bluuebunny/crossref_metadata_2025_split huggingface dataset:
Band Engineering of Quantum Dot Substrates to Utilize QD-Generated Photocarrier for SERS Signal Amplification
Authors: Lim Hunhee , Baek Kwang Min , Jung Yeon Sik 
Published: February 2020

Interacting with light, plasmonic materials generate electric fields induced by localized surface plasmon resonance (LSPR) phenomenon. Electric field generated by plasmonic materials can induce optical phenomena such as light scattering, light emissive recombination and surface-enhanced Raman scattering (SERS). These phenomena grant versatile functionalities to plasmonic materials which can be applied to various devices such as photovoltaics, light emitting diode, meta material, SERS and so on. Amplifying electric field of plasmonic materials can improve the optical phenomenon and applications. Injecting external carriers into plasmonic materials can be good solution to improve electric field generation.
In this research, we used incident light to generate photo-carrier and designed the band structure of the materials to extract photo-carrier into the plasmonic materials. We fabricated the substrate consisting of lead sulfide quantum dot/zinc oxide/plasmonic structure. The bottom quantum dot (QD) layer absorbs light and transfer photo-carrier to zinc oxide and plasmonic structure. For the photo-active material, we selected lead sulfide quantum dot (QD) because the band gap of the QD is conveniently tunable by controlling the size of QD. We synthesized the QD with the band gap around 1.3eV to optimize the light absorption ranging from 400nm to 900nm. Upper ZnO layer forms p-n junction with QD and selectively transports electron to top plasmonic materials. To verify the enhancement of electric field in photo-carrier injected plasmonic structure (PCIPS) substrate, we applied PCIPS substrate to SERS device. We measured 4 different molecules and the SERS signals enhanced from 3 to 7 times. Kelvin probe force microcopy (KPFM) measurement showed the change in surface potential of the substrate with and without light incidence. Our device showed great potential in SERS application because the device showed meaningful improvement in SERS signal simply using incident laser used to detect molecules.

Figure 1
(Invited) Controlling the Carbon Vacancy in 4H-SiC By Thermal Processing
Authors: Ayedh Hussein M. , Baathen Marianne E. , Galeckas Augustinas , Hassan Jawad Ul , Bergman J. P. , Nipoti Roberta , Hallen Anders , Svensson Bengt G 
Published: February 2020

The carbon vacancy (VC) is a major point defect in high-purity 4H-SiC epitaxial layers for bipolar power devices, and it limits the minority charge carrier lifetime. VC exhibits a formation energy of only ~5.0 eV, as confirmed both theoretically and experimentally, and in as-grown layers realized by chemical vapor deposition techniques, the VC concentration is typically in the low 1012 cm-3 range. After high-temperature device processing exceeding 1900 °C, the VC concentration can be enhanced by several orders of magnitude.
Three different approaches are commonly used to minimize the VC content and enhance the carrier lifetime; (i) near-surface ion implantation followed by high-temperature annealing, (ii) thermal oxidation of the Si-terminated epi-layer surface, and the most recent one (iii) ‘equilibrium annealing’ at moderate temperatures (≤1500 °C) under C-rich surface conditions. In the present contribution, we will discuss the advantages and limitations of the different approaches with a particular focus on the approach (iii). New insight into the atomistic processes governing the VC equilibration kinetics is given and how these processes can be tailored by varying the cooling rate after high-temperature treatment. Especially, the diffusivities of both VC and the carbon self-interstitial are found to play a decisive role and where at least the former one displays a substantial anisotropy between directions parallel and perpendicular to the basal c-plane. After thermal treatment of as-grown layers under C-rich surface conditions at 1500 °C for 1 h followed by slow/moderate cooling, the VC concentration is shown to be reduced to ~1x1011 cm-3 enabling a minority carrier lifetime well above 20 µs at room temperature.
(Invited) Microfluidics for Biomedical Devices By Two Examples
Authors: Baysal Oktay 
Published: February 2020

The need and the tremendous value of “very small” machines and devices were realized in late 1980’s. In the following decade, the indispensable utility of micro- or even nano-level transport phenomena in these machines was recognized, leading to the start of research and development in microflows. Researchers started investigating from a point where they deemed relevant body of knowledge on macroflows stood. Over the ensuing years, there has been significant amount of resource investment to, for example, the understanding of how the underlying physics differed as compared to macroflows and, just as importantly, what existing transport phenomena tools would be applicable. It was quickly observed that what significantly changed were the relative effects of, for example, very low Reynolds numbers, the domination of surface and interface tension, and even the continuum assumption. Much happened since then, hence, today we enjoy the ever ubiquities micro- and nano-fluidic devices this body of research and development have produced.
The author took interest in this field in the early 2000’s. This presentation will briefly sample a few of our earlier studies which varied from “design optimization of a micro synthetic jet actuator to control microflow separation,” to “electrodiffusiophoretic motion of charged spherical particle in a nanopore.” The emphasis, however, will be on our current research on two biomedical devices, using in silico approach and collaborating with adjoining experimentations: (i) a convective polymerase chain reactor (cPCR); (ii) microfluidics-aided collagen fiber (MCF) fabrication. Our goal in the first project is to develop a methodology for a portable and affordable c-PCR design intended for point-of-care use. Computational fluid and heat transfer models are developed to simulate the prerequisite convective transport fields. The search space for optimality is determined based on a specified range of the selected design variables. The convection-diffusion equations are then recast to determine and minimize the time-to-double the reagent (in our case, the double-stranded DNA) by the candidate design. For the MCF device, we are developing a new microfluidic methodology to fabricate advanced telocollagen fibers. The ultimate goal is to obtain an advanced microfluidic-based telocollagen manufacturing technology suitable to produce ligament and tendon repair and replacement grafts. Our specific goal is to provide the in silico guidance to the fabrication of collagen fibrils, which are much finer and better axially aligned, since prior research has shown that the mechanical strength of such fibers would be more favorable in achieving their purpose.
(Invited) Hybrid Microfluidic Cell Sorting for Rare Cell Isolation
Authors: Ai Ye 
Published: February 2020

Selective isolation of specific cell subpopulations from highly heterogeneous biological samples is an essential process in various biological studies and clinical applications. The ability to isolate rare cell populations, for example circulating tumor cells, provides unprecedented capabilities for the study of disease progression and better disease assessment. Currently, sorting and isolation of rare cell populations is typically performed using fluorescence-activated cell sorting (FACS) system, a technology developed nearly 60 years ago. These FACS systems are however complex, bulky, and expensive, require highly trained personnel for operation, and may produce bio-hazardous aerosols in open environments.
Microfluidics studies the unique behavior and interactions of fluids and particles at the micrometer length scale, typically in confined microscale channels. Microfluidic technology capable of precise cell manipulation thus has great potential to reinvent the next-generation cell sorting technology. We are currently developing two microfluidic cell sorting technologies including high-throughput hydrodynamic cell sorting and high-accuracy acoustic cell sorting. Hydrodynamic cell sorting is using an interesting inertial particle focusing behavior in an intermediate Reynolds number regime (~100 > Re > ~1). We have designed and fabricated a new type of hydrodynamic sorting device with a series of reverse wavy channel structures. These repeated wavy channels produce periodically reversed Dean secondary flow perpendicular to the main flow direction. The hydrodynamic inertial lift force and the Dean drag force scale with the particle size very distinctively, which leads to distinct equilibrium positions of differently sized particles. We have demonstrated the use of this new hydrodynamic sorting device to isolate cancer cells from blood cells without the use of sheath flows. Acoustic cell sorting is developed based on the study of interactions between high-frequency sound waves and microscale particles. In particular, I will discuss a unique design of a focused interdigital transducer (FIDT) structure, which is able to generate a highly localized acoustic field on the order of 25 µm wide. This highly focused acoustic beam has an effective manipulation area size that is comparable to individual micron-sized particles. We have demonstrated the use of this highly localized acoustic field for fluorescence-activated single cell level sorting with sub-millisecond pulses. By combining the two microfluidic cell sorting technologies, we have demonstrated the capability of enriching target cells by 1,000 to 10,000 times, providing a new solution of rare cell isolation.
High-Throughput Electrochemistry of Li-Mn-Co-Ni-O Positive Electrodes
Authors: McCalla Eric 
Published: February 2020

In the search for high-energy Li-ion positive electrodes, the layered lithium NMC oxides have been studied extensively. Despite wide interest in this system, until recently, the phase diagram remained poorly understood resulting in many conflicting reports in the literature. Combinatorial synthesis, coupled with X-ray diffraction, was used to determine the phase diagrams under various synthesis conditions [1-2]. The unexpected complexity seen in this system included multiple 3-phase regions that transform during cooling along with boundaries to single phase regions which shift during cooling. Despite the deepended understanding of the structural phase diagram, there now remains a very limited exploration of how the electrochemical properties evolve across these complex phase spaces. Herein, we adapt a high-throughput electrochemical testing system wherein 64 samples are cycled simultaneously in order to measure the cycling of the mg-scale powder combinatorial samples. The methodology involves using a solution-dispensing robot is used to make the samples by co-precipitation synthesis followed by high temperature annealing. The samples are subsequently mounted in the combinatorial electrochemical cell and cycled simultaneously. Given that the combinatorial samples here are powders, made using synthesis methods comparable to those used commercially, the results scale-up very well. Beyond the proof-of-concept of the novel high-throughput measurements, results on hundreds of samples in the Li-Mn-Ni-Co-O system of extreme interest as next-generation positive electrodes will be presented. Consequences for further studies in this popular composition space will be discussed.
References:
[1] McCalla, E., Rowe, A. W., Shunmugasundaram, R., & Dahn, J. R. (2013). Structural study of the Li–Mn–Ni oxide Pseudoternary system of interest for positive electrodes of Li-ion batteries. Chemistry of Materials, 25(6), 989-999.
[2] Brown, C. R., McCalla, E., Watson, C., & Dahn, J. R. (2015). Combinatorial study of the Li–Ni–Mn–Co oxide pseudoquaternary system for use in Li–Ion battery materials research. ACS combinatorial science, 17(6), 381-391.
High Energy Density Lithium Secondary Battery with S Cathode and Si Anode Based on Carbon Nanotube Sponge
Authors: Hori Keisuke , Noda Suguru 
Published: February 2020

The lithium secondary batteries with higher energy density is strongly required for electric vehicle application. The sulfur cathode and silicon anode show high theoretical capacity (1675 mAh gsulfur
-1 and 3580 mAh gsilicon
-1). Nevertheless, both active materials change their volume during charge-discharge cycles, which leads to pulverization of electrodes. Therefore, it is difficult to load large amount of active material in the electrode. Limited values of active material results in low capacity in total system of batteries due to the large mass of metal current collector (Al and Cu). To solve the problem, self-supporting, sponge-like paper of carbon nanotubes (CNTs) can be a candidate for non-metal based 3D current collector, which can reduce the mass of current collector. It also accommodates large amount of active material due to high porosity. Previously, we have developed S-CNT cathode and Si-CNT anode [1] and demonstrated high capacity for their individual half cells [1]. In this work, we combined them to achieve higher energy density full cell without any metal current collector.
Submillimeter-long few-wall CNTs produced by fluidized-bed chemical vapor deposition method [2] were used for the 3D current collector. 30-μm-thick CNT paper was fabricated via dispersion and filtration of the CNTs, and the S-CNT cathode was fabricated by sublimation of sulfur into the CNT paper. The Si-CNT anode was fabricated by co-dispersion and co-filtration of Si nanoparticles (50, 100, and 150 nm in diameter) and the CNTs followed by carbon coating by chemical vapor deposition. Lithium was pre-doped to the Si-CNT anode either by contacting it with Li foil in electrolyte or by electrochemically using Li foil as counter electrode. The full cell of the S-CNT cathode (58 mass% S) and the LixSiy-CNT anode (70 mass% Si) showed a high initial discharge capacity and energy density of over 320 mAh/g and 540 Wh/kg based on the total mass of the cathode and anode.
[1] T. Kowase, et al, J. Power Sources, 363, 450 (2017).
[2] Z. Chen, et al., Carbon, 80, 339, (2014)
In-Situ AFM Imaging of Solid Electrolyte Interphase on Silicon Negative Electrodes with an Artificial Surface Layer
Authors: Haruta Masakazu , Kijima Yuki , Ogura Nanako , Konaga Hiroto , Doi Takayuki , Inaba Minoru 
Published: February 2020

Silicon is regarded as the most promising negative electrode material for next-generation lithium-ion batteries because of the high theoretical capacity. We have developed a Si powder with a flake shape (Si LeafPower®, Si-LP, OIKE & Co., Ltd.) that is 100 nm thick with a 3-5 μm lateral dimension.[1-3] The Si-LP electrode demonstrates a superior cycle performances because the unique flake structure resists pulverization during charge and discharge cycling. For further improvement of cycle performances, inhibition of reductive decomposition of electrolytes on the Si negative electrode is necessary. We tried to suppress the electrolyte decomposition by an artificial surface coating on Si thin films and investigated formation of solid electrolyte interphase (SEI) by in-situ atomic force microscopy (AFM) coupled with a potential sweep.
An amorphous Si thin film with the thickness of 100 nm was deposited by RF magnetron sputtering on a mirror polished Cu substrate. After that, LiF layer was sequentially deposited on the Si film electrode by the RF sputtering. AFM observations coupled with cyclic voltammetry were performed in a liquid immersion sample stage equipped with electrochemical connectors. The Si thin film as a working electrode and Li wires as a counter and a reference electrodes were immersed in the electrolyte of 1 M LiTFSI/EC+DEC (1:1 by vol.). AFM scan was conducted with a conventional contact mode at a room temperature in an Ar-filled glovebox. The potential was managed with a potentiostat/galvanostat and the sweep rate was 0.5 mV s-1.
In the first cycle of the cyclic voltammetry for the Si film electrode without LiF, a small cathodic current began to flow ~2 V, and a current peak arose around 0.9 V. This current peak disappeared in the second cycle, which indicated an irreversible reductive decomposition reaction of the electrolyte and formation of SEI on the Si electrode. In the AFM image coupled with the potential sweep, surface deposits emerged from ~0.9 V corresponding to the potential of the electrolyte decomposition. On the other hand, a reductive current peak and surface deposits caused by the electrolyte decomposition were not observed in the Si film electrode with LiF coating. Furthermore, the Coulombic efficiencies of the Si film electrodes improved by the LiF-coating. These results indicated that the LiF layer on the Si electrode prevented the electrolyte decomposition, and thus LiF is a very important component for SEI layer.

Acknowledgments: This work was supported by ALCA-SPRING (JST, Japan) and KAKENHI (JSPS, Japan) Grant Number 16H04649.

References: [1] M. Saito et al., J. Power Sources, 196, 6637 (2011); [2] M. Haruta et al., Electrochimica Acta, 224, 186 (2017).; [3] M. Haruta et al., Electrochimica Acta, 267, 94 (2018).
Electrical Conductivity of Prussian Blue Analogues (Cu, Ni, K Cu, K Ni)
Authors: Kumari Manisha , Redel Engelbert 
Published: February 2020

Prussian Blue, Fe+3₄[Fe+2₆]₃·xH₂O is a typical hexacyanometalate network, in which cyanide ligand coordinates octahedrally with the metal ion. Interstitial cations and metal vacancies balance the local charge in PB structure. This octahedrally coordinated cyanide ligand with metal ion imparts high electrical conductivity to PB. Other than high electrical conductivity, hexacyanometalate offers interesting redox property. That makes PB suitable material for microelectronics applications such as Resistive Random Access Memories (RRAM).
PB shows change in colour during redox transitions when transitions metal cations are associated with it. The change in colour is due to charge transfer between transitions metal cations and hexacyanometalate group. This charge transfer tunes the electrical conductivity of PB compounds. Here we tune the electrical conductivity of PB by adding transition metal cations (Cu, Ni, K Cu, K Ni) into it.
Conduction mechanism will be explained based on ab initio and density of states calculations. From these calculation results, we also explain the contribution of each metal on hopping and band transport, which is the responsible conduction mechanism for varying electrical conductivity in PB analogues.
Thermoelectric Characterization of Copper Hexacyanoferrate
Authors: Hosseini Pouya , Wittstock Gunther , Kumari Manisha , Redel Engelbert , Lin Pengtao , Zhang Kai , Baumgart Helmut 
Published: February 2020

Copper Hexacyanoferrate K2Cu[Fe(CN)6] nH2O forms a typical non-porous coordination network, in which cyanide ligand bridge Cu and Fe ions with octahedral coordination environment. Interstitial cations, e.g. K+ and metal vacancies balances the local charge in metals. This octahedrally coordinated cyanide ligand with metal ions of mixed valence determine the redox properties as well as the high electrical conductivity of these films. The electrical conductivity can be tunes by adding different transition metal cations (e.g. Cu, Ni) within the coordination network.
Crystalline films of K2CuFe(CN)6
were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), X-ray photoelectron spectroscopy to confirm crystallinity, elemental composition and valence states. While the structural properties are understood, little is known about the thermoelectric application potential of these Prussian Blue Analogues. This presentation will report our findings and discuss our electrical characterization measurements utilizing Hall effect measurements to elucidate electrical properties such as carrier concentration, resistivity, mobility, Hall coefficient and an assessment for possible future applications. In addition, a complete thermoelectric characterization is being performed by employing a Lab-on-a-Chip test method, which enables deposition of metal-organic framework compounds through a mask for simultaneous measurements of the Seebeck coefficient and the thermal conductivity.
(Invited) MOF Thin Film Based Chemiresistor Gas Sensors
Authors: Xu Gang 
Published: February 2020

Metal oxide (MOX) semiconducting materials, such as ZnO, SnO2, In2O3 and WO3, are the main active materials for chemresistor gas sensor due to their low cost, portability, real-time operability and ease of use. MOX based gas sensor has been developed for many industrial and domestic applications on detecting volatile organic compounds (VOCs). However, several ways such as cross-sensitivity adjustment, electronic noses and gas pre-separation by other instrument have been developed to optimize its performances, but MOX gas sensor still need to overcome the poor selectivity and high working temperature for broader commercial applications.
Metal organic frameworks (MOFs) feature regular pores, ultra-large surface areas, tuneable framework structures and open-metal sites. These features make MOFs an ideal candidate to overcome the above mentioned long-term bottlenecks of chemiresistor gas sensor . Here, we demonstrate this possiblity by two strategies of material design to optimize the performances of gas sensor:1) high quality semi-conductive MOF thin film was prepared to act as sensing active layer directly; 2) MOX@MOF core-sheath structured nanowire array was design and prepared to act the sensing active layer. The chemiresistor gas sensors based on above materials have not only exhibited improved sensitivity, but also reduced the working temperature.[1,2] Given that MOF material has greatly variable and designable structure and properties, new material designed with MOFs is promising to simplify the structure and decrease the cost of gas sensor for its application on wearable devices, intelligent automobile, smart electrical home appliances and other precise detection fields in future.

Refences:

1. Ming-Shui Yao, Xiao-Jing Lv, Zhi-Hua Fu, Wen-Hua Li, Wei-Hua Deng, Guo-Dong Wu, and Gang Xu* Angew. Chem. Int. Ed.
2017, 56, 16510.
2. Ming-Shui Yao, Wen-Xiang Tang, Guan-E Wang, Bhaskar Nath, and Gang Xu* Adv. Mater. 2016, 28, 5229.

Figure 1
Metal-Organic Frameworks Based Materials for Electrocatalyst
Authors: Li Guangqin 
Published: February 2020

How to design and synthesize of efficient and earth-abundant catalysts for a wide variety of electrochemical energy storage and conversion reactions is a great challenge. Guided by the advantage of component manipulation, morphology control, and structure engineering, advanced MOF-based materials have exhibited remarkable activity, selectivity, and stability for various energy-conversion processes, manifesting great potential for replacing precious-metal-based catalysts in next-generation energy devices. We have studied MOF based materials (Pd@HKUST-1) for hydrogen storage1. Recently, we have synthesized a porous carbon nanomaterial loaded with cobalt nanoparticles (Co@NC-x/y) derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework, which exhibits incredibly high activity as bifunctional oxygen catalysts2. For instance, the optimal catalyst of Co@NC-3/1 has the superb ORR activity with onset potential of ~1.15 V and half-wave potential of ~0.93 V. Moreover, its OER activity is better than commercial IrO2 and it also presents a long-term stability for 2000 circles and a Tafel slope of 85 mV dec-1.

References

[1] Li G., Kobayashi H., Taylor J. M., Ikeda R., Kubota Y., Kato K., Takata M., Yamamoto T., Toh S., Matsumura S., Kitagawa H. *, Nature Mater., 13, 802 (2014).
[2] Li Y., Jia B., Fan Y., Zhu K., Li G. *, Su C.-Y. *, Adv. Energy Mater., 201702048 (2017).