TY - JOUR
T1 - Growth Process Conditions of Tungsten Oxide Thin Films Using Hot-Wire Chemical Vapor Deposition
AU - Houweling, Z.S.
AU - Geus, J.W.
AU - de Jong, M.
AU - Harks, P.P.R.M.L.
AU - van der Werf, C.H.M.
AU - Schropp, R.E.I.
PY - 2011
Y1 - 2011
N2 - We report the growth conditions of nanostructured tungsten oxide (WO3−x) thin films using hot-wire
chemical vapor deposition (HWCVD). Two tungsten filaments were resistively heated to various temperatures
and exposed to an air flow at various subatmospheric pressures. The oxygen partial pressure was
varied from 6.0×10−6 to 1.0 mbar and the current through the filaments was varied from 4.0 to 9.0 A,
which constitutes a filament temperature of 1390–2340 ◦C in vacuum.
It is observed that the deposition rate of the films is predominantly determined by the oxygen partial
pressure; it changes from about 1 to about 36,000nmmin−1 in the investigated range. Regardless of the
oxygen partial pressure and filament temperature used, thin films with a nanogranular morphology are
obtained, provided that the depositions last for 30 min or shorter. The films consist either of amorphous or
partially crystallized WO3−x with high averaged transparencies of over 70% and an indirect optical band
gap of 3.3±0.1 eV. A prolonged deposition time entails an extended exposure of the films to thermal
radiation from the filaments, which causes crystallization to monoclinic WO3 with diffraction maxima
due to the (0 0 2), (2 0 0) and (0 2 0) crystallographic planes, furthermore the nanograins sinter and the
films exhibit a cone-shaped growth.
By simultaneously influencing the surface mobility, by heating the substrates to Tsurface = 700±100 ◦C,
and the deposition rate, a very good control of the morphology of the deposited films is obtained.
Nanowire films, nanocrystallite films and closed crystallite films were thus deposited. These differently
nanostructured c-WO3 films all possess an indirect optical band gap of 2.5±0.1 eV.
AB - We report the growth conditions of nanostructured tungsten oxide (WO3−x) thin films using hot-wire
chemical vapor deposition (HWCVD). Two tungsten filaments were resistively heated to various temperatures
and exposed to an air flow at various subatmospheric pressures. The oxygen partial pressure was
varied from 6.0×10−6 to 1.0 mbar and the current through the filaments was varied from 4.0 to 9.0 A,
which constitutes a filament temperature of 1390–2340 ◦C in vacuum.
It is observed that the deposition rate of the films is predominantly determined by the oxygen partial
pressure; it changes from about 1 to about 36,000nmmin−1 in the investigated range. Regardless of the
oxygen partial pressure and filament temperature used, thin films with a nanogranular morphology are
obtained, provided that the depositions last for 30 min or shorter. The films consist either of amorphous or
partially crystallized WO3−x with high averaged transparencies of over 70% and an indirect optical band
gap of 3.3±0.1 eV. A prolonged deposition time entails an extended exposure of the films to thermal
radiation from the filaments, which causes crystallization to monoclinic WO3 with diffraction maxima
due to the (0 0 2), (2 0 0) and (0 2 0) crystallographic planes, furthermore the nanograins sinter and the
films exhibit a cone-shaped growth.
By simultaneously influencing the surface mobility, by heating the substrates to Tsurface = 700±100 ◦C,
and the deposition rate, a very good control of the morphology of the deposited films is obtained.
Nanowire films, nanocrystallite films and closed crystallite films were thus deposited. These differently
nanostructured c-WO3 films all possess an indirect optical band gap of 2.5±0.1 eV.
U2 - 10.1016/j.matchemphys.2011.09.059
DO - 10.1016/j.matchemphys.2011.09.059
M3 - Article
SN - 0254-0584
VL - 131
SP - 375
EP - 386
JO - Materials Chemistry and Physics
JF - Materials Chemistry and Physics
ER -