Graphene-Based Mixed-Dimensional van der Waals Heterostructures for Advanced Optoelectronics

Advancements and Challenges in the Integration of Indium Arsenide and Van der Waals Heterostructures

The strategic integration of low-dimensional InAs-based materials and emerging van der Waals systems is advancing in various scientific fields, including electronics, optics, and magnetics. With their unique properties, these InAs-based van der Waals materials and devices promise further miniaturization of semiconductor devices in line with Moore's Law. However, progress in this area lags behind other 2D materials like graphene and boron nitride. Challenges include synthesizing pure crystalline phase InAs nanostructures and single-atomic-layer 2D InAs films, both vital for advanced van der Waals heterostructures. Also, diverse surface state effects on InAs-based van der Waals devices complicate their performance evaluation. This review discusses the experimental advances in the van der Waals epitaxy of InAs-based materials and the working principles of InAs-based van der Waals devices. Theoretical achievements in understanding and guiding the design of InAs-based van der Waals systems are highlighted. Focusing on advancing novel selective area growth and remote epitaxy, exploring multi-functional applications, and incorporating deep learning into first-principles calculations are proposed. These initiatives aim to overcome existing bottlenecks and accelerate transformative advancements in integrating InAs and van der Waals heterostructures.

A 1T'-MoTe2/GaN van der Waals Schottky junction for self-powered UV imaging and optical communication

Schottky-type self-powered UV photodetectors are promising for next-generation imaging systems. Nevertheless, conventional device fabrication using high-energy metal deposition brings unintentional interface defects, leading to deteriorated device performance and inhomogeneities. Emerging two-dimensional (2D) metallic materials offer an alternative pathway to overcoming such limitations because of their naturally passivated surfaces and the ease of combining with mature bulk semiconductors via van der Waals (vdW) integration. Here, we report the controllable preparation of MoTe2 in the pure 1T' phase and the fabrication of a high-performance 1T'-MoTe2/GaN vdW Schottky photodiode. With the reduced interface states and suppressed dark current as low as 20 pA at zero bias, the photodiode exhibits a remarkable UV-to-visible (R350/R400) rejection ratio of 1.6 × 104, a stable photoresponsivity of ∼50 mA W-1 and a detectivity of 3.5 × 1012 Jones under 360 nm illumination. The photocurrent ON/OFF ratio reaches ∼4.9 × 106 under 10.5 mW irradiation (360 nm). In particular, the 1T'-MoTe2/GaN Schottky diode shows excellent weak-light detection capability, which could detect a 3 nW 360 nm laser and the light emission from a lighter with a pronounced Ilight/Idark ratio of ∼2. Finally, the applications of the device in self-powered UV imaging and optical communication are demonstrated. These results reveal the great prospects of 2D/3D integration in multifunctional optoelectronics, which may inspire novel 2D-related devices and expand their applications in widespread fields.

Mixed-Dimensional van der Waals Heterostructure (2D ReS2/0D MoS2 Quantum Dots)-Based Broad Spectral Range with Ultrahigh-Responsive Photodetector

The remarkable properties of two-dimensional (2D) materials have led to significant advancements in photodetection and optoelectronics research. Currently, there are many successful methods that are employed to improve the responsivity of photodetectors, but the limited spectral range of the device remains a limitation. This work demonstrates the development of a mixed-dimensional (2D/0D) hybrid photodetector device fabricated using chemical vapor deposition (CVD)-grown monolayer ReS2 and solution-processed MoS2 quantum dots (QDs). The mixed dimensionality of 2D (ReS2) and zero-dimensional (0D) MoS2 QDs assist in improving the spectral range of the device [ultraviolet (360 nm) to near-infrared (780 nm)]. Further, due to the work function difference between ReS2 and MoS2 QDs, the built-in electric field across the mixed-dimensional interface promotes effective charge separation and migration, resulting in improved responsivities of the device. The calculated responsivities of the fabricated photodetector are 5.4 × 102, 3.3 × 102, and 2.6 × 102 A/W when subjected to visible, UV, and NIR light illumination, which is remarkable when compared to the existing reports on broadband photodetection. The mixed-dimensionality heterostructure coupled with contact engineering paves the way for highly responsive broadband photodetectors for potential applications in security, healthcare, etc.

Tunable Adhesion for All-Dry Transfer of 2D Materials Enabled by the Freezing of Transfer Medium

The real applications of chemical vapor deposition (CVD)-grown graphene films require the reliable techniques for transferring graphene from growth substrates onto application-specific substrates. The transfer approaches that avoid the use of organic solvents, etchants, and strong bases are compatible with industrial batch processing, in which graphene transfer should be conducted by dry exfoliation and lamination. However, all-dry transfer of graphene remains unachievable owing to the difficulty in precisely controlling interfacial adhesion to enable the crack- and contamination-free transfer. Herein, through controllable crosslinking of transfer medium polymer, the adhesion is successfully tuned between the polymer and graphene for all-dry transfer of graphene wafers. Stronger adhesion enables crack-free peeling of the graphene from growth substrates, while reduced adhesion facilitates the exfoliation of polymer from graphene surface leaving an ultraclean surface. This work provides an industrially compatible approach for transferring 2D materials, key for their future applications, and offers a route for tuning the interfacial adhesion that would allow for the transfer-enabled fabrication of van der Waals heterostructures.

Single Wavelength Operating Neuromorphic Device Based on a Graphene-Ferroelectric Transistor

As global data generation continues to rise, there is an increasing demand for revolutionary in-memory computing methodologies and efficient machine learning solutions. Despite recent progress in electrical and electro-optical simulations of machine learning devices, the all-optical nonthermal function remains challenging, with single wavelength operation still elusive. Here we report on an optical and monochromatic way of neuromorphic signal processing for brain-inspired functions, eliminating the need for electrical pulses. Multilevel synaptic potentiation-depression cycles are successfully achieved optically by leveraging photovoltaic charge generation and polarization within the photoferroelectric substrate interfaced with the graphene sensor. Furthermore, the demonstrated low-power prototype device is able to reproduce exact signal profile of brain tissues yet with more than 2 orders of magnitude faster response. The reported properties should trigger all-optical and low power artificial neuromorphic development based on photoferroelectric structures.

Organic Bilayer Heterostructures with Built-In Exciton Conversion for 2D Photonic Encryption

Organic multilayer heterostructures with accurate spatial organization demonstrate strong light-matter interaction from excitonic responses and efficient carrier transfer across heterojunction interfaces, which are considered as promising candidates toward advanced optoelectronics. However, the precise regulation of the heterojunction surface area for finely adjusting exciton conversion and energy transfer is still formidable. Herein, organic bilayer heterostructures (OBHs) with controlled face-to-face heterojunction via a stepwise seeded growth strategy, which is favorable for efficient exciton propagation and conversion of optical interconnects are designed and synthesized. Notably, the relative position and overlap length ratio of component microwires (LDSA /LBPEA = 0.39-1.15) in OBHs are accurately regulated by modulating the crystallization time of seeded crystals, resulting into a tailored heterojunction surface area (R = Loverlap /LBPEA = 37.6%-65.3%). These as-prepared OBHs present the excitation position-dependent waveguide behaviors for optical outcoupling characteristics with tunable emission colors and intensities, which are applied into two-dimensional (2D) photonic barcodes. This strategy opens a versatile avenue to purposely design OBHs with tailored heterojunctions for efficient energy transfer and exciton conversion, facilitating the application possibilities of advanced integrated optoelectronics.

Optically Active MXenes in Van der Waals Heterostructures

The vertical integration of distinct 2D materials in van der Waals (vdW) heterostructures provides the opportunity for interface engineering and modulation of electronic as well as optical properties. However, scarce experimental studies reveal many challenges for vdW heterostructures, hampering the fine-tuning of their electronic and optical functionalities. Optically active MXenes, the most recent member of the 2D family, with excellent hydrophilicity, rich surface chemistry, and intriguing optical properties, are a novel 2D platform for optoelectronics applications. Coupling MXenes with various 2D materials into vdW heterostructures can open new avenues for the exploration of physical phenomena of novel quantum-confined nanostructures and devices. Therefore, the fundamental basis and recent findings in vertical vdW heterostructures composed of MXenes as a primary component and other 2D materials as secondary components are examined. Their robust designs and synthesis approaches that can push the boundaries of light-harvesting, transition, and utilization are discussed, since MXenes provide a unique playground for pursuing an extraordinary optical response or unusual light conversion features/functionalities. The recent findings are finally summarized, and a perspective for the future development of next-generation vdW multifunctional materials enriched by MXenes is provided.

Mixed-Dimensional van der Waals Heterostructures for Boosting Electricity Generation

The emerging technology of harvesting environmental energy using hydrovoltaic devices enriches the conversion forms of renewable energy. It provides more concepts for power supply in micro/nano systems, and hydrovoltaic technology with high performance, usability, and integration is essential for achieving sustainable green energy. Comparing the discovery of multiscale nanomaterials, working layers with innovative microstructures have gradually become the dominant trend in the construction of graphene-based hydrovoltaic devices. However, reports on promoting ion/electron redistribution at the solid-liquid interface through the substrate effect of graphene are accompanied by tedious procedures, nondiverse substrates, and monolithic regulation of enhancement mechanisms. Here, the electrophoretic deposition (EPD)-driven SiC whiskers (SiCw)-assisted graphene transfer process is adopted to alleviate the complexity of the device fabrication caused by graphene transfer. The resulting output performance of the graphene/SiCw (GS) mesh films is significantly boosted. The high integrity of graphene and prominent negative surface charge near the graphene-droplet interface are derived from the overlayer and underlayer inside the graphene-based mixed-dimensional van der Waals (vdW) heterostructures, respectively. Additionally, a self-powered desalination-monitoring system is designed based on integrated hydrovoltaic devices. Electricity harvested from the ionic solutions is reused for deionization, representing an efficient strategy for energy conversion and utilization.

Stabilization of transition metal heterojunctions inside porous materials for high-performance catalysis

Transition metal-based heterostructural materials are a class of very promising substitutes for noble metal-based catalysts for high-performance catalysis, due to their inherent internal electric field at the interface in the heterojunctions, which could induce electron relocalization and facilitate charge carrier migration between different metal sites at heterostructural boundaries. However, redox-active metal species suffer from reduction, oxidation, migration, aggregation, leaching and poisoning in catalysis, which results in heavy deterioration of the catalytic properties of transition metal-based heterojunctions and frustrates their practical applications. To improve the stability of transition metal-based heterojunctions and sufficiently expose redox-active sites at the heterosurfaces, many kinds of porous materials have been used as porous hosts for the stabilization of non-precious metal heterojunctions. This review article will discuss recently developed strategies for encapsulation and stabilization of transition metal heterojunctions inside porous materials, and highlight their improved stability and catalytic performance through the spatial confinement effect and synergistic interaction between the heterojunctions and the host matrices.

Ordered Van der Waals Hetero-nanoribbon from Pressure-Induced Topochemical Polymerization of Azobenzene

Pressure-induced topochemical polymerization of molecular crystals with various stackings is a promising way to synthesize materials with different co-existing sub-structures. Here, by compressing the azobenzene crystal containing two kinds of intermolecular stacking, we synthesized an ordered van der Waals carbon nanoribbon (CNR) heterostructure in one step. Azobenzene polymerizes via a [4 + 2] hetero-Diels-Alder (HDA) reaction of phenylazo-phenyl in layer A and a para-polymerization reaction of phenyl in layer B at 18 GPa, as evidenced by in situ Raman and IR spectroscopies, X-ray diffraction, as well as gas chromatography-mass spectrometry and the solid-state nuclear magnetic resonance of the recovered products. The theoretical calculation shows that the obtained CNR heterostructure has a type II (staggered) band gap alignment. Our work highlights a high-pressure strategy to synthesize bulk CNR heterostructures.

2D Material Infrared Photonics and Plasmonics

Two-dimensional (2D) materials including graphene, transition metal dichalcogenides, black phosphorus, MXenes, and semimetals have attracted extensive and widespread interest over the past years for their many intriguing properties and phenomena, underlying physics, and great potential for applications. The vast library of 2D materials and their heterostructures provides a diverse range of electrical, photonic, mechanical, and chemical properties with boundless opportunities for photonics and plasmonic devices. The infrared (IR) regime, with wavelengths across 0.78 μm to 1000 μm, has particular technological significance in industrial, military, commercial, and medical settings while facing challenges especially in the limit of materials. Here, we present a comprehensive review of the varied approaches taken to leverage the properties of the 2D materials for IR applications in photodetection and sensing, light emission and modulation, surface plasmon and phonon polaritons, non-linear optics, and Smith-Purcell radiation, among others. The strategies examined include the growth and processing of 2D materials, the use of various 2D materials like semiconductors, semimetals, Weyl-semimetals and 2D heterostructures or mixed-dimensional hybrid structures, and the engineering of light-matter interactions through nanophotonics, metasurfaces, and 2D polaritons. Finally, we give an outlook on the challenges in realizing high-performance and ambient-stable devices and the prospects for future research and large-scale commercial applications.

Low-Temperature Direct Growth of Amorphous Boron Nitride Films for High-Performance Nanoelectronic Device Applications

We successfully demonstrated the improvement and stabilization of the electrical properties of a graphene field effect transistor by fabricating a sandwiched amorphous boron nitride (a-BN)/graphene (Gr)/a-BN using a directly grown a-BN film. The a-BN film was grown via low-pressure chemical vapor deposition (LPCVD) at a low growth temperature of 250 °C and applied as a protection layer in the sandwiched structure. Both structural and chemical states of the as-grown a-BN were verified by various spectroscopic and microscopic analyses. We analyzed the Raman spectra of Gr/SiO₂ and a-BN/Gr/a-BN structures to determine the stability of the device under exposure to ambient air. Following exposure, the intensity of the 2D/G-peak ratio of Gr/SiO₂ decreased and the position of the G and 2D peaks red-shifted due to the degradation of graphene. In contrast, the peak position of encapsulated graphene is almost unchanged. We also confirmed that the mobility of a-BN/Gr/a-BN structure is 17,941 cm²/Vs. This synthetic strategy could provide a facile way to synthesize uniform a-BN film for encapsulating various van der Waals materials, which is beneficial for future applications in nanoelectronics.

Quasi-2D Mn3Si2Te6 Nanosheet for Ultrafast Photonics

The magnetic nanomaterial Mn₃Si₂Te₆ is a promising option for spin-dependent electronic and magneto-optoelectronic devices. However, its application in nonlinear optics remains fanciful. Here, we demonstrate a pulsed Er-doped fiber laser (EDFL) based on a novel quasi-2D Mn₃Si₂Te₆ saturable absorber (SA) with low pump power at 1.5 μm. The high-quality Mn₃Si₂Te₆ crystals were synthesized by the self-flux method, and the ultrathin Mn₃Si₂Te₆ nanoflakes were prepared by a simple mechanical exfoliation procedure. To the best of our knowledge, this is the first time laser pulses have been generated using quasi-2D Mn₃Si₂Te₆. A stable pulsed laser at 1562 nm with a low threshold pump power of 60 mW was produced by integrating the Mn₃Si₂Te₆ SA into an EDFL cavity. The maximum power of the output pulse is 783 μW. The repetition rate can vary from 24.16 to 44.44 kHz, with corresponding pulse durations of 5.64 to 3.41 µs. Our results indicate that the quasi-2D Mn₃Si₂Te₆ is a promising material for application in ultrafast photonics.

Miniaturized infrared spectrometer based on the tunable graphene plasmonic filter

Miniaturization of a conventional spectrometer is challenging because of the tradeoffs of size, cost, signal-to-noise ratio, and spectral resolution, etc. Here, a new type of miniaturized infrared spectrometer based on the integration of tunable graphene plasmonic filters and infrared detectors is proposed. The transmittance spectrum of a graphene plasmonic filter can be tuned by varying the Fermi energy of the graphene, allowing light incident on the graphene plasmonic filter to be dynamically modulated in a way that encodes its spectral information in the receiving infrared detector. The incident spectrum can then be reconstructed by using decoding algorithms such as ridge regression and neural networks. The factors that influence spectrometer performance are investigated in detail. It is found that the graphene carrier mobility and the signal-to-noise ratio are two key parameters in determining the resolution and precision of the spectrum reconstruction. The mechanism behind our observations can be well understood in the framework of the Wiener deconvolution theory. Moreover, a hybrid decoding (or recovery) algorithm that combines ridge regression and a neural network is proposed that demonstrates a better spectral recovery performance than either the ridge regression or a deep neural network alone, being able to achieve a sub-hundred nanometer spectral resolution across the 8∼14 µm wavelength range. The size of the proposed spectrometer is comparable to a microchip and has the potential to be integrated within portable devices for infrared spectral imaging applications.

Fabrication of r-GO/GO/α-Fe2O3/Fe2TiO5 Nanocomposite Using Natural Ilmenite and Graphite for Efficient Photocatalysis in Visible Light

Hematite (α-Fe₂O₃) and pseudobrookite (Fe₂TiO₅) suffer from poor charge transport and a high recombination effect under visible light irradiation. This study investigates the design and production of a 2D graphene-like r-GO/GO coupled α-Fe₂O₃/Fe₂TiO₅ heterojunction composite with better charge separation. It uses a simple sonochemical and hydrothermal approach followed by L-ascorbic acid chemical reduction pathway. The advantageous band offset of the α-Fe₂O₃/Fe₂TiO₅ (TF) nanocomposite between α-Fe₂O₃ and Fe₂TiO₅ forms a Type-II heterojunction at the Fe₂O₃/Fe₂TiO₅ interface, which efficiently promotes electron-hole separation. Importantly, very corrosive acid leachate resulting from the hydrochloric acid leaching of ilmenite sand, was successfully exploited to fabricate α-Fe₂O₃/Fe₂TiO₅ heterojunction. In this paper, a straightforward synthesis strategy was employed to create 2D graphene-like reduced graphene oxide (r-GO) from Ceylon graphite. The two-step process comprises oxidation of graphite to graphene oxide (GO) using the improved Hummer's method, followed by controlled reduction of GO to r-GO using L-ascorbic acid. Before the reduction of GO to the r-GO, the surface of TF heterojunction was coupled with GO and was allowed for the controlled L-ascorbic acid reduction to yield r-GO/GO/α-Fe₂O₃/Fe₂TiO₅ nanocomposite. Under visible light illumination, the photocatalytic performance of the 30% GO/TF loaded composite material greatly improved (1240 Wcm^-2). Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) examined the morphological characteristics of fabricated composites. X-ray photoelectron spectroscopy (XPS), Raman, X-ray diffraction (XRD), X-ray fluorescence (XRF), and diffuse reflectance spectroscopy (DRS) served to analyze the structural features of the produced composites.

Recent progress of two-dimensional heterostructures for thermoelectric applications

The rapid development of synthesis and fabrication techniques has opened up a research upsurge in two-dimensional (2D) material heterostructures, which have received extensive attention due to their superior physical and chemical properties. Currently, thermoelectric energy conversion is an effective means to deal with the energy crisis and increasingly serious environmental pollution. Therefore, an in-depth understanding of thermoelectric transport properties in 2D heterostructures is crucial for the development of micro-nano energy devices. In this review, the recent progress of 2D heterostructures for thermoelectric applications is summarized in detail. Firstly, we systematically introduce diverse theoretical simulations and experimental measurements of the thermoelectric properties of 2D heterostructures. Then, the thermoelectric applications and performance regulation of several common 2D materials, as well as in-plane heterostructures and van der Waals heterostructures, are also discussed. Finally, the challenges of improving the thermoelectric performance of 2D heterostructures materials are summarized, and related prospects are described.

Polarity-Reversible Te/WSe2 van der Waals Heterodiode for a Logic Rectifier and Polarized Short-Wave Infrared Photodetector

As a p-type elemental material with high carrier mobility, superior ambient stability, and anisotropic crystal structure, emerging two-dimensional (2D) tellurium (Te) has been considered a successor to black phosphorus for developing infrared-related optoelectronics. Nevertheless, the lack of a scalable thickness engineering strategy remains an obstacle to unleashing its full potential. Te-based electronics with logic functions are also less explored. Herein, we propose a novel wet-chemical thinning method for 2D Te, with the merits of scalability and site-specific thickness patterning capability. A polarity-switchable van der Waals (vdW) heterodiode with a high rectification ratio of 2.4 × 10³ is realized on the basis of Te/WSe₂. The electronic application of this unique characteristic is demonstrated by fabricating a logic half-wave rectifier, in which the rectifying states are switchable via electrostatic gating control. Besides, the narrow band gap of Te endows the device with a broad spectral response from visible to short-wave infrared. The room-temperature responsivity reaches 5.2 A W^-1 at the telecom wavelength of 1.55 μm, with an external quantum efficiency of 420% and detectivity of 6.8 × 10⁹ Jones. In particular, owing to the intrinsic in-plane anisotropy of Te, the device exhibits a favorable photocurrent anisotropic ratio of ∼3. Our study demonstrates the enormous potential of Te for novel electronics, promoting the development of elemental 2D materials.

Inducing Strong Light-Matter Coupling and Optical Anisotropy in Monolayer MoS2 with High Refractive Index Nanowire

Mixed-dimensional heterostructures combine the merits of materials of different dimensions; therefore, they represent an advantageous scenario for numerous technological advances. Such an approach can be exploited to tune the physical properties of two-dimensional (2D) layered materials to create unprecedented possibilities for anisotropic and high-performance photonic and optoelectronic devices. Here, we report a new strategy to engineer the light-matter interaction and symmetry of monolayer MoS₂ by integrating it with one-dimensional (1D) AlGaAs nanowire (NW). Our results show that the photoluminescence (PL) intensity of MoS₂ increases strongly in the mixed-dimensional structure because of electromagnetic field confinement in the 1D high refractive index semiconducting NW. Interestingly, the 1D NW breaks the 3-fold rotational symmetry of MoS₂, which leads to a strong optical anisotropy of up to ∼60%. Our mixed-dimensional heterostructure-based phototransistors benefit from this and exhibit an improved optoelectronic device performance with marked anisotropic photoresponse behavior. Compared with bare MoS₂ devices, our MoS₂/NW devices show ∼5 times enhanced detectivity and ∼3 times higher photoresponsivity. Our results of engineering light-matter interaction and symmetry breaking provide a simple route to induce enhanced and anisotropic functionalities in 2D materials.

Dirac Fermion Cloning, Moiré Flat Bands, and Magic Lattice Constants in Epitaxial Monolayer Graphene

Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the 2D material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals, and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different twisted graphene layers. In this work, a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates is proposed. Graphene/SiC heterostructure is taken as a prototypical example and it is demonstrated experimentally that the substrate modulation leads to Dirac fermion cloning and, consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Theoretical modeling captures the cloning mechanism of the Dirac states and indicates that moiré flat bands can emerge at certain magic lattice constants of the substrate, specifically when the period of modulation becomes nearly commensurate with the ( 3   ×   3 ) R 30 o \[(\sqrt 3 \; \times \;\sqrt 3 )R{30^o}\] supercell of graphene. The results show that epitaxial single monolayer graphene on suitable substrates is a promising platform for exploring exotic many-body quantum phases arising from interactions between Dirac electrons.

Enhanced Versatility of Table-Top X-Rays from Van der Waals Structures

Van der Waals (vdW) materials have attracted much interest for their myriad unique electronic, mechanical, and thermal properties. In particular, they are promising candidates for monochromatic, table-top X-ray sources. This work reveals that the versatility of the table-top vdW X-ray source goes beyond what has been demonstrated so far. By introducing a tilt angle between the vdW structure and the incident electron beam, it is theoretically and experimentally shown that the accessible photon energy range is more than doubled. This allows for greater versatility in real-time tuning of the vdW X-ray source. Furthermore, this work shows that the accessible photon energy range is maximized by simultaneously controlling both the electron energy and the vdW structure tilt. These results will pave the way for highly tunable, compact X-ray sources, with potential applications including hyperspectral X-ray fluoroscopy and X-ray quantum optics.

Effects of adatom species on the structure, stability, and work function of adatom-α-borophene nanocomposites

Work function-tunable borophene-based electrode materials are of significant importance because they promote efficient carrier extraction/injection, thereby enabling electronic devices to achieve maximum energy conversion efficiency. Accordingly, determining the work function of adatom-borophene nanocomposites within a series wherein the adatom is systematically changed will facilitate the design of such materials. In this study, we theoretically determined that the M-B bond length, binding energy, electron transfer between adatoms and BBP, and work function (ϕ) are linearly dependent on the ionization potential (IP) and electronegativity for thermodynamically and kinetically stable adatom-α-borophene (M/BBP) systems involving a series of alkali (earth) metal/BBP (M = Li-Cs; Be-Ba) and halogen/BBP (M = F-I), respectively. However, the binding energies of Li/BBP and Be/BBP deviate from these dependencies owing to their super small adatoms and the resulting significantly enhanced effective M-B bonding areas. By interpreting the electron transfer picture among the different parts of M/BBP, we confirmed that metallic M/BBP possesses ionic sp-p and dsp-p M-B bonds in alkali (earth) metal/BBP but covalent-featured ionic p-p interactions in halogen/BBP. In particular, the direct proportionality between IP and ϕ for alkali (earth) metal/BBP originates from the synergistic effect of charge rearrangement and the increased induced dipole moment; however, the inverse proportionality between electronegativity and ϕ for halogen/BBP arises from the adsorption induced charge redistribution. Our results provide guidance for experimental efforts toward the realization of work function-tunable borophene-based electrodes as well as insight into the bonding rules between various adatoms and α-borophene.

In Situ Reduced Graphene Oxide and Polyvinyl Alcohol Nanocomposites With Enhanced Multiple Properties

The nanocomposites formed by graphene oxide (GO) and carbazate-modified polyvinyl alcohol (PVA-N) were developed to investigate their multiple properties for wide applications. Their physicochemical characterizations confirmed that the in situ reduced GO (rGO) not only decreased the crystallization but also induced the porous structures inside the nanocomposites. Significantly, it revealed that the comprehensive performance of PVA-N2-2%GO consisted of PVA-N2 with the carbazate degree of substitution (DS) of 7% and the weight ratio (wt%) of 2% GO displayed 79% of tensile elongation and tensile strength of 5.96 N/mm² (MPa) by tensile testing, glass transition temperature (Tg) of 60.8°C and decomposition temperature (Td) of 303.5°C by TGA and DSC, surface contact angle at 89.4 ± 2.1°, and electrical conductivity of 9.95 × 10⁻¹¹ S/cm. The abovementioned comprehensive performance was enhanced with the increased amount of in situ rGO, contributed by the high DS of the carbazate group in PVA-N and high amount of GO. The rGO by in situ reduction was the main driving force for enhancing the multiple properties inside the nanocomposites.

Fabrication Strategies and Optoelectronic Applications of Perovskite Heterostructures

Metal halide perovskites (MHPs) are emerging low‐cost and multifunctional semiconductor materials. They have been widely used in optoelectronic devices such as perovskite solar cells, light‐emitting diodes, photodetectors, memristors, and lasers. Developing new MHPs, defects passivation, optimizing device structures, and packaging techniques are all effective methods to improve photoelectric performance and stability of perovskite devices. Particularly, the fabrication of perovskite/perovskite heterostructures (PPHSs) is a novel and arresting method to obtain stable and high‐performing optoelectronic perovskite devices since it can passivate defects, regulate energy gaps, and provide new carrier transmission modes of MHPs for multiple semiconductor applications. In this paper, representative fabrication strategies of PPHSs including films and single‐crystal heterostructures are reviewed, and their applications in optoelectronic devices are summarized. Furthermore, the challenges and prospects of PPHSs are discussed based on the current status.

Vertical 1D/2D Heterojunction Architectures for Self-Powered Photodetection Application: GaN Nanorods Grown on Transition Metal Dichalcogenides

Van der Waals (vdW) heterojunctions based on two-dimensional (2D) transition metal dichalcogenide (TMD) materials have attracted the attention of researchers to conduct fundamental investigations on emerging physical phenomena and expanding diverse nano-optoelectronic devices. Herein, the quasi-van der Waals epitaxial (QvdWE) growth of vertically aligned one-dimensional (1D) GaN nanorod arrays (NRAs) on TMDs/Si substrates is reported, and their vdW heterojunctions in the applications of high-performance self-powered photodetection are demonstrated accordingly. Such 1D/2D hybrid systems fully combine the advantages of the strong light absorption of 1D GaN nanoarrays and the excellent electrical properties of 2D TMD materials, boosting the photogenerated current density, which demonstrates a light on/off ratio above 10⁵. The device exhibits a competitive photovoltaic photoresponsivity over 10 A W^-1 under a weak detectable light signal without any external bias, which is attributed to the efficient photogenerated charge separation under the strong built-in potential from the type-II band alignment of GaN NRAs/TMDs. This work presents a QvdWE route to prepare 1D/2D heterostructures for the fabrication of self-powered photodetectors, which shows promising potentials for practical applications of space communications, sensing networks, and environmental monitoring.

Tunable Quantum Tunneling through a Graphene/Bi2Se3 Heterointerface for the Hybrid Photodetection Mechanism

Graphene-based van der Waals heterostructures are promising building blocks for broadband photodetection because of the gapless nature of graphene. However, their performance is mostly limited by the inevitable trade-off between low dark current and photocurrent generation. Here, we demonstrate a hybrid photodetection mode based on the photogating effect coupled with the photovoltaic effect via tunable quantum tunneling through the unique graphene/Bi₂Se₃ heterointerface. The tunneling junction formed between the semimetallic graphene and the topologically insulating Bi₂Se₃ exhibits asymmetric rectifying and hysteretic current-voltage characteristics, which significantly suppresses the dark current and enhances the photocurrent. The photocurrent-to-dark current ratio increases by about a factor of 10 with the electrical tuning of tunneling resistance for efficient light detection covering the major photonic spectral band from the visible to the mid-infrared ranges. Our findings provide a novel concept of using tunable quantum tunneling for highly sensitive broadband photodetection in mixed-dimensional van der Waals heterostructures.

Metallization and Superconductivity in the van der Waals Compound CuP2Se through Pressure-Tuning of the Interlayer Coupling

Emergent layered Cu-bearing van der Waals (vdW) compounds have great potentials for use in electrocatalysis, lithium batteries, and electronic and optoelectronic devices. However, many of their alluring properties such as potential superconductivity remain unknown. In this work, using CuP₂Se as a model compound, we explored its electrical transport and structural evolution at pressures up to ∼60 GPa using both experimental determinations and ab initio calculations. We found that CuP₂Se undergoes a semiconductor-to-metal transition at ∼20 GPa at room temperature and a metal-to-superconductor transition at 3.3-5.7 K in the pressure range from 27.0 to 61.4 GPa. At ∼10 and 20 GPa, there are two isostructural changes in the compound, corresponding to, respectively, the emergence of the interlayer coupling and start of interlayer atomic bonding. At a pressure between 35 and 40 GPa, the vdW layers start to slide and then merge, forming a new phase with high coordination numbers. We also found that the Bardeen-Cooper-Schrieffer (BCS) theory describes quite well the pressure dependence of the critical temperature despite occurrence of a possible medium-to-strong electron-phonon coupling, revealing the determinant roles of the enhanced bulk modulus and electron density of states at high pressure. Moreover, nanosizing of CuP₂Se at high pressure further increased the critical temperature even at sizes approaching the Anderson limit. These findings would have important implications for developing novel applications of layered vdW compounds through simple pressure tuning of the interlayer coupling.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

Direct Charge Trapping Multilevel Memory with Graphdiyne/MoS2 Van der Waals Heterostructure

Direct charge trapping memory, a new concept memory without any dielectric, has begun to attract attention. However, such memory is still at the incipient stage, of which the charge-trapping capability depends on localized electronic states that originated from the limited surface functional groups. To further advance such memory, a material with rich hybrid states is highly desired. Here, a van der Waals heterostructure design is proposed utilizing the 2D graphdiyne (GDY) which possesses abundant hybrid states with different chemical groups. In order to form the desirable van der Waals coupling, the plasma etching method is used to rapidly achieve the ultrathin 2D GDY with smooth surface for the first time. With the plasma-treated 2D GDY as charge-trapping layer, a direct charge-trapping memory based on GDY/MoS2 is constructed. This bilayer memory is featured with large memory window (90 V) and high degree of modulation (on/off ratio around 8 × 107 ). Two operating mode can be achieved and data storage capability of 9 and 10 current levels can be obtained, respectively, in electronic and opto-electronic mode. This GDY/MoS2 memory introduces a novel application of GDY as rich states charge-trapping center and offers a new strategy of realizing high performance dielectric-free electronics, such as optical memories and artificial synaptic.

General synthesis of mixed-dimensional van der Waals heterostructures with hexagonal symmetry

The combination of two-dimensional (2D) materials with non-2D materials (quantum dots, nanowires and bulk materials), i.e. mixed-dimensional van der Waals (md-vdW) heterostructures endow 2D materials with remarkable electronics properties. However, it remains a big challenge to synthesize md-vdW heterostructures because of the difference of crystal symmetry between 2D and non-2D materials. Meanwhile, it is difficult to initiate the nucleation due to the lack of chemical active sites on chemical inert surfaces of 2D materials. Herein, we design a general chemical vapor deposition method for synthesizing a broad class of md-vdW heterostructures with well-aligned hexagonal symmetry including MoS₂/FeS, MoS₂/CoS, MoS₂/MnS, MoS₂/ZnS, Mo(S_xSe_1-x)₂/ZnS_xSe_1-x, Mo(S_xSe_1-x)₂/CdS_xSe_1-x. Combining with DFT calculation, we find that the hexagonal symmetry and the centered clusters of MoS₂and Mo(S_xSe_1-x)₂nanoflakes are two crucial factors to launch the hexagonally oriented growth and nucleation of non-2D materials on 2D materials. Our discovery opens an opportunity for the versatile hetero-integration of 2D materials and allows systematic investigation of physical properties in a wide variety of md-vdW heterostructures.

Black phosphorus for near-infrared ultrafast lasers in the spatial/temporal domain

Two-dimensional (2D) materials have attracted extensive interests due to their wide range of electronic and optical properties. After continuous and extensive research, black phosphorus (BP), a novel member of 2D layered semiconductor material, benefit for the unique in-plane anisotropic structure, controllable direct bandgap characteristic, and high charge carrier mobility, has attracted tremendous attention and successfully applied in ultrafast pulse generation. This article, which focuses on near-infrared ultrafast laser demonstration of BP, present discussion of preparation methods for high quality BP nanosheet, various BP based ultrafast lasers in the spatial/temporal domain, and the future research needs.

Designing New-Generation Piezoelectric Transducers by Embedding Superior Graphene-Based Thermal Regulators

Cascaded-piezoelectric-transducers (CPETs) is a key component in modern energy-conversion fields, possessing versatile applications in ultrasonic scalpels, acoustic levitation, and sonar. However, serious self-heating inevitably occurs inside high-power CPETs, severely limiting their practical applications in broader fields. To tackle this, multidirectional heat-escape channels of multidimensional (multi-D, 3D/2D) graphene films are introduced in designing new-type thermal regulators. A porous AlN-ceramic thermal-sink is creatively selected as a template for directly synthesizing graphene via a two-step chemical vapor deposition strategy. This perfect combination of 3D/2D-graphene and the AlN ceramic can integrate their complementary advantages in uniformizing, transmitting, and releasing heat. Amazingly, in the new-generation CPETs embedded with these graphene-based thermal regulators, the self-heating-induced temperature rise can be substantially reduced by ≈60% (far exceeding actual demand standard). As another kernel parameter, electroacoustic-energy-conversion efficiency is dramatically improved in the new-generation CPETs. Briefly, this research realizes the first synthesis of a novel multi-D-graphene/AlN-ceramic hybrid, and propels its brand-new application directions in new-generation energy-conversion- and thermal-management-related territories.

2D-1D mixed-dimensional heterostructures: progress, device applications and perspectives

Two-dimensional (2D) materials have attracted broad interests and been extensively exploited for a variety of functional applications. Moreover, one-dimensional (1D) atomic crystals can also be integrated into 2D templates to create mixed-dimensional heterostructures, and the versatility of combinations provides 2D-1D heterostructures plenty of intriguing physical properties, making them promising candidate to construct novel electronic and optoelectronic nanodevices. In this review, we first briefly present an introduction of relevant fabrication methods and structural configurations for 2D-1D heterostructures integration. We then discuss the emerged intriguing physics, including high optical absorption, efficient carrier separation, fast charge transfer and plasmon-exciton interconversion. Their potential applications such as electronic/optoelectronic devices, photonic devices, spintronic devices and gas sensors, are also discussed. Finally, we provide a brief perspective for the future opportunities and challenges in this emerging field.

Gate-tunable plasmons in mixed-dimensional van der Waals heterostructures

Surface plasmons, collective electromagnetic excitations coupled to conduction electron oscillations, enable the manipulation of light-matter interactions at the nanoscale. Plasmon dispersion of metallic structures depends sensitively on their dimensionality and has been intensively studied for fundamental physics as well as applied technologies. Here, we report possible evidence for gate-tunable hybrid plasmons from the dimensionally mixed coupling between one-dimensional (1D) carbon nanotubes and two-dimensional (2D) graphene. In contrast to the carrier density-independent 1D Luttinger liquid plasmons in bare metallic carbon nanotubes, plasmon wavelengths in the 1D-2D heterostructure are modulated by 75% via electrostatic gating while retaining the high figures of merit of 1D plasmons. We propose a theoretical model to describe the electromagnetic interaction between plasmons in nanotubes and graphene, suggesting plasmon hybridization as a possible origin for the observed large plasmon modulation. The mixed-dimensional plasmonic heterostructures may enable diverse designs of tunable plasmonic nanodevices.

Chemical Heterointerface Engineering on Hybrid Electrode Materials for Electrochemical Energy Storage

The chemical heterointerfaces in hybrid electrode materials play an important role in overcoming the intrinsic drawbacks of individual materials and thus expedite the in-depth development of electrochemical energy storage. Benefiting from the three enhancement effects of accelerating charge transport, increasing the number of storage sites, and reinforcing structural stability, the chemical heterointerfaces have attracted extensive interest and the electrochemical performances of hybrid electrode materials have been significantly optimized. In this review, recent advances regarding chemical heterointerface engineering in hybrid electrode materials are systematically summarized. Especially, the intrinsic behaviors of chemical heterointerfaces on hybrid electrode materials are refined based on built-in electric field, van der Waals interaction, lattice mismatch and connection, electron cloud bias and chemical bond, and their combination. The strategies for introducing chemical heterointerfaces are classified into in situ local transformation, in situ growth, cosynthesis, and other strategy. The recent progress about the chemical heterointerfaces engineering specially focusing on metal-ion batteries, supercapacitors, and Li-S batteries are introduced in detail. Furthermore, the classification and characterization of chemical heterointerfaces are briefly described. Finally, the emerging challenges and perspectives about future directions of chemical heterointerface engineering are proposed.

Mixed-dimensional Te/CdS van der Waals heterojunction for self-powered broadband photodetector

The 2D layered crystals can physically integrate with other non-2D components through van der Waals (vdW) interaction, forming mixed-dimensional heterostructures. As a new elemental 2D material, tellurium (Te) has attracted intense recent interest for high room-temperature mobility, excellent air-stability, and the easiness of scalable synthesis. To date, the Te is still in its research infancy, and optoelectronics with low-power consumption are less reported. Motivated by this, we report the fabrication of a mixed-dimensional vdW photodiode using 2D Te and 1D CdS nanobelt in this study. The heterojunction exhibits excellent self-powered photosensing performance and a broad response spectrum up to short-wave infrared. Under 520 nm wavelength, a high responsivity of 98 mA W^-1is obtained at zero bias with an external quantum efficiency of 23%. Accordingly, the photo-to-dark current ratio and specific detectivity reach 9.2 × 10³and 1.9 × 10¹¹Jones due to the suppressed dark current. This study demonstrates the promising applications of Te/CdS vdW heterostructure in high-performance photodetectors. Besides, such a mixed-dimensional integration strategy paves a new way for device design, thus expanding the research scope for 2D Te-based optoelectronics.

Self-Powered MXene/GaN van der Waals Heterojunction Ultraviolet Photodiodes with Superhigh Efficiency and Stable Current Outputs

A self-powered, high-performance Ti₃ C₂ T_x MXene/GaN van der Waals heterojunction (vdWH)-based ultraviolet (UV) photodiode is reported. Such integration creates a Schottky junction depth that is larger than the UV absorption depth to sufficiently separate the photoinduced electron/hole pairs, boosting the peak internal quantum efficiency over the unity and the external quantum efficiency over 99% under weak UV light without bias. The proposed Ti₃ C₂ T_x /GaN vdWH UV photodiode demonstrates pronounced photoelectric performances working in self-powered mode, including a large responsivity (284 mA W^-1 ), a high specific detectivity (7.06 × 10¹³ Jones), and fast response speed (rise/decay time of 7.55 µs/1.67 ms). Furthermore, the remarkable photovoltaic behavior leads to an impressive power conversion efficiency of 7.33% under 355 nm UV light illumination. Additionally, this work presents an easy-processing spray-deposition route for the fabrication of large-area UV photodiode arrays that exhibit highly uniform cell-to-cell performance. The MXene/GaN photodiode arrays with high-efficiency and self-powered ability show high potential for many applications, such as energy-saving communication, imaging, and sensing networks.

Interface Engineering Ti3 C2 MXene/Silicon Self-Powered Photodetectors with High Responsivity and Detectivity for Weak Light Applications

Interfacial engineering and heterostructures designing are two efficient routes to improve photoelectric characteristics of a photodetector. Herein, a Ti₃ C₂ MXene/Si heterojunction photodetector with ultrahigh specific detectivity (2.03 × 10¹³ Jones) and remarkable responsivity (402 mA W^-1 ) at zero external bias without decline as with increasing the light power is reported. This is achieved by chemically regrown interfacial SiO_x layer and the control of Ti₃ C₂ MXene thickness to suppress the dark noise current and improve the photoresponse. The photodetector demonstrates a high light on/off ratio of over 10⁶ , an outstanding peak external quantum efficiency (EQE) of 60.3%, while it maintains an ultralow dark current at 0 V bias. Moreover, the device holds high performance with EQE of over 55% even after encapsulated with silicone, trying to resolve the air stability issue of Ti₃ C₂ MXene. Such a photodetector with high detectivity, high responsivity, and self-powered capability is particularly applicable to detect weak light signal, which presents high potential for imaging, communication and sensing applications.

Enhanced performance of ZnO nanorod array/CuSCN ultraviolet photodetectors with functionalized graphene layers

Facile, convenient and low-cost processes, including a chemical hydrothermal method and impregnation technique, were demonstrated to fabricate a self-powered ZnO nanorod array/CuSCN/reduced graphene oxide (rGO) ultraviolet photodetector. ZnO nanorods (NRs) were fully filled and encased by the CuSCN layer, in which CuSCN acts as the primary hole-transport layer and an electron reflection layer, blocking the electron transfer towards the Au electrode and reducing the electron-hole pair recombination. After annealing, this encapsulated structure further reduces the surface state defects of ZnO NRs, which can isolate the electron exchange with oxygen in the air, dramatically reducing the rise and fall time; it also forms a p-n junction, providing a built-in electric field to improve the photoresponse without applying external power. The rGO layer was coated on the surface of CuSCN as the secondary hole-transport layer and then annealed, which could effectively block Au from entering CuSCN and contacting ZnO along cracks and holes during vapor deposition, avoiding the formation of leakage channels. Furthermore, due to the ultra-high carrier mobility and the increase in work function after Au doping, the functionalized graphene could reduce the valence band shift, which is beneficial to enhance hole transport. Meanwhile, rGO obstructs the undesired barrier formed by electrical potential-induced reaction of Au with thiocyanate anions. Finally, the ZnO NR/CuSCN/rGO ultraviolet photodetector exhibits a significant enhancement in device performance (responsivity: 18.65 mA W-1 at 375 nm under 65 mW cm-2 illumination, rectification ratio: 5690 at ±1 V), which is better that of than ZnO NR/CuSCN structure (10.88 mA W-1, 10.22 at ±1 V) and maintains the 100 ms response time.

Photoresponse improvement of mixed-dimensional 1D-2D GaAs photodetectors by incorporating constructive interface states

Mixed-dimensional optoelectronic devices bring new challenges and opportunities over the design of conventional low-dimensional devices. In this work, we develop unreported mixed-dimensional GaAs photodetectors by utilizing 1D GaAs nanowires (NWs) and 2D GaAs non-layered sheets (2DNLSs) as active device materials. The fabricated photodetector exhibits a responsivity of 677 A W-1 and a detectivity of 8.69 × 1012 cm Hz0.5 W-1 under 532 nm irradiation, which are already much better than those of state-of-the-art low-dimensional GaAs photodetectors. It is found that this unique device structure is capable of converting the notoriously harmful surface states of NWs and 2DNLSs into their constructive interface states, which contribute to the formation of quasi-type-II band structures and electron wells in the device channel for the substantial performance enhancement. More importantly, these interface states are demonstrated to be insensitive to ambient environments, indicating the superior stability of the device. All these results evidently illustrate a simple but effective way to utilize the surface states of nanomaterials to achieve the high-performance photodetectors.

The Art of Constructing Black Phosphorus Nanosheet Based Heterostructures: From 2D to 3D

Assembling different kinds of 2D nanosheets into heterostructures presents a promising way of designing novel artificial materials with new and improved functionalities by combining the unique properties of each component. In the past few years, black phosphorus nanosheets (BPNSs) have been recognized as a highly feasible 2D material with outstanding electronic properties, a tunable bandgap, and strong in-plane anisotropy, highlighting their suitability as a material for constructing heterostructures. In this study, recent progress in the construction of BPNS-based heterostructures ranging from 2D hybrid structures to 3D networks is discussed, emphasizing the different types of interactions (covalent or noncovalent) between individual layers. The preparation methods, optical and electronic properties, and various applications of these heterostructures-including electronic and optoelectronic devices, energy storage devices, photocatalysis and electrocatalysis, and biological applications-are discussed. Finally, critical challenges and prospective research aspects in BPNS-based heterostructures are also highlighted.

Mixed-Dimensional In-Plane Heterostructures from 1D Mo6 Te6 and 2D MoTe2 Synthesized by Te-Flux-Controlled Chemical Vapor Deposition

Mixed-dimensional van der Waals heterostructures are scientifically important and practically useful because of their interesting exotic properties resulting from their novel hybrid structures. This study reports the composition- and phase-selective fabrication of low-dimensional molybdenum/tellurium (Mo/Te) compounds and the direct synthesis of mixed-dimensional in-plane 1D-2D Mo₆ Te₆ -MoTe₂ heterostructures. The composition and phase of the Mo/Te compounds are controlled by changing the Te atomic flux that is adjusted by the Te temperature. Metallic 1D Mo₆ Te₆ wires with an intrinsic 1D structure with a diameter of 3-8 nm and length of 100-300 nm are synthesized to form wire networks under low Te flux conditions, whereas the semiconducting few-layer 2H MoTe₂ films preferentially oriented along the <0001> direction are obtained under high Te flux. Under medium Te flux, the mixed-dimensional in-plane 1D-2D Mo₆ Te₆ -MoTe₂ heterostructures are synthesized in which the semiconducting few-layer 2H MoTe₂ circular domains are edge-contacted by the metallic 1D Mo₆ Te₆ wire networks. Furthermore, the present Te-flux-controlled method reveals that the 1D Mo₆ Te₆ networks change to few-layer MoTe₂ films as the Te flux increases. The in-plane 1D-2D Mo₆ Te₆ -MoTe₂ heterostructures synthesized by this method can be considered as advanced edge-contacted 2D semiconductors for high-performance 2D electronics.

Enhancing the Heat-Dissipation Efficiency in Ultrasonic Transducers via Embedding Vertically Oriented Graphene-Based Porcelain Radiators

Ultrasonic transducers with large output power have attracted extensive attentions due to their widespread applications in sonar, acoustic levitation, ultrasonic focusing, and so forth. However, the traditional transducer has almost no heat-dissipation capability itself, strictly relying on the assistant coolant system. Introducing high-performance heat-dissipation component is thus highly necessary. Herein, an embedded porcelain radiator component was designed by combining the excellent thermal conductivity of vertically oriented graphene (VG) with the outstanding heat-dissipation characteristics of thermosensitive ceramics, and a new-type transducer with an embedded VG/ceramic-hybrid radiator was constructed to show high heat-dissipation efficiency (up to ∼5 °C/min). Remarkably, prominent heat-dissipation effectiveness (temperature decline of ∼12 °C), enhanced amplitude and vibration uniformity were also achieved for the new-type transducer along with stabilized operating states. This research should pave ways for extending the applications of VG/ceramic hybrids to heat-dissipation scenarios and provide newfangled thoughts for the performance upgrade of multitudinous high-power devices.

Void-free 3D Bioprinting for In-situ Endothelialization and Microfluidic Perfusion

Two major challenges of 3D bioprinting are the retention of structural fidelity and efficient endothelialization for tissue vascularization. We address both of these issues by introducing a versatile 3D bioprinting strategy, in which a templating bioink is deposited layer-by-layer alongside a matrix bioink to establish void-free multimaterial structures. After crosslinking the matrix phase, the templating phase is sacrificed to create a well-defined 3D network of interconnected tubular channels. This void-free 3D printing (VF-3DP) approach circumvents the traditional concerns of structural collapse, deformation and oxygen inhibition, moreover, it can be readily used to print materials that are widely considered "unprintable". By pre-loading endothelial cells into the templating bioink, the inner surface of the channels can be efficiently cellularized with a confluent endothelial layer. This in-situ endothelialization method can be used to produce endothelium with a far greater uniformity than can be achieved using the conventional post-seeding approach. This VF-3DP approach can also be extended beyond tissue fabrication and towards customized hydrogel-based microfluidics and self-supported perfusable hydrogel constructs.

A WS2-gold nanoparticle heterostructure-based novel SERS platform for the rapid identification of antibiotic-resistant pathogens

The emergence of antibiotic-resistant bacteria is the biggest threat to our society. The rapid discovery of drug resistant bacteria is very urgently needed to guide antibiotic treatment development. The current manuscript reports the design of a 2D-0D heterostructure-based surface enhanced Raman spectroscopy (SERS) platform, which has the capability for the rapid identification of the multidrug resistant strain of Salmonella DT104. Details of the synthesis and characterization of the heterostructure SERS platform using a two dimensional (2D) WS₂ transition metal dichalcogenide (TMD) and zero dimensional (0D) plasmonic gold nanoparticles (GNPs) have been reported. The current manuscript reveals that the 2D-0D heterostructure-based SERS platform exhibits extremely high Raman enhancement capabilities. Using Rh-6G and 4-ATP probe molecules, we determined that the SERS sensitivity is in the range of ∼10^-10 to 10^-11 M, several orders of magnitude higher than 2D-TMD on its own (10^-3 M) or 0D-GNPs on their own (∼10^-6 to 10^-7 M). Experimental and theoretical finite-difference time-domain (FDTD) simulation data indicate that the synergistic effect of an electromagnetic mechanism (EM) and a chemical mechanism (CM) on the heterostructure is responsible for the excellent SERS enhancement observed. Notably, the experimental data reported here show that the heterostructure-based SERS has the ability to separate a multidrug resistance strain from a normal strain of Salmonella by monitoring the antibiotic-pathogen interaction within 90 minutes, even at a concentration of 100 CFU mL^-1.

Reconfigurable 2D/0D p-n Graphene/HgTe Nanocrystal Heterostructure for Infrared Detection

Nanocrystals are promising building blocks for the development of low-cost infrared optoelectronics. Gating a nanocrystal film in a phototransistor geometry is commonly proposed as a strategy to tune the signal-to-noise ratio by carefully controlling the carrier density within the semiconductor. However, the performance improvement has so far been quite marginal. With metallic electrodes, the gate dependence of the photocurrent follows the gate-induced change of the dark current. Graphene presents key advantages: (i) infrared transparency that allows back-side illumination, (ii) vertical electric field transparency, and (iii) carrier selectivity under gate bias. Here, we investigate a configuration of 2D/0D infrared photodetectors taking advantage of a high capacitance ionic glass gate, large-scale graphene electrodes, and a HgTe nanocrystals layer of high carrier mobility. The introduction of graphene electrodes combined with ionic glass enables one to reconfigure selectively the HgTe nanocrystals and the graphene electrodes between electron-doped (n) and hole-doped (p) states. We unveil that this functionality enables the design a 2D/0D p-n junction that expands throughout the device, with a built-in electric field that assists charge dissociation. We demonstrate that, in this specific configuration, the signal-to-noise ratio for infrared photodetection can be enhanced by 2 orders of magnitude, and that photovoltaic operation can be achieved. The detectivity now reaches 10⁹ Jones, whereas the device only absorbs 8% of the incident light. Additionally, the time response of the device is fast (<10 μs), which strongly contrasts with the slow response commonly observed for 2D/0D mixed-dimensional heterostructures, where larger photoconduction gains come at the cost of slower response.

Introducing Electrode Contact by Controlled Micro-Alloying in Few-Layered GaTe Field Effect Transistors

Recently, gallium telluride (GaTe) has triggered much attention for its unique properties and offers excellent opportunities for nanoelectronics. Yet it is a challenge to bridge the semiconducting few-layered GaTe crystals with metallic electrodes for device applications. Here, we report a method on fabricating electrode contacts to few-layered GaTe field effect transistors (FETs) by controlled micro-alloying. The devices show linear I-V curves and on/off ratio of ∼10 4 on HfO 2 substrates. Kelvin probe force microscope (KPFM) and energy dispersion spectrum (EDS) are performed to characterize the electrode contacts, suggesting that the lowered Schottky barrier by the diffusion of Pd element into the GaTe conduction channel may play an important role. Our findings provide a strategy for the engineering of electrode contact for future device applications based on 2DLMs.