L. Nanomaterials and Energy Devices Organizers: Zhiyong Fan, Guozhen Shen, Jiatao Zhang, Yu-Lun Chueh, Hyunhyub Ko, Sang-Woo Kim, Kuniharu Takei, Hong-Ming Lin L-01 Three-dimensional Metal Halide Perovskite Nanowire Arrays and Optoelectronic Devices Zhiyong Fan, Leilei Gu, Mohammad Tavakoli, Aashir Waleed The Hong Kong University of Science and Technology Metal halide perovskite materials are emerging as highly promising materials for high performance optoelectronic devices thus triggered broad attention globally. In this work, we report for the first time a chemical vapor deposition (CVD) process to grow ordered three-dimensional (3-D) metal halide nanowire (NW) arrays in nanoengineering templates. This unique CVD process utilizes metal nanoclusters at the bottom of vertical nanochannels to initiate high quality NW growth. As the nanochannels have largely controllable geometrical factors, namely, periodicity, diameter and depth, NW geometry can also be precisely nanoengineered. As the result, the ordered 3-D NW arrays can achieve ultra-high NW density in the range of 4×108/cm2~109/cm2 at a sizable scale of ~9 cm2. The 3-D NW arrays are conspicuously promising for 3-D integrated nano-electronics/optoelectronics. To further demonstrate the technological potency of the perovskite NW arrays, they have been fabricated into proof-of-concept image sensors. Each image sensor consists of 1,024 photodiode pixels made of vertical perovskite NWs, and the imaging functionality has been verified by recognizing various optical patterns projected on the sensor. In addition, we have also discovered that the chemically and mechanically robust template can effectively protect perovskite NWs from water and oxygen invasion thus the material stability is significantly better than planar perovskite films confirmed by photoluminescence and photoelectric measurements. L-02 Evolution of filament formation in RRAM devices Xing Wu Department of Electrical Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China Objectives: Real-time high-resolution, electrical, chemical, and morphological TEM characterization was carried out on planar FIB-patterned Ni gated dual oxide layers RRAM devices to study the structural and compositional evolution of multiple nanofilaments (MNFs) in the dielectric stack [1]. Methods and Results: We use in-situ TEM to electrically turn on and off the RRAM devices. The formation of single and multiple MNFs were observed, and our results point to the possibility of large variations in the size of different MNFs in the case of multiple filaments formation, as the amount of migrating Ni atoms can greatly vary, leading to different patterns and sizes of MNFs. The MNFs are confirmed to be shaped as “truncated cones,” with the broader side closer to the anode end (i.e., Ni electrode). Furthermore, we observe Ni depletion in the Ni electrode adjacent to the location of the filaments in SET conditions, as well as residual Ni fragments in the dielectric stack after RESET. The unique set of the experimental characterization methods applied in this work and the detailed analysis presented supplies a route to the in-depth characterization of nanoscale filamentation. Conclusions: The presented results directly provide critical information for optimizing the design of future RRAM 1 devices with improved performance and reliability (i.e., narrowing of switching window) and with reduced material/operational variance in both the HRS and LRS. Our following work will involve the TEM-based analysis of the spatial correlation of multiple filaments as well as the size dependence of these nucleated filaments on the compliance setting used for forming and SET events, and future low-power spintronics devices. The experimental routines presented here are broadly applicable for the high-resolution characterization of 2D nanoelectronics devices [2-6], and will lead to new physical insight in a range of 2D layered materials-based polar devices. References: 1. Advanced Electronic Materials 1, 11, (2015). 2. Nano Lett., 16(4), 2548, (2016). 3. Science Advances, 1:e1500462, (2015). 4. Science, 344(6184), 616, (2014). 5. Nat. Comm. 5, 3688, (2014). 6. Nat. Comm. 4, 1776, (2013). Keywords: in-situ TEM; RRAM; dynamic characterization L-03 Hierarchical NiMo-Based 3D Electrocatalysts for Highly-Efficient Hydrogen Evolution in Alkaline Conditions Johnny C. Ho City University of Hong Kong In recent years, electro- or photoelectrochemical water splitting represents a promising route for renewable hydrogen generations but still requires the substantial development of efficient and cost-effective catalysts to further reduce the energy losses and material costs for scalable and practical applications. Here, we report the design and development of a hierarchical electrocatalyst constructed from microporous nickel foam and well-assembled bimetallic nickel-molybdenum (NiMo) nanowires, which are capable to deliver current densities as comparable to those of the state-of-the-art Pt/C catalyst at low overpotentials and even larger current densities at higher overpotentials (> 124 mV). This binder-free 3D hydrogen evolution cathode catalyst also exhibits the excellent stability, without any decay of the current density observed after long-term stability tests at a low current density of 10 mA cm-2 and a high current density of 50 mA cm-2. By pairing this NiMo 3D cathode with a NiFe-based anode, a water electrolyzer can be achieved with a stable current density of 10 mA cm-2 for overall water splitting at a voltage of ~1.53 V, indicating that the water splitting can be indeed realized without any performance sacrifice by using earth abundant electrocatalysts. Keywords: electrocatalysis, nickel-molybdenum alloys, hierarchical nanostrutures, hydrogen evolution L-04 Plasmonic nanoparticles with hidden helicity and optical activity Zhifeng Huang Hong Kong Baptist University The geometrical prerequisite for forming a helix is P (helical pitch) > d (wire diameter). Limited by the current development of nano-fabrication techniques, it is difficult to minimize d and consequently P to the sub-10-nm molecule-comparable scale, preventing the study of chiral plasmonics at dimensions approaching the physical limit. Herein, we operate glancing angle deposition at substrate temperature of 0 °C and high speed of substrate 2 rotation to generate silver nanoparticles (AgNPs) with nominal P < d. The AgNPs have intrinsic chiroptical activity characterized by circular dichroism (CD), originating from the hidden helicity. With increasing P from 3 to 66 nm, the plasmonic mode barely shifts but shows a logarithmic increase in CD amplitude. Immersing AgNPs in water causes the plasmonic mode to redshift and rise in CD amplitude, i.e., a water effect on chiroptical activity. Hydrophilic AgNP arrays with low array porosity show a reversible water effect, but hydrophobic Ag nanospiral arrays with P > d and high array porosity have an irreversible water effect. This work introduces a cost-effective, facile approach to minimize P to sub-10-nm at a regular substrate temperature, paving the way to study chiral plasmonics approaching the physical limit and exploit chirality-related bioapplications typically operated in aqueous solutions to tackle significant health and environmental problems. Keywords: plasmonic nanoparticles, chiroptical activity, reversible water effect, plasmonic nanospirals, glancing angle deposition L-05 Self-assembled BiFeO3-ε-Fe2O3 vertical heteroepitaxy for visible light photoelectrochemistry Ying-Hao Chu National Chiao Tung university Self-assembled vertical heterostructure with a high interface-to-volume ratio offers tremendous opportunities to realize intriguing properties and advanced modulation of functionalities. Here, we design a heterostructure composed of two visible-light photocatalysts, BiFeO3 (BFO) and ε-Fe2O3 (ε-FO), to investigate its photoelectrochemical performance. The structural characterization of the BFO-ε-FO heterostructures confirm the phase separation with BFO nanopillars embedded in the ε-FO matrix. The investigation of band structure of the heterojunction suggests the assistance of photoexcited carrier separation, leading to an enhanced photoelectrochemical performance. The insights into the charge separation are further revealed by means of ultrafast dynamics and electrochemical impedance spectroscopies. This work shows a delicate design of the self-assembled vertical heteroepitaxy by taking the advantage of the intimate contact between two phases that can lead to a tunable charge interaction, providing a new configuration for the optimization of photoelectrochemical cell. Keywords: BiFeO3, photoelectrochemical, water splitting L-06 Controlled Self-assembly of Porphyrin and Applications Jiefei Wang, Yong Zhong, Yanqiu Liu, Na Zhang, Feng Bai Key Laboratory for Special Functional Materials of the Ministry of Education, Henan University Porphyrin self-assembly nanomaterials, as visible-light harvesting materials in the artificial photosynthetic systems that mimic natural photosynthesis, have been well designed and developed via molecular self-assembly with non-covalent interactions including electrostatic force, metal-ligand coordination, π-π stacking, hydrogen bonding as well as host-guest interactions[1-5]. And porphyrin self-assembly with well-defined structures have drawn much attention in a wide range of fields including light-energy conversion, photonics as well as photodynamic therapy due to their attractive photophysical,