Defect-Induced Phase Transformations in CuO Thin Films by Ag Ion Implantation and Their Gas-Sensing Applications

Abstract

The present study is aimed to modify the structural, optical, and morphological properties of CuO thin films with Ag ion implantation toward their potential applications. Fabrication of thin films of CuO was carried out using a thermal evaporation technique on silicon (Si) substrate; post implantation was done with 30 keV Ag ions with varying fluences from 1 × 1014 to 1 × 1016 ions/cm2. The pristine and implanted samples were characterized through X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and diffused reflectance spectroscopy (DRS). SRIM simulation was also carried out to understand the range and other effects. XRD measurements confirmed the formation of the CuO phase for pristine samples, and with the increase in ion fluence, the chemical composition changed from pure CuO to Cu2O + CuO and then to Cu2O + Cu at higher ion fluences. These experimental results from Raman spectroscopy were also consistent with the XRD analysis, which also showed the presence of mixed phases of CuO, Cu2O, and Cu. Results from AFM showed that the value of average roughness increased due to more defects. DRS results revealed the variation in band-gap energy for pristine and implanted samples from 1.96 to 1.71 eV. Density functional theory (DFT) simulations confirmed that Ag ion implantation causes the reduction of CuO surface into Cu2O and Cu. We found that Ag ion implantation-induced defects lead to the mixed phases of CuO, Cu2O, and Cu, which can help in the selective sensing of ethanol and acetone, demonstrating this as a useful technique and having potential applications in energy conversions, and gas and biomolecule sensing.

Spectroscopic ellipsometry modelling of Cr+ implanted copper oxide thin films

“…The ions implanted in the material lose their energy via excitation of target’s electrons or collisions with nuclei. For energies in the range of keV, the nuclear stopping is predominant 26 . Collisions with target atoms cause them to move from their positions in the crystal lattice, the crystal structure is damaged and can be amorphized with enough implanted ions 21 .…”

“…Another utilization of ion implantation was performed by Shi et al 25 , who used argon ions to introduce defects into CuO to study the magnetic properties of the material. High energy 2 MeV Ar ions with doses of 1 × 10 15 and 5 × 10 15 cm −2 produced an increased amount of the Cu vacancies and cause a phase change of CuO into Cu 2 O. Yadav et al 26 implanted CuO thin films of 220 nm thickness with Ag ions of 30 keV energy and doses between 1 × 10 14 and 1 × 10 16 cm −2 . They found that with higher dose the crystallinity of material decreased, and they also noticed a phase change—into Cu 2 O and even Cu for the highest implantation dose.…”