Nanostructured CuO film grown from solution by preferential microwave heating of the conducting glass substrate

Highlights

• CuO films are grown heating preferentially the conducting substrate with microwave radiation during a short time.

• Well-adhered, nanostructured films are obtained at low temperature.

• CuO tenorite phase and gap energy Eg = 1.52 eV are found.

Abstract

Nanostructured Cu(II) oxide receives significant attention because of its possible applications. Very well adhered CuO films have been grown on conducting glass substrates using microwave-activated chemical bath deposition, at low temperature and in a short time. X-ray diffraction and Raman spectroscopy show that only the CuO tenorite phase is present. Scanning electron microscopy reveals a peculiar nanostructured morphology: nanowires or nanobranches that have fallen on the substrate after growing into the precursor solution, perpendicular to it. A gap value, E_g = 1.52 eV, is obtained from the diffused reflectance spectrum. Film characteristics are of interest for some applications, particularly, solar radiation harvesting.

Introduction

Cu(II) oxide or cupric oxide (CuO) has received considerable attention in the literature due to its possible applications: sensors, lithium-ion batteries, supercapacitors, magnetic properties, wetting properties, antibacterial activity, photocatalysis, photodetectors, solar heating, solar cells and water-splitting [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. CuO is a p-type semiconductor with a monoclinic crystal structure (tenorite) [12] and a direct bandgap of 1.2 eV [13]. Direct bandgap values in the range of 1.4 eV–1.6 eV have been reported for nanostructured CuO [14]. These bandgap values imply that CuO can harvest solar radiation with a good efficiency [15].

We report the use of microwave activated chemical bath deposition (MW-CBD) to grow a CuO film on conducting glass. This technique has been previously reported for TiO₂ and ZnO coating on different conducting substrates [16], [17], [18] but not for CuO. Different procedures have been used for CuO thin film deposition [19] [see 19 and references there in]. When using MW-CBD, growth of the oxide on the substrate occurs at an earlier stage than free nucleation in the precursor solution because of a higher temperature of the conducting substrate relative to the precursor solution [20]. Free electrons in the conducting substrate interact with the microwave electric field. They give off the acquired energy to phonons raising the conducting film temperature.