Day 1 - Monday, October 29, 2008

Day 1
Monday, October 29, 2007

The XVI International Materials Research Congress was held in Cancún, México, from October 29 - November 1, 2007. The conference was rescheduled from August because of the threat from Hurricane Dean. The Congress was conducted by the Academia Mexicana de Ciencia de Materiales (MRS-Mexico) in conjunction with the VI Congress of NACE International - Mexico section. This Meeting Scene e-mail and subsequent ones provide a review of the meeting.

There’s plenty of room at the top (of the microchip).
- Plenary speaker Jurrian Schmitz (University of Twente, Netherlands)

  
  Meeting Organizers (l-r): Romeo de Coss, Jose Luis Mora, Juan Mendez
   Nonell, Pedro Hugo Hernandez Tejeda, Jorge Lopes Cuevas

PLENARY LECTURES

Trends in Energy Production
Dr. Alex Freundlich, of the Electrical and Computer Engineering Department, University of Houston, USA, discussed the overall trends in energy production using conventional and unconventional production of energy around the world. This presentation also reviewed trends in global warming as well as the limited availability of coal and other conventional sources of fuels. It was pointed out that nearly 55% of solar cells produced in the world in 2006 were shipped to Germany. The rest of Europe received 11%, USA 8%, and Japan 17% of the total solar cells produced. This presentation also pointed out that current commercially available solar cells are made mainly from crystalline silicon and exhibit efficiencies of ~ 10-20%. The industry is looking for stability for photovoltaic devices to be greater than 25 years and a payback time of less than three years. The polymeric materials being investigated for photovoltaics are promising, however, they do not yet have the long term stability that is needed. It was pointed out that the current trends are toward developing multi-junction solar cells, developing nano-emitters, intermediate band solar cells, and impact ionization cells. He concluded the presentation by indicating that the growth in photovoltaics will continue to be very strong and to meet this demand it would be necessary to develop high efficiency solar cell systems, using stable, naturally abundant and non toxic materials, and low upfront costs and fast payback times.

More Than Moore Creates Opportunities For Materials Science
In an engaging and informative Plenary Speech, Jurrian Schmitz of the University of Twente, Netherlands, gave the audience a unique perspective on Moore’s law. Sure, he agreed, the doubling of the number of transistors on an integrated circuit every two years is great for industrial companies, who make a lot of money from such growth. However, these companies have perfected their technology so much that there is “no freedom for excited researchers to try new ideas,” according to Schmitz. Academic researchers with novel process ideas are allowed nowhere near operating semiconductor fabrication lines (fabs) that have already achieved nanometer precision and sub-ppm materials purity.

Thankfully for academic researchers, there’s “more beyond Moore,” Schmitz said. When transistors reach the 10 nm size level, they will approach quantum limits that will make them ineffective as memory devices. At this point, it will make sense to stop decreasing the size of transistors and start adding functionality to CMOS devices that are already small enough. Instead of being used merely for computing and data storage, integrated circuits could extend their range of functions to include high quality passive devices, wireless communications, optical communications, and sensing and actuating capabilities. “The technological challenge is how to combine electronics with sensors, actuators, and optical components,” Schmitz said. This is where the academic researchers get to step in.

His research group at the University of Twente is concentrating on a technology called “wafer post-processing.” This involves purchasing CMOS wafers right from the fab, adding functionality through a “post-processing step,” dicing the wafer into separate functional components, and then packaging the products. A key consideration in this process is to leave the CMOS intact while adding the functional units. This requires careful treatment involving temperatures less than 400°C, mild (or no) plasmas, maintenance of the hydrogen balance to avoid hydrogen outgassing, and placing little mechanical stress on the wafer. To accomplish this, Schmitz and coworkers have developed a process by which they cool the CMOS substrate while heating the surface using laser annealing. This enables them to build second layers of CMOS devices on top of a first layer. Possible applications involve adding light projectors, CMOS imagers, or radiation imaging detectors on top of CMOS substrates. They have already built a detector that images cosmic radiation better than any device currently available. To paraphrase Richard Feynman, “There’s plenty of room at the top (of the microchip),” Schmitz concluded.

    
    Festivities at the inaugural function.

TECHNICAL SESSIONS

Symposium 1: Nanostructured Materials and Nanotechnology
Ultrathin Helical Nanowires: Structure, Stability, And Nanomechanical Response
Cristian V. Ciobanu of the Colorado School of Mines, USA, discussed the development of novel nanowire structures. He pointed out that tip-suspended nanowires are metastable. The free energy of formation per unit length (f) in the novel helical nanowires is proportional to their radius (R). Research groups in Japan have reported experimental synthesis of helical nanowires and his presentation focused on the challenges in theoretically predicting the metastable structures associated with these.

Two-Dimensional Molecular Networks: A Possible Approach To Molecular Electronics
Dmitrii F. Perepichka of the Department of Chemistry, McGill University, Canada, made a presentation exploring the possibilities of developing microelectronic devices using the bottom-up approach i.e. using polymeric molecules to create devices such as transistors, diodes etc. One of the main techniques discussed was the formation of Langmuir Blodgett (LB) films. Polymers that form rectifying devices were deposited on gold and the other electrode used was mercury. Similarly, carbon nanotubes, appropriately processed and functionalized, were also surface assembled to form rectifier-like devices. A few of the challenges included the yields of such devices and the difficulties in making connections between molecules. One of the conclusions was that even though challenges remain, good progress has been made in devices based on molecular electronics.

  
  Attendees enjoy food and drinks at the Inaugural Toast
   in Tulum Hall, where poster sessions were held.

Characterization Of Epoxy/MWCNT Nanocomposites
A. Hernández-Pérez, of the Centro de Investigación Científica de Yucatán, Mérida, México, presented the use of carbon nanotubes for epoxy composites. Two types of nanotubes (CSD and CMW) that represented nanotubes with aspect ratios of 50 and 857, respectively, were used. The mechanical properties such as tensile strength, elastic modulus, fracture strength, and impact strength of the composites were comparable. However, the conductivity of composites made using CMW tubes was much higher than that for composites made using CSD tubes and epoxy not containing any carbon nanotubes. It was suggested that this enhancement in the conductivity of composites made using CMW nanotubes was due to the alignment of carbon nanotubes.

   
   Putting up posters.

Symposium 3: Theory and Computer Simulation of Materials
Where are Nature's Missing Structures?
Gus Hart of Brigham Young University, USA, gave the audience a preview of a paper soon to appear in the journal Nature Materials, although to hear him talk it might just as well have been accepted by a philosophy or geometry journal. Hart treats alloys as a configurational problem, essentially using geometry to figure out all the different ways he can decorate a lattice with atoms. He avoids chemical complications by using representational red and blue spheres as his atoms. “How many different ways can I arrange two different atoms on an FCC lattice?” he asked himself at the start of this investigation. The answer was only two ways. For three-atom unit cells there are three ways to arrange them. Up to this point all these structures could be found in nature in real crystals. But when he went to four-atom unit cells, things got trickier. There are 12 ways of arranging four atom unit cells on an FCC lattice, but seven of them don’t exist in nature. Data mining has predicted that two of these should exist, but that still leaves five structures missing from nature’s portfolio. These five are A3B1 (110), A3B1 (113), A2B2 (113), A3B1 (111), and A2B2 (111), where A might represent red spheres and B blue spheres. Why are there missing structures? Hart asked himself. Are they somehow defective?

He began exploring the problem by looking at the average bond type, Bavg, for four-atom unit cells on FCC lattices. A red-blue bond was assigned a value of -1, while red-red or blue-blue bonds were assigned bond values of +1. If there are 50% red and 50% blue spheres, the average bond type is zero. Bavg is non-zero for any configuration where the red-blue split is not 50/50. When he looked a the likelihood of any of the 12 four-atom unit cells existing in nature, the non-random structures (as determined by adding up average bond types for a given structure) were most likely to exist, while the random ones were least likely. The five missing structures were highly random. “Geometric simplicity rules the day,” Hart said. The same process works for BCC and perovskite lattices as well, so it’s no fluke for FCC lattices only. What it all means is beyond his—or anyone else’s—understanding right now. It’s almost in the realm of philosophy.

Symposium 7: Ferroelectricity and Piezoelectricity
Magneto-Electric Interactions In Multiferroic Nanostructures And Microwave Devices
G. Srinivasan, of the Physics Department, Oakland University, Rochester, USA, discussed the development of magneto-electric interactions in multiferroic nanostructures and microwave devices. The presentation discussed many such devices such as phase shifters. Examples of materials discussed included yttrium iron garnate (YIG) and lead zirconium titanate (PZT). The speaker pointed out that such devices were tunable using electric and magnetic fields. Important parameters include control of resonant frequency and ability to act as band pass filters. It was pointed out that for such devices temperature stability was not a major concern since tuning could be achieved using an electric field.

Studies On Nanoscale Functional Oxides: Synthesis, High-Resolution Characterization And Electrical Transport
Shriram Ramanathan, of the School of Engineering and Applied Sciences, Harvard University, USA, presented the role of oxygen related point defects in the electronic ceramics, zirconia and vanadium oxides. The focus of this research was on the effect of ultraviolet radiation exposure on incorporation of oxygen in thin films prepared by reactive oxidation of metals. It was shown by analysis using a technique which is a variation of the Rutherford backscattering technique that ultraviolet radiation enhances the incorporation of oxygen in thin films and also enhances the rate of oxidation (for a given partial pressure of oxygen). It was also shown that the insulator to metal-like phase transformation in vanadium oxide can be affected by even a few minutes of exposure to ultraviolet radiation. These effects, such as change in resistivity, are of interest because such phase transformations can be achieved at much lower temperatures.

Symposium 8: Advanced Structural Materials
Scaling Properties Of Machined Surfaces Of Glass Fiber Reinforced Surfaces
M. Hinojosa, of the Universidad Autonoma de Nuevo Leon, Mexico, is examining how machined surface features scale with the size of the glass fibers used to reinforce a polyester resin matrix. Similar studies examining the slow tearing (rupture) of paper have indicated that the scale of the rupture is close to the diameter of the cellulose microfibrils that make up the paper. Experimentally, his group used a polyester resin reinforced with 65% glass fiber. Samples were machined using a polycrystalline diamond tool oriented at 45° and 90° to the long direction of the glass fibers, after which stylus profilometry and atomic force microscopy were used to analyze the machined surfaces. The scale of fracture of the fibers was found to be 22 microns, roughly equivalent to the diameter of the fibers, regardless of machining angle. The roughness exponent as estimated from AFM studies was 0.8, in agreement with values reported in the literature for rapid fracture surfaces in a variety of materials. This implies that machining can be considered a controlled, or at least induced, rapid fracture process.

  
  Tulum Hall bedecked with posters.

Symposium 9: New Trends in Polymer Chemistry and Characterization
From Crystal Engineering To New Dendritic Architectures
In an effort to synthesize dendritic structures that are much more “tree-like” than the traditional sphere-based structures, Charles N. Moorefield and his co-workers at the University of Akron, Ohio, USA, are treating terpyridine complexes with carboxylate moieties. Three-dimensional “shape-persistent” structures have been formed that are essentially terpyridine ligand crystals—the terpyridine moieties are fixed in space relative to the center of the structure. By reacting these with copper, they can produce a “poly-metallated” dendrititic architecture with Cu atoms positioned equidistant from the central moiety. Adding sulfur functional groups permits the attachment of gold particles, and other chemistries allow CdS to be inserted precisely into the dendritic architecture. The researchers have succeeded in attaching these 3D structures to the surfaces of carbon nanotubes,which could be useful in applications such as LEDs, quantum dots, and non-linear optics. They have also used the terpyridine complexes to connect carbon nanotubes end-to-end, end-to-side, and side-to-side.

  
   One attendee made a rather flamboyant
     fashion statement (photo of artwork in
     conference meeting area).

© Materials Research Society, 2007