'자료/연구및기기'에 해당되는 글 37건
- 2009.03.18 :: RAMAN SPECTROSCOPY: Nanowire on a film makes efficient SERS platform 170
- 2009.02.23 :: Gavin Conibeer 1
- 2009.01.06 :: Georgia Tech Professor Walt de Heer holds a proof-of-principle device constructed of graphene
- 2008.12.24 :: [book] Supramolecular Organization and Materials Design
RAMAN SPECTROSCOPY: Nanowire on a film makes efficient SERS platform
Researchers from KAIST (Daejeon, Korea), Korea University, and Soongsil University (both in Seoul, Korea), have developed an efficient and highly reproducible surface-enhanced Raman spectroscopy (SERS) platform for scattering-based sensors in biological and medical applications.1
In SERS, molecules of interest adsorb onto particular nanostructured metal surfaces and create localized surface plasmons that cause a dramatic increase in the incident electromagnetic field–high Raman intensities that can be used to differentiate the spectral fingerprint of many molecules (see www.laserfocusworld.com/articles/317040). Unfortunately, these high Raman intensities or “hot spots” are not easy to reproduce and are highly dependent on the nanostructure platform used. To combat this drawback, the research team developed a simple platform consisting of a metallic nanowire cast onto a metallic film. The single-nanowire-on-a-film (SNOF) architecture is easy to fabricate, reproducible, and provides a line of SERS hot spots at the gap between the nanowire and the film upon optical excitation. In addition, the position of the hot spots can be located in situ using an optical microscope during the SERS measurement.
“SNOF provides an important step toward our main goal to develop simple and atomically well-defined SERS-active nanostructures that actually could be applied as nanobiosensors,” says Ilsun Yoon, postdoctoral researcher at KAIST.
Both finite-difference time-domain (FDTD) modeling and experimental results were used to show how the SNOF architecture could increase Raman gain for improved spectral analysis of three different molecules: benzenethiol, brilliant cresyl blue, and single-stranded DNA. Experimentation included a gold (Au) nanowire fabricated on a Au film as the primary SNOF structure; in addition, a Au nanowire on a silicon substrate was used as a control platform to highlight the Raman gain observed for the primary SNOF structure. Silver (Ag) nanowires and films were also prepared in order to understand the effects of using different metals.
A SNOF architecture (left) produces local Raman gain that enables detection of molecules such as benzenethiol using SERS (a). Optical-microscope (b) and scanning-electron-microscope (c) images confirm that a single gold nanowire is present on the gold film. The SERS spectra of benzenethiol using different nanowire and film materials (right) show the highest Raman gain for the silver nanowire on silver film combination. (Courtesy of KAIST)
Gold nanowires were grown on a sapphire substrate in a horizontal quartz tube furnace using a vapor-transport method. The single-crystalline Au nanowires have a diamond-shaped cross section, are 100 to 200 nm in diameter, and up to tens of micrometers long. Gold 300-nm-thick films were deposited on 10 nm of chromium over silicon substrates, with electron-beam-assisted deposition. A root-mean-square surface roughness of 2.3 to 2.8 nm was sufficiently smooth for the films to be SERS inactive by themselves. To prepare the SNOF structure, Au nanowires were incubated in the solutions containing the analytes and then a drop of the incubated Au nanowire solution was cast on the Au film. The Au nanowires physically adhere on the Au film by the so-called “London force,” a form of intermolecular force.
Surface-plasmon polaritons
A home-built micro-Raman system with a cooled CCD detector and 500-nm-diameter helium-neon laser spot was then used to perform SERS measurements on the adsorbed molecules on the SNOF structure, which was immersed in water. When the SNOF structure is illuminated, an enhanced electric field is induced at the gap between the Au nanowire and the Au film due to excitation of a surface plasmon on the nanowire, which in turn excites surface-plasmon polaritons on the metal film, creating a hot line at the nanowire/film gap.
Experimental
results indicated that the SERS signal increased by a factor of 500 for
the Au nanowire on Au film SNOF compared to the Au nanowire on the
silicon control substrate. Polarization of the input laser source was
also important for Raman enhancement. Raman enhancement of SNOF is
mainly dependent on the material of the nanowire. The Ag nanowire on Ag
film SNOF had the best performance among the SNOF structures, because
the localized surface-plasmon excitation of a Ag nanowire is stronger
upon illumination by 633 nm laser light than that of a Au nanowire.
–Gail Overton
REFERENCE
- I. Yoon et al., J. American Chem. Soc. online, DOI: 10.1021/ja807455s (Dec. 19, 2008).
Sun Feb 01 00:00:00 CST 2009
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Gavin Conibeer University of New South Wales Deputy Director, Photovoltaics Centre of Excellence Presentation Title: Third Generation Photovoltaics (PDF, 1.6Mb) |
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Abstract: To achieve the International Panel on Climate Change recommended 60% reduction in emissions by 2050—the minimum needed to offset the worst effects of climate change—a large scale implementation of sustainable and renewable energy technologies is required. Amongst these renewable energies, photovoltaics is the fastest growing technology with more than 30% growth per year over the last 10 years and more than 60% growth in 2007; although worldwide installation is still small. This growth in manufacture is currently driven by subsidies, primarily in Europe, but the increase itself leads to a learning effect as the technology matures, which brings down the cost per unit. In order to maintain the leverage this steep learning curve applies to unit price, a transition of technology from the first generation approaches based on single crystal wafer based solar cells to second generation thin film, with their much lower energy intensity and material usage, is required. However to project this downward pressure on price onto ever larger production volumes, a further generation change is required to push up efficiencies whilst still maintaining the low cost approaches of thin film cells. The reason that such third generation technologies can achieve such a “best of both worlds” result is that the vast majority of current production cells consist of only one absorbing semiconductor material. But such single semiconductor band gap devices have to compromise in their absorption of the very polychromatic solar spectrum, with a wide range of photon energies. This leads to significant energy losses through two main routes. At first, solar photons at less than the band gap energy are not absorbed at all and are wasted. Secondly, for photons well above the band gap energy, a large fraction of their energy is lost as heat in the device. Third generation devices use multiple energy levels, often in the form of several different semiconductor materials, to extract energy efficiently from a greater fraction of these photons. Examples of such approaches will be discussed, with specific mention of tandem solar cells that use quantum dot nanostructures based on silicon; devices which can up-convert low energy photons such that they are absorbed; and hot carrier cells which seek to extract the energy gained from high energy photons before it can be lost to the lattice. The status of and prospects for these approaches will be assessed. Biography: Dr. Gavin Conibeer received his PhD from Southampton University, UK, in Semiconductor Physics for tandem solar cells in 1995. He also has a BSc in Materials Science and MSc in Polymer Science from London University. Conibeer has held research positions at Oxford, Cranfield, Southampton, and Monash Universities where he has worked on most of the materials systems used in photovoltaics. Conibeer joined the University of New South Wales, Sydney, Australia in 2002 and was appointed a Deputy Director in the Photovoltaics Centre of Excellence in 2003, in charge of Third Generation Photovoltaics. This group of 22 researchers is investigating the fabrication of silicon, germanium and tin nanostructures in oxide, nitride or carbide matrices; up or down conversion of the incident solar spectrum; and hot carrier solar cells. Conibeer’s personal research interests encompass a wide range of third generation and advanced photovoltaic concepts, including silicon quantum dot based tandem solar cells, hot carrier solar cells, up-conversion and photoelectrochemical cells. He is author of over 100 publications including 35 journal articles. | |
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March 14, 2006
Carbon-Based Electronics: Researchers Develop Foundation for Circuitry and Devices Based on Graphite
Graphite, the material that gives pencils their marking ability, could be the basis for a new class of nanometer-scale electronic devices that have the attractive properties of carbon nanotubes – but could be produced using established microelectronics manufacturing techniques.
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Using thin layers of graphite known as graphene, researchers at the Georgia Institute of Technology in the United States, in collaboration with the Centre National de la Recherche Scientifique (CNRS) in France, have produced proof-of-principle transistors, loop devices and circuitry. Ultimately, the researchers hope to use graphene layers less than 10 atoms thick as the basis for revolutionary electronic systems that would manipulate electrons as waves rather than particles, much like photonic systems control light waves.
“We expect to make devices of a kind that don’t really have an analog in silicon-based electronics, so this is an entirely different way of looking at electronics,” said Walt de Heer, a professor in Georgia Tech’s School of Physics. “Our ultimate goal is integrated electronic structures that work on diffraction of electrons rather than diffusion of electrons. This will allow the production of very small devices with very high efficiencies and low power consumption.”
Supported by the U.S. National Science Foundation and the Intel Corporation, the work was described March 13th at the March Meeting of the American Physical Society. Details of fabrication techniques have been reported in the Journal of Physical Chemistry.
Because carbon nanotubes conduct electricity with virtually no resistance, they have attracted strong interest for use in transistors and other devices. However, serious obstacles must be overcome before nanotube-based devices could be scaled up into high-volume industrial products, including:
- An inability to produce nanotubes of consistent sizes and consistent
electronic properties,
- Difficulty integrating nanotubes into electronic devices using processes
suitable for volume production, and
- High electrical resistance that produces heating and energy loss
at junctions between nanotubes and the metal wires connecting them.
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De Heer, who helped discover many properties of carbon nanotubes over the past decade, believes their primary value has been in calling attention to the useful properties of graphene. Continuous graphene circuitry can be produced using standard microelectronic processing techniques, potentially allowing creation of a “road map” for high-volume graphene electronics manufacturing, he said.
“Nanotubes are simply graphene that has been rolled into a cylindrical shape,” de Heer explained. “Using narrow ribbons of graphene, we can get all the properties of nanotubes because those properties are due to the graphene and the confinement of the electrons, not the nanotube structures.”
De Heer envisions using the graphene electronics for specialized applications, potentially within conventional silicon-based systems. Graphene systems could also be used as the foundation for molecular electronics, helping resolve resistance issues that now affect such systems.
“There is a huge advantage to making a system out of one continuous material, compared to having different materials with different interfaces – and large contract resistances to cause heating at the contacts,” he said.
De Heer and collaborators Claire Berger, Nate Brown, Edward Conrad, Zhenting Dai, Rui Feng, Phillip First, Joanna Hass, Tianbo Li, Xuebin Li, Alexei Marchenkov, James Meindl, Asmerom Ogbazghi, Thomas Orlando, Zhimin Song, Xiaosong Wu of Georgia Tech and Didier Mayou and Cecile Naud of CNRS start with a wafer of silicon carbide, a material made up of silicon and carbon atoms. By heating the wafer in a high vacuum, they drive silicon atoms from the surface, leaving a thin continuous layer of graphene.
Next, they spin-coat onto the surface a photo-resist material of the kind used in established microelectronics techniques. Using optical lithography or electron-beam lithography, they produce patterns on the surface, then use conventional etching processes to remove unwanted graphene.
“We are doing lithography, which is completely familiar to those who work in microelectronics,” said de Heer. “It’s exactly what is done in microelectronics, but with a different material. That is the appeal of this process.”
Using electron beam lithography, they’ve created feature sizes as small as 80 nanometers – on the way toward a goal of 10 nanometers with the help of a new nanolithographer in Georgia Tech’s Microelectronics Research Center. The graphene circuitry demonstrates high electron mobility – up to 25,000 square centimeters per volt-second, showing that electrons move with little scattering. The researchers have also shown electronic coherence at near room temperature, and evidence of quantum interference effects. They expect to see ballistic transport when they make structures small enough.
So far, they have built an all graphene planar field-effect transistor. The side-gated device produces a change in resistance through its channel when voltage is applied to the gate. However, this first device has a substantial current leak, which the team expects to eliminate with minor processing adjustments.
The researchers have also built a working quantum interference device, a ring-shaped structure that would be useful in manipulating electronic waves.
The key to properties of the new circuitry is the width of the ribbons, which confine the electrons in a quantum effect similar to that seen in carbon nanotubes. The width of the ribbon controls the material’s band-gap. Other structures, such as sensing molecules, could be attached to the edges of the ribbons, which are normally passivated by hydrogen atoms.
De Heer and collaborators began working on graphene in 2001 and received support from Intel in 2003. They later received a Nanoscale Interdisciplinary Research Team (NIRT) award from the U.S. National Science Foundation. They have filed one patent for their methods of fabricating graphene circuitry.
De Heer and his colleagues expect to continue improving their materials
and fabrication processes, while producing and testing new structures.
“We have taken the first step of a very long road,” de Heer
said. “Building a new class of electronics based on graphene is
going to be very difficult and require the efforts of many people.”
RESEARCH NEWS
& PUBLICATIONS OFFICE
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 100
Atlanta, Georgia 30308 USA
MEDIA RELATIONS CONTACT: John Toon (404-894-6986); E-mail: (jtoon@gatech.edu).
TECHNICAL CONTACTS: Walt de Heer (404-894-7880); E-mail: (deheer@electra.physics.gatech.edu) or Phil First (404-894-0548); E-mail: (first@physics.gatech.edu).
WRITER: John Toon
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Supramolecular Organization and Materials Design
Edited by W. Jones
University of Cambridge
C. N. R. Rao
Indian Institute of Science, Bangalore
Paperback
(ISBN-13: 9780521087810)
£43.00
Supramolecular Chemistry deals with the design, synthesis and study of molecular structures held together by non-covalent interactions. Structures of this type are ubiquitous in nature and are frequently used as blueprints for the design of synthetic equivalents. This book is intended to demonstrate the seminal importance of supramolecular chemistry and self-organization in the design and synthesis of novel organic materials, inorganic materials and biomaterials. With contributions from leading workers in the field, the book shows how the bottom-up approach of supramolecular chemistry can be used to synthesize not only new materials, but function specific molecular devices as well. This book will be of interest to researchers and graduate students in chemistry, materials science and physics who need a summary of the most recent developments in the field.
• Brings out the role and importance of supramolecular design in materials design and synthesis • Contributions from experts in the field • Highly illustrated with over 200 figures
Contents
1. Assembly and mineralization processes in biomineralization Lia Addadi, Elia Beniash and Steve Weiner; 2. Mesoscale materials synthesis and beyond Ivana Soten and Geoffrey A. Ozin; 3. Towards the rational design of zeolite frameworks Paul Wagner and Mark E. Davis; 4. Mesoscale self-assembly Ned Bowden, Joe Tien, Wilhelm T. S. Huck and George M. Whitesides; 5. Design of amphiphiles for the modulation of catalytic membranous and gelation properties Santanu Bhattacharya; 6. Nanofabrication by the surface sol-gel process and molecular imprinting Izumi Kunitake, Sueng-Woo Lee and Toyoki Ichinose; 7. The hierarchy of open-framework structures in metal phosphates and oxalates Srinivasan Natarajan and C. N. R. Rao; 8. Mesoscale self-assembly of metal nanocrystals into ordered arrays and giant clusters G. U. Kulkarni, P. John Thomas and C. N. R. Rao; 9. Layered double hydroxides as templates for the formations of organic-inorganic supramolecular structures Steven P. Newman and William Jones; 10. Molecular machines Francisco M. Raymo and J. Fraser Stoddart; 11. Some aspects of supramolecular design of organic materials Uday Maitra and R. Balasubramanian; 12. Controlling crystal architecture in molecular solids Andrew D. Bond and William Jones.
Reviews
From the hardback review: ‘Supramolecular Organization and Materials Design edited by William Jones and Chintamani Rao demonstrates the importance of supramolecular chemistry and self-organization in the design and synthesis of novel organic, inorganic, and biomaterials. The bottom-up approach of supramolecular context of the synthesis of new materials and function-specific molecular devices … this book will be of interest to researchers and graduate students of chemistry, materials science, and physics who require a summary of the most recent developments in this field.’ Materials Today
From the hardback review: ‘… an excellent overview of the newer facets of materials chemistry, together with challenges for further research … With more than 1100 references, this book should be compulsory reading for any senior university undergraduate on a materials chemistry course and will be an inspiration for any graduate student beginning research in this area.’ Mike Hursthouse, New Scientist
From the hardback review: ‘… this is an excellent book … and contains a wealth of good illustrations … recommended for everyone whose work is concerned with the latest developments in the science of materials.’ Matthias Epple, Angewandte Chemie
From the hardback review: ‘… this book should be compulsory reading for any senior university undergraduate on a materials chemistry course and will be an inspiration for any graduate student beginning research in this area.’ New Scientist
Contributors
Lia Addadi, Elia Beniash, Steve Weiner, Ivana Soten, Geoffrey A. Ozin, Paul Wagner, Mark E. Davis, Ned Bowden, Joe Tien, Wilhelm T. S. Huck, George M. Whitesides, Santanu Bhattacharya, Izumi Ichinose, Sueng-Woo Lee, Toyoki Kunitake, Srinivasan Natarajan, C. N. R. Rao, G. U. Kulkarni, P. John Thomas, Steven P. Newman, William Jones, Francisco M. Raymo, J. Fraser Stoddart, Uday Maitra, R. Balasubramanian, Andrew D. Bond
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