Silicon-rich oxynitride hosts for 1.5 μm Er emission fabricated by reactive and standard RF magnetron sputtering

This study compares the erbium emission from different Si-rich silicon oxynitrides matrices fabricated by magnetron sputtering. The Er-doped layers were grown by two different sputtering configurations: (i) standard co-sputtering of three confocal targets (Er₂O₃, Si₃N₄ and SiO₂) under Ar plasma, and (ii) reactive co-sputtering under Ar + N₂ plasma of either three (Er₂O₃, pure Si and SiO₂) or two targets (Er₂O₃ and pure Si). The last reactive configuration was found to offer the best Er³⁺ PL intensity at 1.5 μm. This highest PL intensity was found comparable to the corresponding emission from Er-doped silicon-rich silicon oxide.     

Structural and luminescent characteristics of macro porous silicon

The results of structural and luminescent study of porous Si prepared by electrochemical etching and containing the pores of micron sizes are presented. The samples demonstrate bright luminescence with external quantum efficiency of 15–20%. Raman scattering spectra contain only one line corresponding to bulk silicon. Atomic force microscopy image shows the structural elements essentially larger than quantum confinement crystallites. However, X-ray diffraction measurements demonstrate the presence of strained Si quantum confinement nanowires. It is shown that the recombination through interface oxide-related centers of the carriers excited due to light absorption in quantum confinement nanowires gives an essential contribution to emission spectra.     

The effects of ABRACADABRA on reading outcomes: An updated meta-analysis and landscape review of applied field research

ABRACADABRA (ABRA) is an evidence-based suite of interactive multimedia that engages learners in the development of core reading skills. This meta-analysis presents an update of the research evidence about the effectiveness of ABRA for elementary students. It reports 91 effect sizes in six reading-related outcomes for a sample of 7,388 students. Regardless of context and measurement type, the studies yielded positive effects of ABRA, ranging in magnitude from g+ = 0.080 for Vocabulary Knowledge to g+ = 0.378 for Phonemic Awareness and reaching statistical significance in four outcome categories. This meta-analysis adds to our understanding of the effectiveness of ABRA-based reading instruction by exploring factors of research design, ABRA design and implementation contexts, and various student characteristics and offers implications for instructional practice.     

Quantum dots for human mesenchymal stem cells labeling. A size-dependent autophagy activation

Lately certain cytotoxicity of quantum dots (QDs) and some deleterious effects of labeling procedure on stem cells differentiation abilities were shown. In the present study we compared cytotoxicity and intracellular processing of two different-sized protein-conjugated QDs after labeling of the human mesenchymal stem cells (hMSC). An asymmetrical intracellular uptake of red (605 nm) and green (525 nm) quantum dots was observed. We describe for the first time a size-dependent activation of autophagy, caused by nanoparticles.     

Atomic scale microstructures of high-k HfSiO thin films fabricated by magnetron sputtering

High-k hafnium-silicate films were deposited by RF magnetron sputtering approach on silicon wafer. The microstructure has been investigated using the combination of transmission electron microscopy and atom probe tomography. It was evidenced that the elaborated HfSiO thin films subsequently annealed at 950 °C during 15 min leads to a complex phase separated nanostructure where silica, hafnia and silicon nanoclusters coexist. The formation of silicon nanoclusters in hafnia-based host was never reported before. The results demonstrate the capability of RF magnetron sputtering to pave the way for realization of nanomemory devices based on silicon clusters embedded in high-k matrix.     

Confined Catalytic Janus Swimmers in a Crowded Channel: Geometry‐Driven Rectification Transients and Directional Locking

Self‐propelled Janus particles, acting as microscopic vehicles, have the potential to perform complex tasks on a microscopic scale, suitable, e.g., for environmental applications, on‐chip chemical information processing, or in vivo drug delivery. Development of these smart nanodevices requires a better understanding of how synthetic swimmers move in crowded and confined environments that mimic actual biosystems, e.g., network of blood vessels. Here, the dynamics of self‐propelled Janus particles interacting with catalytically passive silica beads in a narrow channel is studied both experimentally and through numerical simulations. Upon varying the area density of the silica beads and the width of the channel, active transport reveals a number of intriguing properties, which range from distinct bulk and boundary‐free diffusivity at low densities, to directional “locking” and channel “unclogging” at higher densities, whereby a Janus swimmer is capable of transporting large clusters of passive particles.     

Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

Silicon-rich Al₂O₃ films (Si_x(Al₂O₃)_1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface.     

The effect of oxidation on the efficiency and spectrum of photoluminescence of porous silicon

The photoluminescence spectra of porous silicon and their temperature dependences and transformations on aging are studied. It is shown that the infrared band prevailing in the spectra of as-prepared samples is due to exciton recombination in silicon crystallites. On aging, a well-pronounced additional band is observed at shorter wavelengths of the spectra. It is assumed that this band is due to the recombination of carriers that are excited in silicon crystallites and recombine via some centers located in oxide. It is shown that the broad band commonly observable in oxidized porous silicon is a superposition of the above two bands. The dependences of the peak positions and integrated intensities of the bands on time and temperature are studied. The data on the distribution of oxide centers with depth in the porous layer are obtained.     

Study of the layer-substrate interface in <Emphasis Type="Italic">nc</Emphasis>-Si-SiO<Subscript>2</Subscript>-<Emphasis Type="Italic">p</Emphasis>-Si structures with silicon quantum dots by the method of temperature dependences of photovoltage

Layers grown by magnetron deposition of Si and SiO₂ on a p-type silicon substrate and containing silicon nanocrystals in the oxide matrix have been studied by the method of temperature dependences of the capacitive photovoltage. The effect of the substrate orientation and natural oxidation preceding high-temperature annealing that results in the formation of Si nanocrystals in the SiO₂ matrix on the layer-substrate interface characteristics is studied. The density of fast interface states trapping majority carriers was estimated. It is found that structural changes occur at the layer-substrate interface in the case of a (111) substrate and are caused by stresses appearing upon cooling. It was shown that natural oxidation of the deposited layer, preceding high-temperature annealing, causes an increase in the charge trapped in the oxide.