Chen Peiyu, Murugappan Krishnan, Castell Martin R
Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
Phys Chem Chem Phys. 2020 Feb 26;22(8):4416-4428. doi: 10.1039/c9cp06801e.
Morphological control of gold nanocrystals is important as their catalytic and optical properties are highly shape dependent. In this paper we report the shapes of gold nanocrystals which deviate from the equilibrium Wulff shape due to the influence of the SrTiO3 single crystal substrates. The gold crystals are characterized by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The nanocrystals have an equilibrium shape of a truncated octahedron with {111} and {001} facets. On all three substrate surfaces, i.e., SrTiO3(001)-(2 × 1), SrTiO3(001)-c(4 × 2), and SrTiO3(111)-(4 × 4) + (6 × 6), the height-to-width ratio of the gold crystals is not a constant as would be expected for equilibrium crystals, but instead it increases with crystal height. We propose that as the crystals increase in size, their aspect ratio heightens to relax the interfacial strain. The ratio between the {111} and {001} surface areas of our gold crystals is found to differ on the three substrates, which we speculate is due to the selective adsorption of surfactants on the {111} and {001} gold facets resulting from the different substrate surfaces. Reentrant facets of gold crystals that should be present according to their Wulff shape are not observed because these concave sites typically grow out due to kinetic considerations. This study demonstrates the significant effect of the crystal facet termination and surface reconstruction of an oxide substrate on the shape of supported gold nanocrystals.
金纳米晶体的形态控制非常重要，因为它们的催化和光学性质高度依赖于形状。在本文中，我们报道了由于SrTiO₃单晶衬底的影响而偏离平衡伍尔夫形状的金纳米晶体的形状。通过扫描隧道显微镜（STM）和扫描电子显微镜（SEM）对金晶体进行了表征。纳米晶体的平衡形状为具有{111}和{001}面的截顶八面体。在所有三个衬底表面上，即SrTiO₃(001)-(2×1)、SrTiO₃(001)-c(4×2)和SrTiO₃(111)-(4×4)+(6×6)，金晶体的高宽比不像平衡晶体那样是恒定的，而是随着晶体高度的增加而增加。我们提出，随着晶体尺寸的增加，它们的纵横比会增加以缓解界面应变。我们发现，在这三种衬底上，我们的金晶体的{111}和{001}表面积之比不同，我们推测这是由于不同衬底表面导致表面活性剂在{111}和{001}金面上的选择性吸附。根据其伍尔夫形状应该存在的金晶体的凹角面未被观察到，因为由于动力学考虑，这些凹面通常会生长出来。这项研究证明了氧化物衬底的晶体面终止和表面重构对负载型金纳米晶体形状的显著影响。
