Same Precursor, Two Different Products: Comparing the Structural Evolution of In–Ga–O “Gel-Derived” Powders and Solution-Cast Films Using Pair Distribution Function Analysis

Abstract

Amorphous metal oxides are central to a variety of technological applications. In particular, indium gallium oxide has garnered attention as a thin-film transistor channel layer material. In this work we examine the structural evolution of indium gallium oxide gel-derived powders and thin films using infrared vibrational spectroscopy, X-ray diffraction, and pair distribution function (PDF) analysis of X-ray total scattering from standard and normal incidence thin-film geometries (tfPDF). We find that the gel-derived powders and films from the same aqueous precursor evolve differently with temperature, forming mixtures of Ga-substituted InO and In-substituted β-GaO with different degrees of substitution. X-ray total scattering and PDF analysis indicate that the majority phase for both the powders and films is an amorphous/nanocrystalline β-GaO phase, with a minor constituent of InO with significantly larger coherence lengths. This amorphous β-GaO phase could not be identified using the conventional Bragg diffraction techniques traditionally used to study crystalline metal oxide thin films. The combination of Bragg diffraction and tfPDF provides a much more complete description of film composition and structure, which can be used to detail the effect of processing conditions and structure-property relationships. This study also demonstrates how structural features of amorphous materials, traditionally difficult to characterize by standard diffraction, can be elucidated using tfPDF.

Local atomic structure of thin and ultrathin films via rapid high-energy X-ray total scattering at grazing incidence

“…Aside from the low absolute amount of sample in a thin film, two major aspects have impeded PDF analysis of thin films: (i) the strong scattering from the substrate the film is deposited on, whose thickness exceeds the film thickness usually by at least three orders of magnitude, causing an unfavorable signal-tobackground ratio, and (ii) texture, owing to different growth behavior parallel and perpendicular to the surface and/or in different crystallographic directions. Different approaches have been taken to circumvent these problems, including exfoliating the film off the substrate and grinding it Kurzman et al, 2015) as well as measuring the film on the substrate in transmission and carefully subtracting the dominant background signal of the amorphous substrate (Jensen et al, 2015;Nakamura et al, 2017;Shi et al, 2017;Wood et al, 2017). Both these methods have drawbacks: in the first case, structural changes may occur during the mechanical treatment and, in addition, any texture information is lost completely, whereas in the latter case, the signal-to-background ratio effectively sets a detection limit on the film thickness.…”

Development of low temperature stoichiometric solution combustion derived transparent conductive ternary zinc tin co-doped indium oxide electrodes

“…41 Thus it is important to study thin lm materials as thin lms rather than depending on their bulk counterparts. 42 Although the combustion behavior on thin lms is not clear, 43 but the precursors having fuel-ligand (acetylacetone in this study) can yield crystalline thin lms (Fig. 4a) at signicantly low temperature (200 C), which would have not been possible with conventional sol-gel precursors 44 with large decomposition temperatures (>450 C).…”

Solution-Processed Li2O–Al2O3/TiO2 Nanolaminate Stacks Containing Mobile Lithium Ions and with Increased Breakdown Voltages

“…It is important to emphasize that the DSC and TGA data are on bulk powders and do not fully reflect the dehydration and condensation behavior of the pre-annealed, intimately mixed amorphous thin films that are the precursors to the glassy films we describe in more detail below. The thermal analysis data were useful in identifying temperatures that would likely result in the decomposition of residual nitrates and near complete dehydration of spin-coated thin films, but we do not take, for instance, the mass loss in the TGA data as a characteristic of the processes that occurs in the annealing of spin-coated films, where the precursor has a much greater surface area to volume ratio than the bulk powders …”