| Joseph Halim, Maria R. Lukatskaya, Kevin M. Cook, Jun Lu, Cole R. Smith, Lars-Åke Näslund, Steven J. May, Lars Hultman, Yury Gogotsi, Per Eklund, and Michel W. Barsoum
This study investigates the properties of transparent conductive two-dimensional titanium carbide epitaxial thin films. X-ray reflectometry (XRR) was used to determine the thickness of Ti3AlC2 films before and after etching, showing that the thickness increases with deposition time. XPS analysis was performed to determine the chemical composition and surface characteristics of Ti3AlC2, Ti3C2Tx, and Ti3C2Tx-IC films. The results indicate that the removal of Al leads to a shift in the Ti-C contribution in the XPS spectra toward higher binding energies, suggesting a loss of charge and charge redistribution within the material. The XPS analysis also revealed the presence of surface oxidation and contamination, such as TiO2, H2O, hydrocarbons, alcohols, carboxylates, and aluminum fluoride.
XRD analysis of the byproducts from etching Ti3AlC2 with NH4HF2 showed the presence of (NH4)3AlF6 and AlF3·3H2O, with (NH4)3AlF6 being the major byproduct. Intercalation and de-intercalation of Ti3C2Tx were studied, showing that intercalant compounds such as NH4+ are common to NH4HF2, NH4F, and NH4OH. The XRD patterns confirmed that the c lattice parameter increases with intercalation, and that de-intercalation is possible.
The resistivity of the films increased with etching time, and the etching time required to fully transform Ti3AlC2 to MXenes was determined by XRD analysis. The resistivity of the films was found to be a complex function of film thickness, etching time, and etchant nature. The study also showed that the films exhibit 2D electronic transport properties, with the charge carriers confined and weakly localized within individual Ti3C2Tx layers. The low-temperature resistivity data was consistent with the weak localization model, indicating a truly 2D behavior of the electronic transport properties of Ti3C2Tx.This study investigates the properties of transparent conductive two-dimensional titanium carbide epitaxial thin films. X-ray reflectometry (XRR) was used to determine the thickness of Ti3AlC2 films before and after etching, showing that the thickness increases with deposition time. XPS analysis was performed to determine the chemical composition and surface characteristics of Ti3AlC2, Ti3C2Tx, and Ti3C2Tx-IC films. The results indicate that the removal of Al leads to a shift in the Ti-C contribution in the XPS spectra toward higher binding energies, suggesting a loss of charge and charge redistribution within the material. The XPS analysis also revealed the presence of surface oxidation and contamination, such as TiO2, H2O, hydrocarbons, alcohols, carboxylates, and aluminum fluoride.
XRD analysis of the byproducts from etching Ti3AlC2 with NH4HF2 showed the presence of (NH4)3AlF6 and AlF3·3H2O, with (NH4)3AlF6 being the major byproduct. Intercalation and de-intercalation of Ti3C2Tx were studied, showing that intercalant compounds such as NH4+ are common to NH4HF2, NH4F, and NH4OH. The XRD patterns confirmed that the c lattice parameter increases with intercalation, and that de-intercalation is possible.
The resistivity of the films increased with etching time, and the etching time required to fully transform Ti3AlC2 to MXenes was determined by XRD analysis. The resistivity of the films was found to be a complex function of film thickness, etching time, and etchant nature. The study also showed that the films exhibit 2D electronic transport properties, with the charge carriers confined and weakly localized within individual Ti3C2Tx layers. The low-temperature resistivity data was consistent with the weak localization model, indicating a truly 2D behavior of the electronic transport properties of Ti3C2Tx.