Magneto-optical study of electron occupation and hole wave functions in stacked self-assembled InP quantum dots

We have studied the magnetophotoluminescence of doubly stacked layers of self-assembled InP quantum dots in a GaInP matrix. 4.0±0.1 monolayers of InP were deposited in the lower layer of each sample, whereas in the upper layer 3.9, 3.4, and 3.0 monolayers were used. Low-temperature photoluminescence measurements in zero magnetic field are used to show that, in each case, only one layer of dots is occupied by an electron, and imply that when the amount of InP in both layers is the same, the dots in the upper layer are larger. High-field photoluminescence data reveal that the position and extent of the hole wave function are strongly dependent on the amount of InP in the stack. ©2001 American Institute of Physics

Electron and hole confinement in stacked self-assembled InP quantum dots

We report photoluminescence measurements on stacked self-assembled InP quantum dots in magnetic fields up to 50 T. For triply stacked layers the dots become strongly coupled when the layer separation is 4 nm or less. In contrast, doubly stacked layers show no sign of coupling. We explain this puzzling difference in coupling by proposing a model in which the holes are weakly confined in the GaxIn1-xP layers separating the layers of dots, and are responsible for the coupling. Since only one such intervening layer exists in the doubly stacked dots coupling is excluded. Our model is strongly supported by the exciton masses and radii derived from our experimental results, and is consistent with available theory

Charge confinement and uniformity of stacked InP quantum dots studied by magneto-optical spectroscopy

We have studied the magneto-photo luminescence (PL) of triply stacked layers of self-assembled InP quantum dots, For a small separation of the uppermost dot in (he triple stack from the other two closely stacked layers, only one PL peak is observed, whereas for a large separation two PL peaks are present: a broad low-energy and a narrow high-energy peak. We propose a model in which the low-energy peak is associated with the uppermost dot where alignment faults result in enhanced size fluctuations, broadening the line, The narrow high-energy peak originates from charges located in the double stack. In the large separation regime, an increased broadening of the PL line-width indicates that the size fluctuations are augmented as the layer separation is increased from 15 to 30 nm. (C) 2002 Elsevier Science B.V. All rights reserved

Hole coupling in stacked self-assembled InP quantum dots

We have studied the photoluminescence of doubly stacked layers of InP quantum dots in magnetic fields up to 50T. We find that in contrast to the triply stacked layers studied previously, which were strongly coupled for layer separations of 4 nm or less, the dots in the double layers do not couple. We explain this surprising difference in behaviour by proposing a model in which the holes are confined in the GaInP layers separating the stacked dots. For triply stacked dots two such layers exist, allowing the possibility of coupling via the holes. In doubly stacked dots, there is only one such layer, thus coupling is absent. Our model is consistent with measurements of the exciton masses and radii in the dl,ts, and with calculations of electron and hole wave functions in self-assembled quantum dots. (C) 2000 Elsevier Science B.V. All rights reserved

Photoluminescence of stacked self-assembled InP quantum dots in high magnetic fields

We have measured the photoluminescence of stacked layers of self-assembled InP quantum dots in magnetic fields up to 50 T. In the samples with three stacked layers of dots strong electronic coupling was clearly observed for layer separations of 2 and 4 nm. For a sample with only two stacked layers of dots (separated by 4 nm) no coupling was observed. We attribute this difference in behaviour to a model in which the coupling is via holes that are weakly bound in the GaInP layers between the dots. Since the doubly stacked layers have only one such layer, no coupling is possible. (C) 2000 Elsevier Science B.V. All rights reserved

Guidelines for the use of flow cytometry and cell sorting in immunological studies

International audienceThe classical model of hematopoiesis established in the mouse postulates that lymphoid cells originate from a founder population of common lymphoid progenitors. Here, using a modeling approach in humanized mice, we showed that human lymphoid development stemmed from distinct populations of CD127(-) and CD127(+) early lymphoid progenitors (ELPs). Combining molecular analyses with in vitro and in vivo functional assays, we demonstrated that CD127(-) and CD127(+) ELPs emerged independently from lympho-mono-dendritic progenitors, responded differently to Notch1 signals, underwent divergent modes of lineage restriction, and displayed both common and specific differentiation potentials. Whereas CD127(-) ELPs comprised precursors of T cells, marginal zone B cells, and natural killer (NK) and innate lymphoid cells (ILCs), CD127(+) ELPs supported production of all NK cell, ILC, and B cell populations but lacked T potential. On the basis of these results, we propose a "two-family" model of human lymphoid development that differs from the prevailing model of hematopoiesis