Recent studies of electric conduction of small number molecules are reviewed. Topics of new methods to fabricate nano-gap electrodes, Coulomb blockade phenomena, KONDO effect, negative differential resistance, and temperature dependence are described.
Proteins and enzymes display many functions such as molecular recognition and catalysis. In addition, protein surface recognition via hydrogen bonding, electrostatic interactions and hydrophobic interactions mediate many biological processes including signal transduction, cell growth, and numerous metabolic pathways. In these processes, protein surface/surface interaction plays a key role. Thus, the development of useful strategies to recognize and modify a specific site of protein surface artificially is quite important not only to understand biological systems, but also to create artificial proteins. Here, we describe several new strategies for specific recognition and modification of protein surfaces.
Chemical derivatization of the terminal phosphate group of DNA, as well as the backbone linker phosphates, with sulfur-containing functional groups were developed for covalent attachment of DNA on gold surfaces via chemisorption. Results of IR measurements and quartz crystal microbalance analyses for the DNA-modified gold substrates were described and the immobilization chemistry of the present system was discussed. Next, the techniques of DNA immobilization were applied to develop a biosensor that can discriminate and respond to specific genes (gene sensor). Two examples of gene sensors both of which were coupled with electrochemical signal readouts have been successfully introduced; the first example of gene sensor was taking advantage of a redox-active psoralen compound that binds covalently with DNA and the next was achieved by the use of redox active surface adlayer having a DNA/ferrocene/Au interfacial structure. The basic feasibility of the gene sensor was also discussed.
The formation of ordered dewetted patterns of organic materials on substrates is described. The driving force for dewetting is the interfacial tension between substrate and organic solution. The observed regular order of the formed microdroplets, or “microdomes” can be explained by so-called dissipative structures, a concept developed by Ilya Prigogine. The apparent violation of the second law of thermodynamics (which should prohibit formation of ordered structures from isotropic solution) can be explained by the overall increase of the entropy by the evaporating solvent. The role of the substrate in the formation of ordered dewetted microstructures will be discussed briefly. In the second part of this paper examples for the application of dewetted microstructures in the field of photonics will be given. Special emphasis will be made not only for polymeric but also for low molar mass compounds.
Physical properties of metal nanoparticle superlattices are dependent on the particle size, interparticle spacing, superlattice periodicity and symmetry, among which the control of superlattice symmetry is most difficult to achieve. Various symmetric superlattices of ligand-protected metal nanoparticles, including 2-fold chain, 3-fold quasi-honeycomb, 4-fold square, 6-fold hexagonal and network structures, can be fabricated through interligand interactions and by template methods. The electronic and magnetic properties of 6-fold hexagonal superlattices of metal nanoparticles for the future nanodevice applications are also presented.
Superheterointerfaces have been developed as a new class of engineered interface offering another degree of freedom in the design of semiconductor-based quantum structure. Forced epitaxial mating of non-allied semiconductors provides the superheterointerface that allows self-assembly of quantum dots driven by interface instability. An attempt is made to explore the important functions afforded by these unique quantum dots. Enhancement of the otherwise meager light-emitting capability of Si is demonstrated using column III-V/Si superheterointerfaces.
Simultaneous measuring system of tunneling current and displacement current has been developed for direct detecting the single electron motion in nanomechanical single electron devices. Tunneling current and displacement current staircases have been observed simultaneously in current-voltage characteristics of the double barrier tunneling junctions (DBTJs) that consist of scanning vibrating probe/vacuum/colloidal Au nanoparticles/Au(111) substrate. Single electron motion on and through the colloidal Au nanoparticles has been analyzed by both the displacement current and tunneling current staircases. The negative differential conductance has also been observed in the current-voltage dependence of the same DBTJs. For realizing the nanomechanical single electron device with self-excitation, the utilization of alkanethiol molecules as the tunneling barrier has been discussed.
We discuss recent studies of nano-size mechanics from the stand points of nano-fabrication and nano-machine. First, a nano-mechanical simulator developed by us is explained. Theoretical simulations of noncontact atomic force microscopy images by taking thermal fluctuation into consideration are in very good agreement with experimental results. Next, a new nano-size super-lubricated system that is not subject to friction, “C60 molecular bearing,” is described. This sandwiched structure which confines a C60 monolayer between graphite plates, exhibits superlubrication with zero dynamical frictional forces. Observed results and a theoretical concept of, “step rotation model” to interpret the mechanism of super lubrication, are explained by using a picture of “single molecular bearing.” This research is the first proposal as an artificial nano-machine using fullerene, which can be called the smallest bearing in the world.