bluuebunny/crossref_metadata_2025_split huggingface dataset:
Achieving Surface Finish Requirements on DMLS Parts with Precision Electrochemical Machining
Authors: Risko Donald G 
Published: February 2020

3D Additive Manufacturing is a fast growing technology with metallurgical properties of the “printed” parts achieving manufacturing requirements. Direct Metal Laser Sintering (DMLS) is one of the few additive manufacturing technologies being used in production. This technology is used to manufacture direct parts for a variety of industries including aerospace, dental, medical and other industries that have small to medium size, highly complex geometries. Part tolerance and surface finish are two of the main requirements in addition to metallurgy that must be met by the DMLS parts. Precision Electrochemical Machining (PECM) is a process capable of achieving these requirements on some applications at a significant cost advantage to other methods. One example will be described in detail in this paper of an aerospace application requiring a surface finish of 4 Ra micro inch on a complex surface.
(Invited) Development of High Mobility Polymer Semiconductors for p-Channel, n-Channel, and Ambipolar Thin Film Transistors
Authors: Li Yuning 
Published: February 2020

Polymer semiconductors are enabling materials for a wide range of printed electronics. As channel semiconductors for organic thin film transistors (OTFTs), charge carrier mobility on par with that of amorphous silicon (~0.5 cm2V-1s-1) or higher is required for many applications. The development of polymer semiconductors with high mobility and good ambient stability has been a great challenge. To improve the charge carrier transport, a combination of donor and acceptor units in an alternating fashion in the polymer backbone has been recently found very effective since the intermolecular donor-acceptor attraction can shorten the interchain distance. By utilizing this strategy, we have developed a number of donor-acceptor polymers semiconductors with very high mobility. One particular class of such polymers are based on a diketopyrrolopyrrole (DPP) acceptor building block. By carefully choosing the electron donor blocks, we have successfully developed p-type polymers with high mobility up to 6.9 cm2V-1s-1 and amibipolar polymers with balanced electron and hole mobility of 6.30 cm2V-1s-1 and 2.78 cm2V-1s-1, respectively. By using a ultra-thin layer (~2-5 nm) of polyethylenimine (PEI) to lower the work function of the source and drain contacts, we were able to block the hole injection and successfully transform ambipolar and even p-type transistors unipolar n-type transistors. This general approach to converting the transistor polarity broadens the scope of available polymer semiconductors for constructing n-channel transistors.

References

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Li, Y.; Sonar, P.; Singh, S. P.; Soh, M. S.; van Meurs, M.; Tan, J. J. Am. Chem. Soc. 2011, 133, 2198-2204.

Li, Y.; Sonar, P.; Murphy, L.; Hong, W. Energy Environ. Sci.
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Sun, B.; Hong, W.; Aziz, H.; Abukhdeir, N. M.; Li, Y. J. Mater. Chem. C
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Chen, S.; Sun, B.; Hong, W.; Aziz, H.; Meng, Y.; Li, Y.
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Sun, B.; Hong, W.; Yan, Z.; Aziz, H.; Li, Y. Adv. Mater. 2014, 26, 2636–2642.

Sun, B.; Hong, W.; Thibau, E.; Aziz, H.; Lu, Z.H.; Li, Y. Organic Electronics
2014, 15, pp. 3787-3794.
(Invited) Thin-Film Transistors Based on Donor-Acceptor Polymers
Authors: Dodabalapur Ananth , Kim Seohee , Ha Taejun , Sonar Prashant 
Published: February 2020

In this presentation we will describe device designs, modeling, and experimental results with several new diketopyrrolopyrrole DPP-based polymers and specifically discuss techniques to keep the operating voltage low (< 10 V) in small channel length (< 5 mm) devices. We have been able to obtain mobility values of ~4 cm2/V-s with some of the materials in such devices at low operating voltages for channel lengths of 4 mm in air. These devices possess very high temperature field-induced conductivity of any polymer FET and which exceeds that of most organic single crystal FETs reported so far. Our best devices designs possess a bilayer gate insulator which includes a thin interfacial low- dielectric constant insulator. We will demonstrate that the mobility improvement arises due to the suppression of the formation of Fröhlich polarons, which tend to reduce mobility when polar media such as high-k dielectrics are used with polymer semiconductors. We will also discuss charge transport in such polymers transistors both above and below the threshold voltage.
Solution-Processed Light-Emitting Dielectric Films and Their Applications in Multifunctional Devices
Authors: Li Jing , Dong Guifang , Duan Lian , Wang Liduo 
Published: February 2020

Ionic materials are used as gate dielectric layers for field-effect transistors (FETs) to reduce working voltage. In this paper, we exhibit a newly synthesized ionic iridium complex with interesting multifunction of both insulativity and light emission.1 Based on this material, a multifunctional device which behaves as a normal transistor at low gate voltage and a controllable light emitting device when the voltage is higher has been successfully fabricated. The device achieves area emission and the brightness can be tuned by three electrodes (gate, source and drain electrodes). Other ionic iridium complexes are also investigated. Results demonstrate that when mixed with some polymer, such as polymethyl methacrylate (PMMA), these complexes can form high performance light-emitting dielectric films as well. Through analysis of energy levels, the working mechanism of the device is proposed. Our study verifies that ionic light-emitting complexes have potential to be used in low-voltage multifunctional electronic devices.
This work was financially supported by the National Natural Science Foundation of China (No. 61177023, 51173096, and 61474069).
Reference:
1 J. Li, G. Dong*, L. Duan, D. Ma, T. Hu, Y. Zhang, L. Wang and Y. Qiu, RSC Adv.
2014, 4, 51294.

Figure 1
(Invited) Disentangling the Effects of Gated-Contacts on Transconductance in Organic FETs
Authors: Bittle Emily , Basham James I. , Jackson Thomas N. , Jurchescu Oana D , Gundlach David J. 
Published: February 2020

Recent reports of solution processed organic thin film transistors (TFTs) with exceedingly high field-effect mobility have spurred renewed interest in organic TFTs because of their potential to impact higher performance electronic applications than previously envisioned, while also stimulating considerable debate around the transport physics allowing such high charge carrier mobility in these intriguing material systems. Most reports parameterizing TFT performance make use of DC electrical characterization methods and mathematical relationships that describe transistor current as a function of applied voltage for ideal devices. However, the electrical characteristics reported for many of the highest mobility TFTs exhibit substantial non-ideal behavior. Thus, a detailed investigation of organic transistors with such behavior is needed to discern the transistor channel properties from parasitic device effects that might affect the device operation and give rise to incorrect mobility estimates. We report here on the use of impedance spectroscopy to disentangle the effects of contacts on device operation and extract the electrical properties of the channel. Specifically, we look at the small signal AC impedance of rubrene single crystal transistors to investigate "ideal" low field electronic behavior. The rubrene crystals are grown by vapor transport method and laminated onto prefabricated transistor test structures consisting of a heavily doped silicon substrate (gate electrode), thermally-grown silicon dioxide layer (gate dielectric), and photolithographically-defined metal electrodes (source and drain contacts). The completed rubrene transistors have channel lengths ranging from 50 µm to 100 µm. The impedance response is measured as a function of gate bias and frequency (varied from 20 Hz to 2 MHz). By using a transmission line model to fit the transistor channel coupled with a parallel resistor-capacitor model of the contact impedance, we are able to observe the behavior of the transistor channel and contacts separately as a function of gate bias. We determine the low field mobility of the device independent of contact resistance and show that rapidly changing contact resistance governs the current flow at low gate voltage in DC current-voltage measurements. This effect gives rise to large transconductance near threshold that reflects the “turn-on” of the gated-contacts rather than solely channel response making mobility extracted by using traditional DC current-voltage relationships describing only the channel inappropriate in this bias region.
(Invited) Electrochemical Reaction Induced Amorphization to Complex Oxide Surface and Its Impact to Catalyst Activity for Oxygen Evolution Reaction
Authors: Jia Hongfei , Zhou Li Qin , Ling Chen 
Published: February 2020

Water splitting and artificial photosynthesis systems are proposed as promising approaches to the conversion and storage of solar energy into chemical fuels. However, their efficiency is often limited by the sluggish kinetics of oxygen evolution reaction (OER). Although IrO2 and RuO2 can effectively reduce activation barriers for OER, the scarcity of the materials makes it difficult to use them as OER catalysts for large-scale implementation. Recently there have been a growing interest to investigate complex oxides as alternative OER catalysts and several new catalysts showed activity better or comparable to IrO2 benchmark. Along with these efforts, experimental evidences also indicated many of complex oxides were not stable under reaction conditions, of which amorphization was often observed at catalyst/electrolyte interface after cyclic voltammetry (CV) or potentiostatic measurements [1-3]. Our recent results showed that such type of surface amorphization processes seemed to affect catalyst performance in quite different ways dependent on catalyst material, electrolyte pH and compositions. For instances, in alkaline electrolyte (0.1 M NaOH), the activity of cobalt tungstate reduced after multiple CVs, while copper tungstate, on the other hand, became more active. Under similar conditions, another lithium-containing OER catalyst, Li2CoGeO4, maintained majority of its original activity even after significant loss of lithium and germanium from its surface. In this study, the surface amorphization process is examined by multiple characterization techniques including HR-TEM, XPS, electrochemical and compositional analyses. Possible mechanisms leading to these distinctive behaviors will be discussed in detail.
(1) S. W. Lee, et al., JACS, 2012, 134, 16959-16962
(2) M. Risch, et al., JPCC, 2013, 117, 8628-8635
(3) K. J. McDonald, et al., J. Mater. Chem. A, 2014, 2, 18428-18434
Porous Carbon Hollow Nanospheres for Confining Polysulfide in Lithium Sulfur Batteries
Authors: Zhou Weidong , Xiao Xingcheng , Cai Mei , Yang Li 
Published: February 2020

Lithium–sulfur batteries (Li–S), as one of the most promising candidates, have attracted increasing attention owing to its high theoretical capacity (1675 mAh g-1), low safety concerns/environmental footprint, high natural abundance and competitive cost. Despite these considerable advantages, practical application of Li–S batteries is still hindered currently by several challenges, including low electrical conductivity of sulfur/polysulfides, dissolution of lithium polysulfides and the resulting shuttling effect.
To better confine the sulfur/polysulfides in the electrode of Lithium–Sulfur (Li/S) batteries and improve the cycling stability, we developed a porous carbon shell to confine polysulfide. We systematic investigate the effect of pore size on the confining effect of porous C, and found out small pore size down to 2.8 nm gave the best confining effect. We further developed a core–shell structure with polymer coated porous carbon as shell and S as core. It was first prepared through impregnation of sulfur into hollow carbon spheres under heat treatment, followed by a coating polymerization to give a double layers core–shell structure. From the study of scanning transmission electron microscopy (STEM) images, we demonstrated that the sulfur not only successfully penetrated through the porous carbon shell but also aggregated along the inner wall of the carbon shell, which, for the first time, provided visible and convincing evidence that sulfur preferred diffusing into the hollow carbon rather than aggregating in/on the porous wall of the carbon. Taking advantage of this structure, stable capacity of 900 mAh g-1 at 0.2 C after 150 cycles and 630 mAh g-1 at 0.6 C after 600 cycles could be obtained in Li/S batteries. We also demonstrated the feasibility of full cells using the sulfur electrodes to couple with the silicon film electrodes, which exhibited significantly improved cycling stability and efficiency. The remarkable electrochemical performance could be attributed to the desirable confinement of sulfur through the unique double layers core–shell architectures. [1]

W. Zhou, X. Xiao, M. Cai, Y. Li, Nano Letters, 2014, 14 (9), 5250–5256
Metal Organic Frameworks (MOFs) Cooperated Si Nanorod Arrays Used in Rechargeable Batteries
Authors: Li Jing , Yu Yingjian , Yue Chuang , Sun Shibo , He Xu 
Published: February 2020

Given the large surface area and unique channels, metal-organic frameworks (MOFs),1 have served as a “generalist” in the fields of clean energy,2 such as adsorbents for hydrogen,3 electrolytes for fuel cells,4 electrode materials for supercapacitors5 and so on. However, only a few immature applications of MOFs as electrodes for lithium ion batteries (LIBs) or micro-LIBs have been researched.6-9To the contrary, Si anode, with the highest theoretical capacity, low working potential and feasible integration with other micro- or nano-electronic devices, has been intensively investigated experimentally and theoretically to address the volume expansion issue during discharge/charge processes. But, fully addressing the deterioration of the electrode structures caused by the volume expansion, which would generally results in performance fading and safety issues, is still challenging.
In this work, a novel class of MOFs, was initially proposed to composite/network with Si nanorod (NR) arrays as anodes for LIBs employing the modified nanosphere lithography (NSL) and inductive coupled plasma (ICP) dry etching followed by a method of solution growth. An enhanced capacity was accomplished in this hybrid material nanocomposite electrode compare with that in the only Si NR anodes. In addition, with the employment of a buffer layer of Ti/TiN to modify the electronic conductivity of the interfaces between Si inner core and outer MOFs, a further enhanced capacity was realized accompanied with the high Coulombic Efficiency (CE).First principles calculations were performed to verify the favorable lithium diffusion in the MOF cooperated Si structure.

References:

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[2] Li, S.-L; Xu, Q. Energy. Environ. Sci.
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[9] Han, Y.; Qi, P.; Li, S.; Feng, X.; Zhou, J.; Li, H.; Su, S.; Li, X.; Wang, B. Chem. Commun. 2014, 50, 8057.
Toward a Better Understanding of the Surface Effect through the Design of Conductive Binders in Lithium Sulfur Battery
Authors: Ai Guo , Wang Zhihui , Dai Yiling , Zhao Hui , Chen Yulin , Liu Gao 
Published: February 2020

Li-S battery has attracted much attention, because of the extreme high theoretical capacity and low cost compare to Li-ion battery. But the poor cycling life of lithium sulfur battery kept them from large scale usage. The poor electric conductivity of the charge and discharge product is another limitation for Li-S battery. A lot of research work has focused on the improvement of electrode design, including the combination of porous carbon film, carbon paper, carbon nanotube, graphene or other conductive nanostructure. The design of binder is another effect way to improved the battery performance, because the binder covers up most of the inner surface of the electrode, which has a important effect in surface modification. In Li-S battery, a notable feature of phase transformation will take place, which are from solid phase S8/Li2S8 into soluble Li2S4, then precipitate into solid state Li2S during discharge and the combination of solid phase and liquid phase reaction during charge. The surface effect of binder will have a much bigger influence on Li-S battery performance because this phase transformation.
So in this work, we investigated several binders with different kind of functional group, including both conductive and nonconductive binders, to study the effect of binder on surface modification. A huge difference is observed in electrochemical performance and electrode morphology with different binders. These indicates the different effect of binder on surface modification and therefore in reaction mechanism during charge and discharge. So, we suggest that the designing of binder with preferred physical and electrochemical property in indeed crucial in further improving the performance of Li-S battery.
Carbon Hotels with Nanosulfur Guests: Promising High Capacity Cathode Architecture with Hybrid Electrolyte for Lithium-Sulfur Battery
Authors: Pol Vilas G. , Dysart Arthur , Hong Chulgi , Etacheri Vinodkumar , Tang Jialiang 
Published: February 2020

Lithium-sulfur battery is highly appealing primarily due to its high theoretical specific energy of 2567 Whkg-1 and specific capacity of 1672 mAhg-1, both values an order of magnitude higher than those of commercialized Li-ion systems.1-
2 Despite the wealth of literature demonstrating remarkable carbon-sulfur cathode architectures for Li-S systems, their industrial adoption is limited by performance issues such as low columbic efficiency, poor cycle life, and impractical syntheses. It is imperative that continuing studies on Li-S systems recognize the importance of the underlying fundamental chemistry for progress to be seen. The focus of this work is to develop, characterize, and optimize both Li-S materials and synthesis processes in the pursuit of a practical Li-S rechargeable battery.
Through this work, we understand the shuttle mechanisms and its effect on stable cycling performance and high columbic efficiency in Li-S systems. Initially, we have fabricated carbon hotels using starch based precursor with solid state synthesis approach. These premade hollow carbon particles are filled in situ with sulfur nanoparticles, sonochemically. The electrolyte used is DOL:D2:LiTFSI. The newly developed C-S composite cathode demonstrates high columbic efficiency (minimum 97%) and ~900 mAh/g reversible capacity during long cycling.

References

Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nature Materials
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W. Weng, V. G. Pol, K. Amine, Adv. Mater., 2013, 25, 1608–1615
Li Storage Feasibility of Defected Single- and Bi-Layer Graphene
Authors: Yildirim Handan , Kinaci Alper , Zhao Zhi-Jian , Chan Maria K. Y. , Greeley Jeff 
Published: February 2020

The limited capacity of the intercalation-type graphitic materials has lead to much effort to explore new electrode materials. A natural choice among the carbonaceous materials, graphene, has attracted increased attention for obtaining higher Li storage capacity. The outstanding mechanical strength, electronic conductivity, and ready availability of extra storage sites for Li, has suggested that this material could be an ideal platform for storing more Li. However, for wide range of Li coverages, the calculations predict that defect-free single layer graphene is not thermodynamically favorable for lithiation compared to bulk metallic Li. Thus, exploring ways with which graphene surfaces can be activated such that Li storage capacity can be improved has become a significant focus of research in the field. One such strategy is to activate graphene surface with structural defects. Generally speaking, structural defects can be found nearly in all carbonaceous materials. The presence of such defects can be detrimental for the performance of graphene-based devices. In contrast, however, deviations from the perfection of atomic lattice can also be useful for some applications, as they make it possible to tailor the properties leading to new functionalities.
Following this approach, we performed an extensive series of density functional theory (DFT) calculations for Li adsorption and intercalation in single and bi-layer graphene, which are activated by topological defects for improving Li adsorption. The results confirm that Li adsorption on defect-free single layer graphene is not thermodynamically favorable compared to bulk metallic Li. However, graphene surfaces activated by structural defects are generally found to bind Li more strongly, with the interaction strength sensitive to both the nature of the defects and their densities. The interaction of Li with a one-dimensional extended defect is additionally found to be strong, improving Li storage capacity. The theoretical Li storage capacities of the defected single-layer graphene structures are evaluated with a rigorous thermodynamic analysis, which establishes, in some cases, that these capacities approach, although not exceed, those of graphite. Li storage in bi-layer graphene with and without defects are evaluated in a similar way, and indicate more favorable interaction, and promise for higher Li storage than that of single layer graphene. We will present performance comparisons between defected single- and bi-layer graphene structures, and bulk-graphite for Li storage capacities. A detailed analysis of the effect of the van der Walls (vdW) interactions will also be presented.