An-Ping Li

Bio: An-Ping Li is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Scanning tunneling microscope & Graphene nanoribbons. The author has an hindex of 35, co-authored 146 publications receiving 6849 citations. Previous affiliations of An-Ping Li include Max Planck Society & University of Lyon.

Hexagonal pore arrays with a 50-420 nm interpore distance formed by self-organization in anodic alumina

Abstract: Self-organized hexagonal pore arrays with a 50–420 nm interpore distance in anodic alumina have been obtained by anodizing aluminum in oxalic, sulfuric, and phosphoric acid solutions. Hexagonally ordered pore arrays with distances as large as 420 nm were obtained under a constant anodic potential in phosphoric acid. By comparison of the ordered pore formation in the three types of electrolyte, it was found that the ordered pore arrays show a polycrystalline structure of a few micrometers in size. The interpore distance increases linearly with anodic potential, and the relationship obtained from disordered porous anodic alumina also fits for periodic pore arrangements. The best ordered periodic arrangements are observed when the volume expansion of the aluminum during oxidation is about 1.4 which is independent of the electrolyte. The formation mechanism of ordered arrays is consistent with a previously proposed mechanical stress model, i.e., the repulsive forces between neighboring pores at the metal/oxide interface promote the formation of hexagonally ordered pores during the oxidation process.

Exceptional ballistic transport in epitaxial graphene nanoribbons

Abstract: Graphene nanoribbons will be essential components in future graphene nanoelectronics. However, in typical nanoribbons produced from lithographically patterned exfoliated graphene, the charge carriers travel only about ten nanometres between scattering events, resulting in minimum sheet resistances of about one kilohm per square. Here we show that 40-nanometre-wide graphene nanoribbons epitaxially grown on silicon carbide are single-channel room-temperature ballistic conductors on a length scale greater than ten micrometres, which is similar to the performance of metallic carbon nanotubes. This is equivalent to sheet resistances below 1 ohm per square, surpassing theoretical predictions for perfect graphene by at least an order of magnitude. In neutral graphene ribbons, we show that transport is dominated by two modes. One is ballistic and temperature independent; the other is thermally activated. Transport is protected from back-scattering, possibly reflecting ground-state properties of neutral graphene. At room temperature, the resistance of both modes is found to increase abruptly at a particular length--the ballistic mode at 16 micrometres and the other at 160 nanometres. Our epitaxial graphene nanoribbons will be important not only in fundamental science, but also--because they can be readily produced in thousands--in advanced nanoelectronics, which can make use of their room-temperature ballistic transport properties.

Heteroepitaxial Growth of Two-Dimensional Hexagonal Boron Nitride Templated by Graphene Edges

Abstract: By adapting the concept of epitaxy to two-dimensional space, we show the growth of a single-atomic-layer, in-plane heterostructure of a prototypical material system--graphene and hexagonal boron nitride (h-BN). Monolayer crystalline h-BN grew from fresh edges of monolayer graphene with atomic lattice coherence, forming an abrupt one-dimensional interface, or boundary. More important, the h-BN lattice orientation is solely determined by the graphene, forgoing configurations favored by the supporting copper substrate.

Fabrication and Microstructuring of Hexagonally Ordered Two‐Dimensional Nanopore Arrays in Anodic Alumina

Abstract: washed three times with water, and dried over MgSO4. After removing the solvent, chromatography is carried out on the residue on neutral alox. First, unreacted compound 4 and monoadduct 8 are eluted with pentane, and then bis-adduct 5 with petrolether/ethyl acetate. (54 %, m.p.: 191 C). H NMR (CDCl3, ppm) 3.64 (s, 8 H, CH2), 4.33 (dd, 2 H, CH), 6.99 (dd, 2 H, CH), 7.14 (s, 8 H, aromatic); C NMR (CDCl3, ppm) 33.72, 54.79, 126.37, 129.22, 134.8, 139.74, 140.72. Compound 2: Compound 5 (0.8 g, 2.64 mmol) and chloranil (1.28 g, 5.28 mmol) are dissolved in toluene (150 mL), and heated for 1.5 h under reflux. After removing the solvent, the residue is purified via chromatography (neutral alox/toluene) (75 %, m.p.: 239 C). H NMR (CDCl3, ppm) 5.33 (dd, 2 H, CH), 7.06 (dd, 2 H, CH), 7.37 (AA¢BB¢, 4 H, aromatic), 7.71 (AA¢BB¢, 4 H, aromatic), 7.73(s, 4 H, aromatic); C NMR (CDCl3, ppm) 50.74, 121.71, 126, 127.92, 132.25, 138.73, 142.66. Compound 6a: A solution of compound 2 (100 mg, 0.32 mmol) and 2,3,4,5-tetrachlorothiophenedioxide (167 mg, 0.64 mmol) in CH2Cl2 (4 mL) is heated for 3 days at 70 C under a pressure of 6 kbar. After the reaction is complete, the solvent is removed under vacuum. Chromatography is carried out on the residue on silica gel with hexane/toluene 4/1 as eluent. The first fraction gives the desired product (75 %). The material can be further purified by recrystallization from dichloroethane/ethyl acetate. H NMR (CD2Cl2, ppm) 3.54 (s, 2 H, CH), 5.13 (s, 2 H, CH), 7.45 (AA¢BB¢, 4 H, aromatic), 7.80 (s, 2 H, aromatic), 7.82 (AA¢BB¢, 4 H, aromatic), 7.86 (s, 2 H, aromatic); C NMR (CD2Cl2, ppm) 48.08, 48.86, 122.91, 123.93, 124.29, 126.24, 126.35, 128.02, 128.07, 131.38, 132.91, 133.07, 137.47, 139.58. Compound 6b: Using the procedure described for the synthesis of compound 6a, compound 6b is obtained in a yield of 70 %. H NMR (CD2Cl2, ppm) 3.58 (s, 2 H, CH), 5.19 (s, 2 H, CH), 7.46 (AA¢¢BB¢, 4 H, aromatic), 7.82 (s, 2 H, aromatic), 7.84 (AA¢BB¢, 4 H, aromatic), 7.86 (s, 2 H, aromatic); C NMR (CD2Cl2, ppm) 49.74, 51.89, 120.49, 122.87, 123.96, 126.22, 126.33, 128.02, 128.08, 128.72, 132.90, 133.06, 137.51, 139.73.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Formation of hollow nanocrystals through the nanoscale Kirkendall effect

Abstract: Hollow nanocrystals can be synthesized through a mechanism analogous to the Kirkendall Effect, in which pores form because of the difference in diffusion rates between two components in a diffusion couple. Starting with cobalt nanocrystals, we show that their reaction in solution with oxygen and either sulfur or selenium leads to the formation of hollow nanocrystals of the resulting oxide and chalcogenides. This process provides a general route to the synthesis of hollow nanostructures of a large number of compounds. A simple extension of the process yielded platinum-cobalt oxide yolk-shell nanostructures, which may serve as nanoscale reactors in catalytic applications.

TiO2 nanotubes: synthesis and applications.

Abstract: TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

Formation of hollow nanocrystals through the nanoscale kirkendall effect

Abstract: Formation of Hollow Nanocrystals through the Nanoscale Kirkendall Effect Yadong Yin, Robert M. Rioux, Can K. Erdonmez, Steven Hughes, Gabor A. Somorjai, A. Paul Alivisatos* Department of Chemistry, University of California at Berkeley, and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. *To whom correspondence should be addressed. Email: alivis@uclink4.berkeley.edu Abstract We demonstrate that hollow nanocrystals can be synthesized through a mechanism analogous to the Kirkendall Effect, in which pores form due to the difference in diffusion rates between two components in a diffusion couple. Cobalt nanocrystals are chosen as a primary example to show that their reaction in solution with oxygen, sulfur or selenium leads to the formation of hollow nanocrystals of the resulting oxide and chalcogenides. This process provides a general route to the synthesis of hollow nanostructures of large numbers of compounds. A simple extension of this process yields platinum-cobalt oxide yolk-shell nanostructures which may serve as nanoscale reactors in catalytic applications.