261 research outputs found
Electron Scattering in Intrananotube Quantum Dots
Intratube quantum dots showing particle-in-a-box-like states with level
spacings up to 200meV are realized in metallic single-walled carbon nanotubes
by means of low dose medium energy Ar irradiation. Fourier transform scanning
tunneling spectroscopy compared to results of a Fabry-Perot electron resonator
model yields clear signatures for inter- and intra-valley scattering of
electrons confined between consecutive irradiation-induced defects
(inter-defects distance < 10nm). Effects arising from lifting the degeneracy of
the Dirac cones within the first Brillouin zone are also observed
Indication of Superconductivity at 35 K in Graphite-Sulfur Composites
We report magnetization measurements performed on graphite--sulfur composites
which demonstrate a clear superconducting behavior below the critical
temperature T = 35 K. The Meissner-Ochsenfeld effect, screening
supercurrents, and magnetization hysteresis loops characteristic of type-II
superconductors were measured. The results indicate that the superconductivity
occurs in a small sample fraction, possibly related to the sample surface.Comment: published versio
Electron Wave Function in Armchair Graphene Nanoribbons
By using analytical solution of a tight-binding model for armchair
nanoribbons, it is confirmed that the solution represents the standing wave
formed by intervalley scattering and that pseudospin is invariant under the
scattering. The phase space of armchair nanoribbon which includes a single
Dirac singularity is specified. By examining the effects of boundary
perturbations on the wave function, we suggest that the existance of a strong
boundary potential is inconsistent with the observation in a recent scanning
tunneling microscopy. Some of the possible electron-density superstructure
patterns near a step armchair edge located on top of graphite are presented. It
is demonstrated that a selection rule for the G band in Raman spectroscopy can
be most easily reproduced with the analytical solution.Comment: 7 pages, 4 figure
Chiral Biphenyldicarboxylic Acid Networks Stabilized by Hydrogen Bonding
The self-assembly of 4,4′-biphenyldicarboxylic acid on a Au(111) surface is investigated by means of in situ ultra-high-vacuum scanning tunneling microscopy. Three types of open networks with increasing interpore distance are observed. Experiments and theoretical calculations reveal that the two-dimensional porous networks are stabilized by various types of hydrogen bonds between carboxyl groups and by van der Waals interactions. Cyclic tetrameric and half-cyclic trimeric hydrogen-bonding motifs are shown to induce chirality in the open networks
Tunable quantum dots from atomically precise graphene nanoribbons using a multi-gate architecture
Atomically precise graphene nanoribbons (GNRs) are increasingly attracting
interest due to their largely modifiable electronic properties, which can be
tailored by controlling their width and edge structure during chemical
synthesis. In recent years, the exploitation of GNR properties for electronic
devices has focused on GNR integration into field-effect-transistor (FET)
geometries. However, such FET devices have limited electrostatic tunability due
to the presence of a single gate. Here, we report on the device integration of
9-atom wide armchair graphene nanoribbons (9-AGNRs) into a multi-gate FET
geometry, consisting of an ultra-narrow finger gate and two side gates. We use
high-resolution electron-beam lithography (EBL) for defining finger gates as
narrow as 12 nm and combine them with graphene electrodes for contacting the
GNRs. Low-temperature transport spectroscopy measurements reveal quantum dot
(QD) behavior with rich Coulomb diamond patterns, suggesting that the GNRs form
QDs that are connected both in series and in parallel. Moreover, we show that
the additional gates enable differential tuning of the QDs in the nanojunction,
providing the first step towards multi-gate control of GNR-based multi-dot
systems
Tunable Quantum Dots from Atomically Precise Graphene Nanoribbons Using a Multi‐Gate Architecture
Atomically precise graphene nanoribbons (GNRs) are increasingly attracting interest due to their largely modifiable electronic properties, which can be tailored by controlling their width and edge structure during chemical synthesis. In recent years, the exploitation of GNR properties for electronic devices has focused on GNR integration into field-effect-transistor (FET) geometries. However, such FET devices have limited electrostatic tunability due to the presence of a single gate. Here, on the device integration of 9-atom wide armchair graphene nanoribbons (9-AGNRs) into a multi-gate FET geometry, consisting of an ultra-narrow finger gate and two side gates is reported. High-resolution electron-beam lithography (EBL) is used for defining finger gates as narrow as 12 nm and combine them with graphene electrodes for contacting the GNRs. Low-temperature transport spectroscopy measurements reveal quantum dot (QD) behavior with rich Coulomb diamond patterns, suggesting that the GNRs form QDs that are connected both in series and in parallel. Moreover, it is shown that the additional gates enable differential tuning of the QDs in the nanojunction, providing the first step toward multi-gate control of GNR-based multi-dot systems
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
Self-reported smoking cessation activities among Swiss primary care physicians
ABSTRACT: BACKGROUND: Individual counselling, pharmacotherapy, and group therapy are evidence-based interventions that help patients stop smoking. Acupuncture, hypnosis, and relaxation have no demonstrated efficacy on smoking cessation, whereas self-help material may only have a small benefit. The purpose of this study is to assess physicians' current clinical practice regarding smokers motivated to stop smoking. METHODS: The survey included 3385 Swiss primary care physicians. Self-reported use of nine smoking cessation interventions was scored. One point was given for each positive answer about practicing interventions with demonstrated efficacy, i.e. nicotine replacement therapy, bupropion, counselling, group therapy, and smoking cessation specialist. No points were given for the recommendation of acupuncture, hypnosis, relaxation, and self-help material. Multivariable logistic analysis was performed to identify factors associated with a good practice score, defined as >1. RESULTS: The response rate was 55%. Respondents were predominately over the age of 40 years (88%), male (79%), and resided in urban areas (74%). Seventeen percent reported being smokers. Most of the physicians prescribed nicotine replacement therapy (84%), bupropion (65%), or provided counselling (70%). A minority of physicians recommended acupuncture (26%), hypnosis (8%), relaxation (7%), or self-help material (24%). A good practice score was obtained by 85% of respondents. Having attended a smoking cessation training program was the only significant predictor of a good practice score (odds ratio: 6.24 , 95% CI 1.95-20.04). CONCLUSION: The majority of respondents practice recommended smoking cessation interventions. However, there is room for improvement and implementing an evidence-based smoking cessation-training program could provide additional benefit
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