Investigations on the Crystallographic Orientation Induced Surface Morphology Evolution of ZnO Thin Films and Their Wettability and Conductivity

Abstract

The intrinsic zinc oxide (ZnO) thin films with controllable crystallographic orientation have been synthesized on Si(100) substrates using plasma-enhanced chemical vapor deposition (PECVD) system without any buffer layer. Based on X-ray diffraction (XRD) results, the evolution of crystallographic orientation of ZnO thin films from polar c-plane (0002), polar c-plane and nonpolar m-plane (101̅0) coexist to nonpolar m-plane and a-plane (112̅0) coexist was achieved by a simple factor of controlling synthesized temperature. The plane-view morphological images exhibited that the surface texture and grain shape of ZnO thin films could have evolved from hexagonal to stripelike grains when the ZnO crystallographic orientation changed from perpendicular to parallel to the substrate. The characterization analysis indicated that the zinc precursor [diethylzinc (DEZn), Zn­(C2H5)2] played a key role on the crystallographic orientation evolution of ZnO thin films during the early stage of the growth process because DEZn not only can serve as Zn precursor but also can be employed as passivating agent to influence the crystal growth under different synthesized temperatures. Room-temperature Hall effect measurement showed that intrinsic ZnO thin film with stripelike grains possessed the lowest value of resistivity ∼7.11 × 102 Ω cm, which had an estimated carrier concentration and mobility of about 5.73 × 1014 cm–3 and 15.34 cm2/V s, respectively. The water contact angle (CA) measurement was also provided to determine the surface wettability and surface free energy of ZnO thin films, indicating that CA could be adjusted via different crystallographic orientation of ZnO thin film.

Surface Analysis and Optical Properties of Cu-Doped ZnO Thin Films Deposited by Radio Frequency Magnetron Sputtering

“…Hence, by straightforward analyses, the values of the surface energy obtained for CZO thin film were 12.3, 10.8, and 17.5 mJ•m −2 , respectively, for 2%, 6%, and 10% Cu-doping concentrations. Previous studies have indicated that the surface roughness is directly proportional to the contact angle and thereby inversely proportional to the surface energy of ZnO films [31,32]. Our results, nevertheless, are similar to that reported by Sapkal et al [33].…”

Tuning bandgap and surface wettability of NiFe2O4 driven by phase transition

“…The hydrophobic or hydrophilic materials are usually prepared by modifying their surface with varied surface energy for tunable surface wetting characteristics. The surface characteristics for other oxide materials have also been claimed in our previous work 45 , 46 . In addition, this kind of surface nanostructures could not only be used for self-cleaning 47 – 49 , drug delivery 50 – 54 and biological interactions 55 , but also could be used for other potential surface engineering such as oil-water separation 56 – 58 , self-dustproof surfaces 59 and anti-fogging 60 .…”

Internal stress induced natural self-chemisorption of ZnO nanostructured films

“…2(i) , it was due to internal stress relaxation induced the grain growth from nanograin to micrograin. This transformed process caused the CA decreased, meanwhile, there are many bigger apertures on sub-micrograin surface and liquid may completely penetrate into surface hollows, leading air-pocket loss 39 40 , therefore, the hydrophilic wetting behavior for ZnO nanostructured films occurred at nearly stress-free state (−0.33 GPa). For the purpose of understanding the microstructural features varied boundary from nanograin to micrograin, the obviously different internal stress state for samples Z125 and Z175 effectively induced various surface wetting behavior, the surface morphology, chemical adsorption and optical property of ZnO nanostructured films will be mainly discussed below.…”