Integration of metal oxide nanowires in flexible gas sensing devices

Abstract

Metal oxide nanowires are very promising active materials for different applications, especially in the field of gas sensors. Advances in fabrication technologies now allow the preparation of nanowires on flexible substrates, expanding the potential market of the resulting sensors. The critical steps for the large-scale preparation of reliable sensing devices are the elimination of high temperatures processes and the stretchability of the entire final device, including the active material. Direct growth on flexible substrates and post-growth procedures have been successfully used for the preparation of gas sensors. The paper will summarize the procedures used for the preparation of flexible and wearable gas sensors prototypes with an overlook of the challenges and the future perspectives concerning this field.

Figure 1.

Number of publications as a function of the year from the isiwebofknowledge database 10/06/2013. Right axis: nanowires publications; left axis: nanowires sensors publications.

Figure 2.

SEMimages of (a) cotton fabric substrate in low magnification; (b) bare cotton fibres; (c) ZnO NR-coated cotton fibres and (d) high magnification images of ZnO NRs on a cotton fibre. Scale bar in the inset represents 100 nm; (e) Photograph bare and ZnO NRs coated fabric; (f) Ready-to-wear ZnO NRs-on-fabric multifunctional sensing device sewn on a toy dress. Reprinted from [27] with permission. Copyright Elsevier (2010).

Figure 3.

(a) Representative FESEM image of aligned ZnO nanorods; (b) TEM image of a single nanorod; (c) HRTEM image taken from the edge of the ZnO nanorod. Inset: Corresponding SAED pattern. Reprinted from [32] with permission. Copyright WILEY-VCH Verlag GmbH & Co. KGaA (2010).

Figure 4.

Nanowire device arrays. (a) Dark-field image of silicon nanowire arrays. The anchoring windows were defined by photolithography, and the resist layer (S1805) thickness was 70 nm. Scale bar, 100 mm; (b) SEM image of one of the combed nanowire arrays on the resist layer. Scale bar, 2 mm; (c) Dark-field image of trimmed nanowire arrays (resist layer removed). Scale bar, 40 mm; (d) Optical image of nanowire device arrays connecting to electrode arrays. Scale bar, 200 mm; (e) Representative SEM image of one of the device arrays. Scale bar, 2 mm; (f) I_ds-V_g characteristics (V_ds = 0.1 V) from 20 top-gated Ge/Si nanowire devices assembled by nanocombing. The channel length of the devices is 3.8 mm, with Al₂O₃ (7 nm) serving as the dielectric layer for the top gate (Cr/Au 1/4 5/50 nm). The electrical characterizations were performed in an ambient environment. Reprinted from [35] by permission from Macmillan Publishers Ltd. Copyright (2013).

Figure 5.

Electrical responses of ZnO NR-on-cloth device to (a) various concentrations of H₂ gas and (b) UV irradiation. Clean dry air (CDA) was used to flush the chamber before and after each hydrogen injection. Experiments were performed in room temperature. Reprinted from [27] with permission. Copyright (2010) Elsevier.