锯齿型石墨烯纳米带阵列制备及其自旋逻辑器件研究

Graphene nanoribbons (GNR), known as narrow graphene stripes, has attracted enormous interest from people all over the world because of its outstanding nature in thermal conductivity and electronic properties（e.g. long mean free path of charge carriers, high density of states）. GNRs are therefore believed as one of the most promising alternative materials to use in nanoelectronic devices as channel. However, the properties of GNR depend sensitively on its exact structure. Depending on the nature of chirality, GNRs exhibit metallic properties or semiconductor properties with variable bandgaps. This structure–function relationship can be fully exploited only with access to structurally pure GNRs, but producing just one GNR type remains a considerable challenge. The preparation of controlled chiral GNR arrays in high density not only ensures the homogeneity of the fabricated devices, but also optimizes the current output while increasing the device integration, which is of practical value in the future. Aiming at the above difficulties of GNR preparation, this proposal intends to adopt a chemical vapor deposition method to directly grow zigzag GNR arrays of uniform sizes and high quality on large-size hexagonal boron nitride (h-BN) films that have been pretreated and etched. The investigation on h-BN surface nano-trench array etching and epitaxy of GNR array will be carried out. With the help of simplified density functional theory and reaction kinetics, the mechanisms for nano-trench etching and ribbon growth will be studied. The mechanisms may provide useful guidance for trench etching and GNR growth in large scale with atomic precision. Characterizations e.g. Q-plus AFM, STEM etc. will be carried to determine their lattice structure and fundamental properties, while APRES will be measured to provide the band structure of GNRs. The relationship of GNRs’ structure, their energy bands and their physical properties will be also investigated. GNR device construction methods will be developed and the relationship between GNR device performance and device structure will be explored. This project will provide technical foundation for the development of high-performance GNR-based spin logic devices and integrated circuits in low power.

石墨烯纳米带（GNR）具有载流子长自由程和高态密度，是最具潜力制作未来芯片的沟道材料之一。根据结构不同，GNR表现为金属性或带隙不同的半导体性。GNR结构的多样性和相似性使其可控制备面临着巨大的挑战。制备出高密度受控手性的GNR阵列不但可确保所制器件的均一性，还可以优化电流输出的同时提高器件集成度，极具应用价值。针对上述GNR制备难题，本项目拟采用化学气相沉积法，在经过刻蚀预处理的大尺寸六角氮化硼（h-BN）薄膜上直接生长出阵列规整、尺寸均匀、高质量的锯齿型GNR阵列。开展h-BN表面阵列纳米沟槽刻蚀和阵列GNR外延研究。借助热力学和动力学双重调控，探索沟槽刻蚀与GNR生长机理和控制条件。研究锯齿型GNR微观结构、能带和其物性的内在联系。发展GNR自旋逻辑器件构筑方法，探索GNR器件性能与器件结构之间的关系。该项目将为高性能GNR器件和低功耗集成电路研发奠定技术基础。

石墨烯纳米带（GNR）具有载流子长自由程和高态密度，是最具潜力制作未来芯片的沟道材料之一。石墨烯的锯齿型边缘总是在费米能级附近表现出磁性电子态，从而引起自旋相关现象，这可能为基于石墨烯的自旋电子学提供独特的潜在应用。本项目基于申请人在六角氮化硼表面GNR制备与器件研究方面的长期积累，制备了2-20nm宽的具有原子级平整边缘结构且嵌入h-BN晶格的锯齿型和扶手椅型GNR，并通过微纳器件工艺成功制备室温开关比大于10E5，且迁移率达到1500cm2/Vs，载流子平均自由程超过60nm的场效应器件。嵌入h-BN中的锯齿型GNRs(zGNRs) 的边缘由于面内石墨烯-BN键的稳定性，为探测zGNRs中的磁性提供了可能。项目执行期间共发表了13篇论文，包括Nature Mater., Nat. Rev. Phys.等高水平论文，授权发明专利3件，完成了项目的预期目标，形成一定的国际影响力。主要成果如下：1. 通过磁传输测量来探测弹道状态下嵌入h-BN的zGNR中的磁性特征。将约9 nm宽的zGNR FET中，在4 K温度下观测到其F-P干涉图案。在 4 K 时，~20 mT的磁场能够使器件电阻的变化高达~175 Ω，磁阻比为~1.3%。磁阻的变化可以延伸到室温。它表明即使在室温下zGNR中也存在磁性排序。直接揭示了嵌入h-BN中的zGNR中预测的磁序传输特征，这为探索基于石墨烯的自旋电子器件提供了一个有效的平台。2. 利用过渡金属纳米粒子的催化刻蚀，在h-BN表面得到具有单原子层深度和高长宽比，且取向可控的h-BN纳米沟槽，并进行了系统表征。3. 成功制备出具有GNR边界接触电极的相变存储单元。~3 nm 宽GNR）边界电极相变存储单元在 100 ns 实现~53.7 fJ 写入功耗，并在 6 ns下实现了高低阻值的可逆转变。我们发现单元不对成的物理结构，使其循环寿命及失效机制对输入电压极性具有很强的依赖性。基于石墨烯或 GNR 边界电极的相变存储单元可实现 D型锁存器及D型触发器的逻辑运算功能。针对本重大研究计划的科学问题3取得以下进展和贡献：探寻了具备高载流子自由程和高态密度的GNR体系，提出了实现弹道输运和自旋调控的新方法，为后续进一步研究突破硅基载流子速度极限的GNR自旋逻辑器件提供基础。