Tuning the cooperativity in spin-state switching of molecules in contact to surfaces

调整与表面接触的分子自旋态转换的协同性

• 批准号: 449723616
• 负责人: Professor Dr. Wolfgang Kuch
• 金额: --
• 依托单位: Institut für Experimentalphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/449723616?language=en
• 关键词: Tuning; cooperativity; spin; state; switching

Due to the possibility to switch their molecular magnetic moment on and off by external means, spin-crossover (SCO) molecules are highly interesting candidates for programmable building blocks in molecule-based spin electronics. For that purpose, however, the molecules need to be immobilized and contacted, which implies that they are supported by a solid surface. Correspondingly, mono- and submonolayers of spin-crossover molecules on surfaces have been prepared by, e.g., deposition from the gas phase, and thermal and light-induced spin-state switching could be detected for these systems in recent years by our groups and others. However, the cooperativity, which usually accompanies spin transitions of SCO molecules in solids, is in most cases absent. In order to improve the switching properties of spin-crossover molecules on surfaces, it would be highly desirable to re-establish cooperativity for these systems. This goal, which relates to the general question regarding the ultimate scale limit at which cooperativity becomes effective, is addressed in the present proposal by the stepwise assembly of mononuclear spin-crossover molecules to dimers, trimers, and (ultimately) infinite chains and the deposition as well as characterization of these systems on surfaces. For the multimers, intramolecular cooperativity will emerge, which is studied for the surface-adsorbed molecules. Chain-like, polymeric spin-crossover compounds are in part known to exhibit highly cooperative spin transitions in the solid state, and we want to investigate whether these properties can be retained when depositing monolayers of these polymers on surfaces. To this end, a range of chain-like spin-crossover compounds will be synthesized and investigated regarding their deposition capability on surfaces. Different techniques such as deposition from solids or solution in vacuum as well as by dip or spin coating from solution under ambient pressure, possibly followed by on-surface coupling strategies, are examined to generate such systems. Moreover, horizontal as well as vertical deposition geometries will be explored. The presence of (potentially ordered) monolayers of polymeric spin-crossover compounds on surfaces is examined by atomic force microscopy and scanning tunneling microscopy. The cooperativity in the thermal and light-induced spin transitions of these systems is investigated by x-ray absorption and x-ray photoelectron spectroscopy. The cooperativity is evaluated from the steepness of the thermal spin transition as well as from the detailed analysis of the thermal back-relaxation behavior after an optically induced spin switching at low temperatures. We expect to gain comprehensive knowledge about the factors establishing cooperative spin switching of molecules supported on solid surfaces.

由于可以通过外部手段打开和关闭其分子磁矩，自旋交叉（SCO）分子是基于分子的自旋电子学中可编程构建块的非常有趣的候选者。然而，为此目的，分子需要被固定和接触，这意味着它们由固体表面支撑。相应地，表面上的自旋交叉分子的单层和亚单层已经通过例如，近年来，我们的小组和其他人可以检测到这些系统的气相沉积以及热和光诱导的自旋态转换。然而，通常伴随着固体中SCO分子的自旋跃迁的协同性在大多数情况下是不存在的。为了改善自旋交叉分子在表面上的开关性质，非常需要重新建立这些系统的协同性。这一目标，涉及到的一般问题的最终规模限制，在协同效应变得有效，是解决在本建议的逐步组装单核自旋交叉分子的二聚体，三聚体，和（最终）无限链和沉积以及表征这些系统的表面上。对于多聚体，将出现分子内的协同性，这是研究的表面吸附的分子。链状，聚合物的自旋交叉化合物在某种程度上已知表现出高度合作的自旋跃迁在固态，我们想研究这些特性是否可以保留这些聚合物的表面上沉积单层时。为此，将合成一系列链状自旋交叉化合物，并研究它们在表面上的沉积能力。不同的技术，如沉积从固体或溶液在真空中，以及通过浸或旋涂从溶液在环境压力下，可能其次是表面上的耦合策略，检查生成这样的系统。此外，水平以及垂直沉积的几何形状将进行探讨。原子力显微镜和扫描隧道显微镜检查表面上的聚合物自旋交叉化合物的单层（潜在有序）的存在下。通过X射线吸收谱和X射线光电子能谱研究了这些体系的热致和光致自旋跃迁的协同性。从热自旋转变的陡度以及从详细分析的热回弛豫行为后，在低温下的光诱导自旋切换的协同性进行评估。我们期望获得全面的知识，建立合作的自旋开关的固体表面上支持的分子的因素。