Recent work on glow discharge excitation based on CCD spectra

Z. Weiss
LECO Instrumente Plzen, Plaska 66, 323 25 Plzen, Czech Republic
weissz@leco.cz

The techniques of recording and processing glow discharge spectra on the LECO GDS500A spectrometer will be discussed. Examples of real CCD spectra will be shown and the way from raw spectra to a list of emission yields of different lines will be demonstrated.
Quantitative evaluation of large numbers of emission lines of the same element in different matrices and different discharge gases brings valuable information about excitation processes in the discharge and reveals various matrix effects. Some results of this kind for copper, zinc and aluminium in argon and neon discharges will be shown.
Matrix effects in glow discharge emission spectroscopy is an extensive field, not yet explored. They are interesting from the point of view of analytical applications as well as fundamental processes occurring in the discharges. Examples of matrix effects will be given, some recently proposed explanations will be discussed and various unsolved questions concerning the glow discharge excitation will be mentioned.

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New way to overcome the drawbacks of RSF- and Standard-RSF quantification concepts for VG 9000 and Element GD

T. Gusarova1) , B. Lange1), H. Kipphardt1), C. Venzago2), R. Matschat1) and U. Panne1)
1) Federal Institute for Materials Research and Testing (BAM), Department I Analytical Chemistry, Reference Materials, Richard-Willstaetter-Strasse 11, 12489 Berlin, Germany
2) AQura GmbH, Inorganic Chemical Analysis, Rodenbacher Chaussee 4, 63457 Hanau-Wolfgang, Germany

Glow Discharge Mass Spectrometry (GD-MS) is a very sensitive multielement direct solid sampling technique. The drawback of the method is the lack of a suitable quantification procedure for accurate and traceable analysis of pure materials with small uncertainty. Usually the matrix-specific or not matrix-specific relative sensitivity factors (RSF or Standard-RSF-values, respectively) are used for quantification in GD-MS resulting in uncertainties of ≤ 30 % (RSF) or of at least a factor of two of the true value (Standard-RSF). Often Standard-RSF-values have to be used, because appropriate certified reference materials (CRMs) for the determination of matrix matched RSF-values are lacking. Both concepts (RSF- and Standard-RSF-concept) are based on the following preconditions: 1) linear dependence of Ion Beam Ratio (IBR) on trace element mass fraction, 2) no or negligible blank value, and 3) the same ion source geometry if RSF- or Standard RSF- values achieved with one type of GD mass spectrometer shall be used for the evaluation of  results at another type of GD mass spectrometer. Because of the last precondition the RSF-values, which were investigated and published for different matrices using VG 9000 cannot be used for the new instrument Element GD. Therefore the RSF-values which will be applicable for the evaluation of measurements at Element GD have to be determined at this type of GD mass spectrometer. Furthermore, the applicability of the Standard-RSF-concept for Element GD is not yet fully clear. Thus new suitable quantification procedures should be developed, which allow achieving small uncertainties with both instruments.
To solve the quantification problem of the method especially for very low analyte contents, high purity matrix powders doped with liquids were used as calibration standards. The prepared pellets contained trace elements with mass fractions from 5 µg·kg-1 up to 10 mg·kg-1. This approach ensures direct traceability of measurement results to the International System of Units (SI). Copper, zinc, indium and nickel matrixes were successfully investigated. The suitability of the calibration approach was validated by measurements with CRMs and the results were compared for both instruments. The different RSF-values were estimated and compared.

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Spectroscopic study of a glow discharge-surface interaction using the Balmer alpha line shape of hydrogen isotopes

Nikola Konjević (a), Nikola M. Šišović ( a) and Gordana Lj. Majstorović (b)
a ) Faculty of Physics, University of Belgrade, 11001 Belgrade, P.O.Box 368, Serbia   e-mail: nikruz@ff.bg.ac.yu
b ) Military Academy, 11105 Belgrade, Generala Pavla Jurišića - Šturma 33, Serbia

            We present results of  a discharge-cathode surface interaction study based on comparison of the Hα and Dα Balmer line profiles. Both lines are emitted simultaneously from a low pressure DC hollow cathode (HC) glow discharge (GD). The HC was made of stainless steel (SS) or titanium (Ti) and  the discharge (I=90mA; U=300-350V) was operated with Ar/D2/H2 gas mixture (Ar + 3.5 % vol. D2 + variable vol. percentage of H2). The continuous flow of gas mixture was 20 cm3/min at room temperature and atmospheric pressure. The HCGD was operated in the pressure range 0.5 – 4 mbar.
            The Balmer line shape in low pressure discharges determine several broadening mechanisms, which will be discussed in some details at the Conference. From the point of view of discharge-cathode surface interaction the most important is, so called, excessive Doppler broadening (EDB). The present explanation of this phenomena is based on a sheath collision model (SCM). This model, among other processes, takes into account the influence of gas composition and cathode material to the Balmer line shape. Thus, the experimental Balmer alpha line profile in this study represents a convolution of three Gaussian profiles resulting from different excitation processes. The average energy of excited hydrogen isotope atoms determined from the width of broadest Gaussian induced by EDB are 33 eV (Hα) and 47 eV (Dα). The energy derived from the medium-width Gaussian is 1eV (Hα) and 2 eV(Dα). The width of narrowest Gaussian only slightly exceeds the instrumental broadening and it is always below 0.5 eV.
            It has already been detected with Ti HC that the contribution of the EDB part of Balmer alpha line is smaller than for SS HC. For hydrogen matrix gas, the difference is explained with lower value of number reflection coefficient, RN, for  H+ ions on Ti in comparison with SS. The same argument based on reflection of D+ ions from SS and Ti surface one can use here when discussing the EDB contribution to the Dα line profile. However, in argon gas mixtures with D2 and/or H2 the dominant ion interacting with cathode is H3+ or D3+ and the reflection coefficients of H and H+ or D and D+ are of marginal importance. Unfortunately, the reflection coefficients for the interaction of these ions with polycrystalline metals are not available. The exceptions are experimental and theoretical data for the interaction of H3+ and D3+  with nickel target, which, for low energy incident ions relevant to our experiment, show large discrepancy between theory and experiment.

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Laser ablation pulsed glow discharge mass spectrometry – possibilities and drawbacks

Daniel Fliegel and Detlef Günther
Laboratory for Inorganic Chemistry, ETH Zurich, Switzerland

This contribution presents a laser ablation particle beam pulsed glow discharge time of flight mass spectrometer (LA-PB-GD-TOFMS).
To maintain the low pressure in glow discharge source in combination to use conventional flow conditions for laser ablation, a particle beam interface was constructed and used in-between laser ablation cell and glow discharge. The differentially pumped particle beam on one hand reduces the gas flow into the glow discharge cell and on the other hand generates a focused beam of the aerosol directly into the glow discharge chamber. A hollow cathode glow discharge, operated in He at ms pulse frequency was used and coupled to a fast time of flight mass spectrometer.
To investigate the possibilities of particulate matter exciting and ionizing generated by laser ablation by a pulsed glow discharge, various inorganic material (glass and metal standard reference materials) and organic polymers were analyzed. As a result, for example, the stoichiometric analysis of halogenated polymers and fingerprinting of the polymers will be reported. Upon these experiments the capabilities of pulsed glow discharges for ionizing laser ablated aerosols will be discussed.

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Sputtering Speed and Crater-Geometry as a Function of Current and Voltage in DC-GDS

Wolfgang Verscharen
Robert Bosch GmbH  -  Robert-Bosch-Str. 40  -  96050 Bamberg  -  GERMANY

In the last 8 years I presented our considerations on the correlation between Sputtering-Speed, Voltage and Current on various occasions within the 'Deutsches Anwendertreffen'. In the last months we have been able to complete our work by measuring the sputtering speed of Silicon- resp. Copper-single crystals in different crystallographic orientations.
It appeared, that there is an important influence on sputtering speed concerning absolute value and kind of Voltage-Current-dependence at least for non-directional metallic-bonded materials. For vectored atomic-bonds, as in the case of Silicon, such a dependence could not be found within statistical certainty.
In the first part of my lecture I will present those coherences by means of measured data and discuss the problem of sputtering rates for example. In the second part of my lecture I will try to explain the diversity of crater profiles using a relatively simple electrostatic model. A slight change of the equation, presented in 2004 at the meeting in Dresden, leads to a significantly better match of observed crater profiles and what is more, the parameters of the equation are closely related to the geometry of the GD-lamp and take reasonable values.

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Depth Profile Analysis of Nanoscale Oxide Layers by Glow Discharge Optical Emission Spectrometry (GDOES)

Michael Köster,1 Thomas Asam2, Josef Baiker3
1TAZ GmbH, Hauptstrasse 31A, D-86495 Eurasburg, Germany, mkoester@tazgmbh.de
2TAZ GmbH, Hauptstrasse 31A, D-86495 Eurasburg, Germany, info@tazgmbh.de
3Baiker Analytik, Gampenhof 3, D-88636 Illmensee, Germany, jnfo@baiker.de

Glow discharge optical emission spectrometry is the fastest depth profiling technique but is still believed to be unsuitable for the analysis of thin layers. When thin layer analysis is needed, other, more complex and costly methods, like AES, ESCA or SIMS, are usually preferred. In today´s development of new technological products, the properties and quality of the product depend more and more on their immediate surface. Beside surface analysis in advanced research, the development of a rapid testing method will become necessary. To provide the industry with fast and reliable methods and devices for production control, the sophistication of glow discharge depth profiling methods is of great importance. With the disclosed presentation of in-depth elemental composition of some of the most common metal oxide layers, we like to show the present capabilities of this surface testing method. Therefore, we studied the plasma conditions during the first milliseconds of a glow discharge in dependence on the type of control. Afterwards, thin layers of oxides forming on surfaces of metals or alloys like steel, nickel or chromium were analysed. The best depth resolution and data were obtained with an argon-hydrogen mixture and constant voltage and pressure. A set of correction procedures has been developed by the comparison of the ignition and the steady state. An additional focus has been set on some minor elements and their detection limits within the near-surface region. The results were compared with Auger electron spectrometry depth profiles.

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Depth profile spectral Analysis of New Materials in Hollow Cathode glow Discharge

CANCELED

Renna Djulgerova, Valentin Mihailov, Veselina Gencheva, Zoran Lj. Petrovic1, Tomash Dohnalik2
Georgi Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria

Institute of Physics, Academy of Sciences and Arts, 11080 Zemun, Belgrade, Serbia1

Institute of Physics, Jagellonian University, 30-059 Krakow, Poland2

e-mail: renna@issp.bas.bg; valentine@issp.bas.bg

The hollow cathode discharge turns out to be a plasma source of present interest in the plasma processing technology for deposition of layers, removals of thin films or etching of surfaces, and for different surface treatments.
One of the most attractive features of the hollow cathode discharge is its ability effectively to atomize the substance of the cathode walls or the sample introduced in it. As a very sensitive source for small amount and trace element measurements, the hollow cathode discharge enables fine steps and high sensitivity of the depth profile spectral analysis.
In comparison with the closest technique – the glow discharge optical emission spectrometry (Grimm’s discharge) which is widespread and has already demonstrated its merits for quantitative depth profiling of various materials the application of the hollow cathode discharge is still confined at a laboratory level. However, its high sensitivity, better stability and reproducibility one side, and the good results obtained by now on the other side, justify further investigations and applications of the hollow cathode discharge as a depth profiling technique.
In this work the possibility of hollow cathode discharge for depth profile analysis is demonstrated for several new materials:
planar optical waveguides fabricated by Ag+-Na+ and K+-Na+ ion exchange processes in glass,
SnO2/SiO2/Si structure for gas sensors modified by hexamethildisilazane after rapid thermal annealing,
W- and WC- CVD layers deposited on Co-metalloceramics,
WO3- CVD thin films deposited on glass,
AlN thin films deposited on a glass substrate and
Ag taped BSCCO high temperature superconductive materials.
The results are compared with different standard techniques and confirms that the hollow cathode discharge, in combination with several standard techniques, turns out to be appropriate as a depth profiling technique. These investigations were very useful for finding the optimal technological conditions for fabrication of the materials under interest.

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Effects of fast neutral particles in low-pressure gas discharges

Z. Donko, P. Hartmann, K. Kutasi

Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, 
H-1525 Budapest POB 49, Hungary 

The effects of fast neutral (heavy) particles on the characteristics of low-pressure  noble gas discharges are discussed. Complementing experimental observations, numerical  simulations are applied to demonstrate the importance of these species in the (i) surface reactions  causing electron emission from the cathode and (ii) gas-phase reactions leading to the creation of 
charged particles and to light emission from the discharge through excitation processes.  These processes are found to be important at high values of the electric field to gas density  ratio, E/n, for which conditions positive ions – being the primary species creating fast neutrals in  collision processes – acquire high energy in the cathode region. 

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EMPDA project

Patrick Chapon

HORIBA Jobin Yvon

EMDPA is the acronym for "New Elemental and Molecular Depth Profiling Analysis of Advanced Materials by Modulated Radio Frequency Glow Discharge Time of Flight Mass Spectrometry". EMDPA is a STREP project funded by the EU (contract STRP 032202) in the 6th framework program under the Thematic Priority N°3 - Nanotechnologies and nano-sciences, knowledge-based multifunctional materials and new production processes and devices. The aim of the project is to develop a µ-modulated or pulsed RF glow discharge time of flight mass spectrometer (TOFMS) for all types of layered materials, allowing direct, simultaneous, elemental and molecular quantitative measurements with a sensitivity down to 100 ppb in the depth profiling mode for all elements of the Periodic Table, in observed zones of millimetre dimensions.
EMDPA, which started a year ago, gathers 10 multidisciplinary organisations from 7 countries, carefully selected for the complementary expertise they bring to the project. The partnership embraces experts in plasma physics/chemistry and plasma-surface interactions (CPAT, NILPRP and UNICT), renowned groups in GD-MS design, chemometrics and data handling (ISAS, UNIOVI and EMPA), a recognised research centre with expertise in all aspects of material sciences (UoM), a provider of innovative TOFMS technologies (TW), and a large company manufacturing GD optical spectrometry instruments (HJY).
Two very innovative ideas are the detection of molecular ions allowed by TOFMS and the perfect fit between pulsed discharge and orthogonal TOF for optimized dynamic analysis of multilayered materials.
The objectives are (i) understanding sputtering mechanisms and ionization processes, (ii) characterising sputtered surfaces and molecular chemistry of RF plasma, (iii) understanding transport phenomena and developing detection methods, and (iv) assessing the properties of the prototype.
The organization of the work will be presented.

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Introduction of a novel designed RF-Generator for Glow-Discharge-Sources and demonstration for the practical use in analyzing thin films

Michael Analytis,

Spectruma GmbH

A novel RF-Generator especially designed for Glow Discharge Sources (GDS) will be introduced. This RF-Generator is based on a 'free running' technique, which means that the impedance matching is not performed by an additional electro-mechanical matching network but archived due to slight changes of the operating frequency. This technique has some significant advantages over the 'traditional' matching technique used up to now for GDS systems. In short, the matching speed is almost instantaneously and the probability for a miss matching is virtually nonexistent. Hence the operations of such a source is as simple as the operation of a DC source.
The initial stabilization time of the generator is in the low micro second range which leads to very fast stabilization times of the initial plasma of less the 5 ms. Due to such fast initial stabilization speeds of the plasma the analysis of very thin layers becomes more reliable.
This contribution will introduce the technique of the new RF-Generator and shows the practical application for the analysis of thin films.