Large-Area Uniform 1-nm-Level Amorphous Carbon Layers from 3D Conformal Polymer Brushes. A "Next-Generation" Cu Diffusion Barrier?

A reliable method for preparing a conformal amorphous carbon (a-C) layer with a thickness of 1-nm-level, is tested as a possible Cu diffusion barrier layer for next-generation ultrahigh-density semiconductor device miniaturization. A polystyrene brush of uniform thickness is grafted onto 4-inch SiO2 /Si wafer substrates with "self-limiting" chemistry favoring such a uniform layer. UV crosslinking and subsequent carbonization transforms this polymer film into an ultrathin a-C layer without pinholes or hillocks. The uniform coating of nonplanar regions or surfaces is also possible. The Cu diffusion "blocking ability" is evaluated by time-dependent dielectric breakdown (TDDB) tests using a metal-oxide-semiconductor (MOS) capacitor structure. A 0.82 nm-thick a-C barrier gives TDDB lifetimes 3.3× longer than that obtained using the conventional 1.0 nm-thick TaNx diffusion barrier. In addition, this exceptionally uniform ultrathin polymer and a-C film layers hold promise for selective ion permeable membranes, electrically and thermally insulating films in electronics, slits of angstrom-scale thickness, and, when appropriately functionalized, as a robust ultrathin coating with many other potential applications.

Year-to-year variation in phytoplankton biomass in an anthropogenically polluted and complex estuary: A novel paradigm for river discharge influence.

We examined the effects of nutrient availability and turbidity on phytoplankton biomass over 9 years in Gwanyang Bay, Korea, which is an anthropogenically polluted and complex estuary. While dredging and reclamation shaped geochemical features, river discharge with low-turbidity water and sewage treatment plants contributed to nutrient loading. The replete levels of nutrients and short water-residence time suggest the inapplicability of the washout theory, whereas the presence of NH4+ suppressed the growth of phytoplankton. A reduction in the river discharge caused a concomitant decline in the loading and dilution of suspended particles. All these features led to an increase in SPM, light limitation, and NH4+ concentration. GLM estimates revealed negative effects of NH4+ and SPM on chlorophyll a over 9 years while SEM verified synergistic effects of NH4+ and SPM compared with positive effects of NO2 + NO3-. Our findings provide new insights into phytoplankton bloom dynamics in Gwangyang Bay.

Effect of the Bilayer Period of Atomic Layer Deposition on the Growth Behavior and Electrical Properties of the Amorphous In-Zn-O Film.

This study reports on the effect of a bilayer period on the growth behavior, microstructure evolution, and electrical properties of atomic layer deposition (ALD) deposited In-Zn-O (IZO) films, fixing the ALD cycle ratio of In-O/Zn-O as 9:1. Here, the bilayer period is defined as the total number of ALD cycles in one supercycle of In-O and Zn-O by alternately stacking Zn-O and In-O layers at a temperature of 220 °C. IZO films with a bilayer period from 10 to 40 cycles, namely, IZO[In-O/Zn-O = 9:1] to IZO[36:4], result to form an amorphous phase with a resistivity of 4.94 × 10-4 Ω·cm. However, by increasing the bilayer period above 100 cycles, the IZO films begin to form a mixed amorphous-nanocrystalline microstructure, resulting from the limited intermixing at the interfaces. Concomitantly, the overall film resistivity is considerably increased with a simultaneous decrease in both the carrier mobility and the concentration. These results not only reveal the importance of the bilayer period in designing the ALD stacking sequence in the ALD-IZO, but also provide the possibility of forming various multilayered materials with different electrical properties.

Self-Planarization of High-Performance Graphene Liquid Crystalline Fibers by Hydration.

Graphene fibers (GFs) are promising elements for flexible conductors and energy storage devices, while translating the extraordinary properties of individual graphene sheets into the macroscopically assembled 1D structures. We report that a small amount of water addition to the graphene oxide (GO) N-methyl-2-pyrrolidone (NMP) dispersion has significant influences on the mesophase structures and physical properties of wet-spun GFs. Notably, 2 wt % of water successfully hydrates GO flakes in NMP dope to form a stable graphene oxide liquid crystal (GOLC) phase. Furthermore, 4 wt % of water addition causes spontaneous planarization of wet-spun GFs. Motivated from these interesting findings, we develop highly electroconductive and mechanically strong flat GFs by introducing highly crystalline electrochemically exfoliated graphene (EG) in the wet-spinning of NMP-based GOLC fibers. The resultant high-performance hybrid GFs can be sewn on cloth, taking advantage of the mechanical robustness and high flexibility.

Highly reliable and low-noise solid-state nanopores with an atomic layer deposited ZnO membrane on a quartz substrate.

We present a fabrication scheme for a solid-state ZnO nanopore membrane directly deposited on top of a quartz substrate by atomic layer deposition (ALD) and investigate the characteristics of DNA translocation through the nanopores. We chose a ZnO membrane owing to its high isoelectric point (∼9.5) as well as its chemical and mechanical stability. Aside from the extremely low noise level exhibited by this device on a highly insulating and low dielectric quartz substrate, it also slows down the translocation speed of DNA by more than one order of magnitude as compared to that of a SiNx nanopore device. We propose that the electrostatic interaction between the positively charged ZnO nanopore wall, resulting from the high isoelectric point of ZnO, and the negatively charged phosphate backbone of DNA provides an additional frictional force that slows down the DNA translocation.