Tolerance to Stretching in Thiol-Terminated Single-Molecule Junctions Characterized by Surface-Enhanced Raman Scattering.

We investigated the change in the metal-molecule interaction in a 1,4-benzenedithiol (BDT) single-molecule junction using a combination of surface-enhanced Raman scattering spectra and current-voltage curves. During the stretching process, the conductance of the junction systematically decreased, accompanied by an increase in the vibrational energy of the CC stretching mode. By analyzing the current-voltage curves and Raman spectra, we found that the interaction between the π orbital of BDT and the electronic states of Au was diminished by the orientation change of BDT during the stretching process. A comparison with a 4,4'-bipyridine single-molecule junction revealed that the reduction of coupling of the Au-S contacts was smaller than that of Au-pyridine contacts. Therefore, the electronic states originating from the contact geometry are responsible for the tolerance to the stretching of thiol-terminated molecular junctions.

Investigation of Ag and Cu Filament Formation Inside the Metal Sulfide Layer of an Atomic Switch Based on Point-Contact Spectroscopy.

The atomic switches have attracted wide attention owing to their applications in nonvolatile electric devices. The atomic switch is operated by the formation and dissipation of a metallic filament inside a metal sulfide film, which is controlled by a solid electrochemical reaction. Although the metallic filament is considered to consist of metal atoms, the chemical species of the metallic filament are difficult to be identified due to challenges in observing the metallic filament inside the solid. In this study, we report the investigation on the metallic filament in the atomic switch with metal sulfide based on point-contact spectroscopy (PCS). By cooling the atomic switch, the switch voltage increased to 1 V, which allowed for the PCS measurement. The PCS revealed that the metallic filament was composed of Ag atoms in the case of the Pt/Ag2S/Ag atomic switch. We applied this technique to the Pt/Cu2S/Ag and Pt/Ag2S/Cu atomic switches to uncover the formation process of the metallic filament. In both atomic switches, the chemical species of the metallic filament were Ag. The metal atoms were supplied from both the metal electrode and the sulfide layer.

Stretch dependent electronic structure and vibrational energy of the bipyridine single molecule junction.

We have studied the stretch dependence of the electronic structure and vibrational energy for the 4,4'-bipyridine (BPY) single molecule junction, which was fabricated by the mechanically controllable break junction (MCBJ) using the highly stable nano MCBJ electrodes. The electronic structure and vibrational energy of the single molecule junction were studied by the current-voltage (I-V) curve and surface enhanced Raman scattering (SERS), respectively. The simultaneous SERS and I-V curve measurements revealed the lowest unoccupied molecular orbital (LUMO) and vibrational energy of the C-C stretching mode decreased with an increase in the metal-molecule distance. The molecular orbital energy shift and vibrational energy shift can be explained by the change in the degree of the hybridization of molecular and metal orbitals.

Nutritional assessment using stable isotope ratios of carbon and nitrogen in the scalp hair of geriatric patients who received enteral and parenteral nutrition formulas.

BACKGROUND & AIMS: The δ13C and δ15N values in the scalp hair of geriatric patients in Japan who received the enteral or parenteral nutrition formula were measured to assess nutritional status. METHODS: The relations among δ13C, δ15N, calorie intake, BMI, albumin concentration, total cholesterol (T-CHO) and geriatric nutritional risk index (GNRI) in the patients were investigated. Furthermore, the enrichment of δ13C and δ15N from the nutrients to the hair was investigated. RESULTS: The δ13C values in the hair of patients who received enteral nutrition decreased with decreases in the calories received, while the δ15N values increased, suggesting malnutrition in some patients with a low calorie intake due to a negative nitrogen balance. The distribution of patients with a low calorie intake (below 20 kcal/kg/day) when δ13C was plotted against δ15N differed from that of control subjects, but the distribution of patients with a high calorie intake (above 20 kcal/kg/day) was similar to that of control subjects. No significant differences were observed in BMI, albumin concentration, T-CHO or GNRI between the low and high calorie groups. The enrichment of δ13C and δ15N from the enteral nutrients to the hair were inversely correlated with the δ13C and δ15N in the enteral nutrients. The enrichment levels of δ13C and δ15N tended to be higher and lower, respectively, in the high calorie group. On the other hand, the δ13C and δ15N values in the hair of patients who received parenteral nutrition were higher and lower than those in the control subjects and in the patients who received enteral nutrition, respectively, reflecting the higher δ13C and lower δ15N contents of the parenteral nutrients. CONCLUSIONS: The δ13C and δ15N values in the hair of patients who received enteral nutrition may be effective indicators for evaluating the long-term nutritional status of geriatric patients. A calorie intake of 20 kcal/kg/day may be a cut-off value for malnutrition in Japanese geriatric patients receiving enteral nutrition. However, caution is necessary when dealing with patients switching from parental nutrition as parenteral nutrition resulted in different changes in δ13C and δ15N. The enrichment levels of δ13C and δ15N from the enteral nutrients to the hair may be inversely correlated with the δ13C and δ15N values of enteral nutrients and vary according to the calorie intake.

High-performance top-gated monolayer SnS2 field-effect transistors and their integrated logic circuits.

Two-dimensional (2D) layered semiconductors are very promising for post-silicon ultrathin channels and flexible electronics due to the remarkable dimensional and mechanical properties. Besides molybdenum disulfide (MoS2), the first recognized 2D semiconductor, it is also important to explore the wide spectrum of layered metal chalcogenides (LMCs) and to identify possible compounds with high performance. Here we report the fabrication of high-performance top-gated field-effect transistors (FETs) and related logic gates from monolayer tin disulfide (SnS2), a non-transition metal dichalcogenide. The measured carrier mobility of our monolayer devices reaches 50 cm(2) V(-1) s(-1), much higher than that of the back-gated counterparts (~1 cm(2) V(-1) s(-1)). Based on a direct-coupled FET logic technique, advanced Boolean logic gates and operations are also implemented, with a voltage gain of 3.5 and output swing of >90% for the NOT and NOR gates, respectively. The superior electrical and integration properties make monolayer SnS2 a strong candidate for next-generation atomic electronics.

Origin of the relatively low transport mobility of graphene grown through chemical vapor deposition.

The reasons for the relatively low transport mobility of graphene grown through chemical vapor deposition (CVD-G), which include point defect, surface contamination, and line defect, were analyzed in the current study. A series of control experiments demonstrated that the determinant factor for the low transport mobility of CVD-G did not arise from point defects or surface contaminations, but stemmed from line defects induced by grain boundaries. Electron microscopies characterized the presence of grain boundaries and indicated the polycrystalline nature of the CVD-G. Field-effect transistors based on CVD-G without the grain boundary obtained a transport mobility comparative to that of Kish graphene, which directly indicated the detrimental effect of grain boundaries. The effect of grain boundary on transport mobility was qualitatively explained using a potential barrier model. Furthermore, the conduction mechanism of CVD-G was also investigated using the temperature dependence measurements. This study can help understand the intrinsic transport features of CVD-G.

Toward sub-20 nm hybrid nanofabrication by combining the molecular ruler method and electron beam lithography.

It is of great interest and importance to develop new nanofabrication processes to fabricate sub-20 nm structures with sub-2 nm resolution for next-generation nanoelectronic devices. A combination of electron beam lithography (EBL) and a molecular ruler is one of the promising methods to make these fine structures. Here we successfully develop a hybrid method to fabricate sub-20 nm nanogap devices at the desired positions with a complex structure by developing a post-EBL process, which enabled us to avoid damaging the molecular ruler with the high-energy electron beam, and to fully utilize the EBL resolution. It was found that slight etching of the Ti adhesion layer of the parent metal (Pt) by ACT935J solution assisted the removal of molecular rulers, resulting in improved enhancement in the product yield (over 70%) of nanogap devices.

In-crystal and surface charge transport of electric-field-induced carriers in organic single-crystal semiconductors.

Gate-voltage dependence of carrier mobility is measured in high-performance field-effect transistors of rubrene single crystals by simultaneous detection of the longitudinal conductivity sigma(square) and Hall coefficient R(H). The Hall mobility mu(H) (identical with sigma(square)R(H)) reaches nearly 10 cm(2)/V s when relatively low-density carriers (<10(11) cm(-2)) distribute into the crystal. mu(H) rapidly decreases with higher-density carriers as they are essentially confined to the surface and are subjected to randomness of the amorphous gate insulators. The mechanism to realize high carrier mobility in the organic transistor devices involves intrinsic-semiconductor character of the high-purity organic crystals and diffusive bandlike carrier transport in the bulk.

Consideration on peak shape in a batch-type chemiluminescence detection cell for capillary electrophoresis.

Peak areas, peak heights, and apparent theoretical plate numbers were examined as a function of sample injection times by use of the batch-type CL detection cell. Comparing the experimental data with those obtained by absorption detector, some considerations were carried out about the peak shape. The peak shape in CL detection was influenced by not only concentration distribution of sample in a sample zone but also sample diffusion and CL reaction at the capillary outlet. The sample injection time of ca. 35 s was recommended for the present CE with CL detector. The injection time much influenced peak shape as well as sensitivity in the CL detection cell.

Sensitive determination of metal ions by liquid chromatography with tris(2,2'-bipyridine) ruthenium (II) complex electrogenerated chemiluminescence detection.

Emetine dithiocarbamate metal complex, which is prepared from emetine, carbon disulfide, and metal (II), was found to indicate a large chemiluminescence intensity on the electrogenerated chemiluminescence of tris(2,2'-bipyridine)ruthenium(II). Liquid chromatography equipped with the chemiluminescence detection was developed for analyzing trace metal ions by use of the metal complex formation. The mixture of the Cu(II) and Co(II) complexes as a model sample was injected into the LC system. The two metal complexes and an excess emetine were successfully separated. The Cu(II) and Co(II) complexes were determined over the range 1-300 nM (the detection limit of 650 fg) and 30-5000 nM (the detection limit of 17 pg), respectively.

Microchip capillary electrophoresis using on-line chemiluminescence detection.

Chemiluminescence detection was used in capillary electrophoresis integrated on a microchip. Quartz microchips have two main channels and four reservoirs. Dansyl-lysine and -glycine were separated and detected with bis[(2-(3,6,9-trioxadecanyloxycarbony)-4-nitrophenyl]oxalate as peroxyoxalate chemiluminescent reagent. These dansyl amino acids came into contact with the chemiluminescence reagent to produce visible light at the interface between the separation channel and chemiluminescence reagent-containing reservoir. The detection limit (S/N = 3) for dansyl-lysine was 1 x 10(-5) M, which corresponded to the very small mass detection limit of ca. 0.4 fmol. However, the concentration sensitivity in the present system was approximately two orders of magnitude lower than that in the conventional capillary electrophoresis-chemiluminescence detection system. The relative standard deviations of migration time and peak height for dansyl-lysine were 4.2 and 4.5%, respectively. A channel conditioning before every run and an appropriate control of voltages were needed for the reproducible results. The present system had advantages in rapid separation time (within 40 s), small (several 10 pI) and accurate sample injection method using a cross-shaped injector, and simplification and miniaturization of the detection device.

Chemiluminescence detection of heme proteins separated by capillary isoelectric focusing.

Chemiluminescence detection was combined with capillary isoelectric focusing to perform protein analysis with high sensitivity. Luminol-H2O2 chemiluminescence was utilized, and heme proteins such as cytochrome c, myoglobin and peroxidase were analyzed. The proteins were focused by use of Pharmalyte 3-10 as ampholytes. Hydroxypropylmethyl-cellulose was added to the sample solution in order to easily reduce protein interactions with the capillary wall as well as the electroendoosmotic flow. The focused proteins were transported by salt mobilization to chemiluminescence detection cell equipped with an optical fiber. The present method showed significantly high sensitivity and wide dynamic range; the detection limit for cytochrome c was 6 x 10(-9) M and the linear dynamic range was greater than two-orders of magnitude (up to 2 x 10(-6) M).

Setting up an automated system for evaluation of bone age.

The "Tanner-Whitehouse 2" method is the most popular in evaluating skeletal maturation, but this method has some inherent weak points. We therefore developed the new system to automatically evaluate the skeletal maturation of Japanese children by means of a personal computer. The subjects of this study were 318 healthy Japanese boys and 199 girls ranging from 2 to 15 years of age. The bone age was calculated by multiple regression analysis with parameters for the epiphysis and metaphysis. Successful automatic evaluation was about 80-90% on each phalanx. There was a significant correlation between chronological age and the ratio of epiphyseal width to metaphyseal width. The system developed in this study was useful for evaluating the skeletal maturation.

Standard RUS skeletal maturation of Tokyo children.

A total of 704 girls and 753 boys, all healthy, from 3 to 18 years of age, from Tokyo and its suburbs, were radiographed on the left hand and wrist in 1986. Their RUS (TW2) skeletal maturity was estimated, the 50th-centile skeletal maturity scores were obtained, and the smoothed RUS maturity curves were determined applying the cubic spline function to the 50th-centile scores. On this maturity curve the score at each 0.1 year of chronological age was obtained and allocated as a given RUS skeletal age. This set of scores and ages we termed the TW2-J RUS, i.e. the Japanese TW2 RUS maturity standard. Comparing this RUS standard with the British standard, the Belgian, the southern Chinese, and the northern Indian, it became clear that Japanese children's RUS skeletal maturity progresses rapidly during puberty (after ages 9 in girls and 11 in boys), and that the maximum score difference between neighbouring age groups was observed at ages 12.5 in girls and 14.5 in boys on the spline-smoothed curve. Japanese children attain the adult stage 1 or 2 years earlier than other groups of children (at ages 15 in girls and 16 in boys).

Aberrant expression of a hemidesmosomal protein, bullous pemphigoid antigen 2, in human squamous cell carcinoma.

Through yet unidentified mechanisms, squamous epithelial cells become committed to terminal differentiation after detachment from the basement membrane. In squamous cell carcinoma, these mechanisms seem to be disturbed. A murine monoclonal antibody, designated NCC-Lu-226 (IgG1, K), which recognizes an antigen expressed in basal cells of squamous epithelium at the epithelio-connective tissue border, was obtained. A cDNA clone encoding the antigen was isolated from a cDNA library by immunoselection. DNA sequencing and a database search revealed that this cDNA clone was identical to a hemidesmosomal transmembrane protein, bullous pemphigoid antigen 2 (BPA-2; also known as BPAG2, BP180, or type XVII collagen). Immunoelectron microscopy validated the specific reactivity of this monoclonal antibody with skin hemidesmosomes. Enhanced expression and abnormal distribution of BPA-2 was revealed immunohistochemically in various precancerous and cancerous tissues, including solar keratosis (4 of 5), Bowen's disease (3 of 5), invasive squamous cell carcinoma (7 of 7) of the skin, and squamous cell carcinoma of the lung (14 of 14), esophagus (12 of 13), and cervix (14 of 17). The specific expression of BPA-2 protein in squamous cell carcinoma was confirmed by RT-PCR and Northern hybridization. BPA-2 has possible phosphorylation sites and is actually phosphorylated in cultured keratinocytes and squamous cell carcinoma. The aberrant expression of BPA-2 may reflect dysfunction of the hemidesmosome that occurs as a relatively early event in multistep carcinogenesis of squamous epithelium.