【International Papers】High Shear Thin Film Synthesis of Partially Oxidized Gallium and Indium Composite 2D Sheets

      A paper titled High Paper Thin Film Synthesis of Partially Oxidized Gallium and Indian Composite 2D Sheets published by research teams such as Flinders University in Australia in the scientific journal Wiley Online Library.

Abstract

      Reducing resistance in silicon-based devices is important as they get miniaturized further. 2D materials offer an opportunity to increase conductivity whilst reducing size. A scalable, environmentally benign method is developed for preparing partially oxidized gallium/indium sheets down to 10 nm thick from a eutectic melt of the two metals. Exfoliation of the planar/corrugated oxide skin of the melt is achieved using the vortex fluidic device with a variation in composition across the sheets determined using Auger spectroscopy. From an application perspective, the oxidized gallium indium sheets reduce the contact resistance between metals such as platinum and silicon (Si) as a semiconductor. Current‒voltage measurements between a platinum atomic force microscopy tip and a Si−H substrate show that the current switches from being a rectifier to a highly conducting ohmic contact. These characteristics offer new opportunities for controlling Si surface properties at the nanoscale and enable the integration of new materials with Si platforms.

FIG 1.a) High shear topological fluid flows in thin films of n-propanol in the VFD; spinning top flow generated by the Coriolis force form the hemispherical base of the tube, and double helical flow generated by the eddies from the Faraday waves moving across the thin film, being twisted as such by the Coriolis force from the curved tube; the onset of the formation of the spinning top is associated with a sudden decrease in mixing time, and a slight increase as the Faraday waves form, as represented in (b) which represents the signature of n-propanol in a hemispherical tube for θ 45^o; mixing time is the time for a drop of dye in n-propanol added to the base of the tube to mix halfway up the tube. c) Proposed mechanism of exfoliation. 1. Low pressure zone from the spinning top fluid flow above the eutectic melt which is held against the quartz tube by the centrifugal force. 2. Initial peeling of the gallium oxide layer, due to lateral forces over the surface of the melt and upward lifting and twisting from the low-pressure zone at the center of the spinning top flow. 3. Oxidation of the metal alloy surfaces exposed to n-propanol. 4. Resulting layered sheet structure with indium rich layer above the eutectic melt sandwiched between two layers of gallium oxide.

FIG 2.a) SEM images of exfoliated material. b) AFM image of corrugated 2D sheets formed from a eutectic melt of 85.8% Ga and 14.2% In in the VFD housing a 20 mm O.D (17.5 mm I.D.) diameter quartz tube 18.5 cm in length, θ 45°, ω 7000 rpm. c) AFM height image of the 2D sheet in (b). d) Raman spectra of the In/Ga eutectic melt (— red), and a VFD exfoliated sheet (— blue). e) Optical image of the In/Ga sheet for Raman spectrum recorded in (d).

FIG 3.Auger depth profile graphs, and corresponding SEM of a 2D sheet formed in the VFD according to Figure 1. a–d) Auger depth profiles for locations 1, 2, 3, and 4 in the SEM image, e), with location 4 being on the silicon wafer, the other locations being on the 2D sheet. f) HAADF (High-angle Annular Dark Field) STEM analysis of the eutectic indium gallium derived sheet with the corresponding EDS in g) of a Ga/In sheet outlining the composition of gallium (blue) and indium (red).

Paper Link：https://doi.org/10.1002/smll.202300577