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The administration of intermittent parathyroid hormone (iPTH) is anabolic to the skeleton. Recent studies with cultured osteoblasts have revealed that the expression of PHOSPHO1, a bone-specific phosphatase essential for the initiation of mineralisation, is regulated by PTH. Therefore, this study sought to determine whether the bone anabolic response to iPTH involves modulation of expression of Phospho1 and of other enzymes critical for bone matrix mineralisation. To mimic iPTH treatment, primary murine osteoblasts were challenged with 50 nM PTH for 6 h in every 48 h period for 8 days (4 cycles), 14 days (7 cycles) and 20 days (10 cycles) in total. The expression of both Phospho1 and Smpd3 was almost completely inhibited after 4 cycles, whereas 10 cycles were required to stimulate a similar response in Alpl expression. To explore the in vivo role of PHOSPHO1 in PTH-mediated osteogenesis, the effects of 14- and 28-day iPTH (80 µg/kg/day) administration was assessed in male wild-type (WT) and Phospho1

Fracture burden has created a need to better understand bone repair processes under different pathophysiological states. Evaluation of structural and material properties of the mineralised callus, which is integral to restoring biomechanical is therefore, vital. Micro-CT can facilitate non-invasive imaging of fracture repair, however, current methods for callus segmentation are only semi-automated, restricted to defined regions, time/labour intensive and prone to user-variation. Herein, we share a new automatic method for segmenting callus in micro-CT tomograms that will allow for objective, quantitative analysis of the bone fracture microarchitecture. Fractured and non-fractured mouse femurs were scanned and processed by both manual and automated segmentation of fracture callus from cortical bone after which microarchitectural parameters were analysed. All segmentation and analysis steps were performed using CTAn (Bruker, Belgium) with automatic segmentation performed using the software's image processing plugins. Results showed automatic segmentation reliably and consistently segmented callus from cortical bone, demonstrating good agreement with manual methods with low bias: tissue volume: -0.320mm

The secondary dystroglycanopathies are characterized by the hypoglycosylation of alpha dystroglycan, and are associated with mutations in at least 18 genes that act on the glycosylation of this cell surface receptor rather than the Dag1 gene itself. At the severe end of the disease spectrum, there are substantial structural brain defects, the most striking of which is often cobblestone lissencephaly. The aim of this study was to determine the gene-specific aspects of the dystroglycanopathy brain phenotype through a detailed investigation of the structural brain defects present at birth in three mouse models of dystroglycanopathy-the FKRP(KD) , which has an 80% reduction in Fkrp transcript levels; the Pomgnt1null , which carries a deletion of exons 7-16 of the Pomgnt1 gene; and the Large(myd) mouse, which carries a deletion of exons 5-7 of the Large gene. We show a rostrocaudal and mediolateral gradient in the severity of brain lesions in FKRP(KD) , and to a lesser extent Pomgnt1null mice. Furthermore, the mislocalization of Cajal-Retzius cells is correlated with the gradient of these lesions and the severity of the brain phenotype in these models. Overall these observations implicate gene-specific differences in the pathogenesis of brain lesions in this group of disorders.

Low temperature micro-photoluminescence (μ-PL) has been applied to study GaInNAs bulklike layers grown on GaAs substrates with various crystallographic orientations [(100), (111)A, (311)A, (411)A, and (511)A]. At low excitation conditions, the μ-PL spectra show sharp PL lines of ∼100-300 μeV widths. The density of these lines changes from sample to sample as well as from place to place within one sample. When the excitation power is increased, an additional smooth PL band appears at the higher-energy side. This band is located ∼30-100 meV above the band of sharp PL lines and is attributed to free exciton/carrier recombination. The sharp PL lines are attributed to the recombination of localized excitons trapped at local potential minima. These lines are not resolved in macro-PL spectra because of their high density. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this letter we demonstrate that the N incorporation into (Ga)InAsN quantum dots (QDs), grown on GaAs (100) by radio-frequency (RF) plasma assisted molecular beam epitaxy (MBE), is enhanced as the Ga content increases up to 30% and decreases for Ga contents higher than 30%. Thus, this effect exhibits a maximum N incorporation with a Ga content of 30%. Two sets of (Ga)InAsN QDs samples have been grown under the same growth conditions but with different N contents in one of them and with different Ga concentration in the other set. Optical analysis using Photoluminescence (PL) measurements of the as-grown and post growth rapid thermal annealed samples have been performed. The experimental results show a clear increase of the blueshift with the N concentration as occurred in dilute nitride quantum well (QW) structures. PL peak emission wavelength as high as 1.55 μm has been obtained from QDs capped with GaAs. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a two-colour photocurrent detection method for coherent control of a single InGaAs/GaAs self-assembled quantum dot. A pulse shaping technique provides a high degree of control over picosecond optical pulses. Rabi rotations on the exciton to biexciton transition are presented, and fine structure beating is detected via time-resolved measurements. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

For the formation of large In(Ga)As/GaAs quantum dots, aiming at emission wavelengths of 1.3 μm, strategies like the use of strain reducing diluted InGaAs capping layers or the growth of InAs quantum dots embedded in InGaAs quantum wells are very promising. Using cross-sectional scanning tunneling microscopy we observed for both concepts an increased quantum dot size, but also defective quantum dots, characterized by a material hole or so-called nanovoid. The process of such nanovoid formation is investigated in detail, considering the strain and the limited growth kinetics during capping. The existence of nanovoids impressively shows the limitations of growing larger and thus more strained quantum dots. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, the influence of the diffusion process in the phase separation of GaInNAs layers is analyzed. For this, we have studied by TEM GaInNAs/GaAs quantum wells grown at different temperatures in the range 360-440 °C, finding the existence of periodic strain contrasts in all the wells associated with composition fluctuations in the alloy. These contrasts are more pronounced on increasing the growth temperature, revealing a kinetic influence for the formation of the phase separation. The extrapolation of these results suggests a critical temperature for the beginning of the modulation around 330 °C. The consideration of the growth time and the diffusion time in the epitaxial growth of this alloy suggests that the limiting specie for the formation of the phase separation could be Ga. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on an investigation of capacitance-voltage spectroscopy of electron-hole dynamics in InAs/GaAs self-assembled quantum dots (QDs) under varied reverse bias, and a study of the influence of holes on this process exerted by the Coulomb interactions. The time constant of the electron transport was estimated by making use of the frequency dependence of the capacitance increase due to the InAs dots. The high values found for the tunnelling times suggest that this process is very sensitive to hole accumulation into the dots. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have studied phase separation in Ga0.62In 0.38N0.023As/GaAs (001) multi-quantum wells grown at different temperatures in the range 360°C-460°C. Our results by Transmission Electron Microscopy have shown strain contrasts with 220BF reflection in all the wells, which are more pronounced on increasing the growth temperature. This has been attributed to enhanced phase separation in the alloy. However, contrast modulation was not observed with 002DF reflection. Both results could be explained by the existence of N rich regions and low In segregation regarding the average composition. Experimental and theoretical results point at a large effect of the introduction of N in the phase separation of GaInAsN alloys. However, these models do not explain that the magnitude of the composition modulation increases with the temperature and it is necessary to introduce kinetic factors to predict the phase separation for different growth conditions. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The AlAs-like TO-phonon decay in Al0.7Ga0.3As has been investigated using an infrared four wave mixing technique with picosecond resolution. The low temperature TO-phonon lifetime is found to be ∼5 ps and is significantly shorter than ∼40 ps recently predicted for the TO-phonon in AlAs [A. Debernardi, Phys. Rev. B 57, 12847 (1998)]. In alloy materials Al and Ga atoms are randomly distributed on the Group III sublattice of the zincblende structure. This disorder considerably reduces the lifetime of AlAs phonon mode due to scattering of the TO phonon with Ga atoms which results in an additional decay channel: AlAs-TO GaAs-L(T)O + LA in AlGaAs alloy materials. The new decay channel also leads to stronger temperature dependence of the TO-phonon lifetime. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High pressure provides an efficient way of controlling the electronic properties of semiconductor nanostructures. We use pressure to tune electronic coupling in stacks of self-assembled quantum dots (SAQDs). The coupling occurs as soon as the distance and the height of the barriers between the dots are sufficiently small to permit interaction between the wavefunctions of electrons in adjacent dots. We demonstrate experimental evidence that application of pressure reduces and may quench the coupling. This happens because, under pressure, the inter-dot barriers become higher and hence less transparent for electron wavefunctions. The effect was revealed by means of photoluminescence spectroscopy and confirmed by theoretical modelling.

Using energy and temperature dependent far-infrared pump-probe spectrsocopy we demonstrate that polarons in InAs/GaAs quantum dots decay to two equal energy phonons. An additional decay process involving polaron transfer between closely spaced (∼5meV) excited states has also been observed, for which we find very good agreement between our experimental results and an acoustic phonon assisted transfer model. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical amplification of more than 3 dB is demonstrated using the Hot Electron Light Emitting and Lasing Semiconductor Heterostructure device in a Vertical Cavity Semiconductor Optical Amplifier configuration (HELLISH-VCSOA). The device consists of dilute nitride quantum wells Ga0.35In0.65N0.02As0.08/GaAs multiple quantum well (MQW) layers placed in the active region between the doped GaAs claddings and undoped GaAs/AlAs DBRs. Compared to standard VCSOAs in the HELLISH device, the current here does not flow across the distributed Bragg reflectors (DBR) but is injected longitudinally into the p- and n-doped cladding layers. Therefore DBR layers can be undoped, and heating problems en countered in conventional VCSOAs can be avoided. Current-voltage and spectral characteristics are measured at room temperature under different optical and electrical excitation conditions to demonstrate the possibility of employing this device for amplification purposes (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A photocurrent spectroscopic study of InAs/GaAs self-assembled quantum dots is reported. Under an applied electric field an asymmetry of the quantum confined Stark effect is observed, implying that the dots possess a permanent dipole moment. For zero field the sign of this dipole requires the hole wavefunction to lie above that of the electron, contrary to the predictions of all recent calculations. Comparison with a theoretical model shows that the correct dipole sign can only be reproduced if the dots are of a non-pyramidal shape and contain a non-zero and non-uniform Ga content. Photocurrent spectroscopy is used to determine the absorption and modal gain of dots incorporated into a laser structure.

The authors describe the results of temp. dependent photoluminescence intensity and decay time measurements on InAs/AlGaAs quantum dot structures where the depth of the confinement potential is varied from sample to sample. By comparison with a simple theor. model the temp. dependent behavior is ascribed to a combination of thermally induced occupation of excitonic dark states and thermionic emission of the confined holes. [on SciFinder (R)]

Carrier processes in InAs–GaAs self-assembled quantum dot lasers are investigated via the measurement of the temperature dependence of the current versus integrated spontaneous emission intensity. At high temperatures the rapid increase in threshold current is shown to be due to the non-radiative recombination of carriers at defects or impurities. At low temperatures the threshold current initially decreases with increasing temperature (negative-T0 regime), a behaviour previously attributed to a transition from a non-thermal to quasi-thermal carrier distribution within the dot ensemble. However, the optical results suggest a more complicated behaviour.

Spatially resolved spectroscopy is used to investigate excitation and relaxation mechanisms in individual self-assembled In(Ga)As quantum dots. For low excitation levels (∼1 e-h pair in the dot), both charged (X * ) and neutral (X) single exciton species are observed simultaneously in the μ-photoluminescence (μPL) spectrum. The charge status of X * and X is unambiguously identified using μPL-excitation (μPLE) spectroscopy. At higher excitation levels, additional spectral features appear, red-shifted from X, arising from the recombination of few exciton complexes (2X, 3X). Relaxation mechanisms are investigated using μPL-excitation spectroscopy. For X, the μPLE spectrum exhibits sharp resonances, which are attributed to direct absorption of excitonic states, and broader features due to phonon-assisted absorption, whilst X * is observed only for excitation above the wetting layer energy.

New information on the electron and hole wavefunctions in InAs–GaAs self-assembled quantum dots (SAQD) is obtained from photocurrent spectroscopy of the quantum confined Stark effect. We show that the hole is localised towards the top of the dot, above the electron, an alignment opposite to that predicted by all previous theories. By means of envelope function calculations we show that this alignment can only arise if the nominally InAs dots have a graded GaxIn1–xAs composition with x decreasing from base to apex, and a relatively flat, non-pyramidal shape. In the light of these results most if not all previous modelling of the electronic structure of InAs SAQD needs to be re-examined. The mechanisms involved in the photocurrent process are also discussed.

Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to characterize electron traps in dilute GaAsN epitaxial layers grown by Molecular Beam Epitaxy (MBE) on n+ GaAs substrates. The GaAsN samples used in this study were silicon doped (n-type) and contained nitrogen concentrations ranging from 0.2% to 1.2%. The number of electron traps in each sample detected by the DLTS measurements is found to be dependent on the nitrogen contents. Some of the traps have been identified with previously reported (N-As)spl split interstitial, nitrogen-split interstitial, EL6-like interfacial defect and EL3 defect levels. In a control sample without nitrogen we observed only one deep electron emitting level of energy 0.76 eV and no shallow levels have been seen. However, new shallow traps with energies ranging from 0.036 to 0.13 eV have been detected in samples with nitrogen content in the range 0.2% to 0.4%. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

After a decade of intensive research on GaInNAs(Sb) on GaAs alloys, this paper summarizes some of the key properties of these III-V alloys and presents current progress in their exploitation in a variety of surface-normal operating devices such as Vertical (External)-Cavity Surface-Emitting Lasers (V(E)CSELs) and SEmiconductor Saturable Absorber Mirrors (SESAMs).