We demonstrate the atomic layer deposition of high-quality HfO 2 film on graphene and report the magnitude of remote oxide phonon (ROP) scattering in dual-oxide graphene transistors. Top gates with 30 nm HfO 2 oxide layer exhibit excellent doping capacity of greater than 1.5 × 10 13 /cm 2 . The carrier mobility in HfO 2 -covered graphene reaches 20,000 cm 2 /Vs at low temperature, which is the highest among oxide-covered graphene and compares to that of pristine samples. The temperature-dependent resistivity ρ(T) exhibits the effect of ROP scattering from both the SiO 2 substrate and the HfO 2 over-layer. At room temperature, surface phonon modes of the HfO 2 film centered at 54 meV dominate and limit the carrier mobility to ~ 20,000 cm 2 /Vs. Our results highlight the important choice of oxide in graphene devices. As graphene research rapidly advances towards electronic applications, the need to incorporate high-quality oxides into field effect transistors (FETs) and the understanding of their role in electric transport become imminent. Extensive studies in Si transistors show that charge traps Single layer graphene flakes are prepared by exfoliating HOPG (ZYA grade, SPI supplies) onto SiO 2 (290 nm)/doped Si wafer. We use standard e-beam lithography and metal deposition techniques (Ti 5 nm/ Au 50 nm) to process rectangular pieces into hall bar devices. A second ebeam writing exposes the area to be covered by HfO 2 . Immediately following the development of the resist, HfO 2 films are deposited in a Cambridge Savannah 200 Atomic Layer Deposition system using two precursors: H 2 O and Hf(NMe 2 ) 4 (Sigma-Aldrich). The chamber temperature is 110 ˚C and the growth rate is ~ 1.2 Å/cycle. The device is then soaked in warm acetone (~ 40 °C)for 15 -30 mins, with the aid of ultrasound sonification up to 5 mins when necessary, to release the unwanted HfO 2 film. On some devices, a third e-beam lithography and metal deposition are used to fabricate the top-gate electrode. Growth of HfO 2 on pristine graphene

Materials exhibiting electronic phase transitions have attracted widespread attention. By switching between metallic and insulating states under external stimuli, the accompanying changes in the electrical and optical properties can be harnessed in novel electronic and optical applications. In this work, a laterally confined conductive pattern is inscribed into an otherwise insulating VO2 thin film using ultraviolet light, inducing an almost four orders of magnitude decrease in electrical resistivity of the exposed area. The metallic imprint remains in VO2 after ultraviolet light exposure and can be completely erased by a short low temperature anneal. The ability to optically pattern confined metallic structures provides new opportunities for reconfigurable photonic and plasmonic structures, as well as re‐writable electric circuitry.

Dicyanoacetylene (C4N2) is an unusual energetic molecule with alternating triple and single bonds (think miniature, nitrogen-capped carbyne), which represents an interesting starting point for the transformation into extended carbon–nitrogen solids. While pressure-induced polymerization has been documented for a wide variety of related molecular solids, precise mechanistic details of reaction pathways are often poorly understood and the characterization of recovered products is typically incomplete. Here, we study the high-pressure behavior of C4N2 and demonstrate polymerization into a disordered carbon–nitrogen network that is recoverable to ambient conditions. The reaction proceeds via activation of linear molecules into buckled molecular chains, which spontaneously assemble into a polycyclic network that lacks long-range order. The recovered product was characterized using a variety of optical spectroscopies, X-ray methods, and theoretical simulations and is described as a predominately sp2 network comprising “pyrrolic” and “pyridinic” rings with an overall tendency toward a two-dimensional structure. This understanding offers valuable mechanistic insights into design guidelines for next-generation carbon nitride materials with unique structures and compositions.