Growth of nanoporous high-entropy oxide thin films by pulsed laser deposition

Abstract

High-entropy oxides (HEO) with entropic stabilization and compositional flexibility have great potential application in batteries and catalysis. In this work, HEO thin films were synthesized by pulsed laser deposition (PLD) from a rock-salt (Co0.2Ni0.2Cu0.2Mg0.2Zn0.2)O ceramic target. The films exhibited the target’s crystal structure, were chemically homogeneous, and possessed a three-dimensional (3D) island morphology with connected randomly shaped nanopores. The effects of varying PLD laser fluence on crystal structure and morphology were explored systematically. Increasing fluence facilitates film crystallization at low substrate temperature (300 °C) and increases film thickness (60–140 nm). The lateral size of columnar grains, islands (19 nm to 35 nm in average size), and nanopores (9.3 nm to 20 nm in average size) increased with increasing fluence (3.4 to 7.0 J/cm2), explained by increased kinetic energy of adatoms and competition between deposition and diffusion. Additionally, increasing fluence reduces the number of undesirable droplets observed on the film surface. The nanoporous HEO films can potentially serve as electrochemical reaction interfaces with tunable surface area and excellent phase stability. Graphical abstract

Nucleation and growth behavior of multicomponent secondary phases in entropy-stabilized oxides

“…From Eq. [7], the LSW model estimates that σ = 11 J/m 2 for the rocksalt/tenorite interface and σ = 2.5 J/m 2 for the rocksalt/spinel interface. Both values are significantly higher than the those predicted by Thermo-Calc (Table 1), indicating that Thermo-Calc underestimates the difficulty of forming a new interface for the secondary phase.…”

“…[8] is different from Eq. [7], meaning that Eq. [8] requires an accurate thermodynamic model of σ or ΔG to calculate the other.…”

“…HEO materials show promise in a range of applications, such as electronics [3], batteries [4], and catalysts [5]. Despite their compositional complexity, HEOs can be successfully fabricated in forms other than bulk ceramics, including nanopowders [6] and thin films [7]. Additionally, the concepts behind highentropy design has been applied to non-oxide systems as well, including silicides [8], borides [9], and carbides [10].…”

Progresses on high-entropy nano-catalysts for electrochemical energy conversion reactions

“…Nanoporous HEO films were also prepared via pulse laser ablation using a bulk (Co 0.2 Ni 0.2 Cu 0.2 Mg 0.2 Zn 0.2 )O as the precursor. 52 The authors observed that the lattice mismatch between the substrate and bulk target precursor could trigger the Volmer–Weber growth, resulting in a 3D island structure of HEO film. 79 Increasing the energy fluence not only enhanced nucleation and growth rate but also promoted the coalescence of grains, increasing both the grain size and nanopore diameter (Fig.…”

Exsolution of Core-Shell Nanoparticles in a Complex Concentrated Perovskite Oxide Thin Film Synthesized in One Step

“…Exsolved nanoparticles in thin films are commonly fabricated in multiple steps, first by host oxide film preparation and then by reduction of the host film by heating in a reducing atmosphere such as hydrogen [4][5][6][7]. In this work, exsolved nanoparticles were successfully prepared in polycrystalline perovskite complex concentrated oxide thin films in one step during synthesis using pulsed laser deposition (PLD) and without further reduction [8]. This one-step method for exsolved oxide film fabrication can effectively reduce processing time and cost as well as maintain high density of exsolved metal nanoparticles.…”