窄带大功率高温超导滤波器的研制

本文中,我们介绍一个中心频率大约为2.015GHz,相对带宽小于0.35%,通带内回波损耗大于20dB,带外零点高度大约为-45dB,通带内插损小于0.2dB的窄带四阶双模片型高温超导滤波器.我们对该滤波器在不同输入功率下的传输特性曲线进行了测试,测试结果表明,在输入微波信号功率值为11.7W的情况下,该器件的传输特性曲线没有发生显著退化.     

Effects of Substrates with Different Dielectric Parameters on Left-Handed Frequency of Left-Handed Materials

Wedge-shaped left-handed materials (LHMs) with split ring resonators and wires structures are fabricated by photolithography and lift-off techniques, and the variation of left-handed frequency induced by substrates with different dielectric parameters is investigated. The Snell refraction experiments of the LHM samples are carried out on an angular resoled microwave spectrometer, and the results indicate that the left-handed frequencies of the LHMs shifted downward from 10.57 GHz to 9.74 GHz when the dielectric parameters of the LHM substrates increase from 3.7 to 4.8. Moreover, the finite difference time domain method is used to simulate the microwave transmission properties of the left-handed materials with different substrates, and the experimental results are in agreement with the numerical simulation results. In addition, the reason for the shifting of the left-handed frequency of the LHMs is discussed theoretically.     

Giant magnetic moment at open ends of multiwalled carbon nanotubes

The attractions of cantilevers made of multiwalled carbon nanotubes(MWNTs)and secured on one end are studied in the non-uniform magnetic field of a permanent magnet.Under an optical microscope,the positions and the corresponding deflections of the original cantilevers(with iron catalytic nanoparticles at the free end)and corresponding cut-off cantilevers(the free ends consisting of open ends of MWNTs)are studied.Both kinds of CNT cantilevers are found to be attracted by the magnet,and the point of application of force is proven to be at the tip of the cantilever.By measuring and comparing deflections between these two kinds of cantilevers,the magnetic moment at the open ends of the CNTs can be quantified.Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes,it is called giant magnetic moment,and its possible mechanisms are proposed and discussed.     

微流体芯片中的癌症生物物理研究

文章从生物物理的新角度出发,介绍了如何利用微流体技术研究癌症的一系列重大问题,其中包括:构建三维微型结构体,用于在体外模拟和研究肿瘤细胞侵袭组织的细胞生物行为;开发新型微流体芯片,以检测血液中循环肿瘤细胞,并分析将其应用于临床中的可能性。文章还展望了飞秒激光三维直写技术构建肿瘤细胞转移模型的应用前景。     

Large scale fabrication of nitrogen vacancy-embedded diamond nanostructures for single-photon source applications

Some color centers in diamond can serve as quantum bits which can be manipulated with microwave pulses and read out with laser,even at room temperature.However,the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface.To address this issue,we fabricated arrays of diamond nanostructures,differing in both diameter and top end shape,with HSQ and Cr as the etching mask materials,aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy(NV) embedded diamond.With a mixture of O_2 and CHF_3 gas plasma,diamond pillars with diameters down to 45 nm were obtained.The top end shape evolution has been represented with a simple model.The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement,larger than tenfold,and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected.These results provide useful information for future applications of nanostructured diamond as a single-photon source.     

Aggregation of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite

In this work we report that when ferromagnetic metals (Fe,Co and Ni) are thermally evaporated onto n-layer graphenes and graphite,a metal nanowire and adjacent nanogaps can be found along the edges regardless of its zigzag or armchair structure.Similar features can also be observed for paramagnetic metals,such as Mn,Al and Pd.Meanwhile,metal nanowires and adjacent nanogaps cannot be found for diamagnetic metals (Au and Ag).An external magnetic field during the evaporation of metals can make these unique features disappear for ferromagnetic and paramagnetic metal;and the morphologies of diamagnetic metal do not change after the application of an external magnetic field.We discuss the possible reasons for these novel and interesting results,which include possible one-dimensional ferromagnets along the edge and edge-related binding energy.     

一种结构紧凑的高温超导窄带带通滤波器

研制了一种结构紧凑的高温超导窄带滤波器.该滤波器中心频率为,是在以0.5mm厚的LaAO3(εr≈24)为衬底的YBCO超导薄膜上制作的.测试结果显示该滤波器具有比较好的性能,其插入损耗<0.3dB,反射损耗<-16dB,相对带宽<9‰, 带边陡度>9dB/MHz, 中心频率误差<0.05%.滤波器设计中,利用特殊技术成功地改善了过渡带上的零点特性,为今后研制新型的结构紧凑的滤波器开拓了思路.     

Electrical Conductivity and Current--Voltage Characteristics of Individual Conducting Polymer PEDOT Nanowires

We report the current-voltage （Ⅰ-Ⅴ） characteristics and electrical conductivity of individual template-synthesized poly（3,4-ethylenedioxythiophene） （PEDOT） nanowires （190 ± 6 nm in diameter and δRT = 11.2 ± 2Ω^-1 cm^-1） over a wide temperature range from 300 to 10K. With lowering temperature, the Ⅰ - Ⅴ characteristics become nonlinear around 50K, and a clear Coulomb gap-like structure appears in the differential conductance （dI/dV） spectra. The temperature dependence of the resistance below 70 K follows In R α T^-1/2, which can be interpreted as Efros-Shklovskii hopping conduction in the presence of a Coulomb gap. In addition, the influences of measurement methods such as the applied bias voltage magnitude, the two-probe and four-probe techniques used in the resistance measurements are also reported and discussed.     

适用于3G移动通讯的高温超导窄带滤波器

研制了一种适用于3G移动通讯基站接收机的高温超导窄带带通滤波器.其中心频率为1949.85兆赫兹,带宽为9.7兆赫兹.为了实现极高性能,理论设计了12阶准椭圆(quasi-elliptic)函数型滤波器,引入了3对传输零点.滤波器的计算机仿真是用Sonnet软件完成的.此滤波器是在直径为2英寸、厚度约为0.5毫米的氧化镁双面超导薄膜上制作的.实测表明,达到了极高的性能要求:相对带宽0.49%,带边陡度>150dB/MHZ,带外抑制>60dB,插入损耗<0.2dB,反射损耗<-14dB.     

Absorptive Fabry–Pérot Interference in a Metallic Nanostructure

In conventional optics, the Fabry–Pérot(FP) effect is only considered for transparent materials at a macroscopic dimension. Down to the nanometer scale, for absorptive metallic structures, the FP effect has not been directly observed so far. It is unclear whether such a macroscopic effect still holds for a subwavelength metallic nanostructure. Here, we demonstrate the probing of FP interference in a series of nanometer-thick Au films with subwavelength hole arrays. The evidence from both linear and second harmonic generation signals, together with angle-resolved investigations, exhibit features of a FP effect. We also derive an absorptive FP interference equation, which well explains our experimental results. Our results for the first time experimentally confirm the long-persisting hypothesis that the FP effect holds ubiquitously in a metallic nanostructure.