Atomic and Electronic Structures of Unreconstructed Polar MgO(111) Thin Film on Ag(111)

Atomic and electronic structures of a polar surface of MgO formed on Ag(111) was investigated by using reflection high energy electron diffraction (RHEED), Auger electron spectroscopy, electron energy loss spectroscopy (EELS), and ultraviolet photoemission spectroscopy (UPS). A rather flat unreconstructed polar MgO(111) 1$\times$1 surface could be grown by alternate adsorption of Mg and O$_{2}$ on Ag(111). The stability of the MgO(111) surface was discussed in terms of interaction between Ag and Mg atoms at the interface, and charge state of the surface atoms. EELS of this surface did not show a band gap region, and finite density of states appeared at the Fermi level in UPS. These results suggest that a polar MgO(111) surface was not an insulating surface but a semiconducting or metallic surface.Comment: 6 figures, to be published in Phys. Rev.

Reexamination of the role of hematopoietic organs on the hematopoiesis in the silkworm, Bombyx mori

Larval hematopoietic organs (HPO) are thought as the only source of circulating hemocytes in most insects. In this paper, we re-checked the importance of hematopoietic organs to hematopoiesis in the silkworm through surgical operation to remove the organs from silkworm larvae at 12 h after 5 th ecdysis. We observed that there was no significant decrease of hemocyte density but higher ratio of cell division in the HPO-removed wandering larvae. We checked and compared the total hemocytes in circulation and in 4 hematopoietic organs of each larva and found that even we suppose all hemocytes could be released from 4 organs at one time, it could not meet the circulating hemocytes increase in vivo due to huge difference. In order to monitor hemocytes movement in the hematopoietic organs to get information on hemocytes releasing in vivo, we labeled the dividing hemocytes with 5-bromo-2’-deoxyuridine (BrdU) at 12 h after 5th ecdysis and observed BrdU-positive cells in the organs for several days. Our results show that the BrdU-labeled hemocytes were not released as quickly as we thought because there were still many BrdU-positive cells in the wandering organs and some cells even had almost no changed BrdU labeling. Therefore, the silkworm larvae have a novel hematopoiesis because circulating hemocyte division might contribute huge part to the hematopoiesis

Reexamination of the role of hematopoietic organs on the hematopoiesis in the silkworm, Bombyx mori

Larval hematopoietic organs (HPO) are thought as the only source of circulating hemocytes in most insects. In this paper, we re-checked the importance of hematopoietic organs to hematopoiesis in the silkworm through surgical operation to remove the organs from silkworm larvae at 12 h after 5 th ecdysis. We observed that there was no significant decrease of hemocyte density but higher ratio of cell division in the HPO-removed wandering larvae. We checked and compared the total hemocytes in circulation and in 4 hematopoietic organs of each larva and found that even we suppose all hemocytes could be released from 4 organs at one time, it could not meet the circulating hemocytes increase in vivo due to huge difference. In order to monitor hemocytes movement in the hematopoietic organs to get information on hemocytes releasing in vivo, we labeled the dividing hemocytes with 5-bromo-2’-deoxyuridine (BrdU) at 12 h after 5th ecdysis and observed BrdU-positive cells in the organs for several days. Our results show that the BrdU-labeled hemocytes were not released as quickly as we thought because there were still many BrdU-positive cells in the wandering organs and some cells even had almost no changed BrdU labeling. Therefore, the silkworm larvae have a novel hematopoiesis because circulating hemocyte division might contribute huge part to the hematopoiesis

Utilization of silkworm cocoon waste as a sorbent for the removal of oil from water

ArticleJOURNAL OF HAZARDOUS MATERIALS. 165(1-3):266-270 (2009)journal articl

Electronic properties of metal induced gap states at insulator/metal interfaces -- dependence on the alkali halide and the possibility of excitonic mechanism of superconductivity

Motivated from the experimental observation of metal induced gap states (MIGS) at insulator/metal interfaces by Kiguchi {\it et al.} [Phys. Rev. Lett. {\bf 90}, 196803 (2003)], we have theoretically investigated the electronic properties of MIGS at interfaces between various alkali halides and a metal represented by a jellium with the first-principles density functional method. We have found that, on top of the usual evanescent state, MIGS generally have a long tail on halogen sites with a $p_z$-like character, whose penetration depth ($\lambda$) is as large as half the lattice constant of bulk alkali halides. This implies that $\lambda$, while little dependent on the carrier density in the jellium, is dominated by the lattice constant (hence by energy gap) of the alkali halide, where $\lambda_{\rm LiF} < \lambda_{\rm LiCl} < \lambda_{\rm LiI}$. We also propose a possibility of the MIGS working favorably for the exciton-mediated superconductivity.Comment: 7 pages, 9 figure

Highly Conducting pi-Conjugated Molecular Junctions Covalently Bonded to Gold Electrodes

We measure electronic conductance through single conjugated molecules bonded to Au metal electrodes with direct Au-C covalent bonds using the scanning tunneling microscope based break-junction technique. We start with molecules terminated with trimethyltin end groups that cleave off in situ resulting in formation of a direct covalent sigma bond between the carbon backbone and the gold metal electrodes. The molecular carbon backbone used in this study consist of a conjugated pi-system that has one terminal methylene group on each end, which bonds to the electrodes, achieving large electronic coupling of the electrodes to the pi-system. The junctions formed with the prototypical example of 1,4-dimethylenebenzene show a conductance approaching one conductance quantum (G0 = 2e2/h). Junctions formed with methylene terminated oligophenyls with two to four phenyl units show a hundred-fold increase in conductance compared with junctions formed with amine-linked oligophenyls. The conduction mechanism for these longer oligophenyls is tunneling as they exhibit an exponential dependence of conductance with oligomer length. In addition, density functional theory based calculations for the Au-xylylene-Au junction show near-resonant transmission with a cross-over to tunneling for the longer oligomers.Comment: Accepted to the Journal of the American Chemical Society as a Communication

The number of transmission channels through a single-molecule junction

We calculate transmission eigenvalue distributions for Pt-benzene-Pt and Pt-butadiene-Pt junctions using realistic state-of-the-art many-body techniques. An effective field theory of interacting $\pi$-electrons is used to include screening and van der Waals interactions with the metal electrodes. We find that the number of dominant transmission channels in a molecular junction is equal to the degeneracy of the molecular orbital closest to the metal Fermi level.Comment: 9 pages, 8 figure

Effect of Thermoelectric Cooling in Nanoscale Junctions

We propose a thermoelectric cooling device based on an atomic-sized junction. Using first-principles approaches, we investigate the working conditions and the coefficient of performance (COP) of an atomic-scale electronic refrigerator where the effects of phonon's thermal current and local heating are included. It is observed that the functioning of the thermoelectric nano-refrigerator is restricted to a narrow range of driving voltages. Compared with the bulk thermoelectric system with the overwhelmingly irreversible Joule heating, the 4-Al atomic refrigerator has a higher efficiency than a bulk thermoelectric refrigerator with the same $ZT$ due to suppressed local heating via the quasi-ballistic electron transport and small driving voltages. Quantum nature due to the size minimization offered by atomic-level control of properties facilitates electron cooling beyond the expectation of the conventional thermoelectric device theory.Comment: 8 figure

Evidence for Quantum Interference in SAMs of Arylethynylene Thiolates in Tunneling Junctions with Eutectic Ga-In (EGaIn) Top-Contacts

This paper compares the current density (J) versus applied bias (V) of self-assembled monolayers (SAMs) of three different ethynylthiophenol-functionalized anthracene derivatives of approximately the same thickness with linear-conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) using liquid eutectic Ga-In (EGaIn) supporting a native skin (~1 nm thick) of Ga2O3 as a nondamaging, conformal top-contact. This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts; however, it may also have limited the maximum values of J observed for AC. The measured values of J for AH and AQ are not significantly different (J ≈ 10-1 A/cm2 at V = 0.4 V). For AC, however, J is 1 (using log averages) or 2 (using Gaussian fits) orders of magnitude higher than for AH and AQ. These values are in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules chemisorbed between Au contacts that predict currents, I, that are 2 orders of magnitude higher for AC than for AH at 0 < |V| < 0.4 V. The calculations predict a higher value of I for AQ than for AH; however, the magnitude is highly dependent on the position of the Fermi energy, which cannot be calculated precisely. In this sense, the theoretical predictions and experimental conclusions agree that linearly conjugated AC is significantly more conductive than either cross-conjugated AQ or broken conjugate AH and that AQ and AH cannot necessarily be easily differentiated from each other. These observations are ascribed to quantum interference effects. The agreement between the theoretical predictions on single molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.