Wenhui Wang

Enhancing sensitivity of a single ZnO micro-/nanowire photodetector by piezo-phototronic effect.

We demonstrate the piezoelectric effect on the responsivity of a metal-semiconductor-metal ZnO micro-/nanowire photodetector. The responsivity of the photodetector is respectively enhanced by 530%, 190%, 9%, and 15% upon 4.1 pW, 120.0 pW, 4.1 nW, and 180.4 nW UV light illumination onto the wire by introducing a -0.36% compressive strain in the wire, which effectively tuned the Schottky barrier height at the contact by the produced local piezopotential. After a systematic study on the Schottky barrier height change with tuning of the strain and the excitation light intensity, an in-depth understanding is provided about the physical mechanism of the coupling of piezoelectric, optical, and semiconducting properties. Our results show that the piezo-phototronic effect can enhance the detection sensitivity more than 5-fold for pW levels of light detection.

Light Propagation in Curved Silver Nanowire Plasmonic Waveguides

Plasmonic waveguides made of metal nanowires (NWs) possess significant potential for applications in integrated photonic and electronic devices. Energy loss induced by bending of a NW during light propagation is critical in affecting its performance as a plasmonic waveguide. We report the characterization of the pure bending loss in curved crystalline silver NW plasmonic waveguides by decoupling the energy loss caused by bending and propagation. The energy attenuation coefficiency due purely to bending was also determined, which exhibited an exponential relationship with the bending radius. Finite-difference-time-domain (FDTD) methods were utilized for theoretical simulations, which matched the experimental results well.

Propagating Surface Plasmon Polaritons: Towards Applications for Remote‐Excitation Surface Catalytic Reactions

Plasmonics is a well‐established field, exploiting the interaction of light and metals at the nanoscale; with the help of surface plasmon polaritons, remote‐excitation can also be observed by using silver or gold plasmonic waveguides. Recently, plasmonic catalysis was established as a new exciting platform for heterogeneous catalytic reactions. Recent reports present remote‐excitation surface catalytic reactions as a route to enhance the rate of chemical reactions, and offer a pathway to control surface catalytic reactions. In this review, we focus on recent advanced reports on silver plasmonic waveguide for remote‐excitation surface catalytic reactions. First, the synthesis methods and characterization techniques of sivelr nanowire plasmonic waveguides are summarized, and the properties and physical mechanisms of plasmonic waveguides are presented in detail. Then, the applications of plasmonic waveguides including remote excitation fluorescence and SERS are introduced, and we focus on the field of remote‐excitation surface catalytic reactions. Finally, forecasts are made for possible future applications for the remote‐excitation surface catalysis by plasmonic waveguides in living cells.

Bromide (Br) - Based Synthesis of Ag Nanocubes with High-Yield

The geometry of metal nanoparticles greatly affects the properties of the localized surface plasmon resonance and surface-enhanced Raman scattering. The synthesis of metal nanoparticles with controllable geometry has thus attracted extensive attentions. In this work, we report a modified polyol synthesis approach of silver (Ag) nanocubes through tuning the concentration of bromide ions (Br− ions). We have systematically investigated the effect of Br− ions in the polyol process, and find that higher concentration of Br− ions can enhance oxidative etching effect, which is the dominative factor in determining nanostructure geometry. Therefore, one can realize control over nanostructure geometry by manipulating the concentration of Br− ions. Our work provides an effective approach to control the shape of metallic nanostructures for potential applications.

Control on Surface Plasmon Polaritons Propagation Properties by Continuously Moving a Nanoparticle along a Silver Nanowire Waveguide

Surface plasmon polaritons (SPPs)-based nanowire waveguides possess potential applications for nanophotonic circuits. Precise control on the propagation of SPPs in metal nanowires is thus of significant importance. In this work, we report the control on SPPs propagation properties by moving a silver nanoparticle (Ag NP) along a silver nanowire (Ag NW). The emission intensity at NP can be attenuated to about 25% of the maximum emission value with increasing the distance between excitation end and NP. When NP is gradually moved away from excitation end, the intensity of emission light at Ag NP shows an exponential decay with a superposition of wavy appearance, while the emission at NW end is almost a constant value. It is found that the former is related to the local SPPs field distribution in NW, and the latter is dependent on the distance between excitation end and NW terminal. Moreover, the propagation loss in Ag NP-NW structure has been investigated. Our experiments demonstrate the important role of NP location in NW-based waveguides and provide an effective method of tuning scattering light in NW, which is instructive to design the future specialized function of SPPs-based nanophotonic circuits and devices.

Plasmon Waveguiding in Nanowires

Nanowires supporting propagating surface plasmons can function as nanowaveguides to realize the light guiding with field confinement beyond the diffraction limit, providing fundamental building blocks for nanophotonic integrated circuits. This review covers the recent developments of plasmon waveguiding in nanowires, mainly including plasmon waveguiding in metal nanowires, coupling of nanowire plasmons and emitters, hybrid nanowire waveguides and plasmonic gain, and nanowire photonic devices. We first introduce the main techniques for fabricating metal nanowires, the plasmon modes in metal nanowires and the excitation/detection methods. We then discuss the fundamental properties of plasmon propagation and emission, including zigzag, chiral and spin-dependent propagation, mode conversion, loss and propagation length, group velocity, terminal emission, and leaky radiation. Then the interactions between nanowires and emitters are reviewed, especially the coupling of single nanowires and single quantum emitters. Finally, we briefly introduce the hybrid nanowire waveguide composed of a semiconductor nanowire and a metal film with an intervening thin insulator and highlight a few nanophotonic devices based on plasmonic nanowire networks or plasmonic-photonic hybrid nanowire structures.

Influence of symmetry breaking degrees on surface plasmon polaritons propagation in branched silver nanowire waveguides

Surface plasmon polaritons (SPPs)-based nanowire (NW) waveguides demonstrate promising potentials in the integrated nanophotonic circuits and devices. The realization of controlling SPPs propagation in NWs is significant for the performance of nanophotonic devices when employed for special function. In this work, we report the effect of symmetry breaking degrees on SPPs propagation behavior in manually fabricated branched silver NW structures. The symmetry breaking degree can be tuned by the angle between main NW and branch NW, which influences the emissions at the junction and the main NW terminal in a large extent. Our results illustrate the significance of symmetry breaking degree on SPPs propagation in NW-based waveguides which is crucial for designing the future nanophotonic circuits.

Study of the conductance and structure characteristics of C60/Sb bilayers

The electrical and structural properties of C60/Sb bilayers were investigated. In situ direct-current conductivity measurement results indicate that the doping of Sb into C60 induces the C60 order-disorder phase transition temperature to increase to ~278 K. According to the results of a transmission electron microscope and atomic force microscope study, such a transition (near 278 K) implies the formation of an interfacial structure of Sb-doped C60. Annealing and the absorption of gases destroy the interfacial structure of Sb-doped C60. A possible mechanism for such a phase transition is discussed.