One-dimensional (1D) or quasi-1D semiconductor nanomaterials have attracted much attention in recent years due to their unique properties and numerous applications in opto-electronic nanoscale devices and functional materials. Among these materials, cadmium oxide (CdO) is an important semiconductor with a large direct band gap of 2.5 eV and an indirect band gap of 1.98 eV, which is a promising candidate for opto-electronic applications such as transparent electrodes, solar cells, phototransistors, photodiodes, and gas sensors^[1]. 

Synthesis Methods of Cadmium Oxide with Nanostructure

So far, a number of methods have been used to synthesize the various nanostructures, including the template hydrothermal process, thermal evaporation method, chemical bath deposition method, solvothermal condition, and plasmaassisted approach. Among these methods, the thermal evaporation process is a kind of effective methods in realizing the diversiform cadmium oxide nanostructures. Liu et al. prepared cadmium oxide nanoneedles by catalyst-assistant process at 850–900 ℃. Kou and Huang fabricated necklace-like cadmium oxide nanowire by a vapor transport approach with Au as a catalyst. Pan et al. found that the CdO nanobelts can be realized by evaporating CdO powder at high temperature (1000 ℃). The in-depth understanding for crystal structures is essential to prompt the preparation of nanostructures with controllable morphology^[1].

Crystal Structure

Figure 1. Crystal structure of cadmium oxide (CdO)^[2].

Under normal conditions, cadmium oxide (CdO) crystallizes in the B1 (rock-salt structure) with space group: Fm-3m. As illustrated in figure 1, the atomic positions are at the center (1/2, 1/2, 1/2) for O and the corner (0, 0, 0) for Cd. It is relevant to note that the ionic radius of Cd2+ is much smaller than the one of O2-^[2].

References

[1] Catalyst-free growth and crystal structures of CdO nanowires and nanotubes. Journal of Crystal Growth 311 (2009) 2300–2304.

[2] Effect of zinc concentration on the structural, electronic and elastic properties of Zn x Cd1?x O dilute alloys. Phys. Scr. 90 (2015) 115701.