This section of the article provides detailed supporting information on the preparation, characterization, and properties of transparent conductive two-dimensional titanium carbide (Ti3AlC2) epitaxial thin films. Key points include: 1. **X-ray Reflectometry (XRR) and Thickness Determination**: The thickness of Ti3AlC2 films was determined using XRR before and after etching. For films deposited for 5 and 10 minutes, the thicknesses were 15.2 ± 0.5 nm and 27.7 ± 0.8 nm, respectively. For films deposited for 30 minutes, the thickness was measured directly in TEM. 2. **X-ray Photoelectron Spectroscopy (XPS) Analysis**: High-resolution XPS spectra were analyzed to determine the chemical composition and surface functional groups of Ti3AlC2, Ti3C2Tx, and Ti3C2Tx-IC films. The results showed shifts in binding energies due to charge redistribution and the presence of various functional groups like Ti-C, Ti(II) oxide, Ti(III) oxide, Ti(IV) oxide, Ti-F, and surface oxidation products. 3. **X-ray Diffraction (XRD) Analysis**: XRD patterns of Ti3AlC2 films etched with NH4HF2 revealed the formation of byproducts (NH4)3AlF6 and AlF3. The major byproduct was (NH4)3AlF6. 4. **Intercalation and De-intercalation of Ti3C2Tx**: The intercalation process was confirmed by XRD patterns, showing an increase in c-axis length. De-intercalation was also demonstrated by heating a Ti3C2Tx-IC film in a vacuum at 250 °C, leading to a decrease in c-axis length. 5. **Optimization of Etching Process**: The resistivities of Ti3C2Tx films increased with etching time. The optimal etching time varied depending on the film thickness, with thinner films requiring longer etching times. 6. **Energy-Dispersive X-ray Spectroscopy (EDX) Mapping**: EDX mapping showed the distribution of C, Ti, F, and O atoms in Ti3C2Tx, with fluorine concentrated between Ti-C layers. 7. **Morphologies of Ti3AlC2 and Ti3C2Tx Films**: TEM images revealed the morphology of Ti3AlC2 and Ti3C2Tx films, including the presence of tilted grains and defects. 8. **Comparison with Other Transparent Conductive Materials**: The transmittance and sheet resistance of Ti3C2Tx were compared with other transparent conductors, showing its competitive performance. 9. **Electrical Transport Measurements**: The low-temperature resistivity data for Ti3C2Tx films were fitted to various models, with the weak localization model providing theThis section of the article provides detailed supporting information on the preparation, characterization, and properties of transparent conductive two-dimensional titanium carbide (Ti3AlC2) epitaxial thin films. Key points include: 1. **X-ray Reflectometry (XRR) and Thickness Determination**: The thickness of Ti3AlC2 films was determined using XRR before and after etching. For films deposited for 5 and 10 minutes, the thicknesses were 15.2 ± 0.5 nm and 27.7 ± 0.8 nm, respectively. For films deposited for 30 minutes, the thickness was measured directly in TEM. 2. **X-ray Photoelectron Spectroscopy (XPS) Analysis**: High-resolution XPS spectra were analyzed to determine the chemical composition and surface functional groups of Ti3AlC2, Ti3C2Tx, and Ti3C2Tx-IC films. The results showed shifts in binding energies due to charge redistribution and the presence of various functional groups like Ti-C, Ti(II) oxide, Ti(III) oxide, Ti(IV) oxide, Ti-F, and surface oxidation products. 3. **X-ray Diffraction (XRD) Analysis**: XRD patterns of Ti3AlC2 films etched with NH4HF2 revealed the formation of byproducts (NH4)3AlF6 and AlF3. The major byproduct was (NH4)3AlF6. 4. **Intercalation and De-intercalation of Ti3C2Tx**: The intercalation process was confirmed by XRD patterns, showing an increase in c-axis length. De-intercalation was also demonstrated by heating a Ti3C2Tx-IC film in a vacuum at 250 °C, leading to a decrease in c-axis length. 5. **Optimization of Etching Process**: The resistivities of Ti3C2Tx films increased with etching time. The optimal etching time varied depending on the film thickness, with thinner films requiring longer etching times. 6. **Energy-Dispersive X-ray Spectroscopy (EDX) Mapping**: EDX mapping showed the distribution of C, Ti, F, and O atoms in Ti3C2Tx, with fluorine concentrated between Ti-C layers. 7. **Morphologies of Ti3AlC2 and Ti3C2Tx Films**: TEM images revealed the morphology of Ti3AlC2 and Ti3C2Tx films, including the presence of tilted grains and defects. 8. **Comparison with Other Transparent Conductive Materials**: The transmittance and sheet resistance of Ti3C2Tx were compared with other transparent conductors, showing its competitive performance. 9. **Electrical Transport Measurements**: The low-temperature resistivity data for Ti3C2Tx films were fitted to various models, with the weak localization model providing the