June 2009 - August 2009
Publisher: Chairman Sheng-Lung Huang  Editors: Prof. Jui-che Tsai, Ms. Hsiao-wen Lin  September 30, 2009
May “Photonics Forum” Lecture Highlights


May 1st (Friday), 2009  2:30 PM
Speaker: Prof. Gavin Conibeer (University of New South Wales, Australia)
Topic: Third Generation Photovoltaics

Prof. Gavin Conibeer visited GIPO on May 1st (Friday), 2009, and lectured in room 105, the EE Building II. His lecture, “Third Generation Photovoltaics” elicited enthusiastic participation from GIPO professors and students, and everyone learned much.



Workshop on Display, Lighting, and Solar Cell Optoelectronics Technologies


May 8th (Friday), 2009 10:00 AM ~ 5:50 PM


Deputy Director Chien-Jen Sun (Electronics & Optoelectronics Research Laboratories, Industrial Technology Research Institute)、Professor Jian-Jang Huang (GIPO)、Professor Guo-Dung Su (GIPO)、Professor Hoang-Yan Lin (GIPO)、Professor Ching-Fuh Lin (GIPO)、Director Chung-Wen Lan (Photovoltaics Technology Center, Industrial Technology Research Institute) 


Professor C. C. Yang, Professor Hung-Chun Chang, Professor Jian-Jang Huang, Professor Lung-Han Peng


95 visitors, 60 GIPO students


Auditorium 101, Barry Lam Hall, National Taiwan University


The “Workshop on Display, Lighting and Solar Cell Optoelectronics Technologies”, planned by GIPO professor C. C. Yang, took place on May 8th in auditorium 101 of Barry Lam Hall. From the Industrial Technology Research Institute, Director Chung-Wen Lan of the Photovoltaics Technology Center and Deputy Director Chien-Jen Sun of Electronics and Optoelectronics Research Laboratories were specially invited to speak at this event. In addition, four GIPO professors (Professor Ching-Fuh Lin, Professor Hoang-Yan Lin, Professor Guo-Dung Su, Professor Jian-Jang Huang) also attended as speakers. Visiting participants from all over Taiwan attended the workshop with enthusiasm. Aside from GIPO students and professors, workshop participants included directors and research and development personnel from the industry, professors and master and doctoral students from other schools, and personnel from research institutions. This workshop allowed GIPO professors and students to better understand the current state of this industry and the direction of future development.



~ Self Introduction of the 2009-10 President of the GIPO Student Association ~

Composed by GIPO doctoral student Hsiang-Chun Wei (newly appointed President of the GIPO Student Association)

Hello everyone, it is an honor to serve as the President of the Student Association this year for GIPO professors and students. My name is Hsiang-Chun Wei, and I am a 3rd year doctoral student, studying in Professor Guo-Dong Su’s laboratory. It has been 2 years since I was admitted into GIPO, and I have become accustomed to this environment by degrees. GIPO has the best teachers, best students, and best facilities in the country, and so naturally, concentrating on and excelling in research is a goal that we all strive toward. During those late nights at the laboratory, when anxiety causes pimples to surface on your nose, did you wish that life could be a little more fun and exciting? Have you overlooked the beauty of nature when you are buried under piles of journals? During this one year's term, I would like to bring some amusement to the lives of my fellow classmates.

Please allow me to introduce to you our capable vice-president Jay-Zway Hong, with whom I’m thrilled to work with. He is a 2nd-year master student, studying in Professor Ming-Hua Mao's laboratory. Jay-Zway is a man of enthusiasm with a sense of responsibility and also a sense of humor. With such a strong team, we will work hard to serve you efficiently in building friendships among students, among laboratories, and between GIPO staffers and students.

When I was approached to prepare a self introduction for the GIPO newsletter, I had no idea what to write. I am not quite an outstanding researcher, I am neither well-known nor especially attractive, and I have no fresh and creative political views. Nevertheless, the one guarantee I can make is that I will be working to serve you anywhere, anytime, and that activities and events which should take place, will take place. One for all, all for one!


~ Highlights from GIPO's Summer Photonics Camp, 2009 ~

(Time: July 15th ~ 17th, 2009; Location: Barry Lam Hall and EE Building II, National Taiwan University)

Composed by GIPO master student Jay-Zway Hong (newly appointed Vice President of the GIPO Student Association)

Taiwan’s optoelectronics industry is renowned worldwide, and has become known as the “Taiwan Miracle”. Many students have nevertheless wondered how this industry could thrive during today's financial crisis. The challenges and trends of this industry have been of great interest. The photonics camp, held every year by NTU GIPO, enjoys great popularity among college students across the country, and will answer all your questions.

The summer photonics camp has been a GIPO tradition for years. Students curious about optoelectronics gather from different universities all around the country to unveil the mysteries of Taiwan's optoelectronics industry. With a series of lectures concerning signal transmission and processing, display, optical storage, light-emitting components, energy, and industrial upgrade; the camp provides a detailed and thorough explanation for students.

During the camp, students who are fascinated by the optoelectronics industry learned about the most advanced technological developments and principals, as well as information known only to those inside industrial circles. In these three short days, students filled their brain with optoelectronics knowledge, and their stomach with delicacies. Then, eager to begin work and with a sparkle in their eyes, students returned home and showed off what they have learned in the camp, and shared these with their parents and classmates.

In view of the fact that personal experience always makes a deeper impression than lectures, the camp is designed to provide opportunities for students to do experiments with their own hands. During the afternoon of the first day, we arrived at an optoelectronics laboratory at EE Building I. We then performed three experiments: the first was to evaluate the yield of solar cells, the 2nd was using instruments to evaluate the quality of projectors, and the 3rd was to measure the L-I-V curve (Light-Current-Voltage curve) of a blue LED and use photo luminance to obtain the spectral characteristics of light-emitting components.

Every participating student was eager to try, and asked many questions. Everyone was reluctant to leave when class was over.

Students carefully use probes to make measurements

The awe-inspiring blue light LED

After the experiments, we went to the Demonstration Room of Flat Panel Display. It's a platform created by both academia and industry. The center contains the most advanced display technology research and the most newly-developed materials and products provided by the leading companies in this industry. The students had a lot of fun working with interactive teaching materials, and came to understand that the display device is much more complicated than its light and simple appearance implies. In making display devices, the liquid crystal type, polarizers, driving circuits, back light modules, optical system design, material selection, fabrication, and packaging all play important roles.

Visiting laboratories is an important part of this camp. Generally speaking, laboratories are not open for public visitation, as there are top-secret and hard-won research results inside. In addition, the instruments and equipment are quite valuable; the instruments in clean rooms alone could cost tens of million of dollars. Numerous students wish to visit the NTU laboratories, yet few have had their wish granted. However, through the summer photonics camp, all participants have such opportunity. Special thanks to Professor Gong-Ru Lin, Professor Lung-Han Peng, Professor Sheng-Lung Huang, and Professor Jian-Jang Huang for offering us their laboratories and laboratory guides. Every laboratory guide was passionate about research, energetic, and knowledgeable, inspiring great respect and admiration in the participating students.

Upper and lower classmen interacting and chatting happily


It has been my honor to take part in this three day camp. One of the participants indicated on his feedback form that he wished to be admitted to NTU’s amazing and elegant GIPO next year so that he could work for this camp together with me. I was so touched in reading this that I felt tears came into my eyes. My endeavors had been accepted by fellow students, and that was my greatest gain in running this camp.



~ Symposium and lecture of Academician Yuan-Tseh Lee (former President of Academia Sinica) ~

Time: May 15, 2009

Locations: meeting room, 7th floor & Auditorium 101, Barry Lam Hall, National Taiwan University

In order to give more GIPO students an opportunity to interact with Academician Lee, former president of Academia Sinica and a Nobel Prize laureate in chemistry, we invited him, during our interview with him last September, to speak at our Photonics Forum and share his insights with us. He accepted our invitation instantly, and after consulting his schedule, confirmed that he would visit on May 15.

To make the most of this rare opportunity, we arranged a casual lunchtime exchange between GIPO professors and academician Lee in the 7th floor meeting room of Barry Lam Hall. 16 GIPO professors attended with great enthusiasm, and Dean Soo-Chang Pei of College of Electrical Engineering & Computer Science, was invited to speak at the beginning of the session. During the exchange, professors asked Academician Lee to share his insights on various issues, and discuss his experiences with the dilemma of focusing on research or career advancement, and difficulties with balancing research and family. Academician Lee replied to these questions thoroughly, sharing his thoughts and experiences. The pleasant exchange lasted for one and a half hours, and both parties wished for more time to talk.

Academician Lee and GIPO professors during their lunchtime exchange

The Photonics Forum, beginning at 2:30 pm at auditorium 101, Barry Lam Hall, attracted so many EECS students and teachers that all seats had been taken half an hour before the meeting began. The topic of the day was "My Research Career". After a short opening speech delivered by Chairman Sheng-Lung Huang, Academician Lee began sharing with us his tens of years of research experience and insights. Beginning with his bachelor thesis, the professor’s thirst for learning and knowledge has led him through learning how to solve problems, through how to find his own direction, and through each step toward the summit of his career. Although receiving the Nobel Prize in Chemistry was quite an honor, Academician Lee actually finds more satisfaction in leading the rest of the world in his research fields. After the lecture, participants raised several types of questions. Academician Lee shared his insights with attending teachers concerning how to nurture students. For the students in attendance, he advises that in addition to being passionate about research, having curiosity, and enduring concentration, always believing that there is a better solution would be of great benefit to scientific research.

The lecture lasted for two hours and ended amid eager applause. Through the rare opportunity of this visit, we learned how Academician Lee has devoted himself to study, and how he also paid close attention to other things besides research. It is clear that everyone has been greatly inspired and has gained a lot of fresh ideas and inspiration.

Academician Lee at the Photonics Forum, speaking of his career in research



~ 2009 Academic Exchange with Nanjing University Ph.D. Students ~

Time: July 5th ~ 11th, 2009

Location: Nanjing University

Composed by Jeng-Wei Yu, GIPO Ph.D. candidate (Team Leader of NTU representative student team)

The second doctoral student exchange between National Taiwan University and Nanjing University was held in Nanjing, China. GIPO Chairman Sheng-Lung Huang, Vice Chairman Gong-Ru Lin, Professor C. C. Yang, who was invited to deliver a speech, and ten students visited Nanjing University. I was honored, with the support of other participating students, to have the privilege of serving as the NTU student leader. Therefore, in order to thoroughly draft the details of this exchange, I had talked and exchanged ideas with Kun Tang, the student leader of the Nanjing team. It was a pleasure to work with him, and I would like to thank him for his kind assistance in making preparations and in ensuring that activities proceeded as planned.

The exchange workshop took place on the 6th and 7th of July, 2009. The topics explored were numerous and impressive. They include the four following: quasi-phase-matching nonlinear optics and laser technologies, nanophotonics and artificial bandgap materials, wide bandgap semiconductor materials and micro structures, and novel optical effects in micro structures. Each student had 15 minutes to introduce his laboratory and explain his research achievements. The workshop attracted several other students who weren’t team members to take part in the interaction, which added much interest to the event. Both parties agreed to deliver reports in Chinese, therefore, allowing participants to interact more directly and gain a deeper impression. Each report had aroused animated discussion, which often continued on even during intermissions and break times. It is clear from the fervent discussion amongst members of both teams that NTU and NU are mutually impressed and interested in each other’s research. During these fantastic two days of exchange, we  fully realized that the Department of Physics of NU has worked hard in research and has achieved outstanding results. Each of their student representatives has done some impressive research. We are so glad to have this opportunity to interact with and to learn from such excellent friends, inspiring us to work harder and continue to improve ourselves further.

In interacting with mainland Chinese students, the most sensitive topic is that concerning China and Taiwan. I believe everyone must be curious about how we handled this situation. Basically, the NU students generally did not refer to it, and of course, we did not either. During the exchange, we took special care not to talk about this issue; otherwise, it could cause a lot of other problems and make the situation quite unpleasant. Except for this, getting along with mainland Chinese students was just like getting along with our own classmates, nothing unusual about it. Another topic that might be of special interest to everyone is the differences between universities in China and in Taiwan. It takes mainland Chinese students 3 years to get a master degree, and another 3 years to get a doctoral degree. However, it takes Taiwanese students 2 years to get a master degree and 3 to 7 years, depending on how each individual student performs, to get a doctoral degree. Moreover, I have learned that their master graduates could earn as much as 5,000 RMB per month if they manage to find a good job. However, I have also learned that their doctoral graduates could only earn less than 4,000 RMB monthly if they stay at and work for their universities as instructors (similar to our assistant professors). This is quite surprising, since, in Taiwan, a master graduate would have a difficult time finding a job with a starting salary higher than that of a doctoral graduate.

Through this exchange, we have gotten to know the students of Nanjing University, and furthermore, our ten GIPO students have gotten to know each other better as well. This has somewhat brought me some emotion. GIPO students are increasing, and yet, we are only acquaintances, who rarely interact with one another. Perhaps GIPO could establish a regularly-occurring platform to promote friendship and exchange among students. Finally, I'd like to take this opportunity to thank GIPO Chairman Sheng-Lung Huang, Vice Chairman Gong-Ru Lin, and several other teachers for their assistance in helping us to complete this significant and meaningful exchange successfully. The teachers have worked hard during pre-exchange planning and in their thoughtful guidance during the exchange. We would also like to thank Ms. Hsiao-wen Lin of the GIPO office for her hard work for this event, which has thus led to its success. I hope this meaningful exchange can continue on and allow more and more GIPO students to experience this event and learn from it.

Representative student teams from both parties in front of the Nanjing University entrance


Broad-band anti-reflection effects in self-assembled, subwavelength size of semiconductor nipple array

Professor Lung-Han Peng's group

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We reported the use of recessive size reduction in self-assembled polystyrene sphere mask with anisotropic etching to form lens-like nipple arrays onto the surface of silicon and gallium nitride.  These devices are shown to exhibit a filling factor near to an ideal close-packed condition and paraboloid-like etch profile with slope increased proportionally to the device aspect ratio.  Specular reflectivity less than 3% was observed over the visible spectral range for the 0.35μm-period nipple-lens arrays in Fig.1.  Using two-dimensional rigorous coupled-wave analysis the latter phenomenon can be ascribed to a gradual index matching mechanism accessed by a high surface-coverage semiconductor nipple array structure.

We further compared the weighted surface reflectivity of the following surface textures of (a) paraboloid-like nipple lens, (b) pillar with a cone-shape etch top and (c) pyramidal grating using two-dimensional rigorous coupled-wave analysis (2D-RCWA).  Our calculations show that the use of structure (a) of paraboloid-like nipple lens array renders the lowest reflectivity (<3%) over the 450-700nm spectral range.  The drastic reduction of reflectivity in the 450-900nm spectral range by texture change from pyramid to paraboloid can be ascribed, as referred from the inset of Fig.2, to a linear change in the effective refractive profile and thus a better gradual index matching mechanism provided by the latter.  The oscillatory behavior of reflectivity in the 450-700nm spectral range of the pillar structure (b) reveals subtlety of incomplete destructive interference for lack of continuous change in the effective reflective index.

Fig.1: 0.35μm-period nipple array of (a) Si and (b) GaN showing an aspect ratio of 0.59 and 0.94, (c) Experimental and RCWA-calculated reflectivity spectra for the 0.35μm-period Si nipple array in a near close-packed and non-close-packed condition.

Fig.2: Calculated reflectivity spectra at normal incidence for surface textures composed of (a) paraboloid-like nipple lens, (b) pyramidal grating, and (c) pillar with a cone shape of etch top over Si. Inset: surface profile and effective refractive index profile which are assumed to reside on a square lattice at a periodicity of 0.35μm with a filling ratio~75% and aspect ratio ~0.6.


Yb3+:YAG-silica fiber laser

Professor Sheng-Lung Huang's group

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We demonstrate a compact continuous-wave Yb3+:Y3Al5O12–silica (Yb3+:YAG-silica) fiber laser grown by the codrawing laser-heated pedestal growth (CDLHPG) technique. The threshold is 25 mW, which is an order of magnitude lower than that of previous short-length fiber lasers (Yb3+-doped or Er3+/Yb3+-codoped). A slope efficiency of 76.3% was achieved from a 7-mm-short Yb3+:YAG-silica fiber, corresponding to an extracted power of nearly 1 W/cm. Additionally, low propagation loss and high emission cross section have been determined by analyzing the lasing thresholds and slope efficiencies, and there is an excellent agreement between theoretical results and experimental data.

The CDLHPG technique provides a simple yet effective way to incorporate glass network modifiers (Al2O3 and Y2O3) into SiO2 host through interdiffusion process. Further, Cu-Al alloy packaging is employed to efficiently remove the heat generated inside the fiber compared with previous short-length fibers. To the best of our knowledge, this 7-mm-short Yb3+:YAG-silica fiber laser with record-low threshold down to 25 mW and record-high slope efficiency up to 76.3% is the shortest active fiber reported to date for any short-length fiber laser operated at room temperature.

A 68-μm-diameter Yb3+:YAG single crystal fiber was first grown by the LHPG method from a 20-mol.% doped <111> Yb3+:YAG single crystal with a cross section of 500 μm × 500 μm. The as-grown crystal fiber was then inserted into a fused silica capillary with 76 and 320 μm inner and outer diameters, respectively for redrawing with 5-mm/min growth speed by the CDLHPG technique. The silica diffuses completely into the Yb3+:YAG crystal fiber during redrawing to form the core of the Yb3+:YAG-silica fiber. After the CDLHPG process, the as-grown Yb3+:YAG-silica fiber was packaged by melting Al at 780 °C in a Cu holder to make the Cu-Al alloy. Finally, both ends of the Yb3+:YAG-silica fiber packaged by the Cu-Al alloy were fine polished for dielectric coating on the fiber end faces. The fiber compositions and microstructure were examined by an electron probe micro-analyzer and a high-resolution transmission electron microscopy, and the refractive index measurement was carried out by a home-made confocal microscope using a 635-nm distributed feedback laser. For laser characterization, the fiber was excited by a Ti3+:sapphire laser tuned to 915 nm. Four different output coupler transmittances of 0.7, 1.7, 8.9, and 12.5% were used for optimizing the output powers. The pump was first incident into a standard single-mode fiber (SMF-28) by a 10X objective, and was butt-coupled to the core of a 7-mm-long Yb3+:YAG-silica fiber through a dichroic-coated front face. The fiber laser output and the residual pump beam were collimated by an achromatic lens with 10-mm focal length and further filtered by a long-wavelength-pass filter before detection by a photo detector or an optical spectrum analyzer.

The performance of the Yb3+:YAG-silica fiber laser is shown in Fig. 1. The lasing threshold increases from 25 to 140 mW as the output coupler transmittance increases from 0.7% to 12.5%. The maximum output power of 670 mW was achieved with the output coupler transmittance of 12.5% under 1000-mW incident pump power, corresponding to a power yield of ~1 W/cm.

Fig. 1. Performance of the CW Yb3+:YAG-silica fiber laser at room temperature. Inset: the upper one shows the dependence of slope efficiency on the output coupler transmittance; the lower one shows the side mode suppression ratio of ~70 dB at 1-W incident pump power. The gray dashed and red solid lines are the quantum limit and the best fit to obtain the round-trip loss, respectively.


Aspect Ratio Dependent Ultra-low Reflection and Luminescence of Dry-Etched Si Nano-Pillars on Si Substrate

Professor Gong-Ru Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The Si nano-pillars with high aspect-ratio were fabricated by dry-etching the thin-SiO2 covered Si substrate with rapidly self-assembled Ni nano-dot patterned mask (see Fig. 1). Aspect-ratio dependent ultra-low reflection and anomalous luminescence of Si nano-pillar are analyzed for applications in all-Si-based lighting and energy transferring systems. The Si nano-pillars induce an ultra-low reflectance and refractive index of 0.88% and 1.12, respectively, at 435 nm due to the air/Si mixed structure and highly roughened surface. The reflectance can be <10% with corresponding refractive index of <1.80 between 190 and 670 nm (see Fig. 2). Lengthening the Si nano-pillars from 150±15 to 230±20 nm further results in a decreasing reflectance, corresponding to a reduction in refractive index by Dn/n = 18% in visible and near-infrared wavelength region. After dry etching Si wafer into Si nano-pillars, the weak blue-green luminescence with double consecutive peaks at 418-451 nm is attributed to the oxygen defect (O2-) induced radiation, which reveals less relevance with the ultra-low-reflective Si nano-pillar surface.

Fig.1 SEM surface morphology of Ni nano-dots after different annealing time at 850 oC (a) 30 s and (b) 120 s, and SEM surface morphology of Si nano-pillars




Fig. 2 (a) and (b) Surface reflectance of Si nano-pillars/Si with high of 150±15 nm and 230±20 nm, respectively, and Si wafer (insert) measured by using TM and TE polarized beams at incident angle of 35 degree and (c) the refractive indices of Si nano-pillars/Si.


Partitioning Pixel of Organic Light-Emitting Displays with Patterned Microlens Array Films for Efficiency Improvement

Professor Hoang-Yan Lin’s group

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

A pixel partition scheme assisted with the hollow-arranged or patterned microlens array film (MAF) was proposed to improve the optical characteristics and the lifetime of OLEDs. In our simulation results, a OLED pixel of size 1 mm × 1 mm was equally divided into 10×10 smaller sub-pixels, which was of size 100 μm × 100 μm. The original pixel with emissive edge length of 1 mm covered with patterned MAF have 21% luminance enhancement in the surface normal or 0° direction as compared to bared device. After partitioning it into sub-pixels of 100 μm in edge length, the whole partitioned OLED with patterned MAF can have vast improvement up to 72% under the same total active area and optical power emitted from OLED. To gain higher efficiency, these encouraging results inspire us to apply the patterned MAF to small-size AM- and PM-OLED and to partition large pixel into smaller subpixels for lighting purposes!

Removing microlenses right above the emissive area from the single period or fully-filled MAF is defined as the hollow arranged MAF. Besides, the pixel spacing can be designed as 53 μm, 126 μm or 179 μm, which is corresponding to one, two or three rows of microlenses in between the sub-pixels. Figure 1 shows the pixel-partition configuration of pixel spacing by one row of microlenses, and note that the black circle in each configuration is the viewing aperture of luminance meter for measurement and is equal in size.

Figure 1. Schematic diagram of partitioned pixel units attached hollow-arranged MAF. The unit edge lengthes of sub-pixel are (a) 500 μm, (b) 250 μm, (c) 200 μm and (d) 100 μm. The spacing is one row of microlenses and of 53 μm.

Hollow-arranged and fully-filled MAF with one, two and three rows of microlens in between the sub-pixel spacing were modeled. Considering normal direction luminance ratio, fully-filled MAF shows from 13% to 21% enhancement, which seems irrelevant to the unit edge length of sub-pixel. However, hollow-arranged MAF presents as much as 67% improvement. As the unit edge length of the sub-pixel decreases, the luminance ratio of hollow-arranged MAF will increase linearly; as increment of microlens rows inside the gap in between the sub-pixels, the luminance ratio of hollow-arranged MAF will also increase, as shown in Figure 2.

Figure 2. Luminance ratio of hollow-arranged and fully-filled MAF vs. edge length by varying the sub-pixel spacing in the unit of microlens rows.


The Roles of Thermally Evaporated Cesium Carbonate to Enhance the Electron Injection in Organic Light Emitting Devices

Professor Chih-I Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The properties of thermally evaporated cesium carbonate (Cs2CO3) and its role as electron injection layers in organic light emitting diodes were investigated. According to the ultraviolet photoemission spectra (UPS), the Fermi level of Alq3 after doped with Cs2CO3 shifts toward or into the lowest unoccupied molecular orbital (LUMO) as a result of chemical reaction and charge transfer between Cs2CO3 and Alq3, which lowers the electron injection barrier and improves the current efficiency. As for whether Cs2CO3 being decomposed during the evaporation, we found that Cs2CO3 molecules were deposited on the substrates without decomposition, regardless the evaporation rates, based on the signature features of carbonate groups and ionization energies measured in UPS spectra and the binding energy shifts of core level electrons. The reaction mechanisms between Cs2CO3 and Alq3 are also proposed. Since Cs2CO3 not only being used in the electron injection layer but also in converting high work function materials to cathodes, we further quantitatively investigated the work function modification of indium-tin-oxide (ITO) with deposition of Cs2CO3 at the surfaces. We found that while 0.5 angstrom thick of Cs2CO3 is sufficient to reduce the electron injection barrier of Alq3, the thickness needed to convert ITO surface to low work function cathode is about 10 angstroms.



Fig. 1 (a) UPS spectra of Alq3 near the valence bands with ultra-thin layer of Cs2CO3 deposition. (b) Energy band diagram of Alq3 with Cs2CO3 deposition.



Fig. 2 (a) UPS spectra of Cs2CO3 and Cs2O films on gold samples, near the onset and valence bands. Peaks A and B are the signature features of carbonate. (b) XPS spectra of pristine Cs2CO3 and Cs2O.


Copyright © Graduate Institute of Photonics and Optoelectronics, National Taiwan University