Two-dimensional (2D)
layered materials have stimulated extensive
research interest for their unique thickness-dependent electronic
and optical properties. However, the layer-number-dependent studies
on 2D materials to date are largely limited to exfoliated flakes with
relatively small lateral size and poor yield. The direct synthesis
of 2D materials with a precise control of the number of atomic layers
remains a substantial synthetic challenge. Here we report a systematic
study of chemical vapor deposition synthesis of large-area atomically
thin 2D nickel telluride (NiTe2) single crystals and investigate
the thickness dependent electronic properties. By controlling the
growth temperature, we show that the highly uniform NiTe2 single crystals can be synthesized with precisely tunable thickness
varying from 1, 2, 3, . . . to multilayers with a standard deviation
(∼0.3 nm) of less than the thickness of a monolayer layer NiTe2. Our studies further reveal a systematic evolution of single
crystal domain size and nucleation density with the largest lateral
domain size up to ∼440 μm. X-ray diffraction, transmission
electron microscopy, and high resolution scanning transmission electron
microscope studies demonstrate that the resulting 2D crystals are
high quality single crystals and adopt hexagonal 1T phase. Electrical
transport studies reveal that the 2D NiTe2 single crystals
show a strong thickness-tunable electrical properties, with an excellent
conductivity up to 7.8 × 105 S m–1 and extraordinary breakdown current density up to 4.7 × 107 A/cm2. The systematic study and robust synthesis
of NiTe2 nanosheets defines a reliable chemical route to
2D single crystals with precisely tailored thickness and could enable
the design of new device architectures based on thickness-tunable
electrical properties.
We have fabricated and characterized analog and digital circuits using organic thin-film transistors on polyester film substrates. These are the first reported dynamic results for organic circuits fabricated on polyester substrates. The high-performance pentacene transistors yield circuits with the highest reported clock frequencies for organic circuits.
Developing an effective means for the real-time probing of amyloid β (Aβ) that is closely implicated in Alzheimer's disease (AD) could help better understand and monitor the disease. Here we describe an economic approach based on the simple composition of a natural product, resveratrol (Res), with graphene oxide (GO) for the rapid, fluorogenic recognition of Aβ. The Res@GO composite has proved specific for Aβ over a range of proteins and ions, and could sensitively capture both Aβ monomers and fibers in a physiological buffer solution within only 3 min. The composite can also fluorescently image amyloid deposits in a mouse brain section within 30 min. This new protocol is much cheaper and more timesaving than the conventional immunofluorescence staining technique employed clinically, providing an economic tool for the concise detection of AD.
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