Abstract
Thermochromic undoped and metal (Ti and W)-doped
V
O
2
smart coatings were achieved on Kapton HN by reactive pulsed laser deposition. The optimization of the deposition was conducted with Si (100) substrates. The coatings were deposited at relatively low deposition temperatures (250, 300, and
350
°
C
), which are compatible with the characteristics of Kapton. The stoichiometry of the
V
O
2
-coated Kapton was confirmed by x-ray photoelectron spectroscopy analysis of the vanadium and oxygen bands. Moreover, the single phase
V
O
2
was confirmed by x-ray diffraction of
V
O
2
∕
Si
synthesized at
300
°
C
. Unlike
V
O
2
/Kapton, the
V
O
2
∕
Si
exhibited the well-known semiconductor-to-metallic transition, as shown by the temperature dependence of the infrared transmittance. This coating exhibited a similar transition temperature to that of
V
O
2
single crystal
(
≈
68
°
C
)
, but a small transmittance switching (about 7%) at
2.5
μ
m
. The temperature dependence of the electrical resistivity of all coatings on Kapton was investigated by means of the standard four-point probe technique. The resistivity decreased with increasing temperature. No abrupt semiconductor-to-metallic transition was observed either for undoped or for metal-doped
V
O
2
coatings. It was found that Ti and W dopants have an antagonistic effect on the resistivity. The resistivity was enhanced by the Ti dopant, whereas it was decreased for W-doped
V
O
2
coatings. These results show that the tunability of the resistivity can be tailored either by controlling the deposition temperature or by adjusting the concentration of Ti and W dopants. In addition, at room temperature a much higher temperature coefficient of resistance of
−
3.29
%
∕
°
C
was achieved in W(0.5%)-doped
V
O
2
/Kapton. Finally, these
V
O
2
smart coatings are promising materials for the IR sensing and sunshield applications.