Fabrication of iron carbide by plasma-enhanced atomic layer deposition
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ATOMIC LAYER DEPOSITION FOR EMERGING THIN-FILM MATERIALS AND APPLICATIONS
Fabrication of iron carbide by plasma-enhanced atomic layer deposition Xu Tian1, Xiangyu Zhang1, Yulian Hu1, Bowen Liu1, Yuxia Yuan1, Lizhen Yang1, Qiang Chen1, Zhongwei Liu1,a) 1
Laboratory of Plasma Physics and Materials, Beijing Institute of Graphic Communication, Beijing 102600, China Address all correspondence to this author. e-mail: [email protected]
a)
Received: 8 September 2019; accepted: 7 October 2019
Iron carbide (Fe1−xCx) thin films were successfully grown by plasma-enhanced atomic layer deposition (PEALD) using bis(N,N9-di-tert-butylacetamidinato)iron(II) as a precursor and H2 plasma as a reactant. Smooth and pure Fe1−xCx thin films were obtained by the PEALD process in a layer-by-layer film growth fashion, and the x in the nominal formula of Fe1−xCx is approximately 0.26. For the wide PEALD temperature window from 80 to 210 °C, a saturated film growth rate of 0.04 nm/cycle was achieved. X-ray diffraction and transition electron microscope measurements show that the films grown at deposition temperature 80–170 °C are amorphous; however, at 210 °C, the crystal structure of Fe7C3 is formed. The conformality and resistivity of the deposited films have also been studied. At last, the PEALD Fe1−xCx on carbon cloth shows excellent electrocatalytic performance for hydrogen evolution.
Introduction Over the past several decades, transition metal carbides (TMCs) have attracted much attention due to their unique physicochemical properties and important applications such as low friction interfaces [1, 2], corrosion protection layers [3], fuel cell electrodes [4, 5, 6], biomedical component [7, 8], and catalysts [9]. Generally, the transition metal elements have significant effects on the structure and chemical bonding of binary TMCs [10]. For example, the early transition metals such as Ti, V, and Zr tend to generate strong metal–carbon bonds, which usually have NaCl-type structure. On the other hand, the later transition metals such as Fe, Co, and Ni form weak metal–carbon bonds, demonstrating more complex structures. In the Fe–C system, the carbon can be found in and form various iron carbide phases, including Fe5C2, Fe2C, Fe7C3, Fe3C, and Fe23C6 [11]. For these weak carbide formers, the formation enthalpy is less negative or even positive, so these compounds are thermodynamically unstable. Iron carbide is a particularly important TMC and has promising applications in drug delivery [7], hyperthermia [12], and magnetic storage media [13]. In addition, iron carbide was recently reported to have great potentials for both hydrogen evolution reaction (HER) [5] and COx hydrogenation [14], perhaps because iron
ª Materials Research Society 2019
is an earth-abundant element with promising catalytic activity. However, prior research on the production of iron carbide is still limited compared with iron metal, iron oxide, and iron sulfide. Commonly used methods for the production of bulk and amorphous iron carbides include solution chemistry met
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