Ni-mediated reactions in nanocrystalline diamond on Si substrates: the role of the oxide barrier

Nanocrystalline diamond (NCD) films grown on Si substrates by microwave plasma enhanced chemical vapor deposition (MWPECVD) were subjected to Ni-mediated graphitization to cover them with a conductive layer. Results of transmission electron microscopy including electron energy-loss spectroscopy of cross-sectional samples demonstrate that the oxide layer on Si substrates (∼5 nm native SiO₂) has been damaged by microwave plasma during the early stage of NCD growth. During the heat treatment for graphitizing the NCD layer, the permeability or absence of the oxide barrier allow Ni nanoparticles to diffuse into the Si substrate and cause additional solid-state reactions producing pyramidal crystals of NiSi₂ and SiC nanocrystals. The latter are found impinged into the NiSi₂ pyramids but only when the interfacial oxide layer is absent, replaced by amorphous SiC. The complex phase morphology of the samples is also reflected in the temperature dependence of electrical conductivity, where multiple pathways of the electronic transport dominate in different temperature regions. We present models explaining the observed cascade of solid-state reactions and resulting electronic transport properties of such heterostructures.

Nanocrystalline diamond films grown on Si/native oxide substrates were subjected to Ni-mediated graphitization. Transmission electron microscopy study revealed crystals of NiSi₂ and SiC across the carbon/silicon interface in addition.     

Lung function in children and adolescents with tetralogy of Fallot after intracardiac repair

We studied lung function in 41 patients, aged 6–27 years, 1–5 years after intracardiac surgical repair (ICR) of tetralogy of Fallot (TOF) and about 5 years after the establishment of the Pediatric Cardiac Center in Prague. The measurements included vital capacity (VC). total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), forced expiratory flows (FEF), specific airway conductance (SGaw), lung recoil pressure (Pst), and specific static lung compliance (S_1st). Single or mutiple abnormal lung function parameters were found in 83% of patients. Lung function was not related to shunting operations prior to ICR, hemoglobin concentration, and hematocrit, and had no specific pattern. Pst at 100% TLC and 90% TLC declined with increasing age at ICR and at lung function testing, while SC, rose, as did the ratio FRC/TLC. Fifteen patients were studied before and after surgery. Single or multiple lung function tests were abnormal in 93% before and in 84% after ICR. After ICR the ratios FRC/TLC and also RV/TLC, FEF at 25% VC, and FEF at 60% TLC were less frequently abnormal, while Pst at 100% TLC and at 90% TLC, as well as SGaw and TLC, were more frequently abnormal after ICR. The results indicated a regression of smaller airway obstruction and lung hyperinflation after ICR. The evolution of abnormally compliant (emphysematous) lungs with growth of the patients might be a sign of permanent sequelae of early lung damage from abnormal pulmonary hemodynamics. Pediatr Pulmonol. 1993; 16:23–30. © 1993 Wiley-Liss, Inc.     

Ischemic injury of the developing heart

Cardiac tolerance to ischemia changes significantly during ontogenetic development: the immature heart appears to be more resistant to ischemic injury than the adult myocardium. The mechanisms of the higher tolerance of the developing heart have not yet been satisfactorily clarified; age-dependent changes in energy metabolism have to be taken into consideration. Marked ontogenetic changes are displayed by the mitochondrial membrane potential (MMP): in newborn rats a single population of mitochondria with a relatively high MMP was observed but, with increasing age, the second population with a lower MMP appeared. Adaptation to chronic hypoxia and ischemic preconditioning failed to improve ischemic tolerance of the rat heart on the first postnatal day; the cardioprotective effect only developed at the end of the first postnatal week. Decreasing tolerance of the neonatal heart to ischemia is thus counteracted by the development of endogenous protection. It seems likely that both mitochondrial K_ATP channels and nitric oxide may be involved in the protective mechanisms of adaptation to chronic hypoxia but not to that of ischemic preconditioning, at least in neonatal rats. Basic knowledge of the possible improvements of immature heart tolerance to ischemia may contribute to the design of therapeutic strategies for both pediatric cardiology and cardiac surgery.     

DC potentials in different cells of the stria vascularis measured in vitro

Fine glass microelectrodes were inserted into the stria vascularis (SV) from the endolymphatic side under conditions in vitro. DC potentials were recorded in individual cells of the SV. The electrophoretic dye marking technique was used for identification of cells with different DC potentials. Penetration of the luminal membrane of marginal cells (MC) was accompanied by an unstable transient negative potential of about -15 mV. When the electrode penetrated further into the MC, a positive potential of about +10 mV was recorded. In the basal cells (BC) of the SV a negative DC potential of approx. -45 mV was always measured. Addition of ouabain into the perfusion solution (10(-3) mol/l) abolished the positive potential of MC, whereas the negative potential of BC decreased to approximately one half of the original value. A higher positive potential (+17 mV) was found in the MC of animals which were exposed to noise twenty days before the recording. Results are discussed in the light of the knowledge about localization of different transporting systems within the SV cells.