Undoped and Nd3+ doped Si-based single layers and superlattices for photonic applications

International audienceThis work presents the benefits of the superlattice approach to control light emission properties of materials with Si nanoclusters and rare‐earth ions. The undoped and Nd3+‐doped both Si‐rich‐SiO2 single layers and Si‐rich‐SiO2/SiO2 superlattices were grown by radio frequency magnetron sputtering. Their properties were investigated by means of spectroscopic ellipsometry, Fourier infrared transmission spectroscopy, transmission electron microscopy, and photoluminescence (PL) methods versus deposition conditions, annealing treatment, and superlattice design (doping and thickness of alternated sublayers). An intense Nd3+ emission from as‐deposited single layers and superlattices was observed. The lower annealing temperature (below 900 °C) of the single layers and superlattices favors the formation of amorphous Si clusters that act as effective sensitizers of rare‐earth ions. The highest Nd3+ PL intensity was achieved after a conventional annealing at about 600–800 °C in nitrogen flow for all samples. Crystallized Si‐nanoclusters were formed in Si‐rich‐SiO2 single layers upon annealing at 1000–1100 °C, whereas their formation in the superlattices occurred at higher temperatures (1100–1150 °C). The mechanism of Nd ions' excitation via energy transfer from Si‐nanoclusters and/or matrix defects, if any, is discussed

Nanoscale evidence of erbium clustering in Er-doped silicon-rich silica

International audiencePhotoluminescence spectroscopy and atom probe tomography were used to explore the optical activity and microstructure of Er 3+-doped Si-rich SiO 2 thin films fabricated by radio-frequency magnetron sputtering. The effect of post-fabrication annealing treatment on the properties of the films was investigated. The evolution of the nanoscale structure upon an annealing treatment was found to control the interrelation between the radiative recombination of the carriers via Si clusters and via 4f shell transitions in Er 3+ ions. The most efficient 1.53-μm Er 3+ photoluminescence was observed from the films submitted to low-temperature treatment ranging from 600°C to 900°C. An annealing treatment at 1,100°C, used often to form Si nanocrystallites, favors an intense emission in visible spectral range with the maximum peak at about 740 nm. Along with this, a drastic decrease of 1.53-μm Er 3+ photoluminescence emission was detected. The atom probe results demonstrated that the clustering of Er 3+ ions upon such high-temperature annealing treatment was the main reason. The diffusion parameters of Si and Er 3+ ions as well as a chemical composition of different clusters were also obtained. The films annealed at 1,100°C contain pure spherical Si nanocrystallites, ErSi 3 O 6 clusters, and free Er 3+ ions embedded in SiO 2 host. The mean size and the density of Si nanocrystallites were found to be 1.3 ± 0.3 nm and (3.1 ± 0.2) × 10 18 Si nanocrystallites·cm −3 , respectively. The density of ErSi 3 O 6 clusters was estimated to be (2.0 ± 0.2) × 10 18 clusters·cm −3 , keeping about 30% of the total Er 3+ amount. These Er-rich clusters had a mean radius of about 1.5 nm and demonstrated preferable formation in the vicinity of Si nanocrystallites

Microstructure and optical properties of Pr3+-doped hafnium silicate films

International audienceIn this study, we report on the evolution of the microstructure and photoluminescence properties of Pr 3+-doped hafnium silicate thin films as a function of annealing temperature (T A). The composition and microstructure of the films were characterized by means of Rutherford backscattering spectrometry, spectroscopic ellipsometry, Fourier transform infrared absorption, and X-ray diffraction, while the emission properties have been studied by means of photoluminescence (PL) and PL excitation (PLE) spectroscopies. It was observed that a post-annealing treatment favors the phase separation in hafnium silicate matrix being more evident at 950°C. The HfO 2 phase demonstrates a pronounced crystallization in tetragonal phase upon 950°C annealing. Pr 3+ emission appeared at T A = 950°C, and the highest efficiency of Pr 3+ ion emission was detected upon a thermal treatment at 1,000°C. Analysis of the PLE spectra reveals an efficient energy transfer from matrix defects towards Pr 3+ ions. It is considered that oxygen vacancies act as effective Pr 3+ sensitizer. Finally, a PL study of undoped HfO 2 and HfSiO x matrices is performed to evidence the energy transfer

Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-κ silicates

International audienceHafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO2 and HfO2 phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.960.4) 1017 Si-ncs/cm3, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-j dielectrics with embedded Si nanocluster

Hf-based high-k materials for Si nanocrystal floating gate memories

Pure and Si-rich HfO2 layers fabricated by radio frequency sputtering were utilized as alternative tunnel oxide layers for high-k/Si-nanocrystals-SiO2/SiO2 memory structures. The effect of Si incorporation on the properties of Hf-based tunnel layer was investigated. The Si-rich SiO2 active layers were used as charge storage layers, and their properties were studied versus deposition conditions and annealing treatment. The capacitance-voltage measurements were performed to study the charge trapping characteristics of these structures. It was shown that with specific deposition conditions and annealing treatment, a large memory window of about 6.8 V is achievable at a sweeping voltage of ± 6 V, indicating the utility of these stack structures for low-operating-voltage nonvolatile memory devices

SiOx/SiNy multilayers for photovoltaic and photonic applications

Microstructural, electrical, and optical properties of undoped and Nd3+-doped SiOx/SiNy multilayers fabricated by reactive radio frequency magnetron co-sputtering have been investigated with regard to thermal treatment. This letter demonstrates the advantages of using SiNy as the alternating sublayer instead of SiO2. A high density of silicon nanoclusters of the order 1019 nc/cm3 is achieved in the SiOx sublayers. Enhanced conductivity, emission, and absorption are attained at low thermal budget, which are promising for photovoltaic applications. Furthermore, the enhancement of Nd3+ emission in these multilayers in comparison with the SiOx/SiO2 counterparts offers promising future photonic applications

Corrigendum to “CO–PROX reactions on copper Y2O3-ZrO2 catalysts prepared by a single step co-precipitation technique” [Appl. Catal. B: Environ. 278 (1-12) (2020) 119258]

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CO–PROX reactions on copper Y2O3-ZrO2 catalysts prepared by a single step co-precipitation technique

International audienceNano-sized CuYZr ternary oxides obtained through an original single step co-precipitation synthesis were submitted to an in depth characterization and further tested in the catalytic CO PROX reaction. The tetragonal phase was identified as the main one whatever the calcination temperature. The study of the copper distribution within the crystals through complementary STEM EDX chemical mapping, UV-Vis and H2 Thermo Programmed Reduction (TPR) analysis allowed the identification of at least three distinct sites. The PROX tests revealed interesting properties with CO conversion as high as 95% and relatively high O2 selectivity towards CO2 in the high temperature range. Finally, interesting relationships between relative abundance of copper sites and catalytic activity/selectivity were obtained allowing suggesting relevant active sites

Thermal stability of high-k Si-rich HfO2 layers grown by RF magnetron sputtering

International audienceThe microstructure and optical properties of HfSiO films fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry and attenuated total reflection infrared spectroscopy versus annealing treatment. It was shown that silicon incorporation in the HfO2 matrix plays an important role in the structure stability of the layers. Thus, the increase of the annealing temperature up to 1000 °C did not lead to the crystallization of the films. The evolution of the chemical composition as well as a decrease of the density of the films was attributed to the phase separation of HfSiO on HfO2 and SiO2 phases in the film. An annealing at 1000–1100 °C results in the formation of the multilayer Si-rich/Hf-rich structure and was explained by a surface-directed spinodal decomposition. The formation of the stable tetragonal structure of HfO2 phase was shown upon annealing treatment at 1100 °C