We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By tunneling parallel to the c axis, a single superconducting gap (Delta=2.2 meV) associated with the pi band is observed. The vortices in the pi band have a large core size compared to estimates based on H(c2) and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the pi band is, at least partially, induced by the intrinsically superconducting sigma band.

The terahertz and infrared frequency vibration modes of room-temperature ionic liquids with imidazolium cations and halogen anions were extensively investigated. There is an intermolecular vibrational mode between the imidazolium ring of an imidazolium cation, a halogen atomic anion with a large absorption coefficient and a broad bandwidth in the low THz frequency region (13–130 cm−1), the intramolecular vibrational modes of the alkyl-chain part of an imidazolium cation with a relatively small absorption coefficient in the mid THz frequency region (130–500 cm−1), the intramolecular skeletal vibrational modes of an imidazolium ring affected by the interaction between the imidazolium ring, and a halogen anion with a relatively large absorption coefficient in a high THz frequency region (500–670 cm−1). Interesting spectroscopic features on the interaction between imidazolium cations and halogen anions was also obtained from spectroscopic studies at IR frequencies (550–3300 cm−1). As far as the frequency of the intermolecular vibrational mode is concerned, we found the significance of the reduced mass in determining the intermolecular vibration frequency.

Infrared spectroscopy was performed on ionic liquids (ILs) that had imidazolium cations with different alkyl chain lengths and various halogen or molecular anions with and without a small amount of water. The molar concentration normalized absorbance due to C-H vibrational modes in the range of 3000 to 3200 cm was nearly identical for ILs that had imidazolium cations with different alkyl chain lengths and the same anions. A close correlation was found between the red-shifted C-H vibrational modes, the chemical shift ofC(2)-H proton, and the energy stabilization of the hydrogen-bonding interaction. The vibrational modes of the water molecules interacting with anions in the range between 3300 and 3800 cm was examined. The correlation between the vibrational frequencies of water, the frequencies of C-H vibrational modes, and the center frequency of intermolecular vibrational modes due to ion pairs was discussed.

The terahertz- and infrared-frequency vibrational modes of various room-temperature imidazolium-based ionic liquids with molecular anions were examined extensively. We found that the molar-concentration-normalized absorption coefficient spectra in the low-wavenumber range for imidazolium cations with different alkyl-chain lengths were nearly identical for the same anion. Regarding the overall view of a wide range of imidazolium-based ionic liquids, we found that the reduced mass of the combination of an imidazolium-ring cation and the anion and the force constant play significant roles in determining the central frequency of the broad absorption band. In addition to these findings, we also discuss the correlation between the (+)C-H stretching vibrational modes in the 3000-3300 cm(-1) range of the infrared spectra and the intermolecular vibrational band in the low-wavenumber range. Finally, we describe some interesting characteristics of the intermolecular vibrational band observed in a wide range of imidazolium-based ionic liquids.

Various three-dimensional structures have been created on a nanometer scale using the self-assembly of DNA molecules. However, ordinary DNA structures breakdown readily because of their flexibility. In addition, it is difficult to control them by inputs from environments. Here, we construct robust and photocontrollable DNA capsules using azobenzenes. This provides a method to construct DNA structures that can survive higher temperatures and can be controlled with ultraviolet irradiation.

No abstract

Long/short chain mixed cellulose esters (MCE) are practical, promising polymers with interesting properties. In the molecular design of MCE, using long acyl chains made from renewable resources is important and enhances the value of MCE as sustainable materials. In this study, we focused on two types of renewable long acyl chains for MCE: the aromatic 3-pentadecylphenoxy acetyl (PA) group derived from cardanol extracted from cashew nutshells and the aliphatic stearoyl (St) group made from vegetable oils. Using these long acyl chains and the acetyl (Ac) group as a short acyl chain, we synthesized PA/Ac MCE (P-series) and St/Ac MCE (S-series) in LiCl/DMAc medium. The thermal and mechanical analyses revealed that a mixed substitution of long and short acyl chains prevented the crystallization of the long acyl chain moieties in MCE. The P-series had slightly higher bending strength and glass transition temperature than those of the S-series but showed low impact strength because of the existence of the aromatic ring in the PA group, which caused an increase in the stiffness of the cellulose backbone and the extra intermolecular interaction. However, the S-series without aromatic rings showed remarkably improved impact strength with sufficient balanced mechanical properties for use in durable products due to its composition of low crystalline long acyl chain moieties.

In three-dimensional integration technology, through-silicon vias ͑TSVs͒ with a high aspect ratio in excess of 10 are required, due to a strong demand for a higher packing density. We achieved perfect conformal electroless plating of Cu by the addition of Cl − and bis͑3-sulfopropyl͒ disulfide to a standard plating bath. With this technology, the Cu thickness of the TSV sidewalls remained constant with depth, even for the TSV with an aspect ratio of 20. Perfect conformal plating is a promising technology that could lower the resistance of high aspect ratio TSVs.The formation of through-silicon vias ͑TSVs͒ to enable the stacking of multiple layers of thin Si substrates is a key technology for three-dimensional integration. It is expected that the minimum pitch of TSVs is smaller than 10 m, which will require the diameter of the TSVs to decrease below a few micrometers in the near future. 1,2 In such a structure, the TSV will take the place of a largescale integration circuit global interconnection. Cu filling of the TSV is an important technology because it enables a lower resistance TSV than chemical vapor deposition of tungsten ͑CVD-W͒ filling by an order of magnitude; however, there have been many technical problems in Cu filling of a high aspect ratio TSV. Cu electroplating technology has been studied extensively, 3 and a socalled superconformal deposition that enables a bottom-up fill of submicrometer vias has been proposed. [4][5][6][7][8][9][10][11][12][13] In Cu electroplating, the formation of a sputtered Cu seed layer is very difficult for a high aspect ratio via because the film thickness at the sidewall is much lower than on the flat surface. Therefore, conformal deposition using chemical vapor deposition of titanium nitride ͑CVD-TiN͒ or CVD-W was studied before Cu electroplating. 14-16 However, it is not easy to fill a high aspect ratio via by superconformal Cu electroplating.Cu electroless plating can result in good conformal deposition and is rather insensitive to the electrical conductivity of the seed layer. We found that a bottom-up fill was possible for a submicrometer ultra-large scale integration via using Cu electroless plating with the addition of a sulfuric organic compound with polyethylene glycol ͑PEG͒. We found that a sulfuric organic compound such as bis͑3-sulfopropyl͒ disulfide ͑SPS͒ acted as a strong inhibitor. 17,18 The diffusion of inhibitor molecules into the bottom of fine holes is limited, resulting in faster growth of Cu within the via. Furthermore, Cu can be deposited on TaN, WN, and W barrier layers without a Pd catalyst through displacement plating mechanisms. 19,20 In the preliminary stages of this study, we attempted to use an SPS-contained plating bath to fill TSVs. However, these additives were unable to achieve a bottom-up fill of high aspect ratio TSVs with diameters of a few micrometers. In this study, we investigated Cu-filling characteristics when adding Cl − as a third additive to a PEG and a sulfuric organic compound plating bath. ExperimentalWe prepared the TSV sam...