Interfacial Oxide Film Research Articles

NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure

The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Mössbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using 57Fe-CEMS. An iron oxide phase (Fe3+4Fe2+1O7), as thick as 31 Å, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples.

Polyaniline inhibition of filiform corrosion on organic coated AA2024-T3

Dispersions of the polyaniline emeraldine salt (ES) of paratoluene sulphonic acid (PAni-pTS) effectively inhibit filiform corrosion (FFC) affecting polyvinyl butyral (PVB) coated AA2024-T3 aluminium alloy. An in-situ scanning Kelvin probe (SKP) technique is used to study the effect of systematically varying PAni-pTS volume fraction ( ϕ pa) on FFC initiation and propagation. For ϕ pa < 0.15, there is no evidence of FFC inhibition and E corr values recorded for the intact coated aluminium ( E intact) remain similar to those measured for unpigmented PVB. At ϕ pa ≥ 0.15, a marked rise in E intact is observed, FFC propagation rates decrease and significant oxide growth is observed at the coating-metal interface. For emeraldine base (PAni-EB)-containing coatings, there is no evidence of interfacial oxide film formation, no ennoblement of E intact and minimal inhibition of FFC. Conversely, when a PAni-pTS induced oxide covered surface is re-coated using unpigmented PVB and FFC is initiated as per normal, a substantial reduction in the rate of FFC propagation is observed. It is therefore proposed that inhibition of FFC by PAni-pTS arises principally as a result of the protective nature of the oxide film formed at the metal-coating interface.

Effects of varying interfacial oxide and high-k layer thicknesses for HfO2 metal–oxide–semiconductor field effect transistor

A metal–oxide–semiconductor capacitor and field effect transistor with a hafnium oxide (HfO2) dielectric have been fabricated. Various thicknesses of interfacial oxide and HfO2 film have been used. The results show that the flatband voltage changed due to the change in the physical thickness of the HfO2 film, and not that of the interfacial oxide layer. In addition, the effective channel electron mobility depends on both the amount of fixed charges and the distance from the fixed charges to the Si surface. The results also suggest that the fixed charges are rather uniformly distributed throughout the bulk of high-k layer.

Effects of Environmental Factors on the Electronic Properties of Interfacial Oxide Film on 304L Stainless Steel in High Temperature Pure Water

The electronic properties of the interfacial oxide film formed on 304L stainless steel in high temperature water are investigated by contact electric resistance (CER) measurements. Tests are performed in pure water with a wide range of dissolved oxygen (DO) content at 200, 250, and 288°C. The electrochemical potential (ECP) moves in the noble direction and CER increases when increasing DO. Results show that DO content has a dominant effect on the electronic properties of oxide film. The change of oxide film properties can also be attributed to the variation of the electrochemical potential, which is directly affected by DO content. Critical potentials exist for the formation and reduction of oxide films in high temperature water. Multiple steps are found for the reduction of oxide films due to de-aeration in 200, 250, and 288°C water, implying the presence of multiple-layer interfacial oxide films. The film reduction process is relatively slower than the film formation process. Present results show that even in high purity water, a moderate change of DO content can result in different surface conditions. Dissolved hydrogen has a moderate effect on interfacial surface films in deaerated water. In-situ monitoring of the oxide film properties by CER technique provides information on the interfacial reactions that are related to the SCC behavior of materials in high temperature water environments.

Voltammetry, nanogravimetry and double-layer capacitance studies on chemisorption of Cl − and Br −, competitive with potential-dependent electrosorption of O species at Pt electrodes

The change of double-layer capacitance ( C dl) behaviour of polycrystalline Pt electrodes upon controlled formation of thin oxide films is evaluated. The capacitance behaviour of the oxide film interface with aqueous H 2SO 4 and HClO 4 is quite different from that at the unoxidized Pt surface, while the presence of Cl − ion lowers C dl of the latter interface. This indicates that extrapolation of C dl data for the so-called ‘double-layer region’ into potential ranges where an oxide film exists, would be a quite unreliable basis for double-layer corrections to recorded transient data. The presence of Cl − or Br − ions causes appreciable lowering of C dl until onset of surface oxidation. By means of sensitive EQCN nanogravimetry measurements, the competitive effects of Cl − or Br − adsorption on oxide film formation at Pt can be quantitatively evaluated. Interestingly, adsorption of Cl − leads to net negative mass changes while Br − causes net positive ones over the oxide region. These results are interpreted in terms of specific mass changes due to diminution of O coverage concomitant with increasing halide coverage as a function of potential and Cl − or Br − concentration.

Electrochemical impedance characteristics of pure Al and Al–Sn alloys in NaOH solution

Electrochemical impedance analysis of pure Al and Al–Sn alloys in alkaline solution is reported. The impedance spectrum of pure Al is found to consist of two intersecting capacitive semicircles with a loop at intermediate frequencies. The capacitive semicircles occurring at the high and low frequencies are due to the charge transfer reaction at the metal/surface oxide film interface and the dielectric properties of surface oxide film, respectively. The inductive loop at medium frequencies results from the surface charge build-up at the metal/oxide film interface caused by the rate difference of introduction into and transport through the oxide film of Al 3+ ions. Al–Sn alloys show discrete impedance spectra according to their electrode potential. In the potential range where Al is in the active state and Sn is in immunity, the impedance spectra of Al–Sn alloys are composed of only a capacitive semicircle and then converted into a reverse semicircle indicating a negative polarization resistance with the electrode potential. In addition, Al–Sn alloys have the same impedance spectra as that observed for pure Al at the potentials in which Sn is dissolved.

The effect of interface roughness and oxide film thickness on the inelastic response of thermal barrier coatings to thermal cycling

The effects of interfacial roughness and oxide film thickness on thermally-induced stresses in plasma-sprayed thermal barrier coatings subjected to thermal cycling are investigated using the recently developed higher-order theory for functionally graded materials. The higher-order theory is shown to be a viable alternative to the finite-element approach, capable of modeling different interfacial roughness architectures in the presence of an aluminum oxide layer and capturing the high stress gradients that occur at the top coat–bond coat interface. The oxide layer thickness is demonstrated to have a substantially greater effect on the evolution of residual stresses than local variations in interfacial roughness. Further, the location of delamination initiation in the top coat is predicted to change with increasing oxide layer thickness. This result can be used to optimize the thickness of a pre-oxidized layer introduced at the top coat–bond coat interface in order to enhance TBC durability as suggested by some researchers. The results of our investigation also support a recently proposed hypothesis regarding delamination initiation and propagation in the presence of an evolving bond coat oxidation, while pointing to the importance of interfacial roughness details and specimen geometry in modeling this phenomenon.

Contribution of interface roughness to the infrared spectra of thermally grown silicon dioxide films

Interfacial oxide structures were studied by Infrared reflection absorption spectroscopic analysis. The longitudinal optical mode of the interfacial oxide films arose with lower frequencies and wider widths. We assumed and later verified that these changes resulted from the contribution of interfacial roughness. We therefore examined the contribution of interfacial roughness to the infrared spectra using the effective medium approximation model and via infrared spectra simulation. The experimental results explained by a model of that interface had an atomically roughness of within 1 nm and chemical structure changes effectively little fluctuation.

Hydrous Ir oxide films: the mechanism of the anodic prepeak reaction

The origin and significance of the anodic prepeak (peak A0), seen in cyclic voltammetric studies of hydrous Ir oxide films in acidic solution just prior to the large Ir(III)/(IV) redox peaks (A1/C1), has been examined in this work. By also studying only very thin films, a corresponding cathodic feature (peak C0) has also been identified. The pH dependence of the A0/C0 peaks, assumed to also depict the Ir(III)/(IV) process, has been examined in sulfuric acid solutions, indicating that a ca. −80 mV shift per pH unit applies to this reaction. By also taking into consideration the measured in situ mass changes as the potential is scanned through the A0/C0 peaks, it is shown that these peaks are associated with a greater involvement of anions and more extensive water exchange than is the reaction in the main A1/C1 peaks. Other results also indicate that the film sites that react in the A0/C0 peaks are located deep within the oxide film, likely near the Ir – oxide film interface. Keywords: Ir oxide, hydrous oxide films, cyclic voltammetry, quartz crystal microbalance (QCMB), prepeak, pH dependence, electrochemistry.

Studies of Adhesive Delamination Using DC-Resistance Measurement

Abstract Delamination of three different automotive epoxy adhesives (A, B, and D) from two different steel substrates (cold-rolled steel and electrodeposited zinc steel) upon exposure to distilled water and a 1.0 M NaCl solution was studied using DC-resistance measurements. The DC-resistance measurements were taken on sandwich adhesive bonded specimens having different combinations of adhesive and steel metal substrates upon exposure to a test solution. The measurements were taken on: (i) electrodeposited zinc steel substrates bonded by adhesives A and D in distilled water; (ii) electrodeposited zinc steel substrates bonded by adhesives B and D in a 1.0 M NaCl solution: and (iii) cold-rolled steel substrates bonded by adhesives A and D in a 1.0 M NaCl solution. Four stages of the resistance change across the metal/adhesive/metal specimens were proposed, corresponding to the different stages of bonding degradation. It was found that the initial resistance decrease across an adhesive-bonded specimen was governed by the concentration of the electrolyte produced in the adhesive matrix. The more the water-soluble fillers dissolved in water inside the adhesive, the higher the concentration of the electrolyte and the lower the resistance across the specimen. Hence, the amount of water required to dissolve the water-soluble fillers was governed by the water absorption rate and the rate of adhesive degradation. Adhesive delamination occurred when sharp resistance fluctuations were detected across an adhesive-bonded specimen. The sharp resistance fluctuations were a result of the consecutive breakdown and formation phenomenon of the interfacial secondary oxide or hydroxide film. The magnitude of the resistance fluctuations increased with the degree of adhesive delamination and the area of oxide or hydroxide film breakdown. Anodic delamination was found to occur in the metal/adhesive/ metal specimens according to the crevice corrosion mechanism. The degree of anodic delamination depended on the nature of the secondary oxide or hydroxide film at the adhesive/substrate interface.

Electrochemical lithium intercalation reaction of anodic vanadium oxide film

The electrochemical lithium intercalation reaction of anodic vanadium oxide films in 1 M LiClO 4 propylene carbonate solution has been investigated by the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) as a function of electrode potential. Measured impedance spectra were analysed using the complex non-linear least-squares (CNLS) fitting method. The impedance spectra measured in the potential range from 3.6 to 2.6 V Li/Li + showed that the electrochemical intercalation reaction of lithium ions into the anodic vanadium oxide film consists of three consecutive steps of charge transfer at the electrolyte-oxide film interface, lithium ion incorporation into the oxide film and diffusion through the oxide film. The charge transfer reaction at the electrolyte-anodic vanadium oxide film interface is mainly affected by the valence change of vanadium ions in the anodic vanadium oxide film. In the electrode potential range from 3.0 to 3.6 V Li Li + , i.e., lower lithium content ( δ=0−1) of the oxide film, intercalated lithium ions are highly accumulated in the near-surface region of the anodic vanadium oxide film. The component diffusivity of lithium in the oxide film was determined to be 10 −12–10 −14 cm 2s −1 in the lithium content range investigated, owing to the increased interaction between intercalated lithium ions.

Interface evolution and epitaxial realignment in polycrystal/single crystal Si structures

Our recent work on the poly/single crystal Si interface evolution and on the epitaxial realignment under high temperature (∼ 1000°C) rapid thermal annealing is reviewed. The roles of the mucrystalline morphology, of the interfacial native oxide film, of the doping level and of the processing temperature on the realignment kinetics are addressed. Two different realignment modes are observed. For undoped layers a quasi planar interface motion occurs, while in highly doped polycrystalline layers the realignment proceeds via the formation of epitaxial columns and their lateral growth. These two different modes arise from the doping enhancement of the interface kinetics. It is shown that these processes can be interpreted within an Avrami-Mehl-Johnson nucleation and growth scheme. In the early stages of interface realignment the process is controlled by oxide clustering, arising from the evolution of the native oxide layer, and by the density of grain boundaries intersecting the interface with the single crystal. Once nucleated at specific sites the epitaxial front can then proceed, the kinetics and mode of realignment depending on the density of nucleation sites and on the growth velocity. It is also demonstrated that when narrow (∼ 0.25 μm) polycrystalline strips defined by oxide layers (as in real devices) are used in place of infinite planar layers the realignment mode and kinetics change due to the presence of size effects. These data are presented and their implications for applications to bipolar devices are discussed.

Process and device characterization for a 30-GHz f/sub T/ submicrometer double poly-Si bipolar technology using BF/sub 2/-implanted base with rapid thermal process

Process and device parameters are characterized in detail for a 30-GHz f/sub T/ submicrometer double poly-Si bipolar technology using a BF/sub 2/-implanted base with a rapid thermal annealing (RTA) process. Temperature ramping during the emitter poly-Si film deposition process minimizes interfacial oxide film growth. An emitter RTA process at 1050 degrees C for 30 s is required to achieve an acceptable emitter-base junction leakage current with an emitter resistance of 6.7*10/sup -7/ Omega -cm/sup 2/, while achieving an emitter junction depth of 50 nm with a base width of 82 nm. The primary transistor parameters and the tradeoffs between cutoff frequency and collector-to-emitter breakdown voltage are characterized as functions of base implant dose, pedestal collector implant dose, link-base implant dose, and epitaxial-layer thickness. Transistor geometry dependences of device characteristics are also studied. Based on the characterization results for poly-Si resistors, boron-doped p-type poly-Si resistors show significantly better performance in temperature coefficient and linearity than arsenic-doped n-type poly-Si resistors. >

Kinetic and structural study of the epitaxial realignment of polycrystalline Si films

The epitaxial realignment of undoped and As doped polysilicon films onto crystalline silicon substrates induced by high-temperature rapid-thermal annealing has been investigated. It is shown that the realignment mode and the kinetics of the process are intimately related to the microcrystalline structure of the layers under investigation, to the morphology of the native oxide film present at the interface, and to the presence of As atoms dispersed in the deposited layers. For layers having fine grain dimensions, compared to the film thickness, the realignment takes place via the motion of the crystal-polysilicon interface towards the surface. This is observed in undoped layers and in layers which have been subjected to a high-temperature anneal before As doping. The preimplant anneal disrupts the interfacial oxide film and reduces the thermal cycle needed to complete the realignment of the polysilicon layers. In layers which have not experienced any thermal treatment before As doping, it is seen that the grain size first increases to dimensions on the order of the film thickness, and the realignment transformation then proceeds by lateral growth of epitaxial columns in a manner similar to secondary grain growth. The kinetics of both realignment modes are thermally activated and the atomic limiting processes have been tentatively identified to be As diffusion in bulk Si for As doped layers and Si self diffusion for undoped films. The effect of the microcrystalline structure on the realignment kinetics is attributed to its relationship with the driving force governing the realignment transformation.

Epitaxial realignment of polycrystalline Si layers by rapid thermal annealing

It is shown that both the kinetics and the mode of realignment of As doped polysilicon films deposited onto crystalline silicon substrates, strongly depend on the morphology of the interfacial native oxide film. During rapid thermal annealing the as deposited and doped polycrystalline layers realign via the lateral growth of large epitaxial columns in a way similar to secondary recrystallization. In layers submitted to a high temperature anneal before the As implantation, the realignment occurs by the planar motion of the whole interface towards the surface of the layers, and can be achieved at low annealing temperatures and for short times, with a reduced redistribution of the dopant atoms.

Disbondment Mechanisms for a Heat Shrink Polyethylene Coating on a Cathodically Protected Hot Pipeline

Abstract Interfacial adhesive failure of a pipeline coating was found to be related to the operating temperature of the pipeline, the presence of moisture at the coating/steel interface and cathodic polarisation of the steel. The application of cathodic protection was found to be more detrimental to a pipeline coating than was the immersion of the coating specimens in alkaline environments without polarisation. It is suggested that in the system examined cathodic disbondment is initiated at a coating holiday by the electrochemical reduction of Fe3O4 in the interfacial oxide film and that propagation of the disbondment is associated with electrocapillary action which reduces the surface tension between the steel and the crevice solution. This process increases the thermodynamic disbonding force between the adhesive and the steel in the aqueous environment.

Origin of ion beam mixing effects on morphological features in solid-phase titanium silicide formation

The origin of the ion beam mixing effect, which causes the formation of smooth silicide films, is investigated for the Ti/Si solid-phase silicidation reaction. Ge ion beam mixing of a conventional Ti/c-Si structure with an oxide-contaminated interface shows an obvious effect when the implant conditions are such that the Ti/Si interface is amorphized. On the other hand, silicidation without ion mixing for Ti/a-Si and Ti/c-Si structures with oxide-free interfaces, prepared by sequential deposition in UHV, results in smooth and rough film surfaces, respectively. This strongly suggests that the ion beam mixing effect primarily comes from the amorphization of the Si substrate surface rather than the destruction of the interfacial oxide film.

Dynamic interfacial processes at the amorphous silicon/aqueous electrolyte boundary

The photoelectrochemical behaviour of amorphous hydrogenated silicon (a-Si:H) in aqueous electrolytes has been investigated and the light-induced formation of interfacial oxide films and their dissolution in fluoride-containing solutions have been studied in detail. Three distinctively different surface conditions can be prepared: (i) reduced surfaces which are free of oxidized silicon; (ii) surfaces with natural oxides (d = 1.5 run); and (iii) passivated surfaces exhibiting thick electrochemical oxide films. Photocurrent transients exhibiting a photocurrent doubling, a film formation and a passivation regime are presented. The electrodes under different surface conditions have been analysed by X-ray photoelectron spectroscopy (XPS). Evidence for a non-stoichiometric silicon-rich SiO x, layer, as observed on thermal oxides on silicon, was found. The photoelectrosynthesized oxide films incorporate substantial amounts of water and/or hydroxyl groups as demonstrated by the Ol s binding energy at E B= 533 eV. The photocurrent transients of a-Si:H are compared with those of crystalline silicon. Differences in the temporal evolution of the currents are interpreted assuming a different film growth mechanism. The electronic properties of the samples with differently conditioned surfaces have been investigated. Under reducing conditions at negative potential, a photoconductive gain effect leading to quantum yields of Q > 10 is observed. Schottky barriers have been fabricated and analysed. Generally, oxide-free, slightly fluoride-covered surfaces (≈10% of an atomic layer) show superior electronic behaviour compared to oxidized samples.

Interfacial phenomena involving liquid metals and solid oxides in the Mg–Al–O system

The wetting of ceramic surfaces by aluminum alloys has been reexamined using a chemical system where interfacial reactions and oxide film effects could be isolated. The system Al–Mg–O was chosen since it is technologically important and high-purity, well-characterized materials are readily available. Magnesium alloyed with the aluminum sessile drop and silicon picked up from the experimental apparatus cause an initial reduction in contact angle by altering the protective nature of the oxide film formed on the sessile drop. Evidence of spreading is observed as an intermediate process in the reactive sessile drop pairs. Reaction products formed between the Al–Mg alloys and sapphire (Al2O3), spinel (MgAl2O4), or periclase (MgO) can be interpreted with predicted phase equilibria and the measured loss of magnesium from the sessile drop. Only the rate of the periclase alloy interaction was rapid enough to result in a continuous product layer after 24 h at 800 °C. The volatilization of all of the magnesium from the sessile drop resulted in the formation of a true Al–Al2O3interface. The contact angle for a true Al–Al2O3interface is 88 ± 5 deg at 800 °C. The liquid-solid interfacial energy is 1688 ergs/cm2.

An Epitaxial Regrowth of Polysilicon to Single Crystal Silicon By H2 Annealing Process

ABSTRACTSi epitaxial regrowth was realized through the thick interfacial oxide films of up to 2 nm by H2 annealing. The epitaxy took place in an anomorous region when the oxide was reduced to about a half of its initial peak height, indicating that about a half of the interfacial oxide films in areawise was completely reduced. In this region, redis-tribution or diffusion of super-saturated oxygen was also observed.A schematic model of the epitaxial regrowth by H2 annealing is presented.