Thickness Of Native Oxide Layer Research Articles

Self-sacrificial-reaction guided formation of hierarchical electronic/ionic conductive shell enabling high-performance nano-silicon anode

The inevitable surface oxidation of nano-Si inhibits its practical application as anode for lithium ion battery. Here, a hierarchical electronic/ionic conducting shell is smartly constructed by self-sacrificing reaction of native oxide layer on Si nanoparticles with lithium species. The morphological observation shows that Si nanoparticles are wrapped by lithium ionic conductor Li2SiO3 and amorphous carbon as the interlayer and outer layer, respectively. Such hierarchical structure not only provides a tight bond between Si and coating layer, but also improves the interfacial stability and conductivity of Si nanoparticles. Theoretical calculations demonstrate that the adsorption of Li2SiO3 on Si (111) and the adsorption of C on Si/Li2SiO3 are exothermic and spontaneous, and that the electron transfer and ionic conductivity at the surface of Si/Li2SiO3/C composite is enhanced. As a result, the as-prepared Si/Li2SiO3/C sample exhibits outstanding cycle stability and rate capability. By optimizing the lithium sources and thickness of native oxide layer, the resulted material exhibits 2106 mAh g−1 at 200 mA g−1, remains 1583 mA g−1 at 3000 mA g−1, and maintains 70.2% of capacity retention after 200 cycles. This work provides a robust strategy to promote the practical applications of Si nanoparticles as anode for lithium ion batteries.

Friction and Tribochemical Wear Behaviors of Native Oxide Layer on Silicon at Nanoscale

The friction and tribochemical wear of native oxide (SiO x ) layers formed on a silicon surface were investigated with atomic force microscopy using a silica (SiO2) sphere tip in ambient air (50% relative humidity). The native SiO x layer thickness was determined to be ~0.8 nm with auger electron spectroscopy. The oxide-free Si/H terminated silicon surface was also studied as a reference for comparison. It was found that friction is higher on the Si/SiO x surface than the Si/H surface; but, the wear of the Si/H surface occurs much more readily than that of the Si/SiO x surface when wear depth is less than the thickness of native oxide layer on Si/SiO x surface (~0.8 nm). Based on attenuated total reflection infrared spectroscopy analysis, the friction appears to be governed by the thickness and structure of the adsorbed water layer. Although the wear process in humid conditions is through tribochemical reactions involving the adsorbed water, the removal rate of the substrate layer varies depending on the effective activation energy. These findings are important for the tribological design of silicon-based micro/nanodevices working in humid ambience.

AN EFFECTIVE-SUBSTRATE METHOD TO INVESTIGATE AN IRON NATIVE OXIDE LAYER ON AN IRON SUBSTRATE BY SPECTROSCOPIC ELLIPSOMETRY

An effective-substrate method was presented to obtain the optical constants of an iron native oxide layer with unknown optical constants and film thickness on an iron substrate with unknown optical constants by using spectroscopic ellipsometry (SE). "Thick" iron films were deposited on silicon wafer by magnetron sputtering and were exposed to air at room temperature. They were measured by spectroscopic ellipsometry during this procedure at different time points from ten minutes to seven months. Pseudo optical constants were calculated from the initially measured data and were introduced into the modeling work of subsequent measurements as an effective substrate in order to obtain the optical constants and film thickness of the native oxide layer. After obtaining the optical constants of the subsequent native oxide layer, they were employed in the modeling work of the initially measured data and the optical constants of the iron substrate and the film thickness of the initial native oxide layer was obtained.

A Graphical Analysis of Transient Behavior in SIMS Depth Profiling Using 16O2+.

An attempt to determine the thickness of native oxide layer on a silicon wafer from a graphical analysis of the transient behavior at an earlier stage of SIMS depth profiling using 16O2+ beam has been performed. We found out three specified depths from the characteristic shape of 30Si+ secondary ion intensity vs. depth curves, which strongly depended on the angle of incidence (θ) and the acceleration energy (E) of 16O2+ beam. Good linear relationships were found between the three specified depths and E at low angles of incidence. The linear lines extrapolated coincided triply at E=0, and from this, a value of 0.62 nm was obtained as the thickness of the native oxide layer.