Polymer pre-treatment by linear anode layer source plasma for adhesion improvement of sputtered TiN coatings

The pre-treatment of work-piece surfaces is decisive for improved adhesion of tribological, decorative, sensor, biocompatible, etc. coatings subsequently deposited by vacuum coating techniques. Most current industrial techniques (mainly glow discharges) miss the requirements for activating temperature-sensitive and electrically insulating materials. Gridless plasma sources like the linear anode layer ion source are an excellent alternative due to their low investment and operating costs and scalability to many industrial applications, and also due to the measured plasma characteristics (low surface charging, broad energy distribution). The appreciable increase of adhesion by anode layer source plasma pre-treatment and the effects of ion energy and gas composition are presented for room temperature sputtered titanium nitride coatings polyamide, polycarbonate, and poly(ethyleneterephtalate). For these polymers, the oxygen-based functionalization (chain-scissoring and cross-linking) strongly influence the wetting behaviour and improve the adhesion by suppressing adhesive cracking at low scratching loads. Low O₂ contents in Ar-O₂ discharge of ∼400 eV average ion energy lead to best coating adhesion.     

Synthesis of polypyrrole coated manganese nanowires and their application in hydrogen peroxide detection

This study focuses on the synthesis and application of polypyrrole coated manganese nanowires (Mn/PPy NWs) as an enzyme-less sensor for the detection of hydrogen peroxide (H₂O₂). The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results confirm a core–shell structure with the Mn nanowires encapsulated by the PPy. An electrochemical sensor based on the Mn/PPy NWs for amperometric determination of H₂O₂ is prepared. The electrochemical behaviour of H₂O₂ is investigated by cyclic voltammetry with the use of modified glassy carbon electrode (GCE) with Mn/PPy NWs film. The modified glassy carbon electrode (GCE) with Mn/PPy NWs shows enhanced amperometric response for the detection of H₂O₂. This is due to the high available surface area of Mn/PPy NWs which can provide a suitable area for the reaction of H₂O₂. The detection limit and limit of quantification (S/N = 3) for two linear segments (low and high concentration of H₂O₂) are estimated to be 2.12 μmol L⁻¹, 7.07 μmol L⁻¹ and 22.3 μmol L⁻¹, 74.5 μmol L⁻¹, respectively. In addition, the sensitivity for these two linear segments is 0.4762 μA mM⁻¹ and 0.0452 μA mM⁻¹ respectively.     

Factors affecting the adhesion of microwave plasma deposited siloxane films on polycarbonate

The effects of a radiofrequency oxygen plasma pretreatment and residual water content in the substrate on the adhesion of microwave plasma deposited tetramethyldisiloxane thin films on Bisphenol-A polycarbonate (BPA-PC) were investigated. Samples were characterised using a crosshatch adhesion test, optical and electron microscopy, and X-ray photoelectron spectroscopy. It was found that the use of a low power (5 W) and low treatment time (0.1 s) oxygen plasma can improve adhesion while greater treatment times (1–30 s) and higher oxygen plasma powers (40 W) resulted in a decreased level of adhesion. In addition, it was shown that a BPA-PC water content greater than 90 ppm resulted in rapid adhesion failure of deposited films at the substrate–plasma polymer interface during outdoor weathering. All films degraded substantially when exposed to environmental weathering, indicating ageing reactions within the plasma polymer films themselves, and at the bulk polymer–coating interface.     

Beam plasma discharge at low magnetic field as plasma source for plasma processing reactor

The aims of the research are to study the nature of an effect detected earlier for the formation of ion flows from a beam plasma discharge and to determine possible applications of this effect. These flows propagate in a beam plasma discharge on a normal to the discharge axis. It has been found that the acceleration of ions is a consequence of the potential gradient between an area with a high level of microwave oscillations and a peripheral area of plasma. The results of physical experiments qualitatively correlate with computer simulation data. The analysis of the physical mechanism of the effect has enabled a way of effective control of the flow energy and density to be found. The capability to change the mean energy of the ion flow in the range from 20 up to 70 eV with increase in its density by an order has been demonstrated. A possible application of the effect is a novel plasma processing reactor for treatment of materials used in electronics engineering. In particular, soft etching technology of AlGaAs barrier layers in semiconducting AlGaAs/InGaAs/GaAs heterostructures has been demonstrated.     

Novel silicon carbide/polypyrrole composites; preparation and physicochemical properties

Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon carbide as inorganic substrate. The surface modification of SiC was performed in aqueous solution by oxidative polymerization of pyrrole using ferric chloride as oxidant. Elemental analysis was used to determine the mass loading of polypyrrole in the SiC/PPy composites. Scanning electron microscopy showed the surface modification of SiC by PPy. PPy in composites was confirmed by the presence of PPy bands in the infrared spectra of SiC/PPy containing various amounts of conducting polymer. The conductivity of SiC/PPy composites depends on PPy content on the surface. The composite containing 35 wt.% PPy showed conductivity about 2 S cm⁻¹, which is in the same range as the conductivity of pure polypyrrole powder prepared under the same conditions using the same oxidant. PPy in the composites was clearly detected by X-ray photoelectron spectroscopy (XPS) measurements by its N1s and Cl2p peaks. High resolution scans of the C1s regions distinguished between silicon carbide and polypyrrole carbons. The fraction of polypyrrole at the composite surface was estimated from the silicon and nitrogen levels. The combination of XPS and conductivity measurements suggests that the surface of the SiC/PPy composites is polypyrrole-rich for a conducting polymer mass loading of at least 12.6 wt.%.     

Study on synthesis of poly(GMA)-grafted Fe3O4/SiOX magnetic nanoparticles using atom transfer radical polymerization and their application for lipase immobilization

Functionalized superparamagnetic particles were prepared by atom transfer radical polymerization of glycidyl methacrylate onto the surface of modified Fe₃O₄/SiO_X nanoparticles. The obtained particles were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Candida rugosa lipase was covalently immobilized on the magnetic particles in mild condition via covalent binding with a higher activity recovery. The resulting immobilized lipase had better resistance to pH and temperature inactivation in comparison to free lipase, the adaptive pH and temperature ranges of lipase were widened, and it exhibited good thermal stability and reusability.     

The effects of plasma pre-treatment and post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of plasma pre-treatment and post-treatment on the DLC films were investigated. Experimental results show that the surface roughness of the substrate, ranging from 0.2 to 1.2 nm, created by the plasma pre-treatment, will affect the surface roughness of the DLC films deposited using methane as the carbon source. However, the film surface roughness (0.1-0.4 nm) is much smaller than that of the substrate. Raman analysis and hardness measurement by nanoindentation indicate that the structure and the hardness of the DLC films are relatively unchanged for the film surface roughness investigated. For the argon or hydrogen plasma post-treatment of the DLC films deposited using acetylene as the carbon source, it is found that surface roughness decreases with the post-treatment time. Although the hardness decreases after post-treatment, it remains relatively constant with increasing post-treatment time.     

Low-temperature growth of ZnO nanostructures by oxygen plasma oxidation of ZnCl2

The thermodynamically forbidden reaction between ZnCl₂ and O₂ was able to take place by using oxygen plasma, yielding cone-shaped ZnO nanostructure. In situ optical emission spectroscopy was used to identify the excited species during the plasma enhanced reaction. The determination of excited temperature suggested that the addition of O₂ had great contribution to the enhanced dissociation of ZnCl₂. The successful synthesis of ZnO indicates that the chlorides may replace the organometallics as a new precursor in thin film preparation industry.     

Modelling of plasma etching using a generalized regression neural network

Plasma etching was modelled by using a generalized regression neural network (GRNN). The etching process was characterized with a statistical experimental design. Three etch responses were modelled, which include two etch rates of aluminium and silica and etching profile. GRNN prediction ability was optimized as a function of training factor. Three types of models were constructed depending on the type of prepared data. Type I model corresponds to the model constructed with the original, non-classified data. Type II and III models were built for the classified data without and with the control of data interface, respectively. Compared to type I models, type II models for two etch rates demonstrated more than 25% improvement. By the control of data interface, type III models exhibited more than 15% improvement over type II models. Classification-based models in conjunction with data control thus illustrated much improved prediction of GRNN over those for non-classified models.     

A novel route for the synthesis of processable conducting poly(m-aminophenol)

Polymerization of m-aminophenol (mAP) in aqueous NaOH solution was done chemically by using ammonium persulfate (APS) as an oxidative initiator. The product poly(m-aminophenol) (PmAP) was found to be highly soluble in aqueous sodium hydroxide, dimethyl sulfoxide (DMSO) and N,N-dimethyl formamide (DMF). From the intrinsic viscosity measurement, the optimum condition for the polymerization was established with 0.6 M NaOH medium with the ratio of monomer to oxidant as 1:1.5 (mol:mol). The polymer was characterized by FTIR and ¹H NMR spectroscopy, elemental (CHNS) and thermogravimetric (TGA) analyses. From the spectroscopic analysis the structure of the polymer was found to resemble that of hydroxy polyaniline as the polymer contains free –OH groups attached to o/m position in the phenyl ring. The elemental analysis of the polymer also confirmed the same. From TGA study, the polymer was found to be thermally stable. A freestanding film of poly(m-aminophenol) was cast in DMSO solution followed by solvent removal and drying of the film at 100 °C for 7–8 h in an oven. A dc conductivity of 4.8 × 10⁻⁴ S cm⁻¹ was obtained for the synthesized polymer film after doping with H₂SO₄ solution.     

Facile synthesis of chondroitin sulfate-stabilized gold nanoparticles

A facile and simple method for the synthesis of biocompatible gold nanoparticles (AuNPs) at room temperature has been developed by using sodium borohydride as the reducing agent and employing an inexpensive water-soluble chondroitin sulfate (CS) biopolymer as the stabilizing agent. The as-prepared AuNPs were characterized with ultraviolet–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM). Additionally, the stability of AuNPs in aqueous solution was investigated as a function of the electrolyte sodium chloride concentration. The experimental results showed that even high sodium chloride concentration (1 M) also did not destabilize the colloidal gold solution. So it could be speculated that the high stability of AuNPs should be attributed to the electrostatic repulsion and steric hindrance between the AuNPs stabilized by CS molecules, which wrapped around the surface of as-prepared AuNPs and prevented their agglomeration, and simultaneously improve biocompatibility of AuNPs as well.     

Modification of dispersibility of nanodiamond by grafting of polyoxyethylene and by the introduction of ionic groups onto the surface via radical trapping

To improve the dispersibility of polycrystalline nanodiamond (ND) in solvents, the grafting of polymers and introduction of ionic groups onto ND surface via radical trapping by ND surface were investigated. The grafting of polyoxyethylene (POE) onto ND surface by trapping of POE radicals formed by the thermal decomposition of POE macro azo-initiator (Azo-POE) was examined. The polymer radicals formed by the thermal decomposition of Azo-POE were successfully trapped by ND surface to give POE-grafted ND. The effect of temperature on the grafting of POE onto ND was discussed. In addition, the introduction of cationic protonated amidine groups onto ND was achieved by the trapping of radicals bearing protonated amidine groups formed by thermal decomposition of 2,2′-azobis(2-methylpropionamidine)dihydrochloride (AMPA). The anionic carboxylate groups was introduced onto ND surface by the trapping of the radicals bearing carboxyl groups formed by thermal decomposition of 4,4′-azobis(4-cyonovaleric acid) (ACVA) followed by the treatment with NaOH aqueous solution. The dispersibility of ND in water was remarkably improved by the grafting of POE, based on the steric hindrance of polymer chains and by the introduction of ionic groups, based on the ionic repulsion, onto ND surface.     

Synthesis and characterization of nitrated and aminated poly(phenylene sulfide) derivatives for advanced applications

Nitrated and aminated poly(phenylene sulfide) (PPS) derivatives with different extent of modification were synthesized in a one-pot reaction in suspension. Their substitution degree was determined from both elemental analysis and TGA curves. FT-IR and NMR spectra demonstrated the effectiveness of the functionalization reactions, showing the appearance of bands related to the substituent groups. A progressive reduction in thermal stability was observed as the number of functional groups increased. Aminated derivatives were thermally less stable and exhibited higher solubility in aprotic polar solvents than the corresponding nitrated polymers. DSC thermograms revealed a diminution in the crystallization temperature and a rise in the glass transition with increasing functionalization degree, since the presence of substituent groups inhibits the rotation of consecutive elements of the polymer chain. The level of crystallinity decreased upon increasing chain modification, as evidenced from X-ray diffractograms. The steric hindrance of the substituents disrupts the chain packing, leading to smaller crystals. These derivatives are expected to have applications in electromembranes and as matrix materials for the fabrication of high-performance composites suitable for structural and non-structural components.     

Novel regioregular polythiophenes containing side-chain porphyrin groups for polymeric photovoltaic cells

The paper presents a new strategy for the preparation of porphyrin-functionalized head-to-tail regioregular thiophene copolymers using a simple and effective post polymerization functionalization (PPF) procedure based on the synthesis of a regioregular and soluble polythiophene precursor followed by subsequent reaction with a suitably functionalized porphyrin derivative. Thus, thiophene copolymers poly[3-(6-bromohexyl)thiophene-co-(3-[5-(4-phenoxy)-10,15,20-triphenylporphyrinyl] hexylthiophene)]s at different porphyrin chromophore contents were prepared, obtaining, in all cases, very soluble and easily filmable derivatives. Their thermal, optical and electrochemical properties were determined and their performances as the active layer in bulk heterojunction solar cells tested.     

Effect of microwave remote plasma and radiofrequency plasma on the photoluminescence of (0001) epitaxial ZnO films

Photoluminescence of (0001) epitaxial ZnO films with thicknesses of 10, 30 and 100 nm on C-sapphire substrates have been studied at room temperature and after exposure to Ar, Ar–O₂, Ar–N₂ and Ar–H by remote microwave and radiofrequency plasmas. The photoluminescence are not modified by remote plasma treatments where only neutral species were involved. On the contrary, the photoluminescence signal is enhanced or quenched after radiofrequency plasma treatments when energetic ion species are involved in the surface treatment processes. Little changes of electric properties are observed, however, the optical transmission indicates that the absorption edge and probably also the index of refraction are affected. Photoluminescence peak shifts, widths and intensities changes show very strong similarities with polarized emission of ZnO single crystal where it exists a strong dichroism. The photoluminescence emission properties may then result from this optical modification. However, the plasma treatments on the different samples show very low stability in time, except, for the treatment in argon plasma alone. In this later case, in-situ monitoring of photoluminescence as a function of temperature revealed a partial recovery of the photoluminescence properties after a heat treatment at 400 °C for few minutes. These results indicate that photoluminescence of (0001) ZnO thin film, related to σ-emission polarized emission from c-axis polar surfaces, is highly affected by surface and implanted charged species.     

The influence of crosslinking density on the pore morphology of copolymer beads prepared with a novel pore-forming agent

Macroporous styrene–divinylbenzene (St–DVB) copolymer beads are prepared with a novel pore-forming agent, 1-chlorodecane. Copolymer beads with high specific surface area are obtained although 1-chlorodecane is a typical incompatible solvent of polystyrene. The unexpected behavior of 1-chlorodecane during preparation of copolymer beads is discussed. It is found that the excellent compatibility between the chloro substituents in 1-chlorodecane and phenyl rings in copolymer could be responsible for the unexpected behavior. In addition, the effect of crosslinking density on the pore morphology of the copolymer beads is systematically investigated. The results indicate that the specific surface area, the total pore volume and the average pore diameter of the copolymer beads strongly depend on the crosslinking agent concentration. Overall, the present study provides a novel route to prepare macroporous polymer beads with controllable pore morphology.     

Preparation polystyrene/multiwalled carbon nanotubes nanocomposites by copolymerization of styrene and styryl-functionalized multiwalled carbon nanotubes

Styryl-functionalized multiwalled carbon nanotubes (p-MWNTs) were prepared by esterification based on the carboxylate salt of carbon nanotubes and p-chloromethylstyrene in toluene. Then in situ radical copolymerization of p-MWNTs and styrene initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was applied to synthesize composites of styryl-functionalized multiwalled carbon nanotubes and polystyrene (PS) (p-MWNTs/PS). Characterizations carried out by FT-IR, ¹H NMR, UV–vis show that styryl group covalently bond to the surface of MWNTs. The results of UV showed that the solutions of p-MWNTs/PS in chloroform have the hyperchromic effect. Transmission electron microscopy (TEM) images of p-MWNTs/PS composites and scanning electron microscopy (SEM) images of fracture surface of p-MWNTs/PS composites showed the functionalized nanotubes had a better dispersion than that of the unfunctionalized MWNTs in the matrix. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) suggested that the thermal stability of p-MWNTs/PS composites improved in the presence of MWNTs.     

Synthesis of ferrofluid based nanoarchitectured polypyrrole composites and its application for electromagnetic shielding

The monodispersion of magnetic nanoparticles in conducting polymer is the prerequisite to make a high quality composite for tunable electromagnetic interference (EMI) shielding. To meet this challenge, we have designed and synthesized ferrofluid based nanoarchitectured polypyrrole composites containing Fe₃O₄ (8–12 nm) via in situ oxidative polymerization. To tune the microwave signals, polypyrrole composites (PFF) with different monomer/ferrofluid weight ratios have been prepared and characterized in microwave frequency domain. A maximum shielding effectiveness value of SE_A(max) = 20.4 dB (∼99% attenuation) due to the absorption of microwave has been observed in the frequency range of 12.4–18 GHz and attenuation level varied with ferrofluid loading. The electrical conductivity of PFF composite is of the order of 10⁻² S cm⁻¹ order and having superparamagnetic nature with saturation magnetization (M_s) of 5.5 emu g⁻¹. The lightweight PFF composites with high attenuations can provide full control over the atomic structure and are favorable for the practical EMI shielding application for commercial electronic appliances.     

Microtrenching geometry of 6H-SiC plasma etching

Single-crystal 6H-SiC films were etched in a SF₆/O₂ inductively coupled plasma. Microtrenching which occurred in most experiments at the feet of the profile sidewall was characterized in terms of maximum depth and width. Each characteristic was examined as a function of the process parameters, including ICP coil power, bias voltage, and the O₂ percentage. Experimental results showed that microtrench is caused by the addition of O₂. Apart from the etch mechanisms, relationships between microtrenching and profile angle were also identified. In most cases, the depth and width variations were strongly dependent on the profile angle variation. The statistical experimental design of the process parameters showed that the percentage of O₂ was identified as the most important parameter. The addition of O₂ has influence on the effect of microtrench due to the formation of a SiF_xO_y layer, which have a greater tendency to charge than SiC.