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Abstract We consider the possibility that the neutral-current B anomalies are due to radiative corrections generated by Yukawa interactions of quarks and leptons with new vector-like quark and lepton electroweak doublets and new Standard Model singlet scalars. We show that the restricted interactions needed can result from an underlying Abelian family symmetry and that the same symmetry can give rise to an acceptable pattern of quark and charged lepton masses and mixings, providing a bridge between the non-universality observed in the B-sector and that of the fermion mass matrices. We construct two simple models, one with a single singlet scalar in which the flavour changing comes from quark and lepton mixing and one with an additional scalar in which the flavour changing can come from both fermion and scalar mixing. We show that for the case the new quarks are much heavier than the new leptons and scalars the B anomalies can be due to box diagrams with couplings in the perturbative regime consistent with the bounds coming from $$ {B}_s-{\overline{B}}_s $$ B s − B ¯ s , $$ K-\overline{K} $$ K − K ¯ and $$ D-\overline{D} $$ D − D ¯ mixing as well as other lepton family number violating processes. The new states can be dark matter candidates and, in the two scalar model with a light scalar of O(60) GeV and vector-like lepton of O(100) GeV, there can be a simultaneous explanation of the B-anomalies, the muon anomalous magnetic moment and the dark matter abundance.

We determine the anomaly free discrete R symmetries, consistent with the MSSM, that commute with SU(5) and suppress the μ parameter and nucleon decay. We show that the order M of such Z{double-struck}MR symmetries has to divide 24 and identify 5 viable symmetries. The simplest possibility is a Z{double-struck}4R symmetry which commutes with SO(10). We present a string-derived model with this Z{double-struck}4R symmetry and the exact MSSM spectrum below the GUT scale; in this model Z{double-struck}4R originates from the Lorentz symmetry of compactified dimensions. We extend the discussion to include the singlet extensions of the MSSM and find Z{double-struck}4R and Z{double-struck}8Rare the only possible symmetries capable of solving the μ problem in the NMSSM. We also show that a singlet extension of the MSSM based on a Z{double-struck}24Rsymmetry can provide a simultaneous solution to the μ and strong CP problem with the axion coupling in the favoured window. © 2011 Elsevier B.V.

We consider the possible anomaly free Abelian discrete symmetries of the MSSM that forbid the μ-term at perturbative order. Allowing for anomaly cancellation via the Green-Schwarz mechanism we identify discrete R-symmetries as the only possibility and prove that there is a unique Z4R symmetry that commutes with SO(10). We argue that non-perturbative effects will generate a μ-term of electroweak order thus solving the μ-problem. The non-perturbative effects break the Z4R symmetry leaving an exact Z2 matter parity. As a result dimension four baryon- and lepton-number violating operators are absent while, at the non-perturbative level, dimension five baryon- and lepton-number violating operators get induced but are highly suppressed so that the nucleon decay rate is well within present bounds. © 2010 Elsevier B.V.

Germanium nanocrystals (Ge-ncs) were synthesized by implantation of Ge + ions into the fused silica, followed by a thermal annealing at 1000 °C. High-resolution transmission electron microscopy was employed to characterize both the morphology of the formed Ge-ncs and the evolution of their depth-distribution as a function of annealing durations. The formation of nanocavities in the vicinity of nanocrystal/SiO 2 interface is evidenced, as well as their influence on the release of the compressive stress exerted on Ge-ncs by surrounding SiO 2 . Some Ge-ncs are found inside nanocavities, and can move into the implanted layer through a nanocavity-assisted diffusion mechanism. This finding sheds light on a new process that can explain the non-uniformity of the Ge-nanocrystal spatial distribution.

High-resolution SEM images of germanium nanocrystals (Ge-nc) synthesized by ion implantation in fused silica samples annealed at temperatures below and above the melting point of Ge show a strong size-selective depth-distribution of nanostructures, as evidenced by the correlation between the dimension of the observed objects and the local concentration of implanted Ge measured by Rutherford backscattering spectroscopy (RBS). Whereas the Ge-nc nucleation seems to obey the Ostwald ripening process in samples annealed below 900 °C, Ge desorption effects, non-uniform in depth, in conjunction with the formation of large and spherical nanocavities, become dominant for annealing performed above the solid-liquid phase transition of Ge. Measurements for different annealing times at 1050 °C show two distinct processes in the Ge desorption dynamics: the first is related to direct Ge outgassing effects during the nucleation of Ge-nc, which occurs within the first minutes of the thermal annealing, while the second is due to the release of Ge from Ge-nc, associated with the formation of nanocavities. The formation rate of these nanocavities is more efficient at greater depth than in the vicinity of the sample surface. It appears to be strongly dependent on the local concentration of defects, responsible for the reduction of the Ge diffusion, and to be related to the breaking of Ge-O and Si-Ge bonds at the Ge-nc/SiO(2) interface.

Silicon nanocrystals (Si-nc) embedded in SiO(2) matrix and obtained by ion implantation (50keV, 1.0x10(17)Si/cm(2)) were characterized by means of three different transmission electron microscopy (TEM) techniques: Dark Field (DF), Scanning TEM Annular Dark Field (STEM-ADF) and Z contrast. The strengths and weaknesses of each technique for the characterization of the Si-nc were evaluated and discussed. DF imaging, which has the best contrast, was chosen to give the average Si-nc size evaluated to 5.6nm. On the other hand, STEM-ADF, which is only sensitive to the crystalline phase, provided an evaluation of the Si-nc density of 3.27x10(17)nc/cm(3). Finally, comparison between the STEM-ADF and Z contrast imaging permitted to evaluate the amorphous phase remaining after the annealing to around 12%., (Copyright 2009 Elsevier B.V. All rights reserved.)

Si nanocrystals (Si nc) were formed by the implantation of Si(+) into a SiO2 film on (100) Si, followed by high-temperature annealing. High-resolution transmission electron microscopy has been used to investigate the dislocations in the Si nc produced by a high-dose (ion fluence of 3 x 10(17) cm(-2)) implantation. Three different kinds of dislocations, namely perfect, extended and mismatch dislocations, have been observed in some Si nc. The possible formation mechanism for these dislocations has been discussed. The dislocations in the Si nc are expected to have a great influence on the photoluminescence from Si nc embedded in SiO2.

Room-temperature electroluminescence (EL) has been measured at both macroscopic and microscopic levels from metal-oxide-semiconductor devices containing silicon nanocrystals (Si-nc) embedded in silicon dioxide (SiO(2)) obtained by high-temperature annealing (1050 and 1100 °C) after Si(+) ion implantation. It is found that spatially integrated (macroscopic) EL is dominated by a near-infrared band centered where the photoluminescence (PL) band of Si-nc (from 700 to 1000 nm) is located. However, on a microscopic scale, EL emission is inhomogeneous, the sample surface exhibiting many visible spots of micron-order diameter. EL spectra from a microscopic surface of ∼1 µm(2)(μEL) on visible spots have revealed dominant contributions between ∼550 and ∼650 nm, attributed to oxide defects. These spectral features rapidly decrease with distance from a bright spot, while lower-intensity near-infrared contributions (750-950 nm) remain unaffected up to relatively large distances before eventually becoming extinct. The macroscopic EL measurements can be explained as a superposition of the μEL and PL spectra. A luminescent mechanism is proposed in which charge carriers mostly tunnel through high-defect-density channels in the oxide, yielding bright visible spots, while Si-nc in these channels and their surroundings contribute to the luminescence by hosting electron-hole recombinations (EL) and/or exhibiting PL due to optical excitation from the nearby visible EL spot.

Silicon nanocrystals (Si-nc) and amorphous silicon (α-Si) produced by silicon implantation in fused silica have been studied by micro-Raman spectroscopy. Information regarding the Raman signature of the α-Si phonon excitation was extracted from Raman depth-probing measurements using the phenomenological phonon confinement model. The spectral deconvolution of the Raman measurements recorded at different laser focusing depths takes into account both the Si-nc size variation and the Si-nc spatial distribution within the sample. The phonon peak associated with α-Si around 470 cm(-1) is greatest for in-sample laser focusing, indicating that the formation of amorphous silicon is more important in the region containing a high concentration of silicon excess, where large Si-nc are located. As also observed for Si-nc systems prepared by SiO(x) layer deposition, this result demonstrates the presence of α-Si in high excess Si implanted Si-nc systems.

Surface treatment optimization requires the control of the ion dose and the workpiece temperature, two parameters that are not trivially measurable in plasma-based ion implantation. A temperature and ion fluence monitoring system has been developed and implemented in a plasma-based ion implanter. It is based on the measurement with a thermopile of the radiation emitted from the back face of a thin copper disk inserted in the stainless steel sample holder. Since the incident ions carry practically all the incident power, the measurement of the Cu disk temperature that increases during implantation can provide an evaluation of the ion fluence in real time. A model has been developed for the deconvolution of the temperature data and has been fitted to the temperature behavior during implantation. A good agreement between the total integrated doses, evaluated with Rutherford backscattering spectroscopy characterization, and the ion fluence calculated by means of this model has been obtained with a discrepancy less than 16%.

To study the importance of glucagon and insulin in diabetes, somatostatin (ST) was infused, alone or with insulin or glucagon, in 11 conscious dogs. Plasma immunoreactive insulin (IRI) and glucagon (IRG) levels fell 65 +/- 4% and 33 +/- 3%, respectively, with somatostatin infusion. Glucose production (Ra) assessed by [3-3H]glucose, [2-3H]glucose, or [1-14C]glucose decreased transiently. This is in contrast to the rise in Ra seen after insulin withdrawal in depancreatized dogs, which have normal levels of IRG. Thus, suppression of IRG with somatostatin prevented an increase in Ra in spite of suppression of IRI. When near basal IRG levels were provided during ST infusion in normal dogs, Ra increased, indicating that glucagon contributes to the acute development of diabetes. When basal IRI levels were provided with ST, suppression of Ra was maintained, suggesting that the transience of the metabolic effects of ST-induced glucagon suppression requires concomitant insulin suppression. A comparison of glucose turnover measured using different tracers showed that ST-related hormonal changes did not alter the rate of futile cycling in the liver. ST induced a rise in plasma free fatty acid (FFA) levels, attributed solely to insulin deficiency, as glucagon suppression did not significantly alter FFA concentrations when normal insulin levels were maintained.