Analysis of nitrogen-influenced surface near zones of ferrous materials by glow discharge spectroscopy (GDOS)

Glow discharge spectroscopy (GDOS) will be shown to be a quick, informative and simple method for quantitative depth profile analysis of elements of nitrided layers well suited for their quality control. By systematic variation of all glow discharge determining parameters it is possible to get an excellent depth resolution in the order of sub-m corresponding to a comparatively large analytical activated area (50 mm²). In this paper the behaviour of a number of important parameters related to sputtering of the activated area will be discussed. Some quantitative GDOS depth profiles of carbon and nitrogen of pure iron samples nitrided by different procedures will be shown as examples for application.     

Advanced surface techniques for characterization of Cu-base artefacts

Patinae on Cu-base alloys have been characterized by means of GDOS, SEM, XRD and AFM. The effect of a protective coating was tested in aggressive artificial solutions. Patinae and the bulk of several metal Punic objects were also examined. The GDOS results combined with SEM capabilities allow exhaustive investigation of composition, element distribution and microstructure of modified surface in modern bronzes exposed to accelerated ageing tests as well as in ancient bronzes. The SEM data of the patina thickness agree with the GDOS data. The XRD and SEM investigations allow an exhaustive characterization of corrosion products. Corrosion growth in its early stages determines the effectiveness of the patina's protective role and the AFM is a promising technique for investigating this.     

Eignung von Tiefenprofilanalysen zur Charakterisierung von Oxidschichten an Hochtemperaturlegierungen

Summary The characterization of oxide scales by their composition and structure is necessary in order to predict their protective behaviour for the high temperature alloys in various corrosive media. For this purpose information obtained by classical methods, such as metallography, X-ray diffraction and microprobe analysis can be supplemented by depth profiles determined by various spectroscopical methods.In this paper, HASTELLOY X und INCONEL 617 were oxidized for relatively short times in two different atmospheres. Depth profiles were determined by GDOS (Glow Discharge Optical Spectroscopy), SNMS (Secondary Neutral Mass Spectrometry) and SIMS (Secondary Ion Mass Spectrometry).The measured profiles were compared with the results of non-destructive X-ray diffraction analysis to characterize the scales and the oxide-metal interface.     

Thickness determination from the GDOS depth profiles using piece-wise linear model functions

A data processing method is presented making it possible to determine thin film thickness from GDOS depth profiles. It consists of fitting a piece-wise linear function to the depth profile and in using positions (abscissae) of their knots as parameters which are proportional to film thickness. For thickness calibration, such a linear combination of these parameters is used, which gives minimum variation coefficient of the residuals between the real and the estimated thickness of calibration samples. Relative error lower than 3% was obtained in calibration using 4 samples with nickel film thickness ranging from 0.1 to 8.3 m, each analyzed four times.     

Surface analysis of steel sheets with GDOS and EPMA

Summary In the field of steel sheet characterization, chemical surface analysis plays a very important role. Surface composition effects the surface properties of the final product. At Voest-Alpine Stahl Linz the analysis techniques GDOS and EPMA are routinely used to characterize the steel sheet surface. Some fundamental experiments are here described for the optimization of GDOS depth resolution. In the documentation for a semiquantitative approach for steel sheet analysis, investigations and experience about minimum detection limits are presented. Self developed methods for concentration mapping and thickness mapping are described in the field of electron probe microanalysis; Also an EPMA depth profiling method is highlighted. Finally practical examples demonstrate the wide application range of the analysis methods.     

Calibration standards for composition-depth profiles of non-stoichiometric titanium nitride coatings

Five different TiN_x coatings have been deposited on steel substrates by reactive magnetron sputtering. A quantitative analysis was carried out in two ways. The coatings were initially analysed by GDOS and after removing the coatings from the substrates and digesting the TiN_x powder, nitrogen was quantified by the Kjeldahl technique and titanium by AAS. A comparison of the results shows that AAS and Kjeldahl results correlate very well, whereas GDOS results deviate from these two methods systematically.     

Influence of surface structure on surface analytical statements

The influence of surface structure of technical materials on results and statements of surface analytical methods has been investigated. Especially surface roughness as a typical property of rolled products has been observed. For this purpose samples of steel (technical surface, roughness up to 5 m) and silicon wafers (polished surface) have been analyzed by SNMS and GDOS in order to get information about changes of the surface roughness as function of the sputtering time and their influence on the statements about the depth profiles obtained.     

Heterogeneous element distribution: a contribution to quantitative GDOS depth analysis

Summary The apparent enrichment of Cu, Mg, Mn and Si on the surface of Al cast-alloys, as observed by means of glow discharge optical emission spectrometry (GDOS), could be attributed to the heterogeneous distribution of the alloying elements. The samples under investigation were spectrochemical standards and hence assumed to be homogeneous. Different metallurgical phases were identified which induced selective sputtering. The findings point out that quantitative results obtained by GDOS in-depth analysis can be misleading and should be confirmed by other techniques such as Auger Electron Spectrometry and Energy Dispersive X-ray Spectrometry, which are free from sputter effects.     

Quantitative depth-profiling with GDOS: application to ZnNi-electrogalvanized steel sheets

Summary Studies are made on quantitative GDOS depth profile analysis for ZnNi-coatings. Relative and absolute depth resolution on the interface ZnNi-coating/steel substrate were evaluated in a thickness range of 0.5 to 5 m using two different anode tube diameters. For quantification, an improved approach of the model of constant emission yield was established. The results are demonstrated on ZnNi-electrodeposits with different coating thickness and chemical content.     

Surface analysis on industrial surfaces — now comparable

Interlaboratory test analysis with GDOS and SNMS were conducted by 8 laboratories on certified standard specimens and on a technical steel sheet to determine the elemental concentrations, possible changes of its surface composition due to the manufacturing process and to establish the repeatabilities and reproducibilities under depth profile conditions.     

Depth profile analyses by GDOS on stainless steel surfaces after exposure to liquid lithium

Summary Depth profile analyses by means of glow discharge optical spectroscopy (GDOS) has been performed on stainless steel SS 316 samples after 3 different modes of exposure in liquid lithium at 600° C. The figures represent the qualitative correlation between element concentration (intensity, arbitrary units) and the sputtered depth (sputtertime, seconds). Differences in depletion and enrichment of certain elements amongst others, have been attributed to the differences of the impurities, namely N and C in lithium.

---

Tiefenprofilanalyse an in flüssigem Lithium ausgelagerten Stahlproben mittels Glow Discharge Optical Spectroscopy (GDOS)

Zusammenfassung Es wird über die Tiefenprofilanalyse mittels Glow Discharge Optical Spectroscopy an rostfreiem Stahl SS 316 nach 3 unterschiedlichen Auslagerungen in flüssigem Lithium bei 600° C berichtet. In den Kurven wird qualitativ der Zusammenhang zwischen der Konzentration der Elemente (Intensität in Volt in willkürlichen Einheiten) in Abhängigkeit von der Abtragtiefe (in Sekunden-Sputterzeit) dargestellt. Die Unterschiede in der Anbzw. Abreicherung einzelner Elemente konnten außer der unterschiedlichen Auslagerung, auch auf die Verunreinigungen im Li, insbesondere N und C zurückgeführt werden.

     

Production and characterization of nitrided CVD-SiC films

Silicon Carbide (SiC) and SiC with free silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using a CH₃SiCl₃-H₂-Ar gas mixture at a temperature of 1223 K. Afterwards these layers were gas nitrided in an ammonia-hydrogen-argon mixture at 1273 K. The solid product is an extremely thin film of silicon nitride on SiC or SiC(Si)-basic layers. These ultra thin silicon nitride films were investigated by glow discharge optical spectroscopy (GDOS) and x-ray photoelectron spectroscopy (XPS). The thickness of the layers was determined to a maximum value of 30 nm.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Zur Bestimmung der Zusammensetzung und Homogenit?t reaktiv gesputterter SiNx-Schichten

Summary Thin SiN_x-layers are to be used for joining Si₃N₄ ceramics. For the characterization of such layers produced by reactive sputtering using a RF magnetron cathode, the chemical composition requires determination. Layers were therefore sputtered under various sputtering conditions onto stainless steel, graphite and silicon substrates and then analyzed using three different methods: Glow Discharge Optical Spectrometry (GDOS), Electron Microprobe Analysis (EMPA) and Rutherford-Backscattering (RBS).     

DC-plasma polymerization of pyrrole

DC-plasma-polymerized pyrrole (PP-Py) films deposited on metals were extensively characterized by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Reflection-Absorption IR Spectroscopy (RAIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy (STM), Glow Discharge Optical Spectroscopy (GDOS), electrical conductivity (ASTM Franklin test), and contact angle measurements. TOF-SIMS and RAIR showed no spectroscopic evidence of the presence of the pyrrole ring structure in any of the plasmadeposited films. The major parameter that affected their composition was found to be the pressure. Films deposited at low pressure were less hydrogenated than those polymerized at high pressure or in remote plasma conditions. Although all deposits oxidized slowly in air, their surface energy remained low over an extended period of time. The electrical conductivity of the PP-Py films was in the range of 10⁻³–10⁻⁴ S/cm, i.e., higher than that of amorphous carbon films.     

Point defects in (Ti, Fe)N hard coatings, a Mössbauer study

Reactive magnetron sputtered layers of nitridic hard coatings (e.g. TiN) often show high intrinsic stresses caused by the differences of the thermal expansion coefficients of the layer and the substrate and the incorporation of atoms of sputtering and/or reactive gas atoms in lattice voids. The decrease of hardness and stresses of such layers after heat treatment seems to originate from the out-diffusion of interstitial excess reactive gas atoms (e.g. nitrogen). In this study ⁵⁷Fe Mössbauer spectroscopy on (Ti, Fe)N model layers is used to obtain direct information about the mechanism of the development and variation of intrinsic stresses in nitridic hard coatings in connection with point defects (e.g. excess N). The results of this investigations are supported by X-ray analysis and Glow Discharge Optical Spectroscopy (GDOS).     

Injection profiles in liquid chromatography II: predicting accurate injection-profiles for computer-assisted preparative optimizations

In computer assisted optimization of liquid chromatography it has been known for some years that it is important to use experimental injection profiles, instead of rectangular ones, in order to calculate accurate elution bands. However, the incorrectly assumed rectangular profiles are still mostly used especially in numerical optimizations. The reason is that the acquisition of injection profiles, for each injection volume and each flow rate considered in a computer-assisted optimization requires a too large number of experiments. In this article a new function is proposed, which enables highly accurate predictions of the injection profiles and thus more accurate computer optimizations, with a minimum experimental effort. To model the injection profiles for any injection volume at a constant flow rate, as few as two experimental injection profiles are required. If it is desirable to also take the effect of flow rate on the injection profiles into account, then just two additional experiments are required. The overlap between fitted and experimental injection profiles at different flow rates and different injection volumes were excellent, more than 90%, using experimental injection profiles from just four different injection volumes at two different flow rates. Moreover, it was demonstrated that the flow rate has a minor influence on the injection profiles and that the injection volume is the main parameter that needs to be accounted for.     

Mucin (MUC5AC) expression by lung epithelial cells cultured in a microfluidic gradient device

We have developed a microfluidic gradient device for controlling mucin gene expression of NCI-H292 epithelial cells derived from lung tissues. We hypothesized that gradient profiles would control mucin gene expression of lung epithelial cells. However, it was not possible to generate various stable gradient profiles using conventional culture methods. To address this limitation, we used a microfluidic gradient device to create various gradient profiles (i.e. non-linear, linear, and flat) in a temporal and spatial manner. NCI-H292 lung epithelial cells were exposed to concentration gradients of epidermal growth factor in a microfluidic gradient device with continuous medium perfusion. We demonstrated an effect of gradient profiles on mucin expression of lung epithelial cells cultured in the microfluidic gradient device. It was revealed that NCI-H292 lung epithelial cells exposed to the flat gradient profile of the epidermal growth factor exhibited high expression of mucin as compared with cells exposed to non-linear and linear gradient profiles. Therefore, this microfluidic gradient device could be a potentially useful tool for regulating the mucin expression of lung epithelial cells exposed to chemokine gradient profiles.     

Incorporating high-pressure electroosmotic pump and a nano-flow gradient generator into a miniaturized liquid chromatographic system for peptide analysis

We integrate a high-pressure electroosmotic pump (EOP), a nanoflow gradient generator, and a capillary column into a miniaturized liquid chromatographic system that can be directly coupled with a mass spectrometer for proteomic analysis. We have recently developed a low-cost high-pressure EOP capable of generating pressure of tens of thousands psi, ideal for uses in miniaturized HPLC. The pump worked smoothly when it was used for isocratic elutions. When it was used for gradient elutions, generating reproducible gradient profiles was challenging; because the pump rate fluctuated when the pump was used to pump high-content organic solvents. This presents an issue for separating proteins/peptides since high-content organic solvents are often utilized. In this work, we solve this problem by incorporating our high-pressure EOP with a nano-flow gradient generator so that the EOP needs only to pump an aqueous solution. With this combination, we develop a capillary-based nano-HPLC system capable of performing nano-flow gradient elution; the pump rate is stable, and the gradient profiles are reproducible and can be conveniently tuned. To demonstrate its utility, we couple it with either a UV absorbance detector or a mass spectrometer for peptide separations.