4 research outputs found
Distinctly Improved Photocurrent and Stability in TiO<sub>2</sub> Nanotube Arrays by Ladder Band Structure
Introducing a ternary
interlayer into binary heterostructures to
construct a ladder band structure provides a promising way for photoelectrochemical
water splitting. Here, we design and fabricate a sandwich structure
on TiO<sub>2</sub> nanotubes using CdS<sub><i>x</i></sub>Se<sub>1–<i>x</i></sub> as the interlayer to obtain
a matching band alignment. The photoelectrochemical (PEC) properties
of composite photoanodes are optimized by the order of sensitization
and elements ratio, wherein the TiO<sub>2</sub>/CdS/CdS<sub>0.5</sub>Se<sub>0.5</sub>/CdSe photoanode shows a significantly enhanced photocurrent
of 14.78 mA cm<sup>–2</sup> at −0.2 V vs SCE, exhibiting
a nearly 15-fold enhancement, over 1 order of magnitude. The quantum
efficiency apparently increases to 40% at a range of 400–520
nm, resulting from the fact that a sensitizing layer with a matching
band alignment can facilitate the separation of photogenerated electron–hole
pairs and also extend the absorption range to the visible region due
to its narrow bandgaps. Furthermore, its stability was distinctly
improved by coating MoS<sub>2</sub> on the surface of the TiO<sub>2</sub>/CdS/CdS<sub>0.5</sub>Se<sub>0.5</sub>/CdSe photoanode. Our
findings provide a novel route toward developing a highly efficient
photoelectrode for water splitting
Self-Assembling VO<sub>2</sub> Nanonet with High Switching Performance at Wafer-Scale
Technologically
controlling nanostructures is essential to tailoring the functionalities
and properties of nanomaterials. Various methods free from lithography-based
techniques have been employed to fabricate 2D nanostructures; however
it is still hard to achieve a well interconnected 2D regular nanostructure.
Here, we demonstrate a facile chemical solution method to self-assemble
a regular and interconnected VO<sub>2</sub> nanonet on the wafer scale.
The nanonet shows a well-defined 2D truss network constructed by VO<sub>2</sub> nanorods with twinning relationships. The growth direction
and crystallographic orientation of nanorods are synchronously controlled,
leading to horizontally epitaxial growth of nanorods along three symmetric
directions of the (001) single-crystal sapphire substrate. The unique
nanonets enable the acquisition of excellent resistance switching
properties and dramatic fatigue endurance. A large resistance change
of near 5 orders with a 1.7 °C width of the hysteresis loop is
characterized comparably to the properties of single crystals without
detectable degradation after 500 cycles over the metal-to-insulator
transition. It indicates that the nanonet can serve as an exceptional
candidate for practical application in switching functional devices.
Our findings offer a novel pathway for self-assembly of 2D ordered
nanostructures, which would provide new opportunities for the bottom-up
integration of nanodevices
Highly Efficient Microwave Absorption of Magnetic Nanospindle–Conductive Polymer Hybrids by Molecular Layer Deposition
Oxidative
molecular layer deposition (oMLD) was applied to fabricate conductive
polymer–magnetic material core–shell microwave absorbers
in this work. One dimensional Fe<sub>3</sub>O<sub>4</sub>–polyÂ(3,4-ethylenedioxythiophene)
(PEDOT) nanospindles with controllable PEDOT thickness were successfully
synthesized. Their absorption performance was evaluated in the 2–18
GHz frequency range. With the advantage of oMLD, PEDOT shell thicknesses
can be controlled precisely. Because the permittivity of Fe<sub>3</sub>O<sub>4</sub>–PEDOT nanospindles obviously increases while
their permeability decreases slightly with the PEDOT cycles, the properties
can be tuned effectively by only adjusting the PEDOT cycle number.
With a proper PEDOT shell thickness, excellent reflection characteristics
can be obtained. Remarkably high absorption strength (−55.0
dB at 16.2 GHz) and good absorption bandwidth (4.34 GHz less than
−10 dB) were realized. Such excellent performance is better
than that reported previously for most magnetic material-based absorbers.
Considering the precise controllability and excellent absorption performance
of the prepared microwave absorbers, we believe that oMLD is a facile
synthetic route for microwave absorbers
Evolution of Structural and Electrical Properties of Oxygen-Deficient VO<sub>2</sub> under Low Temperature Heating Process
Structural
stability and functional performances of vanadium dioxide (VO<sub>2</sub>) are strongly influenced by oxygen vacancies. However, the
mechanism of metal–insulator transition (MIT) influenced by
defects is still under debate. Here, we study the evolution of structure
and electrical property of oxygen-deficient VO<sub>2</sub> by a low
temperature annealing process (LTP) based on a truss-structured VO<sub>2</sub> nanonet. The oxygenation process of the oxygen-deficient
VO<sub>2</sub> is greatly prolonged, which enables us to probe the
gradual change of properties of the oxygen-deficient VO<sub>2</sub>. A continuous lattice reduction is observed during LTP. No recrystallization
and structural collapse of the VO<sub>2</sub> nanonet can be found
after LTP. The valence-band X-ray photoelectron spectroscopy (XPS)
measurements indicate that the oxygen deficiency strongly affects
the energy level of the valence band edge. Correspondingly, the resistance
changes of the VO<sub>2</sub> films from 1 to 4.5 orders of magnitude
are achieved by LTP. The effect of oxygen vacancy on the electric
field driven MIT is investigated. The threshold value of voltage triggering
the MIT decreases with increasing the oxygen vacancy concentration.
This work demonstrates a novel and effective way to control the content
of oxygen vacancies in VO<sub>2</sub> and the obvious impact of oxygen
vacancy on MIT, facilitating further research on the role of oxygen
vacancy in structure and MIT of VO<sub>2</sub>, which is important
for the deep understanding of MIT and exploiting innovative functional
application of VO<sub>2</sub>