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Tailoring Physical Properties of Carbon Nanotube Threads During Assembly
摘要： Spinnable carbon nanotubes (CNTs) are useful formats for studying physical properties of CNT fiber assemblies in their pristine states. They are free of catalyst, uniform in length, with a comparatively narrow diameter distribution, and their assembly into thread does not require additional chemicals or solvents. Good quality drawable CNT arrays can be readily assembled into uniform diameter threads with great control over the number of CNTs incorporated into the thread assembly. This uniformity allows study the physical properties that result from changes that occur during thread formation. Here, we report trends of electrical resistivity and mechanical strength that resulted from alterations in their manufacturing parameters, allowing to change intrinsic physical properties of a material such as electrical resistivity. We correlate the electrical resistivity and mechanical strength as a function of diameter, density, and turns/meter. Understanding the effects of dry-spinning parameters will allow a better design of the physical properties of CNT threads for specific applications, such as strain or electrochemical sensors.
关键词： resistivity,threads,and twist angle.,fibers,yarns,Carbon nanotubes,diameter control
更新于2025-09-10 09:29:36
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Raman Spectroscopy of Folded Tetralayer Graphenes Prepared by Atomic Force Microscope
摘要： In this work, we report that when a modulated force is applied to the edge of a bilayer graphene with an atomic force microscope (AFM), two kinds of folded tetralayer graphenes can be obtained: one has one rupture and the other has two ruptures. The twist angle between two bilayer graphenes is found to be in the range of 1.8°～27.7°. Systematic Raman studies show that the position, width, and intensity of 2D and G peaks of the folded tetralayer graphene depend sensitively on these angles. Meanwhile, the intensity enhancement of G mode of twisted tetralayer graphenes has been observed at twist angles of 11.5° and 13.2°. At these two twist angles, the 2D peak of twisted tetralayer graphenes can be fitted by three Lorentzian peaks at laser energy of 2.33 and 2.41 eV. Using an AFM probe to fabricate twisted graphene has the advantages of high yield, controllable positions, and no introduction of chemical pollutants, which has many potentials in future electronics.
关键词： twist angle,atomic force microscope,folded tetralayer graphenes,Raman spectroscopy,2D and G peaks
更新于2025-09-10 09:29:36
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Strain-engineering of twist-angle in graphene/hBN superlattice devices
摘要： The observation of novel physical phenomena such as Hofstadter’s butterfly, topological currents and unconventional superconductivity in graphene have been enabled by the replacement of SiO2 with hexagonal Boron Nitride (hBN) as a substrate and by the ability to form superlattices in graphene/hBN heterostructures. These devices are commonly made by etching the graphene into a Hall-bar shape with metal contacts. The deposition of metal electrodes, the design and specific configuration of contacts can have profound effects on the electronic properties of the devices possibly even affecting the alignment of graphene/hBN superlattices. In this work we probe the strain configuration of graphene on hBN contacted with two types of metal contacts, two-dimensional (2D) top-contacts and one-dimensional (1D) edge-contacts. We show that top-contacts induce strain in the graphene layer along two opposing leads, leading to a complex strain pattern across the device channel. Edge-contacts, on the contrary, do not show such strain pattern. A finite-elements modelling simulation is used to confirm that the observed strain pattern is generated by the mechanical action of the metal contacts clamped to the graphene. Thermal annealing is shown to reduce the overall doping whilst increasing the overall strain, indicating and increased interaction between graphene and hBN. Surprisingly, we find that the two contacts configurations lead to different twist-angles in graphene/hBN superlattices, which converge to the same value after thermal annealing. This observation confirms the self-locking mechanism of graphene/hBN superlattices also in the presence of strain gradients. Our experiments may have profound implications in the development of future electronic devices based on heterostructures and provide a new mechanism to induce complex strain patterns in 2D materials.
关键词： Raman,hBN,Graphene,twist-angle,superlattice,strain
更新于2025-09-09 09:28:46
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Twist-angle Dependent Optoelectronics in a few-layer Transition-Metal Dichalcogenides Heterostructure
摘要： Lattice matching has been supposed to play an important role in the coupling between two materials in vertical heterostructure (HS). To investigate this role, we fabricated a heterojunction device with a few layers of p-type WSe2 and n-type MoSe2 with different crystal orientation angles. The crystal orientations of WSe2 and MoSe2 were estimated by using high-resolution X-ray diffraction. Heterojunction devices were fabricated with twist angles of 0?, 15? and 30?. The I-V curve of the sample with the twist angle of 0° under the dark condition showed a diode-like behavior. The strong coupling due to lattice matching caused a well-established p-n junction. In cases of 15° and 30° samples, the van der Waals gap was built due to lattice mismatching, which resulted in the formation of a potential barrier. However, when the LED light of 365 nm (3.4 eV) was illuminated, excited electrons and holes were possible to jump beyond the potential barrier and the current flowed well in both forward and reverse directions. The effects of the twist angle were analyzed by spectral responsivity and external quantum efficiency, where it was found that the untwisted HS exhibited higher sensitivity under IR illumination while the twisting effect was not noticeable under UV illumination. From the photoluminescence and Raman spectroscopy, it was confirmed that the twisted HS showed a weak coupling due to the lattice mismatch.
关键词： p-n junction,optoelectronics,transition-metal dichalcogenides,heterostructure,a few-layer TMD,twist angle
更新于2025-09-04 15:30:14