[论文解读] Engineering on-surface spin crossover: spin-state switching in a self-assembled film of vacuum-sublimable functional molecule

Senthil Kumar Kuppusamy, Michał Studniarek+8 more|arXiv (Cornell University)|Jan 1, 2018

Molecular Junctions and Nanostructures参考文献 65被引用 66

一句话总结

该论文展示在自组装的、薄膜的、真空升华可得的Fe(II)复合物在弱相互作用表面上的自旋状态切换，显示由于层状双层样组装，在块状材料和10 nm薄膜中具有相当的自旋状态切换。

ABSTRACT

Realization of spin crossover (SCO) based applications requires studying of spin state switching characteristics of SCO complex molecules at nanostructured environments especially on-surface. Except for a very few cases, the SCO of a surface bound thin molecular film is either quenched or heavily altered due to (i) strong molecule-surface interactions and (ii) differing intermolecular interactions in films relative to the bulk. By fabricating SCO complexes on a weakly interacting surface such as highly oriented pyrolytic graphite (HOPG) and copper nitride (CuN), the interfacial quenching problem has been tackled. However, engineering intermolecular interactions in thin SCO active films is rather difficult. This work proposes a molecular self-assembly strategy to fabricate thin spin switchable surface bound films with programmable intermolecular interactions. Molecular engineering of the parent complex system [Fe(H$_{2}$B(pz)$_{2}$)$_{2}$(bpy)] (pz = pyrazole, bpy = 2,2'-bipyridine) with a dodecyl (C$_{12}$) alkyl chain yielded a classical amphiphile-like functional and vacuum sublimable charge neutral Fe$^{\ m II}$ complex, [Fe(H$_{2}$B(pz)$_{2}$)$_{2}$(C$_{12}$-bpy)] (C$_{12}$-bpy = dodecyl[2,2'-bipyridine]-5-carboxylate). The bulk powder and 10 nm thin film, on quartz glass/SiO$_{\ m x}$ surface, of the complex showed comparable spin state switching characteristics mediated by similar lamellar bilayer like self-assembly/molecular interactions in both bulk and thin film states. This unprecedented observation augurs well for the development of SCO based applications, especially in molecular spintronics.

研究动机与目标

• 研究当受限于纳米结构化的表面环境时，SCO络合物的自旋跨越（SCO）行为。
• 开发分子自组装策略以控制薄SCO薄膜中的分子间相互作用。
• 评估薄膜是否保留块状材料那样的SCO切换特性。
• 探索该方法在分子自旋电子学应用中的适用性。

提出的方法

• 将母体SCO络合物 [Fe(H2B(pz)2)2(bpy)] 通过连接一个 C12 直链烷基链来形成 [Fe(H2B(pz)2)2(C12-bpy)]，得到一个真空升华的、两亲体样的 Fe(II)复合物.
• 在石英玻璃/SiOx 上制备薄膜（10 nm）和块状粉末样品以比较SCO行为。
• 表征自旋态切换和归因于层状双层样排列的自组装特征，在块态与薄膜态中。
• 使用弱相互作用衬底（HOPG, CuN）以最大限度减少界面猝灭并保持SCO活性。

实验结果

研究问题

• RQ1 自组装、真空升华的SCO络合物能否在薄膜中保留块状材料那样的自旋跨越行为？
• RQ2 自组装薄膜中的分子间相互作用如何影响表面的SCO切换？
• RQ3 10 nm 薄膜中的自旋态切换是否由层状双层样组装支配，与块状粉末类似？
• RQ4 该方法能否在分子自旋电子学中实现基于SCO的功能？

主要发现

• 块状粉末与10 nm薄膜显示出可比的自旋态切换特性。
• SCO行为在两种状态都由类似的层状双层样自组装和分子相互作用介导。
• 在弱相互作用表面的制备有助于减轻界面猝灭对SCO的影响。
• 分子设计提供了经典的两亲体样功能并保留了自旋切换。
• 结果支持在分子自旋电子学中应用SCO的潜力。