Van der Waals (vdW) solids can be engineered with atomically precise vertical composition through the assembly of layered two-dimensional materials. However, the artisanal assembly of structures from micromechanically exfoliated flakes is not compatible with scalable and rapid manufacturing. Further engineering of vdW solids requires precisely designed and controlled composition over all three spatial dimensions and interlayer rotation.
View Article and Find Full Text PDFThe densification of integrated circuits requires thermal management strategies and high thermal conductivity materials. Recent innovations include the development of materials with thermal conduction anisotropy, which can remove hotspots along the fast-axis direction and provide thermal insulation along the slow axis. However, most artificially engineered thermal conductors have anisotropy ratios much smaller than those seen in naturally anisotropic materials.
View Article and Find Full Text PDFAutonomous electronic microsystems smaller than the diameter of a human hair (<100 μm) are promising for sensing in confined spaces such as microfluidic channels or the human body. However, they are difficult to implement due to fabrication challenges and limited power budget. Here we present a 60 × 60 μm electronic microsystem platform, or SynCell, that overcomes these issues by leveraging the integration capabilities of two-dimensional material circuits and the low power consumption of passive germanium timers, memory-like chemical sensors, and magnetic pads.
View Article and Find Full Text PDFThe large-scale synthesis of high-quality thin films with extensive tunability derived from molecular building blocks will advance the development of artificial solids with designed functionalities. We report the synthesis of two-dimensional (2D) porphyrin polymer films with wafer-scale homogeneity in the ultimate limit of monolayer thickness by growing films at a sharp pentane/water interface, which allows the fabrication of their hybrid superlattices. Laminar assembly polymerization of porphyrin monomers could form monolayers of metal-organic frameworks with Cu linkers or covalent organic frameworks with terephthalaldehyde linkers.
View Article and Find Full Text PDFQuantum computing based on superconducting qubits requires the understanding and control of the materials, device architecture, and operation. However, the materials for the central circuit element, the Josephson junction, have mostly been focused on using the AlO tunnel barrier. Here, we demonstrate Josephson junctions and superconducting qubits employing two-dimensional materials as the tunnel barrier.
View Article and Find Full Text PDFMorphology-retained solid-state photoconversion of anthracene (AN) to 9,10-anthraquinone (PC-ANQ) and dipara-anthracene (PC-DPA) was accomplished by irradiating mercury lamp light to plate-shaped AN single crystal in oxygen and argon atmosphere, respectively. The photoconverted crystals retained the original plate shape morphology of the starting AN crystal, whereas the emission profile and crystal structure were significantly changed. The electrical conductivity of PC-ANQ crystal is 5 orders of magnitude greater than that of the starting AN crystal, whereas the PC-DPA crystal exhibits a decreased conductivity.
View Article and Find Full Text PDFIn this paper, we report an efficient alkali metal doping system for organic single crystals. Our system employs an enhanced diffusion method for the introduction of alkali metal into organic single crystals by controlling the sample temperature to induce secondary thermal activation. Using this system, we achieved intercalation of potassium into picene single crystals with closed packed crystal structures.
View Article and Find Full Text PDFEpitaxy forms the basis of modern electronics and optoelectronics. We report coherent atomically thin superlattices in which different transition metal dichalcogenide monolayers-despite large lattice mismatches-are repeated and laterally integrated without dislocations within the monolayer plane. Grown by an omnidirectional epitaxy, these superlattices display fully matched lattice constants across heterointerfaces while maintaining an isotropic lattice structure and triangular symmetry.
View Article and Find Full Text PDFSolution-phase crystallization of fullerene molecules strongly depends on the types of solvent and their ratios because solvent molecules are easily included in the crystal lattice and distort its structure. The C70 (solute)-mesitylene (solvent) system yields crystals with various morphologies and structures, such as cubes, tubes, and imperfect rods. Herein, using C60 and C70 dissolved in mesitylene, we present a novel way to grow unique flower-shaped crystals with six symmetric petals.
View Article and Find Full Text PDFAtomically thin nanosheets, as recently realized using van der Waals layered materials, offer a versatile platform for studying the stability and tunability of the correlated electron phases in the reduced dimension. Here, we investigate a thickness-dependent excitonic insulating (EI) phase on a layered ternary chalcogenide Ta2NiSe5. Using Raman spectroscopy, scanning tunneling spectroscopy, and in-plane transport measurements, we found no significant changes in crystalline and electronic structures as well as disorder strength in ultrathin Ta2NiSe5 crystals with a thickness down to five layers.
View Article and Find Full Text PDFWe have developed a simple, scalable, transfer-free, ecologically sustainable, value-added method to convert inexpensive coal tar pitch to patterned graphene films directly on device substrates. The method, which does not require an additional transfer process, enables direct growth of graphene films on device substrates in large area. To demonstrate the practical applications of the graphene films, we used the patterned graphene grown on a dielectric substrate directly as electrodes of bottom-contact pentacene field-effect transistors (max.
View Article and Find Full Text PDFWe developed the novel electrode that enables fine control of overpotential by exploiting surface segregation that is the enrichment of one component at the surface of binary alloy. To realize this approach, we controlled the proportion of Si with low Li diffusivity at the surface by annealing the SiGe nanowire in H2 environment at various temperatures. The resulting SiGe nanowires annealed at 850 °C exhibited high reversible capacity (>1031 mA·h·g(-1)), and long cycle life (400 cycles) with high capacity retention (89.
View Article and Find Full Text PDFDuring the past two decades, many materials chemists have focused on the development of organic molecules that can serve as the basis of cost-effective and flexible electronic, optical, and energy conversion devices. Among the potential candidate molecules, metal-free or metal-containing conjugated organic molecules offer high-order electronic conjugation levels that can directly support fast charge carrier transport, rapid optoelectric responses, and reliable exciton manipulation. Early studies of these molecules focused on the design and synthesis of organic unit molecules that exhibit active electrical and optical properties when produced in the form of thin film devices.
View Article and Find Full Text PDFA novel way to grow MoS2 on a large scale with uniformity and in desired patterns is developed. We use Au film as a catalyst on which [Mo(CO)6 ] vapor decomposes to form a Mo-Au surface alloy that is an ideal Mo reservoir for the growth of atomic layers of MoS2 . Upon exposure to H2 S, this surface alloy transforms into a few layers of MoS2 , which can be isolated and transferred on an arbitrary substrate.
View Article and Find Full Text PDFWe report that C60 molecules are spontaneously crystallized into vertical nanowires by the solvent vapor annealing (SVA) process. C60 molecules have been known to be assembled into wire-like crystals by simply dropping and drying C60 solutions in m-xylene on a solid substrate. By the drop-drying process, C60 nanowires have been mostly grown laterally on a solid substrate, as the major force applied to the droplet during the drying process is parallel to the substrate.
View Article and Find Full Text PDFPhenothiazine (PTZ) crystals are grown by a physical vapor transport method in a horizontal tube furnace. The resulting disk-type PTZ single crystals have a layered structure, which can be mechanically exfoliated into stacked individual layers to exhibit various colors depending on the thickness. The PTZ single-crystal field-effect transistor (FET) devices exhibit a p-type semiconducting property with 3.
View Article and Find Full Text PDFWe report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer.
View Article and Find Full Text PDFWe report a novel boiling heat transfer (NBHT) in reduced graphene oxide (RGO) suspended in water (RGO colloid) near critical heat flux (CHF), which is traditionally the dangerous limitation of nucleate boiling heat transfer because of heater failure. When the heat flux reaches the maximum value (CHF) in RGO colloid pool boiling, the wall temperature increases gradually and slowly with an almost constant heat flux, contrary to the rapid wall temperature increase found during water pool boiling. The gained time by NBHT would provide the safer margin of the heat transfer and the amazing impact on the thermal system as the first report of graphene application.
View Article and Find Full Text PDFDirect growth of a single to a few layers of graphene on a germanium nanowire (Gr/Ge NW; see picture) was achieved by a metal-catalyst-free chemical vapor deposition (CVD) process. The Gr/Ge NW was used as anode in a lithium ion battery. This material has a specific capacity of 1059 mA h g(-1) at 4.
View Article and Find Full Text PDFSelf-assembled foam-like graphene (SFG) structures were formed using a simple nucleate boiling method, which is governed by the dynamics of bubble generation and departure in the graphene colloid solution. The conductivity and sheet resistance of the calcined (400°C) SFG film were 11.8 S·cm(-1) and 91.
View Article and Find Full Text PDFMetal catalyst-free growth of large scale single layer graphene film on a sapphire substrate by a chemical vapor deposition (CVD) process at 950 °C is demonstrated. A top-gated graphene field effect transistor (FET) device is successfully fabricated without any transfer process. The detailed growth process is investigated by the atomic force microscopy (AFM) studies.
View Article and Find Full Text PDFLiquid GeCl(4) precursors have been employed to grow into one dimensional Ge nanowires (NWs) via a vapor-liquid-solid (VLS) process, in which Si, supplied as a form of liquid SiCl(4), plays a critical role for the successful formation of Ge NWs.
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