On the Evolution of Copper Oxide Films Grown on α-A1₂O₃ By Pulsed-Laser Ablation

Abstract

Pulsed-laser ablation was used to deposit copper oxide onto single-crystal substrates of (0001) OC-AI2O3 at temperatures ranging up to 900°C. Prior to deposition, the substrates were chemically cleaned and annealed to create a surface structure of low-index terraces separated by crystallographic steps. After deposition, the samples were characterized using transmission electron microscopy and scanning electron Microscopy.The deposited film evolved by an island growth process, with the morphology of the particles being dependent on the growth conditions, substrate orientation, and nature of the substrate surface. Both CuO and Cu2O were produced by the depositions. The phase observed changed from CuO to Cu2O with increasing deposition temperature, as would be expected based on the equilibrium phase diagram. In depositions performed on (0001) alumina substrates with widely spaced surface steps, it was found that on some surface terraces one characteristic particle morphology was produced whereas on others a second morphology was dominant. This suggests that the plane of surface termination in the alumina lattice, which consists of a layer of either Al or O in this orientation, is influencing the growth process.

Orientation Effects on the High‐Temperature Morphological Evolution of Pore Channels in Sapphire

“…Consistent with this prediction, step heights as small as c/6, where c is the unit-cell height in the [0001] direction of sapphire, have been observed by Bench et al 46 and Heffelfinger and Carter 32 for vicinal (0001) sapphire surfaces. However, evidence that suggests the possibility of several distinct surface terminations also exists 42,46 -48 for both basal and nonbasal surfaces.…”

“…The energies of both O-terminated and Al-terminated basal surfaces in sapphire have been calculated, [41][42][43] and termination by a single Al-atom layer is predicted to yield the lowest energy. Consistent with this prediction, step heights as small as c/6, where c is the unit-cell height in the [0001] direction of sapphire, have been observed by Bench et al 46 and Heffelfinger and Carter 32 for vicinal (0001) sapphire surfaces. However, evidence that suggests the possibility of several distinct surface terminations also exists 42,46 -48 for both basal and nonbasal surfaces.…”

The Wulff Shape of Alumina: III, Undoped Alumina

“…The surfaces of alumina have been the subject of numerous experimental studies using a very broad range of tools including low-energy electron diffraction (LEED), [33][34][35][36][37][38][39][40] transmission electron microscopy (TEM), [41][42][43] reflection electron microscopy (REM), 44,45 and atomic force microscopy (AFM). 43,46 -48 LEED studies have shown that a number of low-index surfaces undergo reconstructions at elevated temperatures, and that the ambient oxygen partial pressure during annealing plays a role.…”

“…These experiments have been complemented by studies using TEM and REM, and further evidence indicating surface reconstructions, and spatial variations in the surface termination has been obtained. [43][44][45] AFM has been used to assess the morphologic evolution of several low-index surfaces. Heffelfinger, Bench, and Carter have established that terrace-ledge structures develop on vicinal (0001) surfaces at 1400°C, and concluded that these surfaces are stable.…”