Edge chirality determination of graphene by Raman spectroscopy

Raman imaging on the edges of single layer micromechanical cleavage graphene (MCG) was carried out. The intensity of disorder-induced Raman feature (D band at ~1350 cm-1) was found to be correlated to the edge chirality: it is stronger at the armchair edge and weaker at the zigzag edge. This shows that Raman spectroscopy is a reliable and practical method to identify the chirality of graphene edge and to help in determination of the crystal orientation. The determination of graphene chirality is critically important for fundamental study as well as for applications.Comment: 14 pages, 3 figures, 1 tabl

Using MicroPET Imaging in Quantitative Verification of Acupuncture Effect in Ischemia Stroke Treatment

While acupuncture has survived several thousand years’ evolution of medical practice, its function still remains as a myth from the view point of modern medicine. Our goal in this paper is to quantitatively understand the function of acupuncture in ischemia stroke treatment. We carried out a comparative study using the Sprague Dawley rat animal model. We induced the focal cerebral ischemia in the rats using the middle cerebral artery occlusion (MCAO) procedure. For each rat from the real acupuncture group (n = 40), sham acupoint treatment group (n = 54), and blank control group (n = 16), we acquired 3-D FDG-microPET images at baseline, after MCAO, and after treatment (i.e., real acupuncture, sham acupoint treatment, or resting according to the group assignment), respectively. After verifying that the injured area is in the right hemisphere of the cerebral cortex in the brain by using magnetic resonance imaging(MRI) and triphenyl tetrazolium cchloride (TTC)-staining, we directly compared the glucose metabolism in the right hemisphere of each rat. We carried out t-test and permutation test on the image data. Both tests demonstrated that acupuncture had a more positive effect than non-acupoint stimulus and blank control (P < 0.025) in increasing the glucose metabolic level in the stroke-injured area in the brain, while there was no statistically significant difference between non-acupoint stimulus and blank control (P>0.15). The immediate positive effect of acupuncture over sham acupoint treatment and blank control is verified using our experiments. The long-term benefit of acupuncture needs to be further studied

SEARCH FOR ELECTROWEAK PRODUCTION OF SUPERSYMMETRIC STATES IN NON-UNIVERSAL HIGGS MASS MODEL WITH TWO EXTRA PARAMETERS COMPRESSED SCENARIO WITH THE ATLAS DETECTOR

The ATLAS and CMS collaborations announced the discovery of the Higgs boson in July 2012, completing the particle content of the Standard Model. Although the Standard Model is a great triumph, it is not considered to be the complete theory of particle physics. Among the newly-developed theories, Supersymmetry (SUSY) is one of the most promising ones. SUSY predicts the existence of supersymmetric partner particles and it is one of the best-motivated extensions of the space-time symmetry of particle interactions. There are supersymmetric partner particles associated with each SM particles in which the spin differs by 1/2. This dissertation focuses on a search for electroweak production of supersymmetric particles with compressed mass spectra in the final states with exactly two low-momentum leptons and missing transverse momentum. The proton-proton collision data is recorded by the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to 36.1~{\ifb} of integrated luminosity at $\sqrt{s} = 13$~{\TeV}. Events with same-flavor and opposite electric charge lepton pairs are selected. The data are found to be consistent with the Standard Model prediction. Results are interpreted using the non-universal Higgs mass model with two extra parameters (NUHM2) with small mass differences between the masses of produced supersymmetric particles. Upper limits of the cross-section at 95\% confidence level are set for the NUHM2 model as a function of the universal gaugino mass $m_{1/2}$

Magnetic Oscillation of Optical Phonon in ABA- and ABC-Stacked Trilayer Graphene

We present a comparative measurement of the G-peak oscillations of phonon frequency, Raman intensity and linewidth in the Magneto-Raman scattering of optical E2g phonons in mechanically exfoliated ABA- and ABC-stacked trilayer graphene (TLG). Whereas in ABA-stacked TLG, we observe magnetophonon oscillations consistent with single-bilayer chiral band doublets, the features are flat for ABC-stacked TLG up to magnetic fields of 9 T. This suppression can be attributed to the enhancement of band chirality that compactifies the spectrum of Landau levels and modifies the magnetophonon resonance properties. The drastically different coupling behaviour between the electronic excitations and the E2g phonons in ABA- and ABC-stacked TLG reflects their different electronic band structures and the electronic Landau level transitions and thus can be another way to determine the stacking orders and to probe the stacking-order-dependent electronic structures. In addition, the sensitivity of the magneto-Raman scattering to the particular stacking order in few layers graphene highlights the important role of interlayer coupling in modifying the optical response properties in van der Waals layered materials.Comment: 25 pages, 6 figure

Synthetic Graphene Grown by Chemical Vapor Deposition on Copper Foils

The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interests. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapour deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this chapter, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapour deposition. We also discuss potential applications of such large scale synthetic graphene.Comment: 23 pages, 4 figure

Gold on graphene as a substrate for surface enhanced Raman scattering study

In this paper, we report our study on gold (Au) films with different thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman scattering (SERS) substrates for the characterization of rhodamine (R6G) molecules. We find that an Au film with a thickness of ~7 nm deposited on SLG is an ideal substrate for SERS, giving the strongest Raman signals for the molecules and the weakest photoluminescence (PL) background. While Au films effectively enhance both the Raman and PL signals of molecules, SLG effectively quenches the PL signals from the Au film and molecules. The former is due to the electromagnetic mechanism involved while the latter is due to the strong resonance energy transfer from Au to SLG. Hence, the combination of Au films and SLG can be widely used in the characterization of low concentration molecules with relatively weak Raman signals.Comment: 11 pages, 4 figure