BN/Graphene/BN sandwiches for high mobility nanodevices

石墨烯中载流子的迁移率通常被用作器件质量的优劣系数。在二氧化硅衬底上的宏观结构中可以实现高达10000 cm.V-1s-1的典型迁移率，据报道在大型悬浮结构中的迁移率高达200.000 cm.V-1s-1，然而这种方法显著减少了光刻选项。寻找更合适的衬底介质最近取得了重大突破，六方氮化硼(h-BN)被发现显著提高了石墨烯器件的电子质量，其迁移率约为140.000 cm.V-1s-1，接近电荷中性点。因此，尽管BN在材料质量方面被认为是成功的，但最近对石墨烯BN衬底的纳米结构的实验表明，与SiO_2上的类似结构相比，BN衬底的迁移率和无序密度没有显著改善。该领域的一种普遍猜测是，边缘无序限制了质量，随着设备变得更小，边缘无序发挥着越来越大的作用。虽然这是一种可能性，但它从未得到实验证实，而且众所周知，如果不是超清洁光刻，即使是大型设备的移动性也可能严重恶化。因此，我们假设这些BN-石墨烯纳米结构中的限制因素确实是光刻诱导的，并提出了一种新的加工方案，基于将石墨烯层夹在两个具有保护作用的BN片之间的基本思想，以允许基本上完全清洁的工艺，并有望制造出具有前所未有的流动性的纳米器件。

The mobility of carriers in graphene is commonly used as a figure of merit for the quality of a device. Typical mobilities of up to 10000 cm.V-1s-1 can be achieved in macroscopic structures on SiO2 substrates and up to 200.000 cm.V-1s-1 has been reported in large suspended structures, however this method significantly reduces lithographic options. The search for a more suitable substrate dielectric has recently resulted in a major breakthrough when hexagonal boron nitride (h-BN) was found to significantly increase the electronic quality of graphene devices yielding mobilities of about 140.000 cm.V-1s-1 close to the charge neutrality point. While BN has therefore been seen as a success in terms of material quality, recent experiments on nanostructures of graphene BN substrates revealed no significant improvement in mobilities and disorder density compared to similar structures on SiO2. A general speculation in the field is that the quality is limited by edge disorder, which plays an increasing role as devices are made smaller. While this is a possibility, it has never been confirmed experimentally, and it is also well know that the mobility of even large devices can be seriously deteriorated by anything less than ultra-clean lithography. We therefore postulate that the limiting factor in these BN-graphene nanostructures is indeed lithographically induced, and propose a new processing scheme, based on the basic idea of sandwiching the graphene layer between two protective BN sheets, in order to allow an essentially perfectly clean process, and hopefully produce nanodevices of unprecedented mobility.