Growth and characterization of thin epitaxial Co3O4(1

Abstract

a b s t r a c tThe growth and characterization of epitaxial Co 3 O 4 ð1 1 1Þ films grown by oxygen plasma-assisted molecular beam epitaxy on single crystal a-Al 2 O 3 ð0 0 0 1Þ is reported. The Co 3 O 4 ð1 1 1Þ grows single crystalline with the epitaxial relation Co 3 O 4 ð1 1 1Þ½1 21ka-Al 2 O 3 ð0 0 0 1Þ½1010, as determined from in situ electron diffraction. Film stoichiometry is confirmed by X-ray photoelectron spectroscopy, while ex situ X-ray diffraction measurements show that the Co 3 O 4 films are fully relaxed. Post-growth annealing induces significant modifications in the film morphology, including a sharper Co 3 O 4 =a-Al 2 O 3 interface and improved surface crystallinity, as shown by X-ray reflectometry, atomic force microscopy and electron diffraction measurements. Despite being polar, the surface of both as-grown and annealed Co 3 O 4 ð1 1 1Þ films are ð1 Â 1Þ, which can be explained in terms of a surface inversion in the spinel structure.

Polarity in Oxide Nano-objects

“…Co 3 O 4 (111) films, produced by MBE, grow epitaxially on a single-crystal α-Al 2 O 3 (0001) surface. They are fully relaxed and display a (1 × 1) LEED pattern, which has been explained in terms of a layer inversion in the spinel structure . Similar inversion was also invoked to explain the absence of reconstruction at the surface of polar Co 3 O 4 (110) films produced by the same method on a polar MgAl 2 O 4 (110) substrate .…”

Structure–Property Relationship and Chemical Aspects of Oxide–Metal Hybrid Nanostructures

“…However, this is not always the case, and particularly for transition metals that may adopt more than one oxidation state, alternative approaches are more often followed, in which activated oxygen is supplied during the growth. This can be accomplished by using an electron cyclotron resonance (ECR) oxygen plasma source, − gaseous NO 2 , , or ozone O 3 . , A commercial thermal cracker can be also used as a source of atomic oxygen. , Because the O 2 dissociation step is often rate limiting, the atomic oxygen assisted deposition may facilitate the reaction between individual metal and O atoms before metal cluster formation occurs. In this way, a higher degree of order and a better control on the stoichiometry and morphology of the oxide–metal interface can be achieved, as recently demonstrated for the monolayer of NiO on Ag(001) .…”

Exchange bias and interface electronic structure inNi/Co3O4(011)

“…Also, the direction perpendicular to the (011) surface is characterized by having a repeat period of four atomic planes as opposed to the eight-period repeat along the [100] direction or the eighteen-period repeat of the [111] direction. 32 It therefore should be less susceptible to stacking faults and antiphase boundary formation, leading to fewer defects in the film. The samples in this study were grown by molecular beam epitaxy in a dual ultrahigh vacuum (UHV) system comprising a growth chamber (base pressure ∼ 1 × 10 −9 mbar) equipped with a reflection high energy electron diffraction (RHEED) system, and an analysis chamber (base pressure ∼ 3 × 10 −10 mbar) for low energy electron diffraction (LEED), x-ray photoemission (XPS) and Auger electron spectroscopy (AES).…”