排序方式: 共有72条查询结果,搜索用时 31 毫秒
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H. Weisen F. Hofmann M. J. Dutch J. -M. Moret J. B. Lister A. Pochelon R. A. Pitts M. Anton R. Behn S. Bernel F. Bühlmann R. Chavan B. P. Duval D. Fasel A. Favre S. Franke A. Heym Ch. Hollenstein P. Isoz B. Joye X. Llobet B. Marletaz Ph. Marmillod Y. Martin Ch. Nieswand P. J. Paris A. Perez Z. A. Pietrzyk O. Sauter W. Van Toledo G. Tonetti M. Q. Tran F. Troyon D. J. Ward 《Czechoslovak Journal of Physics》1995,45(12):1095-1110
During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B
tor1.46T,I
p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors (
tor
aB/I
p) up to two and densities up to 2.25×1020m–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×1020m–3 have been obtained in elongated D-shaped plasmas with 360 kAI
P600 kA.Presented at 17th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique. 相似文献
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M. R. Ajayakumar Marco Di Giovannantonio Carlo A. Pignedoli Lin Yang Pascal Ruffieux Ji Ma Roman Fasel Xinliang Feng 《Journal of polymer science. Part A, Polymer chemistry》2022,60(12):1912-1917
The precise introduction of nonplanar pores in the backbone of graphene nanoribbon represents a great challenge. Here, we explore a synthetic strategy toward the preparation of nonplanar porous graphene nanoribbon from a predesigned dibromohexabenzotetracene monomer bearing four cove-edges. Successive thermal annealing steps of the monomers indicate that the dehalogenative aryl-aryl homocoupling yields a twisted polymer precursor on a gold surface and the subsequent cyclodehydrogenation leads to a defective porous graphene nanoribbon containing nonplanar [14]annulene pores and five-membered rings as characterized by scanning tunneling microscopy and noncontact atomic force microscopy. Although the C–C bonds producing [14]annulene pores are not achieved with high yield, our results provide new synthetic perspectives for the on-surface growth of nonplanar porous graphene nanoribbons. 相似文献
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Dr. José I. Urgel Dr. Marco Di Giovannantonio Kristjan Eimre Thorsten G. Lohr Dr. Junzhi Liu Shantanu Mishra Dr. Qiang Sun Amogh Kinikar Dr. Roland Widmer Samuel Stolz Max Bommert Dr. Reinhard Berger Dr. Pascal Ruffieux Dr. Carlo A. Pignedoli Prof. Dr. Klaus Müllen Prof. Dr. Xinliang Feng Prof. Dr. Roman Fasel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13383-13389
Cumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on-surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well-controlled ultrahigh-vacuum conditions. Here we report the on-surface synthesis of a polymer linked by cumulene-like bonds on a Au(111) surface via sequential thermally activated dehalogenative C−C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene-like pentagon–pentagon and heptagon–heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X-ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on-surface synthesis of cumulene-containing compounds, as well as protocols relevant to the stepwise fabrication of carbon–carbon bonds on surfaces. 相似文献
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Luis M. Mateo Qiang Sun Shi‐Xia Liu Jesse J. Bergkamp Kristjan Eimre Carlo A. Pignedoli Pascal Ruffieux Silvio Decurtins Giovanni Bottari Roman Fasel Tomas Torres 《Angewandte Chemie (International ed. in English)》2020,59(3):1334-1339
On‐surface synthesis offers a versatile approach to prepare novel carbon‐based nanostructures that cannot be obtained by conventional solution chemistry. Graphene nanoribbons (GNRs) have potential for a variety of applications. A key issue for their application in molecular electronics is in the fine‐tuning of their electronic properties through structural modifications, such as heteroatom doping or the incorporation of non‐benzenoid rings. In this context, the covalent fusion of GNRs and porphyrins (Pors) is a highly appealing strategy. Herein we present the selective on‐surface synthesis of a Por–GNR hybrid, which consists of two Pors connected by a short GNR segment. The atomically precise structure of the Por–GNR hybrid has been characterized by bond‐resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc‐AFM). The electronic properties have been investigated by scanning tunneling spectroscopy (STS), in combination with DFT calculations, which reveals a low electronic gap of 0.4 eV. 相似文献
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Shantanu Mishra Doreen Beyer Kristjan Eimre Ricardo Ortiz Joaquín Fernndez‐Rossier Reinhard Berger Oliver Grning Carlo A. Pignedoli Roman Fasel Xinliang Feng Pascal Ruffieux 《Angewandte Chemie (International ed. in English)》2020,59(29):12041-12047
Triangular zigzag nanographenes, such as triangulene and its π‐extended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for high‐spin networks with long‐range magnetic order, which are of immense fundamental and technological relevance. As a first step towards these lines, we present the on‐surface synthesis and a proof‐of‐principle experimental study of magnetism in covalently bonded triangulene dimers. On‐surface reactions of rationally designed precursor molecules on Au(111) lead to the selective formation of triangulene dimers in which the triangulene units are either directly connected through their minority sublattice atoms, or are separated via a 1,4‐phenylene spacer. The chemical structures of the dimers have been characterized by bond‐resolved scanning tunneling microscopy. Scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy measurements reveal collective singlet–triplet spin excitations in the dimers, demonstrating efficient intertriangulene magnetic coupling. 相似文献
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Jos I. Urgel Marco Di Giovannantonio Kristjan Eimre Thorsten G. Lohr Junzhi Liu Shantanu Mishra Qiang Sun Amogh Kinikar Roland Widmer Samuel Stolz Max Bommert Reinhard Berger Pascal Ruffieux Carlo A. Pignedoli Klaus Müllen Xinliang Feng Roman Fasel 《Angewandte Chemie (International ed. in English)》2020,59(32):13281-13287
Cumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on‐surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well‐controlled ultrahigh‐vacuum conditions. Here we report the on‐surface synthesis of a polymer linked by cumulene‐like bonds on a Au(111) surface via sequential thermally activated dehalogenative C?C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene‐like pentagon–pentagon and heptagon–heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X‐ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on‐surface synthesis of cumulene‐containing compounds, as well as protocols relevant to the stepwise fabrication of carbon–carbon bonds on surfaces. 相似文献
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Samuel Stolz Marco Di Giovannantonio Jos I. Urgel Qiang Sun Amogh Kinikar Gabriela Borin Barin Max Bommert Roman Fasel Roland Widmer 《Angewandte Chemie (International ed. in English)》2020,59(33):14106-14110
In the emerging field of on‐surface synthesis, dehalogenative aryl–aryl coupling is unarguably the most prominent tool for the fabrication of covalently bonded carbon‐based nanomaterials. Despite its importance, the reaction kinetics are still poorly understood. Here we present a comprehensive temperature‐programmed x‐ray photoelectron spectroscopy investigation of reaction kinetics and energetics in the prototypical on‐surface dehalogenative polymerization of 4,4′′‐dibromo‐p‐terphenyl into poly(para‐phenylene) on two coinage metal surfaces, Cu(111) and Au(111). We find clear evidence for reversible dehalogenation on Au(111), which is inhibited on Cu(111) owing to the formation of organometallic intermediates. The incorporation of reversible dehalogenation in the reaction rate equations leads to excellent agreement with experimental data and allows extracting the relevant energy barriers. Our findings deepen the mechanistic understanding and call for its reassessment for surface‐confined aryl–aryl coupling on the most frequently used metal substrates. 相似文献
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It has been shown theoretically that a light amplifier working on the physical principle of stimulated emission should achieve optimal quantum cloning of the polarization state of light. We demonstrate close-to-optimal universal quantum cloning of polarization in a standard fiber amplifier for telecom wavelengths. For cloning 1-->2 we find a fidelity of 0.82, the optimal value being 5 / 6=0.83. 相似文献