Self-assembled molecular monolayers with ultra-low thermal conductance for energy harvesting (QSAMs)

在单分子中，由于热（声子）和电子的振动都表现出量子力学的波动，因此它们可以表现出干涉，这可以用来操纵它们。事实证明，单个有机分子中声子和电子的相长或相消干涉可以通过向分子中添加各种原子团或通过仔细选择分子与外部电极的连接来精确地设计。虽然最近已经实现了对单分子中电子的室温量子干涉（RTQI）的操纵，并且是英国和国外研究小组之间激烈竞争的主题，但尚未实现对室温声子干涉（RTPI）的同时控制。该项目名为QSAMs，旨在通过设计和实现技术相关的材料和设备来实现下一个突破，利用RTPI和RTQI来产生下一代热电材料。目前，信息技术的电力导致的碳排放量与全球航空业的总排放量相当。QSAMs旨在通过发明新材料来应对大幅减少这些排放的全球挑战，这些新材料可以有效地将数据中心（或示例）产生的废热转化为有用的电力。我们的目标材料是由单层或几层分子形成的薄膜，夹在平面电极之间。干扰将用于优化它们将废热转化为电能和片上冷却的能力。这将通过修改具有高RTQI驱动的塞贝克系数的分子的振动特性来实现，该系数决定了当温度差施加到分子或薄膜的两侧时产生的电压。相反，如果在分子上施加电压，则与之密切相关的珀耳帖系数决定了可以产生的冷却效果的大小。对于热回收来说，一个重要的特性（除了电导率和塞贝克系数之外）是热导率，它需要很低。在块体材料中，难以同时设计高电导率和低热导率。然而，对于附着在电极上的单分子或薄分子膜，可以通过合成圣诞树状分子（在顶部和底部连接到电极）来设计热导，其中分子的主干连接到从侧面出来的分支，这些分支以抵消沿着主干流动的声子波的方式振荡。通过选择用于将分子结合到电极的光滑锚基团，可以进一步减少声子传输，以便在分子和电极之间的接触处散射声子。该提案所涉及的技术挑战有三个方面。首先是从理论上确定具有大RTQI和RTPI效应倾向的分子家族，并预测哪些原子团和哪些锚基团将优化其性质。第二个是合成这些分子，第三个是在一个巨大的平行分子阵列中测量和优化它们的特性，称为自组装单层。了解需要克服的障碍，同时实现RTPI和RTQI在这种宏观超薄膜阵列的分子将有助于确定第一步，以一种新型的技术，具有重要的社会和经济影响，在真实的世界，并解决紧迫的问题，芯片上的冷却和节能热回收。

In single molecules, vibrations due to heat (phonons) and electrons both behave quantum-mechanically like waves and so they can exhibit interference, which can be used to manipulate them. It turns out that constructive or destructive interference of phonons and electrons within individual organic molecules can be engineered precisely by the addition of various atomic groups to the molecule or by carefully selecting the connection of the molecule to external electrodes. Although manipulation of room-temperature quantum interference (RTQI) of electrons in single molecules has been realised recently and is a topic of intense competition between research groups in the UK and abroad, simultaneous control of room-temperature phonon interference (RTPI) has not yet been achieved. This project, called QSAMs, aims to deliver the next breakthrough by designing and realising technologically-relevant materials and devices, which exploit both RTPI and RTQI to yield the next generation of thermoelectric materials.Electricity for information technologies currently results in carbon emissions that are comparable to those of the total global aviation industry. QSAMs aims to address the global challenge of reducing these emissions significantly by inventing new materials that efficiently convert the waste heat produced by data centres (or example) into useful electricity. Our target materials are thin films formed from single layers or a few layers of molecules, sandwiched between flat electrodes. Interference will be used to optimise their ability to convert waste heat into electricity and for on-chip cooling. This will be achieved by modifying the vibrational properties of molecules with a high RTQI-driven Seebeck coefficient, which determines the voltage generated when a temperature difference is applied to the two sides of a molecule or a thin film. Conversely, if a voltage is applied across a molecule, the closely-related Peltier coefficient determines the magnitude of the cooling effect that can be created.A crucial property important for heat recovery (in addition to the electrical conductance and the Seebeck coefficient) is the thermal conductance, which needs to be low. Within a bulk material it is difficult to engineer simultaneously high electrical conductance and low thermal conductance. However, for single molecules or thin molecular films attached to electrodes, the thermal conductance can be engineered by synthesising Christmas-tree-like molecules (connected to the electrodes at top and bottom), in which the trunk of the molecule is connected to branches coming out of the sides, which oscillate in such a way as to cancel out the phonon waves flowing along the trunk. Phonon transport can be further reduced by selecting slippery anchor groups for binding the molecules to the electrodes, in order to scatter phonons at the contacts between the molecules and electrodes. The technical challenges that this proposal addresses are three-fold. The first is to identify theoretically families of molecules that will have the propensity for large RTQI and RTPI effects, and to predict which atomic groups and which anchor groups will optimise their properties. The second is to synthesise these molecules and the third is to measure and optimise their properties in a vast parallel array of molecules, known as a self-assembled monolayer. Understanding the hurdles that need to be overcome to realise simultaneously RTPI and RTQI in such macroscopic ultra-thin-film arrays of molecules will help identify the first steps to a new type of technology that has important societal and economic impacts in the real world and addresses pressing problems of on-chip cooling and energy-efficient heat recovery.