Harnessing the Power of Defect Engineering: Unveiling Oxygen Vacancies in 2D Indium Oxide for Advanced Memory Regions and Pioneering 2D Materials Discovery

The rapid progress in the field of two-dimensional (2D) materials has revolutionized various industries and paved the way for exciting advancements in technology. These materials, with their unique properties and atomic-level thickness, hold immense potential for applications in electronics, optoelectronics, and beyond. To harness the full capabilities of 2D materials, it is crucial to develop effective fabrication techniques that enable their synthesis and manipulation. Among the range of techniques available for the fabrication of 2D materials, liquid metal printing (LMP) has emerged as an innovative approach. This method allows for fast, low-temperature, low-cost, and high-quality exfoliation of metal oxides with atomic-level precision.<br/>One particular 2D material that has attracted significant attention is indium oxide (InO_x). InO_x is a wide bandgap material with remarkable structural stability and tunable electronic properties, making it highly desirable for applications in metal oxide semiconductors. However, the exploration of InO_x in 2D forms remains uncharted territory, presenting a compelling avenue for further development. In the realm of nanoscale memristive devices, the engineering of defects plays a critical role in tailoring the electronic performance. Conducting filaments in insulating oxides, which are essential for memristive behavior, rely on the field-induced migration of oxygen vacancies within the material[1]. Recent studies by Huang et al. shed light on the influence of printing temperatures on the electrical properties of 2D-InO_x. By altering the printing temperatures, they observed variations in the concentration of oxygen vacancies, leading to the presence or disappearance of memristive switching[2].<br/>Building upon this prior research, the present study aims to investigate the defect characteristics of 2D-InO_x in more detail. To achieve this, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were employed. The results revealed that higher printing temperatures led to an increase in the concentration of oxygen vacancies, suggesting that the defect characteristics can be tailored through precise control of the fabrication process. Additionally, the microstructure and crystallinity of 2D-InO_x were analyzed using transmission electron microscopy (TEM) and selected area diffraction patterns (SADP). To gain further insight into the atomic arrangement and defect structures of 2D-InO_x, spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and electron energy loss spectroscopy (EELS) were employed. STEM provides high-resolution images with atomic-level details, enabling the visualization and analysis of crystallographic features, grain boundaries, and defect structures. EELS measurements, on the other hand, offer information about the electronic properties and local chemical environment of the material. Notably, an observable shift in the In-M_4,5 and O-K peaks indicated a preferential segregation of oxygen vacancies at grain boundaries. Peak ratio calculations based on the EELS spectra also provided quantitative information about the defect concentration in 2D-InO_x. Surprisingly, the results suggested a higher defect concentration in 2D-InO_x printed at lower temperatures. The deeper insights gained from this study into the exact nature of oxygen defects and the ability to modify the concentration of oxygen vacancies in atomically-thin oxide films are of great significance. By tailoring defects, researchers can unlock the full potential of 2D-InO_x and pave the way for next-generation memory devices with enhanced performance, energy efficiency, and functional capabilities.<br/><br/><b>References</b>:<br/>1. Waser, R. and M. Aono, <i>Nanoionics-based resistive switching memories.</i> Nature materials, 2007. <b>6</b>(11): p. 833-840.<br/>2. Huang, C.-H., et al., <i>Multiple-State Nonvolatile Memory Based on Ultrathin Indium Oxide Film via Liquid Metal Printing.</i> ACS Applied Materials & Interfaces, 2023.