Optical and morphological properties of thermochromic V2O5 coatings

We present optical and morphological characterizations performed on thermochromic V2O5 coatings. V2O5 coatings were obtained by oxidation of as-deposited VOx films. Comparisons were made among coatings oxidized at various temperatures. Photographic evidence is also shown to provide the reader a clear visual description of the color change that occurs during thermochromic process. Detailed study and analysis regarding this data can be found in Kumar et al. (2017, in press) [1,2].


a b s t r a c t
We present optical and morphological characterizations performed on thermochromic V 2 O 5 coatings. V 2 O 5 coatings were obtained by oxidation of as-deposited VOx films. Comparisons were made among coatings oxidized at various temperatures. Photographic evidence is also shown to provide the reader a clear visual description of the color change that occurs during thermochromic process. Detailed study and analysis regarding this data can be found in Kumar et al. (2017, in press) [1,2].
& 2) The film thickness and roughness were measured using an Alpha step d-500 Profilometer from KLA-Tencor 3) Temperature was controlled by placing the sample on a custom made heating stage with a K type thermocouple for temperature measurement and regulation.

Data format
Treated and analyzed Experimental factors Silicon substrates have been cleaned in Ethanol and later cut into smaller pieces before annealing at different temperatures.

Experimental features
Very brief experimental description

Data source location
Belvaux, Luxembourg Data accessibility The data are available with this article

Value of the data
The data on visible thermochromic behavior of V 2 O 5 coatings provides other researchers an exhaustive view of various methods used to show the thermochromic behavior.
The data can be used by other researchers to compare and verify and improve further on the tunability of V 2 O 5 thermochromism.
This data will be helpful to the scientific community who wishes to use oxygen vacancy generation in metal oxides as a technique to change the optical properties The brightness of the coatings is defined as the total area under the curve over the full range of visible spectrum (400-800 nm). The curve plotted with brightness versus oxidation temperature shown in Fig. 2 has a bell curve profile with maximum at 450°C and a brightness of 50%.
Temperature-dependent optical spectra in the visible region are shown in Fig. 3 for coatings obtained by oxidation at (a) 350°C, and (b) 450°C and (c) 550°C respectively.
THR at specific wavelengths like 535 nm, 555 nm and 575 nm was compared among the films obtained by oxidation at 350°C, 450°C and 550°C in Fig. 4. Lastly Fig. 5 shows the photographic images of thermochromic V 2 O 5 coatings at both room temp and 300°C

Preparation of V 2 O 5 coatings
Thin films of vanadium oxide were deposited on silicon substrates by Direct Liquid Injection (DLI) Metal Organic Chemical Vapor Deposition (MOCVD), the details of which are reported elsewhere [1,2]. Argon was used as the carrier gas at a flow rate of 50 sccm while the chamber pressure was adjusted to 10 mbar. Substrates were maintained at a constant temperature of 500°C during the four hours of deposition.
After deposition, samples were allowed to cool till room temperature in argon atmosphere at low pressure before withdrawing from the chamber. Further handling of the samples was carried out under ambient atmosphere. Post deposition annealing was performed under ambient air at 300-580°C. The annealing time was adjusted to allow a complete oxidation from VOx to V 2 O 5 . While 10 min were sufficient for oxidation at 550°C, significantly longer times were required at lower temperatures; this can be explained by simple temperature dependent oxidation kinetics.
To isolate V 2 O 5 coatings form atmospheric gas phase interactions, Atomic layer deposition (ALD) of Al 2 O 3 was performed using the sequential introduction of Trimethylaluminium (TMA) and water. The pulse times for each reactant were adjusted to 40 ms with a 15 s purge in between each pulse. The rather large pulse and purge times were chosen to achieve complete conformal coverage over the film.

Film characterization
Total hemispherical reflection (THR) measurements were carried out on LAMBDA 1050 UV/Vis/ NIR spectrophotometer from Perkin Elmer with a 150 mm integration sphere in the reflection configuration. Measurements, which correspond to the sum of specular and diffuse reflections, were   performed in the visible spectral range (400-800 nm). Temperature-dependent measurements were carried out with the help of a custom made sample holder with an integrated heating element. Temperature control was achieved by a Horst HT 60 temperature controller coupled to a K-type thermocouple. The film thickness and roughness were measured using an Alpha step d-500 Profilometer from KLA-Tencor.