ADBD plasma surface treatment of PES fabric sheets

Plasma treatment of textile fabrics is investigated as an alternative to the environmentally hazardous wet chemical fabric treatment and pretreatment processes. Plasma treatment usually results in modification of the uppermost atomic layers of a material surface and leaves the bulk characteristics unaffected. It may result in desirable surface modifications, e.g. surface etching, surface activation, cross-linking, chain scission and oxidation. Presented paper contains results of the applicability study of the atmospheric pressure dielectric discharge (ADBD), i.e. dielectric barrier discharge sustaining in air at atmospheric pressure and ambient temperature for synchronous treatment of several sheets of fabric. For tests sheets of polyester fabric were used. Effectivity of the modification process was determined with hydrophilicity measurements evaluated by means of the drop test. Hydrophilicity of individual sheets of fabric has distinctly increased after plasma treatment. Plasma induced surface changes of textiles were also proven by identification of new functional groups at the modified polyester fabric surface. Existence of new functional groups was detected by ESCA scans. For verification of surface changes we also applied high-resolution microphotography. It has shown distinct variation of the textile surface after plasma treatment. Important aspect for practical application of the plasma treatment is the modification effect time-stability, i.e. time stability of acquired surface changes of the fabric. The recovery of hydrophobicity was fastest in first days after treatment, later gradually diminished until reached almost original untreated state.     

Time-resolved,stress-induced,and anisotropic phase transformation of a piezoelectric polymer

We investigate the time-dependent and anisotropic phase transformation of poly (vinylidene difluoride) (PVDF) under bending. Using combined techniques of an atomic force microscope and a Fourier transform infrared spectroscope, observation of surface morphology and phase transformation in time was made. Results showed that bending stress induces the transformation of amorphous, α,β, and γ crystalline phases. Specifically, the amorphous phase was transformed into the β phase when the bending force was applied. In addition, the transformation observed was time and direction dependent. The anisotropic behavior observed brings insights into the origin of the piezoelectricity of PVDF.     

Improved piezoelectric properties of cellular polypropylene ferroelectrets by chemical modification

To improve the thermal stability of piezoelectricity of polypropylene (PP) ferroelectrets, chemical modification of the cellular PP film was performed via chromic acid oxidation and then hydrofluoric acid treatment. Deep chemical modification is achieved as indicated by the energy-dispersive X-ray analyses on the cross-section of the modified cellular PP film. The results of the isothermal decay for piezoelectric d ₃₃-coefficient at 70°C indicate the improved thermal stability of piezoelectricity and the enhanced piezoelectric activity of the modified PP ferroelectrets. The former is attributed to the improvement of thermal stability of the charges trapped in the internal void surface layers as indicated by the thermally stimulated discharge measurements, while the latter results not only from the improved thermal stability of the charges but also from the reduction in Young’s modulus of the PP ferroelectrets due to the chemical modification as revealed by the dielectric resonance analyses.     

Characterization of the ion cathode fall region in relation to the growth rate in plasma sputter deposition

In plasma-assisted magnetron sputtering, the ion cathode fall region is the part of the plasma where the DC electric field and ion current evolve from zero to their maximum values at the cathode. These quantities are straightforwardly related to the deposition rate of the sputtered material. In this work we derive simple relations for the measurable axially averaged values of the ion density and the ion current at the ion cathode fall region and relate them with the deposition rate. These relations have been tested experimentally in the case of an argon plasma in a magnetron sputtering system devoted to depositing amorphous silicon. Using a movable Langmuir probe, the profiles of the plasma potential and ion density were measured along an axis perpendicularly to the cathode and in front of the so-called race-track. The deposition rate of silicon, under different conditions of pressure and input power, has been found to compare well with those determined with the relations derived.     

Micropatterned atmospheric pressure discharge surface modification of fluorinated polymer films for mammalian cell adhesion and protein binding

Micropatterning by an easily accessible atmospheric pressure discharge setup was performed on fluorinated polymer surfaces. Two conductively-coated glass slides are employed, together with the polymer foils to be modified and shadow masks for defining the microstructures. Surface angle measurements indicated the presence of charged groups in the surface of the fluoropolymer, enabling the growth of mammalian cells on arrays of spots with 600 μm diameter. XPS and FTIR spectra revealed the incorporation of oxygen in the surface, while the generation of aldehyde groups on the surface of fluorinated polymer films was demonstrated by selective coupling of fluorescence-labeled aminodextrane to the activated spots. The described method paves the way for producing protein microarray chips on flexible fluoropolymer substrates with standard laboratory equipment.     

Computational study of plasma-solid interaction in argon plasma with inclusion of magnetic field

In the presented contribution two groups of techniques of computational physics were used for the study of sheath structure in the DC glow discharge in argon plasma – the fluid modelling describing macroscopic plasma phenomena and the particle modelling providing more detailed insight into the plasma processes. A comparison of different computational methods is given with attention to the efficiency of computer codes in two dimensions. Another point of interest is the inclusion of external magnetic field into the models and its effect on the sheath structure.     

Carbon-free SiO<Subscript>x</Subscript> films deposited from octamethylcyclotetrasiloxane (OMCTS) by an atmospheric pressure plasma jet (APPJ)

The deposition of carbon-free, silicon oxide (SiO_x) films with a non-thermal, RF capillary jet at 27.12 MHz at normal pressure is demonstrated. The gas mixture for film deposition is constituted of argon, oxygen and small admixtures of octamethylcyclotetrasiloxane (Si₄O₄C₈H₂₄, 0.4 ppm). Surface analysis of the deposited films reveals their exceptionally low carbon content. The XPS atom percentage stays at 2% and less, which is near detection limit. The parametric study reported here focuses on the optimization of the deposition process with regard to the chemical and morphological surface properties of the coating by varying oxygen feed gas concentration (0–0.2%) and substrate temperature (10–50 °C).     

Post-deposition processes for nanostructures formed by electron beam induced deposition with Pt(PF<Subscript>3</Subscript>)<Subscript>4</Subscript> precursor

Electron beam induced deposition was performed using a Pt(PF₃)₄ precursor gas. Self-standing nanowires were produced on the edge of a molybdenum film, followed by two post-deposition processes; electron beam irradiation at room temperature and heating at about 400 K in vacuum. The as-deposited nanowires were composed of an amorphous phase, of which the dominant composition was platinum but containing a small amount of phosphorus impurity. After irradiating with a 300 keV electron beam, the amorphous nanowires were transformed to crystalline ones. By heating, the as-deposited nanowires became single-crystal platinum with a large grain size and the phosphorus content disappeared.     

A study of OH radicals in an atmospheric AC discharge plasma using near infrared diode laser cavity ringdown spectroscopy combined with optical emission spectroscopy

Simultaneous measurements of absolute concentrations of H₂O and OH radicals in an atmospheric AC discharge using continuous wave cavity ringdown spectroscopy (cw-CRDS) are reported. Formation of OH radicals and plasma temperatures are characterized by optical emission spectroscopy. The concentration of OH radical at the edge of the discharge plume at 380 K is measured by the cw-CRDS technique to be 1.1 ×10¹⁵ molecule cm^-3. Ringdown measurements of the H₂O (120-000) band and the OH first overtone around 1515 nm enable us to determine an OH generation yield, , to be 4.8 ×10^-3, where N_OH and are the number densities of OH and H₂O, respectively. The minimum detectable absorption coefficient of the cw-CRDS system is 8.9 ×10^-9  cm^-1, which corresponds to a 1σ detection limit of OH number density of 1.2 ×10¹³ molecule cm^-3 in the discharge. This experimental approach is demonstrated for the first time ever in an AC discharge, and can be applied in general to a variety of atmospheric plasmas to help study OH formation mechanisms and OH-related plasma applications.     

Features of materials alloying under exposures to pulsed plasma streams

Surface modifications and features of materials alloying under pulsed plasma exposures are investigated in this paper. The experiments were carried out with a pulsed plasma gun, which generates plasma streams with ion energies of up to 2 keV, a plasma density of (2–, an average specific power of 10 MW/cm² and plasma energy densities in the range of (5–. Nitrogen, helium, hydrogen, oxygen and different mixtures can be used as working gases. Modification of thin (1–2 μm) PVD coatings of molybdenum coating mixed with substrate in liquid phase under the pulsed plasma processing are analyzed. After alloying of ferritic/martensitic steel EP-823 with Mo the concentration of molybdenum in the modified layer of 15–20 μm achieved 20% for single treatment cycle and 30% after two cycles. Decrease of grain sizes (from tens of μm to hundreds of nm), roughness and porosity were obtained by plasma irradiation of thick (~0.1–0.3 mm) plasma sprayed coatings of Co-32Ni-21Cr-8Al-0.5Y and Ti64. A modified layer with homogeneous structure and thickness up to 50 μm is formed as a result of plasma treatment. Mechanisms of surface modification of WC-Co under irradiation with pulsed plasma streams of different ions are discussed.     

Low-temperature STM/STS investigation of nanostructures created by an STM tip on Au(111) surfaces

The structural stability of rapidly solidified (about 10⁴ K/s) Sn–3.7Ag–0.9Zn eutectic solder was explored by high-temperature annealing. For the as-cast solders, the applied fast cooling rate had a significant influence on the microstructure of the solders. The faster the applied cooling rates, the smaller the β-Sn dendrites. After annealing at 473 K for 20 and 50 h, β-Sn dendrites congregated together into bulk ones for minimizing the interfacial energy, and Ag₃Sn intermetallic compounds (IMCs) as well as ternary Ag–Zn–Sn IMCs segregated on the grain boundary of the β-Sn dendrites. It seems that the coarsening of the β-Sn dendrites in the rapidly solidified specimen brought a significant softening during annealing of the explored Sn–Ag–Zn alloy. Finally, the β-Sn dendrites vanished gradually with increase of the annealing period, which leads to a kind of softening.     

Effect of electron magnetic trapping in a plasma immersion ion implantation system

In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage of 10.0 kV is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform nitrogen plasma. A pair of external coils creates a static magnetic field with main vector component along the axial direction. Thus, a system of crossed E×B field is generated inside the vessel forcing plasma electrons to rotate in azimuthal direction. In addition, the axial variation of the magnetic field intensity produces magnetic mirror effect that enables axial particle confinement. It is found that high-density plasma regions are formed around the target due to intense background gas ionization by the trapped electrons. Effect of the magnetic field on the sheath dynamics and the implantation current density of the PIII system is investigated. By changing the magnetic field axial profile (varying coils separation) an enhancement of about 30% of the retained dose can be achieved. The results of the simulation show that the magnetic mirror configuration brings additional benefits to the PIII process, permitting more precise control of the implanted dose.     

Study of optical properties and molecular structure of plasma polymerized diethylene glycol dimethyl ether

This paper deals with plasma polymerization processes of diethylene glycol dimethyl ether. Plasmas were produced at 150 mtorr in the range of 10 W to 40 W of RF power. Films were grown on silicon and quartz substrates. Molecular structure of plasma polymerized films and their optical properties were analyzed by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy. The IR spectra show C–H stretching at 3000–2900 cm^-1, C=O stretching at 1730–1650 cm^-1, C–H bending at 1440–1380 cm^-1, C–O and C–O–C stretching at 1200–1000 cm^-1. The concentrations of C–H, C–O and C–O–C were investigated for different values of RF power. It can be seen that the C–H concentration increases from 0.55 to 1.0 au (arbitrary unit) with the increase of RF power from 10 to 40 W. The concentration of C–O and C–O–C decreases from 1.0 to 0.5 au in the same range of RF power. The refraction index increased from 1.47 to 1.61 with the increase of RF power. The optical gap calculated from absorption coefficient decreased from 5.15 to 3.35 eV with the increase of power. Due to its optical and hydrophilic characteristics these films can be applied, for instance, as glass lens coatings for ophthalmic applications.     

The influence of hard-baking temperature applied for SU8 sensor layer on the sensitivity of capacitive chemical sensor

SU8, the near-UV photosensitive epoxy-based polymer was used as a sensor layer in the capacitive chemical sensor, ready for integration with a generic double-metal CMOS technology. It was observed that the response of the sensor slowly increases with the temperature applied in hard-baking process as long as it remains below 300°C. At this temperature the response of the sensor abruptly increases and becomes almost threefold. It was shown that fully crosslinked structure of the sensor layer becomes opened and disordered when the sensor is hard-baked at temperatures between 300°C and 320°C, that is, still well below the degradation temperature of the polymer. These changes in chemical structure were analyzed by Fourier-transform infrared spectroscopy. The temperature-dependent changes of the sensor layer structure enable one to prepare a combination of capacitive chemical sensors with good discrimination between some volatile organic compounds.     

Fast solvent-driven micropump fabricated by two-photon microfabrication

A solvent-driven micropump was developed using three-dimensional two-photon microfabrication. The actuation of micropump is utilizing the bending behavior of hydrogel film under asymmetric solvent-stimulus. The micropump could absorb and discharge fluid reversibly by simply alternating solvent composition. Contributing to the thin hydrogel film with the thickness of 2.5 μm, the response time was significantly improved to 0.17 s. The discharge capacity of fluid was estimated to be as low as 9.2×10⁻² pL. The pumping of such ultra-low-volume fluid will be useful for further miniaturization of micro-nanofluidic devices.     

Structure modification of highly ordered pyrolytic graphite by Ar plasma beam scanning at different incident angles

The surface of highly ordered pyrolytic graphite (HOPG) was modified by Ar plasma beam scanning at a controllable angle of incidence. The characteristics of plasma modified HOPG were investigated by atomic force microscope (AFM), micro-Raman, X-ray photoemission spectroscopy (XPS), and grazing incident angle of X-ray diffraction (GIAXRD). A smooth surface of HOPG can be obtained by adjusting the incident angles of Ar plasma beam scanning. The surfaces of HOPG become smoother with increasing angle of incidence after Ar plasma beam scanning. Raman spectra indicate that the plasma beam scanning breaks the hexagonal structures of sp² C=C bonds near the surface of HOPG. The broken hexagonal network structures can form C–O bonds that increase the amount of oxygen on the surface of HOPG, supported by C_1s and O_1s XPS spectra. GIAXRD data support that the co-existence of both crystalline structures of 2H and 3R in HOPG. The carbon bond breaking in 2H and 3R is different and depends on the angle of incidence. Most broken carbon bonds form damaged aromatic rings near the surface of HOPG.     

Effect of cooling rate on microstructural formation and hardness of 30CrNi3Mo steel

The variation of microstructural formation and the hardness of the 30CrNi3Mo steel were systematically explored as a function of applied cooling rates in the range of 1–500°C/min. According to the measured Rockwell hardness results, four characteristic stages could be separated as different ranges of cooling rates, which corresponds well with the microstructural evolution observed. With the applied cooling rate increasing, the transformed structure evolves from granular bainite, lower bainite, self-tempered martensite, to finally martensite without self-tempering. Among them, the self-tempered martensite, obtained in the transformed specimens cooled with rates of 25–80°C/min, exhibits the highest hardness values due to the precipitation of fine carbides within it.     

Effects of carbon fiber surface treatment on the tribological properties of 2D woven carbon fabric/polyimide composites

Polyacrylonitrile (PAN)-based carbon fabric (CF) was modified with strong HNO₃ oxidation and then introduced into polyimide (PI) composites. The friction and wear properties of the carbon fabric reinforced polyimide composites (CFRP), sliding against GCr15 stainless steel rings, were investigated on an M-2000 model ring-on-block test rig under dry sliding. Experimental results revealed that the carbon fiber surface treatment largely reduced the friction and wear of the CFRP. Compared with the untreated ones, the surface-modified CF can enhance the tribological properties of CFRP efficiently due to the improved adhesion between the CF and the PI matrix. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) study of the carbon fiber surface showed that the fiber surface became rougher and the oxygen concentration increased greatly after surface treatment, which improved the adhesion between the fiber and the PI matrix and improved the friction-reduction and anti-wear properties of the CFRP. An erratum to this article can be found at     

Dust particles in collisionless plasma sheath with arbitrary electron energy distribution function

Dust particles often appear in industrial plasmas as undesirable product of the plasma-wall interactions. Large particles of several micrometers in diameter are concentrated in a thin layer (the sheath) above the lower electrode of the rf driven parallel plate device, where the electric force is strong enough to compensate particle’s gravity. Experimental and theoretical uncertainties are significantly increased in the plasma sheath. Common models of dust charging in the plasma sheath suppose the Maxwellian electron energy distribution function (EEDF) in conjunction with a flux of cold ions satisfying classical Bohm criterion at the sheath edge. In this paper we generalize this model to arbitrary EEDF with adapted Bohm criterion. We limit our considerations to collisionless or slightly collisional plasma, where the EEDF inside the sheath is expressed through the EEDF in the plasma bulk. Derived theoretical formulas are incorporated into numerical model, describing collisionless radio frequency (rf) plasma sheath together with the electrical charge, various kinds of forces, balancing radius and oscillation frequency of particles.     

Electrical properties and photoconductivity of polyaniline/sulfonated poly(arylene ether sulfone) composite films

Temperature dependent electrical conductivity of the polyaniline-sulfonated poly(arylene ether sulfone) with 35 mol percent sulfonation (PANI-BPS35) composite films were investigated in the temperature range of 80–380 K. These composite films showed semiconductor behavior with the exponential variation of inverse temperature dependence of electrical conductivity. Calculated Mott’s parameters showed that variable range hopping mechanism is the dominant transport mechanism for the carriers in low temperature region. Photoconductivity of the PANI-BPS35 composite films having 10, 20, and 40 weight percent conductive filler under various illumination intensities was also studied. Photocurrent of the composite films increased with increasing both polyaniline weight fraction and temperature. Finally, the effect of doping on both electrical conductivity and the photoconductivity of the composite films was investigated.