Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography

Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C

A Method for evaluating the effect of blowing agent condensation sprayed polyurethane foams

Peer reviewed: YesNRC publication: Ye

A Method for evaluating the effect of blowing agent condensation on sprayed polyurethane foams

Also published in "CFCs and the Polyurethane Industry : Vol 2 : (A Compilation of Technical Publications, 1988- 1989)"Peer reviewed: YesNRC publication: Ye

Techniques to assess the role of various components in retarding aging of rigid, faced thermal insulating foams

As industry began to evaluate CFC-replacements, it became apparent that foam performance characterizations have been based primarily on empirical evidence collected over a long period of gradualimprovements. Much of the existing wealth of knowledge was simply not applicable to new systems. The development of new products with CFC replacements requires understanding how formulation variables(polyol, isocyanate, blowing agent, catalyst) and manufacturing conditions affect foam properties, how conditions in use affect foam performance and how the process of sample selection and testing may be used to provide feedback to design improved foams.Lorsque l?industrie a commenc\ue9 \ue0 \ue9valuer des solutions de rechange aux chlorofluorocarbures (CFC), il est devenu apparent que les caract\ue9risations de la performance de la mousse \ue9taient jusque l\ue0 fond\ue9es essentiellement sur des preuves empiriques recueillies au fil d?une longue p\ue9riode d?am\ue9liorations graduelles. Une part importante des connaissances existantes n?\ue9tait tout simplement pas applicable aux nouveaux syst\ue8mes. Le d\ue9veloppement de nouveaux produits avec solutions de rechange aux CFC requiert une compr\ue9hension de la fa\ue7on dont les variables de formulation (polyol, isocyanate, agent d?expansion, catalyseur) et les conditions de fabrication influent sur les propri\ue9t\ue9s de la mousse, dont les conditions en service influent \ue0 leur tour sur sa performance et dont le processus de s\ue9lection et de mise \ue0 l?essai des \ue9chantillons peut \ueatre utilis\ue9 pour g\ue9n\ue9rer une r\ue9troaction aux fins de la conception de mousses am\ue9lior\ue9es.Also presented at the World Congress : Polyurethane '93Peer reviewed: YesNRC publication: Ye

Si nanocrystal-based LEDs fabricated by ion implantation and plasma-enhanced chemical vapour deposition

Dept. ElectrònicaAn in-depth study of the physical and electrical properties of Si-nanocrystal-based MOSLEDs is presented. The active layers were fabricated with different concentrations of Si by both ion implantation and plasma-enhanced chemical vapour deposition. Devices fabricated by ion implantation exhibit a combination of direct current and field-effect luminescence under a bipolar pulsed excitation. The onset of the emission decreases with the Si excess from 6 to 3 V. The direct current emission is attributed to impact ionization and is associated with the reasonably high current levels observed in current–voltage measurements. This behaviour is in good agreement with transmission electron microscopy images that revealed a continuous and uniform Si nanocrystal distribution. The emission power efficiency is relatively low, ~10−3%, and the emission intensity exhibits fast degradation rates, as revealed from accelerated ageing experiments. Devices fabricated by chemical deposition only exhibit field-effect luminescence, whose onset decreases with the Si excess from 20 to 6 V. The absence of the continuous emission is explained by the observation of a 5 nm region free of nanocrystals, which strongly reduces the direct current through the gate. The main benefit of having this nanocrystal-free region is that tunnelling current flow assisted by nanocrystals is blocked by the SiO2 stack so that power consumption is strongly reduced, which in return increases the device power efficiency up to 0.1%. In addition, the accelerated ageing studies reveal a 50% degradation rate reduction as compared to implanted structures