Pulsed-plasma polymerization of 1-vinyl-2-pyrrolidone: Synthesis of a linear polymer

The RF plasma induced polymerization of 1-vinyl-2-pyrrolidone was examined under variable duty-cycle pulsed-plasma conditions. Large-scale progressive changes in the composition of the resultant polymeric films were observed with sequential changes in the plasma duty cycle employed during polymerization, all other plasma variables held constant. The film compositional changes obtained are in the direction of increased retention of the lactam ring of the monomer in the resultant polymers as the duty cycles employed (i.e., the ratio of plasma on to plasma off times) were decreased. Particularly significant are the relatively linear polymeric structures obtained under the exceptionally low-average power deposition conditions made accessible with the pulsed plasma technique. XPS and FTIR spectroscopic examination of these latter films reveal compositions that are similar to those obtained by conventional (i.e., nonplasma) synthesis of the linear polymer. The film chemistry controllability demonstrated in the present study is achieved while maintaining the many advantages of the plasma polymerization approach for surface modifications. This work provides additional support for use of the pulsed operational mode as an effective means of film chemistry control, in particular extending the plasma polymerization technique to include synthesis of linear polymers, in lieu of the more highly crosslinked structures typically produced in conventional continuous-wave plasma polymerization processes. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3121–3129, 1998     

Mist separation and sonochemiluminescence under pulsed ultrasound

Differences in the amount of water-mist separation and the intensity of luminol chemiluminescence for pulsed and continuous-wave (CW) ultrasound at 135 kHz have been investigated. The amount of mist generated is estimated using the cooling rate of a copper plate sprayed with the mist. For pulsed operation with an appropriate duty cycle, the cooling rate and the cooling rate per input power to the transducer are higher by 4 and 12 times compared to CW operation, respectively. This is due to the amplitude of the pulsed ultrasound being higher than that for CW ultrasound. Relatively low power pulsed operation can successfully produce both a higher sonochemiluminescence (SCL) intensity and cooling rate than those for CW ultrasound. The sonochemical reaction for pulsed ultrasound occurs at the same input power threshold as that for mist separation, whereas for CW ultrasound, the former threshold is lower than the latter. A higher number of large bubbles is produced with CW ultrasound than that with pulsed ultrasound. To achieve a sound pressure amplitude sufficient for mist separation near the surface of a liquid, it is necessary to expel these bubbles by changing the sound field from resonant standing waves to progressive waves that give rise to capillary waves on the liquid surface.     

Film Chemistry Control and Growth Kinetics of Pulsed Plasma-Polymerized Aniline

The polymerization of aniline under continuous and pulsed RF-plasma conditions is studied using the same plasma reactor. The effects of input power, on and off-times, frequency and duty cycle variations on the growth kinetics and on the chemical structure of the obtained layers are examined. The chemical structure of the films is characterized using Fourier Transform Infra-Red, X-ray photoelectron and UltraViolet?CVisible spectroscopies. The thickness of the films is determined by profilometry. The results show a strong dependence of film chemistry and deposition rates on the discharge power and on-time. The film deposited by pulsed plasma grows mainly during the plasma-on period. Furthermore, this work shows that the retention of aromatic rings can be evaluated by Fourier transform infrared analysis whereas oxidation degree of plasma polyaniline can be determined by X-ray photoelectron and UV?CVis spectroscopies.     

Plasma polymerization using pulsed microwave power

Pulsed microwave power was used to polymerize a variety of monomers containing different functional groups. We examined the effects of pulse frequency and duty cycle on the deposition rates and the composition of the polymers. For monomers that do not contain oxygen we find that there is an increase in deposition rate with increasing pulse frequency and that the pulsed deposition rate is always less than the continuous power deposition rate. For monomers that contain oxygen, or for co-depositions of hydrocarbon monomers with O₂ or CO, we find that there is a decrease in deposition rate with increasing frequency, however the deposition rate using pulsed power is greater than the rate using continuous power. This result is shown to be related to the amount of etching that takes place during the deposition process. Infrared studies reveal that pulsed power can alter the composition of plasma polymers of some oxygen-containing monomers. The presence or absence of vinyl unsaturation, nitrile groups, or a cyclic structure have no effect on the polymerization process.     

Molecular Tailoring of Surfaces: Pulsed Plasma Polymerization of Bromine Containing Monomers

The use of a variable duty cycle pulsed RF plasma is shown to provide film chemistry control during polymerization of saturated (CH₂Br₂) and unsaturated (CH₂=CHCH₂Br) bromine containing monomers. With both monomers, the degree of bromine atom retention in the films is observed to increase in a progressive fashion as the RF duty cycle employed during plasma polymerization is decreased. The film deposition rates, when expressed in terms of thickness per Joule of RF energy input, increase rapidly as the RF duty cycles are reduced. Additionally, the film morphology is observed to become increasingly smooth with decreasing RF duty cycles during deposition, as illustrated with the allyl bromide monomer. The film chemistry controllability of this study is demonstrated with monomers possessing the relatively weak C-Br bond. As such, the present work represents an important extension of the pulsed plasma polymerization approach to include retention of a labile bond during film formation. The introduction of reactive surface functional groups, at controlled densities, provides additional molecular tailoring possibilities via subsequent chemical derivatization processes.     

Design of a nanosecond beam bunching system

A nanosecond proton bunching system has been constructed at Korea Institute of Geoscience and Mineral Resources (KIGAM). This pulsed ion beam will be converted into corresponding duration of neutron pulse, which can reduce the scattered neutron background during neutron spectroscopy. The pulsed beam is obtained by deflection and double bunching by RF field. RF fields are applied to deflection and bunching electrodes as 2 kV p-p, 4 MHz and 2 kV p-p, 8 MHz, respectively. A push-pull RF amplifier has been designed and constructed with a maximum output power of 300 W continuous wave (CW) between 2 and 30 MHz. The main parameters of bunching beam were as follows: 8 MHz repetition rate, 2 ns FWHM, approximately 20% of duty factor and the maximum energy spread of 2 keV within a pulse.     

Atmospheric Pressure Plasma Discharge for Polysiloxane Thin Films Deposition and Comparison with Low Pressure Process

An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film deposition process. The DBD device is enclosed in a vacuum chamber and one of the electrodes is a rotating cylinder. Thus, this device is able to simulate continuous processing in arbitrary deposition condition of pressure and atmosphere composition. A deposition process of thin organosilicon films has been studied reproducing a nitrogen atmosphere with small admixtures of hexamethyldisiloxane (HMDSO) vapours. The plasma discharge has been characterized with optical emission spectroscopy and voltage-current measurements. Thin films chemical composition and morphology have been characterized with FTIR spectroscopy, atomic force microscopy (AFM) and contact angle measurements. A strong dependency of deposit character from the HMDSO concentration has been found and then compared with the same dependency of a typical low pressure plasma enhanced chemical vapour deposition process.     

Quantitative depth profile analysis of metallic coatings by pulsed radiofrequency glow discharge optical emission spectrometry

In recent years particular effort is being devoted towards the development of pulsed GDs because this powering operation mode could offer important analytical advantages. However, the capabilities of radiofrequency (rf) powered glow discharge (GD) in pulsed mode coupled to optical emission spectrometry (OES) for real depth profile quantification has not been demonstrated yet. Therefore, the first part of this work is focussed on assessing the expected advantages of the pulsed GD mode, in comparison with its continuous mode counterpart, in terms of analytical emission intensities and emission yield parameters. Then, the capability of pulsed rf-GD-OES for determination of thickness and compositional depth profiles is demonstrated by resorting to a simple multi-matrix calibration procedure. A rf forward power of 50 W, a pressure of 600 Pa, 1000 Hz pulse frequency and 50% duty cycle were selected. The quantification procedure used was validated by analysing conductive layers of thicknesses ranging from a few tens of nanometer up to about 20 μm and varied compositions (hot-dipped zinc, galvanneal, back contact of thin film photovoltaic solar cells and tinplates).     

Depth profile characterization of Zn-TiO2 nanocomposite films by pulsed radiofrequency glow discharge-optical emission spectrometry

In recent years particular effort is being devoted towards the development of radiofrequency (rf) pulsed glow discharges (GDs) coupled to optical emission spectrometry (OES) for depth profile analysis of materials with technological interest. In this work, pulsed rf-GD-OES is investigated for the fast and sensitive depth characterization of Zn-TiO₂ nanocomposite films deposited on conductive substrates (Ti and steel). The first part of this work focuses on assessing the advantages of pulsed GDs, in comparison with the continuous GD, in terms of analytical emission intensities and emission yields. Next, the capability of pulsed rf-GD-OES for determination of thickness and compositional depth profiles is demonstrated by resorting to a simple multi-matrix calibration procedure. A rf forward power of 75 W, a pressure of 600 Pa, 10 kHz pulse frequency and 50% duty cycle were selected as GD operation parameters.Quantitative depth profiles obtained with the GD proposed methodology for Zn-TiO₂ nanocomposite films, prepared by the occlusion electrodeposition method using pulsed reverse current electrolysis, have proved to be in good agreement with results achieved by complementary techniques, including scanning electron microscopy and inductively coupled plasma-mass spectrometry. The work carried out demonstrates that pulsed rf-GD-OES is a promising tool for the fast analytical characterization of nanocomposite films.     

RF Plasma Deposition of PEO-Like Films: Diagnostics and Process Control

Organic thin films deposited by means of radio-frequency glow discharges fed with Triglyme vapors have been investigated to explore the feasibility for deposition of organic thin films with polyethylene oxide-like features. The film chemical composition has been analyzed by means of X-ray Photoelectron Spectroscopy and FT Infrared Absorption Spectroscopy. Plasma phase diagnostics has been accomplished by means of Optical Emission Spectroscopy. It is shown that the surface density of ether carbon, which is considered the marker of the content of ethylene oxide units in the coating, decreases as the power input is increased. It is also shown that the retention of monomer structure in the film can be easily controlled in situ by actinometric optical emission spectroscopy.     

Time-resolved measurement of emission profiles in pulsed radiofrequency glow discharge optical emission spectroscopy: Investigation of the pre-peak

Radiofrequency glow discharge coupled to optical emission spectroscopy has been used in pulsed mode in order to perform a detailed study of the measured temporal emission profiles for a wide range of copper transitions. Special attention has been paid to the early emission peak (or so-called pre-peak), observed at the beginning of the emission pulse profile. The effects of the important pulse parameters such as frequency, duty cycle, pulse width and power-off time, have been studied upon the Cu pulse emission profiles. The influence of discharge parameters, such as pressure and power, was studied as well.     

Surface reactivity of pulsed-plasma polymerized pentafluorophenyl methacrylate (PFM) toward amines and proteins in solution

Pulsed-plasma polymerization has been used to deposit ultrathin layers of pentafluorophenyl methacrylate by using low duty cycles and low power input. The monomer structure can be retained such that the chemical reactivity of the active ester group could be studied using the reaction with a simple amine. The film properties in aqueous phosphate buffer have been investigated using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and real time surface plasmon resonance spectroscopy. The films react readily with diaminohexane and immunoglobulin (IgG), yet the reactivity shows a dependence on the extent of hydrolysis of the ester group.     

Influence of the Deposition Parameters on the Characteristics of Aerosol-Gel Deposited Thin Films

The aerosol-gel process is a thin film deposition process based on the sol-gel polymerisation of a liquid film deposited from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of sol-gel thin films. The effects of the aerosol deposition route on the film characteristics have been investigated with regard to sol-gel chemistry. TEOS solutions have been studied by viscosimetry and FTIR spectroscopy using an ATR device. Silica xerogel coatings have been studied by transmission FTIR and optical microscopy. Film morphology and uniformity depend closely on the aerosol deposition conditions. The film growth is controlled by a droplet coalescence surface phenomenon.     

Structure–Property Relationship of Thin Plasma Deposited Poly(allyl alcohol) Films

Poly(allyl alcohol) films with a thickness of about 150 nm were deposited by pulse plasma polymerization onto different substrates (inorganic and organic). The structure/property relationships of these samples were studied in dependence on the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time volume sensitive methods (FTIR and dielectric spectroscopy) are combined with surface analytics by employing XPS for that system. FTIR spectroscopy gives qualitatively the same dependence of the concentration of the OH groups on DC like XPS. The observed differences are discussed considering the different analytical depths of both the methods. The dielectric measurements show that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating. The results obtained by dielectric spectroscopy are discussed in detail with the data from FTIR and XPS measurements.     

A comparative study of the polyaniline thin films produced by the cluster beam deposition and laser ablation methods

Polyaniline (PANI) thin films have been prepared by applying the novel neutral and ionized cluster beam deposition (NCBD and ICBD) methods and the pulsed laser deposition (PLD) technique to the PANI samples of half-oxidized emeraldine base (EB-PANI) and protoemeraldine base forms in a high-vacuum condition. Characterization of the oxidation states and structural changes of pristine and doped thin films has been performed by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and x-ray photoelectron spectroscopy. Spectroscopic measurements demonstrate that the dominant structure of NCBD and ICBD thin films corresponds to the reduced leucoemeraldine base state, whereas the chemical composition of PLD thin films depends critically on the laser fluence and the molecular weight of PANI target. The congruent deposition is only obtained for the PLD films deposited by the laser-induced decomposition of the low-molecular-weight targets in the low to intermediate fluence regime (below 100 mJ/cm2 with a pulse duration of 7 ns). The surface morphology examined by atomic force microscopy measurements shows that the cluster and laser beams are effective in producing smooth, uniform polymeric thin films. After I2 and HCl doping, the electrical conductivities of the NCBD, ICBD, and particularly PLD thin films are increased significantly. The higher conductivity of PLD films is ascribed to higher amounts of quinoid di-imine doping sites in the EB-PANI state, and the overall structure-conductivity characteristics are consistent with the spectroscopic observations.     

Growth mechanisms involved in the synthesis of smooth and microtextured films by acetylene magnetron discharges

The growth of hydrogenated amorphous carbons (a-C:H) produced by continuous or pulsed discharges of acetylene (C(2)H(2)) in an unbalanced magnetron setup was investigated. At 5 × 10(-3) Torr, only smooth films are obtained, whereas at 5 × 10(-1) Torr using a pulsed discharge some microtextured films are formed if the duty cycle is low. The morphology of these microtextured films consists of nanoparticles, filamentary particles, and particular agglomerates ("microflowers"). This paper presents a study of acetylene gas phase polymerization by mass spectrometry, and a detailed analysis of bulk structure of films by combining three techniques which include IR spectroscopy, Raman spectroscopy, and laser desorption/ionization Fourier transform mass spectrometry (LDI-FTMS). Finally, based on the study of gas phase and film structure, we propose a model for the growth of both smooth and microtextured films.     

Time Resolved Microwave Interferometry Measurement of the Electron Density in a Pulsed 1,3-Butadiene Discharge

Pulsed plasmas containing organic precursors are becoming increasingly common for multiple applications. To understand the nature of such discharges, in-situ time resolved microwave interferometry measurements of the electron density in a 60 W pulsed inductively coupled 1,3-butadiene discharge have been made. Measurements were also made for continuous wave plasmas at 40, 50, 60 and 70 W power for comparison. The data shows that the time averaged electron densities are independent of pulse width at a particular duty cycle. In addition, time averaged values increase approximately linearly with increasing duty cycle. Such linearity in average density is tied to the ambipolar loss rate. This knowledge is important for understanding the growth kinetics of plasma polymerized films.     

Effect of Showerhead Configuration on Coherent Raman Spectroscopically Monitored Pulsed Radio Frequency Plasma Enhanced Chemical Vapor Deposited Silicon Nitride Thin Films

The effect of showerhead design, number of holes and geometry, in a parallel plate reactor was studied by measuring the concentration of silane reactant by coherent anti-Stokes Raman scattering (CARS) spectroscopy as a function of radio frequency (rf) pulse width and peak power during pulsed power plasma enhanced chemical vapor deposition (PECVD) of silicon nitride thin films. Film deposition rate, stress, SiH/NH ratio, and thickness and index of refraction homogeneity were correlated with the change in silane concentration for each of the three head geometries: radial, square, and asymmetrical. The asymmetrical head caused plasma quality problems which affected the films' qualities. The square pattern showed good mixing qualities, but produced a film with high compressive stress. The radial head provided the most homogenous film, with respect to index of refraction and film thickness. With a 10 ms pulse width, however, the radial head plasma acted as a continuous plasma for depletion and stress data. The showerhead geometry affects plasma qualities, like stability and intensity, and reactant gas velocities, which in turn affect the nitride film thickness, nitride composition, and stress.     

UV-ozone modification of plasma-polymerised acetonitrile films for enhanced cell attachment

Plasma polymerisation is of great interest for modifying the surface properties of biomedical devices in order to control, for example, protein adsorption and cell attachment. In this paper we present results for plasma-polymerised acetonitrile deposited onto silicon or polystyrene substrates. The chemistry of films deposited under a range of experimental conditions was studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). XPS provided evidence that the elemental composition of the films varied with rf power to flow rate parameter (W/F) with films produced at higher W/F being deficient in nitrogen. FTIR revealed that the plasma deposited film contained a wide range of nitrogen functional groups including amine, imine and nitrile. Oxidation of the films by exposure to radiation from a low pressure mercury vapour lamp in an air ambient increased the surface oxygen levels from 3 to 17 at.% after 300 s exposure. XPS also revealed that the oxidation process proceeded via the formation of carbonyl groups at short exposure times (<60 s) while longer treatment times (>60 s) resulted in an increase in the concentration of carboxyl groups. To assess their potential to support cell growth, polystyrene culture dishes coated with plasma deposited films and UV-ozone oxidised films were seeded with 1BR.3.N human fibroblast cells and incubated for up to 72 h. Un-oxidised plasma-polymerised acetonitrile films were found to give comparable cell attachment densities as tissue culture polystyrene. The greatest cell attachment density was found with plasma polymer films which had been UV-ozone treated for the longest time (300 s). Enhanced attachment to this surface was attributed to the high level of carboxylic groups found on this substrate.     

Scanning Raman spectroscopy for characterizing compositionally spread films

Composition-spread La(1-x)SrxMnO3 thin films were prepared by pulsed laser deposition technique from LaMnO3 and SrMnO3 targets. The films were epitaxial with a continuous variation of the out-of-plane lattice parameter along the direction of composition gradient. Scanning Raman spectroscopy has been employed as a nondestructive tool to characterize the composition-spread films. Raman spectra showed the variation of the structural, Jahn Teller distortions and the presence of coexisting phases at particular compositions that are in agreement with the previous observation on the single-crystal samples. Raman spectra on the continuous composition-spread film also reveal the effect of disorder and strain on the compositions.