Electron Assisted Growth of Graphene atop Ir(111) supported Hexagonal Boron Nitride

Abstract

Vertical heterostructures between graphene (Gr) and hexagonal boron nitride (hBN) have attracted a great deal of interest, due to their potential applications in the semiconductor industry as new and superior transistor materials. The direct growth of the heterostucture still remains challenging and in this bachelor thesis, I report a novel electron assisted growth technique, which is used to attempt to grow Gr atop hBN atop an Ir(111) single crystal surface. This technique has already proven to be successful in the opposite order of growing hBN atop Gr/Ir(111)[1].

To properly understand the growth and possible heterostructure formation, pure phases of both hBN and Gr on Ir(111) are characterized first using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). This structural characterization of the pure phases reveals a stronger binding of hBN than Gr to Ir(111) and, therefore, a favored stacking order of Gr atop hBN.

In contrast to this expectation, my STM and LEED results of the electron assisted growth of Gr atop a full hBN layer show, that the temperature required for Gr formation is too high for hBN layer to sustain, and is already complicated by a low sticking coefficient of ethylene atop. After high temperature annealing, the hBN layer is determined to leave behind a (6x2) boron nanoribbon superstructure and no ordered Gr islands are observed. However, the effect of the electron beam in the growth technique is indicated to result in an uneven charging of the hBN layer on Ir(111), and this, in combination with its already highly corrugated pore-wire structure, calls for new research.

Popular Abstract

The end of the Silicon Era

The modern world is on the verge of entering a new era, an era known as, “beyond the Moore’s law”. This law, that has governed the entire computer industry for more than 50 years, predicts that the number of transistors in an integrated circuit will be doubled every two years. By the current rate, the transistors, which are at the very border between nanometres and atomic dimensions, will exceed the physically available sizes of the three-dimensional transistors within the next decade. As a result, fundamentally different sets of materials have to be investigated, will they be the end of the Silicon Era?

In 2010 the Nobel Prize in Physics was awarded to A. Geim and K. Novoselov for the discovery of a new material called “graphene”, a single layer of carbon atoms. By using a simple Scotch Tape, Geim and Noveselov were able to peel off these single atomic layers from a chunk of graphite. This newly found two-dimensional material had very interesting properties, such as an extreme electrical conductivity, which was way beyond any known three-dimensional structure. However, because of its high conductivity, it made it difficult to use by itself within the transistor industry dominated by semiconducting materials, such as silicon. Another intriguing member of the ever-growing family of the two-dimensional materials is an insulator called hexagonal boron nitride. As hexagonal boron nitride shares the same structure as graphene, it becomes interesting to examine if these two atomic layers can be stacked on top of each other, to form so-called two-dimensional heterostructures, with new possibilities and a reduced size way beyond any three-dimensional structure. Furthermore, by a combination of an insulating and a conducting layer, the highly desired semiconducting properties could be achieved, hence creating a structure with a possibility to become the new future of transistors and nanoelectronics.

In my project, I studied how the two-dimensional heterostructure between graphene and hexagonal boron nitride can be formed and characterized it using techniques with resolution on the atomic scale. In addition to contributing to the understanding of stacked two-dimensional materials in general, my study opens new research directions as it surprisingly showed that it is possible to bury and store charge in the hexagonal boron nitride.

• author: Linnala, Lassi
• supervisor: Jan Knudsen
• organization: Synchrotron Radiation Research; Department of Physics
• course: FYSK02 20182
• year: 2019
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: Two-dimensional materials, Two-dimensional heterostructures, Graphene, hexagonal Boron Nitride, STM, LEED
• language: English
• id: 8991361
• date added to LUP: 2019-08-25 14:07:32
• date last changed: 2019-08-25 14:07:32