The electronic behavior of a photosynthetic reaction center monitored by conductive atomic force microscopy.

The conductivity of a photosynthetic reaction center (RC) from Rhodobacter sphaeroides was measured with conductive atomic force microscopy (CAFM) on SAM-modified Au(111) substrates. 2-mercaptoethanol (2ME), 2-mercaptoacetic acid (MAC), 2-mercaptopyridine (2MP) and 4-mercaptopyridine (4MP) were prepared as SAM materials to investigate the stability and morphology of RCs on the substrate by using near-IR absorption spectroscopy and AFM, respectively. The clear presence of the three well known RC near-IR absorption peaks indicates that the RCs were native on the SAM-modified Au(111). Dense grains with various diameters of 5-20 nm, which corresponded to mixtures of single RCs up to aggregates of 10, were observed in topographs of RCs adsorbed on all the different SAM-modified Au(111) substrates. The size of currents obtained from the RC using a bare conductive cantilever were produced in the following order for SAM molecules: 2MP > 2ME > 4MP > MAC. A clear rectification of this current was observed for the modification of the Au(111) substrate with the pi-conjugated thiol, 2MP, indicating that 2MP was effective in both promoting the specific orientation of the RCs on the electrode and electron injection into the RC. Cyclic voltammetry measurements indicate that the 2MP is better mediator for the electron transfer between a quinone and substrate. The current with 2MP-modified cantilever was twice as high as that obtained with the Au-coated one alone, indicating that 2MP has an important role in lowering the electron injection barrier between special pair side of RC and gold electrode.

Fabrication of electrochemical transistor based on pi-conjugate polymer Langmuir-Blodgett film.

We fabricated an efficient organic electrochemical transistor (OECT) composed of polymer Langmuir-Blodgett (LB) film. The pi-conjugated polymer LB film, which was constructed from a poly(N-dodecylacrylamide) (pDDA) and poly(3-hexylthiophene) (PHT) mixture, was used as a conduction channel layer to connect source and drain electrodes. The mixed-polymer LB film was characterized using UV-vis spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), and cyclic voltammetry. Subsequent UV spectra measurements, XRD measurements, and AFM measurements show that PHT forms a crystalline lamellar domain in the layered structure of pDDA. The OECT included 10 layers of the mixed-polymer LB film as the conduction channel layer. The OECT showed an on/off ratio of 1.1x10(4) and mobility of 7.5x10(-2) cm2 V(-1) s(-1) at low gate (VG=-1.2 V) and source-drain voltages (VDS=-0.5 V). Moreover, the necessary charge to operate the OECT was 1.1x10(-9) mol of e(-1) cm(-2), which was 2 orders smaller than the value reported using a similar device structure. The relatively high on/off ratio and low charge consumption suggest that this OECT, which is fabricated from pi-conjugated polymer LB films, is applicable to macroelectronic devices.

Nanoscale actuation of thermoreversible polymer brushes coupled with localized surface plasmon resonance of gold nanoparticles.

This paper describes the fabrication of hybrid nanoassemblies with polymer brushes and gold nanoparticles enabling detection of nanoscale optical changes based on localized surface plasmon resonance. The reversible and thermosensitive nanoscale actuation is achieved by combining stimuli-responsive polymer brushes and gold nanoparticles independently and selectively assembled on substrates. These hybrid nanoassemblies are assembled on numerous substrates and will be applicable for optoelectronics, nanoactuator, and nanosensor applications.

Fabrication of polymer Langmuir-Blodgett films containing regioregular poly(3-hexylthiophene) for application to field-effect transistor.

Semiconducting thin films consisting of regioregular poly(3-hexylthiophene) (RR-PHT) and poly(N-dodecylacrylamide) (pDDA) were constructed by the Langmuir-Blodgett (LB) technique. A mixture of RR-PHT and pDDA spread from a chloroform solution on a water surface forms a stable monolayer, which can be transferred onto solid substrates by the LB method, yielding a well-defined polymer LB film. Surface morphology studies of the LB film indicate that the RR-PHT is dispersed uniformly throughout the surface. The polymer thin film was chemically doped by contacting with FeCl3 acetonitrile solution, and a conductivity of 5.6 S/cm was achieved. Further, the LB film was utilized as the semiconducting film in the field-effect transistor (FET), and mobilities of 2.2 x 10(-4) and 4.4 x 10(-4) cm2 V(-1) s(-1) were obtained by analyzing the saturated and linear regions of the current-voltage characteristic, respectively.