Aparicio-Huacarpuma B D, H Aragón F F, Villegas-Lelovsky L, Soncco C M, Pacheco-Salazar D G, Guerra J A, Morais P C, da Silva S W, Coaquira J A H
Institute of Physics, Applied Physics Division, University of Brasília, Brasília DF 70910-900, Brazil.
Universidad Nacional de San Agustín de Arequipa, Av. Independencia s/n, Arequipa, Peru.
Nanotechnology. 2024 May 24;35(32). doi: 10.1088/1361-6528/ad47cc.
This study investigates the fabrication process of copper thin films via thermal evaporation, with precise control over film thickness achieved through-position adjustment. Analysis of the as-fabricated copper films reveals a discernible relationship between grain size (〈〉) and-position, characterized by a phenomenological equation〈D〉XRDn(Z)=〈D〉0n1+32rZ2+158rZ4, which is further supported by a growth exponent () of 0.41 obtained from the analysis. This value aligns well with findings in the literature concerning the growth of copper films, thus underlining the validity and reliability of our experimental outcomes. The resulting crystallites, ranging in size from 20 to 26 nm, exhibit a resistivity within the range of 3.3-4.6Ω · cm. Upon thermal annealing at 200 °C, cuprite CuO thin films are produced, demonstrating crystallite sizes ranging from ∼9 to ∼24 nm with increasing film thickness. The observed monotonic reduction in CuO crystallites relative to film thickness is attributed to a recrystallization process, indicating amorphization when oxygen atoms are introduced, followed by the nucleation and growth of newly formed copper oxide phase. Changes in the optical bandgap of the CuO films, ranging from 2.31 to 2.07 eV, are attributed mainly to the quantum confinement effect, particularly important in CuO with size close than the Bohr exciton diameter (5 nm) of the CuO. Additionally, correlations between refractive index and extinction coefficient with film thickness are observed, notably a linear relationship between refractive index and charge carrier density. Electrical measurements confirm the presence of a p-type semiconductor with carrier concentrations of ∼10cm, showing a slight decrease with film thickness. This phenomenon is likely attributed to escalating film roughness, which introduces supplementary scattering mechanisms for charge carriers, leading to a resistivity increase, especially as the roughness approaches or surpasses the mean free path of charge carriers (8.61 nm). Moreover,calculations on the CuO crystalline phase to investigate the impact of hydrostatic strain on its electronic and optical properties was conducted. We believe that our findings provide crucial insights that support the elucidation of the experimental results. Notably, thinner cuprite films exhibit heightened sensitivity to ethanol gas at room temperature, indicating potential for highly responsive gas sensors, particularly for ethanol breath testing, with significant implications for portable device applications.
本研究通过热蒸发研究了铜薄膜的制备过程，通过位置调整实现了对薄膜厚度的精确控制。对制备好的铜薄膜进行分析发现，晶粒尺寸（〈〉）与位置之间存在明显的关系，其特征由一个唯象方程〈D〉XRDn(Z)=〈D〉0n1+32rZ2+158rZ4表示，分析得到的生长指数（）为0.41，这进一步支持了该方程。该值与文献中关于铜薄膜生长的研究结果吻合良好，从而突出了我们实验结果的有效性和可靠性。所得微晶尺寸在20至26nm之间，电阻率在3.3 - 4.6Ω·cm范围内。在200°C进行热退火后，生成了氧化亚铜CuO薄膜，随着薄膜厚度增加，微晶尺寸范围为9至24nm。观察到的CuO微晶尺寸相对于薄膜厚度的单调减小归因于再结晶过程，这表明引入氧原子时会发生非晶化，随后是新形成的氧化铜相的成核和生长。CuO薄膜的光学带隙在2.31至2.07eV之间变化，主要归因于量子限制效应，这在尺寸接近CuO的玻尔激子直径（5nm）的CuO中尤为重要。此外，观察到折射率和消光系数与薄膜厚度之间的相关性，特别是折射率与载流子密度之间的线性关系。电学测量证实存在载流子浓度约为10cm的p型半导体，且随着薄膜厚度增加略有下降。这种现象可能归因于薄膜粗糙度的增加，这为载流子引入了额外的散射机制，导致电阻率增加，特别是当粗糙度接近或超过载流子的平均自由程（8.61nm）时。此外，还对CuO晶相进行了计算，以研究静水应变对其电子和光学性质的影响。我们相信我们的发现提供了关键的见解，有助于解释实验结果。值得注意的是，较薄的氧化亚铜薄膜在室温下对乙醇气体表现出更高的灵敏度，这表明对于高响应性气体传感器具有潜力，特别是用于乙醇呼气测试，对便携式设备应用具有重要意义。
