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Conventional Si-based physically unclonable functions (PUFs) take advantage of the unique variations in the fabrication processes. However, these PUFs are hindered by limited entropy sources and susceptibility to noise interference. Here we present a memristive device based on wafer-scale (2-in.) two-dimensional (2D) hafnium disulfide (HfS 2 ) grown by molecular beam epitaxy (MBE). The polycrystalline HfS 2 thin film can offer enhanced entropy sources for PUF applications, such as lattice defects, which can facilitate the random formation of conductive filaments and result in significant device-to-device (D2D) variations. Our proposed PUF design seamlessly integrates two distinct operating modes within a single circuit module. First, a reconfigurable and highly secure mode 1, and second, an ultrareliable mode 2, both with near-ideal Entropy (∼1.0), normalized Hamming distance (∼0.5) and correlation coefficient (∼0.0). Additionally, a predictive Fourier regression model further confirms the unpredictable nature of our dual-mode PUF, with an average prediction accuracy of ∼50%.

Polycrystalline lead halide perovskite finds promising use in fabricating X-ray detectors with a large lateral size, adjustable thickness, and diverse synthesis processes. However, a large dark current hinders its development for weak signal detection. Herein, we propose a multistep pressing strategy for manufacturing a CsPbBr 3 /CsPbCl 3 heterojunction wafer for a reduced dark current X-ray detector, and the device keeps a high sensitivity value after the insertion of a barrier by heterojunction; thus, the trade-off between sensitivity and dark current can be broken. The X-ray detector with a metal-semiconductor-metal structure yields a sensitivity of 6.32 × 10 4 μC Gy air -1 cm -2 at a bias of 12 V, a 1/ f noise of 1.02 × 10 -13 A/Hz -1/2 . These performance parameters are considerably better than those of a similar X-ray detector based on the single-structure wafer. The improved device performance of the heterostructure X-ray detector is ascribed to the suppressed carrier recombination, enhanced carrier transportation of the heterojunction, and strong X-ray attenuation of the CsPbCl -1 layer. The pixel array device is further used in imaging applications. Hence, this study provides an efficient strategy for fabricating heterostructure polycrystalline lead halide perovskite wafers for use in high-performance wafer-based X-ray detectors.3 layer. The pixel array device is further used in imaging applications. Hence, this study provides an efficient strategy for fabricating heterostructure polycrystalline lead halide perovskite wafers for use in high-performance wafer-based X-ray detectors.

The helicity-dependent photocurrent (HDPC) of Fe 4 GeTe 2 (3, 5, 8, 10 nm)/Bi 2 Te 3 (8 nm) heterostructures grown on sapphire substrates was systematically investigated. It is revealed that the HDPC is induced by the interface coupling between the Fe 4 GeTe 2 and Bi 2 Te 3 films, and it is dominated by the circular photogalvanic effect (CPGE) rather than by the circular photodrag effect (circular photon drag effect). As the tensile strain increases, the CPGE current decreases, which can be attributed to the decrease of the interface-induced spin-orbit coupling with increasing tensile strain. In addition, it is demonstrated that by applying appropriate tensile strain, the 5 nm Fe 4 GeTe 2 /Bi 2 Te 3 sample can be used to detect the circular polarization state of a light. Finally, Fe 4 GeTe 2 (5, 8, and 10 nm)/Bi 2 Te 3 (8 nm) heterostructures show a T C larger than 390 K. The dependence of the CPGE on the film thickness of Fe 4 GeTe 2 is different from that of Curie temperature, indicating that the enhanced exchange interaction induced by the interface coupling may be the dominant mechanism for the high- T C ferromagnetism. The large interface-induced CPGE in the Fe 4 GeTe 2 /Bi 2 Te 3 suggests that Fe 4 GeTe 2 /Bi 2 Te 3 heterostructures may provide a good platform for designing novel opto-spintronic devices.

Stretchable organic phototransistor arrays have potential applications in artificial visual systems due to their capacity to perceive ultraweak light across a broad spectrum. Ensuring uniform mechanical and electrical performance of individual devices within these arrays requires semiconductor films with large-area scale, well-defined orientation, and stretchability. However, the progress of stretchable phototransistors is primarily impeded by their limited electrical properties and photodetection capabilities. Herein, wafer-scale and well-oriented semiconductor films were successfully prepared using a solution shearing process. The electrical properties and photodetection capabilities were optimized by improving the polymer chain alignment. Furthermore, a stretchable 10 × 10 transistor array with high device uniformity was fabricated, demonstrating excellent mechanical robustness and photosensitive imaging ability. These arrays based on highly stretchable and well-oriented wafer-scale semiconductor films have great application potential in the field of electronic eye and artificial visual systems.

Electronic devices employing two-dimensional (2D) van der Waals (vdW) transition-metal dichalcogenide (TMD) layers as semiconducting channels often exhibit limited performance (e.g., low carrier mobility), in part, due to their high contact resistances caused by interfacing non-vdW three-dimensional (3D) metal electrodes. Herein, we report that this intrinsic contact issue can be efficiently mitigated by forming the 2D/2D in-plane junctions of 2D semiconductor channels seamlessly interfaced with 2D metal electrodes. For this, we demonstrated the selectively patterned conversion of semiconducting 2D PtSe 2 (channels) to metallic 2D PtTe 2 (electrodes) layers by employing a wafer-scale low-temperature chemical vapor deposition (CVD) process. We investigated a variety of field-effect transistors (FETs) employing wafer-scale CVD-2D PtSe 2 /2D PtTe 2 heterolayers and identified that silicon dioxide (SiO 2 ) top-gated FETs exhibited an extremely high hole mobility of ∼120 cm 2 V -1 s -1 at room temperature, significantly surpassing performances with previous wafer-scale 2D PtSe 2 -based FETs. The low-temperature nature of the CVD method further allowed for the direct fabrication of wafer-scale arrays of 2D PtSe 2 /2D PtTe 2 heterolayers on polyamide (PI) substrates, which intrinsically displayed optical pulse-induced artificial synaptic behaviors. This study is believed to vastly broaden the applicability of 2D TMD layers for next-generation, high-performance electronic devices with unconventional functionalities.

In microelectronics, one of the main 3D integration strategies consists of vertically stacking and electrically connecting various functional chips using through-silicon vias (TSVs). For the fabrication of the TSVs, one of the challenges is to conformally deposit a low dielectric constant insulator thin film at the surface of the silicon. To date, there is no universal technique that can address all types of TSV integration schemes, especially in the case requiring a low deposition temperature. In this work, an organosilicate polymer deposited by initiated chemical vapor deposition (iCVD) was developed and integrated as an insulating layer for TSVs. Process studies have shown that poly(1,3,5-trivinyl-1,3,5-trimethyl cyclotrisiloxane) (P(V 3 D 3 )) can present good conformality on high aspect ratio features by increasing the substrate temperature up to 100 °C. The trade-off is a moderate deposition rate. The thermal stability of the polymer has been investigated, and we show that a thermal annealing at 400 °C (with or without ultraviolet exposure) allows the stabilization of the dielectric films by removing residual oligomers. Then, P(V 3 D 3 ) was integrated in high aspect ratio TSV (10 × 100 μm) on 300 mm silicon wafers using a standard integration flow for TSV metallization. Functional devices were successfully fabricated (including daisy chains of 754 TSVs) and electrically characterized. Our work shows that the metallization barrier should be carefully selected to eliminate the appearance of voids at the top corner of the TSV after the Cu annealing step. Moreover, an appropriate integration process should be used to avoid the appearance of cohesive cracks in the liner. This work constitutes a first proof of concept of the use of an iCVD polymer in a quasi-industrial microelectronic environment. It also highlights the benefit of iCVD as a promising technique to deposit conformal dielectric thin films in a microelectronic pilot line environment.

Flexible electronics have been of great interest in the past few decades for their wide-ranging applications in health monitoring, human-machine interaction, artificial intelligence, and biomedical engineering. Currently, transfer printing is a popular technology for flexible electronics manufacturing. However, typical sacrificial intermediate layer-based transfer printing through chemical reactions results in a series of challenges, such as time consumption and interface incompatibility. In this paper, we have developed a time-saving, wafer-recyclable, eco-friendly, and multiscale transfer printing method by using a stable transferable photoresist. Demonstration of photoresist with various, high-resolution, and multiscale patterns from the donor substrate of silicon wafer to different flexible polymer substrates without any damage is conducted using the as-developed dry transfer printing process. Notably, by utilizing the photoresist patterns as conformal masks and combining them with physical vapor deposition and dry lift-off processes, we have achieved in situ fabrication of metal patterns on flexible substrates. Furthermore, a mechanical experiment has been conducted to demonstrate the mechanism of photoresist transfer printing and dry lift-off processes. Finally, we demonstrated the application of in situ fabricated electrode devices for collecting electromyography and electrocardiogram signals. Compared to commercially available hydrogel electrodes, our electrodes exhibited higher sensitivity, greater stability, and the ability to achieve long-term health monitoring.

Entering an era of miniaturization prompted scientists to explore strategies to assemble colloidal crystals for numerous applications, including photonics. However, wet methods are intrinsically less versatile than dry methods, whereas the manual rubbing method of dry powders has been demonstrated only on sticky elastomeric layers, hindering particle transfer in printing applications and applicability in analytical screening. To address this clear impetus of broad applicability, we explore here the assembly on nonelastomeric, rigid substrates by utilizing the manual rubbing method to rapidly (≈20 s) attain monolayers comprising hexagonal closely packed (HCP) crystals of monodisperse dry powder spherical particles with a diameter ranging from 500 nm to 10 μm using a PDMS stamp. Our findings elucidate that the tribocharging-induced electrostatic attraction, particularly on relatively stiff substrates, and contact mechanics force between particles and substrates are critical contributors to attain large-scale HCP structures on conductive and insulating substrates. The best performance was obtained with polystyrene and PMMA powder, while silica was assembled only in HCP structures on fluorocarbon-coated substrates under zero-humidity conditions. Finally, we successfully demonstrated the assembly of tunable crystal patterns on a wafer-scale with great control on fluorocarbon-coated wafers, which is promising in microelectronics, bead-based assays, sensing, and anticounterfeiting applications.

The outstanding photoelectric properties of perovskites demonstrate extreme promise for application in X-ray detection. However, the soft lattice of the perovskite results in severe ionic migration for three-dimensional materials, limiting the operation stability of perovskite X-ray detectors. Although ligand-decorated nanocrystals (NCs) exhibit significantly higher stability than three-dimensional perovskites, defects remaining on the interface of NCs could still trigger halide migration under a high bias due to the incomplete ligand decoration. Furthermore, it is still challenging to realize sufficient thickness of absorption layers based on NCs for X-ray detectors through traditional methods. Herein, we develop a centimeter-size and millimeter-thick wafer based on CsPbBr 3 NCs through isostatic pressing for X-ray detectors, in which the interfacial defects of NCs are remedied by CsPb 2 Br 5 during aging of wafer in ambient humidity. The wafer shows outstanding sensitivity (200 μC Gy air -1 cm -2 ) and ultralow dark current drift (1.78 × 10 -8 nA cm -1 s -1 V -1 @ 400 V cm -1 ). Moreover, it shows storage stability with negligible performance degradation for 60 days in ambient humidity. Thus, aging perovskite NC wafers for X-ray detection holds huge potential for next-generation X-ray imaging plates.

The interest in the wafer-scale growth of two-dimensional (2D) materials, including transition metal dichalcogenides (TMDCs), has been rising for transitioning from lab-scale devices to commercial-scale systems. Among various synthesis techniques, physical vapor deposition, such as pulsed laser deposition (PLD), has shown promise for the wafer-scale growth of 2D materials. However, due to the high volatility of chalcogen atoms (e.g., S and Se), films deposited by PLD usually suffer from a lack of stoichiometry and chalcogen deficiency. To mitigate this issue, excess chalcogen is necessary during the deposition, which results in problems like uniformity or not being repeatable. This study demonstrates a condensed-phase or amorphous phase-mediated crystallization (APMC) approach for the wafer-scale synthesis of 2D materials. This method uses a room-temperature PLD process for the deposition and formation of amorphous precursors with controlled thicknesses, followed by a post-deposition crystallization process to convert the amorphous materials to crystalline structures. This approach maintains the stoichiometry of the deposited materials throughout the deposition and crystallization process and enables the large-scale synthesis of crystalline 2D materials (e.g., MoS 2 and WSe 2 ) on Si/SiO 2 substrates, which is critical for future wafer-scale electronics. We show that the thickness of the layers can be digitally controlled by the number of laser pulses during the PLD phase. Optical spectroscopy is used to monitor the crystallization dynamics of amorphous layers as a function of annealing temperature. The crystalline quality, domain sizes, and the number of layers were explored using nanoscale and atomistic characterization (e.g., AFM, STEM, and EDS) along with electrical characterization to explore process-structure-performance relationships. This growth technique is a promising method that could potentially be adopted in conventional semiconductor industries for wafer-scale manufacturing of next-generation electronic and optoelectronic devices.

High-performance flexible sensors are essential for real-time information analysis and constructing noncontact communication modules for emerging human-machine interactions. In these applications, batch fabrication of sensors that exhibit high performance at the wafer level is in high demand. Here, we present organic nanoforest-based humidity sensor (NFHS) arrays on a 6 in. flexible substrate prepared via a facile, cost-effective manufacturing approach. Such an NFHS achieves state-of-the-art overall performance: high sensitivity and fast recovery time; the best properties are at a small device footprint. The high sensitivity (8.84 pF/% RH) and fast response time (5 s) of the as-fabricated organic nanoforests are attributed to the abundant hydrophilic groups, the ultra-large surface area with a huge number of nanopores, and the vertically distributed structures beneficial to the transfer of molecules up and down. The NFHS also exhibits excellent long-term stability (90 days), superior mechanical flexibility, and good performance repeatability after bending. With these superiorities, the NFHS is further applied as a smart noncontact switch, and the NFHS array is used as the motion trajectory tracker. The wafer-level batch fabrication capability of our NFHS provides a potential strategy for developing practical applications of such humidity sensors.

The semimetal-based photodetector possesses the intrinsic advantage of high response speed, low power consumption, and wide-range photoresponse. Here, we report the synthesis and application of 1 inch wafer-scale polycrystalline few layer 1T'-MoTe 2 on the SiO 2 /Si substrate by employing a modified chemical vapor deposition method of predeposition of precursors. A continuous film with seamlessly stitched micrometer scale grains has been realized, and the pure 1T' phase was confirmed by Raman spectroscopy. An asymmetric metal electrode photodetector device of Pd-MoTe 2 -Au was designed and fabricated by using shadow mask-assisted UHV deposition. By measuring the self-powered photocurrent under the illumination of Xe lamp, we show that the device is sensitive to a wide spectra range (λ = 320-1200 nm) while maintaining high performance of the ON/OFF ratio (∼10 3 ), responsivity (1.2 A/W), and specific detectivity (7.68 × 10 12 Jones). Under 450, 648, and 850 nm pulsed laser illumination, the response time achieves tens of microsecond scale. The device shows polarized photoresponse as well. Our work may promote the potential application of a self-powered high-performance photodetector based on 1T'-MoTe 2 .

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit promising potential in fabricating highly sensitive photodetectors due to their unique electrical and optoelectrical characteristics. However, micron-sized 2D materials produced by conventional chemical vapor deposition (CVD) and mechanical exfoliation methods fail to satisfy the demands for applications in integrated optoelectronics and systems given their poor controllability and repeatability. Here, we propose a simple selenization approach to grow wafer-scale (2 in.) 2D p -WSe 2 layers with high uniformity and customized patterns. Furthermore, a self-driven broadband photodetector with a p -WSe 2 / n -Si van der Waals heterojunction has been in situ fabricated with a satisfactory responsivity of 689.8 mA/W and a large specific detectivity of 1.59 × 10 13 Jones covering from ultraviolet to short-wave infrared. In addition, a remarkable nanosecond response speed has been recorded under 0.5% duty cycle of the input light. The proposed selenization approach on the growth of 2D WSe 2 layers demonstrates an effective route to fabricate highly sensitive broadband photodetectors used for integrated optoelectronic systems.

Ultra-low-noise solid-state nanopores are attractive for high-accuracy single-molecule sensing. A conventional silicon platform introduces acute capacitive noise to the system, which seriously limits the recording bandwidth. Recently, we have demonstrated the creation of thin triangular membranes on an insulating crystal sapphire wafer to eliminate the parasitic device capacitance. Uniquely different from the previous triangular etching window designs, here hexagonal windows were explored to produce triangular membranes by aligning to the sapphire crystal within a large tolerance of alignment angles (10-35°). Interestingly, sapphire facet competition serves to suppress the formation of more complex polygons but creates stable triangular membranes with their area insensitive to the facet alignment. Accordingly, a new strategy was successfully established on a 2 in. sapphire wafer to produce chips with an average membrane side length of 4.7 μm, an area of <30 μm 2 for 81% chips, or estimated calculated membrane capacitance as low as 0.06 pF. We finally demonstrated <4 μs high-speed and high-fidelity low-noise protein detection under 250 kHz high bandwidth.

Direct chemical vapor deposition of graphene on semiconductors and insulators provides high feasibility for integration of graphene devices and semiconductor electronics. However, the current methods typically rely on high temperatures (>1000 °C), which can damage the substrates. Here, a growth method for high-quality large-area graphene at 300 °C is introduced. A multizone furnace with gradient temperature control was designed according to a computational fluid dynamics model. The crucial roles of the chamber pressure in the film continuity and hydrogen composition in the graphene defect density at low temperature were revealed. As a result, a uniform graphene film with the Raman ratio I D = 0.08 was obtained. Furthermore, a technique of laminating single-crystal Cu foil as a sacrificial layer on the substrate was proposed to realize transfer-free growth, and a wafer-scale graphene transistor array was demonstrated with good performance consistency, which paves the way for mass fabrication of graphene devices.I G = 0.08 was obtained. Furthermore, a technique of laminating single-crystal Cu foil as a sacrificial layer on the substrate was proposed to realize transfer-free growth, and a wafer-scale graphene transistor array was demonstrated with good performance consistency, which paves the way for mass fabrication of graphene devices.

Field-induced nonlinear materials, with extended abilities of manipulating electromagnetic waves, have been widely employed in electromagnetic protection, absorption, and detection. Until now, it was found that the field-induced nonlinearity mainly shows in the optical and terahertz frequency bands. Applying the microwave band into such technical activities is hampered due to a lack of investigations on the nonlinearity caused by microwave electric fields, especially in the ultrawideband and microwave high-frequency bands. In this paper, a nonlinear metamaterial (NLMM) concept based on the integration of metamaterial structures and a semiconductor on the same wafer is proposed, which shows nonlinear behavior to the electromagnetics' field energy in the microwave band. The designed NLMM is transparent to low-density electromagnetic radiation fields, while it adaptively becomes opaque to high-density electromagnetic radiation fields. Two types of NLMM are designed to verify the nonlinear characteristics of ultrawide and narrow bands in the microwave band, respectively. The concept of NLMM can be used for the application of the microwave frequency band in electromagnetic protection and detection.

For decades, photoinhibited two-photon lithography (PI-TPL) has been continually developed and applied into versatile nanofabrication. However, ultrahigh precision fabrication on wafer by PI-TPL remains challenging, due to the lack of a refractive index ( n ) matched photoresist (Rim-P) with effective photoinhibition capacity for dip-in mode. In this paper, various Rim-P are developed and then screened for their applications in PI-TPL. In addition, different lithography methods (in terms of oil-mode and dip-in mode) are analyzed by use of optical simulations combined with experiments. Remarkably, one type of Rim-P ( n = 1.518) shows effective photoinhibition capacity, which represents an outstanding breakthrough in the field of PI-TPL. In contrast to photoresist with an unsuitable refractive index, optical aberrations are almost completely eliminated in the dip-in mode by using the Rim-P. Consequently, features with a minimum critical dimension as small as 39 nm are successfully achieved on wafer by dip-in PI-TPL, which paves the way for subdiffraction silicon-based chip manufacturing by PI-TPL. Moreover, through a combination of the Rim-P and dip-in mode, the ability to achieve tall and high-precision three-dimensional nanostructures is no longer problematic.

Two-dimensional (2D) semiconductors are promising for next-generation electronics that are lightweight, flexible, and stretchable. Achieving stretchability with suppressed crack formation, however, is still difficult without introducing lithographically etched micropatterns, which significantly reduces active device areas. Herein, we report a solution-based hierarchical structuring to create stretchable semiconducting films that are continuous over wafer-scale areas via self-assembly of two-dimensional nanosheets. Electrochemically exfoliated MoS 2 nanosheets with large lateral sizes (∼1 μm) are first assembled into a uniform film on a prestrained thermoplastic substrate, followed by strain relief of the substrate to create nanoscale wrinkles. Subsequent strain-relief cycles with the presence of soluble polymer films produce hierarchical wrinkles with multigenerational structures. Stretchable MoS 2 films are then realized by curing an elastomer directly on the wrinkled surface and dissolving the thermoplastic. Three-generation hierarchical MoS 2 wrinkles are resistant to cracking up to nearly 100% substrate stretching and achieve drastically enhanced photoresponsivity compared to the flat counterpart over the visible and NIR regimes, while the flat MoS 2 film is beneficial in creating strain sensors because of its strain-dependent electrical response.

In this work, we demonstrate the performance of a silicon-compatible, high-performance, and self-powered photodetector. A wide detection range from visible (405 nm) to near-infrared (1550 nm) light was enabled by the vertical p-n heterojunction between the p-type antimony telluride (Sb 2 Te 3 ) thin film and the n-type silicon (Si) substrates. A Sb 2 Te 3 film with a good crystal quality, low density of extended defects, proper stoichiometry, p-type nature, and excellent uniformity across a 4 in. wafer was achieved by atomic layer deposition at 80 °C using (Et 3 Si) 2 Te and SbCl 3 as precursors. The processed photodetectors have a low dark current (∼20 pA), a high responsivity of (∼4.3 A/W at 405 nm and ∼150 mA/W at 1550 nm), a peak detectivity of ∼1.65 × 10 14 Jones, and a quick rise time of ∼98 μs under zero bias voltage. Density functional theory calculations reveal a narrow, near-direct, type-II band gap at the heterointerface that supports a strong built-in electric field leading to efficient separation of the photogenerated carriers. The devices have long-term air stability and efficient switching behavior even at elevated temperatures. These high-performance and self-powered p-Sb 2 Te 3 /n-Si heterojunction photodetectors have immense potential to become reliable technological building blocks for a plethora of innovative applications in next-generation optoelectronics, silicon-photonics, chip-level sensing, and detection.

Self-limiting assembly of particles represents the state-of-the-art controllability in nanomanufacturing processes where the assembly stops at a designated stage, providing a desirable platform for applications requiring delicate thickness control such as optics, electronics, and catalytic systems. Most successes in self-limiting assembly are limited to self-assembled monolayers (SAMs) of small molecules on inorganic, chemically homogeneous rigid substrates (e.g., Au and SiO 2 ) through surface-interaction mechanisms. Similar mechanisms, however, cannot achieve a uniform assembly of particles on flexible polymer substrates. The complex configurations and conformations of polymer chains create a surface with nonuniform distributions of chemical groups and phases. In addition, most assembly mechanisms require good solvent wettability, where many desirable but hard-to-wet particles and polymer substrates are excluded. Here, we demonstrate a collision-based self-limiting assembly (CSA) to achieve wafer-scale, full-coverage, close-packed monolayers of hydrophobic particles on hydrophobic polymer substrates in aqueous solutions. The kinetic assembly and self-limiting processes are facilitated and controlled by the combined acoustic and shear fields. We envision many applications in functional coatings and showcase their feasibility in structural coloration. Importantly, such functional coatings can be repaired using CSA, and both particles and polymer substrate can be recycled.

During the past decades micro-electromechanical microphones have largely taken over the market for portable devices, being produced in volumes of billions yearly. Because performance of current devices is near the physical limits, further miniaturization and improvement of microphones for mobile devices poses a major challenge that requires breakthrough device concepts, geometries, and materials. Graphene is an attractive material for enabling these breakthroughs due to its flexibility, strength, nanometer thinness, and high electrical conductivity. Here, we demonstrate that transfer-free 7 nm thick multilayer graphene (MLGr) membranes with diameters ranging from 85-155 to 300 μm can be used to detect sound and show a mechanical compliance up to 92 nm Pa -1 , thus outperforming commercially available MEMS microphones of 950 μm with compliances around 3 nm Pa -1 . The feasibility of realizing larger membranes with diameters of 300 μm and even higher compliances is shown, although these have lower yields. We present a process for locally growing graphene on a silicon wafer and realizing suspended membranes of patterned graphene across through-silicon holes by bulk micromachining and sacrificial layer etching, such that no transfer is required. This transfer-free method results in a 100% yield for membranes with diameters up to 155 μm on 132 fabricated drums. The device-to-device variations in the mechanical compliance in the audible range (20-20000 Hz) are significantly smaller than those in transferred membranes. With this work, we demonstrate a transfer-free method for realizing wafer-scale multilayer graphene membranes that is compatible with high-volume manufacturing. Thus, limitations of transfer-based methods for graphene microphone fabrication such as polymer contamination, crack formation, wrinkling, folding, delamination, and low-tension reproducibility are largely circumvented, setting a significant step on the route toward high-volume production of graphene microphones.

Transition-metal nitrides (e.g., TiN, ZrN, TaN) are incredible materials with excellent complementary metal-oxide semiconductor compatibility and remarkable performance in refractory plasmonics and superconducting quantum electronics. Epitaxial growth of flexible transition-metal nitride films, especially at the wafer scale, is fundamentally important for developing high-performance flexible photonics and superconducting electronics, but the study is rare thus far. This work reports the high-quality epitaxy of 2-in. titanium nitride (TiN) films on flexible fluorophlogopite-mica (F-mica) substrates via reactive magnetron sputtering. Combined measurements of spectroscopic ellipsometry and electrical transport reveal the superior plasmonic and superconducting performance of TiN/F-mica films owing to the high single crystallinity. More interestingly, the superconductivity of these flexible TiN films can be manipulated by the bending states, and enhanced superconducting critical temperature T C is observed in convex TiN films with in-plane tensile strain. Density functional theory calculations reveal that the strain can tune the electron-phonon interaction strength and the resultant superconductivity of TiN films. This study provides a promising route toward integrating scalable single-crystalline transition-metal nitride films with flexible electronics for high-performance plasmonics and superconducting electronics.

In recent years, two-dimensional (2D) semiconductors have attracted considerable attention from both academic and industrial communities. Recent research has begun transforming from constructing basic field-effect transistors (FETs) into designing functional circuits. However, device processing remains a bottleneck in circuit-level integration. In this work, a non-destructive doping strategy is proposed to modulate precisely the threshold voltage ( V TH -FETs in a wafer scale. By inserting an Al interlayer with a varied thickness between the high- 2 -FETs in a wafer scale. By inserting an Al interlayer with a varied thickness between the high- k dielectric layer, which further leads to stable electron doping. The proposed strategy is then used to optimize an inverter circuit by matching the electrical properties of the load and driver transistors. Furthermore, the doping strategy is used to fabricate digital logic blocks with desired logic functions, which indicates its potential to fabricate fully integrated multistage logic circuits based on wafer-scale 2D semiconductors.k dielectric layer, which further leads to stable electron doping. The proposed strategy is then used to optimize an inverter circuit by matching the electrical properties of the load and driver transistors. Furthermore, the doping strategy is used to fabricate digital logic blocks with desired logic functions, which indicates its potential to fabricate fully integrated multistage logic circuits based on wafer-scale 2D semiconductors.

The metallic nanogap has been proved as an efficient architecture for surface-enhanced Raman scattering (SERS) applications. Although a lot of nanogap fabrication methods have been proposed in the last few decades, the economical and high-yield manufacturing of sub-10 nm gaps remains a challenge. Here, we present a convenient and cost-effective fabrication method for wafer-scale patterning of metallic nanogaps, which simply combines photolithographic metal patterning, swelling-induced nanocracking, and superimposition metal sputtering without requiring expensive nanofabrication equipment. By controlling the swelling time and metal deposition thickness, the gap size can be precisely defined, down to the sub-10 nm scale. Furthermore, we demonstrate that the fabricated nanogap array can be used as an excellent SERS substrate for molecule measurements and shows a high Raman enhancement factor of ∼10 8 and a high sensitivity for the detection of rhodamine 6G (R6G) molecules, even down to 10 -14 M, indicating an extraordinary capability for single-molecule detection. Due to its high controllability and wafer-scale fabrication capability, this nanogap fabrication method offers a promising route for highly sensitive and economical SERS detections.

While two-dimensional (2D) hexagonal boron nitride (h-BN) is emerging as an atomically thin and dangling bond-free insulating layer for next-generation electronics and optoelectronics, its practical implementation into miniaturized integrated circuits has been significantly limited due to difficulties in large-scale growth directly on epitaxial semiconductor wafers. Herein, the realization of a wafer-scale h-BN van der Waals heterostructure with a 2 in. AlGaN/GaN high-electron mobility transistor (HEMT) wafer using metal-organic chemical vapor deposition is presented. The combination of state-of-the-art microscopic and spectroscopic analyses and theoretical calculations reveals that the heterointerface between ∼2.5 nm-thick h-BN and AlGaN layers is atomically sharp and exhibits a very weak van der Waals interaction without formation of a ternary or quaternary alloy that can induce undesired degradation of device performance. The fabricated AlGaN/GaN HEMT with h-BN shows very promising performance including a cutoff frequency ( f T ) as high as 28 and 88 GHz, respectively, enabled by an effective passivation of surface defects on the HEMT wafer to deliver accurate information with minimized power loss. These findings pave the way for practical implementation of 2D materials integrated with conventional microelectronic devices and the realization of future all-2D electronics.f MAX ) as high as 28 and 88 GHz, respectively, enabled by an effective passivation of surface defects on the HEMT wafer to deliver accurate information with minimized power loss. These findings pave the way for practical implementation of 2D materials integrated with conventional microelectronic devices and the realization of future all-2D electronics.

The growth control of a molybdenum disulfide (MoS 2 ) thin film, including the number of layers, growth rate, and electrical property modulation, remains a challenge. In this study, we synthesized MoS 2 thin films using the metal-organic chemical vapor deposition (MOCVD) method with a 2 inch wafer scale and achieved high thickness uniformity according to the positions on the substrate. In addition, we successfully controlled the number of MoS 2 layers to range from one to five, with a growth rate of 10 min per layer. The layer-dependent optical and electrical properties were characterized by photoluminescence, Raman spectroscopy, differential reflectance spectroscopy, and field effect transistors. To guide the growth of MoS 2 , we summarized the relation between the growth aspects and the precursor control in the form of a growth map. Reference to this growth map enabled control of the growth rate, domain density, and domain size according to the application purposes. Finally, we confirmed the electrical performance of MOCVD-grown MoS 2 with five layers under a high-κ dielectric environment, which exhibited an on/off current ratio of 10 ∼6 and a maximum field effect mobility of 8.6 cm 2 V -1 s -1 .

Transition metal dichalcogenides (TMDs) are materials that can exhibit intriguing optical properties like a change of the bandgap from indirect to direct when being thinned down to a monolayer. Well-resolved narrow excitonic resonances can be observed for such monolayers although only for materials of sufficient crystalline quality and so far mostly available in the form of micrometer-sized flakes. A further significant improvement of optical and electrical properties can be achieved by transferring the TMD on hexagonal boron nitride (hBN). To exploit the full potential of TMDs in future applications, epitaxial techniques have to be developed that not only allow the growth of large-scale, high-quality TMD monolayers but also allow the growth to be performed directly on large-scale epitaxial hBN. In this work, we address this problem and demonstrate that MoSe 2 of high optical quality can be directly grown on epitaxial hBN on an entire 2 in. wafer. We developed a combined growth theme for which hBN is first synthesized at high temperature by metal organic vapor phase epitaxy (MOVPE) and as a second step MoSe 2 is deposited on top by molecular beam epitaxy (MBE) at much lower temperatures. We show that this structure exhibits excellent optical properties, manifested by narrow excitonic lines in the photoluminescence spectra. Moreover, the material is homogeneous on the area of the whole 2 in. wafer with only ±0.14 meV deviation of excitonic energy. Our mixed growth technique may guide the way for future large-scale production of high quality TMD/hBN heterostructures.

Lead halide perovskites with good optoelectronic properties and high attenuation of high-energy radiation are great candidates for X-ray radiation detectors. Large area, dense, and thick films or wafers are a prerequisite for these applications. In this paper, a one-step heat-assisted high-pressure press method is developed to directly prepare a large (the largest has a diameter of 80 mm) and thickness- and shape-controlled phase-pure organic-inorganic hybrid CH 3 NH 3 PbI 3 wafer of densely packed large microcrystals from raw powder materials. Meanwhile, this method uses no solvent to achieve essentially 100% material utilization. The obtained wafers show good ambipolar carrier mobilities of ∼20 cm 2 V -1 s -1 and a μτ product as high as 3.84 × 10 -4 cm 2 V -1 . Under an X-ray source using an acceleration voltage of 40 kV, the perovskite wafer-based X-ray detector shows an X-ray sensitivity as large as 1.22 × 10 5 μC Gy air -1 cm -2 under a 10 V bias, the highest reported for any perovskite material. The method provides a convenient strategy for producing large perovskite wafers with good optoelectronic properties, which will facilitate the development of large perovskite devices.

β-phase gallium oxide (Ga 2 O 3 ) is an emerging ultrawide bandgap (UWBG) semiconductor ( E G ∼ 4.8 eV), which promises generational improvements in the performance and manufacturing cost over today's commercial wide bandgap power electronics based on GaN and SiC. However, overheating has been identified as a major bottleneck to the performance and commercialization of Ga 2 O 3 device technologies. In this work, a novel Ga 2 /4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga 3 /4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga 2 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm 3 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm 2 /Vs and a volume charge of ∼3 × 10 17 cm -3 was achieved at a growth temperature of 600 °C. Phonon transport across the Ga 2 O 3 /4H-SiC interface has been studied using frequency-domain thermoreflectance and a differential steady-state thermoreflectance approach. Scanning transmission electron microscopy analysis suggests that phonon transport across the Ga 2 O 3 /4H-SiC interface is dominated by the thickness of the SiN x bonding layer and an unintentionally formed SiO x interlayer. Extrinsic effects that impact the thermal conductivity of the 6.5 μm thick Ga 2 O 3 layer were studied via time-domain thermoreflectance. Thermal simulation was performed to estimate the improvement of the thermal performance of a hypothetical single-finger Ga 2 metal-semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.3 metal-semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.

Inspired by the outstanding properties discovered in two-dimensional materials, the bottom-up generation of molecular monolayers is becoming again extremely popular as a route to develop novel functional materials and devices with tailored characteristics and minimal materials consumption. However, achieving a full-coverage over a large-area still represents a grand challenge. Here we report a molecular self-assembly protocol at the water surface in which the monolayers are strained by a novel solvent surface tension balance (SSTB) instead of a physical film balance as in the conventional Langmuir-Blodgett (LB) method. The obtained molecular monolayers can be transferred onto any arbitrary substrate including rigid inorganic oxides and metals, as well as flexible polymeric dielectrics. As a proof-of-concept, their application as ideal modification layers of a dielectric support for high-performance organic field-effect transistors (OFETs) has been demonstrated. The field-effect mobilities of both p- and n-type semiconductors displayed dramatic improvements of 1-3 orders of magnitude on SSTB-derived molecular monolayer, reaching values as high as 6.16 cm 2 V -1 s -1 and 0.68 cm 2 V -1 s -1 for pentacene and PTCDI-C8, respectively. This methodology for the fabrication of wafer-scale and defect-free molecular monolayers holds potential toward the emergence of a new generation of high-performance electronics based on two-dimensional materials.

Platinum diselenide (PtSe 2 ) is an emerging class of two-dimensional (2D) transition-metal dichalcogenide (TMD) crystals recently gaining substantial interest, owing to its extraordinary properties absent in conventional 2D TMD layers. Most interestingly, it exhibits a thickness-dependent semiconducting-to-metallic transition, i.e., thick 2D PtSe 2 layers, which are intrinsically metallic, become semiconducting with their thickness reduced below a certain point. Realizing both semiconducting and metallic phases within identical 2D PtSe 2 layers in a spatially well-controlled manner offers unprecedented opportunities toward atomically thin tailored electronic junctions, unattainable with conventional materials. In this study, beyond this thickness-dependent intrinsic semiconducting-to-metallic transition of 2D PtSe 2 layers, we demonstrate that controlled plasma irradiation can "externally" achieve such tunable carrier transports. We grew wafer-scale very thin (a few nm) 2D PtSe 2 layers by a chemical vapor deposition (CVD) method and confirmed their intrinsic semiconducting properties. We then irradiated the material with argon (Ar) plasma, which was intended to make it more semiconducting by thickness reduction. Surprisingly, we discovered a reversed transition of semiconducting to metallic, which is opposite to the prediction concerning their intrinsic thickness-dependent carrier transports. Through extensive structural and chemical characterization, we identified that the plasma irradiation introduces a large concentration of near-atomic defects and selenium (Se) vacancies in initially stoichiometric 2D PtSe 2 layers. Furthermore, we performed density functional theory (DFT) calculations and clarified that the band-gap energy of such defective 2D PtSe 2 layers gradually decreases with increasing defect concentration and dimensions, accompanying a large number of midgap energy states. This corroborative experimental and theoretical study decisively verifies the fundamental mechanism for this externally controlled semiconducting-to-metallic transition in large-area CVD-grown 2D PtSe 2 layers, greatly broadening their versatility for futuristic electronics.

The development of highly conductive electrodes with robust mechanical durability and clear transmittance in the visible to IR spectral range is of great importance for future wearable/flexible electronic applications. In particular, low resistivity, robust flexibility, and wide spectral transparency have a significant impact on optoelectronic performance. Herein, we introduce a new class of covellite copper monosulfide (CuS) nanosheet films as a promising candidate for soft transparent conductive electrodes (TCEs). An atmospheric sulfur adsorption-corrosion phenomenon represents a key approach in our work for the achievement of wafer-scale CuS nanosheet films through systematic control of the neat Cu layer thickness ranging from 2 to 10 nm multilayers at room temperature. These nanosheet films provide outstanding conductivity (∼25 Ω sq -1 ) and high transparency (> 80%) in the visible to infrared region as well as distinct flexibility and long stability under air exposure, yielding a high figure-of-merit (∼60) that is comparable to that of conventional rigid metal oxide material-based TCEs. Our unique room temperature synthesis process delivers high quality CuS nanosheets on any arbitrary substrates in a short time (< 1 min) scale, thus guaranteeing the widespread use of highly producible and scalable device fabrication.

Van der Waals heterostructures have attracted increasing interest, owing to the combined benefits of their constituents. These hybrid nanostructures can be realized via epitaxial growth, which offers a promising approach for the controlled synthesis of the desired crystal phase and the interface between van der Waals layers. Here, the epitaxial growth of a continuous molybdenum disulfide (MoS 2 ) film on large-area graphene, which was directly grown on a sapphire substrate, is reported. Interestingly, the grain size of MoS 2 grown on graphene increases, whereas that of MoS 2 grown on SiO 2 decreases with an increasing amount of hydrogen in the chemical vapor deposition reactor. In addition, to achieve the same quality, MoS 2 grown on graphene requires a much lower growth temperature (400 °C) than that grown on SiO 2 (580 °C). The MoS 2 /graphene heterostructure that was epitaxially grown on a transparent platform was investigated to explore its photosensing properties and was found to exhibit inverse photoresponse with highly uniform photoresponsivity in the photodetector pixels fabricated across a full wafer. The MoS 2 /graphene heterostructure exhibited ultrahigh photoresponsivity (4.3 × 10 4 A W -1 ) upon exposure to visible light of a wide range of wavelengths, confirming the growth of a high-quality MoS 2 /graphene heterostructure with a clean interface.

The perovskite single-crystalline thin films, which are free of grain boundaries, would be highly desirable in boosting device performance due to their high carrier mobility, low trap density, and large carrier diffusion length. Herein, a facile room-temperature approach to epitaxially grow MAPbBr 3 single-crystalline films on CsPbBr 3 substrates by the droplet-evaporated crystallization method is reported. A large-area continuous MAPbBr 3 single-crystal film about 15 × 15 mm 2 in size has been heteroepitaxially grown on CsPbBr 3 substrates. The surface morphology, composition, and single crystallinity were characterized by a scanning electron microscope, an energy-dispersive spectrometer, an electron probe microanalyzer, and high-resolution X-ray diffractions, respectively. The thickness of the films could be adjusted from 1 to 18 μm by varying the concentration of the solution from 10 to 50 wt %. The epitaxial relationship of MAPbBr 3 (010)∥CsPbBr 3 (010), MAPbBr 3 [101]∥CsPbBr 3 [200] was authenticated using XRD, pole figure, and TEM. The low defect density of 4.6 × 10 11 cm -3 and high carrier mobility of 261.94 cm 2 V -1 s -1 of the MAPbBr 3 film measured by the SCLC method are comparable to those of bulk single crystals. An on/off ratio of ∼113 was achieved according to current-voltage curves. Our research demonstrates the first large-area single-crystal heterojunction of a hybrid perovskite with an all-inorganic perovskite, which may show unique properties in optoelectronic applications.

Graphdiyne is a new two-dimensional carbon allotrope with many attractive properties and has been widely used in various applications. However, the synthesis of large-area, high-quality, and ultrathin (especially monolayer) graphdiyne and its analogues remains a challenge, hindering its application in optoelectronic devices. Here, a wafer-scale monolayer pyrenyl graphdiyne (Pyr-GDY) film is obtained on hexagonal boron nitride (hBN) via a van der Waals epitaxial strategy, and top-floating-gated multibit nonvolatile optoelectronic memory based on Pyr-GDY/hBN/graphene is constructed, using Pyr-GDY as a photoresponsive top-floating gate. Benefiting from the excellent charge trapping capability and strong absorption of the graphdiyne film, as well as the top-floating-gated structure and the ultrathin hBN film used in the device, the optoelectronic memory exhibits high storage performance and robust reliability. A huge difference in the current between the programmed and erased states (>26 μA μm -1 at V ds = 0.1 V) and a prolonged retention time (>10 5 s) enable the device to achieve multibit storage, for which eight and nine distinct storage levels (3-bit) are obtained by applying periodic gate voltages and optical pulses in the programming and erasing processes, respectively. This work provides an important step toward realizing versatile graphdiyne-based optoelectronic devices in the future.

Liquid fouling can reduce the functionality of critical engineering surfaces. Recent studies have shown that minimizing contact angle hysteresis is a promising strategy for achieving omniphobic (all-liquid repellent) properties, thereby inhibiting fouling. Prior omniphobic films can repel a broad range of liquids, but the applicability of these coatings has always been limited to silicon wafers or smooth glass. Here we develop a facile procedure to generate an omniphobic coating on any surface, including metals, paper, ceramics, etc. The coating involves depositing an ultrasmooth, silicon wafer-like silica layer and then treating this layer with a highly reactive chlorosilane, which grafts polydimethylsiloxane chains onto the surface. Negligible contact angle hysteresis (≤1°) for various liquids, including ultralow surface tension oils, alcohols, and fluoro-solvents, was achieved on many different substrates regardless of their initial roughness or chemistry. In fact, the contact angle hysteresis was so low we were forced to propose an alternate measurement technique, using tilt angles, that reduced the inherent errors associated with traditional contact angle goniometry. The coating's durability was characterized and, when it was damaged, could be repeatedly repaired, fully restoring the omniphobic properties to their initial state.

We explored the feasibility of wafer-scale two-dimensional (2D) molybdenum disulfide (MoS 2 ) layers toward futuristic environmentally friendly electronics that adopt biodegradable substrates. Large-area (> a few cm 2 ) 2D MoS 2 layers grown on silicon dioxide/silicon (SiO 2 /Si) wafers were delaminated and integrated onto a variety of cellulose-based substrates of various components and shapes in a controlled manner; examples of the substrates include planar papers, cylindrical natural rubbers, and 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers. The integrated 2D layers were confirmed to well preserve their intrinsic structural and chemical integrity even on such exotic substrates. Proof-of-concept devices employing large-area 2D MoS 2 layers/cellulose substrates were demonstrated for a variety of applications, including photodetectors, pressure sensors, and field-effect transistors. Furthermore, we demonstrated the complete "dissolution" of the integrated 2D MoS 2 layers in a buffer solution composed of baking soda and deionized water, confirming their environmentally friendly transient characteristics. Moreover, the approaches to delaminate and integrate them do not demand any chemicals except for water, and their original substrates can be recycled for subsequent growths, ensuring excellent chemical benignity and process sustainability.

Platinum ditelluride (PtTe 2 ) is an emerging semimetallic two-dimensional (2D) transition-metal dichalcogenide (TMDC) crystal with intriguing band structures and unusual topological properties. Despite much devoted efforts, scalable and controllable synthesis of large-area 2D PtTe 2 with well-defined layer orientation has not been established, leaving its projected structure-property relationship largely unclarified. Herein, we report a scalable low-temperature growth of 2D PtTe 2 layers on an area greater than a few square centimeters by reacting Pt thin films of controlled thickness with vaporized tellurium at 400 °C. We systematically investigated their thickness-dependent 2D layer orientation as well as its correlated electrical conductivity and surface property. We unveil that 2D PtTe 2 layers undergo three distinct growth mode transitions, i.e., horizontally aligned holey layers, continuous layer-by-layer lateral growth, and horizontal-to-vertical layer transition. This growth transition is a consequence of competing thermodynamic and kinetic factors dictated by accumulating internal strain, analogous to the transition of Frank-van der Merwe (FM) to Stranski-Krastanov (SK) growth in epitaxial thin-film models. The exclusive role of the strain on dictating 2D layer orientation has been quantitatively verified by the transmission electron microscopy (TEM) strain mapping analysis. These centimeter-scale 2D PtTe 2 layers exhibit layer orientation tunable metallic transports yielding the highest value of ∼1.7 × 10 6 S/m at a certain critical thickness, supported by a combined verification of density functional theory (DFT) and electrical measurements. Moreover, they show intrinsically high hydrophobicity manifested by the water contact angle (WCA) value up to ∼117°, which is the highest among all reported 2D TMDCs of comparable dimensions and geometries. Accordingly, this study confirms the high material quality of these emerging large-area 2D PtTe 2 layers, projecting vast opportunities employing their tunable layer morphology and semimetallic properties from investigations of novel quantum phenomena to applications in electrocatalysis.

Two-dimensional (2D) metal dichalcogenides have drawn considerable interest because they offer possibilities for the implementation of emerging electronics. The emerging electronics are moving toward two major directions: vertical expansion of device space and flexibility. However, the development of a synthesis method for 2D metal dichalcogenides that meets all the requirements remains a significant challenge. Here, we propose a promising method for wafer-scale, conformal, and low-temperature (≤240 °C) synthesis of single-phase SnS 2 via the atomic layer deposition technique. There is a trade-off relationship between the crystallinity and orientation preference of SnS 2 , which is efficiently eliminated by the two-step growth occurring at different temperatures. Consequently, the van der Waals layers of the highly crystalline SnS 2 are parallel to the substrate. Thin-film transistors (TFTs) comprising the SnS 2 layer show reasonable electrical performances (field-effect mobility: ∼0.8 cm 2 V -1 s -1 and on/off ratio: ∼10 6 ), which are comparable to that of a single-crystal SnS 2 flake. Moreover, we demonstrate nonplanar and flexible TFTs to identify the feasibility of the implementation of future electronics. Both the diagonal-structured TFT and flexible TFT fabricated without a transfer process show electrical performances comparable to those of rigid and planar TFTs. Particularly, the flexible TFT does not exhibit substantial degradation even after 2000 bending cycles. Our work would provide decisive opportunities for the implementation of future electronic devices utilizing 2D metal chalcogenides.

Despite high potential, the promise of 2D materials has not been realized practically because of limits of tiny grown size and difficult manipulation of the active spot. The utilization of 2D layers is the ultimate approach, which should be supported by large-scale production. In this very first report, we demonstrate the wafer-scale production of ReS 2 using the conventional sputtering method. The controllability of ReS 2 geometry has been investigated to form typical thin films or vertically aligned layers that are further applied for field emission. The vertically aligned ReS 2 layers exhibit ultralow turn-on electric field (0.6 V μm -1 ) with the current density (0.6 mA cm -2 ) and significantly low threshold electric field (0.8 V μm -1 ), respectively, along with outstanding emission stability. The results are attributed to weakly coupled ReS 2 layers and the high geometrical field enhancement factor (∼1.08 × 10 5 ). Further, Kelvin probe force microscopy measurements confirm that lowering the work function is not solely responsible to achieve the ultralow operative field. Moreover, finite element simulation suggests that not only the length, width, and separation of the nanostructures but also the local slope plays an important role in suppressing screening effects.

Two-dimensional transition-metal dichalcogenides (TMDCs) possess unique electronic and optical properties, which open up a new opportunity for atomically thin optoelectronic devices. Synthesizing large-scale monolayer TMDCs on the SiO 2 /Si substrate is crucial for practical applications, however, it remains a big challenge. In this work, a method which combines chemical vapor deposition (CVD) and thermal evaporation was employed to grow monolayer tungsten disulfide (WS 2 ) crystals. Through controlling the density and the distribution of W precursors, a wafer-scale continuous uniform WS 2 film was achieved, with the structural and spectral characterizations confirming a monolayer configuration and a high crystalline quality. Wafer-scale field-effect transistor arrays based on the monolayer WS 2 were fabricated. The devices show superior electrical performances, and the maximal mobility is almost 1 order of magnitude higher than those of CVD-grown large-scale TMDC devices reported so far.

The substitutional doping method is ideally suited to generating doped two-dimensional (2D) materials for practical device applications as it does not damage or destabilize such materials. However, recently reported substitutional doping techniques for 2D materials have given rise to discontinuities and low uniformities, which hamper the extension of such techniques to large-scale production. In the current work, we demonstrated uniform substitutional doping of monolayer MoS 2 in a 2 in. wafer of area >13 cm 2 . The devices based on doped MoS 2 showed extremely high uniformity and stability in electrical properties in ambient conditions for 30 days. The photodetectors based on the doped MoS 2 samples showed an ultrahigh photoresponsivity of 5 × 10 5 A/W, a detectivity of 5 × 10 12 Jones, and a fast response rate of 5 ms than did those based on undoped MoS 2 . This work showed the feasibility of real-life applications based on functionalized 2D semiconductors for next-generation electronic and optoelectronic devices.

We demonstrated a simple and scalable fabrication route of a nitrogen-doped reduced graphene oxide (N-rGO) photodetector on an 8 in. wafer-scale. The N-rGO was prepared through in situ plasma treatment in an acetylene-ammonia atmosphere to achieve an n-type semiconductor with substantial formation of quaternary-N substituted into the graphene lattice. The morphology, structural, chemical composition, and electrical properties of the N-rGO were carefully characterized and used for the device fabrication. The N-rGO devices were fabricated in a simple metal-semiconductor-metal structure with unconventional metal-on-bottom configuration to promote high-performance photodetection. The N-rGO devices exhibited enhanced photoresponsivity as high as 0.68 A W -1 at 1.0 V, which is about 2 orders of magnitude higher compared to a pristine graphene and wide-band photoinduced response from the visible to the near-infrared region with increasing sensitivity in the order of 785, 632.8, and 473 nm excitation wavelengths. We also further demonstrated a symmetric characteristic of the photoinduced response to any position of local laser excitation with respect to the electrodes. The excellent features of wafer-scale N-rGO devices suggest a promising route to merge the current silicon technology and two-dimensional materials for future optoelectronic devices.

Silk fibroin is an excellent candidate for biomedical implantable devices because of its biocompatibility, controllable biodegradability, solution processability, flexibility, and transparency. Thus, fibroin has been widely explored in biomedical applications as biodegradable films as well as functional microstructures. Although there exists a large number of patterning methods for fibroin thin films, multilayer micropatterning of fibroin films interleaved with metal layers still remains a challenge. Herein, we report a new wafer-scale multilayer microfabrication process named aluminum hard mask on silk fibroin (AMoS), which is capable of micropatterning multiple layers composed of both fibroin and inorganic materials (e.g., metal and dielectrics) with high-precision microscale alignment. To the best of our knowledge, our AMoS process is the first demonstration of wafer-scale multilayer processing of both silk fibroin and metal micropatterns. In the AMoS process, aluminum deposited on fibroin is first micropatterned using conventional ultraviolet (UV) photolithography, and the patterned aluminum layer is then used as a mask to pattern fibroin underneath. We demonstrate the versatility of our fabrication process by fabricating fibroin microstructures with different dimensions, passive electronic components composed of both fibroin and metal layers, and functional fibroin microstructures for drug delivery. Furthermore, because one of the crucial advantages of fibroin is biocompatibility, we assess the biocompatibility of our fabrication process through the culture of highly susceptible primary neurons. Because the AMoS process utilizes conventional UV photolithography, the principal advantages of our process are multilayer fabrication with high-precision alignment, high resolution, wafer-scale large area processing, no requirement for chemical modification of the protein, and high throughput and thus low cost, all of which have not been feasible with silk fibroin. Therefore, the proposed fabrication method is a promising candidate for batch fabrication of functional fibroin microelectronics (e.g., memristors and organic thin film transistors) for next-generation implantable biomedical applications.

This paper demonstrates, for the first time, wafer-scale graphene/MoS 2 heterostructures prepared by chemical vapor deposition (CVD) and their application in vertical transistors and logic gates. A CVD-grown bulk MoS 2 layer is utilized as the vertical channel, whereas CVD-grown monolayer graphene is used as the tunable work-function electrode. The short vertical channel of the transistor is formed by sandwiching bulk MoS 2 between the bottom indium tin oxide (ITO, drain electrode) and the top graphene (source electrode). The electron injection barriers at the graphene-MoS 2 junction and ITO-MoS 2 junction are modulated effectively through variation of the Schottky barrier height and its effective barrier width, respectively, because of the work-function tunability of the graphene electrode. The resulting vertical transistor with the CVD-grown MoS 2 /graphene heterostructure exhibits a current density exceeding 7 A/cm 2 , a subthreshold swing of 410 mV/dec, and an on-off current ratio exceeding 10 3 . The large-area synthesis, transfer, and patterning processes of both semiconducting MoS 2 and metallic graphene facilitate construction of a wafer-scale array of transistors and logic gates such as NOT, NAND, and NOR.

PtS 2 is a newly developed group 10 2D layered material with high carrier mobility, wide band gap tunability, strongly bound excitons, symmetrical metallic and magnetic edge states, and ambient stability, making it attractive in nanoelectronic, optoelectronic, and spintronic fields. To the aim of application, a large-scale synthesis is necessary. For transition-metal dichalcogenide (TMD) compounds, a thermally assisted conversion method has been widely used to fabricate wafer-scale thin films. However, PtS 2 cannot be easily synthesized using the method, as the tetragonal PtS phase is more stable. Here, we use a specified quartz part to locally increase the vapor pressure of sulfur in a chemical vapor deposition furnace and successfully extend this method for the synthesis of PtS 2 thin films in a scalable and controllable manner. Moreover, the PtS and PtS 2 phases can be interchangeably converted through a proposed strategy. Field-effect transistor characterization and photocurrent measurements suggest that PtS 2 is an ambipolar semiconductor with a narrow band gap. Moreover, PtS 2 also shows excellent gas-sensing performance with a detection limit of ∼0.4 ppb for NO 2 . Our work presents a relatively simple way of synthesizing PtS 2 thin films and demonstrates their promise for high-performance ultrasensitive gas sensing, broadband optoelectronics, and nanoelectronics in a scalable manner. Furthermore, the proposed strategy is applicable for making other PtX 2 compounds and TMDs which are compatible with modern silicon technologies.

Two-dimensional (2D) van der Waals (vdW) heterostructures exhibit novel physical and chemical properties, allowing the development of unprecedented electronic, optical, and electrochemical devices. However, the construction of wafer-scale vdW heterostructures for practical applications is still limited due to the lack of well-established growth and transfer techniques. Herein, we report a method for the fabrication of wafer-scale 2D vdW heterostructures with an ultraclean interface between layers via the aid of a freestanding viscoelastic polymer support layer (VEPSL). The low glass transition temperature ( T g ) and viscoelastic nature of the VEPSL ensure absolute conformal contact between 2D layers, enabling the easy pick-up of layers and attaching to other 2D layers. This eventually leads to the construction of random sequence 2D vdW heterostructures such as molybdenum disulfide/tungsten disulfide/molybdenum diselenide/tungsten diselenide/hexagonal boron nitride. Furthermore, the VEPSL allows the conformal transfer of 2D vdW heterostructures onto arbitrary substrates, irrespective of surface roughness. To demonstrate the significance of the ultraclean interface, the fabricated molybdenum disulfide/graphene heterostructure employed as an electrocatalyst yielded excellent results of 73.1 mV·dec -1 for the Tafel slope and 0.12 kΩ of charge transfer resistance, which are almost twice as low as that of the impurity-trapped heterostructure.

The fabrication of van der Waals heterostructures mainly extends to two-dimensional (2D) materials that are exfoliated from their bulk counterparts, which is greatly limited by high-volume manufacturing. Here, we demonstrate multilayered PtS 2 /PtSe 2 heterojunctions covering a large area on the SiO 2 /Si substrate with a maximum size of 2″ in diameter, offering throughputs that can meet the practical application demand. Theoretical simulation was carried out to understand the electronic properties of the PtS 2 /PtSe 2 heterojunctions. Zero-bias photoresponse in the heterojunctions is observed under laser illumination of different wavelengths (405-2200 nm). The PtS 2 /PtSe 2 heterojunctions exhibit broad band photoresponse and high quantum efficiency at infrared wavelengths with lower bounds for the external quantum efficiencies being 1.2% at 1064 nm, 0.2% at 1550 nm, and 0.05% at 2200 nm, and also relatively fast response time at the dozens of millisecond level. The large area, broad band 2D heterojunction photodetector demonstrated in this work further corroborates the great potential of 2D materials in the future low-energy optoelectronics.

Wafer-scale MoS 2 growth at arbitrary integer layer number is demonstrated by a technique based on the decomposition of carbon disulfide on a hot molybdenum filament, which yields volatile MoS x precursors that precipitate onto a heated wafer substrate. Colorimetric control of the growth process allows precise targeting of any integer layer number. The method is inherently free of particulate contamination, uses inexpensive reactants without the pyrophoricity common to metal-organic precursors, and does not rely on particular gas-flow profiles. Raman mapping and photoluminescence mapping, as well as imaging by electron microscopy, confirm the layer homogeneity and crystalline quality of the resultant material. Electrical characterization revealed microampere output current, outstanding device-to-device consistency, and exceptionally low noise level unparalleled even by the exfoliated material, while other transport properties are obscured by high-resistance contacts typical to MoS 2 devices.

The availability of an accurate, nondestructive method for measuring thickness and continuity of two-dimensional (2D) materials with monolayer sensitivity over large areas is of pivotal importance for the development of new applications based on these materials. While simple optical contrast methods and electrical measurements are sufficient for the case of metallic and semiconducting 2D materials, the low optical contrast and high electrical resistivity of wide band gap dielectric 2D materials such as hexagonal boron nitride (hBN) hamper their characterization. In this work, we demonstrate a nondestructive method to quantitatively map the thickness and continuity of hBN monolayers and bilayers over large areas. The proposed method is based on acquisition and subsequent fitting of ellipsometry spectra of hBN on Si/SiO 2 substrates. Once a proper optical model is developed, it becomes possible to identify and map the commonly observed polymer residuals from the transfer process and obtain submonolayer thickness sensitivity for the hBN film. With some assumptions on the optical functions of hBN, the thickness of an as-transferred hBN monolayer on SiO 2 is measured as 4.1 Å ± 0.1 Å, whereas the thickness of an air-annealed hBN monolayer on SiO 2 is measured as 2.5 Å ± 0.1 Å. We argue that the difference in the two measured values is due to the presence of a water layer trapped between the SiO 2 surface and the hBN layer in the latter case. The procedure can be fully automated to wafer scale and extended to other 2D materials transferred onto any polished substrate, as long as their optical functions are approximately known.