Layer-by-layer thinning of two-dimensional materials.

Etching technology - one of the representative modern semiconductor device makers - serves as a broad descriptor for the process of removing material from the surfaces of various materials, whether partially or entirely. Meanwhile, thinning technology represents a novel and highly specialized approach within the realm of etching technology. It indicates the importance of achieving an exceptionally sophisticated and precise removal of material, layer-by-layer, at the nanoscale. Notably, thinning technology has gained substantial momentum, particularly in top-down strategies aimed at pushing the frontiers of nano-worlds. This rapid development in thinning technology has generated substantial interest among researchers from diverse backgrounds, including those in the fields of chemistry, physics, and engineering. Precisely and expertly controlling the layer numbers of 2D materials through the thinning procedure has been considered as a crucial step. This is because the thinning processes lead to variations in the electrical and optical characteristics. In this comprehensive review, the strategies for top-down thinning of representative 2D materials (e.g., graphene, black phosphorus, MoS2, h-BN, WS2, MoSe2, and WSe2) based on conventional plasma-assisted thinning, integrated cyclic plasma-assisted thinning, laser-assisted thinning, metal-assisted splitting, and layer-resolved splitting are covered in detail, along with their mechanisms and benefits. Additionally, this review further explores the latest advancements in terms of the potential advantages of semiconductor devices achieved by top-down 2D material thinning procedures.

Enhancing control in spatial atomic layer deposition: insights into precursor diffusion, geometric parameters, and CVD mitigation strategies.

In recent years, spatial atomic layer deposition (SALD) has gained significant attention for its remarkable capability to accelerate ALD growth by several orders of magnitude compared to conventional ALD, all while operating at atmospheric pressure. Nevertheless, the persistent challenge of inadvertent contributions from chemical vapor deposition (CVD) in SALD processes continues to impede control over film homogeneity, and properties. This research underscores the often-overlooked influence of diffusion coefficients and important geometric parameters on the close-proximity SALD growth patterns. We introduce comprehensive physical models complemented by finite element method simulations for fluid dynamics to elucidate SALD growth kinetics across diverse scenarios. Our experimental findings, in alignment with theoretical models, reveal distinctive growth rate trends in ZnO and SnO2films as a function of the deposition gap. These trends are ascribed to precursor diffusion effects within the SALD system. Notably, a reduced deposition gap proves advantageous for both diffusive and low-volatility bulky precursors, minimizing CVD contributions while enhancing precursor chemisorption kinetics. However, in cases involving highly diffusive precursors, a deposition gap of less than 100µm becomes imperative, posing technical challenges for large-scale applications. This can be ameliorated by strategically adjusting the separation distance between reactive gas outlets to mitigate CVD contributions, which in turn leads to a longer deposition time. Furthermore, we discuss the consequential impact on material properties and propose a strategy to optimize the injection head to control the ALD/CVD growth mode.

Controlled growth of ultrasmall Cu2O clusters on TiO2nanoparticles by atmospheric-pressure atomic layer deposition for enhanced photocatalytic activity.

This work presents a gas-phase approach for the synthesis of Cu2O/TiO2powder-based photocatalysts using atomic layer deposition (ALD). The process is carried out in a fluidized bed reactor working at atmospheric pressure using (trimethylvinylsilyl)-hexafluoroacetulacetonate copper(I) as the Cu-precursor and H2O vapor as the oxidizer. The saturating regime of the chemical reactions and the linear growth of ALD are achieved. In combination with the unsaturated regime, the ALD approach enables the deposition of ultrasmall Cu2O clusters with average diameters in the range of 1.3-2.0 nm, narrow particle size distributions and tunable Cu2O loadings on P25 TiO2nanoparticles. The photocatalytic performance of Cu2O/TiO2photocatalysts is investigated by the degradation of organic dyes, including Rhodamine B (RhB), methyl orange, and methylene blue; the results demonstrate that the surface modification of TiO2nanoparticles by Cu2O nanoclusters significantly enhances the photocatalytic activity of TiO2. This is attributed to the efficient charge transfer between Cu2O and TiO2that reduces the charge recombination. The photocatalytic reaction mechanism is further investigated for the degradation of RhB, revealing the dominating role of holes, which contribute to both direct hole oxidation and indirect oxidation (i.e. via the formation of hydroxyl radicals). Our approach provides a fast, scalable and efficient process to deposit ultrasmall Cu2O clusters in a controllable fashion for surface engineering and modification.

Titanium Nitride Nanodonuts Synthesized from Natural Ilmenite Ore as a Novel and Efficient Thermoplasmonic Material.

Nanostructures of titanium nitride (TiN) have recently been considered as a new class of plasmonic materials that have been utilized in many solar energy applications. This work presents the synthesis of a novel nanostructure of TiN that has a nanodonut shape from natural ilmenite ore using a low-cost and bulk method. The TiN nanodonuts exhibit strong and spectrally broad localized surface plasmon resonance absorption in the visible region centered at 560 nm, which is well suited for thermoplasmonic applications as a nanoscale heat source. The heat generation is investigated by water evaporation experiments under simulated solar light, demonstrating excellent solar light harvesting performance of the nanodonut structure.