Ferroelectric thin film has attracted great interest for nonvolatile memory applications and can be used in either ferroelectric Schottky diodes or ferroelectric tunneling junctions due to its ...promise of fast switching speed, high on-to-off ratio, and nondestructive readout. Two-dimensional α-phase indium selenide (In2Se3), which has a modest band gap and robust ferroelectric properties stabilized by dipole locking, is an excellent candidate for multidirectional piezoelectric and switchable photodiode applications. However, the large-scale synthesis of this material is still elusive, and its performance as a ferroresistive memory junction is rarely reported. Here, we report the low-temperature molecular-beam epitaxy (MBE) of large-area monolayer α-In2Se3 on graphene and demonstrate the use of α-In2Se3 on graphene in ferroelectric Schottky diode junctions by employing high-work-function gold as the top electrode. The polarization-modulated Schottky barrier formed at the interface exhibits a giant electroresistance ratio of 3.9 × 106 with a readout current density of >12 A/cm2, which is more than 200% higher than the state-of-the-art technology. Our MBE growth method allows a high-quality ultrathin film of In2Se3 to be heteroepitaxially grown on graphene, thereby simplifying the fabrication of high-performance 2D ferroelectric junctions for ferroresistive memory applications.
Lithium ion (Li-ion) batteries are an integral part of electric vehicles and hybrid electric vehicles because of their high energy and power density. These batteries suffer from a high temperature ...rise during operation, thus affecting their life span and efficiency. In this study, thermal management of Li-ion batteries was accomplished by using a novel material (Graphene coated nickel (GcN) foam saturated with paraffin). The growth of graphene coated on nickel foam was carried out using chemical vapor deposition. The thermal conductivity of the pure paraffin wax was enhanced by 23 times after infiltrating it into the GcN foam. The paraffin was used as a phase change material (PCM). The melting and freezing temperatures of the GcN foam saturated with paraffin were increased and decreased respectively as compared to pure paraffin. The latent heat and specific heat of the GcN foam saturated with paraffin is decreased by 30% and 34% respectively as compared to pure paraffin. The thermal management for Li-ion batteries is also compared among five materials: nickel foam, paraffin wax, GcN foam, nickel foam saturated with paraffin and GcN foam saturated with paraffin. The battery surface temperature rise is 17% less using graphene coated nickel foam saturated with PCM as compared to using nickel foam under 1.7 A discharge current.
•A graphene coated nickel (GcN) foam as thermal management for batteries is studied.•Temperature is 17% lower using GcN-paraffin composite comparing to nickel foam.•The GcN foam enhances the thermal conductivity of pure paraffin wax by 23 times.•The latent heat of GcN foam-paraffin composite is 30.41% lower than that of paraffin.
Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the ...monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B–C bonds and 1.6-fold for N–C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/μm2. Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering.
Luminescent defects in hexagonal boron nitride (hBN) have emerged as promising single photon emitters (SPEs) due to their high brightness and robust operation at room temperature. The ability to ...create such emitters with well‐defined optical properties is a cornerstone toward their integration into on‐chip photonic architectures. Here, an effective approach is reported to fabricate hBN SPEs with desired emission properties in distinct spectral regions via the manipulation of boron diffusion through copper during atmospheric pressure chemical vapor deposition (CVD)—a process termed gettering. Using the gettering technique the resulting zero‐phonon line is deterministically placed between the regions 550 and 600 nm or from 600 to 650 nm, paving the way for hBN SPEs with tailored emission properties. Additionally, rational control over the observed SPE density in the resulting films is demonstrated. The ability to control defect formation during hBN growth provides a cost effective means to improve the crystallinity of CVD hBN films, and lower defect density making it applicable to hBN growth for a wide‐range of applications. The results are important to understand defect formation of quantum emitters in hBN and deploy them for scalable photonic technologies.
Controlling the emission frequency of single photon emitters (SPEs) in hexagonal boron nitride has been a critical goal since their discovery in 2016. This work demonstrates a robust chemical vapor deposition method for producing SPEs of a preselectable frequency and density, based on modification of the catalytic behavior of copper using a gettering effect during growth.
The atomic thin, vertically-stacked 2H-MoTe2/MoS2 heterostructures are successfully synthesized using the single step chemical vapor deposition (CVD) method and a magnet-assisted secondary precursor ...delivery tool. The second material (MoTe2) was grown in a well-controlled, unique and epitaxial 2H-stacking mode atop the first material (MoS2), starting from the edges. This led to the construction of a vertical p-n junction with a broadband photoresponse from the ultraviolet (UV, 200 nm) to the near-infrared (IR, 1100 nm) regions. The high crystallinity of MoTe2/MoS2 heterostructures with a modulation of sulfur and tellurium distribution is corroborated by multiple characterization methods, including Raman spectroscopy, photoluminescence (PL) spectroscopy and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Furthermore, the photoelectrical measurements exhibit a tremendous photoresponsivity with an external quantum efficiency (EQE) as high as 4.71 A/W and 532% at 1100 nm, while as 4.67 A/W and 1935% at 300 nm, one to two orders of magnitude higher than other exfoliated MoTe2 heterostructure devices have been reported so far. This synthetic method is a controllable stacking mode confined synthesis approach for 2D heterostructures, and paves the way for the fabrication of high-performance functional telluride-based broadband photodetectors.
Highly crystallized bilayer MoTe2/MoS2 p-n heterojunctions with advanced photoresponsivity are for the first time synthesized by a single-run chemical vapor deposition method. The photodetectors exhibit a tremendous photoresponsivity as 4.71 A/W and an external quantum efficiency (EQE) as 532% at 1100 nm, while 4.67 A/W and 1935% at 300 nm, which are one to two orders of magnitude higher than other transition-metal dichalcogenides (TMDs) heterostructures reported so far. Display omitted
Development of next-generation porous sorbents to overcome the challenges, such as low uptake capacity, slow sorption rate, and non-recyclability, associated with conventional sorbents is of utmost ...importance. Herein, we report the synthesis of a highly porous graphene aerogel (GA) with a unique three-dimensional hierarchical bimodal porous network of macro and meso-pores via a facile hydrothermal technique; this aerogel has sorption capacity that is more than 5 times that of conventional commercial sorbents. Fluoroalkyl silane functionalization of the GA surface results in a significant reduction in its water sorption from 20 g g −1 to 5 g g −1 due to the GA surface becoming more hydrophobic, which renders it useful in practical application to selectively remove oil from seawater. Moreover, the sorption rate of the GA for oils and organic solvents has been found to be extremely fast, and saturation of the GA is completed in a few seconds. This is attributed to its unique meso–macro bimodal porous structure with large pore channels called macro-pores or voids of various sizes ranging from 300 nm to over 10 μm, which facilitate mass transport into its inner mesopores of 14–18 nm at high rate. Finally, the GA is shown to be a highly recyclable material due to its good mechanical strength, where the oil- and organic solvent-sorbed GA can be efficiently recovered using thermal or chemical methods for several sorption–desorption cycles without significant loss in its capacity, which also makes the process cost effective and environmentally friendly.
Miniaturization and energy consumption by computational systems remain major challenges to address. Optoelectronics based synaptic and light sensing provide an exciting platform for neuromorphic ...processing and vision applications offering several advantages. It is highly desirable to achieve single‐element image sensors that allow reception of information and execution of in‐memory computing processes while maintaining memory for much longer durations without the need for frequent electrical or optical rehearsals. In this work, ultra‐thin (<3 nm) doped indium oxide (In2O3) layers are engineered to demonstrate a monolithic two‐terminal ultraviolet (UV) sensing and processing system with long optical state retention operating at 50 mV. This endows features of several conductance states within the persistent photocurrent window that are harnessed to show learning capabilities and significantly reduce the number of rehearsals. The atomically thin sheets are implemented as a focal plane array (FPA) for UV spectrum based proof‐of‐concept vision system capable of pattern recognition and memorization required for imaging and detection applications. This integrated light sensing and memory system is deployed to illustrate capabilities for real‐time, in‐sensor memorization, and recognition tasks. This study provides an important template to engineer miniaturized and low operating voltage neuromorphic platforms across the light spectrum based on application demand.
Optoelectronic vision and synaptic devices can help overcome high energy requirements of computation and enable miniaturised, precise, real‐time vision systems. Herein, atomically thin layers of Sb doped In2O3 are utilised as ultraviolet‐active optoelectronic synapses with recognition and prolonged memory capabilities. The material is devised into an imaging array of photo‐active pixels capable of pattern recognition and memorization at low power with very few training cycles.
Photodetector technology has evolved significantly over the years with the emergence of new active materials. However, there remain trade-offs between spectral sensitivity, operating energy, and, ...more recently, an ability to harbor additional features such as persistent photoconductivity and bidirectional photocurrents for new emerging application areas such as switchable light imaging and filter-less color discrimination. Here, we demonstrate a self-powered bidirectional photodetector based on molybdenum disulfide/gallium nitride (MoS2/GaN) epitaxial heterostructure. This fabricated detector exhibits self-powered functionality and achieves detection in two discrete wavelength bands: ultraviolet and visible. Notably, it attains a peak responsivity of 631 mAW–1 at a bias of 0V. The device’s response to illumination at these two wavelengths is governed by distinct mechanisms, activated under applied bias conditions, thereby inducing a reversal in the polarity of the photocurrent. This work underscores the feasibility of self-powered and bidirectional photocurrent detection but also opens new vistas for technological advancements for future optoelectronic, neuromorphic, and sensing applications.
A unique strategy is reported to constrain the nucleation centers for multilayer graphene (MLG) and, later, single‐crystal graphene domains by gettering carbon source on backside of the flat Cu foil, ...during chemical vapor deposition. Hitherto, for a flat Cu foil, the top‐surface‐based growth mechanism is emphasized, while overlooking the graphene on the backside. However, the systematic experimental findings indicate a strong correlation between the backside graphene and the nucleation centers on the top‐surface, governed by the carbon diffusion through the bulk Cu. This understanding steers to devise a strategy to mitigate the carbon diffusion to the top‐surface by using a carbon “getter” substrate, such as nickel, on the backside of the Cu foil. Depth profiling of the nickel substrate, along with the density functional theory calculations, verifies the gettering role of the nickel support. The implementation of the backside carbon gettering approach on single‐crystal graphene growth results in lowering the nucleation density by two orders of magnitude. This enables the single‐crystal domains to grow by 6 mm laterally on the untreated Cu foil. Finally, the growth of large‐area polycrystalline single layer graphene, free of unwanted MLG domains, with significantly improved field‐effect mobility of ≈6800 cm2 V−1 s−1 is demonstrated.
A backside carbon gettering approach is implemented to manipulate top‐surface CVD graphene growth on Cu foil using a Ni support substrate. This strategy limits the nucleation centers for multilayer and single‐crystal graphene domains at the top‐surface through gettering the carbon source at backside of the Cu foil, resulting in high quality uniform single‐crystal graphene.
Ferroelectric thin film has attracted great interest for nonvolatile memory applications and can be used in either ferroelectric Schottky diodes or ferroelectric tunneling junctions due to its ...promise of fast switching speed, high on-to-off ratio, and nondestructive readout. Two-dimensional α-phase indium selenide (In
Se
), which has a modest band gap and robust ferroelectric properties stabilized by dipole locking, is an excellent candidate for multidirectional piezoelectric and switchable photodiode applications. However, the large-scale synthesis of this material is still elusive, and its performance as a ferroresistive memory junction is rarely reported. Here, we report the low-temperature molecular-beam epitaxy (MBE) of large-area monolayer α-In
Se
on graphene and demonstrate the use of α-In
Se
on graphene in ferroelectric Schottky diode junctions by employing high-work-function gold as the top electrode. The polarization-modulated Schottky barrier formed at the interface exhibits a giant electroresistance ratio of 3.9 × 10
with a readout current density of >12 A/cm
, which is more than 200% higher than the state-of-the-art technology. Our MBE growth method allows a high-quality ultrathin film of In
Se
to be heteroepitaxially grown on graphene, thereby simplifying the fabrication of high-performance 2D ferroelectric junctions for ferroresistive memory applications.
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