ELECTRONIC AND TRANSPORT PROPERTIES OF ARMCHAIR GRAPHENE NANORIBBON JUNCTIONS INVOLVING ZIGZAG EDGE INTERFACES

Ph.DDOCTOR OF PHILOSOPH

Low-bias Negative Differential Resistance effect in armchair graphene nanoribbon junctions

Graphene nanoribbons with armchair edges (AGNRs) have bandgaps that can be flexibly tuned via the ribbon width. A junction made of a narrower AGNR sandwiched between two wider AGNR leads was recently reported to possess two perfect transmission channels close to the Fermi level. Here, we report that by using a bias voltage to drive these transmission channels into the gap of the wider AGNR lead, we can obtain a negative differential resistance (NDR) effect. Owing to the intrinsic properties of the AGNR junctions, the on-set bias reaches as low as ~ 0.2 V and the valley current almost vanishes. We further show that such NDR effect is robust against details of the atomic structure of the junction, substrate and whether the junction is made by etching or by hydrogenation.Comment: The following article has been submitted to Applied Physics Letters (http://scitation.aip.org/content/aip/journal/apl). Copyright (2014) Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported Licens

Band Structure Mapping of Bilayer Graphene via Quasiparticle Scattering

A perpendicular electric field breaks the layer symmetry of Bernal-stacked bilayer graphene, resulting in the opening of a band gap and a modification of the effective mass of the charge carriers. Using scanning tunneling microscopy and spectroscopy, we examine standing waves in the local density of states of bilayer graphene formed by scattering from a bilayer/trilayer boundary. The quasiparticle interference properties are controlled by the bilayer graphene band structure, allowing a direct local probe of the evolution of the band structure of bilayer graphene as a function of electric field. We extract the Slonczewski-Weiss-McClure model tight binding parameters as $\gamma_0 = 3.1$ eV, $\gamma_1 = 0.39$ eV, and $\gamma_4 = 0.22$ eV.Comment: 12 pages, 4 figure

PET/CT Imaging of Zr-89-N-sucDf-Pembrolizumab in Healthy Cynomolgus Monkeys

PURPOSE: Programmed cell death-1 receptor (PD-1) and its ligand (PD-L1) are the targets for immunotherapy in many cancer types. Although PD-1 blockade has therapeutic effects, the efficacy differs between patients. Factors contributing to this variability are PD-L1 expression levels and immune cells present in tumors. However, it is not well understood how PD-1 expression in the tumor microenvironment impacts immunotherapy response. Thus, imaging of PD-1-expressing immune cells is of interest. This study aims to evaluate the biodistribution of Zirconium-89 (89Zr)-labeled pembrolizumab, a humanized IgG4 kappa monoclonal antibody targeting PD-1, in healthy cynomolgus monkeys as a translational model of tracking PD-1-positive immune cells. PROCEDURES: Pembrolizumab was conjugated with the tetrafluorophenol-N-succinyl desferal-Fe(III) ester (TFP-N-sucDf) and subsequently radiolabeled with 89Zr. Four cynomolgus monkeys with no previous exposure to humanized monoclonal antibodies received tracer only or tracer co-injected with pembrolizumab intravenously over 5 min. Thereafter, a static whole-body positron emission tomography (PET) scan was acquired with 10 min per bed position on days 0, 2, 5, and 7. Image-derived standardized uptake values (SUVmean) were quantified by region of interest (ROI) analysis. RESULTS: 89Zr-N-sucDf-pembrolizumab was synthesized with high radiochemical purity (> 99 %) and acceptable molar activity (> 7 MBq/nmol). In animals dosed with tracer only, 89Zr-N-sucDf-pembrolizumab distribution in lymphoid tissues such as mesenteric lymph nodes, spleen, and tonsils increased over time. Except for the liver, low radiotracer distribution was observed in all non-lymphoid tissue including the lung, muscle, brain, heart, and kidney. When a large excess of pembrolizumab was co-administered with a radiotracer, accumulation in the lymph nodes, spleen, and tonsils was reduced, suggestive of target-mediated accumulation. CONCLUSIONS: 89Zr-N-sucDf-pembrolizumab shows preferential uptake in the lymphoid tissues including the lymph nodes, spleen, and tonsils. 89Zr-N-sucDf-pembrolizumab may be useful in tracking the distribution of a subset of immune cells in non-human primates and humans. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02760225

Epidemiological and risk analysis of the H7N9 subtype influenza outbreak in China at its early stage

Dozens of human cases infected with H7N9 subtype avian influenza virus (AIV) have been confirmed in China since March, 2013. Distribution data of sexes, ages, professions and regions of the cases were analyzed in this report. The results showed that the elderly cases, especially the male elderly, were significantly more than expected, which is different from human cases of H5N1 avian influenza and human cases of the pandemic H1N1 influenza. The outbreak was rated as a Grade III (severe) outbreak, and it would evolve into a Grade IV (very severe) outbreak soon, using a method reported previously. The H7N9 AIV will probably circulate in humans, birds and pigs for years. Moreover, with the driving force of natural selection, the virus will probably evolve into highly pathogenic AIV in birds, and into a deadly pandemic influenza virus in humans. Therefore, the H7N9 outbreak has been assumed severe, and it is likely to become very or extremely severe in the future, highlighting the emergent need of forceful scientific measures to eliminate any infected animal flocks. We also described two possible mild scenarios of the future evolution of the outbreak

Oxygen-vacancy-mediated ferromagnetism in Fe:In2O3 (IFO) and exchange bias effect in IFO/NiO system.

Diluted magnetic semiconductor (DMS) with high TC finds significant applications in Spintronics, where both electron charge and electron spin can be manipulated. Exchange bias (EB) effect plays a very important role in many magnetic devices (e.g. spin valve) by pinning or stabilizing a ferromagnetic layer. However, the origin of ferromagnetism in many DMSs and the physics of EB effect are still not clear. In this final year project, both the ferromagnetism in IFO (Fe:In2O3) and the EB effect in IFO/NiO system are studied through a series of well-designed experiments. For the first part, we aim to clarify the roles of carrier and oxygen vacancy in ferromagnetism of IFO. We designed our experiments such that carrier concentration is varied by doping different concentrations of Sn into the usual IFO samples and oxygen vacancy concentration is varied by annealing the samples in air or high vacuum. The structure, magnetic and electrical transport properties of the samples have been characterized by XRD and Physical Property Measurement System. Based on the experimental results, we have concluded that ferromagnetism in IFO should be attributed to oxygen vacancies. To understand the mechanism, we have proposed a modified oxygen-vacancy model, where the oxygen vacancies contribute to both ferromagnetism and conduction. This model is consistent with both our results and experimental data reported by other groups. For the EB effect, we have employed our diluted ferromagnetic oxide IFO as the F layer and fabricated a IFO/NiO exchange bias heterostructure by sputtering deposition. The samples have been field cooled (FC) from 350K to 10K and hysteresis loops at various temperatures are collected by PPMS. The results show that we have established exchange bias below the Neel temperature . These results can be explained in our own model and the Spin Galss model.Bachelor of Science in Physic

Exploration and Practice of Rigid Restraint System of Water Resources at County Level: A case study of Yongkang City

General Secretary Xi Jinping proposed to take water resources as the maximum rigid restriction, emphasize using water resources as its capacity permits, and actively explore new ways of high-quality development with regional characteristics. Yongkang is a water shortage county in the southern water-rich area. The contradiction between insufficient water supply and rapid economic and social development and continuous improvement of ecological environment is more prominent. In this paper, industrial water users are taken as the key control objects, and the added value of unit water consumption is taken as the rigid constraint index of water resources. It is incorporated into the reform of “heroes per acre” and integrated with the existing water resources management system to design the collaborative promotion mechanism framework of general rigid constraint of water resources. Then, the application practice in Yongkang is carried out, and the responsibilities of various administrative departments are clarified

Large magnetoresistance from long-range interface coupling in armchair graphene nanoribbon junctions

10.1063/1.4904830APPLIED PHYSICS LETTERS1052