bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemically Modified Graphene and Carbon Quantum Dots: Structural, Electronic and Chiroptical Characterization
Authors: Herranz Mª Ángeles , Ferrer-Ruiz Andres , Vázquez-Nakagawa Mikiko , Rodríguez-Pérez Laura , Martín Nazario 
Published: February 2020

Graphene Quantum Dots (GQDs) and Carbon Quantum Dots (CQDs) are nanomaterials with rising popularity as an alternative to traditional semiconductor quantum dots and organic dyes.1 In addition to simple fabrication methods and low production costs, GQDs and CQDs exhibit a good chemical stability and solubility, unique photophysical properties, photochemical stability, and biocompatibility. These are remarkable properties for applications in fields such as catalysis, photovoltaic devices, bioimaging or medical diagnosis.2

With the objective of constructing versatile and functional ensembles for nanoelectronics and optoelectronics, we lately embarked in the synthesis of these carbon nanomaterials and their covalent or supramolecular modification with ligands that modify their fundamental properties. For instance, adding a chiroptical response to the semiconductor properties of GQDs will provide the extra value of their potential application in photonics. In this sense, we recently proof the concept that GQDs are able to become chiral and that this property can be transferred to a supramolecular structure built with pyrene molecules, where the chiral-GQDs/pyrene ensembles show a characteristic chiroptical response depending on the configuration of the introduced organic ligands.3

We have also combined GQDs and CQDs materials with p-quinonoid π-extended tetrathiafulvalenes (exTTFs)4 in the search for new electron donor-acceptor systems (Figure). The electronic interactions between the CQDs and exTTF have been investigated in the ground and excited states.
The characterization of the obtained GQDs and CQDs nanomaterials by a combination of analytical, microscopic and spectroscopic techniques will be presented and discussed, along with the photophysical properties of some of the aggregates formed.

References

[1]. (a) A. Cayuela, M. L. Soriano, C. Carrillo-Carrión, M. Valcárcel, Chem. Commun., 2016, 52, 1311. (b) X. T. Zheng, A. Ananthanarayanan, K. Q. Luo, P. Chen, Small,
2015, 11, 1620. (c) L. Li, G. Wu, G. Yang, J. Peng, J. Zhao, J.-J. Zhu, Nanoscale, 2013, 5, 4015.
[2]. (a) X. Wang, G. Sun, N. Li, P. Chen, Chem. Soc. Rev.,
2016, 45, 2239. (b) Y. Du, S. Guo, Nanoscale, 2016, 8, 2532. (c) Y. Wang, A. Hu, J. Mater. Chem. C, 2014, 2, 6921
[3]. M. Vázquez-Nakawaga, L. Rodríguez-Pérez, M. A. Herranz, N. Martín, Chem. Commun.,
2016, 52, 665.
[4]. J. Mateos-Gil, L. Rodríguez-Pérez, M. Moreno Oliva, G. Katsukis, C. Romero-Nieto, M. A. Herranz, D. M. Guldi, N. Martín, Nanoscale, 2015, 7, 1193.

Figure 1
(Invited) Probing the Dielectric Response of Exfoliated Black Phosphorous in Free Standing Conditions
Authors: Gaufres Etienne , Fossard Frederic , Favron Alexandre , Gosselin Vincent , Côté Michel , Martel Richard , Loiseau Annick 
Published: February 2020

Ultra-thin Black Phosphorus (BP) is a 2D semiconductor characterized by a direct and tunable band gap associated to high carriers mobility (1-3). Studying suspended thin layers of pristine BP is however challenging due to its strong degradation through a thickness dependent and photo-assisted oxidation reaction by adsorbed moisture oxygen (4). Using a protective transfer procedure from glovebox to our TEM-EELS operating at 40kV, we probe the dielectric response of suspended BP down to the monolayer in the range 0.5-40 eV, that include band gaps thresholds and surface/volume plasmons energies for BP. The dispersion of the plasmons as a function of the momentum is also measured and simulated for both in-plane crystallographic directions.
(1)Liu et al, ACS Nano (2014)
(2)Qiao et al, Nature Comm. (2014)
(3) Long et al, Nano Letter (2016)
(4)Favron et al, Nature Mater. (2015)
Electrostatic Double Layer Flash Memory Based on Two-Dimensional Crystals
Authors: Fullerton Susan , Xu Ke , Liang Jierui , Lu Hao , Wang Weihua , Kim Hanchul , Kwak Iljo , Cho Kyeongjae , Kummel Andrew , Seabaugh Alan 
Published: February 2020

A new type of flash memory will be presented based on the electrostatic doping of two-dimensional crystals using ions. The proposed device consists of two, 2D crystals separated by a 2D electrolyte through which the ions can pass. The top 2D crystal comprises the channel of a field-effect transistor (FET), while bottom 2D crystal is a backgate. When the ions are near the surface of the channel, they induce image charge in the channel and the device is the low resistance, or ON state. When the ions are pulled back to the backgate by an applied field, the device is in the high resistance or OFF state. The 2D electrolyte is cobalt crown ether phthalocyanine (CoCrPc) plus a salt, which can be deposited on the surface of 2D crystals simply by drop casting and annealing. The crown ethers solvate metal ions, and the ions can pass through the cavity of the crowns. Density functional theory (DFT) calculations show that the crown ethers present a small barrier to ion transport required for fast (nanosecond) switching, but the height of the barrier will be increased for long retention both by the image charge induced in the channel and by modulating the gate bias. The current-voltage characteristics of a simplified device architecture (monolayer CoCrPc:LiClO4 on graphene) will be presented. The graphene FET can be reconfigureably programmed by the 2D electrolyte, achieving sheet carrier densities of 4 x 1012 cm-2 at a low lithium concentration of 5 crown ethers to 1 Li+. Based on the geometric packing of the molecules, as determined by scanning tunneling microscopy, the doping density is predicted to increase to 5 x 1013 cm-2 at a crown ether to lithium ratio of 1:1. State retention measurements show that the two states can be retained for at least 30 minutes (maximum time measured to date) with a memory window of 10 uA. To increase the ON/OFF ratio and therefore the memory window, MoS2 FETs doped with the 2D electrolyte were also fabricated and similar bistable behavior is observed.
This work was supported in part by the Center for Low Energy Systems Technology (LEAST), one of six SRC STARnet Centers, sponsored by MARCO and DARPA, and NSF grant #ECCS-GOALI-1408425.

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(Invited) Rare Earth Doped Light Emitting Thin Film Materials for Silicon Photonics
Authors: Bradley Jonathan D. B. 
Published: February 2020

Silicon photonic technology is becoming ubiquitous for data center, sensing and advanced photonic applications. However, one of the key challenges for silicon photonic microsystems is integrating materials which can provide optical gain. The leading approach involves hybrid bonding of III-V materials to silicon chips, which is expensive and difficult to scale. Alternatively, rare-earth-doped materials are promising for active device applications on silicon. Rare earth doped oxide thin films can be deposited using standard, low-cost, and wafer-scale methods directly on silicon and emit light in important bands for communications and other emerging applications.
This presentation will cover recent progress on integrating rare-earth-doped materials into silicon photonic microsystems. It will focus on fabrication and integration methods, particularly reactive magnetron co-sputtering, which yields low-loss, high-gain thin films which can be deposited using a single post-processing step onto silicon photonic chips that have been fabricated in a silicon foundry. The fabrication challenges, spectroscopic properties, and device design requirements related to prospective materials, including ytterbium-, erbium- and thulium-doped oxides will be discussed. The talk will review the application of such films in light-emitting rare-earth-doped devices, including amplifiers and continuous-wave and pulsed lasers.
(Invited) Electrolysis with Plasma Cathodes: Modeling and Experiments to Understand the Electrochemical Interface
Authors: Go David B. 
Published: February 2020

In the conventional picture of electrolysis, two metal electrodes are submerged into an electrolyte solution and an applied voltage drives redox reactions at the cathode and anode, respectively. Plasma electrolysis, also called glow discharge electrolysis, changes this convention by replacing one or both of the solid electrodes with a plasma or gas discharge. Reduction and/or oxidation reactions, therefore, are no longer mediated by a solid/liquid interface but by a gaseous/liquid interface, requiring that free charges traverse from the gas to liquid and vice versa. The plasma cathode configuration replaces the typical metal cathode with a plasma, such that free gaseous electrons in the plasma must be injected into the solution phase to initiate reduction reactions at the “cathode”. Recently, this approach to electrolysis has received significant attention for nanomaterials synthesis and emerging applications include the ‘catalyst-free’ electrochemical processing of carbon dioxide (CO2) into useful chemicals.
However, there are significant questions that persist about the nature of the electron reactions at the plasma-liquid interface. Recent studies have confirmed that the plasma electrons solvate in the solution before reacting with other dissolved species, and interfacial measurements of the absorption spectrum show that it is similar to, but different from, the standard solvated electron spectrum measured using radiolysis techniques. This anomaly suggests that the plasma-liquid interface is a wholly different environment for solvated electrons from that they experience in bulk radiolysis. To understand this interface, a model of the interfacial electrostatic Debye layer was constructed by considering both the electrostatic potential variation on the plasma side and the liquid side along with electron injection across the liquid interface. This analytical model predicts a non-linear scaling relationship between the plasma current density and electrolyte conductivity, and experimental measurements confirm the model. Extracted values from the model, including the interfacial electric field (~105 V/m) and the electrolyte cation concentration, offer insight into the electrochemical interface, but do not fully resolve questions regarding the anomalous absorption spectrum of plasma-injected solvated electrons.
Plasma Oxidation of Liquid Precursors
Authors: Sunkara Mahendra Kumar , Ajayi Babajide , Jaramillo-Cabanzo Daniel Felipe 
Published: February 2020

Several grand challenges in energy storage and conversion involve the discovery functional materials which many agree will be multi-element solid solution of metal oxides. The conventional wet chemical methods for synthesis of multi-metal oxide often require time-consuming high pressure and temperature processes, and so the challenge is to develop rapid and scalable techniques with precise compositional control.
This presentation will discuss the concept of plasma oxidation of liquid precursors for making mixed metal oxides with compositional control and rapid time scales. The concept is demonstrated with binary, ternary and quaternary metal oxide with control over entire composition range using metal precursor solutions.1 For the ternary system, the results show the selective formation of metastable spinel solid solution phases with compositions over the entire range by tuning the metal precursor composition.
The concept of plasma oxidation of liquid precursors is investigated to produce a number of materials systems for electrocatalysts, lithium ion batteries and heterogeneous catalysts. For example, in terms of oxygen evolution reaction, ternary alloys involving manganese doped nickel ferrite nanoparticles, NiMnzFe2-zO4 (01), exhibited considerable electrocatalytic activity achieving an overpotential of 0.39V at a benchmarking current density of 10 mAcm-2 for low manganese content at z = 0.2.1 Lithiated NMC compounds exhibit about 220 mAh/g capacity after 50 cycles.

Acknowledgements

The authors acknowledge support from NSF EPSCoR (1355438) and access to facilities at the Conn Center for Renewable Energy Research.

Reference

B.P. Ajayi, S. Kumari, D. Jaramillo-Cabanzo, J. Spurgeon, J. Jasinski and M.K. Sunkara, “A rapid and scalable method for making mixed metal oxide alloys for enabling accelerated materials discovery”, J. of Materials Research, DOI: http://dx.doi.org/10.1557/jmr.2016.9231 (11), 1596-1607(2016)
(Invited) Nanotip-Defined High Local Electric Fields Accelerate CO2 Reduction Heterogeneous Catalysts
Authors: Liu Min , Sargent Edward H. 
Published: February 2020

The electrochemical reduction of carbon dioxide (CO2) provides a promising path towards the storage of renewable energy and to the sustainable synthesis of carbon-based chemical feedstocks. A key challenge for such a process is the low activity and selectivity of the CO2 reduction reaction (CO2RR). It is intensely desired to reduce CO2 at low overpotentials, generating desired products at high current densities over extended periods, and reacting selectively without the formation of undesired byproducts. However, CO2RR today is hindered by the low local concentration of CO2 in aqueous electrolytes, in which more kinetically favorable reduction of protons to H2 often outcompetes CO2RR, eroding reaction selectivity. We developed a field-induced reagent concentration (FIRC) method to enhance the CO2RR process. Through shaping electrodes into arrays of nanoneedles, we generated a high local electric field even when using low applied overpotentials. The high field concentrates electrolyte cations, and the cations bring with these a high local concentration of CO2 to the active CO2RR surface. Simulations revealed that 10-fold higher electric fields can be achieved on nanometrically sharp tips compared to that of quasi-planar regions. Utilizing bottom-up synthesized gold nanoneedle electrodes, record-low onset potential and record-high geometric current density at the low potential of −0.35 V with nearly quantitative (>95%) Faradaic efficiency (FE) for CO2 reduction to CO conversion were achieved (1). This current density surpasses by an order of magnitude the performance of the best previously-reporeted gold nanorods, nanoparticles, and oxide-derived noble metal catalysts. The nanoneedle electrodes exhibited robust continuous reactions over 8 hours in an inorganic aqueous electrolyte. The FIRC concept has also be leveraged to build other metal nanoneedles and metal or metal sulfide covered gold nanoneedles. These electrodes exhibit much enhanced CO2to hydrocarbon conversion efficiencies, proving the wider application of the FIRC concept.
References:
(1) M. Liu, Y. Pang, B. Zhang, P. D. Luna, O. Voznyy, J. Xu, X. Zheng, C. T. Dinh, F. Fan, C. Cao, F. P. Arquer, T. S. Safaei, A. Mepham, A. Klinkova, E. Kumacheva, T. Filleter, D. Sinton, S. O. Kelley, E. H. Sargent, Nature, 2016, 537, 382.
Understanding of Transition from Gas-Phase to Material-Kinetic Limitations for Nonstoichiometric Oxides
Authors: Ji Ho-Il , Davenport Tim , Haile Sossina M 
Published: February 2020

Oxygen nonstoichiometric oxides are important materials in technologies such as fuel cells, permeation membranes, and solar-driven thermochemical fuel production owing to their reversible redox characteristics. The material kinetic properties of the oxides, the surface reaction rate constant at the solid/gas interface and the chemical diffusion in the bulk, have been widely investigated for the understanding of chemical redox kinetics. However, under certain conditions, insufficient oxidant/reductant supply hinders the overall redox kinetics in which the oxides accompany relatively large nonstoichiometry (δ) deviations during the reaction. Furthermore, since the oxides are usually structured as mesoporous or microporous forms to enhance the effective surface reaction rate and thereby enhance kinetics, understanding the correlation among the material kinetic properties, the morphology of the oxides, and the oxidant/reductant gas supply is essential for establishing the strategy for maximizing global reaction rates.
We will present the effects of morphology, temperature and gas flow rate on the global redox kinetics of porous undoped ceria (CeO2-δ) as a model system. Using the reticulated porous ceramic (RPC) approach, and the morphology of the samples was controlled by modifying the starting ceria slurry with/without pore-formers. Kinetic behavior was examined as a function of temperature and gas flow rate by the electrical conductance relaxation technique, which is attractive due to its ease for extracting the kinetic parameters. The validity of the electrical conductance relaxation technique for assessing the kinetic behavior of the porous oxides in the limits of the gas-phase supply and the surface reaction of material will be discussed, and the theoretically anticipated transition behavior from the gas-phase to the material kinetic limits will be shown in comparison to the experimental result.
Integration of Upscaled Microbial Fuel Cells in Real Municipal Sewage Plants
Authors: Muddemann Thorben , Jiang Bolong , Kunz Ulrich , Bormann Hinnerk , Haupt Dennis René , Niedermeiser Michael , Schlaefer Ottmar , Sievers Michael 
Published: February 2020

In search for appropriate processes to enhance the efficiency of municipal sewage plants, microbial fuel cells (MFC) have moved into research focus. Due to the MFC characteristic, which is able to treat wastewater while generating power simultaneously, it is also a promising approach to change the energy balance of sewage plants – switching from the biggest municipal energy consumer to an energy producer.
Owing to the small power density of MFCs in comparison to chemical fuel cells, large active surface areas and therefore low-cost cell constructions, electrodes and catalysts are necessary.
Challenges in MFC upscaling have been overcome and a functional and less price intensive cell design for integration in existing aeration tanks of municipal wastewater treatment plants has been developed (figure left). The new cell design integrates a double-sided graphite/polymer composite anode between two cathodes, to enlarge the surface area. It allows online half-cell potential measurement and biofilm flushing by nitrogen (figure right), among other options. High performance catalytic active cathodes are used, which are produced in-house by a semi-automatic production line.
A fuel cell stack of up to fifty MFCs, each with an active area of 6000 square centimeters respectively, has successfully started operation with real municipal wastewater at the wastewater treatment plant in Goslar, Germany.
In addition to the technical cell design, the wastewater parameters strongly affect the electrochemical performance of microbial fuel cells. Therefore the influences of process parameters (temperature, pH, O2, TOC etc.) were measured to determine optimized operating points when fed by real wastewater.
Additionally cathodic catalysts influence the MFC performance considerably, so the electrode-performance of the scaled up microbial fuel cells were investigated by half-cell measurements.

Figure 1
Quantitative Microstructure Characterization of a NMC Electrode
Authors: Usseglio-Viretta François Laurent Emilien , Smith Kandler 
Published: February 2020

Performance of lithium-ion batteries (LIBs) is strongly influenced by the porous microstructure of their electrodes. In this work, the microstructure of a non-calendared LiNi1/3Mn1/3Co1/3O2 (NMC) electrode has been investigated in order to extract relevant properties useful for battery modeling. At first, the image level of detail has been evaluated (using original criteria based upon edge detection) to assess the overall data quality available for the study. Then, transport properties (volume fraction, connectivity, particle size and tortuosity) and electrochemical property (specific surface area) have been calculated for the pore and the active material. Figure 1 shows concentration field calculated within the pore (used to determine the effective diffusion coefficient) and the active material particle size.
Special attention has been paid to determine (i) the size of the so-called representative volume element (RVE) required to be statistically representative of the heterogeneous medium and (ii) the voxel size dependence for each properties. Both analyses are essential since they allow checking the relevance of the calculated values, before actually using them in macroscopic models. It has been found that the investigated properties exhibit different RVE sizes and image resolution dependences. Several properties have been calculated using a panel of different numerical methods in order to compare their results. Indeed, some of these methods rely on different assumptions and exhibit intrinsic bias, leading as a consequence to different outcomes as established in this work.
Properties have been calculated on the whole domain and have been then plotted along the electrode thickness to evaluate their overall heterogeneity and assess the presence of edge effects, if any. It is then possible to introduce subsequently these spatially-dependent properties into 1D macroscopic battery model in order to take into consideration the heterogeneity, between each slice, of the electrode material while retaining the advantage of an inexpensive CPU time macroscopic model. This approach is particularly relevant for graded electrode materials that exhibit microstructure gradients. Edge effects, as well as property gradients, are shown for the investigated electrode material.
An additional microstructure analysis has been performed on a calendared NMC electrode. Indeed, in industrial LIB electrode manufacturing, the cast electrode undergoes a compression step (calendaring) in order to improve particle connectivity and reduce the electrode’s porosity which increases battery capacity. The effect of this compression step on the material properties have been quantified in this work and significant microstructure properties change are shown.

Figure 1