Optical Properties of Tetrahedral Amorphous Carbon Films and Their Potential for Lab-on-a-Chip

In this study, tetrahedral amorphous carbon (ta-C) films with thicknesses between several 100 nm and several micrometers have been deposited onto polished tungsten carbide and steel substrates by pulsed laser deposition (PLD) using an excimer laser (248 nm wavelength). We investigate the optical properties (e.g. the refractive index (n) and extinction coefficient (k) in the visible and near-infrared wavelength range) of these layers in dependence of the used laser ablation fluence on the target. It is shown that n of ~2000 nm thick ta-C films can be tuned, depending on the sp3-content, between n = 2.5 and 2.8 at a wavelength of 632 nm. Besides of this k reduces with the sp3-content and is as low as 0.03 at sp3-contents of more than 75%. We proof that this gives the opportunity to prepare coating with tailored optical properties. Furthermore, it is shown that the ta-C films have low background fluorescence in the wavelengths range of 380 - 750 nm, which make this thin films attractive for certain optical, medical and biotechnological applications. We present for the first time that one possible application is the use in Lab-on-a-Chip-systems (LOC). Within these systems, the ultrasensitive detection of fluorescence markers and dyes is a challenge. In order to increase the signal-to-noise-ratio, a setup was developed, that used the specific optical properties of ta-C films produced by PLD. We used the ta-C film as an integrated reflector that combined low background fluorescence, a low reflectivity at the excitation wavelength and the high reflectivity at the emission wavelength. We prove that this setup improves the detection of fluorescence photons.

Targeting new ways for large-scale,high-speed surface functionalization using direct laser interference patterning in a roll-to-roll process

Direct Laser Interference Patterning(DLIP)is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm.The raw beam having a diameter of 3 mm@1/e^(2) is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS■-L element and cylindrical telescopes.The shaped beam is split into its diffraction orders,where the two first orders are parallelized and guided into a galvanometer scanner.The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern.The DLIP spot has a line-like interference pattern with about 15μm spatial period.Laser fluences of up to 8 J cm^(-2) were achieved using a maximum pulse energy of 0.6 mJ.Furthermore,an in-house built roll-to-roll machine was developed.Using this setup,aluminum and copper foil of 20μm and 9μm thickness,respectively,could be processed.Subsequently to current collector structuring coating of composite electrode material took place.In case of lithium nickel manganese cobalt oxide(NMC 622)cathode deposited onto textured aluminum current collector,an increased specific discharge capacity could be achieved at a C-rate of 1℃.For the silicon/graphite anode material deposited onto textured copper current collector,an improved rate capability at all C-rates between C/10 and 5℃ was achieved.The rate capability was increased up to 100%compared to reference material.At C-rates between C/2 and 2℃,the specific discharge capacity was increased to 200 mAh g^(-1),while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 m Ah g^(-1),showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.

Influence of Deposition Temperature on the Electrical and Electrochemical Properties of Carbon-Based Coatings for Metallic Bipolar Plates, Prepared by Cathodic Arc Evaporation

Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the deposition of tribological coatings. In this study, anti-corrosive and electrical conductive carbon-based coatings with a metallic interlayer were prepared on stainless steel substrates as surface modification for metallic bipolar plates. Hereby, the influence of the deposition temperature during the deposition of the carbon top layer was investigated. Raman spectroscopy revealed differences in the microstructure at 200°C compared to 300°C and 100°C. Measurements of the interfacial contact resistance showed that the deposited coatings significantly improve the electrical conductivity. There are only minor differences between the different carbon top layers. The corrosion resistance of the coatings was studied via potentiodynamic polarization at room temperature and 80°C. Experiments showed that the coating with a carbon top layer deposited at 200°C, considerably reduces the current density and thus corrosion of the substrate is suppressed.

Development of a Graphite Coating and Its Transfer from Batch to Coil Process for Application in PEMFC for Hydrogen-Powered Vehicles

In the present paper, coating systems consisting of a metallic corrosion barrier and a conductive graphitic carbon layer were deposited by a DC vacuum arc process. The coatings were developed in a batch process for application in the polymer electrolyte membrane fuel cell (PEMFC), and transferred to a continuous coil process to facilitate industrial mass production. The coating samples in the coil process had to achieve comparable results to the samples produced in the batch process, to meet the requirements of the environment prevailing in the fuel cell.The transfer to roll-to-roll processes is a crucial factor for commercial upscaling of PEMFC production. The experimental results showed that the electrical conductivity and corrosion resistance of the samples in the coil process were significantly improved compared to the uncoated base material and showed comparable performance to batch coated samples. X-ray photoelectron spectroscopy (XPS) was performed to determine the depth profile and the surface composition. Additional measurements were recorded for the contact resistances using the four-wire sensing method as well as corrosion resistance using potentiodynamic methods.

A Mixed Ether Electrolyte for Lithium Metal Anode Protection in Working Lithium-Sulfur Batteries

Lithium-sulfur(Li-S) battery is considered as a promising energy storage system to realize high energy density.Nevertheless,unstable lithium metal anode emerges as the bottleneck toward practical applications,especially with limited anode excess required in a working full cell.In this contribution,a mixed diisopropyl ether-based(mixed-DIPE) electrolyte was proposed to effectively protect lithium metal anode in Li-S batteries with sulfurized polyacrylonitrile(SPAN) cathodes.The mixed-DIPE electrolyte improves the compatibility to lithium metal and suppresses the dissolution of lithium polysulfides,rendering significantly improved cycling stability.Concretely,Li | Cu half-cells with the mixed-DIPE electrolyte cycled stably for 120 cycles,which is nearly five times longer than that with routine carbonate-based electrolyte.Moreover,the mixedDIPE electrolyte contributed to a doubled life span of 156 cycles at 0.5 C in Li | SPAN full cells with ultrathin 50 μm Li metal anodes compared with the routine electrolyte.This contribution affords an effective electrolyte formula for Li metal anode protection and is expected to propel the practical applications of high-energy-density Li-S batteries.

Mechanical Properties of Remote-Laser Cut CFRP and Thermographic Laser-Process Monitoring

Remote-laser beam cutting is a productive technology without tool wear. Especially when cutting carbon fiber reinforced polymers (CFRP), it offers constant manufacturing quality. Since it is a thermal process, a heat-affected zone (HAZ) is formed at the edge of the cut. Based on quasi-static and cyclic mechanical tests on open-hole specimens, the influence of the process on the mechanical properties of CFRP is shown. The quasi-static tests are in good correlation with results from other researchers by indicating an increase in the maximum tensile stress of the test specimens, cut by remote-laser. The reason is the rearrangement of the shear stresses and a reduction of the notch stress concentration. However, the results of the present study show that excessive expansion of the HAZ leads to a reduction in the maximum tensile stress compared to milled test specimens. Under cyclic load conditions, remote-laser beam cutting does not lead to a more pronounced degradation than milling. The mechanical properties of the notched test pieces are sensitive to the expansion of the HAZ. For the production of components it is therefore necessary that the remote-laser beam cutting is carried out under controlled and documentable conditions. For this purpose, process thermography was tested as a tool for quality assurance. The results show that the technology is basically suitable for this task.

陶瓷基体热喷涂涂层的研究进展

由于表面改性的需要,陶瓷基体对热喷涂涂层方案的需求也在日益增加。根据基体结构和性能的不同,需要开发特殊的基体相关的制备概念。本文展示一些在烧结氮化硅和AlN陶瓷上沉积涂层的概念。使用传统的喷砂工艺处理的基体近表面区域粗糙度低并会带来损害。作为替代方法 ,激光刻蚀被用来改变陶瓷基体的热喷涂表面特性。通过选择适当的激光刻蚀参数和喷涂方法,成功地制备了与陶瓷基体具有良好结合性能的大气等离子喷涂(APS)和悬浮液超音速火焰喷涂(suspension-HVOFAl2O3)涂层。

Measurement and analysis technologies for magnetic pulse welding： established methods and new strategies

Magnetic pulse welding （MPW） is a fast and clean joining technique that offers the possibility to weld dissimilar metals, e.g., aluminum and steel. The high-speed collision of the joining partners is used to generate strong atomic bonded areas. Critical brittle intermetallic phases can be avoided due to the absence of external heat. These features attract the notice of industries performing large scale productions of dissimilar metal joints, like automo- tive and plant engineering. The most important issue is to guarantee a proper weld quality. Numerical simulations are often used to predict the welding result a priori. Nevertheless, experiments and the measurement of process parameters are needed for the validation of these data. Sensors nearby the joining zone are exposed to high pressures and intense magnetic fields which hinder the evaluation of the electrical output signals. In this paper, existing analysis tools for process development and quality assurance in MPW are reviewed. New methods for the process monitoring and weld characterization during and after MPW are introduced, which help to overcome the mentioned drawbacks of established technologies. These methods are based on optical and mechanical measuring technologies taking advantage of the hypervelocity impact flash, the impact pressure and the deformation necessary for the weld formation.

The role of polysulfide-saturation in electrolytes for high power applications of real world Li-S pouch cells

The lithium-sulfur(Li-S)technology is the most promising candidate for next-generation batteries due to its high theoretical specific energy and steady progress for applications requiring lightweight batteries such as aviation or heavy electric vehicles.For these applications,however,the rate capability of Li-S cells requires significant improvement.Advanced electrolyte formulations in Li-S batteries enable new pathways for cell development and adjustment of all components.However,their rate capability at pouch cell level is often neither evaluated nor compared to state of the art(SOTA)LiTFSI/dimethoxyethane/dioxolane(LITFSI:lithium-bis(trifluoromethylsulfonyl)imide)electrolyte.Herein,the combination of the sparingly polysulfide(PS)solvating hexylmethylether/1,2-dimethoxyethane(HME/DME)electrolyte and highly conductive carbon nanotube Buckypaper(CNT-BP)with low porosity was evaluated in both coin and pouch cells and compared to dimethoxyethane/dioxolane reference electrolyte.An advanced sulfur transfer melt infiltration was employed for cathode production with CNT-BP.The Li+ion coordination in the HME/DME electrolyte was investigated by nuclear magnetic resonance(NMR)and Raman spectroscopy.Additionally,ionic conductivity and viscosity was investigated for the pristine electrolyte and a polysulfide-statured solution.Both electrolytes,DME/DOL-1/1(DOL:1,3-dioxolane)and HME/DME-8/2,are then combined with CNT-BP and transferred to multi-layered pouch cells.This study reveals that the ionic conductivity of the electrolyte increases drastically over state of(dis)charge especially for DME/DOL electrolyte and lean electrolyte regime leading to a better rate capability for the sparingly polysulfide solvating electrolyte.The evaluation in prototype cells is an important step towards bespoke adaption of Li-S batteries for practical applications.

Mechanism of superlubricity of a DLC/Si_(3)N_(4) contact in the presence of castor oil and other green lubricants

To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbon coatings with varying fraction of sp^(2) and sp^(3) hybridized carbon in presence of a commercially available silicon nitride bulk ceramic,castor oil provides superlubricity although the liquid vegetable oil film in the contact is only a few nanometres thick at most.Besides a partial liquid film possibly separating surfaces in contact,local tribochemical reactions between asperities are essential to maintain superlubricity at low speeds.High local pressure activates chemical degradation of castor oil generating graphitic/graphenic-like species on top of asperities,thus helping both the chemical polishing of surface and its chemical passivation by H and OH species.Particularly,the formation of the formation of–(CH_(2)–CH_(2))n–noligomers have been evidenced to have a major role in the friction reduction.Computer simulation unveils that formation of chemical degradation products of castor oil on friction surfaces are favoured by the quantity of sp^(2)-hybridized carbon atoms in the amorphous carbon structure.Hence,tuning sp^(2)-carbon content in hydrogen-free amorphous carbon,in particular,on the top layers of the coating,provides an alternative way to control superlubricity achieved with castor oil and other selected green lubricants.

Life cycle safety issues of lithium metal batteries:A perspective

The rising lithium metal batteries(LMBs)demonstrate a huge potential for improving the utilization duration of energy storage devices due to high theoretical energy density.Benefiting from the designs in the electrolyte,interface,and lithium host,several attempts have been made in the commercial application of LMBs.However,the application of lithium anode introduces additional safety risks and potential catastrophic accidents due to the high activity of lithium metal and dendrite during the electrochemical cycles.A comprehensive understanding of challenges and design issues on the safety hazards of LMBs in life cycle management is imperative for safe and commercial applications of LMBs.This paper first reviews emerging key safety issues and promising corresponding enhancements of LMBs during their production,utilization,and recycling.The wet air instability of lithium metal anode and gas production during activation have undoubtedly become the most intractable problems in LMBs production.It is necessary to use spraying technology to build a good protection layer upon lithium metal anode.Then,the growth of lithium dendrites poses a higher challenge to the utilization of LMBs,which requires the design of better electrolyte,anode skeleton,and other strategies as well as the prediction of LMBs life through big data and other methods.As for LMBs recovery,it is of great significance to choose the solvent to effectively control the consumption rate and temperature of highly reactive lithium metal powder.At last,further appeals and improvements are proposed for inspiring more related research to push forward the commercial use of LMBs.