into account. The native oxide should be routinely removed if possible—implying that appropriate chemically-resistant metallisation be chosen, or fabrication processes should incorporate stable passivation of silicon surfaces between CPW tracks to avoid native oxide growth. Conversely, the increased sensitivity of attenuation to surface effects by shrinking CPW dimensions suggests that CPW-based sensors could benefit from miniaturization.

Evaluation and mitigation of reactive ion etching-induced damage in AlGaN/GaN MOS structures fabricated by low-power inductively coupled plasma

AlGaN/GaN metal-oxide-semiconductor (MOS) structures were fabricated by low-power inductively coupled plasma reactive ion etching (ICP-RIE) and chemical vapor deposition of SiO2 dielectrics on the etched surfaces, and they were systematically investigated by physical and electrical characterizations in an effort to develop a low-damage recessed gate process. Although ICP-RIE with reduced bias power was able to suppress nitrogen deficiencies and native oxide growth on damaged AlGaN surfaces, compositional changes due to selective aluminum removal were found to be inevitable. On the other hand, thin damaged layers were completely oxidized to form GaOx interface layers at the initial stage of SiO2 deposition, leading to dielectric/etched-AlGaN interfaces with excellent electrical properties. Furthermore, Hall-effect measurements showed negligible impact on the two-dimensional electron gas beneath the AlGaN layers etched under very low bias conditions. The current comprehensive research demonstrates the significant advantages of the proposed low-damage recessed gate process for fabricating next-generation AlGaN/GaN MOS-HFET devices.

Impact of doping and silicon substrate resistivity on the blistering of atomic-layer-deposited aluminium oxide

Aluminium oxide (Al2O3) thin films grown at low temperatures using atomic layer deposition (ALD) are known to often suffer from local delamination sites, referred to as “blisters”, after post-deposition annealing during device processing. In this work, we report our observation that doping of the silicon substrate has an effect on blister formation. The introduction of a highly doped layer by diffusion or implantation is found to significantly reduce blistering, compared to the non-doped regions in the immediate vicinity. Similar behavior is observed for both phosphorus and boron doping. Further investigation of this phenomenon using substrates with different resistivities reveals that even when introduced already during silicon crystal growth, doping affects the blistering of aluminium oxide films. Changes in several properties of silicon affected by doping, most importantly surface terminating groups, native oxide growth, and passivation of defects with hydrogen, are discussed as potential reasons behind the observed effect on blistering.

Facile Process for Surface Passivation Using (NH4)2S for the InP MOS Capacitor with ALD Al2O3.

Ammonium sulfide ((NH4)2S) was used for the passivation of an InP (100) substrate and its conditions were optimized. The capacitance–voltage (C–V) characteristics of InP metal-oxide-semiconductor (MOS) capacitors were analyzed by changing the concentration of and treatment time with (NH4)2S. It was found that a 10% (NH4)2S treatment for 10 min exhibits the best electrical properties in terms of hysteresis and frequency dispersions in the depletion or accumulation mode. After the InP substrate was passivated by the optimized (NH4)2S, the results of x-ray photoelectron spectroscopy (XPS) and the extracted interface trap density (Dit) proved that the growth of native oxide was suppressed.

XPS Study of the Process of HgCdTe Oxidation in a Glow Discharge Oxygen Plasma

Initial stages of HgCdTe oxidation in a glow discharge plasma in O2 atmosphere are first studied using the XPS method. The chemical composition of the growing native oxide layer is investigated and the oxidation kinetics is revealed. It is experimentally established that the mechanism of HgCdTe oxidation changes as the oxide thickness reaches 2-3 nm due to the change of the limiting stage of the chemical reaction. The composition of the formed oxide is varies with depth and is characterized by low mercury content. It is suggested that the diffusion of oxygen to the oxide–semiconductor interface and its predominant interaction with tellurium are the main mechanism of the native MCT oxide growth, so that the oxide region bordering the substrate is ∼10% oxygen depleted. The obtained results are discussed and compared with previously reported data on MCT oxidation in RF plasma and in liquid electrolytes.

Effects of Hf buffer layer at the Y-doped HfO2/Si interface on ferroelectric characteristics of Y-doped HfO2 films formed by reactive sputtering

10 nm-thick ferroelectric (FE) HfO2 films with 1.5 mol% yttrium-doping were fabricated by mid-frequency reactive magnetron co-sputtering deposition on bare Si and underlying metal Hf. Yttrium was incorporated into the HfO2 layers by simultaneously sputtering from Y and Hf metal targets under oxygen atmosphere. The effects of interfacial layer on structural and electrical properties of Y:HfO2 films have been systemically studied using high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrical measurements. Based on TEM and XRD measurements, the presence of a non-centrosymmetric orthorhombic phase which is responsible for ferroelectricity in yttrium-doped HfO2 (Y:HfO2) films could be detected. As an initial protective layer, the ultra-thin metal Hf (~1 nm) layer covers the silicon surface and prevents the native oxide growth during the deposition and post-annealing process. Results reveal that the thickness of interfacial layer is significantly reduced by deposit a Hf buffer layer and a remanent polarization Pr of up to 14 μC/cm2 can be detected in P-V measurement. The strategy of using Hf buffer layer to improve electrical properties of HfO2 film is a feasible method for the fabrication of metal-insulator-semiconductor (MIS) capacitor based on FE-HfO2/Si gate stack.

High performance graphene-silicon Schottky junction solar cells with HfO2 interfacial layer grown by atomic layer deposition

Among the limiting factors that affect the performance of Graphene (Gr)/ Silicon (Si) Schottky barrier solar cells (SBSC) - are the high recombination at Gr/Si interface and the growth of undesirable native oxide that resulted in instability issue. In this work, hafnium oxide (HfO2) grown by atomic layer deposition (ALD) has been investigated as an interfacial layer for Gr/Si Schottky junction solar cells. Engineering the interface with HfO2 contributed to enhancing the power conversion efficiency remarkably from 3.9% to 9.1%. The obtained efficiency with HfO2 interfacial layers grown by ALD is considered among the highest reported for Gr/Si SBSC using pristine graphene.

Oxidization of Al0.5Ga0.5As(001) surface: The electronic properties

AlGaAs materials are used in a variety of cutting-edge devices and the band gap states after the surface oxidization is found with Fermi level pinning. With first-principle calculations, we explore the formation of gap states during the initial stage of native-oxide growth on Al0.5Ga0.5As (001) surface. The results indicate that oxygen adsorption at the bridge sites of Al (Ga)-As satisfies the bond saturation and doesn't lead to any effect on the surface gap states. The breaking of As-As dimer results in the defect states in band gap with Fermi level pining due to the replacement of oxygen. In the oxidization process, it is found that the As-As dimer is very easy to be broken. In addition, the defect states in band gap maybe disappear after the full oxidization of surface with the elimination of unsaturated As on surface. With these gap states, some absorption peaks are found to appear in the range of 0–1eV in the absorption spectra.

Easy Plating—A Simple Approach to Suppress Parasitically Metallized Areas in Front Side Ni/Cu Plated Crystalline Si Solar Cells

Plated silicon solar cells with nonoptimized antireflective coatings (ARCs) may feature parasitic plating (PP), i.e., unwanted metal depositions in ARC defects/pinholes. The present work introduces the easy plating sequence that takes advantage of native oxide growth to avoid plating in unwanted ARC pinholes or defects due to the electrical insulation of these defects. This prevents PP for plated solar cells. Independent of the ARC pinhole density, an aesthetic immaculate appearance can be achieved using easy plating. It is shown that it is possible to gain up to 0.5 mA/cm2 in short-circuit current density and 6 mV in open-circuit voltage compared to the reference plating sequence at Fraunhofer ISE. The importance to avoid drawbacks in terms of contact resistance and contact adhesion due to laser-induced or native oxide at the Si–Ni interface in the easy plating sequence is discussed in detail and important influencing factors in the process chain are lined out. At this stage of development, low contact resistances are possible in some cases but further research is necessary to fully understand the impact of solar cell design and process-related influencing factors. Easy plating can be an option to avoid PP independent of prior ARC pinhole density.

Impact of Native Oxide Growth on the Capacitance-Voltage Characteristic of Pseudo-MOS Structure

Influence of native oxide growth on the top and/or the back surface(s) of the pseudo-MOS structure on impedance is analyzed. This impedance analysis reveals a definite reduction in resistance is achieved with the removal the surface native oxide by HF cleaning. The resistance increased with the time spent after HF treatment. These suggest the native oxide will induce erroneous estimations of surface carrier density when attempting to use the pseudo-MOS structure to extract the universal effective mobility.

Self-assembly and electrical characteristics of 4-pentynoic acid functionalized Fe3O4-γ-Fe2O3 nanoparticles on SiO2/n-Si

A novel investigation on a relationship between temperature-influential self-assembly (70–300°C) of 4-pentynoic acid functionalized Fe3O4-γ-Fe2O3 nanoparticles (NPs) on SiO2/n-Si with electrical properties was reported with the interests for metal-oxide-semiconductor applications. X-ray diffractometer (XRD) analysis conveyed that 8±1nm of the NPs were assembled. Increasing heating temperature induced growth of native oxide (SiO2). Raman analysis confirmed the coexistence of Fe3O4-γ-Fe2O3. Attenuated Total Reflectance Infrared (ATR-IR) spectra showed that self-assembly occurred via SiOC linkages. While SiOC linkages were broken down at elevated temperatures, formations of Si-OH defects were amplified; a consequence of physisorbed surfactants disintegration. Atomic force microscopy (AFM) showed that sample with more physisorbed surfactants exhibited the highest root-mean-square (RMS) roughness (18.12±7.13nm) whereas sample with lesser physisorbed surfactants displayed otherwise (12.99±4.39nm RMS roughness). Field Emission Scanning Electron Microscope (FE-SEM) analysis showed non-uniform aggregation of the NPs, deposited as film (12.6μm thickness). The increased saturation magnetization (71.527Am2/kg) and coercivity (929.942A/m) acquired by vibrating sample magnetometer (VSM) of the sample heated at 300°C verified the surfactants’ disintegration. Leakage current density-electric field (J-E) characteristics showed that sample heated at 150°C with the most aggregated NPs as well as the most developed SiOC linkages demonstrated the highest breakdown field and barrier height at 2.58×10−3 MV/cm and 0.38eV respectively. Whereas sample heated at 300°C with the least SiOC linkages as well as lesser aggregated NPs showed the lowest breakdown field and barrier height at 1.08×10−3 MV/cm and 0.19eV respectively. This study opens up better understandings on how formation and breaking down of covalent linkages as well as accumulation of defects, particularly prior temperature influential self-assembly at the interfaces, affected electrical breakdown field and barrier height. Hence, possible future development of self-assembly silicon-based metal-oxide-semiconductor (MOS) structure particularly in the presence of SiO2 can be deliberated.

Native Oxide Growth on Silicon Micro-Pillars

This paper presents a study on monitoring the native oxide growth on silicon micro-pillars. It also presents a comparison between the rates of oxide growth on pillars fabricated using the reactive ion etching (RIE) approach and the metal assisted chemical etching (MACE) approach. The native oxide growth is monitored using photoluminescence (PL) measurements. PL measurements showed that native silicon oxide grows at a higher rate on MACE pillars compared to RIE pillars. SEM images showed that the MACE pillars exhibit a porous outer layer while the RIE pillars show a dense outer layer. It is concluded that the porosity of the pillars enhances the native oxide growth.

Dynamics of native oxide growth on CdTe and CdZnTe X-ray and gamma-ray detectors

We studied the growth of the surface oxide layer on four different CdTe and CdZnTe X-ray and gamma-ray detector-grade samples using spectroscopic ellipsometry. We observed gradual oxidization of CdTe and CdZnTe after chemical etching in bromine solutions. From X-ray photoelectron spectroscopy measurements, we found that the oxide consists only of oxygen bound to tellurium. We applied a refined theoretical model of the surface layer to evaluate the spectroscopic ellipsometry measurements. In this way we studied the dynamics and growth rate of the oxide layer within a month after chemical etching of the samples. We observed two phases in the evolution of the oxide layer on all studied samples. A rapid growth was visible within five days after the chemical treatment followed by semi-saturation and a decrease in the growth rate after the first week. After one month all the samples showed an oxide layer about 3 nm thick. The oxide thickness was correlated with leakage current degradation with time after surface preparation.

Self-protective Oxide Nano-Coatings for Enhanced Surface Biocompatibility of Titanium

ABSTRACTThe biocompatibility of an implant material depends on the bulk physical properties in addition to the surface properties. In biomedical engineering and industry Ti and Ti-alloys are very popular biological implant material for their bulk physical properties and strength to weight ratio resembling those of nature bone. It is possible to modify the surface properties of titanium for enhanced surface biocompatibility. The main objective of the this study is to engineer a smart Ti-based prosthesis surface by self induced chemically modified titanium oxide nano-film by the chemical mechanical polishing process (CMP). This new process applied on bio-implants aims at significantly reducing the out-diffusion of Ti and other metallic impurities from prosthesis in contact with body fluids and tissue and simultaneously enhancing the surface mechanical, chemical and biological properties. CMP technique enables the growth of a thicker and denser self-protective native oxide on Ti and Ti alloy samples, while simultaneously inducing a controlled surface roughness. It is demonstrated that the Ti based dental implants with self-protective oxide induced surfaces help minimize chemical and bacterial reactivity in addition to Ti ion dissolution while promoting their biocompatibility through surface patterning. The studied self-protective oxide films can also be utilized for many additional applications including bio-sensors.

Ultra-thin oxide growth on silicon during 10keV x-ray irradiation

Abstract Surface effects on silicon wafers irradiated by 10 keV x-rays at room temperature were characterized using x-ray photoelectron spectroscopy and spectroscopic ellipsometry. The samples were exposed to total ionizing doses ranging from 1.0 to 12 Mrad(SiO2) at x-ray dose rates ranging from 5.8 krad(SiO2)/min to 67 krad(SiO2)/min. Accelerated thin oxide growth on irradiated samples compared to natural native oxide growth under room temperature conditions was demonstrated, and the composition of the irradiation-accelerated oxide was investigated. The presence of suboxides along with silicon dioxide was confirmed on the irradiated silicon sample. Two thin oxide growth models were applied to characterize the enhanced oxidation rate observed for irradiated wafers.