Electrical conduction of silicon oxide containing silicon quantum dots

Current-voltage measurements have been made at room temperature on a Si-rich silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$^\circ$C. The thickness of oxide between Si quantum dots embedded in the film increases with the increase of annealing temperature. This leads to the decrease of current density as the annealing temperature is increased. Assuming the Fowler-Nordheim tunneling mechanism in large electric fields, we obtain an effective barrier height $\phi_{eff}$ of $\sim$ 0.7 $\pm$ 0.1 eV for an electron tunnelling through an oxide layer between Si quantum dots. The Frenkel-Poole effect can also be used to adequately explain the electrical conduction of the film under the influence of large electric fields. We suggest that at room temperature Si quantum dots can be regarded as traps that capture and emit electrons by means of tunneling.Comment: 14 pages, 5 figures, submitted to J. Phys. Conden. Mat

Light emission from hydrogenated and unhydrogenated Si-nanocrystal/Si dioxide composites based on PECVD-grown Si-Rich Si oxide films

Hydrogenated and unhydrogenated Si-nanocrystal/Si dioxide (Si-nc/SiO2) composites were obtained from SiyO1-y (y=0.36, 0.42) thin films deposited by plasma-enhanced chemical vapor deposition. The unhydrogenated composites were fabricated by promoting the Si precipitation through thermal annealing of the films in flowing pure Ar at temperatures up to T=1100oC. Fourier transform infrared spectroscopy (FTIR) and elastic recoil detection analysis (ERDA) did not detect any trace of H in these samples. The hydrogenated composites were obtained from identical films by replacing the Ar with (Ar+5%H2) in the annealing step. The photoluminescence (PL) of the composites was studied as a function of the annealing temperature, annealing time and pump laser power. The PL intensity in the Ar-annealed samples increases with increasing annealing temperature, and it increases and then tends to saturation as a function of the annealing time at 1100oC. For the samples annealed in (Ar+5%H2), a qualitatively similar behavior is observed, however, the PL intensity is several hundreds percent larger. The FTIR spectra show that H in these samples incorporates as Si-H bonds. The analysis of the Si-H stretching band, in conjunction with results from previous studies of the Si/SiO2 phase separation process, suggests that a fraction of these bonds are located in the Si/SiO2 interface regions. The dependence of the PL spectra on y, T, and laser power are consistent with the assumption that light emission in both hydrogenated and unhydrogenated Si-nc/SiO2 composites originates from bandgap transitions involving electron quantum confinement in the Si-ncs, the details of the recombination mechanism still being unclear. The PL spectra from the hydrogenated films are skewed to the red as compared to those from the unhydrogenated ones. The bulk of the data indicates that H passivates nonradiative recombination centers, mostly probably Si dangling bonds in the Si-nc/SiO2 regions, thus increasing the number of Si-ncs that contribute to the PL and modifying the distribution of emission wavelengths. The PL intensity in the Ar-annealed samples increases with increasing annealing temperature, and it increases and then tends to saturation as a function of the annealing time at 1100oC. For the samples annealed in (Ar+5%H2), a qualitatively similar behavior is observed, however, the PL intensity is several hundreds percent larger. The FTIR spectra show that H in these samples incorporates as Si-H bonds. The analysis of the Si-H stretching band, in conjunction with results from previous studies of the Si/SiO2 phase separation process, suggests that a fraction of these bonds are located in the Si/SiO2 interface regions. The dependence of the PL spectra on y, T, and laser power are consistent with the assumption that light emission in both hydrogenated and unhydrogenated Si-nc/SiO2 composites originates from bandgap transitions involving electron quantum confinement in the Si-ncs, the details of the recombination mechanism still being unclear. The PL spectra from the hydrogenated films are skewed to the red as compared to those from the unhydrogenated ones. The bulk of the data indicates that H passivates nonradiative recombination centers, mostly probably Si dangling bonds in the Si-nc/SiO2 regions, thus increasing the number of Si-ncs that contribute to the PL and modifying the distribution of emission wavelengths.Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Zalloum, O. H. Y.. McMaster University; CanadáFil: Wojcik, J.. McMaster University; CanadáFil: Mascher, P.. McMaster University; Canad

H-Induced effects in luminescent silicon nanostructures obtained from PECVD grown SiyO1-y:H (y>1/3) thin films annealed in (Ar+5%H2)

SiyO1−y:H (y=0.36 and 0.42) alloy films were fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition and subsequently annealed in (Ar+5%H2) at different temperatures. Glancing angle x-ray diffraction and Fourier transform infrared spectroscopy measurements revealed the formation of silicon nanoclusters (Si-ncl) in an amorphous SiO2 matrix for films annealed at temperatures of 900  °C and above. Negligible photoluminescence (PL) was observed at room temperature for the as-grown samples; however, PL bands appeared in the visible after the annealing treatments. The PL intensities are much higher and the spectra skewed to the red as compared to data obtained for similar samples annealed in pure Ar. These effects are attributed to the passivation by H atoms of nonradiative recombination centers in the materials annealed in (Ar+5%H2). The overall analysis of the PL data indicates that both quantum confinement and defect states contribute to the luminescence. Two-step annealing procedures [in Ar and then in (Ar+5%H2)] were found to yield slightly higher passivation efficiencies than single annealing steps in (Ar+5%H2).Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Zalloum, O. H. Y.. Mc Master University; CanadáFil: Irving, E. A.. Mc Master University; CanadáFil: Wojcik, J.. Mc Master University; CanadáFil: Mascher, P.. Mc Master University; Canad

X-ray diffraction study of crystalline Si nanocluster formation in annealed silicon-rich silicon oxides

The formation and subsequent growth of crystalline silicon nanoclusters (Si-ncs) in annealed silicon-rich silicon oxides (SRSOs) were studied by glancing angle x-ray diffraction. SRSO samples with Si concentrations (y) of 0.40, 0.42, and 0.45 were grown by inductively coupled plasma-enhanced chemical-vapor deposition (PECVD). Samples with y=0.42 grown by electron-cyclotron-resonance PECVD were also studied. Annealing treatments were performed at temperatures (T) of 900, 1000, and 1100 °C for times (t) between 0.5 and 3 h in flowing Ar. As-grown SRSO films did not present signs of Si clusters (amorphous or crystalline); however, (111), (220), and (311) Bragg peaks corresponding to c-Si were clearly seen after annealing at 900 °C for the y=0.45 sample, but only barely seen for the y=0.42 and undetected for the y=0.40 samples. For T=1000 °C, all studied SRSO samples clearly showed the c-Si diffraction peaks, which became narrower with increasing t and T. From the width of the Si (111) peaks, the mean size of Si-ncs and their dependence on T and t was determined. Activation energies were deduced from the T dependence by fitting the results to two growth models of Si precipitates in an a-SiO2 matrix reported in the literature. The activation energies qualitatively agree with values deduced from transmission electron microscopy studies of annealed SRSO reported in the literature. However, they are significantly lower than Si diffusion activation energies available in the literature for SiO2 with low excess Si. A broad feature is also observed in the x-ray diffractograms for as-grown samples with low y, which shifts to the peak position corresponding to a-SiO2 with increasing T. This behavior is explained by the formation of a well-defined a-SiO2 phase with increasing T, where mixed Si-O4-nSin (n=1,2,3) tetrahedra in the as-grown alloy are gradually converted into Si-O4 and Si-Si4 as phase separation of Si and SiO2 proceeds. From the measured Si (111) peak positions, small Si-ncs are found to be tensilely strained by as much as ~0.8%. This effect becomes insignificant as Si-ncs become larger with increasing y or T.Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Zalloum, O. H. Y.. Mc Master University; CanadáFil: Irving, E. A.. Mc Master University; CanadáFil: Wojcik, J.. Mc Master University; CanadáFil: Roschuk, T.. Mc Master University; CanadáFil: Flynn, M. J.. Mc Master University; CanadáFil: Mascher, P.. Mc Master University; Canad

Physicians' guideline adherence is associated with long-term heart failure mortality in outpatients with heart failure with reduced ejection fraction: the QUALIFY international registry

Background: Physicians' adherence to guideline-recommended therapy is associated with short-term clinical outcomes in heart failure (HF) with reduced ejection fraction (HFrEF). However, its impact on longer-term outcomes is poorly documented. Here, we present results from the 18-month follow-up of the QUALIFY registry. Methods and results: Data at 18 months were available for 6118 ambulatory HFrEF patients from this international prospective observational survey. Adherence was measured as a continuous variable, ranging from 0 to 1, and was assessed for five classes of recommended HF medications and dosages. Most deaths were cardiovascular (CV) (228/394) and HF-related (191/394) and the same was true for unplanned hospitalizations (1175 CV and 861 HF-related hospitalizations, out of a total of 1541). According to univariable analysis, CV and HF deaths were significantly associated with physician adherence to guidelines. In multivariable analysis, HF death was associated with adherence level [subdistribution hazard ratio (SHR) 0.93, 95% confidence interval (CI) 0.87–0.99 per 0.1 unit adherence level increase; P = 0.034] as was composite of HF hospitalization or CV death (SHR 0.97, 95% CI 0.94–0.99 per 0.1 unit adherence level increase; P = 0.043), whereas unplanned all-cause, CV or HF hospitalizations were not (all-cause: SHR 0.99, 95% CI 0.9–1.02; CV: SHR 0.98, 95% CI 0.96–1.01; and HF: SHR 0.99, 95% CI 0.96–1.02 per 0.1 unit change in adherence score; P = 0.52, P = 0.2, and P = 0.4, respectively). Conclusion: These results suggest that physicians' adherence to guideline-recommended HF therapies is associated with improved outcomes in HFrEF. Practical strategies should be established to improve physicians' adherence to guidelines. © 2019 The Authors. European Journal of Heart Failure © 2019 European Society of Cardiolog