Takashi Sambongi

Elasticity mapping of living fibroblasts by AFM and immunofluorescence observation of the cytoskeleton

Using the force mapping mode of atomic force microscopy (AFM), we measured spatial distribution of elastic moduli of living mouse fibroblasts (NIH3T3) in a physiological condition. The nuclear portion of the cellular surface is about 10 times softer than the surroundings. Stiffer fibers are confirmed in the elastic images. In order to investigate origin of the softer nuclear portion and the stiffer fibers, we fixed the identical cells imaged by the AFM, and carried out immunofluorescence observation for three types of cytoskeletal filaments--actin filaments, microtubules, and intermediate filaments, using confocal laser scanning microscopy (CLSM). A comparison between the AFM and the CLSM images revealed that the elasticity of the cells was concerned not only with the distribution of actin network, but also with intermediate filaments, whereas microtubules had no large effect on the measured elasticity.

Peierls transition in TaS3

Abstract Transition-metal trichalcogenide, TaS 3 , with an orthorhombic structure was found to undergo a metal-semiconductor transition at 270 K. Electron diffraction reveals diffuse scattering above room temperature and superlattice spots at a lower temperature. These phenomena are interpreted in terms of Peierls transition.

Non-ohmic conductivity of TaS3 in the low-temperature semiconducting regime

Abstract Electrical conductivity of the quasi one-dimensional conductor TaS3 was measured in the low-temperature semiconducting regime. Below 100K, the conductivity along c-axis (l-d axis) in the low field limit is characterized by the activated process with the activation energy of 250K, and the current-field (I-E) characteristic is nonlinear, dI dE increasing with the field strength. These results can be explained by the excitation of phase solitons associated with pinned CDW condensates.

Giant Resistivity Anomaly in ZrTe5

The group-IV transition-metal penta-chalcogenide, ZrTe 5 , shows a giant peak of the electrical resistivity around 150 K, suggestive of a structural phase transition.

X-Ray Study of Charge Density Wave Structure in 1T-TaS2

Positions of satellite reflections in charge density wave (CDW) phases of 1T-TaS 2 were measured by X-ray diffraction. In the commensurate (C-) phase, stacking of CDW layers is considerably disordered. On heating from the C-phase there appears a new incommensurate triclinic structure up to 280 K, where anomalies have been observed in various properties.

Non-linear conductivity in the spin density wave phase of (TMTSF)2ClO4

Abstract Electrical conductivity was measured in the spin-density wave phase of (TMTSF)2ClO4, which is induced in zero magnetic field when ordering of ClO4 ions is suppressed by rapid quenching. The conductivity along the one-dimensional axis increases above a threshold field, in the range of 10–40mV cm-1. The threshold field increases slightly with increasing temperature. The conductivity increase is presumably assigned to the sliding motion of the spin-density wave, as suggested by Tomic et al. for (TMTSF)2NO3. Significant sample dependence is observed in threshold field-temperature and conductance-field relations; important effects of the interaction between the deformable spin-density wave and pinning centers are inferred.

Narrow band noise in SDW sliding

Narrow band noise was observed in the spin-density-wave (SDW) phase of quenched (TMTSF)2ClO4, when electric current larger than the threshold for non-ohmicity was passed parallel to the one-dimensional axis. The noise frequency F increases linearly with the excess current density JSDW with a slope FJSDW = 240 kHz (Acm-2)-1. It is confirmed that the non-linear excess current is carried by the SDW condensate and that the narrow band noise is generated by the sliding motion of the SDW.

Comparing microscopic with macroscopic elastic properties of polymer gel

Measurements of the local elastic modulus of agar gels obtained with atomic force microscope (AFM) force mapping were compared with values obtained by the tensile creep method. The observed spatial distributions of the local elastic modulus over the gel surface in AFM elastic images clearly corresponded to the network structure of agar fibers observed both in AFM topographic and scanning electron microscope (SEM) images. Both peak and average values of distribution functions in the histograms of local elastic modulus increase monotonically with the agar concentration. Values obtained by AFM force mapping were found to be proportional to values obtained from creep experiments.

Negative Evidences for Charge/Spin Density Wave in ZrTe5

Experimental searches were made for evidences for the charge- or spin-density wave state in the trigonal-prismatic pseudo-linear chain compound ZrTe 5 . Negative evidences for such phase transitions were provided by the absence of lattice modulation, ohmic resistivity at high electric fields, and by temperature and angular dependences of electrical resistivity and magnetic susceptibility.

Superconductivity in One-Dimensional TaSe3

Monoclinic TaSe 3 was found to be superconducting below 2.1 K. The effect of magnetic field on the transition curve is very anisotropic. One-dimensional behavior is expected.