Epitaxial Ni_xPd_1–x (111) Alloy Substrates with Continuously Tunable Lattice Constants for 2D Materials Growth

Abstract

Epitaxial strain can be a powerful parameter for directing the growth of thin films. Unfortunately, conventional materials only offer discrete choices for setting the lattice strain. In this work, it is demonstrated that epitaxial growth of transition metal alloy solid solutions can provide thermally stable, high-quality growth substrates with continuously tunable lattice constants. Molecular beam epitaxy was used to grow NiPd(111) alloy films with lattice constants between 3.61 and 3.89 Å on the hexagonal (0001) basal planes of α-AlO and CrO (grown as epitaxial films on α-AlO (0001)). The CrO acted as an adhesion layer, which not only improved the high-temperature stability of the films but also produced single-domain films with NiPd [112̅] parallel to CrO [112̅0], in contrast to growth on α-AlO that yielded twinned films. Surface characterization by electron diffraction and scanning tunneling microscopy (STM) as well as bulk X-ray diffraction analysis indicated that the films are suitable as inexpensive and stable substrates for thin-film growth and for surface science studies. To demonstrate this suitability, bilayer SiO, a two-dimensional van der Waals material, was grown on a NiPd(111) film tuned to closely match the film's lattice constant, with STM and electron diffraction results revealing a highly ordered, single-phase crystalline state.

Growth and Atomic‐Scale Characterization of Ultrathin Silica and Germania Films: The Crucial Role of the Metal Support

“…Moreover, in addition to the growth of silica bilayer films on Ru(0001), the film has been prepared on graphene, [86] Pt(111), [16] Pd(111), [87, 80] Pd(100), [88, 89] and Ni x Pd 1− x (111) [90] . The impact of the metal support on the silica film structure is the topic of the next section.…”

“…[76] Moreover,i na ddition to the growth of silica bilayer films on Ru(0001), the film has been prepared on graphene, [86] Pt(111), [16] Pd 111, [87,80] Pd(100), [88,89] and Ni x Pd 1Àx (111). [90] The impact of the metal support on the silica film structurei st he topic of the next section. Understanding the mechanisms that determine the structure of the films when preparedo nd ifferent substrates is important to predict the structures of germania films on metal supports, discussed in the following sections.…”

“…The structure andp roperties of metal-supported silica films are strongly influenced by the compositiono ft he metal substrate. [16,90,77,91,87,90] The films adopt different atomic arrangements when prepared on different metal substrates.…”

“…[91] Experimentally,azero-strain film has been grown on aN i 0.48 Pd 0.52 (111)s urface, resulting in ac rystalline phase, in agreement with this argument. [90] One must clarify,t hat when the film-interaction is too strong, this argumenti sn olonger valid, because then chemicali nteractions govern the structure, as it has been shown by doping the silica film with Al. [87] Monolayer Films:AComparison…”

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

“…2D silica and silicate films can be prepared on metal substrates, including Pd(100) and Pd(111), and Ru(0001) and metal alloys . While it is good approach to study 2D materials by combination of experimental and theoretical techniques, it is not a practical method for the preparation of 2D zeolites.…”