Wafer-Scale Freestanding Monocrystalline Chalcogenide Membranes by Strain-Assisted Epitaxy and Spalling.

Monocrystalline chalcogenide thin films in freestanding forms are very much needed in advanced electronics such as flexible phase change memories (PCMs). However, they are difficult to manufacture in a scalable manner due to their growth and delamination challenges. Herein, we report a viable strategy for a wafer-scale epitaxial growth of monocrystalline germanium telluride (GeTe) membranes and their deterministic integrations onto flexible substrates.

High Mobility Transistors and Flexible Optical Synapses Enabled by Wafer-Scale Chemical Transformation of Pt-Based 2D Layers.

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.

Defect Passivation of 2D Semiconductors by Fixating Chemisorbed Oxygen Molecules via h-BN Encapsulations.

Hexagonal boron nitride (h-BN) is a key ingredient for various 2D van der Waals heterostructure devices, but the exact role of h-BN encapsulation in relation to the internal defects of 2D semiconductors remains unclear. Here, it is reported that h-BN encapsulation greatly removes the defect-related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer WS crystals. Electron energy loss spectroscopy (EELS) combined with theoretical analysis clearly confirms that the oxygen molecules are chemisorbed onto the defects of WS crystals and are fixated by h-BN encapsulation, with excluding a possibility of oxygen molecules trapped in bubbles or wrinkles formed at the interface between WS and h-BN.

Reversible Transition of Semiconducting PtSe and Metallic PtTe for Scalable All-2D Edge-Contacted FETs.

Two-dimensional (2D) transition metal dichalcogenide (TMD) layers are highly promising as field-effect transistor (FET) channels in the atomic-scale limit. However, accomplishing this superiority in scaled-up FETs remains challenging due to their van der Waals (vdW) bonding nature with respect to conventional metal electrodes. Herein, we report a scalable approach to fabricate centimeter-scale all-2D FET arrays of platinum diselenide (PtSe) with in-plane platinum ditelluride (PtTe) edge contacts, mitigating the aforementioned challenges.

In situ synthesis of hierarchically-assembled three-dimensional ZnS nanostructures and 3D printed visualization.

Nanomaterials have gained enormous interest in improving the performance of energy harvest systems, biomedical devices, and high-strength composites. Many studies were performed fabricating more elaborate and heterogeneous nanostructures then the structures were characterized using TEM tomographic images, upgrading the fabrication technique. Despite the effort, intricate fabrication process, agglomeration characteristic, and non-uniform output were still limited to presenting the 3D panoramic views straightforwardly.

Large-area vertically aligned 2D MoSlayers on TEMPO-cellulose nanofibers for biodegradable transient gas sensors.

Crystallographically anisotropic two-dimensional (2D) molybdenum disulfide (MoS) with vertically aligned (VA) layers is attractive for electrochemical sensing owing to its surface-enriched dangling bonds coupled with extremely large mechanical deformability. In this study, we explored VA-2D MoSlayers integrated on cellulose nanofibers (CNFs) for detecting various volatile organic compound gases. Sensor devices employing VA-2D MoS/CNFs exhibited excellent sensitivities for the tested gases of ethanol, methanol, ammonia, and acetone; e.

Multiwavelength Optoelectronic Synapse with 2D Materials for Mixed-Color Pattern Recognition.

Neuromorphic visual systems emulating biological retina functionalities have enormous potential for in-sensor computing, with prospects of making artificial intelligence ubiquitous. Conventionally, visual information is captured by an image sensor, stored by memory units, and eventually processed by the machine learning algorithm. Here, we present an optoelectronic synapse device with multifunctional integration of all the processes required for real time object identification.

Peel-and-Stick Integration of Atomically Thin Nonlayered PtS Semiconductors for Multidimensionally Stretchable Electronic Devices.

Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled electromechanical properties have been explored for transformative devices. Currently, the availability of 2D vdW crystals is rather limited in nature as they are only obtained from certain mother crystals with intrinsically possessed layered crystallinity and anisotropic molecular bonding. Recent efforts to transform conventionally non-vdW three-dimensional (3D) crystals into ultrathin 2D-like structures have seen rapid developments to explore device building blocks of unique form factors.

MoS Synapses with Ultra-low Variability and Their Implementation in Boolean Logic.

Brain-inspired computing enabled by memristors has gained prominence over the years due to the nanoscale footprint and reduced complexity for implementing synapses and neurons. The demonstration of complex neuromorphic circuits using conventional materials systems has been limited by high cycle-to-cycle and device-to-device variability. Two-dimensional (2D) materials have been used to realize transparent, flexible, ultra-thin memristive synapses for neuromorphic computing, but with limited knowledge on the statistical variation of devices.

Efficient Suppression of Charge Recombination in Self-Powered Photodetectors with Band-Aligned Transferred van der Waals Metal Electrodes.

Recombination of photogenerated electron-hole pairs dominates the photocarrier lifetime and then influences the performance of photodetectors and solar cells. In this work, we report the design and fabrication of band-aligned van der Waals-contacted photodetectors with atomically sharp and flat metal-semiconductor interfaces through transferred metal integration. A unity factor α is achieved, which is essentially independent of the wavelength of the light, from ultraviolet to near-infrared, indicating effective suppression of charge recombination by the device.

Crystal Phase Transition Creates a Highly Active and Stable RuC Nanosurface for Hydrogen Evolution Reaction in Alkaline Media.

Although metastable crystal structures have received much attention owing to their utilization in various fields, their phase-transition to a thermodynamic structure has attracted comparably little interest. In the case of nanoscale crystals, such an exothermic phase-transition releases high energy within a confined surface area and reconstructs surface atomic arrangement in a short time. Thus, this high-energy nanosurface may create novel crystal structures when some elements are supplied.

Efficient and additive-free synthesis of morphology variant iron oxyhydroxide nanostructures for phosphate adsorption application.

Iron oxyhydroxide (FeOOH) nanostructures of different shapes were successfully synthesized on flexible textile cloth of polyester using a novel and simple technique based on hydrolysis method. The technique used herein is newly designed specifically to improve the efficiency in terms of energy, simplicity and cost involved in large scale synthesis of nanostructured thin films. Additionally, the morphology of nano-sized iron oxyhydroxide could be tuned into different shapes through variation in the type of precursors used for synthesis.

Mechanically rollable photodetectors enabled by centimetre-scale 2D MoS layer/TOCN composites.

Two-dimensional (2D) molybdenum disulfide (MoS) layers are suitable for visible-to-near infrared photodetection owing to their tunable optical bandgaps. Also, their superior mechanical deformability enabled by an extremely small thickness and van der Waals (vdW) assembly allows them to be structured into unconventional physical forms, unattainable with any other materials. Herein, we demonstrate a new type of 2D MoS layer-based rollable photodetector that can be mechanically reconfigured while maintaining excellent geometry-invariant photo-responsiveness.

Scalable Van der Waals Two-Dimensional PtTe Layers Integrated onto Silicon for Efficient Near-to-Mid Infrared Photodetection.

In recent years, there has been increasing interest in leveraging two-dimensional (2D) van der Waals (vdW) crystals for infrared (IR) photodetection, exploiting their unusual optoelectrical properties. Some 2D vdW materials with small band gap energies such as graphene and black phosphorus have been explored as stand-alone IR responsive layers in photodetectors. However, the devices incorporating these IR-sensitive 2D layers often exhibited poor performances owing to their preparation issues such as limited scalability and air instability.

Large-area 2D PtTe/silicon vertical-junction devices with ultrafast and high-sensitivity photodetection and photovoltaic enhancement by integrating water droplets.

2D PtTe2 layers, a relatively new class of 2D crystals, have unique band structure and remarkably high electrical conductivity promising for emergent opto-electronics. This intrinsic superiority can be further leveraged toward practical device applications by merging them with mature 3D semiconductors, which has remained largely unexplored. Herein, we explored 2D/3D heterojunction devices by directly growing large-area (>cm2) 2D PtTe2 layers on Si wafers using a low-temperature CVD method and unveiled their superior opto-electrical characteristics.

Vertically Aligned 2D MoS Layers with Strain-Engineered Serpentine Patterns for High-Performance Stretchable Gas Sensors: Experimental and Theoretical Demonstration.

Two-dimensional (2D) molybdenum disulfide (MoS) with vertically aligned (VA) layers exhibits significantly enriched surface-exposed edge sites with an abundance of dangling bonds owing to its intrinsic crystallographic anisotropy. Such structural variation renders the material with exceptionally high chemical reactivity and chemisorption ability, making it particularly attractive for high-performance electrochemical sensing. This superior property can be further promoted as far as it is integrated on mechanically stretchable substrates well retaining its surface-exposed defective edges, projecting opportunities for a wide range of applications utilizing its structural uniqueness and mechanical flexibility.

High-performance flexible asymmetric supercapacitor based on rGO anode and WO/WS core/shell nanowire cathode.

Flexible smart electronics require their energy storage device to be flexible in nature. Developing high-performance flexible energy storage devices require direct integration of electrode active materials on current collectors to satisfy the high electronic/ionic conductivity and long-term durability requirements. Herein, we develop a flexible all-solid-state asymmetric supercapacitor comprised of reduced graphene oxide (rGO) and core/shell tungsten trioxide/tungsten disulfide (WO/WS) nanowire based electrodes.

Wafer-Scale Two-Dimensional MoS Layers Integrated on Cellulose Substrates Toward Environmentally Friendly Transient Electronic Devices.

We explored the feasibility of wafer-scale two-dimensional (2D) molybdenum disulfide (MoS) layers toward futuristic environmentally friendly electronics that adopt biodegradable substrates. Large-area (> a few cm) 2D MoS layers grown on silicon dioxide/silicon (SiO/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.

Wafer-scale 2D PtTe layers for high-efficiency mechanically flexible electro-thermal smart window applications.

Two-dimensional (2D) transition metal dichalcogenide (TMD) layers have gained increasing attention for a variety of emerging electrical, thermal, and optical applications. Recently developed metallic 2D TMD layers have been projected to exhibit unique attributes unattainable in their semiconducting counterparts; e.g.

Automated Assembly of Wafer-Scale 2D TMD Heterostructures of Arbitrary Layer Orientation and Stacking Sequence Using Water Dissoluble Salt Substrates.

We report a novel strategy to assemble wafer-scale two-dimensional (2D) transition metal dichalcogenide (TMD) layers of well-defined components and orientations. We directly grew a variety of 2D TMD layers on "water-dissoluble" single-crystalline salt wafers and precisely delaminated them inside water in a chemically benign manner. This manufacturing strategy enables the automated integration of vertically aligned 2D TMD layers as well as 2D/2D heterolayers of arbitrary stacking orders on exotic substrates insensitive to their kind and shape.

Thickness-Independent Semiconducting-to-Metallic Conversion in Wafer-Scale Two-Dimensional PtSe Layers by Plasma-Driven Chalcogen Defect Engineering.

Platinum diselenide (PtSe) 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.

Wafer-Scale Growth of 2D PtTe with Layer Orientation Tunable High Electrical Conductivity and Superior Hydrophobicity.

Platinum ditelluride (PtTe) 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 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 layers on an area greater than a few square centimeters by reacting Pt thin films of controlled thickness with vaporized tellurium at 400 °C.

An unexpected surfactant role of immiscible nitrogen in the structural development of silver nanoparticles: an experimental and numerical investigation.

Artificially designing the crystal orientation and facets of noble metal nanoparticles is important to realize unique chemical and physical features that are very different from those of noble metals in bulk geometries. However, relative to their counterparts synthesized in wet-chemical processes, vapor-depositing noble metal nanoparticles with the desired crystallographic features while avoiding any notable impurities is quite challenging because this task requires breaking away from the thermodynamically favorable geometry of nanoparticles. We used plasma-generated N atoms as a surface-active agent, a so-called surfactant, to control the structural development of Ag nanoparticles supported on a chemically heterogeneous ZnO substrate.

Simultaneous and synergistic effect of heavy metal adsorption on the enhanced photocatalytic performance of a visible-light-driven RS-TONR/TNT composite.

A hydrothermally synthesized rhodium/antimony co-doped TiO nanorod and titanate nanotube (RS-TONR/TNT) composite was prepared for removal of heavy metals and organic pollutants from water under visible light irradiation. The composite provides the dual function of simultaneous adsorption of heavy metal ions and enhanced degradation of dissolved organic compounds. Acid treatment transformed titanate nanotubes to irregular tubular structures distributed homogeneously over untransformed RS/TONRs.