Exciton Spin Dynamics in Semiconductor Quantum Wells

In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum Wells. The spin properties of excitons in nanostructures are determined by their fine structure. We will mainly focus in this review on GaAs and InGaAs quantum wells which are model systems.Comment: 55 pages, 27 figure

Two distinct patterns of treatment resistance:clinical predictors of treatment resistance in first-episode schizophrenia spectrum psychoses

BACKGROUND: Clozapine remains the only evidence-based antipsychotic for treatment-resistant schizophrenia (TRS). The ability to predict which patients with their first onset of schizophrenia would subsequently meet criteria for treatment resistance (TR) could help to diminish the severe functional disability which may ensue if TR is not recognized and correctly treated. METHOD: This is a 5-year longitudinal assessment of clinical outcomes in a cohort of 246 first-episode schizophrenia spectrum patients recruited as part of the NIHR Genetics and Psychosis (GAP) study conducted in South London from 2005 to 2010. We examined the relationship between baseline demographic and clinical measures and the emergence of TR. TR status was determined from a review of electronic case records. We assessed for associations with early-, and late-onset TR, and non-TR, and differences between those TR patients treated with clozapine and those who were not. RESULTS: Seventy per cent (n = 56) of TR patients, and 23% of the total study population (n = 246) were treatment resistant from illness onset. Those who met criteria for TR during the first 5 years of illness were more likely to have an early age of first contact for psychosis (years) [odds ratio (OR) 2.49, 95% confidence interval (CI) 1.25-4.94] compared to those with non-TR. The relationship between an early age of first contact (years) and TR was significant in patients of Black ethnicity (OR 3.71, 95% CI 1.44-9.56); and patients of male gender (OR 3.13 95% CI 1.35-7.23). CONCLUSIONS: For the majority of the TR group, antipsychotic TR is present from illness onset, necessitating increased consideration for the earlier use of clozapine

Antikinetoplastid SAR study in 3-nitroimidazopyridine series: identification of a novel non-genotoxic and potent anti-T. b. brucei hit-compound with improved pharmacokinetic properties

To study the antikinetoplastid 3-nitroimidazo[1,2-a]pyridine pharmacophore, a structure-activity relationship study was conducted through the synthesis of 26 original derivatives and their in vitro evaluation on both Leishmania spp and Trypanosoma brucei brucei. This SAR study showed that the antitrypanosomal pharmacophore was less restrictive than the antileishmanial one and highlighted positions 2, 6 and 8 of the imidazopyridine ring as key modulation points. None of the synthesized compounds allowed improvement in antileishmanial activity, compared to previous hit molecules in the series. Nevertheless, compound 8, the best antitrypanosomal molecule in this series (EC50 = 17 nM, SI = 2650 & E° = -0.6 V), was not only more active than all reference drugs and previous hit molecules in the series but also displayed improved aqueous solubility and better in vitro pharmacokinetic characteristics: good microsomal stability (T1/2 > 40 min), moderate albumin binding (77%) and moderate permeability across the blood brain barrier according to a PAMPA assay. Moreover, both micronucleus and comet assays showed that nitroaromatic molecule 8 was not genotoxic in vitro. It was evidenced that bioactivation of molecule 8 was operated by T. b. brucei type 1 nitroreductase, in the same manner as fexinidazole. Finally, a mouse pharmacokinetic study showed that 8 displayed good systemic exposure after both single and repeated oral administrations at 100 mg/kg (NOAEL) and satisfying plasmatic half-life (T1/2 = 7.7 h). Thus, molecule 8 appears as a good candidate for initiating a hit to lead drug discovery program

Real-time investigation of In surface segregation in chemical beam epitaxy of In0.5Ga0.5P on GaAs (001)

Surface segregation processes during the growth of Ga0.5In0.5P/GaAs heterostructures by chemical beam epitaxy have been investigated in real time using reflection high-energy electron diffraction (RHEED). It is shown that In segregation occurs at both GaInP on GaAs and GaAs on GaInP interfaces. Resulting composition profiles are deduced from the RHEED data. (C) 1996 American Institute of Physics

Interface effects on the photoluminescence of GaAs/GaInP quantum wells

The influence of indium surface segregation, As-P exchange at the interfaces and residual incorporation of As and P on the photoluminescence properties of GaAs/GaInP quantum wells, is investigated both theoretically and experimentally. It is shown that these effects may lead to an important energy shift or compensate each other depending on growth conditions. As a consequence the exploitation of photoluminescence spectra in such heterostructures have to be carefully carried out. Four samples have been especially designed to study, in addition to indium segregation, the As-P exchange at the GaAs on GaInP interface. Their low temperature photoluminescence study illustrates the complex behaviours observed in this material system. Photoluminescence spectra are shown to be very sensitive to the interface chemistry, in particular As-P exchange

Photoluminescence energy and interface chemistry of GaInP/GaAs quantum wells

It is shown that the unusual scattering of the currently reported photoluminescence energy of GaInP/GaAs quantum wells (QWs) can be well accounted for by considering the combined effect of In surface segregation and As/P exchange at the interfaces. The resulting chemical modification of the interfaces being strongly growth procedure dependent, can explain the observed dispersion of the experimental results. This is demonstrated by experiments in which different growth switching procedures are used at the GaInP/GaAs QW interfaces. (C) 1997 American Institute of Physics. [S0003-6951(97)03450-5]

Indium surface segregation during chemical beam epitaxy of Ga1-xInxAs/GaAs and Ga1-xInxP/GaAs heterostructures

We report on the investigation of In surface segregation in GaInP/GaAs and GaInAs/GaAs heterostructures grown by chemical beam epitaxy (CBE). Owing to the peculiarities of CBE growth, it is shown that In segregation can be quantitatively evaluated in real-time by using reflection high-energy electron diffraction (RHEED). A segregation coefficient and its variation with the growth temperature is extracted from the RHEED data. It is used to determine the In composition profiles at the interfaces of GaInAs/GaAs quantum well (QW) structures as a function of the growth temperature. A good agreement is found between optical transition energies calculated from these profiles and the experimental photoluminescence (PL) energies. PL energy shifts observed in GaInP/GaAs QW's as a function of the growth temperature are qualitatively explained by In segregation