The effect of cerium and lanthanum surface treatments on early stages of oxidation of A361 aluminium alloy at high temperature

X-ray photoelectron spectroscopy analysis has been used to study the surface of A361 aluminium alloy after electrodeposition of cerium and lanthanum compounds followed by oxidation tests in air at 100-500 °C for 2 h. Cerium and lanthanum oxide deposits are found on the β-AlFeSi second phase particles and to a lesser extent on the eutectic Al-Si areas, while the α-Al phase is covered with a thin aluminium oxide film. This uneven deposition may be related either to a preferential nucleation and growth process on active interfaces or to the differing electrical conductivity of the phases and intermetallic compounds of the alloy. Initial stages of oxidation of A361 alloy disclosed thickening of the aluminium oxide layer and Mg enrichment at the surface, especially above 400 °C. Rare earth deposits revealed two different effects: reduced Mg diffusion and enhanced thickening of the aluminium oxide film. A distinctive behaviour of Ce oxide appears at 300-500 °C related with Ce(III) to Ce(IV) transition.     

Thermal conductivity of isotopically enriched Si: revisited

The thermal conductivity of isotopically enriched ²⁸Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of four samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched ²⁸Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 10±2%. This finding is in disagreement with an earlier report by Ruf et al. At ∼26 K the thermal conductivity of ²⁸Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of ∼8 for a 99.982% ²⁸Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be ∼3% lower than the values recommended in the literature.     

Electrical Characterization of Metal-Insulator-Metal Capacitors with Atomic-Layer-Deposited HfO2 Dielectrics for Radio Frequency Integrated Circuit Application

Metal-insulator-metal （MIM） capacitors with atomic-layer-deposited HfO2 dielectric and TaN electrodes are investigated for rf integrated circuit applications. For 12nm HfO2, the fabricated capacitor exhibits a high capacitance density of 15.5fF/μm2 at 100kHz, a small leakage current density of 6.4 × 10^-9 A/cm^2 at 1.8V and 125℃, a breakdown electric field of 2.6 MV//cm as well as voltage coefficients of capacitance （VCCs） of 2110ppm/V^2 and -824 ppm/V at 100kHz. Further, it is deduced that the conduction mechanism in the high field range is dominated by the Poole-Frenkel emission, and the conduction mechanism in the low field range is possibly related to trap-assisted tunnelling. Finally, comparison of various HfO2 MIM capacitors is present, suggesting that the present MIM capacitor is a promising candidate for future rf integrated circuit application.     

Initial oxidation of Mn surface studied by ultraviolet photoelectron spectroscopy and metastable induced electron spectroscopy

Metastable induced electron spectroscopy (MIES) was combined to ultraviolet photoelectron spectroscopy (UPS) to study the initial steps of manganese oxidation. Oxygen exposure directly led to the formation of MnO with no intermediate states. The MnO feature saturation observed by MIES and UPS techniques showed noticeable differences and proved the formation of several oxide layers. The oxidation kinetics was studied by measuring MnO features by UPS, which depend on the surface coverage by oxygen. We observe a decrease of oxygen adsorption probability with oxygen exposure. Oxidation proceeds by oxygen dissolution into the first layers to form a three-dimension MnO. This hypothesis was confirmed by our work function measurements.     

Heat capacity of isotopically enriched Si, Si and Si in the temperature range 4 K<T<100 K

The heat capacity of isotopically enriched ²⁸Si, ²⁹Si, ³⁰Si samples has been measured in the temperature range between 4 and 100 K. The heat capacity of Si increases with isotopic mass. The values of the initial Debye temperature Θ_D(0) for the three isotopic varieties of silicon have been determined. Good agreement with the theoretical dependence of the heat capacity on isotopic mass has been found.     

Effects of interface on the dielectric properties of Ba0.6Sr0.4TiO3 thin film capacitors

Ba_0.6Sr_0.4TiO₃ thin films were deposited on Pt/SiO₂/Si substrate by radio frequency magnetron sputtering. High-resolution transmission electron microscopy (HRTEM) observation shows that there is a transition layer at BST/Pt interface, and the layer is about 7-8 nm thickness. It is found that the transition layer was diminished to about 2-3 nm thickness by reducing the initial RF sputtering power. X-ray photoelectron spectroscopy (XPS) depth profiles show that high Ti atomic concentration results in a thick interfacial transition layer. Moreover, the symmetry ν of ?_r-V curve of BST thin film is enhanced from 52.37 to 95.98%. Meanwhile, the tunability, difference of negative and positive remanent polarization (P_r), and that of coercive field (E_C) are remarkably improved.     

Effects of anodizing conditions on bond strength of anodically oxidized film to titanium substrate

The bond strength of the oxide film to the titanium substrate and its inherent structural characteristics are very important preconditions for the success of titanium implants. The purpose of this study was to evaluate the micro-morphologies, crystalline structures, and bond strengths of the anodically oxidized films formed on titanium with the variation of electrolytes and applied current densities. In contrast to the specimens produced using sulfuric acid as the electrolyte, those produced using phosphoric acid showed quite different shapes and densities of the pores as the applied current densities were varied. The oxide films anodized in sulfuric acid consisted of anatase and rutile TiO₂, whileTiP₂O₇ was predominantly formed on the Ti surfaces anodized using phosphoric acid as the electrolyte. The oxide films, which did not experience spark deposition showed amorphous shape and their bond strengths were significantly lower than those of the other groups (p < 0.05). Those specimens which experienced initial spark deposition with a low current condition showed the highest bond strengths (34.2 MPa) within each electrolyte sub-set. The growing rates of the oxide film thicknesses in relation to the electric current changes varied according to the type of electrolyte, and the oxide film thickness influenced the bond strength.     

A combined study of the oxidation mechanism and resistance of AISI D6 steel exposed at high temperature environments

In this work it is thoroughly examined the oxidation performance of D6 tool steel under isochronal and isothermal oxidations. Isochronal oxidation tests, from ambient temperature to 1000 °C, revealed the oxidation rate of the coupons at different temperatures. Four different temperatures were selected for the isothermal oxidation test, which correspond to different oxidation rates. The oxidation and the examination of the samples were accomplished by thermogravimetric analysis (TG) in air with which the mass gain of the samples due to oxidation was simultaneously acquired. The samples were, also, examined by scanning electron microscopy (SEM), in order to observe their surface before and after the oxidation tests. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used for the accurate identification of the as formed oxides. The results revealed that in every case two distinct layers of oxides were formed while their composition was different, depending on the temperature of oxidation. Furthermore, the thickness of the as formed oxides is increased when the oxidation is performed at higher temperatures.     

Photoacoustic measurements of the thermal properties of AlyGa1-yAs alloys in the region 0<y<0.5

y Ga_1-yAs alloys grown by liquid phase epitaxy on GaAs substrates, by means of the open photoacoustic cell detection technique and the temperature-rise method under continuous light illumination. The values of the thermal conductivity, diffusivity and specific heat were obtained in the 0<y<0.5 region, where the Al_yGa_1-yAs band gap is mainly direct. The technique presented here is based upon an effective sample model which is shown to be suitable for the determination of the thermal properties of two layer semiconductor specimens. Received: 15 November 1996/Accepted: 5 March 1997     

AC plasma electrolytic oxidation of magnesium with zirconia nanoparticles

The incorporation of monoclinic zirconia nanoparticles and their subsequent transformation is examined for coatings formed on magnesium by plasma electrolytic oxidation under AC conditions in silicate electrolyte. The coatings are shown to comprise two main layers, with nanoparticles entering the coating at the coating surface and through short-circuit paths to the region of the interface between the inner and outer coating layers. Under local heating of microdischarges, the zirconia reacts with magnesium species to form Mg₂Zr₅O₁₂ in the outer coating layer. Relatively little zirconium is present in the inner coating layer. In contrast, silicon species are present in both coating layers, with reduced amounts in the inner layer.     

Dielectric relaxation measurements on nonlinear side-chain polymers

Dynamic dielectric relaxation measurements in the frequency range from 0.001 Hz to 5 kHz have been performed on an amorphous nonlinear optical side-chain polymer, containing the active molecule 4-dimethylamino-4-nitrostilbene as pendant group. The results yielded the relaxation times of the group in the temperature region from 20° below to 40° above the glass-transition temperature of the polymer. The temperature dependence could be described well by the Williams-Landel-Ferry (WLF) equation. It is shown that the relaxation times have a distribution, which could be fit to the form of Cole and Cole with a parameter =0.55. Consequently a substantial part of the active molecules will not be aligned when the polymer is subjected to a poling procedure.     

Phase evolution of an aluminized steel by oxidation treatment

Effects of temperature and time on the microstructure and phase evolution for different thermal treatments were investigated with respect to the measurement of intermetallic layer thickness, phase identification and microhardness distribution in the aluminized zone of a steel substrate. The intermetallic phases present in the aluminized region after hot dip aluminizing is mainly Fe₂Al₅. The thickness of the intermetallic layers increases with increasing oxidation temperature and time. In the oxidation treatments of the aluminized steel in air, the initial Fe₂Al₅ phase remains at the temperature below 950 °C in 2-h, and the Fe₂Al₅ phase is completely transformed into low iron content Fe-Al intermetallics due to oxidation at 950 °C for 4 h. However, the Fe₂Al₅ phase remains in the outer layer of the aluminized samples diffusion-treated in vacuum regardless of diffusion time. The microhardness values of the Al₂O₃ and the intermetallic Fe₂Al₅, FeAl₂, FeAl and Fe₃Al phases are HV1150, HV1010, HV810, HV650 and HV320, respectively. The oxide layer formed on the steel substrate has an extremely fast adherence to the steel substrate and excellent properties of thermal shock resistance, high temperature oxidation resistance and anti-liquid aluminum corrosion.     

Dynamic and static contributions to the zero-field splitting term of divalent nickel in fluosilicate crystals

Previously published electron paramagnetic resonance (EPR) data for Ni²⁺(3d⁷) in hydrated and deuterated crystals of zinc and nickel fluosilicate have been re-analyzed to separate the static and dynamic contributions to the fine-structure (or axial zero-field-splitting) term D in the spin-Hamiltonian. While the Debye parameters of ZnSiF₆·6H₂O and ZnSiF₆·6D₂O were determined in an earlier low-temperature study¹, those of the undiluted nickel crystals, for which good data between 4 and 77 K is lacking, have been estimated here by comparison of the data above 60 K with those for the corresponding zinc compounds. The numerical results indicate that the measured values of D are composed of a negative dynamical contribution produced by the rotational motions of the water ligands, together with both negative and positive static contributions produced by the water ligands, and the more distant [SiF₆]²⁻ and [Ni.6H₂O]²⁺ complexes, respectively. A point-charge calculation shows the contribution of the latter to be roughly +2.5 cm⁻¹ in NiSiF₆·6H₂O. The exceptionally large temperature variations of D in these crystals is attributed to the near-cancellation of the positive and negative static contributions, leaving the effect of the dynamical contribution dominant.     

Praseodymium silicide formation at the Pr2O3/Si interface

The interface and layer structure of praseodymium (Pr) oxide layers grown on Si(0 0 1) from a high-temperature effusion cell are studied using grazing incidence X-ray diffraction. Due to the interdiffusion of praseodymium and silicon atoms, Pr silicide forms in the layers. We find that Pr silicide is the favorable structure under oxygen deficient growth conditions in the Pr oxide layer. To avoid the silicidation, additional oxygen must be supplied. The formation of Pr silicide is suppressed for layers grown with an oxygen partial pressure of 10⁻⁷ mbar at a substrate temperature of 700 °C.     

Gadolinium oxide high-k gate dielectrics prepared by anodic oxidation

The growth and properties of gadolinium oxide (Gd₂O₃) films prepared by anodic oxidation were investigated. Uniform Gd₂O₃ thin film with good oxide quality was obtained. The X-ray diffraction (XRD) pattern of the Gd₂O₃ films showed that they had a poly-crystalline structure. The dielectric constants of Gd₂O₃ films oxidized at 30 and 60 V are 9.4 and 12.2, respectively. The equivalent oxide thickness (EOT) of the Gd₂O₃ stacked oxide is in the range of 5.8-9.4 nm. The MOS capacitor with Gd₂O₃ exhibits interesting electrical properties. Longer oxidation time reduced the leakage current density for 30 V anodic oxidation but increased the leakage current density for 60 V anodic oxidation. This work reveals that Gd₂O₃ could also be an alternative dielectric for Si substrate and therefore, might pave the way to fabricate CMOS devices in the future.     

Influence of thermal annealing on oxidation states of Al-oxide in spin tunneling junctions

The dielectric constant in annealing coercive differential spin tunneling junctions Co/Al-oxide/Co has been investigated in order to clear the influence of thermal annealing on oxidation states. Al oxidized naturally in pure O₂ shows the relative dielectric constant of 10–40 before annealing. It indicates that Al oxidized in pure O₂ can be AlO₂ because the dielectric constant of AlO₂ is approximately 22.7. This dielectric measurement result is in good agreement with XPS analysis results that O/Al ratio is 1.9–2.0. After annealing at temperature ranging from room temperature up to 250 °C, the relative dielectric constant approaches approximately 8.0, which is equal to that of Al₂O₃. This indicates that the phase of Al-oxide is changing from AlO₂ to Al₂O₃ by annealing. This dielectric measurement will help investigate the oxidation state, such as chemical composition for junctions themselves.     

Violet luminescence in Ge nanocrystals/Ge oxide structures formed by dry oxidation of polycrystalline SiGe

Nanocrystals of Ge surrounded by a germanium oxide matrix have been formed by dry thermal oxidation of polycrystalline SiGe layers. Violet (3.16 eV) luminescence emission is observed when Ge nanocrystals, formed by the oxidation of the Ge segregated during the oxidation of the SiGe layer, are present, and vanishes when all the Ge has been oxidized forming GeO₂. Based on the evolution of the luminescence intensity and the structure of the oxidized layer with the oxidation time, the recombination of excitons inside the nanocrystals and the presence of defects in the bulk oxide matrix are ruled out as sources of the luminescence. The luminescence is attributed to recombination in defects at the Ge sub-oxide interface between the Ge nanocrystals and the surrounding oxide matrix, which is GeO₂.     

F2 laser induced oxidation of inorganic material

Transparent SiO₂ thin films were selectively fabricated on Si wafer by 157 nm F₂ laser in N₂/O₂ gas atmosphere. The F₂ laser photochemically produced active O(¹D) atoms from O₂ molecules in the gas atmosphere; strong oxidation reaction could be induced to fabricate SiO₂ thin films only on the irradiated areas of Si wafer. The oxidation reaction was sensitive to the single pulse fluence of F₂ laser. The irradiated areas were swelled and the height was approximately 500-1000 nm at the 205-mJ/cm² single pulse fluence for 60 min laser irradiation. The fabricated thin films were analytically identified to be SiO₂ by the Fourier-transform IR spectroscopy. The SiO₂ thin films could be also removed by subsequent chemical etching to fabricate micro-holes 50 nm in depth on Si wafer for microfabrication.