Oxide Growth Kinetics Research Articles

Metal-organic chemical vapor deposition of Cr 2O 3 and Nd 2O 3 coatings. Oxide growth kinetics and characterization

Thin oxide films of Cr 2O 3 and Nd 2O 3 were prepared, using Metal-Organic Chemical Vapor Deposition (MOCVD) technique, to protect stainless steels against corrosion at high temperature. The conditions of precursor volatilization were studied by thermogravimetry. Deposited film growth kinetics depended on the deposition parameters, particularly substrate temperature, gas flow rate and location of substrate in the coating reactor. The influence of the deposition parameters on the deposition rate and the uniformity of the films is discussed. The oxide films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The aim of this work was to optimize coating parameters in order to prepare mixed Nd 2O 3–Cr 2O 3 films, leading to the most important protective effects under high temperature corrosion conditions.

Surface Oxidation Kinetics of GaAs Oxide Growth by Liquid Phase Chemical-Enhanced Technique

The initial stage of GaAs oxidation by a near-room-temperature liquid phase chemical-enhanced technique has been studied. Based on the experimental results of X-ray photoelectron spectroscopy, a complete model illustrating the chemical composition of the grown oxide film has been established. To clarify the kinetics of oxide growth in a liquid solution in more detail, we have also performed selective oxidation and surface profile measurements. Unusual features of the oxide growth kinetics have been observed by investigating the physical structure of oxide at the edge of mask in the selective oxidation.

Ar/N 2 O remote plasma-assisted oxidation of Si(100): Plasma chemistry, growth kinetics, and interfacial reactions

The kinetics of Ar/N2O remote plasma-assisted oxidation of Si(100) and the mechanism of nitrogen incorporation at the Si–SiO2 interface were investigated using mass spectrometry, optical emission spectroscopy, and on-line Auger electron spectroscopy. N2, O2, and NO are the stable products of N2O dissociation in the plasma. The maximum NO partial pressure occurs at 10 W applied rf power; N2 and O2 are the predominant products for applied powers greater than 50 W. Ar/N2O remote plasmas are prolific sources of atomic O; in contrast, atomic N is not produced in significant concentrations. Ar/N2O remote plasma-assisted oxidation was investigated at 300 °C for applied rf powers of 5, 20, and 50 W. The oxide growth kinetics are slower than expected for a purely diffusionally controlled process. A diffusion-reaction model that incorporates first-order loss of the oxidizing species as it diffuses through the growing oxide layer fits the data very well. The initial oxidation rate increases linearly with plasma density, suggesting that the near-surface concentration of oxidizing species scales with the surface flux of plasma electrons. Nitrogen is incorporated at the Si–SiO2 interface in direct proportion to the N2 partial pressure in the Ar/N2O remote plasma. Molecular NO does not react at the Si–SiO2 interface at 300 °C, its role in Si thermal oxynitridation notwithstanding. Nitrogen incorporation at the Si–SiO2 interface was also achieved by exposure of ultrathin Ar/O2 plasma oxides to a remote 20 W Ar/N2 plasma.

Oscillatory kinetics of anodic oxidation of silicon – influence of the crystallographic orientation

This work describes the oscillatory kinetics of the anodic oxide growth on silicon with crystallographic orientations (111) and (100). Although the oscillations are observed for two orientations if the experimental variables are properly chosen, their shape, amplitude and period are essentially different. It is shown that the oscillations are caused by a continuous growth of thin oxide layers at the sample surface and their peeling off.An analysis of the morphology of the samples and their kinetics of growth shows that the oscillatory anodization kinetics is a self-organizing phenomenon emerging as a result of collective interactions in the electrolyte/Si system. These interactions are influenced by the crystallography of silicon. The case of (111) Si shows the presence of the correlation links in a sequence of individual oscillations nearly two times longer than in the case of (100) Si . These differences are attributed to different mechanisms of the pore formation in (111) and (100) silicon wafers.

Effect of crystal orientation and doping on the activation energy for GaAs oxide growth by liquid phase method

We have investigated the oxide growth kinetics of near-room-temperature liquid phase chemical enhanced oxidation on differently oriented and doped GaAs substrates. Oxidation reactions have been studied by analyzing their activation energies and have been found to depend on the bond configuration of crystal planes. Experimental results indicate that the activation energies are independent of the doping of GaAs. The oxidation rates are dopant selective (n−:p+-GaAs∼4:1 at 30 °C under illumination) and sensitive to illumination (without:with illumination∼1:25 at 30 °C for a n+-doped GaAs). In the oxidation reactions, photogenerated holes are found to play an important role. Finally, we have proposed a mechanism based on the band bending and the carrier transport near the oxide-GaAs interface to interpret the experimental observations.

A study on the oxidation kinetics of silicon in inductively coupled oxygen plasma

The oxidation kinetics of silicon in inductively coupled oxygen plasma (ICP) was studied at temperatures ranging from 350 to 450 °C. The oxide growth kinetics was described by a linear-parabolic growth law, with a rapid initial growth and a negative linear-rate constant. Under oxygen pressure of 10 mTorr, the initial oxide growth at 350 °C (thickness below 25 nm) was faster than at 400 °C. An analysis of transverse-optical mode frequencies and etch rates indicated that the density of the surface oxide was lower than that of the bulk oxide. The oxidation kinetics was explained qualitatively by assuming that the ICP oxide consisted of a surface layer with a larger diffusion coefficient and a bulk layer with a smaller diffusion coefficient. On the other hand, the ICP oxidation of silicon with a thin chemical oxide showed a positive linear-rate constant and no surface layer effect, supporting the fact that the oxide grown by the ICP oxidation has a low-density surface layer with a larger diffusion coefficient.

Transmission electron microscope study of the dry oxidation kinetics of WSi2 on (001)Si and polycrystalline silicon

Cross-section transmission electron microscopy has been applied to study the growth kinetics of oxide of WSi2 on (001)Si and polycrystalline silicon (poly Si) in the dry oxidation process. The linear activation energy and the parabolic activation energy of WSi2 on (001)Si were found to be 0.8±0.2 and 1.0±0.2 eV for samples dry oxidized at 800–890 °C for 10–60 min, respectively. On the other hand, the linear activation energy and parabolic activation energy of WSi2 on polycrystalline silicon for samples dry oxidized at 800–890 °C for 10–60 min were 1.0±0.2 and 1.8±0.2 eV. The linear activation energy is attributed to the diffusion of Si atoms from the substrate to the reaction interface. The different parabolic activation energies of 1.0 and 1.8 eV for WSi2 on (001)Si and poly Si, respectively, indicate significant difference in diffusion of O2 through grown SiO2. It is conceivable that stress generated during oxidation and the amount of fluorine atoms, introduced during the low pressure chemical vapor deposition process, present in the silicide layer and grown oxide, can influence the oxide quality and oxidation kinetics.

X-ray spectroscopy of the oxidation of 6H-SiC(0001)

Chemically abrupt ${\mathrm{SiO}}_{2}/6\mathrm{H}\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{C}(0001)$ interfaces have been obtained after thin (\ensuremath{\cong}5 nm) oxide thermal growth of the Si-terminated face. The originality of the paper resides in a simultaneous use of standard technological conditions for this oxidation (dry ${\mathrm{O}}_{2}$ oxidation at 1 atmosphere and 1000 \ifmmode^\circ\else\textdegree\fi{}C) and in control and characterization of the starting substrates taken from in situ, ultrahigh vacuum-surface techniques. The oxidation of $3\ifmmode\times\else\texttimes\fi{}3$ Si-rich and $6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3}R30\ifmmode^\circ\else\textdegree\fi{}$ C-rich reconstructed surfaces is compared. In both cases no C-C bonds or C enrichment are observed at the ${\mathrm{SiO}}_{2}/\mathrm{S}\mathrm{i}\mathrm{C}$ interface by x-ray photoelectron spectroscopy $\mathrm{C}1s$ analysis, the C-C bonds of the initially graphitized C-rich surface being removed during the first nanometer oxide growth. The interfacial suboxide components with binding energy between the substrate and ${\mathrm{SiO}}_{2}\mathrm{}\mathrm{Si}2p$ features remain below our detection limit. X-ray photoelectron diffraction analyses indicate that, below the oxide layer, the ordering and polarity of the 6H-SiC(0001) are maintained. These results allow us to conclude that there is probably no fundamental contraindication to obtain nearly ideal ${\mathrm{SiO}}_{2}/\mathrm{S}\mathrm{i}\mathrm{C}$ interfaces on flat SiC terraces. Two growth regimes are observed in the oxide growth kinetics. They are discussed to determine the possible reasons of carbon exodiffusion or previously observed C enrichments at the ${\mathrm{SiO}}_{2}/\mathrm{S}\mathrm{i}\mathrm{C}$ interface.

Grain boundary character distribution in oxides formed on (100) and (111) nickel single crystals coated with ceria gel

A numerical analysis of texture data was conducted to assess the grain boundary character distribution in oxides formed at 1073 K on the (100) and (111) crystal faces of nickel coated with ceria gel. As input data were used the orientation distribution functions of oxide grains derived from three basic pole figures, measured by the X-ray technique. As an output of the calculations, the grain boundary misorientation functions and frequencies of coincidence site lattice boundaries were obtained. The results revealed that the substrate crystallographic orientation exerted an essential influence on oxide grain boundary structure. The presence of ceria introduced some changes; however, they are rather small and cannot explain the existing differences in oxide growth kinetics. An implication of this finding for the explanation of the `reactive element effect' is discussed.

Grain boundaries and growth kinetics of polycrystalline ferrimagnetic oxides with chemical additives

Grain boundaries and grain growth kinetics of two ferrimagnetic oxides, Y2Gd1Fe5O12 and Li0.3Zn0.4Fe2.3O4, modified by a sol–gel particulate coating process were investigated on the basis of their microstructural characteristics. Interestingly, the addition of small amounts of MnO2 and SiO2 using the sol–gel coating process led to different results for the two magnetic materials. In the case of Y2Gd1Fe5O12, the additives had a role as a grain growth inhibitor because Si-rich precipitates were segregated along the grain boundary and exerted a drag force against grain boundary movement. On the other hand, the same additives acted as an accelerator for grain growth by forming a glassy phase at the grain boundaries for Li0.3Zn0.4Fe2.3O4. The results were analyzed quantitatively by calculating activation energies for grain growth and grain boundary mobilities. For example, the calculated grain boundary mobilities, i.e., 5.6×10−15 m3/N s at 1400 °C for Y2Gd1Fe5O12 and 22.3×10−15 m3/N s at 1150 °C for Li0.3Zn0.4Fe2.3O4, supported the microstructural observation.

Wet oxidation of Ti34Si23N43

The wet oxidation of magnetron-sputtered x-ray-amorphous Ti34Si23N43 films at temperatures from 500 to 1000 °C and ambient pressure was investigated by backscattering spectrometry, x-ray diffraction analysis, and step profilometry. Up to 800 °C, the oxidation yields x-ray-amorphous oxide scales of atomic composition Ti20Si13O67. At 500 and 550 °C the oxide growth kinetics is parabolic. At 700 and 800 °C, the oxidation kinetics is well described by a logarithmic time dependence. At 1000 °C, the oxide scale has a layered structure with a crystalline TiO2 layer on top of Ti–Si–O.

Growth Kinetics Of SiO2 On (001)Si Catalyzed By Cu3Si At Elevated Temperatures

AbstractThe oxidation of Si catalyzed by 170-nm-thick Cu3Si at elevated temperatures has been investigated by transmission electron microscopy and Auger electron spectroscopy. For wet oxidation at 140–180 °C, the growth rate of the oxide layer was increased with the temperature. On the other hand, as the temperature was increased above 200 °C, the growth rate slowed down. The growth kinetics of oxide was investigated. Controlling mechanisms for the growth of oxide owing to the grain growth of Cu3Si are discussed. The activation energy for the linear growth of oxide was measured to be 0. 19 ± 0.1 eV.

Role of impurities on Mg surfaces under ambient exposure conditions

The long-term oxide growth kinetics under atmospheric ambient conditions has been studied for pure magnesium and several magnesium alloys. Oxide thicknesses in the range of 1–15 nm are measured using X-ray photoelectron spectroscopy, making use of the inelastic mean free paths for magnesium and MgO. On pure magnesium, the oxide growth rate is slow, following logarithmic kinetics during exposure periods as long as 10 months. On samples containing iron or manganese as inclusions, an increased oxidation rate was noted following exposure periods as short as several hours. Evidence of localised oxidation around such inclusions could be observed from secondary ion mass spectrometry (SIMS) images of the near-surface region. High purity aluminum–magnesium alloys exhibit lower oxide growth rates than pure magnesium; the initially thicker oxide film contains aluminum ions which are believed to increase the activation energy for ion movement.

Contact Electric Resistance (CER) Technique for In-Situ Characterisation of Surface Films

In this paper a new in situ contact electric resistance (CER) technique for the measurement of electric resistance of surface films is described in detail. The applicability of this technique to characterise electrochemical phenomena is evidenced. Also the complementary nature of the CER technique to other electrochemical techniques is shown. The CER measurement enables monitoring of e.g. adsorption, oxide growth and reduction processes. It can also be applied at negative potentials where hydrogen evolution occurs and in electrolytes which contain a redox-couple having a significant exchange current density. The application areas of the CER technique include e.g. investigation of the role of adsorption in electrocatalysis, characterisation of conducting polymers, optimisation of electroplating processes, investigation of the effectiveness of inhibitors and monitoring of the kinetics of oxide growth in high temperature water. Correlation of CER results with practical corrosion phenomena such as weight gain and stress corrosion cracking susceptibility have been established. In this paper CER results on AISI 316 stainless steel in a borate buffer solution at 200°C are compared with a current-voltage curve and capacitance measurements in the same environment. As another example the electric resistance of the surface film on nickel and Inconel 600 are shown as a function of time in a high temperature (320°C) aqueous environment with varying dissolved hydrogen content.

Measurement of oxide film growth on Mg and Al surfaces over extended periods using XPS

X-ray photoelectron spectroscopy (XPS) has been used to follow oxide film growth on pure magnesium and pure aluminum surfaces across 12 orders of magnitude exposure to water vapour and humid air. Both Mg and Al exhibited logarithmic-type oxide growth kinetics. Oxide film growth was observed to continue well into the ambinent exposure range, suggesting the possibility for modifying the oxide film chemistry while still under atmospheric conditions. The chemistry of the films was monitored as a function of exposure by examining the changes in the core-level O 1s spectra and the associated oxidised metal/oxygen stoichiometry. It was observed that both Mg and Al surfaces initially formed partially hydrated oxide surfaces which became progressively more hydrated at longer exposures.

Limit to extent of formation of the quasi-two-dimensional oxide state on Au electrodes

Potentiostatic polarization of Au electrodes in 0.5 M aqueous H2SO4 and KOH solutions at polarization potentials Ep between 2.00 and 2.43 V (RHE) for polarization times tp up to 104 s leads to the formation of thick oxide films which comprise up to four oxide states, designated OC1, OC2, OC3 and OC4, as resolved from linear sweep voltammetry oxide reduction profiles. The oxide growth proceeds by inverse logarithmic kinetics with two distinguishable kinetic regions leading to linear relations between 1/qox and log tp. The first 1/qox vs. log tp linear region corresponds to development of the quasi-2D state (OC1) and the very initial growth of the OC2 state, and the oxide growth in this tp domain is slow. Further growth of OC2 and formation of the OC3 and OC4 states is significantly faster. The oxide growth kinetics change when 1/qox reaches a value of ca. 0.10 mC−1 cm2. In situ ellipsometry measurements indicate the presence of two distinct layers within the oxide films, the inner layer designated α and the outer one designated β. The α film corresponds to the OC1 state whereas the β film corresponds to the OC2, OC3 and OC4 states. The OC1 state reaches a limiting thickness of 3 equiv. monolayers of AuO or Au(OH)2 in aqueous H2SO4 and 1 monolayer of AuO or Au(OH)2 in aqueous KOH. The β state which resides on top of the α one grows without reaching any limiting thickness and up to 100 equiv. monolayers of Au2O3 or Au(OH)3, depending on the electrolyte composition, can be formed under the conditions described in the present paper.

Atomically flat, ultrathin-SiO 2/Si(001)interface formation by UHV heating

Conventional wet cleaning and ultrahigh vacuum (UHV) heated cleaning prior to thermal oxidation were compared with respect to their effects on extremely thinSiO 2/Si(001)interface roughness. Atomically flatSiO 2/Si(001)interfaces were realized by preparing theSi(001)−2 × 1surface in UHV followed by thermal oxidation. This planarization is significant in the range of oxide thickness ( T ox < ∼ 9nm). As for the ‘wet-cleaned’ surfaces, a wide variety of the interface roughness was observed at T ox < ∼ 4nmwhich corresponds to the ‘initial oxide thickness ( T io)’ which appeared in the oxide growth kinetics. The electron scattering caused by the interface roughness might degrade the inversion electron mobility for the ‘wet-cleaned’ sample at T ox < T io.

Rapid thermal N2O oxynitride on Si(100)

High-resolution x-ray photoelectron spectroscopy (XPS) in conjunction with secondary-ion-mass spectrometry was used to study the chemical nature and distribution of N in oxynitride films formed by rapid thermal N2O processes (RTPs) or conventional furnace methods. The kinetics of furnace oxide growth in N2O are slower than that in O2. During reoxidation the oxidation rate increased to that in pure O2 and the N in the SiO2–Si interface region is displaced into the bulk of the oxide. High-resolution synchrotron Si 2p core-level photoemission spectroscopy (PES) was used to study the oxide–Si(100) interface suboxide structures produced by RTP with and without the presence of N. XPS N 1s studies indicated that there are two types of N in the RTP oxynitride films. The chemical bond configuration of the first type of N is similar to that of N in Si3N4 and is mainly distributed within the first 1 nm from the interface. The second type of N is distributed mainly outside of the first 1 nm region, and the N is likely bonded to two Si and one oxygen atom. PES studies showed that Si formed suboxides with oxygen at the interface for all oxynitride films. It is found that there is no change in the Si+1 structure while there is a dramatic decrease in the Si+2 and Si+3 states with the inclusion of N in the oxide. Both the XPS and PES results are explained in terms of a strain reduction as N is incorporated in the film near the interface region, where Si3N4 functions as a buffer layer which reduces the stress caused by the large Si lattice mismatch between the bulk Si and the oxide overlayer. About 1/5 of the Si+2 and 1/3 of Si+3 atoms at the SiO2–Si interface have been replaced by the Si3N4 buffer layer at the oxynitride–Si interface.

Low-temperature oxidation of Si in a microwave electron cyclotron resonance excited O2 plasma

The kinetics of the oxidation of Si in a microwave excited O2 plasma have been studied at temperatures in the range of 260–390 °C. The substrate was positively biased and the total electron and O− ion current maintained constant by application of an electric field ∼5 MV cm−1 across the growing oxide. This field was established for thicknesses ≥10 nm. Total current densities were 2–6 mA cm−2 while the O− current was estimated to be 0.02–0.04 mA cm−2. Oxide growth kinetics are discussed in terms of a recent physical model. Chemical etch rates and refractive indices were measured and although similar to those of thermal oxide, infrared absorption spectra suggest that the internal network structure is not the same.

Nanometer-scale field-induced oxidation of Si(111):H by a conducting-probe scanning force microscope: Doping dependence and kinetics

Hydrogen-terminated Si(111) was patterned on the nanometer scale by field-induced oxidation using a biased conducting-probe scanning force microscope. The kinetics of oxide growth as well as its dependence on doping are investigated. Field-induced oxidation is observed for voltages exceeding a doping dependent threshold above which oxidation kinetics follows a power law.