Fabrication of ultrasensitive hexagonal disc structured ZnO thin film sensor to trace nitric oxide

Figures & data

Figure 1. XRD spectra of as-prepared ZnO and annealed ZnO Thin film

Figure 2. Diffraction Spectra of (101) orientation of ZnO and annealed ZnO Thin film

Table 1. Lattice parameters using XRD

	Preferred orientation (101)		Lattice parameters
Film Sample	Bragg’s Angel (2θ)	FWHM	a = b (nm)	c (nm)	c/a	V (nm^3)	L (nm)
As Prepared	36.36	0.21489	0.28506	0.49374	1.73207	34.744	0.16881
Zn4	36.33	0.19383	0.28529	0.49414	1.73200	34.828	0.16873
Zn5	36.34	0.18655	0.28522	0.49401	1.73202	34.802	0.16870
Zn6	36.35	0.18578	0.28515	0.49387	1.73198	34.775	0.16876
Zn7	36.35	0.18576	0.28515	0.49387	1.73198	34.775	0.16876

Table 2. Microstructure analysis using XRD

Film Sample	Crystallite size D (nm)	Tensile strain (ε)	Dislocation density (δ)line/m^2	Texture coefficient (TC) for (101) plane
As prepared	70.89	5.1 × 10^−2	1.98 × 10^−4	0.964
Zn4	78.73	4.6 × 10^−2	1.6133 × 10^−4	1.161
Zn5	81.37	4.43 × 10^−2	1.510 × 10^−4	1.14
Zn6	82.14	4.41 × 10^−2	1.482 × 10^−4	0.94
Zn7	82.135	4.41 × 10^−2	1.482 × 10^−4	0.895

Figure 3. Effect of annealing temperature on grain size and texture coefficient of ZnO thin film samples

Figure 4. (a) Absorbance spectra (b) Tauc’s plot of ZnO Thin Film Samples

Figure 5. Effect of annealing on energy band gap of ZnO thin film

Figure 6. (a) FESEM and (b) Energy dispersive spectroscopy images of as-prepared ZnO thin film

Figure 7. Structural variation of ZnO thin film after annealing for an hour at various temperatures: (a) 400° C (b) 500° C (c) 600° C (d) 700° C

Table 3. EDS analysis

	Element Weight%			Atomic%
Film Samples	O(K shell)	Zn(L shell)	C	Zn	O
As prepared	0.84	2.6	0.31	33.66	44.23
Zn4	0.18	0.7	0.07	38.33	41.11
Zn5	0.25	0.92	0.09	37.56	41.62
Zn6	0.2	0.57	0.08	31.18	45.88
Zn7	3.18	6.94	1.2	26.23	49.18

Figure 8. Gas sensing setup (a) Gas chamber (b) Electrode assembly (CeNSE Lab, Indian Institute of Science, Bangalore)

Figure 9. Nitric oxide gas response – ZnO thin film sensors at an operating temperature of 150°C

Figure 10. At an operating temperature of 150°C (a) Sensitivity (b) Response and recovery time of various ZnO sensors

Figure 11. (a) Sensitivity curve (b) Response time and recover time – Zn4 sensor at different operating temperatures

Table 4. Response and recovery time for ZnO and other material-based sensors toward NO gas

Sl. No	Materials	Target gas	Response Time(s)	Recovery Time (s)	Concentration (ppm)	Operating Temperature	References
1.	WO3 (Tungsten trioxide)	NO	45	152	20 ppm	200°C	[47]
2.	Copper- Ion -Doped Polyaniline/Tungsten Oxide Nanocomposite (SAW Sensor)	NO	97	37	10ppb	RT	[48]
3.	ZnO NR	NO	80	140	100ppb	RT	[49]
4.	TiO2 (Titanium dioxide)	NO	91	184	10ppm	310 nm-light activation	[50]
5.	MoS2 (Molybdenum disulfide)	NO	300	900	100ppm	RT	[51]
6.	Flower like ZnO	NO	22.1 min	51.7 min	1000 ppm	RT	[52]
7.	Ag doped ZnO	NO	60	102	21.6ppb	200° C	[53]
8.	Zn4 sensor	NO	52s	19s	2.75 ppm	150°C	Present work

Foot note: RT-Room temperature; ppm-parts per million; ppb-parts per billion, NR-Nano rods, Ag-silver.

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