Characterizing top gated bilayer graphene interaction with its environment by Raman spectroscopy

In this work we study the behavior of the optical phonon modes in bilayer graphene devices by applying top gate voltage, using Raman scattering. We observe the splitting of the Raman G band as we tune the Fermi level of the sample, which is explained in terms of mixing of the Raman (Eg) and infrared (Eu) phonon modes, due to different doping in the two layers. We theoretically analyze our data in terms of the bilayer graphene phonon self-energy which includes non-homogeneous charge carrier doping between the graphene layers. We show that the comparison between the experiment and theoretical model not only gives information about the total charge concentration in the bilayer graphene device, but also allows to separately quantify the amount of unintentional charge coming from the top and the bottom of the system, and therefore to characterize the interaction of bilayer graphene with its surrounding environment

Advances in martensitic transformations in Cu-based shape memory alloys achieved by in situ neutron and synchrotron X-ray diffraction methods

This article deals with the application of several X-ray and neutron diffraction methods to investigate the mechanics of a stress induced martensitic transformation in Cu-based shape memory alloy polycrystals. It puts experimental results obtained by two different research groups on different length scales into context with the mechanics of stress induced martensitic transformation in polycrystalline environment

On the inner Double-Resonance Raman scattering process in bilayer graphene

The dispersion of phonons and the electronic structure of graphene systems can be obtained experimentally from the double-resonance (DR) Raman features by varying the excitation laser energy. In a previous resonance Raman investigation of graphene, the electronic structure was analyzed in the framework of the Slonczewski-Weiss-McClure (SWM) model, considering the outer DR process. In this work we analyze the data considering the inner DR process, and obtain SWM parameters that are in better agreement with those obtained from other experimental techniques. This result possibly shows that there is still a fundamental open question concerning the double resonance process in graphene systems.Comment: 5 pages, 3 figure

Relationship between the volume of the unit cell of hexagonal-close-packed Ti, hardness and oxygen content after α-case formation in Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy

In this study, the influence of oxygen diffusion on the physical properties of Ti–6Al–2Sn–4Zr–2Mo–0.1Si was examined. Measurements were carried out directly on sample cross sections which were preoxidized at high temperature. The lattice parameter evolution was measured using synchrotron X-ray diffraction and was coupled with microhardness and electron probe microanalyzer results with the aim of highlighting their relationships. The results show that the hardness and oxygen gradients along the oxygen diffusion zone in the alloy are similar to the evolution of the [alpha]α-phase unit-cell volume quantified by X-ray diffraction. Linear relationships were found between these three parameters