California NanoSystems Institute

Title:
Studies of charge-transport mechanisms in thin organic films and at interfaces using advanced photoelectron spectroscopies

Abstract:
In the rapidly developing field of organic electronics, many elementary processes involving the transport of charge carriers within the bulk of the materials and at interfaces are only partially understood. In this presentation, I review our recent studies of parameters essential for the charge transport in well-defined mono- and multilayer films of polyaromatic molecules, using (angle-resolved) ultraviolet photoelectron and resonant photoelectron spectroscopic techniques. In particular, the intramolecular charge-vibrational coupling related to the geometric relaxation accompanying a charge, the dynamic screening of individual charge carriers, the intermolecular band width related to the charge transfer integral, as well as structure- and orbital-dependent femtosecond charge transfer processes at organic/inorganic interfaces are discussed.

Taku Hasobe, JAIST
Lecturer, School of Materials Science

Title:
Construction of Supramolecular Nanoarchitectures for Light Energy Conversion

Abstract:
In recent years, increased efforts to assemble organic dye moiety into desired structures have been made because of their extended p-electron conjugation. Such organization of molecular assembly is an interesting topic because of a variety of applications such as optical and electronic devices. Construction of organized assemblies makes it possible to show the new property and phenomenon in comparison with those of monomeric forms. In particular, porphyrins and nanocarbon materials such as fullerenes and carbon
nanotubes are often organized into nanoscale superstructures which perform many of the essential lightharvesting and electronand energy-transfer functions. Based on these ideas, we have recently reported new types of supramolecular nanoassemblies such as porphyrin nanorods and nanofibers, porphyrin nanoparticles, porphyrin-carbon nanotube composites and porphyrin-fullerene composites. The details of preparation method, structural and photoelectrochemical properties will be discussed in this presentation.

Yuichi Hiratsuka, JAIST
Lecturer, School of Materials Science

Title:
Micro-mechanical devices powered by biological motors

Abstract:
Living system use many types of micro or nano-mechanical systems known as "motor proteins". These biological motors have unique features, such as nano-meter scaled molecular motors, high efficiently energy transduction from chemical energy or having a capacity for self-assembly. The realization of bio-hybrid micro-machines which integrate such motor proteins and micro- or nano-structures fabricated from inorganic materials, would offer some capabilities that are not achieved by traditional electronic, magnetic or optical devices. In this seminar, I will introduce three mechanical devices driven by biological motors: 1) a micro-transporter driven by kinesin-microtubule based motor proteins which has the potential for use in lab-on-a-chip devices, 2) micro-rotary motors driven by bacteria, 3) our current research on optical devices driven by motor proteins (mimic fish melanophore cell system). We believe that these studies demonstrate the development of micro-devices based on bottom-up assembly.

Publication list:
1) Yuichi Hiratsuka, Shoji Takeuchi, "Towards a microrotary motor driven by motor proteins", MEMS2007, pp.695-698, 2007
2) Yuichi Hiratsuka, Takashi Kamei, Noboru Yumoto, and Taro Q.P. Uyeda, "Three Approaches to Assemble Nano-Bio-Machines using Protein Molecular Motors.", Nanobiotechnology 2, pp.1551-1286, 2006 (Review)
3) Yuichi Hiratsuaka, Makoto Miyata, Tetsuya Tada and Taro Q.P. Uyeda "Micro-rotary motor powered by bacteria", Proc. Nati. Acad. Sci. USA 103, pp.13618-1363, 2006
4) Yuichi Hiratsuka, Makoto Miyata, and Taro Q.P. Uyeda, "Living microtransporter by uni-directional gliding of Mycoplasma along microtracks", Biochem. Biophys. Res. Commun. 331. pp. 318-324, 2005



Masaru Kawakami, JAIST
Lecturer, School of Materials Science

Title:
Study of the single molecule dynamics of biomolecules using atomic force microscopy

Abstract:
To carry out their biological function, most protein molecules have to fold into a unique and highly-ordered structure. Consequently much work has been carried out involving the determination of the three dimensional structures of proteins. However, the three-dimensional structure of proteins reveals only the "static" properties of proteins and it does not tell the dynamic "fluctuations" of their structures that are so important to their biological function.
Until recently, almost all measurements of protein dynamics have been obtained using ensemble measurements. These techniques yield the average properties of the system: information about individual molecules is hidden and rarely populated conformational states, which might be of functional relevance, are extremely difficult to characterize. Techniques which can explore the behavior of single molecules are, therefore, essential for developing new insights into the relationship between the dynamics and function of proteins.
Single molecule techniques such as optical/magnetic tweezers have recently been used to investigate the mechanical properties of various kinds of biomolecules, but these techniques are not capable of investigating the "internal" dynamics of molecules. Since its conception, there have been many studies of biological molecules at single molecule resolution using AFM. We have developed new AFM techniques using thermal/magnetic spontaneous/forced oscillation of an AFM cantilever which are capable of quantitatively measuring the internal conformational dynamic changes of a single molecule. Quantitative analysis of single molecule viscoelasticity provides dynamic information on the minor intra-molecular motions of protein molecules, which are regarded to be important to their biological function. Recent progress of our new technique for biomolecules (polysaccharides, poly-ethylene glycol, titin I27 domain and myosin) will be presented.

J.D. Lee, JAIST
Lecturer, School of Materials Science

Title:
Ultrafast mobility control of a polar semiconductor: finding the ultimate method for mobility control

Abstract:

Using the nonperturbative many-body time-dependent approach (1), we investigated the nonequilibrium dynamics of two coherent longitudinal optical phonon-plasmon coupled (LOPC) modes in a polar semiconductor: carrier-relevant mode and lattice-relevant mode. In this study, the basic idea for control of the carrier mobility is to manipulate the ultrafast relaxation dynamics of the coherent carrier-relevant LOPC mode. Using our simulation and modeling approaches, we propose two possible options to achieve control of carrier mobility. One option is to optimize the semiconductor by tuning the carrier doping to a given optically pumped laser, where the relaxation of the coherent carrier-relevant LOPC mode would respond in a critical fashion (2). With this approach, it is found that the carrier mobility could be enhanced by dozens of percent. The other option is to optimize the optically pumped laser. In this case, the pulse train of below-band-gap excitation would be incorporated for optical pumping, which can make possible the dephasing-free dynamics of the coherent carrier-relevant LOPC mode by keeping synchronization of the pulse train with coherent oscillation (3). This approach could lead to the ultimate method for controlling the carrier mobility of the semiconductor.

FIG.1: Dynamics and fate of LOPC modes in GaAs (with doped carriers of 2x1018 cm-3) under the below-band-gap excitation of the pulse-train of N=8 with respect to the pulse interval (in the upper right corner of each figure). The mode near 17THz is the carrier-relevant LOPC mode.

Ryo Maezono, JAIST
Lecturer, School of Information Science

Title:

Abstract:

Electronic properties of materials have been have been well studied in a number of research communities. In the computational field, there recently has been increased interest in using ab-initio simulations as one of the recent trends of materials science is to identify novel mechanisms and functionalities in more complicated interacting systems. Density functional theory (DFT) provides a firm theoretical foundation to provide the treatment of complicated many-body interactions, thus stimulating the ab-initio research field. Although a majority of computational studies emphasize the response and excitation of materials by external fields, there still remains challenging research problems concerning the ground state properties. The quantum Monte Carlo (QMC) method discussed in my talk is one of the more appropriate approaches for this purpose as the method is used to evaluate the ground state mean value of physical quantities.

My recent studies include the application of the QMC method to atomic systems, molecular systems including biomolecules, and extended periodic systems. Other topics of interest include methodologies for stable calculations and high performance computing.

Yukiko Yamada-Takamura, JAIST
Lecturer, School of Materials Science

Title:
Surface and interface studies of GaN growth on silicon

Abstract:
Gallium nitride (GaN)-based materials are attractive for applications in short-wavelength light emitting diodes, laser diodes, and high power devices. Commonly used substrates for GaN growth are single crystal sapphire and silicon carbide. Silicon is an attractive candidate for substrates because of its major role in electronics and its availability as high quality, low cost and large diameter single crystal wafers. However, it is difficult to grow high quality GaN directly on Si substrates because of the large lattice mismatch and difference in thermal expansion coefficients between the two materials. Also, the wurtzite structure of GaN has freedom in its polarity, which is largely influenced by the choice of substrates and buffer layers as well as the nucleation condition. In the case of a non-polar substrate like Si, it is especially important to control the nucleation stage to grow a mono-polar film. This presentation will report the results of our studies of GaN growth on various silicon substrates, including Si(111)[1), Si(111) with zirconium diboride (ZrB2) buffer layer, which is a conductive, reflective and lattice-matched buffer layer for GaN[2, 3), and symmetry-converted silicon-on-insulator (SOI), SOI(111) with Si(001) as a handling wafer[4). All the experiments were carried out using our ultrahigh vacuum molecular beam epitaxy-scanning probe microscopy (UHV MBE-SPM) system.