bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Processing Routes on Structural and Electrical Properties of High Energy-Density Oxide Cathode Materials
Authors: Fung Kuan-Zong , Tsai Shu-Yi , Kenneth Fung , Chang Chia-Chin
Published: July 2021

Cathode materials with high energy density for Li ion batteries have received great attention due to the high demand in transportation applications. Although several crystal structures have been demonstrated and shown reversible capabilities during lithiation/delithiation processes in cathode of Li ion batteries; oxides with layered/spinel structure still remain the ones that provide higher energy densities.

However, higher energy density means the creation of more ionic/electronic defects in both cation and/or anion sublattices of layered/spinel structures. Higher defect concentration in either cation or anion sublattices tend to destabilize its crystal structure. As a result, the phase change is frequently observed in repeatedly cycled cathode. Furthermore, the phase-changing cathode tends to show the capacity fading after cycling tests. Based on defect consideration, the stability of highly defective materials may be enhanced by using dopant and/or better processing routes. In this study, the electrical/electrochemical/structural properties of oxide cathodes will be investigated.

First, the electrical measurement of spinel/layered oxides are conducted using sintered disc. Assembled cells using above-mentioned cathode and Li anode with desired liquid electrolyte will be tested and cycled. XPS, SEM and XRD analyses will be conducted on as-assembled as well as cycled cells. The analyzing results will be illustrated based on the processing parameters and defect chemistry of doping ions and the accompanying defects created.
A New Method for Evaluating Li-Ion Battery Anode Materials Based on Surface Compositional and Structural Characterization
Authors: Ociepa Jozef
Published: July 2021

There is a global effort to develop safer lithium-ion batteries (LIB) with a high energy density and long lifetime. Material properties, their mutual interactions, and active interfaces are key factors in battery performance. Popular methods involve the mixing of different ingredients and development of a suitable fabrication process. Significant effort has been spent to understand the reaction mechanism of battery materials, but this is very challenging due to high system complexity. Different techniques have been developed to follow these reactions, and most significantly, the reactions between Li and electrode materials. Our team has developed a new method to characterize Li thermal diffusion and structural interaction on the surfaces of potential anode and cathode materials. This method is based on surface crystallographic and compositional characterization of deposited ultra-thin film of Li on potential single crystal or polycrystalline anode material. Surface crystallography characterization is done with w Low Energy Electron Diffraction (LEED) and surface composition with Auger Electron Spectroscopy (AES). This characterization monitors Li thermal diffusion into the electrode surface at room temperature and changes in surface crystalline structure and composition. The data provides a strong link between Lithium thermal diffusion and lithiation processes in LIB. The dynamic interaction of Li is monitored at the nanoscale level and gives the direct response how Li atoms interact with the substrate. The diffusion of evaporated Li on single crystals of HOPG, Si(111)-(211)-(100), SiC-6H, CVD-Diamond and LiNbO3 have been performed. The results shows that HOPG is the excellent reference substrate for this method as Li diffuses at room temperature and surface crystallography of HOPG remains unchanged. The structural reaction of Li with Si is very strong causing LEED pattern to disappear and there is no Li diffusion at room temperature as indicated from AES data. The data for SiC-6H and LiNbO3 shows better Li diffusional behavior than on Si but not as good as on HOPG. This method of using a single crystal substrate and basic surface characterization techniques is providing simple nanoscale access into the chemical reactions between Li and the substrate material that will result in better understanding of Lithium diffusion in the fabricated battery electrodes. The initial material classification for “native” Lithium thermal diffusion properties is proposed.
(Invited) Characterization of Graphite Anode Architectures for Extreme Fast Charge Using Rapid EIS and Differential Coulometry
Authors: Torres-Castro Loraine , Karulkar Mohan , Lamb Joshua , Chen Kuan-Hung (Michael) , Dasgupta Neil P.
Published: July 2021

The ability to fast charge automotive lithium-ion batteries is key to enabling wide-scale adoption by consumers. A primary challenge to fast charging is lithium plating due to insufficient lithium diffusion rates into the graphite anode. Plating and subsequent poor cycling of plated lithium leads to capacity loss over time and possible failure due to dendrite-induced short circuit. Sandia National Laboratories and the University of Michigan have worked together to develop advanced anode architectures, known as Highly Ordered Laser Electrode (HOLE), to increase lithium diffusion rates and avoid lithium plating. This work will describe Sandia's latest efforts to characterize and quantify the improvements brought on by these advanced anode structures. High precision cycling, rapid EIS, and isothermal control during fast charging allow precise tracking of cycle-to-cycle efficiency and intra-cycle differential coulometry. These methods are used to detect and quantify lithium plating at the earliest stages and provide a quantitative basis for evaluating lithium plating dependence on anode architecture, temperature, and current. A thorough discussion of experimental conditions will also be conducted to aid others in performing similar measurements.

Sandia National Laboratories is a multimission 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.
Thermal Characterization of Large-Format Li-Ion Pouch Cells with Transient Cooling and Lock-in Thermography
Authors: Lin Jie , Chu Howie , Monroe Charles W. , Howey David
Published: July 2021

Electrification of transport and heating is an important part to combat climate change. This leads to an increasing demand for energy storage options for power grids and electric vehicles.

Recent progress in battery management systems, and energy density improvements, have favored the deployment of Li-ion batteries as the leading electrochemical energy storage technology [1]. At the same time, battery thermal management is a critical challenge due to inevitable heat generation from ohmic, reaction and entropic heating [2]. If the amount of heat generated is not sufficiently dissipated from the battery, it could substantially increase the cell temperature which leads to severe degradation and even catastrophic thermal runaway [3, 4]. Especially for large-format pouch cells, high temperature and large temperature non-uniformity are common issues and thus require careful battery thermal design. One tool to address this is by establishing an electrochemical-thermal model of performance – but this requires accurate knowledge of various battery properties. Commercial Li-ion batteries have a multi-layered unit-cell structure in jelly roll or stack, with each unit cell containing current collectors, cathode, anode and separator. The cell components with different properties, multiphase electrodes and complex electrode morphology have made it difficult to obtain battery properties without proper characterization methods.

Therefore, in this study, we propose novel thermal characterization approaches to measuring the specific heat capacity and anisotropic thermal conductivity of large-format Li-ion pouch cells. The specific heat is characterized via a transient cooling method together with an analytical model, while the thermal diffusivity can be obtained by fitting a 3D thermal model to the dynamic surface temperature response measured with lock-in thermography. A nonlinear least-squares optimization algorithm is used to parameterize the battery thermal diffusivity. After that, the battery thermal conductivity can be decoupled from the measured specific heat and thermal diffusivity. Validated with aluminum reference samples, the present characterization methods have the merits of fast speed and good accuracy, which will be appealing to both scientific research and engineering practice.

References

G. Zubi, R. Dufo-López, M. Carvalho and G. Pasaoglu, Renewable and Sustainable Energy Reviews, 89, 292 (2018).

D. Bernardi, E. Pawlikowski and J. Newman, J Electrochem Soc, 132, 5 (1985).

D. P. Finegan, E. Darcy, M. Keyser, B. Tjaden, T. M. M. Heenan, R. Jervis, J. J. Bailey, R. Malik, N. T. Vo, O. V. Magdysyuk, R. Atwood, M. Drakopoulos, M. DiMichiel, A. Rack, G. Hinds, D. J. L. Brett and P. R. Shearing, Energy & Environmental Science, 10, 1377 (2017).

Y. Zhu, J. Xie, A. Pei, B. Liu, Y. Wu, D. Lin, J. Li, H. Wang, H. Chen, J. Xu, A. Yang, C. L. Wu, H. Wang, W. Chen and Y. Cui, Nat Commun, 10, 2067 (2019).
(Invited) Precursors for the Thermal Atomic Layer Deposition of Cobalt Metal Films and Alloys Thereof
Authors: Winter Charles H. , Hollin Jonathan , Khine Linn Nyi Myat , Devereaux Zachary
Published: July 2021

Herein, we will describe recent progress in our laboratory on the development of chemical precursors for the thermal atomic layer deposition (ALD) of cobalt metal, titanium metal, cobalt-titanium alloy, and other metal and metal alloy films. The nanoscale dimensions of current and future microelectronics devices now require alternative, ultrathin barrier materials for copper and other interconnect metals as well as new ultrathin liner materials. Sputtered cobalt-titanium alloys have been demonstrated to function as barrier materials and liners at dimensions as small as 1 nm. Hence, these materials may replace current barrier and liner materials such as TiN, TaN, and W metal. However, the narrow and deep nanoscale features require growth of cobalt-titanium alloy films by ALD to meet the strict conformality and thickness requirements. Moreover, thermal ALD is preferred over plasma-based processes, since recombination of atomic hydrogen on feature walls can afford poor conformal coverage. Thermal ALD processes for Co and Ti metal films are poorly developed, because the negative electrochemical potentials of the ions in precursors (Co2+ ↔ Co, E° = -0.280 V, Ti2+ ↔ Ti, E° = -1.628 V) require strong reducing co-reactants, which are not available. We will report new thermal ALD processes for cobalt metal films that employ various ligands, in combination with hydrazine-based co-reactants. These processes afford high purity cobalt metal films. We will also describe our efforts to develop new precursors for the thermal ALD of titanium metal films. Initial depositions of cobalt-titanium metal films will also be described.
Modelling the Growth and Etch of Thin Film Metal Oxides
Authors: Mullins Rita , Kondati Natarajan Suresh , Nolan Michael
Published: July 2021

HfO2 and ZrO2 are two high-k materials that are crucial in semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Atomic layer deposition (ALD) and thermal atomic layer etching (ALE) allow fabrication of ultra-thin films for semiconductor device processing. ALD is a well-known metal oxide thin film deposition technique in which metal and oxygen containing precursors are added sequentially to the reactor to ensure self-limiting precursor adsorption and reaction to enable a high level of control over film thickness. Thermal ALE, which is a relatively modern technique, uses self-limiting fluorination (using hydrogen fluoride exposure) and subsequent ligand exchange reactions at elevated temperatures to remove up to a monolayer of the metal oxide material. This modern approach for controlled etching is the reverse of ALD and removes only the fluorinated layer.

Given that it is difficult to investigate ALD and ALE reactions directly using experimental techniques, first-principles-based atomic-level simulations using density functional theory (DFT) can give deep insights into the precursor chemistry and the reactions that drive the deposition and etch of different materials. This contribution presents first principles density functional theory modelling to examine the growth and etch of thin films of HfO2 and ZrO2. Concerning the ALD reaction, the adsorption mechanism of precursors TDMAHf and TDMAZr are studied at the bare and hydroxylated surfaces of HfO2 and ZrO2 respectively. Stable OH coverages of 0.50 ML and 0.63 ML on the surfaces of HfO2 and ZrO2 were found respectively. Ligand loss from the metal precursor can be achieved by protonation from the OH terminated surface of both metal oxides. Concerning the ALE reaction, HF exposures on the surfaces of HfO2 and ZrO2 are studied. HF coverages ranging from 1.0 ± 0.3 to 17.0 ± 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 ± 0.02 Å /cycle for HfO2 and -0.57 ± 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 ± 0.3 and 6.5 ± 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).
(Invited) Area-selective spatial ALD of SiO2 interleaved with back-etch corrections: Selectivity and surface inspection of non-growth area
Authors: Mameli Alfredo , Karasulu Bora , van Es Maarten , Roozeboom Fred
Published: July 2021

The combination of area-selective ALD intermitted with back-etching steps has recently attracted much interest because of its potential in achieving high selectivity. Compared to non-interrupted area-selective ALD this supercycle approach has proven to be very effective in reducing the defectivity on the non-growth areas and thickening the layers on the growth areas.1, 2

In this work we studied the case of selective SiO2 deposition on silicon substrate wafers (growth area) with large ZnO patterns (non-growth area). We will demonstrate the effectiveness of this complementary approach, i.e., deposition and etch-back corrections in a rotary atmospheric-pressure all-spatial processing (= ‘dep/etch’) reactor (Fig. 1) to maximize SiO2 selectivity while obtaining high deposition rates. For the selective spatial ALD part of the supercycle a three-step (‘ABC’-type) recipe was adopted,3 consisting of exposure to: A) inhibitor, B) silicon precursor (BDEAS) and C) O2 plasma. The periodic back-etch intermissions in the supercycle were carried out in the same integrated spatial process reactor by exposing the substrate to a CF4-O2-N2 plasma. The plasma source used for both O2-plasma and the back-etch was of the atmospheric-pressure Dielectric Barrier Discharge (DBD) type4.

Figure 2 gives an illustration for a supercycle process with the substrate rotating at 20 rpm and using 3 repetitions of 40 ‘ABC’-cycles and 6 corrective back-etch cycles. During the each set of 40 ‘ABC’-cycles we could selectively grow sufficient (i.e., up to ~3.5 nm) SiO2 layer thickness on the growth area before the first nucleation of SiO2 became apparent on the ZnO non-growth areas. This way some selectivity is gradually lost with the number of ALD cycles increasing. As shown in Fig. 2 the selectivity loss can be repeatedly restored by a CF4-O2-N2 plasma back-etch with no silicon detected on the non-growth area by XPS. We demonstrated that with 3 repeated ‘dep/etch’ supercycles up to 10 nm thick SiO2 could be grown on the growth area.

We will discuss how Low Energy Ion Spectroscopy (LEIS), with its extreme sensitivity to the top monolayer(s) of a thin film, can give more and reliable quantitative information on the process selectivity and the defectivity on the non-growth area in terms of surface coverage and derived thickness. In addition, scanning probe FTIR-AFM microscopy can give information about the defects and contaminants at the substrate surface. Furthermore, we extended the selective spatial ALD of SiO2 to other oxidic non-growth areas like Al2O3, IGZO, SnO2, Ta2O5 and ZrO2.

1. R. Vallat, et al., J. Vac. Sci. Technol. A, 35, 01B104 (2017).

2. S. K. Song, et al., Chem. Mater. 31, 4793-4804 (2019).

3. A. Mameli, et al., ACS Nano, 11, 9303-9311 (2017).

4. Y. Creyghton, P. Poodt, M. Simor, F. Roozeboom, US Patent Application 20170137939.

Figure 1
Structure and Emission Evolution in Si-Rich HfO2:Pr Films Versus Annealing Temperature
Authors: Vega-Macotela Leonardo Gabriel , Torchynska Tetyana , Oliveros-García José , Khomenkova Larysa , Gourbilleau Fabrice
Published: July 2021

Pr-doped Si-rich-HfO2 films with specific emitting and structural properties have been prepared by radio-frequency magnetron sputtering using standard pure argon plasma approach. The effect of post-deposition thermal annealing on the transformation of crystalline phases, their compositions and photoluminescence spectra was investigated by means of the Energy Dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electronic microscopy (SEM), Raman scattering and photoluminescence (PL) methods. Thermal annealing was carried out at 800 °C, 900 °C, 1000 °C and 1100 °C within time of 30 min in nitrogen atmosphere. The SEM images demonstrate the grains with the size about 40 nm. It was observed that the influence of temperature at annealing causes the phase transformation and separation processes. In studied samples, the formation of the tetragonal HfO2 and SiO2 phases, were detected at XRD study after the annealing at 1000 and 1100 °C. PL spectra of these films are complex and demonstrate several PL bands centered at 442, 479, 523, 607, 637 and 716 nm. Their contribution depends on the annealing temperature and governs the shape of total PL spectra. The impact of crystalline phase separation on the peculiarities of PL spectra and XRD are analyzed and discussed.
Microplasma-Engineered Nanoassembly of Core-Shell Plasmonic Nanoparticles for Ultrasensitive Flexible Surface-Enhanced Raman Scattering Substrates
Authors: Yeh Yi-Jui , Chiang Wei-Hung , Tung Kuo-Lun
Published: July 2021

Surface enhance Raman scattering (SERS) is emerging as a powerful technology for the label-free detection of various biological and chemical species. One of the important but often overlooked considerations in the design of surface-enhanced Raman scattering (SERS) substrates for trace detection is the efficiency of sample collection. Conventional designs based on rigid substrates such as silicon, alumina, and glass resist conformal contact with the surface under investigation, making the sample collection inefficient.

The aim of our work is to develop an effective paper-based test strip to achieve high SERS performance for biosensing. Here we present one-step green-fabrication of bimetallic nanoparticles Au/Ag (3D porous stricture) loaded on filter paper using microplasma system. This approach requires a minimal fabrication effort and cost, also contains nanoisland and nanogaps (<20nm) on paper substrate to generate a high density of hot spot(~2000/um2). The 3D biomimetric substrate shows a low detection limit for Rhodamine 6G, high averaged enhancement factor, excellent signal uniformity, good stability and suitability in biosensing. In addition, the novel substrate was applied in label-free folic acid, dopamine and other Raman probe detection with small amount and low concentration of analyte, and it exhibited effective SERS platform potential for bio-detection and bio-sensing.

Figure 1
Plasma and Thermal Processing for Designing Hybrid Carbon-Nickel Sulfide Composite Electrodes
Authors: Santhosh Neelakandan M , Filipič Gregor , Zavašnik Janez , Cvelbar Uros
Published: July 2021

There are enormous efforts being made to develop alternative energy storage devices and to meet the energy needs beyond consumer electronics and electric vehicles. Considering batteries and supercapacitors as one of the best performing energy storage devices with high specific energy and power density, there are lots of efforts have been applied to improve the electrochemical features. Amide the different approaches, one of the direct method to improve the performance of such devices are by employing potential electrode materials. Transition metal sulfides are considered as the potential candidates for the next-generation energy storage electrodes. The conversion-reaction induced charge storage mechanism makes them as a promising material for designing high-capacity electrodes for electrochemical energy storage devices. However, poor conductivity and pulverization during the cycling process limits their applications as energy storage devices by limiting the cycle life, capacity and energy density. Thus a combination of metal sulfide phases with hierarchical carbon nanostructures is proposed to address these limitations. Additionally, the direct growth of electrode material on the current collector can overcome the issues related to the binders and internal resistance. In this aspect combining metal sulfides with carbon nanostructures directly grown on current collectors can be used as an advanced electrode material for energy storage applications. Herein, a fast, two-step approach is demonstrated for fabricating a hybrid electrode, consisting of trinickel disulfide (Ni3S2), metallic Ni nanoparticle and vertically aligned multi-walled carbon nanotubes (VCN) in the form Ni3S2/Ni@VCN. The VCN structure is prepared by plasma-assisted techniques, and the nickel sulfide is anchored by the thermal annealing. These Ni3S2/Ni@VCN composites can be directly used as a binder-free electrode for energy storage devices without any further processing, which makes the procedure as a promising technique for the fast fabrication of electrode materials for energy storage devices.
(Invited) Closed Loop Lithium Ion Battery Recycling Process
Authors: Wang Yan
Published: July 2021

Lithium-ion batteries (LIBs) is widely used in every aspect of our life due to its high energy density and long cycle life. However, the large demand of LIBs will also lead to a substantial end-of-life (EOL) batteries which requiring proper treatment. Recycling EOL LIBs not only mitigates the production of hazardrous waste caused by improper disposal, it also can recover the value from strategic materials. A closed-loop recycling process developed in WPI has demonstrated its success in synthesizing different cathode materials with excellent electrochemical performance when compared with a commercially available cathode. In this presentation, we will discuss the various efforts in our team to recover high quality cathode materials from spent lithium ion batteries and determine the impacts of some potential impurities.
Digging in Documents: Using Text Mining to Reveal Hidden Knowledge in the Lithium-Ion Battery Literature
Authors: EL-Bousiydy Hassna , Lombardo Teo , N. Primo Emiliano , Duquesnoy Marc , Morcrette Mathieu , Johansson Patrik , Simon Patrice , Grimaud Alexis , A. Franco Alejandro
Published: July 2021

Scientific publications constitute the main information source of battery-related data for academic research. There is an impressive number of papers published on Lithium Ion Batteries (LIBs) for instance. Such impressive amount of data in principle could be used by machine learning (ML) methods in order to optimize efforts and even make possible the discovery of new optimal experimental conditions. Yet, the majority is published as unstructured data, making ML analysis difficult. Here, in order to unravel researchers’ habits when reporting their results, we present a text mining study using primarily publications containing original experimental data from the LIB field. We analyze the reported data structure and we discuss the remaining challenges for applying automated knowledge discovery techniques. We then present a Named Entity Recognition approach to automatically extract quantified parameters from the battery literature and how to build an in house generated database containing a wide diversity of materials, experimental parameters and conditions. Our in house approach achieves a data extraction F-scores ≥ 90% and can thereby pave the way towards an automatized way of generating large databases for use in battery ML models.

References
El-Bouysidy, H., Lombardo, T., Primo, E. N., Duquesnoy, M., Morcrette, M., Johansson, P., Simon, P.,
Grimaud, A., & Franco, A. A. submitted (2020).

Torayev, Amangeldi, Pieter CMM Magusin, Clare P. Grey, Céline Merlet, and Alejandro A. Franco. Journal of Physics: Materials 2, no. 4 (2019): 044004.
Evaluating the Entropy of Reaction of a Custom Lithium-Ion Pouch Cell By Coupling a Frequency-Domain Method and Physics-Based Thermoelectrochemical Model
Authors: Hammond Jonathan , Abbasalinejad Armin , Christensen Jake , Kim Sun Ung Ung
Published: July 2021

It is necessary to measure the entropy of reaction to determine the thermal and electric performances of a lithium-ion battery. It is possible to measure the entropy of reaction at 100 times the speed of traditional methods using a frequency-domain method; in which, a sinusoidal current of the angular frequency is applied to the cell and resulting temperature signals of and 2 are observed due to reversible entropic heating and irreversible Joule heating, respectively. In this project, a physics-based model with coupled thermo- and electrochemical components was built to determine the internal states of a lithium-ion cell at different open-circuit potentials. In a previous work, this model has been employed to evaluate the entropy of reaction on a commercial pouch cell. This work seeks to further demonstrate the validity of the model by employing a series of custom pouch cells, that were built and tested for their entropy of reactions at different temperatures and open circuit potentials, using frequency-domain method. The results of the study were further experimentally validated by applying traditional entropy measurement methods to custom coin cells of the same chemistry as the pouch cells. Preliminary results of these exercises indicate a precise correlation of entropy of reaction values between the two methods. Ultimately, this work demonstrates that entropy of reaction can be accurately extracted using a frequency-domain method at lower time costs than traditional methods.
Microplasma Assembly a High-Efficient and Catalytic Platform Reduction 4-Nitrophenol Based on Reusable Au@Ag Nanoparticle / Cellulose Paper
Authors: Yeh Yi-Jui , Chiang Wei-Hung , Tung Kuo-Lun
Published: July 2021

Grafting metal nanoparticles (NPs) on flexible platforms is being increasingly attempted to advance their usage in the field of catalysis, sensing, energy storage, etc. However, anchoring NPs on substrates is nontrivial as it involves surface modification of the NPs and/or the substrate, which makes the whole process tedious. On the other hand , Bimetallic nanoparticles, which are composed of two metal elements in a particle, exhibit much higher catalytic activity than respective monometallic ones due to new bi-functional or synergistic effects, so-called a ligand and/or an ensemble effect.

Here we present the green, facile, less-time, one-step process fabrication of 3-dimension porous Au(core)@Ag(shell) NP /filter paper by Microplasma-assisted system. The aim of our work is to develop a high efficient catalytic substrate on common filter paper loaded on Au@Ag NPs. In our work, we found Au@Ag NP /filter paper can be synthesized and in a minute time scale. We further extend this technology to fabricated Au@Ag NP /paper and characterized them by SEM, Raman, XRD and UV-Vis spectroscopies. Besides, The as-prepared Au@Ag NP / filter paper is stable, uniform, and exhibits high efficiency and reusability in the catalytic reduction of 4-nitrophenol (4-NP) with a high rate constant as well as an average conversion of 96% in 3 minutes during 6 times. While acting as catalysts, the composites display excellent surface enhanced Raman scattering (SERS) efficiency, allowing the real-time monitoring of chemical reactions. The obtained Au@Ag bimetallic catalysts /filter paper show an exceptional superior catalytic activity for the reduction of 4-nitrophenol (4-NP) which can be completely reduced to 4-aminophenol (4-AP) in a single step within seconds., surpassing most reported noble metal nanoparticle catalysts. The results have not only paved the way for the wide application of Au@Ag NPs / filter paper but also provide a new road for the application of other bimetallic NPs

Figure 1
(Invited) Chemical Modulation of Precursor Reactivity for Systematic Synthesis of High-Quality Quantum Dots
Authors: Han Hee-Sun
Published: July 2021

With their size-dependent electronic properties, solution processability, and synthetic tunability, quantum dots (QDs) have been heavily studied for fundamental research and commercial applications. The performance of QD-based devices and QD probes are greatly affected by their size distribution and structural quality. To date, extensive studies have investigated size control, allowing us to grow QDs with less than a single monolayer difference in their size variation. In contrast, high quality QD growth is achieved
mostly by trial-and-error and a reaction condition optimized for a specific QD system cannot be adapted to QDs of different sizes or materials. To address this critical gap in QD synthesis, we first identified the key parameters contributing to the structural quality of QDs and examined how they affect QD growth. Our study shows that the reaction temperature governs the instability of the QD surface and the level of lattice relaxation, while precursor reactivity impacts the reaction kinetics at the surface as well as satellite particle formation. Systematic optimization of growth conditions requires independent tuning of these two parameters. Unfortunately, conventional precursors do not allow temperature-independent modulation of their reactivity, requiring new precursors to be synthesized for different reaction conditions. This approach is inherently low throughput and labor-intensive.

To enable temperature-independent modulation of precursor reactivity, we designed a new sulfur precursor that has a reactivity that can be chemically tuned in a predictable manner. The additives used for this reaction are commercially available, making the new chemistry highly accessible. The new precursor chemistry
represents a new paradigm for QD growth: chemically-induced precursor conversion. We show that the new precursor allows systematic growth of high quality QDs of various sizes and materials for both core-only and core-shell QDs. Moreover, a close examination of the growth results provided invaluable insight into the nanoparticle growth process, enabling logical tuning of the reaction condition. We also show that this new precursor chemistry employs completely different reaction mechanisms for nucleation and growth. By effectively separating growth and nucleation even at a high concentration of precursors, the new precursor allows heat-up-based growth of high quality shells that are comparable to those created by the injection method. Our study inspires the design of other precursors to systematically grow high quality nanocrystals and achieve the heat-up-based growth of high quality shells, a highly economical and scalable approach for large-scale synthesis.
Silicon-Tin Alloyed Nanocrystals by Femtosecond Laser Plasma
Authors: Svrcek Vladimir , Buerkle Marius , Lozach Mickael , McDonald Calum , Mariotti Davide
Published: July 2021

Silicon’s (Si) indirect bandgap limits its absorption and possible applications, and therefore remarkable efforts are put into the possibility of fabricating a material compatible with the existing silicon technology that is also a direct bandgap material. Tin (Sn) alloying with silicon represents an exciting possibility to tune Si properties. In addition, at the quantum confinement size (<10 nm) when the material becomes a quantum dot, it becomes possible to control the electronic structure of a material by varying the size. Although the possibility to tailor the bandgap of elemental Si over a wide range has been demonstrated, it is very challenging to obtain stable alloyed SiSn quantum dots. In particular, alfa Sn has a crystal structure similar to Si with zero band gap: a diamond cubic crystal structure, and importantly affected by the crystal configuration and a possible change to a direct energy gap at sufficiently high Sn concentration. This therefore makes Sn a favorable element to create an alloy with a lower bandgap than Si. Exploiting these features would make alloyed SiSn NCs an important candidate for a broad range of applications such as next generation photovoltaic cells based on carrier multiplication, super high efficient photodetectors, fluorescent tags for biomedical applications etc. In this contribution we will discuss the synthesis paths and optoelectrical properties in the context of silicon, tin, and silicon/tin alloyed nanocrystals at high alloying concentrations. Our results show that plasma-based processes allow the synthesis of alfa tin alloyed SiSn QDs with unprecedented dimensions and alloying concentrations. We will present SiSn-QDs as the world’s highest alloys fabricated by confined plasma from femtosecond (fs) laser in liquid media with a high tin concentration of approximately 17% ever reported in literature to our knowledge. We have demonstrated for the first time the experimental and exact theoretical calculation determination of the thermal stability of the SiSn-NCs at those concentrations. We study their electronic properties by means of an approximate band structure suitable for finite-sized systems (quasi-band structure) derived from first-principles calculations. This work therefore advances the current state of the art, provides opportunities to compare and verify theoretical results and offer important directions for applications.
(Invited) Thermal Transport in Multi-component Nanoparticle Superstructures
Authors: Stahley James B , Zanjani Mehdi
Published: July 2021

Engineering nanoscale structures and interfaces through self-assembly of quantum dots and nanoparticles is a powerful approach in material design and processing. Nanoscale building blocks, with a variety of shapes, sizes, and compositions, can self-assemble into different structures with desirable electronic, photonic, and phononic properties. Recent advances in synthesis and characterization of complex nano-scale units has provided a large library of multi-component building blocks that can significantly expand the current scope of colloidal self-assembly. However, the complexity of these building blocks makes it significantly harder to predict the resulting self-assembled structures and their transport properties. Therefore, developing predictive tools based on computational and machine learning approaches becomes a necessity for successful implementation of new material design procedures.

In this work, we utilize a combination of Molecular Dynamics simulations and Machine Learning-based approaches to investigate the self-assembly process of multi-component nanoparticles. We establish a computational framework to help identify feasible multi-component superstructures, and investigate various designs as a function of shape and size of the building blocks. Additionally, our approach transforms the high-dimensional energy landscapes of nanoparticles into low-dimensional parameter spaces by using Manifold Learning techniques. This illustration of the phase space compresses the full energy profile of the system into a single snapshot that contains important information regarding the assembly process and allows the comparison of the behavior of constructs with different geometric features in the same abstract space. This approach also facilitates the discovery of intuitive self-assembly pathways based on the energy footprint of nanoparticles.

Furthermore, we develop a computational framework to predict transport properties of the identified multi-component superstructures. Band structure calculations are performed to capture the influence of key parameters such as building block size/shape on the photonic and phononic properties of various structural designs. Finally, we present a Genetic Algorithm (GA)-based platform to implement an inverse material-design process where superstructures with desired transport properties are obtained from the available building blocks. Our results provide new insight into designing multi-component nano-scale structures and will help pave the way for developing powerful tools for material discovery and identification.
(Keynote) Electrochemistry Insights into the Development of Colloidal Quantum Dot Infrared Photodetectors
Authors: Guyot-Sionnest Philippe
Published: July 2021

Colloidal quantum dots may provide a cheap and versatile approach to infrared detection and light sources. Indeed, advances in the past few years have led to commercial high definition shortwave infrared imaging with PbS quantum dots as well as academic demonstrations of solution processed mid-wave thermal imaging with HgTe quantum dots, dual band detection, flexible and hyperspectral sensors.

This talk will start by describing how this progress derived from insights gained by electrochemical studies of colloidal quantum dots. Following a path previously traced for conducting polymers, solution phase electrochemical reduction and spectroscopy allowed the first observation of redox stability in quantum dot states of the colloidal quantum dots. This then led to electrochemical studies in films which confirmed ambipolar stability in the lead chalcogenides. The next key electrochemistry contribution was the development of the “solid-state ligand exchange” which increased 1000-fold the charge transfer rates across quantum dots. This led to the first observation of ohmic conduction in films of quantum dots and subsequent studies of hopping transport in these materials, before photoconductivity studies and translation to solid state gating. Electrochemistry is still routinely used to extract mobility in a state resolved manner, while that has only been recently realized with solid state gating. Electrochemistry is easily coupled with spectroscopy, and this allows much information on the states and their related interband and intraband transitions. Electrochemistry and photoluminescence have even been applied to single dots microscopy in the visible, which was used to study blinking and its elimination under reducing conditions. Electrochemistry also allowed to lower the laser threshold of quantum dot films under reducing conditions and this approach is now being translated to solid state devices by others. Finally, controlled doping is essential for devices and this is another area where electrochemistry provides much insights.

This talk will then briefly describe the status of infrared photodetection beyond silicon with colloidal quantum dots, and emphasize the performance metrics and potential avenue for improvements.
(Invited) Conduction Band Structure of Colloidal Quantum Wells
Authors: Diroll Benjamin T.
Published: July 2021

Similar to epitaxial quantum wells, colloidal quantum wells display electron intersubband transitions when photoexcited or electrochemically charged. Compared to epitaxial quantum wells, the strong confinement effect of thin, monodisperse colloidal quantum wells results in narrow intersubband transitions which reach high energies spanning the near-infrared spectral range. The composition of surface ligand chemistry subtly tunes the strain of the colloidal quantum wells to generate intersubband transitions over nearly continuously tunable energies. The divergent behavior of the band gap energy and intersubband transition energy implicates a substantial role of biaxial (in-plane) strain on the valence band structure. Multiple pump transient spectroscopy was furthermore employed to examine the lifetime of intersubband transitions, which is critical to their implementation in quantum cascade lasers or infrared detectors. In all cases, including core/shell samples, the lifetime of intersubband transitions is limited by surface or LO phonons to 1 ps or less, much shorter than comparable intraband transitions in quantum dots.
(Invited) Electronic and Optical Properties of Quantum-Confined Nanoparticles
Authors: Buerkle Marius , Lozach Mickaël , McDonald Calum , Mariotti Davide , Svrcek Vladimir
Published: July 2021

We discuss the electronic and optical properties of semiconducting nanoparticles in the quantum-confinement regime and how they can be modeled accurately using first-principles calculations. We address how band-like features emerge from finite electronic states with increasing particle size and how we can control the characteristics of the electronic band structure by means of surface chemistry and alloying. In particular, we are focusing on technological important issues such as bandgap engineering of both magnitude of the bandgap as well as transition type (indirect vs. direct bandgap) and process stability of nanoparticles. We discuss this for several type of semiconducting nano particles composed of environmentally friendly materials, namely we discuss: (i) the origin of the experimentally observed change of the bandgap silicon (Si) nanoparticles upon functionalization with OH groups. We show that the decisive factor here is not as previously proposed surface-strain but charge transfer from the OH groups to the surface electronic states of the particle. (ii) How surface states control the optical properties of silicon carbide (SiC) nano particles, which can lead to in terms of quantum-confinement counter intuitive level diagrams We correlate the frontier electronic states to the measured absolute positions of the conductance band minimum and valance band maximum. (iii) Transition from indirect to direct bandgaps in ultrasmall tin (Sn) and alloyed silicon-tin (SixSn1-x) nanoparticles. Ultrasmall tin nanoparticles are found to have indeed a direct bandgap as recent measurements have proposed but its comparable small bandgap make applications difficult. We show that also for high enough Sn concentration binary silicon-ton alloyed nanoparticles can change their bandgap characteristic from indirect to direct, however the required tin concentration is larger than what one would expect from what is know for bulk silicon-tin. (iv) Lastly, we also investigate the thermal stability of silicon and tin nanoparticles which is especially important for high temperature processing necessary for in cooperating the nanoparticles into existing silicon technologies such as photovoltaic devices. We show that depending on the nanoparticles crystal structure they can remain stable up to several hundred degrees Celsius.
Ionic Mass Transfer Accompanied with Electrodeposition of Li Metal in Solvate Ionic Liquid
Authors: Miki Akinori , Nishikawa Kei , Kamesui Go , Matsushima Hisayoshi , Ueda Mikito
Published: July 2021

Li metal is a promising negative electrode candidate for next-generation rechargeable batteries. However, the non-uniform electrochemical reaction induces dendrite formation during charging operation and dead lithium during discharging operation, respectively. Many researchers tried to control the morphological variation of electrodeposited Li metal by using additives and artificial interface layer. In general, the electrodeposition of metals are governed by the ionic mass transfer rate in the vicinity of the electrode. In this study, we focused on the Li+ ionic mass transfer phenomenon during the electrodeposition and electrochemical dissolution of Li metal in solvate ionic liquid. The solvate ionic liquid is new electrolyte candidate for the batteries. Especially, it is good candidate for Li-S batteries due to the suppression of dissolution of poly-sulfide. However, the mechanism of electrodeposition of Li metal has not been cleared in solvate ionic liquid system. Here, two in-situ techniques were applied to discuss the mechanism of Li metal electrodeposition from the viewpoint of ionic mass transfer. One is the digital holographic interferometry microscope which can visualize the Li+ concentration profile near the electrode. Another is micro-Raman spectroscopy which can detect the bonding of the chemical species in the electrolyte. We would like to discuss the ionic mass transfer phenomenon in the vicinity of the electrode during the electrodeposition and electrochemical dissolution of Li metal in solvate ionic liquid based on these in-situ measurement results.
Controlling the Spatial Dimensions of Nanostructured Electrolytes to Stabilize Dendritic Electrodeposition of Silver
Authors: Sharon Daniel , Bennington Peter , Nealey Paul F. , Patel Shrayesh N.
Published: July 2021

The tendency of metals to form uncontrolled dendritic morphologies during electrodeposition hinders the development of safe and reliable metal batteries. Multiphase nanostructured electrolytes can suppress dendritic growth if the mechanical modulus of the electrolyte is high relative to that of the metal or if the conducting channels are confined to nanoscale dimensions. Direct visualization and analysis of electrodeposition within polymeric nanostructures elucidates the structure−property relationships and mechanisms underlying the suppression of dendrite growth. To overcome these challenges, we introduce here a generalizable platform by which we can directly characterize electrodeposited metal morphologies in well-defined, multiphase nanostructured electrolytes by top-down SEM imaging [1]. This approach requires no destructive sample preparation techniques between electrodeposition and imaging. The platform consists of coplanar electrodes coated by polymeric structures consisting of alternating ion conducting and nonconducting material which are precisely created by lithography and etch techniques. These fabricated polymeric structures are designed to carefully model deposition of metals in nanostructured polymeric separators and electrolytes.

In this study we track the electrodeposition of silver ions (Ag+) dissolved in dry, aprotic poly(ethylene oxide) (PEO) polymer electrolyte confined within channels that are defined by a microfabricated nonconductive polystyrene structures. We find that Ag metal electrodeposition occurs only in the conductive domains with no significant deformation of the adjacent low-modulus nonconductive and confining domains. Moreover, we have shown that the Ag metal deposit morphology was strongly dependent on the dimensions of the conducting domains. When confinement width was similar in scale to the critical length scale for unstable deposition, the metal morphology was dense, unbranched filaments. Gradually increasing the confinement width led to branched dendritic deposition, although the side branch feature size was limited by the size of the confinement. These results demonstrate that in addition to mechanical and transport properties, the nanodimension of the structured electrolyte can also serve to stabilize dendritic morphology growth. This work highlights critical parameters for design of structured battery components such as solid-electrolytes, separators, and current collectors.

[1] Sharon, D.; Bennington, P.; Patel, S.N.; Nealey, P.F.*, “Stabilizing Metal Electrodeposition by Limiting Spatial Dimensions in Nanostructured Electrolytes,” ACS Energy Lett. 2020, 5, 2889−2896.

Figure 1