Multi-scale order in amorphous transparent oxide thin films

Abstract

Nominally “diffraction amorphous” materials represent a pervasive challenge in establishing classical structure-property relationships. This stems from the difficulty in defining the structure of nominally amorphous materials and experimentally differentiating the short-range (<10 Å) and medium-range (10 to 30 Å) order as a function of process parameters which are important due to their influence on physical, chemical, or transport properties. Herein, we report on the determination of short- and medium-range order in nominally amorphous zinc and tin co-substituted indium oxide In1.4Zn0.3Sn0.3O3 (a-ZITO) thin films grown by pulsed laser deposition. These thin films are being explored as transparent conductors that exhibit changes in transport properties depending on deposition temperature while remaining “diffraction amorphous.” Reduced density function (RDF) analysis from electron diffraction accompanied by density functional theory molecular dynamics simulation of a liquid quench suggests ordering at short range. Scanning transmission fluctuation electron microscopy (STFEM) indicates the presence of ordered ZITO regions at medium range. For a-ZITO films grown at different temperatures, RDF analysis showed no significant change in the short range order. However, STFEM revealed notable structural (and symmetry) differences at medium range. The existence of this type of multi-scale local order in amorphous ZITO thin films highlights the importance of a combined approach to unravel the structures of nominally amorphous materials and to understand structure-properties correlations.

Towards quantitative treatment of electron pair distribution function

“…As the medium-range order has a significant effect on the physical behavior of the material (Pagon et al, 2010;Bassiri et al, 2011Bassiri et al, , 2013Yan et al, 2012;Hart et al, 2016), studies of fine details of amorphous structures were triggered with the development of a dedicated method -Fluctuation Electron Microscopy (FEM), which demonstrated the paracrystalline nature of amorphous silicon (Borisenko et al, 2012;. Ishimaru (2006) demonstrated the importance of energy filtering for the PDF analysis: the unfiltered data of amorphous SiC showed a significantly different behavior for Q below 10 Å À1 , while the high-Q regions of filtered and unfiltered data were the same (energy slit used was 20 eV).…”

Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing

“…This measure of mechanical stability and its relationship to Brownian thermal noise is quantified through the fluctuation dissipation theorem by Callen and Greene [10]. In general, only small changes are observed in the atomic structure of the coatings of the same material prepared by different methods when studied by electron diffraction reduced density function (RDF) analysis (which appear to be only sensitive to short range order, principally around the 1st and 2nd nearest neighbours, and up to a maximum of about 1 nm, and consequently cannot distinguish between atomistic models that contain or do not contain nanoscale order) [11][12][13]. A previous study using this technique has however demonstrated a correlation between mechanical loss and the concentrations of titania in titania-doped tantala [14].…”

“…Quantitative FEM analysis has thus far proven challenging, but with recent developments such as variable resolution FEM, information about the extent of the nanometre-scale ordering can be extracted [26,34]. Nevertheless, a number of recent studies have been successful in relating the scattering covariance and angular correlations in FEM data to structural information [13,35,36].…”

The Importance of Averaging to Interpret Electron Correlographs of Disordered Materials

“…It can be primarily used for characterizing local diffraction symmetry of disordered solid materials, such as amorphous semiconductors, oxides, and metallic glasses (Yan et al, 2012). It can be primarily used for characterizing local diffraction symmetry of disordered solid materials, such as amorphous semiconductors, oxides, and metallic glasses (Yan et al, 2012).…”