Oxide Growth Mechanism Research Articles

ToF-SIMS depth profiling of alumina scales formed on a FeCrAl high-temperature alloy

The thickness and composition of thin oxide scales formed on a powder metallurgical FeCrAl alloy isothermally oxidised between 0.5 and 192 h at 900 °C have been investigated using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show that the oxide scale grows according to a parabolic law during oxidation times up to 192 h. The oxide scales mainly consist of alumina, with the accumulation of Fe and Cr oxides both within the scale and at the oxide scale/metal substrate interface. Furthermore, elements such as Mg, Si, K, Ca, Ti, Mn, Ni and Zr are also found within the oxide scale which indicates that these elements may also influence the oxide scale growth rate and growth mechanisms. The results demonstrate the usefulness of ToF-SIMS analysis for characterisation of the initial stages of oxidation of FeCrAl alloys at elevated temperatures.

Oxide growth and its dielectrical properties on alkylsilated native-SiO 2/Si surface

The kinetics and mechanism of probe-induced oxide growth on an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) passivated native-SiO 2/Si surface have been investigated using atomic force microscopy (AFM). It was found that oxidation strongly depends on tip polarity and the local chemistry of OTS molecules. At negative tip voltage, oxide grows and the oxidation involves a decomposition and depletion of OTS SAM. While under positive tip bias, OTS molecules are partially degraded. The dielectrical properties of the oxide were characterized by I– V measurements using current sensing AFM. The barrier height of AFM grown oxide, in comparison with thermal oxide and OTS SAM, was determined. Current spikes relating to the release of single charge were also observed on the I– V curves of AFM oxide.

Influence of Deuterium and Platinum on the Thermal Oxidation of GaAs

The thermal oxidation of GaAs at 500°C in labeled has been studied with gas phase analysis, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy. The influence of a few hundred atomic parts per million of deuterium in the GaAs substrate and of surface platinum have been evaluated with respect to oxide growth mechanisms and the degree of As buildup. Deuterium increased the transport from the substrate interface of both Ga and As toward the gas interface thereby lowering the degree of preferential Ga oxidation and As buildup at the substrate interface. Platinum, on the other hand, catalyzed the dissociation of the oxygen molecule at the gas interface and thereby facilitated an increased transport of oxygen toward the substrate interface. That results in an increased overall oxidation rate with a high degree of preferential Ga oxidation and concomitant As buildup. When the oxygen pressure was increased from 20 to 720 mbar, a lowered degree of As buildup was observed due to the lower degree of preferential Ga oxidation. © 2003 The Electrochemical Society. All rights reserved.

Role of oxidizer in the chemical mechanical planarization of the Ti/TiN barrier layer

The electrochemical parameters controlling the polishing rates of Ti and TiN are investigated. In this paper, alumina containing slurry was studied at pH 4 with 5% H 2O 2 as the oxidizer. Passive film formation on the surface during chemical mechanical polishing (CMP) plays an important role. To understand the oxide growth mechanism and the surface chemistry, X-ray photoelectron spectroscopy was performed. It was found that in the absence of an oxidizer, the removal of Ti and TiN is mainly due to mechanical abrasion of oxide layer or metal layer. However, in the presence of 5% H 2O 2 as the oxidizer, different removal behavior was observed for Ti and TiN. The removal mechanism of Ti during CMP is mainly due to mechanical abrasion of the oxide layer whereas for TiN it could be attributed to the formation of metastable soluble peroxide complexes.

Oxidation of AISI 304L stainless steel surface with atomic oxygen

Oxidation of stainless steel surface in oxygen atmosphere was investigated by Auger electron spectroscopy (AES) depth profiling. The samples made of AISI 304L stainless steel were exposed to highly non-equilibrium oxygen atmosphere at different temperatures between 300 and 800 K and for different periods between 5 and 600 s. The degree of dissociation of oxygen molecules was of the order of 10%. A thin oxide layer formed on the stainless steel surface consisted of the iron oxide. The thickness depended on the sample temperature. At room temperature it was 7 nm, and it remained the same up to 200 °C. With further increase of temperature, the thickness of the oxide layer increased and reached 40 nm at 450 °C. The thickness was independent of exposure time. The results were explained by two mechanisms of oxide growth. Up to 200 °C the oxidation was run by electro-migration, while at higher temperatures the thermal induced migration prevailed.

Use of isotopic tracers and SIMS analysis for evaluating the oxidation behaviour of protective coatings on nickel based superalloys

In this investigation, the oxide growth mechanisms of a Pt–aluminide type coating were investigated using a two-stage oxidation treatment. The samples are first oxidised in unlabelled 16 O 2 , followed by a second oxidation in 18 O 2 enriched tracer gas. Oxygen diffusion characteristics through the oxide scale were determined by SIMS depth profiling. Focused ion beam analysis was also conducted using a Ga + ion beam to mill cross-sections and then perform elemental mapping. Encouraging results have been obtained from this series of experiments and have clearly shown the two different oxidation mechanisms that occur at temperatures above and below approximately 1000 °C which are associated with the formation of θ and α alumina scales.

Stress generation during high-temperature oxidation of metallic alloys

During high-temperature oxidation, constraint stresses are generated in the growing oxide in response to a lateral growth strain mechanism. Substantial progress has been made in recent years in clarifying the mechanisms of oxide growth that sets the stage for understanding the origin of the lateral growth strain. Nevertheless, identification of the lateral growth mechanisms remains elusive.

Iron oxide nanoparticles hosted in silica aerogels

The investigated hybrid materials consist of non-agglomerated iron oxide particles hosted in silica aerogels. The composite material can be produced as a monolith, in any shape, and with different dilutions of the iron oxide phase. Two sol–gel chemistry routes have been followed: a solution of Fe(NO3)3·9H2O has been added either to the silica gel or to the initial sol; in the latter, the iron salt provided the water required for the gel polymerisation. To obtain monolithic aerogels, the gels were dried by hypercritical solvent evacuation. On the other hand, some gels were dried by slow and controlled evaporation of the solvent, resulting in xerogels. Several heat treatments have been performed and the iron oxide particle phase, growth mechanism and crystallinity have been analysed. The composite materials were characterised by means of X-ray diffraction, Mossbauer spectrometry and superconducting quantum interference device magnetometry. It was observed that the particle sizes (in the nanometre range) and the thermal stability of the iron oxide phases strongly depend on the preparation method that determines the microstructure of the host material. Consequently, the magnetic properties of the nanoparticles can be controlled via synthesis conditions, matrix properties and thermal treatments.

Oxygen isotopic exchange occurring during dry thermal oxidation of 6H SiC

SiC is a large band gap semiconductor, promising for high power and high frequency devices. The thermal oxide is SiO 2 however the growth rates of thermal oxide on SiC are substantially slower than on Si, and different along the polar directions ( 〈0 0 0 1〉 and 〈0 0 0 1〉 in the hexagonal polytypes). Thorough understanding of the oxide growth mechanisms may give us new insights into the nature of the SiO 2/SiC interface, crucial for device applications. We have determined growth kinetics for ultra-dry thermal oxidation of 6H SiC at 1100 °C for pressures from 3 to 200 mbar. At 3 mbar, the lowest pressure studied, the oxide growth rates along the two polar directions are virtually the same. At higher pressures growth is faster on the carbon-terminated (0 0 0 1 ) face. After consecutive oxidations at 1100 °C and 100 mbar in 18 O 2 and 16 O 2 gases, 18 O depth profiles show significant isotopic exchange and oxygen movement within the oxide during oxidation.

Characterization and growth of oxide films

Surface-analytical techniques are useful to characterize oxide films and to study growth processes on metals and semiconductors. This paper will summarize work at the National Research Council of Canada on the high temperature oxidation of nickel, chromium, FeCrAl alloys (with and without yttrium additions), β-NiAl and silicon. The application of secondary ion mass spectrometry, reflection high energy electron diffraction, and transmission electron microscopy is emphasized. Also considered is the thermal oxidation of III–V semiconductors, indium phosphide and gallium arsenide. X-ray photoelectron spectroscopy provides additional useful information on the chemical composition of the oxides. The often complementary information provided by the various techniques leads to (i) a better understanding of oxidation processes and of oxide growth mechanisms on an atomic scale, (ii) interfacial segregation phenomena, and (iii) the role of reactive elements like yttrium in modifying transport processes in oxides.

Investigation of oxide growth and stability on n-GaAs and n-InP by coupling transient photocurrent and surface analysis

Investigation of oxide chemistry and reactivity of III–V semiconductors has been undergone with an electrochemical approach coupled with surface analysis. Growth and stability of anodic oxides obtained on n-GaAs and n-InP was investigated with potensiostatic mode under illumination at pH 9. For the two compounds, the transient photocurrent, the recovery of the photocurrent and XPS analysis were performed in the same conditions. InP and GaAs present very different behaviours, which are linked to the stability of the oxidised interface. InP evidences a thin, stable and electrically blocking oxide film, while GaAs exhibits a thicker, unstable and porous oxide layer. This work point out that XPS analysis has to be coupled with in situ techniques as transient photocurrent, to understand accurately the oxide growth mechanism.

Studies on the surface chemistry of oxide films formed on IN-738LC superalloy at elevated temperatures in dry air

The oxidation behavior of IN-738LC was studied to develop high-temperature materials for low cost and highly efficient turbine systems. The present study was undertaken to investigate the kinetics and the surface chemistry of the oxide films formed during isothermal oxidation of IN-738LC superalloy in the temperature range 1123–1223 K in dry air. The oxidation kinetics followed the parabolic law. The activation energy of oxidation was 264 kJ mol−1. The scaling process is controlled mainly by the diffusion of chromium ions through the intermediate chromia layer in the scale. The surface morphology and the oxide phases of the scale were characterized by SEM, XRD, and EDS studies. XRD analysis revealed the presence of NiO, NiAl2O4, NiCr2O4 spinel, Al2O3, and Cr2O3 on the top-scale surface. The scale surface and cross section were further characterized using X-ray photoelectron spectroscopy (XPS), which revealed the presence of NiO, Ni2O3, NiAl2O4, Al2O3, and TiO2 on the top-oxide surface. The chromia layer was found to be underneath the top scale. The chromia layer also contains NiCr2O4 and NiAl2O4 spinels along with Al2O3. Application of XPS was found to be successful to understand the oxide-scale chemistry in terms of the oxide-growth mechanism of IN-738LC at elevated temperatures.

Initial Kinetics of Copper Oxidation in Different Oxidizing Atmospheres as Studied by In Situ UHV-TEM

Abstract It is of fundamental and practical interest to understand the oxidation process since a desirable property for metals is resistance to corrosion. But there is a wide gap between information provided by surface science methods and that provided by bulk oxidation studies. The former have mainly examined the adsorption of ∼ 1 ML of oxygen on the metal surface, where as both low and high temperature bulk oxidation studies have mainly focused on the growth of an oxide layer at the later stages of oxidation. We are probing the initial oxidation stage of a model metal system by in situ ultra-high vacuum (UHV) transmission electron microscopy (TEM) in order to gain insights into the initial kinetics of oxidation. We have previously shown that the growth mechanism of the cuprous oxide is initially dominated by oxygen surface diffision.

Analysis of Thin Oxide Growth Mechanisms in Partial-Pressure Rapid-Thermal Oxidation of Silicon

In this paper we analyze the growth mechanism of extremely thin silicon-oxide layers, formed by rapid thermal oxidation under various oxygen partial pressures, on the basis of the Deal-Grove model and the silicon-fragment model. It is determined that the silicon-fragment model gives an acceptable interpretation of the experimental results concerning the linear rate constant.

Surface and interface segregation in the oxidation of metals

For the protection of high-temperature alloys against corrosion, a slowly growing, dense, well-adherent scale must be formed. At elevated to high temperatures either chromia (Cr2O3) or alumina (Al2O3) can act as such a protective scale. Surface and interface phenomena in the nucleation, growth and adherence of oxide scales have been studied, mainly by AES; these phenomena are described and their mechanisms are discussed. Various positive effects on nucleation, growth and adherence are exerted by alloying with reactive elements (i.e. Ce, Y, La, Ti, Zr …) in small concentrations. They are acting in their oxidized state, segregated on the metal surface in oxide nucleation and segregated in oxide grain boundaries in the oxide growth mechanism. Non-metal elements such as nitrogen and carbon can enhance Cr2O3 nucleation by intermediate co-segregation with chromium, in contrast sulphur impedes chromia formation. Segregation of sulphur to the surface of voids and cracks forming at the metal/oxide interface deteriorates the scale adherence. The detrimental sulphur can be scavenged in precipitates formed by the reactive elements (oxides and oxysulphides) and at their interfaces. Copyright © 2000 John Wiley & Sons, Ltd.

Application of surface techniques to study oxide growth processes

Surface-analytical techniques are useful to characterize oxide films and to study oxide growth processes on metals and semiconductors. This paper will summarize work at NRC on the high-temperature oxidation of both FeCrAl alloys and silicon, as well as the thermal and UV ozone oxidation of III–V semiconductors. In these studies, surface-analytical data complemented by information provided by other techniques, e.g., TEM, lead to a better understanding of oxidation phenomena and oxide growth mechanisms for a wide variety of materials and applications.

Studies on passivation behavior of tungsten in application to chemical mechanical polishing

Chemical mechanical polishing (CMP) is considered to be the enabling technology for meeting the planarization requirements in <0.35 μm feature sized multilevel semiconductor device fabrication. CMP of tungsten is done in order to planarize and remove excess tungsten in the process to form inter-level contacts. Considerable importance is given to the role played by the passive oxide film formation on the surface during tungsten CMP. In this study, x-ray photoelectron spectroscopy (XPS) is used to understand the oxide growth mechanism in tungsten. Tungsten wafers are polarized to different anodic potentials in static pH 4 solutions of KIO3 and H2O2, two commonly used oxidizers in CMP. XPS measurements are employed to probe the chemical and stoichiometric changes in the surface oxide films treated under these conditions. These results are then compared with the electrochemical polarization results.

Investigation of the incorporation of electrolyte anions in porous anodic Al 2 O 3 films by employing a suitable probe catalytic reaction

A new method has been developed capable of describing the incorporation of electrolyte anions along the pore wall surface and across both the barrier layer and the pore wall oxide after the establishment of the steady state of growth of porous anodic Al2O3 where other methods cannot be applied to obtain reliable results. The knowledge of the nature/composition of anodic oxides as regards the incorporation of species like electrolyte anions is of specific importance for both the understanding of the electrochemical mechanism of oxide production and growth and the scientific and technological applications of porous anodic Al2O3 films. The method consists of the selection and use of a suitable catalytic probe reaction on porous anodic oxides at thicknesses varying from a value near zero up to the maximum limiting thickness and the treatment of the experimental reaction rate results by a properly developed mathematical formalism. This method was employed in anodic Al2O3 films prepared in H2SO4 anodizing electrolyte at a constant bath temperature and different current densities using as a probe reaction the decomposition of HCOOH on these oxides, which is almost exclusively a dehydration reaction, at relatively high reaction temperatures, 350 °C and 390 °C, where the effect of other species except SO4 2− incorporated in the oxide on the reaction rate is eliminated. It has been shown that the fraction of the intercrystallite surfaces occupied by SO4 2− follows a parabola-like distribution. It has a significant value at the pore base surface, depending on the current density, then it passes through a maximum along the pore wall surface and across both the barrier layer and the pore walls near the pore bases at positions depending on the current density and then becomes almost zero at the mouths of the pores of the oxide with the maximum limiting thickness and at both the Al2O3/Al interface and cell boundaries. The maximum value of the surface coverage is almost independent of the current density and is always near 1, showing an almost complete saturation of intercrystalline surfaces at these positions. The above distribution of surface coverage predicts a qualitatively similar distribution of the SO4 2− bulk concentration across both the barrier layer and pore wall oxide around the pore bases. The method may be improved and developed further either for a more detailed investigation of the above films or to investigate films prepared in other pore-forming electrolytes.

X-ray photoelectron spectra of low temperature plasma anodized Si0.84Ge0.16 alloy on Si(100): Implications for SiGe oxidation kinetics and oxide electrical properties

The material properties of low-temperature plasma-grown oxide on gas-source molecular beam epitaxial Si0.84Ge0.16 have been investigated. X-ray photoelectron spectra studies show that plasma anodization leads to no segregation of Ge species during thin oxide growth with the onset of partial segregation occurring for thicker oxides. Depth profiling shows that the plasma oxide is stoichiometric in form with the exception of a small percentage of Ge atoms left in their unoxidized state. The density of these Ge atoms agrees with that measured in previous electron trapping studies. In addition, oxide growth rate enhancement of SiGe is observed. These phenomena are explained using a qualitative model for the mechanism of oxide growth of SiGe which is consistent with published results for SiGe: oxides grown with other systems.

Oxidation kinetics of hydrogen-enriched Si(100) and Si(111) surfaces

Hydrogen-enriched Si(100) and Si(111) wafers were thermally oxidized and the growth kinetics were studied by measuring the thickness and the refractive index of the oxide. The oxidation was performed in dry oxygen at temperatures of 800, 845 and 855 °C Prior to oxidation the Si surfaces were hydrogen-enriched by hydrogenation in hydrogen plasma in a planar r.f. unit. The substrates were kept at the lower electrode without heating or at a temperature of 100 °C. In the investigated thickness range of 40–200 Å the growth was linear with time. The rate constant was smaller and the zero time thickness higher (as obtained from the fit of the experimental points) as compared with the case of the Si surface with wet RCA preoxidation clean only. A discussion on the role of the hydrogen in oxide growth mechanisms is included.