Identification of the mechanism-limiting nitrogen diffusion in metallic alloys by in situ photoemission electron spectroscopy

In situ photoemission electron spectroscopy is used to identify the mechanism limiting the thermally activated nitrogen diffusion in metallic alloys. The samples were prepared by bombarding stainless steel with a broad ion source in a high-vacuum chamber. The photoemission spectra evolution on increasing controlled oxygen partial pressure is correlated with bulk material properties. The presence of oxygen inhibits the formation of iron nitrides and gamma(N)-phase (austenitic face-centered-cubic lattice containing nitrogen), which proved to be fundamental for efficient nitrogen penetration in the alloy. (C) 2003 American Institute of Physics.9485435543

Vapor-solid-solid growth mechanism driven by epitaxial match between solid AuZn alloy catalyst particles and ZnO nanowires at low temperatures

A comprehensive explanation for the precise mechanism of ZnO nanowire growth at low temperatures (T<400 degrees C) is presented. Experimental data and theoretical considerations evidence that ZnO nanowires originate from solid gamma-AuZn catalyst particles. A model is proposed to describe such growth. An original feature of the model concerns the formation of nanowire, which occurs via preferential oxidation of specific gamma-AuZn surfaces induced by epitaxial-like growth mechanism

Probing the Electronic Properties of Monolayer MoS<inf>2</inf> via Interaction with Molecular Hydrogen

This work presents a detailed experimental investigation of the interaction between molecular hydrogen (H2) and monolayer MoS2 field effect transistors (MoS2 FET), aiming for sensing application. The MoS2 FET exhibits a response to H2 that covers a broad range of concentration (0.1–90%) at a relatively low operating temperature range (300–473 K). Most important, H2 sensors based on MoS2 FETs show desirable properties such as full reversibility and absence of catalytic metal dopants (Pt or Pd). The experimental results indicate that the conductivity of MoS2 monotonically increases as a function of the H2 concentration due to a reversible charge transferring process. It is proposed that such process involves dissociative H2 adsorption driven by interaction with sulfur vacancies in the MoS2 surface (VS). This description is in agreement with related density functional theory studies about H2 adsorption on MoS2. Finally, measurements on partially defect-passivated MoS2 FETs using atomic layer deposited aluminum oxide consist of an experimental indication that the VS plays an important role in the H2 interaction with the MoS2. These findings provide insights for future applications in catalytic process between monolayer MoS2 and H2 and also introduce MoS2 FETs as promising H2 sensors

Asymmetric effect of oxygen adsorption on electron and hole mobilities in bilayer graphene: Long- and short-range scattering mechanisms

We probe electron and hole mobilities in bilayer graphene under exposure to molecular oxygen. We find that the adsorbed oxygen reduces electron mobilities and increases hole mobilities in a reversible and activated process. Our experimental results indicate that hole mobilities increase due to the screening of long-range scatterers by oxygen molecules trapped between the graphene and the substrate. First principle calculations show that oxygen molecules induce resonant states close to the charge neutrality point. Electron coupling with such resonant states reduces the electron mobilities, causing a strong asymmetry between electron and hole transport. Our work demonstrates the importance of short-range scattering due to adsorbed species in the electronic transport in bilayer graphene on SiO2 substrates. © 2013 American Chemical Society