Metal-insulator-metal (MIM) tunnel diodes on a variety of high and low work function metals with various levels of root-mean-square roughness are fabricated using high quality atomic layer deposited Al 2 O 3 as the insulating tunnel barrier. It is found that electrode surface roughness can dominate the current versus voltage characteristics of MIM diodes, even overwhelming the impact of metal work function. Devices with smoother bottom electrodes are found to produce current versus voltage behavior with higher asymmetry and better agreement with Fowler-Nordheim tunneling theory, as well as a greater percentage of functioning devices. V

We have developed a kinetic model to describe the oxidation behavior of Si1−xGex alloys during Ge segregation, which compares the Deal–Grove flux of oxidant diffusing through the oxide to the maximum flux of Si diffusing through the Ge-rich layer. This is motivated by thermal oxidation experiments on Si1−xGex alloys (x<0.17) using a fluorine-containing ambient (O2 and 200 ppm of NF3). The fluorine is known to modify point defect generation during oxidation of pure Si toward vacancy production, which is also the case for Ge in Si. We demonstrate that fluorinated oxidation of Si1−xGex enhances the oxidation rate by 25%–40% in the temperature range of 700–800 °C. Oxides formed at these temperatures were SiO2, while those formed at 600 °C exhibited a transition from SiO2 to mixed oxide growth at some point during the very early phase of oxidation, depending on the alloy composition. Consideration of these data suggests that other factors in addition to oxidation temperature must be considered in predicting which oxide type will be produced, in contrast to most previous reports. Our model, indeed, shows that alloy composition, oxide thickness, and oxidant partial pressure are also important parameters. We believe that the model is very useful in predicting the oxide type that should result from a given set of growth conditions, and in particular, it suggests that a changeover from SiO2 to mixed oxide formation is likely at some point during the oxidation process, particularly if carried to larger thicknesses.

No abstract

A modified version of the carburization process, a widely established technique used in the steel industry for case hardening of components, is used for the growth of graphene on stainless steel. Controlled growth of high-quality single- and few-layered graphene on stainless steel (SS) foils through a liquid-phase chemical vapor deposition (CVD) technique is reported. Reversible Li intercalation in these graphene-on-SS structures is demonstrated, where graphene and SS act as electrode and current collector, respectively, providing very good electrical contact. Direct growth of an active electrode material, such as graphene, on current-collector substrates makes this a feasible and efficient process for developing thin-film battery devices.

No abstract