In this work, Bi
2Se
3 nanoplates were grown by the chemical vapor deposition (CVD) method
via a horizontal tube furnace as shown in
Fig. 1a. The flexible device with Bi
2Se
3 nanoplates grown on copper interdigital electrodes (IDEs) pre-patterned on polyimide (PI) substrate was schematically exhibited in
Fig. 1b. And the optical photograph of the as-prepared Bi
2Se
3 device and SEM image of the sensing area were displayed in Fig. S3 (Supporting information). As for the characterization of the as-synthesized Bi
2Se
3, firstly, randomly-distributed and free-standing Bi
2Se
3 nanoplates were observed from the SEM image (
Fig. 1c). A large coverage and high yield of Bi
2Se
3 nanoplates were achieved. An approximate atomic ratio of Bi to Se at 2:3 from EDS spectra (Fig. S4 in Supporting information) was consistent with Bi
2Se
3 configuration. Moreover, the TEM image (
Fig. 1d) exhibited a clear nanoplate structure of the obtained Bi
2Se
3 with the lateral size of ~350 nm. High-resolution TEM image (
Fig. 1e) and the relevant fast fourier transform (FFT) forms revealed the lattice spacings of 0.30 nm corresponding to the crystal plane of (015) for Bi
2Se
3, indicative of the successful synthesis. Afterwards, XRD measurements were employed to verify the crystalline structure of the Bi
2Se
3 nanoplates in Fig. S5 (Supporting information). After deducting the background of the PI substrate underneath, the main diffraction peaks at 9.1°, 18.3°, 29.2° and 47.3° were respectively assigned to (003), (006), (015) and (0015) crystal planes of hexagonal Bi
2Se
3 (JCPDS card No. 33–0214) [
37]. Moreover, the Raman spectrum of the prepared Bi
2Se
3 was shown in
Fig. 1f. Three peaks at 69, 127, and 172 cm
−1 were respectively assigned to the A
1g1, E
g2 and A
1g2 vibrational modes, which were accorded with the previous result of Bi
2Se
3 nanoplates [
38]. Besides, the elemental compositions and chemical states of the as-prepared Bi
2Se
3 nanoplates were explored by XPS measurements. The survey spectrum (Fig. S6 in Supporting information) confirmed the successful synthesis of pure Bi
2Se
3 material. Herein, Bi 4f spectrum can be divided into two peaks at 158.3 eV (Bi 4f
7/2) and 163.6 eV (Bi 4f
5/2) as shown in
Fig. 1g. And the peaks at 53.7 eV and 54.5 eV in Se 3d spectrum were assigned into Se 3d
5/2, and Se 3d
3/2, respectively (
Fig. 1h). Note that recognizable bismuth oxide (BiO
x) and selenium oxide (SeO
x) peaks were separately observed in
Figs. 1g and
h, consistent with previous reports about Bi
2Se
3 nanoflakes [
39]. This phenomenon indicated the surface oxidation of Bi
2Se
3 nanoplates within air, which led to an
n-type doping in Bi
2Se
3 [
40]. Subsequently, the
I-V characteristic of the as-prepared Bi
2Se
3 device was explored by an electrochemical analyzer (voltage: −2 V to + 2 V, sample interval: 0.001 V). A nice linear ohmic behavior was observed in Fig. S7 (Supporting information), stating that the resistance variation when adsorbing/desorbing gas molecules was mainly resulted from gas-solid film interaction rather than the interfacial contact [
41].