bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Study of LSCF and LSM-YSZ Cathode Microstructure by FIB/SEM Tomography
Authors: Wankmüller Florian , Joos Jochen , Meffert Matthias , Gerthsen Dagmar , Ivers-Tiffée Ellen
Published: February 2020

The mixed ionic-electronic conducting cathode (La, Sr)(Co, Fe)O3-δ (LSCF) is utilized worldwide for solid oxide fuel cells (SOFCs) operated at intermediate temperatures [1] because of its excellent oxygen reduction reaction rate. The challenge of using LSCF as cathode material is the complex nature of the interface to Zirconia-based electrolytes, which may counteract this advantage [2, 3]. The composite cathode (La, Sr)MnO3 (LSM) – Y2O3 doped ZrO2(YSZ) is an adequate alternative for higher temperatures only. LSM-YSZ offers fewer regions of oxygen reduction (triple phase boundaries) due to spatially separated ionically (YSZ) and electronically (LSM) conductive phases. If electrochemical and microstructural parameters of both types of electrodes are quantified by appropriate techniques, the performance can be modeled and compared for different operating conditions. Advanced imaging techniques such as focused ion beam/scanning electron microscopy (FIB/SEM) or X-ray tomography are promising techniques for microstructure quantification enabling 3D reconstructions of µm- and sub-µm-scaled multiphase electrodes [4, 5, 6]. Reconstructing the composite cathode, in particular, comprises the challenge of overcoming the weak material contrast between LSM and YSZ using scanning electron microscopy.

This contribution will show how FIB/SEM tomography can help to identify different microstructural parameters such as porosity, particle size, surface area and tortuosity. We will compare LSCF and LSM-YSZ cathodes and enlighten new challenges in image reconstruction, parameter acquisition and parameter interpretation for the different material sets.

[1] H. Yokokawa, et al., J. Power Sources, 182, p. 400 (2008)

[2] J. Szasz, et al., ECS Trans., 66(2), p. 79 (2015)

[3] Yokokawa, et al., Solid State Ionics, 262, p. 454 (2014)

[4] J.R. Wilson, et al., Nature Materials
5(17), p. 541 (2006)

[5] J. Joos, et al., Electrochim. Acta
82, p. 268 (2012)

[6] Y. C. K. Chen-Wiegart, et al., J. Power Sources, 218, p. 348 (2012)

Figure 1
Chemical Analysis of Activation Process of LSM Thin Film Electrode
Authors: Yu Yang , Liu Jian , Finklea Harry O. , Abernathy Harry , Ohodnicki Paul R , Kalapos Thomas , Hackett Gregory A
Published: February 2020

Strontium-doped lanthanum manganite (LSM) is one of the most widely used cathode material for yttria-stabilized zirconia (YSZ)-based solid oxide fuel cells (SOFCs), due to its superior chemical stability and small coefficient of thermal expansion (TEC) mismatch with YSZ. The activation process of the cell, which can be attributed to the cathode and cathode electrode interface, has a significant effect on the long-term electrochemical performance and stability of SOFCs. Therefore, it is essential to understand the origin of this underlying activation process. In this study, thin film LSM on YSZ half cells were fabricated with an LSCF counterelectrode and the effects of cathodic current density and overpotential on the polarization behavior of the LSM thin film electrode were investigated. The surface morphology as well as surface chemistry and bonding environment of LSM before and after polarization was investigated using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The formation of SrO was found on the LSM surface after polarization. The cross-section microstructure of LSM, as well as interfacial chemistry of LSM/YSZ, were investigated using transmission electron microscope (TEM) and TEM-based energy dispersive X-ray spectroscopy (EDS). The presence of Mn-rich phases were observed before and after polarization. The pre- and post-activation electrode performances were investigated at various temperatures and oxygen partial pressures, which helps reveal the nature of the activation mechanism in combination with the microstructural and chemical analysis.
Removal of Gaseous Hexavalent Chromium Species in a SOFC System By a Chromium Getter
Authors: De Vos Yves
Published: February 2020

Chromium containing alloys release hexavalent chromium species, which degrade SOFC stacks, and are hazardous for human health. Cathode air preheaters are a known source for hexavalent chromium, as they have a large surface area, consisting of austenitic steel, containing 22% chromium. The preheaters in this study use 0.5 – 1.0 m² steel surface, with maximum wall temperatures of 700 – 900 °C. These preheaters release 0.05 – 0.1 g hexavalent chromium in 1000 h. Improved alloy selection reduces this by a factor 15 – 20.

Higher reduction is required, depending on the operating temperatures in the SOFC stack, and for automotive applications such as SOFC APU’s. Hexavalent chromium at end of life is a hazardeous waste, and might complicate the recycling strategy for used vehicles.

 

The design and performance of a Chromium Getter is presented: this component captures hexavalent chromium, as released by a cathode air preheater or another steel component. The Getter is a catalyst: it reduces hexavalent chromium to trivalent chromium, which is stored on a Ti/TiO2 surface in the component.

 

Lab tests were executed during 1000 h, at 750°C, 4 g/s mass flow, 3% moisture. The source of the hexavalent chromium is a plate heat exchanger, with contains 0.6 m² heat exchanging walls, consisting of austenitic alloy. These walls were kept at 780°C overall. This was done for accelerated testing. Chromium was analyzed at 7 collection runs, each taking 20h. During the collection runs, the outflowing hot gas was cooled in a Liebig cooler. The Liebig coolers were rinsed with acid, and the total chromium amount in the acid was measured using ICP-OES. The hexavalent fraction was determined by photometry after derivatization.

 

The concentration of hexavalent chromium species at the outlet of the Chromium Getter is below the analytical detection limit during the 1000h test. This corresponds to a conversion by a factor 650 or higher, as compared to measurements on heat exchangers without chromium getter.

 

Post mortem analysis shows that the chromium stored on the active surface is trivalent chromium, as desired. Therefore, the component can be recycled as regular metal at the end of life. The storage capacity of the component is calculated for a 1.2 kWe SOFC system, using a Chromium Getter with 0.17 l volume.

Figure 1
Progress in HEXIS’ Development: Galileo 1000 N and HEXIS' Next Generation SOFC System
Authors: Mai Andreas , Fleischhauer Felix , Denzler Roland , Schuler Alexander
Published: February 2020

HEXIS is developing and manufacturing SOFC-based micro-CHP systems for single-family or small multi-family houses. Galileo 1000 N with an output of 1 kW electrical power was brought into the market 2013. Since then, HEXIS together with other members of the Viessmann Group have been developing the next generation of the Viessmann/HEXIS SOFC system.

The paper and presentation will report on the newest results of the short-stack tests, fullscale-stack tests as well as on system tests based on the established Galileo systems as well as on Hexis’ next generation systems. These include results of Galileo tests running for more than 23’000 h, electrical efficiencies of the new generation of 40 % AC, net and total efficiencies of 95 % (LHV). An electrical efficiency of 54 % (DC) was demonstrated on fullscale-stack level with steam reforming.

The tests showed that the electrical efficiency is rather constant in the desired operation window. Degradation rates as low as approx. 0.3 % / kh, i.e. 10 mΩ cm² / kh could be shown on short-stack level over 19’000 h. As a consequence, the next generation will be operating at higher power densities, allowing a higher electrical power output at unchanged stack size. The results of tests concentrating on Redox and on-off cycles will be another topic of the contribution.

HEXIS’ next generation systems are being developed together with other group companies of the Viessmann Group leading to a new system architecture. The contribution will give a first glance into this new architecture and will show first test results obtained.
Durability of PEMFC Electrodes and Reduction of Pt Loading
Authors: Gazdzicki Pawel , Mitzel Jens , Sanchez Daniel G , Dreizler Andreas M. , Schulze Mathias , Friedrich Kaspar Andreas
Published: February 2020

A particular challenge related to low temperature polymer electrolyte fuel cells (PEMFC) is to maintain high performance and long-term durability concurrently with the further reduction of Pt loading. These are conflicting goals because of a direct correlation of Pt surface with activity and Pt amount with durability. Moreover the lack of common procedures to reliably determine voltage loss rates leads to severe difficulties in the comparison of results obtained by different institutions or projects. Accordingly, special attention is devoted to the discrimination between irreversible and reversible voltage losses [1].

Regarding the influence of Pt loading on PEMFC performance and durability our recent rainbow stack study [2] performed in dynamic operation shows that for Pt/C based cathodes a sudden drop of performance is observed for loadings <=0.2 mgPtcm-2 and current densities >1 Acm-2. A similar threshold value is found for the increase of irreversible voltage losses which lead to a reduction of PEMFC durability for cathodes with <=0.2-0.3 mgPt/cm2 (see Fig. 1). Another durability issue at cathodic loadings <0.4 mgPt/cm2 is the acceleration of reversible degradation leading to a significant voltage drop at continuous fuel cell operation. The results show that the Pt loading of Pt/C based electrodes cannot be reduced below 0.2-0.3 mgPtcm-2 by just varying the thickness of the catalyst layers without suffering durability issue. To go below 0.2 mgPtcm-2 new electrode designs are needed. A special combination of coating techniques is also considered as promising approach to solve this issue.

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303452 (Impact).

References:

[1] P. Gazdzicki, J. Mitzel, D. Garcia Sanchez, M. Schulze, K. A. Friedrich, J. Power Sources, 327, 85 (2016).

[2] P. Gazdzicki, J. Mitzel, A. M. Dreizler, M. Schulze, K. A. Friedrich, Fuel Cells, DOI: 10.1002/fuce.201700099

Figure 1
Surface Modification of Porous Foam Electrodes: Stabilization of Solid Electrolyte Interphase Formation in Li-Metal Batteries
Authors: Day Brian A , Gattu Bharat , Shanthi Pavithra Murugavel , Datta Moni Kanchan , Kumta Prashant N
Published: February 2020

The formation of the solid electrolyte interphase (SEI) is critical to stabilization of lithium metal electrodes.1,2 When the electrodes contact electrolyte, a thin solid layer is immediately deposited on the surface. Ideally, this layer should be electronically insulating, while conducting Li-ions, and only a few nanometers thick to ensure that lithium can diffuse to the electrode surface without the reduction of any electrolyte components.2 Unfortunately, much research has shown that even after initial formation, the SEI layer continues to grow, and eventually leads to cell failure by limiting the ability of lithium to diffuse to the electrode surface.3,4 In order make electrodes practical for use in lithium metal batteries, the growth of the SEI needs to be well controlled and limited in thickness.

Previous work has shown that the use of high surface area porous metal anodes can prevent dendrite formation, another key barrier to commercialization of lithium metal batteries.5 However, as the number of cycles increases and the SEI layer on the electrode grows too thick, the pore network fills and lithium diffusion is limited, and plating subsequently reverts to unwanted dendritic growth.

In this work, a method for improving the cycling stability of these porous foam electrodes by controlling the SEI is examined. Accordingly, the work focuses on the utilization of novel surface additives to achieve this goal. The approach has shown to greatly increase the number of achievable cycles. The engineered systems already show ~99% efficiency over 100 cycles, far better than the 70 cycles at ~95% efficiency previously obtained using unmodified foams. By controlling the initial SEI formation and limiting its thickness, saturation of the pore network can be inhibited, thus extending the stable cycling window.

Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0007797, Edward R. Weidlein Chair Professorship funds, and the Center for Complex Engineered Multifunctional Materials (CCEMM).

References

Aurbach, E. Zinigrad, Y. Cohen, H. Teller, Solid State Ionics, 148, 405-416 (2002).

Peled, S. Menkin, J. Electrochem. Soc., 164 (7), A1703-1719 (2017).

Zheng, S. W. Lee, Z. Liang, H. Lee, K. Yan, H. Yao, H. Wang, W. Li, S. Chu, and Y. Cui, Nature Nanotech.
9, 618-623 (2014)

Vetter et al., Journal of Power Sources
147, 269–281 (2005)

A. Day, P. Jampani, P. M. Shanthi, B. Gattu, P. N. Kumta. ECS 232, National Harbor Maryland (2017).
(Invited) Functionalization of 2D Materials: A Molecular Approach
Authors: De Feyter Steven
Published: February 2020

In this presentation, I will focus on the functionalization and nanostructuring of graphite, graphene, and other 2D materials using two approaches. A first approach is based on molecular self-assembly at the interface between a liquid or air, and the 2D material. I will discuss concepts of nanostructuring emphasizing the effect of solvent, solute concentration and temperature, and self-assembly under nanoconfinement conditions. A second approach is based on grafting molecules on 2D materials via covalent chemistry. In addition to a discussion on the functionalization principles, it will be demonstrated how also nanolithography can be used to nanostructure such covalently modified 2D materials. Advanced interface specific methods such as scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) provide structural and other types of information at the nanoscopic level.

Figure 1
Novel Strategies to Interface Molecules and 2D Materials
Authors: Perez Emilio M
Published: February 2020

One of the most attractive areas of research in Nanoscience is the combination of 2D materials through van der Waals forces to form heterostructures (Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H. Science 2016, 353, DOI: 10.1126/science.aac9439). Here, we present strategies beyond dispersion forces to interface 0D (molecules) and 2D materials.

We will show examples of 0D-2D heterostructures connected through covalent and noncovalent chemistry. In the first example, we will show a method to functionalize graphene covalently with exquisite atomic selectivity and yield (NanoLett. 2016, Chem. Commun. 2017). In the second example, we will show that the photoresponse of MoS2 photodetectors can be enhanced by simple and reversible supramolecular functionalization with organic dyes (Chem. Commun. 2016). We will also show the example of a naturally occurring van der Waals heterostructure, franckeite, an air stable, p-doped semiconductor with photoresponse in the far IR (Nat. Comms. 2017). Finally, we will present strategies for the self assembly of liquid-phase exfoliated 2D materials from suspension into functioning electronic devices (Chem. Commun. 2017).
Piezopotential-Driven Efficient Piezocatalytic Activity By Single- and Few-Layered MoSe2 Nanoflowers
Authors: Chung Yun-Jung , Wu Jyh-Ming
Published: February 2020

Recently, developing a catalyst system without the demand of light irradiation has received a great attention. Here, we report the new advances in the piezoelectric properties of two-dimensional MoSe2 in the application of degradation and further investigate the reactive oxygen species as results from the active sites of the single- and few-layered structure. This work successfully synthesized non-centrosymmetric single- and few-layered MoSe2 nanoflowers by a hydrothermal method. The single- and few-layered structure of MoSe2 nanoflowers were discovered to have a highly efficient piezo-catalyst effect, which possessed a superior piezo-catalyst activity toward decomposition of Rhodamine B dye by imposing an ultrasonic-wave in the dark. In the presence of mechanical force, the spontaneous polarization establish an internal electric field in the non-centrosymmetric structure, which acts as an efficient driven force for the separation of the electrons and holes in an opposite direction. Consequently, the surface of polarized MoSe2 nanoflowers emerges the strain-induced charges that are available for generating hydroxyl radical to oxidize the Rhodamine B dye. The piezoresponse force microscopy (PFM) and the tunneling atomic force microscopy (TUNA) confirmed that the MoSe2 nanoflowers exhibited a significantly piezoelectric potential. The electron paramagnetic resonance (EPR) spectra further proved that the hydroxyl radicals were generated when the mechanical force applied to the nanoflowers. The degradation ratio reached 100% within 120 s for destroying the Rhodamine B dye and showed an ultra-fast degradation rate at 69,889 ppm L mole −1 s −1. Compared to the commercial bulk MoSe2, the nanoflowers showed a better performance due to the single layer and odd layer structure as observed in the HRTEM images. Furthermore, the piezocatalytic effect of MoSe2 nanoflowers has a potential in exhibiting an efficient piezocatalytic activity in hydrogen evolution. Ultrasonic waves lead to a strain-induced electrons and holes on their surface, which create the redox reaction on the water molecules. The higher amount of hydrogen gas output has been observed at the higher frequency of ultrasonic-wave system. This work provides a great possibility for the future application in hydrogen production by using energy waste from the environment, such as vibration. In summary, this research demonstrates the evident structure of single- and few-layered MoSe2 nanoflowers with piezoelectric potential output and reveals the fastest degradation rate among the reported value. In addition, the piezo-catalyst effect of MoSe2 nanoflowers offers a future promising candidate for hydrogen production.
(Invited) Out-of-Plane Polarization of 2D Layers
Authors: Zhu Hanyu , Zhang Xiang
Published: February 2020

Symmetry of atomic lattices determines a variety of fundamental optical and electronic properties such as second harmonic generation (SHG) and piezoelectricity. The diversity of layered materials presents a unique opportunity to control the lattice symmetry in low dimension. We present our recent discoveries of intrinsic out-of-plane asymmetric structures in atomically thin layered materials. The strong covalent component of the chemical bonding in these materials maintains the vertical polarization, which is usually electrostatically unstable. We further prove that the polarization is reversible by electric field in quintuple layers with SHG and piezoresponse. Our results have potential for 2D memories and switchable electrochemistry.
Metal Semiconductor Field Effect Transistors with Conducting NbS2/n-MoS2 Van Der Waals Schottky Junction and Graphene Contact
Authors: Shin Hyung Gon , Lim June Yeong , Park Sam , Im Seongil
Published: February 2020

We have fabricated van der Waals (vdW) Schottky junction between high work function conducting NbS2 transition metal dichalcogenide (TMD) and semiconducting n-MoS2 TMD for metal semiconductor field effect transistors (MESFETs). The Schottky barrier between NbS2 and MoS2 appeared as large as ~0.5 eV due to their work function difference, as measured by scanning Kelvin probe. Schottky effect MESFET operates with a low threshold gate voltage of -0.5 ~ -1 V exhibiting easy saturation. Since this FET contains low density traps at the vdW interface, little gate hysteresis and ideal subthreshold swing of 60~80 mV/dec are expected. In addition, source/drain (S/D) contact for n-channel MoS2 could significantly affect device mobility. In the case of the graphene S/D contact, the device shows the highest mobility of more than 800 cm2/V s, although the device shows the lowest mobility of ~15 cm2/V s in the case of Au/MoS2 contact without an annealing process. TMD-based MESFET with NbS2/n-MoS2 junction is considered novel and promising in future 2D device electronics.
(Invited) Exploitation of Nanomaterials and Interfacial Engineering in Perovskite Solar Cells
Authors: Jung Hyun Suk
Published: February 2020

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 22% and further improvements are expected up to 25%. These novel organometal halide perovskite absorbers which possess exceptionally strong and broad light absorption enable to approach the performances of the best thin film technologies. To commercialize these great solar cells, there are many bottlenecks such as long term stability, large scale fabrication process, and environmental issues.

In this presentation, we introduce our recent efforts to facilitate commercialization of perovskite solar cells.1-5 For examples, we introduce a recycling technology of perovskite solar cells, which will facilitate the commercialization as well as solve the environmental issues of perovskite solar cells.4 Moreover, we are going to discuss about stability issue of perovskite materials regarding charge generation and extraction.

(1) B. J. Kim, D.H. Kim, Y.-Y. Lee, H.-W. Shin, G. S. Han, J. S. Hong, K. Mahmood, T. Ahn, Y.-C. Joo, K. S. Hong, N.-G. Park, S. Lee and H. S, Jung, Energy Environ. Sci., 2015, 8, 916.

(2) M.-C. Kim, B. J. Kim, J. Yoon, J.-W. Lee, D. Suh, N.-G. Park, M. Choi and H. S. Jung, Nanoscale , 2015, 7, 20725.

(3) S. Jang, J. Yoon, K. Ha, M.-C. Kim, D. H. Kim, S. M. Kim, S. M. Kang, S. J. Park, H. S. Jung, and M. Choi, Nano Energy, 2016, 22, 499.

(4) B. J. Kim, D. H. Kim, S. L. Kwon, S. Y. Park, Z. Li, K. Zhu and H. S. Jung, Nature Communications, 2016, 7, 11735.

(5) M.-C Kim, B. Jo Kim, D.-Y. Son, N.-G. Park, H. S. Jung, and M. Choi, Nano Lett., 2016, 16, 5756.
(Invited) Linker Group Effects of Linearly Pi-Extended Porphyrins for Solar Energy Conversion
Authors: Hu Yi , Jinadasa R.G. Waruna , Yellappa Shivaraj , Webre Whitney , Thomas Michael , D'Souza Francis , Wang Hong
Published: February 2020

Linearly pi-extended porphyrins often show significantly broadened and red-shifted absorption bands due to the largely extended pi-system. As such, linearly pi-extended porphyrins appear to be attractive candidates as sensitizers for dye-sensitized solar cells.1-3 Linearly pi-extended porphyrins, such as benzoporphyrins, are generally very difficult to synthesize and functionalize. In this presentation, we present concise and versatile synesthetic methods to access different types of benzoporphyrins. Push-pull porphyrins, in which the push (electron-donating) and pull (electron-withdrawing) groups are installed at the porphyrin beta-positions are also designed and synthesized.4-6 These porphyrins are evaluated as sensitizers for dye-sensitized solar cells. Significant linker effects and push-pull effects were observed for these porphyrins. Systematic investigation on linker groups, electron-donating groups as well as electron-withdrawing groups are performed using UV-Vis spectroscopy, life-time and steady state fluorescence spectroscopy, cyclic voltammetry and DFT calculations.

Figure 1
Growth of Hybrid Metal-Organic Perovskites with Controlled Crystal Orientation
Authors: Ozden Sehmus , Mohite Aditya D.
Published: February 2020

The organic–inorganic hybrid perovskites have gained a great attention because of their superior optoelectronic properties such as high absorption coefficient, bandgap, long carrier lifetime, electron mobility, low cost and facile deposition technique. Because of their extraordinary properties, they have been widely investigated for a variety of applications such as photovoltaics, light emitting diodes, photodetectors, thermoelectric devices, lasers and X-ray detectors. Among these applications, perovskites have made breakthrough in solar cells devices. In a short time, this class of materials has demonstrated impressive potential to achieve high conversion efficiency, which has increased from 3.5% to ~22%. The ability to control the crystal orientation of perovskites crystals is crucial for achieving directional high mobility of charge carriers in the direction of the electrodes in optoelectronic devices. However, even though there is an important progress on the synthesis of metal-halide hybrid perovskite films, it still remains a big challenge to control-over the crystal orientation and anisotropy during crystal growth. Here, we will discuss the synthesis of two-dimensional and three-dimensional perovskite films with control over crystal orientation to achieve a strong anisotropy of certain planes in the resultant thin film perovskites. We anticipate that this method could be applicable as a general method for the growth of thin film perovskites with any combination of the compounds such as cations, divalent metals, and halides, which otherwise may be limited kinetically and also will allow for the tuning of their crystalline orientation based on the desired device functionalities.
(Invited) Controlling Energy Flow in Plasmonic Photocatalysis through the Design of Hybrid Plasmonic Nanostructures
Authors: Linic Suljo
Published: February 2020

It has been shown that photo-excitation of plasmonic metal nanoparticles (Au, Ag, and Cu) can induce direct photo-chemical reactions on the nanoparticles. However, the widespread application of this technology in catalysis has been limited by the relatively poor chemical reactivity of noble metal surfaces. In this presentation, we present our recent work in which we conceptualized and designed hybrid nanostructures in which a plasmonic metal harvests the energy of visible light photons and selectively channels that energy into catalytically active centers on the nanostructure. To accomplish this, we developed a synthetic protocol to deposit a few monolayers of Pt onto plasmonic Ag nanocubes. This model system allows us to conclusively separate the optical and catalytic functions of the hybrid nanomaterial and analyze the interaction between the two functions. Through experimental and theoretical studies of the optical properties of these nanostructures, we show that the flow of energy is strongly biased towards absorption (i.e. excitation of energetic charge carriers) in the thin Pt shell. We demonstrate the utility of these nanostructures for photo-catalytic chemical reactions in the preferential oxidation of CO in excess H2. The reactor studies conclusively show that photo-excitation of these nanostructures results in photo-chemical reactions on the Pt surface. We describe the fundamental physical reasons for the observed directed flow of energy and discuss how these discoveries impact the field of plasmonic catalysis.

U. Aslam, S. Chavez, S. Linic, Nature Nanotechnology, 2017 (10.1038/nnano.2017.131)

C Boerigter, R Campana, M Morabito, S Linic, Nature communications, 7, 2016

C. Boerigter, U Aslam, S Linic, ACS Nano 10 (6), 6108-6115, 2016

S. Linic, U Aslam, C Boerigter, M Morabito, Nature Materials 14 (6), 567-576

Andiappan, S. Linic Science, 339, 1590, 2013

D. B. Ingram, S. Linic, JACS, 133, 5202, 2011

Suljo Linic, Phillip Christopher and David B., Nature Materials,
10, 911, 2011.

P. Christopher, H. Xin, S. Linic, Nature Chemistry, 3, 467, 2011.

P. Christopher, H. Xin, M. Andiappan, S. Linic, Nature Materials, 11, 1044, 2012.
(Invited) Probing Charge Density and Surface Chemistry of Nanostructured Electrodes Using Single-Particle Spectro-Electrochemistry
Authors: Link Stephan
Published: February 2020

A surface plasmon in a metal nanoparticle is the coherent oscillation of the conduction band electrons leading to both absorption and scattering as well as strong local electromagnetic fields. These fundamental properties have been exploited in many different ways, including for example surface enhanced spectroscopy and sensing, photothermal cancer therapy, and color display generation. The performance of plasmonic nanoparticles for a desired application not only depends on the particle size and shape, but is tunable through nanoparticle interactions on different length scales that support near- and far-field coupling. Chemical synthesis and assembly of nanostructures are able to tailor plasmonic properties that are, however, typically broadened by ensemble averaging. Single particle spectroscopy together with correlated imaging is capable of removing heterogeneity in size, shape, and assembly geometry and furthermore allows one to separate absorption and scattering contributions. In this talk I will discuss our recent work on using the surface plasmon resonance to follow as well as initiate electrochemical processes including charging, physio- and chemisorption of analytes and reactants, and redox reactions.
(Invited) Light-Driven H2 Generation Using 1D and 2D Multicomponent Semiconductor/Catalyst Nanoheterostructures
Authors: Lian Tianquan
Published: February 2020

Quantum confined semiconductor nanocrystals have been widely investigated as light harvesting and charge separation components in photovoltaic and photocatalytic devices. The efficiency of these semiconductor nanocrystal-based devices depends on many processes, including light harvesting, carrier relaxation, charge separation and charge recombination. The competition between these processes determines the overall solar energy conversion (solar to electricity or fuel) efficiency. Compared with single component quantum dots (QDs), semiconductor nanoheterostructures, combining two or more materials, offer additional opportunities to control their charge separation properties by tailoring their compositions and dimensions through relative alignment of conduction and valence bands. Further integration of catalysts (heterogeneous or homogeneous) to these materials form multifunctional nanoheterostructures. Using Pt tipped CdSe/CdS dot-in-rod nanorods(NRs) and CdS nanoplatelets as model systems for 1D and 2D hetersotrtuctures, we are examining the mechanism of long-lived charge separation and H2 generation in the presence of sacrificial electron donor. The rates of carrier transport, interfacial charge (electron and hole) transfer, and charge recombination can be directly monitored by transient absorption and time-resolved fluorescence spectroscopy. In this talk, we will discuss how the rates of these elementary carrier transfer and transport processes depend on the dimension (size and length), morphology and band alignment in these materials, affect the overall H2 generation efficiency and can be optimized through rational material design.
(Invited) Synthesis and Redox Property of Sumanenyl Trication
Authors: Sakurai Hidehiro , Ohigashi Yuya , Ikuma Naohiko , Yakiyama Yumi
Published: February 2020

Sumanene, a bowl-shaped aromatic molecule, possesses the partial structure of C60 and shows unique structural and physical properties based on its curved pi-conjugated system. One of the characteristic features of sumanene is the presence of three benzylic carbons, which allow us to generate the corresponding cation, anion, and carbene species. Here we report the successful generateon, isolateon and redox property of sumanenyl tri-cations.

Sumanenyl tri-cations (1) were obtained in high yield by acid-triggered generateon o\from the corresponding hydroxyl-substituted sumanene derivative as a precursor. 1 reacted with the hydride donor, giving a tri-phenyl sumanene (2, 2’) and quinoidal sumanene (3’) in the presence and the absence of acid, respectively. Cyclic voltammetry revealed multi-step redox property of 1. Reductive wave at −1.28 V was observed as 2 electrons reduction without acid. In contrast, reductive wave at −1.17 V and −1.68 V were observed as 1 electron reduction with acid.

Figure 1
(Invited) Controlling the Properties of Colloidal Quantum Dots for Energy Conversion Applications
Authors: Beard Matthew C
Published: February 2020

Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells, and light emitting diodes.We studied the how the optical absorption enhancement and bandage positions of PbS QDs are modified upon ligand exchange from oleate to a series of cinnamate ligands. We find that band edge positions of PbS QDs, can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust, and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. We find that within the cinnamate/PbS QD system the optical absorption is enhanced and the enhancement scales linearly with the HOMO/LUMO gap of the ligand and not their electron donating/withdrawing character, indicating that the ligand/QD coupling occurs equally efficient between QD VB/ligand HOMO levels and the QD CB/ligand LUMO levels. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the resulting emergent optical and electrical properties. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. We demonstrate that the optical enhancement can be used to extract the ligand binding isotherms for a given QD/ligand complex by following the absorption enhancement during ligand exchange reactions. We expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.
(Invited) Optical Phenomena in Bio-Assembled Nanostructures with Plasmonic and Excitonic Resonances
Authors: Govorov Alexander O.
Published: February 2020

Metal nanocrystals and semiconductor quantum dots and have the ability to absorb and scatter light very efficiently. This study concerns special designs of hybrid nanostructures with electromagnetic hot spots, where the electromagnetic field becomes strongly enhanced. Overall plasmonic nanostructures with hot spots demonstrate strongly amplified optical and energy-related effects.

Using nanoparticle arrays made of different metals, one can transfer plasmonic signals coherently and with small losses [1].

Plasmonic hot spots efficiently generate energetic electrons, which can be used for photochemistry and photodetection [2,3].

Using nanostructures with hot spots, one can strongly enhance optical generation of heat and also confine high photo-temperatures in small volumes [4,5].

Colloidal nanocrystal assemblies with plasmon resonances allow us to strongly enhance chiral optical responses (circular dichroism) of biomolecules and drugs [6,7].

[1] E.-M. Roller, et al., Nature Physics 13, 761 (2017).

[2] A.O. Govorov, H. Zhang, H.V. Demir and Y. K. Gun’ko, Nano Today 9, 85 (2014).

[3] H. Harutyunyan, et al., Nature Nanotech. 10, 770 (2015).

[4] A. O. Govorov and H. Richardson, Nano Today 2, 20 (2007).

[5] C. Jack, et al., Nat. Commun. Volume:7, 10946 (2016).

[6] A. O. Govorov, et al., Nano Letters
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, 1374–1382 (2010).

[7] A. Kuzyk, et al., Nature 483, 311 (2012).
(Invited) Semiconductor Nanowires for Optoelectronics Applications
Authors: Jagadish Chennupati , Smith Leigh M. , Jackson Howard E.
Published: February 2020

Semiconductors have played an important role in the development of information and communications technology, solar cells, solid state lighting. Nanowires are considered as building blocks for the next generation electronics and optoelectronics. In this talk, I will introduce the importance of nanowires and their potential applications and discuss about how these nanowires can be synthesized and how the shape, size and composition of the nanowires influence their structural and optical properties. I will present results on axial and radial heterostructures and how one can engineer the optical properties to obtain high performance lasers, THz detectors and solar cells. Use of nanowires for engineering of neuronal networks will be discussed. Future prospects of the semiconductor nanowires will be discussed.
Reaction Mechanisms of Halogenated Silanes on N-Rich Surfaces during Atomic Layer Deposition of Silicon Nitride
Authors: Hartmann Gregory Peter , Ventzek Peter , Iwao Toshihiko , Ishibashi Kiyotaka , Hwang Gyeong S
Published: February 2020

Atomic layer deposition (ALD) has recently received increasing attention for the growth of high-conformity silicon nitride (SiN) thin films. In particular, plasma enhanced ALD (PEALD) allows SiN deposition at substantially lower temperatures (< 400 °C) with better film properties, compared to thermal ALD. These advantages make PEALD more attractive for ultra large scale integrated circuit (ULSI) device fabrication where the growth of aspect ratio independent and high-quality conformal thin dielectric films is tremendously important. The PEALD of SiN films involves a repetitive two-step process: (1) adsorption and decomposition of silicon-containing precursors and ii) nitridation of the Si-rich surface by active N species emanating from the plasma. Halogenated silanes such as hexachlorodisilane, bis(tertiary-butyl-amino)- silane, and dicholorosilane (DCS, SiH2Cl2) have been utilized as Si precursors. Despite previous studies, the underlying reaction mechanisms of these Si precursors with a N-rich SiN surface during PEALD still remain uncertain. Parameters controlling the rate of growth and uniformity have been demonstrated experimentally, but without knowledge of the reaction mechanisms, direct contributions of specific process conditions cannot be explained. Using first-principles density functional theory (DFT) calculations combined with experimental characterization, we have examined and identified a novel mechanism for the adsorption and decomposition of DCS on a N-rich SiN surface. Our study predicts that the DCS adsorption and dissociation can occur by overcoming a moderate barrier (~ 0.3 eV), far lower than the prohibitively large barriers predicted for previously proposed mechanisms. Through a detailed electronic structure analysis of the reaction intermediates, we have also elucidated the principles underlying the reaction mechanism, notably the hypervalent nature of Si which permits the facile reaction of molecularly adsorbed DCS with primary and secondary amines on the surface, followed by simultaneous Cl release and deportation steps and subsequent HCl formation and desorption. We have examined the same mechanism utilizing alternative precursors and the predicted trends are found to be corroborated with the important properties of the system. Understanding these principles allows us to develop guidelines for processing conditions, such as the importance of maintaining the proper surface composition to facilitate Si precursor adsorption and dissociation. Our study provides insight into the SiN ALD process via chlorosilanes and guidelines to control the deposition for high-quality SiN films and provides a framework for future theoretical studies of surface reactions during ALD.
A-Si Planarization By Inductively Coupled Plasma Etch with Advanced Process Control
Authors: Wang Yan , Zhang Dongping , Zhang Haiyang
Published: February 2020

Since fin field effect transistors (FinFET) has been widely adopted in 16/14nm technology node and beyond, the process control becomes more and more critical. [1] A-Si thickness as well as uniformity control is rather rigorous.

In previous report, we have demonstrated the planarization of a-Si by inductively coupled plasma (ICP) with a fixed time [2]. Indeed, due to the process variation, the wafer level control of CMP cannot be too precise without specific process control. The temperature-only controlled etch amount to target thickness is limited and process window is restricted. Thus, one more etch factor need to be introduced for wider process window and more accurate control.

In this paper, a dynamic process time name as “trimming” function is simulated based on the incoming thickness and ‘trmming’ rate for better control the thickness after etching process. Trimming, namely time dependent etching, is more effective to the incoming thickness variation. In this planarization process, the process control focuses on two performances: the uniformity and the mean value. The uniformity is mainly control the “Hydra” parts, wlhich is equipped in the commercial ICP tools and can supply more than 100 temperature control units, while the mean value is mainly controlled by etching time. Our experimental results shows the temperature dependency of thickness control is -26.3Å/℃, while the trimming rate is -1.35 Å/s. Based on the experimental data, the time–dependent etching based on the input thickness is realized.

This work was partially sponsored by Shanghai Rising-Star Program(B type). The authors would like to thank Mr. Jiangang Liu, and Tongxun Guo from Lam research for the support of constructive discussion.

Reference:

[1] C. Auth et al., “A 22 nm high performance and low-power CMOS technology featuring fully-depleted tri-gate transistors, self-aligned contacts and high density MIM capacitors,” in VLSI Symp. Tech. Dig., pp. 131–132, 2012.

[2] Y. Wang et al., “Poly-Si Planarization by ICP Plasma Etch at FinFET Technology”, ECS Trans. 77(3), 71-76, 2017.
Alloying Effects on Superionic Conductivity in Lithium Indium Halides for All-Solid-State Batteries
Authors: Adelstein Nicole , Zevgolis Alysia , Wood Brandon C. , Mehmedović Zerina , Hall Alex Thomas , Alves Thomaz Coelho
Published: February 2020

The low ionic conductivity in solid electrolytes is a limiting factor for commercial implementation of all solid state batteries. Through understanding Li+ ion diffusion by using first-principles molecular dynamics, significant insights in developing new battery materials can be achieved. For example, alloying of anions is a promising engineering strategy for tuning ionic conductivity in halide-based inorganic solid electrolytes. We explain the alloying effects in Li3InBr6−xClx, in terms of strain, chemistry, and microstructure, using first-principles molecular dynamics simulations and novel electronic structure analysis. We find that strain and bond chemistry can be tuned through alloying and affect the activation energy and maximum diffusivity coefficients. The similar conductivities of the x=3 and x=6 compositions can be understood by assuming the alloy separates into Br-rich and Cl-rich regions. Phase-separation increases diffusivity at the interface and in the expanded Cl-region, suggesting microstructure effects are critical.
Phase Field Modeling of Eletrochemical Phenomena
Authors: Zerihun Nega Alemayehu
Published: February 2020

Rational design of novel electrochemical energy storage systems with flexible designs, cheaper prices and more efficiency to meet the power storage needs of everything from handheld gadgets to electric cars heavily relies on the availability of advanced experimental and computational tools. One of the emerging computational tools in the discovery and design of materials is the phase field method. It is widely used for describing phase transformations and kinetics of microstructural evolution in materials sciences. One of its features is the diffuse interface, i.e. a region of space where two (or more) phases are assumed to mix. For electrochemical systems, the interface as the reacting zone plays a very important role. The diffusive nature of the electrical double layer across the electrode-electrolyte interface makes it more suitable for a description with phase field.

In this work, the phase field method is employed to study the kinetics of intercalation. The classical and the finite interface dissipation (FID) phase field methods are used. With the former, a systematic assumption of a linear temperature vs. concentration phase diagram for modeling the electrode-electrolyte coexistence is found to work well for higher partitioning coefficient. It was found that the rate constant is an exponential function of the partitioning coefficient. Moreover, it is possible to see that the activation energy required for intercalation is lower than the activation energy for de-intercalation, which is in agreement with both experiments and atomistic calculations. This work emphasizes on the non-equilibrium behavior especially at the beginning of interaction between electrode particles and electrolyte, with slow evolution of equilibrium. This was investigated using the FID model. One of its pivotal flux contributions is permeation which is caused by chemical potential difference across the interface. It is scaled by a material parameter dubbed “permeability”, which was originally estimated by the interdiffusion coefficient. A new approach to estimate this quantity for non-equilibrium electrochemistry is formulated based on the Butler-Volmer kinetics and its estimation from electrochemical measurement systems such as cyclic voltammetery and electrochemical impedance spectroscopy is shown. The simulation results on the influence of size, morphology and distribution of active particles on the kinetics of intercalation will be discussed. Furthermore, industrial exploitation of the simulation results for reverse engineering of electrode materials for high performance batteries will be described.
A Multiscale Method for Multiphase Pore-Scale Simulation of the Polymer Electrolyte Fuel Cell Catalyst Layer
Authors: Zheng Weibo , Kim Seung Hyun
Published: February 2020

The cost and durability of polymer electrolyte fuel cells (PEFCs) are critical to their massive commercialization. To further reduce the cost of PEFCs, optimized catalyst layers (CLs) with low Pt loading and high performance are necessary. For the CL with low Pt loading, mass transport loss is a critical factor and limits the performance at high current density conditions. The micro-structure of a CL needs to be optimized to reduce the transport loss through heterogeneous porous structures and make reactants more accessible to the Pt sites. Pore-scale simulation directly computes detailed multiphysics phenomena occurring inside the heterogeneous nanoscale structure of the CL [1], thereby improving our understanding of micro-structural effects and guiding the design of an optimized CL. However, for the wide-spread use of pore-scale simulation in the design process, the computational cost needs to be reduced.

In this work, the multiscale method developed in Zheng and Kim [2] is used to accelerate multiphase pore-scale simulation, where water generation and liquid water transport processes in the CL micro-structure are explicitly computed. In the multiscale method, a physical quantity is decomposed into macroscopic and local variations. The macroscopic variations occur at the scale of the CL thickness, and are described by the volume-averaged equation as in the macroscopic method [3]. The local variations are due to the complex micro-structure of CL, and are captured by pore-scale simulation. The multiscale method is applied to the governing equations of electrolyte phase potential and gas phase oxygen concentration in the multiphase pore-scale simulation. The calculation of the electrolyte phase potential shows that the multiscale method substantially increases the convergence rate without sacrificing the accuracy. The application of the multiscale method to the oxygen concentration will be presented. The performance and computational cost of the multiscale method in simulating multiphase transport-electrochemistry coupling in the cathode CLs will be discussed.

Reference:

[1] J. Kang, K. Moriyama, S. H. Kim, An extended stochastic reconstruction method for catalyst layers in proton exchange membrane fuel cells, Journal of Power Sources 325 (2016) 752-761.

[2] W. Zheng, S. H. Kim, A multiscale approach to accelerate pore-scale simulation of porous electrodes, Journal of Power Sources 348 (2017) 21 - 29.

[3] D. M. Bernardi, M. W. Verbrugge, A mathematical model of the solid-polymer-electrolyte fuel cell, Journal of the Electrochemical Society 139 (9) (1992) 2477-2491.