Supplementary Material
Conductive SnO2:Sb Nanobelts as Electrodes for Detection of
NO2 in ppb Level with Ultrahigh Sensitivity
Bin Cai, Xiaoli Zhao, Tengfei Pei, Ermes Toninelli, Qingxin Tanga), Yanhong Tonga), and Yichun
Liu
Key Laboratory of UV Light Emitting Materials and Technology under Ministry of Education,
Northeast Normal University, Changchun 130024, P. R. China
*Corresponding author E-mail: (Q. X. Tang) tangqx@nenu.edu.cn;
(Y. H. Tong) tongyh@nenu.edu.cn
Table S1: Performance list for the reported metal oxide sensors for detection of NO2 at the ppb
level.
Figure S1: SEM images of SnO2 and SnO2:Sb nanobelts.
Figure S2: Fabrication process of SnO2 nanobelt FET device with SnO2:Sb nanobelt electrodes.
Figure S3: The electrical characteristics of the SnO2(NBE) device.
Figure S4: Stability of the SnO2(NBE) device.
Figure S5: Schematic representation of the experimental system for gas sensing.
Figure S6: Performance of MiCS-2714 to NO2.
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1. Table S1: Performance list for the reported metal oxide sensors for detection of NO2 in ppb
level:
material
principle
operating
temperature (℃)
LOD
(ppb)
sensitivity
at LOD
dimension
（nm）
ref
SnO2
multi-nanowires
Resistance
400
500
1650%(a)
-1550%(b)
200
1
SnO2 networked
nanowires
Resistance
200
500
1800%(a)
80-100
2
InGaZnO4 networked
nanotubes
Resistance
300
400
1680%(a)
50-200
3
WO3 film
Resistance
125
100
9200%(a)
-
4
SnO2 networked
nanowires
Resistance
200
100
1900%(a)
80-100
5
ZnO networked
nanowires
Resistance
190
58
3000%(a)
1000-2000
6
B doped CNTs/
SnO2 film
Resistance
Room
Temperature
50
159%(a)
59%(b)
-
7
ZnO networked
nanowires
Resistance
210
30
158%(a)
140-210
8
ZnO film
Resistance
300
20
110%(a)
-
9
In2O3 film
Resistance
Room
Temperature
20
120%(a)
20%(c)
-
10
Single In2O3
nanowire
FET
Room
Temperature
20
125%(a)
25%(c)
10
11
In2O3 networked
nanowires
Resistance
Room
Temperature
5
120%(a)
20%(c)
10
11
Si networked
nanowires
Resistance
Room
Temperature
10
100.02%(a)
0.02%(c)
100-200
12
Note: a:S=Pg/Pa×100%; b:S= (Pa-Pg)/Pg×100%,c:S=(Pg-Pa)/Pa×100%, Pg is the test signal of the
sensor in the target gas, Pa is the test signal of the sensor in carrier gas. LOD: Limit of detection.
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2. SEM images of SnO2 and SnO2:Sb nanobelts
Single-crystal nanobelts of SnO2 and SnO2:Sb were synthesized by vapor-transport, as
previously reported.13 The nanobelts have the regular shape and the smooth surface with
diameters of 100-800 nm and lengths of tens of micrometers.
(a)
(b)
Figure S1. (a) SEM image of SnO2 nanobelts. (b) SEM image of SnO2:Sb nanobelts
3. Fabrication process of SnO2 nanobelt FET device with SnO2:Sb nanobelt electrodes
The nanobelt electrodes were transferred by nanomechanical manipulation. The details about
the procedure were shown in the Figure S2. (a) A SnO2 single-crystal nanobelt was first
transferred onto the gate insulator (Si/SiO2) by nanomechanical manipulation. Then the SnO2:Sb
nanobelt was transferred and placed into contact with the SnO2 nanobelt. It was found in our
experiment that point contact between two nanobelts can be easily achieved owing to the Van
der Waals force. b) Taken the contact point as the center, adjust the position of the probe in the
xy plane to rotate the SnO2:Sb nanobelt until the SnO2:Sb nanobelt just suspended above the
SnO2 nanobelt. c) Manipulating the probe station towards the direction of the arrow which was
shown in the figure S2c, larger contact area between the SnO2:Sb and SnO2 nanobelts can be
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realized. The SnO2:Sb nanobelt can be fully transferred onto the substrate as a sufficient contact
area formed. (Contact area contain: SnO2 and SnO2:Sb nanobelt; SnO2:Sb nanobelt and substrate)
d) Another SnO2:Sb nanobelt electrode can be realized by repeat the steps from a to c.
In summary, high accuracy of the probe station (200 TPI, 0.35 micron per degree) and the
experience of nanomechanical manipulation are indispensable for the whole process.
(a)
(b)
z
y
x
SnO2:Sb
SnO2
Si/SiO2
(c)
(d)
Figure S2. Schematic representations of the device fabrication process.
4. The electrical characteristics of the SnO2(NBE) device
The electrical characteristics of the SnO2(NBE) device tested in air at room temperature are
shown in Figures S3. The output curves in Figure S3a show the typical linear characteristic at
low VSD and reach saturation at high VSD. The transfer curves of Figure S3b show the typical
field-effect characteristics with respect to the gate voltage (VG) modulated current. According to
the transfer curves, the field-effect mobility (μ), on/off ratio, and threshold voltage (VT) of the
device were calculated to be respectively 66.34 cm2V-1s-1, 107, and -18.5 V. The high mobility,
on/off ratio, and highly repeatable electrical characteristics, not only confirm the high
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performance of the SnO2(NBE) device, but also provide a fundamental premise to ensure the
device reliability for the further sensing detection.
3
2
1
0
-0.5 V
(b) 10-6
-1 V
-1.5 V
0 1 2 3 4 5
VSD (V)
0.8
0.6
-9
10
0.4
-12
10
0.2
-15
10
-30 -15
0
VG (V)
ISD (μA)
0V
ISD (A)
ISD (nA)
(a) 4
0.0
15
Figure S3. Output (a) and transfer (b) curves of the FET in air at room temperature.
5. Multiple measurements in dry air and N2
As shown in Figures S4a and b, the electrical characteristics of the FET sensor with the
SnO2:Sb nanobelts as electrodes (SnO2(NBE) device) were first measured in dry air and then in
N2. Through multiple measurements both in dry air and N2, the performance is shown to be
highly repeatable. The gate leakage current (IGS) is found to be in the order of 10-13 A (Figure
S4a, green squares). Figure S4c shows that all transfer curves measured in 20 days are
overlapped well and hence shows the good air stability of our device.
5
ISD (A)
-9
10
(b)
Dry air
N2 1h
N2 2h
|IGS|
Dry air
N2 1h
N2 2h
0.2
-11
0.0
-8
10
-12
-13
-0.4
10
-15
-0.6
10
10
10
-40 -30 -20 -10
VG (V)
0
1 days
5 days
10 days
15 days
20 days
-10
10
-0.2
10
(c)
ISD (A)
-7
10
I (μA)
(a)
-14
-4 -2 0 2 4
V (V)
-20 -10
0
10
VG (V)
Figure S4. (a) Transfer curves of the SnO2(NBE) device tested in dry air and N2, Corresponding
Gate leakage current (IG) is also shown (green squares). (b) I-V curves of the SnO2(NBE) device
tested in dry air and N2. (c) Transfer curves of the SnO2(NBE) device measured in 20 days.
5. Testing process of the device to NO2
Figure S5 shows a schematic representation of the experimental setup for gas detection. The
device was placed into the stainless testing chamber and its leading wires were connected to a
Keithley 4200-SCS station, for semiconductor characterization. The testing gas was introduced
to the chamber by means of stainless pipes. Prior to the testing, pure dry N2 was led into the
chamber for 2 hours, so as to purge the testing chamber of undesired residual gases. The
electrical characteristics of the FET nanosensor were first measured in the N2 for 2 hours to
confirm the stability of devices. Subsequently, NO2 of 10 ppm in N2 was introduced to the
chamber and diluted by N2. The stream of N2 and NO2 was kept under controlled flow rate
conditions, by using a pair of Mass Flow Controllers (MFC CS200A). In this way a variable
concentration of NO2 in N2 was gradually obtained. The total gas flow rate was kept within a 500
sccm value. All of the data were collected in real time. At the end of the testing cycle, the NO 2
was collected by an alkaline solution.
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Keithley 4200-SCS station
Gas in
MFC
N2 and NO2
gas cylinders
Mass Flow Controllers
Gas out
Testing chamber
Alkaline solution
Flow adjustment
Figure S5. Schematic representation of the experimental setup used for gas sensing.
6. Performance of MiCS-2714 to NO2.
The MiCS-2714 is a robust MEMS sensor for nitrogen dioxide and leakage detection. (SGX
Sensortech, Switzerland). The detailed performance was shown in Figure S6. It is observed a
Figure S6. The sensing performance of MiCS-2714 (25°C, 50% RH)
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LOD of 50 ppb with a 30% resistance change can be obtained at room temperature.14 (blue circle)
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