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KAIST announced a novel technology to produce gasoline by a metabolically engineered microorganism
A major scientific breakthrough in the development of renewable energy sources and other important chemicals; The research team succeeded in producing 580 mg of gasoline per liter of cultured broth by converting in vivo generated fatty acids
For many decades, we have been relying on fossil resources to produce liquid fuels such as gasoline, diesel, and many industrial and consumer chemicals for daily use. However, increasing strains on natural resources as well as environmental issues including global warming have triggered a strong interest in developing sustainable ways to obtain fuels and chemicals.
Gasoline, the petroleum-derived product that is most widely used as a fuel for transportation, is a mixture of hydrocarbons, additives, and blending agents. The hydrocarbons, called alkanes, consist only of carbon and hydrogen atoms. Gasoline has a combination of straight-chain and branched-chain alkanes (hydrocarbons) consisted of 4-12 carbon atoms linked by direct carbon-carbon bonds.
Previously, through metabolic engineering of Escherichia coli (E. coli), there have been a few research results on the production of long-chain alkanes, which consist of 13-17 carbon atoms, suitable for replacing diesel. However, there has been no report on the microbial production of short-chain alkanes, a possible substitute for gasoline.
In the paper (entitled "Microbial Production of Short-chain Alkanes") published online in Nature on September 29, a Korean research team led by Distinguished Professor Sang Yup Lee of the Department of Chemical and Biomolecular Engineering at the Korea Advanced Institute of Science and Technology (KAIST) reported, for the first time, the development of a novel strategy for microbial gasoline production through metabolic engineering of E. coli.
The research team engineered the fatty acid metabolism to provide the fatty acid derivatives that are shorter than normal intracellular fatty acid metabolites, and introduced a novel synthetic pathway for the biosynthesis of short-chain alkanes. This allowed the development of platform E. coli strain capable of producing gasoline for the first time. Furthermore, this platform strain, if desired, can be modified to produce other products such as short-chain fatty esters and short-chain fatty alcohols.
In this paper, the Korean researchers described detailed strategies for 1) screening of enzymes associated with the production of fatty acids, 2) engineering of enzymes and fatty acid biosynthetic pathways to concentrate carbon flux towards the short-chain fatty acid production, and 3) converting short-chain fatty acids to their corresponding alkanes (gasoline) by introducing a novel synthetic pathway and optimization of culture conditions. Furthermore, the research team showed the possibility of producing fatty esters and alcohols by introducing responsible enzymes into the same platform strain.
Professor Sang Yup Lee said, "It is only the beginning of the work towards sustainable production of gasoline. The titer is rather low due to the low metabolic flux towards the formation of short-chain fatty acids and their derivatives. We are currently working on increasing the titer, yield and productivity of bio-gasoline. Nonetheless, we are pleased to report, for the first time, the production of gasoline through the metabolic engineering of E. coli, which we hope will serve as a basis for the metabolic engineering of microorganisms to produce fuels and chemicals from renewable resources."
This research was supported by the Advanced Biomass Research and Development Center of Korea (ABC-2010-0029799) through the Global Frontier Research Program of the Ministry of Science, ICT and Future Planning (MSIP) through the National Research Foundation (NRF), Republic of Korea. Systems metabolic engineering work was supported by the Technology Development Program to Solve Climate Changes on Systems Metabolic Engineering for Biorefineries (NRF-2012-C1AAA001-2012M1A2A2026556) by MSIP through NRF.
Short-Chain Alkanes Generated from Renewable Biomass
This diagram shows the metabolic engineering of Escherichia coli for the production of short-chain alkanes (gasoline) from renewable biomass.
Nature Cover Page (September 29th, 2013)
2013.11.04 View 10936 -
KAIST Hosted the 6th International Presidential Forum on Global Research Universities
More than 120 global leaders from higher education, private and public sectors, to discuss the promotion of economic growth through knowledge creation and entrepreneurship
The Korea Advanced Institute of Science and Technology (KAIST) held the 6th International Presidential Forum on Global Research Universities (IPFGRU) on October 15th at the Westin Chosun Hotel in Seoul, Republic of Korea.
About 64 presidents and vice presidents from 57 research universities in 28 nations attended for a presentation and panel discussion on the topic of “The Role and Responsibility of Research Universities: Knowledge Creation, Technology Transfer, and Entrepreneurship.”Annually held, the forum is organized to promote excellence and innovation in higher education and provide a place for discussion among prominent research university leaders and key policy-makers in the private and public sectors from across the world.Among the notable universities attending the 2013 forum were the University of California, Irvine, the École Polytechnique Fédérale de Lausanne, Technische Universität Berlin, Technion-Israel Institute of Technology, Tokyo Institute of Technology, Rice University, the University of Waterloo, and Massachusetts Institute of Technology (MIT). Government officials as well as representatives from business and industry such as Samsung Electronics, Korea Telecom, and Elsevier also joined the event.
The forum was proceeded with three separate sessions: Enabling Knowledge Creation, Entrepreneurship & University-Based Technology Transfer, and Higher Education & Strategic Knowledge Creation: Specialization & Performance, through which speakers and panelists examined how universities have played a role in knowledge creation and technology transfer, and ultimately how they have contributed to the development of national economies.
Keynote speakers were Michael Drake, chancellor of UC Irvine, and Jörg Steinbach, president of Technische Universität Berlin. Forum participants shared their experiences and insights in starting up knowledge- and technolgy-based new businesses.
Steve Kang, president of KAIST, talked about the purpose of the 2013 IPFGRU:
“In the face of an ever-changing economic climate driven by shifts in technological advancement, demographic trends, and global integration, the role of research universities is becoming ever more significant in achieving sustainable economic growth. This forum will help participants from around the world to define the choices ahead as universities seek the most productive and beneficial models for cooperation with industry, venture startups, and government.”For the 2013 IPFGRU, Ministry of Science, ICT, and Future Planning, ROK, Saudi Aramco, Samsung Heavy Industries, S-Oil, Elsevier, Thomson Reuters, and the Korea Economic Daily were forum sponsors.
2013.11.04 View 9500 -
First Prize in the 2013 International Military Science and Technology Contest
Professor James R. Morrison and his students of the Industrial and Systems Engineering Department at KAIST were awarded the first prize in the 2013 International Military Science and Technology Contest organized by the Defense Acquisition Program Administration held in COEX from July 11 to 14.
The research group, Byungduk Song (Ph.D candidate), Jonghoe Kim (Ph.D candidate), Hyolin Park (MS candidate) and Professor James R. Morrison, received the first prize with their paper entitled “Automated and persistent UAV system for a complementary method for border patrol and target tracking.”
The Defense Acquisition Program Administration is the host of the annual contest which aims to contribute to the future of the defense industry and to expand technology exchange between private institutes and the military through the coordination of defense technology and advanced technology from industrial and educational cooperation.Professor Morrison’s team received the honor of the first-place prize out of 56 competitors from within Korea and 7 from overseas in the field of Synthetic New Technology/Academic Thesis.
2013.10.31 View 8158 -
Distinguished Professor Sang Yup Lee appointed as an advisor for Shanghai Jiao Tong University in China
In recognition of his outstanding accomplishments in the area of bioengineering, specializing in metabolic engineering, Sang Yup Lee, a distinguished professor of Chemical & Biomolecular Engineering at KAIST, was assigned as an advisory professor for the bioengineering department at Shanghai Jiao Tong University in China for five years from August 2013 to July 2018.
Together with Peking University and Tsinghua University, Shanghai Jiao Tong University is one of the top three universities in China.
The advisory professors carry out collaborated research programs in special areas and provide advice on education and research issues.
Professor Lee, a specialist in metabolic engineering, has initiated systems metabolic engineering which integrates metabolic engineering, systems biology, and synthetic biology and has applied it to various chemical production systems to develop bio fuel and many eco-friendly chemical production processes. Recently, he received the Marvin J. Johnson Award from the American Chemistry Society, the Charles Thom Award from the American Society for Industrial Microbiology, as well as the Amgen Biochemical Engineering Award. As a global leader in the area of bioengineering, Professor Lee is a member of the Korean Academy of Science & Technology, the National Academy of Engineering of Korea, the US National Academy of Engineering, and is the chairman of the Global Agenda Council on Biotechnology at the World Economic Forum.
2013.10.31 View 8176 -
Core Technology for Lithium Air Secondary Battery Developed
KAIST-Kyonggi University joint research team developed composite catalyst out of nano fiber and graphene
Five times improvement in capacity compared to lithium-ion secondary battery, driving 800 km at maximum
The core technology for lithium air secondary battery, the next generation high capacity battery, has been developed.
A research team formed by KAIST Department of Materials Science’s Professors Il-Doo Kim and Seokwoo Jeon, and Kyonggi University Department of Materials Science’s Professor Yong-Joon Park has created a lithium air secondary battery, with five times greater storage than the lithium-ion secondary battery, by developing a nano fiber-graphene composite catalyst. The research results are published in the August 8th online edition of Nano Letters.
A cathode of a lithium-ion battery consists of graphite and an anode of the battery consists of a lithium transition metal oxide. Lithium-ion batteries are widely used in mobile phones and laptops. However, lithium-ion batteries cannot support electric vehicles, providing energy for only 160 kilometers on one full charge. The lithium air secondary battery just developed by the research team uses lithium on the cathode and oxygen on the anode. It is earning a popular acknowledgement among the next generation secondary battery research community for having lightweight mass and high energy density.
However, lithium-ion batteries remain difficult to commercialize because of their short lifespan. Lithium and oxygen meet up to form lithium oxide (Li2O2) at discharge, and decompose again at charge. In a traditional lithium air battery, this cycle does not occur smoothly and results in high resistance, thereby reducing the lifespan of the battery. It is thus essential to develop high efficiency catalyst that facilitates the formation and decomposition of lithium oxides.
The research team used electric radiation to develop a nano composite catalyst by mixing cobalt oxide nano fiber and graphene. The performance of the battery has been maximized by settling nonoxidative graphene, which has high specific surface area and electrical conductivity, on catalyst active cobalt oxide nano fiber. Applying the nano composite catalyst on both poles of the lithium air battery resulted in an improved lifespan of over 80 recharge cycles with capacity greater than 100mAh/g, five times greater than a lithium ion battery. The newly discovered charge-discharge property is the highest among the reported performances of the lithium air battery so far.
The lithium air battery is cheap to make, as the main materials are metal oxide and graphene. “There are yet more issues to resolve such as stability, but we will collaborate with other organizations to open up the era of electronic vehicles,” said Professor Il-Doo Kim. “We hope to contribute to vitalizing the fields of next generation lithium air battery by leading nanocatalyst synthesis technology, one of the core materials in the fields of secondary battery,” Professor Kim spoke of his aspiration.
The graduate students participated in the research are Won-Hee Ryu, a postdoctorate at KAIST Department of Materials Science, Sungho Song, a PhD candidate at KAIST Department of Materials Science, and Taek-Han Yoon, a graduate student at Kyonggi University.
Picture I: Schematic Diagram of Lithium Air Battery Made of Nano Composite Catalysts
Picture II: Images of Cobalt Oxide Nano Fibers and Graphene Nano Composite Catalysts
Picture III: Images of Manufacturing Process of Cobalt Oxide Nano Fibers and Graphene Nano Composite Catalysts for Lithium Air Battery
2013.10.18 View 11021 -
Nanowire Made of Diverse Materials May Become Marketable
- Technology to commercialize nanowire developed after 2 years of industrial-academic joint research -
- 2 million strands of 50nm-width, 20 cm-length nanowire mass producible in 2 hours –
A South Korean joint industrial-academic research team has developed the technology to put forward the commercialization of nanowire that is only a few nanometers wide. It is expected to be applied in various fields such as semiconductors, high performance sensors, and biodevices.
In cooperation with LG Innotek and the National Nanofab center, Professor Jun-Bo Yoon, from KAIST Department of Electrical Engineering, developed the technology to mass produce nanowire at any length with various materials. The research results are published on the online edition of Nano Letters on July 30th.
Nanowire has a long linear structure with its width at 100 nanometers at maximum. It is a multifunctional material that has yet undiscovered thermal, electric, and mechanical properties. Nanowire is highly acclaimed as a cutting-edge material with unique nano-level properties that can be applied in semiconductors, energy, biodevices, and optic devices.
Previously, nanowires had an extremely low synthesis rate that required three or four days to grow few millimeters. It was therefore difficult to produce the desired products using nanowires. Moreover, nanowires needed to be evenly arranged for practical application, but the traditional technology required complex post-treatment, not to mention the arrangement was not immaculate.
The research team applied semiconductor process instead of chemical synthesis to resolve these issues. The team first formed a pattern greater that of the target frequency by using a photo-engraving process on a silicon wafer board whose diameter was 20 centimeters, then repeatedly reduced the frequency to produce 100 nm ultrafine linear grid pattern. Based on this pattern, the research team applied the sputtering process to mass-produce nanowires in perfect shapes of 50 nm width and 20 cm maximum length.
The new technology requires neither a lengthy synthesis process nor post-cleaning to attain a perfectly aligned state. Thus, academic and industrial circles consider the technology has high possibilities for commercialization.
“The significance is in resolving the issues in traditional technology, such as low productivity, long manufacturing time, restrictions in material synthesis, and nanowire alignment,” commented Professor Yoon on this research. “Nanowires have not been widely applied in the industry, but this technology will bring forward the commercialization of high performance semiconductors, optic devices, and biodevices that make use of nanowires.”
2013.10.18 View 8601 -
Therapy developed to induce Angiogenesis of Retina
- Junyeop Lee, Graduate School of Medical Sciences and Engineering
- Research results expected to be applied for treatment of diabetic retinopathy
A major clue to treatment of retinovascular disease, which causes blindness, has been found. The key to protection of the retinal nerve is the angiogenic protein that promotes healthy retinal vessel growth around the retina, which usually does not receive blood supply readily. This research offers a beginning to the possible improvement of therapy for diabetic retinopathy1 and retinopathy of prematurity2. Also important to the research is the fact that the ophthalmology specialist researcher, currently undergoing professional training, provided the results.
KAIST Graduate School of Medical Sciences and Engineering’s Junyeop Lee is the opthalmology specialist, who carried out the research under supervision by academic advisers Gyuyeong Go and Wookjun Yoo. The Ministry of Science, ICT and Future Planning as well as the National Research Foundation of Korea have funded his research. The research results have been published as a cover paper on ‘Science Translational Medicine’ on 18th August. This journal is a sister publication of Science, which is prestigious in the field of translational medicine that ties the basic science with clinical medicine. (Thesis title: Angiopoietin-1 Guides Directional Angiogenesis Through Integrin αvβ5 Signaling for Recovery of Ischemic Retinopathy)
The traditional treatment of diabetic retinopathy includes laser photocoagulation to destroy the retinal tissues or antibody therapeutics, which prevents vessel proliferation and blood leaking. The advantage of antibody therapeutics3 is that it retains the retinal nerves, however, it is not the fundamental solution but merely a temporary one, which requires repeated treatments.
The research team identified that Angiopoietin-14 protein, known as essential for growth and stabilization of vessels, also plays an important role in retinal vessel growth. The protein protects the retinal nerves, as well as provides improvement for retinal ischemia5 that is the root cause of vision loss due to retinal hemorrhages. It is expected to become a key to finding fundamental treatment method – by providing sufficient blood supply to the retina, thereby preserving the retinal nerve functions.
The results show that administration of Angiopoietin-1 to retinopathy mouse model promotes growth of healthy vessel growth, further preventing abnormal vessel growth, retinal hemorrhage and vision loss due to retinal ischemia.
Junyeop Lee said, “This research has identified that Angiopoietin-1 is an important factor in retinal vessel generation and stabilization. The paradigm will shift from traditional treatment method, which prevents vessel growth, to a new method that generates healthy vessels and strengthens vessel functions.”
1 Diabetic retinopathy: This retinovascular disease is a diabetic complication caused by insufficient blood supply. It is the major causes of blindness in adults.
2 Retinopathy of prematurity: The retinal vascular disease that occurs in premature infants with incomplete retinal vascular development. It is also the most common cause of blindness in children.
3 Antibody Therapeutics: Antibody developed to selectively inhibit abnormal blood vessel growth and leakage. Typical antibody therapeutics is Avastin and Lucentis, which hinder vascular endothelial growth factor (VEGF).
4 Angiopoietin-1: A critical growth factor that induces the production of healthy blood vessels and maintains the stability of the created vessel.
5 Retinal ischemia: State of ailment where retinal tissue blood supply is not sufficient.
Figure 1. Retinopathy mouse models show that, in comparison to the control group, the VEGF-Trap treatment and Angiopoietin-1 (Ang1) treatment groups significantly suppresses the pathological vascular proliferation. In addition, the Ang 1 group show vessel growth toward the central avascular area (region of retinal ischemia), which is not observed in VEGF-Trap treatment.
Figure 2. Reduced retinal ischemia, retinal bleeding and blood vessel normalization by Angiopoietin-1. Retinal ischemic region (arrow) and retinal bleeding significantly reduced in the Angiopoietin-1 (Ang1) treatment model in comparison to control group (left). The newly generated vessels in Ang 1 model are structurally supported by perivascular cells as normal retinal vessels do (right).
2013.10.12 View 10488 -
KAIST to establish Ombudsperson system
KAIST has recently undergone a massive reorganization to achieve a streamlined system and highly efficient administration; and it will now implement the new “Ombudsperson” system to hear the opinions of the members of the university.
On September 9th, President Sungmo Kang held a ceremony to appoint Professors Sang-Young Shin and Hong-Gu Shim as the new “Ombudspersons”.
The previous Shinmungo system raised complaints and recommendations for improvements by members of the university, but this is the first time that KAIST has assigned a direct department for handling such matters.
The newly appointed Ombudspersons will review for the possibility of any unjust, irrational systems, violations of research ethics and such. It is their role to take a neutral stance and advise on the correction and improvement.
The merit of the Ombudsperson system is that diverse opinions can be reflected on the policy. The Ombudsperson guarantees the security of the contents of discussion so that anyone can share his or her opinion without fear of being recorded in documents.
It is expected that the Ombudsperson system will protect the interests of the individuals and thus contribute to making a “happy campus”.
President [Sungmo] Kang has said that the reason establishing the office of the Ombudsperson is “In order for KAIST to take a new leap toward the world, it is crucial to bring the minds of the members together…. Even the smallest voices must be heard to present solutions to make the university where everyone’s happy.”
In 1809, the Swedish Parliament appointed the first “Ombudsperson” to investigate and resolve civil complaints. Now, it is widely used in public institutions, corporations and universities to improve the communication and work efficiency of the members.
The new Ombudsmen: Prof. Sang-Young Shin (left) and Prof. Hong-Gu Shim (right)
2013.09.27 View 9982 -
Jellyfish Exterminator Robot Developed
Formation Control demonstrated by JEROS
- Trial performance successfully completed with three assembly robots -
A team led by KAIST Civil and Environmental Engineering Department’s Professor Hyeon Myeong has just finished testing the cooperative assembly robot for jellyfish population control, named JEROS, in the field.
The rising number of accidents and financial losses by fishing industry, estimated at 300 billion won per year, caused by the recent swarm of jellyfish in coastal waters has been a major problem for many years. The research team led by Prof. Hyeon Myeong began developing an unmanned automated system capable of eradicating jellyfishin in 2009, and has since completed field-tests last year with success.
This year, JEROS’s performance and speed has been improved with the ability to work in formation as a cooperative group to efficiently exterminate jellyfish.
An unmanned aquatic robot JEROS with a mountable grinding part is buoyed by two cylindrical bodies that utilizes propulsion motors to move forward and reverse, as well as rotate 360 degrees. Furthermore, GIS (geographic information system)-based map data is used to specify the region for jellyfish extermination, which automatically calculates the path for the task. JEROS then navigates autonomously using a GPS (Global Positioning System) receiver and an INS(inertial navigation system).
The assembly robots maintain a set formation pattern, while calculating its course to perform jellyfish extermination. The advantage of this method is that there is no need for individual control of the robots. Only the leader robot requires the calculated path, and the other robots can simply follow in a formation by exchanging their location information via wireless communication (ZigBee method).
JEROS uses its propulsion speed to capture jellyfish into the grinding part on the bottom, which then suctions the jellyfish toward the propeller to be exterminated.
The field test results show that three assembly robots operating at 4 knots (7.2km/h) disposes jellyfish at the rate of about 900kg/h.
The research team has currently completed testing JEROS at Gyeongnam Masan Bay and is expected to further experiment and improve the performance at various environment and conditions.
JEROS may also be utilized for other purposes including marine patrols, prevention of oil spills and waste removal in the sea.
JEROS research has been funded by Ministry of Science, ICT and Future Planning and Ministry of Trade, Industry and Energy.
2013.09.27 View 16198 -
Transparent Glass Wall as a Touch Game Media
Professor Woo-hoon Lee
- Selected as the “Highlight” at SIGGRAPH emerging technology conference
- “An excellent example of the transparent display panel in everyday life”
A joint research team led by KAIST Industrial Design Department’s Prof. Woo-hoon Lee and Computer Sciences Prof. Ki-hyuk Lee has developed a brand new concept game media “TransWall”, which utilizes both sides of the glass wall as the touch medium.
TransWall has been chosen as the “highlight” of 2013 SIGGRAPH emerging technology conference. SIGGRAPH is a world-renowned conference in the area of computer graphics and interaction technique, last held 21st-25th July at Anaheim, in the United States.
It all started with the thought, wouldn’t it be possible to turn the glass walls surrounding us into a medium for entertainment and communication?
TransWall utilizes holographic screen film inserted between two glass sheets with a multi-touch function, onto which the image can be projected using the beam projector from both sides. Furthermore, an additional Surface Transducer attached to the glass can deliver the sound and vibration.
What seemed as an ordinary glass wall has been transformed into a multi-sensory media that can transmit and receive visual, auditory and tactile information.
TransWall can be implemented at public places such as theme parks, large shopping malls and subway stations, providing the citizens with a new form of entertainment. This touch-interaction method can also be applied to developing a variety of cultural contents in the future.
Professor Lee said, “TransWall shows an example of near-future where touch-interaction method can be utilized with the soon-to-be commercialized transparent display panel in everyday lives.”
TransWall Introduction video (https://vimeo.com/70391422)
TransWall at SIGGRAPH 2013 Display (https://vimeo.com/71718874)
Picture 1. Both sides of the glass wall can be used as a touch platform for various medias, including games.
Picture 2. TransWall attracts the interests of the audience at SIGGRAPH emerging technology.
Picture 3. Structure of TransWall
Picture 4. Photo of TransWall from side
2013.09.19 View 8894 -
Secondary, High Capacity Battery developed from Rice Husks
Rice husks, a waste product from rice polishing, has been successfully utilized as the silicon anode for use in high capacity lithium ion secondary batteries. The new silicon anode derived from rice husks exhibit superior output and lifespan.
Professor Choi Jang Wook (The Graduate School of Energy, Environment, Water and Sustainability (EEWS)) and Professor Park Seung Min (Department of Biochemistry) and their respective research teams separated naturally occurring, highly porous silica material within the rice husks and developed a 3-dimensional, highly porous silicon anode material.
The result of the research effort was published in the online edition of the Proceedings of the National Academy of Sciences (PNAS) journal, a world renowned journal in the field of natural sciences.
Silicon has attracted much attention as anode material for next generation lithium ion secondary batteries because it exhibits 3~5 times higher capacity than conventional graphene. The high capacity will pave the way to lithium secondary batteries with higher energy densities than conventional batteries. It is anticipated that the application of silicon batteries will yield electronic devices with a longer duration for use in addition to electronic vehicles boasting longer mileage.
The silicon anode is based on the 3-dimensional, highly porous structure of rice husks which remedies the problematic extreme volume expansion of conventional silicon anodes.
Utilization of inexpensive rice husks to create high value silicon anodes will cause a ripple effect on the industry and academia.
2013.08.23 View 9705 -
Short Wavelength, Ultra-High Speed Quantum Light Source based on Quantum Dot Developed
Professor Yong Hoon, Cho (Department of Physics) and his research team synthesized an obelisk nanostructure and successfully formed a single semiconductor quantum exhibiting high reliability to realize an ultra-high speed, highly efficient, release of quantum dots.
The result of the research effort was published in the July 5th online edition of Scientific Reports published by Nature.
Semiconductor Quantum Dots restrict electrons within a cubic boundary of few nanometers thereby exhibiting similar properties to an atom with discontinuous energy levels. Exploitation of this characteristic makes possible the development of quantum light source, critical for next generation quantum information communication and quantum encryption.
High operational temperatures, stability, rapid photon release, electric current capability, and other advantages are reasons why semiconductor quantum dots are regarded as next generation core technology.
However conventional, spontaneously formed quantum dots are densely packed in a planar structure rendering the analysis of a single quantum dot difficult and result in the poor efficiency of photon release. In addition, the internal electromagnetic effect which is caused by inter-planar stress results in low internal quantum efficiency due to the difficulty in electron-hole recombination.
Professor Cho’s research team synthesized an obelisk shaped nanostructure using nitrides that emit short wavelengths of light. The activation layer was grown on the tip of the nanostructure and the team succeeded in placing a single quantum dot on the nano-tip. The team was therefore able to confirm the ultra-high speed single photon characteristics which occur at low energy levels.
Use of unique nanostructures makes synthesis of single atomic structures without processes like patterning while enabling the release of light emitted by the quantum dot.
Using this unique method the team showed the increase in internal quantum efficiency. The electromagnetic forces apparent in thin films no longer affects the quantum dot greatly due to the obelisk structure’s reduced inter planar stress.
The newly developed quantum light source emits visible light (400nm range) and not the conventional infrared light. This characteristic makes possible it use in communication in free space and enables use of highly efficient, visible range photon detector.
Professor Cho commented that “the developed method makes quantum dot growth much easier making single photon synthesis much faster to contribute to the development of practical quantum light source.” And that “the characteristics of the obelisk nanostructure enable the easy detachment from and attachment to other substrates enabling its use in producing single chip quantum light source.”
The research was conducted under the supervision of Professor Cho. The researchers werey Jae Hyung, Kim (first author) and Yong Ho, Ko (second author), both Ph.D. candidates at KAIST. The Ministry of Science, ICT and Future Planning, the National Research Foundation, and WCU Program provided support to the research effort.
2013.08.23 View 7960