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Maternal perinatal depression exerts pervasive effects on the developing brain, as evidenced by electroencephalographic (EEG) patterns that differ between children of women who do and do not meet DSM or ICD diagnostic criteria. However, little research has examined if the same EEG pattern of right-frontal alpha asymmetry exists in newborns and thus originates in utero independent of postnatal influences, and if depressive symptoms are associated with this neural signature. Utilizing 125-lead EEG (n=18), this study considered clinician-rated maternal prenatal depressive symptoms in relation to newborn EEG. Maternal depressive symptomatology was associated with greater relative right-frontal alpha asymmetry during quiet sleep. These results suggest that even subclinical levels of maternal depression may influence infant brain development, and further support the role of the prenatal environment in shaping children’s future neurobehavioral trajectories.
To assess the burden of bloodstream infections (BSIs) among pediatric hematology-oncology (PHO) inpatients, to propose a comprehensive, all-BSI tracking approach, and to discuss how such an approach helps better inform within-center and across-center differences in CLABSI rate
Prospective cohort study
US multicenter, quality-improvement, BSI prevention network
PHO centers across the United States who agreed to follow a standardized central-line–maintenance care bundle and track all BSI events and central-line days every month.
Infections were categorized as CLABSI (stratified by mucosal barrier injury–related, laboratory-confirmed BSI [MBI-LCBI] versus non–MBI-LCBI) and secondary BSI, using National Healthcare Safety Network (NHSN) definitions. Single positive blood cultures (SPBCs) with NHSN defined common commensals were also tracked.
Between 2013 and 2015, 34 PHO centers reported 1,110 BSIs. Among them, 708 (63.8%) were CLABSIs, 170 (15.3%) were secondary BSIs, and 232 (20.9%) were SPBCs. Most SPBCs (75%) occurred in patients with profound neutropenia; 22% of SPBCs were viridans group streptococci. Among the CLABSIs, 51% were MBI-LCBI. Excluding SPBCs, CLABSI rates were higher (88% vs 77%) and secondary BSI rates were lower (12% vs 23%) after the NHSN updated the definition of secondary BSI (P<.001). Preliminary analyses showed across-center differences in CLABSI versus secondary BSI and between SPBC and CLABSI versus non-CLABSI rates.
Tracking all BSIs, not just CLABSIs in PHO patients, is a patient-centered, clinically relevant approach that could help better assess across-center and within-center differences in infection rates, including CLABSI. This approach enables informed decision making by healthcare providers, payors, and the public.
We studied the effect of a cross-conjugated bridging group (χC) on charge-transfer in a push-pull chromophore system. The hyperpolarizability of such molecules was found to be comparable to that of a fully π-conjugated molecule (πC) with the same donor and acceptor. The cross-conjugated moiety was then applied as a pendant to a fully π-conjugated chromophore containing a tricyanopyrroline acceptor (TCP). The addition of a χC moiety did not alter the intrinsic hyperpolarizability and provides an avenue for extending and aiding πC systems. The molecules were examined by X-ray diffraction (XRD), hyper-Raleigh scattering (HRS) and UV-visible (UV-vis) spectroscopy. Experimental results were compared with the predictions of density functional theory (DFT). Cross-conjugated molecules have comparable β values, relative to πC molecules, due to reduced spatial overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Thus, the χC architecture could facilitate independent modification of donor and acceptor strengths while minimizing unfavorable effects on electronic transitions and dipole moments.
Highly carbon doped GaAs layers grown by metal organic vapor phase epitaxy (MOVPE) have been investigated by transmission electron microscopy (TEM). Electron irradiation has been applied to generate point defects interacting with native defects, e.g., substitutional carbon. This irradiation induces periodically arranged striations perpendicular to the growth direction, which were observed in situ by TEM. Furthermore, precipitates (Ø= 10–15nm) were formed containing non-crystalline material, which most likely is gallium. To explain these phenomena a precipitation mechanism is proposed. It involves small fluctuations of the incorporated C as well as the interaction of irradiation induced point defects, mainly As and C interstitials and As vacancies.
A new model for carbon diffusion in silicon that explains carbon diffusion during annealing at 850°C and 900°C in superlattice carbon structures grown by MBE is implemented using the Monte Carlo atomistic simulator DADOS. Carbon concentrations in the delta layers are 2×1020 cm−3, exceeding by far the solid solubility. The simple kick-out mechanism which incorporates the well established values of the product of diffusivity and equilibrium concentrations of intrinsic point defects and in-diffusion experiments of carbon in silicon does not explain the observed C diffusion profiles. A more detailed analysis of the experiments shows that, in order to fit them, a more unstable Ci is required. Therefore, we include the formation of clusters in the simulations. The formation of carbon/Si self-interstitial clusters promotes the premature break-up of Ci and the increase of the Si self-interstitial concentration in the carbon rich regions and, consequently, provides a better fit to the experiments. The low solubility of carbon in silicon at the annealing temperatures explains why these clusters are formed, even under conditions where the self-interstitial concentration is below the equilibrium value.
The structure of undoped Si:H films deposited at a high rate of 6-9 Å/s in an RF (13.56 MHz) plasma from hydrogen-silane gas mixtures at various substrate temperatures was studied using TEM (with in-situ annealing), XRD, Raman spectroscopy, optical absorption and hydrogen effusion. It is found that under our conditions the amorphous to crystalline transition occurs in a relatively narrow range of parameters, influenced mainly by hydrogen dilution and to a lesser degree by the substrate temperature. In the crystalline range the material is found to be nanocrystalline (average grain size 20 nm) and the crystals are essentially stable up to 800°C annealing. The crystal structure of a mixed amorphousnanocrystalline phase of samples deposited near the edge of crystallinity is also found to be rather stable. Nanocrystalline Si films deposited under these latter deposition conditions reveal in hydrogen effusion a relatively compact material and show high solar cell efficiencies (6-8%) when incorporated as i-layers in pin solar cells.
The possibility to suppress undesirable diffusion of the base dopant boron in siliconbased bipolar transistor structures by the incorporation of a high concentration of carbon has lead to renewed interest in the behavior of carbon in crystalline silicon. The present paper will review essential features of carbon in silicon including solubility, diffusion mechanisms and precipitation behavior. Based on this information the possibilities to use carbon to influence diffusion of dopants in silicon by the introduction of non-equilibrium concentrations of intrinsic point defects will be discussed as well as the reason for the relatively high resilience against carbon precipitation. Interactions between carbon and oxygen will be mentioned, especially in the context of an as yet unexplained fast out-diffusion of carbon close to the surface.
Macroscopic poly(ether ether ketone) (PEEK) and polypropylene (PP) nanocomposites containing vapour-grown carbon nanofibres (CNF) were produced using standard polymer processing. Tensile tests revealed a linear increase in composite stiffness with nanofibre content. A detailed DSC study verified that under standard processing conditions the degree of crystallinity and the crystalline structure of these semicrystalline thermoplastics were not affected by the nanofibres. Nevertheless, we provide evidence that the nanoscale filler can alter the polymer morphology under certain conditions, an effect which needs to be considered when evaluating nanocomposite properties. Given the absence of morphological changes in the standard nanocomposites we were able to calculate the intrinsic nanofibre modulus using short fibre theory; both distinctively different matrix systems show a similar effective nanofibre modulus.
We crystallize amorphous silicon films with a frequency doubled Nd:YVO4 laser operating at a repetition frequency of up to 50 kHz. A sequential lateral solidification process yields polycrystalline silicon with grains longer than 100 μm and a width between 0.27 and 1.7 μm depending on film thickness and laser repetition frequency. The average grain size is constant over the whole crystallized area of 25 cm2. Thin film transistors with n- type and p-type channels fabricated from the polycrystalline films have average field effect mobilities of μn = 467 cm2/Vs and μp = 217 cm2/Vs respectively. As a result of the homogeneous grain size distribution, the standard deviation of the mobility is only 5%.
We introduce a new quantitative description for electronic noise at Schottky contacts. The model combines spatially inhomogeneous current transport across the interface with the modulation of the local barrier height due to trapping dynamics of charged states located at or close to the interface. The experimentally observed increase of noise power with decreasing temperature is explained by the inhomogeneity of the interface. Our model fits experimental data obtained from different silicide/silicon Schottky contacts and the detailed analysis of measured noise spectra yields information about the interfacial potential fluctuations.
The deposition process of multiple layer structures of intrinsic and p-type hydrogenated amorphous silicon was followed by measuring the microwave detected transient photoconductivity (TRMC) during the film growth. In an i-p-i structure we can show that after deposition of an upper layer of about 500 nm, former deposited layers do not influence the TRMC-signal any more. In an i-p+-i-p structure we can clearly distinguish between p-layers of different doping concentration.
Several stationary and transient techniques are used to characterize a large number of intrinsic a-Si:H films prepared in a narrow range of production conditions. Correlation between stationary photoconductivity, the activation energy of the dark conductivity and the long-time range decay of the transient photoconductivity and photoinduced absorption is observed. The applicability of a-Si:H films for solar cells in view of these properties is discussed.
We present a new analytical theory of electronic transport for inhomogeneous Schottky contacts. Our model combines a novel method to solve Poisson's equation for the space charge region of an inhomogeneous contact with thermionic emission theory. We explain quantitatively the temperature and voltage dependences of the ideality factor n of current/voltage characteristics, and we are able to extract from experimental data information on the characteristic size of the inhomogeneities. Our measurements on polycrystalline and epitaxial Schottky contacts yield values in the range of 200–500nm as the typical size of inhomogeneities, covering a fraction of 0.1–1% of the total interface area.
Evaluating either curved Richardson plots or temperature-dependent ideality data allows for a quantitative characterization of spatial inhomogeneities at Schottky contacts. Applying the two independent methods to PtSi/Si diodes we obtain a standard deviation around 70mV for the barrier fluctuations. These results agree with those from the comparison of temperature-dependent current and capacitance barriers. We discuss also flat band barrier heights which should be used if one investigates the temperature dependence of fundamental Schottky barrier heights. Their temperature coefficients depend on metallization. For epitaxial NiSi2/Si contacts on (100) oriented Si we find a strong influence of interface crystallography on the temperature coefficients.
Molecular beam deposition (MB) of thin film metal oxide is prospective for application in gas sensor technology due to the well-controlled oxide molecular fluxes during creation of multi-oxide structures with improved characteristics. However, the MB process leads to some oxygen deficiency in the oxide. Further application of the MB technology (and, in general, the e-beam oxide deposition in vacuum) for processing of sensor structures needs the control and correction of the oxygen stoichiometry by adding in-situ atomic oxygen to the growing material or via the thin film oxidation after deposition.
Thin films (50 to 500 nm) of SnOx and TiOx were deposited on SiO2/(001)Si substrates at 100°C by MB from SnO2 and TiO2 sources. The film stoichiometry in the as-deposited state and after annealing in vacuum and in oxygen is characterized by XRD, TEM and RBS. Oxygen annealing transformed the strongly non-stoichiometric SnO (Romarchite) in the as-deposited state to Cassiterite, SnO2. Structure transformations in the TiO2 films during annealing are also discussed.
The crystallization behavior (ordering) of undoped and boron-doped Si0.5Ge0.5 films, deposited on SiO2/Si(001) substrate by molecular beam epitaxy in hish vacuum at room temperature, were studied by XRD, HRTEM and in situ by Doppler broadening spectroscopy using monoenergetic positrons. Some decomposition features of SiGe solid solutions were demonstrated via splitting the XRD peaks at high temperatures. The SiGe decomposition was detected in the precrystalline state of the SiGe undoped and doped films in the temperature range from 450 to 600 K by compaering S- and W-parameters of SiGe with that of amorphous silicon and germanium. In conclusion, we discuss model of internim ordering states before crystallization.
The objective of this work was to study by transmission electron microscopy the lattice defects in GaAs bulk crystals and heterostructures formed by In diffusion. In such samples hints for the existence of superconductivity have been found. Indium was found to move more than 100 μm into bulk GaAs during lh annealing at 550ºC (such conditions are typical for molecular beam epitaxy growth on GaAs wafers). This rapid diffusion is accompanied by the creation of dislocation networks and metallic In droplets that show evidence for lattice strain. To study the interaction of In with the GaAs lattice, In/GaAs multi-layers were grown by MBE at about 450ºC on a GaAs buffer layer. The interfaces of these structures showed misfit dislocations at islands of InAs besides the presence of lattice strain. Both types of samples showed microwave absorption signals typical for superconductivity. The most likely superconductive phases are small metastable inclusions, probably consisting of amorphous Ga or In.
We deposit phosphorus-doped, amorphous Si by low pressure chemical vapor deposition and subsequently crystallize the films by furnace annealing at a temperature of 600°C. Optical in-situ monitoring allows one to control the crystallization process. Phosphorus doping leads to faster crystallization and a grain size enhancement with a maximum grain size of 15 μm. Using transmission electron microscopy we find a log-normal grain size distribution in our films. We demonstrate that this distribution not only arises from solid phase crystallization of amorphous Si but also from other crystallization processes based on random nucleation and growth. The log-normal grain size distribution seems to be a general feature of polycrystalline semiconductors.
Highly doped (∼1018 to 1021cm−3) polycrystalline Si1-xGex films, crystallized from amorphous (a) state at relative low temperatures, are prospective materials in a variety of applications, such as liquid-crystal displays, solar cells and integrated thermoelectric sensors on large-area glass substrates. Since the nature of the grains in the crystallized film defines properties such as carrier mobility, the nucleation and growth process of the a-SiGe films is of fundamental interest. We have studied the crystallization of undoped and highly doped (B or Ga) amorphous SiGe films. The films were deposited by RFCVD or molecular beam on oxidized (001)Si and for TEM study on cleaved NaCl. The incubation time and grain growth rate were studied by means of in situ TEM using a heating stage. The crystallization process in undoped SiGe followed Avrami relationship. An average grain size between 0.1 and 2μm was observed. However, the highly p-doped (with B or Ga) SiGe films crystallized to a stable nanocrystalline structure (grain size <10nm). The process of the a-SiGe crystallization is explained on the basis of self-diffusion. During the first stage, the nucleation of crystals is accompanied with nonequilibrium vacancy generation at the amorphous/crystalline interface. During the second stage, the growth of crystals takes place by vacancy outdiffusion which is hindered by B and Ga interaction with vacancies.