A study of the density of sputtered atoms in the plasma of the modified Grimm-type glow discharge source

The sputtering of atoms from the cathode of a modified Grimm-type glow discharge source was studied using hollow cathode lamps as primary sources. Absorption of copper atoms at a distance of 1.5 mm from the cathode was measured, using different discharge conditions, with helium, neon, argon, krypton and nitrogen as carrier gases. For conditions with voltages at and above 800 V, the greatest absorption (copper atom concentration) was obtained using argon as carrier gas. Absorption by copper and chromium, measured at varying distances from the cathode and at different discharge conditions, shows a maximum between 1 and 2 mm from the cathode. This phenomenon can only be explained by cluster sputtering or cluster formation in the plasma. By using the Doppler temperatures of the emission and absorption sources to calculate line profile halfwidths, measured absorbances can be converted to atom number densities.A diffusion model has been formulated to describe the diffusion of sputtered atoms through the plasma which is in a steady state. From the agreement obtained with experimental results, it is concluded that in principle this diffusion model can be used to predict the spatial distribution of sputtered atoms in the plasma.     

Morphology of tellurium electrolytically deposited in a pulsed mode

Morphology of tellurium deposits produced by pulsed electrolysis of 0.005–0.05 M TeCl₄ solutions in dimethyl sulfoxide was studied. The effect of the TeCl₄ concentration and pulsed current parameters on the structure of electrolytically deposited tellurium films was examined.     

The formation of ozone and UV radiation from high-power pulsed electric discharges

High-power electric discharges with pulse energies of from 0.15 J to 4 kJ were studied. The yields of UV photons and ozone were found to be approximately equal, which led us to conclude that discharge conditions under which UV radiation and ozone fully destroyed each other were possible. If ozone formation was suppressed, as when a negative volume charge was created in the spark gap region, the flux of UV photons reached 3 × 10²³ photons/(cm² s).     

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.     

Application of a modulated Grimm-type glow discharge plasma as primary light source for simultaneous reading atomic absorption spectrometry

Summary The Grimm-type glow discharge lamp (GDL) working in a modulated way can be used as primary light source for atomic absorption measurements. The number of element radiations is given by the composition of the target (sample on GDL) which becomes sputtered. Its composition can be adopted to the analytical problem to be solved. It is easy to change the target.The glow discharge source generated at relatively low power (10–24 W) is burning stable for >20 min on the same spot. This is time enough to operate atomic absorption measurements of 10 samples simultaneously, for example, by using the normal flame technique or the graphite tube furnace or the atomsource sputter method to generate atoms of the sample material. The monochromator device of an AA spectrometer has to be replaced by a polychromator one.The spectral behaviour of the glow discharge source compared to that of the hollow cathode lamps of the elements studied is described here by using a double beam two channel AA spectrometer for simultaneous reading of both the signals. In most cases the glow discharge source is the better one. Home-made targets are used to measure first analytical results.

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Einsatz einer modulierten Glimmentladungslampe als Primärlichtquelle zur simultan messenden Atomabsorptionsspektrometrie

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We have to thank the Spectruma company and Bernhard Bogdain especially for supporting this work.     

Evaluation of a pulsed EIMAC source for atomic-fluorescence spectrometry

An EIMAC xenon arc continuum source operated in the pulsed mode has been evaluated for potential use as a source of excitation in atomic-fluorescence spectrometry. The results were compared with those obtained with a similar lamp operated in the continuous-wave mode; little or no improvement was evident from this comparison. The lamp was found to be unstable in the pulsed mode, requiring the use of a rather large residual d.c. current in conjunction with a relatively low amplitude power-pulse in order to sustain the arc. Moreover, the pulsed source yielded a large background signal because of scattering of source-radiation in the flame; the background spectrum (with source "on") contained numerous large peaks due to fluorescence of molecular species in the flame and to irregularities in the spectral distribution of the pulsed lamp output transmitted to the signal detector by scatter.     

Spectroscopic investigations of a cathode fall region of the Grimm-type glow discharge

This paper presents the results of the spectroscopic study of the cathode fall region of a plane cathode Grimm-type glow discharge in pure hydrogen and in argon with small admixtures of hydrogen. In contrast with the discharge in an argon-hydrogen mixture, the volt-ampere characteristics of the pure hydrogen discharge show a maximum typical for an abnormal glow-to-arc transition. This maximum in the V-A curve is explained here as being due to the increasing role of self-sputtering of the cathode material in sustaining the discharge at higher currents.For the measurements of the electric fields in the cathode fall region, Stark spectroscopy of the hydrogen Balmer lines is employed. Consistent results were obtained from H_β and H_γ recordings in a pure hydrogen discharge. Some of the difficulties in applying Stark spectroscopy for the diagnostics of a spatially inhomogeneous electric field inherent to Grimm glow discharges are discussed in detail. The experimental results are used to test the theoretical predictions of the electric field distribution in the cathode fall region. Reasonable agreement between theories and experiment is reported.Doppler spectroscopy of the same Balmer lines is used to determine the energies of the excited hydrogen atoms in the discharge. In the cathode fall region of a pure hydrogen discharge, two groups of excited atoms are detected: “slow”, in the range 3.4–8.2 eV, and “fast”, in the range 80–190 eV. The relative concentrations of “slow” and “fast” excited hydrogen atoms in the cathode fall region are determined. In addition, the relative concentration of hydrogen atoms with temperatures around 0.1 eV, excited in the plasma of the negative glow region, is also determined. The origin of these “slow” and “fast” hydrogen atoms is related to the presence of H⁺ and H₃⁺ ions, respectively. In the cathode fall region of an argon-hydrogen mixture discharge, only excited hydrogen neutrals with energies of 32–43 eV are detected. Their origin is related to the dominant role of H₃⁺ ions in this discharge. For both gases, in the negative glow region, an increase in the temperature of excited hydrogen atoms is detected, and is explained by the additional excitation of energetic neutrals in collisions with electrons.The axial intensity distributions of the hydrogen Balmer lines, in comparison with other atomic and ionic lines, show different shapes with maxima in the vicinity of the cathode surface. These shapes are explained by the excitation of reflected high-energy neutral atoms in collisions with the matrix gas.     

Kinetic temperatures and electron densities in the plasma of a side view Grimm-type glow discharge

A special source in which the Grimm-type plasma is viewed side-on for spectroscopic measurements was constructed. The kinetic gas temperatures and electron densities were derived from the line profiles of Ar I 415.8 nm and He I 447.1 nm respectively.     

Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated.The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10¹²cm^?3 for metastable argon atoms, 10¹⁶cm^?3 for neutral argon atoms, 10¹³ cm^?3 for sputtered copper atoms and 10¹⁴cm^?3for electrons.     

Free sodium-water clusters: photoionisation studies in a pulsed molecular beam source

Neutral Na·(H₂O) _n clusters are studied by near-uv one-photon ionisation and time-of-flight mass spectroscopy. The clusters are formed in a “pickup source” by injection of a beam of Na atoms into the expansion zone of a pulsed nozzle beam of water vapour seeded into an argon carrier gas. The performance of this novel technique for studying cold aggregates of potentially reactive species is discussed in detail. The photoion efficiency (PIE) spectrum of the monomer near its ionisation threshold (4.379(2) eV) shows a rich structure. Vibrational frequencies of the ion can be deduced and some indication of molecular Rydberg states is seen. Ionisation potentials for larger clusters and the binding energies of the neutral clusters up ton=5 are reported.     

On the theory of the radical radiation formation in a solid host

The calculation of the radical formation rate constant in solid organic compounds is carried out. This formation is a result of the cleavage of the hydrogen atom from the carbon atom via a radiationless electronic transition in an electronically excited molecule. The electronic transition is supposed to be stipulated by the nonadiabaticity operator and the perturbation theory with respect to this operator is supposed to be applicable. The vibrational interaction of an electronically excited molecule with the host environment is assumed not to be small. The calculation is carried out within the framework of a model in which the whole molecule is represented by a CH group this being treated as a Morse oscillator. The specific features of the different substances in such a model are simulated by different values of the CH bond parameters.     

Factors affecting the capillary electrophoresis of ricin, a toxic glycoprotein

Conditions for the analysis of ricin with capillary electrophoresis were investigated. Uncoated and coated columns were tested with a variety of different buffer combinations which included different principal components, pH, ionic strength, and additives. Of the combinations tested, uncoated columns used with either zwitterionic salts or putrescine gave the best results. Multiple peaks were resolved with these conditions. Coated columns generally yielded between 1000 and 5000 plates with several buffer combinations. Ricin may be analyzed faster and with greater resolution with capillary electrophoresis employing untreated fused-silica columns than by using other chromatographic techniques.     

Factors affecting the detection limit of a flow- injection spectrophotometric procedure

Design criteria for manifolds to obtain adequated sensitivity and freedom from certain types of noise are discussed. For the determination of chloride by the mercury(II) thiocynate method, the mergin-streams manifold, needed to eliminated negative peaks at low concentrations and refractive index effects, increased the baseline noise because of inefficient mixing at the confluence point. Packed-bed reactors and single-bead-string reactors (SBSR) significantly improved the baseline noise. Refractive index effects caused by sample concentration gradients were eliminated by the injection of large volumes (>500 μl), so that the detector could view a homogeneous central part of the sample zone. This approach maximises the signal because the dispersion is governed only by the relative flow rates of the carrier and reagent streams. The detection limits for chloride were improved to 40 ng l^?1 in aqueous solutions of low ionic strength and to 1.3 mg l^?1 in 5.25% (w/v) potassium sulphate.     

Factors affecting the electrodeposition of226Ra

The electrodeposition of²²⁶Ra for -spectrometry was reinvestigated to improve reproducibility and yield. Electrodeposition is from 20 ml of 90% propan-2-ol10% 0.05M HNO₃ onto stainless steel disks, using 100 mA at 35 V for 20 minutes and a platinum anode. Half deposition time is 3–4 minutes. The following factors were found important: 1. Maintaining the same anode position. 2. Rotation of cathode. 3. Exclusion of sulphate. 4. Avoiding heating the HNO₃/propan-2-ol plating solution. 5. Exclusion of solubilised resin resulting from passage through ion-exchange columns. 6. Maintaining other impurities at less than 10 g. If these precautions are followed yields are greater than 90%.     

Study of a pulsed glow discharge ion source for time-of-flight mass spectrometry

This paper describes a new type of glow discharge (GD) ion source coupled to a time-of-flight mass spectrometer (TOFMS). The GD is operated in the microsecond pulse (μs-pulse) mode. The operational parameters of the μs-pulse GD were optimized against the ion signals, giving 180 Pa for the discharge pressure, 3 A for the transient discharge current, 1.75 kHz for the discharge frequency and 2 μs for the discharge pulse duration. Experimental results show that the discharge current in the μs-pulse mode can be one order of magnitude higher than that obtained in the d.c. mode. The structure of the interface between the μs-pulse GD and the mass spectrometer was found to be critical, and a Macor disc must be applied in front of the sampling orifice in order to shield the sampling plate from the anode of the GD to achieve both a good vacuum and the best sputtering. A transient sputtering rate of 24.4 μs s⁻¹ mm⁻² was reached in the μs-pulse mode and was significantly higher than that for the d.c.-GD. Typical mass spectra of brass and nickel samples were studied and are discussed. © 1997 Elsevier Science B.V.     

Factors affecting the bioavailability of soy isoflavones in humans

To fully evaluate the potential risks and benefits of isoflavones to human health, an understanding of the physiological behavior of these compounds following ingestion is required. Numerous researchers have investigated the kinetics and extent of polyphenol absorption by measuring plasma concentrations and/or urinary excretion among adults after the ingestion of a single dose of polyphenol, provided as either a pure compound, plant extract, or whole food/beverage. Available data suggest isoflavones are more bioavailable than other flavonoid subclasses. This review will focus on our current understanding of factors affecting isoflavone absorption and metabolism in humans.     

A new pulsed light source for lifetime studies and time resolved spectroscopy: the synchrotron radiation from an electron storage ring

Synchrotron radiation from the Orsay Storage Ring (ACO) has been used as a repetitive source for lifetime and time resolved fluorescence studies. Our measurements and results concern: (1) Lifetime of standard compounds (quinine sulfate and fluorescein anion); (2) single vibronic level fluorescence (aniline and pyrazaine in the vapor phase; pyrazine lifetime has been measured for the first time to be 0.5 ± 0.2 ns); and (3) reactivity of excited molecules (decay time and time resolved spectra of 2-naphthol and fluorescein both undergoing fast protolytic reactions in the excited state). Storage ring synchrotron radiation characteristics and performances are discussed and compared to those of conventional “nanosecond” flash lamps. Possible new applications are foreseen.