Masashi Horikiri

Third-order nonlinear optical properties of didodecyldimethylammonium–Au(dmit)2

The third-order optical nonlinearity of metal(dmit)2 was investigated with femtosecond optical Kerr effect at 830 nm wavelength. The nonresonant second-order hyperpolarizability for the didodecyldimethylammonium–Au(dmit)2 (2C12–Au) molecule was estimated to be as large as 2.2×10−32 esu.

Investigation on ultrafast third-order optical nonlinearity of metal(dmit)2/(mnt)2 charge transfer complexes

We have investigated the transient third-order optical nonlinearity of the solutions of Metal(dmit)2/(mnt)2 salts in acetone by employing femtosecond optical Kerr gate measurement at 830 nm wavelength. An order of enhancement on the second-order hyperpolarizability is found for the above salts with central atoms of Cu and Ni. We have suggested an explanation for the enhancement based on the extension of electronic conjugation by the centring Cu or Ni atom.

Crystal Structure of Dioctadecyldimethylammonium-Au(dmit)2 Salt

The crystal of the dioctadecyldimethylammonium-Au(dmit)2 (2C18-Au(dmit)2) salt has been found to be composed of alternate sheets of Au(dmit)2 anions and dioctadecyldimethylammonium cations with a pronounced interdigitation of the alkyl chains. The planar Au(dmit)2 anions are dimerized by face-to-face stacking and further forming extended columns along the a-axis with short side-by-side contacts by sulfur atoms.

Superconductivity in Au(dmit)2 Langmuir-Blodgett films

The resistivity of the LB film of ditetradecyldimethylammonium-Au(dmit) 2 (2C 14 -Au(dmit) 2 ) was measured in the temperature range 2-300 K. A resistivity drop or an appreciable change of the temperature derivative is seen at 3.9 K, suggesting the existence of superconducting phase below that temperature.

Possible superconductivity in Au(dmit)2 Langmuir-Blodgett films

The resistance of the Langmuir-Blodgett films of ditetradecyldimethylammonium-Au(dmit) 2 has been measured under hydrostatic pressure up to 0.7 GPa. The room-temperature resistance decreases with increasing pressure and reaches a 0.6-times smaller value compared to that at ambient pressure. The film under the pressure shows a clear resistance decrease below 1.4 K on cooling, while that under ambient pressure shows a blunt decrease below 0.85 K and it turns to increase below 0.65 K. These results suggest the existence of the pressure-induced superconducting phase together with the earlier results of the ac magnetic susceptibility measurement.

Time-domain control of conductive LB films based on alkylammonium-metal(dmit)2

Abstract The conductive Langmuir–Blodgett (LB) films based on dioctadecyldimethylammonium-Au(dmit) 2 salt were studied. ‘Waiting time ( T w )’, which is defined as the time between the application of the salts on the water surface and the onset of the compression, was introduced as a film-forming parameter. The film quality at the air/water interface was greatly improved by changing T w . Furthermore, the atomic force microscope (AFM) images of the LB film indicated that the film forms quasi-three-dimensional (Q-3D) structure in case T w =5 min but the structure tends to be two-dimensional (2D) with increasing T w . The resultant conductivity of the LB film also depends on the T w and the highest conductivity was obtained in case T w =90 min. The IR absorption spectra suggest that the driving force of the morphological improvement is the oxidation of the Au(dmit) 2 moiety proceeding at the air/water interface before the onset of compression.

Structural Control of Alkylammonium-Au(dmit)2 LB Films

Abstract The structure of conductive LB films based on dioctadecyldimethylammonium-Au(dmit)2 (2C18-Au(dmit)2) is studied by introducing into a parameter, “waiting time”, which is defined as the time between the application of spreading solvent and the onset of compression. The π-A isotherms and the Brewster angle microscopy suggest that 2C18-Au(dmit)2 complex forms multi-layered films on the water surface, whereas, the in-plane conductivity of the LB films after anodic oxidation increases with increasing the “waiting time”.