Optimization in the Technological Steps for the Fabrication of Large Area Micromirror Arrays

Micromirror arrays are a very strong candidate for future energy saving applications. Within this work, the fabrication process for these micromirror arrays has been optimized and some steps for the large area fabrication of micromirror modules were performed. At first the surface roughness of the insulation layer of silicon dioxide (SiO2) was investigated. This SiO2 thin layer was deposited on three different type of substrates i.e. silicon, glass and Polyethylene Naphthalate (PEN) substrates. The deposition techniques which has been used are Plasma Enhanced Chemical Vapor Deposition (PECVD), Physical Vapor Deposition (PVD) and Ion Beam Sputter Deposition (IBSD). The thickness of the SiO2 thin layer was kept constant at 150nm for each deposition process. The surface roughness was measured by Stylus Profilometry and Atomic Force Microscopy (AFM). It was found that the layer which was deposited by IBSD has got the minimum surface roughness value and the layer which was deposited by PECVD process has the highest surface roughness value. During the same investigation, the substrate temperature of PECVD was varied from 80° C to 300° C with the step size of 40° C and it was found that the surface roughness keeps on increasing as the substrate holder temperature increases in the PECVD process. A new insulation layer system was proposed to minimize the dielectric breakdown effect in insulation layer for micromirror arrays. The conventional bilayer system was replaced by five layer system but the total thickness of insulation layer remains the same. It was found that during the actuation of micromirror arrays structure, the dielectric breakdown effect was reduced considerably as compared to the bilayer system. In the second step the fabrication process of the micromirror arrays was successfully adapted and transferred from glass substrates to the flexible PEN substrates by optimizing the conventional process recipe. In the last section, a large module of micromirror arrays was fabricated by electrically interconnecting four 10cm×10cm micromirror modules on a glass pane having dimensions of 21cm×21cm.

Development of hybrid UV VCSEL with organic active material and dielectric DBR mirrors for medical, sensoric and data storage applications

Lasers play an important role for medical, sensoric and data storage devices. This thesis is focused on design, technology development, fabrication and characterization of hybrid ultraviolet Vertical-Cavity Surface-Emitting Lasers (UV VCSEL) with organic laser-active material and inorganic distributed Bragg reflectors (DBR). Multilayer structures with different layer thicknesses, refractive indices and absorption coefficients of the inorganic materials were studied using theoretical model calculations. During the simulations the structure parameters such as materials and thicknesses have been varied. This procedure was repeated several times during the design optimization process including also the feedback from technology and characterization. Two types of VCSEL devices were investigated. The first is an index coupled structure consisting of bottom and top DBR dielectric mirrors. In the space in between them is the cavity, which includes active region and defines the spectral gain profile. In this configuration the maximum electrical field is concentrated in the cavity and can destroy the chemical structure of the active material. The second type of laser is a so called complex coupled VCSEL. In this structure the active material is placed not only in the cavity but also in parts of the DBR structure. The simulations show that such a distribution of the active material reduces the required pumping power for reaching lasing threshold. High efficiency is achieved by substituting the dielectric material with high refractive index for the periods closer to the cavity. The inorganic materials for the DBR mirrors have been deposited by Plasma- Enhanced Chemical Vapor Deposition (PECVD) and Dual Ion Beam Sputtering (DIBS) machines. Extended optimizations of the technological processes have been performed. All the processes are carried out in a clean room Class 1 and Class 10000. The optical properties and the thicknesses of the layers are measured in-situ by spectroscopic ellipsometry and spectroscopic reflectometry. The surface roughness is analyzed by atomic force microscopy (AFM) and images of the devices are taken with scanning electron microscope (SEM). The silicon dioxide (SiO2) and silicon nitride (Si3N4) layers deposited by the PECVD machine show defects of the material structure and have higher absorption in the ultra violet range compared to ion beam deposition (IBD). This results in low reflectivity of the DBR mirrors and also reduces the optical properties of the VCSEL devices. However PECVD has the advantage that the stress in the layers can be tuned and compensated, in contrast to IBD at the moment. A sputtering machine Ionsys 1000 produced by Roth&Rau company, is used for the deposition of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3) and zirconium dioxide (ZrO2). The chamber is equipped with main (sputter) and assisted ion sources. The dielectric materials were optimized by introducing additional oxygen and nitrogen into the chamber. DBR mirrors with different material combinations were deposited. The measured optical properties of the fabricated multilayer structures show an excellent agreement with the results of theoretical model calculations. The layers deposited by puttering show high compressive stress. As an active region a novel organic material with spiro-linked molecules is used. Two different materials have been evaporated by utilizing a dye evaporation machine in the clean room of the department Makromolekulare Chemie und Molekulare Materialien (mmCmm). The Spiro-Octopus-1 organic material has a maximum emission at the wavelength λemission = 395 nm and the Spiro-Pphenal has a maximum emission at the wavelength λemission = 418 nm. Both of them have high refractive index and can be combined with low refractive index materials like silicon dioxide (SiO2). The sputtering method shows excellent optical quality of the deposited materials and high reflection of the multilayer structures. The bottom DBR mirrors for all VCSEL devices were deposited by the DIBS machine, whereas the top DBR mirror deposited either by PECVD or by combination of PECVD and DIBS. The fabricated VCSEL structures were optically pumped by nitrogen laser at wavelength λpumping = 337 nm. The emission was measured by spectrometer. A radiation of the VCSEL structure at wavelength 392 nm and 420 nm is observed.

Optimization of the Mechanical and Optical Properties of Tunable Optical Sensor Arrays (TOSA) for a Nanospectrometer in the Visible and Near Infrared Spectral Range

Tunable Optical Sensor Arrays (TOSA) based on Fabry-Pérot (FP) filters, for high quality spectroscopic applications in the visible and near infrared spectral range are investigated within this work. The optical performance of the FP filters is improved by using ion beam sputtered niobium pentoxide (Nb2O5) and silicon dioxide (SiO2) Distributed Bragg Reflectors (DBRs) as mirrors. Due to their high refractive index contrast, only a few alternating pairs of Nb2O5 and SiO2 films can achieve DBRs with high reflectivity in a wide spectral range, while ion beam sputter deposition (IBSD) is utilized due to its ability to produce films with high optical purity. However, IBSD films are highly stressed; resulting in stress induced mirror curvature and suspension bending in the free standing filter suspensions of the MEMS (Micro-Electro-Mechanical Systems) FP filters. Stress induced mirror curvature results in filter transmission line degradation, while suspension bending results in high required filter tuning voltages. Moreover, stress induced suspension bending results in higher order mode filter operation which in turn degrades the optical resolution of the filter. Therefore, the deposition process is optimized to achieve both near zero absorption and low residual stress. High energy ion bombardment during film deposition is utilized to reduce the film density, and hence the film compressive stress. Utilizing this technique, the compressive stress of Nb2O5 is reduced by ~43%, while that for SiO2 is reduced by ~40%. Filters fabricated with stress reduced films show curvatures as low as 100 nm for 70 μm mirrors. To reduce the stress induced bending in the free standing filter suspensions, a stress optimized multi-layer suspension design is presented; with a tensile stressed metal sandwiched between two compressively stressed films. The stress in Physical Vapor Deposited (PVD) metals is therefore characterized for use as filter top-electrode and stress compensating layer. Surface micromachining is used to fabricate tunable FP filters in the visible spectral range using the above mentioned design. The upward bending of the suspensions is reduced from several micrometers to less than 100 nm and 250 nm for two different suspension layer combinations. Mechanical tuning of up to 188 nm is obtained by applying 40 V of actuation voltage. Alternatively, a filter line with transmission of 65.5%, Full Width at Half Maximum (FWHM) of 10.5 nm and a stopband of 170 nm (at an output wavelength of 594 nm) is achieved. Numerical model simulations are also performed to study the validity of the stress optimized suspension design for the near infrared spectral range, wherein membrane displacement and suspension deformation due to material residual stress is studied. Two bandpass filter designs based on quarter-wave and non-quarter-wave layers are presented as integral components of the TOSA. With a filter passband of 135 nm and a broad stopband of over 650 nm, high average filter transmission of 88% is achieved inside the passband, while maximum filter transmission of less than 1.6% outside the passband is achieved.

Low-Cost Micromechanically Tunable Optical Devices: Strained Resonator Engineering, Technological Implementation and Characterization

The rapid growth of the optical communication branches and the enormous demand for more bandwidth require novel networks such as dense wavelength division multiplexing (DWDM). These networks enable higher bitrate transmission using the existing optical fibers. Micromechanically tunable optical microcavity devices like VCSELs, Fabry-Pérot filters and photodetectors are core components of these novel DWDM systems. Several air-gap based tunable devices were successfully implemented in the last years. Even though these concepts are very promising, two main disadvantages are still remaining. On the one hand, the high fabrication and integration cost and on the other hand the undesired adverse buckling of the suspended membranes. This thesis addresses these two problems and consists of two main parts: • PECVD dielectric material investigation and stress control resulting in membranes shape engineering. • Implementation and characterization of novel tunable optical devices with tailored shapes of the suspended membranes. For this purposes, low-cost PECVD technology is investigated and developed in detail. The macro- and microstress of silicon nitride and silicon dioxide are controlled over a wide range. Furthermore, the effect of stress on the optical and mechanical properties of the suspended membranes and on the microcavities is evaluated. Various membrane shapes (concave, convex and planar) with several radii of curvature are fabricated. Using this resonator shape engineering, microcavity devices such as non tunable and tunable Fabry-Pérot filters, VCSELs and PIN photodetectors are succesfully implemented. The fabricated Fabry-Pérot filters cover a spectral range of over 200nm and show resonance linewidths down to 1.5nm. By varying the stress distribution across the vertical direction within a DBR, the shape and the radius of curvature of the top membrane are explicitely tailored. By adjusting the incoming light beam waist to the curvature, the fundamental resonant mode is supported and the higher order ones are suppressed. For instance, a tunable VCSEL with 26 nm tuning range, 400µW maximal output power, 47nm free spectral range and over 57dB side mode suppresion ratio (SMSR) is demonstrated. Other technologies, such as introducing light emitting organic materials in microcavities are also investigated.

The Surface Plasmon Resonance of Supported Noble Metal Nanoparticles: Characterization, Laser Tailoring, and SERS Application

This work deals with the optical properties of supported noble metal nanoparticles, which are dominated by the so-called Mie resonance and are strongly dependent on the particles’ morphology. For this reason, characterization and control of the dimension of these systems are desired in order to optimize their applications. Gold and silver nanoparticles have been produced on dielectric supports like quartz glass, sapphire and rutile, by the technique of vapor deposition under ultra-high vacuum conditions. During the preparation, coalescence is observed as an important mechanism of cluster growth. The particles have been studied in situ by optical transmission spectroscopy and ex situ by atomic force microscopy. It is shown that the morphology of the aggregates can be regarded as oblate spheroids. A theoretical treatment of their optical properties, based on the quasistatic approximation, and its combination with results obtained by atomic force microscopy give a detailed characterization of the nanoparticles. This method has been compared with transmission electron microscopy and the results are in excellent agreement. Tailoring of the clusters’ dimensions by irradiation with nanosecond-pulsed laser light has been investigated. Selected particles are heated within the ensemble by excitation of the Mie resonance under irradiation with a tunable laser source. Laser-induced coalescence prevents strongly tailoring of the particle size. Nevertheless, control of the particle shape is possible. Laser-tailored ensembles have been tested as substrates for surface-enhanced Raman spectroscopy (SERS), leading to an improvement of the results. Moreover, they constitute reproducible, robust and tunable SERS-substrates with a high potential for specific applications, in the present case focused on environmental protection. Thereby, these SERS-substrates are ideally suited for routine measurements.

Surface modifications of nanocrystalline diamond films and their functionalization with phthalocyanines

Boron-doped diamond is a promising electrode material for a number of applications providing efficient carrier transport, a high stability of the electrolytic performance with time, a possibility for dye-sensitizing with photosensitive molecules, etc. It can be functionalized with electron donor molecules, like phthalocyanines or porphyrins, for the development of light energy conversion systems. For effective attachment of such molecules, the diamond surface has to be modified by plasma- or photo-chemical processes in order to achieve a desired surface termination. In the present work, the surface modifications of undoped and boron-doped nanocrystalline diamond (NCD) films and their functionalization with various phthalocyanines (Pcs) were investigated. The NCD films have been prepared by hot filament chemical vapor deposition (HFCVD) on silicon substrates and were thereafter subjected to modifications with O2 or NH3 plasmas or UV/O3 treatments for exchange of the H-termination of the as-grown surface. The effectiveness of the modifications and their stability with time during storage under different ambients were studied by contact angle measurements and X-ray photoelectron spectroscopy (XPS). Furthermore, the surface roughness after the modifications was investigated with atomic force microscopy (AFM) and compared to that of as-grown samples in order to establish the appearance of etching of the surface during the treatment. The as-grown and the modified NCD surfaces were exposed to phthalocyanines with different metal centers (Ti, Cu, Mn) or with different side chains. The results of the Pc grafting were investigated by XPS and Raman spectroscopy. XPS revealed the presence of nitrogen stemming from the Pc molecules and traces of the respective metal atoms with ratios close to those in the applied Pc. In a next step Raman spectra of Ti-Pc, Cu-Pc and Mn-Pc were obtained with two different excitation wavelengths (488 and 785 nm) from droplet samples on Si after evaporation of the solvent in order to establish their Raman fingerprints. The major differences in the spectra were assigned to the effect of the size of the metal ion on the structure of the phthalocyanine ring. The spectra obtained were used as references for the Raman spectra of NCD surfaces grafted with Pc. Finally, selected boron doped NCD samples were used after their surface modification and functionalization with Pc for the preparation of electrodes which were tested in a photoelectrochemical cell with a Pt counter electrode and an Ag/AgCl reference electrode. The light sources and electrolytes were varied to establish their influence on the performance of the dye-sensitized diamond electrodes. Cyclic voltammetry measurements revealed broad electrochemical potential window and high stability of the electrodes after several cycles. The open circuit potential (OCP) measurements performed in dark and after illumination showed fast responses of the electrodes to the illumination resulting in photocurrent generation.

Mikromechanisch durchstimmbare, dielektrische Fabry-Pérot-Filter im nahen Infrarot-Bereich: Konzept, Herstellung und Charakterisierung

Das Ziel der vorliegenden Arbeit war die Herstellung und Charakterisierung mikromechanisch durchstimmbarer, dielektrischer Fabry-Pérot-Filter im nahen Infrarot-Bereich bei einer Zentralwellenlänge von λc = 950 nm. Diese Bauelemente wurden auf Basis kostengünstiger Technologien realisiert, dank deren Entwicklung extreme Miniaturisierung und gleichzeitig hohe spektrale Anforderungen möglich sind. Der Vorteil solcher Filter liegt darin, dass sie direkt in einen Photodetektor integriert werden können und mit ganz wenigen Komponenten zu einem kompakten Spektrometermodul zusammengesetzt werden können. Die Baugröße ist nur durch die Größe des Photodetektors limitiert und die gesamte Intensität des einfallenden Lichts kann vorteilhaft auf eine einzelne Filtermembran des Fabry-Pérot-Filters fokussiert werden. Für den Filteraufbau werden zwei hochreflektierende, dielektrische DBR-Spiegel, ein organisches Opferschichtmaterial, welches zur Erzeugung einer Luftkavität im Filter dient, und zwei unterschiedliche Elektroden aus ITO und Aluminium verwendet. Die mikromechanische Auslenkung der freigelegten Filtermembran geschieht mittels elektrostatischer Aktuation, wobei auf diese Weise die Kavitätshöhe des Fabry-Pérot-Filters geändert wird und somit dieser im erforderlichen Spektralbereich optisch durchgestimmt wird. Das in dieser Arbeit gewählte Filterkonzept stellt eine Weiterentwicklung eines bereits bestehenden Filterkonzepts für den sichtbaren Spektralbereich dar. Zum Einen wurden in dieser Arbeit das vertikale und das laterale Design der Filterstrukturen geändert. Eine entscheidende Änderung lag im mikromechanisch beweglichen Teil des Fabry-Pérot-Filters. Dieser schließt den oberen DBR-Spiegel und ein aus dielektrischen Schichten und der oberen Aluminium-Elektrode bestehendes Membranhaltesystem ein, welches später durch Entfernung der Opferschicht freigelegt wird. Die Fläche des DBR-Spiegels wurde auf die Fläche der Filtermembran reduziert und auf dem Membranhaltesystem positioniert. Zum Anderen wurde im Rahmen dieser Arbeit der vertikale Schichtaufbau des Membranhaltesystems variiert und der Einfluss der gewählten Materialien auf die Krümmung der freistehenden Filterstrukturen, auf das Aktuationsverhalten und auf die spektralen Eigenschaften des gesamten Filters untersucht. Der Einfluss der mechanischen Eigenschaften dieser Materialien spielt nämlich eine bedeutende Rolle bei der Erhaltung der erforderlichen optischen Eigenschaften des gesamten Filters. Bevor Fabry-Pérot-Filter ausgeführt wurden, wurde die mechanische Spannung in den einzelnen Materialien des Membranhaltesystems bestimmt. Für die Messung wurde Substratkrümmungsmethode angewendet. Es wurde gezeigt, dass die Plasmaanregungsfrequenzen der plasmaunterstützten chemischen Gasphasenabscheidung bei einer Prozesstemperatur von 120 °C die mechanische Spannung von Si3N4 enorm beeinflussen. Diese Ergebnisse wurden im Membranhaltesystem umgesetzt, wobei verschiedene Filter mit unterschiedlichen mechanischen Eigenschaften des Membranhaltesystems gezeigt wurden. Darüber hinaus wurden optische Eigenschaften der Filter unter dem Einfluss des lateralen Designs der Filterstrukturen untersucht. Bei den realisierten Filtern wurden ein optischer Durchstimmbereich von ca. 70 nm und eine spektrale Auflösung von 5 nm erreicht. Die erreichte Intensität der Transmissionslinie liegt bei 45-60%. Diese Parameter haben für den späteren spektroskopischen Einsatz der realisierten Fabry-Pérot-Filter eine hohe Bedeutung. Die Anwendung soll erstmalig in einem „Proof of Concept“ stattfinden, wobei damit die Oberflächentemperatur eines GaAs-Wafers über die Messung der spektralen Lage seiner Bandlücke bestimmt werden kann.

Optical Characterization of Organic Gain Materials for UV-emitting Hybrid Complex Coupled VCSELs

In this thesis, optical gain measurement setup based on variable stripe length method is designed, implemented and improved. The setup is characterized using inorganic and organic samples. The optical gain of spiro-quaterphenyl is calculated and compared with measurements from the setup. Films with various thicknesses of spiro-quaterphenyl, methoxy-spiro-quaterphenyl and phenoxy-spiro-quaterphenyl are deposited by a vacuum vapor deposition technique forming asymmetric slab waveguides. The optical properties, laser emission threshold, optical gain and loss coefficient for these films are measured. Additionally, the photodegradation during pumping process is investigated.

Further investigations on doubly excited four-electron ions: beam-foil experiment and MCDF theory

In continuation of our previous work on the quintet transitions 1s2s2p^2 ^5 P-1s2s2p3d ^5 P^0, ^5 D^0, results on other n = 2 - n' = 3 quintet transitions for elements N, 0 and F are presented. Assignments have been established by comparison with Multi-Configuration Dirac-Fock calculations. High spectral resolution on beam-foil spectroscopy was essential for the identification of most of the lines. For some of the quintet lines decay curves were measured, and the lifetimes extracted were found to be in reasonable agreement with MCDF calculations.

Molecular Beam Epitaxial Growth of III-V Semiconductor Nanostructures on Silicon Substrates

The main focus and concerns of this PhD thesis is the growth of III-V semiconductor nanostructures (Quantum dots (QDs) and quantum dashes) on silicon substrates using molecular beam epitaxy (MBE) technique. The investigation of influence of the major growth parameters on their basic properties (density, geometry, composition, size etc.) and the systematic characterization of their structural and optical properties are the core of the research work. The monolithic integration of III-V optoelectronic devices with silicon electronic circuits could bring enormous prospect for the existing semiconductor technology. Our challenging approach is to combine the superior passive optical properties of silicon with the superior optical emission properties of III-V material by reducing the amount of III-V materials to the very limit of the active region. Different heteroepitaxial integration approaches have been investigated to overcome the materials issues between III-V and Si. However, this include the self-assembled growth of InAs and InGaAs QDs in silicon and GaAx matrices directly on flat silicon substrate, sitecontrolled growth of (GaAs/In0,15Ga0,85As/GaAs) QDs on pre-patterned Si substrate and the direct growth of GaP on Si using migration enhanced epitaxy (MEE) and MBE growth modes. An efficient ex-situ-buffered HF (BHF) and in-situ surface cleaning sequence based on atomic hydrogen (AH) cleaning at 500 °C combined with thermal oxide desorption within a temperature range of 700-900 °C has been established. The removal of oxide desorption was confirmed by semicircular streaky reflection high energy electron diffraction (RHEED) patterns indicating a 2D smooth surface construction prior to the MBE growth. The evolution of size, density and shape of the QDs are ex-situ characterized by atomic-force microscopy (AFM) and transmission electron microscopy (TEM). The InAs QDs density is strongly increased from 108 to 1011 cm-2 at V/III ratios in the range of 15-35 (beam equivalent pressure values). InAs QD formations are not observed at temperatures of 500 °C and above. Growth experiments on (111) substrates show orientation dependent QD formation behaviour. A significant shape and size transition with elongated InAs quantum dots and dashes has been observed on (111) orientation and at higher Indium-growth rate of 0.3 ML/s. The 2D strain mapping derived from high-resolution TEM of InAs QDs embedded in silicon matrix confirmed semi-coherent and fully relaxed QDs embedded in defectfree silicon matrix. The strain relaxation is released by dislocation loops exclusively localized along the InAs/Si interfaces and partial dislocations with stacking faults inside the InAs clusters. The site controlled growth of GaAs/In0,15Ga0,85As/GaAs nanostructures has been demonstrated for the first time with 1 μm spacing and very low nominal deposition thicknesses, directly on pre-patterned Si without the use of SiO2 mask. Thin planar GaP layer was successfully grown through migration enhanced epitaxy (MEE) to initiate a planar GaP wetting layer at the polar/non-polar interface, which work as a virtual GaP substrate, for the GaP-MBE subsequently growth on the GaP-MEE layer with total thickness of 50 nm. The best root mean square (RMS) roughness value was as good as 1.3 nm. However, these results are highly encouraging for the realization of III-V optical devices on silicon for potential applications.

Piezoresistive cantilevers with an integrated bimorph actuator

Scanning Probe Microscopy (SPM) has become of fundamental importance for research in area of micro and nano-technology. The continuous progress in these fields requires ultra sensitive measurements at high speed. The imaging speed limitation of the conventional Tapping Mode SPM is due to the actuation time constant of piezotube feedback loop that keeps the tapping amplitude constant. In order to avoid this limit a deflection sensor and an actuator have to be integrated into the cantilever. In this work has been demonstrated the possibility of realisation of piezoresistive cantilever with an embedded actuator. Piezoresistive detection provides a good alternative to the usual optical laser beam deflection technique. In frames of this thesis has been investigated and modelled the piezoresistive effect in bulk silicon (3D case) for both n- and p-type silicon. Moving towards ultra-sensitive measurements it is necessary to realize ultra-thin piezoresistors, which are well localized to the surface, where the stress magnitude is maximal. New physical effects such as quantum confinement which arise due to the scaling of the piezoresistor thickness was taken into account in order to model the piezoresistive effect and its modification in case of ultra-thin piezoresistor (2D case). The two-dimension character of the electron gas in n-type piezoresistors lead up to decreasing of the piezoresistive coefficients with increasing the degree of electron localisation. Moreover for p-type piezoresistors the predicted values of the piezoresistive coefficients are higher in case of localised holes. Additionally, to the integration of the piezoresistive sensor, actuator integrated into the cantilever is considered as fundamental for realisation of fast SPM imaging. Actuation of the beam is achieved thermally by relying on differences in the coefficients of thermal expansion between aluminum and silicon. In addition the aluminum layer forms the heating micro-resistor, which is able to accept heating impulses with frequency up to one megahertz. Such direct oscillating thermally driven bimorph actuator was studied also with respect to the bimorph actuator efficiency. Higher eigenmodes of the cantilever are used in order to increase the operating frequencies. As a result the scanning speed has been increased due to the decreasing of the actuation time constant. The fundamental limits to force sensitivity that are imposed by piezoresistive deflection sensing technique have been discussed. For imaging in ambient conditions the force sensitivity is limited by the thermo-mechanical cantilever noise. Additional noise sources, connected with the piezoresistive detection are negligible.

Values for the electron screening in muonic atoms for all Z

The electron screening correction in the X-ray transitions in muonic atoms is calculated within a relativistic SCF Hartree-Fock procedure for many transitions and all Z.

First results of experimental and theoretical investigations on sextet states of doubly-excited five-electron ions

In continuation of our previous work on doubly-excited ions with three and four electrons we present the first results on optical transitions in the term system of doubly-excited ions with five electrons. Transitions between such sextet states were identified in beam-foil spectra of the ions nitrogen, oxygen and fluorine. Assignments were first established by comparison with Multi-Configuration Dirac-Fock calculations. Later assignments were aided by Multi-Configuration Hartree-Fock calculations (see the contribution by G. Miecznik et al. in this issue). Decay curves were recorded for all six candidate lines. The lifetime results are compared to theoretical values which confirm most of the assignments qualitatively.

Beam-foil-excited auger transitions in neon

Energy spectra of electrons ejected from collisions between a carbon foil and Ne projectiles with energies between 1.4 and 20 MeV have been measured. Continuous and discrete electron energy distributions are observed. Auger transitions of foil-excited Ne have been studied. Using relativistic Dirac-Fock multiconfiguration calculations, most of the measured Auger transitions have been identified.

Precise calculations of atomic electron binding energies in fermium

The comparison between the experimental binding energies for the K, L, and M electrons for fermium and the results of our Dirac-Fock calculation, taking into account all tractable corrections, leads to agreement within about 20 eV. This shows that the present method of calculation is an adequate description of this problem and that nonlinear electrodynamical effects will not be present in nature or will be smaller than 1% compared to the values recently proposed. It is found that the energies of electronic transitions can now be used to estimate the nuclear radius.