The temperature cycling mode was used to
measure ozone, and the low power sensor was
shown to be stable. The reproducibility was
greatly improved when compared to standard
constant voltage operation. Furthermore, crosssensitivity could be reduced by simple adaptations. The study also showed disadvantages by
using temperature modulation in one-minute
Low-Cost Sensors for Indoor and Outdoor Pollution, Table 3 Compounds used as sensors and their corresponding
bandgaps, and the gases they sense
Sensor
Specific
compound Sensing [53]
z/eV
Tin oxides (35%)
SnO 2
NH 3 , CH 3 CHO, CH 3 SH, H 2 S, NO 2 , C 2 H 5 OH, CO 2 ,
CO, benzene, o-xylene, SO 2 , O 2 , H 2 , H 2 O, C 4 H 10 , CO
and NO 2 , NO x , petrol, CH 4 , O 3 , C 3 H 8
3.6 [58]
Mixed oxides (13%)
–
Humidity, CO 2 , NO x , hydrocarbons, C 2 H 5 OH, NH 3 ,
NO, O 3 , NO 2 , SO 2 , CH 4 , LPG (liquefied petroleum
gas), H 2 S
–
Zinc oxides (10%)
ZnO
O 2 (in water), CO, CH 4 , H 2 , H 2 O, C 2 H 5 OH, C 3 H 8 ,
NO, NO 2 , CO 2 , O 3 , C 2 H 6 , n-C 4 H 10
3.3 [59]
Titanium oxides (7%)
TiO 2
H 2 , CO 2 , O 2 , CO, CH 4 , ethanol, methanol, propanol
3.0–3.2 [60]
Tungsten oxides (7%)
WO 3
H 2 S, O 3 , NO, NO 2 , NO x , NH 3
2.6–3.0 [61]
Indium oxides (5%)
In 2 O 3
O 3 , H 2 , CO, C 3 H 8 , NO 2
2.7 [62]
Niobium oxides (3%)
Nb 2 O 5
NH 3 , CO, C 2 H 5 OH
3.4 [63]
Iron oxides (3%)
Fe 2 O 3
H 2 , CO 2 , O 2 , CO, CH 4
2.2 [64]
Gallium oxides (3%)
b-Ga 2 O 3
O 2
4.8–4.9 [65]
Cerium oxides (2%)
CeO 2
O 2
3.2 [66]
Molybdenum oxides (2%) MoO 3
NH 3 , NO 2
3.2 [53]
Copper oxides (2%)
CuO 2
H 2 , CO 2 , O 2 , CO, ethanol
1.4 [53]
Aluminum oxides (2%)
Al 2 O 3
Humidity
am-Al 2 O 3 : 7.0
[67], g-Al 2 O 3 :
7.6 [67]
Zirconium oxides (2%)
ZrO 2
O 2 , hydrocarbons, NO x , CO, O 2 , alcohol
3.84–4.51 [68]
Energy
CBM
VBM
CuO 2
In 2 O 3
SnO 2
ZnO
Energy
Donor band
Acceptor band
A
B
Low-Cost Sensors for Indoor and Outdoor Pollution,
Fig. 7 The figure to left [1] displays two bands: one that
accepts electrons from the valence band (p-type semiconductor (A)) and one that transfers electrons to the
conduction band (n-type semiconductor (B)). The figure
to the right [58] shows the band gaps of four different metal
oxides
Low-Cost Sensors for Indoor and Outdoor Pollution
435
measure ozone, and the low power sensor was
shown to be stable. The reproducibility was
greatly improved when compared to standard
constant voltage operation. Furthermore, crosssensitivity could be reduced by simple adaptations. The study also showed disadvantages by
using temperature modulation in one-minute
Low-Cost Sensors for Indoor and Outdoor Pollution, Table 3 Compounds used as sensors and their corresponding
bandgaps, and the gases they sense
Sensor
Specific
compound Sensing [53]
z/eV
Tin oxides (35%)
SnO 2
NH 3 , CH 3 CHO, CH 3 SH, H 2 S, NO 2 , C 2 H 5 OH, CO 2 ,
CO, benzene, o-xylene, SO 2 , O 2 , H 2 , H 2 O, C 4 H 10 , CO
and NO 2 , NO x , petrol, CH 4 , O 3 , C 3 H 8
3.6 [58]
Mixed oxides (13%)
–
Humidity, CO 2 , NO x , hydrocarbons, C 2 H 5 OH, NH 3 ,
NO, O 3 , NO 2 , SO 2 , CH 4 , LPG (liquefied petroleum
gas), H 2 S
–
Zinc oxides (10%)
ZnO
O 2 (in water), CO, CH 4 , H 2 , H 2 O, C 2 H 5 OH, C 3 H 8 ,
NO, NO 2 , CO 2 , O 3 , C 2 H 6 , n-C 4 H 10
3.3 [59]
Titanium oxides (7%)
TiO 2
H 2 , CO 2 , O 2 , CO, CH 4 , ethanol, methanol, propanol
3.0–3.2 [60]
Tungsten oxides (7%)
WO 3
H 2 S, O 3 , NO, NO 2 , NO x , NH 3
2.6–3.0 [61]
Indium oxides (5%)
In 2 O 3
O 3 , H 2 , CO, C 3 H 8 , NO 2
2.7 [62]
Niobium oxides (3%)
Nb 2 O 5
NH 3 , CO, C 2 H 5 OH
3.4 [63]
Iron oxides (3%)
Fe 2 O 3
H 2 , CO 2 , O 2 , CO, CH 4
2.2 [64]
Gallium oxides (3%)
b-Ga 2 O 3
O 2
4.8–4.9 [65]
Cerium oxides (2%)
CeO 2
O 2
3.2 [66]
Molybdenum oxides (2%) MoO 3
NH 3 , NO 2
3.2 [53]
Copper oxides (2%)
CuO 2
H 2 , CO 2 , O 2 , CO, ethanol
1.4 [53]
Aluminum oxides (2%)
Al 2 O 3
Humidity
am-Al 2 O 3 : 7.0
[67], g-Al 2 O 3 :
7.6 [67]
Zirconium oxides (2%)
ZrO 2
O 2 , hydrocarbons, NO x , CO, O 2 , alcohol
3.84–4.51 [68]
Energy
CBM
VBM
CuO 2
In 2 O 3
SnO 2
ZnO
Energy
Donor band
Acceptor band
A
B
Low-Cost Sensors for Indoor and Outdoor Pollution,
Fig. 7 The figure to left [1] displays two bands: one that
accepts electrons from the valence band (p-type semiconductor (A)) and one that transfers electrons to the
conduction band (n-type semiconductor (B)). The figure
to the right [58] shows the band gaps of four different metal
oxides
Low-Cost Sensors for Indoor and Outdoor Pollution
435