Liquid metal reaction platforms: exploring the 2D oxidation products of liquid metal alloys for potential future use in more than Moore-based low-energy devices
Creators: name: Goff, Abigail
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400499
subject: Chemical engineering not elsewhere classified

description: Current electronic technologies consume a large percentage of our energy and materials1, 2. Researchers are therefore working towards the implementation of low-energy alternatives that may conserve resources that would otherwise be used in powering the devices used across the globe. Transistors are the main component in electronic technologies and were the focal point of “Moore’s Law” which states the number of components of an integrated circuit will double every two years. This law has held true for over 50 years, however, it’s logarithmic trend is predicted to plateau within the next 5 years3. As such, the miniaturisation (more Moore) and diversification (more than Moore) of our technology is needed4. Transistors are being adapted for improvement, either by creating new configurations, utilising different materials as Silicon alternatives, or by creating completely new devices that harness the various material properties of new materials.

To generate and utilise different materials within these devices, new synthesis methods are being applied, including the liquid metal (LM) touch printing method – an alternative to traditional bottom-up and top-down methods, such as chemical vapour deposition (CVD) or exfoliation, respectively. LM touch printing is a hybrid two-step synthesis method where the liquid is exposed to oxygen – growing an oxide “skin” from bottom-up (following Cabrera-Mott oxidation), before being exfoliated from the droplet surface in a top-down manner. LMs such as Ga, In, Bi, and Sn are ideal for the growth of new materials as they can be alloyed with high melting point metals prior to oxidation5, 6.

The preferential oxide “skin” that forms on the surface of a LM alloy can be approximated via a simple set of equations (developed within this Master’s Thesis) that predict, thermodynamically, what is more likely to form6. In this manner, experimentalists can save time on trial-and-error experiments determining what LM solvent is appropriate for the formation of high melting point metal oxides. This equation does not account for the kinetics of the systems, nor does it account for potential mixed oxides or the potential for intermetallic states within the LM alloy, however there is room for expansion of this prediction, which will further our understanding of the LM alloy system. The predictive equation created in this work has been tested in the case of Mn oxide printing. Mn was alloyed with Sn, as the prediction results indicated the formation of Ga2O3 when Mn is alloyed with Ga, but MnO2 when alloyed with Sn. This Masters project highlights the useful nature of the equation, as time was saved in trial-and-error testing, however, it highlights the issues with the equations also: The MnSn alloy did not, in fact, form MnO2, instead it was found to form MnSnOx. This mixed oxide was found to be ultrathin (~8nm thick), paramagnetic, insulating, and piezoelectric (d33 = ~42 pm/V). The crystal structure of the material could not fully be elucidated, and this is believed to be due to the potential formation of an intermetallic phase during the cooling of the MnSn alloying process. The MnSn2 intermetallic cannot be broken down to a homogeneous MnSn liquid alloy at the low temperatures needed for Cabrera-Mott oxidation, meaning that the oxide “skin” formed and printed is not homogeneous and likely contains oxides of MnSn, MnSn2 and Sn. There is still much that needs to be done within the LM touch printing field to fully understand the processes that take place within these systems. Oxide predictions should be expanded to account for the aforementioned variables, intermetallic formation in LM systems should be examined further, and the MnSn mixed oxides synthesised above should also be further characterised to identify their structure before piezoelectric devices are produced to confirm their use in the energy generation field as energy generation is a component of the more than Moore/diversification goal post toward keeping Moore’s Law alive.