Growth, Properties, and Applications of Pulsed Laser Deposited Nanolaminate Ti3AlC2 Thin Films

Recently, nanolaminated ternary carbides have attracted immense interest due to the concomitant presence of both ceramic and metallic properties. Here, we grow nanolaminate ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}$ thin films by pulsed laser deposition on c-axis-oriented sapphire substrates and, surprisingly, the films are found to be highly oriented along the (103) axis normal to the film plane, rather than the (000l) orientation. Multiple characterization techniques are employed to explore the structural and chemical quality of these films, the electrical and optical properties, and the device functionalities. The 80-nm thick ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}$ film is highly conducting at room temperature, with a resistivity of about 50 \textmu{}\ensuremath{\Omega} cm and a very-low-temperature coefficient of resistivity. The ultrathin (2 nm) ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}$ film has fairly good optical transparency (\ensuremath{\sim}70%) and high conductivity (sheet resistance \ensuremath{\sim}735 \ensuremath{\Omega}/sq) at room temperature. Scanning tunneling microscopy reveals the metallic characteristics (finite density of states at the Fermi level) at room temperature. The metal-semiconductor junction of the p-type ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}$ film and n-$\mathrm{Si}$ show the expected rectification (diode) characteristics, in contrast to the ohmic contact behavior in the case of ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}/$p-$\mathrm{Si}$. A triboelectric-nanogenerator-based touch-sensing device, comprising of the ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}$ film, shows a very impressive peak-to-peak open-circuit output voltage (\ensuremath{\sim}80 V). These observations reveal that pulsed laser deposited ${\mathrm{Ti}}_{3}{\mathrm{Al}\mathrm{C}}_{2}$ thin films have excellent potential for applications in multiple domains, such as bottom electrodes, resistors for high-precision measurements, Schottky diodes, ohmic contacts, fairly transparent ultrathin conductors, and next-generation biomechanical touch sensors for energy harvesting.