Inelastic scattering in a monolayer graphene sheet; a weak-localization study

Charge carriers in a graphene sheet, a single layer of graphite, exhibit much distinctive characteristics to those in other two-dimensional electronic systems because of their chiral nature. In this report, we focus on the observation of weak localization in a graphene sheet exfoliated from a piece of natural graphite and nano-patterned into a Hall-bar geometry. Much stronger chiral-symmetry-breaking elastic intervalley scattering in our graphene sheet restores the conventional weak localization. The resulting carrier-density and temperature dependence of the phase coherence length reveal that the electron-electron interaction including a direct Coulomb interaction is the main inelastic scattering factor while electron-hole puddles enhance the inelastic scattering near the Dirac point.Comment: 12 pages, 3 figures, submitted to PR

Observation of Supercurrent in PbIn-Graphene-PbIn Josephson Junction

Superconductor-graphene-superconductor (SGS) junction provides a unique platform to study relativistic electrodynamics of Dirac fermions combined with proximity-induced superconductivity. We report observation of the Josephson effect in proximity-coupled superconducting junctions of graphene in contact with Pb1-xInx (x=0.07) electrodes for temperatures as high as T = 4.8K, with a large IcRn (~ 255 microV). This demonstrates that Pb1-xInx SGS junction would facilitate the development of the superconducting quantum information devices and superconductor-enhanced phase-coherent transport of graphene.Comment: 8 pages, 7 figures, accepted in PR

Evaluation of Adhesion Properties of Thin Film Structure through Surface Acoustic Wave Dispersion Simulation

A theoretical simulation study of the dispersion characteristic of the surface acoustic wave (Rayleigh wave) was conducted by modeling the adhesion interlayer with stiffness coefficients to evaluate the bonding properties of nano-scale thin film structures. For experimental validation, a set of thin film specimens were fabricated—637 nm, 628 nm, 637 nm, 600 nm, and 600 nm thick titanium (Ti) films were deposited on silicon (Si) (100) substrate using a DC Magnetron sputtering process with DC power from 28.8 W, 57.6 W, 86.4 W, 115.2 W, and 144 W. The thicknesses of the Ti films were measured using a scanning electron microscope (SEM). Surface acoustic wave velocity for each of the manufactured thin film specimens was measured by using a V(z) curve technique of a Scanning Acoustic Microscope. The measured velocity, transducer frequency, and thickness of the film were applied to dispersion characteristic simulation for a given stiffness coefficient to calculate adhesion strength of each specimen. To verify the simulation result, the adhesion force of each specimen was measured using a nano-scratch test and then compared with the calculated values from the dispersion characteristic simulation. The value of adhesion strength from the dispersion characteristic simulation and the value of adhesion force of the nano-scratch test were found to have a similar tendency according to the process variable of the thin film. The results demonstrated that the adhesion strength of a thin film could be evaluated quantitatively by calculating the dispersion characteristics with the adhesion interlayer stiffness model

Through-Silicon via Device Non-Destructive Defect Evaluation Using Ultra-High-Resolution Acoustic Microscopy System

In this study, an ultra-high-resolution acoustic microscopy system capable of non-destructively evaluating defects that may occur in thin film structures was fabricated. It is an integrated system of the control module, activation module, and data acquisition system, in which an integrated control software for controlling each module was developed. The control module includes the mechanical, control, and ultrasonic parts. The activation module was composed of the pulser/receiver, and the data acquisition system included an A/D board. In addition, the integrated control software performs system operation and material measurement and includes an analysis program to analyze the obtained A-Scan signals in various ways. A through-silicon via (TSV) device, which is a semiconductor structure, was prepared to verify the performance of the developed system. The TSV device was analyzed using an ultra-high-resolution acoustic microscope. When the C-Scan images were analyzed, void defects with a size of 20 μm were detected at a depth of approximately 32.5 μm. A similar result could be confirmed when the cross section was measured using focused ion beam (FIB) microscopy

Grain Scale Representative Volume Element Simulation to Investigate the Effect of Crystal Orientation on Void Growth in Single and Multi-Crystals

Crystal plasticity finite element (CPFE) simulations were performed on the representative volume elements (RVE) modeling body centered cubic (bcc) single, bi- and tri-crystals. The RVE model was designed to include a void inside a grain, at a grain boundary and at a triple junction. The effect of single crystal orientation on the flow strength and growth rate of the void was discussed under prescribed boundary conditions for constant stress triaxialities. CPFE analyses could explain the effect of inter-grain orientations on the anisotropic growth of the void located at the grain boundaries. The results showed that the rate of void growth had preferred orientation in a single crystal, but the rate could be significantly different when other orientations of neighboring crystals were considered

Tuning locality of pair coherence in graphene:based andreev interferometers

We report on gate-tuned locality of superconductivity-induced phase-coherent magnetoconductance oscillations in a graphene-based Andreev interferometer, consisting of a T-shaped graphene bar in contact with a superconducting Al loop. The conductance oscillations arose from the flux change through the superconducting Al loop, with gate-dependent Fraunhofer-type modulation of the envelope. We confirm a transitional change in the character of the pair coherence, between local and nonlocal, in the same device as the effective length-to-width ratio of the device was modulated by tuning the pair-coherence length ξ(T) in the graphene layer

PT702. Hippocampal subfields volume reduction in high schoolers with previous verbal abuse experiences

Objective: Reduced hippocampal volume and alterations in white matter tracts have been frequently reported in adults having the history of emotional maltreatment. We investigated whether these structural change occur in adolescents with previous verbal abuse (VA) experiences. Methods: Hippocampal subfield volume and white matter structural connectivity measures were assessed in 31 first year male high school students with various degrees of exposure to parental and peer VA. Results: The high VA group showed significant volume reduction in the left cornu ammonis (CA) 1 and left subiculum compared to the low VA group (p<0.05). Volumes of left hippocampal subfields CA1 and subiculum were negatively correlated with previous VA experiences (p<0.05). Increased mean diffusivity (MD) of the splenium of the corpus callosum was related to high VA score across all subjects (p<0.05). There was an inverse relationship between volume of the CA1 and subiculum and MD of the splenium (p<0.05). Conclusion: Exposure to parental and peer VA may affect development of the left hippocampal subfields and the splenium of corpus callosum. These structural alterations can be discernible during adolescence