다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The ultimate aim of any detection method is to achieve such a level of sensitivity that individual quanta of a measured entity can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity1, 2, 3, 4. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects5, which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here, we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

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Detection of individual gas molecules adsorbed on graphene

The surface science of titanium dioxide

The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphenes surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

Detection of Individual Gas Molecules Absorbed on Graphene

[Chen, Zongping; Ren, Wencai; Gao, Libo; Liu, Bilu; Pei, Songfeng; Cheng, Hui-Ming] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition

We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can significantly improve the thickness uniformity. As a result, one- or two- layer graphene regions occupy up to 87% of the film area. Single layer coverage accounts for 5%–11% of the overall film. These regions expand across multiple grain boundaries of the underlying polycrystalline Ni film. The number density of sites with multilayer graphene/graphite (>2 layers) is reduced as the cooling rate decreases. These films can also be transferred to other substrates and their sizes are only limited by the sizes of the Ni film and the CVD chamber. Here, we demonstrate the formation of films as large as 1 in2. These findings represent an important step towards the fabrication of large-scale high-quality graphene samples.

/pdf/growth-of-large-area-single-and-bi-layer-graphene-by-5fpaabm4da.pdf

Growth of large-area single- and Bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces

If the rich functionality of organic molecules is to be exploited in devices such as light-emitting diodes or field-effect transistors1,2,3,4,5,6,7, interface properties of organic materials with various (metallic and insulating) substrates must be tailored carefully7,8,9,10. In many cases, this calls for well-ordered interfaces. Organic epitaxy11,12,13—that is, the growth of molecular films with a commensurate structural relationship to their crystalline substrates—relies on successful recognition of preferred epitaxial sites. For some large π-conjugated molecules (‘molecular platelets’) this works surprisingly well14,15, even if the substrate exhibits no template structure into which the molecules can lock13,15,16. Here we present an explanation for site recognition in non-templated organic epitaxy, and thus resolve a long-standing puzzle11. We propose that this form of site recognition relies on the existence of a local molecular reaction centre in the extended π-electron system of the molecule. Its activity can be controlled by appropriate side groups and—in a certain regime—may also be probed by molecularly sensitized scanning tunnelling microscopy. Our results open the possibility of engineering epitaxial interfaces, as well as other interfacial nanostructures for which specific site recognition is essential.

Understanding and tuning the epitaxy of large aromatic adsorbates by molecular design

A quasianalytical modeling approach for graphene metal-oxide-semiconductor field-effect transistors (MOSFETs) with gapless large-area graphene channels is presented. The model allows the calculation of the I-V characteristics, the small-signal behavior, and the cutoff frequency of graphene MOSFETs. It applies a correct formulation of the density of states in large-area graphene to calculate the carrier-density-dependent quantum capacitance, a steady-state velocity-field characteristics with soft saturation to describe the carrier transport, and takes the source/drain series resistances into account. The modeled drain currents and transconductances show very good agreement with experimental data taken from the literature {Meric et al., [Nat. Nanotechnol. 3, 654 (2008)] and Kedzierski et al., [IEEE Electron Device Lett. 30, 745 (2009)]}. In particular, the model properly reproduces the peculiar saturation behavior of graphene MOSFETs with gapless channels.

Modeling of graphene metal-oxide-semiconductor field-effect transistors with gapless large-area graphene channels

Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device for low (9%) and high (95%) relative humidity for shorter (450 min) and longer (1800 min) time periods. At constant exposure time a characteristic increase of viscosity is observed with increasing humidity. For high humidity, high viscosity is obtained after a short time. Assuming that the measured viscosity change is strongly related to the absorption of oxygen, XPS was applied to the chemical and quantitative analysis of differently prepared samples. In all cases, Ga is predominantly oxidized at the surface whereas Ga atoms in the metallic state are located deeper inside. Besides Ga 2 O 3 (the most stable oxide phase), the less stable Ga 2 O is detected. Indium and tin are almost stable in their metallic state. With increasing humidity the thickness of the oxide film increases in our case from about 19 A to 25 A, assuming a layer-by-layer model. The presented results confirm our assumption of the increase in viscosity of the GaInSn system as a consequence of the preferential oxidation of gallium in the near-surface region.

Viscosity effect on GaInSn studied by XPS

This paper is a summary of a series of experiments studying the exposure of hydrogen, oxygen, and water, on the (2×1) surfaces of Si(100) and Si(111). While the primary focus has been on high resolution electron energy loss (EELS) results, low energy electron diffraction (LEED) and x‐ray photoelectron spectroscopy (XPS) are also used in the studies. Both the (100) and cleavage (111) surfaces form a monohydride and a dihydride exhibiting a (2×1) and a (1×1) LEED pattern, respectively. These systems exhibit saturation, which is consistent with the model of hydrogen saturation of the dangling bonds. Upon water adsorption the Si–H and Si–OH vibronic modes are observed, indicating that water is decomposed. On the cleavage surface only, there is evidence of a very weak scissor mode, allowing for the possibility of a few percent of molecular water adsorption. Oxygen adsorption is complex. For samples formed at high temperatures (∼1000 K) the observed vibronic features are similar to those known for the Si–O–Si c...

Juergen A. Schaefer

Papers

Growth of large-area single- and Bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces

Understanding and tuning the epitaxy of large aromatic adsorbates by molecular design

Modeling of graphene metal-oxide-semiconductor field-effect transistors with gapless large-area graphene channels

Viscosity effect on GaInSn studied by XPS

Adsorption of H, O, and H2O at Si(100) and Si(111) surfaces in the monolayer range: A combined EELS, LEED, and XPS study