Kammarchedu Vinay, Butler Derrick, Rashid Asmaul Smitha, Ebrahimi Aida, Kayyalha Morteza
Department of Electrical Engineering, The Pennsylvania State University, University Park, PA 16802, United States of America.
Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, United States of America.
Nanotechnology. 2024 Sep 18;35(49):495701. doi: 10.1088/1361-6528/ad7853.
Engineering superlattices (SLs)-which are spatially periodic potential landscapes for electrons-is an emerging approach for the realization of exotic properties, including superconductivity and correlated insulators, in two-dimensional materials. While moiré SL engineering has been a popular approach, nanopatterning is an attractive alternative offering control over the pattern and wavelength of the SL. However, the disorder arising in the system due to imperfect nanopatterning is seldom studied. Here, by creating a square lattice of nanoholes in the SiOdielectric layer using nanolithography, we study the SL potential and the disorder formed in hBN-graphene-hBN heterostructures. Specifically, we observe that while electrical transport shows distinct SL satellite peaks, the disorder of the device is significantly higher than graphene devices without any SL. We use finite-element simulations combined with a resistor network model to calculate the effects of this disorder on the transport properties of graphene. We consider three types of disorder: nanohole size variations, adjacent nanohole mergers, and nanohole vacancies. Comparing our experimental results with the model, we find that the disorder primarily originates from nanohole size variations rather than nanohole mergers in square SLs. We further confirm the validity of our model by comparing the results with quantum transport simulations. Our findings highlight the applicability of our simple framework to predict and engineer disorder in patterned SLs, specifically correlating variations in the resultant SL patterns to the observed disorder. Our combined experimental and theoretical results could serve as a valuable guide for optimizing nanofabrication processes to engineer disorder in nanopatterned SLs.
工程超晶格（SLs）——电子的空间周期性势场——是在二维材料中实现包括超导性和关联绝缘体在内的奇异特性的一种新兴方法。虽然莫尔超晶格工程一直是一种流行的方法，但纳米图案化是一种有吸引力的替代方法，它能控制超晶格的图案和波长。然而，由于纳米图案化不完善而在系统中产生的无序现象很少被研究。在这里，通过使用纳米光刻技术在SiO2介电层中创建纳米孔的方形晶格，我们研究了hBN-石墨烯-hBN异质结构中形成的超晶格势和无序现象。具体而言，我们观察到，虽然电输运显示出明显的超晶格卫星峰，但该器件的无序程度明显高于没有任何超晶格的石墨烯器件。我们使用有限元模拟结合电阻网络模型来计算这种无序对石墨烯输运性质的影响。我们考虑三种类型的无序：纳米孔尺寸变化、相邻纳米孔合并和纳米孔空位。将我们的实验结果与模型进行比较，我们发现无序主要源于纳米孔尺寸变化，而不是方形超晶格中的纳米孔合并。我们通过将结果与量子输运模拟进行比较，进一步证实了我们模型的有效性。我们的研究结果突出了我们这个简单框架在预测和设计图案化超晶格中的无序现象方面的适用性，特别是将所得超晶格图案的变化与观察到的无序现象联系起来。我们的实验和理论相结合的结果可以为优化纳米制造工艺以设计纳米图案化超晶格中的无序现象提供有价值的指导。
