Reversible local-modification of surface structure on clean Ge(0 0 1) by scanning tunneling microscopy below 80 K

The structure of the clean Ge(0 0 1) surface is locally and reversibly changed between c(4×2) and p(2×2) by controlling the bias voltage of a scanning tunneling microscopy (STM) below 80 K. It shows hysteresis for the direction of the sample bias voltage change. The c(4×2) structure is observed with the sample bias voltage V_b?−0.7 V. This structure is maintained at V_b?0.7 V with increasing the bias voltage from −0.7 V. When V_b is higher than 0.8 V, the structure changes to p(2×2). This structure is then maintained at V_b?−0.6 V with decreasing the bias voltage from +0.8 V. The area of the structure change can be confined in the single dimer row just under the STM tip using a bias voltage pulse. In particular, the minimum transformed length is four dimers along the dimer row in the transformation from p(2×2) to c(4×2). The observed local change of the reconstruction with hysteresis is attributed to the energy transfer process from the tunneling electron to the Ge lattice in the local electric field due to the STM bias voltage. A phenomenological model is proposed for the structure changes. It is based on a cascade inversion of the dimer buckling orientation along the dimer row.     

Incident-angle dependence of the phase conjugate reflectivity by nonlinear piezoelectric interaction in PZT ceramics.

The reflectivity of an acoustic phase conjugator by nonlinear piezoelectric interaction in PZT ceramics was measured as a function of the incident angle. The phase conjugator was designed as a solid block with a flat surface for the acoustic incidence from water. The phase conjugate reflectivity showed incident angle dependence, which is mainly determined by the transmissivity of the acoustic waves, together with some effects of anisotropy. The field-reconstructing ability of this phase conjugator was simulated for focused incident beams.     

Absolute Measurement of Second-Order Nonlinear Optical Coefficient of LiNbO3 by Parametric Processes

We have redetermined the absolute values of the nonlinear optical coefficient, d₃₁, of LiNbO₃ by parametric fluorescence and, for the first time, by difference frequency generation measurements to resolve the considerable discrepancy that existed between the values determined by second-harmonic generation (SHG) and parametric fluorescence. We obtain d₃₁ = 4.8±0.5 and 4.3±0.5 pm/V at the pump wavelengths of 488 and 532 nm, respectively, in reasonable agreement with the SHG data. It appears that the previous parametric fluorescence value, d₃₁=5.8 pm/V, was overestimated.Author to whom correspondence should be addressed.     

Synthesis and DNA damaging ability of enediyne-polyamine conjugates

Polyamine-enediyne conjugates were synthesized and exhibited potent DNA damaging ability under physiological conditions. The extent of their activity was shown to depend upon the polyamine length that regulates the DNA binding affinity of the conjugates, and enhanced DNA damaging activities were observed under slightly acidic conditions.     

Highly efficient chiral resolution and determination of absolute configuration of 2-alkanols by using a cyclopenta[b]furan derivative

The reaction of 3a-benzhydryl-3,3a,4,5-tetrahydro-2H-cyclopenta[b]furan and various 2-alkanols in the presence of a catalytic amount of pyridinium 4-tolunesulfonate in dichloromethane gave 3a-benzhydryl-6a-(1-methyl-aloxy)-hexahydrocyclopenta[b]furan in more than 90% chemical yields. The resulting diastereomeric mixture is easily separable on silica gel chromatography because of the large ΔR_f value (briefly 0.1). Absolute configuration of the 2-alkanols can be easily estimated by the chemical shifts of ¹H and ¹³C NMR of methyne group of the benzhydryl moiety.