bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) How Beneficial Is Reduced Graphene Oxide (RGO) for Long-Term Photo Generated Charge Transport in Inorganic Oxide - Rgo Nanocomposites? a Case Study of Bismuth Titnate - Rgo Films?
Authors: Selvaraj Josephine , Gupta Satyajit , Fiechter Sebastian , Subramanian Vaidyanathan
Published: February 2020

This work begins with a summary of the role of reduced graphene oxide (RGO) in promoting the photoactivity of oxides and chalcogenides. Initial indicators suggest that RGO is a good material for promoting charge speration over short time scales. However the story over long term illumination is different. This presentation delineates the results of a systematic analysis of the photoelectrochemical (PEC) and optical responses of RGO combined with a representative multimetal oxide – bismuth titanate (BTO) on films. We investigated the role of RGO as a promoter of charge separation and transport, by suppressing recombination loss of carriers in BTO. The micro-structure of the BTO/RGO composite observed using transmission, scanning electron, and atomic force microscopy, revealed a well-integrated, and highly porous morphology compared to pristine BTO film. The integration of BTO with RGO resulted in a ~ 7 fold increase in photocurrent density with an optimal RGO loading of 2 wt%. The performance of the BTO/RGO interface was further examined to obtain critical insights on: (i) how the electrolyte influences the stability of the BTO/RGO composite and (ii) what interactions prevail at the BTO/RGO interface, under long-term illumination to impact the RGO stability. This work assumes immediate significance because implementation of RGO as a charge transport agent in oxidative systems is heavily researched currently. Unless a mechanism to protect RGO is determined, its long-term stability, especially under oxidative conditions of any form, has to be thoroughly investigated on a case-to-case basis to ensure composite longevity.
Carbon Nitride (C3N4) Photocatalysts Synthesized from Different Methods for Photocatalytic Reaction Under Visible Light Irradiation
Authors: Hu Che-Chia , Wang Mao-Sheng , Guo Zheng-Wei
Published: February 2020

C3N4 photocatalyst powders have generally been synthesized with a solid-state (SS) method, which formed a graphitic feature with tri-s-triazine (C6N7) units as elementary building blocks. The present work reports a solvothermal (ST) synthesis, in which the yellow powders were obtained as low as 150-220 °C using cyanuric chloride (C3N3Cl3) and sodium azide (NaN3) as the starting materials and acetonitrile as the solvent. X-ray diffraction analyses showed that the crystalline structure of ST samples changed from pseudocubic-C3N4 to beta-C3N4 with increasing the solvothermal temperature, and powders obtained from SS method displayed a graphitic-C3N4 structure with diffraction angles at ca. 13.1° and 27.5°. The two distinct diffraction angles represented (100) plane of tri-s-triazine units and (002) plane of stacking of the conjugated aromatic system, respectively. UV-Vis absorbance spectra showed that the band gap of SS was estimated to be 2.6 eV, and that of ST samples were estimated to be 1.9 to 2.45 eV, varied with solvothermal tempearture. To evaluate the visible-light-responded photocatalytic activity of the samples, degradation of methylene orange dyes was conducted using a 200 W Xenon lamp. ST samples showed a higher photocatalytic activity on degradation of methylene orange, which can be attributed to its larger light absorbance in the visible regime compared to that of SS ones.

Figure 1
(Invited) Bodipy Dyes for Solar Energy Conversion
Authors: He Hongshan , Klfout Hafsah A , Elkhalifa Mahmoud , Stewart Adam
Published: February 2020

BODIPY, abbreviation for boron-dipyrromethene, is a class of fluorescent dyes. They exhibit several unique characteristics including tunable spectral coverage, high absorption capability, exceptional chemical and photo-resistance in solution and in solid state, very good solubility in organic solvents, and easy structural modification making them attractive for many applications. However, in the past thirty years, the research on BODIPY dyes is heavily focused on development of new molecules for imaging and labeling of biological substrates, and only a few reports are related to solar energy conversion. In this talk, I will  present our recent studies on several functionalized BODIPY dyes with a donor-π-acceptor configuration for dye-sensitized solar cells. Those highly functionalized BODIPY dyes exhibit strong absorption in the visible region and very interesting photovoltaic and sensitization behaviors. Synthesis, single-crystal structures, photophysical and photovoltaic properties will be discussed. The findings from our study will be of great interests to researchers who are working in the fields of solar energy conversion.
(Invited) Metalation of Porphyrins on Surfaces in Liquid and Vacuum
Authors: Lytken Ole
Published: February 2020

Adsorption and metalation of porphyrins on metal single-crystal surfaces under ultrahigh vacuum has been studied extensively, but less is known about the adsorption behavior of porphyrins on oxide surfaces. On metal surfaces porphyrin molecules will react with coadsorbed metal atoms or the surface itself, producing the metalated molecules and coadsorbed hydrogen atoms, which subsequently combine and desorb as hydrogen molecules. Examples will be given of 5,10,15,20-tetraphenylporphyrin (2HTPP) on Cu(111). A similar reaction is also possible for oxide surfaces. As 2HTPP is adsorbed on MgO an ion-exchange reaction happens already at room temperature and the two aminic protons of the porphyrin molecule are exchanged with a Mg2+ ion from the oxide surface, producing MgTPP and, locally, Mg(OH)2. Examples will be given of adsorption on both single-crystal MgO(100) substrates and nanostructured powders. Examples will also be given of metalation of 2HTPP adsorbed on a Au(111) surface immersed in an aqueous zinc acetate solution, metal-exchange reactions with Cu2+ and unsuccessful attempts to demetalate the adsorbed metalloporphyrins in acidic solutions.
(Invited) Molecular Mechanism of NO Reduction By Bacterial Nitric Oxide Reductases
Authors: Shiro Yoshitsugu
Published: February 2020

Bacterial nitric oxide reductase (NOR) catalyzes the NO reduction reaction (2NO + 2H+ + 2e- --> N2O + H2O) at its active site, which is a binuclear center comprised by heme (heme b
3) and non-heme iron (FeB).  In the enzymatic reaction by NOR, three short-lived intermediates have been proposed for the coordination of two molecules of NO to the binuclear center; i.e., trans-, cis-heme b
3- and cis-FeB-coordinations.  To establish the molecular mechanism of the NO reduction by NOR, we have been studying the time-resolved spectroscopies to characterize the coordination and electronic structures of the intermediates, which are appeared in the micro- to milli-second time region after the reaction of the ferrous enzyme with the NO molecule(s).  On the basis of the time-resolved optical, ESR and IR spectral changes, we have proposed that the trans-mechanism seem favorable for the NO reduction mechanism by bacterial NOR.  We will discuss the NOR reaction with referring their crystallographic structural data which we reported.
Scale-up of Rechargeable Mutivalent Batteries Via Pouch Cells Development
Authors: Ha Seungbum , Gallagher Kevin G.
Published: February 2020

Lithium ion batteries are now deployed to various portable electric devices and electric vehicles. However, the energy density, especially the volumetric energy density of the battery does not reach ideal target from a consumer perspective. The multivalent metal batteries are one of the promising candidates as a beyond lithium ion battery with 2–3 times the energy density of what lithium ion can offer.

Among multivalent metals, magnesium provides double the volumetric capacity of lithium. However, the standard reduction potential of magnesium is 700 mV less negative than that of lithium. Therefore, the approach to increasing its operating voltage is very important to increase energy density of battery.

Due to the demand for high voltage operation, comprehensive efforts have been demonstrated for high voltage electrolyte. The oxidative stability of many magnesium electrolytes is reported to be over 3 V vs Mg when tested by cyclic voltammetry on a Pt working electrode. However, their window of operation when assembled in coin cells and operated at constant current using typical stainless steel current collector and case is rarely above 2.0 V.

We demonstrated assembly of pouch cells for multivalent metal batteries and performed electrochemical testing. Initial work to identify high-performing materials, composition, fabrication variables and cycling conditions is conducted in cyclic voltammetry and coin cell test. The resulting information is then used for the pouch cell demonstration.
Core-Shell Structural Evolution of Crystalline Silicon Nanoparticles upon Lithiation/Delithiation By Ex Situ Raman Spectroscopy and Operando Synchrotron X-Ray Diffraction
Authors: Pavlenko Ekaterina , Quazuguel Lucille , Boniface Maxime , Tardif Samuel , Rieutord François , Marechal Manuel , Micha Jean-Sébastien , Mareau Vincent , Gonon Laurent , Lyonnard Sandrine
Published: February 2020

Core-shell structural evolution of crystalline silicon nanoparticles upon lithiation/delithiation by ex situ Raman spectroscopy and operando synchrotron X-ray diffraction

Silicon has attracted substantial attention as an alternative anode material for next-generation Li-ion batteries (LiBs) as it has a high theoretical capacity of 3580 mA h g-1 that is about ten times that of the commonly used graphite. (1) Upon charging, Si and Li react via an alloying process with a sharp interphase separating the growing LixSi amorphous phase from the pristine crystalline Si. In case of spherical particles this leads to a core-shell structure captured in Figure1b and c. An enormous volume expansion of Si associated with alloying leads to cracking of the electrode material and rapid fading of its performance. This hinders Si from being widely used in LiBs. It has been reported that for Si nano-particles (diameter<150nm) volume expansion does not lead to cracking (2). To benefit from silicon unique properties and enable realization of smart electrode design, an enhanced understanding of structural evolution along charging/discharging is required.

In the present work we were able to evidence the gradual amorphisation of crystalline Si nanoparticles upon cycling using ex situ Raman spectroscopy. Furthermore we probed the resulting stresses found in cores of the core-shell structures of Si nanoparticles and their evolution along lithiation/delithiation. Operando synchrotron X-ray diffraction (XRD) has also been performed to monitor the changes of the crystalline lattice during the initial cycles and to further quantify the constrained/unconstrained state of the silicon core. By means of combined ex situ Raman spectroscopy and in situ XRD we were able to provide in-depth understanding of the nanoparticles evolution.

Figure
1
. Schematic representation of silicon electrodes: a) pristine b)
after 1 cycle lithiation 
c)
after 100 cycles lithiation
d) corresponding Raman spectra. Black, blue and green, respectively.
(All spectra were normalized to the maximum of the c-Si peak)

1. Obrovac, M. N., and Leif Christensen. "Structural changes in silicon anodes during lithium insertion/extraction." Electrochemical and Solid-State Letters 7.5 (2004): A93-A96.

2. Liu, Xiao Hua, et al. "Size-dependent fracture of silicon nanoparticles during lithiation." Acs Nano 6.2 (2012): 1522-1531.

Figure 1
Characterizing the Stability and Kinetics of Hybrid Oxide-Sulfide Solid Electrolyte Cells
Authors: Taylor Nathan J , Thompson Travis , Garcia-Mendez Regina , Sakamoto Jeff
Published: February 2020

Growing energy applications and markets demand safer and higher performance Li-ion batteries. All solid-state batteries (ASSBs) represent a significant step forward in Li-ion battery technology. We have recently described the production of Li6.25La3Al0.25Zr2O12 (LLZO) solid state electrolyte (SSE). LLZO provides high room temperature ionic conductivities as well as chemical and mechanical stability towards metallic Li, which has 10X the specific capacity of a carbon anode. Sulfide based SSEs have high room temperatures conductivities, but their chemical and mechanical stability towards metallic Li has not been well defined. Here, we describe the construction of ASSBs with a metallic Li anode, a solid oxide electrolyte (LLZO), and a composite cathode consisting of an 75Li2S:25P2S5 sulfide electrolyte and TiS2 cathode. This architecture isolates the Li anode from the sulfide SSE and allows for facile assembly with a cold-pressed composite cathode powder. Electrochemical impedance spectroscopy (EIS) was used to probe the electrochemistry of the LLZO/Li2S:P2S5 interface as a function of temperature, pressure, and current density. DC cycling at 70°C and post mortem materials characterization were performed to determine the long-term stability of the hybrid oxide/sulfide interface.
Advanced Processing and Electrochemical Analysis of Novel Sodium-Rich Anti-Perovskites Via Conventional Sintering and Spark Plasma Sintering Methods
Authors: Wu Erik , Nguyen Han , Hy Sunny , Yersak Thomas A. , Meng Ying Shirley
Published: February 2020

Interest in non-flammable solid-state battery electrolytes continues to grow as they hold promise for batteries with increased safety, reliability, and energy density. They are nonflammable, stable over a wide temperature range, have a large electrochemical window, and potentially allow for the use of metallic Li anodes [1].

One particular solid-state electrolyte is the Lithium-rich anti-perovskite (LiRAP) with the formula Li3OX where X is a halogen or a mixture of halogens. Conductivities of >1 mS/cm were previously reported [2]. Interest in the material grew as the conductivity varied with different processing conditions thus opening the door to improvement with structura tweaking and optimization [3].

Whenever new a lithium compound is discovered in the battery field, interest in a sodium analog also arises. Na-ion batteries are considered a possible lower-cost alternative to lithium ion batteries due to the abundance of sodium. The conductivity of various Na-rich anti-perovskite (NaRAP) compounds with varying halogens were also previously reported [4]. 

Here we compare different synthesis methods for the Na3OBr compound, namely conventional cold-pressed sintering and spark plasma sintering. Spark plasma sintering enables a shorter processing time and more tightly-packed, dense pellets [5]. We report that the Na ionic conductivity for Na3OBr remained at similar values regardless of the synthesis method.

Acknowledgements

This work was supported by the National Science Foundation under grant number ACI-1053575.

References

[1] Thangadurai, V., Pinzaru, D., Narayanan, S., Baral, A. “Fast Solid State Li Ion Conducting Garnet-Type Structure Metal Oxides for Energy Storage”. J. Phys. Chem. Lett., 2015, 6 (2), pp 292–299. doi: 10.1021/jz501828v

[2] Wang, Y, Richards, W. D., Ong, S. P., Miara, L. J., Kim, J. C., Mo, Y., and Ceder, G. “Design principles for solid-state lithium superionic conductors”. Nature Materials, 2015, 14, pp 1026-1031. doi: 10.1038/nmat4369

[3] Deng, Z., Radhakrishnan, B., Ong, S. P. “Rational Composition Optimization of the Lithium-Rich Li3Ocl1-xBrx Anti-Perovskite Superionic Conductors”. Chem. Mater.
2015, 27(10), pp 3749-3755. doi: 10.1021/acs.chemmater.5b00988

[4] Wang, Y., Wang, Q., Liu, Z., Zhou, Z., Li, S., Zhu, J., Zou, R., Wang, Y., Lin, J., Zhao, Y.  “Structural manipulation approaches towards enhanced sodium ionic conductivity in Na-rich antiperovskites.” J. Power Sources
2015, 293, pp 735–740. doi: 10.1016/j.jpowsour.2015.06.002

[5] Sairam, K., Sonber, J. K., Murthy, T.S.R.Ch., Subramanian, C., Fotedar, R. K., Nanekar, P., Hubli, R.C. “Influence of spark plasma sintering parameters on densification and mechanical properties of boron carbide”. Int. Journal of Refractory Metals and Hard Materials, 2013, 42, pp 185-192. doi: 10.1016/j.ijrmhm.2013.09.004
Electrochemical Characterization of Advanced Sulfur Cathode Materials for Li-S Batteries
Authors: Nguyen Dan Thien , Hoefling Alexander , Lee Young Joo , Theato Patrick , Song Seung-Wan
Published: February 2020

Lithium-ion batteries are promising energy storage systems for electric vehicles and smart-grid storage systems. However, the needs for new batteries with higher energy than that of the current lithium-ion batteries are increasing. Among many battery systems, lithium-sulfur (Li-S) batteries are one of the most attractive candidates for next-generation high-energy density batteries due to high theoretical capacity of sulfur of 1672 mAh/g.1 However, commercialization of Li-S batteries has been hindered by  the issues such as the insulating nature of sulfur and lithium sulfide (Li2S) and polysulfide shuttle electrode-electrolyte interfacial instability. In order to achieve high performance Li-S batteries, much research efforts have devoted to solve those problems by preparing sulfur-based composite with porous carbon, and optimizing electrolyte composition and concentration and functional binder.2,3 However, report of the development of new sulfur material, and its electrochemical behavior and reaction mechanism, and correlation to the cycling performance of Li-S batteries is limited. Herein, we report on the improvement of electrochemical performance of an advanced sulfur cathode material by optimizing the cathode composition and electrolyte concentration. Correlation between the cycling performance and the changes in surface property and particle morphology of sulfur cathode material with cycling, which is obtained through ex situ X-ray photoelectron spectroscopy and scanning electron microscopy, would be presented in the meeting.

Acknowledgements

This work was supported under the framework of international cooperation program managed by National Research Foundation of Korea (2015K2A5A3000068) and German Academic Exchange Service (57141898).

 

References

1. Y.S. Su, Y. Fu, T. Cochell, and A. Manthiram, Nat. Commun., 4, 2985 (2013).

2. N. Jayaprakash, J. Shen, S. S. Moganty, A. Corona, and L. A. Archer, Angew. Chemie, 123, 6026 (2011).

3. S. Urbonaite, and P. Novák, J. Power Sources, 249, 497 (2014).
Fe2O3/Carbon Nanocomposite As Cathode Catalyst for Non-Aqueous Lithium-Air Batteries
Authors: Wu Maochun , Zhao Tianshou
Published: February 2020

Thanks to the highest capacity of lithium metal (3.86 × 103 mA h g-1) and inexhaustible oxygen in the atmosphere, lithium-air battery offers the promise of a remarkably high theoretical specific energy density up to ~11 kW h g-1, which is comparable to that of conventional fuels [1]. However, the development of lithium-air batteries is hindered by the high overpotential, low rate capacity, and poor cycling performance. The cathode has been shown to be the bottle-neck of rechargeable lithium-air batteries, wherein the sluggish oxygen reduction/evolution reaction (ORR/OER, especially OER) kinetics not only results in a large overpotential, but also causes the poor rechargeability. Thus, it is of great significance and urgency to enhance the electrochemical performances of the cathode. One effective way is to design high efficient catalysts to reduce the charge overpotential. Despite the precious Ru based catalysts have shown promising results as a catalyst for lithium-air batteries, its scarcity and high price will restrict the wide application. As a result, other non-noble transition metal/metal oxides (e.g., MnOx, CoOx) with activities for ORR and/or OER have drawn great interests for lithium-air batteries [2, 3]. Oxides of iron, which in the same group of Ru in the periodic table, however, is less investigated.

Herein, we proposed a facile method to fabricate Fe2O3/carbon nanocomposite cathode materials in which Fe2O3 nanoparticles with a diameter of 4-6 nm are deposited onto the carbon surface, as shown in Figure 1. The electro-catalytic activities were investigated by linear sweeping voltammetry (LSV) and discharge-charge profiles. The results show a lower onset potential and a larger OER current density, suggesting that Fe2O3 is an effective OER catalyst. Moreover, a non-aqueous lithium-oxygen battery with this cathode demonstrates a remarkably 430 mV lower charge overpotential and a dramatically improved cycling life.

More detailed experimental results will be presented in the meeting. And some possible mechanisms of the catalytic effect will also be discussed.

Figure 1
A Novel Strategy for Configuration of an Integrated Flexible Sulfur Cathode for High-Performance Lithium-Sulfur Batteries
Authors: Wang Hongqiang , Zhang Wenchao
Published: February 2020

Lithium-sulfur batteries are regarded as promising candidates for energy storage devices due to their high theoretical energy density. The practical application is hindered, however, by low active material utilization and unsatisfactory capacity retention caused by the diffusion of polysulfides. Herein, we present a novel strategy for the configuration of the sulfur cathode, which is composed of an integrated carbon/sulfur/carbon sandwich structure on polypropylene separator (CSC@separator) that is produced via the simple doctor blade technique. The integrated electrode exhibits excellent flexibility and high mechanical strength. The upper and bottom carbon layers of the sandwich-structured electrode not only work as double current collectors which effectively improve the conductivity of the electrode, but also serve as good barriers, suppressing the diffusion of the polysulfide and buffering the volume expansion of the active materials during cycling. The CSC@separator cathode delivers high reversible capacity of 730 mAh g-1 after 500 cycles with a small capacity decay of 0.058% per cycle, and also demonstrates low self-discharge behaviour.
Ether Degradation Thermodynamics in Li-O2 Redox Environments: A Computational Study
Authors: Brutti Sergio , Carboni Marco , Marrani Andrea Giacomo , Spezia Riccardo
Published: February 2020

The reaction thermodynamics of the 1,2-dimethoxi-ethane (DME) in a highly oxidizing environment has been studied by first principles methods to predict the spontaneous degradation processes of this model solvent molecule commonly used in electrolytes for Li-O2 rechargeable batteries. The potential energy surfaces of the reactivity of DME towards the O2
- superoxide radical anion in oxygen-poor or oxygen rich environments have been calculated by quantum chemistry techniques. A large set of density functional theory (DFT) methods has been used and compared to post-Hartree-Fock predictions to evaluate their predictive relative performances and select the best for the calculation of the full reactivity. Solvation effects have been considered by employing self-consistent reaction field in a continuum solvation model. The onset reaction of the degradation of the DME model molecule is the H-extraction by the O2
- superoxide anion to form an ether radical with an unpaired electron on a carbon atom. The subsequent reactivity of this radical molecule differs depending on the availability of molecular oxygen molecules. In oxygen rich environment this radical species follow multistep paths to give formaldehyde and alkyl carbonates whereas in oxygen poor environment the final products are alkyl oxalates or alkyl formates.
Performance of Li-Air Battery Cell with Folded Structure
Authors: Park Jung Ock , Kim Joon-Hee , Choi Kyoung Hwan , Lee Heung Chan , Im Dongmin
Published: February 2020

The Li-Air batteries which convert the electrochemical reactions of lithium and O2 into electrical energy have high theoretical gravimetric capacity (3861 mAh/gLi) that is ten times higher than that of lithium ion batteries (372 mAh/gc).  Its potential to generate high energy density makes it a promising candidate to replace the lithium ion batteries which practically reached the gravimetric energy density limit in the electric vehicle applications.  To meet the requirements of the electric vehicle applications, the Li-Air batteries need to overcome the technical barriers that limit the cycle life such as electrolyte and cathode instability.  Although recent developments have been focused on improving the cycle life (1) and safety (2) of Li-Air battery in efforts to extend its application into the electric vehicle, it is also important to design a cell structure that can achieve the highest possible energy density.  The Li-Air battery uses lithium metal, porous carbon layer, protective layer and gas diffusion layer (GDL).  The properties of lithium metal anode and porous carbon cathode layer are well known, and the cell design will mainly be affected by the mechanical property of the electrolyte, protective layer and GDL. 

Figure 1 shows the schematic of a Li-Air fold cell where the Li metal anode, protective layer, and cathode are folded.  The oxygen can be distributed to the cathode through the GDL which is inserted between the two cathode layers that are formed from folding.  The cell design enables the two layers of the cathode to share one common GDL layer and thus increasing energy density of the cell.  The capacity of the Li-Air fold cell can be controlled by changing the length (L) and the number of folds of the cell.  The width (W) of the cell affects the O2 distribution in cathode, thus the choice of W is limited.  Figure 2 shows the areal capacity of three Li-Air fold cells which contained polyethylene oxide with LiTFSI as electrolyte in the cathode and protective layer.  The cells were tested in 1 atm O2 at 60 C.  The capacities of the cells were adjusted by changing the number of folds.  For the cells in Figure 2, the three cells had WxL dimension of 1x5 cm and were folded 1, 10 and 50 times which resulted in the cells with capacity values of 0.02, 0.2 and 1 Ah, respectively.  Figure 2 indicates that the performance of the Li-Air fold cell is reproducible as the number of folds increase.   In the presentation, the effects of cell dimension on cell performance, the technical difficulties of manufacturing Li-Air cells with high energy density as well as the issues that need to be overcome to improve the cycle life will be discussed.

References

1. A. J. Smith, , J. C. Burns, , S. Trussler, , J. R. Dahn , J. Electrochem. Soc. 157, A196−A202 (2010).

2. S. Menkin, D. Golodnitsky,  E. Peled , Electrochem. Commun. 11, 1789−1791 (2009).

Figure 1
Analysis of the Active Material Microstructure Constituting the Positive Electrode in Lithium-Ion Batteries Application
Authors: Cabelguen Pierre-Etienne , Peralta David , Cugnet Mikaël , Badot Jean-Claude , Dubrunfaut Olivier , Mailley Pascal
Published: February 2020

Our project aims to complete an experimental study supported by computer modeling to bring a better understanding of the impact of the microstructure on electrochemical behavior. Research has shown in particular that the material microstructure is of tremendous importance to fully exploit its electrochemical capabilities. Indeed, a same chemical and crystallographic phase can exhibit vastly different energy densities, power capabilities and capacity retention depending on its microstructure.

LiNi1/3Mn1/3Co1/3O2materials (NMC) consisting of different microstructure are used as a model compounds. NMC synthesis is set up via co-precipitation route which allows the adjustment of different synthesis parameters such as the pH, concentrations of reactants and feeding and stirring rates, to obtain different morphologies. It gives the possibility to tune the primary particle crystallinity and morphology from thin nanosized pellets to large micrometric cuboids. The differences in the resulting electrochemical performances are discussed regarding the diffusion of lithium in both solid and liquid phases, the wettability and the electronic conductivity of the material by

By coupling electroanalytical techniques, microscopy and computer simulations, we show that the microstructure induces a fundamental difference in the rate-limiting step of the electrochemical process. The microstructure is first qualitatively and quantitatively investigated using mercury porosimetry, helium pycnometry helium pycnometry and FIB-SEM reconstruction. Cyclic voltammetry shows that porous materials behaviour is indeed limited by charge-transfer over a wide range of scan rates whereas dense materials are rapidly limited by solid-state diffusion. The support of modelling allows us to quantify important kinetics parameters such as diffusion coefficients, diffusion length and exchange surface areas and currents. The electronic conductivity investigated using broadband dielectric spectroscopy. This technique allows to separate and treat individually the different relaxations arising from the different length scales: crystallite, nanostructure, and microstructure. It is shown that the electronic conductivity is highly dependent on the microstructure of the primary particles. Flake-shape particles exhibit a higher conductivity, which has an effect at all larger scales. This study shows that the application of electroanalytical techniques must take into account carefully the microstructure of the studied materials and need the support of modelling to fully understand the electrochemical process.

Figure 1
(Invited) Pixel-Parallel CMOS Image Sensors with 16-Bit A/D Converters Developed by 3-D Integration of SOI Layers with Au/SiO2 Hybrid Bonding
Authors: Goto Masahide , Hagiwara Kei , Honda Yuki , Nanba Masakazu , Iguchi Yoshinori , Saraya Takuya , Kobayashi Masaharu , Higurashi Eiji , Toshiyoshi Hiroshi , Hiramoto Toshiro
Published: February 2020

To meet the increasing demands for higher performance of video imaging, several 3D integrated CMOS image sensors have been recently studied by using through-silicon vias (TSVs) and micro-bumps [1-2]. Although these sensors improved some of their performances by 3D integration, in-pixel interconnection was not realized because the TSV or bump size was larger than the imaging pixel size.

We have studied on the pixel-parallel 3D integrated CMOS image sensors by using embedded Au electrodes [3-5] suitable for high density integration instead of TSVs or bumps. Fig. 1(a) shows a schematic of the developed CMOS image sensor. Pixels including 128 × 96 photodiodes (PDs) and A/D convertors (ADCs) in the upper layer were connected to 16-bit counters in the lower layer for each pixel. The two functional layers were formed on silicon-on-insulator (SOI) wafers and directly bonded, mediated by Au electrodes embedded in the intermediate SiO2 layer by electroplating and chemical mechanical polishing (CMP). Each pixel size was 80 μm square with a Au electrode of 10 μm in diameter. No voids were observed at the bonded interface.

By measuring the input–output response of the developed sensor, we obtained a linear output to the light illumination intensity. The sensor also had a wide dynamic range of 96 dB, which corresponds to the 16-bit output. Signals were detected even under low illumination of 0.1 lx. Fig. 1(b) demonstrates an example of video images captured by the developed sensor. The 16-bit digital output contrast was adjusted to the standard display by compressed to 8-bit data. We confirmed the pixel-parallel operation without any pixel defects.

In summary, a 128 × 96 pixel-parallel 3D integrated CMOS image sensor with 16-bit A/D converters was successfully demonstrated by applying Au/SiO2 hybrid bonding of SOI layers. The developed process is promising for CMOS image sensors of higher performance and More-than-Moore type devices for the next generation electronics.

References

[1] J. Aoki et al., ISSCC, p.482, 2013.

[2] S. Sukegawa et al., ISSCC, p. 484, 2013.

[3] M. Goto et al., ECS trans., 61(6), p.87, 2014.

[4] M. Goto et al., IEDM, 4.2, 2014.

[5] M. Goto et al., IEEE S3S, 7c.3, 2015.

Figure 1
(Invited) Progress in Process Technologies for SiC Power Devices
Authors: Kimoto Tsunenobu
Published: February 2020

Power semiconductor devices have attracted increasing attention as key components in a variety of power conversion systems. Although the performance of Si power devices has remarkably been improved, silicon carbide (SiC) (and gallium nitride (GaN)) is promising for advanced low-loss and fast power devices, which can substantially outperform Si-based power devices [1-3]. Because of its strong bonding energy and thermal stability, however, special cares must be paid for fabrication process of SiC devices. This paper reviews present status and challenges of device processing technologies in SiC. In particular, ion implantation and MOS technologies are highlighted, because of their uniqueness, importance, and difficulty.

Ion implantation is a key process in fabrication of almost all kinds of SiC devices, due to the extremely small diffusion constants of dopants in SiC. Wide-range doping control of both n- and p-type conductivity can be achieved by ion implantation, but post-implantation annealing at unusually high temperature over 1650 oC is required to achieve nearly perfect electrical activation. Such high-temperature annealing may cause incongruent evaporation of silicon and surface roughening. The surface roughening can be significantly minimized by using a carbon cap. If the as-implanted lattice damage is of near-amorphous level, lattice recovery is very difficult. Therefore, implantation at elevated temperature is often employed, especially when the implant dose is very high. A variety of extended and point defects are generated by ion implantation in SiC and many of these defects survive after the post-implantation annealing. Thus, designing of device structure (implanted regions) and the process control are critical for fabrication of high-performance SiC devices.

SiC power MOSFETs are an ideal power switch owing to the low on-resistance and fast switching. However, the interface properties of SiO2/SiC MOS structures are still far from a satisfactory level, severely affecting the performance and reliability of SiC power MOSFETs. As in the case of Si power MOSFETs, high dielectric property of the gate oxide, high channel mobility, high threshold voltage and its stability are required. Though recent study on MOS structures formed on nonpolar SiC faces (a- and m-faces) has exhibited some promise (reasonably high mobility of 100 cm2/Vs and threshold-voltage stability), basic understanding of SiC MOS physics is still missing. To overcome the limitations of interface characterization techniques, a new method has been developed to accurately characterize the interface states near the band edge, and a clear correlation with channel mobility has been found. Based on these results, several trials to further improve the SiC MOS interface are under investigation.

[1] J.A. Cooper, Jr. and A. Agarwal, Proc. IEEE 90, 956 (2002).

[2] T. Kimoto, Jpn. J. Appl. Phys. 54, 040103 (2015).

[3] T. Kimoto and J.A. Cooper, Fundamentals of Silicon Carbide Technology (John Wiley & Sons, 2014).
(Invited) Intrinsic Reliability Assessment of 650V Rated AlGaN/GaN Based Power Devices: An Industry Perspective
Authors: Moens Peter , Banerjee Abhishek , Constant Aurore , Coppens Peter , Caesar Markus , Li Zilan , Vandeweghe Steven , Declercq Frederick , Padmanabhan Balaji , Jeon Woochul , Guo Jia , Salih Ali , Tack Marnix , Meneghini Matteo , Dalcanale Stefano , Tajilli A , Meneghesso Gaudenzio , Zanoni Enrico , Uren Mike , Chatterjee Indranil , Karboyan Serge , Kuball Martin
Published: February 2020

GaN devices are promising candidates for the next generation power devices for energy efficient applications. Although astounding performance is already proven by many research papers, the widespread adoption of GaN power devices in the market is still hampered by (1) yield and reproducibility ; (2) cost ; (3) reliability. All three factors are to be considered, but to convince customers to adopt GaN power devices in their next generation products, proven device and product reliability is a must.  Cost is kept acceptably low by growing the GaN epi stack on 6inch and 8inch Si substrates, and by processing the GaN power device technology in standard CMOS production lines, with a proper contamination control protocol in place.

This paper will focus on the most important intrinsic reliability mechanisms for GaN power devices. It will cover gate dielectric reliability, Ohmic contact reliability, accelerated drain stress testing (high temperature reverse bias--HTRB) and high voltage device wear-out testing (high voltage off-state stress--HVOS). The need to do reliability investigations based on statistical data on large area power transistors (100+ mm gate width) instead of small test structures will be emphasized. Acceleration models and statistical distribution models (Weibull, lognormal) are discussed.  The correlation between the GaN buffer stack vertical leakage and the parametric drift in prime device parameters under accelerated stress will be highlighted.

Furthermore, since the MOCVD epi layers of the GaN-on-Si buffer stack are key to the device performance, a measurement strategy to extract valuable information about the physical properties of the buffer layers (e.g. activation energies of the traps, conduction mechanisms, …) based on simple transmission line structures, is outlined.  This information will also be linked to the so-called “dynamic Ron”, a recoverable reduction in on-state current due to the trapping of charges in the buffer stack and/or the interface.

Finally, it will be shown that through proper engineering of the epi buffer stack, device layout and device passivation scheme, dynamic Ron-free power transistors can be obtained.
(Invited) Role of Interfaces in Achieving Self-Compliance Controlled Resistive Random Access Memory Devices for Low-Power Embedded Applications
Authors: Jha Rashmi , Lu Wenchao , Chen Wenbo
Published: February 2020

Resistive Random Access Memory (ReRAM) devices are considered promising candidates for emerging Non-Volatile Memory (NVM) applications. ReRAM devices can be switched at very low voltages using ultra-fast pulses. In addition, these devices can be easily integrated in Complementary Metal Oxide Semiconductor (CMOS) process-flow due to simplistic configuration, materials and process compatibility. These properties make them attractive for not only stand-alone off-chip memory applications but also for low-power embedded memory applications. However, there are several challenges that need to be addressed to take the complete benefit of this enabling technology. For example, currently available ReRAM devices suffer from variability and limited endurance. Additionally, these devices need a careful control of current, referred to as compliance current (CC), during electroforming and set operations which is typically achieved using a current limiting circuitry or an on-chip transistor. A tight control of CC is needed to control the filament dimension during forming and set operations of ReRAM to prevent the permanent breakdown of the device. However, the necessity of current limiting circuitry or transistor makes the integration of ReRAM devices in crossbar architectures difficult in 1Diode-1ReRAM (1D1R) configuration using bidirectional diodes as selector devices. Therefore, there is an urgent need to develop ReRAM devices which are self-compliance current (SCC) controlled where no additional current limiting circuitry or transistor is needed to limit the current through the device. This paper will discuss the role of interfacial layer (IL) engineering between electrodes and switching oxides towards achieving SCC ReRAM devices. Experimental results will be presented to show routes to scale down the switching currents in SCC ReRAM devices via the control of compositions and thicknesses of IL. Device performance parameters including endurance, retention, and reliability characteristics of these devices will be discussed. Finally, mechanism behind SCC and device models will be discussed which can be used for circuit level simulations.
(Invited) Challenges and Opportunities for GaN on Diamond Devices
Authors: Graham Samuel
Published: February 2020

The integration of CVD diamond is seen as an important technology for the passive thermal management of high power GaN devices.  Diamond films are often attached to GaN devices either through direct growth on the GaN or through a plasma activated attachment process.  Regardless of the method used, a thermal resistance between the GaN and diamond will exist at the interface either through the nucleation and growth of low thermal conductivity diamond at the interface or through a large phonon mismatch at the GaN diamond interace for the bonded approach.  While recent demonstrations have shown the benefits of using CVD diamond in lowering the temperature of GaN HEMTs, the theoretical benefits of CVD diamond have not been achieved due to the need to control thermal boundary resistance and the elimination of low conductivity diamond near the interace with GaN.

In this work, we will present data on the thermal performance of GaN on Diamond HEMTs fabricated using bonding as well as CVD growth on the GaN.  To better understand the thermal response of these devices, the thermal conductivity of the diamond and quality of the diamond measured using Raman spectroscopy and microscopy approaches will be presented.  In addition, the thermal boundary resistance between the GaN and diamond will be presented.  A link between the thermal conductivity, thermal boundary resistance, and the bonding or growth approach will be used to elucidate their impact on the total thermal resistance of the GaN on Diamond system.  Furthermore, the mechanical integrity of the GaN on diamond interface which can lead to a degradation in TBR measured using a transient thermoreflectance method will be shown.  Finally, the temperature distribution in GaN on Diamond HEMTs will be measured and correlated to models of the devices employind properties measured in our experiments.  Finally, the propspects for GaN on Diamond based on CVD growth and direct bonding approaches will be discussed.
(Invited) Recent Progress in GaN Power Devices with BV > 1200 V
Authors: Xing Huili Grace , Nomoto Kazuki , Hu Zongyang , Song Bo , Zhu Mingda , Jena Debdeep
Published: February 2020

Rapid progress has been made on GaN based power devices with breakdown voltage > 600 V. More recently, the vertical power devices have received increasing amount of attention in the community since 1) high quality GaN bulk substrates are readily available commercially, and 2) vertical power devices promise higher power handling capabilities. In this talk, I will present the recent progress made in our group on this topic: from lateral HEMT based SBDs with BV > 1.9 kV to vertical p-n junction based diodes with BV > 3.4 kV, as well as first demonstrations of polarization-doped power devices. I will also show the near unity ideality factor achieved in GaN-on-GaN p-n diodes, which subsequently enabled us to extract SRH nonradiative lifetime in GaN for the first time.
(Invited) New Directions in GaN Photonics Enabled by Electrochemical Processes
Authors: Zhang Cheng , Yuan Ge , Xiong Kanglin , Park Sung Hyun , Han Jung
Published: February 2020

So far the impact and promise of GaN devices are focused mainly on optoelectronic and microelectronic devices. The blue LEDs and their inventors have been recognized with Nobel prizes, and GaN power transistors are positioned to play a key role in compact energy efficient power electronics.

The exploration of GaN in photonic devices and structures, which seeks to manipulate optical density of states and propagation properties through linear and non-linear optical index engineering, has received much less attention. In this talk we will summarize our effort in making GaN resonators in one, two, and three dimensions. We will review the performance and challenges associated with different fabrication pathways. With the use of a novel electrochemical process, we are able to selectively porosify or electro-polish GaN. The electrochemical process enables unprecedented tuning in the index of refraction, making it possible to create optical confined structures and laser diodes.

The research is supported by US Department of Energy, National Science Foundation, and DARPA.
Investigation on Alumina Passivation for Improved IGZO TFT Performance
Authors: Mudgal Tarun , Edwards Nicholas , Ganesh Prashant , Bharadwaj Anish , Manley Robert G. , Hirschman Karl D
Published: February 2020

A study on the influence of the back-channel interface on the operation of bottom-gate indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) is presented.  TFTs without any passivation material deposited typically exhibit best-case initial results.  However a passivation layer is required for device stability and process integration.  The surface of IGZO is very sensitive to deposition conditions of passivation materials; in general additional oxygen vacancies are created which renders the IGZO conductive.  Annealing in an oxidizing ambient may reverse this effect and result in devices which exhibit appropriate semiconducting properties. 

The impact of passivation using alumina deposited via electron beam evaporation and atomic layer deposition (ALD) has been investigated.  A decrease in TFT channel mobility is attributed to the IGZO/alumina back-channel interface degradation associated with the alumina passivation process.  Low temperature ALD (e.g. T ≤ 150°C) has been explored to minimize this degradation effect.  Pre-passivation and post-passivation anneal treatments have also been explored to better understand the mechanisms involved.  Improvements in the back-channel interface were shown to depend on the thickness and deposition method of the alumina passivation layer.  Temperature-dependent measurements reveal differences in electrical characteristics including bias-stress stability.  Modifications in the passivation and annealing procedures and process integration details have resulted in a marked improvement in the performance of passivated devices.
ZnO Nanowires Synthesis and Characterization
Authors: Tsai Ping-Hsin , Wang Chiu-yen
Published: February 2020

In this study, a two-zone furnace had been used to grow ZnO nanowires (NWs) on Si (100) substrates by thermal evaporation method via the vapor-solid (VS) mechanism. We mixed zinc oxide powder and graphite powder as source. By controlling the growth temperature, source temperature, growth pressure, source amount, growth time, growth position and carrier gas, ZnO NWs had been grown a variety of condition. When growth temperature was set at 500 oC, ZnO were grown disorderly. Nanobelts and nanowires were grown simultaneously on silicon substrate. As growth temperature increasing to 700 oC, uniform ZnO NWs had been grown with 10-20 μm in length and 80-100 nm in diameter. But when growth temperature was increased continuously to 900 oC, the silicon substrate didn’t have ZnO NWs trace. Not only growth temperature but also other parameters had a lot of influences on growing ZnO NWs. Such as source amount, it mainly affects nanowire’s morphology and density of nanowires. Source temperature affects the source vapor pressure to adjust the atmosphere in tube. Growth time was related to the length of ZnO NWs. The position was associated with the deposit of source vapor. Therefore, we can grow appropriate ZnO NWs to increase the diversity of the research on electrical application part in the future. ZnO NWs were characterized by field-emission scanning electron microscope (FE-SEM), x-ray diffractometer (XRD), and transmission electron microscope (TEM) about the morphology and crystal structure.