52 research outputs found
RoomâTemperature Transport Properties of Graphene with Defects Derived from OxoâGraphene
In recent years, graphene oxide has been considered as a soluble precursor of graphene for electronic applications. However, the performance lags behind that of graphene due to lattice defects. Here, the relation between the density of defects in the range of 0.2â% and 1.5â% and the transport properties is quantitatively studied. Therefore, the related flakes of monolayers of graphene were prepared from oxoâfunctionalized graphene (oxoâG). The morphologic structure of oxoâG was imaged by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Fieldâeffect mobility values were determined to range between 0.3â
cm2âVâ1âsâ1 and 33.2â
cm2âVâ1âsâ1, which were inversely proportional to the density of defects. These results provide the first quantitative description of the density of defects and transport properties, which plays an important role for potential applications
A Study on High-Speed Rail Pricing Strategy in the Context of Modes Competition
High-speed rail (HSR) has developed rapidly in China over the recent years, for the less pollution, faster speed, comfort, and safety. However, there is still an issue on how to improve the seat occupancy rates for some HSR lines. This research analyzes the pricing strategy for HSR in Wuhan-Guangzhou corridor based on the competition among different transport modes with the aim of improving occupancy rates. It starts with the theoretical analysis of relationship between market share and ticket fare, and then disaggregate choice models with nested structure based on stated preference (SP) data are established to obtain the market share of HSR under specific ticket fare. Finally, a pricing strategy is proposed to improve the occupancy rates for Wuhan-Guangzhou HSR. The results confirm that a pricing strategy with floating fare should be accepted to improve the profit of HSR; to be specific, the ticket fare should be set in lower level on weekdays and higher level on holidays
Nanoscale Investigation of Defects and Oxidation of HfSe<sub>2</sub>
HfSe2 is a very good candidate for a transition metal dichalcogenide-based field-effect transistor owing to its moderate band gap of about 1 eV and its high-Îș dielectric native oxide. Unfortunately, the experimentally determined charge carrier mobility is about 3 orders of magnitude lower than the theoretically predicted value. This strong deviation calls for a detailed investigation of the physical and electronic properties of HfSe2. Here, we have studied the structure, density, and density of states of several types of defects that are abundant on the HfSe2 surface using scanning tunneling microscopy and spectroscopy. Compared to MoS2 and WSe2, HfSe2 exhibits similar type of defects, albeit with a substantially higher density of 9 Ă 1011 cm-2. The most abundant defect is a subsurface defect, which shows up as a dim feature in scanning tunneling microscopy images. These dim dark defects have a substantially larger band gap (1.25 eV) than the pristine surface (1 eV), suggesting a substitution of the Hf atom by another atom. The high density of defects on the HfSe2 surface leads to very low Schottky barrier heights. Conductive atomic force microscopy measurements reveal a very small dependence of the Schottky barrier height on the work function of the metals, suggesting a strong Fermi-level pinning. We attribute the observed Fermi-level pinning (pinning factor âŒ0.1) to surface distortions and Se/Hf defects. In addition, we have also studied the HfSe2 surface after the exposure to air by scanning tunneling microscopy and conductive atomic force microscopy. Partly oxidized layers with band gaps of 2 eV and Schottky barrier heights of âŒ0.6 eV were readily found on the surface. Our experiments reveal that HfSe2 is very air-sensitive, implying that capping or encapsulating of HfSe2, in order to protect it against oxidation, is a necessity for technological applications
Kinkless electronic junction along one dimensional electronic channel
Here we report the formation of type-A and type-B electronic junctions
without any structural discontinuity along a well-defined 1-nm-wide
one-dimensional electronic channel within a van der Waals layer. We employ
scanning tunneling microscopy and spectroscopy techniques to investigate the
atomic and electronic structure along peculiar domain walls formed on the
charge-density-wave phase of 1T-TaS2. We find distinct kinds of abrupt
electronic junctions with discontinuities of the band gap along the domain
walls, which do not have any structural kinks and defects. Our
density-functional calculations reveal a novel mechanism of the electronic
junction formation; they are formed by a kinked domain wall in the layer
underneath through substantial electronic interlayer coupling. This work
demonstrates that the interlayer electronic coupling can be an effective
control knob over several-nanometer-scale electronic property of
two-dimensional atomic monolayers
Robust Luttinger liquid state of 1D Dirac fermions in a van der Waals system NbSiTe
We report on the Tomonaga-Luttinger liquid (TLL) behavior in fully degenerate
1D Dirac fermions. A ternary van der Waals material NbSiTe
incorporates in-plane NbTe chains, which produce a 1D Dirac band crossing
Fermi energy. Tunneling conductance of electrons confined within NbTe2 chains
is found to be substantially suppressed at Fermi energy, which follows a power
law with a universal temperature scaling, hallmarking a TLL state. The obtained
Luttinger parameter of ~0.15 indicates strong electron-electron interaction.
The TLL behavior is found to be robust against atomic-scale defects, which
might be related to the Dirac electron nature. These findings, as combined with
the tunability of the compound and the merit of a van der Waals material, offer
a robust, tunable, and integrable platform to exploit non-Fermi liquid physics
Spatially resolved electronic structure of twisted graphene
We have used scanning tunneling microscopy and spectroscopy to resolve the
spatial variation of the density of states of twisted graphene layers on top of
a highly oriented pyrolytic graphite substrate. Owing to the twist a moire
pattern develops with a periodicity that is substantially larger than the
periodicity of a single layer graphene. The twisted graphene layer has
electronic properties that are distinctly different from that of a single layer
graphene due to the nonzero interlayer coupling. For small twist angles (about
1-3.5 degree) the integrated differential conductivity spectrum exhibits two
well-defined Van Hove singularities. Spatial maps of the differential
conductivity that are recorded at energies near the Fermi level exhibit a
honeycomb structure that is comprised of two inequivalent hexagonal
sub-lattices. For energies |E-E_F|>0.3 eV the hexagonal structure in the
differential conductivity maps vanishes. We have performed tight-binding
calculations of the twisted graphene system using the propagation method, in
which a third graphene layer is added to mimic the substrate. This third layer
lowers the symmetry and explains the development of the two hexagonal
sub-lattices in the moire pattern. Our experimental results are in excellent
agreement with the tight-binding calculations.Comment: To appear in Phys. Rev.
Identification of semiconductive patches in thermally processed monolayer oxoâfunctionalized graphene
The thermal decomposition of graphene oxide (GO) is a complex process at the atomic level and not fully understood. Here, a subclass of GO, oxoâfunctionalized graphene (oxoâG), was used to study its thermal disproportionation. We present the impact of annealing on the electronic properties of a monolayer oxoâG flake and correlated the chemical composition and topography corrugation by twoâprobe transport measurements, XPS, TEM, FTIR and STM. Surprisingly, we found that oxoâG, processed at 300â°C, displays CâC sp3âpatches and possibly CâOâC bonds, next to graphene domains and holes. It is striking that those CâOâC/CâC sp3âseparated sp2âpatches a few nanometers in diameter possess semiconducting properties with a band gap of about 0.4â
eV. We propose that sp3âpatches confine conjugated sp2âC atoms, which leads to the local semiconductor properties. Accordingly, graphene with sp3âC in double layer areas is a potential class of semiconductors and a potential target for future chemical modifications
Identifizierung von halbleitenden Bereichen in thermisch behandeltem monolagigem Oxo-funktionalisiertem Graphen
Human CIK Cells Loaded with Au Nanorods as a Theranostic Platform for Targeted Photoacoustic Imaging and Enhanced Immunotherapy and Photothermal Therapy
How to realize targeted photoacoustic imaging, enhanced immunotherapy, and photothermal therapy of gastric cancer has become a great challenge. Herein, we reported for the first time that human cytokine-induced killer cells (CIK) loaded with gold nanorods were used for targeted photoacoustic imaging, enhanced immunotherapy, and photothermal therapy of gastric cancer. Silica-modified gold nanorods were prepared; then incubated with human cytokine-induced killer cells (CIK), resultant human CIK cells loaded with Au nanorods were evaluated for their cytotoxicity, targeted ability of gastric cancer in vitro and in vivo, immunotherapy, and photothermal therapy efficacy. In vitro cell experiment shows that human CIK cells labeled with gold nanorods actively target gastric cancer MGC803 cells, inhibit growth of MGC803 cells by inducing cell apoptosis, and kill MGC803 cells under low power density near-infrared (NIR) laser treatment (808-nm continuous wave laser, 1.5 W/cm2, 3 min). In vivo experiment results showed that human CIK cells labeled with gold nanorods could target actively and image subcutaneous gastric cancer vessels via photoacoustic imaging at 4 h post-injection, could enhance immunotherapy efficacy by up-regulating cytokines such as IL-1, IL-12, IL-2, IL-4, IL-17, and IFN-Îł, and kill gastric cancer tissues by photothermal therapy via direct injection into tumor site under near-infrared (NIR) laser irradiation. High-performance human CIK cells labeled with Au nanorods are a good novel theranostic platform to exhibit great potential in applications such as tumor-targeted photoacoustic imaging, enhanced immunotherapy, and photothermal therapy in the near future
- âŠ