Epitaxial Calcium and Strontium Fluoride Films on Highly Mismatched Oxide and Metal Substrates by MOCVD: Texture and Morphology

Abstract

The growth of epitaxial CaF2 and SrF2 thin films on single crystalline r-cut sapphire, MgO (001) and biaxially textured Ni−W polycrystalline tape by low-temperature MOCVD is reported. A novel and efficient combination of alkaline-earth and fluorine precursors was used for deposition. A comprehensive study regarding the out- and in-plane orientation of the films and their surface morphology is presented using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), energy-dispersive X-ray analysis (EDX), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and electron backscatter diffraction (EBSD). The grown films are shown to have different crystallographic orientation depending on the film−substrate lattice mismatch and growth rate. Both types of films were obtained with pure c-axis orientation on all used substrates by either choosing the appropriate deposition conditions or postdeposition treatment. Epitaxial relations for all grown films are determined. A film−substrate interaction is described for the case of Ni−W substrate; a way to avoid it is proposed and successfully implemented. Certain growth conditions are shown to result in a unique three-dimensional ordered nanogrid structure of the films, making them perfect nanotemplated substrate for the epitaxial growth of other functional layers.

CaF2and CaF2:Ln3+(Ln = Er, Nd, Yb) hierarchical nanoflowers: hydrothermal synthesis and luminescent properties

“…3 Nanoscale CaF 2 , a very important fluoride, has attracted increasing interest with respect to UV lithography, UV-transparent optical lenses, the surface conditioning of glass, promoting agents for bone/teeth reconstruction, and biocompatible luminescent markers. [4][5][6] Due to these important properties, various CaF 2 structures, such as nanocrystals, [7][8][9] nanoparticles, 4,10 nanowires, 11 films, 12 and nanocubes 13 have been successfully fabricated by a variety of methods. Very recently, Zhen et al have reported the aqueous solution synthesis of CaF 2 hollow microspheres via an Ostwald ripening process at room temperature.…”

Calcium fluoride as high-k dielectric for 2D electronics

“…Makarevich et al 47 reported the successful growth of CaF 2 (001) films (confirmed by XRD spectra) on single-crystalline SrTiO 3 (00l) and Ni-W (00l) substrates by water-assisted MOCVD at 400 C. CaF 2 films were deposited with a rate of 5 A ˚/s under 1 Torr using calcium hexafluoroacetone [Ca(HFAC) 2 ] as the precursor and the surface of CaF 2 films deposited on SrTiO 3 (00l) surface exhibit a small roughness value of 10 nm. Later, thin (10-15 nm) CaF 2 (100) films were successfully deposited on polycrystalline Ni 0.95 W 0.05 alloy in Ar atmosphere under 16 mbar by MOCVD followed by recrystallization annealing at 700 C. 48 In this synthesis process, two precursors, calcium dipivaloylmethanates with bidentate neutral ligand 1,10-phenantroline [M(tmhd) 2 Á2Phen] and hydrofluoric were used. With a deposition rate > 3.5 A ˚/s, CaF 2 film surface exhibit a 3D grid morphology formed by rectangularbased bars along [110] and [1 1 0] axes (100-200 nm long and 30-50 nm wide) and a roughness value of 8 nm.…”

Nanostructured CaF2:Ln3+ (Ln3+ = Yb3+/Er3+, Yb3+/Tm3+) Thin Films: MOCVD Fabrication and Their Upconversion Properties

“…The first report on the deposition of CaF 2 with MOCVD dates back to 1989 when the bis(pentamethyl‐cyclopentadienyl)calcium was applied as calcium source together with SiF 4 or NF 3 as the fluorine source . More recently, fluorine free β‐diketonate has been applied as calcium source combined with the use of ammonium hydrogen fluoride as the fluorine source . A few reports are described in the application of fluorinated precursors to the fabrication of thin films where polyether adducts of the Ca bis‐hexafluoroacetylacetonate have been applied, namely, the Ca(hfa) 2 •tetraglyme and the Ca(hfa) 2 •diglyme•H 2 O …”