H. Holzbrecher

Electroluminescence of erbium–oxygen‐doped silicon diodes grown by molecular beam epitaxy

We have fabricated erbium–oxygen‐doped silicon light emitting diodes with molecular beam epitaxy by simultaneously evaporating erbium and silicon and providing a suitable background pressure of oxygen. In reverse bias, the diodes show intense room‐temperature electroluminescence at λ=1.54 μm, originating from the intra‐4f transition of erbium. This luminescence does not show temperature quenching between 4 and 300 K. In forward bias the erbium peak intensity is reduced by a factor of 30 at low temperatures and shows temperature quenching.

Quantitative analysis of oxide films on ODS-alloys using MCs+-SIMS and e-beam SNMS

SummaryAttempts to obtain a quantitative analysis of depth profiles of oxide films on iron-based ODS-alloys using MCs+-SIMS and e-beam SNMS are presented. Since the oxide films of the alloys consist mainly of alumina, implantation standards in Al2O3(sapphire) were used for the quantification of the measured depth profiles. The so-called matrix effect, normally present in SIMS analysis, is strongly reduced by recording the MCs+-secondary ions. Over a wide concentration range, agreement between SIMS and SNMS data is obtained within a factor 2–3. The evaluated concentration profiles for the main alloying elements in combination with 18O tracer-experiments have been used to give an interpretation of the growth processes of the oxide films for Fe-based ODS-alloys, with and without the addition of an yttria dispersion. The results show that the addition of yttria dispersion is responsible for the dramatic change observed in the oxide growth mechanism.

Analysis of composition and growth mechanisms of oxide scales on high temperature alloys by SNMS, SIMS, and RBS

Composition and growth phenomena of alumina scales on a conventional wrought alloy Fe-20Cr-5Al and an yttria containing ODS alloy with the same base composition were investigated. The alloys were oxidized in a twostage oxidation process at 1000 °C in air and air containing18O-tracer. By using secondary neutrals and secondary ion mass spectrometry in combination with RBS, the in-depth concentration of main and minor alloying elements as well as the oxygen isotope distribution in the alumina scale could be determined. It is shown, that the difficulties in deriving the exact growth processes of the scales from the oxygen tracer profiles can be overcome by using the time dependance of the iron and chromium distribution in the alumina. From these results it could be derived that growth of the oxide scales formed on the ODS and the conventional alloy mainly differ in the relative contribution of aluminium diffusion. The mechanisms which lead to these differences in scale growth phenomena will be discussed.

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on LaxSryMnO3 cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.

Influence of germanium content on the photoluminescence of erbium- and oxygen-doped SiGe grown by molecular beam epitaxy

The photoluminescence at 1.54 μm of erbium- and oxygen-doped Si/Si1−xGex samples grown completely by molecular beam epitaxy has been investigated for germanium concentrations ranging from x=0 to x=0.165. The dopants were either placed into the Si1−xGex or into the Si layers of an alternating Si/Si1−xGex layer structure. Because of the good crystal quality after growth, it was possible to obtain all luminescence data from as-grown samples without annealing. We observed a decrease in photoluminescence (PL) intensity and a stronger temperature dependence with increasing Ge content. For samples with the same Si/Si1−xGex layer structure, an enhancement of PL intensity at low temperature was seen when erbium and oxygen were placed into the Si1−xGex layers rather than into the Si layers. We attribute this effect to a capture of photogenerated carriers in the Si1−xGex layers.

SIMS investigations on the growth mechanisms of protective chromia and alumina surface scales

The oxidation behaviour of the oxide-dispersion strengthened (ODS) high-temperature alloys MA 956 (an aluminium oxide former) and MA 754 (a chromium oxide former) has been compared with that of two model alloys, Fe-20Cr-5Al and Ni-25Cr. The morphology and composition of the oxide scales were investigated by metallography, X-ray diffraction analysis and scanning electron microscopy. For analysis of the oxide layer growth mechanisms, twostage oxidation experiments with18O as tracer were used, the distribution of the oxygen isotopes in the oxide scale being determined by SIMS. The ODS alloys show a more selective oxidation than the two model alloys; moreover, the protective oxides on the ODS alloys have a lower growth rate and better adhesion than those on the two model alloys. From the SIMS investigations it can be deduced that the improved properties of the layers on the ODS alloys result from a change in the transport processes in the protective layer; whereas the aluminium and chromium oxide films on the conventional alloys grow by cation and anion transport, the scales on the ODS alloys grow almost exclusively by anion transport. It is shown that the observed properties of the oxide scales on the ODS alloys can be explained by this change in transport mechanism.

Quantitative SIMS-analysis of erbium profiles in LiNbO3

Modern fiberoptic communication technology uses light of 1.5 μm wavelength and Er3+ is the laser active ion for this wavelength. Doping of crystalline LiNbO3 (an electrooptical material) with erbium ions permits the fabrication of signal-amplifying electrooptic devices. Novel results of three different approaches have been presented to dope the near surface area of LiNbO3 for its application in planar optoelectronics: erbium indiffusion from the surface, implantation of erbium into LiNbO3 and subsequent annealing schemes, and the homoepitaxial growth of Er-doped LiNbO3 on LiNbO3 single crystalline material by a laser deposition method. These experiments are not only useful for creating integrated optical devices with active amplifying functions, but they are also important examples for fabricating and studying novel thin ferroelectric films. Secondary ion mass spectrometry (SIMS) has been employed as the main analytical tool for quantitative determination of the erbium concentration profiles.

Photo- and electroluminescence characterization of erbium doped SiGe

We have performed photo- and electroluminescence measurements on erbium doped silicon and SiGe samples containing different amounts of germanium. All samples were grown completely by molecular beam epitaxy. Oxygen was used as a codopant to enhance the luminescence efficiency. The photoluminescence data show a systematic variation of the thermal activation energy obtained from temperature dependent intensity measurements with varying germanium contents. For samples with an alternating Si/SiGe layer structure stronger photoluminescence is observed when the erbium ions are incorporated into the SiGe layers rather than into the silicon layers. We attribute this to the capture of photogenerated carriers in the SiGe layers. Electroluminescence from erbium doped SiGe samples which have been processed as diodes has been observed up to room temperature in both surface and edge emitting geometries.

Eignung von Tiefenprofilanalysen zur Charakterisierung von Oxidschichten an Hochtemperaturlegierungen

SummaryThe 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.

Improvement of the detection limit of carbon in metal alloys by Ion Microprobe Analysis

SummaryAn important aim of materials research is the detection of dependencies between local carbon distributions and mechanical characteristics. Because of the small concentration of carbon the methods of analysis for the detection of local element distributions-e.g. Auger Spectroscopy, Electron Microprobe, and Ion Microprobe Analysis-are not directly suitable.This paper presents results of examinations with Ion Microprobe Analysis which improve the detection limit of carbon by a factor of 100. Thus the aim to detect local distributions of carbon in high temperature alloys seems to be possible for concentrations above 200 ppm.ZusammenfassungEin wichtiges Ziel der Werkstofforschung ist der Nachweis von Abhängigkeiten zwischen lokalen Kohlenstoffverteilungen und mechanischen Werkstoffeigenschaften. Wegen der kleinen Kohlenstoffgehalte sind die Verfahren zur Bestimmung lokaler Elementverteilungen — Auger-Spektroskopie, Elektronenmikrosonde und Ionenmikrosonde — nicht direkt geeignet. Es werden Untersuchungsergebnisse angegeben, die eine Verbesserung der Nachweisgrenze für Kohlenstoff mit der Ionenmikrosonde um den Faktor 100 ermöglichen. Damit erscheint der Nachweis lokaler Kohlenstoffverteilungen in Hochtemperaturwerkstoffen für Konzentrationen ≥200 ppm möglich.