Abstract Among quantum devices based on 2D materials, gate-defined quantum confined 1D channels are much less explored, especially in the high-mobility regime where many-body interactions play an important role. We present the results of measurements and theory of conductance quantization in a gate-defined one-dimensional channel in a single layer of transition metal dichalcogenide material WSe 2 . In the quasi-ballistic regime of our high-mobility sample, we report conductance quantization steps in units of e 2 / h for a wide range of carrier concentrations. Magnetic field measurements show that as the field is raised, higher conductance plateaus move to accurate quantized values and then shift to lower conductance values while the e 2 / h plateau remains locked. Based on microscopic atomistic tight-binding theory, we show that in this material, valley and spin degeneracies result in 2 e 2 / h conductance steps for noninteracting holes, suggesting that symmetry-breaking mechanisms such as valley polarization dominate the transport properties of such quantum structures.
The ability to tune the twist angle between different layers of two-dimensional (2D) materials has enabled the creation of electronic flat bands artificially, leading to exotic quantum phases. When a twisted blilayer of graphene (tBLG) is placed at the van der Waals proximity to a semiconducting layer of transition metal dichalcogenide (TMDC), such as WSe<sub>2</sub>, the emergent phases in the tBLG can fundamentally modify the functionality of such heterostructures. Here we have performed photoresponse measurements in few-layer-WSe<sub>2</sub>/tBLG heterostructure, where the mis-orientation angle of the tBLG layer was chosen to lie close to the magic angle of 1.1°. Our experiments show that the photoresponse is extremely sensitive to the band structure of tBLG and gets strongly suppressed when the Fermi energy was placed within the low-energy moiré bands. Photoresponse could however be recovered when Fermi energy exceeded the moiré band edge where it was dominated by the photogating effect due to transfer of charge between the tBLG and the WSe<sub>2</sub> layers. Our observations suggest the possibility of the screening effects from moiré flat bands that strongly affect the charge transfer process at the WSe<sub>2</sub>/tBLG interface, which is further supported by time-resolved photo-resistance measurements.
Abstract A semiconductor/dielectric interface is one of the dominant factors in device characteristics, and a variety of oxides with high dielectric constants and low interface trap densities have been used in carbon nanotube transistors. Given the crystal structure of nanotubes with no dangling bonds, there remains room to investigate unconventional dielectric materials. Here, we fabricate carbon nanotube transistors with boron nitride nanotubes as interfacial layers between channels and gate dielectrics, where a single semiconducting nanotube is used to focus on switching behaviors at the subthreshold regime. The subthreshold swing of 68 mV·dec −1 is obtained despite a 100-nm-thick SiO 2 dielectric, corresponding to the effective interface trap density of 5.2 × 10 11 cm −2 ·eV −1 , one order of magnitude lower than those of carbon nanotube devices without boron nitride passivation. The interfacial layers also result in the mild suppression of threshold voltage variation and hysteresis. We achieve Ohmic contacts through the selective etching of boron nitride nanotubes with XeF 2 gas, overcoming the trade-off imposed by wrapping the inner nanotubes. Negligible impacts of fluorinating carbon nanotubes on device performances are also confirmed as long as the etching is applied exclusively at source/drain regions. Our results represent an important step toward nanoelectronics that exploit the advantage of one-dimensional van der Waals heterostructures.
Ambipolar dual-gate transistors based on low-dimensional materials, such as graphene, carbon nanotubes, black phosphorus, and certain transition metal dichalcogenides (TMDs), enable reconfigurable logic circuits with a suppressed off-state current. These circuits achieve the same logical output as complementary metal–oxide semiconductor (CMOS) with fewer transistors and offer greater flexibility in design. The primary challenge lies in the cascadability and power consumption of these logic gates with static CMOS-like connections. In this article, high-performance ambipolar dual-gate transistors based on tungsten diselenide (WSe2) are fabricated. A high on–off ratio of 108 and 106, a low off-state current of 100 to 300 fA, a negligible hysteresis, and an ideal subthreshold swing of 62 and 63 mV/dec are measured in the p- and n-type transport, respectively. We demonstrate cascadable and cascaded logic gates using ambipolar TMD transistors with minimal static power consumption, including inverters, XOR, NAND, NOR, and buffers made by cascaded inverters. A thorough study of both the control gate and the polarity gate behavior is conducted. The noise margin of the logic gates is measured and analyzed. The large noise margin enables the implementation of VT-drop circuits, a type of logic with reduced transistor number and simplified circuit design. Finally, the speed performance of the VT-drop and other circuits built by dual-gate devices is qualitatively analyzed. This work makes advancements in the field of ambipolar dual-gate TMD transistors, showing their potential for low-power, high-speed, and more flexible logic circuits.
Read moreAlkyne polymerizations are effected by tungsten- and tantalum-based catalysts, giving linear polyacetylenes(LPAs)and hyperbranched polyarylenes(HPAs)of high molecular weights(Mwup to 2.5 × 105)in high yields(up to 93%). All the LPAs and HPAs are thermally stable and completely soluble in common solvents such as THF, toluene, dichloromethane, and chloroform. Incorporation of biphenyl mesogenic pendants into poly(1-phenyl-1-hexyne)structure endows the LCPA with nematicity. Upon photoexcitation, the LPAs and HPAs emit strong UV and blue lights with high quantum yields(up to 94%). Multilayer electroluminescence devices of LPAs emit blue light with maximum luminance and external quantum efficiency of 1065 cd/m2and 0.86%, respectively. The HPAs attenuate strong laser pulses, with optical limiting performances comparable to that of C60, a well-known optical limiter.
Read moreFluorescence correlation spectroscopy (FCS) was used to study the nano-clusters of silole molecules formed by aggregation from solutions in acetone-water mixtures. It allowed the determination of the size of clusters in nanometer scale. Aggregate formation was investigated systematically by measuring the cluster sizes made at different silole concentrations and water contents.
Read moreSliding ferroelectricity in 2D materials, arising from interlayer sliding-induced interlayer hybridization and charge redistribution at the van der Waals interface, offers a means to manipulate spontaneous polarization at the atomic scale through various methods such as stacking order, interfacial contact, and electric field. However, the practical application of extending 2D sliding ferroelectricity remains challenging due to the contentious mechanisms and the complex device structures required for ferroelectric switching. Here, a sliding memristor based on a graphene/parallel-stacked hexagonal boron nitride/graphene tunneling device, featuring a stable memristive hysteresis induced by interfacial polarizations and barrier height modulations, is presented. As the tunneling current density increases, the memristive window broadens, achieving an on/off ratio of ≈10<sup>3</sup> and 2 order decrease of the trigger current density, attributed to the interlayer migration of positively charged boron ions and the formation of conductive filaments, as supported by the theoretical calculations. The findings open a path for exploring the sliding memristor via a tunneling device and bridge the gap between sliding ferroelectricity and memory applications.
Read moreTwo-dimensional (2D) materials have attracted attention for quantum information science due to their ability to host single-photon emitters (SPEs). Although the properties of atomically thin materials are highly sensitive to surface modification, chemical functionalization remains unexplored in the design and control of 2D material SPEs. Here, we report a chemomechanical approach to modify SPEs in monolayer WSe<sub>2</sub> through the synergistic combination of localized mechanical strain and noncovalent surface functionalization with aryl diazonium chemistry. Following the deposition of an aryl oligomer adlayer, the spectrally complex defect-related emission of strained monolayer WSe<sub>2</sub> is simplified into spectrally isolated SPEs with high single-photon purity. Density functional theory calculations reveal energetic alignment between WSe<sub>2</sub> defect states and adsorbed aryl oligomer energy levels, thus providing insight into the observed chemomechanically modified quantum emission. By revealing conditions under which chemical functionalization tunes SPEs, this work broadens the parameter space for controlling quantum emission in 2D materials.
Read moreCFC syndrome is a genetically heterogenous condition. Missense mutations have been identified in BRAF, KRAS, MEK1 and MEK2. We have reported here a KRAS mutation in a baby girl with an early clinical diagnosis of CFC syndrome associated with a large ulcerating hemangioma. Although ectodermal abnormalities have been described in all individuals with this condition, features such as ichthyosis and hemangioma have been previously found only in those patients carrying a mutation in BRAF, and not in KRAS. The findings we have described contrast with these observations. The relatively high frequency of hemangiomas in CFC syndrome suggests that defects in the expression of the MAPK pathway may alter endothelial cell proliferation. Increased understanding of how the molecular pathways with which defects in CFC syndrome predispose affected individuals to hemangiomas might offer insights into the pathogenesis of this common childhood tumour in the general population.
Read moreThe risk of HIV infection does not increase linearly with the number of sexual partners in this population. This is reasonable, as the prevalence of HIV infection in this population is essentially determined by drug use. Caution is needed in the interpretation of these results since the analysis of role of number of sexual partners in male intravenous drug users is impaired by low statistical power.
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