Polymer screening by radiofrequency glow discharge time-of-flight mass spectrometry.

The aim of this work is to optimise and evaluate radiofrequency glow discharge (RF GD) time-of-flight mass spectrometry (TOFMS) for identification of organic polymers. For this purpose, different polymers including poly[methylmethacrylate], poly[styrene], polyethylene terephthalate-co-isophthalate and poly[alpha-methylstyrene] have been deposited on silicon wafers and the RF GD-TOFMS capabilities for qualitative identification of these polymeric layers by molecular depth profiling have been investigated. Although some molecular information using the RF continuous mode is available, the pulsed mode offers a greater analytical potential to characterise such organic coatings. Some formed polyatomic ions have proved to be useful to identify the different polymer layers, confirming that layers having similar elemental composition but different polymer structure could be also differentiated and identified.

Direct chemical in-depth profile analysis and thickness quantification of nanometer multilayers using pulsed-rf-GD-TOFMS.

Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer (pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer thickness, t(Al). Samples with t(Al) = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness t(Nb) = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which are optimized for the in-depth profile analysis with high depth resolution.

Analysis of small bubbles in glass by glow discharge--time-of-flight mass spectrometry.

The chemical reactions occurring during the glass manufacturing processes can give rise to small bubbles, damaging the required glass properties. To avoid eventual bubbles formation, the chemical composition of the bubbles should be known to trace back the gas sources and take appropriate corrective actions. Mass spectrometry is a most adequate detection technique for such purpose due to its ability to provide the required information in a short time. Analysis of these small bubbles in glass requires a system incorporating a very small volume (for a fast evacuation of the entire line and low dilution of the analytes) and a fast mass analyser allowing the quasi-simultaneous detection of the whole spectral interval of interest, such as a time-of-flight mass spectrometer (TOFMS). In this work, the analytical potential of a radiofrequency glow discharge (rf-GD) coupled to a TOFMS was evaluated for the first time for the analysis of bubbles in glasses. The operating conditions of the rf-GD (pressure and applied power) were optimized by introducing into the system known volumes of air. Detection limits in the order of nL were obtained for molecular nitrogen, oxygen and carbon dioxide. Finally, a stainless steel bellows valve was modified to serve as glass breaker for the sampling process. This valve was connected on-line to the mass spectrometer inlet line and proved to be most appropriate for the analysis of the gaseous content of bubbles (with diameters below 0.5mm) entrapped in industrial glasses.

Spectroscopic evaluation of a compact magnetically boosted radiofrequency glow discharge for time-of-flight mass spectrometry.

A compact magnetically boosted radiofrequency glow discharge (GD) has been designed, constructed and its analytical potential evaluated by its coupling to a mass spectrometer (MS). Simple modifications to the original source configuration permitted the insertion of permanent magnets. Small cylindrical Nd-Fe-B magnets (diameter = 4 mm, h = 10 mm) were placed in an in-house-modified GD holder disc that allows easy and fast exchange of the magnets. The different processes taking place within the GD plasma under the influence of a magnetic field, such as sputtering, ionisation processes and ion transport into the MS, were studied using different GD operating conditions. Changes to the ionisation and ion transport efficiency caused by the magnetic field were studied using an rf-GD-TOFMS setup. A magnetic field of 60-75 gauss (G) was found not to affect the sputtering rates but to enhance the analyte ion signal intensities while decreasing the Ar species ion signals. Moreover, magnetic fields in this range were shown not to modify the crater shapes, enabling the fast and sensitive high depth resolved analysis of relatively thick coated samples (micrometre) by using the designed compact magnetically boosted rf-GD-TOFMS.

Amplification of noble gas ion lines in the afterglow of a pulsed hollow cathode discharge and possible benefit for analytical glow discharge mass spectrometry.

A high-current pulsed hollow cathode discharge was used to study the role of atomic and ionic metastables involved in ionization plasma processes. We observed the enhancement of the spectral emission lines of noble gas ions in the afterglow. A study of the processes that involve atomic and ionic metastables is of great interest since it should lead to a better understanding of and enhanced control over the ionization mechanisms crucial to analytical glow discharge mass spectrometry (GDMS) analysis.

Matrix implanted laser desorption ionization (MILDI) combined with ion mobility-mass spectrometry for bio-surface analysis.

The implantation of low velocity massive gold cluster ions allows homogeneous incorporation of a metallic matrix into the near-surface region of rat brain tissues. Subsequent analysis by laser desorption ionization mass spectrometry yields spectra exhibiting molecular ion peaks in the mass range up to 35 kDa similar to those observed by matrix-assisted LDI. Matrix-implanted LDI when combined with ion-mobility preseparation promises to be a useful technique for molecular imaging of biotissues with a laser microprobe.