Electron transport with mobility above 10–3 cm2/Vs in amorphous film of co‐planar bipyridyl‐substituted oxadiazole

We demonstrate that a bipyridyl substituted oxadiazole (Bpy‐OXD) shows high electron mobility that reached above 10^–3 cm²/Vs. We believe that the high mobility results from both the hybrid molecular structure of the two electron‐accepting units: bipyridyl and oxadiazole, and the planar molecular structure based on its lack of sterically hindered bulky substituent. The computational analysis elucidates that the amorphous nature of Bpy‐OXD in thin‐film state probably results from the polymorphic effect in isolated state and the volume effect in solid state. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The origin of spectral distortion in electric field modulation spectroscopy based on scanning tunneling microscopy

Electric field modulation spectroscopy using scanning tunneling microscopy (STM-EFMS) measurements were performed for a Si(1 1 1) surface with epitaxially-grown β-FeSi₂ islands. STM-EFMS spectra acquired around the indirect energy gap of Si reproduced the photon energy peak position observed in conventional macroscopic EFMS experiments. However, a considerable discrepancy was found in the energy position of the accompanying spectral dip. We examined two possibilities for the cause of this discrepancy. The first interpretation is that the STM-‘EFMS’ spectra may simply reflect the local density of states based on essentially the same principle as that of tunneling spectroscopy. However, this interpretation is ruled out by the facts that almost identical STM-EFMS spectra are obtained also out of the regime of tunneling. The second interpretation is a spectral distortion due to a large electric field steadily built in the sample surface, which is supported experimentally by a spectral shift of the dip energy that is induced by altering the tip-induced band bending.     

Thermodynamic properties of ethanol solution of chiral camphors and its derivatives

Enthalpies of mixing and the densities of ethanol solution of R- and S-enantiomers of camphor, 10-camphorsulfonamide, 10-camphorsulfonic acid, camphorquinone, and 10-camphorsulfonyl chloride have been measured for a wide range of mole fractions of heterochiral components at 298.15 K. Enthalpies of mixing were exothermic for all concentrations and heterochiral solutions were more stable than each of the homochiral solutions. Enthalpic stabilization of mixing of heterochiral solutions was increased with a decreasing concentration of all the camphor derivatives measured. The sequence of enthalpic stabilization on mixing was 10-camphorsulfonyl chloride, 10-camphorsulfonic acid, 10-camphorsulfonamide, camphor, and camphorquinone. Apparent molar volumes were determined and excess volumes of mixing of heterochiral solutions were small and negative. Enthalpic stabilizations were found to be dependent on dipole–dipole interaction between solutes and solvents.     

Enthalpies of mixing of ethanol solution of chiral limonenes at 298.15 K

Enthalpies of mixing of ethanol solution of R- and S-enantiomers of limonene in large concentration have been measured at 298.15 K. The enthalpies of mixing were negligibly small for all concentrations. Enthalpies of mixing showed negative in less than 30 mol%, but positive in more than the high concentration of limonenes. The heterochiral solutions were more stable than each of the homochiral solutions in dilute solutions. The concentration dependence on enthalpies of mixing in dilute concentration of less than 10 mol% was much sharper in inclination than the dense solutions limonene.