Synthesis and Characterization of Large‐Area Nanometer‐Thin β‐Ga₂O₃ Films from Oxide Printing of Liquid Metal Gallium

Abstract

Herein, wafer‐scale Ga2O3 films are shown, which are synthesized by oxide printing of liquid metal Ga on SiO2/Si and sapphire substrates. This process enables highly uniform ≈2 nm‐thick films over ≫1 mm2 areas. The physical properties of these films (as‐deposited and after annealing in ambient conditions) are investigated. X‐ray photoelectron spectroscopy indicates that the as‐prepared films contain significant fractions (up to 8% wt) of Ga metal residue, which completely converts to Ga2O3 after annealing. Results from Raman spectroscopy confirm the presence of β‐phase in annealed samples. Transmission electron microscopy images indicate that the films are composed of polycrystalline domains. Photoluminescence is observed in all samples, depicting the typical spectrum of Ga2O3 with four emission bands. After annealing, the luminescence intensity increases across all samples, which is attributed to an enhancement in crystallinity. Also, the relative intensity of the blue emission decreases after annealing, which is consistent with a transition from bluish to greenish color in the films. This observation is associated with a change in defect population upon annealing. Overall, these results demonstrate that oxide printing of liquid metal gallium is a simple process that, upon annealing of the resulting films, leads to nanometer‐thin β‐Ga2O3 films over wafer‐scale areas.

Applications of liquid metals in nanotechnology

“…60,61 Other stamping, brushing, squeegeeing and high shear methods were devised for oxide skin collection from LM melts. [62][63][64][65][66][67][68] The ultra-smooth and reactive surface of LMs can also be used for templating 2D materials. In contrast to solid metals, LMs possess a dynamic electrical double layer (EDL).…”

Liquid Metals: A Novel Possibility of Fabricating 2D Metal Oxides

“…[ 68,74 ] This technique involves contacting the liquid metal droplet with a target substrate, as shown in Figure a. Various thin oxide sheets were obtained by utilizing the skin of liquid metals, such as Ga 2 O 3 , [ 69,70,75–77 ] Bi 2 O 3 , [ 57 ] SnO, [ 53,58 ] and SnO 2 . [ 53 ] They can be utilized for next‐generation power, radio‐frequency electronics, ultraviolet photodetectors, field‐effect transistors, ferroelectric field‐effect memory, and complementary metal‐oxide‐semiconductor transistor devices, respectively.…”

Liquid metals: an ideal platform for the synthesis of two-dimensional materials

“…3a). 40,44,69 However, one should always be aware of the potential for introducing undesired cracks into the synthesised 2D sheets, which has been observed in previous work. 40 Brushing, on the other hand, is carried out by placing the substrate with fully oxidised liquid metal on it facing down, followed by gently brushing on to another substrate.…”