Realizing perfect light absorption in stacked thin films of dielectrics and metals through critical light coupling has recently received intensive research attention. In addition, realizing ...ultra‐thin perfect absorber and tunable perfect absorber in the visible spectrum is essential for novel optoelectronics applications. However, the existing thin film stacks cannot show tunable perfect absorption in a wide‐angle range. Here, a tunable perfect absorption from normal incidence to a wide‐angle range (0° to 70°) by utilizing a two‐layer stack consisting of a high refractive index low‐loss dielectric on a high reflecting metal is proposed. This is experimentally demonstrated by depositing a thin layer of low‐loss phase change material such as stibnite (Sb2S3) on a thin layer of silver. This structure shows tunable perfect absorption with large spectral tunability in the visible wavelength. Furthermore, the absorption enhancement in 2D materials by transferring monolayer molybdenum disulfide on the stack, which shows 96% light absorption with enhanced photoluminescence, is demonstrated. In addition, the thin film stack can work as a scalable phase modulator offering a maximum phase tunability of ≈140° by changing the structural state of Sb2S3 from amorphous to crystalline.
Tunable critical light coupling from normal incidence to a wide‐angle range using a thin‐film cavity consisting of a high refractive index low‐loss dielectric on a high reflecting metal is experimentally presented. The thin‐film cavity is proposed to demonstrate a 2D material‐based ultra‐thin perfect absorber operating at room temperature and a scalable phase modulator for tunable visible photonic applications.
Abstract
Exploiting solid electrolyte (SE) materials with high ionic conductivity, good interfacial compatibility, and conformal contact with electrodes is essential for solid-state sodium metal ...batteries (SSBs). Here we report a crystalline Na
5
SmSi
4
O
12
SE which features high room-temperature ionic conductivity of 2.9 × 10
−3
S cm
−1
and a low activation energy of 0.15 eV. All-solid-state symmetric cell with Na
5
SmSi
4
O
12
delivers excellent cycling life over 800 h at 0.15 mA h cm
−2
and a high critical current density of 1.4 mA cm
−2
. Such excellent electrochemical performance is attributed to an electrochemically induced in-situ crystalline-to-amorphous (CTA) transformation propagating from the interface to the bulk during repeated deposition and stripping of sodium, which leads to faster ionic transport and superior interfacial properties. Impressively, the Na|Na
5
SmSi
4
O
12
|Na
3
V
2
(PO
4
)
3
sodium metal batteries achieve a remarkable cycling performance over 4000 cycles (6 months) with no capacity loss. These results not only identify Na
5
SmSi
4
O
12
as a promising SE but also emphasize the potential of the CTA transition as a promising mechanism towards long-lasting SSBs.
The synthesis of graphene in both high quality and quantity via economic ways is highly desirable and meaningful for practical applications. Here we report a simple, green and cost- effective ...multiple electrochemical exfoliation approach to high quality and high yield (nearly 50%) graphene flakes by using graphite rod from spent zinc–carbon as graphene source. The graphite rod (anode) and platinum (cathode) were placed vertically at bottom and top of the electrochemical cell, with protonic acid (i.e, H2SO4, H3PO4 or H2C2O4) aqueous solution as electrolyte. The vertical cell configuration enables multiple exfoliation process to improve both the quality and yield of graphene sheets from electrochemical exfoliation of graphite. After nitrogen doping, the exfoliated graphene flakes processes excellent electrocatalytic activity, stability and toxicity tolerance for oxygen reduction reaction in alkaline solution.
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► A simple, green and cost-effective multiple electrochemical exfoliation approach to high quality and yield graphene was proposed. ► The exfoliation mechanism and optimized conditions were explored in detail. ► The N-doping exfoliated graphene flakes has demonstrated excellent electrocatalytic activity, stability and toxicity tolerance.
MnO
2
supported on graphene oxide (GO) made from different graphite materials has been synthesized and further investigated as electrode materials for supercapacitors. The structure and morphology of ...MnO
2
-GO nanocomposites are characterized by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Nitrogen adsorption-desorption. As demonstrated, the GO fabricated from commercial expanded graphite (denoted as GO(1)) possesses more functional groups and larger interplane gap compared to the GO from commercial graphite powder (denoted as GO(2)). The surface area and functionalities of GO have significant effects on the morphology and electrochemical activity of MnO
2
, which lead to the fact that the loading amount of MnO
2
on GO(1) is much higher than that on GO(2). Elemental analysis performed via inductively coupled plasma optical emission spectroscopy confirmed higher amounts of MnO
2
loading on GO(1). As the electrode of supercapacitor, MnO
2
-GO(1) nanocomposites show larger capacitance (307.7 F g
-1
) and better electrochemical activity than MnO
2
-GO(2) possibly due to the high loading, good uniformity, and homogeneous distribution of MnO
2
on GO(1) support.
Abstract Van der Waals semiconductors exemplified by two-dimensional transition-metal dichalcogenides have promised next-generation atomically thin optoelectronics. Boosting their interaction with ...light is vital for practical applications, especially in the quantum regime where ultrastrong coupling is highly demanded but not yet realized. Here we report ultrastrong exciton-plasmon coupling at room temperature in tungsten disulfide (WS 2 ) layers loaded with a random multi-singular plasmonic metasurface deposited on a flexible polymer substrate. Different from seeking perfect metals or high-quality resonators, we create a unique type of metasurface with a dense array of singularities that can support nanometre-sized plasmonic hotspots to which several WS 2 excitons coherently interact. The associated normalized coupling strength is 0.12 for monolayer WS 2 and can be up to 0.164 for quadrilayers, showcasing the ultrastrong exciton-plasmon coupling that is important for practical optoelectronic devices based on low-dimensional semiconductors.
Layered vanadium‐based oxides are the promising cathode materials for aqueous zinc‐ion batteries (AZIBs). Herein, an in situ electrochemical strategy that can effectively regulate the interlayer ...distance of layered NH4V4O10 quantitatively is proposed and a close relationship between the optimal performances with interlayer space is revealed. Specifically, via increasing the cutoff voltage from 1.4, 1.6 to 1.8 V, the interlayer space of NH4V4O10 can be well‐controlled and enlarged to 10.21, 11.86, and 12.08 Å, respectively, much larger than the pristine one (9.5 Å). Among them, the cathode being charging to 1.6 V (NH4V4O10‐C1.6), demonstrates the best Zn2+ storage performances including high capacity of 223 mA h g−1 at 10 A g−1 and long‐term stability with capacity retention of 97.5% over 1000 cycles. Such superior performances can be attributed to a good balance among active redox sites, charge transfer kinetics, and crystal structure stability, enabled by careful control of the interlayer space. Moreover, NH4V4O10‐C1.6 delivers NH4+ storage performances whose capacity reaches 296 mA h g−1 at 0.1 A g−1 and lifespan lasts over 3000 cycles at 5 A g−1. This study provides new insights into understand the limitation of interlayer space for ion storage in aqueous media and guides exploration of high‐performance cathode materials.
Here, it is shown that via increasing the cutoff voltage from 1.4, 1.6, to 1.8 V, the interlayer space of NH4V4O10 can be well‐controlled and enlarged quantitatively to 10.21, 11.86, and 12.08 Å, respectively, much larger than the pristine one (9.5 Å), resulting in better zinc‐ion storage performance.
Large‐scale synthesis of single‐layer graphene (SLG) by chemical vapor deposition (CVD) has received a lot of attention recently. However, CVD synthesis of AB stacked bi‐layer graphene (BLG) is still ...challenging. Here, we report synthesis of BLG homogeneously at large scale by thermal CVD. The 2D Raman band of CVD BLG splits into four components, suggesting splitting of electronic bands due to strong interlayer coupling. The splitting of electronic bands in CVD BLG is further evidenced by the study of near infrared absorption and carrier dynamics are probed by transient absorption spectroscopy. UV photoelectron spectroscopy invesigation also indiates CVD BLG possesses different electronic structures to those of CVD SLG. The growth mechanism of BLG is found to be related to catalytic activity of the copper (Cu) surface, which is determined by the purity of Cu foils employed in the CVD process. Our work shows that strongly coupled or even AB stacked BLG can be grown on Cu foils at large scale, which is of particular importance for device applications based on their split electronic bands.
Bilayer graphene (BLG) is synthesized homogeneously on a large scale by thermal CVD. The splitting of electronic bands in BLG is demonstrated using Raman spectroscopy and optical absorbtion spectroscopy, and carrier dynamics are probed by transient absorption spectroscopy. The successful synthesis of BLG on a large scale is of particular importance for device applications based on their degenerate electronic bands.
Interlayer electronic and mechanical couplings of transitional metal dichalcogenides due to Van der Waals force determine their band structure and Raman modes evolution, respectively. Twist‐stacked ...WS2 bilayers have been synthesized with twist angles of 0°, 13°, 30°, 41°, 60°, and 83° via chemical‐vapor depositon, which allows us to study the coupling effect by Raman and photoluminescence spectroscopy and density function calculation. The photoluminescence property implies that these random‐twisted WS2 bilayers behave as quasi‐direct bandgap material due to weakened interlayer coupling as a result of larger interlayer distances than the nontwisted 0° and 60° stacked WS2 bilayers (with an indirect band gap). In addition, an additional small peak (AI) near the excitonic transition peak (A) is observed from the twisted bilayers, which can be attributed to the interlayer exciton transition.
WS2 bilayers with different twist angles are observed in high‐temperature chemical vapor deposition growth. The random twisted WS2 bilayers show enhanced photoluminescence and absence of the indirect transition peak, which is due to weakened interlayer coupling as a result of larger interlayer distances than the nontwisted AA and AB stacking bilayers.
Considerable attention has been paid recently to coherent control of plasmon resonances in metadevices for potential applications in all-optical light-with-light signal modulation and image ...processing. Previous reports based on out-of-plane coherent control of plasmon resonances were established by modulating the position of a metadevice in standing waves. Here we show that destructive and constructive absorption can be realized in metallic nano-antennas through in-plane coherent control of plasmon resonances, which is determined by the distribution rule of electrical-field components of nano-antennas. We provide proof-of-principle demonstrations of plasmonic switching effects in a gold nanodisk monomer and dimer, and propose a plasmonic encoding strategy in a gold nanodisk chain. In-plane coherent control of plasmon resonances may open a new avenue toward promising applications in optical spectral enhancement, imaging, nanolasing, and optical communication in nanocircuits.
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