Shirsath Sagar E, Liu Xiaoxi, Assadi M H N, Younis Adnan, Yasukawa Yukiko, Karan Sumanta Kumar, Zhang Ji, Kim Jeonghun, Wang Danyang, Morisako Akimitsu, Yamauchi Yusuke, Li Sean
School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2502, Australia.
Nanoscale Horiz. 2019 Mar 1;4(2):434-444. doi: 10.1039/c8nh00278a. Epub 2018 Nov 19.
For the first time, this work presents a novel room temperature time-effective concept to manipulate the crystallization kinetics and magnetic responses of thin films grown on amorphous substrates. Conventionally, metal-induced crystallization is adopted to minimize the crystallization temperature of the upper-layer thin film. However, due to the limited surface area of the continuous metal under-layer, the degree of crystallization is insufficient and post-annealing is required. To expose a large surface area of the metal under-layer, we propose a simple and novel approach of using an Au nanodots array instead of a continuous metallic under-layer to obtain crystallization of upper-layer thin films. Spinel cobalt ferrite (CFO) thin film as a 'model' was deposited on an Au nano-dots array to realize this methodology. Our findings revealed that the addition of quantum-sized Au nano-dots as a metal under-layer dramatically enhanced the crystallization of the cobalt ferrite upper layer at room temperature. The appearance of major X-ray diffraction peaks with high intensity and well-defined crystallized lattice planes observed via transmission electron microscopy confirmed the crystallization of the CFO thin film deposited at room temperature on 4 nm-sized Au nano-dots. This crystallized CFO thin film exhibits 18-fold higher coercivity (H = 4150 Oe) and 4-fold higher saturation magnetization (M = 262 emu cm) compared to CFO deposited without the Au under-layer. The development of this novel concept of room-temperature crystallization without the aid of additives and solvents represents a crucial breakthrough that is highly significant for exploring the green and energy-efficient synthesis of a variety of oxide and metal thin films.
这项工作首次提出了一种新颖的室温时效概念，用于操控在非晶衬底上生长的薄膜的结晶动力学和磁响应。传统上，采用金属诱导结晶来降低上层薄膜的结晶温度。然而，由于连续金属下层的表面积有限，结晶程度不足，需要进行后退火处理。为了暴露出金属下层的大表面积，我们提出了一种简单新颖的方法，即使用金纳米点阵列代替连续的金属下层来实现上层薄膜的结晶。以尖晶石钴铁氧体（CFO）薄膜作为“模型”，沉积在金纳米点阵列上以实现该方法。我们的研究结果表明，添加量子尺寸的金纳米点作为金属下层，在室温下显著增强了钴铁氧体上层的结晶。通过透射电子显微镜观察到的高强度主要X射线衍射峰的出现以及明确的结晶晶格平面，证实了在4纳米尺寸的金纳米点上室温沉积的CFO薄膜的结晶。与没有金下层沉积的CFO相比，这种结晶的CFO薄膜表现出高18倍的矫顽力（H = 4150奥斯特）和高4倍的饱和磁化强度（M = 262电磁单位/立方厘米）。这种无需添加剂和溶剂辅助的室温结晶新概念的发展代表了一个关键突破，对于探索各种氧化物和金属薄膜的绿色和节能合成具有极其重要的意义。
