Measurement of the nonlinear conducting states of α-(BEDT-TTF)2I3 using electronic Raman scattering.

Nonlinear conducting states in a strongly correlated organic electronic system α-(BEDT-TTF)2I3 [BEDT-TTF=bis(ethylenedithio)-tetrathiafulvalene] are studied by Raman spectroscopy. Wide-range Raman spectra of nonlinear conducing states provide direct information about conducting properties through the electronic Raman process. A comparison between the behaviors of the electronic modes of BEDT-TTF layers and the vibrational mode of I3 molecules reveals the formation of nonequilibrium states in which only the electronic parts show the change of states.

Near-Infrared photoluminescence in the femtosecond time region in monolayer graphene on SiO₂.

We investigate the dynamical properties of photoexcited carriers in a single monolayer of graphene at room temperature in air using femtosecond time-resolved luminescence spectroscopy. The luminescence kinetics are observed in the near-infrared region of 0.7-1.

Ultrafast energy transfer of one-dimensional excitons between carbon nanotubes: a femtosecond time-resolved luminescence study.

Excitation energy transfer has long been an intriguing subject in the fields of photoscience and materials science. Along with the recent progress of photovoltaics, photocatalysis, and photosensors using nanoscale materials, excitation energy transfer between a donor and an acceptor at a short distance (≤1-10 nm) is of growing importance in both fundamental research and technological applications. This Perspective highlights our recent studies on exciton energy transfer between carbon nanotubes with interwall (surface-to-surface) distances of less than ∼1 nm, which are equivalent to or shorter than the size of one-dimensional excitons in carbon nanotubes.

Ultrafast exciton energy transfer between nanoscale coaxial cylinders: intertube transfer and luminescence quenching in double-walled carbon nanotubes.

We study exciton energy transfer in double-walled carbon nanotubes using femtosecond time-resolved luminescence measurements. From direct correspondence between decay of the innertube luminescence and the rise behavior in outertube luminescence, it is found that the time constant of exciton energy transfer from the inner to the outer semiconducting tubes is ∼150 fs. This ultrafast transfer indicates that the relative intensity of steady-state luminescence from the innertubes is ∼700 times weaker than that from single-walled carbon nanotubes.

Ga and As composition profiles in InP/GaInAs/InP heterostructures--x-ray CTR scattering and cross-sectional STM measurements.

Changes of composition profiles in GaInAs layers sandwiched by InP, due to the layer thicknesses, were measured by the x-ray CTR scattering and cross-sectional STM techniques. Both techniques showed quite similar results, which indicates that the x-ray CTR scattering measurements and analyses give us correct composition profiles both for group-III and group-V atoms in the buried heterostructures non-destructively. Limits of the CTR analysis are discussed, especially on the spatial resolution and composition grading below the bottom interface.

pi-Conjugated multidonor/acceptor arrays of fullerene-cobaltadithiolene-tetrathiafulvalene: from synthesis and structure to electronic interactions.

The synthesis, structure, photoelectrochemical behavior, and nonlinear optical (NLO) properties of a symmetric acceptor-acceptor-donor-acceptor-acceptor array, C(60)-Co-TTF-Co-C(60), have been described. The precursors, namely, cobalt dicarbonyl complexes Co(C(60)Ar(5))(CO)(2) were synthesized from the penta(organo)[60]fullerenes, C(60)Ar(5)H, as starting materials. In the next step, two cobalt-fullerene complexes were connected to a tetrathiafulvalene (TTF) tetrathiolate bridge to obtain the C(60)-Co-TTF-Co-C(60) array.

Pressure-induced phase transitions on a liquid crystalline europium(III) complex.

The effect of pressure on the phase behavior of the liquid crystalline complex [Eu(bta)(3)L(2)] (bta is benzoyltrifluoroacetonate, and L is the Schiff base 2-hydroxy-N-octadecyl-4-tetradecyloxybenzaldimine) was studied by X-ray diffraction, Raman spectroscopy, and luminescence spectroscopy. The pressure was varied between ambient pressure and 8.0 GPa.

Direct observation of dark excitons in micelle-wrapped single-wall carbon nanotubes.

We have performed electroabsorption spectroscopy on micelle-wrapped single-wall carbon nanotubes. In semiconducting nanotubes, many oscillating structures composed of the increase and decrease of absorption are observed in the spectra in the region of the first and second absorption bands, E11 and E22. The spectral shape is reproduced mainly by the second-derivative curve of the absorption spectrum, which indicates the presence of nearly degenerate bright and dark excitonic states.