12/28 Seminar Speech

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Speaker：Mr. Tsai Song Jau 

Organization：China Steel Corporation

Topic：Open Innovation-China Steel Corporation Industry-University Cooperation Model, which will use the cooperation with schools to develop AHSS lightweight steel and silicon steel sheets for electric vehicle motors as examples.

 Date：10:20 am , 2020.12.21

Location：Room 203, College of Engineering

12/21 Seminar Speech

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Speaker：Professor Yi-Chia Chou

Organization：Department of Electrophysics, National Chiao Tung University  

Topic：Direct Growth of Flexible GaN Film via van der Waals Epitaxy

 Date：10:20 am , 2020.12.21

Location：Room 203, College of Engineering

Abstract；A flexible gallium nitride thin film was obtained on mica through van der Waals epitaxy. A hydride vapor phase epitaxy was applied to fabricate such flexible GaN thin film directly on substrate suing an optimized two-step growing process to form LT-GaN and HT-GaN sequentially. The interfacial stress caused by the mismatches of thermal expansion coefficient and lattice were significantly reduced via van der Waals epitaxy and the proposed two-step growth. A critical (minimum) growth pressure was found to grow the HT-GaN. The optical performance was controlled by interface and surface roughness. For poor-quality LT-GaN, it quickly decomposed during HT-GaN growth and induced high density of defects near the LT-GaN/HT-GaN interface. The defects then caused the GaN film non-transparent. The surface roughness also controlled the transmittance. In the measurement region, the average transmittance decreased linearly as the GaN surface became rougher. A reliability test was approached where the strong bending caused slight PL peak shift, but did not significantly reduced the peak intensity. Thus, such direct grown GaN film on F-mica substrate can be evaluated as a reliable optical device.

12/14 Seminar Speech

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Speaker：Mr. Yiren Wu

Organization：Phrozen 

Topic：Looking at the development of Taiwan's 3D printing industry from Phrozen's founding to the world.

 Date：10:20 am , 2020.12.14

Location：Room 203, College of Engineering

12/07 Seminar Speech

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Speaker：Professor Chen-Tsyr Lo

Organization：Department of Materials and Optoelectronic Science, National Sun Yat-Sen University  

Topic：Synthesis and Applications of Functional Cross-linked Core-shell Block Copolymers

 Date：10:20 am , 2020.12.07

Location：Room 203, College of Engineering

Abstract；A series of high-performance cross-linked core-shell block copolymers as charge-storage or ion-conductive materials will be introduced. We have been studied in the functional core-shell block-copolymer nanoparticles with cross-linking conjugating cores surrounding by hydrophilic shells via Suzuki-coupling reaction, while the nanoparticles with cross-linked cores using triazole-based comprising several ion-conductive functional groups, such as the zwitterionic groups or triazolium groups with salts or ion liquids were also studied. The nanoparticles presented uniform size distribution and well-defined core-shell nanostructure, while the intra-molecular charge transfer was effectively enhanced due to the incorporation of conjugating groups. Both the conjugating-core sizes and π-π interaction of the prepared nanoparticles were effectively controlled by the block composition. Moreover, the studied transistor memory devices embedded with these solution-process-able nanoparticles exhibited non-volatile flash-type memory characteristics and presented both amphiphilic carrier-trapping abilities. For those ionic-conductive nanoparticles, the highest ionic conductivities of 1.26 × 10^–3 S/cm were achieved at 90 ^oC with the presence of 30 wt.% ionic liquid, which are due to the enhanced segmental molecular motion and the formation of a preferable ionic-conductive path composed of the hydrophobic ionic-liquid based shell with the added ionic liquid. We believe this achievement provides multiple applications of cross-linked nanoparticles as a promising candidate for both charge-storage and ion-conductive materials in the future organic technology.

11/30 Seminar Speech

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Speaker：Professor PI-HO HU

Organization：Department of Electrical Engineering, National Taiwan University  

Topic：Ferroelectric FET Non-volatile Memory

 Date：10:20 am , 2020.11.30

Location：Room 203, College of Engineering

Abstract；Artificial intelligence (AI) and Internet-of-Things (IoT) play a vital role in the future. For the von Neumann architecture, communication bottleneck between memory and processors becomes one of the most series problems due to low data throughput and high-power consumption. Non-volatile memory (NVM) based synapse and logic-in-memory circuit have been proposed to alleviate these problems. Ferroelectric Field-Effect-Transistor (FeFET) has been explored actively for emerging non-volatile memory and neuromorphic computing due to its high compatibility with CMOS platform. In this talk, I will introduce the operation principles and the challenges of FeFET memory. We have proposed a novel split-gate FeFET (SG-FeFET) for non-volatile memory and neuromorphic applications, which significantly improves the energy efficiency and reduces the power consumption. The reliability and endurance of SG-FeFET memory have also been improved owing to the lowered write voltage. SG-FeFET as a synaptic device has also been investigated including the non-linearity, asymmetry, and dynamic range of conductance updates.

11/23 Seminar Speech

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Speaker：Professor Chia-Shain Chuang

Organization：Department of Electronic Engineering, Chung Yuan Christian University  

Topic：Investigations for magnetoresistance of ultralow-hole-density monolayer epitaxial graphene grown on SiC systems

 Date：10:20 am , 2020.11.23

Location：Room 203, College of Engineering

Abstract；In this talk, I focus on detailed measurements on ultralow-density p-type monolayer epitaxial graphene, which has yet to be extensively studied. The measured resistivity ρxx shows insulating behavior in the sense that ρxx decreases with increasing temperature T over a wide range of T (1.5 K ≤ T ≤ 300 K). The crossover from negative magnetoresistivity (MR) to positive magnetoresistivity at T = 40 K in the low-field regime is ascribed to a transition from low-T quantum transport to high-T classical transport. For T ≥ 120 K, the measured positive MR ratio [ρxx(B) − ρxx(B = 0)]/ρxx(B = 0) at B = 2 T decreases with increasing T, but the positive MR persists up to room temperature. Our experimental results suggest that the large MR ratio (~100% at B = 9 T) is an intrinsic property of ultralow-charge-density graphene, regardless of the carrier type. This effect may find applications in magnetic sensors and magnetoresistance devices.
Keywords: epitaxial graphene, resistance standard, magnetoresistance, quantum hall

11/16 Seminar Speech

Hits:375

Speaker：Professor Pin-Jui Hsu

Organization：Department of Physics, National Tsing Hua University  

Topic：Proximity-Effect-Induced Superconductivity in Monatomic Ni-Pb Alloy and Ni Nanoislands

 Date：10:20 am , 2020.11.16

Location：Room 203, College of Engineering

Abstract；Proximity effect facilitates the penetration of Cooper pairs that permits superconductivity in normal metal with reduced dimensionality, offering a promising approach to develop novel quantum phenomena and emergent phases of matters in hybrid magnetic/superconducting nanostructures. Here, we have investigated proximity-induced superconductivity in monatomic Ni-Pb alloy and Ni nanoislands grown on Pb(111) by scanning tunneling microscopy/ spectroscopy (STM/STS) combined with theoretical calculations. Through elemental Pb superconducting substrate, tunneling conductance spectra have resolved an induced superconductivity with a gap size Δ about 0.85 meV in Ni-Pb alloy, which is about 0.11 meV smaller than Pb(111). On the contrary, Ni nanoislands with honeycomb lattice display a superconductivity gap with the same size of the Pb(111) substrate. From spatially monotonic decrease of Δ across the interface between Ni-Pb alloy and Pb(111), the decay length ξ_L about 5 nm has been extracted. According to the Usadel fittings and the BdG model, a weak ferromagnetism with an effective temperature about 6 ~ 15 K explains such rather short decay length as well as reduced superconductivity gap in the Ni-Pb surface alloy. As for honeycomb-structured Ni nanoislands, asymmetric edge scattering of surface electrons on Pb(111) has been revealed and further theoretical insights on the details of strong suppression of backscattering at the bearded type of edges are currently in progress.

11/02 Seminar Speech

Hits:372

Speaker:Dr. Tien-Ming Chuang

Topic: Visualizing Emergent Superconductivity by Spectroscopic Imaging - Scanning Tunneling Microscopy

10/26 Seminar Speech

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Speaker: Professor Hsin-Jay Wu

Topic: Phase diagram engineering - A New Avenue Towards High Performance Thermoelectric Materials