In our previous study, electrically induced mechanical stress was produced on monolithic polycarbonate (PC) films under a DC voltage using a needle‐plane electrode setup. This study investigated other materials with various structures and dielectric constants, in order to further understand the deformation mechanism. It was found that the elastic behavior occurred at electric fields intensities below that initiating measurable surface deformation. The amorphous materials, PS, and the semi‐crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar observable deformation onset electric field at 200 MV/m. While PVDF, having a dielectric constant of 10.0–12.0, showed an onset at only 30 MV/m. The data was also compared to our previous study on PC. The depth and diameter of the deformation for all materials increased relative to the applied electric field up to film breakdown. Thermal annealing of the deformed films revealed a recoverable “delayed elastic” component and an irreversible “plastic” component. A three‐stage electrically induced mechanical deformation mechanism was proposed for amorphous materials, while a two‐stage mechanism was proposed for the semi‐crystalline materials. The difference on the energy loss versus deformed volume for amorphous and semi‐crystalline polymers was also determined and discussed.
Layer thickness was found to have a significant effect on the irreversible electromechanical deformation and the failure mechanism in polycarbonate (PC)/poly (vinylidene fluoride) (PVDF) multilayered films when subjected to an electrical impulse in a DC needle‐plane configuration. Three distinct regions of behavior were observed. Region I comprised thick layer systems that exhibited only irreversible center deformation. The improvement to failure resistance compared to the monolithic films was attributed to the interphase between the two components. Region II films with an intermediate layer thickness showed both an irreversible center deformation and a treeing mechanism which were observed to simultaneously occur. The surface treeing mechanism, similar to the lightning treeing phenomena in nature, occurs only at impact rates. The tree morphology showed large amounts of plowing, indicating that this damage mechanism can dissipate a large amount of energy prior to electromechanical fracture of the film. Region III films comprise ultrathin layers in the nanoscale and showed no treeing. The unique interphase region between these ultrathin layers was estimated to be at least ten percent of the overall layered structure. These films behaved similar to monolithic materials with improved electromechanical failure characteristics. This work complements the enhanced dielectric performance of multilayer films observed in earlier investigations.
more » « less- NSF-PAR ID:
- 10454599
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Applied Polymer Science
- Volume:
- 138
- Issue:
- 17
- ISSN:
- 0021-8995
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Plasma-enhanced atomic layer deposition (PEALD) enables the epitaxial growth of ultrathin indium nitride (InN) films at significantly reduced process temperatures and with greater control of layer thickness compared to other growth methods. However, the reliance on plasma-surface interactions increases the complexity of the growth process. A detailed understanding of the relationship between the plasma properties and the growth kinetics is therefore required to guide the tuning of growth parameters. We present an in situ investigation of the early-stage PEALD growth kinetics of epitaxial InN within three different plasma regimes using grazing incidence small-angle x-ray scattering (GISAXS). The GISAXS data are supported by diagnostic studies of the plasma species generation in the inductively coupled plasma source as a function of the relative concentrations of the nitrogen/argon gas mixture used in the growth process. The growth mode is found to be correlated to the production of nitrogen species in the plasma, with high concentrations of the atomic N species promoting Volmer–Weber growth (i.e., island growth) and low concentrations promoting Stranski–Krastanov growth (i.e., layer-plus-island growth). The critical thickness for island formation, island center-to-center distance, and island radius are found to increase with ion flux. Furthermore, the island center-to-center distance and areal density are observed to change only during plasma exposure and to continue changing with exposure even after the methylindium adlayer is believed to have fully reacted with the plasma. Our results demonstrate the potential to control the growth kinetics during PEALD of epitaxial films by intentionally accessing specific regimes of plasma species generation.
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Abstract The structural properties of co-deposited ultrathin PtSe 2 films grown at low temperatures by molecular beam epitaxy on c-plane Al 2 O 3 are studied. By simultaneously supplying a Se flux from a Knudsen cell and Pt atoms from an electron-beam evaporator, crystalline (001)-oriented PtSe 2 films were formed between 200 °C and 300 °C. The long separation between substrate and electron beam evaporator of about 60 cm ensured minimal thermal load. At optimum deposition temperatures, a ten times or even higher supply rate of Se compared to Pt ensured that the pronounced volatility of the Se was compensated and the PtSe 2 phase was formed and stabilized at the growth front. Postgrowth anneals under a Se flux was found to dramatically improve the crystalline quality of the films. Even before the postgrowth anneal in Se, the crystallinity of PtSe 2 films grown with the co-deposition method was superior to films realized by thermal assisted conversion. Postgrowth annealed films showed Raman modes with narrower peaks and more than twice the intensity. Transmission electron microscopy investigations revealed that the deposited material transitioned to a two-dimensional layered structure only after the postgrowth anneal. PtSe 2 growth was found to start as single layer islands that preferentially nucleated at atomic steps of the substrate and progressed in a layer-by-layer like fashion. A close to ideal wetting behavior resulted in coalesced PtSe 2 films after depositing about 1.5 PtSe 2 layers. Detailed Raman investigation of the observed PtSe 2 layer breathing modes of films grown under optimized co-deposition conditions revealed an interlayer coupling force constant of 5.0–5.6 × 10 19 N m −3 .more » « less
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Ever-increasing demands for energy, particularly being environmentally friendly have promoted the transition from fossil fuels to renewable energy.1Lithium-ion batteries (LIBs), arguably the most well-studied energy storage system, have dominated the energy market since their advent in the 1990s.2However, challenging issues regarding safety, supply of lithium, and high price of lithium resources limit the further advancement of LIBs for large-scale energy storage applications.3Therefore, attention is being concentrated on an alternative electrochemical energy storage device that features high safety, low cost, and long cycle life. Rechargeable aqueous zinc-ion batteries (ZIBs) is considered one of the most promising alternative energy storage systems due to the high theoretical energy and power densities where the multiple electrons (Zn2+) . In addition, aqueous ZIBs are safer due to non-flammable electrolyte (e.g., typically aqueous solution) and can be manufactured since they can be assembled in ambient air conditions.4As an essential component in aqueous Zn-based batteries, the Zn metal anode generally suffers from the growth of dendrites, which would affect battery performance in several ways. Second, the led by the loose structure of Zn dendrite may reduce the coulombic efficiency and shorten the battery lifespan.5
Several approaches were suggested to improve the electrochemical stability of ZIBs, such as implementing an interfacial buffer layer that separates the active Zn from the bulk electrolyte.6However, the and thick thickness of the conventional Zn metal foils remain a critical challenge in this field, which may diminish the energy density of the battery drastically. According to a theretical calculation, the thickness of a Zn metal anode with an areal capacity of 1 mAh cm-2is about 1.7 μm. However, existing extrusion-based fabrication technologies are not capable of downscaling the thickness Zn metal foils below 20 μm.
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Obama, B., The irreversible momentum of clean energy.
Science 2017, 355 (6321), 126-129.Goodenough, J. B.; Park, K. S., The Li-ion rechargeable battery: a perspective.
J Am Chem Soc 2013, 135 (4), 1167-76.Li, C.; Xie, X.; Liang, S.; Zhou, J., Issues and Future Perspective on Zinc Metal Anode for Rechargeable Aqueous Zinc‐ion Batteries.
Energy & Environmental Materials 2020, 3 (2), 146-159.Jia, H.; Wang, Z.; Tawiah, B.; Wang, Y.; Chan, C.-Y.; Fei, B.; Pan, F., Recent advances in zinc anodes for high-performance aqueous Zn-ion batteries.
Nano Energy 2020, 70 .Yang, J.; Yin, B.; Sun, Y.; Pan, H.; Sun, W.; Jia, B.; Zhang, S.; Ma, T., Zinc Anode for Mild Aqueous Zinc-Ion Batteries: Challenges, Strategies, and Perspectives.
Nanomicro Lett 2022, 14 (1), 42.Yang, Q.; Li, Q.; Liu, Z.; Wang, D.; Guo, Y.; Li, X.; Tang, Y.; Li, H.; Dong, B.; Zhi, C., Dendrites in Zn-Based Batteries.
Adv Mater 2020, 32 (48), e2001854.Acknowledgment
This work was partially supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 22011044) by KRISS.
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In the limit of a large yield stress, or equivalently at the initiation of motion, viscoplastic flows can develop narrow boundary layers that provide either surfaces of failure between rigid plugs, the lubrication between a plugged flow and a wall or buffers for regions of predominantly plastic deformation. Oldroyd ( Proc. Camb. Phil. Soc. , vol. 43, 1947, pp. 383–395) presented the first theoretical discussion of these viscoplastic boundary layers, offering an asymptotic reduction of the governing equations and a discussion of some model flow problems. However, the complicated nonlinear form of Oldroyd’s boundary-layer equations has evidently precluded further discussion of them. In the current paper, we revisit Oldroyd’s viscoplastic boundary-layer analysis and his canonical examples of a jet-like intrusion and flow past a thin plate. We also consider flow down channels with either sudden expansions or wavy walls. In all these examples, we verify that viscoplastic boundary layers form as envisioned by Oldroyd. For each example, we extract the dependence of the boundary-layer thickness and flow profiles on the dimensionless yield-stress parameter (Bingham number). We find that, while Oldroyd’s boundary-layer theory applies to free viscoplastic shear layers, it does not apply when the boundary layer is adjacent to a wall, as has been observed previously for two-dimensional flow around circular obstructions. Instead, the boundary-layer thickness scales in a different fashion with the Bingham number, as suggested by classical solutions for plane-parallel flows, lubrication theory and, for flow around a plate, by Piau ( J. Non-Newtonian Fluid Mech. , vol. 102, 2002, pp. 193–218); we rationalize this second scaling and provide an alternative boundary-layer theory.more » « less
