Spectroscopic imaging- and micro-ellipsometry of MXene-based microelectronic devices

MXenes are two-dimensional (2D) nanomaterials whose optical, structural, and charge-transport properties can be finely tuned through composition and surface chemistry. MXetronics builds on this tunability to develop microscale electronic and photonic devices based on MXene thin films. Here, we demonstrate that imaging spectroscopic ellipsometry (ISE) and spectroscopic micro-ellipsometry (SME) provide two complementary, fully non-invasive optical approaches for characterization and process control of MXene-based comb-shaped backside electrodes used in photodetector and gas-sensing applications. SME enables sub-minute high-throughput probing of multiple representative sample sites, offering rapid assessment of fabrication quality. ISE delivers device-scale or micrometer-resolved imaging, allowing precise visualization of MXene film uniformity, structural integrity, composition, and transport-related properties throughout device processing. Leveraging SME's and ISE's high sensitivity toward these properties, we show that electrode regions altered during photoresist lithography are readily identified by their increased thickness, reduced conductivity, and distinct optical fingerprints, arising from tetramethylammonium hydroxide (TMAOH) intercalation into Ti₃C₂T_x. These results represent the comprehensive application of microscopic ellipsometry techniques to MXene microsystems, establishing a powerful metrology pathway for the rapidly growing fields of MXene 2D materials and MXetronics.