Pulsed Radiofrequency Glow Discharge Research Articles

Challenging identifications of polymer coatings by radiofrequency pulsed glow discharge-time of flight mass spectrometry

Radiofrequency pulsed glow discharge (RF-PGD) coupled to time of flight mass spectrometry (TOFMS) has become a powerful tool for obtaining both elemental and molecular information directly from solid samples. Two GD Grimm-type based designs coupled to TOFMS are compared for the analysis of polymers. One of the chambers is an in-house design (“UNIOVI GD”), while the other (named “GD.1”) corresponds to the source included in the initial GD-TOFMS prototype. Operating conditions were similar for both GD designs (15 W of applied power with both chambers, 200 Pa of pressure for GD.1 and 150 Pa for the UNIOVI GD), with argon being the plasma gas used. Experimental results showed that the GD.1 design provides richer molecular information and also better detection limits for polyatomic ions (in the low μg g−1 range); this fact could be attributed to higher distance between the sample and the mass spectrometric interface in GD.1 design. Furthermore, this GD source contains a flow tube inside the anode favouring the formation of polyatomic ions and, thus, providing higher molecular information. Moreover, the use of an argon pre-chamber to minimize the entry of external air, which could interfere in the sought polymer identification, has been successfully evaluated as well. Finally, four conductive polymers (polyaniline, polyphenylene sulfide, polypyrrole and polythiophene) containing carbon, hydrogen and either sulphur or nitrogen have been characterized using RF-PGD-TOFMS (using the GD.1 chamber and the Ar pre-chamber). Results showed that some of the polyatomic ions can be eventually considered as fragments coming from the structures of the corresponding monomers constituting each polymer. Thus, the molecular information provided by RF-PGD-TOFMS under appropriate experimental conditions enables a fast and reliable identification of the studied polymers.

The 7th international conference on instrumental methods of analysis: modern trends and applications (IMA 2011)

The 7th international conference “IMA 2011, Instrumental methods of analysis: modern trends and applications” was held from 18–22 September, 2011, in Chania (west Crete), which presents an excellent combination of cultural life, natural beauty (numerous beaches, gorges such as the renowned Samaria gorge, high mountains, biodiversity, etc.), a Venetian old town and many archaeological sites. The conference was held at the Conference Centre of theMediterraneanAgronomic Institute of Chania/Centre International de Hautes Etudes Agronomiques Mediterraneennes (MAICh/CIHEAM). This is a conference centre conceived with respect for the environment, situated 3 km from the centre of Chania on the campus of the institute. IMA 2011 is the seventh conference in this series, which started in 1999 in Chalkidiki, Macedonia, Greece, under the chairmanship of Professor M. Ochsenkuhn-Petropoulou and there has been a conference every 2 years since then organized by different other Hellenic academic institutions. IMA 2011 provided an excellent framework for the presentation of new concepts, instruments, methods, systems and applications in the area of modern chemical analysis. Researchers and scientists from universities, research institutions, state organizations and industry were in attendance and presented their experiences in the current state of the art in the area of instrumental methods of analysis. Furthermore, IMA 2011 provided grounds for graduate and postgraduate students to disclose their projects, discuss scientific collaborations with other groups, as well as to explore employment opportunities. IMA 2011 was organized with the cooperation of two of the most important Cretan institutes: the Technical University of Crete (Analytical and Environmental Chemistry Laboratory) and the MAICh/CIHEAM. Co-organizers were other Hellenic academic analytical chemistry institutions actively involved in former IMA conferences. The conference was opened by Professor Y. Phillis, Rector of the Technical University of Crete. Honorary prizes were awarded to Professor Elo Hansen, Denmark, and Professor Antonius Kettrup, Germany, for their top contributions in the field of analytical chemistry. Presentations were given in the fields of bioanalytics, speciation, sensors, materials science and nanomaterials, mass spectrometry, environmental analysis, chromatography, X-ray analysis and atomic absorption spectrometry over the 5 days of the conference. The scientific framework consisted of 14 sessions, 2 of which were held in parallel. Each session was introduced by a plenary lecture conducted bywell-known invited scientists experienced in the respective fields from all over the world, for example, A. Sanz-Medel (Pulsed radiofrequency glow discharge time-of-flight mass spectrometry for isotopes, elements, molecules and nanostructured materials), R. Lobinski (High-resolution molecular mass spectrometry in the analysis of heteroatom-containing molecules), B.Michalke (Element speciation in neurodegenerative disease investigation—focus on manganese), G. Hieftje (New instruments for mass spectrometry),W. Lindner (Potential of chiral ion exchanger for chromatographic resolution of stereoisomers), and chaired by experts in instrumental methods of analysis. Published in the special paper collection Instrumental Methods of Analysis (IMA 2011) with guest editors Maria OchsenkuehnPetropoulou, Nikos Kallithrakas and Panagiotis Kefalas

Depth-profile analysis of thermoelectric layers on Si wafers by pulsed r.f. glow discharge time-of-flight mass spectrometry

In this work the depth-profile analysis of thermoelectric layers deposited on Au and Cr covered Si wafers with the aid of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (pulsed RF-GD-TOFMS also called plasma profiling TOFMS (PP-TOFMS™)) is described. For thermoelectric materials the depth resolutions obtained with both PP-TOFMS and secondary ion mass spectrometry (SIMS) are shown to be well comparable and in the order of the roughness of the corresponding layers (between 20 and 3700nm). With both methods a direct solid analysis without any preparation steps is possible. In addition, the analysis of the samples with PP-TOFMS proved to be faster by a factor of 26 compared to SIMS, as sputtering rates were found to be 80nms−1 and 3nms−1, respectively.For the analyzed samples the results of PP-TOFMS and SIMS show that a homogeneous deposition was obtained. Quantitative results for all samples could also be obtained directly by PP-TOFMS when the stoichiometry of one sample was determined beforehand for instance by inductively coupled plasma optical emission spectrometry (ICP-OES) and scanning electron microscopy energy dispersive X-ray fluorescence spectrometry (SEM-EDX). For Bi2Te3 the standard deviation for the main component concentrations within one sample then is found to be between 1.1% and 1.9% and it is 3.6% from sample to sample. For Sb2Te3 the values within one sample are from 1.7% to 4.2% and from sample to sample 5.3%, respectively.

Spatial emission distribution of a pulsed radiofrequency glow discharge: Influence of the pulse frequency

A pulsed radiofrequency Glow Discharge (pulsed rf GD) plasma has been spectroscopically characterized by performing side-on measurements of the emitted radiation. The effect of varying the pulse frequency (e.g. between 100 and 10,000Hz), while keeping the duty cycle constant at 25%, has been investigated on different argon and analyte (i.e. copper) emission lines, at different plasma locations. In particular, it is observed that an intermediate frequency of 2.5kHz favors the excitation of the argon atoms, while the argon ions are preferably excited by lower frequencies (e.g. longer pulse widths). Moreover, the excitation of copper atoms has a strong dependence on the upper energy level, and it has been noticed that the emission from higher levels is favored by the use of lower pulsed-rf frequencies. On the other hand, it has been found that the spatial distribution of the gas species and the analyte species (i.e. Ar and Cu, respectively) differ from each other: the atomic argon emission extends longer along the plasma plume than the atomic copper emission. Furthermore, ionic species have their maximum emission signal in the region close to the anode; however, their emission signal decay quite fast at increasing distances to the anode. Nevertheless, it should be highlighted that it is possible to detect ionic emission at distances far away from the negative glow; in regions where usually the sampler cone interface is placed in GD-MS instruments.

Influence of the hydrogen contained in amorphous silicon thin films on a pulsed radiofrequency argon glow discharge coupled to time of flight mass spectrometry. Comparison with the addition of hydrogen as discharge gas

Thin film solar cells technology based on hydrogenated amorphous silicon (a-Si:H) has undergone a great expansion during recent years. Pulsed radiofrequency glow discharge time-of-flight mass spectrometry (rf-PGD-ToFMS) is able to perform depth profiling analysis of coated materials, providing an excellent tool for rapid and high sensitive chemical characterisation of photovoltaic devices. The hydrogen concentration on a-Si:H thin films is around 10%, which represents a challenge for quantitative depth profile analyses by using GD sources due to the so-called “hydrogen effect”. It is well-known that when hydrogen is present in the Ar discharge, even in small quantities, significant changes can occur in the ion signal intensities and sputtering rates measured. Therefore, a critical comparison has been carried out by rf-PGD-ToFMS in terms of pulse profiles, spectral interferences and depth resolution for two modes of hydrogen introduction in the discharge, exogenous hydrogen in molecular gaseous form (using the mixture 0.2% H2 + Ar as discharge gas) or endogenous hydrogen, sputtered as a sample constituent. For this purpose, non-hydrogenated materials (containing B, P and Si) and three types of a-Si:H thin films were investigated. Exogenous hydrogen was found to produce a noteworthy influence on the pulse profiles of the analytes, whereas the effect of the hydrogen sputtered from the samples could be considered less notorious. Moreover, the proper selection of the after-peak region was found to be critical to obtain optimum mass spectra (i.e. high analyte sensitivities free of interferences).

Pulsed glow discharge time of flight mass spectrometry for the screening of polymer-based coatings containing brominated flame retardants

There is an increasing concern regarding the toxicity, environmental distribution and impact of organic compounds employed today as flame retardants. Along these lines, the potential of radiofrequency pulsed glow discharge (rf-PGD) time-of-flight mass spectrometry for mass spectrometric fingerprinting and quantification of brominated flame retardants (BFRs) into polymers is investigated here. Tetrabromobisphenol A was chosen as a “model” BFR compound for system optimisation and analytical characterisation purposes. After optimisation of power and pressure operation conditions of the rf-PGD, 15 W forward power and 200 Pa were chosen with the aim of attaining good sensitivity for elemental and polyatomic ions and long-term signal stability. Then, analytical performance of micro- and milli-second GD pulse regimes was compared and better detection limits were obtained using the millisecond pulse regime (a higher number of polyatomic ions was observed as well). Under the selected optimum conditions, linear calibration graphs were obtained for elemental bromine as well as for several polymer fragments. Limits of detection well below 0.1% were obtained both for elemental bromine and for the fragments investigated. Finally, a comparison of the mass spectra obtained for some polymeric samples containing different BFR compounds was carried out. The signals of polyatomic ions, related to the BFRs, can be successfully applied to the identification and discrimination among the different polymers.

Pulsed rf-GD-TOFMS for depth profile analysis of ultrathin layers using the analyte prepeak region

Direct solid analysis of ultrathin layers is investigated using pulsed radiofrequency (rf) glow discharge (GD) time-of-flight mass spectrometry (TOFMS). In particular, previous studies have always integrated the detected ion signals in the afterglow region of the rf-GD pulse, which is known to be the most sensitive one. Nevertheless, the analytical capabilities of other pulse time regions have not been evaluated in detail. Therefore, in this work, we investigate the analyte prepeak region, which is the pulse region where the analyte ions peak after the initial sputtering process of each GD pulse, aiming at obtaining improved depth profile analysis with high depth resolution and with minimum polyatomic spectral interferences. To perform these studies, challenging ultrathin Si-Co bilayers deposited on a Si substrate were investigated. The thickness of the external Si layer was 30 nm for all the samples, whilst the internal Co layer thicknesses were 30, 10, 5, 2 and 1 nm, respectively. It should be remarked that the top layer and the substrate have the same matrix composition (Si > 99.99%). Therefore, the selected samples are suitable to evaluate the response of the Si ion signal in the presence of an ultrathin Co layer as well as the possible oxygen contaminations or its reactions. Additionally, these samples have been evaluated using time-of-flight secondary ion mass spectrometry, and the results compare well to those obtained by our pulsed rf-GD time-of-flight mass spectrometry results.

Endogenous and exogenous hydrogen influence on amorphous silicon thin films analysis by pulsed radiofrequency glow discharge optical emission spectrometry

During the last decade the photovoltaic industry has been growing rapidly. One major strategy to reduce the production costs is the use of thin film solar cells based on hydrogenated amorphous silicon (a-Si:H). The potential of pulsed radiofrequency glow discharge coupled to optical emission spectrometry (rf-PGD-OES) for the analysis of such type of materials has been investigated in this work. It is known that when hydrogen is present in the argon discharge, even in small quantities, significant changes can occur in the emission intensities and sputtering rates measured. Therefore, a critical comparison has been carried out by rf-PGD-OES, in terms of emission intensities, penetration rates and depth resolution for two modes of hydrogen introduction in the discharge, manually external hydrogen in gaseous form (0.2% H 2–Ar) or internal hydrogen, sputtered as a sample constituent. First, a comparative optimisation study (at 600 Pa and 50 W) was performed on conducting materials and on a silicon wafer varying the pulse parameters: pulse frequency (500 Hz–20 kHz) and duty cycle (12.5–50%). Finally, 600 Pa, 50 W, 10 kHz and 25% duty cycle were selected as the optimum conditions to analyse three types of hydrogenated samples: an intrinsic, a B-doped and a P-doped layer based on a-Si:H. Enhanced emission intensities have been measured for most elements in the presence of hydrogen (especially for silicon) despite the observed reduced sputtering rate. The influence of externally added hydrogen and that of hydrogen sputtered as sample constituent from the analysed samples has been evaluated.

Investigation of the afterglow time regime in pulsed radiofrequency glow discharge time‐of‐flight mass spectrometry

The pulsed power operation mode of a radiofrequency (rf) glow discharge time-of-flight mass spectrometer was investigated, for several ions, in terms of intensity profiles along each pulse period. Particular attention was paid to the plateau and transient afterglow regions. An rf pulse period of 4 ms and a duty cycle of 50% was selected to evaluate the influence of discharge parameters in the afterglow delay and shape of Ar(+), Ar(2)(+) and several analytes (Br, Cl, Cu) contained in polymeric layers. Pulse shapes of Ar(+) and Ar(2)(+) ions vary with pressure and power. At low pressures the highest intensity is observed in the plateau while at higher pressures (>600 Pa) the afterpeak is the dominant region. Although the influence of the applied power is less noticeable, a widening of the afterglow time regime occurs for Ar(+) when increasing the power. Maximum intensity of the argon signal is measured in the afterglow at 30 W, while the area of such afterpeak increases with power. The maximum intensity of Ar(2)(+) is obtained at the highest power employed (60 W) and the ratio maximum intensity/afterglow area remains approximately constant with power. Analytes with ionization potentials below (Cu) or just above (Br) the argon metastable energy show maxima intensities after argon ions decay, indicating they could be ionized by collisions with metastable Ar atoms. Chlorine signals are observed in the afterglow despite their ionization potential is well above the energy of argon metastable levels. Moreover, they follow a similar pattern to that observed for Ar(2)(+) , indicating that charge-transfer process with Ar(2)(+) could play a significant role.

Analytical performance of pulsed radiofrequency glow discharge optical emission spectrometry for bulk and in-depth profile analysis of conductors and insulators

Radiofrequency glow discharge (rf-GD) coupled to optical emission spectrometry (OES) has proved to be a powerful tool for the direct solid bulk materials and in-depth profile analysis. Rf-GD is generally operated in continuous mode, but the interest in pulsed (P) rf-GD is steadily increasing. So far, however, investigations to assess the analytical performance of rf-PGD-OES are scarce and systematic studies to analyse homogeneous and/or coated samples are still lacking. This work aims at critical comparison of the practical analytical performance characteristics of rf-GD-OES operated in continuous and pulsed modes. Pulsed rf-GD was carefully evaluated for the analysis of three conducting materials with different matrices (copper, steel and aluminium) and for bulk homogenous non-coated glasses of varying thicknesses (1, 1.8 and 2.8 mm). The comparison was performed in terms of crater shapes, sputtering rates and emission yields, demonstrating that increased emission yields could be obtained in pulsed mode working with small pulse widths (i.e. at high pulse frequency and relatively short duty cycle). Further, the potential of the pulsed rf-GDs has been studied also for depth profiling analysis of a thin gold layer (∼30 nm) deposited on conductive and insulating substrates. An improvement in the depth-resolution, under selected experimental conditions, was clearly observed. Finally, those observed advantages of pulsed rf-GD-OES were successfully tested by analysing real-life samples including commercial tinplates and a multilayered glass.

Pulsed Radiofrequency Glow Discharge Time-of-Flight Mass Spectrometry for Nanostructured Materials Characterization

Progress in the development of advanced materials strongly depends on continued efforts to miniaturizing their structures; thus, a great variety of nanostructured materials are being developed nowadays. Metallic nanowires are among the most attractive nanometer-sized materials because of their unique properties that may lead to applications as interconnectors in nanoelectronic, magnetic, chemical or biological sensors, and biotechnological labels among others. A simple method to develop self-ordered arrays of metallic nanowires is based on the use of nanoporous anodic alumina (NAA) and self-assembled nanotubular titanium dioxide membranes as templates. The chemical characterization of nanostructured materials is a key aspect for the synthesis optimization and the quality control of the manufacturing process. In this work, the analytical potential of pulsed radiofrequency glow discharge with detection by time-of-flight mass spectrometry (pulsed rf-GD-TOFMS) is investigated for depth profile analysis of self-assembled metallic nanostructures. Two types of nanostructured materials were successfully studied: self-assembled NAA templates filled with arrays of single metallic nanowires of Ni as well as arrays of multilayered Au/FeNi/Au and Au/Ni nanowires and nanotubular titanium dioxide templates filled with Ni nanowires, proving that pulsed rf-GD-TOFMS allows for fast and reliable depth profile analysis as well as for the detection of contaminants introduced during the synthesis process. Moreover, ion signal ratios between elemental and molecular species (e.g., (27)Al(+)/(16)O(+) and (27)Al(+)/(32)O(2)(+)) were utilized to obtain valuable information about the filling process and the presence of possible leaks in the system.

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).

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. Results have shown that the intensity observed in the pre-peak can be 10 times as large as the plateau value for resonant lines and up to 5 times in case of transitions to the metastable levels. Increasing pressure or power increased the pre-peak intensity while its appearance in time changed. The pre-peak decreased when the discharge off-time was shorter than 100 μs. According to such results, the presence of the pre-peak could be probably due to the lack of self-absorption during the first 50 μs, and not to the ignition of the plasma. Under the selected operation conditions, the use of the pre-peak emission as analytical signals increases the linearity of calibration curves for resonant lines subjected to self-absorption at high concentrations.

Quantitative depth profile analysis of boron implanted silicon by pulsed radiofrequency glow discharge time-of-flight mass spectrometry

The analytical potential of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (pulsed-rf-GD-TOFMS) is investigated for fast quantitative analysis of major and dopant elements in bulk and thin film layers. This technique does not require sampling at ultra-high vacuum conditions and so it facilitates high sample throughput compared to reference techniques as secondary ionization mass spectrometry (SIMS). In this paper, bulk and boron implanted silicon samples are analyzed. Boron concentration in Si samples is calculated from calibration curves obtained using solar grade silicon and B doped silicon wafers as calibrating materials, and using 29Si + ion signal as internal standard. Qualitative depth profiles of 10B implanted silicon are determined in a few seconds using the low-pressure pulsed-rf-GD-TOFMS system. Additionally, quantitative depth profiles are easily determined making use of the calibration curves. A good agreement with the depth profiles measured using SIMS was obtained, demonstrating the analytical potential of the pulsed-GD-TOFMS system for fast, sensitive and high depth resolution analysis of implanted silicon samples.

Pulsed radiofrequency glow discharge optical emission spectrometry for the direct characterisation of photovoltaic thin film silicon solar cells

The increasing demand for photovoltaic devices has created a silicon supply shortage, providing a great opportunity for hydrogenated amorphous silicon (a-Si:H) used in thin film technology. The potential of continuous and pulsed radiofrequency glow discharge optical emission spectrometry (rf-GD-OES) for the characterisation of thin film solar cells (TFSC), based on a-Si:H, has been investigated in this work. Qualitative in-depth profiles of TFSC obtained by both GD modes were carefully compared, in terms of signal intensity, penetration rate, emission yield, and depth resolution. The influence of rf-GD parameters operating in continuous mode was studied using three types of samples: B doped, P doped and the complete photovoltaic TFSC device based on a-Si:H. Moreover, the effect of different roughness of the Zn substrate on the depth resolution of the a-Si:H layer was evaluated, along with plasma cleaning conditions optimisation. Additionally, intensity signals and relative depth resolution were investigated for different pulsed GD experimental conditions, such as the pulse frequency (from 500 Hz to 10 kHz), duty cycle (in the range of 0.1875-0.5) and rf forward power (from 25 W to 75 W). 450 Pa and 25 W were selected as the optimum conditions for continuous rf-GD-OES analysis, whereas 450 Pa, 75 W, 1000 Hz and a duty cycle of 0.5 were selected for pulsed rf-GD-OES work. Results show that rf-GD-OES is a powerful tool for direct depth-profiling analysis of a-Si:H TFSC, allowing to discriminate the different parts of the photovoltaic devices: the first contact layer with ZnO2 and Al2O3, the a-Si:H layer (where it can be distinguished between the B doped, the intrinsic a-Si:H and the P doped films), the back contact layer and, finally, the Zn substrate. Moreover, diffusion processes between the coating layers, which could have an important influence on the final efficiency of photovoltaic devices, can be identified and could be studied by rf-GD-OES.

18O/16O isotopic separation in anodic tantala films by glow discharge time‐of‐flight mass spectrometry

AbstractGlow discharge mass spectrometry has been widely used for trace and ultra‐trace element analysis of high‐purity alloys. A novel pulsed radio frequency glow discharge time‐of‐flight mass spectrometer (rf GD TOFMS) has been developed that retains the pulsed radio frequency analytical ion source to provide ion signal enhancement due to processes involving Penning ionisation. A time‐resolved detection mode has been implemented to sample the afterglow regime of the pulse profile, corresponding to the highest ion signal intensities. Here, the performance of rf GD TOFMS in isotope differentiation is discussed. Anodic tantala films, comprising 18O‐rich layers of controlled thicknesses and locations, were formed by appropriate combination of anodising of tantalum in electrolytes enriched with 18O isotopes and of natural O isotopic abundance. Transmission electron microscopy (TEM) and radio frequency glow discharge optical emission spectrometry (rf GD OES) analyses were performed to examine the morphology and elemental distributions of the specimens, while the content of 18O in the 18O‐rich layers was determined by elastic recoil detection analysis(ERDA). In pulsed rf GD TOFMS analysis, characteristic ionic species formed in the glow discharge allows differentiation of 18O‐rich layers. Particularly, the location of 18O‐rich layers was determined from the 16O18O and Ta18O ion signals at masses m/z 34 and 199, respectively. The locations of 18O‐rich layers in anodic films, controlled by the selected anodising conditions, were probed precisely. The 18O profiles in anodic tantala were directly compared with those obtained by dual beam time‐of‐flight SIMS. Copyright © 2009 John Wiley & Sons, Ltd.

High-Precision Detection Method of Emission Signals from a Pulsed Radio-Frequency Glow Discharge Plasma by Using a Fast Fourier Transform Analyzer

A fast Fourier transform (FFT) analyzer was employed to estimate the emission intensity from a radio-frequency (RF)-powered glow discharge plasma for atomic emission analysis. A bias current induced by a self-bias voltage in the RF plasma was pulsated to modulate the emission intensity, and then the modulated component was selectively detected with the FFT analyzer. This method greatly improved the data precision of the emission intensity, thus contributing to better detection ability. The emission intensity of the Mn I 403.08-nm line in an Fe-0.2 mass % Mn alloy sample could be determined with a relative standard deviation of 0.060%. The 3-sigma detection limit of manganese in Fe-based alloys could be obtained to be 1.6 x 10(-5) mass %, when Mn I 403.08 nm was selected as the analytical line.

Pulsed radiofrequency glow discharge time‐of‐flight mass spectrometry for molecular depth profiling of polymer‐based films

We demonstrate the potential of an innovative technique, pulsed radiofrequency glow discharge time-of-flight mass spectrometry, for the molecular depth profiling of polymer materials. The technique benefits from the presence, in the afterglow of the pulsed glow discharge, of fragment ions that can be related to the structures of the polymers under study. Thin films of different polymers (PMMA, PET, PAMS, PS) were successfully profiled with retention of molecular information along the profile. Multilayered structures of the above polymers were also profiled, and it was possible to discriminate among layers having similar elemental composition but different polymer structure.

Potential analytical applications of negative ions from a pulsed radiofrequency glow discharge in argon

Detection of negative ions from a conventional analytical glow discharge source using argon as the working gas is reported. The negative ions are recorded using a pulsed discharge source coupled with a time-of-flight mass spectrometer. A considerable enhancement in the “afterglow” region of the negative ion signal for halogens and halogenated molecules and reduction in background is observed. This is the first time when negative ions have been reported for halogen containing materials and we illustrate our findings with results from the polytetrafluoroethene polymer (PTFE).

A comparison of non-pulsed radiofrequency and pulsed radiofrequency glow discharge orthogonal time-of-flight mass spectrometry for analytical purposes

The analytical potential of a radiofrequency glow discharge orthogonal time-of-flight mass spectrometer (RFGD-TOFMS) has been evaluated in both pulsed and non-pulsed modes. A certified reference steel was selected for this study. The operating conditions of the GD plasma (pressure and applied power) were optimized in terms of sensitivity. Additionally, duty cycle and pulse width parameters were investigated in the pulsed RF mode. In this case, high analyte ion signals and improved signal to background ratios were measured after the end of the pulse, in the so-called afterglow domain. The analyte ion signals were normalized to sputtering rates to compare different operating conditions. It was found that the sensitivity in the pulsed mode was improved in comparison to the non-pulsed mode; however, the factor of enhancement is element dependent. Moreover, improved analytical performance was obtained in terms of ion separation capabilities as well as in terms of accuracy and precision in the evaluation of the isotopic ratios, using the pulsed RFGD-TOFMS. Additionally, depth profile analyses of a Zn/Ni coating on steel were performed and the non-pulsed and pulsed RFGD-TOFMS analytical performances were compared.