bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Photophysics of Hybrid Semiconductor Nanostructures in Photocatalytic Hydrogen Generation
Authors: Kuno Masaru 
Published: February 2020

Semiconductor nanostructures possess a number of applications in solar energy conversion. This includes using colloidal quantum dots in solar cells and, more recently, using analogous nanostructures such as nanowires (NWs) and nanosheets (NSs) in photocatalytic applications. Here we describe recent work to understand the photocatalytic response of solution-synthesized cadmium chalcogenide NWs and NSs within the context of hydrogen generation. Various CdX (X = S, Se) systems such as core/shell NWs and hybrid metal nanoparticle decorated NWs and NSs have been studied. In all cases, femtosecond transient differential absorption spectroscopy has been used to reveal relevant carrier relaxation processes in these materials as well as the flow of charges across the different heterointerfaces that are present. By correlating these transient absorption results to results from accompanying hydrogen generation efficiency measurements, we have, in turn, rationalized the response of these materials, clarifying the role that different heterojunctions play in establishing both charge separation and hydrogen generation efficiencies.
Investigation of Graphene Oxide-TiO2 Photoelectrodes with Different Compact Layers and Counter Electrodes
Authors: Devarepally Kishore Kumar 
Published: February 2020

Modified Hummer’s method was adopted for the preparation of graphene oxide (GO) using graphite flakes. Graphene-oxide was incorporated in the TiO2 paste and the films are prepared by screen printing on FTO glass (TEC8) substrates. The screen printed films were subjected to heat treatment cycle at 375°C for 5 min, 375 °C for 5 min, 450°C for 15 min and finally at 500°C for 15 minutes. The crystallinity and phase purity of the GO samples were characterised by X-ray diffraction using Cu-Kα radiation. The morphology of the GO is investigated using transmission electron microscopy and the chemical structures of GO are analysed by XPS.
Photovoltaic properties were measured by a computer-controlled digital source meter (Keithley 2400) under simulated one sun illumination at AM 1.5G (100mW/cm2) from a solar simulator (92250 A, Newport, USA). The electrochemical impedance spectroscopy (EIS) is carried out using Metrohm Autolab in the frequency range of 1MHz to 0.1Hz with amplitude of 20 mV under dark conditions. The device was assembled by coupling GO-TiO2 films soaked in N719 dye with Surlyn as the spacer between the electrodes. The performance of the GO-TiO2 composite photoelectrodes were tested with different compact layers and different counter electrodes. The DSSC fabricated with graphene oxide as counter electrode exhibited photoconversion efficiency of 4.6% whereas, platinum based devices showed photoconversion efficiency of 4.7%. The present study suggests that graphene oxide counter electrodes can be considered as a promising alternative to platinum, with further optimisation, which clearly has advantages in terms of its abundance and low cost processing towards industrial prospects.
(Invited) Electrochemistry of Nitrophenylcorroles in Nonaqueous Media
Authors: Jiang Xiaoqin , Shan Wenqian , Pacquelet Sandrine , Desbois Nicolas , Gros Claude , Kadish Karl M. 
Published: February 2020

Nitrocorroles have recently been studied as potential agents against human cytomegalovirus infection for their antiviral activity.1 They have also been incorporated into triple-decker complexes containing phthalocyanine macrocycles.2 The nitrophenyl corroles can undergo multiple redox reactions at the conjugated macrocycle in addition to one or more reductions at the meso-nitrophenyl groups. Metal-centered reactions can also occur for some transition metal corroles. As part of our continuing studies into elucidating the electrochemistry of porphyrins, corroles and related macrocycles, we have synthesized a series of free-base and metallated nitrophenylcorroles which were electrochemically characterized in a variety of nonaqueous solvents. The structures of the investigated compounds are shown in Chart 1. The redox potentials for each electrode reaction of the above compounds were measured by cyclic voltammetry and spectra of the electroreduced and electroxidized forms of the corrloles were obtained by thin-layer UV-visible spectroelectrochemistry under the same solution condition. This data was then analyzed as a function of the solvent properties, the number and position of the meso-nitrophenyl substituents and the type or oxidation state of the central metal ion. Protonation and deprotonation constants of the free-base corroles were also determined by monitoring changes in the UV-visible spectra during titrations with different acids or bases. The free-base corroles can add one proton to form CorH4
+ and they can also lose one or two protons to form CorH2
- and possibly CorH-. These positively and negatively charged corroles are also electroactive and were characterized as to their electrochemistry and spectral properties.
1. Gros, C. P.; Desbois, N.; Michelin, C.; Demilly, E.; Tilkin-Mariame, A.-F.; Mariame, B.; Gallardo, F. ACS Infect. Dis.
2015,
1(8), 350-356.
2. Lu, G.; Li, J.; Jiang, X.; Ou, Z.; Kadish, K. M. Inorg. Chem.
2015,
54 (18), 9211-9222.

Figure 1
(Invited) Phthalocyanine Monolayer Nucleation of Gate Oxide ALD on Single Layer Graphene and TMD Surfaces
Authors: Kummel Andrew , Park Jun Hong , Kwak Iljo , Chagarov Evgeniy , Movva Hema , Chou Harry , Banerjee Sanjay K , Fathipour Sara , Seabaugh Alan , Fullerton Susan , Vishwanath Suresh , Xing Huili Grace , Choudhury Pabitra 
Published: February 2020

Several proposed beyond-CMOS devices based on two-dimensional (2D) heterostructures require the deposition of thin dielectrics between 2D semiconductor layers as an interlayer, or on the 2D semiconductor as a gate. However the direct deposition of dielectrics on 2D materials is challenging due to their inert surface chemistry. To deposit subnanometer EOT dielectrics on 2D semiconductors, a flat lying titanyl phthalocyanine (TiOPc) monolayer was employed to functionalize the 2D materials via non-bonding interaction for atomic layer deposition (ALD), and the initial stage of growth was probed using in-situ STM. ALD pulses of trimethyl aluminum and H2O resulted in the uniform deposition of AlOx on the TiOPc/HOPG via dissociative chemisorption onto TiOPc reactive sites. The uniformity of the dielectric is consistent with DFT calculations showing multiple reaction sites on each TiOPc molecule for reaction with TMA.
In order to deposit dielectrics with low leakage and low equivalent oxide thickness (EOT) on WSe2, a flat-lying titanyl phthalocyanine (TiOPc) monolayer (ML), deposited via molecular beam epitaxy (MBE), was integrated to create a seed layer for atomic layer deposition (ALD) on WSe2 surfaces. TiOPc molecules formed a flat lying monolayer on WSe2 ML, with four fold crystal structure in scanning tunneling microscopy. ALD pulses of trimethyl aluminum and H2O resulted in the uniform deposition of Al2O3 on TiOPc/WSe2, confirmed by AFM and cross sectional TEM. After deposition of 50 cycles of the Al2O3 onto the TiOPc/multilayer WSe2, top gated FETs were fabricated. The top gated leakage current was measured 0.046 pA/µm2 at 1 V gate bias with 2.4 nm EOT, which is lower leakage current than previous results. A subthreshold swing of 80 mV/dec was measured in n-branch of dual gated device.

Figure 1
(Invited) Electrogeneration and Electrochemistry of Sigma-Bonded Cobalt Porphyrins with Pi-Extended Systems and/or Highly Electron-Withdrawing Pyrrole Substituents
Authors: Kadish Karl M. , Ke Xiangyi , Cong Lei , Kumar Ravi , Sankar Muniappan 
Published: February 2020

A series of cobalt β-substituted nitroporphyrins were investigated as to their electrochemistry, spectroelectrochemistry and reactivity with alkyl halides in nonaqueous media. Selected structures of the examined compounds are shown in Chart 1. Each porphyrin contains cobalt(II) in its neutral air-stable form and is characterized by multiple redox reactions, some of which involve the conjugated π-ring system and others, the central metal ion which can be converted to its Co(III) and Co(I) forms under the application of an applied oxidizing or reducing potential. The half-wave potentials for each redox reaction were measured by cyclic voltammetry and spectra of the oxidized and reduced compounds were obtained by thin-layer UV-visible spectroelectrochemistry under the same solution conditions. The electrogenerated Co(I) porphyrins are highly reactive in the presence of methyl iodide and a rapid reaction occurs to generate a new series of σ-bonded Co(III) methyl derivatives, which were also characterized as to their electrochemistry and spectroscopic properties in nonaqueous media. These data were then analyzed as a function of the solvent properties, the nature of the β-pyrrole substituents and the oxidation state of the central metal ion.

Figure 1
(Invited) Carbon-Rich Porphyrins
Authors: Jux Norbert , Lungerich Dominik , Hölzel Helen , Reger David , Ruppel Michael , Martin Max 
Published: February 2020

We will present new carbon-rich porphyrins and tetrabenzoporphyrins some of which carry hexabenzocoronene units as well as other aromatic species.
We report on the synthesis, characterization, and properties of some of these novel systems.[1,2]

References

[1] J. M. Englert, J. Malig, V. A. Zamolo, A. Hirsch, N. Jux, Chem. Commun. 2013, 49, 4827 – 4829.
[2] D. Lungerich, J. F. Hitzenberger, M. Marcia, F. Hampel, T. Drewello, N. Jux, Angew. Chem. Int. Ed..
2014,
53, 12231-12235.

Figure 1
Modeling and Experimental Study of Micro Enzymatic Biofuel Cells
Authors: Song Yin , Wang Chunlei 
Published: February 2020

Miniaturized enzymatic biofuel cells (EBFCs) converting biological energy into electrical energy by using enzyme-modified electrodes are considered as a candidate to power implantable medical devices and portable electronics. In this study, modeling of the EBFC system has been conducted using finite element analysis based on COMSOL Multiphysics 4.3a in terms of cell performance, efficiency and optimum cell configurations. Two modules have been applied to obtain the maximum theoretical cell performance of on-chip microelectrodes: 1) diffusion module to incorporate the mass transport and enzymatic kinetics; 2) conductive module to integrate concentration and potential. The design rule has been developed in the steady state. The effect of orientation of the microelectrode arrays in blood artery has been studied. In the experimental part, integration of the high surface area nanomaterials such as carbon nanotubes (CNTs) and graphene could be one of the effective solutions to further improve the performance of current EBFCs. The EBFC systems employing 3D carbon micropillar arrays integrated with different nanomaterials, such as graphene, reduced graphene oxide (rGO) and rGO/CNTs composite have been investigated. The fabrication process of this micro-system combined top-down carbon microelectromechanical system (C-MEMS) technology to fabricate the 3D micropillar arrays platform and bottom-up electrophoretic deposition (EPD) to deposit various carbon based nanomaterials onto the 3D micropillar arrays. The materials characterization, electrochemical characterization and device evaluation have been conducted. Upon comparison among bioelectrodes integrated with different nanomaterials, the amperometric response of the rGO/CNTs based bioelectrodes exhibited the best electrochemical performance and the as-resulted 3D micro EBFC generated a maximum power density of 196.04 µWcm-2 at 0.61 V. In addition, modeling of the rGO/CNTs EBFC system based on finite element analysis has also been conducted to predict the theoretical cell performance. The power density of actual device has been noted to be 71.1% of the modeling result.
Porous Carbon Interdigitated Electrode Arrays for Electrochemical Biosensors
Authors: Ibrahim Fatimah , Selvarajan Reena Sri , Yafouz Bashar , Madou Marc J , Azari Pedram , Abd Hamid Sharifah Bee , Gan Seng Neon 
Published: February 2020

In this paper, three-dimensional (3D) porous carbon interdigitated electrode arrays (IDEAs) are developed utilizing standard photolithography of electrospun mats of SU-8 photoresist nanofibers. Porous IDEAs have the potential to produce higher aspect ratio than non-porous electrode due to the reduced stress at the interface between the substrate and the carbon structure [1]. In a first step, a layer of polymeric nanofibers is deposited on a silicon substrate by optimizing the conditions for far-field electrospinning of SU-8 photoresist. Subsequently, the SU-8 mat is patterned using conventional photolithography to generate the polymer precursor for the carbon electrode structure. Finally, the polymer precursor is pyrolysed at 900°C in an inert atmosphere to produce a porous carbon IDEA [2]. The porous carbon IDEAs were optimized as a function of the nanofibers diameter, thickness of the electrospun SU-8 mat and width/gap ratio of the IDEAs. To characterize the porous carbon IDEAs, electrochemistry studies (cyclic voltammetry and electrical impedance spectroscopy) were conducted and the results were compared with traditional flat carbon IDEAs (the latter was fabricated by spin coating a non-porous SU-8 film on a silicon substrate). The redox amplification factor of both porous and flat carbon IDEAs was studied to gain an understanding of the effect of electrode porosity on the redox amplification. This factor was optimized for width and gap of the IDEAs and the nanofibers diameter.

Acknowledgments

This research is supported by Flagship grant project number FL001A-14AET, Transdisiplinary Research Grant Scheme (TRGS TR002A-2014B) from University of Malaya and Ministry of Science Technology and Innovation (MOSTI) Science Fund (SF-020-2014).

References

1. Sharma, C.S., A. Sharma, and M. Madou, Multiscale carbon structures fabricated by direct micropatterning of electrospun mats of SU-8 photoresist nanofibers. Langmuir, 2010. 26(4): p. 2218-2222.
2. Kamath, R.R. and M.J. Madou, Three-Dimensional Carbon Interdigitated Electrode Arrays for Redox-Amplification. Analytical chemistry, 2014. 86(6): p. 2963-2971.
Environmental Friendly Fluorine Mixture for CVD Cleaning Processes to Replace C2F6, CF4 and NF3
Authors: Wieland Robert , Boudaden Jamila , Pittroff Michael 
Published: February 2020

Since the beginning of the 1980’s per fluorinated carbons (PFC’s) such as C2F6 and CF4 have been used as cleaning gases in thin film deposition technology and since the 1990’s NF3 has been used in the same way. PFC’s and NF3 have long atmospheric lifetimes and therefore high global warming potentials. The main applications of these gases are to remove residual films left behind after a chemical vapor deposition process (CVD). The most important materials to remove are dielectric layers like silicon oxides (SiO2), carbon-containing silicon oxides, silicon nitrides (Si3N4) and, to a certain extent, conducting films like doped poly-silicon and silicide layers. According to the World Semiconductor Council the semiconductor industry in 2013 used 7512 t NF3, 1133 t CF4 and 708 t C2F6 on a global basis. Approximately 72% of all semiconductor industry gaseous emissions are caused from these three gases (C2F6, CF4 and NF3). Fraunhofer EMFT and Solvay Special Chem have developed an alternative cleaning process, which can be a replacement for the currently used PFC’s and NF3in semiconductor CVD tools.
The target of this work was to find viable alternative gas mixtures for the semiconductor industry, which could be used as a “drop in” to avoid additional high investment costs from equipment modification. Our study has demonstrated that these more environment friendly gas mixtures also provide a more efficient and faster cleaning behavior for most applications. A cleaning efficiency gain of a factor 1.3 up to 17 can be expected, relative to the F2-amount required for cleaning; this gain in efficiency depends on the cleaning gas to be replaced and on the reactor type. A shorter cleaning time can lead directly into a higher equipment throughput and more cost effective usage of thin film tools. To generate data on particle and tool attrition, a first “mini marathon” test run has been performed. The test reactor, a 200mm wafer size CVD tool, was equipped with a mass spectrometer, to verify the end point of the chamber cleaning and to gain an overview of the waste gases going into the abatement system.

Figure 1
In Operando Studies of Electrode-Electrolyte Interfaces for Magnesium Batteries
Authors: Hahn Nathan T , Zavadil Kevin R 
Published: February 2020

The development of rechargeable Mg batteries, driven by the desire to overcome the limiting specific energy density and high cost of Li ion batteries, is currently frustrated by the lack of stable, functional electrolytes compatible with high voltage cathodes. Successful electrolytes have typically employed chloride complexes as the Mg cation delivering species in order to avoid the formation of Mg cation blocking films on the anode surface. However, such electrolytes exhibit questionable compatibility with the high voltage cathodes and current collector materials needed to attain large energy density and low cost in a complete magnesium battery system. Motivated by this problem, novel “conventional” electrolytes resembling those used in Li-ion batteries have been proposed, including those based on the weakly coordinating bis(trifluoromethylsulfonyl)imide (TFSI) and monocarborane (CB11H12
-) anions. The electrochemical behavior and stability of such electrolytes is not well understood, and their study is necessary in order to guide magnesium battery development efforts.
In this presentation we describe the results of in operando studies focused on evaluating the relationship between interfacial speciation and electrochemical behavior from the perspective of the efficiency of magnesium electrodeposition and dissolution in novel electrolyte chemistries. The techniques utilized by these studies include Raman spectroscopy and X-ray absorption spectroscopy, conducted in such a way as to provide interfacial or near-interfacial information concerning the interactions of the Mg cation with the solvent and anion species in the presence of the electrified interface. We demonstrate that these in situ experiments provide a level of insight that is not attained by bulk or otherwise ex situ electrolyte characterization techniques. In particular, we find that interfacial changes in MgTFSI2/glyme electrolyte speciation promote instability in the TFSI anion contributing to the poor reversibility of the Mg metal deposition process. We further demonstrate that the addition of chloride species to the TFSI-based electrolyte modifies these interfacial processes, suppressing the TFSI decomposition pathway. We will also discuss how the nature of the specific ether solvent employed influences these findings. We believe that this information provides important insight into the design and implementation of electrolytes for future magnesium batteries.
This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000.

Figure 1
Mesoscale Interplay of Physicochemical Processes in Li-S Battery Electrodes
Authors: Mistry Aashutosh , Liu Zhixiao , Chen Chien-Fan , Mukherjee Partha P. 
Published: February 2020

Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density [1-6]. A typical Li-S battery operation includes multi-step electrochemical reactions and transport phenomena relevant to the “internal shuttle effect”. The insoluble final product, such as Li2S, can passivate the active cathode surface, block mass transfer channels and induce mechanical degradation, all of which negatively impact the cell performance. Each of these phenomena takes place at different spatial and temporal scales which necessitates a mesoscale approach to understand the implications of physicochemical coupling.
In this regard, a coupled mesoscale model has been developed in order to study physicochemical interactions in the cathode microstructure. At the interface level, the mechanism of chemical interactions between discharge products and cathode surface is fundamentally investigated. The growth rates of precipitation thickness and coverage are predicted. At the cathode microstructure level, the surface passivation and pore blockage induced by Li2S precipitation are systematically studied. At the cell level, the mechanisms of discharge capacity loss are revealed.
In summary, this mesoscale modeling framework can be employed to quantify the capacity loss due to the internal shuttle effect and other electrochemical degradation mechanisms and understand the effect of cathode microstructure (i. e. sulfur loading, specific surface area, pore size distribution) on the electrochemical performance.

Acknowledgement:

Financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, grant DE-EE0006832 (Program manager: Tien Duong) is gratefully acknowledged.

References:

P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, Nat. Mater., 11(1), 19-29 (2012).

F. Y. Fan, W. C. Carter, and Y. M. Chiang, Adv. Matter., 27, 5203-5209 (2015)

R. Cao, W. Xu, D. Lv, J. Xiao, and J. G. Zhang, Adv. Energy Matter., 5, 1402273 (2015)

Y. X. Yin, S. Xin, Y. G. Guo, and L. J. Wan, Angew. Chem., 52(50), 13186-13200 (2013)

Y. Yang, G. Y. Zheng, and Y. Cui, Chem. Soc. Rev., 42(7), 3018-3032 (2013).

Z. Liu, D. Hubble, P. B. Balbuena, and P. P. Mukherjee, Phys. Chem. Chem. Phys., 17, 9032 (2015).

Figure 1