Epitaxial stabilization of orthorhombic cuprous oxide films on MgO(110)

Abstract

Continuous epitaxial films of cuprous oxide (Cu 2 O) have been formed by the thermal oxidation of 1.5-m-thick Cu metal films deposited on MgO(110) substrates. These films melted at 1118°C in air, in agreement with equilibrium phase diagrams. Upon cooling from the liquid, a highly crystalline, epitaxial, 2.5-m-thick Cu 2 O film was formed. X-ray diffraction spectroscopy revealed that the Cu 2 O film crystal structure was orthorhombically distorted from the bulk cubic crystal structure. High-resolution transmission electron microscopy showed that the film is coherent, and energy dispersive x-ray spectroscopy showed that interdiffusion is limited to the interface. These results suggest that a new epitaxially stabilized phase of Cu 2 O has been formed. a)

Strain splitting of1syellow orthoexciton of epitaxial orthorhombicCu2Ofilms on MgO [110]

“…The specimens were then heated and cooled according to various protocols described elsewhere. 17 The key requirement is that the sample be heated to a temperature at or slightly above the melting temperature but not so high as to cause the film to ''bead up'' into islands. Under this condition smooth shiny, epitaxial Cu 2 O films often resulted.…”

“…By subtly controlling the temperature and partial pressure near the solid-liquid transition, we earlier achieved the growth of high-quality epitaxial orthorhombic Cu 2 O thin films on MgO͓110͔ substrates. 17 In this paper, we report the excitonic structure observed in such epitaxial films. The splitting and shift of the 1s orthoexciton energy level were analyzed in terms of the distortion from the cubic structure of the bulk material.…”

Nonlinear optical processes at quadrupole polariton resonance inCu2Oas probed by a Z-scan technique

“…Figure 4͑d͒ plots the n = 84 cavityphoton mode for a 10-m-thick Cu 2 O platelet that form a Fabry-Perot cavity ͑blue dashed curve͒ sitting just above the bare exciton mode ͑red dashed curve͒. 28 ͑Matching of the mode frequency with the polariton frequency can be achieved by adjusting the propagation direction relative to the plane normal.͒ Then, the lower polariton branch ͑red solid curve͒ would develop a local minimum via quadrupole coupling associated with a very small effective mass ͑Ӎ10 −5 m e ͒ in which long-lived polaritons can condense.…”

Two-dimensional growth of continuous Cu2O thin films by magnetron sputtering

“…8͒ compared to the thermal energy ͑0.1 eV͒ provided by the high growth temperature of 1180°C in the liquid-phase growth. 7 Although further characterization would be desirable, we believe that the qualitative improvement achieved in the hardness of our Cu 2 O films is relevant to the evolution of device quality material. Figure 1͑a͒ shows the result of an XRD -2 scan of a Cu 2 O film on MgO͑011͒, which was deposited at 700°C with a deposition rate of ϳ0.02 m per min, and a growth time of 20 min.…”

“…We also did scratch tests. Comparing with those films deposited by the ex situ liquid-phase growth technique 7 and laser ablation, the Cu 2 O films obtained by magnetron sputtering are functionally much harder, i.e., much more difficult to be scratched and removed from the MgO substrates. This indicates that a denser film with better adhesion to the substrate has been synthesized.…”