In this Special Issue “2D Nanostructures for Optoelectronic and Green Energy Devices”, we have collected nine high-quality, original research papers and one comprehensive review paper by outstanding ...scientists and engineers from relevant fields, covering the topics in optical properties and couplings in 2D nanostructures, spectroscopic analysis in atomic scale, 2D transistors, 2D optoelectronics, and 2D energy storage applications. This Special Issue is expected to attract and enrich readers by providing innovative research articles and a review paper in the field of 2D nanostructures.
Atomically thin layers of two-dimensional materials can be assembled in vertical stacks that are held together by relatively weak van der Waals forces, enabling coupling between monolayer crystals ...with incommensurate lattices and arbitrary mutual rotation
. Consequently, an overarching periodicity emerges in the local atomic registry of the constituent crystal structures, which is known as a moiré superlattice
. In graphene/hexagonal boron nitride structures
, the presence of a moiré superlattice can lead to the observation of electronic minibands
, whereas in twisted graphene bilayers its effects are enhanced by interlayer resonant conditions, resulting in a superconductor-insulator transition at magic twist angles
. Here, using semiconducting heterostructures assembled from incommensurate molybdenum diselenide (MoSe
) and tungsten disulfide (WS
) monolayers, we demonstrate that excitonic bands can hybridize, resulting in a resonant enhancement of moiré superlattice effects. MoSe
and WS
were chosen for the near-degeneracy of their conduction-band edges, in order to promote the hybridization of intra- and interlayer excitons. Hybridization manifests through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle, which occurs as hybridized excitons are formed by holes that reside in MoSe
binding to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures in which the monolayer pairs are nearly aligned, resonant mixing of the electron states leads to pronounced effects of the geometrical moiré pattern of the heterostructure on the dispersion and optical spectra of the hybridized excitons. Our findings underpin strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructures
.
A very simple, as well as sensitive and selective, sensing protocol was developed on a pre-anodized graphite pencil electrode surface coated using poly(thionine) (APGE/PTH). The poly(thionine) coated ...graphite pencil was then used for simultaneous sensing of 3-nitrophenol (3-NP) and 4-nitrophenol (4-NP). The poly(thionine) coated electrode exhibited an enhanced electrocatalytic property towards nitrophenol (3-NP and 4-NP) reduction. Redox peak potential and current of both nitrophenols were found well resolved and their simultaneous analysis was studied. Under optimized experimental conditions, APGE/PTH showed a long linear concentration range from 20 to 230 nM and 15 nM to 280 nM with a calculated limit of detection (LOD) of 4.5 and 4 nM and a sensitivity of 22.45 µA/nM and 27.12 µA/nM for 3-NP and 4-NP, respectively. Real sample analysis using the prepared sensor was tested with different environmental water samples and the sensors exhibited excellent recovery results in the range from 98.16 to 103.43%. Finally, the sensor exposed an promising selectivity, stability, and reproducibility towards sensing of 3-NP and 4-NP.
•Zinc electrodes for energy storage devices.•Surface modification for rough surface and high surface area.•Improved ionic diffusion ability at the high current densities.•Enhanced energy storage ...performance of Zinc ion capacitors.
Zinc (Zn) ion based capacitors (ZICs) have been considered to be a new emerging energy storage device due to their high energy density and long cycle life. However, it is still challenging to overcome the limitation of ZICs with the low power densities and poor rate performance because of their low ion diffusion ability at high current densities during the cycling. Hence, we propose a novel surface modification strategy for the development of the rough surface and high surface area of Zn electrodes as the anode material so as to improve the ion diffusion ability at the high current densities. The energy storage performance of the surface-tailored Zn electrodes is significantly improved with the high specific capacitance (353 F g−1 at the current density of 0.5 A g−1), excellent high-rate performance (62 F g−1 at the current density of 10.0 A g−1), and remarkable cycling stability of 99% after 2000 cycles. This improved electrochemical performance is discussed and explained in terms of surface roughness and surface area. Our fining suggests that the surface engineering is a powerful approach for the potential applications of ZICs.
Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter ...interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS
optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ∼4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 10
s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices.
van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having ...great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS2 to MoS2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices.
Rational three-dimensional nitrogen doped mesoporous carbon nanostructured surfaced Nickel metal (Ni) nanoparticles (nps), NCNP composites have been developed using nickel organic complex and ...utilized as an electrocatalyst for oxygen evolution reaction. The NCNP composites of tunable physio-chemical characteristics, such as Ni nps size (∼18–∼42 nm), surface area (∼18–∼43 m2 g−1), pore size (3.23–3.84 nm) and nitrogen doping amount (1.20–3.87 wt%) have been achieved via controlled carbonization temperature. An optimized NCNP composite of favorable physio-chemical properties has delivered good oxygen evolution kinetics such as a lower overpotential value (370 mV) at 10 mA cm−2, a minimum Tafel slope value (55 mV dec−1), and relatively a higher electrochemical surface area (0.6325 cm−2) than the other NCNP composites. Moreover, the best NCNP electrocatalyst has shown a comparable overpotential value with the benchmarking catalyst at 10 mA cm−2, equivalent to ∼10% solar photoelectrical conversion efficiency. In addition, the best NCNP electrocatalyst has exhibited excellent accelerated degradation test for 24 h at a constant current density of 10 mA cm−2 with an increase overpotential value of 0.029 V.
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•N-doped mesoporous NCNP electrocatalyst prepared by a simple cost-effective approach.•NCNP delivers comparable overpotential value with the benchmark electrocatalyst.•NCNP exhibits excellent accelerated degradation test for 24 h at a 10 mA cm−2.
The rapid growth of the global economy and urbanization have resulted in major worldwide issues such as greenhouse gas emission, air pollution and the energy crisis. Artificial ambient light is one ...of the greatest inventions in human history, but it is also one of the primary energy consumption constituents and a focus of the global grand energy challenge. Therefore, low cost and low energy consumption lighting technology is in high demand. In this review, we will summarise and discuss one of the emerging lighting technologies - white electroluminescence light-emitting diodes enabled by hybrid colloidal quantum dots (WQLEDs), which have attracted intense attention because of promising potential in both flat-panel backlighting and solid-state lighting. WQLEDs have unique high luminescence efficiency, broad colour tunability and solution processability. Over the past few decades, the development of colloidal quantum dot synthesis, material engineering and device architecture has highlighted the tremendous improvements in WQLED formation. As WQLED efficiencies approach those of molecular organic LEDs, we identify the critical scientific and technological challenges and provide an outlook for ongoing strategies to overcome these challenges.
Electroluminescence light-emitting diodes enabled by hybridising colloidal quantum dots is an emerging technology for large-area and foldable ambient lighting. We summerise state-of-the-art scientific challenges and prospect their future development.
In this work, we develop a Ag@Al
O
@Ag plasmonic core-shell-satellite (PCSS) to achieve highly sensitive and reproducible surface-enhanced Raman spectroscopy (SERS) detection of probe molecules. To ...fabricate PCSS nanostructures, we employ a simple hierarchical dewetting process of Ag films coupled with an atomic layer deposition (ALD) method for the Al
O
shell. Compared to bare Ag nanoparticles, several advantages of fabricating PCSS nanostructures are discovered, including high surface roughness, high density of nanogaps between Ag core and Ag satellites, and nanogaps between adjacent Ag satellites. Finite-difference time-domain (FDTD) simulations of the PCSS nanostructure confirm an enhancement in the electromagnetic field intensity (hotspots) in the nanogap between the Ag core and the satellite generated by the Al
O
shell, due to the strong core-satellite plasmonic coupling. The as-prepared PCSS-based SERS substrate demonstrates an enhancement factor (EF) of 1.7 × 10
and relative standard deviation (RSD) of ~7%, endowing our SERS platform with highly sensitive and reproducible detection of R6G molecules. We think that this method provides a simple approach for the fabrication of PCSS by a solid-state technique and a basis for developing a highly SERS-active substrate for practical applications.
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