To measure the electrical property of the films, Au top electrodes were patterned and deposited by sputtering using a metal shadow mask. Voltage–current curves Daporinad clinical trial of the films were measured using an Autolab 302 N electrochemical workstation controlled with Nova software (with a possible error in current and voltage values as ±5%; Nova Software, Chongqing, China). All measurements were repeated at least twice to confirm the results. During measurement, the working electrode and sensor electrode were connected to the top Au electrode, and the reference and counter electrode were connected to the ITO substrate. X-ray photoelectron spectroscopy (XPS) was performed with an ESCALAB250Xi spectrometer (Thermo Fisher Scientific, Waltham,

MA, USA) using a monochromatized Al K alpha X-ray source (hV) 1486.6 eV with 20 eV pass energy. Hall effect measurements were carried out by the Accent HL5500PC (Nanometrics, SRT1720 clinical trial Milpitas, CA, USA). All measurements were performed at room temperature. Results and discussion The electrochemical synthesis of ZnO is a four-step process: First, nitrate ions and H2O are electrochemically reduced at the surface of the working electrode, resulting in an increase in the local pH value in the vicinity of the electrode

(Equations 1 and 2). Then, the increase in the local pH leads to the precipitation of zinc ions as zinc hydroxide (Zn(OH)2, Equation 3) at a suitable temperature, and Zn(OH)2 can be transformed into ZnO. In the presence of Ti4+, part of the Ti4+ ions can be incorporated into ZnO lattices. (1) (2) (3) (4) (5) Figure 1a shows the SEM images of Ti-ZnO film. It is apparent that the grains are formed by many small crystallites aggregated with irregular shapes. In the inset of the same figure, a cross-sectional image was presented which shows film thickness as approximately 330 nm. EDS elemental maps are shown in Figure 1b,c,d. The O, Zn and Ti Vitamin B12 elemental maps have the same spatial distribution. This indicates a quite uniform distribution of elements in the synthesized products

and demonstrates that the ZnO films are homogenously doped with Ti. The EDS spectra and element atomic percentage compositions were presented in the supporting information in Additional file 1: Figure S1. Figure 1 The surface morphology of Ti-ZnO film. (a) The SEM (inset cross-sectional image) and EDS mapping (b, c and d) images of Ti-ZnO films. The XRD pattern of the Ti-doped ZnO film (inset pure ZnO film) was displayed in Figure 2. The XRD patterns of the films are consistent with the hexagonal lattice structure, and a strong (002) preferential orientation is observed. It implies that the Ti atoms may substitute the zinc sites substitutionally or incorporate interstitially in the lattice. From Figure 2, it can be found that the locations of the diffraction peaks slightly shift towards higher diffraction angles, which illustrate the change in interplanar spacing (d-value). This is because of the different ionic radii between Ti4+ (0.