Functionalized Bilayer Graphene Devices: Achieving Selectivity and Sensitivity

石墨烯是一种原子薄的碳原子表面，具有显著的电输运特性，对附近分子种类的分布很敏感；这使得石墨烯在传感器设备的概念中成为一种令人兴奋的材料。然而，为了赋予这些设备任何选择性，表面的功能化是必要的，这意味着在石墨烯表面涂上能够选择性捕获目标分析物的化学基团。虽然各种气体、离子和生物分子传感器已经被证明使用功能化石墨烯器件，但绝大多数都依赖于非共价吸附将官能团固定在表面，这带来了稳定性和可重复性的问题。共价化学可以通过直接将官能团结合到碳晶格中来改善固定化，但这会产生不利于石墨烯导电的缺陷。因此，在石墨烯传感器的概念中，对选择性和灵敏度的需求之间存在着根本的对立。为了解开这个难题，我们提出了一种基于功能化双层石墨烯的原始架构。在这种设计中，即使在高密度的情况下，共价功能位点也可以固定在顶层，而底层则保持其导电性。此外，两层取向之间的扭转角在设计中成为一个新的自由度，在传感器的背景下未被探索。在这个项目中，我们的团队将研究功能化石墨烯双层作为传感器应用中的两个关键挑战：(1)如何控制顶层表面功能位点的分布，以及(2)如何模拟底层对这些功能位点捕获分析物的敏感性。为了解决这些问题，我们的团队汇集了大量的实验和数值技术，包括从头计算、分子动力学模拟、扫描探针和高光谱成像、光电子和阻抗谱以及电传输测量，这些技术将在战略上相互关联，以产生对官能化双层结构和扭曲角度影响的独特多维理解。

Graphene is an atomically-thin surface of carbon atoms with remarkable electrical transport properties that are sensitive to the nearby distribution of molecular species; this makes graphene an exciting material in the conception of sensor devices. Functionalization of the surface is however necessary to impart any selectivity to these devices, which means dressing the graphene surface with chemical groups able to capture selectively the target analyte. While various gas, ion and biomolecular sensors have been demonstrated using functionalized graphene devices, the vast majority rely on non-covalent adsorption to immobilize the functional groups onto the surface, which raises issues of stability and reproducibility. Covalent chemistry could improve immobilization by binding directly the functional groups into the carbon lattice, but this creates defects that are detrimental to the electrical conduction of the graphene. There is thus a fundamental opposition between the needs for selectivity and sensitivity in the conception of graphene sensors. To unlock this conundrum, we propose an original architecture based on functionalized bilayer graphene. In this design, covalent functional sites can be tethered to the top layer, even at high densities, while the bottom layer preserves its electrical conduction. In addition, the twist angle between the orientation of the two layers becomes a new degree of freedom in the design, unexplored in the context of sensors. In this project, our team will investigate two key challenges in the application of functionalized graphene bilayers as sensors: (1) how to control the distribution of functional sites at the surface of the top layer, and (2) how to model the sensitivity of the bottom layer to the capture of an analyte by these functional sites. To address these, our team brings together a very large range of experimental and numerical techniques, including ab initio calculations, molecular dynamics simulations, scanning probes and hyperspectral imaging, photoelectron and impedance spectroscopy as well as electrical transport measurements, that will be strategically correlated to generate a unique multidimensional understanding of the functionalized bilayer structure and the impact of the twist angle.