Fabrication of Thin Films of α-Fe₂O₃ via Atomic Layer Deposition Using Iron Bisamidinate and Water under Mild Growth Conditions

Abstract

Atomic layer deposition (ALD) has been shown to be an excellent method for depositing thin films of iron oxide. With limited iron precursors available, the methods widely used require harsh conditions such as high temperatures and/or the use of oxidants such as ozone or peroxide. This letter aims to show that bis(N,N'-di-t-butylacetamidinato) iron(II) (iron bisamidinate or FeAMD) is an ideal ALD precursor because of its reactivity with water and relative volatility. Using in situ QCM analysis, we show outstanding conformal self-limiting growth of FeOx using FeAMD and water at temperatures lower than 200 °C. By annealing thin films of FeOx at 500 °C, we observe the formation of α-Fe2O3, confirming that we can use FeAMD to fabricate thin films of catalytically promising iron oxide materials using moderate growth conditions.

Nanostructured Fe2O3 Processing via Water‐Assisted ALD and Low‐Temperature CVD from a Versatile Iron Ketoiminate Precursor

“…The constant growth rate of 0.47 Å per cycle was confirmed again, leading to 90 nm thick films by applying 2000 cycles. The growth rates obtained are comparable to the results of Avila et al when using iron bisamidinate and water as precursors and are among the highest observed for ALD grown iron oxide so far . As expected for surface controlled ALD‐type growth, the surface roughness of the films was low and did not vary as a function of the deposition temperature inside the ALD window.…”

“…After annealing (500 °C) at ambient atmosphere and pressure for 1 h, however, the amorphous deposits were transformed to crystalline hematite ( Figure ). The amorphous appearance of the ALD grown iron oxides originates from the low deposition temperature and the low layer thickness, which hinders the crystallization as already reported by Avila et al previously . All deposits have been characterized in terms of composition by Rutherford backscattering (RBS) and nuclear reaction analysis (NRA) (Figure S9 and Table S5, Supporting Information).…”

“…Some of them have been used successfully for ALD of other transition metal oxides . Very recently, Avila et al adopted the approach to specifically choose [bis(amidinate) iron] that exhibits promising reactivity and was thereby tested in water‐assisted ALD of iron oxide wherein growth rates of the order of 0.47 Å per cycle at temperatures between 130 and 200 °C were obtained …”

Area Selective Chemical Vapor Deposition of Metallic Films using Plasma Electrons as Reducing Agents

“…To address these issues and to meet such requirements, thermal ALD and PEALD can be used. For instance, iron oxide films can be deposited at temperatures ranging from 150 °C to 500 °C by thermal ALD [36][37][38][70][71][72], and by PEALD [73]. Cobalt and nickel films can be deposited at temperatures ranging from 125 °C to 350 °C by thermal ALD [41,[74][75][76][77][78], and PEALD [39,[79][80][81].…”

Facile aerobic construction of iron based ferromagnetic nanostructures by a novel microbial nanofactory isolated from tropical freshwater wetlands

“…Due to its widespread application potential, the synthesis of well-defined ferromagnetic IONP’s has emerged as a widely investigated research niche. Currently, most synthesis protocols rely heavily on chemical methods including co-precipitation [ 11 ], thermal decomposition [ 12 ], atomic layer deposition, [ 13 ] and sol–gel processes [ 14 ], or physical protocols such as ball milling [ 15 ], electron beam evaporation [ 16 ], radio frequency (RF) sputtering [ 17 ] or sonochemical synthesis [ 18 ]. Although these methods produce predictable outcomes, they require rigorous adherence to stringent protocols and entail a high cost and energy investment.…”