Local structure relaxation in nanocrystalline Ni1−xO thin films

Abstract

Non-stoichiometric nickel oxide (Ni 1-x O) thin films were prepared by DC magnetron sputtering technique in mixed Ar/O 2 atmosphere and studied by synchrotron radiation Ni K-edge x-ray absorption spectroscopy, x-ray diffraction and scanning electron microscopy. The use of advanced modelling technique, combining classical molecular dynamics with ab initio multiplescattering extended X-ray absorption fine structure (EXAFS) calculations, allowed us to describe the structure relaxation and dynamics in nanocrystallites and to estimate their size and the concentration of nickel vacancies. Highlights Nickel oxide thin films were prepared by DC magnetron sputtering. Local structure of Ni 1-x O thin films was studied by x-ray absorption spectroscopy. The atomic structure of Ni 1-x O thin films is strongly relaxed. Ni vacancies in Ni 1-x O thin films play important role in atomic structure relaxation.

EXAFS and XANES analysis of oxides at the nanoscale

“…). In addition, it was found that, while the temperature dependence of the MSRD for the Ni-O 1 and Ni-Ni 2 atom pairs is close and can be described by the correlated Debye model, there is some additional static disorder ( st ) 2 in nanosized NiO (Anspoks et al, 2012;Anspoks, Kalinko, Kalendarev & Kuzmin, 2014) (Fig. 8).…”

“…However, even in the nanosized oxide, the structural peaks are well visible up to $6 Å , thus making the use of the MD-EXAFS approach feasible. A more detailed analysis of the first two peaks due to the first two coordination shells (Ni-O 1 and Ni-Ni 2 ) indicates that, in the nanosized oxide, the R(Ni-Ni 2 ) distance increases slightly, whereas the R(Ni-O 1 ) distance contracts (Anspoks et al, 2012;Anspoks, Kalinko, Kalendarev & Kuzmin, 2014). Such a result is not trivial, since in bulk NiO the two distances are proportional:…”

“…The use of classical MD simulations for the interpretation of EXAFS (the MD-EXAFS method) in nanomaterials will be discussed below for the example of Ni K-edge EXAFS in nanosized nickel oxide (nano-NiO) (Anspoks et al, 2010(Anspoks et al, , 2012Anspoks & Kuzmin, 2011;Anspoks, Kalinko, Kalendarev & Kuzmin, 2014).…”

“…EXAFS spectroscopy has been used to study local structure in nickel oxide for a long time. Most works have been dedicated to an investigation of NiO thin films (Kuzmin et al, 1997;Avendañ o et al, 2005;Jang et al, 2009Jang et al, , 2011Gutié rrez et al, 2013;Anspoks, Kalinko, Kalendarev & Kuzmin, 2014;Domínguez-Cañ izares et al, 2014), NiO monolayers on Ag(001) (Luches et al, 2003;Groppo et al, 2003Groppo et al, , 2004Lamberti et al, 2003;Luches, Groppo et al, 2004;Lamberti, 2004) and NPs (Hattori et al, 2002;Meneses et al, 2007;Mandal et al, 2009;Anspoks et al, 2010Anspoks et al, , 2012Anspoks & Kuzmin, 2011). One can also mention the work that has been done on ultrathin MgO epilayers on Ag(001) (Luches, D'Addato et al, 2004), which have a rock-salt crystal structure similar to NiO and thus a closely related behaviour of the EXAFS signal.…”

EDA: EXAFS data-analysis software package

“…Application examples of this method cover several compounds: SrTiO 3 , ReO 3 (Kalinko et al, 2009), Ge (Timoshenko et al, 201), NiO (Anspoks et al, 2010;Anspoks et al, 2012;Anspoks et al, 2014a) The case of microcrystalline and nanocrystaline (6 nm) NiO (Anspoks et al, 2012) is illustrated in Fig. 5.…”