Physical+Review+Letters
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Ultra-high Resolution 2-dimentional Real-time Image Capture with Super Lens
Ultra-high Resolution 2-dimentional Real-time Image Capture with Super Lens
Applications to high-precision semiconductor processing or intracellular structures observation are possible.
A joint research team led by Professors Yongkeun Park and Yong-Hoon Cho from the Department of Physics, KAIST, has succeeded in capturing real-time 2D images at a resolution of 100 nm (nanometers), which was impossible with optical lens due to the diffraction limit of light until now. Its future application includes high-precision semiconductor manufacturing process or observation of intracellular structures.
This research follows the past research of the super-lens developed by Professor Park last April, using paint spray to observe images that have three times higher resolution than those discovered by conventional optical lens.
Since optical lens utilize the refraction of light, the diffraction limit, which prevents achieving focus smaller than the wavelength of light, has always been a barrier for acquiring high-resolution images. In the past, it was impossible to observe objects less than the size of 200 to 300 nm in the visible light spectrum.
In order to solve the problem of near-field extinction due to scattering of light, the research team used spray paint consisting of nano-particles massed with dense scattering materials to obtain high-resolution information.
Then, by calculating and restoring the first scattering shape of light using the time reversibility of light, the researchers were able to overcome the diffraction limit. The original position of an object to be observed is obtained by deriving the complex trajectory of the light, and reversing the time to locate the particular position of the object.
Professor Park said, “This new technology can be used as the core technology in all fields which require optical measurement and control. The existing electron microscopy cannot observe cells without destroying them, but the new technology allows us to visualize at ultra-high resolution without destruction.”
The research results were published online in the 9th edition of Physical Review Letters, a prestigious international journal in the field of physics.
2014.09.23 View 8931 -
An Electron Cloud Distribution Observed by the Scanning Seebeck Microscope
All matters are made of small particles, namely atoms. An atom is composed of a heavy nucleus and cloud-like, extremely light electrons.
Korean researchers developed an electron microscopy technique that enables the accurate observation of an electron cloud distribution at room-temperature. The achievement is comparable to the invention of the quantum tunneling microscopy technique developed 33 years ago.
Professor Yong-Hyun Kim of the Graduate School of Nanoscience and Technology at KAIST and Dr. Ho-Gi Yeo of the Korea Research Institute of Standards and Science (KRISS) developed the Scanning Seebeck Microscope (SSM). The SSM renders clear images of atoms, as well as an electron cloud distribution. This was achieved by creating a voltage difference via a temperature gradient.
The development was introduced in the online edition of Physical Review Letters (April 2014), a prestigious journal published by the American Institute of Physics.
The SSM is expected to be economically competitive as it gives high resolution images at an atomic scale even for graphene and semiconductors, both at room temperature. In addition, if the SSM is applied to thermoelectric material research, it will contribute to the development of high-efficiency thermoelectric materials.
Through numerous hypotheses and experiments, scientists now believe that there exists an electron cloud surrounding a nucleus. IBM's Scanning Tunneling Microscope (STM) was the first to observe the electron cloud and has remained as the only technique to this day. The developers of IBM microscope, Dr. Gerd Binnig and Dr. Heinrich Rohrer, were awarded the 1986 Nobel Prize in Physics.
There still remains a downside to the STM technique, however: it required high precision and extreme low temperature and vibration. The application of voltage also affects the electron cloud, resulting in a distorted image.
The KAIST research team adopted a different approach by using the Seebeck effect which refers to the voltage generation due to a temperature gradient between two materials.
The team placed an observation sample (graphene) at room temperature (37~57℃) and detected its voltage generation. This technique made it possible to observe an electron cloud at room temperature.
Furthermore, the research team investigated the theoretical quantum mechanics behind the electron cloud using the observation gained through the Seebeck effect and also obtained by simulation capability to analyze the experimental results.
The research was a joint research project between KAIST Professor Yong-Hyun Kim and KRISS researcher Dr. Ho-Gi Yeo. Eui-Seop Lee, a Ph.D. candidate of KAIST, and KRISS researcher Dr. Sang-Hui Cho also participated. The Ministry of Science, ICT, and Future Planning, the Global Frontier Initiative, and the Disruptive Convergent Technology Development Initiative funded the project in Korea.
Picture 1: Schematic Diagram of the Scanning Seebeck Microscope (SSM)
Picture 2: Electron cloud distribution observed by SSM at room temperature
Picture 3: Professor Yong-Hyun Kim
2014.04.04 View 12921 -
New Era for Measuring Ultra Fast Phenomena: Atto Science Era
Domestic researchers successfully measured the exact status of the rapidly changing Helium atom using an atto second pulse. Thanks to this discovery, many ultrafast phenomena in nature can now be precisely measured. This will lead to an opening of a new "Atto Science" era.
Prof. Nam Chang Hee led this research team and Ph.d Kim Kyung Taek and Prof. Choi Nak Ryul also participated in this research. They have conducted the research under the support of the Researcher Support Program initiated by The Ministry of Education and Science and Korea Research Foundation. The research result was published in the prestigious journal "Physical Review Letters" on March 2nd. (Title: Amplitude and Phase Reconstruction of Electron Wave Packets for Probing Ultrafast Photoionization Dynamics)
Prof. Nam Chang Hee"s research team used atto second pulse to measure the ultrafast photoionization.
His team used atto second X-ray pulse and femto second laser pulse to photoionize Helium atoms, and measure the wave speed of the produced electron to closely investigate the ultrafast photoionization process.
Atom"s photoionization measurement using an atto second pulse was possible using the research team"s high-energy femto second laser and high-performance photo ion measurement device. This research team succeeded in producing the shortest 60 atto second pulse in the world using high-harmonic waves.
The research team used high-power femto second laser to produce atto second high-harmonic pulse from argon gas, used this to photoionize Helium atoms, and measured the ultrafast photoionization of the atoms.
Prof. Nam Chang Hee said, "This research precisely measured the exact status of rapidly changing Helium atoms. I am planning to research on measuring the ultrafast phenomena inside atoms and molecules and controlling the status of the atoms and molecules based on the research result."
2012.04.04 View 9587 -
The thermal fluctuation and elasticity of cell membranes, lipid vesicles, interacting with pore-forming peptides were reported by a research team at KAIST.
A research team from KAIST, consisted of Sung-Min Choi, Professor of Nuclear and Quantum Engineering Department, and Ji-Hwan Lee, a doctoral student in the Department, published a paper on the “thermal fluctuation and elasticity of lipid vesicles interacting with pore-forming peptides.” The paper was carried by Physical Review Letters, an internationally renowned peer-review journal on physics on July 16, 2010.
Cell membranes, which consist of lipid bilayers, play important roles in cells as barriers to maintain concentrations and matrices to host membrane proteins. During cellular processes such as cell fission and fusion, the cell membranes undergo various morphological changes governed by the interplay between protein and lipid membranes. There have been many theoretical and experimental approaches to understand cellular processes driven by protein-lipid membrane interactions. However, it is not fully established how the membrane elastic properties, which play an important role in membrane deformation, are affected by the protein-membrane interactions.
Antimicrobial peptides are one of the most common examples of proteins that modify membrane morphology. While the pore-forming mechanisms of antimicrobial peptides in lipid bilayers have been widely investigated, there have been only a few attempts to understand the mechanisms in terms of membrane elastic properties. In particular, the effects of pore formation on the membrane fluctuation and elastic properties, which provide key information to understand the mechanism of antimicrobial peptide activity, have not been reported yet. The research team reports the thermal fluctuation and elasticity of lipid vesicles interacting with pore-forming peptides, which were measured by neutron spin-echo spectroscopy.
The results of this study are expected to pay an important role in understanding the elastic behavior and morphological changes of cell membranes induced by protein-membrane interactions, and may provide new insights for developing new theoretical models for membrane fluctuations which include the membrane mediated interaction between protein patches.
(a) (b)
Figure
(a) Schematics for bound melittin and pores in lipid bilayers
(b) P NMR signal ratio (with/without Mn2+) of DOPC LUV-melittin vs P/L at 30˚C. The dashed line is a guide for eyes.
2010.07.23 View 11182 -
KAIST Professor Finds Paradox in Human Behaviors on Road
-Strange as it might seem, closing roads can cut delays
A new route opened to ease traffic jam, but commuting time has not been reduced.Conversely, motorists reached their destinations in shorter times after a big street was closed. These paradoxical phenomena are the result of human selfishness, according to recent findings of a research team led by a KAIST physics professor.
Prof. Ha-Woong Jeong, 40, at the Department of Physics, conducted a joint research with a team from Santa Fe Institute of the U.S. to analyze the behaviors of drivers in Boston, New York and London. Their study found that when individual drivers, fed with traffic information via various kinds of media, try to choose the quickest route, it can cause delays for others and even worsen congestion.
Prof. Jeong and his group"s study will be published in the Sept. 18 edition of the authoritative Physical Review Letters. The London-based Economist magazine introduced Prof. Jeong"s finding in its latest edition.
Prof. Jeong, a pioneer in the study of "complex system," has published more than 70 research papers in the world"s leading science journals, including Nature, PNAS and Physical Review Letters. "Initially, my study was to reduce annoyance from traffic jam during rush hours," Prof. Jeong said. "Ultimately, it is purposed to eliminate inefficiency located in various corners of social activities, with the help of the network science."
The Economist article read (in part):
"...when individual drivers each try to choose the quickest route it can cause delays for others and even increase hold-ups in the entire road network.
"The physicists give a simplified example of how this can happen: trying to reach a destination either by using a short but narrow bridge or a longer but wide motorway. In their hypothetical case, the combined travel time of all the drivers is minimized if half use the bridge and half the motorway. But that is not what happens. Some drivers will switch to the bridge to shorten their commute, but as the traffic builds up there the motorway starts to look like a better bet, so some switch back. Eventually the traffic flow on the two routes settles into what game theory calls a Nash equilibrium, named after John Nash, the mathematician who described it. This is the point where no individual driver could arrive any faster by switching routes.
"The researchers looked at how this equilibrium could arise if travelling across Boston from Harvard Square to Boston Common. They analysed 246 different links in the road network that could be used for the journey and calculated traffic flows at different volumes to produce what they call a “price of anarchy” (POA). This is the ratio of the total cost of the Nash equilibrium to the total cost of an optimal traffic flow directed by an omniscient traffic controller. In Boston they found that at high traffic levels drivers face a POA which results in journey times 30% longer than if motorists were co-ordinated into an optimal traffic flow. Much the same thing was found in London (a POA of up to 24% for journeys between Borough and Farringdon Underground stations) and New York (a POA of up to 28% from Washington Market Park to Queens Midtown Tunnel).
"Modifying the road network could reduce delays. And contrary to popular belief, a simple way to do that might be to close certain roads. This is known as Braess’s paradox, after another mathematician, Dietrich Braess, who found that adding extra capacity to a network can sometimes reduce its overall efficiency.
"In Boston the group looked to see if the paradox could be created by closing any of the 246 links. In 240 cases their analysis showed that a closure increased traffic problems. But closing any one of the remaining six streets reduced the POA of the new Nash equilibrium. Much the same thing was found in London and New York. More work needs to be done to understand these effects, say the researchers. But even so, planners should note that there is now evidence that even a well intentioned new road may make traffic jams worse."
2008.09.18 View 13258