Yunying Wu

Preparation of hard and ultra water-repellent silicon oxide films by microwave plasma-enhanced CVD at low substrate temperatures

Hard silicon dioxide (SiO2) films were prepared by means of microwave plasma-enhanced CVD (MPECVD) using trimetylmethoxysilane (TMMOS) and CO2 as a row material and as an additive gas, respectively. The substrate temperature remained below 373 K. After preparation of the SiO2 films, the film surfaces were treated through a chemical method, that is, preparation of self-assembled monolayers of fluoroalkylsilane on the surfaces, in order to improve water repellency. This process was also conducted below 373 K. As a result of the chemical treatment, the water contacts angle of the films increased up to 150°. By this combined method, hard and ultra water-repellent silicon oxide films were successfully prepared. The films had high optical transparency. The high performance of the films was realized based on the mutual effect of surface hydrophobic groups and surface nanotextures. The films are expected to have wide applications in many engineering fields.

Characteristics of ultra water-repellent thin films prepared by combined process of microwave plasma-enhanced CVD and oxygen-plasma treatment

Transparent thin films with ultra water-repellency were prepared by a combined process of microwave plasma-enhanced CVD (MPECVD) and oxygen-plasma treatment. An organosilicon compound was used as a raw material for MPECVD. Mechanical properties, that is, hardness and wear resistance, of the ultra water-repellent thin films prepared by the combined process were improved in comparison with the films prepared by MPECVD without the oxygen-plasma treatment. The optical performance of the films remained unchanged.

Characteristics and high water-repellency of a-C:H films deposited by r.f. PECVD

Abstract Hydrogenated amorphous carbon (a-C:H) films have been prepared by r.f. plasma-enhanced chemical vapor deposition at low bias voltage from 0 to −40 V with CH 4 and H 2 as raw materials. The a-C:H films deposited with no bias applied showed characteristics of polymeric films with a large fluorescence level while the a-C:H films deposited at a bias voltage of r.f. 150 W showed characteristics from diamond-like carbon to graphitic nature with a significantly reduced fluorescence level. High water-repellency of over 140° in a contact angle obtained at a-C:H/trimetylmethoxysilane/Si structures. This high water-repellency is due to CH groups on surfaces and the roughness.

Nanotextures fabricated by microwave plasma CVD: application to ultra water-repellent surface

Nanotextured surfaces of polymer sheets with high water-repellency were fabricated through a nano-replica process. First, ultra water-repellent silica thin films were deposited onto Si substrates by microwave plasma-enhanced CVD (MPECVD) using an organosilicon compound as a raw material. The nanotextures of the film surface were controlled by changing deposition pressure. Second, the surface nanotextures of the films were replicated to Ni molds by electroforming. Third, polystyrene (PS) was coated on the Ni molds by spin coating and the nanotextured PS replicas were fabricated by this process. The contact angles of the nanotextured PS replicas were 130°, while 90° were obtained for PS flat sheets.

Highly efficient treatment of industrial wastewater by solution plasma with low environmental load

Advanced oxidation techniques are efficient processes to dispose of organic contaminants in industrial wastewater with low secondary pollution. The solution plasma technique was featured as an advanced oxidation technique with low secondary pollution and high efficiency. However, the solution plasma technique reported previously could only treat wastewater of less than 200 mL owing to the limited plasma generated by only one pair of electrodes. In this work, multiple pairs of electrodes were installed at the bottom of the reaction vessel to generate plasma for decomposing methylene blue trihydrate (MB) and methyl orange (MO) solutions with a batch amount of 18 L/batch. The solution plasma technique was compared with direct ozonation in decomposition of MB and MO wastewater. A surprising phenomenon is that MO was more readily decomposed than MB by using direct ozonation, whereas the removal of MO was too low, and MB was more readily decomposed than MO by using the solution plasma technique.

A novel 3-dimensional cell culture system for embryoid bodies' formation

Nano-structured films with super hydrophobic surfaces were fabricated by microwave-plasma enhanced chemical vapor deposition (MPECVD) method. It was found that water droplets with a volume from 10 to 30 µl rolled and bounced without wetting or spreading on the surfaces of the nano-structured films (nano films). After 3 days of cultivation, aggregation of embryoid body (EB) cells from embryonic stem (ES) cells were formed as microspheres on nano films coating in petri disks. Growth of ES cells was shown to be the best on the nano films with a 150° water contact angle. The EBs derived from ES cells cultured in droplets on the nano films grew over the cultivation time until the 7th day on which EBs began to spread out. The results showed that the nano-structured film with a super-hydrophobic surface is a useful material for obtaining EBs from undifferentiated ES cells, this is anticipated to be a stem cell source for transplantation due to their pluripotency and indefinite proliferation.

Low Temperature Deposition of Transparent Ultra Water-Repellent Thin Films by Microwave Plasma Enhanced Chemical Vapor Deposition

One of the most common methods for obtaining water repellent surfaces is spreading fluoropolymer or fluoroalkylsilane onto substrates. However, this method is not applicable to low heat-resistant substrates such as plastics, since after spreading, the method requires a heating process which is generally conducted at a temperature of about 600K. The objective of this study is the preparation of ultra water-repellent and optically transparent thin films at low temperatures below 373K. The films were deposited by means of microwave plasma enhanced plasma chemical vapor deposition (MPECVD) using organosilane, that is, trimethylmethoxysilane (TMMOS) as a source with adding Ar, CO 2 , N 2 , O 2 or air as an excitation gas. Under optimized preparation conditions, films with water contact angles more than 150 degrees and optical transparencies more than 90% were successfully fabricated.