Wide process temperature of atomic layer deposition for In2O3thin-film transistors using novel indium precursor (N,N'-di-tert butylacetimidamido)dimethyllindium.

This study introduces a novel heteroleptic indium complex, which incorporates an amidinate ligand, serving as a high-temperature atomic layer deposition (ALD) precursor. The most stable structure was determined using density functional theory and synthesized, demonstrating thermal stability up to 375 °C. We fabricated indium oxide thin-film transistors (In2O3TFTs) prepared with DBADMI precursor using ALD in wide range of window processing temperature of 200 °C, 300 °C, and 350 °C with an ozone (O3) as the source. The growth per cycle of ALD ranged from 0.06 to 0.1 nm cycle-1at different deposition temperatures. X-ray diffraction and transmission electron microscopy were employed to analyze the crystalline structure as it relates to the deposition temperature. At a relatively low deposition temperature of 200 °C, an amorphous morphology was observed, while at 300 °C and 350 °C, crystalline structures were evident. Additionally, x-ray photoelectron spectroscopy analysis was conducted to identify the In-O and OH-related products in the film. The OH-related product was found to be as low as 1% with an increase the deposition temperature. Furthermore, we evaluated In2O3TFTs and observed an increase in field-effect mobility, with minimal change in the threshold voltage (Vth), at 200 °C, 300 °C, and 350 °C. Consequently, the DBADMI precursor, given its stability at highdeposition temperatures, is ideal for producing high-quality films and stable crystalline phases, with wide processing temperature range makeing it suitable for various applications.

c-Axis Aligned 3 nm Thick In2O3 Crystal Using New Liquid DBADMIn Precursor for Highly Scaled FET Beyond the Mobility-Stability Trade-off.

Oxide semiconductors (OS) are attractive materials for memory and logic device applications owing to their low off-current, high field effect mobility, and superior large-area uniformity. Recently, successful research has reported the high field-effect mobility (µFE) of crystalline OS channel transistors (above 50 cm2 V-1 s-1). However, the memory and logic device application presents challenges in mobility and stability trade-offs. Here, we propose a method for achieving high-mobility and high-stability by lowering the grain boundary effect. A DBADMIn precursor was synthesized to deposit highly c-axis-aligned C(222) crystalline 3 nm thick In2O3 films. In this study, the 250 °C deposited 3 nm thick In2O3 channel transistor exhibited high µFE of 41.12 cm2 V-1 s-1, Vth of -0.50 V, and SS of 150 mV decade-1 with superior stability of 0.16 V positive shift during PBTS at 100 °C, 3 MV cm-1 stress conditions for 3 h.

Polyvinylalcohol (PVA)-Assisted Exfoliation of ReS2 Nanosheets and the Use of ReS2-PVA Composites for Transparent Memristive Photosynapse Devices.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant attention for their outstanding optoelectrical properties. Unlike most TMDs with layer-dependent photoresponsivity, rhenium disulfide (ReS2) shows excellent thickness-independent photoresponsivity. Herein, we show a surfactant-free polyvinyl alcohol (PVA)-assisted exfoliation method for 2D-TMDs in aqueous solution and a transparent photosensitive memristor synapse device based on ReS2 nanosheets composited with PVA. ReS2 nanosheets are obtained via PVA-assisted exfoliation. After exfoliation, the ReS2-PVA dispersion solution is spin-coated on a substrate and dried to form a nanocomposite film without additional processing. Transparent memristors are then fabricated on plastic or glass substrates to demonstrate the applicability of the ReS2-PVA film. The devices show "write once, read many" memory behavior with a high ON/OFF current ratio (1.0 × 104 at 0.5 V) during electrical operation. In the high resistive state, synaptic functions with long-term memory behavior are successfully mimicked by applying photonic stimuli to the transparent ReS2-PVA memristors. The excitatory postsynaptic current stimulated by the photosignal is gradually reduced by electric stimuli. The proposed PVA-assisted exfoliation method is cost-effective, environmentally friendly, and applicable to various TMD nanomaterials. Furthermore, the ReS2-PVA nanocomposite film obtained via a simple solution-based process demonstrates excellent photosynaptic behavior.

Na-Cation-Assisted Exfoliation of MX2 (M = Mo, W; X = S, Se) Nanosheets in an Aqueous Medium with the Aid of a Polymeric Surfactant for Flexible Polymer-Nanocomposite Memory Applications.

2D nanosheets of transition metal dichalcogenides (TMDCs) have been attracting attention due to their sizable band gap. Facile and effective Na-cation-assisted exfoliation of TMDC (MX2 , M = Mo, W; X = S, Se) nanosheets in an aqueous medium and their application as a composite filler in a polyvinyl alcohol (PVA) matrix are explored in this work. The presence of Na cations is highly beneficial for exfoliating defect-free and few-layer MX2 nanosheets in water in the presence of small-sized micelles of polymeric surfactant, and significantly elevates the exfoliation yield by more than one order of magnitude compared to a conventional surfactant-assisted exfoliation. The strategy suggested in this work is very advantageous compared to both Li cation intercalation in organic solvents and conventional low-yield surfactant-assisted exfoliations. As an application of the exfoliated nanosheets, the fabrication of memory devices with the configuration of Ga-doped ZnO/MX2 -PVA/Ag is demonstrated, and they exhibit bistable and write-once-read-many-times resistive switching behavior with a high ON/OFF current ratio of 3 × 103 at -1.0 V (for WS2 ) and 2.0 V (for MoS2 ). Furthermore, MX2 -PVA nanocomposite fibrous films and mats are successfully fabricated using an electrospinning technique, which can expand the use of TMDC nanofillers in applications involving highly flexible polymer-based MX2 composites.

Unimer-Assisted Exfoliation for Highly Concentrated Aqueous Dispersion Solutions of Single- and Few-Layered van der Waals Materials.

We suggest a unimer-assisted exfoliation method for the exfoliation of van der Waals two-dimensional (2D) materials such as graphene, MoS2, and h-BN and show that the micellar size is a critical parameter for enhancing the exfoliation efficiency. To explain the effectiveness of the unimers in the exfoliation, the influence of the micellar size of a biocompatible block copolymer, Pluronic F-68, is evaluated in view of the yield and thickness of exfoliated 2D flakes. By the addition of water-soluble alcohols, the surfactants exist in the form of a unimer, which facilitates the intercalation into the layered materials and their exfoliation. The results showed that the high exfoliation efficiency could be achieved by controlling the micellar size mostly to be unimers; the average yield rate of MoS2 exfoliation was 4.51% per hour, and the very high concentration of 1.45 mg/mL was obtained by sonication for 3 h. We also suggested the dielectrophoresis technique as a method for forming a film composed of 2D flakes for diverse applications requiring electrical signals. The unimer-assisted exfoliation method will be substantially utilized to achieve highly concentrated aqueous dispersion solutions of 2D materials.