Fig. 1. Experimental setup of chemical vapour transition deposition

Fig. 2. SEM images of (a) porous silicon and porous silicon/VO₂ composite structure deposited at (b) 65 Pa; (c) 330 Pa; (d) 530 Pa; (e),(f), (g) are enlarged views of (c)

Fig. 3. XRD patterns of (a) porous silicon and porous silicon/VO₂ composite structure deposited at (b) 65 Pa; (c) 330 Pa; (d) 530 Pa

Fig. 4. EDS pattern of porous silicon/VO₂ composite structure deposited at 330 Pa

Fig. 5. TEM images of porous silicon/VO₂ composite structure deposited at 330 Pa. (a) High resolution transmission electron microscope (HRTEM) image; (b) FFT corresponding to square area in (a)

Fig. 6. Response curves of different NO₂ concentrations of porous silicon/VO₂ composite structure deposited at 65 Pa, 330 Pa, and 530 Pa, respectively

Fig. 7. Dynamic response curves of samples with deposition pressure of 330 Pa. (a) Dynamic response curves of porous silicon/VO₂ composite structure; (b) response curve of different NO₂ concentrations of porous silicon/VO₂ composite structure

Fig. 8. Sensitivites of porous silicon/VO₂ composite structure for different gases deposited at 330 Pa

Fig. 9. Energy bands of P-type porous silicon and N-type VO₂. (a) Before contact; (b) after contact

Fig. 10. Response mechanism of porous silicon and porous silicon/VO₂ composite structure. (a) Response mechanism diagram of porous silicon; (b)-(c) response mechanism diagram of larger particles of VO₂ after composited with porous Si; (d)-(e) response mechanism diagram of smaller particles of VO₂ after composited with porous Si

Fig. 11. Change of barrier height of porous silicon/VO₂ composite structure to different gases