Initial oxidation rate of metals and the logarithmic equation

Chemical Analysis of the Gallium Surface in a Physiologic Buffer

Gallium and its alloys have been regarded as one of the promising materials for flexible bioelectronics due to their liquid-like mechanical properties, excellent electrical property, and low toxicity. Although many studies have fabricated bioelectronics from gallium-based liquid metals, gallium surface chemistry in physiologic conditions is rarely investigated. Here, we investigated the chemical change of the gallium surface in a physiologic buffer at 37 °C over 45 days. The gallium ion concentration and pH measurement indicated that the oxidation and corrosion progressed more rapidly in the physiological buffer than in air. Also, the release of gallium ions and protons followed a square root of time growth. Various spectroscopic techniques were used to measure the chemical composition change on the gallium surface. The FT-IR study indicated that the GaOOH-rich gallium surface produced Ga³⁺ and OH^- ions. The XPS study indicated the oxide layer formation within 5 days, and then the contamination layer was deposited over time, which includes different ions and organic materials derived from the physiologic buffer. This study provides a detailed chemical analysis of the gallium surface in a physiological buffer. These fundamental studies would be a cornerstone for understanding the complex interaction between the gallium surface and the biological environment.

Comparison of oxidation in uni-directionally and randomly oriented Cu films for low temperature Cu-to-Cu direct bonding

Cu-to-Cu direct bonding has attracted attention because it has been implemented in CMOS image sensors. Prior to the bonding, the oxides on the Cu surface needs to be removed, yet the surface may oxidize right after cleaning. Thus, oxidation is an inherent issue in the application of Cu direct bonding. Our previous study reported that Cu direct bonding can be achieved below 250 °C by using (111)-oriented nanotwinned Cu because it has the fastest surface diffusivity. However, the oxidation behavior of the nanotwinned Cu is unclear. Here, we examined the oxidation behavior of highly (111) and (200) oriented, and randomly-oriented Cu films at temperatures ranging from 120 to 250 °C. Transmission electron microscopy was used to measure the oxide thickness. The results show that the oxidation rate of (111)-oriented nanotwinned Cu has the lowest oxidation rate among them. Together, it is unique to possess the combination of the fastest surface diffusivity and the lowest oxidation rate.

Tunable plasmonic resonance of gallium nanoparticles by thermal oxidation at low temperaturas

The effect of the oxidation of gallium nanoparticles (Ga NPs) on their plasmonic properties is investigated. Discrete dipole approximation has been used to study the wavelength of the out-of-plane localized surface plasmon resonance in hemispherical Ga NPs, deposited on silicon substrates, with oxide shell (Ga₂O₃) of different thickness. Thermal oxidation treatments, varying temperature and time, were carried out in order to increase experimentally the Ga₂O₃ shell thickness in the NPs. The optical, structural and chemical properties of the oxidized NPs have been studied by spectroscopic ellipsometry, scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. A clear redshift of the peak wavelength is observed, barely affecting the intensity of the plasmon resonance. A controllable increase of the Ga₂O₃ thickness as a consequence of the thermal annealing is achieved. In addition, simulations together with ellipsometry results have been used to determine the oxidation rate, whose kinetics is governed by a logarithmic dependence. These results support the tunable properties of the plasmon resonance wavelength in Ga NPs by thermal oxidation at low temperatures without significant reduction of the plasmon resonance intensity.

Role of stress in the self-limiting oxidation of copper nanoparticles

The oxidation process of Cu nanoparticles has been investigated by means of an in-situ X-ray diffraction method. A self-limiting oxidation process involving an unusually drastic decrease (about 4 orders in magnitude) in the oxidation rate was observed at 298 K, whereas a non-self-limiting oxidation emerged at 323 K with a rate of at least 4 orders in magnitude faster than 298 K. The drastic slowing at 298 K and the big differences between the two close temperatures in the oxidation kinetics were found to be directly correlated to whether the compressive stress in the Cu(2)O(111) layers that commensurately formed on the Cu(111) surface is relaxed or not.

THE THEORY OF FORMATION OF HIGH RESISTANCE ANODIC OXIDE FILMS

Various models are considered for the growth of anodic oxide films (metal ions mobile). In general, a transition is expected, as the thickness of the film is increased, from control by the metal/oxide interface (Cabrera and Mott) with very thin films to control by the movement of ions through the body of the film (Verwey), with the concentration of mobile ions taking up the value (p, say) which gives electroneutrality. The field strength only varies with thickness in the transition region of thickness. Dewald's theory is the special case of p zero, which gives a field increasing continuously to infinite thickness. The high field production of Frenkel defects (with the vacant cation sites immobile and the interstitial ions mobile) as postulated by Bean, Fisher, and Vermilyea, and a slight mobility of oxygen ions are two processes which would allow p to vary with the field strength, and which would, therefore, give rise to "overshoot" in the transients in the field strength which occur when the applied current is suddenly changed. However, if the field strength is sufficiently great to produce Frenkel defects it would be expected to be sufficiently great to cause the vacancies to be mobile. This case is considered. Finally, it is noted that in an amorphous oxide it is difficult to maintain a distinction between lattice and interstitial ions, and, in fact, a range of site energies and jump distances would be expected. Some of the observed features (including "overshoot", and Tafel slope anomalies) of the kinetics for tantalum may, therefore, be due simply to the fact that the oxide is amorphous.