bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Constructing Photocatalyst with Visible Light Response
Authors: Sun Zaicheng
Published: February 2020

Solar-driven production of hydrogen (H2) from water splitting is considered as one of the promising ways to provide clean fuels. There are two critical issues for high efficient photocatalytic solar energy conversion. One is the extension of light absorption into visible light region, and the other is the enhancement of quantum efficiency at each wavelength. In the former case, the light absorption band strongly depends on the intrinsic band gap of the photocatalyst materials. Regarding to the latter case, enhancement of quantum efficiency has been attempted by improving the methods of modification and synthesis. In this presetation, defects, like oxygen vacancies, have been demonstrated to enhance photocatalytic activity for TiO2, SrTiO3 and other oxides due to excellent charge separation efficiency within their whole absorption band.[1-3] besides the surface defect, bulk defect like Ti3+ doped TiO2 can be treated as another kind of bulk defect also were invstigated.[4] Normally, these oxides only absorb UV light due to their large band gap. We also investigated the effect of defects on the photocatalytic activity of visible light photocatalyst, like sulfides, which have an extended visible light absorption from UV to visible light region (~ 550 nm).[5] The results indicate that the defects within a certain concentration can promote the charge separation and enhance the photocatalytic performance.

[1] Huaqiao Tan, Zhao Zhao, Mang Niu, Chengyu Mao, Dapeng Cao, Daojian Cheng, Pingyun Feng and Zaicheng Sun. Nanoscale, 2014, 2：10216-10223

[2] Huaqiao Tan, Zhao Zhao, Wan-bin Zhu, Eric N. Coker, Binsong Li, Min Zheng, Weixing Yu, Hongyou Fan, and Zaicheng Sun, ACS Appl. Mater. Interfaces:
2014, 6
：19184-19190

[3] Zhao Zhao, Huaqiao Tan, Haifeng Zhao, Yang Lv, Li-Jing Zhou, Yujiang Song and Zaicheng Sun, Chemical Communications, 2014, 50
： 2755-2757

[4] Zhao Zhao, Xiaoyan Zhang, Guoqiang Zhang, Zhenyu Liu, Dan Qu, Xiang Miao, Pingyun Feng, Zaicheng Sun. Nano Research: 2015, 8(12): 4061-4071

[5] Xiaoyan Zhang, Zhao Zhao, Wanwan Zhang, Guoqiang Zhang, Dan Qu, Xiang Miao, Shaorui Sun, Zaicheng Sun*. Solution Small:
2016 ,12: 10.1002/smll.201503067
(Invited) Atomic Layer Deposited Oxides on Silicon for Enhanced Solar Energy Conversion
Authors: Strandwitz Nicholas C
Published: February 2020

Dielectric-semiconductor interfaces are integral to photovoltaic and photoelectrochemical systems. These interfaces provide electronic passivation, chemical protection, and can influence charge carrier collection at interfaces. Here we present two aspects of our work on dielectric-semiconductor interfaces: The impact of non-hydrolytic atomic layer deposition (NH ALD) chemistries and the role of fixed charge at metal-alumina-silicon tunnel contacts.

There is significant interest in minimizing oxidative damage to substrate semiconductors (e.g., Si) during ALD. Non-hydrolytic ALD chemistries utilize oxygen sources other than water or oxygen and have been shown inflict less oxidative damage to substrates. We directly compare NH and traditional ALD aluminum oxide chemistries and have found the NH ALD films have a larger fixed negative charge and larger interface trap state density. The understanding and control of semiconductor-dielectric interfaces is critical for controlling charge transport, possibly through leaky dielectrics, and for minimizing interface recombination.

Tunnel layer dielectrics (thickness < 2 nm) have been recently examined for protection and for increasing energy conversion figures of merit. In principle, fixed charge within such dielectrics can influence the electrostatic barrier in the semiconductor, which will have a direct impact on these figures of merit. We have examined alumina-silicon interfaces, in which the fixed charge can be tuned over a large range (+1E12 to -5E12 charges cm-2) by changing processing conditions. Based on an electrostatic model, these changes in fixed charge density should shift barrier heights by nearly 200 meV. In MIS stacks, we have found no evidence of changes in fixed charge in metallized, ultra-thin aluminum oxide layers. We will present several possibilities for why the fixed charge that is otherwise always found at these interfaces may be absent in metallized layers. Use of fixed charge to tune barrier heights could allow for large energy conversion figures of merit by simply tuning surface tunnel dielectrics in a manner similar to interfacial dipoles.
Enhanced Photoelectrochemical Efficiency of Self-Organized TiO2 Nanotube Layers Due to Secondary Materials
Authors: Macak Jan M. , Krbal Milos , Sopha Hanna , Prikryl Jan , Zazpe Raul , Ng Siowoon
Published: February 2020

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 10 years motivated for their possible range of applications including photo-catalysis, solar cells, hydrogen generation and biomedical uses [1]. The synthesis of 1D TiO2 nanotube structure is carried out by a conventional electrochemical anodization of valve Ti metal sheet. The main drawback of TiO2 is its applicability in the UV light (wavelengths < 390 nm). In order to enhance the efficiency, TiO2 has been doped by N [2] or C [3] o to shift its absorption into the visible light.

Except of doping, one of the major issues to extend the functional range of nanotubes is to coat homogenously tube interiors by a secondary material. It has been shown that additional ultrathin surface coating of TiO2 by secondary materials such as Al2O3 [4], ZnO [5] or MgO [6] annihilates electron traps at the TiO2 surface and thus increases the photogenerated concentration of charge carriers. Recently, it has been demonstrated that just a single cycle of Al2O3 [7] or ZnO [5] deposited by atomic layer deposition (ALD) efficiently improve charge transport properties of the heterostructure while gradual passivation appears with increasing ZnO thickness due to stronger band-bending [5].

The presentation will focus in detail on the coating of the nanotube arrays by secondary materials using ALD. The deposited materials influence strongly photo-electrochemical properties of nanotube films. Experimental details and some very recent photocatalytic [8] and sensing [9] results will be presented and discussed.

References:

[1] J. M. Macak et al., Curr.
Opin. Solid State Mater.
Sci. 1-2 (2007) 3.

[2] C. Burda et al., Nano Lett. 3 (2003) 1049.

[3] S. Sakthivel et al., Angew. Chem., Int. Ed. 42 (2003) 4908.

[4] R. Zazpe et al., Langmuir, in press, DOI:10.1021/acs.langmuir.6b03119.

[5] A. Ghobadi et al., Scientific Reports 6 (2016) 30587

[6] H. Park, et al., Journal of Electroceramics 23 (2009) 146.

[7] J-Y. Kim et al., Nanotechnology 25 (2014) 504003.

[8] M. Krbal et al., Ms submitted.

[9] S. Ng et al., Ms in preparation.
Argon Annealed ALD-ZrO2/SiON Gate Stack for Advanced CMOS Devices
Authors: Gupta Richa , Saikia Dulen , Vaid Rakesh
Published: February 2020

Now-a-days, high-k dielectric materials are in demand as they not only inhibit direct tunneling but also ensures relatively thicker oxides. To replace SiO2 as gate dielectric, a number of high-k materials have been extensively studied such as aluminum oxide (Al2O3), zirconium dioxide (ZrO2), cerium oxide (CeO2), hafnium oxide (HfO2) and titanium dioxide (TiO2). Among them, ZrO2 is one of the most outstanding candidates due to its excellent chemical, physical and electrical properties such as good thermodynamic stability with silicon, high dielectric constant, high melting point, high refractive index, and sufficient band gap. Atomic layer deposition (ALD) method having the benefit of low temperature deposition and extremely precise thickness control has been utilized for the deposition of ZrO2 film. Additionally, the post deposition annealing (PDA) of ZrO2in argon (Ar) ambient has been performed along with Ti-Pt as bilayer metal gate.

Taking into consideration the state-of-the-art research progress, we report the fabrication of ultra-thin silicon oxynitride (SiON) as a sacrificial layer (SL) for n-Si/ALD-ZrO2 gate stackfollowed by post deposition annealing (PDA) of ZrO2 in argon (Ar) ambient. The surface roughness for the Ar annealed ZrO2 film measured using atomic force microscopy (AFM) was found to be 0.796 nm whereas the thicknesses of SiON SL ~ 5.34 nm and ZrO2 film ~ 11.63 nm were corroborated by field emission scanning electron microscope (FESEM) and spectroscopic ellipsometer (SE). Electrical characterizations such as capacitance voltage and current voltage measurements indicates the improved results for n-Si/ALD-ZrO2/Ti-Pt MOS capacitor in terms of various performance parameters such as dielectric constant (K), effective oxide thickness (EOT), leakage current density (J), effective oxide charge (Qeff) and series resistance (Rs) and their determined values are 26, 2.1 nm, 8.75 × 10-9 A/cm2, 0.42 × 1013 cm-2 and 4.54 KΩ respectively. The noble concept of SiON SL along with the PDA of ZrO2 in Ar ambient can enable the further scaling of n-Si/SiON/ZrO2 gate stack without the adverse effects of gate leakage current. Some of the important results obtained from the reported work have been exemplified in the figures below.

Figure 1
Cobalt CMP Development for 7nm Logic Device
Authors: Wu Changhong , Han Ja-Hyung , Shi Xingzhao , Koli Dinesh R , Penigalapati Dinesh
Published: February 2020

Cobalt metallization for CA (contacts) and TS (trench silicide) of 7nm logic device may dramatically reduce resistance and improve 5-7% performance compared to its counterpart tungsten. This new integration scheme requires novel cobalt deposition, CMP, cleaning and etching processes. This study presents the advancement of cobalt CMP development in GLOBALFOUNDRIES Inc.. Two-step CMP process was developed. Overburden cobalt was removed and polishing was stopped on the liner material via endpoint detection during the bulk CMP. Bulk CMP was followed by buff CMP, where the liner material and a certain amount of ILD films were removed. At first, the effect of polish pressure and sliding velocity on blanket cobalt removal rate was investigated. Results showed the prestonial relationship. Subsequently, process parameters (polish pressure, sliding velocity, over polish time, etc.) were optimized for the bulk CMP. End point was captured successfully and was stable at the optimized process conditions. In addition, process had wide over polish time window due to good stop ability of the bulk slurry on the liner material. During buff CMP, removal rate selectivity between cobalt, liner, and ILD films were studied and compared for different types of slurries with different components concentration. Higher liner removal rate and lower cobalt/ILD rate were achieved at an optimized slurry components concentration. Finally, cleaning solutions and process parameters were optimized. Surface topography (dishing, erosion, etc.) and defects post cobalt CMP were extensively characterized. Results demonstrated comparable CMP performance between cobalt and tungsten.

Figure 1
(Gordon E. Moore Medal for Outstanding Achievement in Solid State Science and Technology Address) Transient Polymers for Low-k Dielectrics and Vaporizing Devices
Authors: Kohl Paul A
Published: February 2020

Dielectric materials provide critical functions throughout the interconnect hierarchy, including on-chip dielectrics, package substrates, and printed wiring boards. Transient polymers, those which vaporize on command, can be used to form ultra low-k dielectrics, such as porous materials or air-cavities. Transient polymers can also be used as coatings or structural materials in electronic packages and devices enabling the disappearance of the device when the collection, recovery or disposal of the device is difficult.

In this presentation, the motivation and opportunity for improved electronic materials will be presented. The nature of transient polymers will be described including their synthesis, physical properties, and chemical reactivity. Transient polymers can be decomposed into liquids or gases when exposed to a thermal, chemical or photo-chemical stimulus. Finally, several applications for transient polymers in the fabrication of unique electronic devices, structures or packages will be described.
GaN Based Hydrogen Sensor in Humid Ambient
Authors: Jung Sunwoo , Baik Kwang Hyeon , Jang Soohwan
Published: February 2020

Hydrogen gas is a pollutant-free energy source that is closely related to industry and human life. Recently, intensive research has been conducted on hydrogen as an alternative fuel. Hydrogen gas is used in various fields such as refinery process, cooling system in nuclear power plant, semiconductor process and hydrogen fuel cell vehicle. However, hydrogen is the highly explosive gas with wide explosion range and low ignition energy. Thus, hydrogen gas detection in various conditions is very important for hydrogen-related industry. Especially for hydrogen sensors in hydrogen fuel cell vehicle, proper monitoring of the feed stream is critical to ensure highly efficient energy conversion. In this environment, accurate and reliable detection of hydrogen in highly humid ambient is vital. AlGaN/GaN high electron mobility transistor (HEMT) structure has high density and mobility carriers at 2 dimensional electron gas channel (2-DEG) induced by piezoelectric and spontaneous polarization of AlGaN and GaN interface, from which the drain current response can be amplified through a functionalized gate electrode. Most of GaN based hydrogen sensors including nanowires, Schottky diode, metal oxide semiconductor (MOS) diode, and AlGaN/GaN HEMT employ platinum thin films as catalytic active layer. Hydrogen molecules are dissociated on active Pt surface, influence the channel conductance or Schottky barrier height, and induce the current response.

 In this work, AlGaN/GaN HEMT based hydrogen sensors incorporating nano-porous membrane was demonstrated. Platinum thin film serves as both Schottky contact and sensing material simultaneously. The device showed the excellent sensitivity for 500 ppm hydrogen even in 100% relative humidity. The nano-porous membrane coated on the sensor area effectively permits the approach of hydrogen gas molecules to sensing area while blocking water molecules which tend to cover the active sites of the sensor. The device showed reliable hydrogen gas sensing characteristics even after 25℃ ~ 100℃ heating cycle stress. This results support the potential use of AlGaN/GaN HEMT hydrogen sensor with nano-porous membrane in the applications of fuel cell vehicle.
Optical and Electrical Changes in 2-Dimentional Black Phosphorus Under Electron-Beam Irradiation
Authors: Kim Suhyun
Published: February 2020

Black phosphorus (BP) has a puckered honeycomb structure with a tunable bandgap (direct bandgap from 0.3 eV (bulk) to 2.0 eV (monolayer)), where each layer is held together by a weak van der Waals interaction. With its high surface to volume ratio, tunable direct bandgap, excellent electrical and optical properties, BP is expected to greatly contribute to the improvement in nanotechnology. In previous studies, the properties of BP were studied using different characterization methods including transmission electron microscopy and scanning electron microscopy (SEM) and various nanoscale devices were fabricated by electron beam lithography (EBL) process. Thus widely used technologies that utilize electron beam (e-beam) in semiconductor fields imply that discovering the influence of electron-beam irradiation on BP would attribute to better understanding and make use of full potential that BP contains. In our experiment we have employed EBL equipment in order to irradiate e-beam onto BP flakes with precisely controlled beam intensity and area dose. As BP tends to degrade rapidly with the presence of oxygen and water, the vulnerability of BP under e-beam irradiation was also investigated with increasing exposure time under air condition. The mechanically exfoliated BP flakes were irradiated with e-beam after storing each sample in air ambient for different periods of time. It was found that the degradation of BP under e-beam irradiation is highly dependent on the degree of oxidation (air exposure time). The surface morphology was observed in situ by SEM while e-beam was irradiated inside EBL chamber while optical and electrical properties of the BP samples were analyzed using Raman spectroscopy and electrostatic force microscopy, respectively. Realizing the role of e-beam, accurate results can be obtained from further researches on BP. Further results and discussion will be presented in detail.
GaN Based Carbon Dioxide Sensor
Authors: Jung Sunwoo , Baik Kwang Hyeon , Jang Soohwan
Published: February 2020

It is necessary to detect promptly amounts of carbon dioxide for the safety of workplace and the health of workers because concentrations of 7 to 10% may cause an acute symptom such as unconsciousness even in the presence of high concentration of oxygen. It is colorless and odorless. Also, its density is higher than common air, so that it is easily accumulated on the ground in the enclosed construction. Carbon dioxide is used in chemical, biomedical, energy and food industries as a reactant, an intermediate, and a final product. Recently, there are growing market-driven demands for the carbon dioxide gas sensors to detect early risk of high concentration of carbon dioxide exposure and to monitor quality of air in daily lives. In this applications, low power consumption, compact size, as well as reliability and sensitivity of the sensor are required to be integrated with IoT (internet of things) devices. Semiconductor type gas sensors satisfy these requirements, and GaN based gas sensors shows many superior performances including reliability and sensitivity to other semiconductors.

ZnO is a direct bandgap II-V compound semiconducting material with wide bandgap energy of 3.37 eV and large exciton binding energy of 60 meV. One of the advantages of ZnO is facile nanorod growth via hydrothermal method, which is low cost, non-toxic, low temperature, and scalable process. In hydrothermal growth, growth rate of c-plane is faster than m-plane in wurtzite crystal structure due to the higher surface energy of c-plane, hence ZnO nanowires or or bundle of nanorods along c-axis are generally formed. These ZnO nanorods with high surface to volume ratio can be employed in the gas sensor device as a sensing material to obtain high sensitivity for target gas.

In this study, AlGaN/GaN HEMT (high electron mobility transistor) based carbon dioxide sensor using ZnO nanorods as sensing material was fabricated, and the response of the device to carbon dioxide gas was investigated. The device showed current increase in carbon dioxide ambient due to the increase enhanced channel conductivity from 150oC, and fast reliable repeatability to cyclic exposures of various concentrations of carbon dioxide gas. Also, effect of humidity on sensing behavior was discussed.
Photon Absorption Enhancement of TiO2 Nanotube Arrays Decorated with Aluminum Nanoparticles
Authors: Zhang Shuai , Du Kang , Liu Guohua , Yang Changping , Wang Kaiying
Published: February 2020

Highly ordered TiO2 nanotube (NT) arrays fabricated by electrochemical anodization have shown promising potential for photocatalystic applications [1]. Loading metallic nanoparticles has been introduced to enhance photocatalytic activity of the TiO2 nanotubes. However, the applications are primarily focused on silver or gold due to their strong plasmonic behaviors at visible wavelength [2]. As a low cost alternative, nanoparticles Al exhibit strong plasmon resonances spanning much of visible region of the spectrum as well. In this paper, we fabricated nanoparticles Al on the wall of TiO2nanotube arrays by magnetron sputtering technique and investigated their optical characteristics.

A representative SEM (Scanning Electron Microscope) image of TiO2 nanotube structure is shown Fig.1. [3] The nanoparticles Al were deposited on TiO2 nanotubes by a radio frequency (RF) reactive magnetron sputtering system (Sputter AJA 4050). The deposition parameters were kept at pressure (4.2 mTorr), power (120 W), gas (10 sccm), stable deposition rate (0.4Å/S). The nanoparticle thin films Al have been calibrated on glass substrates and TiO2 with thickness from 0 to 20 nm, which can be well-controlled by the sputtering time, the photographs of various nanoparticles Al on glass (22 mm × 22 mm) and TiO2 (10 mm × 20 mm) are shown in the Fig. 2. Compared with pure TiO2 nanotubes, the absorbance spectra (400 - 850 nm) confirms that the absorption intensity of Al/TiO2 NTs increases with increasing the thickness of Al NPs. The 10 nm Al/TiO2 NTs sample exhibits a broad absorption peak centered close to 550 nm in the visible light region. The enhanced visible light absorption peak is ascribed to the enhancement of localized surface plasmon resonance of nanoparticle Al. These results indicate that the photo-response of TiO2 NTs could be easily extended to the visible-light region through the aid of nanoparticles Al (Fig. 3).

In summary, well-dispersed distribution of nanoparticles Al have been assembled on the TiO2 NTs by RF magnetron sputtering technique. The nanoparticles Al are readily controlled with thickness from 5 to 20 nm. The visible light absorption have been systematically studied. The optimized thickness is ~10 nm, which efficiently absorb light over a broad range of wavelength.

References

[1] Z. Endut, M. Hamdi, W.J. Basirun, Supercapacitance of bamboo-type anodic titania nanotube arrays, Surf. Coat. Tech. 215 (2013) 75–78.

[2] M.W. Knight, N.S. King, Lifei Liu, H.O Everitt, P. Nordlander and N.J. Halas, Aluminum for plasmonics. ACS Nano 8 (2013) 834-840.

[3] Kang Du, Guohua Liu, Xuyuan Chen, Kaiying Wang, PbS Quantum Dots Sensitized TiO2 Nanotubes for Photocurrent Enhancement, Journal of The Electrochemical Society,162(2015) E251-E257.

Figure 1
Aptamer Functionalized AlGaN/GaN HEMT Biosensor Array for Electrical Enumeration of Circulating Tumor Cells
Authors: Pulikkathodi Anil Kumar , Sarangadharan Indu , Chen Yi-Hong , Lee Gwo-Bin , Wang Yu-Lin
Published: February 2020

This paper demonstrates a novel high sensitive FET biosensor array that can capture as well as count the number of captured Circulating Tumor Cells (CTCs) by the aptamer immobilized on the sensor. The FET used for this purpose is AlGaN/GaN HEMT (High Electron Mobility Transistor) because of its high sensitivity. Using a new and robust sensing technique the cell capture was able to be measured electrically and analyzed. The array enhances the capturing and detection capability of the sensors. The advantage of this sensor array is that the detection can be extended to any type of cells and cell lines to differentiate the normal and abnormal cells among them, and the behavior of cells can be studied in different kinds of mediums in which the cells are suspended.

Biosensors can be used as point of care testing devices. In order to do so, they must be compact, portable, highly sensitive and user friendly. Along with being highly sensitive, GaN HEMT also are biocompatible, high temperature tolerant, chemically resistive and have excellent electrical properties. These properties of HEMT makes it a candidate for rapid biosensing. CTC enumeration has been used as a prognostic marker for metastatic colorectal cancer (m-CRC). CTCs are migrating cells that are shed into the blood stream from primary and metastatic tumors. But cancer patients have only 1-10 CTCs per cc of blood which makes them hard to be detected among plethora of other blood cells. The HEMT biosensor array developed by our group overcomes this drawback by capturing CTCs and counting them electrically, with an accuracy of single cell binding.

The fabrication of AlGaN/GaN HEMT is done by forming mesa islands by ICP etching of epi-wafer which is followed by ohmic metal deposition, annealing and probing pad deposition. Finally individual chips of size 1mm X 1mm are embedded onto an epoxy substrate and interconnects are deposited making a planar sensing device. This fabricated chip is then passivated and only the gate electrode and channel regions are opened with an area of 10X60µm2 using photolithography.

Aptamer is immobilized on the gate electrode and CTCs are allowed to be captured for 5~10 minutes. The cells bound on the aptamer are observed and the capture can be confirmed electrically by measuring the change in current gain compared to the aptamer current level and the change in current gain of HEMT sensor corresponds to the number of CTCs captured by the aptamer. In this way, CTC enumeration can be carried out using electrical measurement. This sensing technique is highly sensitive and can provide up to single cell resolution. Apart from rare migrating cells, abnormal cells and other cell based disease biomarkers can be detected and enumerated using our GaN HEMT based biosensor array.

Figure 1
(Invited) Mesoscale Modeling Approaches for Hydrogen Generation and Storage
Authors: Heo Tae Wook , Ogitsu Tadashi , Wood Brandon C.
Published: February 2020

Many of the biggest challenges in the hydrogen energy research are associated with the fact that the operating mechanisms often involve the complicated coupling of chemical/physical processes over vast ranges of multiple length and time scales. These kinetic phenomena tend to occur at or near several types of solid/solid, solid/liquid, and solid/gas interfaces, which in turn play key roles in determining the overall performance of hydrogen generation and storage processes. Examples include surface reactions with hydrogen gas or water; surface, bulk, and interface mass transport processes; structural modifications occurring under operation; and intermediate phase nucleation-and-growth processes associated with hydrogen incorporation or corrosion. Essentially, these are collective dynamic processes of atomic/molecular species that determine the thermodynamics and kinetics of nano- or micro-level characteristics. However, the lack of clear understanding of associated mechanisms and their impacts on hydrogen generation and solid-state storage reactions has hampered the acceleration of materials discovery and development. Therefore, it is obvious that several modeling approaches that cover different length and time scales ought to be properly integrated in order to comprehensively explore the underlying mesoscale science during the co-evolution of relevant processes. Mesoscale continuum modeling frameworks can provide a unified platform for integrating the necessary atomistic approaches, which typically provide higher accuracy for nanoscale chemical processes, and continuum approaches, which offer far greater flexibility and scalability and can describe materials at the microstructural level. In this talk, we present our integrated effort as part of the new DOE Advanced Water Splitting Materials consortium (HydroGEN) and Hydrogen Storage Materials—Advanced Research Consortium (HyMARC) under the Energy Materials Network (EMN) towards the multiscale modeling of solid-state hydrogen storage and hydrogen production via water splitting. In particular, we will discuss our recent efforts on the development of an integrated mesoscale modeling framework that can directly incorporate parameters derived from predictive atomistic modeling approaches such as ab initio calculations and molecular dynamics simulations. Several case studies will be presented, such as modeling phase transformations of complex metal hydrides during the (re/de)hydrogenation and modeling physical/chemical processes during the water splitting and corrosion.

*This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
(Invited) Large Scale Many-Body Perturbation Theory Calculations: Methodological Developments, Data Collections, Validation and Applications
Authors: Govoni Marco , Galli Giulia
Published: February 2020

One of the main tools used in first principle simulations of materials is Density Functional Theory; however, several of the approximate exchange and correlation functionals do not provide the level of accuracy required for predictive calculations of excited state properties. The application to large systems of more accurate post-DFT approaches such as Many-Body Perturbation Theory (MBPT) -- for example to heterogeneous systems, nanostructured, disordered, and defective materials -- has been hindered by high computational costs. In this talk recent methodological developments in MBPT calculations will be discussed, as implemented in the open source code WEST [1]. Results using a formulation that does not require the explicit calculation of virtual states will be presented for photoelectron spectra of aqueous solutions [2]. We will discuss online data collections which contain benchmarking results. Simplifications of MBPT calculations based on the use of static response properties, such as dielectric-dependent hybrid functionals [3], will also be presented. We will also briefly discuss the ongoing activities of the Midwest Integrated Center for Computational Materials (MICCoM) [4].

[1] www.west-code.org; M. Govoni et al., J. Chem. Theory Comput. 11, 2680 (2015).

[2] A. Gaiduk et al., J. Am. Chem. Soc. Commun. 138, 6912 (2016).

[3] J. Skone et al., Phys. Rev. B 89, 195112 (2014); J. Skone et al., Phys. Rev. B 93, 235106 (2016); N. Brawand et al., Phys. Rev. X 6, 041002 (2016).

[4] www.miccom-center.org.

In collaboration with: N. Brawand, A. Gaiduk, F. Gygi, I. Hamada, T.A. Pham, P. Scherpelz, H. Seo, J. Skone, M. Vörös.

Figure 1
(Invited) A New Model for Materials Genome Initiative - Driven Research: The High Throughput Experimental Materials Science Virtual Laboratory
Authors: Green Martin L.
Published: February 2020

The main goal of the Materials Genome Initiative (MGI) is the discovery, optimization, and commercial deployment of novel materials twice as fast as today’s practice, and at reduced cost. Since its inception in 2011, the MGI has resulted in significant progress in computational simulation and modeling to enable predictions of materials properties. More recently, an experimental component, based on high-throughput experimental (also known as combinatorial) materials science has been added. However, there remain serious challenges that the materials community must overcome to enable widespread deployment of an MGI-type approach to novel materials development. For example, data, both experimental and simulated, must be made discoverable, accessible, and interoperable. Further, even one “brick and mortar” high-throughput experimental facility would be very costly, whereas multiple facilities dedicated to different materials classes (e.g., catalysts, photovoltaics, lightweight structural materials) would be needed. Therefore, we propose a “High Throughput Experimental Materials Science Virtual Laboratory” (HTEMSVL) to facilitate MGI-driven research. The virtual laboratory would consist of an integrated, delocalized network of high-throughput synthesis and characterization tools, as well as a best-in-class, configurable data curation system, consisting of NIST (and other) materials resource registries and materials data repositories. Thus, data generated in the HTEMSVL could readily be made discoverable and accessible, at the discretion of the owner. Ultimately, users of the HTEMSVL, such as researchers at national labs, universities, and industry could leverage it to facilitate the rapid development and commercialization of novel materials and products.
Decomposition of Strong Carboxylic Acids Redox Catalyzed By Carboxylate Ions; Chemical Grafting of Carbon Surfaces
Authors: González Felipe J , Ramírez Vanessa , Mendez Alia
Published: February 2020

In mixtures of trichloroacetate ion and trichloroacetic acid in acetonitrile, trichloromethyl radicals are produced as a result of the redox reaction between the acid and its conjugated base. The reaction follows a loop mechanism in which the trichloroacetic acid is slowly consumed by proton reduction while the trichloroacetate ion is oxidized like in an electrochemical Kolbe reaction [1]. The hydroquinone-trichloroacetate complex was a good sensor of this unexpected self-decarboxylation redox reaction [2]. According to the conceptual framework of this reaction, the acid-base mixture was also tested but using the compounds derived from 4-nitrophenylacetic acid. The reaction ocurrs also in this system, however, when a glassy carbon electrode was present in the reaction solution, the grafting of nitrobenzyl groups on the surface was detected, whereas 4-nitrotoluene was detected as the product of a paralel reaction in solution. Therefore, the reaction represent an alternative to the covalent modification of carbon substrates without electrochemical induction.

[1] Drochss P. Valencia, Pablo D. Astudillo, Annia Galano, Felipe J. González, Org. & Biomol. Chem., 2013, 11, 318-325

[2] Pablo D. Astudillo, Annia Galano, Jorge Tiburcio, Felipe J. González, J. Electroanal. Chem., 2007, 604, 57-64

Figure 1
Invited: Ammonia Generation at Algae Modified Electrodes: Some Mechanistic Considerations Drawn from Redox Potentials
Authors: Leddy Johna , Lyon Jacob , Paschkewitz Timothy
Published: February 2020

Nature designs eloquent systems to effect electrochemical changes that pose daunting objectives for address by simple electrodes. In a sequence of electrochemical steps in a highly structured, bio-matrix, biological systems provide energy and kinetic control that yields important products from oxidized reactants. Examples are CO2 and water to form O2 and sugars and dinitrogen to form ammonia. By capturing these biological matrices on electrodes, the biomachines can generate products important in energy and materials.

Minteer and coworkers have demonstrated many systems of this type, including capture of the entire Krebs cycle on an electrode where the various components of the cycle are captured in a modified Nafion membrane. By analogy, we have captured algae on electrodes to generate ammonia. Cyanobacteria generates ammonia from dinitrogen with nitrogenase enzyme and from fixed nitrogen of nitrate and nitrite with nitrate and nitrite reductase.

Thermodynamically, the conversion of dinitrogen to ammonia is not energetically taxing, but the energetic cost to break the nitrogen nitrogen triple bond is high. In review of the kinetics for ammonia generation from N2, NO3
-, and NO2
- reactants, the thermodynamics were reviewed. From a potential axis and speciation diagram, some reactions are identified with sufficient energy to break the nitrogen triple bond. These reactions and other mechanistic steps in ammonia generation are presented and the role of local pH is considered. The protocol is anticipated applicable to identifying energy generating reactions important in other bioelectrochemical systems.
Real-Time Imaging of Oxygenic Photosynthesis in Spinach Using Bio-LSI
Authors: Kasai Shigenobu , Sugiura Yamato , Prasad A. , Sato Teruya , Inoue Kumi Y. , Ino Kosuke , Matsue Tomokazu
Published: February 2020

In the present study, we used a large-scale integration (LSI)-based amperometric sensor array system, designated Bio-LSI, to image in-vivo light-induced oxygen release from Spinach Leaves. The Bio-LSI device consists of 400 sensor electrodes with a pitch of 250 μm for rapid electrochemical imaging of large areas. Fig.1 shows schematic diagram for detection of oxygen production from Spinach leaves during photosynthesis using Bio-LSI. The imaging of oxygen production from Spinach leaves using Bio-LSI was also measured at light intensities of 20 and 30 klx (Fig 2, A3; a and b) which was found to be considerably higher as compared to the dark control (Fig 2, A2). The real-time monitoring of oxygen reduction current in control and light illuminated samples has also been presented (Fig. 2B). The results shows almost no changes in oxygen reduction current in non-illuminated Spinach leaves while a considerable changes have been observed in leaves illuminated with intensities of either 20 klx and 30 klx which was found to drop immediately at the switching off of the light source.

Our results show that light induced oxygen release can be monitored using the device, suggesting that the Bio-LSI is a promising tool for real time imaging of oxygen release and the effects of stresses in whole Spinach leaf under in-vivo conditions. To the best of our knowledge, this report is the first to describe real time electrochemical imaging of light induced oxygen release in Spinach leaves using LSI-based amperometric sensors.

References

(1) T. Yasukawa, et al., Chem. Lett., 28,975-976, 1999.

(2) K.Y.Inoue, et al. Lab Chip. 5, 848-856, 2015.

Figure 1
Electrodeposited Cadmium Oxide Semiconductor Electrodes for Protein Redox Characterization
Authors: Peters Dennis G , Gerroll Benjamin
Published: February 2020

Semiconductor films have previously shown promise for the measurement of protein reduction potentials.1,2 An advantage gained with semiconductor working electrodes is the ability to take measurements while adsorption phenomena that occur at bare metal electrodes are avoided, which denature the protein and make sample recovery impossible. This denaturation may also affect the redox potentials.3 Thus, an ability to measure redox potentials accurately while maintaining protein integrity can find many applications in bioanalytical systems.

In this work we have synthesized and characterized cadmium oxide (CdO) working electrodes for electrochemical studies of native biomolecules in aqueous systems. Electrodeposited CdO films were generated through application of a constant current (4.5 mA/cm2) to an indium-doped tin oxide (ITO) working electrode immersed in a 0.1 M cadmium chloride (CdCl2) solution and subsequently annealed at 450 ˚C for 1.5 h. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy methods were employed to characterize deposited material. As proof of concept, cyclic voltammetry of redox dyes with CdO working electrodes was performed to determine their redox potentials. Azurin, a copper blue protein from Pseudomonas aerunginosa,and cytochrome c, a small heme protein purified from bovine heart, were among the metalloproteins investigated. A novel small volume (50 and 750 µL) cyclic voltammetry cell was employed that facilitates sample recovery. Cyclic voltammograms were recorded at 10 mV/s for each sample with a CdO working electrode, a saturated Ag/AgCl reference electrode (–0.044 V vs. SCE), and a platinum counter electrode in aqueous solutions containing 100 mM Tris buffer and 200 mM KCl.

References

1. Valincius, G.; Reipa, V.; Mayhew, M. P.; Vilker, V. L. Electro. Chem. Comm.
2002,
4, 314-317.

2. Valincius, G.; Repia, V.; Vilker, V.; Woodward, J.; Vaudin, M. J. Electrochem. Soc.
2001, 148, E341-E347.

3. Hosseinzadeh, P.; Lu, Y. Biochimica et Biophysica Acta. 2015.

Figure 1. Small volume CV designed and used for metalloprotein analysis.

Figure 1
Extracellular Electron Transfer in Mixed Species Biofilms: The Role of Rikenella Microfusus
Authors: Grattieri Matteo , Abdellaoui Sofiene , Hasan Kamrul , Minteer Shelley D.
Published: February 2020

The capability of microorganisms to transfer electrons to/from an electrode surface is critical for the development of bioelectrochemical systems. However, the extracellular electron transfer (EET) mechanisms have been elucidated only for few microorganisms, in particular Geobacter sulfurreducens (Sh.) and Shewanella oneidensis (G.S.) respectively. A Microbial fuel cell (MFC) is a bioelectrochemical system that couples the possibility to directly convert chemical energy from civil and industrial wastewater into electrical energy thank to the bioelectrocatalytic activity of bacteria colonizing the electrodes. For on-field application of the technology, a mixed bacterial community will be most likely obtained, since wastewater solutions and biomasses are commonly utilized as inoculum. The presence of mixed-species biofilm can also facilitate the oxidation of complex substrates, since many microorganisms capable of EET can only use low-molecular organic acids and alcohols provided by fermenting bacteria. Accordingly, it is important to understand how microorganisms rather than Sh. and G.S. can contribute to the EET process.

Different studies have reported a particularly high presence of Bacteroidetes in the microbial community at the anode and the cathode of MFCs. The biological characterizations have indicated an high percentages of Rikenella Microfusus (R.M.), which belong to the order of Bacteroidales, but only few information about its metabolism are available. R.M. was isolated by fecal materials, it is an obligated anaerobic, nonmotile and gram-negative bacterium, which is capable to oxidize a number of substrates as glucose, mannose, lactose producing acids.

Herein, a pure culture of R.M. (ATCC® 29728™) was anaerobically grown and the EET was investigated on carbon cloth electrodes (non-wet proofed, E-TEK) potentiostatically polarized at a positive potential (+0.2 V vs. Ag|AgCl Sat.) and maintained in anaerobic conditions by constant purging of nitrogen gas. For the study, glucose was used to provide the substrate for the bacterium. Electrochemical experimental evidences revealed that flavins might be involved in the EET, facilitating the communication of the bacterium with the electrode surface. Moreover, oxygen influence on the current response was detected, critically affecting the capability of the bacterium to perform EET. The impact of the new finding on future researches devoted to clarify the EET for real application of bioelectrochemical systems will be discussed.
Tunable Pt Alloys for Oxygen Reduction and Alcohol Oxidation
Authors: Co Anne C. , Coleman Eric J. , Choi Heewon
Published: February 2020

Herein, we report the tunable properties of electroactive PtCu alloys made by galvanic displacement of Pt onto Cu metallic foams and their effect on the electrocatalytic activity of O2 reduction to form water or peroxide and the electrooxidation reaction of alcohols and organic acids to CO2.
Nanocellulose-Photoactive Oxide Composites for Efficient Photoelectrochemical Water Splitting
Authors: Choi Taekjib
Published: February 2020

Large porous nanostructures based electrode with high electrochemical activity are attracting a great interest in various energy conversion and storage applications. Recently, three dimensional nanostructured composites have been extensively utilized for high performance photoelectrodes of photoelectrochemical water splitting because of their large surface area and improved electron transport properties. In this work, we fabricated high porous semiconducting transition metal oxides, such as TiO2 (anatase phase) and Fe2O3 (hematite) nanostructures through soft-templating methods using sol-gel process. The cellulose nanofiber was used as template, which exhibits low thermal expansion, high surface area and good mechanical and optical properties. We investigated photoelectrochemical performances for nanocellulose- templated TiO2 and Fe2O3 nanostructures and thermal treated nanostructures. We found that thermal treatments enable rapid photogenerated electron-hole separation and transport, leading to higher photoelectrochemical efficiency, which are associated with carbonization of cellulose nanofibers. Nanocelluose-photoactive oxide composites are promising candidate for high efficient photoelectrode for solar water splitting.
NBD-Ferrocene: A New Fluorescence Redox Molecular Switch Based on Photoinduced Electron Transfer
Authors: Čížková Martina , Cattiaux Laurent , Mallet Jean-Maurice , Labbé Eric , Buriez Olivier
Published: February 2020

Fluorimetric redox switches, sensitive to external electrochemical stimuli, belong to a wide family of molecular sensors in which the switching process is achieved by shifting the molecules between two or more stable states. While the area of pH and ligand-based chemosensors has been extensively explored,[1] the topic on luminescent molecular redox switches has remained rather underdeveloped[2] even though redox modulation of fluorescence affords considerable opportunities in optoelectronic and biological applications.[3]In this context, the development of new electrochemically switchable fluorescent probes is of high interest. Based on DFT calculation, an original nitrobenzoxadiazole (NBD) system containing a redox active ferrocene unit was designed (Figure 1) and its optical, electrochemical, and spectroelectrochemical properties were investigated. The system was nonfluorescent in its initial reduced state as a result of photoinduced electron transfer from ferrocene moiety to the photoexcited NBD part and considerable enhancement of emission intensity was observed during oxidation of NBD-ferrocene to NBD-ferrocenium, in which photoinduced electron transfer was disabled electrochemically.

References

[1]
(a) de Silva, A. P.; Gunaratne, H. Q. N. ; Gunnlaugsson, T. ; Huxley, A. J. M. ; McCoy, C. P. ; Rademacher, J. T.; Rice, T. E. Chem.
Rev.
1997, 97, 1515-1566; (b) Gale, P. A.; Caltagirone, C. Chem. Soc. Rev.
2015, 44, 4212-4227.

[2]
(a) Magri, D. C. Analyst
2015, 140, 7487-7495; (b) Audebert, P.; Miomandre, F. Chem. Sci.
2013, 4, 575-584.

[3]
Liu, Z.; Qi, W.; Xu, G. Chem. Soc. Rev. 2015, 44, 3117-3142.

Acknowledgement

The financial support from the EU Research and Innovation programme Horizon 2020 through the Marie Skłodowska-Curie action (H2020-MSCA-IF-2014, ID 656519) is gratefully acknowledged.

Figure 1 a) Electrochemical oxidation of the new NBD-ferrocene system. b) DFT calculations of orbital energy levels. c) Electrochemically mediated fluorescence enhancement.

Figure 1
The Influence of Anions on the Release of Ag(I) Ions from Silver Nanoparticles (AgNPs)
Authors: Nomor Aondoakaa Steve , Horrocks Benjamin Richard
Published: February 2020

Silver nanoparticles (AgNPs) are widely being incorporated into products such as socks [1, 2], sports wears and wound dressings [3, 4] to serve as antibacterials and to inhibit unwanted odours. As these products are washed, the silver nanoparticles leach out, dispersing in water where they may release silver ions. Although the only contraindication of high levels of silver in humans is argyria [5], it is said to be very toxic to aquatic organisms that make up the base of a series of food chains. In this study, silver nanoparticles were synthesised by the citrate reduction method following the procedure of Lee and Meisel [6]. The nanoparticles were prepared in the presence of various anions and in pure water in order to examine the effect of the medium on the release of Ag(I). AgNPs were characterised by UV-Vis spectrometry, dynamic light scattering (DLS) and atomic force microscopy (AFM). The decrease in surface plasmon resonance (SPR) peak of the nanoparticles after dialysis indicates that quite a number of conduction electrons have gone into reaction, hence lowering of resonant frequency. The diameters of the nanoparticles as measured by DLS ranged from 102 nm in the 10 mM chloride AgNPs before dialysis to 892 nm in the 50 mM sample after dialysis, indicating aggregation over the dialysis period. On the other hand, particle sizes in terms of both height and diameter as measured by AFM decreased after dialysis. This could be explained that in spite of aggregation in solution, the AgNPs deposit as islands about 1 particle in height on the AFM substrate (Si wafer). Release of Ag(I) from the NPs was monitored by anodic stripping voltammetry at glassy carbon electrodes. Two interesting observations were made: (i) there is substantial (90 mM) Ag(I) present in the initial NP preparation and (ii) the concentration of Ag(I) after 73 h of dialysis remained easily detectable at about 4 µM irrespective of the concentration of chloride present.

References

1 T.M. Benn, P.Westerhoff. Environ. Sci. Technol. 2008, 42, 4133-4139.

2 D.E Meyer, M.A. Curran, M.A. Gonzalez. J Nanopart Res. 2011, 13, 147-156.

3 A. Hebeish, M.H. El-Rafie, M.A. El-Sheikh, A.A. Saleem, M.E. El-Naggar. Intnal. Journ. of Macromolecules. 2014, 65, 509-515.

4 T. Maneerung, S. Tokura, R. Rujiavanit. Carbohydrate Polymers. 2008, 72, 43-51.

5 WHO Guidelines for Drinking-water quality. 2003. World Health Organisation, Geneva.

6 P.C. Lee, D. Meisel. J. Phys. Chem. 1982, 86, 3391-3395.

Figure 1