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分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

Incorporating noble metal nanoparticles on the surface or inner side of semiconductors to form a hybrid nanostructure is an effective route to improve the gas sensing performance of these semiconductors. In this study, we present novel Au-decorated ZnO nanospheres (Au-ZnO NSs) obtained by laser irradiation of liquids. Structural characterization indicated that the Au-ZnO NSs consisted of single crystalline ZnO NSs with few Au nanoparticles decorated on their surfaces and abundant encapsulated Au nanoparticles with relatively small sizes. Laser irradiation-induced heating–melting–evaporating processes are responsible for the formation of unique Au-ZnO NSs. Gas sensing properties of the Au-ZnO NSs, as gas sensing materials, were investigated and compared with those of pure ZnO NSs. The former showed lower working temperature, higher sensitivity, better selectivity, and good reproducibility. The response values of Au-ZnO NSs and pure ZnO NSs sensors to ethanol of 100 ppm were 252 and 75 at working temperature of 320 °C and 360 °C, respectively. The significant enhancements in gas sensing performance should be attributed to the electronic sensitization induced by the depleted layers between encapsulated Au nanoparticles and ZnO and chemical sensitization originating from the catalytic effects of Au nanoparticles decorated on the surfaces that dissociated molecular oxygen. |

提交时间：
2017年08月18日
点击量:*31*，
下载量:*20*

Monodispersed Carbon Nanodots Spontaneously Separated from Combustion Soot with Excitation.pdf

张豪分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

We present a facile, low-cost procedure by simple one-step combustion of small organic molecules to obtain ultrafine, hydrophobic, and fluorescent carbon nanodots (CNDs). Without further centrifugation and dialysis, we could easily separate CNDs from combustion soot through spontaneous sedimentation. Transmission electron microscopy and photoluminescence characterization demonstrated that the collected CNDs possessed a monodispersed size distribution with a diameter of 1.9 ± 0.5 nm and excitation-independent luminescent properties. Furthermore, after oxidization treatment, the oxidized CNDs displayed good water solubility and the highest fluorescent intensity at neutral solution. |

提交时间：
2017年08月16日
点击量:*45*，
下载量:*30*

分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

Great effort is made to maximize the surface area and expose active sites of a catalyst by distributing it over a suitable electronic conducting support. We present a design and eco-friendly construction of a two-dimensional Pt/SnO2/reduced-graphene-oxide (rGO) nanocomposite to study the strong metal-semiconductor-support interactions as candidate highly active and durable electrocatalyst. Distinctively, highly reactive SnOx nanoparticles (NPs) induced by laser ablation in liquids were used as a precursor to transform the graphene oxide (GO). Simultaneously, the initial amorphous-like SnOx further crystallized into SnO2 NPs, which were uniformly anchored onto rGO sheets. Afterward, the photo-excited electrons from semiconductor SnO2 were used as green reducing agents. Ultrafine Pt NPs with an average size of about 1–2 nm were in situ reduced and uniformly anchored on the surface of crystallized SnO2 NPs. Compared with the Pt/rGO catalysts without SnO2 modification, the prepared Pt/SnO2/rGO catalysts not only show larger electrochemical active surface area and higher catalytic activity toward methanol oxidation but also exhibit better tolerance toward CO and long-term cycle stability. The significantly enhanced electrochemical performance should be attributed to the uniformly dispersed Pt NPs with ultrafine size and the synergetic effect from the hybrid noble metal-semiconductor-carbon network components, which possess promising potential applications as electrocatalysts for methanol oxidation. |

提交时间：
2017年08月15日
点击量:*46*，
下载量:*31*

Exact Solution of the Generalized Rabi Model

Degang Zhang分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

The generalized Rabi model is exactly solved by employing the unitary transformation method in the occupation number representation. The analytical expressions for the complete energy spectrum consisting of two sub-energy spectra are presented in the whole range of all the physical parameters. Each energy level possesses twofold degeneracy and is determined by the parameter in the unitary transformation, which obeys a highly nonlinear equation. The corresponding eigenfunction is a convergent infinite series in terms of these physical parameters. Due to the level crossings between the neighboring eigenstates at certain parameter values, such the degeneracies could lead to novel physical phenomena in these quantum systems with the light-matter interaction. |

提交时间：
2017年08月07日
点击量:*16*，
下载量:*14*

Analytical result on the supercurrent through a superconductor/quantum-dot/superconductor junction

Wei Li, Yu Zhu, Tsung-han Lin分类： 物理学 >> 基本粒子与场物理学

We present an analytical result for the supercurrent across a superconductor/quantum-dot/superconductor junction. By converting the current integration into a special contour integral, we can express the current as a sum of the residues of poles. These poles are real and give a natural definition of the Andreev bound states. We also use the exact result to explain some features of the supercurrent transport behavior. |

提交时间：
2017年08月05日
点击量:*14*，
下载量:*12*

分类： 物理学 >> 基本粒子与场物理学

Using the nonequilibrium Green function, we show that microwave irradiation can reverse the supercurrent flowing through a superconductor / quantum-dot / superconductor structure. In contrast with the conventional sideband effect in normal-metal / quantum-dot / normal-metal junctions, the photon-assisted structures appear near E0=n2ℏω(n=±1,±2...), where E0 is the resonant energy level of the quantum dot and ω is the frequency of microwave field. Each photon-assisted structure is composed of a negative and a positive peak, with an abrupt jump from the negative peak to the positive peak around E0=n2ℏω. The microwave-induced π-junction transition is interpreted in the picture of photon-assisted Andreev bound states, which are formed due to multiple photon-assisted Andreev reflection between the two superconductors. Moreover, the main resonance located at E0=0 can also be reversed with proper microwave strength and frequency. |

提交时间：
2017年08月05日
点击量:*15*，
下载量:*13*

ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions

Yu Zhu, Qing-feng Sun, Wei Li, Zhong-shui Ma, Tsung-han Lin分类： 物理学 >> 基本粒子与场物理学

We investigate ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions. In the presence of microwave irradiation, we show that the trajectory of multiple Andreev reflections can be closed by emitting or absorbing photons. Consequently, photon-assisted Andreev states are formed and play the role of carrying supercurrent. On the Shapiro steps, dc component appears when the resonant level is near a series of positions with spacing of half of the microwave frequency. Analytical result is derived in the limit of infinite superconducting gap, based on which new features of ac Josephson effect are revealed. |

提交时间：
2017年08月05日
点击量:*16*，
下载量:*14*

Supersymmetric Probes in a Rotating 5D Attractor

Wei Li, Andrew Strominger分类： 物理学 >> 基本粒子与场物理学

Supersymmetric zero-brane and one-brane probes in the squashed AdS2譙3 near-horizon geometry of the BMPV black hole are studied. Supersymmetric zero-brane probes stabilized by orbital angular momentum on the S3 are found and shown to saturate a BPS bound. We also find supersymmetric one-brane probes which have momentum and winding around a U(1)L譛(1)R torus in the S3 and in some cases are static. |

提交时间：
2017年08月05日
点击量:*11*，
下载量:*9*

Non-Supersymmetric Attractor Flow in Symmetric Spaces

Davide Gaiotto, Wei Li, Megha Padi分类： 物理学 >> 基本粒子与场物理学

We derive extremal black hole solutions for a variety of four dimensional models which, after Kaluza-Klein reduction, admit a description in terms of 3D gravity coupled to a sigma model with symmetric target space. The solutions are in correspondence with certain nilpotent generators of the isometry group. In particular, we provide the exact solution for a non-BPS black hole with generic charges and asymptotic moduli in N=2 supergravity coupled to one vector multiplet. Multi-centered solutions can also be generated with this technique. It is shown that the non-supersymmetric solutions lack the intricate moduli space of bound configurations that are typical of the supersymmetric case. |

提交时间：
2017年08月05日
点击量:*13*，
下载量:*13*

Non-Supersymmetric Attractors in Symmetric Coset Spaces

Wei Li分类： 物理学 >> 基本粒子与场物理学

We present a method of constructing generic single-centered and multi-centered extremal black hole solutions in a large class of 4D N=2 supergravities coupled to vector-multiplets with cubic prepotentials. The method is applicable to models for which the 3D moduli spaces obtained via c*-map are symmetric coset spaces. The attractor solutions are generated by certain nilpotent elements in the coset algebra. We present explicit computations in 4D N=2 supergravity coupled to one vector-multiplet, whose 3D moduli space is the symmetric coset space G_{2(2)}/SL(2,R)^2. The non-supersymmetric multi-centered black holes in this model are found to lack the intricate moduli space of bound configurations that are typical of the supersymmetric case. |

提交时间：
2017年08月05日
点击量:*13*，
下载量:*13*