Modern electronics based on semiconductors is meeting the fundamental speed limit caused by the interconnect delay and large heat generation when the sizes of components reach nanometer scale. Photons as a carrier of the information are superior to electrons in bandwidth, density, speed, and dissipation. More over, photons could carry intensity, polarization, phase, and frequency information which could break through the limitation of binary system as in electronic devices. But due to the diffraction limitation, the photonic components and devices can not be fabricated small enough to be integrated densely. Surface plasmon polariton is quanta of collective oscillations of free electrons excited by photons in metal nanostrucrures, which offers a promising way to manipulate light at the nanoscale and to realize the miniaturization of photonic devices. Hence, plasmonic circuits and devices have been proposed for some time as a potential strategy for advancing semiconductor-based computing beyond the fundamental performance limitations of electronic devices, as epitomized by Moore's law. A variety of individual plasmonic nanodevices have been intensively studied recently, but the crucial and necessary step to enable nanophotonic circuits for future information technology, namely cascade logics integrated on-chip, has not been achieved. Here we demonstrate that a nanophotonic binary logic NOR gate can be realized by cascading plasmonic OR and NOT gates in four-terminal nanowire networks. We explain the operating principle for the device based on quantum dot luminescence imaging, which reveal the interferences for different logic functions between propagating plasmon wave packets in the nanowire network in great detail. Since the NOR gate is logic complete, i.e. any Boolean logic gate can be constructed from it, our results could have a key role in defining a viable path for the development of novel subwavelength optical processor architectures.

Cascaded Logic Gates in Nanophotonic Plasmon Networks

農林水産省経営局長賞 尿石症により尿道閉塞した雄子牛に対するバルーンカテーテルを用いた膀胱-皮膚フィステル装着による治療法の考案 (平成26年度家畜診療等技術全国研究集会・入賞論文)

Interaction of light pulses of various durations and intensities with nanoscale photonic structures plays an important role in many applications of nanophotonics for high-density data storage, ultra-fast data processing, surface coloring and sensing. A design of optically tunable and reconfigurable structures made from different materials is based on many important physical effects and advances in material science, and it employs the resonant character of light interaction with nanostructures and strong field confinement at the nanoscale. Here we review the recent progress in physics of tunable and reconfigurable nanophotonic structures of different types. We start from low laser intensities that produce weak reversible changes in nanostructures, and then move to the discussion of non-reversible changes in photonic structures. We focus on three platforms based on metallic, dielectric and hybrid resonant photonic structures such as nanoantennas, nanoparticle oligomers and nanostructured metasurfaces. Main challenges and key advantages of each of the approaches focusing on applications in advanced photonic technologies are also discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201700108

Light-Induced Tuning and Reconfiguration of Nanophotonic Structures

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 emitte...

Plasmon Waveguiding in Nanowires.

We demonstrate a device geometry for single-molecule electronics experiments that combines both the ability to adjust the spacing between the electrodes mechanically and the ability to shift the energy levels in the molecule using a gate electrode. With the independent in-situ variations of molecular properties provided by these two experimental \"knobs\", we are able to achieve a much more detailed characterization of electron transport through the molecule than is possible with either technique separately. We illustrate the performance of the device using C(60) molecules.

http://absimage.aps.org/image/MAR05/MWS_MAR05-2004-002899.pdf

Mechanically-Adjustable and Electrically-Gated Single-Molecule Transistors

Optical force, coming from momentum exchange during light-matter interactions, has been widely utilized to manipulate microscopic objects, though mostly in vacuum or in liquids. By contrast, due to the light-induced thermal effect, photophoretic force provides an alternative and effective way to transport light-absorbing particles in ambient gases. However, in most cases these forces work independently. Here, by employing the synergy of optical force and photophoretic force, we propose and experimentally demonstrate a configuration which can drive a micron-size metallic plate moving back and forth on a tapered fiber with supercontinuum light in ambient air. Optical pulling and oscillation of the metallic plate are experimentally realized. The results might open exhilarating possibilities in applications of optical driving and energy conversion.

Light-Induced Pulling and Pushing by the Synergic Effect of Optical Force and Photophoretic Force.

Leaky plasmon modes (LPMs) in metal nanowires (NWs), which combine the physical characteristic of both “plasmonics” and “leaky radiation”, present distinguished performances in terms of guiding and radiating light. In contrast to traditional light-guiding in metal NWs with one single LPM, multiple LPMs are crucial for advanced uses such as augmenting data transmission channels, enhancing sensing performance, manipulating polarization and converting mode. Here, we demonstrate experimentally the control over multiple LPMs in pentagonal silver NWs. By combining far-field real-space imaging and leakage radiation microscopy, the three typical LPMs with fields mainly concentrating in corners surrounded by air are specifically identified. By manipulating excitation wavelengths and NW diameters, the number of the excited LPMs can be controlled. These findings reveal the physics of LPMs in silver NWs, thereby paving the way towards applying the high-order leaky modes in silver NWs for photonic integrated circuits, nanoscale confinement, plasmonic sensing, QD-nanowire coupling, etc.

Identification and control of multiple leaky plasmon modes in silver nanowires

Nanowelding of nanomaterials opens up an emerging set of applications in transparent conductors, thin-film solar cells, nanocatalysis, cancer therapy, and nanoscale patterning. Single point nanowelding (SPNW) is highly demanded for building complex nanostructures. In this letter, the precise control of SPNW of silver nanowires is explored in depth, where the nanowelding is laser-induced through the plasmonic resonance enhanced photothermal effect. It is shown that the illumination position is a critical factor for the nanowelding process. As an example of performance enhancement, output at wire end can be increased by 65% after welding for a plasmonic nanocoupler. Thus, single point nanowelding technique shows great potentials for high-performance electronic and photonic devices based on nanowires, such as nanoelectronic circuits and plasmonic nanodevices.

Laser-induced single point nanowelding of silver nanowires

Nanojoining (including nanowelding, nanosoldering, etc.) of metal nanomaterials offers the opportunity of constructing complex structures and advanced functional devices at the nanoscale. In comparison with nanowelding, nanosoldering does not involve the melting of base metal and shows considerable mechanical strength and good thermal and electrical conductivity. Here, an optically controlled local nanosoldering technique, which ensures the nanostructures to be bonded while their original structural integrity is retained, is proposed and demonstrated. Typical elemental devices (V-shaped, T-shaped, and X-shaped nanostructures) are formed with this nanosoldering technique. The conductivity of one V-shaped junction is enhanced by 500 times after nanosoldering. This facile nanosoldering technique provides an avenue to locally manipulate light, charge, heat, and mass transport at the nanoscale and is thereby expected to benefit the development of nanophotonics and nanoelectronics.

Optically controlled local nanosoldering of metal nanowires

DOI: 10.1002/aelm.201700614 to develop an adequate method to combine them together and understand its charge transport mechanisms. Recent advancements in the field of welding of NWs research indicate its potential capabilities in fabrication and repairing nanoelectronics,[16–19] nanophotonics,[20] nanomedicine,[21] and nanoelectromechanical systems.[22] There are reports of successful nanowelding following various techniques, including thermal annealing,[23] optical welding,[24–28] capillarity-driven welding,[29] chemical welding,[30] spot welding,[31] stretchinduced cold-welding,[32–34] and welding by Joule heating.[35,36] Although much progress has been achieved in this field, there remains many cumbersome issues, such as necessitating complicated and expensive experimental setup, use of chemicals which can contaminate the system, and lack of robustness corresponding to mechanical strength and electrical connectivity, yet to be addressed. Furthermore, the joining of semiconductor and metal NWs remains a challenging issue for miniaturization and integration of next generation nanodevices as the melting points of these two different types of materials are different. In this article, we present a relatively simple technique to achieve adequate welding of ZnO NW with Ag NW and also both type of NWs with Au electrode toward realizing heterojunction-based electronic nanodevices. The effects of local heat generation in closely spaced semiconductor and metal nanostructures due to strong optical interactions have been utilized for melting and eventually welding these nanostructures. Following this technique, four different electronic devices (two devices consisting of one Schottky and two ohmic junctions, one device with two back-to-back Schottky junctions, and another one with three ohmic contacts) have been fabricated. The devices with one Schottky and two ohmic junctions have been fabricated following two different approaches for two different orientations of the ZnO (top/bottom) and Ag (bottom/top) NWs. Although the temperature difference between the melting points of ZnO and Ag NWs is about 1000 K, it has been demonstrated that the melting points of both NWs are reached simultaneously when ZnO NW in on top of Ag NW, which results in superior quality of welding. Thereafter, toward understanding the transport mechanisms of all these devices, the obtained current– voltage (I–V) characteristic curves are analyzed in detail. This photothermal nanowelding technique paves the path for realizing heterostructure-based 1D electronic nanodevices. An improvised and comparatively inexpensive method for welding semiconductors and metal nanowires (NWs) utilizing a plasmon-enhanced photothermal effect is presented in this article. Different types of heterojunction-based (single Schottky junction and back-to-back Schottky junctions) electronic nanodevices are fabricated by welding various combinations of silver and ZnO NWs on two gold electrodes using continuous wave laser (λ = 532 nm) shots. It is inferred from the current–voltage characteristic curves of these devices that the junction formed between the ZnO nanowire (NW) and the gold electrode demonstrates Schottky barrier-like behavior, whereas the junctions between silver-and-gold and silver-and-ZnO behave like ohmic contacts. The maximum currents obtained for a single Schottky junction and back-to-back Schottky junctions corresponding to the applied bias voltage 40 V are 42 μA and 7 μA, respectively. This plasmon-enhanced nanowelding technique extends the range of applications of nanowelding in fabrication of electronic nanodevices.

Hangbo Yang

Papers

Light-Induced Pulling and Pushing by the Synergic Effect of Optical Force and Photophoretic Force.

Identification and control of multiple leaky plasmon modes in silver nanowires

Laser-induced single point nanowelding of silver nanowires

Optically controlled local nanosoldering of metal nanowires

Photothermal‐Induced Nanowelding of Metal–Semiconductor Heterojunction in Integrated Nanowire Units