2D materials are layered crystalline materials and are the most attractive nanomaterials due to their potentials in next-generation electronics. Because most 2D materials are atomically thin, a suitable fabrication process without degradation of the original properties of the material is required to realize 2D-material-based devices. Atomic layer deposition (ALD) is an ideal technique for adding materials with atomic scaling precision to nanomaterials. Due to the surface-sensitive reactions of ALD, growth on 2D materials is strongly affected by the surface properties of the 2D materials. In this Perspective, ALD growth on 2D materials is reviewed and discussed with previously reported results to provide insights to readers who are investigating 2D materials and relevant topics.

Thermal atomic layer deposition (ALD) of metal has generally been achieved at high temperatures of around 300°C or at relatively low temperatures with highly reactive counter reactants, including plasma radicals and O 3 , which can induce severe damage to substrates. Here, the growth of metallic Pt layers by ALD at a low temperature of 80°C is achieved by using [(1,2,5,6-η)-1,5-hexadiene]-dimethyl-platinum(II) (HDMP) and O 2 as the Pt precursor and counter reactant, respectively. ALD results in the successful growth of continuous Pt layers at the low temperature without any reactive reactants owing to the low activation energy of the HDMP precursor for surface reactions. Because of the high reactivity of the precursor, the growth of a pure Pt layer is achieved on various thermally weak substrates, leading to the fabrication of high-performance conductive cotton fibers by ALD. A capacitive-type textile pressure sensor is successfully demonstrated by stacking elastomeric rubber-coated conductive cotton fibers perpendicularly and integrating them onto a fabric with a 7 × 8 array configuration to identify the features of the applied pressure, which can be effectively utilized as a new platform for future wearable and textile electronics. INTRODUCTIONAtomic layer deposition (ALD) has widely attracted considerable interest for various high technologies, such as semiconductor devices and display devices, 1-3 because of its superb ability to deposit ultrathin films with excellent controllability and conformality even on complex three-dimensional (3D) structures. 1-8 Based on these superior properties, ALD has been intensively studied for several applications. In particular, textile electronics using the ALD is one of the promising fields since several materials can be readily deposited at temperatures lower than 150°C by ALD, leading to the effective functionalization of thermally fragile substrates such as plastics, cellulose papers and polymeric textiles. [9][10][11][12] Chen et al. 13 demonstrated hydrophobic silk fabrics with a high laundering durability and robustness due to a TiO 2 coating deposited by ALD. However, in the case of metal ALD, since temperatures as high as 300°C are generally required to achieve successful deposition with the thermal energy of the precursor reactions, it is difficult to deposit conformal metal films onto thermally weak substrates using ALD, causing difficulties in a wide range of applications, including textile electronics. 14,15 To ensure successful metal ALD at low temperatures, ALD in which the

Area-selective atomic layer deposition (AS-ALD) is a promising bottom-up patterning approach for fabricating conformal thin films. One of the current challenges with respect to AS-ALD is the deficiency of the surface inhibitor used for fabricating nanoscale three-dimensional structures. In this study, a vapor-deliverable small inhibitor called ethanethiol (ET) that thermally adsorbs on surfaces was used for the AS-ALD of Al2O3. The inhibitor selectively adsorbed on Co and Cu substrates but not on the SiO2 substrate, allowing for the selective deactivation of Co and Cu substrates in Al2O3 ALD. The use of dimethylaluminum isopropoxide (DMAI) as the Al precursor resulted in better inhibition than the use of trimethylaluminum (TMA). Various experimental and theoretical methods, including water contact angle measurements, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, density functional theory calculations, and Monte Carlo simulations, were used to elucidate the process of AS-ALD using ET. Dimerization of the DMAI precursor is considered to be a governing factor for its high deposition selectivity, while the probability of this phenomenon is very low for the TMA precursor. The current study provides insight into the selectivity of AS-ALD from the perspective of the chemical reaction and an opportunity to improve selectivity via precursor selection.

Small machines are highly promising for future medicine and new materials. Recent advances in functional nanomaterials have driven the development of synthetic inorganic micromachines that are capable of efficient propulsion and complex operation. Miniaturization and large-scale manufacturing of these tiny machines with true nanometer dimension are crucial for compatibility with subcellular components and molecular machines in operation. Here, block copolymer lithography is combined with atomic layer deposition for wafer-scale fabrication of ultrasmall coaxial TiO 2 /Pt nanotubes as catalytic rocket engines with length below 150 nm and a tubular reactor size of only 20 nm, leading to the smallest man-made rocket engine reported to date. The movement of the nanorockets is examined using dark-field microscopy particle tracking and dynamic light scattering. The high catalytic activity of the Pt inner layer and the reaction confined within the extremely small nanoreactor enable highly efficient propulsion, achieving speeds over 35 µm s −1 at a low Reynolds number of <10 −5 . The collective movements of these nanorockets are able to efficiently power the directional transport of significantly larger passive cargo.