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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. 

2D native surface oxides formed on low melting temperature metals such as indium and gallium offer unique opportunities for fabricating high-performance flexible electronics and optoelectronics based on a new class of liquid metal printing (LMP). An inherent property of these Cabrera-Mott 2D oxides is their suboxide nature (e.g., In2O3−x), which leads high mobility LMP semiconductors to exhibit high electron concentrations (ne > 1019 cm−3) limiting electrostatic control. Binary alloying of the molten precursor can produce doped, ternary metal oxides such as In-X-O with enhanced electronic performance and greater bias-stress stability, though this approach demands a deeper understanding of the native oxides of alloys. This work presents an approach for hypoeutectic rapid LMP of crystalline InGaOx (IGO) at ultralow process temperatures (180 °C) beyond the state of the art to fabricate transistors with 10X steeper subthreshold slope and high mobility (≈18 cm2 Vs−1). Detailed characterization of IGO crystallinity, composition, and morphology, as well as measurements of its electronic density of states (DOS), show the impact of Ga-doping and reveal the limits of doping induced amorphization from hypoeutectic precursors. The ultralow process temperatures and compatibility with high-k Al2O3 dielectrics shown here indicate potential for 2D IGO to drive low-power flexible transparent electronics. 

Lithium-ion batteries have received significant research interest due to their advantages in energy and power density, which are important to enabling many devices. One route to further increase energy density is to fabricate thicker electrodes in the battery cell; however, careful consideration must be taken when designing electrodes as to how increasing the thickness impacts the multiscale and multiphase molecular transport processes, which can limit the overall battery operating power. Design of these electrodes necessitates probing the molecular processes when the battery cell undergoes electrochemical charge/discharge. One tool for in situ insights into the cell is neutron imaging, because neutron imaging can provide information of where electrochemical processes occur within the electrodes. In this manuscript, neutron imaging is applied to track the lithiation/delithiation processes within electrodes at different current densities for a full cell with a thick sintered Li 4 Ti 5 O 12 anode and LiCoO 2 cathode. The neutron imaging reveals that the molecular distribution of Li + during discharge within the electrode is sensitive to the current density, or equivalently discharge rate. An electrochemical model provides additional insights into the limiting processes occurring within the electrodes. In particular, the impact of tortuosity and molecular transport in the liquid phase within the interstitial regions in the electrodes are considered, and the influence of tortuosity was shown to be highly sensitive to the current density. Qualitatively, the experimental results suggest that the electrodes behave consistent with the packed hard sphere approximation of Bruggeman tortuosity scaling, which indicates that the electrodes are largely mechanically intact but also that a design that incorporates tunable tortuosity could improve the performance of these types of electrodes.