bluuebunny/crossref_metadata_2025_split huggingface dataset:
Instability and Degradation Mechanism of Platinum-Group Metal (PGM)-Based Carbon Supported Electrocatalysts in Alkaline Medium
Authors: Lafforgue Clémence , Dubau Laetitia , Maillard Frederic , Chatenet Marian 
Published: February 2020

Direct liquid alkaline fuel cells (DLAFC) are considered high-energy density generators and arouse interest because (i) their energy density can be higher than for closed systems like Li-ion batteries, and (ii) they do not suffer from issues related to H2 compression, storage and delivery as for proton-exchange membrane fuel cells (PEMFC). Moreover, electrocatalyst commonly used for PEMFC suffer from a poor durability in operation [1]. In the case of alkaline fuel cells, despite few studies, the common belief supposes a larger stability of electrocatalysts in alkaline medium compared to acidic medium, owing to the better thermodynamic stability of many metals and oxides at high pH, as predicted by Pourbaix [2].
In reality, some recent studies showed that the state-of-the-art carbon-supported platinum nanocatalysts are subjected to severe degradations upon a mild potential cyclic procedure in 0.1 M NaOH at 25°C [3]. The loss of electrochemical surface area (ECSA) reaches 60 % after 150 cycles in the range 0.1 - 1.23 V vs. RHE at 100 mV s-1. Herein, the same degradation procedure has been performed with Pd/C and PtRu/C: non-negligible ECSA loss (ca. 35 %) is monitored for Pd/C, whereas very harsh degradation is noted for PtRu/C.
Identical-location transmission electron microscopy studies (ILTEM) revealed that the main degradation mechanism is, whatever the electrocatalyst, the detachment of the nanoparticles from the carbon substrate (Figure 1 D-E-F). It is suspected that this detachment follows the rupture of the binding between the PGM nanoparticles and the carbon support, triggered by the formation of carbonates originating from PGM-assisted corrosion of the carbon support. The CO-stripping experiments performed in NaOH 0.1 M (Figure 1 A-B-C) confirm that the ability of each electrocatalysts to form CO2 is linked to the observed degradations.
This work was partly supported by an ONR-global grant (project ONR N62909-16-1-2137).

References

[1] L. Dubau, L. Castanheira, F. Maillard et al., WIREs Energy and Environment 2014, 540, 3.
[2] M. Pourbaix, National Association of Corrosion Engineers 1979, 453.
[3] A. Zadick, L. Dubau, N. Sergent, G. Berthomé, M. Chatenet, ACS Catalysis 2015, 4819, 5.

Figure 1
Metal-Organic-Frameworks-Modified Separator for Lithium–Oxygen Batteries with Long Cycle Life
Authors: Zhang Xiahui , Cha Younghwan , Dong Panpan , Lee Jung-In , Song Min-Kyu 
Published: February 2020

Lithium-ion batteries (LIBs) are reaching their theoretical energy limit, but still cannot meet the needs for all-electric vehicles. Owing to their five times higher energy density (~3500 W h/kg) than that of LIBs, lithium–air (Li–O2) batteries have been considered as one of most promising next-generation energy storage devices.1 However, Li–O2 batteries still suffer from several challenges that hinder their practical applications, such as low energy efficiency and poor cycle life.2 Recently, it has been demonstrated that the gradual accumulation of side products due to parasitic reactions can result in the failure of Li–O2 batteries.3 Therefore, the cyclic performance of Li–O2 batteries can be significantly improved by preventing the accumulation of side products.
Metal–organic frameworks (MOFs), a novel type of crystalline porous materials, have been widely studied as adsorbents for gas separation or storage due to their large surface area, high micro-porosity, and chemically unsaturated metal sites.4 Recently, MOFs-modified separators have been reported as molecular sieves to mitigate the shuttling effect of polysulfides in lithium–sulfur batteries.5 Herein, we report a MOFs-modified separator for Li–O2 batteries. In this work, nanocrystalline MOFs are prepared and then coated on a GF/D separator by a facile method. The as-fabricated MOFs-modified separator showed much-improved cycle life up to 200 cycles at a current rate of 125 mA/g, compared to untreated GF/D separator. The mechanism of how MOFs mitigate the accumulation of side products on the cathode will be also discussed in this presentation.

Reference

1 Bruce, P. G., Freunberger, S. A., Hardwick, L. J. & Tarascon, J. M. Li–O2 and Li–S batteries with high energy storage. Nat Mater
11, 19-29, doi:10.1038/nmat3191 (2012).
2 Luntz, A. C. & McCloskey, B. D. Nonaqueous Li–air batteries: a status report. Chem Rev
114, 11721-11750, doi:10.1021/cr500054y (2014).
3 Kim, B. G. et al. Ordered Mesoporous Titanium Nitride as a Promising Carbon-Free Cathode for Aprotic Lithium–Oxygen Batteries. ACS nano
11, 1736-1746 (2017).
4 Furukawa, H., Cordova, K. E., O’Keeffe, M. & Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science
341, 1230444 (2013).
5 Bai, S., Liu, X., Zhu, K., Wu, S. & Zhou, H. Metal–organic framework-based separator for lithium–sulfur batteries. Nat. Energy
1, 16094 (2016).
Dual Color Bioimaging with Nanocarbon Quantum Dots
Authors: Hasan Md Tanvir , Gonzalez-Rodriguez Roberto , Sizemore Elizabeth , Naumov Anton V 
Published: February 2020

Since a number of medical conditions require simultaneous treatment and diagnostics, the field of molecular therapeutics has recently turned to multifunctional approaches allowing for both therapy and biomedical imaging. A number of such molecular and nanoformulations are combined with fluorophores that allow for imaging of the delivery pathways of the drug in the visible. This is optimal for in-vitro or ex-vivo work, however, can not be utilized well in-vivo. Thus there is a need in nanoformulations optimized for both in-vitro and in-vivo studies. Nanocarbons, possessing intrinsic stable fluorescence in the visible and near-IR stand out as candidates for such complex application.
In this work, we for the first time produce a biocompatible nanocarbon quantum dots (NCQDs) that exhibit two-color emission both in visible and NIR possess a capability for biological pH sensing. These NCQDs show the crystalline graphitic structure in TEM and average sizes of c.a. 5 nm beneficial for cellular internalization. As opposed to related structures such as graphene oxide and other graphene derivatives NCQDs show high quantum yield in green (~500 nm) of 68.1% calculated via a comparative method using Coumarin-153 as a basis. Near-IR emission at ~860 nm shows lower relative quantum yield but is located in the water window with reduced absorption and lower autofluorescence backgrounds providing a promising potential route for in-vivo studies. Emission of NCQDs also depends on pH of the surrounding medium. The change in pH of as-prepared NCQDs from 2.71 to 8.2 yields an increase of fluorescence intensity up to ~60%. The actual spectral signature of NCQD emission also changes with pH: upon spectral decomposition of the broad emission feature the green component (470-514 nm) shows an increase at higher pH with respect to the red component (846-888 nm). Biocompatibility of NCQDs is verified by the MTT assay showing a low cytotoxic response. As potential drug delivery agents, NCQDs also show efficient cellular internalization assessed via in-vitro imaging in green. Additionally, pH-dependent shifts of the spectral features allow differentiating between acidic cancerous and neutral healthy exocellular environments allowing to use NCQDs for cancer detection. Therefore, our results indicate that NCQDs have a significant potential in bio-applications because of their capacity for dual color green/near-IR imaging for in-vitro/in-vivo studies, pH sensitivity, water solubility, low cytotoxicity and high capacity for cellular internalization.
Nickel Nanoparticles Synthesized Via Novel Alcogel Electrolysis for the Growth of Multi-Walled Carbon Nanotubes (MWCNTs) By Chemical Vapor Deposition (CVD) Technique
Authors: Ali Zulfiqar 
Published: February 2020

Facile Ni-silica nanocomposite synthesis method via alcogel electrolysis and their subsequent use for growth of multiwalled carbon nanotubes (MWCNTs) by conventional chemical vapor deposition (CVD) setup is reported. As the nature of nickel nanoparticles is magnetic so after synthesis amidst silica network these were magnetically separated. The catalysts were characterized by x-ray diffraction (XRD) and crystallite size was calculated from peak broadening of XRD data by using Sherr’s formula which was found to be 18-20 nm. Moreover, ethanol was employed as precursor of carbon along with Argon as inert carrier gas in CVD and three experiments on nickel nanocatalysts were performed in different temperature ranges i.e. 650 oC, 750 oC and 850 oC.
The grown multiwalled carbon nanotubes (MWCNTs) by CVD were characterized by XRD, Raman spectroscopy and Secondary Electron Microscopy (SEM). Raman spectroscopy confirms the high purity of grown MWCNTS on nickel nanocatalysts while from the SEM images the average diameter was found to be 25 nm and morphology of CNTs of grown carbon nanotubes on synthesized nickel nanoparticles were elucidated which shows nest type morphology characteristics of MWCNTs.
Key words: Alcogel Electrolysis, CVD, MWCNTS, Raman Spectroscopy.
(Invited) Functionalization of Carbon Nanotubes in a Micellar Environment
Authors: Orcin-Chaix Lucile , Delport Géraud , Campidelli Stephane , Voisin Christophe , Lauret Jean-Sébastien 
Published: February 2020

A key issue for applications of colloidal nanoobjects is related to their solubility in water. Indeed, their aggregation results in the deterioration of their intrinsic properties. In order to solve this problem, many strategies have been developed. As far as carbon nanotubes are concerned, the best way to solubilize them in water while preserving their outstanding properties is to use a micellar environment. As a consequence the chemistry of carbon nanotubes in micelles is a growing field of research. For instance, people have grafted photoswitches on the wall of nanotubes, have doped nanotubes with diazonium and even performed polymerization in micelles [1-4].
In this presentation, we will present our recent results on the functionalization of carbon nanotubes with different kind of molecules in a micellar environment (porphyrins [5, 6], polymers [7]…). In particular, we will focus on the influence of the molecules on the optical properties of carbon nanotubes both on ensemble and at the single object level.

References

[1] AJ. Hilmer et al. Langmuir 28(2), 1309-1321 (2012)
[2]S. Kreft et al., J.Phys.Chem.C,119.27 (2015): 15731-15734
[3] G. Clavé, et al, Chem. of Mat. 25.13 (2013): 2700-2707
[4] Y. Tsutsumi RSC Advances 4, 6318 (2014)
[5] G. Delport et al, NanoLetters 17, 6778 (2017)
[6] G. Delport et al, Nanoscale 9, 2646-2651 (2017)
[7] L. Orcin-Chaix et al, submitted
(Invited) Long-Lived Charge Separation across Interfaces with Semiconducting Single-Walled Carbon Nanotubes
Authors: Blackburn Jeffrey L. , Kang Hyun Suk , Ferguson Andrew John , Arias Dylan , Johnson Justin C. 
Published: February 2020

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive absorbers for use in solar energy harvesting schemes because of their strong and energetically tunable optical absorption, and high charge carrier mobilities due to the delocalized nature of the π-electron system. Beyond their technological potential, s-SWCNTs offer attractive properties for fundamental studies of charge generation in strongly confined nanoscale systems and photoinduced electron transfer (PET) processes. For example, strong quantum confinement and low dielectric screening impart single-walled carbon nanotubes with exciton-binding energies substantially exceeding kBT at room temperature. Additionally, the energetically narrow and distinct spectroscopic signatures for excitons and charges within s-SWCNT thin films enables the unambiguous temporal tracking of fundamental photophysical processes occuring at important photoactive heterojunctions designed for charge separation.
In this presentation, I will discuss recent studies that probe the generation and recombination of long-lived charges in samples consisting of heterojunctions between s-SWCNTs and various electron acceptors. I will focus on the roles of important interfacial properties that can influence the kinetics and efficiency of the interfacial PET process and recombination of the resulting separated charges. These properties include the energetic energetic driving force for exciton dissociation, the amount of residual wrapping polymer on the highly enriched s-SWCNTs, the local dielectric enrivonrment, the presence or absence of an electric field, and geometrical factors of the interface that can be modified via structural properties of the acceptors. Better fundamental understanding of these model interfaces can inform the design of more efficient solar energy harvesting systems, photodetectors, and other opto-electronic devices.
Multiple-Heterojunction in Single Titanium Dioxide Nanoparticle for Novel Metal-Free Photocatalysis
Authors: Cho Yoonjun , Kim Sungsoon , Park Jong Hyeok 
Published: February 2020

Despite longstanding controversy, TiO2 polymorphs heterojunction composed of anatase and rutile outperform the individual ones because of the energetic type-II band alignment at the heterojunction interface. Apart from the conventional polymorphs interface, the surface disordered TiO2 has been drawing interest and considered as an unpredictable strategy while is regarded as a fact for dramatically enhancing photocatalytic activity. However, introduction and localization of the disordered layer within conventional TiO2 nanoparticles with the heterojunction has remained a big challenge.
Here we report a selective positioning of a disordered layer with different thickness ranges in between the anatase and rutile phases by a conceptually different synthetic route for highly efficient novel metal-free photocatalytic H2 production (denoted as DE-P25). With two step disorder engineering: Phase selective disordering of rutile TiO2 and thermal annealing process at temperature lower than phase transformation, the multiple heterojunction in DE-P25 single nanoparticle with the disordered layer of 2~3 nm could be synthesized which is confirmed by high resolution-TEM, electron energy loss spectroscopy (EELS) and inline electron holography mapping for the first time. EELS Ti-L2,3 spectrum geometry of DE-P25 showed distinctive oxygen-deficient variation between the two crystals which corresponds with the drastic decrease of potential and negative charge density within the disordered layer due to localized unpaired electrons. PL decay profiles exhibiting ultra-fast charge migration of DE-P25 indicate that the rutile phase incorporated with the disordered layer in the TiO2 nanoparticle induces dominant direct excition formation and reduces the self-trap of charge carriers, thus suppressing the electron/hole recombination, which perfectly coincides with the holography mapping analysis.
This multiple heterojunction in single TiO2 nanoparticles composed of crystalline anatase/disordered rutile/ordered rutile demonstrate not only superior interfacial charge separation efficiency, but also novel-metal free surface reactivity, which synergistically yields ~140 times higher H2 production rate than conventional anatase and rutile single heterojunction system.

Figure 1
(Invited) Paramagnetic Endohedral Fullerenes for Biomedical Applications
Authors: Cornes Stuart , Zhou Shen , Barendt Timothy , Zheng Xiaoyu , Eaton Sandra , Eaton Gareth , Davis Jason , Beer Paul , Porfyrakis Kyriakos 
Published: February 2020

N@C60 is a paramagnetic endohedral fullerene species comprised of a single nitrogen atom incarcerated within a C60 carbon cage. Shielding of the nitrogen from the external environment results in extremely long relaxation times of its electron spin (T1 = 0.375 ms, T2 = 0.25 ms). This provides the molecule with a very sharp EPR signal,1 which undergoes observable dipolar broadening in the presence of other paramagnetic species, suggesting that N@C60 derivatives would be ideal candidates as spin probes for biological applications.2–4 In order for this to be realised functionalisation of the inherently hydrophobic fullerene cage must be undertaken to render it compatible with aqueous environments.
Several methodologies for the solubilisation of empty cage and other endohedral fullerene species have been demonstrated,5–7 however many of these are unsuitable for use with N@C60 due to its instability at elevated temperatures.8 Herein we report the first examples of water-soluble derivatives of N@C60, prepared using an adaptation of the widely used Bingel reaction.9 Preliminary investigations towards the use of these materials as electron paramagnetic resonance imaging (EPRI) agents is also discussed.10

1 J. J. L. Morton, A. M. Tyryshkin, A. Ardavan, K. Porfyrakis, S. A. Lyon and G. Andrew D. Briggs, J. Chem. Phys., 2006, 124, 014508.
2 K.-P. Dinse, H. Käß, C. Knapp and N. Weiden, Carbon, 2000, 38, 1635–1640.
3 G. Liu, A. N. Khlobystov, G. Charalambidis, A. G. Coutsolelos, G. A. D. Briggs and K. Porfyrakis, J. Am. Chem. Soc., 2012, 134, 1938–1941.
4 S. Zhou, M. Yamamoto, G. A. D. Briggs, H. Imahori and K. Porfyrakis, J. Am. Chem. Soc., 2016, 138, 1313–1319.
5 J. Li, A. Takeuchi, M. Ozawa, X. Li, K. Saigo and K. Kitazawa, J. Chem. Soc. Chem. Commun., 1993, 0, 1784–1785.
6 M. Brettreich and A. Hirsch, Tetrahedron Lett., 1998, 39, 2731–2734.
7 I. Rašović, Mater. Sci. Technol., 2016, 0, 1–18.
8 A. Iwasiewicz-Wabnig, K. Porfyrakis, G. A. D. Briggs and B. Sundqvist, Phys. Status Solidi B, 2009, 246, 2767–2770.
9 S. Zhou, I. Rašović, G. A. D. Briggs and K. Porfyrakis, Chem. Commun., 2015, 51, 7096–7099.
10 S. P. Cornes, S. Zhou and K. Porfyrakis, Chem. Commun., 2017, DOI:10.1039/C7CC07106J.

Figure 1
Highly Selective Silicon Dry Chemical Etch Technique for Advanced FinFET Technology
Authors: Bi Zhenxing , Loubet Nicolas J , Greene Andrew , Yeung Chunwing , Zhang Jingyun , Devarajan Thamarai , Sankarapandian Muthumanickam , Zhou Huimei , Wang Miaomiao , Conti Richard , Saulnier Nicole , Stolfi Michael , Bhatnagar Ajay , Cogorno Matt , Zhang Jingchun 
Published: February 2020

With transistor scaling in 7nm technology and beyond, sacrificial silicon materials etches (e.g. dummy poly silicon gate removal) are considered to be among the most challenging hurdle in FinFET process development. In this paper, we present a dry chemical etch technique for selective etching of single crystal, poly-crystal and amorphous silicon on various FinFET device process steps. It was demonstrated that this technique could completely remove poly silicon in vertically high aspect ratio (AR>5) FinFET gates with a large process window (over-etch budget ~200%) while achieving the lowest gate leakage current and best short channel FET yield. Proper surface preparation, queue time control and etch by-product removal strategies are discussed. The residue free etch and etch by-product sublimation mechanisms are also investigated by High Resolution Electron Microscopy (HREM) and Fourier Transform Infrared Spectroscopy (FTIR) surface analysis.
This work was performed by the IBM Research at various IBM Research and Development Facilities.
Simulations of Correlative Defect Forming in Hafnia
Authors: Pil'nik Andrey A. , Chernov Andrey A. , Perevalov Timofey V. , Islamov Damir R. 
Published: February 2020

High-κ hafnium oxide is widely used in different electronic devices. The electronic properties of HfO2 (e.g. leakage currents, optics) are defined by defects and traps, namely by oxygen vacancies (VO). Generation of new defects leads to breakdown, increasing the leakage, that leads to the FET and FRAM degradation. On the other hand, active layers in RRAM devices use traps as precursors for HRS/LRS switch. The aim of the work is predicting the defect forming in dielectrics in strong electric fields using analytical, numerical and ab initio simulations. Despite the advances in computational performance, the ab initio simulations still require large time and efforts. Analytical and half-analytical solutions of the problem can be helpful in a way of predicting conditions for defect formation.
The rate of new defect generation in the hafnium oxide with only one VO was calculated using the heat transfer equation with a strong positive loopback. The analytical and half-analytical solutions were found and compared with numerical ones. The most probable positions of new defect at specific electric field were found. These results were compared with ab initio (DFT) calculations of oxygen polyvacancy structure in monoclinic HfO2. It was found that the most favorable spatial configuration of an oxygen polyvacancy is a chain, where the next vacancy is formed near the already existing one, and no more than 2 removed O atoms are related to a Hf atom. Found distances between neighboring VO are (4.05-4.21) Å.
The work was supported by the Russian Science Foundation, grant #16-19-00002.
(Invited) Surface Free Energy and Interfacial Strain in HfO2 and Hzo Ferroelectric Formation
Authors: Chagarov Evgueni , Kavrik Mahmut , Katz Michael , Stanford Norman , Davydov Albert , Lee Min-Hung , Kummel Andrew C 
Published: February 2020

The mechanism of stability of the phases of HfO2, ZrO2, and HZO (HfxZr1-xO2) were systematically investigated with density functional theory molecular dynamics (DFT-MD) to determine the mechanism for HZO having a much larger process window for formation the ferroelectric phase as compared to doped HfO2 or ZrO2. For the bulk states, the monoclinic phase (“m”) is about 80 mV per formula unit more stable than either the orthorhombic ferroelectric (“f”) phase or tetragonal (t-phase) for all three oxides. The surface free energies of the (001), (110), and (111) surfaces of all three oxides were calculated using an identical DFT technique. For all three oxides, the (111) face has the lowest surface free energies consistent with experimental data on columnar HZO grains showing [111] is the preferred growth direction. However, the surface free energy for all direction are nearly degenerate between HfO2, ZrO2, and HZO; therefore, even for nanocrystal formation the surface free energy does not favor f-phase formation. The effect of stress/strain was calculated by determining the free energy of formation as a function of the volume of the unit cell. When the oxides are grown in the low density amorphous phase but a post deposition anneal is perform for crystallization. The crystalline forms are more dense than the amorphous forms and the DFT calculation show that a higher surface area per unit cells will greatly favor f-phase formation. However, the effect is nearly identical for HfO2, ZrO2, and HZO; this is consistent with experiments showing the molar volumes of HfO2 and ZrO2 being within 2%. Instead, formation of nanocrystalites is hypothesized to be the source of the enhanced processing window for HZO. Experimental data is consistent with partial phase separation in HZO. Atom probe tomography imaging of the chemical composition of TiN/5 nm HZO/Si(001) ferroelectric films show an asymmetric distribution of the Hf and Zr within the HZO layer with the Zr being concentrated near the TiN/HZO interface; this is consistent with ZrO2 having a 100C lower crystallization temperature than HfO2 and therefore initiate the crystallization starting on the TiN(111) surface. It is hypothesized that the nanocrystals which template on TiN(111) can produce the interfacial stress/strain needed to stabilize f-phase formation; high resolution TEM shows regions of epitaxial alignment between HZO and TiN consistent with this mechanism. In addition atom probe tomography (APT) was performed on TiN/HZO/Si structures to determine the film composition of the interfaces for indication of possible phase separation of HZO since phase separation could promote nanocrystal formation.
Funding by LAM Research is gratefully acknowledged.