The effect of excitation frequency in the 13.56–60 MHz range on the electron energy distribution function (EDF) of capacitively coupled plasma is investigated. Under a fixed rf voltage (50–130 V peak-to-peak) and argon pressure (100 mTorr), a remarkable change in the EDF is observed: a Druyvesteyn type at low frequencies (≃13.56 MHz) evolves into a bi-Maxwellian type in a very high frequency (VHF) above 30 MHz. The transition frequency decreases with increasing the rf voltage. The observed frequency effect on the EDF is tentatively explained in terms of the transition of electron heating mode from the collisional ohmic heating at low frequencies into the plasma surface heating in the VHF range.

The atmospheric pressure of Ar + H 2 O plasma jet has been analyzed and its effects on the poly(methyl methacrylate) (PMMA) surface has been investigated. The PMMA surface treatment was performed at a fixed gas flow-rate discharge voltage, while varying the plasma treatment time. The Ar + H 2 O plasma was studied with optical emission spectroscopy (OES). Optimum plasma conditions for PMMA surface treatment were determined from relative intensities of Argon, hydroxyl radical (OH), oxygen (O) I emission spectra. The rotational temperature T rot of Ar + H 2 O plasma was determined from OH emission band. The PMMA surfaces before and after plasma treatment were characterized by contact angle and surface free energy measurements, X-ray photoelectrons spectroscopy (XPS), atomic force microscope (AFM) and UV-spectroscopy. The contact angle decreased and surface free energy increased with plasma treatment time. XPS results revealed the oxygen to carbon ratio (O/C) on plasma-treated PMMA surfaces remarkably increased for short treatment time ≤60 s, beyond which it has weakly dependent on treatment time. The carbon C1s peak deconvoluted into four components: C–C, C–C=O, C–O–C and O–C=O bonds and their percentage ratio vary in accordance with plasma treatment time. AFM showed the PMMA surface roughness increases with plasma treatment time. UV-visible measurements revealed that plasma treatment has no considerable effect on the transparency of PMMA samples.

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Porous biphasic bioceramics that contain hydroxyapatite and tricalcium phosphate were synthesized in this study using luffa cylindrical fibres (LCF) as the template. In addition to improving the pore structure, using this template led to a chemical coating of the pores´ internal surfaces by important minerals such as magnesium and phosphorous from the LCF residue. Evaluation of our preliminary results suggests promising applications in bone tissue engineering. The synthesized porous bioceramics were characterized in view of their microstructural, physical, and in vitro features. They showed a trimodal pore system comprising a nano-pore network, smaller macropore with diameters of 5 to 100 μm, and cylindrical macropores with diameters from 100 to 400 μm; and 75% of interconnected porosity was confirmed by Mercury intrusion porosimetry and SEM images. Enhanced cell adhesion of the internal pore surfaces generated long and extended cells inside the macropores. SEM images show how the cells adhered to bioceramic surfaces and developed cytoplasmic extensions. Their proliferation in vitro demonstrates that the scaffold architecture and mineral composition are suitable for mesenchymal stem cell seeding and growth.

The effect of excitation frequency on the electron distribution function (EDF) in the 13.56-60 MHz range capacitive discharge at a fixed voltage of 80 V (peak-to-peak) in the 50-200 mTorr range of argon and helium was investigated. A marked difference in the frequency dependence of the EDF was observed between the argon and the helium discharge. In the case of argon, the EDF at low pressures (50 mTorr) is bi-Maxwellian type irrespective of the frequency while the EDF at high pressures (100 and 150 mTorr) changes from Druyvesteyn type at low frequencies to bi-Maxwellian type in the VHF range (>30 MHz). In the case of helium, however, the EDF resembles Maxwellian type over a wide frequency range, although the EDF is weakly biMaxwellian at frequencies higher than 40 MHz. The observed results are discussed taking into account surface heating, Ramsauer effect and two different electron heating modes (collisional ohmic heating and collisionless surface heating).

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Surface wave plasmas (SWPs) of large area and high density are conventionally produced under a flat dielectric window for microwave irradiation through slot antennas. However, the SWPs often show discontinuous jumps in plasma density, and they tend to localize near the slots in the case of electronegative gas discharge. In this letter we report that such problems can be avoided by using a corrugated dielectric window with a periodicity of ∼ 10 mm pitch and 5 mm depth. Compared with the conventional flat plate, the corrugated plate gives a widely spreading uniform plasma with higher power efficiency and no density jump. Three-dimensional numerical simulations of microwave excitation under the experimental conditions clearly show a dramatic change in the wave propagation along the corrugated surface, supporting the experimental observations.