Soft-lithographically line-patterned In-doped ZnO quantum dots with hydrothermally grown ZnO nanocolumns for acetone detection

We introduced a new approach to enhance the sensing performance of sensors based on metal oxide semiconductors. We synthesized In-doped ZnO quantum dots (IZO QDs) by a hydrothermal method and fabricated line-patterned IZO QD layers with polydimethylsiloxane (PDMS) molds. Additional hydrothermal growth was conducted to create ZnO nanocolumns (NCs) on the patterned surfaces. Thus, drop-cast and line-patterned sensors and line-patterned samples with NCs grown for 0.5 h (NC(0.5 h)/Line) and 4 h (NC(4 h)/Line) were prepared. Among these four different sensors, the NC(0.5 h)/Line sensor exhibited an excellent response of 26,000 with fast response times of less than 1 s to 10 ppm of acetone. In addition, the detection limit was approximately 0.1 ppm of acetone, and the resistance was almost constant even after repeatability tests. According to UV–vis and X-ray photoelectron spectroscopic analyses, the extraordinary sensing characteristics of NC(0.5 h)/Line were mainly because this sensor had the largest optical band energy and the highest ratio of oxygen vacancies among the tested sensors. On the other hand, the NC(4 h)/Line sensor showed the lowest response of the four sensors. During the long-term growth of NCs, [sbnd]OH groups are produced on the surface of the material, and Zn(OH)₂ NCs are formed instead of ZnO NCs, resulting in a large decrease in the carrier concentration and active sites. In conclusion, we developed highly sensitive acetone sensors by constructing special morphologies.