Phonon gated electronics: Changing the electrical transport in molecular devices with vibrations generated via magnetic power absorption

由于材料科学和制造工艺的进步，电子设备的尺寸和速度在过去几十年里呈指数级增长。尽管如此，这些越来越小和更快的组件正在向量子力学的基本边界推进，这很快就会导致过热、有缺陷的元件和/或处理能力受损。此外，性能限制并不是传统电子产品的唯一问题。随着产品范围和市场基础的不断扩大，人们越来越担心电子产品对环境和健康的影响，因为我们生活的方方面面几乎都依赖于电子产品。电子设备中使用的许多材料都是有害的，制造这些材料所采用的浪费方法，再加上每隔几年就无法阻止的电子设备的更新，意味着产生大量的危险废物。与传统的半导体器件相比，分子电子学具有更小的内部尺寸和潜在的可生物降解元件的优势。然而，到目前为止，这些研究主要集中在模拟标准器件和p-n结的操作，而不是基于分子结构的独特性质来开发新的功能。再加上金属-分子接触问题，以及有机结构在运行过程中经历的化学和结构退化，分子器件仍然落后于传统结构的效率和耐用性。因此，电子行业不能从采用新一代混合电子产品中获利。该项目旨在通过利用分子和分子动力学的内在属性来解决这些缺陷，而不是模仿半导体器件。为了将分子电子学作为一个具有内在特征的独立领域来实现，混合电子学需要一个定性的概念步骤。分子动力学，即原子由于热能而以特征频率振动，通常被认为是旨在模拟半导体结构的分子设备的麻烦。然而，分子中丰富的振动性质，从低频呼吸模式到超快氢键振动，如果我们能够在不改变宏观温度的情况下产生甚至人工控制选定化学键的振动，那么开发新的范例是一个有吸引力的可能性。为此，我们可以利用磁性材料在暴露在交变磁场中时所耗散的能量来产生或猝灭磁体功能化或与磁体接触的分子中的简正模。这种功率取决于外部直流磁场、交流磁场的频率和磁各向异性，这些参数可以由外部磁场控制或改变材料成分或形状。这将使我们能够通过控制电压和振动光谱来研究电子输运和分子动力学之间的相互作用。从应用于电子器件的角度来看，我提出的方法不会受到与分子结构变化和电极宏观冷却相关的长松弛时间的阻碍，而不仅仅是改变系统的温度。这是因为声子将通过第三个不与电极接触的绝缘磁端直接注入分子。与简单地用微波场辐照分子相比，该技术还可以克服有机分子对微波的低吸收率，并将操作扩展到任意分子体系，在微波场照射下产生光学范围内的振动模。然后，我们可以制造在分子尺度上工作的晶体管，并在几个GHz的频率上驱动磁场。

The size and speed of electronic appliances have improved exponentially in the last few decades thanks to the advances in materials science and fabrication processes. Nonetheless, these ever smaller and faster components are pushing at the fundamental boundaries of quantum mechanics, which will soon result in excessive heating, defective elements and/or impaired processing. Furthermore, performance limitations are not the only problem for conventional electronics. There is an increasing concern about the environmental and health repercussions for a society that depends on electronics in almost every aspect of our life, with an ever-expanding product range and market base. Many of the materials used in electronic devices are harmful, and the wasteful methods employed for their fabrication, together with the unstoppable updating of electronic gadgets every few years mean that large amounts of hazardous waste is produced.Molecular electronics has the advantages over conventional semiconducting devices of small intrinsic size and potentially biodegradable components. However, the research has so far focused in emulating the operation of standard devices and p-n junctions, rather than developing new functionalities based on the unique properties of molecular structures. Added to metal-molecular contact problems, and the chemical and structural degradation that organic structures undergo during operation, molecular devices still lag the efficiency and durability of conventional structures. Therefore, the electronics industry cannot profit from adopting a new generation of hybrid electronics. This project aims to address these drawbacks by using the intrinsic properties of molecules and molecular dynamics, instead of mimicking semiconductor devices.To bring molecular electronics to fruition as an independent field with intrinsic features, a qualitative conceptual step in hybrid electronics is required. Molecular dynamics, where the atoms vibrate at a characteristic frequency due to the thermal energy, are usually considered a nuisance for molecular devices aiming to emulate semiconducting structures. However, the rich range of vibrational properties in molecules, from low-frequency breathing modes to ultrafast hydrogen bond vibrations, is an attractive possibility to develop new paradigms if we could generate or even artificially control the vibrations at chosen chemical bonds without changing the macroscopic temperature. For this purpose, we can use the power dissipated by magnetic materials during exposure to alternating magnetic fields to generate or quench normal modes in molecules functionalized to, or in contact with the magnet. This power is dependent on an external DC magnetic field, the frequency of the AC magnetic field and the magnetic anisotropy, parameters which can be controlled by external fields or modifying the material composition or shape. This will allow us to study the interaction between electronic transport and molecular dynamics by having control over both voltage andvibrational spectrum.From the point of view of applications to electronic devices, rather than just changing the temperature of the system, the method I put forward will not be hampered by the long relaxation times associated with structural changes in the molecules and the macroscopic cooling of the electrodes. This is because the phonons will be injected directly to the molecules through a third insulating magnetic terminal not in contact with the electrodes. As compared with simply irradiating the molecules with microwave fields, the technique will also allow us to overcome the low microwave absorption of organic molecules, and extend the operation to arbitrary molecular systems, where we will generate vibrational modes in the optical range with exposure to microwave fields. We can then fabricate transistors operating at the molecular scale and with driving magnetic fields at frequencies of several GHz.