bluuebunny/crossref_metadata_2025 huggingface dataset:
Advances and Application of Conformal Mesoscale Modeling to Battery Electrodes
Authors: Roberts Scott A. , Trembacki Bradley L. , Ferraro Mark E. , Mistry Aashutosh N , Brunini Victor E. , Mukherjee Partha P. , Noble David R.
Published: February 2020

Advances in x-ray computed tomography (XCT) with sub-micron resolution and millimeters of field-of-view have enabled imaging of battery electrodes in sufficient detail to elucidate the mesostructure of the percolated particle network. Most often the secondary conductive binder phase is not visible using XCT and its structure can only be observed using electron-based techniques (e.g. scanning electron microscopy), which typically have a field-of-view too small for meaningful reconstructions. This secondary phase, however, is thought to be critically important for understanding electrode performance at the mesoscale.

We have developed a computational approach to creating computable three-dimensional (3D) mesoscale representations of the active material (particle), conductive binder, and electrolyte/void phases. This approach is built upon the Conformal Decomposition Finite Element Method (CDFEM) and combines 3D XCT image data for the active material phase and a novel “binder bridge” placement algorithm for the conductive binder. This approach enables the calculation of effective transport properties, such as electrical and ionic conductivity and mechanical moduli, that can be upscaled to macroscale battery simulations. Coupled electrochemical and mechanical simulations can also be performed to predict (dis)charge performance and degradation mechanisms of the electrode.

In this work, we discuss the computational requirements, in terms of mesh resolution and domain size, to reasonably minimize computational errors. We also compare our “binder bridge” approach to other approaches in the literature, including a popular stochastic representation. The effect of nano-porosity within the conductive binder phase is explored. As part of this comparison, we explore the differences between smooth and voxelated particle representations along with differences between finite element and finite volume methods. Finally, we discuss upscaling of some of these effective properties into functional forms that can be implemented in macroscale battery simulation platforms.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Effect of Graphene Oxide on Electrochemical Behavior of MnO2/GO Supercapacitor
Authors: Singhal Rahul , Fagnoni Justin T.
Published: February 2020

Supercapacitors have received a lot of attention due to their high-power performance, long cycle life low maintenance, and for applications in hybrid electric vehicles, portable electronic devices, and power back-up devices [1-3]. Various researchers studied MnO2 cathode materials for application in electrochemical capacitors, because of its low cost and natural abundance [2, 3]. However, MnO2 has limited electrochemical performance because of its poor conductivity and low surface area. To improve the electrochemical performances of MnO2, we have synthesized MnO2/graphene oxide (GO) nanocomposite with varying concentration of GO (0.4 mg/ml and 0.8 mg/ml).

GO/MnO2 nanocomposite was synthesized by adding KMnO4 in a solution of water and ethanol (3:1), containing desired amount of GO. The brown precipitates were obtained after a continuous stirring for 1 hr. The precipitate was washed and dried to obtain the GO/MnO2 nanocomposites. The electrodes were prepared by spreading a slurry of GO/MnO2 powder, carbon black, PTFE binder (80:15:5 weight ratio) onto Ni mesh. The electrochemical characterizations were carried out in an aqueous solution of 1M Na2SO4. The charge discharge studies were carried out between 100 mA/g to 5A/g current range. The discharge capacities were found to be 230 F/g and 105 F/g at a current of 100 mA/g and 5A/g, respectively for 20mg GO. The detailed results will be presented at the 233rd Electrochemical Society Meeting.

References:

P. Iamprasertkun, A. Krittayavathananon, A. Seubsai, N. Chanlek, P. Kidkhunthod, W. Sangthong, S. Maensiri, R. Yimnirun, S. Nilmoung, P. Pannopard, S. Ittisanronnachai, K. Kongpatpanich, J. Limtrakul, M. Sawangphruk, Sci. Rep. 6, 37560; doi: 10.1038/srep37560 (2016).

M. Toupin, T. Brousse, D. Be´langer, Chem. Mater.16 3184 (2004).

Y. Zhang, G. Li, Y. Lv, L. Wang, A. Zhang, Y. Song, B. Huang, International J. Hydrogen Energy 36 11760 (2011).

Figure 1
Hetero-Atom Doped Highly Conductive Porous Carbon for Exceptional Electrochemical Performance
Authors: Mangisetti Sandhya Rani , Ramaprabhu Sundara , M Kamaraj
Published: February 2020

In response to the growing global energy needs, the dependency on fossil fuels can lead to the harsh effects on the environment. Thus, it is crucial to recognize continuously growing energy demand by expanding the energy conversion and storage technologies, which exploit clean and renewable energy resources. In this concern, the progress of new energy conversion and storage devices are detected as one of the most important topics in clean energy applications. To efficiently use the produced energy in automobiles, portable applications, it must be stored absolutely so that it can be reproduced when required. Supercapacitors are new class of energy storage devices, in which carbon nanomaterials with controlled porous structure and unique physicochemical properties are among the crucial components. Supercapacitors have the benefit of rapid recharge ability, greater stability, and long cycle life. However, further enhancement of the electrochemical performance, particularly improving the energy density, is a quite challenging. To deal this difficulty, several approaches such as the utilization of carbon materials with high active surface area and studies in various non-aqueous electrolytes also have been attempted. Further, electrochemically energetic materials such as conducting polymers have been developed to enhance the specific capacitance. But they found limited practical applications due to the deterioration of the rate capability and cycle stability. Hetero-atom doping is another productive approach to modify the properties of the carbon nanomaterials and their electrochemical performance. Conductive polymers specifically, polypyrrole is ideal precursor for preparation of hetero-atom doped carbon nanomaterials. However, there is a demand to develop highly conductive porous carbon nanomaterials with high active surface area and hetero-atom doping using a simple method. Here, we present a simple yet productive method for synthesizing hetero-atom doped highly conductive porous carbon with high specific surface area and unique hierarchical pore structure. We prepared the large-scale synthesis of nitrogen-doped porous carbon wrapped reduced graphene oxide-partially exfoliated carbon nanotubes (NP-(rGO-PECNT)) with interconnected hierarchical porous structure. Here, the polypyrrole conductive polymer acts as both nitrogen and carbon source, thereby contributing to pseudocapacitance while, rGO-PECNT conductive matrix provides a high specific surface area for ion and charge transportation. The derived porous (NP-(rGO-PECNT)) displays 7 at % nitrogen content with a specific surface area 2400 m2 g-1, and pore volume 1.81 cm3 g-1. The fabricated supercapacitor using (NP-(rGO-PECNT)) as an electrode material exhibits excellent specific capacitance of 800 F g-1 at 2 A g-1, with high cycling stability of 96 % over 10000 cycles.
Pseudocapacitor Based on Mediators Attached to CNTs
Authors: Yan Zhiwei , Zhang Chen , Qiao Xiaoyao , Zhou Xiangyang
Published: February 2020

Recent study has demonstrated that addition of metal cyanide mediators or redox species into polymer electrolytes can effectively increase the specific enrgy and power of supercapacitor to the levels of 30 Wh/kg at 1 kW/kg or 15 Wh/kg at 15 kW/kg. In order to further enhance the performance of the supercapacitors, the mediator-containg polymer electrolyte was absobed into a matrix of carbon nanotubes (CNTs) grown on carbon paper or metal foils (Fig. 1). A CVD process is optimized to ordered carbon nanotubes on the substrates with capability of controlling the ratio of semiconductor versus conductor CNTs. The electrode materials were used to fabricate full-cell supercapacitors with symetric or asymetric configurations. Three-electrode and full-cell electrochemical measurements were conducted to evaluate the performances of the supercapacitors. Galvanostatic charge-discharge results indicate that the specific energy was 39 Wh/kg at 1 kW/kg or 18 Wh/kg at 15 kW/kg. The cyclic voltammtry data show that the pseudocapacitors behave similarly as an electric double layer capacitor (EDLC). Self-discharge of the pseudocapacitors was also evaluated using open circuit voltage monitoring method. The self-discharge resistance was evaluated using an equivalent circuit model. The analytical results indicate that the self-discharge was improved by at least 1.5 times showing the effect of absorption of mediators into the CNT matrix.

Figure 1
Lifecycle Comparison and Degradation Mechanisms of Li-Ion Battery Chemistries Under Grid and Electric Vehicle Duty Cycle Combinations
Authors: Choi Daiwon , Crawford Alasdair J. , Viswanathan Vish , Huang Qian , Kintner-Meyer Michael CW. , Zhang Ji-Guang , Reed David , Sprenkle Vincent
Published: February 2020

Energy is the essential resource for modern society, but recent growing concern over limited fossil-fuel resources, pollution, and global warming by greenhouse gas emissions has introduced the need to use renewable energy at a large scale, together with the widespread use of HEVs and EVs. Among energy storage technologies, Li-ion batteries, backed by their success in electric vehicles and associated mass production, have gained interest for stationary applications because of their high energy/power density and greater than 90% energy efficiency. Currently, 77% of electrochemical ESSs operated for grid stabilization in United States use Li-ion batteries-mostly for frequency regulation service, which is a high-value market. To maximize benefits, the use of single Li-ion battery chemistry for both stationary as well as electric vehicle applications is being considered. Because of the dual use of Li-ion batteries in electric vehicles (EVs) and in stationary applications, this study focuses on the performance and degradation of two different Li-ion battery chemistries when exposed to (1) selected grid services, (2) typical EV use patterns, and (3) a combination of grid services and EV applications, sometimes referred to as vehicle to grid (V2G). Therefore, high-energy LiNi0.8Co0.15Al0.05O2 (NCA) and high-power LiFePO4 (LFP) based advanced Li-ion battery chemistries were chosen for our reliability studies under three scenarios: (1) frequency regulation, and EV drive cycle coupled with either (2) frequency regulation or (3) peak shaving to understand the degradative effect of grid service that can increase lifecycle cost. The NCA-based cell has good power and energy characteristics and has been used in EVs, but it tends to release significant amounts of oxygen from its cathode, resulting in oxidation of the electrolyte and thermal runaway. In contrast, the LFP-based has been widely deployed for stationary energy storage because the LFP electrode provides high power, stability, and does not generate oxygen during heating; thus, safer than the NCA electrode. The reliability of these two battery chemistries was evaluated by analyzing lifecycle performance factors such as capacity/energy fade, round-trip efficiency (RTE), resistance change, and calendar aging behavior will be presented.
Facile, Green, Low-Cost Fabrication of Silicon/Carbon Nanocomposites for Lithium-Ion Battery Anode Applications
Authors: Ashuri Maziar , He Qianran , Shaw Leon
Published: February 2020

Hybrid Si/C materials have attracted huge attentions during the past 20 years. The attempts include core/shell, yolk/shell, nanotubes, nanowires and etc. However, the cost of the synthesis of these materials are high and requires complex methods and sufficient time. Therefore, the researchers switched to micron-size silicon as starting material and tried to fabricate composites of silicon with other conductive materials. It was proven that silicon, with more than 300% volume change during charge/discharge process, and low conductivity, cannot satisfy the needs, individually. Among the conductive materials, graphite (Gr) was the first choice. However, the Si/Gr composites did not deliver significant capacity in the first experiments. Here, we looked at the problem again and proposed a new method to elaborate the capacity of Si/Gr composites. This approach is based on size reduction and uniform mixing of silicon and graphite at first stage, followed by conformal carbon coating and creating empty voids inside the composite at the last step. The obtained results are comparable to previous experiments and the whole synthesis can be done with minimum cost in reasonable time.
Trench-Wall Carbon Nanotube Sponges As Effective Dual Hosts for High-Areal-Capacity Sulfur Cathodes and Lithium Anodes
Authors: Yang Gang , Tan Jian , Yu Choongho
Published: February 2020

High-energy-density batteries are seeing increasingly demand for many applications. Traditional Li-ion batteries based on metal oxide cathode and graphite anode, though under continuous improvement, cannot meet the requirement in the long term due to the theoretical limitation on reaction chemistry. The lithium-sulfur battery is a promising candidate for future energy storage because of its high energy density in theory. However, to achieve high energy density in practical applications, a high areal loading (~10 mg cm-2) of active material – sulfur is required, which is hindered by deteriorating polysulfides shuttle and lithium dendrite formation. Previous research tackled the problems from either cathode side or anode side, and showed performance improvement based on a low areal loading (<3 mg cm-2) of sulfur. Here we report a novel trench-wall carbon nanotube sponge acting as a dual host for high-areal-capacity sulfur cathodes and lithium anodes. Created by a controllable mechano-chemical method, the unique trench-wall structure provides nano-reactors for active materials with shortened diffusion length, polysulfides-philic and lithiophilic surface for hosting active materials, and increased surface area for promoting electrochemical reactions. The cell showed excellent areal capacity (10.3 mAh cm-2) after 100 cycles under a high current density of 4.8 mA cm-2, demonstrating both high “cell-level” energy density and power. The trench-wall CNT sponge is, to our best knowledge, the first single material used to simultaneously and effectively tackle the problems from both cathode and anode sides of lithium-sulfur batteries. The strategy of creating nano-trenches on the wall of carbon nanotubes paves a new way for designing new materials for high-energy-density batteries.
Size-Controlled Carbon Catalysts Derived from Metal-Organic Frameworks for Non-Aqueous Li-Air Battery
Authors: He Yanghua , Wang JIngyun , Wu Gang
Published: February 2020

The excessive use of fossil fuels has led to increasing concerns about global climate change and national energy storage. It is urgent to develop some clean, efficient, and reliable technologies to harvest and store the clean energy generated from solar and wind. Electrochemical energy technology such as batteries and fuel cells can serve as an ideal medium to store and release electricity. Among various electrochemical systems, Li-air battery has attracted wide attention to be a promising next-generation energy storage device due to its high theoretical capacity (11,000 Wh/kg). Thus, one of the most important topics is to develop an efficient, economical and safe Li-air battery. Here, we develop a series of Co-doped metal-organic frameworks derived carbon catalysts (Co-MOFs) of different sizes, which can be employed as the high-performance bifunctional cathode catalysts for Li-air battery. Controlled by anion type and the amount of 1-methyl imidazole, Co-MOFs catalysts can be obtained with various sizes, ranging from 50 nm to 5 µm. Further optimization of the Co content and thermal activation procedure can produce a highly active Co-N-C catalyst, showing a half-wave potential of 0.818 V vs. RHE in aqueous solution and high selectivity for four-electron reduction, mainly due to the influence of the final morphology and structure including surface area, pore structure and nitrogen doping. Co-N-C catalyst also exhibits a higher performance in terms of onset potential, half-wave potential and current density in non-aqueous solution when compared with non-metal-MOFs derived catalysts. The high oxygen reduction reaction (ORR) activity of this catalyst could be attributed to the Co-Nx active sites embedded in the porous carbon matrix. In the battery, the cathode consisting of Co-MOFs catalysts shows a high discharged capacity of 13,000 mAh/g and a relative stable cycling performance up to 50 cycles, which implies that Co-MOFs catalysts could be a promising candidate as the replacement of platinum group metal catalysts for Li-air battery applications.
Chemical Vapor Synthesis and Electrochemical Studies of Ru+4O2 Reactions with Lithium Ion
Authors: Merrell Asriel R. , Williams Jere A. , Adkins Joshua Willis , Douglas Lacey D , Dangerfield Aaron , Yang Yiqun , Meda Lamartine
Published: February 2020

Nanostructured pyramidal shape ruthenium oxide (Ru+4O2) was studied electrochemically using cyclic voltammetry (CV) and cyclic charge-discharge (CCD) experiments at five different cut-off voltages (1.5, 1.0, 0.80, 0.4, and 0.1 V) versus Li/Li+. CCD experiments performed at cut off voltages of 1.5 V and 1.0 V showed a plateau at approximately 2.1 V that corresponds to 100 and 350 mAh g-1, respectively, with no significant formation of solid electrolyte interface (SEI). CV experiments performed in the same voltage range showed a reduction and an oxidation peak at 2.1 and 2.5 V, respectively, that corroborated the CCD experiments. At cut off voltages below 1.0 V, the CV showed two peaks current at 1.0 V (Ru0/Li2O) and 0.6 V (SEI) during the first forward potential sweep. The SEI disappeared during the second cycle and beyond. On the other hand, during the reverse potential sweep two peak currents are observed at 1.2 V and 2.7 V. The latter represents the oxidation of Ru0 to Ru+4 and the former is assigned to the decomposition of the SEI. The CCD experiments revealed a total capacity of approximately 1200 mAh g-1 (~6 Li+ per mol of Ru+4O2). However, the expected capacity is 806 mAh g-1 (4 Li+ per mol of Ru+4O2) as described by the conversion reaction of lithium with Ru+4O2 (Ru+4O2 + 4Li++4e- <-->Ru0 + 2Li2O). Therefore, there is an excess capacity of ~600 mAh g-1. To understand the source of the excess capacity, CCD experiments were performed in the range of 2.0 to 0.1 V vs. Li/Li+ which revealed that the material is behaving as a pseudo-capacitor. The calculated capacity in this range is only 90 mAh g-1. This value is too small to account for the excess capacity.

Figure 1
Effect of High Current Density on the Performance in a Molten Carbonate Fuel Cell
Authors: Lee Choong-Gon
Published: February 2020

The effect of current density on the cell performance was investigated in a coin type molten carbonate fuel cell. The cell temperature was 700oC under atmospheric condition. The three different of current densities, 150, 300, and 450 mA/cm2 were used. The cell performance with respect to the current density was analysed via steady-state polarization, step-chronopotentiometry, and impedance methods. The electrochemical analyses revealed that cell performance rapidly degraded by increasing current density. This may result from decrease of active surface area caused by electrolyte loss. This work reports that life of MCFC strongly depends on current density.
Enhanced Cycling Stability of SiOx/Si/Nickel Foam Thin Film Anodes for Lithium Ion Batteries
Authors: Chiu Kuo-Feng , Li Kun-Che , Leu Hoang-Jyh
Published: February 2020

Silicon has been known as the next generation anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity (4200 mAh/g). However silicon anodes face the challenge of large volume change over 300 % during lithiation/delithiation cycles, leading to the pulverization of the silicon based electrodes. In this study, radio frequency (RF) magnetron sputtering is used to deposit amorphous silicon thin films on nickel foam current collectors. This flexible three-dimensional structure is found to relieve stress caused by the volume expansion. Furthermore, SiOx is coated on the previously fabricated silicon anodes as a buffer layer. The oxygen contents and the thickness of the SiOx are controlled by depositing under different Ar/O2 ratios, and depositing times. The electrochemical behaviors of the SiOx/Si/nickel foam electrodes toward lithium are studied. It is found that the SiOx/Si/nickel foam electrodes with optimized oxygen contents and thickness of SiOx films exhibit high cycling stability and coulombic efficiency. The results are attributed to the stress relaxation effect provided by the flexible nickel foams and the SiOx buffer layers.
Synthesis and Transfer of High-Quality Graphene Grown on Al2O3(0001)/Pt(111) Template Wafers
Authors: Verguts Ken , Coroa Joao , Peters Lisanne , Wu Cheng Han , Huyghebaert Cedric , Brems Steven , De Gendt Stefan
Published: February 2020

Today, CMOS compatible routes to grow and transfer large graphene sheets are still missing. Chemical vapor deposition (CVD) is the main synthesis technique yielding high-quality wafer-scale graphene. Platinum is expected to be an excellent catalyst to grow monolayer, large scale and high-quality graphene. Moreover, electrochemical graphene transfer methods are demonstrated, which facilitate the reusability of this expensive Pt template.

A process window is studied to grow graphene on platinum foils. The influence of growth temperature and time as well as the methane to hydrogen ratio is optimized. Moreover CO2 can be used as a graphene defect etching gas to replace hydrogen, resulting in successful graphene syntheses conditions.

It is shown that the polycrystalline nature of the Pt foil makes it extremely difficult to grow a uniform monolayer graphene sheet. It is also demonstrated that a smooth Pt(111) thin film on sapphire (Rrms = 0.2 nm) decreases the amount of graphene nucleation centres and thus strongly reduce the graphene multilayer areas. Therefore, a Pt(111) thin film appears ideally suited to grow millimetre-sized graphene islands in reasonable time frame (< 1 hour growth time).

To promote graphene delamination from the platinum growth template, it is of prime importance that an interfacial water (IFW) layer is formed. This IFW layer serves as a pathway for charged ions to intercalate between graphene and its CVD growth substrate. It is demonstrated that only a selection of ions succeed in intercalating and thus in a successful graphene delamination. The ions that are able to intercalate are electro-active outside the electrochemical window of the used solvent.

Figure 1
(Invited) Anomalous Corrosion of Bulk 2D Materials Leading to Stable Monolayers
Authors: Das Saptarshi
Published: February 2020

In this talk, I will elucidate on a recently discovered, unprecedented, substrate assisted, anomalous corrosion or self-limiting electrochemical ablation (EA) process that transforms bulk layers of various two- dimensional (2D) transition metal dichalcogenides (TMDCs) into their corresponding monolayers quickly and at room temperature when subjected to a high anodic potential. In particular I will explain what role does the substrate, pH, electrolyte solution, applied anodic potential, temperature and finally, in specific cases, self-assemble monolayers (SAMs) play in determining the corrosion rates for the bulk and monolayer which ultimately leads to successful conversion of multilayer TMDCs into their corresponding monolayer. I will also talk about thin film transistors (TFTs) based on these monolayers which demonstrate current ON-OFF ratios in excess of 107 along with ON currents in the range of ~100µA/µm which is on-par with any state-of-the-art TFT technology.
Protected Metallic MoS2 Nanosheets Outlast Pristine Metallic MoS2 Nanosheets for Hydrogen Evolution Reaction
Authors: Benson Eric E. , Zhang Hanyu , Schuman Samuel , Nanayakkara Sanjini U. , Bronstein Noah D. , Ferrere Suzanne , Blackburn Jeffrey L. , Miller Elisa M.
Published: February 2020

Functionalizing nanosheets of metallic molybdenum disulfide (MoS2) provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state. Metallic MoS2 nanosheets have been studied for HER due to their higher reactivity for HER, earth abundance, low-cost, and non-toxicity, which makes metallic MoS2 a candidate to replace platinum for HER. The functionalized nanosheets are more stable to the thermally initiated phase transformation from the metallic 1T phase to the semiconducting 2H phase. Furthermore, we show for an exemplary functionalized sample (Et2NPh-MoS2) that functionalization leads to better stability and long-term performance under HER conditions. These results provide a framework for understanding and controlling the balance between catalytic activity and stability for these unique 2D materials. Chemically-exfoliated, metallic (1T) MoS2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS2 functionalized with the most electron donating functional group (p-(CH3CH2)2NPh-MoS2) is the most efficient catalyst for HER in this series, with initial activity similar to the pristine metallic phase of MoS­­­­­­
2. The p-(CH3CH2)2NPh-MoS2 is more stable than unfunctionalized metallic MoS2 and outperforms unfunctionalized metallic MoS2 for continuous H2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the pendant group on the phenyl ring. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS2 sheet. We show that the functional groups preserve the metallic feature of the MoS2 films, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when annealed at 150 °C for 24 h in a nitrogen atmosphere. We propose that this protection is critical to maintaining the catalytically active state of 1T MoS2 nanosheets. Our results demonstrate a strong correlation between the electron donating strength of substituents and the surface energetics, electron transfer resistance, and the HER catalytic activity of functionalized MoS2 nanosheets.
Charges, Defects and Interfaces in Two-Dimensional Materials and Devices
Authors: Liu Yuanyue
Published: February 2020

Two-dimensional semiconductors show great promise for next-generation electronics and optoelectronics, yet they still face significant challenges to realize their potential. Here I will discuss our recent theoretical/computational studies on the charges carriers, defects and interfaces in two-dimensional materials and devices. Specifically, I will show (i) how to estimate the electron/hole mobility with reasonable accuracy; (ii) the role of defects and how to passivate the harmful ones [1,2]; and (ii) how to lower the metal-semiconductor resistance [3,4].

[1] Y. Liu, P. Stradins, S. Wei, Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201508828

[2] Y. Liu, H. Xiao, W. A. Goddard III, Nano Lett. 2016, 16, 3335

[3] Y. Liu, P. Stradins, S. Wei, Science Advances 2016, 2, e1600069

[4] Y. Liu, H. Xiao, W. A. Goddard III, JACS, 2016, 138, 15853
(Invited) Theory and Device Concepts of Novel Electronic, Optoelectronic, and Topological 2D Materials
Authors: Qian Xiaofeng
Published: February 2020

2D materials provide extraordinary materials platform with many interesting physical properties distinct from their bulk counterpart and offer unprecedented opportunities for ultrathin electronic and optical applications. Here I will present our recent theoretical works on novel 2D multiferroics and 2D topological materials as well as a few device concepts. First, I will highlight our discoveries on 2D topological materials including binary and ternary transition metal dichalcogenides etc. Our works show that electric field, elastic strain, and van der Waals stacking can be utilized to introduce topological phase transition [1,2]. In particular, the electric field induced topological phase transition offers a possibility for realizing topological field effect transistor, which will be fundamentally different from conventional transistors. In the second example, I will introduce the discovery of 2D multiferroics in semiconducting group IV monochalcogenide monolayers [3]. These 2D materials exhibit giant spontaneous ferroelastic lattice strain and ferroelectric polarization. Both are strongly coupled, accompanied with large anisotropic 2D excitonic responses and nonlinear optical responses [4]. Our theoretical findings indicate that these multiferroic 2D materials possess low domain wall energy and migration barrier, suggesting great opportunities for multifunctional opto-electronic-mechanical devices such as 2D ferroelectric and ferroelastic memory and 2D ferroelectric excitonic photovoltaics. Finally, relevant experimental progresses as well as some critical challenges and opportunities in 2D materials and their nanostructures will be discussed.

1. Xiaofeng Qian, Junwei Liu, Liang Fu, and Ju Li. Quantum spin Hall effect in two-dimensional transition metal dichalcogenides.
Science
346, 1344-1347 (2014).

2. Junwei Liu, Hua Wang, Chen Fang, Liang Fu, and Xiaofeng Qian. van der Waals Stacking-Induced Topological Phase Transition in Layered Ternary Transition Metal Chalcogenides.
Nano Letters
17, 467-475 (2017).

3. Hua Wang and Xiaofeng Qian. Two-dimensional multiferroics in monolayer group IV monochalcogenides.
2D Materials
4, 015042 (2017).

4. Hua Wang and Xiaofeng Qian. Giant Optical Second Harmonic Generation in Two-Dimensional Multiferroics.
Nano Letters
17, 5027-5034 (2017).
(Invited) Lead-Free Perovskite Solar Cells Based on Various Contact Electrodes
Authors: Diau Eric Wei-Guang
Published: February 2020

Perovskite solar cells (PSC) have attracted much attention in recent years due to the rapid progress on the performance of PSC to attain PCE over 22 % within 5 years. Our group follows this trend working on PSC but with emphasizing on three major directions (i) lead-free PSC, (ii) carbon-based mesoscopic PSC and (iii) planar heterojunction PSC with the p-contact layer using graphene oxide (GO) and reduced GO (rGO) derivatives. For the tin-rich perovskites, we designed and synthesized alloyed Sn-Pb mixed halide perovskites by dipping the precursor solutions on the mesoporous films with the TiO2/Al2O3/C configuration to form solar cells free of organic HTM. The photovoltaic performance was further improved on adding 30 mol % of tin fluoride (SnF2) with device configuration FTO/TiO2/Al2O3/NiO/C producing best power conversion efficiency 5.2 % with great reproducibility and intrinsic stability. To make a stable pure tin perovskite free of lead, we varied SnCl2/SnBr2 ratios to yield tin perovskites with three halides (I, Br and Cl) co-crystallized inside the tin-perovskite crystals according to the stoichiometric ratios of the precursors. A device with MASnIBr1.8Cl0.2 (SnCl2 = 10 %) showed the best photovoltaic performance with PCE 3.2 % with great reproducibility and long-term stability. We also investigated inverted planar heterojynction (PHJ) PSC with PEDOT:PSS, GO and rGO as potential p-contact electrodes. The devices made of 2D or 2D/3D hybrid tin perovskite solar cells will be introduced and discussed. Electrochemical impedance spectra (EIS), transient photoelectric decays and transient PL decays were performed to understand the charge transfer mechanism in related to their device performances.
(Invited) Colloidal Pb-Free Perovskite Nanocrystals for Optoelectronic Energy Applications
Authors: Nag Angshuman
Published: February 2020

Pb-halide perovskites exhibit defect-tolerant behaviour resulting into efficient optoelectronic properties. We have worked on various aspects of material design, optical and optoelectronic properties of colloidal cesium lead halide perovskite nanocrystals.1-5 The key aspects that make Pb-halides an unique class of optoelectronic materials are: (i) Pb2+ exhibit stable nS2 electronic configuration in the outermost orbital, (ii) small effective masses of charge carriers because of 3-D structural network of [PbBr6]4- octahedra with Pb-Br-Pb bond angles close 180o, and (iii) strong spin-orbit splitting of Pb 6p states (conduction band minimum).

From last couple of years, we have started searching for colloidal Pb-free metal halide nanocrystals that can exhibit the combination of these three properties.6-7 In this talk, I will discuss about our experiences on Pb-free metal halide nanocrystals. The Pb-free materials that will be discussed are colloidal thallium halide (TlX), cesium antimony halide (M3Sb2X9; M = Cs and Rb), and cesium bismuth halide (Cs3Bi2X9) nanocrystals, where X signifies halides. Intrinsic issues regarding material design and photophysical properties relevant for optoelectronic applications will be discussed.

References:

1. Swarnkar, A; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag A. Angew. Chem.
Int. Ed.
2015, 53, 15424.

2. Yettapu, G. R.; Talukdar, D.; Sarkar, S.; Swarnkar, A.; Nag, A.; Ghosh, P.; Mandal, P. Nano
Lett.
2016, 16, 4838.

3. Ravi, V. K.; Markad, G. B.; Nag, A. ACS Energy Lett.
2016, 1, 665.

4. Mir, W. J.; Jagadeeswarara, M.; Das, S.; Nag, A. ACS Energy Lett., 2017, 2, 537.

5. Sarkar, S.; Ravi, V. K.; Banerjee, S.; Yettapu, G. R.; Markad, G. B.; Nag, A.; Mandal, P. Nano
Lett., 2017, 16, 5402.

6. Swarnkar, A.; Ravi, V. K.; Nag, A. ACS Energy Lett., 2017, 2, 1089.

7. Mir, W. J; A. Warankar, A.; Acharya, A.; Mandal, P.; Nag, A. Chem. Sci.
2017
, 8, 4602.

8. Pal, J.; Manna, S.; Mondal, A.; Das, S.; Adarsh, K. V.; Nag, A. Angew. Chem.
Int. Ed.
2017, 56, 14187.
(Invited) Near Infrared Plasmon-Induced Charge Separation in Heterostructured Nanoparticles
Authors: Teranishi Toshiharu
Published: February 2020

The structure of nanomaterial determines their individual properties and assembled structures they can form [1,2]. Highly efficient photoenergy conversion in heterostructured nanoparticle (NP) assemblies requires the formation of epitaxial heterointerfaces and band alignment engineering. This requirement has led to attention being given to recent advances and prospects in the charge separation properties of both type-II semiconductor/semiconductor NPs [3-6] and plasmon/semiconductor NPs [7,8]. Special attention has been given to plasmonic semiconductor/semiconductor combinations [7,8], where the near infrared plasmon-induced carriers in the plasmonic semiconductor phase are injected into the conduction band of another semiconductor phase.

[1] Wu, H.-L.; Sato, R.; Yamaguchi, A.; Kimura, M.; Haruta, M.; Kurata, H.; Teranishi, T. Science
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[2] Kanehara, M.; Arakawa, H.; Honda, T.; Saruyama, M.; Teranishi, T. Chem. Eur. J.
2012, 18, 9230.

[3] Saruyama, M.; So, Y.-G.; Kimoto, K.; Taguchi, S.; Kanemitsu, Y.; Teranishi, T. J. Am. Chem. Soc.
2011, 133, 17598.

[4] Sakamoto, M.; Inoue, K.; Saruyama, M.; So, Y.-G.; Kimoto, K.; Okano, M.; Kanemitsu, Y.; Teranishi, T. Chem. Sci.
2014, 5, 3831.

[5] Teranishi, T.; Samamoto, M. J. Phys. Chem. Lett.
2013, 4, 2867. (Perspective)

[6] Sakamoto, M.; Inoue, K.; Okano, M.; Saruyama, M.; Kim, S.; So, Y.-G.; Kimoto, K.; Kanemitsu, Y.; Teranishi, T. Nanoscale
2016, 8, 9517.

[7] Lian, Z.; Sakamoto, M.; Matsunaga, H.; Vequizo, J. J. M.; Yamakata, A.; Haruta, M.; Kurata, H.; Teranishi, T., under revision.

[8] Sakamoto, M.; Kimura, M.; Kawawaki, T.; Matsunaga, H.; Ranasinghe, C. S. K.; Yamakata, A.; Matsuzaki, H.; Furube, A.; Teranishi, T., submitted.
(Invited) Light on EuOx Nanostrutured Films
Authors: Mariscal Antonio , Serna Rosalia
Published: February 2020

Europium monoxide (EuO) is a well-known ferromagnetic semiconductor with single crystal band-gap similar to Si (1.12 eV) and is compatible with the actual semiconductor technology, and suited for the development of integrated spintronics components. However, very little is known of the optical properties of this notable material in thin film configuration, and especially nanostructured. Only very recently some evidence on possible quantum confinement in EuO nanostructures has been reported [1]. In part, this is because EuO high quality films and nanostructures are very difficult to obtain and preserve. Indeed the only data available on its dielectric function are for single crystal EuO and dates from the 70’s from reflectance measurements.

Recently we have been able to prepare high quality textured nanocrystalline EuOx films by pulsed laser deposition in vacuum at room temperature through a reduction process. Because the EuO films rapidly oxidize under exposure to ambient, we have encapsulated them with a 10 nm thick Al2O3 layer. This has allowed us to preserve the EuOx nanostructures and to study both their linear optical and luminescent properties. In this contribution, we will show the optical dielectric function of thin nanocrystalline EuOx films in the NUV-VIS-NIR, using spectroscopic ellipsometry measurements with perfect Kramers-Kronig consistency. The results show how tweaking the EuOx composition and nanostructure modifies its dielectric function, and therefore it enables the control of the excitonic response modifying the band-gap of the films. We will show the photoluminescent emission of these films, and discuss its excitonic or ionic (Eu2+) origin. We believe that the knowledge of the optical properties of this unique material will open a new route for the integration with commercial semiconductors (Si, GaAs, GaN) for novel spintronics and photonics combined devices.

[1] G.M. Prinz, T. Gerber, A. Lorke, M. Müller, Quantum confinement in EuO heterostructures, Appl. Phys. Lett. 109 (2016). doi:10.1063/1.4966223.
Carbon Dots Based Fluorescence Nanoprobe for Cell Imaging and Single Particle Tracking
Authors: Song Yang , Du Dan , Lin Yuehe
Published: February 2020

School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164

Advances in real-time imaging in living cells have enabled tracking of individual molecules over time and space. Single particle tracking (SPT) technique enables the imaging and mapping of functional biomolecules directly in living cells at unprecedented spatial and temporal resolution [1-4]. This technique has provided a powerful tool to reveal the dynamic structure-function relationships in complex biological systems and dramatically advanced the fundamental understanding of biological systems and medical diagnose [5-7]. The fluorescent probe, which tags the molecules of interest and allows the fluorescent emission, is crucial for intercellular imaging. The considerable interest in intercellular trafficking sparked sustained research efforts on developing of fluorescent probes with high quantum yield, excellent stability and biocompatibility.

Carbon dots (CDs) exhibit controlling size and shape, surface heteroatom doping, tunable photoluminescence (PL) and efficient multiphoton up-conversion. These CDs exhibit excellent biocompatibility, high photostability, enhanced brightness and high quantum yields [8]. Therefore, CDs will provide a new platform as versatile probes for single particle tracking (SPT) in various biological and medical areas. In our previous studies [9-10], we synthesis the CDs with optimized remarkable quantum confinement effect, surface effect and surface defect state are expected to present (1) low cytotoxicity and excellent biocompatibility. (2) Capability of precisely controlling the functional-group and feasible labeling of biomolecule for enhanced specificity. (3) Enhanced optical properties. (4) High stability. The CDs are highly chemically and thermally stable. We found that the endosome escape most probably because that the untreated surface group of CDs could provide high buffering capacity to trigger the osmotic swelling and physical rupture of the lysosomes in acid vesicle [9]. This technology can be easily extended to the mobility of molecules and proteins in the cell membrane with the same principle. This new technology will be a major breakthrough of real-time, high resolution of intercellular imaging.
(Invited) Luminescent Rare Earth Doped Nanoparticles
Authors: Vetrone Fiorenzo
Published: February 2020

In recent years, rare earth doped nanoparticles have been proposed for a number of exciting applications in a wide-range of fields including nanomedicine, nanoelectronics, biosensing, bioimaging, photovoltaics, photocatalysis, etc. This is due, primarily, to their interesting and versatile optical properties including their inherent ability to convert low-energy near-infrared (NIR) light to higher energies spanning the UV, visible, and NIR regions of the spectrum via a process known as upconversion. Upconversion, inherent to the rare earths, results from the multitude of 4f electronic energy states, many of which are spaced equally and long-lived, that facilitate the absorption of multiple low energy photons to populate the higher energy emitting states. Thus, upconversion is a multiphoton process, but unlike other two-photon excited materials, the need for expensive ultrafast lasers is eliminated since the simultaneous absorption of multiple photons is not required; due to the long lifetimes of the rare earth ion excited states, sequential absorption occurs efficiently. Moreover, following NIR excitation, these nanoparticles can also undergo conventional luminescence and emit in the three NIR biological windows where tissues are optically transparent. Here, we will discuss the luminescence properties of rare earth doped nanoparticles and present a perspective on both their applicability as well as drawbacks for use in various applications. Finally, we will demonstrate that the intelligent combination of diverse materials, with different properties, will allow for the engineering of novel multifunctional nanostructures, which can usher in a new era for rare earth doped nanoparticles.
Influence on the Porous Silicon Photoluminescence By Magnetic Nanostructures
Authors: Granitzer Petra , Rumpf Klemens , Poelt Peter , Reissner Michael
Published: February 2020

In this framework luminescent porous silicon (PSi) is filled with a magnetic metal (e.g. Ni) to influence the photoluminescence due to the presence of metal deposits. This happens in two ways. On the one hand the surface plasmon of the metal deposits is exploited to modify the luminescence and on the other hand it is influenced by an external magnetic field. Due to the metal filling of the porous silicon the photoluminescence is blue-shifted and furthermore an increase of the intensity is observed. The influence of the magnetic metal filling on the optical properties is discussed and the magnetic characterization of the nanocomposits is presented.

The porous silicon is fabricated by anodization of a moderately doped p-silicon wafer. The electrolyte consists of hydrofluoric acid, Ethanol and distilled water (1:2:1). The metal deposition has been performed by pulsed electrodeposition in using a NiCl2 and NiSO4 solution.

First the optical properties of the luminescent PSi are investigated, second Ni is deposited within the porous silicon samples and subsequently the nanocomposite specimens are characterized optically again and also magnetically. The samples are structurally characterized by SEM, EDX and TEM.

The optical properties are investigated with respect to the shift of the photoluminescence due to the metal filling. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm and the luminescence intensity is increased. Figure 1 shows the comparison of the photoluminescence of two Ni-filled samples with different metal deposition time.

Concerning the magnetic properties of the nanocomposite the embedded Ni structures can be superparamagnetic from the size of the pore diameters but due to the branched morphology the achieved deposits tend to be interconnected and thus do not offer necessarily a superparamagnetic behavior. Also temperature dependent magnetization measurements give no hint for a superparamagnetic behavior. Field dependent magnetization measurements performed with the magnetic field applied perpendicular and parallel to the sample surface show a high magnetic anisotropy. It can be clearly seen that the samples offer a film-like behavior due to the interconnected Ni structures which is represented by the easy axis parallel to the surface. In the frame of this work the optical characterization of luminescent PSi with respect to its photoluminescence compared with Ni filled samples is discussed in detail as well as the corresponding magnetic properties of the nanocomposites. Furthermore the influence of an external magnetic field on the optical properties is elucidated. The presented systems are promising candidates for applications in optoelectronics and also for magneto optical integrated devices.

Figure 1. Photoluminescence spectra of porous silicon with incorporated Ni for two different deposition times.

Figure 1
(Invited) Fundamentals and Applications of Directional and Isotropic Atomic Layer Etching
Authors: Vahedi Vahid , Lill Thorsten
Published: February 2020

Atomic Layer Etching (ALE) is a cyclic process comprised of a self-limited surface modification step followed by a self-limited step to remove the modified layer. Based on this definition, there are several approaches to realize and classify ALE. For instance, one can distinguish between directional and isotropic ALE depending on whether the removal of the activated layer is accomplished by ion bombardment or thermal energy.

Thanks to such salient performance benefits as uniformity across all length scales and selectivity, atomic layer etching is being proliferated in production. Directional ALE was the first process to go into production because most critical etch applications require directionality. Isotropic ALE is an emerging branch based on chemical reactions akin to those uses in thermal ALD. The term “isotropic” means that the etch proceeds in all directions. This property is particularly valued in vertical device integration where materials need to be removed from vertical and concealed surfaces.

In this talk, a conceptual framework for directional and isotropic ALE will be introduced to explain the performance benefits and limitations of both technologies. Experimental and theoretical results as well as applications examples will be presented to illustrate the concepts.