October 2015 - December 2015
 
 
 
Publisher: Chairman Gong-Ru Lin  Editors: Professor Chao-Hsin Wu, Ms. Hsiao-wen Lin  February 29, 2016
 
 

Congratulations to GIPO professor Gong-Ru Lin! A collaborative paper authored by Professor Lin and other international scholars has been quoted and was the subject of a focused report by Nature Photonics.

For further information, please refer to the following GIPO website: http://gipo.ntu.edu.tw/p5news-detail.php?sn=8647

Congratulations to the following graduate students on being awarded, under the instruction of Professor Chi-Kuang Sun and Professor Gong-Ru Lin, the “2015 Youth Theses Prize of the Chinese Institute of Electrical Engineering”. The winners’ list is as follows:

The 1st place:

Winner Adviser Thesis title
Chung-Yu Lin (Master student)

Professor Gong-Ru Lin

Directly Modulated Dual-wavelength Laser Carrier Based MMWoF Wireless Communication Network

The 3rd place:

Winner Adviser Thesis title
Szu-Yu Lee (Master student)

Professor Chi-Kuang Sun

Realization and Implementation of Two-photon Acoustic Microscopy

Congratulations to Chun-Yen Lin, GIPO master student, on being awarded, under the instruction of Professor Gong-Ru Lin, the “ACP 2015 Best Student Paper” prize!

Congratulations to Shu-Ming Hsu, GIPO master student, on being awarded, under the instruction of Professor I-Chun Cheng, the “TVS-2015, Taiwan Vacuum Society 2015, Excellent Thesis Prize” and the “IEDMS-2015, International Electron Devices and Materials Symposium 2015, Best Paper Award”!

Congratulations to GIPO professors Lon A. Wang, Lung-Han Peng, Jui-Che Tsai, Yuh-Renn Wu and Chao-Hsin Wu, all members of EECS slow-pitch softball team, for placing 2nd at the “2015 NTU College of Engineering, EECS, College of Law & College of Science Teachers/Staff Slow-pitch Softball Tournament”!

Congratulations to GIPO professors Lung-Han Peng and Yuh-Renn Wu, and Ms. Li-Chi Yao, all members of the EECS track & field team, for winning the “Teachers/Staff 1200m Relay Race of the 66th NTU Games”!

Congratulations to GIPO professor Hung-Chun Chang on being awarded the “2015 Photonics Engineering Prize” from Taiwan Photonics Society!

Congratulations to Hsiang-Yu Chen, GIPO master student, on being awarded, under the instruction of Professor Gong-Ru Lin, the “Optic 2015 Student Paper Award” from Taiwan Photonics Society!

Congratulations to the following master/doctoral students on being awarded the “OPTIC 2015 Student Paper Award”, under the instruction of each of the following advisers:

 Student

 Award

 Adviser

Cheng-Ting Tsai

OPTIC 2015 Student Paper Award, doctoral student

Gong-Ru Lin

Yun-Shiuan Li

OPTIC 2015 Student Paper Award, doctoral student

I-Chun Cheng

Chen-Yen Lin

OPTIC 2015 Student Paper Award, doctoral student

Chi-Kuang Sun

Ting-Yang Chen

OPTIC 2015 Student Paper Award, master student

Jian-Jang Huang

Wen-Yi Lan

OPTIC 2015 Student Paper Award, master student

Jian-Jang Huang

Jia-Wei Wu

OPTIC 2015 Student Paper Award, master student

Ching-Fuh Lin

Shang-Pang Lin

OPTIC 2015 Student Paper Award, master student

Ching-Fuh Lin

 

 
 

September “GIPO Colloquium” Highlights (Compiled by Li-Chi Yao)

Time:

4:30 pm, Sept. 18 (Fri.), 2015
Speaker: Professor Feng-Huei Lin (Institute of Biomedical Engineering, NTU)
Topic: The Development of Nanoparticles on Cell Imaging Tracking
  Professor Feng-Huei Lin visited GIPO on Sept. 18 (Fri.) and delivered a speech concerning “The Development of Nanoparticles on Cell Imaging Tracking” at auditorium 101, Barry Lam Hall. His speech was informative and the professor interacted well with participants. GIPO teachers and students participated with enthusiasm and learned a great deal.
 

Professor Feng-Huei Lin (right) and Professor Sheng-Lung Huang (left), the host of this speech

 

Time:

10:30 am, Sept. 22 (Tue.), 2015
Speaker: Professor Mona Jarrahi (Electrical Engineering Department, University of California Los Angeles)
Topic: New Frontiers in Terahertz Technology
  Professor Mona Jarrahi visited GIPO on Sept. 22 (Tue.) and delivered a speech concerning “New Frontiers in Terahertz Technology” at auditorium 101, Barry Lam Hall. Her speech was interesting, and the professor interacted well with her audience. GIPO teachers and students participated with enthusiasm and learned a great deal.
 

Professor Mona Jarrahi (right) and GIPO chairman, Professor Gong-Ru Lin (left)

 

Time:

4:30 pm, Sept. 25 (Fri.), 2015
Speaker: Professor Shoou-Jinn Chang (Dept. of Electrical Engineering, National Cheng Kung University)
Topic: InGaN-based Photonic Devices with tunnel-junction-cascaded structure
  Professor Shoou-Jinn Chang visited GIPO on Sept. 25 (Fri.) and delivered a speech concerning “InGaN-based Photonic Devices with tunnel-junction-cascaded structure” at auditorium 101, Barry Lam Hall. His speech was informative, and the professor interacted well with his audience. GIPO teachers and students learned a great deal from the event.

 

Professor Shoou-Jinn Chang (right) and GIPO chairman, Professor Gong-Ru Lin (left)

 

October、November “GIPO Colloquium” Highlights (Compiled by Li-Chi Yao)

Time:

4:30 pm, Oct. 30 (Fri.), 2015
Speaker: Professor Jia-Ming Liu (Electrical Engineering Department, UCLA)
Topic: Terahertz Graphene Photonics and Plamsonics
 

Professor Jia-Ming Liu visited GIPO on Oct. 30 (Fri.) and delivered a speech concerning “Terahertz Graphene Photonics and Plamsonics” at auditorium 105, EE Building II. His speech was fascinating and the professor interacted well with students. GIPO teachers and students were happy to participate in this event, and learned a great deal.

 

Professor Jia-Ming Liu (left) and GIPO chairman, Professor Gong-Ru Lin (right)

 

Time:

4:30 pm, Nov. 6 (Fri.), 2015
Speaker: Professor Arthur Chiou (Biophotonics and Molecular Imaging Research Center , National Yang-Ming University)
Topic: How Optical Microrheology & Microscopy Quantify Biophysical Markers to Complement the Biochemical at Cellular and Sub-cellular Level?
 

Professor Arthur Chiou visited GIPO on Nov. 6 (Fri.) and delivered a speech concerning “How Optical Microrheology & Microscopy Quantify Biophysical Markers to Complement the Biochemical at Cellular and Sub-cellular Level?” at auditorium 101, Barry Lam Hall. His speech was excellent and the professor interacted very well with students. GIPO teachers and students participated with enthusiasm and learned a great deal.

 

Professor Arthur Chiou (right) and GIPO Professor Si-Chen Lee (left)

 

Time:

2:30 pm, Nov. 16 (Mon.), 2015
Speaker: Professor David J. Hagan (CREOL, UCF)
Topic: Nonlinear refraction and absorption: Mechanisms, Characterization and Applications
 

Professor David J. Hagan visited GIPO, in answer to GIPO professor Jiun-Haw Lee’s invitation, on Nov. 16 (Mon.) and delivered a speech concerning “Nonlinear refraction and absorption: Mechanisms, Characterization and Applications” at auditorium 105, EE Building II. His speech was informative and the speaker interacted very well with students. GIPO teachers and students attended this event with enthusiasm and learned a great deal.

 

Professor David J. Hagan (left) and Professor Jiun-Haw Lee (right), the host of this speech

 

Time:

4:30 pm, Nov. 20 (Fri.), 2015
Speaker: Professor Wood-Hi Cheng (visiting professor, Graduate Institute of Optoelectronic Engineering, National Chung Hsing University)
Topic: The Art and Science of Packaging High-Coupling Photonics Devices
  Professor Wood-Hi Cheng visited GIPO on Nov. 20 (Fri.) and delivered a speech concerning “The Art and Science of Packaging High-Coupling Photonics Devices” at auditorium 101, Barry Lam Hall. His speech was excellent, and the professor interacted well with his audience. GIPO teachers and students were happy to attend this event and learned a great deal.

 

Professor Wood-Hi Cheng (middle), GIPO Professor Hung-Chun Chang (left), and Professor Sheng-Lung Huang (right), the host of this speech

 

December “GIPO Colloquium” Highlights (Compiled by Li-Chi Yao)

Time:

4:30 pm, Dec. 4 (Fri.), 2015
Speaker: Professor Ursula J. Gibson (Department of Physics, Norwegian University of Science and Technology)
Topic: New materials for Solar Energy and Mid-infrared applications
  Professor Ursula J. Gibson visited GIPO, in answer to GIPO professor Lon A. Wang’s invitation, on Dec. 4 (Fri.) and delivered a speech concerning “New materials for Solar Energy and Mid-infrared applications” at auditorium 101, Barry Lam Hall. Her speech was fascinating and the professor interacted well with students. GIPO teachers and students participated with enthusiasm and learned a great deal.
 

Professor Ursula J. Gibson (right) and Professor Lon A. Wang (left), the host of this speech

 

Time:

4:30 pm, Dec. 18 (Fri.), 2015
Speaker: Professor Bing Sheu (emeritus chair professor, National Chiao Tung University)
Topic: In digital era, the best role and strategy for one to play and integrate with information
  Professor Bing Sheu visited GIPO on Dec. 18 (Fri.) and delivered a speech concerning “In digital era, the best role and strategy for one to play and integrate with information” at auditorium 101, Barry Lam Hall. His speech was interesting, and the speaker interacted very well with students. GIPO teachers and students participated with enthusiasm and benefited a great deal.
 

Professor Bing Sheu (right) and Professor Chih-I Wu (left), the host of this speech

 

Time:

4:30 pm, Dec. 25 (Fri.), 2015
Speaker: Professor Yuan Luo (Institute of Medical Device and Imaging, NTU)
Topic: Spatial-spectral biomedical imaging
  Professor Yuan Luo visited GIPO on Dec. 25 (Fri.) and delivered a speech concerning “Spatial-spectral biomedical imaging” at auditorium 101, Barry Lam Hall. His speech was fascinating and the professor interacted well with his audience. GIPO teachers and students were happy to attend this event and learned a great deal.
 

Professor Yuan Luo (right) and Professor Sheng-Lung Huang (left), the host of this speech

 

 

 
 

~ 2015 Ph.D. Student Academic Exchange with Nanjing University ~

(The 8th Cross-Strait Ph.D. Student Forum on Photonic Science and Technology, 2015)

(Time: Nov. 15-20, 2015; Location: Nanjing University)

Composed by Chia-Ying Su, GIPO Ph.D. student

The Cross-Strait Ph.D. Student Forum on Photonic Science and Technology has entered its 8th year in 2015. This excellent long-term relationship can be attributed to hard work from both GIPO, NTU, and the School of Physics, NJU. It is a student-oriented activity, and each year, NTU and NJU take turns to sponsor it. Its purpose is to inspire, through workshops and cultural interactions, more comprehensive study inspirations and more opportunities for cooperation. Five out of the ten NTU students who are participating this year have already attended last year’s symposium, and I’m honored to be one of them and to be able to help in passing down this tradition. In addition to their own outstanding students, NJU has also invited students of other neighboring universities, including Nanjing Tech University, Southeast University, Nanjing University of Aeronautics and Astronautics, and Soochow University, to participate in this event. Therefore, there were 21 mainland students attending this symposium.

A group photo of all attendants of the Ph.D. Student Forum

In mid-November, our GIPO chairman, several professors and the doctoral students set out to Nanjing University, Jiangsu province, to begin this 6 days’ activity. It was already Sunday afternoon when we finally arrived at Nanjing Lukou International Airport. As soon as we entered the arrival hall, all we saw were smiling faces of NJU students’. Most of them were students who had visited Taiwan last year. The moment we saw these familiar faces once again after a whole year, laughter and greetings burst out all over the hall. Our friendship with NJU students developed from last year was not diminished by time. And, at this very moment, time seemed to have drawn us back to the scene of one year ago, in Taipei, so lovely, so familiar.

NJU students enthusiastically pick us up at the airport

The academic discussion lasted for 2 whole days; the agenda was packed with fascinating topics. The symposium did not appear to be inferior to other international conferences. There were both universities professors’ lectures and students’ study reports covering the following 6 subjects: “solid state lighting and display”, “nonlinear optics”, “two-dimensional materials and devices”, “physics optics and laser technology”, “plasmonics and metamaterials”, and “photoelectric energy conversion, solar cell and battery”.

 

Professors addressed the opening ceremony

Six professors gave us lectures on academic studies. Professor Jian-Jang Huang lectured on the study of “Enhancement-mode GaN on Si HEMTs”, which led to the production of high breakdown voltage device when a layer of pGaN was inserted under gate electrode. Professor Xing-Long Wu, NJU, lectured on the characters of oxygen creation and facet-cutting in the production of core/shell ZnO mesocrystal in terahertz frequency range with radiative emission and cubic In2O3 microparticles. He also lectured on the study of β-FeSi2 nanocubes, which produced very strong ferromagnetism even at room temperature. Professor Hoang-Yan Lin lectured on the study of a vision field calculation model displayed in 3D image. Professor Xiaoyong Wang, NJU, lectured on his study in a series of perovskite new materials. Professor Chao-Hsin Wu lectured on the exploration of achieving Giga-Hz spontaneous optical bandwidth by virtue of modulating base-collector voltage of light-emitting transistor. Professor Jia Zhu, NJU, showed us the way of using metal nanosphere to increase absorption and field strength, so as to enhance the solar energy transform efficiency to 90%.

A snapshot of professors lecturing

In the students’ study reports, each student had to report on his or her study and answer questions in 15 minutes. Besides answering other students’ questions, reporting students would also receive suggestions and advice from Professor Tao Yu, NJU, and Professor Jia Zhu, NJU. In the reporting, through academic exchange, students could realize the most advanced research of different fields, and could also gain valuable knowledge from related fields, which would of course benefit their future researches. I had noticed some differences between Taiwan and Mainland students. Generally speaking, Mainland students spoke faster, more smoothly, with full confidence, and used lots of references; therefore, I had to pay close attention to follow their reports. Taiwan students, on the other hand, paid more attention to interactions with the audience. While reporting, they observed the audience from time to time, detected audiences’ spontaneous reactions, and thereby modulated their tempo. The result was that all attendants of the report felt quite comfortable and at ease.

A snapshot of NTU students reporting

During lunchtime at the symposium, the NJU students gave up their breaks to take us around their large campus for some sightseeing. Because of its high latitude, Nanjing was of the most beautiful during those early winter days. Rolls of yellow-leaved gingko trees stood along both sides of the trail. Lots of yellow leaves fell on the ground forming a beautiful blanket. Some leaves were just turning from green into brown, and their motley colors beautified the whole campus. We visited some historical buildings, such as Beidalo, a landmark building built in 1919, the small auditorium, and the library. We also took a group photo in front of NJU south gate.

A view of NJU campus scenery

At the end of the symposium, students from both sides exchanged presents, and voted for the 2 best theses and 2 best personality students from each side. Among Mainland students, Xiao-Chen Sun and Liangliang Sun were chosen the best thesis students. It’s the second time Xiao-Chen won the best thesis; he won for the first time last year. His distinct speech and steady style impressed me greatly. And, Liangliang’s poised manners and systematic reporting style has become our goal to learn. The Mainland’s 2 best personality winners were Chong Sheng, the well-known captain of the Mainland team, and Jin-Hui Chen. It’s the second time that Chong Sheng participated in this symposium. After forming good friendships from last year, he further took on the captain’s responsibility to take care of everything. Jin-Hui looked after the Taiwan students thoroughly, leading us on the tour of the NJU campus, sending us to the conference room and back to the hotel and ensuring that we would return to the hotel in time every night. Among the Taiwan students, Tsung-Chin Cheng won the best thesis prize because his report was considered very comprehensive. Li-Jen Hsiao, the captain of the Taiwan team, won the best personality prize because he took on the laborious responsibility to take care of the whole team. I would like to thank the Mainland students’ for their kindness in conferring both the best thesis and the best personality prizes upon me. It was such a great honor! I was grateful and also under pressure, being the first student to report on stage. Nevertheless, the pressure inspired me to maximize my potential. And, I would like to thank my instructing professor for his assistance and effective training during the process, which made it possible for me to win this prize. Furthermore, I was the only girl on Taiwan team; perhaps that made me stand out during the activities at the symposium. Perhaps that is the real reason that I won the best personality prize.

Students from both sides exchanging gifts

A snapshot of the awarding ceremony, (left) NJU best thesis winners – Xiao-Chen Sun & Liangliang Sun, and (right) NJU best personality winners – Chong Sheng & Jin-Hui Chen

A snapshot of the awarding ceremony, NTU winners – Chia-Ying Su, Li-Jen Hsiao & Tsung-Chin Cheng

Finally, we would like to thank GIPO office for providing this rare opportunity for students from both sides to meet and exchange ideas, appreciate each other’s culture and establish friendship. Although it lasted for 6 days only, I do believe that the wonderful memories and the academic value it created is worth far more than the 6 days we spent. Therefore, I would suggest that GIPO junior students strive for the opportunities to join this symposium, so as to improve yourselves, increase your knowledge and enhance your personal connections.

 

 
 
Plasmon-enhanced Photoluminescence of an Amorphous Silicon Quantum Dot Light-Emitting Device by Localized Surface Plasmon Polaritons in Ag/SiOx:a-Si QDs/Ag Sandwich Nanostructures

Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We investigated experimentally the plasmon-enhanced photoluminescence of the amorphous silicon quantum dots (a-Si QDs) light-emitting devices (LEDs) with the Ag/SiOx:a-Si QDs/Ag sandwich nanostructures (Fig. 1), through the coupling between the a-Si QDs and localized surface plasmons polaritons (LSPPs) mode, by tuning a one-dimensional (1D) Ag grating on the top. The coupling of surface plasmons at the top and bottom Ag/SiOx:a-Si QDs interfaces, resulting in the localized surface plasmon polaritons (LSPPs) confined underneath the Ag lines, which exhibit the Fabry–Pérot resonance. From the Raman spectrum, it proves that the existence of a-Si QDs embedded in Si-rich SiOx film (SiOx:a-Si QDs) at a low annealing temperature (300℃) to prevent the possible diffusion of Ag atoms from Ag film. The photoluminescence (PL) spectra of a-Si QDs can be precisely tuned by a 1D Ag grating with different pitches and Ag line widths (Fig. 2) were investigated. An optimized Ag grating structure, with 500 nm pitch and 125 nm Ag line width, was found to achieve up to 4.8-fold PL enhancement at 526 nm and 2.46-fold PL integrated intensity compared to the a-Si QDs LEDs without Ag grating structure, due to the strong a-Si QDs–LSPPs coupling (Fig. 3). (International Journal of Photoenergy (Volume 2015 (2015), Article ID 140617)

Fig. 1. Schematic view of a-Si QDs LEDs with a Ag/SiOx:a-Si QDs/Ag sandwich nanostructures

Fig. 2. SEM images of a series of Ag gratings (samples B-E). Scale bar is 1 μm

Fig. 3. The plots of the PL enhancement factor of samples B-E

 

Direct QAM-OFDM Encoding of a Master-to-Slave Injection-Locked WRC-FPLD Pair for 28×20 Gbit/s DWDM-PON Transmission

 Professor Gong-Ru Lin’s laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

This work demonstrated a master-to-slave injection-locked weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) pair, which is capable of carrying an orthogonal frequency division multiplexed 16-quadrature amplitude modulation (16-QAM OFDM) data at 20 Gbit/s/channel for 28 channels in a dense wavelength division multiplexing passive optical network (DWDM-PON), as illustrated in Fig. 1. Since the lower front-facet reflectance and longer cavity features of WRC-FPLD, it reveals broader gain spectrum with denser longitudinal modes and higher injection efficiency than a typical FPLD for supporting more DWDM channels. As a result, the optical spectra of master and slave WRC-FPLDs are shown in Fig. 2. After passing through a demultiplexer with a channel spacing of 50 GHz for the central mode of master WRC-FPLD, the filtered single-mode master with a peak power of -4 dBm was employed to injection-lock the slave WRC-FPLD, which achieves a side-mode suppression ratio (SMSR) of 50 dB. Moreover, the bit error rate (BER) performances of back-to-back and 25-km single-mode fiber (SMF) transmitted 20-Gbit/s OFDM data carried by the master-to-slave injection-locked WRC-FPLD pair at different channels are shown in Fig. 3. For the central mode injection case, the back-to-back transmitted BER of 1.6×10-5 can be improved to 2.9×10-7 by employing the OFDM subcarrier per-leveling technique, and it is inevitably degraded to 2.1×10-4 due to the fiber dispersion after 25-km SMF transmission. To meet the forward error correction (FEC) the required BER of 3.8×10-3, 28 DWDM channels can be obtained to reveal a total data-rate of 28×20=560 Gbit/s. Therein, a slightly decreased SMSR of 35 dB is also obtained for the farthest side-mode injection case. In conclusion, the master-to-slave injection-locked WRC-FPLD pair has shown its competitive performance and superior flexibility to fit multi-channel DWDM-PON transmission.

Fig. 1. The schematic diagram of the master-to-slave injection-locked WRC-FPLD pair based DWDM-PON system for direct 16-QAM OFDM modulation and transmission.

Fig. 2. The optical spectra of master and slave WRC-FPLDs.

Fig. 3. The BER performances of back-to-back and 25-km SMF transmitted 28-Gbit/s 16-QAM OFDM data.

 

Enhancing Light Out-Coupling of Organic Light-Emitting Devices with Nanostructured Composite Electrodes

Professor Chung-Chih Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Due to their various merits, organic light-emitting devices (OLEDs) have posed as promising candidates for the next-generation display and lighting technologies. All these applications have been imposing increasing efficiency requirements on OLEDs. While internal quantum efficiencies close to 100% have been reported with phosphorescent or other triplet-harvesting OLEDs, typical OLEDs suffer from a poor extraction efficiency of internally generated photons, resulting from a large mismatch of the refractive indices between organic layers, indium tin oxide, glass, and air. The total internal reflection at the interfaces of devices strongly traps photons inside the device, which significantly limits the external quantum efficiency (EQE) of OLEDs. It is known that ~70-80% of the generated photons are trapped in conventional OLED structures due to total internal reflection or coupling to surface plasmon polaritons (SPPs) at the metallic surface. In our studies, we have developed a novel internal extraction structure using a nanostructured composite transparent electrode (Figure 1), which not only functions as the current conductor/injector for the device but also significantly enhances out-coupling of OLED internal radiation. With such a technique, we have realized a very high externalquantum efficiency of 62% and a very high luminous efficiency of 264 lm/W in OLEDs (Figure 1).

Figure 1. Achieving very high external quantum and power efficiencies of OLEDs with nanostructured composite electrodes

 

Flexible Transparent Graphene-based Composite Transparent Electrode Prepared with Copper Vapor Assisted CVD and Innovative Polymer-free Transfer Method

Professor Chih-I Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The major tasks of this research project is to fabricate flexible or transparent perovskite halogenide solar cells by whole solution processes for high enough energy conversion efficiency at low sun luminance condition. The initial achievements of whole solution processes and optoelectronic characterization include one-step precursor deposition, solvent induced fast crystallization, vapor assisted solution process. Each of these processing technologies resulted in the analyses comparing their I-V curves, fill factor, open-circuit voltage, optoelectronic energy conversion efficiency. These measurements were done for different fil thickness, since the correlation between characterizations and thickness is important to evaluate the flexibility and transparency of perovskite solar cells.

Transparent graphene electrode materials have been improved by innovative copper vapor assisted C. V. D. for graphene/Cu composite thin film synthesis. Such grown composite electrode were transferred by special "Protective Frame Transfer Method" to form double layered composite electrode material that held transmittance 94.4% and low electric sheet resistance as 0.1 k ohm/sqare. 2D-band to G-band peak ratio of 1.8 measured by Raman spectroscopy, and X-ray Photoelectron Spectroscopy (X.P.S.) showed minor existence of copper on graphene, such evidence of Cu on graphene surface was supported with photograph taken using scanning electron microscopy. Those peak positions of 2D-band and G-band were found shifted to higher Raman Shift (1/cm) side. These phenomena imply that C-C bonding strength of graphene intra-plane and inter-layer van der Waal bonding could be enhanced at those portions where copper particles/islands are bonded to graphene. Comparing graphene/Cu composite and that etched off copper with nitric acid solution, their density of states analyses for valence band using Ultraviolet Photoelectron Spectroscopy showed that semi-metallic graphene’s valence band structure had no significant rising 1~2 eV near Fermi Level for this composite thin film. Thus, the enhanced electric conductivity could majorly be attributed to the bridging effect of lower resistant copper particles/islands across high resistant domain boundaries of graphene leading to increased electric current paths through low electric sheet resistance. Resulted in much higher successful film transfer ratio, this bridging effect had been supported by enhanced mechanical strength effect of graphene/Cu composite films than pure graphene films.

Fig. 1. SEM photographs: (a) Near; (b) farther from, (c) near, uniform temperature zone

Fig. 2. Raman spectroscopic plots

Fig. 3. X-ray Photoelectron Spectroscopic plots showing work function increase with graphene/copper composites

Fig. 4. Ultraviolet Photoelectron Spectroscopic plots showing no density of states increase near Fermi Level with graphene/copper composites

 

A Circular-Ring Miniaturized-Element Metasurface With Many Good Features for Frequency Selective Shielding Applications

 Professor Yih-Peng Chiou's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

A novel circular-ring miniaturized-element (CRME) metasurface is proposed for frequency selective electromagnetic shielding applications in this paper. The proposed structure exhibits good performance in many aspects. The CRME size can be easily reduced to 0.088rx0.088r, where r is the wavelength at resonance. Such small size can be useful in applications with limited space. The newly proposed metasurface not only shows the stability to incidence angles and polarizations, but also demonstrate negligible polarization crossing. The metasurface also presents low coupling between elements, which leads to the insensitivity of periodicity fluctuation in fabrication process. Moreover, the frequency responses can be varied through the modification of the element pattern of the metasurface. It provides flexible frequency responses to use in frequency selective shielding applications. Also, this element is suitable for constructing a metasurface aligned in either square or even hexagonal lattice, which owns the best adaptability to a doubly curved surface or a spherical one. Without revising the CRME, both the squareand hexagonal-lattice metasurfaces constructed can perform competently at the same time. Finally, the metasurface prototype is fabricated and tested in a fully anechoic chamber to verify the design. The measured results well agree with the simulated ones. This work is published in IEEE Transaction on Electromagnetic Compatibility, June 2015.

Left: The fabricated prototype of the eight-turn CRME metasurface with the line width of 0.15 mm and Λ = 6.7 mm. Right: Eight-turn CRME metasurface at normal incidence. Simulated and measured results are very consistent.

 

Improvement of color stability in white organic light-emitting diode by phosphor dopant

 Professor Jiun-Haw Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

With the incorporation of thin (4 nm) and lightly doped (1%) phosphor, tris(phenylpyridine)iridium (Ir(ppy)3), inside the emitting layer close to the electron transporting layer interface of an organic light-emitting diode (OLED), electron injection characteristic was improved. Together with the recombination zone shift under different voltage driving, a white OLED with stable electroluminescence (color coordinate shift (0.012, 0.002) from 100 to 10000 cd/m2) was demonstrated.

Fig. 1. Electroluminescence spectra of OLED (a) without and (b) with interface phosphor dopant

 

 
 
 
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