For info on how to attend via videoconference, email andrew.b.hamlin.th@dartmouth.edu

"Liquid Metal Printing of Ultrathin Conductive Metal Oxide"

Abstract

Widegap metal oxides are a critical semiconducting material in solar power generation, transparent electronics and displays. Ultrathin versions of these materials are poised to be at the forefront of next generation technology due to their high transparency, flexibility, and capacity to advantageously use backchannel sensitivity and quantum confinement. Liquid metal printing fundamentally yields 2-3 nm electronic materials, which provides the ability to understand the properties of 2D oxides. This process involves the facile, instantaneous delamination and deposition of the oxide shell that encompasses molten metals. Relevant metals such as indium, tin and gallium possess low melting temperatures, introducing compatibility with flexible substrates.

Our work in this field includes the invention of two liquid metal printing techniques, heated press printing and continuous roller-based printing. These techniques are discussed in depth, and their resultant oxide films are structurally and chemically analyzed. Press printed InO_x films imaged using transmission electron microscopy revealed large plate-like overlapping grains. Assessment of the electronic density of states and transfer characteristics of InO_x thin film transistors (TFTs) demonstrated that the 2D nature of these films yielded quantum confinement effects. High mobilities of up to 67 cm²/Vs were achieved, which is in part due to the unique grain structure achieved with press printing. To leverage the importance of the backchannel of these ultrathin materials and tailor TFT device characteristics, heterostructure InO_x / GaO_x channels were fabricated and analyzed. These tunable devices demonstrated enhancement mode operation, excellent switching properties, and improved device variability. Increased InO_x carrier concentration via modulation doping due to a work function mismatch between InO_x and GaO_x is also observed. Utilization of alloys to create desirable electronic materials is a natural progression of this work. However, the oxide shell composition typically differs from the alloy, leading to the need for a deeper knowledge on the physics of liquid metal oxidation. Investigation of the oxidation rate as a function of temperature and dopant concentration will also lead to a better understanding of the effect of thickness, physical structure, and composition on electronic behavior.

Thesis Committee

• Prof. Will Scheideler (Chair)
• Prof. Jifeng Liu
• Prof. Geoffroy Hautier
• Prof. Julia Hsu

Contact

For more information, contact Theresa Fuller at theresa.d.fuller@dartmouth.edu.