Research in semi-crystalline polymer thin films has seen significant growth due to their fascinating thermal, mechanical, and electronic properties. In all applications, acquiring precise control over the film morphology atop various substrates or in the free-standing film geometry is key to advancing product performance. This article reviews the crystallization of polymer thin films processed via physical vapor deposition (PVD). Classical PVD techniques are briefly reviewed, highlighting their working principles as well as successes and challenges to achieving morphological control of polymer films. Subsequently, the recent development of a unique PVD technique termed Matrix Assisted Pulsed Laser Evaporation (MAPLE) is highlighted. The non-destructive technology overcomes the major drawback of polymer degradation by classical PVD. Recent advances highlighting how MAPLE can be exploited to control polymer film morphology in ways not achievable by other methods are presented. Challenges and future scope of PVD for polymer film deposition concludes the review.
Lithium-ion batteries are widely used in many applications and it is important to monitor battery aging over time. However, it remains challenging to quickly and accurately measure aging. The correlation between battery mechanics and capacity fade can be a useful tool in battery diagnosis [1]. In this work, we present a method which uses the coupling between mechanics and electrochemistry to measure aging of a pouch cell. To quantify aging, state of health (SOH) measurements are often used. By measuring the initial peak stress and peak stress at later times, with the known stress-SOH relationship, the amount of aging can be determined [2]. We investigate the relationship between stress and SOH in different types of commercial batteries under various cycling ranges. A lithium ion pouch cell was constrained inside a fixture along with a sensor that monitors stresses. Pouch cells were cycled at two different rates, C/2 and C/4, under Constant Current Constant Voltage charging scheme. Every 50 cycles, capacity was accurately measured through a slow discharge. In this presentation, we present the stress evolutions of pouch cells cycled at various ranges, shown in Figure 1 [3]. Using a model, we show that the observed stress-SOH relationship is composed of a long term linear film growth and a short term non-linear stress relaxation, as indicated in Figure 2 [3]. The various cycling ranges cause the average stress level inside the batteries to vary, which leads to different levels of softening. Such stress relaxation mechanism first dominates the overall stress behavior, but is gradually overtaken by the linear stress-increasing mechanism due to film growth. Commercial batteries with different compositions exhibit qualitatively similar results on stress-SOH, but vary quantitatively due to differences in their mechanical properties. We characterize the mechanical responses of individual components and compare their softening behaviors under low stress ranges. Reference: Cannarella, John, and Craig B. Arnold. "Stress evolution and capacity fade in constrained lithium-ion pouch cells." Journal of Power Sources 245 (2014): 745-751. Cannarella, John, and Craig B. Arnold. "State of health and charge measurements in lithium-ion batteries using mechanical stress." Journal of Power Sources 269 (2014): 7-14. Liu, Xinyi M., and Craig B. Arnold. "Effects of Cycling Ranges on Stress and Capacity Fade in Lithium-Ion Pouch Cells." Journal of The Electrochemical Society 163.13 (2016): A2501-A2507. Figure Captions: Figure 1. a) Representative stress evolution profiles plotted using maximum and minimum stresses during each cycle for batteries cycled between 1) 75-100% SOC 2) 50-100% SOC 3) 25-100% SOC 4) 0-100% SOC. For every 50 cycles, capacity is measured at a C/10 rate through a full discharge. b) A comparison between stress evolution profiles of batteries cycled from 0% to 100% SOC and from 75% to 100% SOC. Figure 2. A comparison between experimental results and the fitted stress-SOH model. Figure 1
In this Research Article, we demonstrate pulsed laser processing of a silver nanowire network transparent conductor on top of an otherwise complete solar cell. The macroscopic pulsed laser irradiation serves to sinter nanowire-nanowire junctions on the nanoscale, leading to a much more conductive electrode. We fabricate hybrid silicon/organic heterojunction photovoltaic devices, which have ITO-free, solution processed, and laser processed transparent electrodes. Furthermore, devices which have high resistive losses show up to a 35% increase in power conversion efficiency after laser processing. We perform this study over a range of laser fluences, and a range of nanowire area coverage to investigate the sintering mechanism of nanowires inside of a device stack. The increase in device performance is modeled using a simple photovoltaic diode approach and compares favorably to the experimental data.
The Global Positioning System (GPS) has become a mature technology and is continually being applied in new and more demanding applications. A current effort in this area is the development of compact, durable but lightweight GPS antennas on conformal surfaces for handheld devices. Because modeling the electromagnetic performance of these antennas is often difficult, prototypes are typically built, measured and redesigned in an iterative process. We demonstrate the fabrication of a GPS conformal antenna under ambient-temperature conditions using a combination of laser micromachining and/or laser direct-write processes. The electromagnetic behavior of the antennas is then characterized and the design of the antenna structures is further optimized. Pattern simulations and input impedance measurements of the antenna are presented that demonstrate the usefulness and success of the iterative process made possible with this fabrication technique
Poly(vinyl chloride) (PVC) is being considered for use as a flow frame material in a developmental zinc/bromine battery. The choice of PVC was based on its low cost and the ease with which it can be molded into complex parts. The electrolyte used in this battery is a highly corrosive mixture of bromine, zinc bromide, zinc chloride, potassium bromide, potassium chloride and a quaternary amine salt. The quaternary salt serves to reduce the concentration of free bromine in the electrolyte by virtue of its complexing capability. It is well known that aqueous bromine is capable of oxidizing organic compounds. The purpose of the current study was to investigate the effect of a bromine electrolyte on two PVC formulations, PVC-1 and PVC-4. PVC-1 is the designation given to one of B.F. Goodrich's commercial formulations and is the present baseline material for the flow frame. PVC-4 is an experimental B.F. Goodrich formulation that was developed especially for battery applications. We sought answers to such questions as (1) does oxidation and/or bromination take place. (2) does bromine penetrate into the sample and, if so, how far. (3) how are the mechanical and morphological properties affected. and (4) are there differences in stability betweenmore » PVC-1 and PVC-4. To accelerate the aging processes we aged the PVC samples at an elevated temperature in an electrolyte which did not contain any complexing agent. 5 refs., 6 figs.« less
By employing different laser forward-transfer techniques, we probe the effects of transfer mechanism on the damage of sensitive organic molecules. Thick-film polymer absorbing layers provide the maximum optical and thermal protection for the molecules.
Traditional white-light and fluorescent imaging techniques provide powerful methods to extract high-resolution information from two-dimensional (2-D) sections, but to retrieve information from a three-dimensional (3-D) volume they require relatively slow scanning methods that result in increased acquisition time. Using an ultra-high speed liquid lens, we circumvent this problem by simultaneously acquiring images from multiple focal planes. We demonstrate this method by imaging microparticles and cells flowing in 3-D microfluidic channels.
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