bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative Study of Titanium Nitride ALD using High Purity Hydrazine vs Ammonia
Authors: Alvarez Daniel , Andachi Keisuke , Tsuchibuchi Gaku , Suzuki Katsumasa , Spiegelman Jeffrey , Murata Hayato 
Published: December 2020

Emerging devices (Logic and Advanced Memory) require high quality thin (5-20 Å) electrode and barrier films. Difficult thermal budget constraints are now being placed on well-known materials such as TiN and TaN. Deposition temperature limitations have reached 350°C and below while very low resistivity (<100 micro-ohm/cm) must be achieved. Novel Ti precursors are being explored.1 Our approach has focused on hydrazine (N2H4) as an alternative nitrogen source to NH3.
Hydrazine is generally difficult to handle from a safety perspective due to its flammability and toxicity. We have developed a novel method to store and generate hydrazine in situ as a high purity gas which is then delivered to ALD process chambers.2 In this study, we examine the effect that hydrazine has on low deposition temperature TiN ALD processes. We experimentally evaluate TiN ALD growth and film characteristics using TiCl4/ N2H4 in comparison to that using TiCl4/NH3.
Titanium Nitride films were deposited using the hot wall type tubular furnace and a sequential gas supply system. Deposition temperature was set to predetermined value in the range from 250°C to 400°C. In the case of TiCl4/NH3, GPC was 0.10-0.27 Å/cycle at 250-400°C, where a decrease is noted as the deposition temperature is reduced. With the use of hydrazine, an increase in GPC is observed at each deposition temperature vs NH3. Moreover, the temperature dependence of GPC moved in the opposite direction of TiCl4/NH3. Specifically, GPC of TiCl4/N2H4 ALD was 19% higher at 400°C while an increase of 310% was seen at 250°C versus NH3. In the case of TiCl4/N2H4, the ALD window appears in the range of 250-400°C, where TiCl4 adsorption saturation curves are observed at 250°C and 400°C. Refractive index (R.I.) of TiCl4/N2H4 ALD was about 1.68-1.73 at 250-400°C. These values were approximately equal to R.I. of typical sputtered TiN which was about 1.66. In contrast, R.I. of TiCl4/NH3 ALD was larger than 2.00 in the 250- 300°C range. Because of R.I. of typical titanium oxide is about 2.4-2.5, it is assumed that the TiCl4/NH3 ALD film is contaminated by oxygen. In the ammonia case, background contaminants in the reactor appear to compete with low reactivity NH3 for reaction sites on the ALD surface. In the TiCl4/N2H4 case, higher temperature is not required to form high quality TiN films compared to TiCl4/NH3 ALD.
From the above results, the use of high purity hydrazine is beneficial to maintaining high throughput and good film quality under the new constraints for emerging devices. Film composition by XPS and Resistivity measurements consistent with this conclusion will also be presented.

References

[1] Klesko J.P., Thrush C.M., Winter C.H., Chemistry of Materials. 27: 4918-4921, (2015).
[2] J. Spiegelman, Daniel Alvarez et al., 18th International Conference on Atomic Layer Deposition (2018) AMTuP2.

Figure 1
Atomic Layer Etching of Silicon Oxide with CF3I and O2 Plasma
Authors: Kim Seon Yong , Lee Taehoon , Park In-Sung , Ahn Jinho 
Published: December 2020

Perfluorinated compounds (PFCs) such as CF4, C2F6, C3F8, and C4F8 have been widely used in plasma dry etching and in-situ deposition chamber cleaning processes.[1] More recently, the PFCs have been used in atomic layer etching (ALE), which is considered the promising etching technique that can control the etched thickness in atomic scale levels.[2] However, PFCs generally have a high global warming potential (GWP), which is a significant figure of merit concerned with global warming.
CF3I has been studied as a dry etching gas to replace PFCs because of its ultra-low GWP (GWP100=0.3). However, most of the results have been required at high plasma power over 1000 W, which made it difficult to commercialize.[3] Therefore, the feasibility of applying CF3I to ALE processed at low plasma power (400 W or less) is an important factor to replace PFCs.
In this study, ALE of SiO2 was performed with CF3I as an etchant gas. In the ALE process, one cycle involved two steps: surface modification and removal steps. In the first step, surface modification, CF3I plasma was treated on the SiO2 surface to deposit fluorocarbon polymer. In the second step, removal step, O2 plasma was used to remove the deposited polymer. When fluorocarbon polymer was removed by O2 plasma, SiO2 film was etched by the byproduct of volatile SiFx generated in the interlayer between fluorocarbon polymer and SiO2. The surface change in the respective modification and removal step was confirmed by X-ray photoelectron spectroscopy (XPS), and the etched thickness of SiO2 film during ALE process was measured by using ellipsometry and transmission electron microscopy (TEM).
As a result of SiO2 ALE using CF3I, etched thickness per cycle (EPC) saturation with both CF3I plasma treatment time and O2 plasma treatment time shows that etching was proceeding to atomic scale. When the plasma power is 300 W, the EPC is 0.93 nm/cycle. It means the fast etch rate enough to replace other PFCs at a low power condition.[2]

References

[1] C. J. Mogab, et. al., J. Appl. Phys. 49, 3796 (1978).
[2] D. Metzler, et. al., J. Vac. Sci. Technol. A 32, 020603 (2014).
[3] A. Misra, et. al., D. Rufin, Mat. Let. 34 415 (1998).
(Invited) Controlled Assembly of 3D Graphene Electrodes for Enhanced Alkali Metal Storage
Authors: Lee Michael J , Lee Hoyoung , Lee Kyungbin , Lee Byeongyong , Lee Seung Woo 
Published: December 2020

Graphene has been intensively investigated as an electrode material for energy storage devices thanks to its large surface area and excellent electrical conductivity. However, the restacking of graphene sheets is inevitable during the solution process due to π–π and hydrophobic interactions, which reduces the available surface area. Recently, 3D structured crumpled graphene has emerged as an promising electrode material due to its aggregation-resistive property.
In this study, we will introduce our recent efforts to assemble 3D structured crumpled graphene anodes through the stacking engineering process for Li-, Na-, K-ion batteries. We reveal the role of defects in improving the charge storage performance through the surface-controlled charge storage mechanism. The crumpled graphene anodes exhibited high capacity with excellent rate-performance and cycling stability. We further evaluate the temperature-dependent performance of 3D graphene anodes, demonstrating their superior charge storage performance in extreme cold environments. Finally, we will discuss anodic electrochemical exfoliation of graphite for the fast production of graphene at low cost with moderate quality.
Chemical Manipulation Towards High Performance Li-S Batteries
Authors: Xie Jia , Jiang Zhipeng , Zeng Ziqi , Zhang Wei , Li Shuping 
Published: December 2020

Lithium-sulfur batteries have been regarded as one of the most promising new battery technologies due to their high theoretical energy density (2600 Wh kg-1) and the abundant resource as well as the low cost of sulfur. However, current sulfur cathodes and lithium metal anodes can’t meet the design requirements for high specific energy batteries. In this talk we will introduce several chemical manipulation methods for high performance Li-S batteries. On the sulfur cathode side, a new reaction pathway is proposed and Se or Te as eutectic accelerator is introduced to boost reaction kinetics. It is possible to eliminate polysulfide dissolution while under the dissolution deposition mechanism and obtain high performance sulfur cathodes compatible with both ether and carbonate electrolytes.[1-5] For lithium metal anodes, we have developed a couple of multifunctional artificial layers through simple and facile chemical methods. The multifunctional layers are beneficial not only for uniform deposition of lithium, but also for prolonged cycling performance.[6-7] With the newly developed anode and cathode materials, a high energy lithium-sulfur battery with significantly improved performance is obtained under the conditions of high areal capacity loading (> 10 mAh cm-2), lead electrolyte (3 ul/mgS) and low N/P ratio (~ 3: 1). The energy density and cycle life are expected to show breakthrough in large Li-S batteries.
References

Chen, L. Peng, L. Wang, K. Yuan, Y.H. Huang, B. Shan, L.X. Yuan*, and J. Xie*, Nature Communications, 2019, 10, 1021

Zhang, Y. Sun, H. Jia, Z. Zhang, B. Shan, and J. Xie*, Energy Storage Materials, 2019, 21, 287-296

Li, Z. Han, W. Hu, L. Peng, J. Yang, L. Wang, Y. Zhang, B. Shan and J. Xie*, Nano Energy, 2019, 60, 153-161

Li, Z. Zeng, J. Yang, Z. Han, W. Hu, L. Wang, J. Ma, B. Shan and J. Xie*, ACS Applied Energy Materials, 2019, 2(4), 2956-2964

Wang, X. Chen, S. Li, J. Yang, Y. Sun, L. Peng, B. Shan and J. Xie*, Journal of Materials Chemistry A, 2019, 7, 12732-12739

Jiang, J. Liu, Z. Han, W. Hu, Z. Zeng, Y. Sun and J. Xie*, Angewandte Chemie International Edition, 2019, 58(33), 11374-11378

Jiang, Z. Zeng, C. Yang, Z. Han, W. Hu, J. Lu, and J. Xie*, Nano Letters,
2019, DOI:10.1021/acs.nanolett.9b03562
Study on the Effect of Surface Area on the ORR Performance of Perovskite Catalyst for High Performance Lithium-Oxygen Batteries
Authors: Kim Jiyoun , Choi Yusong , Ahn Tae-Young , Cho Jang-Hyeon 
Published: December 2020

Lithium oxygen(Li-O2) batteries have been recognized as one of the next-generation power sources, capable of supplying power for a long time even in an independent extreme environment. In spite of the theoretical advantage, Li-O2 batteries face technical and economical challenges that must be addressed to promote them as commercially variable techcologies for future energy system. Above all, battery performance largely depends on the activities of the cathode during discharge and charge, respectively. The undesirable overpotential caused by sluggish reaction kinetics assiciated with the ORR and OER greatly limit the current performance of Li-O2 batteries, which must be improved by efficient catalyzing the reactions. Among the numerous catalysts, perovskite oxides have attention for candidate electrocatalyst for Li-O2 batteries due to their high electronic/ionic conductivity, high electrochemical stability, and catalytic activity. Especially, La0.6Sr0.4Co0.2Fe0.8O3(LSCF) is considered as a typical catalyst for Li-O2 batteries, which and provide high oxygen surface exchange coefficient for fast kinetics at the gas/electrode interface. The surface area is significantly related on the ORR and OER performance, which influences on the active area for reactions. In this study, we have tried to utilize a simple high energy ball milling process to investigate the electrochemical properties of LSCF catalyst. Through the BET analysis, it was confirmed that the specific area significantly was increased after ball milling due to the reduced particle size, obtaining the optimized milling time with the higher ORR performance. The electrochemical activities have been measured with rotating disk electrode(RRDE) method. Well-ball milled LSCF catalyst has resulted in the enlargement of specific surface area and increased defective sites, which improve the catalytic activity.
To investigate the influence of LSCF oxides on the ORR process, the performance of composite electrode with LSCF catalyst in LITFSI in either solvents has been compared with a carbon based cathode(carbon nano tube(CM130)). From the discharge results, the composite electrode showed the superior performance as well as higher specific capacitance (more than 1.6 times) than carbon based electrode dye to the altered transport and reaction kinetics due to LSCF. In this study, we have proposed the processes of obtaining a catalyst with optimal electrochemical properties through a relatively simple process and applied it to electrode for lithium oxygen batteries.
Evaluation of Thermal Expansion Coefficient in Ge1-x
Sn
x
Nanowire Using Reciprocal Space Mapping
Authors: Ogasawara Gai , Yokogawa Ryo , Hirosawa Ichiro , Yoshioka Kazutoshi , Takahashi Yuki , Suda Kohei , Ogura Atsushi 
Published: December 2020

Ge1-x
Sn
x
is expected to be a new material for next-generation electronic and thermoelectric device because it has higher carrier mobilities and lower thermal conductivity than pure Si and Ge. Here, strain is an important factor for designing electric and thermoelectric devices. It has been reported that there is a correlation between strain and thermal conductivity for group IV semiconductors [1]. In plane compressive strain is induced in epitaxially grown GeSn thin film on a Ge substrate due to the difference in lattice parameter. Anisotropic strain relaxation has been occurred in the GeSn nanowires. Anisotropic strain may cause anisotropic thermal expansion and thermal conductivity. In this study, we evaluated the thermal expansion of Ge1-x
Sn
x
nanowire fabricated on Ge substrate using reciprocal space mapping (RSM) by synchrotron radiation X-ray diffraction (XRD) measurement.
The Ge1-x
Sn
x
thin films were epitaxially grown on Ge (001) substrate for 34 and 45 nm by home-made metal organic chemical vapor deposition [2]. Sn concentrations (x) is 3.2% as confirmed by Rutherford backscattering spectrometry. Then, the nanowires were fabricated by electron beam lithography and dry etching as shown in Fig. 1. The major axis length (L) parallel to [110] were fixed at 10 µm while the minor axis width (W) parallel to [-110] were 200 or 500 nm. For the measurement of RSM, multi-axis diffractometer in BL19B2 of SPring-8 was used. The photon energy was 10 keV, which is just under the K-edge of Ge at 11 keV. We fabricated many nanowires to obtain sufficiently strong X-ray diffraction. The sample temperature was controlled using a heating stage (Anton Paar DHS1100).
Figure 2 shows the relationship between temperature and the lattice parameters in Ge0.968Sn0.032
nanowire with W=500 nm. Thermal expansion for the sample with W=200 nm showed an isotropic change. However, it was revealed that the thermal expansion between the in-plane minor axis [-110] and the out-of-plane [001] directions were different for the sample with W=500 nm. In the previous study, we have confirmed the uniaxial strain relaxation (minor axis direction [-110]) has been occurred with decreasing W for Ge1-x
Sn
x
nanowire [3]. Thus, it is considered that the thermal expansion become isotropic as the nanowire width gets shorter.

References

Xu et al., J. Appl. Phys. 106, 114302 (2009).

Suda et al., ECS Trans. 64 (6). 697 (2014).

K. Yoshioka et al., Thin Solid Films 697, 137797 (2020).

Figure 1
Functionalized Magnetic 3D Printing of High Performance Electrodes for Lithium Battery
Authors: Sarkar Abhishek , Shrotriya Pranav , Nlebedim Ikenna C 
Published: December 2020

With the trend for rapid prototyping of parts and systems, additive manufacturing process like three-dimensional (3D) printing can advance the fabrication of shape-specific architectures for anisotropic permanent magnets involving expensive and critical rare-earth elements1,2. Although in-situ alignment will open new horizons for manufacturing of complex permanent magnets, integration of alignment systems into 3D printing processes is still a challenge. In our former works, we have demonstrated a mechanism to address this challenge accomplished by integration of bonded magnet production, 3D printing, finite element modeling and system development3.
Alignment of electrode pores, (e.g. using magnetic field) allow from better electrochemical transport of electrolyte through the electrode, thereby improving cell performance. The formerly developed magnetic field alignment model for 3D printed material in my postdoctoral program will be modified and used to predict the degree-of-alignment in electrodes for lithium-ion battery. The relationship between pore tortuosity and degree-of-alignment was modeled using a power law with the effect of exponent compared in Fig. 1a.
A coupled electrochemical-thermal-mechanical modeled is developed to predict the cell capacity loss due to above-mentioned anodic degradation mechanisms. Keeping the porosity, the tortuosity is altered between aligned and non-aligned states, to evaluate the electrochemical transport properties like diffusivity and ionic conductivity in the electrode. The model predicts an increase in cell capacity for lower tortuosity (aligned) electrodes, which is further amplified at faster charging conditions (Fig. 1b). It is generally observed that fast charging induces a steep non-uniform charge distribution in the unaligned electrodes. With increase in alignment, the electrolyte has easier pathways leading to a more uniform charge distribution and therefore a larger capacity. An immediate impact of a more uniform charge distribution is the lowering of tendency for lithium-ions to deposit in metallic form on the anode (called lithium plating).
These results provide an indication that alignment of electrodes will be beneficial towards designing a higher capacity and faster charging battery. Experimental validations are the next step towards validating the model predictions.

Huber, C. et al. 3D print of polymer bonded rare-earth magnets, and 3D magnetic field scanning with an end-user 3D printer. Appl. Phys. Lett.
109, 162401 (2016).

Li, L., Post, B., Kunc, V., Elliott, A. M. & Paranthaman, M. P. Additive manufacturing of near-net-shape bonded magnets: Prospects and challenges. Scr. Mater. (2017) doi:10.1016/j.scriptamat.2016.12.035.

Sarkar, A. et al. Functionalizing magnet additive manufacturing with in-situ magnetic field source. Addit. Manuf.
34, 101289 (2020).

Figure 1
(Invited) Nanostructured Rocksalt-Based Positive Electrode Materials for Rechargeable Li/Na Batteries
Authors: Yabuuchi Naoaki 
Published: December 2020

In the past decade, lithium-enriched compounds, Li2MO3 (M = Mn4+, Ru4+
etc.), have been extensively studied for high-capacity positive electrode materials of lithium batteries. Although the origin of high reversible capacities was a debatable subject for a long time, recently it has been evidenced that charge compensation is partly achieved by solid-state redox of non-metal anions, i.e., oxide ions (anionic redox), coupled with redox reaction of transition metal ions (cationic redox), which is the basic theory used for classical lithium/sodium insertion materials. Recently, many cation-disordered rocksalt oxides have been proposed as a new series of electrode materials, which utilize reversible anionic redox. Nevertheless, insufficient electrode kinetics for the cation-disordered rocksalt system limits its use for practical applications. One simple strategy is to synthesize nanosized materials, which overcomes a problem of electrode kinetics (for electrons, holes and ions), and indeed electrode kinetics is significantly improved through nanosizing even for a non-lithium-excess and stoichiometric system.1) Moreover, Nanosized Li/Na-excess oxides also deliver large reversible capacities even at room temperature,2, 3) which shows much better electrode kinetics compared with as-prepared submicrometer-sized samples.
From these findings, we discuss the advantages/disadvantages of “nanostructured” rocksalt-based electrode materialsto develop high energy Li/Na-ion batteries in the future.
References

Sato et al., and N. Yabuuchi., Journal of Materials Chemistry A, 6, 13943 (2018).

Kobayashi et al., and N. Yabuuchi, Small, 15, 1902462 (6 pages) (2019).

Kobayashi et al., and N. Yabuuchi, Materials Today, in-press, DOI: 10.1016/j.mattod.2020.03.002
A Simple One-Dimensional Transport Model to Explain Inverse Signatures in Lithium-Metal Batteries
Authors: Uppaluri Maitri , Subramaniam Akshay , Subramanian Venkat R. 
Published: December 2020

Lithium metal as the negative electrode in lithium batteries provides high theoretical capacity (3,860 mAh g–1) and negative electrochemical potential (-3.040 V vs standard hydrogen electrode) 1. However, using lithium metal poses several challenges, including dendritic electrodeposition and accumulation of dead lithium. These phenomena can cause the cell to short, and also contribute to poor cyclability 2.
Lithium deposition and stripping can be observed on the cell’s voltage response as unique signatures. These signatures can give insight on the morphology of the deposit 3. Physics-based continuum models can be used to understand lithium ion transport effects on deposition and stripping, and on the emergent voltage signatures.
Our past work studied one-dimensional models for lithium symmetric cells to model charge transport and capture the transitions in voltage observed experimentally 4. In this work, we propose a simple diffusion-based one-dimensional moving boundary that shows inverse signatures of lithium ion concentration and overpotential for the lithium deposition reaction. We show that using a transport model alone can produce unique inverse voltage signatures. The deposition of lithium is modeled as a moving interface.
The model was tested with different design parameters such as salt concentration, and different applied current densities and ion diffusivities to study their effect on the formation of signatures. These parameters affect the interface motion and ion transport in the electrolyte. The interplay between these two phenomena then determines characteristic signatures of the overpotential and the cell voltage.

Acknowledgement

This work at the University of Texas at Austin was supported by U.S. DOE award DEAC05- 76RL01830 through PNNL subcontract 475525 and the assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the US Department of Energy (DoE) through the Advanced Battery Materials Research Program (Battery500 Consortium).

References

1. W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, and J. G. Zhang, Energy Environ. Sci., 7, 513–537 (2014).
2. D. Lin, Y. Liu, and Y. Cui, Nat. Nanotechnol., 12, 194–206 (2017).
3. K. N. Wood, M. Noked, and N. P. Dasgupta, ACS Energy Lett., 2, 664–672 (2017).
4. A. Subramaniam, J. Chen, R. M. Kasse, M. F. Toney, T. Jang, and N. R. Geise, J. Electrochem. Soc., 166, A3806–A3819 (2019).