Borophene sheets have been synthesized in recent experiments, but the metallic nature and structural instability of the sheets seriously prevent emerging applications. Hydrogenated borophene has been predicted as an ideal material for nanoelectronic applications due to its high stability as well as excellent electronic and mechanical properties. However, the fabrication of hydrogenated borophene is still a great challenge. Here, we demonstrate that hydrogenated borophenes in large quantities can be prepared without any metal substrates by a stepwise in‐situ thermal decomposition of sodium borohydride under hydrogen as the carrier gas. The borophenes with good crystallinity exhibit superior stability in strong acid or base solvents. The structure of the grown borophene is in good agreement with the predicted semiconducting α‐boron sheet. A fabricated borophene‐based memory device shows a high ON/OFF‐current ratio of 3×103 and a low operating voltage of less than 0.35 V as well as good stability.
Zero-dimensional
boron structures have always been the focus of
theoretical research owing to their abundant phase structures and
special properties. Boron clusters have been reported extensively
by combining structure searching theories and photoelectron spectroscopy
(PES) experiments; however, crystalline boron quantum dots (BQDs)
have rarely been reported. Here, we report the preparation of large-scale
and uniform crystalline semiconductor BQDs from the expanded bulk
boron powders via a facile and efficient probe ultrasonic approach
in the acetonitrile solution. The obtained BQDs have 2.46 nm average
lateral size and 2.81 nm thickness. Optical measurements demonstrate
that a strong quantum confinement effect occurs in the BQDs, implying
the increase of the band gap from 1.80 eV for the corresponding bulk
to 2.46 eV for the BQDs. By injecting the BQDs into poly(vinylpyrrolidone)
as an active layer, a BQD-based memory device is fabricated that shows
a rewriteable nonvolatile memory effect with a low transition voltage
of down to 0.5 V and a high on/off switching ratio of 103 as well as a good stability.
The emergence of borophene has triggered
soaring interest in the
investigation of its superior structural anisotropy, a novel photoelectronic
property for diverse potential applications. However, the structural
instability and need of a metal substrate for depositing borophene
restrict its large-scale applications toward high-performance electronic
and optoelectric devices. van der Waals epitaxy is regarded as an
efficient technique for growing superb two-dimensional materials onto
extensive functional substrates, but the preparation of stable and
controllable borophene on nonmetallic substrates is still not reported.
Here, we demonstrate that borophene films can be synthesized onto
a mica substrate by van der Waals epitaxy, where hydrogen and NaBH4 are respectively used as the carrier gas and the boron source.
The lattice structure of the as-synthesized borophene coincides with
the predicted α′-boron sheet. The borophene-based photodetector
shows an excellent photoresponsivity of 1.04 A W–1 and a specific detectivity of 1.27 × 1011 Jones
at a reversed bias of 4 V under illumination of a 625 nm light-emitting
diode, which are remarkably superior to those of reported boron nanosheets.
This work facilitates further studies of borophene toward its attractive
properties and applications in novel optoelectronic devices and integrated
circuits.
Borophenes (2D boron sheets) have triggered a surge of interest both theoretically and experimentally because of its distinct structural, optical and electronic properties for extensive potential applications. Although theoretical efforts have guided the research directions of borophene, only few synthetic borophene sheets have been demonstrated experimentally. Borophene sheets have been successfully synthesized experimentally on metal substrates until 2015. Afterwards, more efforts were put on the controlled synthesis of crystalline and semiconducting borophene sheets as well as on the investigation of their novel and fascinating physical properties. This report provides a brief review on theoretical and experimental progress in borophene research. Some typical structures and properties of borophenes have been reviewed. The focus is laid on summarizing the experimental synthesis of borophene in recent years, and on showing some ultrastable and semiconducting borophenes which have been applied in electronic information devices. Finally, the future challenges and opportunities regarding experimental realization and practical applications of borophenes are presented.
Two-dimensional boron sheets with a quasicubic structure have been synthesized on a Ni foil substrate by chemical vapor deposition, and possess a direct bandgap of around 2.4 eV.
Borophene
has been predicted to have outstanding catalytic activity
owing to its extreme electron deficiency and abundant active sites.
However, no experimental results have been still reported for borophene
application in high-efficiency catalysis. Here, a borophene nanosheet
was prepared on a carbon cloth surface via chemical vapor deposition.
The boron source is sodium borohydride and the carrier gas is hydrogen
gas. The crystal structure of the borophene nanosheet highly matches
that of a theoretical α′-borophene nanosheet. Borophene
shows good electrocatalytic hydrogen evolution reaction (HER) ability
with a 69 mV/dec Tafel slope and good cycling stability in a 0.5 M
H2SO4 solution. The enhanced performance is
ascribed to an abundant electrocatalytic active area and low resistance
of charge transfer, which results from its rich surface active sites.
The improvement has been revealed by first-principles calculations,
which is originated from their inherent metallicity and abundant electrocatalytic
active sites on the nanosheets’ surface. Borophene’s
extraordinarily high activity and stability give rise to extensive
investigation of the application of borophene in high-efficiency energy
applications such as catalysts and batteries.
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