The strong metal–support interaction (SMSI) is the encapsulation of a supported metal particle by an oxide layer that diffuses from the substrate. This process is usually described as being driven by a reduction in the surface energy of the metal particle and has a significant influence on the catalytic activity of the metal. Here, epitaxial Pd nanocrystals grown in ultrahigh vacuum on $\mathrm{SrTi}{\mathrm{O}}_3\left(001\right)$ and anatase $\mathrm{Ti}{\mathrm{O}}_2\left(001\right)$ substrates are studied by scanning tunneling microscopy. At annealing temperatures above ∼600 ºC, the Pd crystals can become encapsulated by a $\mathrm{Ti}{\mathrm{O}}_x$ monolayer originating from the substrates. For both bare and encapsulated Pd crystals, their height-to-width ratio increases with the crystal height as a mechanism to partially release their interfacial misfit strain with the substrate. However, the rate of this increase is lower for encapsulated crystals, indicating that during the SMSI process the interface between the particle and the oxide is modified to form a lower energy interfacial structure which also results in less strain in the encapsulated particle. The SMSI is found to preferentially occur on larger crystals, driven by the reduction in their elastic strain energy, which scales with the crystal volume. Compared with the traditional view of SMSI our results provide a more complete description of the encapsulation process.

中文翻译：

---

驱动强金属-载体相互作用的热力学：负载型 Pd 纳米晶体的钛酸盐封装

强金属-载体相互作用 (SMSI) 是由从基材扩散的氧化物层封装支撑的金属颗粒。该过程通常被描述为由金属颗粒表面能的降低驱动，对金属的催化活性有显着影响。在这里，在超高真空中生长的外延 Pd 纳米晶体$\mathrm{钛酸锶}{\mathrm{哦}}_3\left(001\right)$ 和锐钛矿 $钛{\mathrm{哦}}_2\left(001\right)$通过扫描隧道显微镜研究基材。在高于 600 ºC 的退火温度下，Pd 晶体可以通过$钛{\mathrm{哦}}_X$源自基板的单层。对于裸露和封装的 Pd 晶体，它们的高宽比随着晶体高度的增加而增加，这是部分释放其与基板的界面错配应变的机制。然而，对于封装的晶体，这种增加的速率较低，这表明在 SMSI 过程中，粒子和氧化物之间的界面被修改以形成较低能量的界面结构，这也导致封装粒子中的应变较小。发现 SMSI 优先出现在较大的晶体上，这是由它们的弹性应变能降低驱动的，这与晶体体积成比例。与 SMSI 的传统观点相比，我们的结果对封装过程提供了更完整的描述。