Silicon oxide

Abstract: Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage. Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles. Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).

Abstract: We employ scanning probe microscopy to reveal atomic structures and nanoscale morphology of graphene-based electronic devices (i.e., a graphene sheet supported by an insulating silicon dioxide substrate) for the first time. Atomic resolution scanning tunneling microscopy images reveal the presence of a strong spatially dependent perturbation, which breaks the hexagonal lattice symmetry of the graphitic lattice. Structural corrugations of the graphene sheet partially conform to the underlying silicon oxide substrate. These effects are obscured or modified on graphene devices processed with normal lithographic methods, as they are covered with a layer of photoresist residue. We enable our experiments by a novel cleaning process to produce atomically clean graphene sheets.

Abstract: Single nanometre-sized pores (nanopores) embedded in an insulating membrane are an exciting new class of nanosensors for rapid electrical detection and characterization of biomolecules. Notable examples include α-hemolysin protein nanopores in lipid membranes1,2 and solid-state nanopores3 in Si3N4. Here we report a new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy. First, a pore of 20 nm is opened in a silicon membrane by using electron-beam lithography and anisotropic etching. After thermal oxidation, the pore can be reduced to a single-nanometre when it is exposed to a high-energy electron beam. This fluidizes the silicon oxide leading to a shrinking of the small hole due to surface tension. When the electron beam is switched off, the material quenches and retains its shape. This technique dramatically increases the level of control in the fabrication of a wide range of nanodevices.

Abstract: Pressurized blister tests show that the adhesion energies of graphene samples on silicon oxide are much higher than those measured in typical micromechanical structures.

Abstract: The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n +‐Si in ultrapure water saturates at 10 A. The native oxide growth on n‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure waterdrops and chemical binding energy. These chemical bond structures for native oxide filmsgrown in air and in ultrapure water are also discussed.