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Abstract 2D metal oxides (2DMOs) have recently emerged as a high‐performance class of ultrathin, wide bandgap materials offering exceptional electrical and optical properties for a wide area of device applications in energy, sensing, and display technologies. Liquid metal printing represents a thermodynamically advantageous strategy for synthesizing 2DMOs by a solvent‐free and vacuum‐free scalable method. Here, recent progress in the field of liquid metal printed 2D oxides is reviewed, considering how the physics of Cabrera‐Mott oxidation gives this rapid, low‐temperature process advantages over alternatives such as sol‐gel and nanoparticle processing. The growth, composition, and crystallinity of a burgeoning set of 1–3 nm thick liquid metal printed semiconducting, conducting, and dielectric oxides are analyzed that are uniquely suited for the fabrication of high‐performance flexible electronics. The advantages and limitations of these strategies are considered, highlighting opportunities to amplify the impact of 2DMO through large‐area printing, the design of doped metal alloys, stacking of 2DMO to electrostatically engineer new oxide heterostructures, and implementation of 2D oxide devices for gas sensing, photodetection, and neuromorphic computing. 

We present a method of fabricating uniform, large area indium oxysulfide (InOxSy) films using a vacuum-free continuous liquid metal printing method (CLMP) and sulfurization process for high-performance multi-wavelength photodetection. CLMP enables rapid printing of wide area (>10 cm2/s) metal oxide films of single nm-scale thickness at process temperatures just above 150 °C, which can be partially converted to metal oxy-chalcogenide thin films at back-end-of line (BEOL) process temperatures. Phototransistors fabricated from 16 nm-thick InOxSy achieved responsivities as high as 280 A/W and respond to wavelengths as long as 630 nm, enabling both classification of multiple wavelengths and readout of intensity assisted by machine learning models. 

Transparent conductive oxides (TCOs) are a high-performance material system that could enable new wearable sensors and electronics, but traditional fabrication methods face scalability and performance challenges. In this work, we utilize liquid metal printing to produce ultrathin two-dimensional (2D) indium tin oxide (ITO) films with superior microstructural, optical, and electrical properties compared to conventional techniques. We investigate the dynamics of grain growth and its influence on conductivity and the optical properties of 2D ITO, demonstrating the tunability through annealing and multilayer deposition. Additionally, we develop Au-decorated transparent electrodes, showcasing their adhesion and flexibility, low contact impedance, and biocompatibility. Leveraging the transparency of these electrodes, we enable enhanced simultaneous multimodal biosignal acquisition by integrating biopotential-based methods, such as electrocardiogram (ECG) or bioimpedance sensing (e.g., impedance plethysmography, IPG), with optical modalities like photoplethysmography (PPG). This study establishes CLMP-fabricated flexible 2D TCOs as a versatile platform for advanced bioelectronic systems and multimodal diagnostics. 

Two-dimensional (2D) metal oxide semiconductors offer a superlative combination of high electron mobility and visible-range transparency uniquely suitable for flexible transparent electronics. Synthesis of these ultrathin (<3 nm) semiconductors by Cabrera-Mott oxidation of liquid metals could enable emerging device applications but requires the precise design of their electrostatics at the nanoscale. This study demonstrates sub-nanometer-level control over the thickness of semiconducting 2D antimony-doped indium oxide (AIO) by manipulating the kinetics of Cabrera-Mott oxidation through variable-speed liquid metal printing at plastic-compatible temperatures (175°C). By modulating both the growth kinetics and doping, we engineer the conductivity and crystallinity of AIO for integration in ultrathin channel transistors exhibiting exceptional steep turn-on, on-off ratios > 106 and an outstanding average mobility of 34.7 ± 12.9 cm2/Vs. This result shows the potential for kinetically controlling 2D oxide synthesis for various high-performance optoelectronic device applications. 

Abstract— In this study, we present continuous liquid metal printing (CLMP) to produce flexible and transparent indium tin oxide (ITO) layers compatible with plastic substrates with low glass transition temperatures. By leveraging the low melting point of an indium-tin (In-Sn) alloy, we achieve spontaneous two-dimensional (2D) oxide growth at low temperatures, following Cabrera-Mott (CM) oxidation kinetics. A robotically controlled roller deforms the molten alloys, depositing a thin native oxide (ITO) via van der Waals adhesion across large areas (approximately 1200 cm²) in mere seconds. The printed 2D ITO is highly crystalline with large plate-like grains with an average size of 55 nm. They demonstrate low resistivity (approximately 714 μΩ⋅cm) and transparency (>92% in visible light) with an optical bandgap of 3.71 eV. Mechanical testing reveals superior adhesion, 2X greater bendability, and 3X better scratch resistance of flexible 2D ITO. Finally, we demonstrate an application towards flexible transparent electrocardiogram electrodes based on flexible 2D ITO. 

We present a rapid liquid metal printing process (CLMP) enabling fabrication of high-mobility metal oxide semiconducting channels in less than 3 seconds. We use this process to engineer heterostructure TFTs with channels consisting of 3 nm layers of In2O3 and Ga2O3 with improved subthreshold slope and enhanced on-state performance (uave∼14cm2/Vs) . We report the influence of deposition temperature and speed, investigating crystallinity and grain morphology of this class of 2D oxide semiconductors.