Czyszczon-Burton Thomas M, Montes Enrique, Prana Jazmine, Lazar Sawyer, Rotthowe Nils, Chen Sully F, Vázquez Héctor, Inkpen Michael S
Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10, Prague 16200, Czech Republic.
J Am Chem Soc. 2024 Oct 4;146(41):28516-26. doi: 10.1021/jacs.4c11241.
Chemical groups capable of connecting molecules physically and electrically between electrodes are of critical importance in molecular-scale electronics, influencing junction conductance, variability, and function. While the development of such linkage chemistries has focused on interactions at gold, the distinct reactivity and electronic structure of other electrode metals provides underexplored opportunities to characterize and exploit new binding motifs. In this work we show that α,ω-alkanedibromides spontaneously form well-defined junctions using silver, but not gold, electrodes through application of the glovebox-based scanning tunneling microscope-based break junction method. We systematically evaluate, through a series of additional studies, whether these molecular components form physisorbed or chemisorbed contact geometries, and if they undergo secondary chemical reactions at the silver surface. Critically, we find that the same junctions form when using different halide, or trimethylstannyl, terminal groups, suggestive of an electronically transparent silver-carbon(sp) contact chemistry. However, the experimental conductance of the junctions we measure with silver electrodes is ∼30× lower than that observed for such junctions comprising gold-carbon(sp) contacts, which does not align with predictions based on first-principles calculations. We further exclude the possibility that the proposed silver alkyl species undergo α- or β-hydride elimination reactions that result in a distinct contact chemistry through conductance measurements of control molecules that cannot undergo such processes. Applying insights provided from prior temperature-programmed desorption studies and a robust series of atomistic simulations, we ultimately propose that in these experiments we measure alkoxide-terminated junctions formed from the reaction of the chemisorbed alkyl with oxygen that is coadsorbed on the silver surface. This work, in demonstrating that high conductance contact chemistries established using model gold electrodes may not be readily transferred to other metals, underscores the need to directly characterize the interfacial electronic properties and reactivity of electrode metals of wider technological relevance.
在分子尺度电子学中，能够在电极之间物理和电气连接分子的化学基团至关重要，它们会影响结电导、变异性和功能。虽然此类连接化学的发展主要集中在与金的相互作用上，但其他电极金属独特的反应性和电子结构为表征和利用新的结合基序提供了尚未充分探索的机会。在这项工作中，我们表明，通过基于手套箱的扫描隧道显微镜断结方法，α,ω-链烷二溴化物使用银电极而非金电极自发形成定义明确的结。我们通过一系列额外的研究系统地评估这些分子组件是否形成物理吸附或化学吸附的接触几何结构，以及它们是否在银表面发生二次化学反应。至关重要的是，我们发现使用不同的卤化物或三甲基锡基端基时会形成相同的结，这表明存在一种电子透明的银 - 碳（sp）接触化学。然而，我们用银电极测量的结的实验电导比包含金 - 碳（sp）接触的此类结低约30倍，这与基于第一性原理计算的预测不一致。我们通过对无法进行此类过程的对照分子进行电导测量，进一步排除了所提出的银烷基物种发生α-或β-氢化物消除反应从而导致不同接触化学的可能性。应用先前程序升温脱附研究提供的见解以及一系列强大的原子模拟，我们最终提出，在这些实验中，我们测量的是由化学吸附的烷基与共吸附在银表面的氧反应形成的醇盐端结。这项工作表明，使用模型金电极建立的高电导接触化学可能不容易转移到其他金属上，强调了直接表征具有更广泛技术相关性的电极金属的界面电子性质和反应性的必要性。
