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Meeting Days Four and Five: Thursday, July 4 and Friday, July 5

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While some scientific conferences begin tapering off in activity on Thursday and fading away silently on Friday, ICMAT 2013 continued at high speed all the way through Friday morning, with two final Plenary Lectures and the Poster Award session closing out the meeting. Couple this with Thursday’s pair of Plenary Lectures and one Theme Lecture, along with full schedules in most of the symposia, and the attendees were kept very busy in the final days of the conference. Thursday night’s Conference Banquet at the grand Resorts World Sentosa complex, featuring fine food, speeches, toasts, and an entertaining native folk dance performed by a local dance troupe, was just the icing on the cake.

Congratulations and thanks are due to Professor B.V.R. Chowdari, the Organizing Chairman of this and all the previous ICMAT conferences, and President of MRS-Singapore. A more gracious host and organizer could not possibly be found. To discover this for yourself, make plans to attend ICMAT 2015, scheduled to take place from June 28th to July 3rd. Hope to see you there!



The VIPs of ICMAT 2013: B.V.R Chowdari (in front, under the "I" in
the ICMAT logo overhead), with Nobel Laureates Yuan-Tseh Lee and
Alan Heeger next to him in the middle of the group. The rest of the VIPs
are Plenary Lecturers, Theme Lecturers, Guests of Honor, and spouses.

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Professor Chowdari closes a successful ICMAT 2013 with thanks to all participants.



Sixth Plenary Lecture

The Next Life of Silicon

Gabriel Aeppli, University College London

 

The ability to etch ever finer features into silicon has driven the technology industry forward. But in the not-too-distant future, we will hit several major roadblocks. Electronics are requiring more power and giving off more heat, while the decreasing size of circuits means we are physically running out of switchable electrons to actually create the 0s and 1s of computer language. Aeppli is working to make the transition from existing technology to new types of computing, namely through quantum information processing.

 

Quantum computing involves replacing classical bits with quantum qubits. These qubits are in a superposition of both 0s and 1s, with brings about two exciting features: the information storing potential is much larger than the classical analogue, and the entanglement can be exploited to provide natural parallelization. But quantum states are fragile and can break, losing all stored information, “if you just look at them,” Aeppli quipped. By using ion and atom traps—“perhaps the most successful [method] determined by the number of Nobel prizes awarded”—robust qubits can be made.

              

Modern atomic physics has a large library of ion hosts, but, looking for a material that can be readily fabricated, Aeppli has chosen to work with silicon. Adding a donor atom, such as P or Bi, to silicon yields a spare electron with a very low binding energy of 0.07 eV (for comparison, the H electron is bound at 27 eV). The spin, as well as the orbital, can be manipulated with lifetimes in the millisecond range—long enough to be usable for computing. And the fabrication of traps is exceedingly simple. Scanning tunneling microscopy can ablate dangling hydrogen atoms from specific points on the silicon surface, and exposure to PH3 replaces an Si atom with P to create the trapped state. With ion trap computing, “silicon could represent the future as well as the past,” Aeppli concluded.



 Seventh Plenary Lecture

Films and Capsules from Polyelectrolytes and Nanoparticles for Biomedical and Materials Applications
Helmuth Mohwald, Max Planck Institute of Colloids and Interfaces, Potsdam

Mohwald and his group are fabricating core/shell multilayer capsules for controlled release of their contents at a desired rate. Such capsules could be used in the food, pharmaceuticals, coatings, cleaning, and cosmetics industries, among others. He is particularly interested in developing this technology for self-healing coatings.

The researchers chose the core/shell design because “you can manipulate the properties of the shell in a detailed way on the surface,” Mohwald said. They start with sacrificial particles of polymer or carbonate in the core, then coat these particles with a polyelectrolyte material having the desired properties of permeability and decay-rate under the prospective operating conditions. Removal of the core leaves a hollow capsule that can be filled with a therapeutic agent for biomedical purposes or perhaps with glue for self-healing coating applications.

The strength or weakness of the polyelectrolyte shell makes it susceptible to controlled permeation of the active agent from inside the capsule to the external area of interest.  The permeation can be controlled chemically by varying the pH, the salt level, and the electrochemistry of the region surrounding the capsule. Temperature, light, ultrasound, and microwaves can also be used to control the permeation.

Mohwald is particularly interested in developing an active feedback coating, in which a stimulus to the capsule induces a change in its shell structure, and this change is fed back to the capsule to perhaps induce more change, in a continuous loop. He envisions using this concept in an anti-corrosion self-healing coating. In this case, the stimulus produced by a defect created in the coating would cause a change in the structure of the capsule’s shell, releasing the anti-corrosion repairing agent inside to fix the defect. The process would stop—no more capsules would open—when feedback indicated that the repair had been made.


 Eighth Plenary Lecture

Properties of Glassy Polymers at the Nanoscale versus the Bulk State

Donald R. Paul, University of Texas at Austin

“In modern materials it’s quite common to think about size effects,” Paul started his talk. “Typically in inorganic materials, as things approach the nanoscale we experience confinement effects and quantum effects that make these materials interesting.” Such size effects are not typically present in organic polymers, but Paul has found another kind of size effect in thin films of glassy-state polymers.

 

Initially, he was interested in researching UV-induced crosslinking in thin films for permeable membranes. To be able to uniformly crosslink a film, it needed to be thin, typically on the 100 nm scale. The graduate student working on the problem became increasingly frustrated, because every film he studied gave different results. The permeability of the same films was extraordinarily scattered. But the student kept careful data and found that the permeability changed with age in a predictable fashion. He started to track the permeability versus the film’s age, finding that thinner films aged much faster than thicker ones, although effects can be seen for films up to 1 micron thick. Further experiments showed that the annealing step, done above the glass transition temperature to remove the solvent effects and thermal history of the film, accelerated the aging effect. In bulk films, the aging process is negligible over the lifetime of the membrane.

              

But permeability isn’t the only factor affected by aging; younger films were found to be more responsive to CO2 plasticization. Paul expressed caution in testing new materials for membranes, saying that the thickness and age of the film must be carefully monitored. Glassy polymer films are dependent on their history, and evaluating thin films can give very different behaviors depending on protocol. Paul cautioned that “making thin films is not for the weak hearted,” but great steps can be made in thin film membranes with careful experimentation.


 Ninth Plenary Lecture

Molecular Design of Catalytic Materials through Intelligent Hybrid Ligands
Andy Hor, National University of Singapore

Andy Hor is doing materials science research at the most basic level—the ligand level—according to his own viewpoint. His group is synthesizing multifaceted hybrid ligands from a wide variety of elements and molecules. The requirements for these ligands is that they must have hetero-donating capability; coordinative flexibility and structural diversity; and comparative and synergistic effects with donors in their proximity. A final requirement, and the most important one from Hor’s perspective, is that the ligands must be stimulus-sensitive and environmentally responsive intelligent complexes.

“In a catalytic cycle, at different stages the catalyst must do different things, so the ligand must be responsive,” Hor said.

He gave many examples of the  ligands his team is creating, including Cr(III) pyrazolyl hybrids, Na(I) cubanes, all-nitrogen hybrids, Cu4X4 cubanes, and polymers of oligomers (POLOS) from basic pyridyl carboxylate hybrids. Looking ahead, they are planning to investigate self-assembly of magnetically active chiral Co3Ln cubanes, metal transplant in ligands through self-assembly, and functional engineering of spacer molecules that could be inserted in many of these hybrid ligands to provide different catalytic properties. “Everything boils down to ligand construction,” Hor concluded.


Fourth Theme Lecture

The Science of Magnetic Skyrmions
Yoshi Tokura, University of Tokyo

Skyrmions are named in honor of their discoverer, Tony Hilton Royle Skyrme, (1922–1987), a British physicist who developed a new way to describe the state of the nucleon. In his abstract for this talk, Tokura referred to skyrmions as “nanomentric spin-swirling vortex objects, in terms of k-space and real space.” They are highly magnetic particles: one skyrmion in a volume of one nm2 has an effective magnetic field, Beff, of 4,000 Tesla—an extremely high value. Skyrmions manifest themselves in many materials, but Tokura focused on B20-type crystals, such as MnGe, FeGe, CoGe, and Fe 0.5Co 0.5Si, among others. The vortices can be observed in some crystals using a Lorentz TEM, which Tokura demonstrated by showing some videos of the formation and movement of these swirling particles. Phase mapping of skyrmions has been done using topological Hall resistivity; in MnGe, the topological Hall effect is nearly temperature independent.

Perhaps most importantly in terms of possible applications, translational motion of skyrmions can be driven by an ultra-low polarized electron current, making them candidates as information carriers in spintronics. Skyrmions cannot be intrinsically pinned—they can flow to avoid any pinning centers—which should give them a distinct advantage in potential device applications.


Poster Awards


Poster Award winners with Dr. Alan Heeger

Nobel Laureate Alan Heeger presented 33 Best Poster Awards to outstanding students whose posters stood out from a total of 765 on display at ICMAT 2013. “The poster sessions are the heart of any conference,” Heeger said, because there you can find the freshest research results of the meeting. The winners in attendance were:

Prabeer Barpanda

Xiaofei Sun

Guangyuan Zheng                   

Yong Wang

Fei Yan                       

Hiromi Tanaka

Lin Sun                                   

Teck Wee Goh

Lin Ma                                     

Chan La-o-vorakiat

Weiqiang Chen                       

Yao-Wei Huang

Yu Zhang                                

Purushothaman Varadhan

Kunal Mondal                          

Madiel Inggrid Setyawati

Liangxing Lu                           

Xiaomei Zeng

Yong Yang                               

Y. Zhou

Sara Adibi                               

Tamas Panda

Ferhan Abdul Rahim               

Man Ying Lam

James Kah                              

Zhiyong Lam

Soumik Siddhanta

 



Technical Program

Symposium E7: Multifunctional Materials II

Van der Waals Epitaxy of MoS2 Layers Using Graphene as Growth TemplatesYumeng Shi, Singapore University of Technology and Design

As a monolayer, molybdenum disulfide (MoS2) is a direct band gap material, which gives it interesting applications in optoelectronics. MoS2 consists of a central layer of hexagonal Mo sandwiched between two layers of S atoms. Multiple layers are held together by van der Waals forces, making it easy to separate the bulk material into single layers. Shi uses chemical vapor deposition to deposit MoS2, from an ammonium tetrathiomolybdate precursor, onto graphene sheets; with this method, he is able to obtain wafer-sized, single-layer sheets of MoS2. The wrinkles in graphene serve as nucleation sites to produce MoS2 films oriented directly over the graphene pattern, as shown by bright-field STEM. Shi is working toward developing a high-performance anode from this material for use in lithium ion batteries.

 

  

 

Symposium J9.2: Flexible Electronics

 

Nanomaterials for Printed Electronics

Shlomo Magdassi, Hebrew University of Jerusalem

 

Magdassi’s research is focused on functional printing of conductive materials. He has synthesized highly concentrated dispersions of silver nanoparticles by passivating the particles with an organic ligand, with the side effect of making the ink non-conductive. The organics can be removed by heating to 300°C, but this is only good for heat-resistive substrates. To get conductivity without heating, Magdassi took advantage of the “coffee ring effect” to form a condensed layer of nanoparticles where the outer ring is conducting due to particles coalescing in close contact. Printing micron-sized rings in an overlapping "Olympic-ring-type" pattern formed a transparent electrode able to be used in place of ITO. To demonstrate the functionality of his electrode, he removed the touchscreen of an iPhone and replaced it with a touchscreen made of the printed silver coffee rings. He proved his screen worked with a video of someone playing on the phone.

              

Magdassi is working on moving past metal inks into the world of carbon nanotubes (CNTs), the advantage being that the CNTs will form a flexible electrode. Ever the entrepreneur, he is also developing methods for 3D-printing of conductive inks by forming an emulsion of nanoparticles and water-soluble monomers that are able to undergo UV-initiated polymerization. The 3D structure would be built up by printing each layer while irradiating the ink to form conducting 3D objects.

 

 



 

Symposium P8: Novel Materials

 

Novel Biosensing Applications of Graphene

Shyam Mohapatra, University of South Florida

 

Add another possibility to the list of exceptional applications of graphene. Mohapatra is utilizing graphene for biosensors, motivated by its lack of cytotoxicity and inertness in physiological conditions. Graphene also has the advantage of low thermal and electrical noise, which provides the high sensitivity needed for biosensing. Different enzymes, dependent on the sensing application, are immobilized on graphene, and changes in the cyclic voltammogram are monitored to detect the presence of an analyte. With this method, he was able to sense glucose oxidase with a level of detection of 3 µM. Now, Mohapatra is developing “point-of-care diagnostics” to sense DNA mutations to provide personalized therapy. He was able to show that his graphene sensing methods could, in fact, distinguish mutated DNA from normal DNA. In the future, he plans to develop detection methods for microorganisms that could “revolutionize the infectious disease field in a big way,” he said.

 

  

 

 

Symposium V8: Techniques to Fabricate Special Structures for Plasmonics and Metamaterials

Resonant Mode Switchable Metamaterial Through MEMS Fabrication
Wu Zhang, Nanyang Technological University

Zhang and his colleagues are experimenting with MEMS to change the shape of the unit cells of metamaterials and thus tune the metamaterial’s resonance. The metamaterial they fabricated consists of two-layers of metal resonators, with the two metals having different coefficients of thermal expansion. Split ring resonators (SRRs) are fixed onto a silicon oxide substrate, while slabs of the metamaterial are suspended on the substrate. A comb drive MEMS actuator deforms the metamaterial’s unit cell structure, causing the resonant mode to switch at 2.6 THz. An analytical model of this phenomenon postulates that the SRRs, the slabs, and the substrate are coupled, behaving like three resonant oscillators. It is this coupling of oscillators that affects the metamaterial’s resonant mode.



Symposium W8: Synthesis, Processing, and Characterization II

Graphitic Carbon Synthesis and Molecular Assembly for Functional Nanocomposites
Sang Ouk Kim, KAIST, Republic of Korea

Carbon in its many forms displays a wide range of properties. Fullerenes are n-type semiconductors; carbon nanotubes can be conductors or semiconductors; and graphene is a zero-gap semi-metal. Kim demonstrated that doping carbon materials with B or N atoms can permit the tuning of work functions, charge densities, and electrical conductivities, rendering them useful for carbon-based electronics applications. Unfortunately, these materials tend to aggregate and are hard to separate.

Graphene oxide also displays useful properties. Importantly, it can be dispersed in solution by dialysis in concentrations as high as 5 wt%. This technique produced the first reported graphene oxide liquid crystal. This material can be spin-coated to form wrinkle-free graphene oxide films, which could be used as flexible layers in polymeric composites. These graphene oxide films can be tuned for desired electrical properties as discussed above, and can be easily transferred to substrates of any form, including complex structures.

Kim also demonstrated that his group can control the number of walls of a carbon nanotube (CNT), called “wall-number CNT growth,” through directed growth on a monodisperse nanocatalyst array. The number of walls is controlled by the duration of the metal ion loading time. Finally, B- and N-doped CNTs are useful for tuning organic solar cells through CNT-assisted carrier transport enhancement. Undoped CNTs fail in this application because electrons and holes tend to recombine instead of being transported for energy generation. But controlling the work function of the CNTs through careful doping with B or N atoms permits selective transfer of either electrons or holes in the system, thus avoiding undesirable recombination.

  

 

Symposium DD10: Nanostructures for Biosensing and Detection

 

Design of Conjugated Polymers for Biosensing and Biofunction Regulation

Shu Wang, Chinese Academy of Sciences

 

Conjugated polymers are most famous for their use in organic electronics, but Wang is finding that these unique materials are also useful in biomedical applications. He uses water soluble conjugated polymers, typically polyelectrolytes, to diagnose cancer, image cells, and kill bacteria.

 

Methylated DNA is a marker for various forms of cancer (prostate, colon, bladder, etc.). A polyfluorene derivative, with ammonium bromide pendant chains for water-solubility, can complex with DNA. The conjugated polymer undergoes fluorescence resonance energy transfer with the DNA to allow for detection by UV-Vis spectroscopy. Methylated DNA can be distinguished from regular DNA by a peak, only present in the methylated version, at 530 nm. With their system, colon cancer could be detected with 87% sensitivity.

 

Wang also found that using a poly(p-phenylene vinylene) derivative, he could kill more than 70% of Gram-negative bacteria, E. coli. By exciting the polymer with UV light, charge transfer from the polymer to molecular oxygen forms singlet oxygen, which then ruptures the bacteria membrane, effectively killing the microorganism.

 


Scanning the Meeting

 


  

  



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The Meeting Scene e-newsletter of the Materials Research Society (MRS) presents news from MRS and other conferences directly from the conference venue.

This work was partially supported by the IMI Program of the National Science Foundation under Award No. DMR 08-43934. Specifically, the work of Apprentice Science Reporter Jenna Bilbrey was funded under this NSF award, which is managed by the International Center for Materials Research (ICMR), University of California, Santa Barbara, USA. MRS thanks the NSF and the ICMR for their continued support, without which the Meeting Scene would not be possible.

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