Temperature dependence of formation of nanorods and dots of iodine compounds on an H-terminated Si(111) surface in a concentrated HI solution

Immersion of atomically flat, H-terminated Si(111) surfaces in 7.6 M HI for 0.5 - 4 h caused spontaneous formation of nanosized clusters at the Si surface. X-ray photoelectron spectroscopy analysis suggested that the clusters were composed of silicon iodides (such as SiHxI4-x), produced most probably by Si etching with HI. Atomic force microscopy inspection revealed that the immersion at a low temperature below about 30 degrees C led to the formation of long rod-shaped clusters, oriented in the (112) direction or equivalents, whereas the immersion at a high temperature above 30 degrees C led to the formation of circular dot clusters, their size and shape changing abruptly at about 70 degrees C. It is shown experimentally that the formation of dot clusters at a high immersion temperature is explained on the basis of thermodynamics, whereas that of oriented rod clusters at a low temperature is explained by a kinetics-controlled mechanism.     

Electronic properties of CrF and CrCl in the X 6Sigma+ state: observation of the halogen hyperfine structure by Fourier transform microwave spectroscopy

The rotational spectra of the CrF and CrCl radicals in the X 6Sigma+ state were observed by employing a Fourier transform microwave spectrometer. The CrF and CrCl radicals were generated by the reaction of laser-ablated Cr with F2 and Cl2, respectively, diluted in Ar. A chromium rod made of chromium powder pasted with epoxy resin was ablated by a Nd:YAG laser. Rotational transitions were measured in the region between 8 and 26 GHz. Several hyperfine constants due to the halogen nuclei were determined by a least-squares analysis. The electronic properties of CrF and CrCl were derived from their hyperfine constants and were compared with those of other 3d transition metal monohalides: TiF, MnF, FeF, CoF, NiF, and FeCl.     

Fourier transform microwave spectroscopy of the Rg-SH(2Pi(i)) complexes (Rg:Ne, Kr): determination of the intermolecular potential energy surfaces

Pure rotational spectra of Ne-SH and Kr-SH have been studied by Fourier transform microwave spectroscopy. R-branch transitions in the lower-spin component (Omega=3/2) corresponding to a linear (2)Pi(i) radical were observed for J(")=1.5-4.5 in the region 11-25 GHz for Ne-SH and for J(")=1.5-6.5 in the region 5-20 GHz for Kr-SH, respectively, with parity doublings and hyperfine splittings associated with the H nucleus. Although the spectral pattern of Kr-SH is relatively regular, that of Ne-SH is irregular with the J dependence of the parity doublings quite different from other Rg-SH or Ar-OH complexes. Two-dimensional intermolecular potential energy surfaces (IPSs) for both of the species have been determined from the least-squares fittings of the observed rotational transitions utilizing results of high-level ab initio calculations. These IPSs reproduce the observed transition frequencies within the experimental error and provide accurate knowledge on the intermolecular interaction and internal dynamics. Systematic comparisons of Rg-SH complexes have clarified various features of this series of complexes.     

An HPLC assay of hydroxyl radicals by the hydroxylation reaction of terephthalic acid

An HPLC assay for hydroxyl radicals is described. The hydroxyl radical was trapped by terephthalic acid (non-fluorescent), and 2-hydroxyl terephthalic acid (fluorescent) was quantitated by HPLC-fluorescence detection. At a terephthalic acid concentration of 4.25 mmol/L, the hydroxyl radical formed in the Fenton reaction was successfully assayed in the concentration range of hydrogen peroxide of 2.5-50 micro mol/L, where the concentration of Fe(II) was 50 micro mol/L. The fluorescence of 2-hydroxy terephthalate was stable at 24 h, and its detection limit by this method was 5 nmol/L (100 fmol).     

Laser terahertz-emission microscope for inspecting electrical faults in integrated circuits

A laser terahertz-emission microscope (LTEM) system is proposed and developed for inspecting electrical faults in integrated circuits (IC). We test a commercial operational amplifier while the system is operating. Two-dimensional terahertz-emission images of the IC chip are clearly observed while the chip is scanned with a femtosecond laser. When one of the interconnection lines is cut, the damaged chip has a LTEM image different from that of normal chips. The results indicate that the LTEM system is a potential tool for IC inspection.     

Excitation and decay of the isovector giant monopole resonances via the 208Pb(3He,t p) reaction at 410 MeV

The excitation and subsequent proton decay of the isovector spin-flip giant monopole resonance (IVSGMR) is studied via the 208Pb(3He,t) reaction at 410 MeV. In the inclusive spectrum (60+/-5)% of the non-energy-weighted sum-rule strength for this 2 variant Planck's over 2h omega resonance was found in the region 29相似文献   

Lipase TL-mediated kinetic tesolution of 5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol at low temperature: concise asymmetric synthesis of both enantiomers of a piperazic acid derivative

Lipase TL-mediated kinetic resolution of (+/-)-5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol (5) at low temperature proceeded to give the corresponding (S)-alcohol 5 and (R)-acetate 6 in quantitative yields with high enantiomeric purity. The addition of bases such as pyridine, DMAP, 2,4- and 2,6-lutidines, or triethylamine considerably enhanced the rate of kinetic resolution. The alcohol (S)-5 and the acetate (R)-6 were converted to piperazic acid derivatives (R)- and (S)-3, respectively, via the intramolecular Mitsunobu reaction as a key step.     

Synthesis and properties of novel thiaarenecyclynes

Novel thiaarenecyclynes 3 and 4 in which two thioether units and two benzene rings are alternately inserted into the single bonds of cyclooctatetrayne are synthesized. Their unique properties are described.     

In situ FTIR studies of primary intermediates of photocatalytic reactions on nanocrystalline TiO2 films in contact with aqueous solutions

Multiple internal reflection infrared spectroscopy was applied to in situ investigations of surface intermediates of photocatalytic reactions on nanocrystalline TiO(2) films in contact with aqueous solutions. UV irradiation in the presence of dissolved O(2) caused the appearance of new bands peaked at 943, 838, and 1250-1120 cm(-)(1) together with intensity changes in other bands. Investigations of influences of the solution pH, the presence or absence of hole and electron scavengers, and isotopic H(2)O --> D(2)O exchange on the spectral changes have revealed that the primary step of photocatalytic O(2) reduction is the formation of the surface peroxo species, Ti(O(2)), giving the 943 cm(-)(1) band, probably with the surface superoxo species, TiOO., as a precursor, in neutral and acidic solutions. The surface peroxo species is then transformed to the surface hydroperoxo, TiOOH, giving the 838 and 1250-1120 cm(-)(1) bands, by protonation in the dark. This is, to our knowledge, the first direct in situ spectroscopic detection of primary intermediates for the photocatalytic O(2) reduction in aqueous solutions. On the basis of the assignment, a possible reaction scheme for various processes of the photocatalytic O(2) reduction is proposed, which is in harmony with other spectral changes induced by the UV irradiation.