Synthesis of zinc oxide nanocrystals by thermal decomposition of Zn-oleate in organic medium

We report the synthesis of uniform-sized hexagonal ZnO nanocrystals by the thermolysis of Zn-oleate complex, which was prepared from the reaction of inexpensive and environmentally friendly reagents such as zinc nitrate and sodium oleate. Two organic compounds with different boiling points, octadecene and octylether, were selected as the medium for thermolysis of Zn-oleate complex. Under optimized reaction conditions, we were able to synthesize ZnO nanoparticles with the size being about 10 nm. X-ray diffraction and transmission electron micrograph (TEM) images confirmed the high crystallinity of the nanocrystals.     

Simulation of coupled heat and moisture transfer in air-conditioned buildings

The simultaneous heat and moisture transfer in the building envelope has an important influence on the indoor environment and the overall performance of buildings. In this paper, a model for predicting whole building heat and moisture transfer was presented. Both heat and moisture transfer in the building envelope and indoor air were simultaneously considered; their interactions were modeled. The coupled model takes into account most of the main hygrothermal effects in buildings. The coupled system model was implemented in MATLAB-Simulink, and validated by using a series of published testing tools. The new program was applied to investigate the moisture transfer effect on indoor air humidity and building energy consumption under different climates. The results show that the use of more detailed simulation routines can result in improvements to the building's design for energy optimisation through the choice of proper hygroscopic materials, which would not be indicated by simpler calculation techniques.     

Rubrene as an additive in M-phthalocyanine/fullerene organic solar cells

Photovoltaic devices made from metallo-phthalocyanine/fullerene (M-Pc/C₆₀) with 5,6,11,12-tetraphenylnaphthacene (rubrene) as an additive are fabricated and characterized. The effect of rubrene is examined for 4 different M-phthalocyanines – H₂Pc, ZnPc, ClInPc, and VOPc – to represent 4 different valencies of the central moiety of M-Pc. In each case, rubrene has shown a notable increase in the open circuit voltage and in the case of the ClInPc and VOPc results in an increase in the overall power conversion efficiency. Through measurement of external quantum efficiency, it is shown that the increased efficiency is due to increased V_oc and not due to the photocurrent contribution from the complementary absorption profile of rubrene. Finally, the photostability of rubrene-based cells is studied, showing that unencapsulated devices decay rapidly in air as a result of the formation of rubrene peroxide, as evidenced by significant decay of the UV–vis absorption and direct measurement of the cell performance over a time period as short as several minutes.     

Heteromorphic chloroindium phthalocyanine films for improved photovoltaic performance

A new structure incorporating multiple phases of chloroindium phthalocyanine (ClInPc) is fabricated and tested in photovoltaic devices. This so-called heteromorphic structure includes as-deposited and THF vapor treated ClInPc films to improve absorption and photovoltaic (PV) performance in devices. Absorption of the polymorphic phases of ClInPc are complementary and lead to improved current generation. Short circuit current is improved by over 70% using the heteromorphic structure, while power conversion efficiency (PCE) improves by more than 40% versus solely as-deposited devices. Advantages of the heteromorphic structure include broader spectral response, improved interfacial contact area and an intermediary open circuit voltage (V_oc).     

Unified soft breakdown MOSFETs compact model: From experiments to circuit simulation

Several simplifications on MOSFET compact model for oxide breakdown degradation are presented. The current partitioning coefficient is systematically investigated, including influence of drain voltage and increasing breakdown strength. It reveals that several conduction paths are formed during breakdown and that the reduction of channel conductance is the dominant phenomenon at operating voltages. Based on these observations, a new physically based compact model including soft breakdown (SBD) is proposed. KW: soft breakdown, characterization, modeling, reliability.     

Optical and electrical characterization of thin films based on anthracene polyether polymers

Two new anthracene derivatives were characterized to improve the optoelectronic properties of π-conjugated anthracene polymers. The optical properties of the polymers were investigated by UV-visible absorption and photoluminescence (PL) spectroscopy. The energy bandgaps of anthracene-based polyether thin films were in the range 2.8–2.97 eV. Green emission (504 nm) was observed for anthracene/bisphenol A (An-BPA) and green-yellow emission (563 nm) for anthracene/fluorinated bisphenol A. (An-BPAF) Organic diodes formed by sandwiching anthracene layers between indium–tin oxide (ITO) and aluminum contacts were characterized. The dc electrical properties of ITO/anthracene derivatives/Al diodes were studied using current–voltage measurements and showed ohmic behavior at low voltage. The conduction mechanism seems to be a space-charge-limited current with exponential trap distribution at high applied bias voltage. The ac electrical transport of the anthracene derivatives was studied as a function of frequency (100 Hz–10 MHz) and applied bias in impedance spectroscopy analyses. We interpreted Cole–Cole plots in terms of the equivalent circuit model as a single parallel resistance and a capacitance network in series with a relatively small resistance. The evolution of the electrical parameters deduced from fitting of the experimental data is discussed. The conduction mechanism revealed by I–V characteristics is in agreement with the impedance spectroscopy results.     

Performance and reliability of advanced High-K/Metal gate stacks (Invited Paper)

This paper provides a systematic study of mobility performance and Bias Temperature Instabilities (BTI) reliability in advanced dielectrics stacks. By studying a large variety of dielectric stacks we clearly demonstrate that mobility performance, interface defects Nit and Negative BTI reliability are strongly correlated. All are affected by nitrogen species N which is clearly identified as the main mobility killer when it reaches unintentionally the Si interface during the deposition of nitrided gates or the nitridation steps.     

Modelling solar effects on the heat and mass transfer in a street canyon, a simplified approach

In urban areas, the climatic loads on buildings in summer conditions are largely affected by solar radiation. In this paper a modified simplified method for radiant interchange determination is used in a solar energy study. The good agreement with the radiosity method allows one to use this simplified method in the street canyon case. In a building pilot study, parametric analysis and building thermal behaviour can be assessed by simplified models which are useful for long-period simulation. Then this radiant interchange model is introduced in a zonal model of a canyon street and performed with a variable climatic conditions show case. The solar radiation is the only driving force in the street air movement. The interest of such approach for complex coupled phenomena studies is highlighted by obtained results and the assessment of variable climatic loads for different building zones can be considered with the model detailed herein. Future developments are planned in order to improve simulation accuracy by the addition of other local phenomena.     

Assessment of temperature gradient effects on moisture transfer through thermogradient coefficient

The objective of this paper is to describe moisture transfer through porous material due to temperature gradient. For that purpose, an experimental device was set up to assess moisture flux under isothermal and non-isothermal conditions. This involves placing samples between two compartments with controlled air conditions and monitoring relative humidity and temperature profiles inside the samples over the time. To interpret these results, we proposed to express the mass flux in terms of two driving potentials: water vapor content gradient and temperature gradient. Accordingly, thermogradient coefficient was calculated and discussed. It represents the difference between the moisture fluxes under isothermal and non-isothermal conditions. The impact of temperature gradient on the moisture buffer value (MBV) was also considered through a numerical experiment taking into account thermogradient coefficient. Results show that temperature gradient implies a relative variation of the MBV for about 14%. Thus, it would be better to consider non-isothermal conditions for its assessment.     

Engineering the Surface Chemistry and Morphology of Polymeric Carbon Nitrides Towards Greener Heterogeneous Catalysts for Biodiesel Synthesis

Biodiesel remains one of the most promising alternatives to replace fossil fuel-derived petrodiesel. Nonetheless, conventional biodiesel synthesis relies on homogeneous alkali-based catalysts that involve long and tedious purification steps , increasing biodiesel production costs. Heterogeneous catalysts have emerged as promising alternatives to circumvent these drawbacks, as they can easily be recovered and reused. Herein, polymeric carbon nitride dots and nanosheets are synthesized through a solid-phase reaction between urea and sodium citrate. Their morphology and surface chemistry are tuned by varying the precursor's ratio, and the materials are investigated as catalysts in the transesterification reaction of canola oil to biodiesel. A conversion of > 98% is achieved using a 5 wt% catalyst loading, oil to methanol ratio of 1:36 at 90 °C for 4 h, with the performance maintained over at least five reuse cycles. In addition, the effect of the transesterification reaction parameters on the reaction kinetics is evaluated, which follows a pseudo-first-order (PFO) regime. Combined with a deep understanding of the catalyst's surface, these results have allowed us to propose a reaction mechanism similar to the one observed for homogenous alkali catalysts. These carbon nitride-based nanoparticles offer a metal-free and cost-effective alternative to conventional homogeneous and metal-based heterogeneous catalysts.