Yoou-Bin Guo

Adhesion improvements for diamond-like carbon films on polycarbonate and polymethylmethacrylate substrates by ion plating with inductively coupled plasma

Abstract An inductively coupled plasma (ICP) ion plating method using hexamethyldisiloxane (HMDSO) and oxygen reactants was employed to deposit hard diamond-like carbon (DLC) coatings on polycarbonate (PC) and polymethylmethacrylate (PMMA) substrates. O2 plasma was the most effective pretreatment method for improving the adhesion of the DLC on the polymer by removing the contaminants and forming the polar functional groups on the surfaces. The adhesion of the DLC film on the PMMA substrate was always much worse than that on the PC substrate. To improve the DLC film adhesion on the PMMA substrate, interfacial layers were deposited by remote plasma polymerization in order to avoid the destruction of the functional groups in the monomer precursors. Interfacial layers deposited using HMDSO/C2H5OH mixture, methylmethacrylate and propylene oxide monomers were successful to improve the adhesion of the DLC films on the PMMA from 1A (with no interfacial layer) to 4A–5A, as measured by the X-cut method. The adhesion abilities of the interfacial layers were strongly dependent on the gas phase reactions during depositions. To understand the critical roles of the interfacial layers, the effects of the deposition conditions as well as the structures of the interfacial layers were studied.

Radio-frequency microdischarge arrays for large-area cold atmospheric plasma generation

By flowing gases through arrays of microhollow cathode holes, large area (12 mm in diameter) uniform and stable discharges could be generated by a rf power supply. Both the rf power and the gas flow through the cathode holes played key roles in maintaining uniform and stable discharges. The discharges could be stable for a period longer than one hour in pure helium (He) and in He containing 1% hexamethyldisiloxane (HMDSO). By using a third steel electrode biased with a pulse power supply (100 kHz, 50% duty cycle), the plasma from arrays of cathode holes could be extended to 20 mm in length. Amorphous carbon films deposited by the extended atmospheric plasma using 1% HMDSO/He reactants exhibited the same structure as those by low pressure plasma chemical vapor deposition.

Transparent Ultrahigh-Strength Moisture Barrier Film Fabricated by Lamination Process

Multilayer barrier films were fabricated by stacking multiple pairs of inorganic and organic layers on organic-treated poly(ethylene terephthalate) (PET) substrates. The inorganic and organic moisture barrier layers were prepared by plasma-enhanced chemical vapor deposition (PECVD) and bar coating, respectively, at room temperature. The water vapor transmission rate (WVTR) through six pairs of inorganic/organic stacking layers can reach 2.1×10-5 g m-2 day-1. By laminating two PET substrates, both coated with two pairs of inorganic/organic barrier layers, individually achieving a WVTR of 5 ×10-3 g m-2 day-1, an ultrahigh-strength moisture barrier film could be produced with the WVTR significantly lowered to as much as 4×10-5 g m-2 day-1, which was in the same order of magnitude as a single PET film coated with six pairs of inorganic/organic stacking layers. Even after bending 5,000 times, the laminated barrier film maintained not only the high moisture barrier strength but also the good optical transparency and flexibility. The possible reason for the significant improvement of the moisture barrier strength by lamination is also proposed.

Characteristics of Large-Area Cold Atmospheric Discharges from Radio-Frequency Microdischarge Arrays

Uniform and homogeneous large-area cold atmospheric discharges were produced by arrays of radio-frequency (rf) microhollow cathode discharges. A high flow rate of helium through the cathode holes was necessary to maintain stable and uniform discharges. The rf power also played a key role in sustaining the homogeneous and uniform discharges due to its efficiency being higher than that of the dc or pulse discharges. The rf microdischarges under various conditions were characterized by optical emission spectroscopy and by measuring the electrode voltage with an oscilloscope. Due to the higher concentration of Ag contaminants in the plasma, the optical emission intensity from the discharge using silver paste as the cathode was lower than that using silver paste as the anode. The electron temperature and the plasma density increased with increasing rf power and helium flow rate. The dc self-bias of the rf-powered electrode for the atmospheric discharge could be either negative or positive depending on the plasma density. A mechanism was proposed to explain the positive self-bias characteristic of the atmospheric discharge. Using a third electrode powered by a pulse power supply (100 kHz, 50% duty cycle), the rf microdischarge sheet was extended into a stable and homogeneous volume discharge with the thickness increased from 3 mm to 20 mm.

Modifications of DLC films for MEMS applications

SiOx-containing DLC films are deposited by plasma enhanced chemical vapor deposition on Si substrate. The effect of SiOx dopants on the stress, adhesion and hydrophobicity of the DLC films are studied. The incorporation of SiOx in the DLC films deposited by using hexamethyldisiloxane and CH4 mixture reduces the residual stress as well as enhances adhesion of the film on the substrate. Besides, the thermal stability of the film also improves.