Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis
Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis
复制标题
DOI：
10.1016/j.apsusc.2021.151068
复制
发表时间：
2021-09-15
影响因子：
6.7
通讯作者：
Cortie, David
中科院分区：
文献类型：
--
作者：
Bake, Abdulhakim;Rahman, Md Rezoanur;Cortie, David
金属钴纳米颗粒具有吸引人的磁性，但容易氧化，从而抑制其磁化。在这篇文章中，我们报道了使用离子束合成来生产超小的，抗氧化的，钴纳米颗粒嵌入在亚化学计量的TiO2-delta薄膜中。在20 ~ 60 keV的高通量注入下，组装得到的粒子平均尺寸为1.5 +/- 1 nm。利用扫描透射电子显微镜研究了纳米颗粒的几何形状和结构。L-2、L-3钴边缘的近边缘x射线荧光光谱证实，表面下的大多数颗粒是金属的、未氧化的钴。小颗粒的金属性质的进一步证据是通过它们在3到300 K之间的高磁化和超顺磁响应，以及4.5 K的低阻滞温度提供的。利用振动样品磁强计、元素分辨x射线磁圆二色性和深度分辨偏振中子反射法对其磁性进行了研究。这些技术提供了磁性金属Co颗粒的统一图像。我们认为，基于这些实验观察和热力学计算，由于TiO2在CoO上的焓稳定性抑制了固态反应，钴被保护免受二氧化钛表面下的氧化。
Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra-small, oxidation-resistant, cobalt nanoparticles embedded within substoichiometric TiO2-delta thin films. Using high fluence implantation of cobalt at 20-60 keV, the particles were assembled with an average size of 1.5 +/- 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near-edge X-ray fluorescence spectroscopy on the L-2,L-3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and super paramagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element-resolved X-ray magnetic circular dichroism, and depth-resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reactions.