One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the d...
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One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the dielectric interface. Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered single-crystalline mono- to tetralayer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to bandlike in subsequent layers. Such an abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ∼3 nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals.
A stibarsen [derived from Latin stibium (antimony) and arsenic] or allemontite, is a natural form of arsenic antimonide (SbAs) with the same layered structure as arsenic and antimony. Thus, exploring the two-dimension...
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A stibarsen [derived from Latin stibium (antimony) and arsenic] or allemontite, is a natural form of arsenic antimonide (SbAs) with the same layered structure as arsenic and antimony. Thus, exploring the two-dimensional SbAs nanosheets is of great importance to gain insights into the properties of group V-V compounds at the atomic scale. Here, we propose a class of two-dimensional V-V honeycomb binary compounds, SbAs monolayers, which can be tuned from semiconductor to topological insulator. By ab initio density functional theory, both α-SbAs and γ-SbAs display a significant direct band gap, while others are indirect semiconductors. Interestingly, in an atomically thin β-SbAs polymorph, spin-orbital coupling is significant, which reduces its band gap by 200 meV. Especially under biaxial tensile strain, the gap of β-SbAs can be closed and reopened with concomitant change of band shapes, which is reminiscent of band inversion known in many topological insulators. In addition, we find that the Z2 topological invariant is 1 for β-SbAs under the tensile strain of 12%, and the nontrivial topological feature of β-SbAs is also confirmed by the gapless edge states which cross linearly at the Γ point. These ultrathin group-V-V semiconductors with outstanding properties are highly favorable for applications in alternative optoelectronic and quantum spin Hall devices.
Diamond coatings were prepared on alumina by hot filament chemical vapor deposition, which constituted an insulator used in a laser pump. The composition and morphologies of the diamond coatings were characterized by ...
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We report an angle-resolved photoemission spectroscopy study of a ThCr2Si2-type superconductor YFe2Ge2 (Tc≈1.8 K) in the normal state. The resolved low-energy band structure mainly consists of several flat Fe bands, ...
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We report an angle-resolved photoemission spectroscopy study of a ThCr2Si2-type superconductor YFe2Ge2 (Tc≈1.8 K) in the normal state. The resolved low-energy band structure mainly consists of several flat Fe bands, while the renormalization factors of different bands range from 1.7 to 2.8. Around the Fermi level, these bands contribute to a high density of states, which may account for the unusually high Sommerfeld coefficient γ. Besides, a 30 meV kink is observed, which is probably induced by electron-phonon interactions. Our results indicate that YFe2Ge2 is a moderately correlated compound, while electron-phonon coupling should be taken into account to better understand its properties.
We demonstrate a high-repetition-rate, high-peak-power diode-pumped passively Qswitched ceramic Nd:YAG quasi-three-level laser at 946 nm. The maximum peak power reaches 12.4 kW with a pulse width of 13.0 ns at 3.3 kHz...
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Yttrium silicate(YSiO)coating was fabricated on C/SiC composites through dip-coating route for the sake of improving oxidation resistance of the ***"silicone resin+Y2O3 powder"slurry with ethanol as solvent ...
Yttrium silicate(YSiO)coating was fabricated on C/SiC composites through dip-coating route for the sake of improving oxidation resistance of the ***"silicone resin+Y2O3 powder"slurry with ethanol as solvent was used to synthesize *** synthesis of YSiO phase and the microstructure and oxidation resistance of coating were investigated,and the anti-oxidation mechanism was discussed.
The thermal stability of carbon fiber in PIP-processed C/SiC composites under high temperature envir onment was studied. The microstructure evolution of carbon fiber in PIP-C/SiC composites was characterized. T he res...
The thermal stability of carbon fiber in PIP-processed C/SiC composites under high temperature envir onment was studied. The microstructure evolution of carbon fiber in PIP-C/SiC composites was characterized. T he results showed that the microstructure of carbon fiber gradually destroyed with the elevation of annealing tem perature. When the annealing temperature reached 1800 ℃,the integrity of carbon fiber was destroyed,which corresponding to the descend of mechanical properties. Further study on the mechanisms of c arbon fiber is needed and is in progress.
To satisfy consumers' requirement of less smoke, vegetable oils should possess certain thermal stability, which was evaluated by smoke point and dependent on the content of the minor compounds. As the proposal of ...
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