THE SEMICONDUCTOR-METAL TRANSITION IN V
2
O
5
THIN FILMS DEPOSITED
BY RF MAGNETRON SPUTTEIRNG: THE INFLUENCE OF OXYGEN CONTENT
IN PHYSICAL PROPERTIES .
Dwight Acosta, Argelia Pérez, Carlos Magaña, Francisco Hernández,
Instituto de Física, Universidad Nacional Autónoma de México
A. P. 20 364, 01000, México D.F., MEXICO
Vanadium pentoxide (V
2
O
5
) thin films were deposited by RF magnetron sputtering with
two deposition conditions: with and without O
2
, atmosphere using a V
2
O
5
target .The thin
films deposition was carried out using a 5 cm diameter and 3 mm thick target 99.95% pure
vanadium pentoxide target (Goodfellow). The substrates were placed 50 mm in front of the
magnetron and not heating was applied during the deposition. Sputtering deposition was
carried out with a power of 100 W for 15 min, in a controlled Ar/O
2
atmosphere with an
oxygen concentration of 10%. The base pressure in the chamber was 10
-6
Torr and the
working pressure was 10
-3
Torr. The V
2
O
5
thin films were deposited simultaneously on
corning glass substrates with and without conductive layer of fluorine doped tin oxide (SnO2
:F or FTO), with a sheet resistance of 7 ohm/sq.The V
2
O
5
films thickness was determined
with optical perfilometry and runs from 360 to 400 nm
Different bits of the same sample were heated at a constant heating rate (from RT to
500
o
C in 100
o
C steps) and at atmospheric pressure in order to determine their
thermolectrical with a Jandel Multi Height Microposition probe equipment, using the four-
probe method. The optical measurements were carried out using an Agilent HP 8453 UV-
Vis spectrophotometer within the 300–1000 nm spectral range.. V
2
O
5
composition details
were derived from X-Rays Photoelectron Spectroscopy (XPS) and Energy Dispersive
Spectroscopy (EDS). XRD patterns reveal low crystallinity in all the cases. In HREM
micrographs nano crystallinity nature in V
2
O
5
grains was observed. SEM micrographs
obtained before and after voltammetry cycling reveal, V
2
O
5
films look regular and compact,
with an uniform grain size distribution. In SEM micrographs of films observed after cyclic
voltammetry experiments, were detected modifications in grains configuration and eroded
surface details that might be related with sample degradation and loss of electrochromic
activity as a consequence of mass and charge transport during the experiment.Noticeable
changes in resistivity as a function of temperature can be observed:For both type of
samples ( the ones deposited with an O
2
and those without an O
2
flow) the resistivity grows
linearly up to 200 ºC , then a sharp decrease up to 255 ºC is observed; after a soft increase
up to 300 ºC; ,the resistivity, again grows abruptly up to a 500 ºC. The change of resistivity
around the 255 ºC is related with the change of a semiconductor to metallic phase .The
electrochomic properties of our V
2
O
5
films were studied in an electrochemical cell with a
three electrodes configuration using the Cyclic Voltammetry (CV) method. The CV
experiments were performed in a potential range: E
0
= -2800mV to E
1
= potential 2800 mV
using platinum wire as reference electrode with a scanning rate of 1000 mV/s. Cycling runs,
were performed from 1, to 60 cycles respectively and the coloration and decoloration
processes at different rates, were observed for all the cases
PS1 10
-166-
