Molecular Spintronics

在过去的十年里，自旋电子学和有机电子学领域有了巨大的发展。单独而言，这些领域有望解决现代无机半导体电子学面临的两个方面的挑战：首先是需要利用电子电荷以外的自由度，这是由不断增加的功率密度和对量子计算机的追求驱动的；第二个是对非常便宜、普遍可打印电路的渴望。尽管“自旋电子学”这个术语相对较新，指的是对自旋的操纵和测量，而不仅仅是电子的电荷，但信息技术长期以来一直依赖于电子自旋来存储数据。可以说，第一个先进的自旋电子器件是磁阻式（外部磁场调节材料的电阻）读磁头，它彻底改变了硬盘数据存储。自旋电子学的下一个主要用途几乎肯定是磁随机存取存储器（MRAM），它将DRAM的许多优点（特别是存取速度）与硬盘驱动器的非易失性结合起来。由于其低成本，易于加工，化学通用性和与柔性衬底的兼容性，分子半导体，如酞菁，卟啉和苝，其主要特征是碳原子环，正在成为无机半导体（如硅）的有吸引力的替代品，用于各种光电器件，例如有机发光二极管（oled）和光伏（OPV）。这些材料用途广泛，在生物医学领域有着悠久的历史；事实上，叶绿素（在植物中将光转化为能量）是一种卟啉衍生物，酞菁衍生物被用于癌症治疗。它们也有一些特性，使它们成为自旋电子学的理想选择。它们的长自旋松弛时间已经被利用，例如，在自旋阀装置中，非晶有机薄膜被用作间隔。此外，与无机晶格相比，它们具有较高的分子纯度，并且与自旋电子学中最广泛使用的无机半导体材料砷化镓（GaAs）相反，它们具有将磁性实体插入分子框架的巨大灵活性，可以随意定制。有机分子的其他主要优点是高度可调谐的光学特性和在光谱可见区域的大磁光效应，这与离散局部开关兼容。我们的研究将发展分子自旋电子学的新领域，具体目标是为磁光学、电子学和分子识别创建一个平台技术。该平台将针对有机物具有独特优势的地区开发。我们期待对生物学产生特别巨大的影响，因为功能化比无机物更直接，而对量子信息技术来说，磁性离子和配体子系统的分离提供了量子比特（磁性离子可以随意定位在碳环中心）和控制比特（重叠的配体-碳环-轨道）的独立寻址能力，这在无机固体中是不容易实现的。为了实施该计划，我们已经从伦敦和沃里克组建了一个跨学科的团队，他们已经非正式地联合起来进行开创性的概念验证工作，包括酞菁纳米线的制造和分子薄膜中高信息磁共振的观察。该项目有一组非常具体的目标，从光控磁相互作用到依靠磁共振的新型生物测定芯片。为了便于管理，将会有关于薄膜沉积和表征、器件、生物学和理论的工作包。

Over the last decade there has been tremendous growth in the fields of spintronics and organic electronics. Individually, these fields promise to deal with two aspects of the challenges now facing modern inorganic semiconductor electronics: the first being the need - driven by ever increasing power densities and the quest for quantum computers - to exploit degrees of freedom other than the electron charge; the second being the desire for very cheap, universally printable circuits. Although the term 'spintronics' is relatively new, and refers to the manipulation and measurement of the spin rather than just the charge of the electron, information technology has long depended on the electron spin for data storage. Arguably the first advanced spintronic devices are the magnetoresistive (where an external magnetic field modulates the electrical resistance of a material) read heads which have revolutionised hard-drive data storage. The next major use of spintronics will almost certainly be in magnetic random access memory (MRAM), which will combine many of the advantages (notably access speed) of DRAM with the non-volatility of hard drives.Thanks to their low cost, ease of processing, chemical versatility and compatibility with flexible substrates, molecular semiconductors such as phthalocyanines, porphyrins and perylenes, whose key features are rings of carbon atoms, are establishing themselves as attractive alternatives to inorganic semiconductors, such as silicon, for a variety of optoelectronic devices, e.g. organic light emitting diodes (OLEDs) and photovoltaics (OPV). These materials are extremely versatile, with a long history in biomedicine; indeed chlorophyll (which converts light into energy in plants) is a porphyrin derivative and phthalocyanine derivatives are used in cancer therapy. They also have properties that make them desirable for spintronics. Their long spin relaxation times are already being exploited, for example, in spin valve devices where amorphous organic films are used as spacers. Furthermore, they are endowed with high molecular purity compared to inorganic crystal lattices, and display tremendous flexibility for insertion of magnetic entities into molecular frameworks which can be tailored at will, contrary to what can be attained in gallium arsenide (GaAs), the most widely used inorganic semiconductor material for spintronics. Other major advantages of organic molecules are highly tuneable optical properties and large magneto-optic effects in the visible region of the spectrum, which are compatible with discrete local switching.Our research will develop the new field of molecular spintronics, with the specific aim of creating a platform technology for magneto-optics, electronics, and molecular recognition. The platform will be developed for areas where organics have unique advantages. We look forward to particularly dramatic impacts on biology where functionalization is more straightforward than for inorganics, and for quantum information technology where the separation into magnetic ion and ligand subsystems provides independent addressability of qubits (the magnetic ions which can be positioned at will in the carbon ring centers) and control bits (the overlapping ligand - carbon ring - orbitals) which cannot be readily achieved in inorganic solids. To carry out the programme, we have assembled an interdisciplinary team from London and Warwick which has already combined informally to perform groundbreaking proof of concept work, including the fabrication of phthalocyanine nanowires and observation of highly informative magnetic resonance in molecular thin films, for the current proposal. The project has a very specific set of objectives, ranging from optically controlled magnetic interactions to a novel bioassay chip relying on magnetic resonance. To facilitate management, there will be work-packages for film deposition and characterization, devices, biology and theory.