This paper describes a simple, low-temperature, and environmentally friendly aqueous route for the layer-by-layer nanometric growth of crystalline α-Fe₂O₃. The formation mechanism involves alternative sequences of the electrostatic adsorption of Fe²⁺ ions on the surface and the subsequent onsite oxidation to Fe³⁺. A combination analysis of X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy, and X-ray photoelectron spectroscopy revealed that α-Fe₂O₃ is directly formed without post-growth annealing via designed chemical reactions with a growth rate of ca. 1.7 nm per deposition cycle. The obtained α-Fe₂O₃ layer exhibits electrocatalytic activity for water oxidation and, at the same time, insignificant photo-electrocatalytic response, indicating its defective nature. The electrocatalytic activity was tailored by annealing up to 500 °C in air, where thermal diffusion of Sn⁴⁺ into the α-Fe₂O₃ lattice from the substrate probably provides an increased electrical conductivity. The subsequent surface-modification with Ni(OH)₂ lowers the overpotential (250 mV at 0.5 mA cm⁻²) in a 1 M KOH solution. These findings open direct growth pathways to functional metal oxide nanolayers via liquid phase atomic layer deposition.

中文翻译：

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溶液介导的 α-Fe2O3 纳米生长具有电催化水氧化活性

_{本文介绍了一种简单、低温、环保的水性路线，用于晶体 α-Fe 2} O ₃的逐层纳米生长。形成机制涉及Fe ²⁺离子在表面上的静电吸附和随后的现场氧化成Fe ³⁺的交替序列。X 射线衍射、扫描电子显微镜、UV-Vis 光谱和 X 射线光电子能谱的组合分析表明，α-Fe ₂ O ₃是通过设计的化学反应直接形成的，无需生长后退火，生长速率约为. 每个沉积周期 1.7 nm。得到的α-Fe ₂O ₃层表现出对水氧化的电催化活性，同时，光电催化反应不显着，表明其存在缺陷。^{电催化活性是通过在空气中退火至 500 °C 来调整的，其中 Sn 4+}从基底热扩散到 α-Fe ₂ O ₃晶格中可能会提高电导率。随后用 Ni(OH) ₂进行的表面改性降低了 1 M KOH 溶液中的过电位（0.5 mA cm ^-2时为 250 mV ）。这些发现开辟了通过液相原子层沉积直接生长到功能性金属氧化物纳米层的途径。