Rasheed Atif
Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom.
Microscopy (Oxf). 2021 Aug 9;70(4):e1-e5. doi: 10.1093/jmicro/dfaa078.
Nickel nanocrystals have received much attention for their ferromagnetic properties. The crystal properties are strongly dependent on their facets and therefore detailed study of their morphology, facets and orientation is critical for magnetic applications. In this work, equilibrium crystal shapes of self-assembled nickel nanocrystals on the (111) termination of strontium titanate (SrTiO3) at room temperature and under ultra-high vacuum (UHV) conditions have been investigated using scanning tunneling microscope. SrTiO3 (111) substrate was sputtered (0.5 keV, 2.5 µA, 10 min) and annealed (900°C, 1 h) under UHV conditions. Three different periodicities were observed: 2.21 ± 0.01 nm corresponding to (4 × 4) reconstruction, 3.31 ± 0.02 nm corresponding to (6 × 6) reconstruction and 2.85 ± 0.05 nm, rotated at 30° with respect to (4 × 4) reconstruction, corresponding to (3√3 × 3√3)R30° reconstruction. Nickel (∼1 ml) was deposited using an e-beam evaporator on the substrate preheated to 320°C and the sample was post-annealed multiple times. Nickel took platonic shapes of supported icosahedron comprising of (111) facets and truncated octahedron comprising of (001) and (111) facets. Based on surface energy ratios of truncated octahedrons at equilibrium, the work of adhesion was calculated to be 3.889 ± 0.167 J/m2.
镍纳米晶体因其铁磁性能而备受关注。晶体特性强烈依赖于其晶面，因此对其形态、晶面和取向进行详细研究对于磁学应用至关重要。在这项工作中，利用扫描隧道显微镜研究了室温及超高真空（UHV）条件下，自组装在钛酸锶（SrTiO₃）（111）晶面上的镍纳米晶体的平衡晶体形状。SrTiO₃（111）衬底在超高真空条件下进行溅射（0.5 keV，2.5 μA，10分钟）并退火（900°C，1小时）。观察到三种不同的周期性：2.21±0.01 nm对应于（4×4）重构，3.31±0.02 nm对应于（6×6）重构，以及相对于（4×4）重构旋转30°的2.85±0.05 nm，对应于（3√3×3√3）R30°重构。使用电子束蒸发器在预热至320°C的衬底上沉积镍（约1毫升），并对样品进行多次后退火。镍呈现出由（111）晶面组成的支撑二十面体和由（001）及（111）晶面组成的截角八面体的柏拉图形状。根据平衡时截角八面体的表面能比，计算得出粘附功为3.889±0.167 J/m²。
