Results 1 - 10 of 19
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[en] We demonstrate the multiazimuth observation (360 deg. in principle) of InGaAs/GaAs quantum dots (QDs) by means of a 300 kV scanning transmission electron microscope (STEM), where both cross-sectional and plan-view observations are performed on a single STEM specimen for the first time. A cylindrical specimen with a diameter of 200-300 nm including the QD layer inside along the rotation axis was fabricated by the focused ion beam (FIB) technique, with the application of a newly developed mesa-cutting method to adjust the position and angle of the QD layer precisely. The 360 deg. STEM observation is realized by mounting the cylindrical specimen on a holder equipped with a specimen-rotation mechanism. High potential of 3D-STEM observation is briefly presented by showing high contrast images of QDs, dark field images, and moire fringes with various incident angles
[en] Multi-detector computed tomography (MDCT) has been used to provide diagnostic information after heart valve replacements such as prosthetic valve dysfunction. However, only few data are available about aortic paraprosthetic regurgitation (APR). The aim of this study is to assess the feasibility, accuracy, and reproducibility of the existence of APR using contrast-enhanced 64-row MDCT. We retrospectively evaluated 20 consecutive patients who underwent both 64-row MDCT and two-dimensional transthoracic echocardiography (2D-TTE) after aortic valve replacement. The presence of APR was evaluated with 64-row MDCT, and validated with 2D-TTE, two-dimensional transesophageal echocardiography (2D-TEE), or intraoperative findings if available. If APR was present, we also evaluated paraprosthetic anatomical regurgitation orifice (PARO) area to quantify the prognostic impact of APR or for surgical planning such as closure device sizing. Overall, 12 of 20 valves showed beam-hardening artifact (BHA) which made the reliable evaluation of APR difficult. The presence of artifact seemed to depend on valve types. Among 8 patients who did not show BHA, there were perfect agreements between MDCT and 2D-TTE, 2D-TEE, or intra-operative findings about APR. There were excellent inter-observer agreements in the evaluation of APR and PARO area. PARO area was consistent with the echocardiographic severity of APR in this study. Our retrospective data suggest that MDCT could be a reliable technique for the evaluation of APR after On-X standard or St. Jude Medical (SJM) standard valve replacement. MDCT can become a novel quantitative tool for the evaluation of PARO area. (author)
[en] The optical properties of polyvinylpyrrolidone (PVP)-adsorbed and silica-coated Y2O3:Er,Yb nanoparticles produced by using PVP were studied for potential bio-applications of upconversion nanoparticles. We utilized PVP to better disperse Y2O3:Er,Yb nanoparticles in solution and to prepare silica-coated Y2O3:Er,Yb nanoparticles. The fluorescent intensity of PVP-adsorbed Y2O3:Er,Yb nanoparticles was 1.25 times higher than non-adsorbed Y2O3:Er,Yb nanoparticles, which was probably due to surface defects in Y2O3:Er,Yb nanoparticles being covered by the PVP. However, the fluorescent intensity of silica-coated Y2O3:Er,Yb nanoparticles decreased as silica layer thickness increased. This could be ascribed to the higher vibrational energy of PVP than that of the silica structure. Therefore, the optimum silica layer thickness is important in bio-applications to avoid deterioration of the optical properties of Y2O3:Er,Yb nanoparticles. - Highlights: • We prepared the silica-coated upconversion nanoparticles by using PVP. • We showed that PVP played an important role in coating nanoparticles. • PL intensity of silica-coated nanoparticles decreased as silica layer thickness increased
[en] Epitaxial growth of an organic ultrathin film has been confirmed for the first time by reflection high-energy electron diffraction (RHEED) during film growth. Copper phthalocyanine(CuPc) films were grown heteroepitaxially on a cleaved face of MoS2, under high vacuum of ca.4x10-9 torr by a newly developed organic molecular beam epitaxy technique. The RHEED pattern revealed that epitaxially grown CuPc has its own lattice constant, which is completely different from that of MoS2 even at the initial deposition stage. (author)
[en] Tip-enhanced Raman scattering microscopy, a family of scanning probe microscopy techniques, has been recognized as a powerful surface analytical technique with both single-molecule sensitivity and angstrom-scale spatial resolution. This review covers the current status of tip-enhanced Raman scattering microscopy in surface and material nanosciences, including a brief history, the basic principles, and applications for the nanoscale characterization of a variety of nanomaterials. The focus is on the recent trend of combining tip-enhanced Raman scattering microscopy with various external stimuli such as pressure, voltage, light, and temperature, which enables the local control of the molecular properties and functions and also enables chemical reactions to be induced on a nanometer scale. (author)
[en] Hybrid interface structures consisting of organic copper-phthalocyanine (CuPc) and ferromagnetic metal Fe(001) with and without a MgO(001) cover were investigated by using surface sensitive techniques of X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. A systematic study of the energy level alignment at the interfaces was carried out. For the hybrid interfaces considered here, our results indicate that the insertion of an artificially-grown ultra-thin oxide layer MgO(001) can prevent Femi level pinning and induce a rather large interface dipole, thereby resulting in remarkable CuPc Fermi level shifts when the thickness of the CuPc film is less than 3 nm. This study provides a better understanding of spin filtering in MgO-based organic spin devices and a new way to alter the interface electronic structure of metal/organic semiconductor hybrid systems.
[en] Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 x 2√3) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and π-conjugated TP ring in the SAMs were calculated to be about 30 .deg. and 40 .deg. , respectively, from the surface normal. It was also observed that the π* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between π-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated
[en] The formation and structure of self-assembled monolayers (SAMs) by the adsorption of acetyl-protected octylthioacetate (OTA) on Au(111) in a catalytic tetrabutylammonium cyanide (TBACN) solution were examined by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Molecular-scale STM imaging revealed that OTA molecules on Au(111) in a pure solvent form disordered SAMs, whereas they form well-ordered SAMs showing a c(4 x 2) structure in a catalytic TBACN solution. XPS and CV measurements also revealed that OTA SAMs on Au(111) formed in a TBACN solution have a stronger chemisorbed peak in the S 2p region at 162 eV and a higher blocking effect compared to OTA SAMs formed in a pure solvent. In this study, we clearly demonstrate that TBACN can be used as an effective deprotecting reagent for obtaining well-ordered SAMs of thioacetyl-protected molecules on gold
[en] The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at 50 .deg. C formed well-ordered SAMs with a (2√3 x √5)R41".deg. packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments (C_5H_9 "+, m/e = 69) generated via C-S bond cleavage and the parent molecular species (C_5H_9SH"+, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs
[en] Highlights: ► We prepared a Y2O3:Er,Yb nanoparticles by laser ablation in liquid. ► The particle size increased with the increasing energy density of the laser. ► At low energy density, dot-like nanoparticles were observed. At high energy density, worm-like nanoparticles were observed. ► In the photoluminescence spectra, green and red fluorescence were observed using a 980 nm laser diode as the excitation source. ► The fluorescence intensity increased with increasing energy density of the laser. - Abstract: We prepared a Y2O3:Er,Yb nanoparticles by laser ablation in liquid. The laser used the second harmonic generation Nd:YAG (532 nm). A preparation process and measurement of upconversion properties were performed by varying the range of the energy density of the laser. Images from scanning electron microscopy (SEM) indicated that two types of nanoparticles existed in the product of laser ablation in liquid. We concluded the following: one type of nanoparticles was prepared from the nucleation of materials in a plume and the other was prepared by fragmentation. In the photoluminescence spectra, green (2H11/2, 4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) fluorescence were observed using a 980 nm laser diode (LD) as the excitation source. We confirmed that the fluorescence intensity increased with increasing energy density of the laser. Thus, we concluded that the number of the nanoparticles increased as the energy density of the laser was increased.