Transmission electron microscope specimen preparation of Zn powders using the focused ion beam lift-out technique

Particles of Zn powder have been studied to show that high-quality scanning electron microscope (SEM) and transmission electron microscope (TEM) specimens can be rapidly produced from a site-specific region on a chosen particle by the focused ion beam (FIB) lift-out technique. A TEM specimen approximately 20-μm long by 5-μm wide was milled to electron transparency, extracted from the bulk particle, and micromanipulated onto a carbon coated copper mesh TEM grid. Using the FIB lift-out method, we were able to prepare a site-specific TEM specimen from a difficult material in under 3 hours. The TEM analysis of the lift-out specimen revealed a large amount of thin area free from characteristic signs of damage that may be observed as a result of conventional argon ion milling. The overall microstructure of the specimen prepared by the FIB lift-out method was consistent with samples prepared by conventional metallographic methods. A grain size of ∼10 to 20 μm was observed in all specimens by both TEM and SEM analysis. Light optical microscopy revealed the presence of internal voids in ∼10 to 20 pct of all particles. The SEM analysis showed the voids to extend over ∼70 pct of the particle volume in some cases.     

Single wall nanotube and vapor grown carbon fiber reinforced polymers processed by extrusion freeform fabrication

Single wall carbon nanotubes (SWNTs) and vapor grown carbon fibers (VGCFs) were compounded with poly(acrylonitrile-co-butadiene-co-styrene) (ABS) to create composite materials for use with Extrusion Freeform Fabrication (EFF). The composite materials possessed homogeneously dispersed fibers that were oriented with EFF processing. The VGCF and SWNT reinforced materials processed by EFF displayed improved tensile modulus compared to similarly processed ABS and composite material with isotropic fiber orientation, and the SWNT reinforced material displayed the highest properties, strength and modulus, of the materials studied. The materials containing oriented VGCFs and SWNTs showed modulus improvements of 44 and 93%, respectively.     

Comparative study on the effect of misalignment on bordered and borderless contacts

Continued shrinking of feature sizes in integrated circuits has raised increasing reliability concern. In order to achieve higher packing density, interconnects are migrating toward borderless contacts and vias. The penalty with the absence of metal extension, however, is the decrease in electromigration lifetimes. The issue is particularly critical when there is a misalignment between the contact and metal line, which may occur due to process variability. In this paper, we studied the effect of misalignment on the electromigration lifetimes for bordered and borderless contacts. We found that the misalignment effect becomes more pronounced in borderless contacts. We also studied the case of multiple contact configuration. The results indicate that electromigration lifetimes increase with increasing number of contacts in series. The experimental data is consistent with finite element modeling results.     

Chemically Functionalized Reduced Graphene Oxide as Additives in Polyethylene Composites for Space Applications

The discovery of radiation-shielding materials remains a critical technology to enable long-term space travel and extraterrestrial colonization. Hydrocarbon polymers, such as high-density polyethylene (HDPE), are among the best radiation attenuators due to their rich H content and lightweight. Due to their simple chemical structure that lacks larger heteroatoms, HDPE is also resistant to numerous radiation-induced degradation pathways that often limit the applicability of more sophisticated polymers. One drawback of hydrocarbon polymers is their inferior mechanical properties, such as tensile strength and impact toughness, relative to metals and other high-performance polymer systems. In this report, we develop an alkylated reduced graphene oxide that is used as an additive to enhance the storage and tensile moduli of HDPE by 10–15% across the lunar temperature range. These additives outperform unmodified reduced graphene oxide by 30% due to better dispersion through the polymer matrix as observed by cross-sectional scanning electron microscopy. POLYM. ENG. SCI., 60:86–94, 2020. © 2019 Society of Plastics Engineers     

Plasma-induced fluctuations in CO2lasers

Data giving the parametric dependence of plasma-induced fluctuations termed random noise and striation oscillations are presented for CO2lasers and compared to He-Ne devices.     

Network behavior of thermosetting polyimide/multiwalled carbon nanotube composites

In previous published research, network formation has been used to understand morphology and properties in polymer nanocomposites containing carbon nanotubes (CNTs) through measurements of rheological and electrical percolation thresholds, largely in thermoplastic matrices. In this research, these tools are explored as a means to understand network transport mechanisms and changes in CNT dispersion during curing in a thermosetting matrix. Specifically, rheological and electrical measurements were performed on the uncured nanocomposites, and electrical measurements were performed on the cured nanocomposites. The resulting data were applied to a percolation model. The results showed that the uncured resin played a limited role in mediating rheological transport and that little CNT aggregation occurred during curing. The results of this initial work suggest that such a combination of techniques is applicable to understanding dispersion changes resulting from curing and provides complementary insight to that provided by electron microscopy imaging of the same phenomenon.     

Membranes for Kraft black liquor concentration and chemical recovery: Current progress,challenges, and opportunities

Membranes can significantly reduce energy consumption during concentration of black liquor (BL) in the Kraft papermaking process, but the harsh conditions (pH ~12, 80°C–95°C, ~15 wt% solids) make this challenging. We elucidate challenges and opportunities for membranes in BL applications. We critically review membrane materials, processes, and operational modes investigated in the literature. Future advances will involve fabrication of higher-rejecting (≥95% lignin and inorganics), BL-resistant, NF, and RO membranes. Opportunities exist for molecular sieving and electrically driven membranes to recover other valuable chemicals such as carboxylic acids. We also discuss the economics of BL concentration with a single-stage membrane process.