28 research outputs found
Exchange-biased NiFe2O4/NiO nanocomposites derived from NiFe-layered double hydroxides as a single precursor
Strong interlayer coupling in monoclinic GaTe
Recently, emerging intriguing physical properties have been unraveled in
anisotropic layered semiconductors, with their in-plane anisotropy often
originated directly from the low crystallographic symmetry. However, little has
been known in the case where interlayer couplings dominate the anisotropy of
electronic band structures in them. Here, by both experiment and theory, we
show rather than geometric factors, the anisotropic energy bands of monoclinic
gallium telluride (GaTe) are determined by a subtle bulk-surface interaction.
Bulk electronic states are found to be the major contribution of the highest
valence band, whose anisotropy is yet immune to surface doping of potassium
atoms. The above peculiar behaviors are attributed to strong interlayer
couplings, which gives rise to an inverse of anisotropy of hole effective
masses and a direct-indirect-direct transition of band gap, depending on the
number of layers. Our results thus pave the way for future applications of
anisotropic layered semiconductors in nanoelectronics and optoelectronics.Comment: 3 figure
Quasi-Two-Dimensional Fermi Surface and Heavy Quasiparticles in CeRh2As2
The recent discovery of multiple superconducting phases in CeRh2As2 has
attracted considerable interest. These rich phases are thought to be related to
the locally noncentrosymmetric crystal structure, although the possible role of
a quadrupole density wave preceding the superconductivity remains an open
question. While measurements of physical properties imply that the Ce 4f
electrons could play an essential role, the momentum-resolved electronic
structure remains hitherto unreported, hindering an in-depth understanding of
the underlying physics. Here, we report a high-resolution angle-resolved
photoemission study of CeRh2As2. Our results reveal fine splittings of
conduction bands, which are directly related to the locally noncentrosymmetric
structure, as well as a quasi-two-dimensional Fermi surface, implying weak
interlayer hopping and possible nesting instabilities. Our experiments also
uncover the fine structures and pronounced temperature evolution of the Kondo
peak, demonstrating strong Kondo effect facilitated by excited crystal electric
field states. Our results unveil the salient electronic features arising from
the interplay between the crystal structure and strong electron correlation,
providing spectroscopic insight for understanding the heavy fermion physics and
unconventional quadrupole density wave in this enigmatic compound
Morphologies, Preparations and Applications of Layered Double Hydroxide Micro-/Nanostructures
Layered double hydroxides (LDHs), also well-known as hydrotalcite-like layered clays, have been widely investigated in the fields of catalysts and catalyst support, anion exchanger, electrical and optical functional materials, flame retardants and nanoadditives. This feature article focuses on the progress in micro-/nanostructured LDHs in terms of morphology, and also on the preparations, applications, and perspectives of the LDHs with different morphologies
Preparation of Nickel–Aluminum-Containing Layered Double Hydroxide Films by Secondary (Seeded) Growth Method and Their Electrochemical Properties
Thin
films of nickel–aluminum-containing layered double
hydroxide (NiAl-LDH) have been prepared on nickel foil and nickel
foam substrates by secondary (seeded) growth of NiAl-LDH seed layer.
The preparation procedure consists of deposition of LDH seeds from
a colloidal suspension on the substrate by dip coating, followed by
hydrothermal treatment of the nanocrystals to form the LDH film. The
secondary grown film is found to provide a higher crystallinity and
more uniform composition of metal cations in the film layer than the
in situ grown film on seed-free substrate under identical hydrothermal
conditions. A systematic investigation of the film evolution process
reveals that the crystallite growth rate is relatively fast for the
secondary grown film because of the presence of LDH nanocrystal seeds.
Electrochemical performance of the resulting NiAl-LDH films as positive
electrode material was further assessed as an example of their practical
applications. The secondary grown film electrode delivers improved
recharge–discharge capacity and cycling stability compared
with that of the in situ grown film, which can be explained by the
existence of a unique microstructure of the former. Our findings show
an example for the effective fabrication of LDH film with controllable
microstructure and enhanced application performance through a secondary
(seeded) growth procedure
Morphologies, Preparations and Applications of Layered Double Hydroxide Micro-/Nanostructures
Triple-Confined Well-Dispersed Biactive NiCo<sub>2</sub>S<sub>4</sub>/Ni<sub>0.96</sub>S on Graphene Aerogel for High-Efficiency Lithium Storage
Layered
double hydroxides (LDHs), also known as hydrotalcite-like anionic
clay compounds, have attracted increasing interest in electrochemical
energy storage, in the main form of LDH precursor-derived transition
metal oxides (TMOs). One typical approach to improve cycling stability
of the LDH-derived TMOs is to introduce one- and two-dimensional conductive
carbonaceous supports, such as carbon nanotubes and graphene. We herein demonstrate an effective
approach to improve the electrochemical performances of well-dispersed
biactive NiCo<sub>2</sub>S<sub>4</sub>/Ni<sub>0.96</sub>S as anode
nanomaterials for lithium-ion batteries (LIBs), by introducing a three-dimensional
graphene aerogel (3DGA) support. The resultant 3DGA supported NiCo<sub>2</sub>S<sub>4</sub>/Ni<sub>0.96</sub>S (3DGA/NCS) composite, obtained
by sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor
in situ grown on the 3DGA support (3DGA/NiCo-LDH). Electrochemical
tests show that the 3DGA/NCS composite indeed delivers the greatly
enhanced electrochemical performances compared with the NiCo<sub>2</sub>S<sub>4</sub>/Ni<sub>0.96</sub>S counterpart on two-dimensional graphene
aerogel, i.e., a high reversible capacity of 965 mA h g<sup>–1</sup> after 200 cycles at 100 mA g<sup>–1</sup> and especially
a superlong cycling stability of 620 mA h g<sup>–1</sup> after
800 cycles at 1 A g<sup>–1</sup>. The enhancements could be
ascribed to the compositional and structural advantages of boosting
electrochemical performances: (i) well-dispersed NiCo<sub>2</sub>S<sub>4</sub>/Ni<sub>0.96</sub>S nanoparticles with interfacial nanodomains
resulting from both the dual surface confinements of the 3DGA support
and the crystallographic confinement of NiCo-well-arranged LDH crystalline
layer, (ii) an appropriate specific surface area and a wide pore size
distribution of mesopores and macropores, and (iii) highly conductive
3DGA support that is measured experimentally by using electrochemical
impedance spectra to underlie the enhancement. Our results demonstrate
that the tunable LDH precursor-derived synthesis route may be extended
to prepare various transition metal sulfides and even transition metal
phosphides for energy storage with the aid of tunable cationic type
and molar ratio
Solid-Solution Sulfides Derived from Tunable Layered Double Hydroxide Precursors/Graphene Aerogel for Pseudocapacitors and Sodium-Ion Batteries
Transition-metal
sulfides (TMSs) are suggested as promising electrode materials for
electrochemical pseudocapacitors and lithium- and sodium-ion batteries;
however, they typically involve mixed composites or conventionally
stoichiometric TMSs (such as NiCo<sub>2</sub>S<sub>4</sub> and Ni<sub>2</sub>CoS<sub>4</sub><b>)</b>. Herein we demonstrate a preparation
of solid-solution sulfide (Ni<sub>0.7</sub>Co<sub>0.3</sub>)ÂS<sub>2</sub> supported on three-dimensional graphene aerogel (3DGA) via
a sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor/3DGA.
The electrochemical tests show that the (Ni<sub>0.7</sub>Co<sub>0.3</sub>)ÂS<sub>2</sub>/3DGA electrode exhibits a capacitance of 2165 F g<sup>–1</sup> at 1 A g<sup>–1</sup>, 2055 F g<sup>–1</sup> at 2 A g<sup>–1</sup>, and 1478 F g<sup>–1</sup> at
10 A g<sup>–1</sup>; preserves 78.5% capacitance retention
upon 1000 cycles for pseudocapacitors; and in particular, possesses
a relatively high charge capacity of 388.7 mA h g<sup>–1</sup> after 50 cycles at 100 mA g<sup>–1</sup> as anode nanomaterials
for sodium-ion batteries. Furthermore, the electrochemical performances
are readily tuned by varying the cationic type of the tunable LDH
precursors to prepare different solid-solution sulfides, such as (Ni<sub>0.7</sub>Fe<sub>0.3</sub>)ÂS<sub>2</sub>/3DGA and (Co<sub>0.7</sub>Fe<sub>0.3</sub>)ÂS<sub>2</sub>/3DGA. Our results show that engineering
LDH precursors can offer an alternative for preparing diverse transition-metal
sulfides for energy storage
A Method of High Throughput Monitoring Crop Physiology Using Chlorophyll Fluorescence and Multispectral Imaging
We present a high throughput crop physiology condition monitoring system and corresponding monitoring method. The monitoring system can perform large-area chlorophyll fluorescence imaging and multispectral imaging. The monitoring method can determine the crop current condition continuously and non-destructively. We choose chlorophyll fluorescence parameters and relative reflectance of multispectral as the indicators of crop physiological status. Using tomato as experiment subject, the typical crop physiological stress, such as drought, nutrition deficiency and plant disease can be distinguished by the monitoring method. Furthermore, we have studied the correlation between the physiological indicators and the degree of stress. Besides realizing the continuous monitoring of crop physiology, the monitoring system and method provide the possibility of machine automatic diagnosis of the plant physiology.Highlights: A newly designed high throughput crop physiology monitoring system and the corresponding monitoring method are described in this study. Different types of stress can induce distinct fluorescence and spectral characteristics, which can be used to evaluate the physiological status of plants