Folded acoustic phonons in InAs-AlAs strained-layer superlattices
Raman spectroscopy is used to characterize highly mismatched (7%) InAs‐AlAs superlattices grown by atomic layer molecular beam epitaxy. In particular, folded acoustic modes are presented and compared with two different theoretical models (Rytov and linear chain). We find good agreement between theory and experiments. We estimate, with a simple model, the magnitude of the effect of the strain on the phonon frequency shifts.
Lattice vibration in alternating monolayers of ZnSe and ZnTe
Lattice vibration in alternating monolayers of ZnSe and ZnTe is studied. Optical vibrational modes observed from (ZnSe)n‐(ZnTe)n (n=2, 3, 4) short‐period superlattice are evaluated by a theoretical analysis using the linear‐chain model. A method of the calculation which can take into account lattice strain is proposed. It is found that the zeroth‐ and the first‐order folded phonons in the ZnSe layer are observed in Raman scattering. By investing the displacement of the atoms, it is also found that the ZnSe‐like LO mode is localized in the ZnSe layer, whereas no mode is localized in the ZnTe layer. This characterization is attributed to an overlap of the dispersion curves for ZnSe‐ and ZnTe‐LO modes in the strained layer.
Investigation of scatter radiation of non-circular X-ray scan trajectories
Modern interventional X-ray devices are highly maneuverable and allow complex 3D imaging trajectories. New scan trajectories enable not only optimized object sampling but also introduce new approaches for dynamic 3D imaging. In this paper, we investigated the scatter radiation of two different scan trajectories. The scatter radiation was sampled by a rail setup with dosimeters at defined positions. After data analysis, contour maps were generated which show for four exemplary heights the scatter radiation distribution. The alternative scan trajectory showed smaller dose exposures at heights correlated to upper torso and head areas of a model physician. Keywords—Image acquisition, alternative scan trajectory, circular tomosynthesis, scatter radiation distribution