Laser ablation particle beam glow discharge time of flight mass spectrometry for the analysis of halogenated polymers and inorganic solid material

A laser ablation particle beam pulsed glow discharge mass spectrometer (LA-PB-GD-TOFMS) was designed and used for fundamental studies. The instrument consists of a three stage aerodynamic lens system, a hollow cathode pulsed glow discharge and a time-of-flight mass spectrometer. The particle beam interface was constructed to provide an efficient particle transfer into the hollow cathode. Calculations showed that particles between 1 and 3000 nm in diameter are able to pass through this interface.     

Model of microsecond pulsed glow discharge in hollow cathode for mass spectrometry

A new model for microsecond pulsed glow discharge in a hollow cathode and its afterglow is described. The model is based on the Monte-Carlo method together with a new method for electrical field calculation, which is based on some phenomenological laws of plasma behavior. The afterglow model uses continuity and Poisson equations. A qualitative agreement between the model results and results published in experimental and theoretical works is demonstrated. Some processes in the microsecond pulsed discharge in the hollow cathode, such as sputtering, ionization and transfer of sample, are investigated. The model is successfully used for the optimization of the operational parameters of the time-of-flight mass spectrometer with ionization by microsecond pulsed glow discharge in a hollow cathode.     

Experimental measurement of the intensity of the spectral line CuI 324.7 nm and the concentration of Cu atoms in a hollow cathode discharge under pulsed and steady-state conditions

The intensity of the spectral line CuI 324.7 nm and the concentration of Cu atoms in a hollow cathode discharge were measured when operating the lamp under pulsed and steady-state conditions. The influence of the temperature regime of the cathode walls on the effect of the applied operation mode was investigated.     

Depth profile analysis of surface modified SnO2 gas sensors in a hollow cathode discharge

Depth profile analysis of a SnO₂/SiO₂/Si structure, modified with hexamethildisilazane and processed with rapid thermal annealing (RTA) in the temperature range of 800–1200 °C, is investigated in a hollow cathode discharge for the purpose of characterizing gas sensing solid state devices. The depth behavior of the elements tin, nitrogen, carbon and silicon in this structure is deduced from their emission spectra in the hollow cathode plasma. The hollow cathode used is a liquid nitrogen - cooled Al cylinder having 4 mm inner diameter and 12 mm length. Spectrally pure Ne at a pressure of 130 Pa is used as working gas. The hollow cathode discharge is supplied by a pulse generator with 10 μs pulse width, 4 kHz pulse frequency and 0.5 A pulse amplitude. The results are interpreted by possible reconstruction of hexamethyldisilazane molecule.     

Time-of-flight mass spectrometry with pulsed gas-discharge ionization: Study of relative sensitivities of components

The potential of the relative sensitivity method was assessed for the direct analysis of solid samples using time-of-flight mass spectrometry with pulsed glow discharge ionization in a combined hollow cathode. Relative sensitivity factors of sample elements were obtained for various samples (copper, steel, nickel, lead, and silicon). For the majority of elements, these factors appeared to be close to unity. The factors were compared with the similar data obtained for direct current (DC) glow discharge; the range of factors obtained in the present work was significantly narrower. This opens up new prospects for pulsed gas-discharge ionization in semiquantitative analysis without using certified reference samples strictly corresponding to the test sample in composition and structure.     

High frequency excitation of vapours produced by hollow cathode sputtering

Using a hollow cathode discharge for producing a suitable atomic vapour, the spectral lines of elements were excited by a high frequency discharge of 2450 MHz. These lamps were used as primary light sources for atomic absorption spectroscopy and were compared with conventional hollow cathode lamps. Higher intensity of radiation as well as higher sensitivity was obtained with the high frequency discharge. The interaction of the microwave field with the hollow cathode discharge limits the ultimate intensity. The stability of radiation from these sources is good. Measurements of line halfwidths indicate gas temperatures of approximately 500°K for both the high frequency and conventional hollow cathode discharges.     

A pulsed arc-glow hollow cathode lamp

A copper pulsed arc-glow discharge has been designed, and time-resolved Fabry-Perot emission line profiles have been obtained for the Cu(I) 324.7 nm doublet. Results when compared to a standard copper hollow cathode lamp operated under the same pulsed conditions showed that the arc-glow lamp gave 17 per cent greater time- and wavelength-integrated intensity, and a line profile that was not as severely self-reversed. Total radiant power emitted by the arc-glow lamp was less because of the reduced size of the emission region. Line widths during the first 21 μsec of a pulse were in the range 0.0012–0.0025 nm including an instrumental broadening contribution estimated to be less than 0.0004 nm. Argon pressures for the discharge ranged from 15 to 26 Torr. Pulse durations of 300 μsec with a repetition rate of 100 Hz and pulse currents up to 300 mA were used.     

The formation of an oscillating system during the sputtering of sapphire single crystal with pulsed glow discharge

Sapphire (α-Al₂O₃, transparent corundum) single crystals were analyzed with pulsed direct current glow discharge mass spectrometry. Combined hollow cathode was used as a discharge cell. To obtain stable sputtering of dielectric material, a formation of initial surface conductivity via preliminary vacuum deposition of thin metallic layer was proposed. Al and Ta film of different thickness (30–200 nm) were considered for this purpose. The approach was found to provide the effective sputtering of dielectrics. The formation of an oscillating system was shown during the sputtering of sapphire samples in a tantalum combined hollow cathode cell. For oriented sapphire single crystals, periodic oscillations of ²⁷Al⁺ intensity were acquired. This phenomenon was observed only for dielectric single crystals and not for other dielectric samples, e.g. alumina ceramic or fused quartz. The linear dependence of oscillation period on the duration of discharge pulse was found. The origin of these oscillations seems to be attributed to periodic fluctuations of surface conductivity. Oscillation periods calculated for two different orientations of sapphire single crystals (001 and 012) were found to be proportional to the main period of sapphire lattice. Therefore, an assumption that the crystal internal structure of the sample might be the cause of the oscillations is discussed.     

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. Figure Time profile of Ti, Ti⁺, and Ne⁺ spectral lines     

A line profile study of the 193.76 nm arsenic emission line from lamps used in atomic absorption spectroscopy

The width of the 193.7 nm line of arsenic has been measured for a commercial hollow cathode lamp (HCL), a pumped hollow cathode lamp and a commercial electrodeless discharge lamp (EDL). The measurements were made using an echelle spectrometer and operating the lamps under a wide range of conditions. The line widths for the commercial HCL and for the EDL were found to be 0.91 pm (9.10 mÅ) and 0.895 pm (8.95 mÅ) respectively when operated under the recommended unpulsed operating conditions, and the EDL line was seven times as intense as that from the HCL. When the lamps were pulsed, the widths of the lines increased to 1.009 pm (10.09 mÅ) in the case of the HCL and to 0.904 pm (9.04 mÅ) for the EDL. The arsenic HCL, with neon as a carrier gas, suffers from severe spectral interference which arises from the presence of the 193.89 nm and 193.01 nm Ne II lines. This could account for most of the curvature of the absorbance-vs-concentration calibration curve.     

Development of a laser ablation-hollow cathode glow discharge emission source and the application to the analysis of steel samples.

A novel atomic emission spectrometry comprising laser ablation as a sampling source and hollow cathode plasma for the excitation of ablated sample atoms is proposed. In this arrangement, a conventional Grimm-type discharge lamp is employed, but the polarity of the power supply is reversed so that the cylindrical hollow tube acts as a cathode and the glow discharge plasma is produced within this tube. A laser is irradiated to introduce sample atoms into the discharge plasma. Ablated atoms are excited by collisions with electrons and gas species, and emit characteristic radiation upon de-excitation. The experiments were conducted only in an atmosphere of helium gas so as to avoid a rapid erosion of the cathode hollow tube. Phase-sensitive detection with a lock-in amplifier was utilized to reject the continuous background emission of the plasma gas and emissions of sputtered atoms from the tube material. The unique feature of this technique is that the sampling and excitation processes can be controlled independently. The proposed technique was employed for the determination of Cr, Mn, and Ni in low-alloyed steel samples. The obtained concentrations are in good agreement with the reported values. The relative standard deviation (RSD), a measure of the analytical precision, was estimated to be 2-9% for Cr, 3-4% for Mn, and 4-11% for Ni determination.     

Evaluation of a hollow cathode atomic emission source designed for continuous solution sample introduction

A hollow cathode discharge capable of continuous operation with solution sample introduction is described. Discharge current densities up to 0.64 are maintained in a helium plasma. Analyte emission intensities are optimized in terms of anode placement in relation to the hollow cathode, carrier gas flow rate, discharge current and sample solution flow rate. Detection limits for selected elements are reported and range from 0.03 for Li to 200 for Zn. Temporal stability of the discharge is examined and a calibration curve for Li is presented.     

Formation and Role of a Hollow-Cathode Plasma Plug in Mass-Spectrometric Analysis

The use of plasma electron and ion sources based on a glow discharge is often restricted by a too high plasma-forming gas pressure in the process volume. Experiments with a new design of a hollow cathode, a type of glow discharge, are described in this paper. It was found that, if a cap with an orifice is arranged at the vertex of a cylindrical hollow cathode (the orifice diameter is 10 to 90% of the inner diameter of the hollow cathode), a plasma plug, which offers resistance to a plasma-forming gas flow from the cathode hole to the vacuum chamber, is formed in the cathode hole near the orifice. As a result, a pressure drop is formed between the cathode hole and the vacuum chamber. This pressure drop depends on the orifice diameter, and it can be as high as three orders of magnitude with the use of a hollow cathode with an internal diameter of 20 mm and an orifice diameter of 4 mm in the cap at the cathode vertex.     

The hollow cathode plume: A plasma emission source for solids

A hollow cathode discharge serves to form an energetic plasma plume which exhibits intense emission characteristics. The sample cathode is sputtered in the discharge to produce an atomic population which then flows into the plume through an exit orifice for subsequent excitation. Atomic absorption and emission profiles in the plume are shown. Emission spectra of major and minor elements show strong atomic and ionic lines of sputtered species, particularly from the inner core of the plume. A sample in the form of a small disc can serve as the base of the hollow cathode for more convenient sample preparation. The source is believed to have potential also in elemental analysis by mass spectrometry.     

Determination of Nd,Ho, Er,Tm and Y in Solutions by Hollow Cathode Discharge with Copper Cathodes

Abstract

A hollow cathode discharge has been applied to the determination of Nd, Ho, Er, Tm and Y in solutions using copper cathodes and argon as a carrier gas. The solutions were evaporated to dryness in the cathodes without a pretreatment. Absolute detection limits for the elements studied here were found to be lower in the copper cathode by about one order than those obtained in previous studies in graphite hollow cathodes.     

Time- and wavelength-resolved emission line profiles for pulsed Cu and Ag hollow cathode lamps

Time-resolved, line emission wavelength profiles were obtained for a copper and a silver pulsed hollow cathode lamp with the use of a piezoelectrically driven interferometer. A computer was used to control the timing of the sweep of the interferometer, the pulsing of the source, and the acquisition, averaging, sorting and display of data. Minor manipulation of the data stored in core facilitated the presentation of intensity vs wavelength emission profiles in a time-resolved form. Ten sequential line profiles spaced at 21 μsec time intervals were obtained.The copper hollow cathode lamp was driven at 100 Hz with pulse currents of up to 400 mA. Pulses lasted for up to 300 μsec. Line profiles changed dramatically during a pulse and showed extreme self-reversal of the resonance emission lines after 100 μsec. Variations of line profile with dc background current level and spatial position within the discharge were also investigated. Uncorrected line widths of each of the doublets of the Cu(I) 324.7 nm resonance line measured during the first 21 μsec of the discharge, where they were narrowest, ranged from 0.0012 to 0.0022 nm, including an instrumental broadening contribution estimated to be less than 0.0004 nm. The silver lamp showed extreme self-reversal even during the first 21 μsec.     

Study of some excitation characteristics of the discharge in a hot hollow cathode

Some excitation characteristics of the discharge in a hot hollow cathode were investigated. A graphite cathode coated with evaporated films of copper, iron, manganese or titanium, and argon or helium fill gas were applied. The dependence of spectral-line intensities on fill gas pressure and discharge current were studied. At 0.4 A discharge current and various fill gas pressures, the excitation temperatures for iron, manganese and titanium were determined.     

The design and characteristics of direct current glow discharge atomic emission source operated with plain and hollow cathodes

A compact direct current glow discharge atomic emission source has been designed and constructed for analytical applications. This atomic emission source works very efficiently at a low-input electrical power. The design has some features that make it distinct from that of the conventional Grimm glow discharge source. The peculiar cathode design offered greater flexibility on size and shape of the sample. As a result the source can be easily adopted to operate in Plain or Hollow Cathode configuration. I-V and spectroscopic characteristics of the source were compared while operating it with plain and hollow copper cathodes. It was observed that with hollow cathode, the source can be operated at a less input power and generates greater Cu I and Cu II line intensities. Also, the intensity of Cu II line rise faster than Cu I line with argon pressure for both cathodes. But the influence of pressure on Cu II lines was more significant when the source is operated with hollow cathode.     

Comparison of trace analytical results obtained with different hollow cathode discharge lamps

Summary Detection limit and sensitivity of trace analysis of powdered samples have been tested using hollow cathod discharge lamps made in our laboratory. We found some special problems for trace analysis with hollow cathode excitation; such problems are the energy tuning and the pressure dependence of spectral lines. Results obtained with improved hollow cathode discharge lamp and with water cooled hollow cathode discharge lamp are compared to each other.

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Vergleich spurenanalytischer, mit verschiedenen Hohlkathodenlampen erzielter, Ergebnisse

Zusammenfassung In Pulveranalysenergebnissen wurde die mit den von uns entwickelten Entladungsröhren erzielten Nachweisgrenzen sowie die Veränderung des Nachweisvermögens geprüft. Es wurde experimentell nachgewiesen, daß bei der Hohlkathodenentladung auch spezielle spurenanalytische Probleme entstehen, wie die Energieabstimmung und die Druckabhängigkeit der Spektrallinien. Die Ergebnisse der modifizierten und die der wassergekühlten Hohlkathodenentladung wurden zusammengestellt und verglichen.

     

A glow discharge device for atomic emission spectrometry of microliter solution samples

A novel glow discharge device designed specifically for solution analysis is described. The detection limits obtained are comparable to those obtained with demountable hollow cathode lamps, but with better precision. Rotational and excitation temperatures are examined as functions of fill gas pressure and discharge current. A sputtering constant is presented and the technique for measuring this parameter is described.