Gheorghiu Cristina C, Ionescu Aurelia, Zai Maria-Iulia, Iancu Decebal, Burducea Ion, Velisa Gihan, Vasile Bogdan S, Ianculescu Adelina C, Bobeica Mariana, Popa Daniel, Leca Victor
Extreme Light Infrastructure-Nuclear Physics (ELI-NP), "Horia Hulubei" National Institute for R&D in Physics and Nuclear Engineering, 30 Reactorului Street, 077125 Măgurele, Romania.
Faculty of Physics, University of Bucharest, 077125 Măgurele, Romania.
Materials (Basel). 2022 Sep 4;15(17):6134. doi: 10.3390/ma15176134.
The use of Fe films as multi-element targets in space radiation experiments with high-intensity ultrashort laser pulses requires a surface structure that can enhance the laser energy absorption on target, as well as a low concentration and uniform distribution of light element contaminants within the films. In this paper, (110) preferred orientation nanocrystalline Fe thin films with controlled morphology and composition were grown on (100)-oriented Si substrates by oblique angle RF magnetron sputtering, at room temperature. The evolution of films key-parameters, crucial for space-like radiation experiments with organic material, such as nanostructure, morphology, topography, and elemental composition with varying RF source power, deposition pressure, and target to substrate distance is thoroughly discussed. A selection of complementary techniques was used in order to better understand this interdependence, namely X-ray Diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Non-Rutherford Backscattering Spectroscopy. The films featured a nanocrystalline, tilted nanocolumn structure, with crystallite size in the (110)-growth direction in the 15-25 nm range, average island size in the 20-50 nm range, and the degree of polycrystallinity determined mainly by the shortest target-to-substrate distance (10 cm) and highest deposition pressure (10 mbar Ar). Oxygen concentration (as impurity) into the bulk of the films as low as 1 at. %, with uniform depth distribution, was achieved for the lowest deposition pressures of (1-3) × 10 mbar Ar, combined with highest used values for the RF source power of 125-150 W. The results show that the growth process of the Fe thin film is strongly dependent mainly on the deposition pressure, with the film morphology influenced by nucleation and growth kinetics. Due to better control of film topography and uniform distribution of oxygen, such films can be successfully used as free-standing targets for high repetition rate experiments with high power lasers to produce Fe ion beams with a broad energy spectrum.
在高强度超短激光脉冲的空间辐射实验中，将铁膜用作多元素靶材，需要一种能够增强靶材对激光能量吸收的表面结构，以及薄膜内轻元素污染物的低浓度和均匀分布。本文在室温下，通过倾斜角射频磁控溅射在（100）取向的硅衬底上生长了具有可控形貌和成分的（110）择优取向纳米晶铁薄膜。深入讨论了薄膜关键参数的演变，这些参数对于使用有机材料进行类似空间辐射实验至关重要，例如纳米结构、形貌、表面形貌以及随射频源功率、沉积压力和靶材到衬底距离变化的元素组成。为了更好地理解这种相互依存关系，使用了一系列互补技术，即X射线衍射、原子力显微镜、扫描和透射电子显微镜、能量色散X射线光谱和非卢瑟福背散射光谱。这些薄膜具有纳米晶倾斜纳米柱结构，（110）生长方向的晶粒尺寸在15 - 25纳米范围内，平均岛尺寸在20 - 50纳米范围内，多晶度主要由最短的靶材到衬底距离（10厘米）和最高的沉积压力（10毫巴氩气）决定。对于（1 - 3）×10毫巴氩气的最低沉积压力，结合125 - 150瓦的最高射频源功率使用值，薄膜主体中的氧浓度（作为杂质）低至1原子百分比，且具有均匀的深度分布。结果表明，铁薄膜的生长过程主要强烈依赖于沉积压力，薄膜形貌受成核和生长动力学影响。由于对薄膜表面形貌的更好控制和氧的均匀分布，这种薄膜可成功用作高功率激光器高重复率实验的独立靶材，以产生具有宽能谱的铁离子束。
