Characterization of defects in curved CFRP samples using pulsed thermography and 3D Finite Element Simulation

Active thermography is a technique for non-destructive testing used for a contact-free inspection of components and materials. Thermographic methods are considered as an alternative to the state of the art techniques of ultrasonic- or X-raytesting. In particular, composite materials like Carbon Fibres Reinforced Plastics (CFRP), are increasingly analyzed by means of Active Thermography in order to detect defects like voids, delaminations or inclusions of foreign materials. Although much progress has been achieved in these fields in the last years, the studies and applications of thermographic detection of flaws are restricted to specimens with simple geometries in most cases found in literature. For industrial applications, however, components with complex geometries are of even prior importance [1]. In complex structures the temperatures after thermal excitation are influenced not only by material and defect properties but also by geometry effects and details of the excitation conditions. Thus the evaluation procedures used in the case of simple geometries cannot be applied in complex structures

Influence of Coimplantation on Activation of Er Emission in Si

The results of high resolution photoluminescence studies of erbium implanted silicon are presented. We show that the apparent enhancement of Er emission by coimplantation with light elements is not due to formation of Er-dopant complexes, but rather to Er forming complexes with defects induced by the implantation process alone

Erbium related centers in CZ-silicon

CZ Si implanted with Er shows the same cubic crystal field splitting of the 1.54 mu m luminescence as FZ-SI together with otter, defect- and oxygen correlated Pr complexes. The cubic centers exhibit somewhat shorter radiative life- and excitation times. The 100 times higher luminescence yield of CZ samples is thus attributed to the improved incorporation and to the passivation of recombination centers. The latter conclusion is supported by DLTS results which indicate complicated annealing behaviour.</p

Optically Active Centers in Er-Implanted Silicon

We show that of all the optically active Er centers in silicon found after ion implantation and optimum annealing (900°C) the isolated cubic interstitial Er is the dominant PL center above 100 K. At lower anneal temperatures ( ≈ 600°C) with later rapid thermal anneal at 900°C oxygen related centers also emit

Two-dimensional hole gas and Fermi-edge singularity in Be delta-doped GaAs

The subband structure of the quasi-two-dimensional hole gas (2DHG) formed at a single Be Delta-doped layer in GaAs has been studied by photoluminescence spectroscopy. To confine the photogenerated minority carriers, and thus to enhance the efficiency of radiative recombination form the 2DHG, the Delta-doping spike was placed in the center of an AlsubxGasub1-xAs/GaAs/AlsubxGasub1-xAs double heterostructure. Recombination involving different hole subbands has been resolved which enabled us to analyze the subband occupation as a function of dopant concentration and sample temperature. In sample structures where the Fermi level is located close to unoccupied subbands, a pronounced Fermi-edge singularity (FES) is observed in the low-temperature (Smaller than 20 K) luminescence spectrum. The temporal evolution of the FES has been studied by time-resolved luminescence spectroscopy. The enhancement in emission intensity at the Fermi edge can be understood in terms of a transfer of excitonic os cillator strength from the unoccupied subbands to nearby occupied states at the Fermi energy. Self-consistent subband calculations have been performed to compute the hole confining potential and the subband energies for the present Delta-doped structures. The results of these calculations, which take into account the finite spread of the dopant atoms in accordance with secondary-ion-mass spectroscopic data, are in good agreement with the measured subband spacings. The assignment of light- and heavy-hole transitions is supported by luminescence measurements using circularly polarized light

Erbium related centers in CZ-silicon

CZ Si implanted with Er shows the same cubic crystal field splitting of the 1.54 mu m luminescence as FZ-SI together with otter, defect- and oxygen correlated Pr complexes. The cubic centers exhibit somewhat shorter radiative life- and excitation times. The 100 times higher luminescence yield of CZ samples is thus attributed to the improved incorporation and to the passivation of recombination centers. The latter conclusion is supported by DLTS results which indicate complicated annealing behaviour