While the Tc of VO2 is convenient for many applications, it is desirable to modify the Tc to other values for either new applications or improved performance in the previously stated applications. The Tc of VO2 is known to be strain-mediated. Strain in VO2 has been induced via deposition of thin films onto lattice mismatched epitaxial substrates, as well as by doping with other transition metal elements besides vandium., 
For the first time, we are investigating digital doping of ALD VO2 using other elements such as Al, Ti, Nb, and W by incorporation of their oxides into the binary ALD VO2 process (TEMAV + O3). We will discuss the fundamentals and limitations of doped ALD VO2 growth and basic materials characterization, and will demonstrate the impact of dopant concentration and identity on the optical and electrical phase transition properties of the resulting films.
Generally, inclusion of dopants such as Ti and Al into the ALD VO2 process in amounts between 1% and 10% results in surfactant-like film growth behavior, with increasing dopant concentrations reducing RMS roughness of the ALD films from ~2 nm to ~0.2 nm. Higher concentrations of dopants also interfere with film crystallization during annealing, inhibiting the magnitude of the metal-insulator transition. Smaller concentrations of dopants, between 1% and 3%, can lower the Tc of the VO2 films while maintaining acceptable optical behavior, depending on dopant identity and concentration. In particular, we find that Nb doping at these low concentrations decreases Tc of VO2 by -13.5˚C/Nb%.
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