Enhanced Spin Injection in Molecularly Functionalized Graphene via Ultrathin Oxide Barriers
Enhanced Spin Injection in Molecularly Functionalized Graphene via Ultrathin Oxide Barriers
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DOI：
10.1103/physrevapplied.15.054018
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发表时间：
2021-04
影响因子：
4.6
通讯作者：
J. Toscano-Figueroa;N. Natera-Cordero;D. Bandurin;C. R. Anderson;V. Guarochico-Moreira;I. Grigorieva;I. J. Vera-Marun
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文献类型：
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作者：
J. Toscano-Figueroa;N. Natera-Cordero;D. Bandurin;C. R. Anderson;V. Guarochico-Moreira;I. Grigorieva;I. J. Vera-Marun
实用自旋电子器件的实现依赖于产生和检测纯自旋电流的能力。在基于石墨烯的自旋阀中，这通常是通过隧道势垒从铁磁接触注入自旋极化电子来实现的，其中 Al2O3 和 MgO 最广泛用作势垒材料。然而，使这些势垒足够薄的要求通常会导致针孔和低接触电阻，从而导致自旋注入效率低，由于所谓的电阻失配问题，在室温下通常为 5%。在这里，我们展示了另一种制造石墨烯超薄隧道势垒接触的方法。我们证明，具有 sp 键合苯基的石墨烯的激光辅助化学功能化有效地为超薄 Al2O3 薄膜的生长提供了种子层，确保了光滑、高质量的隧道势垒并提高了自旋注入效率。重要的是，功能化对石墨烯通道本身自旋输运的影响相对较弱，因此增强的自旋注入占主导地位并导致自旋信号增加一个数量级。此外，使用聚焦激光束和光刻技术对功能化进行空间控制原则上可用于将功能化仅限于接触区域，进一步减少对石墨烯通道的影响。我们的研究结果为规避基于容易获得且高度稳定的Al2O3的石墨烯自旋电子器件中的电阻失配问题开辟了一条新途径，并促进其实际应用的发展向前迈进了一步。
Realisation of practical spintronic devices relies on the ability to create and detect pure spin currents. In graphene-based spin valves this is usually achieved by injection of spin-polarized electrons from ferromagnetic contacts via a tunnel barrier, with Al2O3 and MgO used most widely as barrier materials. However, the requirement to make these barriers sufficiently thin often leads to pinholes and low contact resistances which in turn results in low spin injection efficiencies, typically 5% at room temperature, due to the so-called resistance mismatch problem. Here we demonstrate an alternative approach to fabricate ultra-thin tunnel barrier contacts to graphene. We show that laser-assisted chemical functionalization of graphene with sp-bonded phenyl groups effectively provides a seed layer for growth of ultrathin Al2O3 films, ensuring smooth, high quality tunnel barriers and an enhanced spin injection efficiency. Importantly, the effect of functionalization on spin transport in the graphene channel itself is relatively weak, so that the enhanced spin injection dominates and leads to an order of magnitude increase in spin signals. Furthermore, spatial control of functionalization using a focused laser beam and lithographic techniques can in principle be used to limit functionalization to contact areas only, further reducing the effect on the graphene channel. Our results open a new route towards circumventing the resistance mismatch problem in graphene-based spintronic devices based on the easily available and highly stable Al2O3, and facilitate a step forward in the development of their practical applications.