Continuous Liquid Metal Printed 2D Transparent Conductive Oxide Superlattices

Abstract

2D conducting metal oxides offer unprecedented control of thin film electrostatics at the nanoscale. A scalable, rapid, and low‐cost approach is presented to printing transparent conductive oxides (TCOs) via spontaneous low‐temperature Cabrera‐Mott oxidation of compliant liquid metals. Repeating heterostructures of these 2D oxide layers are exploited to produce an exceptional, 100× increase in conductivity while simultaneously raising the visible range optical transmittance. This innovative approach employs defect modulation doping at the type I heterojunction between InOx/GaOx, exceeding the achievable performance with ITO, which is otherwise limited by poor dopant activation at low temperatures. The exceptional performance of these multilayer 2D TCO superlattices exceeds that of competing TCOs printed from sol‐gels and nanoparticles, establishing a 100× faster process to fabricate flexible inorganic electronics.

Heterojunction Transistors Printed via Instantaneous Oxidation of Liquid Metals

“…15,16,18,24−26 In our recent work (Ye et al), we applied this effect to increase carrier concentration (>10 20 cm −3 ) and conductivity (>600 S/cm) through the fabrication of a layered InO x /GaO x superlattice using continuous liquid metal printing (CLMP). 18 However, the electrostatic control offered by these heterointerfaces can also be utilized for improving InO x TFT performance through enhancement of the free carrier concentration, as shown previously for InO x /ZnO x heterojunctions. 15,24 A remaining challenge for heterostructure TFTs is capturing the advantages of higher mobility while controlling the turn on (V on ) voltage toward the goal of enhancement mode operation.…”

“…23−25 Heterostructure channels integrating layers with dissimilar work functions can also result in band bending due to Fermi level pinning at the heterointerface. 24 This phenomenon, referred to as modulation doping, 18,24,26 has been utilized to increase the carrier concentration in heterojunctions between InO x , SnO x , ZnO x , AlO x , and GaO x . 15,16,18,24−26 In our recent work (Ye et al), we applied this effect to increase carrier concentration (>10 20 cm −3 ) and conductivity (>600 S/cm) through the fabrication of a layered InO x /GaO x superlattice using continuous liquid metal printing (CLMP).…”

“…14,17 Liquid metal printing is an emerging vacuumfree, solvent-free, scalable method that offers the ability to deposit crystalline films in-air at low temperatures (<200 °C). 10,11,18 This method operates based on Cabrera-Mott oxidation, which is responsible for the formation of an oxide skin on the surface of liquid metal, which can readily be adhered to a target substrate via van der Waals adhesive forces. 11 Previously, we printed large area, two-dimensional (2D) nanosheets that can be rapidly fabricated via continuous rolling deposition, making this approach a breakthrough in the scalable production of metal oxide semiconductors.…”

“…11 Previously, we printed large area, two-dimensional (2D) nanosheets that can be rapidly fabricated via continuous rolling deposition, making this approach a breakthrough in the scalable production of metal oxide semiconductors. 18 inverters, amplifiers, dielectrics, and touch capacitive sensors. 4,11,13,18−22 Recent reports of ultrathin channel TFTs demonstrate the importance of the passivation of the backchannel for achieving high mobility and good operational stability.…”

CO2 reduction on the Li–Ga liquid metal surface

“…9 Liquid metals offer unique bulk chemistry and interfacial properties due to the adjustable composition achieved by selective alloying, hence providing a high degree of interfacial physicochemical tunability. 10 In addition, liquid metals have more accessible delocalized metal atoms and electrons for catalysis and chemical reactions than their solid counterparts. [11][12][13][14][15][16] Therefore, using metals in their liquid state, enables efficient liquid interface reactions, which provides tremendous opportunities in chemical synthesis.…”