Santiago-Santos, Juan A.

Profile Picture

Filters

20151
Reset filters

Settings

Citations

Publication Search Results

Now showing 1 - 1 of 1
  • Thumbnail Image
    Publication
    Fabrication and characterization of VO2 thin films using pulsed DC magnetron sputtering
    (2015) Santiago-Santos, Juan A.; Fernández, Félix E.; College of Arts and Sciences - Sciences; Marrero, Pablo; Lysenko, Sergiy; Department of Physics; Palomera, Rogelio
    Vanadium dioxide (VO2) is one of the many oxide phases of vanadium, which exhibits a semiconducting monoclinic stable phase up to 68°C. At temperatures over ~68°C the stable phase for VO2 is tetragonal and exhibits metallic conduction. Accompanying the abrupt and reversible phase change, the electrical resistivity and infrared transmittance changes substantially. Physical vapor deposition of VO2 thin films is often performed successfully by Pulsed Laser Deposition (PLD), but this technique is not easily scaled up for large substrate areas. Sputtering can offer an alternate route which is easily scalable up to arbitrary size, but presents a challenge due to the technical difficulties that arise when depositing dielectric materials and, in the particular case of VO2 requires very good control of film oxidation. Pulsed-DC reactive sputtering can solve the question of efficiently depositing uniform films of poorly conducting materials, but so far conditions have not been achieved to produce VO2 films with electrical and optical response comparable to those obtained from PLD. The present work further investigated adequate parameters for VO2 deposition via Pulsed-DC reactive sputtering. We were able to successfully deposit monoclinic VO2 on glass at relatively low temperatures of ~400°C with a partial oxygen pressure of 0.5mTorr, but initial results were not easily reproducible, apparently because of the need to control the oxygen pressure very accurately. The results were improved by implementing post-deposition annealing methods. For measuring the electrical and optical changes of the films as a function of temperature, a software application was developed using the LabVIEW platform. The software allowed for automatic data acquisition while the system took repeatable and accurate measurements. Electrical resistance characterization showed changes as high as three orders of magnitude with sharp hysteresis ~11°C wide. The optical transmittance in the infrared range also exhibited abrupt reductions of 36% during phase transition with similar hysteresis. Structural characterization by x-ray diffraction (XRD) showed that both, annealed and non-annealed samples exhibited the presence of monoclinic VO2 with a high preference for alignment along the (100) plane. Estimates for grain size were also obtained from XRD and showed a slight reduction in grain size perpendicular to the (100) plane as the annealing time was increased. Further analysis was done on the samples with Atomic Force Microscopy techniques which revealed lateral grain sizes of 110 nm for samples annealed during 20 minutes and an increase to 300 nm for samples annealed for 45 minutes.