Perspectives on the design and control of multiscale systems

New applications in materials, medicine, and computers are being discovered where the control of events at the molecular and nanoscopic scales is critical to product quality, although the primary manipulation of these events during processing occurs at macroscopic length scales. This motivates the creation of tools for the design and control of multiscale systems that have length scales ranging from the atomistic to the macroscopic. This paper describes a systematic approach that consists of stochastic parameter sensitivity analysis, Bayesian parameter estimation applied to ab initio calculations and experimental data, model-based experimental design, hypothesis mechanism selection, and multistep optimization.     

Auger electron spectroscopy study of reactive ion etched silicon carbide

Reactive ion etching (RIE) of bulk 4H-SiC based on CHF₃-O₂ plasma was studied by varying the rf power and process pressure. The elements on the etched surface and the surface roughness were characterized by Auger electron spectroscopy and atomic force microscopy, respectively. It was found that the surface roughening is mainly caused by Al contamination and C rich layer (C residues) induced micromasking effect. The micromasking effect is in turn determined by the dc self-bias developed at the substrates. A threshold dc self-bias exists at around −320 to −330 V, beyond which no micromasking effect was observed. This observation is explained in terms of physical ion bombardment and sputtering in the RIE process.     

Deposition of polymeric nitrogenated amorphous carbon films (a-C:H:N) using electron cyclotron resonance CVD

In this paper the deposition of polymeric nitrogenated amorphous carbon (a-C:H:N) films from a mixture of hydrogen, methane and nitrogen, using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) system is reported. Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA) measurements were used to determine the actual amount of nitrogen, carbon and hydrogen in the films. The results showed that there is insignificant change in the atomic concentration of C but a slight decrease in the atomic concentration of H with increasing N incorporation. A slight decrease in the amount of bonded H and an increase in the C=N bond was also observed as deduced from infrared (IR) absorption measurements. The optical gap was found to decrease and the Urbach band tail width increase at larger N₂ flow ratio. The conductivity increased by three orders of magnitude compared to that of films prepared in the absence of N₂. The results suggest that the observed C=N double bond effectively bridges the aromatic rings resulting in a delocalization of carriers.     

Stabilization of oils by microencapsulation with heated protein-glucose syrup mixtures

The use of proteins [whey protein isolate (WPI) or soy protein isolate (SPI) in combination with dried glucose syrup (DGS) for stabilization of microencapsulated spray-dried emulsions containing tuna oil, palm stearin, or a tuna oil-palm stearin blend was investigated. Pre-emulsions containing heated (100°C/30 min) protein-DGS mixtures and oils at oil/protein ratios of 0.75∶1 to 4.5∶1 were homogenized at two passes (35+10 or 18+8 MPa) and spray-dried to produce 20–60% oil powders. Microencapsulation efficiency decreased at lower homogenization pressure and as the oil load in the powder was increased beyond 50% but was independent of the type of oil encapsulated and the total solids (TS) content of the emulsions (24–33% TS) prior to drying. Oxidative stabilities of the powders, as indicated by headspace propanal values and PV after 4 wk of storage at 23°C, generally decreased with increasing oil content and homogenization pressure but increased with increasing TS of the emulsion prior to drying. Powder containing palm stearin was more stable to oxidation than powders containing a 1∶1 ratio of palm stearin and tuna oil or only tuna oil. Heated WPI-DGS formulations were superior to corresponding formulations stabilized by heated SPI-DGS, producing spray-dried powders with higher microencapsulation efficiency and superior oxidative stability.     

Tensile,thermal, flammability and morphological properties of sepiolite filled ethylene propylene diene monomer (EDPM) rubber composites

The effect of sepiolite loading content on the curing characteristics, tensile mechanical, thermal, swelling, flammability and morphological properties of sepiolite-filled ethylene propylene diene monomer (EPDM) composites was investigated. The composites were prepared with sepiolite loadings of 0–70 part per hundred (phr) of rubber using a two-roll mill. The results highlighted the improvement in the tensile properties and cross-link density values peaked at 60 phr of sepiolite loading. The scorch time, curing time, swelling percentage, and linear burning rate of the composites decreased with an increase in sepiolite loading. Thermogravimetric analysis showed an increasing trend with increase in sepiolite loading. The temperatures corresponding to 5, 25 and 50% weight loss (T_5wt%, T_25wt% and T_50wt%) and the percentage of char residue gradually increased with increase in sepiolite loading. The homogenous dispersion of the sepiolite particles in the EPDM matrix and the formation of zigzag structures, especially at 60 phr, were the main reasons of the improvement of mechanical properties which were confirmed by the morphological studies. The formation of a protective layer, which acted as a barrier against heat transfer into the deeper layers, enhanced the flammability resistance of the composites. Notably, the EPDM filled with 60 phr sepiolite exhibited excellent performance in the aspects of mechanical, thermal stability and flammability properties and resistance towards swelling.