Chem
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Extremely Thin and Highly Flexible Graphene-Based Thermoacoustic Speakers
A joint research team led by Professors Jung-Woo Choi and Byung Jin Cho of the School of Electrical Engineering and Professor Sang Ouk Kim of the Material Science and Engineering Department, all on the faculty of the Korea Advanced Institute of Science and Technology (KAIST), has developed a simpler way to mass-produce ultra-thin graphene thermosacoustic speakers.
Their research results were published online on August 17, 2016 in a journal called Applied Materials & Interfaces. The IEEE Spectrum, a monthly magazine published by the Institute of Electrical and Electronics Engineers, reported on the research on September 9, 2016, in an article titled, “Graphene Enables Flat Speakers for Mobile Audio Systems.” The American Chemical Society also drew attention to the team’s work in its article dated September 7, 2016, “Bringing Graphene Speakers to the Mobile Market.”
Thermoacoustic speakers generate sound waves from temperature fluctuations by rapidly heating and cooling conducting materials. Unlike conventional voice-coil speakers, thermoacoustic speakers do not rely on vibrations to produce sound, and thus do not need bulky acoustic boxes to keep complicated mechanical parts for sound production. They also generate good quality sound in all directions, enabling them to be placed on any surface including curved ones without canceling out sounds generated from opposite sides.
Based on a two-step, template-free fabrication method that involved freeze-drying a solution of graphene oxide flakes and the reduction/doping of oxidized graphene to improve electrical properties, the research team produced a N-doped, three-dimensional (3D), reduced graphene oxide aerogel (N-rGOA) with a porous macroscopic structure that permitted easy modulation for many potential applications.
Using 3D graphene aerogels, the team succeeded in fabricating an array of loudspeakers that were able to withstand over 40 W input power and that showed excellent sound pressure level (SPL), comparable to those of previously reported 2D and 3D graphene loudspeakers.
Choong Sun Kim, the lead author of the research paper and a doctoral student in the School of Electrical Engineering at KAIST, said:
“Thermoacoustic speakers have a higher efficiency when conducting materials have a smaller heat capacity. Nanomaterials such as graphene are an ideal candidate for conductors, but they require a substrate to support their extremely thinness. The substrate’s tendency to lose heat lowers the speakers’ efficiency. Here, we developed 3D graphene aerogels without a substrate by using a simple two-step process. With graphene aerogels, we have fabricated an array of loudspeakers that demonstrated stable performance. This is a practical technology that will enable mass-production of thermosacoustic speakers including on mobile platforms.”
The research paper is entitled “Application of N-Doped Three-Dimensional Reduced Graphene Oxide Aerogel to Thin Film Loudspeaker.” (DOI: 10.1021/acsami.6b03618)
Figure 1: A Thermoacoustic Loudspeaker Consisted of an Array of 16 3D Graphene Aerogels
Figure 2: Two-step Fabrication Process of 3D Reduced Graphene Oxide Aerogel Using Freeze-Drying and Reduction/Doping
Figure 3: X-ray Photoelectron Spectroscopy Graph of the 3D Reduced Graphene Oxide Aerogel and Its Scanning Electron Microscope Image
2016.10.05 View 13941 -
Direct Utilization of Elemental Sulfur for Microporous Polymer Synthesis
Using elemental sulfur as an alternative chemical feedstock, KAIST researchers have produced novel microporous polymers to sift CO2 from methane in natural-gas processing.
Methane, a primary component of natural gas, has emerged recently as an important energy source, largely owing to its abundance and relatively clean nature compared with other fossil fuels. In order to use natural gas as a fuel, however, it must undergo a procedure called “hydrodesulfurization” or “natural gas sweetening” to reduce sulfur-dioxide emissions from combustion of fossil fuels. This process leads to excessive and involuntary production of elemental sulfur. Although sulfur is one of the world’s most versatile and common elements, it has relatively few large-scale applications, mostly for gunpowder and sulfuric acid production.
Thus, the development of synthetic and processing methods to convert sulfur into useful chemicals remains a challenge. A research team led by Professor Ali Coskun from the Graduate School of EEWS (Energy, Environment, Water and Sustainability) at Korea Advanced Institute of Science and Technology (KAIST) has recently introduced a new approach to resolving this problem by employing elemental sulfur directly in the synthesis of microporous polymers for the process of natural-gas sweetening.
Natural gas, containing varying amounts of carbon dioxide (CO2) and hydrogen sulfide (H2S), is generally treated with amine solutions, followed by the regeneration of these solutions at increased temperatures to release captured CO2 and H2S. A two-step separation is involved in removing these gases. The amine solutions first remove H2S, and then CO2 is separated from methane (CH4) with either amine solutions or porous sorbents such as microporous polymers.
Using elemental sulfur and organic linkers, the research team developed a solvent and catalyst-free strategy for the synthesis of ultramicroporous benzothiazole polymers (BTAPs) in quantitative yields. BTAPs were found to be highly porous and showed exceptional physiochemical stability. In-situ chemical impregnation of sulfur within the micropores increased CO2 affinity of the sorbent, while limiting diffusion of CH4. BTAPs, as low-cost, scalable solid-sorbents, showed outstanding CO2 separation ability for flue gas, as well as for natural and landfill gas conditions.
The team noted that: “Each year, millions of tons of elemental sulfur are generated as a by-product of petroleum refining and natural-gas processing, but industries and businesses lacked good ideas for using it. Our research provides a solution: the direct utilization of elemental sulfur into the synthesis of ultramicroporous polymers that can be recycled back into an efficient and sustainable process for CO2 separation. Our novel polymeric materials offer new possibilities for the application of a little-used natural resource, sulfur, to provide a sustainable solution to challenging environmental issues.”
This work was published online in Chem on September 8, 2016 and also highlighted in C&EN (Chemical & Engineering News) by the American Chemical Society (ACS) on September 19, 2016. The research paper was entitled “Direct Utilization of Elemental Sulfur in the Synthesis of Microporous Polymers for Natural Gas Sweetening.” (DOI: 10.1016/j.chempr.2016.08.003)
Figure 1. A Schematic Image of Direct Utilization of Elemental Sulfur
This image shows direct utilization of elemental sulfur in the synthesis of microporous polymers and its gas separation performance.
Figure 2. BTAP’s Breakthrough Experiment under Pre-mixed Gas Conditions
This data presents the breakthrough measurements for CO2-containing binary gas-mixture streams with different feed-gas compositions to investigate the CO2 capture capacity of ultramicroporous benzothiazole polymers (BTAPs) for large-scale applications under simulated conditions of natural and landfill gases.
2016.10.05 View 9107 -
Continuous Roll-Process Technology for Transferring and Packaging Flexible Large-Scale Integrated Circuits
A research team led by Professor Keon Jae Lee from KAIST and by Dr. Jae-Hyun Kim from the Korea Institute of Machinery and Materials (KIMM) has jointly developed a continuous roll-processing technology that transfers and packages flexible large-scale integrated circuits (LSI), the key element in constructing the computer’s brain such as CPU, on plastics to realize flexible electronics.
Professor Lee previously demonstrated the silicon-based flexible LSIs using 0.18 CMOS (complementary metal-oxide semiconductor) process in 2013 (ACS Nano, “In Vivo Silicon-based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Biocompatible Liquid Crystal Polymers”) and presented the work in an invited talk of 2015 International Electron Device Meeting (IEDM), the world’s premier semiconductor forum.
Highly productive roll-processing is considered a core technology for accelerating the commercialization of wearable computers using flexible LSI. However, realizing it has been a difficult challenge not only from the roll-based manufacturing perspective but also for creating roll-based packaging for the interconnection of flexible LSI with flexible displays, batteries, and other peripheral devices.
To overcome these challenges, the research team started fabricating NAND flash memories on a silicon wafer using conventional semiconductor processes, and then removed a sacrificial wafer leaving a top hundreds-nanometer-thick circuit layer. Next, they simultaneously transferred and interconnected the ultrathin device on a flexible substrate through the continuous roll-packaging technology using anisotropic conductive film (ACF). The final silicon-based flexible NAND memory successfully demonstrated stable memory operations and interconnections even under severe bending conditions. This roll-based flexible LSI technology can be potentially utilized to produce flexible application processors (AP), high-density memories, and high-speed communication devices for mass manufacture.
Professor Lee said, “Highly productive roll-process was successfully applied to flexible LSIs to continuously transfer and interconnect them onto plastics. For example, we have confirmed the reliable operation of our flexible NAND memory at the circuit level by programming and reading letters in ASCII codes. Out results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing.”
Dr. Kim added, “We employed the roll-to-plate ACF packaging, which showed outstanding bonding capability for continuous roll-based transfer and excellent flexibility of interconnecting core and peripheral devices. This can be a key process to the new era of flexible computers combining the already developed flexible displays and batteries.”
The team’s results will be published on the front cover of Advanced Materials (August 31, 2016) in an article entitled “Simultaneous Roll Transfer and Interconnection of Silicon NAND Flash Memory.” (DOI: 10.1002/adma.201602339)
YouTube Link: https://www.youtube.com/watch?v=8OJjAEm27sw
Picture 1: This schematic image shows the flexible silicon NAND flash memory produced by the simultaneous roll-transfer and interconnection process.
Picture 2: The flexible silicon NAND flash memory is attached to a 7 mm diameter glass rod.
2016.09.01 View 11604 -
IdeasLab Presents Biotechnology Solutions for Aging Populations at 2016 Davos Forum
KAIST researchers will discuss how biological sciences and health technologies can address challenges and opportunities posed by aging populations in an era of increasing longevity.
Many countries around the world today are experiencing the rapid growth of aging populations, with a decline in fertility rate and longer life expectancy.
At this year's Annual Meeting of the World Economic Forum (a.k.a. Davos Forum) on January 20-23, 2016 in Davos-Klosters, Switzerland, four researchers in the field of biological sciences and biotechnology at the Korea Advanced Institute of Science and Technology (KAIST) will discuss the implications of an aging population and explore possible solutions to provide better health care services to the elderly.
KAIST will host an IdeasLab twice on the theme "Biotechnology Solutions for Ageing Populations" on January 21st and 23rd, respectively.
Professor Byung-Kwan Cho of the Biological Sciences Department will give a presentation on "Rejuvenation via the Microbiome," explaining how microorganisms in the human gut play an important role in preventing aging, or even rejuvenating it.
Distinguished Professor Sang Yup Lee of the Chemical and Biomolecular Engineering Department will talk about "Traditional Medicine Reimagined through Modern Systems Biology." Professor Lee will introduce his research results published in Nature Biotechnology (March 6, 2015) and some more new results. He discovered the mechanisms of traditional oriental medicine's (TOM) efficacy by applying systems biology to study structural similarities between natural and nontoxic multi-compounds in the medicine and human metabolites. He will discuss TOM's multi-target approach, which is based on the synergistic combinations of multi-compounds to treat symptoms of a disease, can contribute to the development of new drugs, cosmetics, and nutrients.
Professor Youn-Kyung Lim of the Industrial Design Department will speak about a mobile and the Internet of Things-based health care service called "Dr. M" in her presentation on "Advanced Mobile Healthcare Systems."
Professor Daesoo Kim of the Biological Sciences Department will share his research on human's happiness and greed in the context of nueroscience and behavioral and biological sciences in a talk entitled "A Neural Switch for Being Happy with Less on a Crowded Planet."
KAIST has hosted IdeasLabs several times at the Summer Davos Forum in China, but this is the first time it will participate in the Davos Forum in January.
Professor Lee said, "Just like climate change, the issue of how to address aging populations has become a major global issue. We will share some exciting research results and hope to have in depth discussion on this issue with the leaders attending the Davos Forum. KAIST will engage actively in finding solutions that benefit not only Korea but also the international community."
2016.01.19 View 11478 -
KAIST Develops New Technique for Chiral Activity in Molecules
Professor Hyunwoo Kim of the Chemistry Department and his research team have developed a technique that can easily analyze the optical activity of charged compounds by using nuclear magnetic resonance (NMR) spectroscopy. The research finding entitled “H NMR Chiral Analysis of Charged Molecules via Ion Pairing with Aluminum Complexes” was published online in the October 19th issue of The Journal of the American Chemical Society.
The technique relies on observation of the behavior of optical isomers. Molecules with the same composition that are mirror images of each other are optical isomers. For example, the building blocks of all living organisms, amino acids, are a single optical isomer. In our bodies, optical isomers bring different physiological changes due to their distinct optical activities. Therefore, controlling and analyzing the optical activities are critical when developing a new drug.
High-performance liquid chromatography (HPLC) is the de facto standard of analyzing the optical activity of a compound. However, HPLC is very expensive that many laboratories can’t afford to have. In addition, with the machine, one analysis may take 30 minutes to one hour to complete. It lacks in signal sensitivity and chemical decomposition, and the application is limited to nonpolar compounds.
Usually adopted in analyzing the structure of a chemical compound, NMR spectroscopy requires only one to five minutes per single analysis. Since it is essential for analyzing the molecular structure, many chemistry labs have NMR equipment. However, until this technique was invented, no other research team had reported an effective way of using the NMR spectroscopy to decompose the signal of chiral activity of a compound.
The research team uses negatively-charged metal compounds in NMR spectroscopy. The technique employs negatively-charged metal compounds which bond ionically to positively- and negatively-charged optical compounds. As a result, the NMR spectroscopy can distinguish the signal from chiral activity. Not only can it analyze various chemicals without structural constraints, but it can also be used for both nonpolar and polar solvents.
As many compounds for new drugs have functional groups, which can be charged, this analysis method can be directly employed in the development process of drugs. Professor Kim said, “A revolutionary analysis method has been developed using simple chemical principles. I hope that our method will be applied to the development of new medicine.”
This research was sponsored by the Center for Nanomaterials and Chemical Reactions at the Institute for Basic Science and the Supercomputing Research Center of KAIST.
Picture 1: Separations of NMR Signals of Chemicals due to Interaction with Metal Compounds
Picture 2: Separations of NMR Signals in Different Chemicals
2015.11.20 View 11847 -
Using Light to Treat Alzheimer's Disease
Medical application of photoactive chemicals offers a promising therapeutic strategy for neurodegenerative diseases.
A research team jointly led by Professor Chan Beum Park of the Materials Science and Engineering Department at KAIST and Dr. Kwon Yu from the Bionano Center at the Korea Research Institute of Bioscience and Biotechnology (KRIBB) conducted research to suppress an abnormal assembly of beta-amyloids, a protein commonly found in the brain, by using photo-excited porphyrins.
Beta-amyloid plaques are known to cause Alzheimer's disease. This research finding suggests new ways to treat neurodegenerative illnesses including Alzheimer's disease. It was published online as the lead article in the September 21th issue of Angewandte Chemie. The title of the article is “Photo-excited Porphyrins as a Strong Suppressor of ß-Amyloid Aggregation and Synaptic Toxicity.”
Light-induced treatments using organic photosensitizers have advantages to managing the treatment in time and area. In the case of cancer treatments, doctors use photodynamic therapies where a patient is injected with an organic photosensitizer, and a light is shed on the patient’s lesion. However, such therapies had never been employed to treat neurodegenerative diseases.
Alzheimer's starts when a protein called beta-amyloid is created and deposited in a patient’s brain. The abnormally folded protein created this way harms the brain cells by inducing the degradation of brain functions, for example, dementia. If beta-amyloid creation can be suppressed at an early stage, the formation of amyloid deposits will stop. This could prevent Alzheimer’s disease or halt its progress.
The research team effectively prevented the buildup of beta-amyloids by using blue LED lights and a porphyrin inducer, which is a biocompatible organic compound. By absorbing light energy, a photosensitizer such as porphyrin reaches the excitation state. Active oxygen is created as the porphyrin returns to its ground state. The active oxygen oxidizes a beta-amyloid monomer, and by combining with it, disturbs its assembly.
The technique was tested on drosophilae or fruit flies, which were produced to model Alzheimer on invertebrates. The research showed that symptoms of Alzheimer's disease in the fruit flies such as damage on synapse and muscle, neuronal apoptosis, degradation in motility, and decreased longevity were alleviated. Treatments with light provide additional benefits: less medication is needed than other drug treatments, and there are fewer side effects. When developed, photodynamic therapy will be used widely for this reason.
Professor Park said, “This work has significance as it was the first case to use light and photosensitizers to stop deposits of beta-amyloids. We plan to carry the research further by testing compatibility with other organic and inorganic photosensitizers and by changing the subject of photodynamic therapy to vertebrate such as mice.”
Picture 1 – Deposits of Beta-Amyloid in Fruit Flies Stopped by Using Porphyrin and Blue LED Lights
Picture 2 – The Research Finding Published as the Lead Article in Angewandte Chemie (September 2015)
2015.11.11 View 11464 -
KAIST and Hanwha Chemical Agree on Research Collaboration
KAIST signed a memorandum of understanding (MOU) with Hanwha Chemical Co., Ltd., a Korean chemical and auto manufacturer, on November 2, 2015 to establish a research center on campus.
The research center, which will be named “KAIST-Hanwha Chemical Future Technology Research Center,” will implement joint research projects for five years beginning from 2016 to develop innovative, green technologies that will help the Korean chemical industry boost its global competitiveness and to nurture top researchers and engineers in chemical engineering.
The research center will lead the development of next-generation petrochemical materials and manufacturing technology and the establishment of pure high-refining processes which are more energy-efficient and environmentally friendly. KAIST and Hanwha will strive to secure new technologies that have the greatest commercialization potential in the global market. They will also establish a scholarship fund for 15 KAIST doctoral students in the Department of Chemical and Biomolecular Engineering.
Many professors from the Chemical and Biomolecular Engineering Department including Distinguished Professor Sang Yup Lee, who was listed in the Top 20 Translational Researchers of 2014 by Nature Biotechnology this year, and Professor Hyunjoo Lee who received the Woman Scholar award at the 2015 World Chemistry Conference, will work at the research center.
Professor Lee, the head of the research center, said, “Collaborating with Hanwha will give us a strong basis for our efforts to carry out original research and train the best researchers in the field.”
Chang-Bum Kim, the Chief Executive Officer (CEO) of Hanwha Chemical, said,
“We hope our collaborations with KAIST will go beyond the typical industry and university cooperation. The two organizations will indeed jointly operate the research center, and this will become a new model for industry and university cooperation. We expect that the research center will play a crucial role in the development of new products and technologies to grow the Korean chemical industry.”
In the photo, President Steve Kang of KAIST (fourth from left) and CEO Chang-Bum Kim of Hanwha Chemical (fifth from left) hold the MOU together.
2015.11.01 View 11758 -
Professors Sukbok Chang and Jang-Wook Choi Receive the 2015 Knowledge Award from the Korean Government
The Ministry of Science, ICT and Future Planning (MISP) of the Republic of Korea announced the 2015 Knowledge Awards on October 20, 2015. Two KAIST professors received the award.
Established in 2009, the awards are presented to Korean scientists whose publications have contributed to the international science community. Specifically, the MISP used the two biggest science databases, Science Citation Index Expanded (SCIE) and Scopus, to identify ten highly cited papers ranked in the top 1% by total citations in the past ten years.
Professor Sukbok Chang of Chemistry (left in the picture below) is a global authority in the field of catalytic hydrocarbon functionalization. His paper entitled “Palladium-catalyzed C-H Functionalization of Pyridine N-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arenes,” which was published in the Journal of the American Chemical Society in 2008, was once selected by Thomson Reuters as one of the “Most Influential Research Papers of the Month.” In 2011, the American Chemical Society included his paper in the list of the top 20 research papers that were most frequently cited in the last three years.
Professor Jang-Wook Choi of the Graduate School of EEWS (Energy, Environment, Water, and Sustainability) has been known for his leading research in rechargeable battery, supercapacitor, and materials chemistry. In particular, his work on secondary fuel cells attracted significant attention from academia and industry in Korea. Professor Choi developed a super-thin flexible lithium-ion battery this year, thinner than a credit card, which lasts longer than the existing batteries and with greater performance. He also developed new electrode materials for next-generation sodium-ion and magnesium secondary fuel cells.
Professor Sukbok Chang (left) and Professor Jang-Wook Choi (right)
2015.10.23 View 12217 -
Affordable Genetic Diagnostic Technique for Target DNA Analysis Developed
Professor Hyun-Gyu Park of the Department of Chemical and Biomolecular Engineering at KAIST has developed a technique to analyze various target DNAs using an aptamer, a DNA fragment that can recognize and bind to a specific protein or enzyme. This technique will allow the development of affordable genetic diagnoses for new bacteria or virus, such as Middle Ease Respiratory Syndrome (MERS). The research findings were published in the June issue of Chemical Communications, issued by the Royal Society of Chemistry in the United Kingdom. The paper was selected as a lead article of the journal.
The existing genetic diagnosis technique, based on molecular beacon probes, requires a new beacon probe whenever a target DNA mutates. As a result, it was costly to analyze various target DNA fragments. To address this problem, Professor Park’s team designed an aptamer that binds and deactivates DNA polymerase. The technique was used in reverse, so that the aptemer did not bind to the polymerase, maintaining its activated state, only if the target DNA was present. These probes are called TagMan probes.
The controlled activation and deactivation of DNA polymerase enables nucleic acid to elongate or dwindle, making it possible to measure fluorescence signals coming from TaqMan probes. This same probe can be used to detect various target DNAs, leading to the development of a new and sensitive genetic diagnostic technique.
Unlike the existing molecular beacon probe technique which requires a new probe for every target DNA, this new technique uses the same fluorescent TaqMan probe, which is cheaper and easier to detect a number of different target nucleic acid fragments. The application of this technique will make the process of identifying and detecting foreign DNAs from pathogens such as virus and bacteria more affordable and simple.
Professor Park said, “This technique will enable us to develop simpler diagnostic kits for new pathogens, such as MERS, allowing a faster response to various diseases. Our technology can also be applied widely in the field of genetic diagnostics.”
Picture: A schematic image of target nucleic acid extracted through the activation and deactivation of DNA polymerase
2015.07.31 View 10445 -
3D Plasmon Antenna Capable of Focusing Light into Few Nanometers
Professors Myung-Ki Kim and Yong-Hee Lee, both of the Physics Department at KAIST, and their research teams have developed a three dimensional (3D) gap-plasmon antenna which can focus light into a space a few nanometers wide. Their research findings were published in the June 10th issue of Nano Letters.
Focusing light into a point-like space is an active research field with many applications. However, concentrating light into a smaller space than its wavelength is often hindered by diffraction. To tackle this problem, many researchers have utilized the plasmonic phenomenon of a metal where light can be confined to a greater extent by overcoming the diffraction limit.
Many researchers have focused on developing a two dimensional (2D) plasmon antenna and were able to focus a light under 5 nanometers wide. However, this 2D antenna revealed a challenge: the light disperses to the opposite end regardless of how small its beam was focused. To solve this difficulty, a 3D structure had to be employed to maximize the light's intensity.
Adopting the proximal focused-ion-beam milling technology, the KAIST research team developed a 3D four nanometer wide gap-plasmon antenna. By squeezing the photons into a 3D nano space of 4 x 10 x 10 nm3 size, the researchers were able to increase the intensity of light by 400,000 times stronger than that of the incident light. Capitalizing on the enhanced intensity of light within the antenna, they intensified the second-harmonic signal and verified that the light was focused in the nano gap by scanning cathodoluminescent images.
The researchers anticipate that this technology will improve the speed of data transfer and processing up to the level of a terahertz (one trillion times per second) and to enlarge the storage volume per unit area on hard disks by 100 times. In addition, high definition images of submolecule size can be taken with actual light, instead of with an electron microscope, while improving the semiconductor process to a smaller size of few nanometers.
Professor Kim said, “A simple yet ingenious idea has shifted the research paradigm from 2D gap-plasmon antennas to 3D antennas. This technology will see numerous applications including in the field of information technology, data storage, imaging medical science, and semiconductor processes.”
The research was sponsored by the National Research Foundation of Korea.
Figure 1: 3D Gap-Plasmon Antenna Structure and Simulation Results
Figure 2 – Constructed 3D Gap-Plasmon Antenna Structure
Figure 3 – Amplified Second Harmonic Signal Generation and Light Focused in the Nano Gap
2015.06.24 View 10436 -
KAIST Team Develops Flexible PRAM
Phase change random access memory (PRAM) is one of the strongest candidates for next-generation nonvolatile memory for flexible and wearable electronics. In order to be used as a core memory for flexible devices, the most important issue is reducing high operating current. The effective solution is to decrease cell size in sub-micron region as in commercialized conventional PRAM. However, the scaling to nano-dimension on flexible substrates is extremely difficult due to soft nature and photolithographic limits on plastics, thus practical flexible PRAM has not been realized yet.
Recently, a team led by Professors Keon Jae Lee and Yeon Sik Jung of the Department of Materials Science and Engineering at KAIST has developed the first flexible PRAM enabled by self-assembled block copolymer (BCP) silica nanostructures with an ultralow current operation (below one quarter of conventional PRAM without BCP) on plastic substrates. BCP is the mixture of two different polymer materials, which can easily create self-ordered arrays of sub-20 nm features through simple spin-coating and plasma treatments. BCP silica nanostructures successfully lowered the contact area by localizing the volume change of phase-change materials and thus resulted in significant power reduction. Furthermore, the ultrathin silicon-based diodes were integrated with phase-change memories (PCM) to suppress the inter-cell interference, which demonstrated random access capability for flexible and wearable electronics. Their work was published in the March issue of ACS Nano: "Flexible One Diode-One Phase Change Memory Array Enabled by Block Copolymer Self-Assembly."
Another way to achieve ultralow-powered PRAM is to utilize self-structured conductive filaments (CF) instead of the resistor-type conventional heater. The self-structured CF nanoheater originated from unipolar memristor can generate strong heat toward phase-change materials due to high current density through the nanofilament. This ground-breaking methodology shows that sub-10 nm filament heater, without using expensive and non-compatible nanolithography, achieved nanoscale switching volume of phase change materials, resulted in the PCM writing current of below 20 uA, the lowest value among top-down PCM devices. This achievement was published in the June online issue of ACS Nano: "Self-Structured Conductive Filament Nanoheater for Chalcogenide Phase Transition." In addition, due to self-structured low-power technology compatible to plastics, the research team has recently succeeded in fabricating a flexible PRAM on wearable substrates.
Professor Lee said, "The demonstration of low power PRAM on plastics is one of the most important issues for next-generation wearable and flexible non-volatile memory. Our innovative and simple methodology represents the strong potential for commercializing flexible PRAM."
In addition, he wrote a review paper regarding the nanotechnology-based electronic devices in the June online issue of Advanced Materials entitled "Performance Enhancement of Electronic and Energy Devices via Block Copolymer Self-Assembly."
Picture Caption:
Low-power nonvolatile PRAM for flexible and wearable memories enabled by (a) self-assembled BCP silica nanostructures and (b) self-structured conductive filament nanoheater.
2015.06.15 View 15347 -
Anti-Cancer Therapy Delivering Drug to an Entire Tumor Developed
KAIST’s Department of Bio and Brain Engineering Professor Ji-Ho Park and his team successfully developed a new highly efficacious anti-cancer nanotechnology by delivering anti-cancer drugs uniformly to an entire tumor. Their research results were published in Nano Letters online on March 31, 2015.
To treat inoperable tumors, anti-cancer medicine is commonly used. However, efficient drug delivery to tumor cells is often difficult, treating an entire tumor with drugs even more so.
Using the existing drug delivery systems, including nanotechnology, a drug can be delivered only to tumor cells near blood vessels, leaving cells at the heart of a tumor intact. Since most drugs are injected into the bloodstream, tumor recurrence post medication is frequent.
Therefore, the team used liposomes that can fuse to the cell membrane and enter the cell. Once inside liposomes the drug can travel into the bloodstream, enter tumor cells near blood vessels, where they are loaded to exosomes, which are naturally occurring nanoparticles in the body. Since exosomes can travel between cells, the drug can be delivered efficiently into inner cells of the tumor.
Exosomes, which are secreted by cells that exist in the tumor microenvironment, is known to have an important role in tumor progression and metastasis since they transfer biological materials between cells. The research team started the investigation recognizing the possibility of delivering the anti-cancer drug to the entire tumor using exosomes.
The team injected the light-sensitive anti-cancer drug using their new delivery technique into experimental mice. The researchers applied light to the tumor site to activate the anti-cancer treatment and analyzed a tissue sample. They observed the effects of the anti-cancer drug in the entire tumor tissue.
The team’s results establish a ground-breaking foothold in drug delivery technology development that can be tailored to specific diseases by understanding its microenvironment. The work paves the way to more effective drug delivery systems for many chronic diseases, including cancer tumors that were difficult to treat due to the inability to penetrate deep into the tissue.
The team is currently conducting experiments with other anti-cancer drugs, which are being developed by pharmaceutical companies, using their tumor-penetrating drug delivery nanotechnology, to identify its effects on malignant tumors.
Professor Park said, “This research is the first to apply biological nanoparticles, exosomes that are continuously secreted and can transfer materials to neighboring cells, to deliver drugs directly to the heart of tumor.”
Picture: Incorporation of hydrophilic and hydrophobic compounds into membrane vesicles by engineering the parental cells via synthetic liposomes.
2015.04.07 View 12200