US-Japan young scientists symposium on nano-mechanics related systems

A joint US-Japan nanotechnology meeting was held on 8 October 2008 at the National Institute for Materials Science (NIMS). This one-day meeting is a part of one-week visit of US team to several Japanese institutions, including University of Tokyo (6 October), AIST (Tsukuba, 7 October), NIMS (8 October), Kyoto University (10 October) and Osaka University (11 October). The visit is sponsored by Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the US National Science Foundation (NSF). The visit is a part of a US-Japan exchange program. As a part of this program, between 2 and 16 March 2008 a Japanese team led by Prof. Yasuhiro Horiike (NIMS) has visited 7 US universities. During the visit, a one-day meeting has been held at Northwestern University, which included 16 talks given in four sessions: Nanoscale devices, Hybrid Nanomaterials, Nano-biomedical materials and devices and Nano tools.

Conference overview

The meeting was started by the opening greetings from Yutaka Shimooka (deputy director of the office for nanotechnology and materials research of MEXT) and Kazuko Shinohara (scientific affairs assistant at the Tokyo office of NSF). Then the leaders of the Japanese and US teams, Prof. Yasuhiro Horiike (NIMS Fellow) and Prof. Teri Odom (Northwestern University) have introduced the team members.

The introduction was followed by eleven 20-minute talks split up into three sessions. Remarkably, despite the young age of the participants (most of them have defended their PhD between 2000 and 2007), most of them already hold posts of professor or associated professor leading a personal research group. Most talks have summarized the results obtained by the group within the last few years. Every session was followed by a round-table discussion. In addition, much communication occurred during the breaks, lunch and dinner. All talks were devoted to nanoscience and a bigger half (6 out of 11) focused on biological applications. The biology- related talks reported few technical achievements and rather borrowed previously developed nanotechniques. However, their concentration on vital applications, such as cure of major deceases (AIDS, cancer, obesity, etc.) was remarkable. The presentation level was rather high and corresponded to a major international conference. Seven talks were given by US and four by Japanese scientists. Japanese speakers reported important technical advances but could benefit from presentation experience.

The talks were summarized by Yasuhiro Horiike. He stressed the importance of the conducted joint meetings and asked the organizers to continue this exchange program. He mentioned that the meetings are especially useful for the Japanese teams, which is less experienced than US participants and can learn much from them.

Summary of the talks

First session - novel imaging techniques. Chair Prof. Teri Odom

The first talk by Prof. Lincoln Lauhon (Northwestern University), a last-minute substitution in the program, introduced two imaging techniques: local electrode atomic probe tomography (LEAP) and scanning photo-current microscopy (SPCM). Both techniques are well known and are considered mediocre. However, Prof. Lauhon demonstrated that when combined with clever research strategy, any technique can bring important information. In particular, LEAP images of semiconducting nanowires resulted in three-dimensional single-atomic resolution. However, because of the destructive nature of the technique, those images brought relatively little information. Meanwhile, SPCM images of the nanowires had resolution of only ~0.5 micron, but when acquired before and after etching of the wires, they demonstrated that the nanometer-thin surface layers of the studied nanowires were highly doped by impurities, and that doping had a gradient from the base to the tip of the wire.

The following presentation by Dr. Kazushi Sumitani (Saga Light Source, Japan) introduced novel advanced X-ray imaging techniques employing a synchrotron as an X-ray source. In particular, X-ray holography reached spatial resolution of 0.1 A and allowed 3D imaging of individual germanium atoms on silicon.

The third talk by Prof. Vinothan Manoharan (Harvard University) again showed that good old imaging techniques, with a clever use, can outperform novel and fancy microscopies. His group exploits a standard laser diffraction scheme where interference between the incident and diffracted laser beams allows 3D shape reconstruction of the scattering object. It is generally believed that the spatial resolution of this technique is limited by the laser wavelength to several hundreds nanometers. However, Prof. Manoharan demonstrated that if the diffraction pattern is imaged with an ultrafast CCD (~500 fs) and analyzed with a powerful computer then 10-nm resolution can easily be achieved. This resolution corresponds not to absolute positions of the studied particles, but to the relative changes in their positions. Those changes transform into fluctuations of the laser diffraction, which allow time-resolved study of such important biological phenomena as migration and Brownian motion of particles inside living cells. This technique has the following advantages:

• The corresponding setup consists of only a laser, CCD camera and a computer. Thus it can be cheap, simple and small; it can be home made and embedded into virtually any experiment.
• Optional utilization of pulsed laser allows to improve signal to noise ratio, reduce radiation damage and study delicate biological objects.
• Measurements are fast - 1000 times faster than conventional confocal microscopy, which is routinely used for 3D imaging in biology.

A disadvantage of the technique is extensive computing demands - even a modern computer needs ~100 s to process a single image frame.

Second session - hybrid nanomaterials. Chair Prof. Linda Peteanu

The session was opened by Prof. Yasuo Azuma (Osaka University) - a young scientist who has just defended his PhD in 2007 at Tokyo Institute of Technology. His research is devoted to low-temperature single-electron tunneling (Coulomb blockade regime) from a studied material into a tip of a scanning tunneling microscope (STM). He successfully solved one of the notorious experimental problems associated with this phenomenon - low signal-to-noise ratio due to weak single-electron tunneling currents. He has prepared his samples on top of quartz oscillators having certain eigen frequencies thereby increasing the tunneling current. In addition, a novel phenomenon - frequency dependent electron tunneling - has been characterized.

The second talk by Prof. Andrew Lyon (Georgia Institute of Technology) went into a completely different area - design of peptide-modified hydrogels aiming at selective delivery of drugs into certain cells inside a human body. Andrew is a former chemist, but he has shifted toward biology after recognizing the importance of the associated research for curing ovarian cancer - a lesser known among cancers, but nevertheless the second most common gynecologic malignancy after the breast cancer. The ovarian cancer is notoriously difficult to cure because it often avoids detection and, as a result, its cells are rather resistant to common drugs. That is why the selective drug delivery is especially important for this decease.

The third talk was given by Kotone Akiyama (Tohoku University), again, a young researcher who has defended her PhD in 2007. Her talk spreaded over three different topics: (i) manufacturing STM tips, (ii) synchrotron-radiation STM and (iii) AFM lithography. In the first part, a procedure has been described to produce high-quality tungsten STM tips: tungsten wire is glued on a commercial Si cantilever. It is then cut and milled using focused ion beam setup resulting in superior STM tips (apex ~22 deg, curvature ~3 nm, STM energy resolution <3 meV at room temperature). Part (ii) briefly covered photoconductivity measurements using STM tip as a contact and synchrotron radiation as a light source, whereas part (iii) was focused on depositing metal nano-dots using an atomic force microscope (AFM).

The last talk by Prof. Heather Maynard (University of California) demonstrated a successful direct application of physics into biology: using standard electron lithography setup, she makes matrixes of active sites with a pre-designed pattern. Then single protein molecules are attached to those sites resulting in a functional array of aligned proteins, which can be applied to various biological tasks.

Third session - Nano-biomedical materials and devices. Chair Chikara Dohno

The first speaker, Prof. Jongyoon ("Jay") Han (Massachusetts Institute of Technology) again demonstrated how biological applications can benefit from nanotechnology. He has developed an efficient routine to make nanochannels of certain diameter and applied them as filters for transporting biological molecules and fluids. Important detail of his approach was electric field, which was applied across the nanochannels thus allowing flow control by electrical double layers.

The talk by Prof. Christina Smolke (California Institute of Technology) was devoted to design of "biological computers". In particular, she demonstrated that logical operations (AND, OR, etc.) on biomolecules can be performed by selecting appropriate RNA fragments. Biological "computers" are much slower than conventional semiconductor processors, however, they can operate directly with bio-objects, inside living cells.

Prof. Koji Sugano (Kyoto University) has developed an efficient lithography-based procedure of manufacturing large arrays of gold nanodots with certain diameter (in the range of several tens nanometers) and relative distances. Individual nanodots can then be utilized as plasmonic devices, where, e.g., single biomolecules are detected through surface plasmon resonances.

The last speaker, Prof. Christopher Love (Massachusetts Institute of Technology), concentrated on vital immunology problems associated with AIDS and diabetes. Here again, standard physical tools, such as microfluidic systems and fluorescent imaging helped studying the time evolution of various processes in living cells.

(text and photos by Kostya Iakoubovskii)