The energy storage performance of lithium-ion batteries (LIBs) depends on the electrode capacity and electrode/cell design parameters, which have previously been addressed separately, leading to a ...failure in practical implementation. Here, we show how conformal graphene (Gr) coating on Ni-rich oxides enables the fabrication of highly packed cathodes containing a high content of active material (~99 wt%) without conventional conducting agents. With 99 wt% LiNi
Co
Al
O
(NCA) and electrode density of ~4.3 g cm
, the Gr-coated NCA cathode delivers a high areal capacity, ~5.4 mAh cm
(~38% increase) and high volumetric capacity, ~863 mAh cm
(~34% increase) at a current rate of 0.2 C (~1.1 mA cm
); this surpasses the bare electrode approaching a commercial level of electrode setting (96 wt% NCA; ~3.3 g cm
). Our findings offer a combinatorial avenue for materials engineering and electrode design toward advanced LIB cathodes.
The electrocatalytic activity of a CuO flower-like nanostructured electrode was investigated in terms of its application to enzyme-less amperometric H
2O
2 sensors. The CuO nanoflowers film was ...directly formed by chemical oxidation of copper foil under hydrothermal condition and then used as active electrode material of non-enzymatic electrochemical sensors for H
2O
2 detection under alkaline conditions. The sensitivity of the sensor with CuO nanoflowers electrode was 88.4
μA/mM
cm
2 with a linear response in the range from 4.25
×
10
−5 to 4
×
10
−2
M and a detection limit of 0.167
μM (
S/
N
=
3). Excellent electrocatalytic activity, large surface-to-volume ratio and efficient electron transport property of CuO nanoflowers electrode have enabled stable and highly sensitive performance for the non-enzymatic H
2O
2 sensor.
The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based ...on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.
Two-dimensional transition metal dichalcogenides (TMDCs) have emerged as promising materials for next-generation electronics due to their excellent semiconducting properties. However, high contact ...resistance at the metal–TMDC interface plagues the realization of high-performance devices. Here, an effective metal–interlayer–semiconductor (MIS) contact is demonstrated, wherein an ultrathin ZnO interlayer is inserted between the metal electrode and MoS2, providing damage-free and clean interfaces at electrical contacts. Using TEM imaging, we show that the contact interfaces were atomically clean without any apparent damages. Compared to conventional Ti/MoS2 contacts, the MoS2 devices with a Ti/ZnO/MoS2 contact exhibit a very low contact resistance of 0.9 kΩ μm. These improvements are attributed to the following mechanisms: (a) Fermi-level depinning at the metal/MoS2 interface by reducing interface disorder and (b) presence of interface dipole at the metal/ZnO interface, consequently reducing the Schottky barrier and contact resistance. Further, the contact resistivity of a Ti/ZnO/MoS2 contact is insensitive to the variation of ZnO thickness, which facilitates large-scale production. Our work not only elucidates the underlying mechanisms for the operation of the MIS contact but also provides a simple and damage-free strategy for conventional aggressive metal deposition that is potentially useful for the realization of large-scale 2D electronics with low-resistance contacts.
Transition metal dichalcogenides (TMDs) are of great interest owing to their unique properties. However, TMD materials face two major challenges that limit their practical applications: contact ...resistance and surface contamination. Herein, a strategy to overcome these problems by inserting a monolayer of hexagonal boron nitride (h‐BN) at the chromium (Cr) and tungsten disulfide (WS2) interface is introduced. Electrical behaviors of direct metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) contacts with mono‐ and bilayer h‐BN in a four‐layer WS2 field‐effect transistor (FET) are evaluated under vacuum from 77 to 300 K. The performance of the MIS contacts differs based on the metal work function when using Cr and indium (In). The contact resistance is significantly reduced by approximately ten times with MIS contacts compared with that for MS contacts. An electron mobility up to ≈115 cm2 V‐1 s‐1 at 300 K is achieved with the insertion of monolayer h‐BN, which is approximately ten times higher than that with MS contacts. The mobility and contact resistance enhancement are attributed to Schottky barrier reduction when h‐BN is introduced between Cr and WS2. The dependence of the tunneling mechanisms on the h‐BN thickness is investigated by extracting the tunneling barrier parameters.
Inserting an atomic hexagonal boron nitride layer at the interface of metal and WS2 to form a metal–insulator–semiconductor (MIS) contact is a practical method to improve mobility and contact resistance of four‐layer WS2 transistors. This study provides an opportunity to understand the impact of the metal work‐function and the mechanism of the Schottky barrier reduction of the MIS‐structured WS2 transistors.
In this work, we developed an atomically thin (∼2.5 nm) heterostructure consisting of a monolayer rhodamine 6G (R6G) film as a photoactive layer that was sandwiched between graphene films functioning ...as channels (graphene–R6G–graphene, G–R–G). Through a comparison of results of both photocurrent measurements and chemically enhanced Raman scattering (CERS) experiments, we found that our G–R–G heterostructure exhibited ∼7 and ∼30 times better performance than R6G-attached single-graphene (R6G–graphene, R–G) and MoS2 devices, respectively; here, the CERS enhancement factor was highly correlated with the relative photoinduced Dirac voltage change. Furthermore, the photocurrent of the G–R–G device was found to be ∼40 times better than that of the R–G photodetector. The top graphene was highly operative in the monolayer, of which the performance is significantly deteriorated by fluorescence and tailored charge transfer efficiency with the increment of R6G film thickness. Overall, the responsivity of the G–R–G photodetector was ∼40 times higher than that of the R–G photodetector because of the more efficient carrier transfer between the organic dye and graphene induced by weaker π–π interactions between the top and bottom graphene channels in the former device. This atomically thin (∼2.5 nm) and highly photosensitive photodetector can be employed for post-Si-photodiode (PD) image sensors, single-photon detection devices, and optical communications.
The strongly correlated thermoelectric properties have been a major hurdle for high-performance thermoelectric energy conversion. One possible approach to avoid such correlation is to suppress phonon ...transport by scattering at the surface of confined nanowire structures. However, phonon characteristic lengths are broad in crystalline solids, which makes nanowires insufficient to fully suppress heat transport. Here, we employed Si–Ge alloy as well as nanowire structures to maximize the depletion of heat-carrying phonons. This results in a thermal conductivity as low as ∼1.2 W/m-K at 450 K, showing a large thermoelectric figure-of-merit (ZT) of ∼0.46 compared with those of SiGe bulks and even ZT over 2 at 800 K theoretically. All thermoelectric properties were “simultaneously” measured from the same nanowires to facilitate accurate ZT measurements. The surface-boundary scattering is prominent when the nanowire diameter is over ∼100 nm, whereas alloying plays a more important role in suppressing phonon transport for smaller ones.
Due to the vulnerability of organic optoelectronic devices to moisture and oxygen, thin-film moisture barriers have played a critical role in improving the lifetime of the devices. Here, we propose a ...hexagonal boron nitride (hBN) embedded Al2O3 thin film as a flexible moisture barrier. After layer-by-layer (LBL) staking of polymer and hBN flake composite layer, Al2O3 was deposited on the nano-laminate template by spatial plasma atomic layer deposition (PEALD). Because the hBN flakes in Al2O3 thin film increase the diffusion path of moisture, the composite layer has a low water vapor transmission ratio (WVTR) value of 1.8 × 10−4 g/m2 day. Furthermore, as embedded hBN flakes restrict crack propagation, the composite film exhibits high mechanical stability in repeated 3 mm bending radius fatigue tests.
The assembly of nanowires and nanotubes into arrays patterned on multiple length scales is critical to the realization of integrated electronic and photonic nanotechnologies. A general and efficient ...solution-based method for controlling organization and hierarchy of nanowire structures over large areas has been developed. Nanowires were aligned with controlled nanometer to micrometer scale pitch using the Langmuir−Blodgett technique and transferred to planar substrates in a layer-by-layer process to form parallel and crossed nanowire structures. The parallel and crossed nanowire structures were efficiently patterned into repeating arrays of controlled dimensions and pitch using photolithography to yield hierarchical structures with order defined from the nanometer through centimeter length scales. In addition, electrical transport studies show that reliable electrical contacts can be made to the hierarchical nanowire arrays prepared by this method. This solution-based process offers a flexible pathway for bottom-up assembly of virtually any nanowire material into highly integrated and hierarchically organized nanodevices needed for a broad range of functional nanosystems.
We have developed thin zinc oxide (ZnO) layers protected highly conductive p-type silicon (Si) electrodes and investigated their diode and photoanode characteristics. ZnO layers have been deposited ...on the glass as well as p-Si substrates at a temperature of 400 °C by pulsed spray pyrolysis method. The crystal structure, surface morphology, and phase purity of the layers along with electrical characteristics of the heterostructures were investigated. Finally, the photocatalytic water oxidation performance of the ZnO/Si structures was studied in an alkaline electrolyte solution (pH = 10). The as-grown devices exhibited excellent diode characteristics with a turn-on voltage of 4.5 V, and applied bias-voltage dependent carrier transport mechanisms. As compared to bare Si, ZnO coated Si-based PEC devices showed good stability and durability along with very low onset potential of 0.07 V versus Ag/AgCl.
Ultrathin ZnO layers coated Si electrodes prepared by pulsed spray pyrolysis. These heterostructures exhibited excellent p-n junction diode characteristics along with good stability as well as durability as photoanodes in an alkaline electrolyte. Display omitted
•Si/ZnO heterostructures are developed and investigated.•Structures possess significant diode and PEC properties.•As compared to bare Si, good photoanodes stability and durability are observed.
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