The area-selective ALD has been applied to fabricate defect-free 3D patterns and nanostructures for electronic applications. 31,32 Then during the deposition, materials can be deposited only where needed. A patterned area of substrate is initially activated or passivated with assistance of electron/ion beam, self-assembled monolayers (SAMs), or polymer resists. Area-selective ALD has been developed to exert spatial control to fabricate 3D nanostructures. In fabrication of composite catalysts, the selective approaches of ALD are of importance and necessary. So far, the development of ALD for the synthesis of catalytic materials (metal and oxide) has aroused great interests in the design and controllable fabrication of unique catalytic structures. The heterointerfaces between metal and oxides are also beneficial for activity enhancement. 30 In detail, the oxide coating layers could serve as physical barriers, or form strong metal-oxide interactions to anchor metal nanoparticles. The well-engineered oxide overcoating layers could encapsulate supported nanoparticles to enhance the catalytic performance in both thermal stability and activity. 30 Besides metal ALD processes, ALD of oxides has demonstrated a great potential in preventing catalysts from sintering. 26–29 By adjusting different ALD processes, it is possible to fabricate core–shell structured or alloys nanoparticles with well-defined compositions ratio. 21–25 Recently, ALD has shown its potential in synthesizing single atom catalysts as well. 19,20 For instance, ALD was utilized to fabricate highly dispersed, size controllable metal nanoparticles, such as Ru, Pd, Pt, Ir, and Ni, during the nucleation stage. The use of ALD for synthesis of heterogeneous catalysts has been developed rapidly in the past few years. Thus, it enables direct modification of the surfaces and structures, 18 as well as adjustment of the shape and size of materials deposited on complex substrates. 15–17 Taking the advantage of self-limiting surface adsorption nature of ALD, the target materials can be deposited with controllability and uniformity in atomic level. So far, significant number of elements and their oxides can be synthesized via ALD. 8–14 ALD is based on successive and alternative surface reactions from gas phase to fabricate thin films and overlayers in the nanometer range. Among various synthesis methods, atomic layer deposition (ALD) has been recently developed as an effective method to synthesize composite catalysts. 5–7 To design and obtain catalysts with the desired activity, selectivity, and stability, synthesis strategies to build precise configurations with direct modulation of reactive sites are of great importance. 1–4 The catalytic performance of composite catalysts strongly depends on their size, heterointerfaces, active sites, etc. Composite catalysts based on metal-oxide with designed structures perform an irreplaceable role for most applications. Catalysts are widely utilized to accelerate chemical reactions by decreasing reaction barriers in various industrial syntheses, environment pollution control, energy conversion, and so on.
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