Non-hydraulic mortars contain datable binder carbonate with a direct relation to the time when it was used in a building, but they also contain contaminants that disturb radiocarbon dating attempts. The most relevant contaminants either have a geological provenance and age or they can be related to delayed carbonate formation or devitrification and recrystallization of the mortar. We studied the mortars using cathodoluminescence (CL), mass spectrometry (MS), and accelerator mass spectrometry (AMS) in order to identify, characterize, and date different generations of carbonates. The parameters—dissolution rate, 13C/12C and 18O/16O ratios, and 14C age—were measured or calculated from experiments where the mortars were dissolved in phosphoric acid and each successive CO2 increment was collected, analyzed, and dated. Consequently, mortar dating comprises a CL characterization of the sample and a CO2 evolution pressure curve, a 14C age, and stable isotope profiles from at least 5 successive dissolution increments representing nearly total dissolution. The data is used for modeling the interfering effects of the different carbonates on the binder carbonate age. The models help us to interpret the 14C age profiles and identify CO2 increments that are as uncontaminated as possible. The dating method was implemented on medieval and younger mortars from churches in the Åland Archipelago between Finland and Sweden. The results are used to develop the method for a more general and international use.
The electron-hole correlation effects on the energy levels and the wave functions of a strain-induced quantum dot containing 1 to 10 electron-hole pairs have been studied using large scale configuration-interaction calculations. The results show the importance of including the correlations in order to reproduce the experimentally measured quantum dot spectra and to obtain bound multi-exciton complexes. Increasing the number of electron-hole pairs in the quantum dot a transition from a strongly correlated system to the one approximated by the Hartree-Fock theory is observed. IntroductionThe possibility to observe and study individual quantum dots (QD) [1][2][3], and thereby probe the details of their electronic structure, has made it increasingly relevant to include the carrier-carrier correlation in the theoretical calculation of the QD energy spectra. To fully treat the correlations one would have to solve the Hamiltonian for the QD system exactly, a task that is clearly impossible without using simplifying assumptions. The most widely used approximation for large, weakly confining QD's (%10-100 nm) is the effective mass approximation [4][5][6]. Within the effective mass model, the electrons and holes in the QD can be treated as an interacting fewbody system situated in an external potential. This few-body problem can be solved using the full configuration interaction (FCI) model [7], which represents an exact solution of the effective mass Schr€odinger equation. In this article we present the results of FCI and truncated CI calculations performed on a QD formed by the self-organizing growth of an InP island (base diameter %80 nm) on top of a GaAs/In 0:1 Ga 0:9 As/GaAs quantum well (width 7 nm) [8]. The CI results are compared with those obtained within the Hartree-Fock (HF) approximation.
The size dependence of the radiative recombination rates of electrons and holes confined in a semiconductor InGaAs/GaAs quantum dot has been studied using large configuration interaction ͑CI͒ expansions. The confinement potentials were modeled by employing truncated two-dimensional parabolas. The calculations show that the radiative recombination rates from the ground states of the ͑multi͒excitons are rather smooth functions of the dot size; no ''magic'' dot sizes with exceptional fast radiative recombination rates were found, but level crossings cause significant variations. The recombination rates calculated at the CI level are much larger than those obtained at the self-consistent-field ͑SCF͒ and free-particle ͑FP͒ levels. The exciton ground-state recombination rate increases monotonously with increasing dot radius, whereas at the SCF and FP levels the recombination rate is independent of the dots radius. Thus Coulomb correlation effects are necessary for explaining the predicted size dependences.
We report experimental observation and theoretical interpretation of temperature-dependent, time-resolved luminescence from strain-induced quantum dots. The experimental results are well described by a master equation model for the electrons. The intraband relaxation in the conduction band and the radiative recombination rate are governed by the hole populations resulting in prominent temperature dependence of the relaxation process. Even when only a few electrons and holes are confined in a single quantum dot the Auger-like process provides a rapid intraband relaxation channel for electrons that can replace the phonon scattering as the dominant relaxation mechanism. ͓S0163-1829͑98͒51148-4͔ RAPID COMMUNICATIONS R15 994 PRB 58 M. BRASKÉ N et al. RAPID COMMUNICATIONS R15 996 PRB 58 M. BRASKÉ N et al.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.