•Non-uniform plasma was used to modify PET films.•The treated film surface can be divided into typical three regions.•In these regions, gradient roughness surface was created.•Homogenous surface chemistry was also generated in these regions.•The experimental results were explained by theoretical plasma-etching mechanism.Dielectric barrier discharge (DBD) plasma was used to modify polyethylene terephthalate (PET) films with gradient roughness and homogenous surface chemistry. Based on asymmetric electrode arrangement, the spatial distribution of the plasma on the films surface was non-uniform, leading to the formation of typical three discharge regions (central zone, boundary zone and diffuse zone). The experimental results showed that the plasma induced significant morphological and chemical changes onto the surfaces. Furthermore, a gradient surface roughness from central zone to diffuse zone was formed, while surface chemistry was relatively homogenous in these regions, which can be explained by theoretical plasma-etching mechanism.Download high-res image (67KB)Download full-size image

At atmospheric pressure, anatase TiO2 films with various nano-morphologies have been grown on quartz substrate by non-thermal TiCl4–O2–Ar reactive plasma vapor deposition. High concentration of oxygen vacancies and undercoordinated Ti atoms are incorporated into the crystal lattice of the deposited films, which can be tuned by changing the discharge conditions such as temperature and vapor flow rate. Strong visible luminescence is found for the deposited films, originating from the radiative recombination of trapped electrons due to uncoordinated Ti atoms and oxygen vacancies. To clarify the growth mechanism, an analytical model is proposed to explain the corresponding discharging process. We find the theoretical predictions agree well with experimental results. By effectively adjusting the morphology and lattice crystallinity, we believe this work can provide an expedient and controllable way to fabricate anatase films with interesting optical properties, which can meet the demands of complex practical situations to the maximum degree.

Micro-scale TiO2 crystal trees were fabricated on quartz glass substrates via atmospheric pressure plasma jet (APPJ) from the mixture gas of titanium tetrachloride (TiCl4) vapor, argon and oxygen by one step. Small variations in deposition parameters have a dramatic effect on the structure of the deposits. The heights of these TiO2 trees vary from several micrometers to over one hundred micrometers. The high resolution transmission electron microscope of the TiO2 trees (HRTEM) clearly shows the lattice fringes, which serves as evidence that the TiO2 trees are quite crystalline. The X-ray diffraction (XRD) and the selected area diffraction (SAED) results confirm the composition of anatase and rutile phase of these TiO2 trees. This particular tree-like structure of TiO2 shows a superhydrophobicity with water contact angle as high as 170°.

In this research, the dispersion of TiO2 nanoparticles coated by acrylic acid (AA)-plasma-polymers in glycol solution is investigated by ultraviolet absorbency and particle size distribution measurement. The results show that the dispersion of TiO2 nanoparticles is greatly improved after AA-plasma-polymer coating. It depends on the discharge parameters to a great extent and there exists an optimal dispersion value. The potentials in the DLVO theory between particles are calculated using the surface energy of nanoparticles as a main entrance, and first applied in estimation the dispersion behaviors of nanoparticles. It is found that the potential maxima in the DLVO curves match well with the optimal experimental dispersion values. This indicates the success of DLVO theory in explaining the dispersion improvement of surface-coated TiO2 nanoparticles. It also displays that the surface energy plays an important role in the dispersion behaviors of TiO2 nanoparticles. It is an effective way to improve the dispersion of nanoparticles through changing their surface energy by plasma polymer coating.

The surface structures of hexamethyldisiloxane (HMDSO) films prepared by rf plasma polymerization are investigated by Fourier transform infrared, solid-state 29Si CP/MAS nuclear magnetic resonance and scanning electron microscope. The reactive species in HMDSO plasma and the mechanism of HMDSO plasma synthesis are studied by optic emission spectrum. The effect of continuous wave discharge and different pulse discharge parameters especially plasma “high power” time on chemical structure and physical morphology modifications of HMDSO polymer film is compared elaborately. The results show that HMDSO-continuous-wave polymer is an organic film without SiO group. Its surface consists of several microscale islands with many clustered rods. While HMDSO-pulse-polymer is a network of interconnected primary methylsiloxane units and minor hydroxyl, oxymethylene, hydrogen and carbonyl groups. The ratio of SiOSi to Si(CH3)n and new functional groups of OH, CO and CO are effectively “tailored” by changing plasma “high power” time. Moreover, HMDSO-pulse-polymer is a continuous, regular and compact film with a few asteroid protuberances. This deposited film becomes more regular after increasing plasma “high power” time and gradually presents perfect “straw-mat” morphology. It is indicated that pulse plasma polymerization is an effective way to tailor the surface structures of plasma polymer films through controlling plasma “high power” time.

Pulsed RF plasma polymerization using vinyl acetic acid as a prototype precursor was investigated in order to evaluate the applicability of the pulsed RF discharge to obtain plasma polymers with less cross-linked structure and high degree retention of the groups in the starting monomer. The chemical structure and the surface morphology of the polymerized vinyl acetic acid were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscope (XPS) and scanning electron microscope (SEM). At all other plasma parameters remaining constant, the chemical structure was observed to vary with the plasma duty cycles. The FTIR results showed that more carboxylic groups could be ‘retained’ with the decreasing of the duty cycles. The XPS results were consistent with the FTIR measurements. Surface energy measurements indicated that the plasma films were hydrophilic. The plasma polymerized films at continuous discharge mode show higher thermal stability than the films polymerized at pulsed discharge mode. But the later is less cross-linked. So it is possible to control the chemical composition of the plasma film with the same surface functional groups as its monomer being ‘retained’ by pulse plasma technologies. Some regular graft ‘lightning’ network patterns were interestingly found in the plasma films kept at room temperature for some time by SEM. It was estimated that the mechanism of the plasma polymerization is different along the ‘lightning’ network and on the valley of the pattern.

At atmospheric pressure, anatase TiO2 films with various nano-morphologies have been grown on quartz substrate by non-thermal TiCl4–O2–Ar reactive plasma vapor deposition. High concentration of oxygen vacancies and undercoordinated Ti atoms are incorporated into the crystal lattice of the deposited films, which can be tuned by changing the discharge conditions such as temperature and vapor flow rate. Strong visible luminescence is found for the deposited films, originating from the radiative recombination of trapped electrons due to uncoordinated Ti atoms and oxygen vacancies. To clarify the growth mechanism, an analytical model is proposed to explain the corresponding discharging process. We find the theoretical predictions agree well with experimental results. By effectively adjusting the morphology and lattice crystallinity, we believe this work can provide an expedient and controllable way to fabricate anatase films with interesting optical properties, which can meet the demands of complex practical situations to the maximum degree.