Scanning tunneling microscopy and spectroscopy of metallic features and nanocontacts for atomically precise graphene nanoribbons on silicon surface

This thesis investigates the fabrication and electronic properties of metallic nanostructures and nanocontacts formed with atomically precise graphene nanoribbons (GNRs) on silicon surfaces. Scanning tunneling microscope (STM)-based electron beam induced deposition (EBID) was employed to write sub-5 nm metallic magnesium boride (MgBx) nanostructures directly onto hydrogen-passivated Si(100) surfaces. The effects of deposition parameters like voltage, current, writing speed, and repetition cycles on the dimensions and uniformity of the MgBx nanostructures were systematically investigated. Pre-fabricated niobium contact electrodes with narrow gaps were utilized to measure the conductivity of the MgBx nanowires and explore their potential superconducting behavior at cryogenic temperatures, though no superconductivity was observed. The STM-EBID technique using a hafnium precursor was further applied to form metallic nanocontacts directly onto individual solution-synthesized GNRs exfoliated on Si(100) surfaces. Scanning tunneling spectroscopy revealed induced p-n junction formation at the metal-GNR interface due to work function differences, creating a local band-bending effect useful for engineering the electronic properties. Moreover, strategies were developed to fabricate large-area metal electrode arrays on insulating silicon dioxide layers, enabling the precise writing of HfB2 interconnects to bridge individual GNRs with the electrodes for in-situ transport measurements. Finally, a simplified cleaning process combining high-temperature ultra-high vacuum annealing with piranha solution or UV ozone treatment was demonstrated for preserving atomically flat hydrogen-passivated Si(100) surfaces, facilitating GNR deposition and surface characterization after device fabrication steps.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Sun, Hongye

Contributors dc:contributor

• Lyding, Joseph W
• Abelson, John R
• Girolami, Gregory S
• Cao, Qing
• Zhang, Yingjie

• Graphene Nanoribbon
• Scanning Tunneling Microscopy
• Scanning Tunneling Spectroscopy
• Electron-beam-induced Deposition
• Hafnium Diboride
• Magnesium Boride
• Silicon
• Nanotechnology

Statement dc:rights

• Copyright 2024 Hongye Sun

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125752

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125752