To understand this phenomenon, it is worthwhile to notice that the valence of Ti tends to be +4 in the TZO films made by atomic layer deposition. Along the [100] direction, the film layer is composed of the line of Zn2+ ions or the line of O2−. If Ti4+ ions take the place of Zn2+ sites, the repulsive force in this direction would increase because of extra positive charge. This effect can enlarge the interplanar spacing along the [100] direction, thus leading to the observed decrease of the diffraction angle. The AFM images of the

films deposited on silicon substrate were measured to further characterize the effect of Ti doping concentration on the surface morphology of TZO films. Figure 3 shows the AFM images of these films and their root mean square (rms) surface Akt inhibitor roughness in a scan size of 2 × 2 μm2. It was found that the rms roughness value of the LY2835219 films except for the sample with N = 1 is in the range of 1.65 to 1.80 nm. The surfaces of these films are evidently smoother than those deposited by RF reactive magnetron sputtering [10]. It highlights the potential use of TZO films made by ALD as TCO, where precise control over film uniformity and smoothness is required. The film with N = 1 shows the lowest surface Integrin inhibitor roughness

with its rms roughness value to be 0.59 nm. In addition, no etching effect on the film is found in the experiment [17]. Figure 3 AFM images of TZO films with rms surface roughness Dichloromethane dehalogenase in a scan area of 2 × 2 μm 2 . Figure 4 displays the transmission spectra of TZO films grown on quartz. It is obvious that an average optical transmittance more than 80% in the visible range is obtained

for the samples with N from 20 to 2, which is valuable for TCO applications such as liquid crystal displays. The relatively low transmission for the sample grown with N = 1 resulted from the high concentration of Ti in the TZO films. Moreover, all the films show a sharp absorption edge in the ultraviolet range, which shifts to the lower wavelength side with Ti concentration increase. The optical band gap of TZO thin films can be calculated according to the transmission spectra. As a direct-band gap material [18], it is reasonable to assume that the absorption coefficient (α) is proportional to − ln(T), where T is the optical transmission. According to the Tauc relationship, the relation between the optical band gap (E g) and absorption coefficient is given by [19] (4) where h is Planck’s constant and v is the frequency of the incident photon. The E g of the TZO films can be obtained by drawing the plot of (α × hv)2 versus the photon energy (hv) and extrapolating a straight line portion of this plot to the axis of photon energy, as is indicated in the inset of Figure 4. It can be found that the band gap energy increases from 3.26 eV for pure ZnO film to 3.99 eV for the film with N = 1. The widening of band gaps with the increase of titanium concentration is generally attributed to the Burstein-Moss band-filling effect.