Hydroelectric power is the most important and wildly-used renewable energy source in the environment. In this paper, we propose the concept of using a multi-layered triboelectric nanogenerator (TENG) to effectively harvest the water wave and water drop energy. For a single-layered TENG, interdigital electrodes are incorporated in order to generate multiple electric outputs under one water wave or water drop impact. For the collection of water wave energy, a polyurethane (PU) coated copper rod is used to roll and contact with the polytetrafluoroethylene (PTFE) film covered interdigital electrodes. The surface of the PU and PTFE film are fabricated as porous structures and nanowire arrays, which provide the advantage of large contact area. Under one water wave impact, the single-layered TENG composed of 9 pairs of interdigital electrodes can provide 9 pulses of electric outputs (voltage can reach 52V). The output current density and instantaneous output power density of a 5-layered TENG are 15.3 mA/m2 and 1.5 W/m2, respectively. The rectified electric outputs have been applied to drive light emitting diodes and charge commercial capacitors. In addition, the part of the polytetrafluoroethylene (PTFE) film covered interdigital electrodes has been successfully used to harvest water drop energy, whcih can also generate 9 pulses of electric outputs upon one water drop falling. All these results show the developed TENG has great potential to harvest the hydroelectric power of ocean wave and raindrop in the near future. References: 1. Lin, Z.-H.; Cheng, G.; Lin, L.; Lee, S.; Wang, Z. L. Angew. Chem. Int. Ed. 2013, 52, 12545�12549. 2. Lin, Z.-H.; Cheng, G.; Lee, S.; Wang, Z. L. Adv. Mater. 2014, 26, 4690�4698. 3. Lin, Z.-H.; Cheng, G.; Wu, W.; Pradel, K. C.; Wang, Z. L. ACS Nano 2014, 8, 6440�6448. 4. Cheng, G.; Lin, Z.-H.; Du, Z.; Wang, Z. L. ACS Nano 2014, 8, 1932�1939.

Over the last two decades, III-V compound semiconductor nanowires (NWs) have been the focus of extensive research efforts. III-V NWs are particularly attractive for a wide variety of next-generation nanoelectronics and optoelectronics applications, in part due to their proven potential for unprecedented freedom in bandgap engineering, monolithic heteroepitaxial integration, and materials cost reduction. Of further interest is the technologically relevant subset of laterally-grown or planar epitaxial NWs, which hold the promise for nanoscale transistor scaling beyond the limits of the current Si-based roadmap. However, to date, in-situ doping dynamics and the effects of non-steady state dopant incorporation on the morphology and structure of planar III-V NWs has remained relatively unexplored, partially based on the shortcomings of conventional dopant profilometry techniques. Using planar GaAs NWs containing multiple, laterally isolated p-n junctions, we show that microwave impedance microscopy coupled with atomic force microscopy (MIM-AFM) has the capability of non-destructively spatially mapping charge carrier density profiles with nanoscale resolution. Particular attention is given to a novel observation of cyclical Zn impurity incorporation enhancement during vapor-liquid-solid (VLS) growth of p-type NW segments, simultaneously associated with the formation of a laterally twinned planar NW crystal structure. Our results are validated through correlation of MIM-AFM data with near-field infrared spectroscopy (NFIR) measurements, which reveals chemical information with ~ 10 nm spatial resolution. A theoretical model of the nanoprobe-NW interaction for both scan probe techniques is presented, which allows for the qualitative correlation of the collected data to doping signatures. These techniques, coupled with helium ion microscopy (HIM) and conventional transmission electron microscopy (TEM), allow us to validate the impact of the doping process on the structural topology of the NWs. The above microscopy techniques are pivotal to developing a new understanding of the growth dynamics of lateral VLS multi-junction GaAs NWs, and are likewise applicable for the direct measurement of composition and dopant distribution profiles in a wide variety of inorganic nanostructures.

Nanostructured Mn3O4 was introduced to activated carbon by a novel sonochemical reaction and the resulting nanocomposites were investigated as supercapacitor electrodes. Not only does the sonication catalyze the redox reaction, but also promote the diffusion of the precursors, resulting in the formation of coherent nanocomposites with Mn3O4 nanoparticles grown and uniformly distributed inside the mesopores of activated carbon. This novel microstructure endows the sample with a superior performance, the specific capacitance is 150 F/g against 93 F/g of activated carbon at a charge/discharge rate of 100mA/g, and the energy density of 228 Wh/Kg against 178 Wh/Kg of activated carbon at a power density of 273W/kg in Li ion capacitors.

Diamond has an attractive interest as one of next-generation power electronics materials. Recently, development of thermally-stable, high-current diamond field effect transistors (FETs) with Al2O3 gate and passivation dielectrics deposited by an atomic layer deposition (ALD) technique were reported to be as large as 1 A/mm by Waseda Univ. and NTT groups. In addition, since the sheet hole density in the hydrogenated-diamond surface was reported to be as high as 1E14 cm-2 which was one or two orders larger than other semiconductors. Therefore, we should use such the big advantage and then have to develop the high-k gate dielectric for diamond in order to control the high-density hole carrier. Since the high-k dielectric provides the large capacitance at a given gate voltage, the controllable carrier density is predicted to be increased with increasing the dielectric constant. For this purpose, as a first step to search the best high-k insulator material to the diamond, we have demonstrated the diamond FETs with high-k HfO2/HfO2, LaAlO3/Al2O3 Ta2O5/Al2O3, and ZrO2/Al2O3 stack gates prepared by a combination of sputter-deposition (SD) and ALD techniques. Since the FET property is sensitive to the interfacial states between the diamond and dielectric and the border traps in the dielectrics, it is essential to obtain the guideline for developing the excellent gate dielectric for diamond. In this paper, we will show why the high-k dielectric insulator is required for diamond and demonstrate the LaAlO3, HfO2, Ta2O5, and ZrO2 as the gate insulator of the FETs using the hydrogenated diamond (H-diamond) p-type channel. In addition, to understand the interface property between the diamond and dielectric, we will investigate the electric properties of interface between the H-diamond and insulator.

Ferroelectric generators are used to generate large magnitude current pulse by impacting a polarized ferroelectric material like PZT (lead zirconate titanate) 95/5. The impact induced shock wave induces a ferroelectric to anti-ferroelectric phase transition in the material causing depolarization. At high impact speeds, the material undergoes breakdown leading to charges to appear inside the material. Depending on the loading conditions and the electromechanical boundary conditions, the current or voltage profiles obtained vary. The exact physics of this process is largely unknown. In this paper, we explore the large deformation dynamic response of a ferroelectric material. Using the Maxwell�s equations, conservation laws and the second law of thermodynamics, we derive the governing equations for the phase boundary propagation as well as the driving force acting on it. We allow for the phase boundary to contain surface charges which introduces the contribution of curvature of phase boundary in the governing equations and the driving force. This type of analysis accounts for the dielectric breakdown of the material and resulting conduction in the ferroelectric. Next, we implement the equations derived to solve a one dimensional impact problem on a ferroelectric material under different electrical boundary conditions. The constitutive law is chosen to be piecewise quadratic in polarization and quadratic in the strain. We adopt a shock capturing finite volume scheme to solve the phase boundary propagation problem. We solve for the current profile generated in short circuit case and for voltage profile in open circuited case.

Natural particles, such as pollen, diatoms, and fungal spores, exhibit a remarkable breadth of complex solid surface ornamentations as well as a nanoscale thin liquid glues. This talk will examine pollen, and show that these features combine to yield a natural pressure-sensitive adhesive system. In particular, we have discovered that the combination of solid spines or reticulate structures with the nanometric liquid pollenkitt gives pollen a load-sensitive adhesion on rough surfaces. A second discovery is that the pollen adhesion can be optimized when the adhesion surface patterns form a negative impression of the pollen spine features. These results are derived from measurements of pollen adhesion and detachment from surfaces with controlled roughness and pattern regularity, by using AFM and centrifuge methods. Three pollen species were investigated, each having a unique surface morphology and pollenkitt volume. Surface patterning of the test substrate was controlled by using blends of poly(styrene) with poly(styrene-b-isoprene) copolymer. Significant enhancement in the adhesion was observed for pollen deposited on rough patterned surfaces owing to multiple spine interactions with a rough surface. The adhesion was optimized when the counter surface pattern matched the spacing of the pollen spines. Modeling of pollen detachment behavior under centrifugal forces shows that the mechanism of pollen detachment switches from sliding to rolling as roughness increases. The pollen adhesion system provides a natural model for development of novel pressure-sensitive adhesives on rough or patterned surfaces.

We have performed a number of experiments to examine the mechanical behavior of high capacity anodes. In particular, using two separate techniques, we have measured the fracture energy of lithiated silicon thin-film electrodes as a function of lithium concentration. The fracture energy is found to be similar to that of pure silicon and essentially independent of the concentration of lithium. Thus, while lithiated silicon can flow plastically, it appears to fracture in a brittle manner. Additionally, we have measured stresses that develop during lithiation/delithiation of germanium electrodes. We have performed complementary XRD experiments to determine the phases that develop during lithiation/delithiation. These measurements demonstrate plastic flow in germanium, which limits the stresses, thus reducing the driving force for crack propagation. Overall, these experiments provide key insight into the development of high-capacity anode systems that avoid fracture and thereby enable long cycle life.

Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D�TMDs, much less is known about exciton dynamics and radiative recombination. In this talk, we show first principles calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with chemical formula MX2 (M=Mo,W and X=S,Se), in bilayer and bulk MoS2, and in two MX2 hetero-bilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs, which have been the subjects of recent intense investigation. We find radiative lifetimes of a few ps at low temperature and a few ns at room temperature in the monolayers, and slower radiative recombination in bulk and bilayer than in monolayer MoS2. The MoS2/WS2 and MoSe2/WSe2 hetero-bilayers exhibit very long-lived (~30 ns at room temperature) inter-layer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer; this finding agrees with very recent ultrafast spectroscopy experiments, and helps resolve a controversy on the topic. In closing, we discuss how the radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, can be employed to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion.

One-dimensional ZnO nanostructures were considered as promising semiconductor materials for potential applications in optoelectronics. A number of methods have been used to fabricate ZnO nanostructures, such as chemical vapor deposition, vapor-phase transport, thermal evaporation, etc. However, these methods always have some disadvantage including the complex process, low reproducibility, high cost, etc, leading to the failures in the industrial applications. In this research, we developed a novel technique in which the ZnO rods were fabricated by re-crystallized from ZnO thin film. The ZnO nanorods with controllable density, growth direction, and high transparent were achieved. Finally, a dye-sensitized solar cell using obtained ZnO nanorods as photo electrodes was demonstrated, showing very good performance. Firstly, ZnO thin ?lms were deposited on TCO glasses by a conventional 13.56 MHz radio frequency magnetron sputtering system with optimized deposition condition. Secondly, the novel annealing processes were carried out for obtained ZnO thin films in a conventional furnace. The reducing annealing and oxygen annealing processes were shifted in order to control the balance of recrystallization of ZnO nanoros and reducing effect of ZnO thin film. The reducing gas was forming gas setting the ratio of 1.9% H2 in N2. According to the requirement of the different morphology (density, length, diameter, etc) of ZnO nanorods, the annealing temperature, time, and pressure were adjusted individually for each annealing process. As the summary, the ZnO nanorods could be grown in the novel annealing processes with well-controlled growth direction. The obtained ZnO nanorods showed good crystallinity and high transmittance. Through the investigation for different parameters during annealing processes, it was found that the oxygen annealing process between reducing annealing processes contributed to efficiently introduce the oxygen. With the annealing time controlling, the different morphologies of ZnO nanorods could be obtained. The low-temperature (less than 420�C) initial reducing annealing process contributed to control the density of ZnO nanorods. Moreover, the properties of different substrates were also found influencing on ZnO nanorods fabrication. The lower mismatch of the lattice imperfections and matching thermal expansion coefficient between ZnO film and substrates contributed to better crystallinity and vertical-alignment of ZnO rods. Finally, the obtained ZnO nanorods were used as photoelectrodes demonstrated in a dye-sensitized solar cell, which achieved the overall conversion efficiency of 5.48%.