Quantum-Enhanced Molecular Piezoresistivity

压阻率是材料在施加机械应变时的电阻率(电导率)的变化，对现代传感器的发展起着重要的作用。具有压阻特性的器件可用于检测应变、压力、加速度和力，在许多应用中用作传感器。我们中的许多人都在口袋里放了一套，因为我们智能手机中检测方向和运动的加速度计实际上是基于硅半导体微结构中的压阻(或压电容)效应。其他应用包括车辆技术(例如，负责展开安全气囊的力传感器)、建筑(例如，监测桥梁中预应力混凝土的性能)、机器人(例如，第二代机器人中手和钳子的触觉感知)、液压技术(例如，控制释放阀的压力传感器)、玩具(一个著名的例子是任天堂游戏机，其控制器中包括一组加速计和测功器)和健康技术(例如，远程手术中的感官反馈，“智能”可穿戴式健康监测和药物输送设备)。这份清单绝不是详尽的，因为力传感器是最常见的传感器类型之一。尽管压阻效应是在150多年前被发现的，但这类器件的发展仍然活跃和热门，特别是在当前不断需要小型化和降低功耗的情况下。我建议开发一种新型的压阻传感器，以分子为活性成分。一些分子在被压缩或拉伸时会经历构象变化(原子在其结构中的相对位置的变化)，其电学性质(电导/电阻)也会相应地改变。这种行为是由纳米领域特有的效应引起的，在纳米领域，电荷通过量子隧道流动，并导致对非常小的力的敏感度极高。压阻现象最初将在单分子水平上进行研究，方法是利用扫描隧道显微镜中的纳米操纵技术制造单分子结(仅由1个分子组成的电子设备)，以识别最有希望的结构。随后将使用原子力显微镜对少数分子进行测量，以提取力参数并验证它们是否适合用于功能电子传感器。最后，将柔性分子的自组装单分子层(一分子厚的一层)夹在两个金属薄膜之间来制备原型器件，并将评估它们在机械载荷/应力下的电学性能。从技术角度来看，该项目的最终目标是开发超薄(&lt；100 nm，人类头发厚度的1/1000)、精确和灵敏的力传感器，可用于前面提到的需要缩小尺寸和增强性能的应用。从科学角度来看，该项目将产生有关分子机械行为的前所未有的详细数据，这些数据将对催化和聚合物降解等领域产生影响。

Piezoresistivity, the change in electrical resistivity (conductivity) of a material when a mechanical strain is applied, is an important effect for the development of modern sensors. Devices with piezoresistive behaviour, that can be used to detect strain, pressure, acceleration and force, are used as sensors in many applications. Many of us carry a set of them in our pockets, as the accelerometers in our smartphones that detect orientation and movement are in fact based on the piezoresistive (or piezocapacitive) effect in silicon semiconducting microstructures. Other applications include vehicle technology (e.g. force sensors responsible for deploying the airbag), construction (e.g. to monitor the performances of pre-stressed concrete in bridges), robotics (e.g. tactile perception of hands and pincers in second-generation robots), hydraulics (e.g. pressure sensors to control release valves), toys (a notable example are the Nintendo consoles that include in their controllers sets of accelerometers and dynamometers) and health technology (e.g. sensory feedback in remote surgery, "smart" wearable health monitoring and drug delivery devices). This list is by no means exhaustive, as force sensors are among the most common type of sensors. Despite the fact that the piezoresistive effect was discovered more than 150 years ago, the development of such devices remains active and topical, especially with the current, constant need for miniaturisation and reduced power consumption.I propose here to develop a new kind of piezoresistive sensors, based on molecules as active components. Some molecules undergo a conformational change (a change in the relative position of the atoms in their structure) as they are compressed or stretched, and their electrical properties (conductance / resistance) change accordingly. This behaviour arises from effect unique to the nanoscale realm, where charge flows by quantum tunnelling, and results in extremely enhanced sensitivity to very small forces. Piezoresistive phenomena will be initially investigated at the single-molecule level, by fabricating single-molecule junctions (electrical devices made of 1 molecule only) employing nanomanipulation techniques in a scanning tunnelling microscope to identify the most promising structures. Few-molecules measurements will follow using an atomic force microscope, to extract force parameters and verify their suitability to be used in functional electronic sensors. Finally, prototype devices will be prepared by sandwiching a self-assembled monolayer (a 1-molecule thick layer) of flexible molecules between two metallic films, and their electrical properties under mechanical load/stress will be assessed. From a technological point of view, the final aim of the project is to develop ultra-thin (<100 nm, 1/1000 the thickness of a human hair), precise and sensitive force sensors that could be used in the applications mentioned earlier, where reduced size and enhanced performances are required. From a scientific point of view, the project will yield unprecedentedly detailed data about the mechanical behaviour of molecules, that will have impact in fields such as catalysis and polymer degradation.