CA was measured by fitting a circle equation to the shape of the sessile drop
(due to the sphere-like shape of the drop) and then calculating the slope of the tangent to the drop at the liquid-solid vapor interface line. The camera was positioned in order to observe the droplet under an angle of about 2° to 4° with respect to the plane of the sample surface supporting the droplet. Roll-off angles were measured with a goniometer in order to control the tilt angle. The orthoscopic images were obtained using a commercial photocamera. Results and discussion The samples’ structure was examined by X-ray diffraction, the XRD patterns being presented in Figure 2. Four peaks can be readily indexed to hexagonal wurtzite ZnO (JCPDS file no. 36-1451) corresponding to the Miller indexes of the reflecting planes for selleck ZnO (100), (002), (101), and (102). The strong and sharp diffraction peaks suggest that the as-obtained products are well crystallized. Interestingly, the intensity distribution of some XRD peaks deviates drastically from what is characteristic to standard ZnO where (101) is the strongest XRD line and the intensity ratio [I(002)/I(101)] = 0.56 is the value for non-preferred orientation. For example, in the case of sample b and sample e, the intensity ratio [I(002)/I(101)] increases, its
values larger than 1 being correlated with a high degree of orientation ATM Kinase Inhibitor clinical trial on the c-axis of the ZnO crystallites. The peak at 2θ = 38.3° is assigned to Au (111). With the increase of the reactants’ concentration Pomalidomide and the reaction time, the peak intensity corresponding to gold decreases, suggesting a better covering of the substrate. Figure 2 The XRD patterns of all ZnO samples. The room temperature reflectance and photoluminescence (PL) spectra of the synthesized samples are shown in Figure 3. A strong decrease of reflectance can be noticed at approximately 380 nm in all sample spectra, this being attributed to the band-to-band transition in ZnO. Indeed, the bandgap value was estimated at around 3.27
eV by using the Kubelka-Munk function F(R) = (1 – R)1/2/2R, R being the observed diffuse reflectance. The PL spectra exhibit a strong, broad emission band centered at about 550 nm (2.17 eV) and a weak (or very weak) emission band centered at about 380 nm (3.27 eV). The UV emission has an excitonic origin, being attributed to the recombination of free excitons. Usually, the green emission is linked to some defects, being related to the incorporation of hydroxyl groups in the crystal lattice during the growth process and to the oxygen defects (interstitial ions or vacancies) [36–39]. Due to the fact that when employing wet chemical methods the ZnO crystallites are formed by Zn(OH)2 dehydration, traces of this compound on the ZnO surface lead to the quenching of the ZnO exciton emission . Consequently, we may say that the optical properties of our ZnO samples are typical for this semiconductor.