Low-power Plasma Treatment Research Articles

Improvement of conductivity of graphene-silver nanowire hybrid through nitrogen doping using low power plasma treatment

Graphene-silver nanowire (AgNW) hybrid structure is a potential candidate to replace indium tin oxide (ITO) owing to its high conductivity, transparency, and flexibility. The thin insulating polyvinylpyrrolidone (PVP) residual surfactant coating that forms on AgNW weakens the wire-to-wire and wire-to-graphene contact, resulting in a higher sheet resistance. For this reason, a post-processing treatment such as high-temperature annealing is usually carried out to reduce the sheet resistance. In this paper, low power nitrogen plasma is utilized to increase the electrical conductivity of the hybrid through the partial removal of PVP and simultaneous doping of graphene without employing any high-temperature annealing treatment. A reduction of over 34% in sheet resistance is obtained for the hybrid compared with a 17% reduction for the AgNW electrode alone. The hybrid electrode, in comparison to the AgNW electrode alone, results in an electrical to optical conductivity ratio (σDC/σOP) of 234 in 45 s without losing its transparency. In comparison to the 4% reduction of sheet resistance caused by high temperature annealing at 180 °C for 30 min, nitrogen plasma treatment results in a substantially higher reduction (>34%) of the sheet resistance of hybrids in a substantially shorter processing time (45 s).

Optical Emission Spectroscopy Study and 3-D Surface Characterization of Silicone Rubber Exposed to Different Argon RF Plasma Powers

The present study was undertaken to investigate the effect of argon plasma treatment on the extent of Foley catheter surface modification. Foley catheter (flexible tube made of silicone rubber, used for urinary catheterization) surface was treated at different argon (Ar) RF plasma powers. The surface modification was assessed by measurement of contact angle. Contact angle study shows decrease in contact angle and increase in surface free energy shows more polar group incorporation at low power plasma treatment. Atomic force microscopy (AFM) revealed an increased average surface roughness proportional to plasma power. Optical emission spectroscopy (OES) shows various states of argon causing surface modification.

Imparting electrical conductivity to a plastic optical fibre based on poly(methyl methacrylate)

In this study, as a preliminary work on the realisation of an optical/electrical acupuncture needle, we have attempted to impart electrical conductivity to a plastic optical fibre (POF) by coating a thin gold layer on its surface. First, we investigated the adhesion between the gold and two different substrates, poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)), which were used as the core and the cladding of POF, respectively. To enhance the interfacial adhesion between the gold layer and the substrates, the following two different approaches were applied: low-power plasma treatment and physical surface roughening. A 50 nm-thick gold layer was deposited by ion sputtering onto both the substrates and also onto the 0.5 mm-diameter POF. The variation of wettability and adhesion according to the plasma conditions were investigated through water contact angle measurement and cross-hatch cut testing. Despite the decreased contact angles of the substrates after Ar or O2 plasma treatment, both polymers exhibited very poor adhesion to the gold layer. However, substrates roughened by sandblasting showed 3B class adhesion to gold in the cross-hatch tape test results. The POF that was gold-sputtered after sandblasting showed an electrical conductivity of 1.35 × 103 S cm−1 without any significant optical loss. This fabrication technique may be used for developing a medical needle capable of simultaneously applying electrical and optical stimulus.

Hysteresis and Reversibility of a Superhydrophobic Photopatternable Silicone Elastomer

We report upon the wetting property of layers of a micropatterned photodefinable silicon elastomer, PDSE, repetitively and alternatively treated with oxygen plasma and temperature cycles. At low power plasma treatments, we observed a hysteresis in terms of contact angle between phases lowering the contact angle and phases of recovery. As opposed to high power plasma for which we show that by generating fissures on the surface, the structure can be cycled between superhydrophobic and superhydrophilic states. The plasma-generated diffusion paths were characterized by electron microscopy and were found to be directly related to the recovery of the wetting properties of the plasma treated layers of PDSE. The cycling between the superhydrophobic and superhydrophilic states was dependent on the power of the applied plasma as well as the condition during the contact angle recovery amplified by a temperature-controlled baking step.

Polymer Surface Functionalization Using Plasma, Ultraviolet and Synchrotron Radiation

Polyurethane (PU) and polystyrene (PS) films were functionalized by ultraviolet (UV) or selective synchrotron radiations (SR) in the presence of reactive gases. The UV-PU results were compared with lowpressure plasma treatments of the same films. Oxygen or acrylic acid vapours (AA) were used as reactive gases. X-ray photoelectron spectroscopy measurements of UV modified films in the presence of oxygen or AA matched the RF-plasma treatments results. It is shown that COO and C=O functional groups were incorporated at the polymer surface efficiently with both methodologies. In addition, near-edge X-ray absorption fine structure showed that a thin film of poly(acrylic acid) is formed over the PU and PS films during the UV irradiation in the presence of AA vapours. These results resemble previous AA low-power plasma treatments. PU and PS films were also selectively functionalized by SR using oxygen as reactive gas. Surface concentrations of COO and C=O functional groups were enhanced by C1s → σ* C–C excitation after irradiation and oxygen introduction. This efficient surface functionalization was clearly observed in PS films which do not have CO and COO groups in their molecular structure. Excitations involving transitions to π* orbital (π*C=C, π*C=O) led to much lower functionalization efficiency. The SR results can be explained by taking into account previous photon stimulated ion desorption studies of polymers. SR results may open new ways to functionalize polymer surfaces selectively and efficiently.

Ultraviolet-induced surface modification of polyurethane films in the presence of oxygen or acrylic acid vapours

An efficient surface functionalization of polyurethane (PU) films has been obtained by ultraviolet (UV)-assisted modification in the presence of oxygen or acrylic acid (AA) vapours. Film analyses were carried out by water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and Near-edge X-ray absorption fine structure (NEXAFS). Film hydrophilicity increased with photolysis time in the presence of oxygen or AA vapours. Incorporation of COO and C O functional groups at the polymer surface after the UV-assisted treatments was observed. In addition, High resolution XPS and NEXAFS results showed that a thin film of poly (acrylic acid) (PAA) is formed over the PU films during the UV irradiation with AA vapours. The obtained results are compared with previous published oxygen and AA low-power plasma treatments. Similarity between both treatment methodologies is shown. UV surface functionalization and polymerization of PAA can be used instead of a traditional plasma treatment with the advantage of set-up simplicity and lower costs.

High Pressure Plasma Treatment for Controlling the Surface Activity and Optical Properties of TiO2 Nanoparticles

The effect of high pressure radio frequency (RF) plasma treatment on TiO2 surface and photocatalytic property has been investigated. X-ray photoelectron spectroscopy (XPS) measurements have shown the two different oxidation states of oxygen in the untreated TiO2 powder. Its relative proportion changes with the different dose of plasma treatments. The proportion of Ti3+ surface states also changes after plasma treatment and strongly depends on combination of plasma power and treatment time. The photocatalytic activity of plasma-untreated and -treated samples was measured by observing the relative degradation of methylene blue. The result showed about 50% increase in photoactivity at the sample treated with 10 W RF power plasma. Low power plasma treatment is a more efficient process for achieving a photoactive surface. The effect of total dose (power and treatment time) and power has been also studied to modify the surface activity of TiO2 nanoparticles.

A Study of the Effects of Low Power Plasma Treatment on Graphite and Highly Orientated Pyrolytic Graphite (HOPG) Surfaces

Abstract We have studied both the chemical and topographical changes induced on graphitic surfaces by low power plasmas using surface-sensitive X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and atomic force microscopy (AFM). Evidence is presented for two totally different reaction mechanisms for air plasma and nitrogen plasma interactions with these surfaces. Both plasmas chemically alter the first few atomic layers of the surface; however, air plasma treatment results in the formation of an oxidised layer, whereas nitrogen plasma treatment generates a much more open structure of loosely adhered material.

The effect of low power plasmas on carbon fibre surfaces

The effect of a variety of low power plasma treatments (e.g., NH 3, N 2, air and Ar) on low modulus carbon fibre surfaces have been examined using X-ray photoelectron spectroscopy. Grazing angle techniques have been used to probe only the first 12–15A of the fibre surface. Plasma treatments were carried out in an in situ plasma cell which was attached to a PHI 5400 X-ray photoelectron spectrometer. This enabled the immediate effects of the plasma to be studied before the treated surface was exposed to air. Air plasmas introduced both alcohol and carboxyl groups onto the fibre surfaces. Nitrogen plasmas gave very similar results to ammonia plasmas with the formation of three nitrogen containing species on the fibre surface. The signal at 398.9eV was assigned to a combination of aromatic amines (-NH 2), and -CNH groups. Its relative intensity, as expected was greater for fibres treated in ammonia plasmas. Air exposure of these activated surfaces results in a strongly bound -O-H layer. Significant etching or pitting was not observed in the scanning electron micrographs of these treated fibres. Comparing XPS spectra of the immediate surface with those taken at bulk sensitive angles, it can be concluded that chemical change only occurred in the first few atomic layers.