bluuebunny/crossref_metadata_2025_split huggingface dataset:
Importance of Polymer Backbone Stability of Anion Exchange Polymer Electrolytes
Authors: Kim Yu Seung , Lee Kwan-Soo , Choe Yoong-Kee , Fujimoto Cy 
Published: February 2020

Anion exchange membranes have received attention for solid-state alkaline membrane water electrolysis. However, the harsh operating condicitions of alkaline membrane water electrolysis require good chemical stability of the membrane. Chemical degradation of anion exchange membranes can occur in the cationic functional group, cationic functional group-polymer linkage, and polymer backbone. The alkaline stability of cation-functionalized polyaromatic membranes has mainly been discussed in the context of cation stability. Thus far, lifetime studies of cation-fucntinalized polyaromatics indicate that cation stability is of paramount importnace for stable operation of alkaline membrane water electrolysis. However, equally important is the stability of the polymer backbone which may impact the key membrane properties such as mechanical toughness, hydroxide conductivity and water uptake.[1]
In this study, comparative studies on cationic group vs. polymer backbone stabilities of cationic group functionalized polyaromatic membranes were made by computational modeling and experimenatal method. The computational modeling study suggests that the facile backbone degradation of anion exchange membranes is not only due to the electron deficincy of the polymer backbone but also due to the low bond dissociation energy of the molecular stucture. The relatively lower bond dissociation energy of heteroatom substitutuents in the polymer backbone of anion exchange membranes caused facile backbone degradation before cationic functional group degradation. For example, benzyl trimethyl ammonium has very high electonegativity but the degradation occurs after aryl-ether degradation due to the high bond dissociation energy of carbon-carbon or carbon-nitrogen bonds.
Experimental study on degradation of benzyl trimethyl ammonium functionalized fluoirnated poly(arylene ether) membranes suggests further insight regarding polymer backbone degradation. The C-N stretching peaks of the poly(arylene ether) membranes is shifted to the higher wave number (blue shift) due to the cationic group degradation of the cationic group attached to the phenolic structure occurs before that of the cationic group attached to the un-degraded polymer backbone. This inidcates accessibility of water molecules also play a critical role in polymer backbone degradation. We will provide some other evidences on facile backbone degradation of polyaromatic polymers and their impact on membrane properties at the meeting. This presentation emphasizes on the importance of polymer backbone stability.
[1] Fujimoto, C.; Kim, D. S.; Hibbs, M.; Wrobleski, D.; Kim, Y. S. J. Membr. Sci. 2012, 423, 438−449.
Conductivity and Mechanical and Thermal Stability of Polyelectrolyte-Functionalized Anion Exchange Membranes
Authors: Rodriguez-Silva Allen , Movil-Cabrera Omar , Staser John A 
Published: February 2020

Recent studies have shown that anion exchange membranes (AEMs) surpass cation exchange membranes (CEMs) in that they reduce fuel crossover and facile electrochemical kinetics in alkaline solution which makes possible the use of non-precious metal electrocatalysts. However, the chemical and mechanical stability of AEMs is generally poor compared to CEMs. Our research has focused on developing porous AEMs utilizing a stable, nonconductive polymer (polysulfone) as the structural matrix functionalized with an ion-conducting polyelectrolyte filling the pores. We have synthetized these membranes via a simple phase-inversion process. Preliminary results using electrochemical impedance spectroscopy (EIS) indicate that the membrane conductivity is not always proportional to the quantity of polyelectrolyte in the phase inversion solution, which has led us to believe that non-homogeneous distribution of the polyelectrolyte may be taking place due to the polarity difference of these molecules. These results are shown in Figure 1 [1].
Continuous analysis and study of the conductive properties as a function of the amount of polyelectrolyte will be performed. Surface and cross-sectional images to identify the porous structure of these AEMs, as well as thermal gravimetric analysis (TGA) investigating thermal stability of these membranes will be presented. Finally, water diffusion anisotropy data will be collected by nuclear magnetic resonance (NMR) technique.
Figure 1: Rodríguez. A., Staser, J. (2015). “Synthesis of polyelectrolyte-functionalized anion exchange membranes and conductive, mechanical and thermal properties study”. (Manuscript is currently in progress)

Figure 1
Status of Vertical Electroplishing at Cornell University
Authors: Furuta Fumio 
Published: February 2020

Cornell's SRF group has continued R&D on vertical electropolishing (VEP) of Niobium SRF Cavity with electrolyte of HF(40w%):H2SO4(96w%) in Volume proportions 1: 9. Compared with conventional horizontal EP system for SRF cavities, VEP could eliminate rotary acid seals, sliding electrical contact, cavity vertical/horizontal position control fixtures. And also, the acid plumbing/containment could be simplified. So, the cost reduction of capital equipment is highly expectable. Many of single- and multi-cell cavities have been processed with VEP and performed RF test at Cornell. VEP’ed multi-cell cavity performance was limited by too much Qo degradation above 25MV/m before. But in the analysis of removal vs. field gradient against previous VEP’ed cavity tests, we have found a tendency that small removal as final etches could provide high gradient without Qo degradation. The ILC 9-cell cavity “ACCEL9” with TESLA shape processed by VEP at Cornell achieved Eacc of about 40MV/m by minimizing final removal. This is the first 9-cell cavity that achieved ILC base-line specification (Qo=1.0e10 at 31.5MV/m, Qo=8.0e9 at 35MV/m) by VEP in the world. We have also fabricated demountable half-cell coupon cavity. This cavity consists of Nb half-cell and dummy cavity assemblies. This coupon cavity provides us more information about VEP process details, such as the difference of I-V curve between cell orientations. Four demountable Nb coupons with diameter of 11mm are attached on half-cell and processed. These coupons are very strong tool for further surface analysis to optimize process parameters. We will present our current status of VEP R&D, cavity test results, and fundamental study results with Nb coupons.
(Invited) Operating Mechanisms of Organic Bulk-Heterojunction Solar Cells
Authors: Garcia-Belmonte Germa 
Published: February 2020

Bulk-heterojunction solar cells contains an interpenetrated blend of donor-acceptor molecules that assists photogeneration and carrier transport. We show for thinner films in which transport or outer interface extracting limitation is not severe that carrier recombination is easily accessible from impedance analysis, and permits evaluating losses in (Fermi level) voltage. As a result reconstruction of the current-voltage characteristics in any required conditions based on a restricted set of measurements is possible. The analysis highlights carrier recombination current as the determining mechanism of organic solar cell performance. In addition the influence of the electronic density-of-states (DOS) caused by the inherent energy disorder on open-circuit voltage and fill factor is highlighted. The connection between DOS and the capacitive response is also addressed.
A discussion of impedance analysis in the much less studied case of collection-limited solar cells is discussed. Recent experimental analyses of transport processes are presented. We show how by incorporating blocking electrodes into the cell structure transport mechanisms can be understood in terms of diffusion-recombination models. Impedance spectra reveal carrier diffusion signature when blocking or extracting cathode contacts are employed. Finally contact effects are also addressed. The energy level alignment at the contacts is of primary importance in establishing the contact extracting ability and carrier selectivity. Several characterization techniques of the contact properties are explored.
(Invited) Unexpected Molecular Interfaces: SAMs on Cobalt
Authors: Pookpanratana Sujitra , Richter Curt A. , Hacker Christina A. 
Published: February 2020

Molecular-based materials are appealing for many applications due to their diverse composition, which in turn impacts physical and electronic properties. Often, the interaction between an organic layer and an inorganic substrate is unpredictable once the interface is formed. We use a holistic approach to investigate the molecular interfaces – photoelectron spectroscopies and electrical characterization to probe the interface and buried junction, respectively. Thus, molecular-based interfaces provide a unique platform to investigate the ensemble-scale impact molecules which provide basic physical insights and ideas for potential applications.
An emerging field is to combine the flexibility of organic materials into spin-based electronics. Most research in this field implement organic semiconductors as the non-magnetic spacer in a spin-valve device configuration. While there are many proposed mechanisms regarding spin-transport in organic materials, there is no doubt that the interface between the magnetic electrode and organic material is an important aspect for the success of an organic spintronic device. In addition to potentially altering the electronic structure at the interface, SAMs could serve as a tunneling barrier for spintronics due to their insulating nature and discrete thickness. Inorganic tunnel junctions have improved spin-injection into organic spin-valve devices.
We have explored self-assembled monolayers (SAM) on a template-stripped and oxidized cobalt surface to understand the molecular-metal interface from a structural, chemical, and electronic point of view. We find that the self-assembly of the bifunctional molecule is profoundly different than the thiol-alone species. In particular, the cobalt surface exhibits a very different interface following self-assembly of a carboxylic acid-bearing species. We find that a thiol-carboxylic acid monolayer reacts with oxidized Co surface atoms in such a way that metallic Co atoms are detected at the surface. We propose two different models of the interface formation based on the results, and suggest that the MHA/ethanol removes the cobalt oxide during the self-assembly as the prevailing model. We also discuss the impact of this Co/molecule interface on electron transport through Co/molecule/Si molecular junctions. Our results provide insight into ex-situ modification and functionalization of ferromagnetic interfaces impacting an important aspect of spin-based devices. Interfaces are not always straight forward – they can have unforeseen impact and influence.

Figure 1
Synthesis, Characterization, Electrochemical and Optoelectronic Properties and LED Device Fabrication of Low Band-Gap Donor-Acceptor Organic Semiconducting Small Molecules
Authors: Dhamodharan Ragavachari , Ramachandran Elumalai 
Published: February 2020

Organic fluorophores that exhibit efficient emission in the NIR region, especially in the solid state, are scarce. The design of organic materials towards efficient solid state emission has gained immense importance [1] due to their applications in various fields, such as organic light emitting devices (OLEDs), flat panel displays, organic solid-state lasers and fluorescent sensors [2]. Among the various fluorophores, red emitters have acquired a great deal of importance since red is one of the three primary colors used for white light emission [3]. The development of p-conjugated systems emitting in the NIR region is of great importance as they are often used in bio-imaging, laser printers, optical disks, plasma panel displays and heat absorbers [4]. For low energy emission such as red and NIR, planar molecular architecture with extended conjugation is inevitable for lowering the band-gap. But this extended planar architecture often leads to a strong intermolecular p-p interaction, a detrimental phenomenon by which the molecule loses its excitation energy through a non-radiative emission, resulting in weak emission. In the light of these facts it is a challenging task to design molecules that would exhibit efficient emission in the solid state, especially in the red to NIR region.
This presentation will discourse upon the synthesis, characterization, electrochemical, optoelectronic properties and LED device fabrication of low band-gap donor-acceptor organic semiconducting small molecules that exhibit solid state emission in the yellow to NIR region.

References

a) Shimizu, M.; Hiyama, T. Chem. Asian. J.
2010, 5, 1516; b) Sreejith, S.; Divya, K. P.; Ajayghosh, A. Chem. Commun. 2008, 2903; c) Zhang, Z.; Xu, B.; Su, J.; Shen, L.; Xie, Y.; Tian, H. Angew. Chem.
2011, 123, 11858; d) Zhou, Y.; Kim, J. W.; Kim, M. J.; Son, W. J.; Han, S. J.; Kim, H. N.; Han, S.; Kim, Y.; Lee, C.; Kim, S. J.; Kim, D. H.; Kim, J. J.; Yoon, J. Org. Lett.
2010, 12,1272.

a) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Chem. Mater. 2004, 16, 4556; b) Justel, T.; Nikol, H.; Ronda, C. Angew. Chem.
1998, 110, 3250; c) Samuel, I. D. W.; Turnbull, G. A. Chem. Rev. 2007, 107, 1272; d) Zhang, S. W.; Swager, T. M. J. Am. Chem. Soc.
2003, 125, 3420.

a) Adhikari, R. M.; Duan, I.; Hou, L.; Qiu, Y.; Neckers, D. C.; Sha, B. K. Chem. Mater. 2009, 21, 4638; b) Park, M. J.; Lee, J.; Park, J. H.; Lee, S. K.; Lee, J. I.; Chu, H. Y.; Hwang, D. H.; Shim, H. K. Macromolecules. 2008, 41, 3063.

Qian, G.; Wang, Z. U. Chem. Asian J. 2010, 5, 1006.

Figure 1
Photoelectrochemical Studies and Capacitance Measurements during the Nitride Passivation of InP in Liquid Ammonia (-55°C)
Authors: Njel Christian , Bakas Idriss , Aureau Damien , Gonçalves Anne-Marie , Etcheberry Arnaud 
Published: February 2020

This work presents a fundamental photo-electrochemical process at the interface SC/electrolyte. The photoelectrochemical passivation of n-InP is reported in liquid ammonia (-55 °C) during an anodic treatment[1]. The extraction of InP sample from the solvent is successfully performed at ambient temperature. Thanks to XPS (X-ray Photoelectron Spectroscopy), a reproducible polyphosphazene like film is reported on InP (-[(H2N)-P=N]n-)[2]. A soft anodic electrochemical treatment under illumination is applied at the interface to provide a gradual controlled coverage ratio of the surface by the film. This quantitative study requires a chronopotentiometry process with a constant anodic current of 1µA.cm-2 under illumination. An anodic charge around 0.3 mC.cm-2 is enough to ensure a complete coverage of the surface by the film. According to the anodic charge a gradual striking flat band potential shift is observed (Fig. 1). A flat C-2 = f(V) is extended over 1 volt leading to a high interfacial capacitance (» 2µF.cm-2). From the analysis of capacitance-potential curves, the interface appears to be under accumulation conditions after the film formation. A significant drop of the resulting photo potential is then observed (Fig. 2). However, under a strong positive overvoltage (» 1V), a stationary anodic photocurrent is recovered.

[1] A-M. Gonçalves, N. Mézailles, C. Mathieu, P. Le Floch, A. Etcheberry, « «Fully Protective yet functionalizable monolayer onto InP” Chemistry of Materials.22(2010) 3114-3120.

[2] A-M. Gonçalves, C.Njel, C. Mathieu, D.Aureau, A. Etcheberry.
« Phosphazene like film formation on InP in liquid ammonia (223K) . Thin Solid Films 538 (2013) 21–24.

Figure 1
An Attractive Wet Route for Nitriding III-Vs
Authors: Njel Christian , Aureau Damien , Gonçalves Anne-Marie , Etcheberry Arnaud 
Published: February 2020

The control of surface quality or interface chemistry is one of the key steps for a lot of new advanced industrial products with high added value. This is particularly true in the case of III-V semiconductors (III-Vs) technology for which surface passivation plays a key role in device performances, low temperature and low damage processes having been developed over time to reduce surface effects.
With the introduction of III-V’s on large scale Silicon platforms and device scaling to nanometer range, passivation question will be on the front page again
[1]
. Phosphorus nitride insulating films as passivation layers on InP seem to be very attractive to realize MISFETs with high channel electron mobilities and low interface state densities. This paper presents an original electroless approach of polyphosphazen film formation on InP in liquid ammonia (-55 °C). The chemical surface modifications are closed to those observed by electrochemistry[2],[3]. These findings are protected by a CNRS patent filed by us in 2013
[4]
. Moreover, the chemical stability of the surface is also demonstrated by XPS analyses. Indeed no air ageing of the surface is observed after three months of air exposure. The electroless mode is attractive to the industry since it avoids any electrical (potential and current) control at the interface.
This paper proposes a novel electroless passivation route in liquid ammonia through a “Polyphosphazen like” film formation which could be adapted to a large scale production since no electrical contact is involved at the interface to provide a full and efficient chemical passivation.

[1]“Interface engineering and chemistry of Hf-based high-k dielectrics on III–V substrates”, G. He, X. Chen, Z. Sun, Surface Science Reports 68 (2013) 107.
[2] A-M. Gonçalves, N. Mézailles, C. Mathieu, P. Le Floch, A. Etcheberry, « «Fully Protective yet functionalizable monolayer onto InP” Chemistry of Materials.22 (2010) 3114-3120.
[3] A-M. Gonçalves, C.Njel, C. Mathieu, D.Aureau, A. Etcheberry.
« Phosphazene like film formation on InP in liquid ammonia (223K). Thin Solid Films 538 (2013) 21–24.
[4] “Polyphosphazène electroless sur semiconducteurs III-P”, réf CNRS 03024-01 BFF100427CG
A. Etcheberry, A-M. Gonçalves, C. Mathieu, J. Vigneron, N. Mézailles, P. Le Floch
(Invited) Use of the Doping Dependence of Collection Efficiencies for Dye Sensitized Photocurrents to Demonstrate Physical Models for Charge Transfer at Single Crystal Oxide Semiconductor Surfaces
Authors: Spitler Mark T , Parkinson Bruce A , Watkins Kevin 
Published: February 2020

The different physical limits of an Onsager-based model for charge collection at a semiconductor electrode are revealed through an experimental examination of the doping density dependence of photocurrents at single crystal ruitile TiO2 electrodes sensitized with the N3 chromophore and a trimethine cyanine dye. As the doping density of the electrodes was varied from 1015 cm-3 to 1020 cm-3, three different regimes of behavior were observed for the magnitude and shape of the dye sensitized current-voltage curves. Low-doped crystals produced current-voltage curves with a slow rise of photocurrent with potential. At intermediate doping levels, Schottky barrier behavior was observed producing a photocurrent plateau at an electrode bias in the depletion region. At highly doped electrodes tunneling currents played a significant role, especially in the recombination processes. The fitting revealed the role of the various physical parameters that govern photoinduced charge collection in sensitized systems.
Pseudocapacitive Charge Storage at Nanoscale Silicon Electrodes
Authors: McSweeney William , Geaney Hugh , Glynn Colm , McNulty David , O'Dwyer Colm 
Published: February 2020

Current lithium-ion battery anode research involves significant investigations of semiconducting materials, particularly Si as its theoretical specific capacity is >4000 mAh/g1. Previous theoretical studies showed that porous Si with a large pore size and high porosity can maintain its structure after Li ion induced alloying and swelling. Metal-assisted chemical (MAC) etching is shown here to form internally mesoporous nanowires in the form of a layer, etched from highly doped Si2-4. Some porous materials are well known to exhibit pseudocapacitive behaviour in aqueous electrolytes5,6. Maintaining the structure without stress-induced cracked caused by volumetric changes in material is crucial in achieving a high capacity and long cycle retention. Almost all investigations of nanoscale Si involve their deposition onto a metallic current collector electrode within the battery cell. Here, we demonstrate that pseudocapacitive behaviour can be harnessed when Si nanowires are etched to maximum mesoporosity, forming an electrically dead layer on silicon current collector electrodes. This limits insertion or alloying processes to form Li-Si phases7and charge is stored within the electric double layer, even in Li-ion containing electrolytes. Measurements using cyclic and linear voltammetry supported by Raman scattering spectroscopy and electron microscopy confirm surface charge storage mechanisms; pseudocapacitance is not observed when the same nanowires are used on stainless steel current collectors. In such cases, the rate of lithiation is shown to be related to the degree of porosity and the net surface electronic density of the porous silicon in accumulation mode during charging.
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W. McSweeney, O. Lotty, C. Glynn, H. Geaney, J. D. Holmes and C. O'Dwyer, Electrochim. Acta, 135, 356 (2014).
Enabling Overall Water Splitting By Iron Oxide and Silicon
Authors: Wang Dunwei 
Published: February 2020

Photoelectrochemical water splitting promises a large-scale solar energy storage solution. Its development has been impeded by poor performance of photoanodes, particularly in the capabilities of photovoltage generation. Using the prototypical photoanode material of hematite as a study tool, we show that structural disorders on or near the surfaces are an important reason for the low photovoltages. A facile re-growth strategy was developed to readily alter the surfaces for reduced disorders. A record-low turn-on voltage of 0.45 V (vs. reversible hydrogen electrode) was measured. The result permitted us to construct devices made of three most abundant elements on the Earth crust (O, Si, and Fe) to split water with only sunlight as the energy input at an overall efficiency of 0.91%.