Research
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We are studying nanomaterials and nanoelectronics based on a synergistic combination of molecular chemistry and low-dimensional inorganic materials. Our research spans the interdisciplinary fields of chemistry, materials science, physics, electronics and fluidics engineering. We believe that conducting hybrid research in multiple fields will realize game-changing materials and devices.
Control Carrier Behavior in 2D materials
Carrier control of inorganic materials is important in applications of optoelectronic devices such as transistors, light emitting diodes and photovoltaics. Two-dimensional inorganic materials (2D materials) are attracting attention as next-generation device materials due to their thin crystal structures (several atomic layers) and various physical properties (semiconducting to metallic). However, the conventional carrier injection methods, such as ion plantation, cannot apply the thin bodies, and it is difficult to control the behavior of carriers. We are exploring a convenient, nondestructive method using molecules to control and modify the carrier behavior of 2D materials.
We succeeded in developing a MOSFET (metal-oxide-semiconductor field-effect-transistor) with high performance using molecular interaction. A 2D material, MoS2, shows semiconducting-to-metallic conversion by contact with a molecular viologen. We achieved a low-contact resistance and a high-performance device with a sub-threshold swing of ~77 mV/decade. In another case, a molecular treated MoS2 showed a near-unity optical property. Usually, the pristine MoS2 monolayer shows a quantum yield of ~1%, whereas a molecular superacid-treated MoS2 shows a quantum yield of up to ~100%.
2D Devices and Molecular Doping
Metallic transport in monolayer and multilayer molybdenum disulfides by molecular surface-charge transfer doping, ACS Appl. Mater. Interfaces, 2022, 14, 8163.
Single-layered assembly of vanadium pentoxide nanowires on graphene for nanowire-based lithography technique, Nanotechnology, 2022, 33, 075602.
Electronic Structure Mosaicity of Monolayer Transition Metal Dichalcogenides by Spontaneous Pattern Formation of Donor Molecules, ACS Appl. Mater. Interfaces, 2019, 11, 15922.
Tuning Transition-Metal Dichalcogenide Field-Effect-Transistor by Spontaneous Pattern Formation of an Ultrathin Molecular Dopant Film, ACS NANO, 2018, 12, 10123.
Oriented Growth of Gold Nanowires on MoS2, Adv. Funct. Mater. 2015, 25, 6257.
Air-stable surface charge transfer doping of MoS2 by benzyl viologen, J. Am. Chem. Soc. 2014, 136, 7853.
2D Optical Properties
Ultralarge Photoluminescence Enhancement of Monolayer Molybdenum Disulfide by Spontaneous Superacid Nanolayer Formation, ACS Appl. Mater. Interfaces, 2021, 13, 25280.
Photoactivation of Strong Photoluminescence in Superacid-Treated Monolayer Molybdenum Disulfide, ACS Appl. Mater. Interfaces, 2020, 12, 36496.
Solvent engineering for strong photoluminescence enhancement of monolayer molybdenum disulfide in redox-active molecular treatment, Appl. Phys. Express, 2019, 12, 051014.
Systematic Study of Photoluminescence Enhancement in Monolayer Molybdenum Disulfide by Acid Treatment, Langmuir, 2018, 34, 10234.
Near-Unity Photoluminescence Quantum Yield in MoS2, Science, 2015, 350, 1065.
Controlled assembly
Materials growth is important for developing physical and chemical properties. We are developing material growth systems on 2D material surfaces and in 1D fluidic channels. On one 2D material's surface, we found that molecules/atoms were spontaneously assembled to form an ordered/oriented morphology. Using the technique, we have developed Au nanowire growth on a 2D material, MoS2, using an inorganic molecular AuCl3 (Link). The nanowires can be grown on MoS2 lattice in a triangle manner (C3 symmetry-like). Strong Au-S interaction generates this unusual behavior.
We are also pursuing a fluidic assembly system. Microfluidics (channel diameter of ~200 um) are used to continuously introduce molecules into the fluidic channel and dynamically control concentration and composition. We developed a microfluidic assembly system of molecules and nanomaterials (carbon nanotubes, inorganic nanowires) and realized an asymmetric 1D assembly along the streamline in the fluidic channel. It demonstrated various internal morphologies such as (i)core-shell structures (see the right image, Link) and (ii)vertical/parallel orientation of nanowires along the streamline (Link).
Single-layered assembly of vanadium pentoxide nanowires on graphene for nanowire-based lithography technique, Nanotechnology, 2022, 33, 075602.
General Thermal Texturization Process of MoS2 for Efficient Electrocatalytic Hydrogen Evolution Reaction, Nano Lett. 2016, 16, 4047.
Oriented Growth of Gold Nanowires on MoS2, Adv. Funct. Mater. 2015, 25, 6257.
Microfluidic Control of the Internal Morphology in Nanofiber-based Macroscopic Cables, Angew. Chem. Int. Ed., 2012, 51, 7942.
Meter-Long and Robust Supramolecular Strands Encapsulated in Hydrogel Jackets, Angew. Chem. Int. Ed., 2012, 51, 1553.
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