Pure ε- and β-phase gallium oxide (Ga2O3) films have been successfully grown on Al2O3 (001) substrate via metal–organic chemical vapor deposition (MOCVD) at a growth temperature of 500 °C. Growth pressure controlled nucleation is the dominant controlling parameter for pure phase Ga2O3 film growth. Due to the biaxial stress induced by lattice mismatch, heteroepitaxial ε-phase Ga2O3 is grown on Al2O3 by heterogeneous nucleation at low pressure. However, film growth is dominated by spherical nuclei homogeneous nucleation at a pressure higher than 100 mbar, and β-phase Ga2O3 film is grown with a mosaic surface. The optimum pressure for the growth of pure ε-Ga2O3 films with superior crystallinity is 35 mbar, whereas the pressure window for pure β-Ga2O3 growth is between 100 mbar and 400 mbar. The growth rate of β-Ga2O3 film is much lower than ε-Ga2O3 film at high pressure. On the other hand, all Ga2O3 films have shown good optical properties with a band gap of about 4.9 eV. This fundamental research will help to understand the mechanism of MOCVD growth involving high quality and pure phase ε- and β-Ga2O3 film.

Inspired by nature, tunable wettability has attracted a lot of attention in both academia and industry. Various methods of polymer surface tailoring have been studied to control the changes in wetting behavior. Polymers with a precisely controlled wetting behavior in a specific environment are blessed with a wealth of opportunities and potential applications exploitable in biomaterial engineering. Controlled wetting behavior can be obtained by combining surface chemistry and morphology. Plasma assisted polymer surface modification technique has played a significant part to control surface chemistry and morphology, thus improving the surface wetting properties of polymers in many applications. This review focuses on plasma polymerization and investigations regarding surface chemistry, surface wettability and coating kinetics, as well as coating stability. We begin with a brief overview of plasma polymerization; this includes growth mechanisms of plasma polymerization and influence of plasma parameters. Next, surface wettability and theoretical background structures and chemistry of superhydrophobic and superhydrophilic surfaces are discussed. In this review, a summary is made of recent work on tunable wettability by tailoring surface chemistry with physical appearance (i.e. substrate texture). The formation of smart polymer coatings, which adjust their surface wettability according to outside environment, including, pH, light, electric field and temperature, is also discussed. Finally, the applications of tunable wettability and pH responsiveness of polymer coatings in real life are addressed. This review should be of interest to plasma surface science communality particularly focused controlled wettability of smart polymer surfaces.

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