bluuebunny/crossref_metadata_2025 huggingface dataset:
Fast and Reversible Four-Electron Storage Enabled By Ethyl Viologen for Rechargeable Magnesium Batteries
Authors: Sun Yue , Lu Yi-Chun
Published: December 2020

Magnesium (Mg) batteries have been considered one of the most promising “post-lithium-ion” energy storage technologies owing to their high theoretical energy density, earth abundance, and intrinsic safety with air and moisture. However, the cell performance of Mg batteries has been limited to cathode materials leading to sluggish kinetics, low reversible energy density, and poor cycling stability. The development of Mg intercalation cathode materials[1–3] has been impeded by slow Mg2+ solid diffusion due to high charge density, sluggish charge redistribution, and strong electrostatic interaction with host and anions.[4] Many of the Li+-intercalation cathodes are not suitable for Mg2+ insertion.[5] Organic materials with high tunability have attracted significant attention,[6] but it has been challenging to achieve organic Mg batteries with a satisfactory energy density as the commercial lithium-ion battery (100-170 Wh kg-1
[7]) with high power and long cycle life. Here, a new organic cathode for rechargeable Mg batteries is reported based on ethyl viologen (EV), which not only has a fast redox couple EV2+/EV0 but also is capable of coupling with redox-active anions, such as iodide (I-), achieving a total four-electron storage. The EV2+/EV0 redox couple demonstrates a stable cycle life (500 cycles) with a superior rate performance (10 C) owing to intrinsic fast electrode kinetics, and a high material utilization (>80%) was achieved at 1.0 C under a high areal loading of 5 mg cm−2. When coupling with iodide I-, a reversible four-electron storage is achieved with a high energy density (304.2 Wh kg-1) and a stable cycle life (>100 cycles). This study provides effective strategies for designing reversible multielectron storage for high-rate and high-energy rechargeable Mg batteries.[8]

Reference
s
:

[1] X. Sun, P. Bonnick, V. Duffort, M. Liu, Z. Rong, K. A. Persson, G. Ceder, L. F. Nazar, Energy Environ. Sci. 9 (2016) 2273-2277.

[2] X. Sun, P. Bonnick, L. F. Nazar, ACS Energy Lett. 1 (2016) 297-301.

[3] B. Liu, T. Luo, G. Mu, X. Wang, D. Chen, G. Shen, ACS nano 7 (2013) 8051-8058.

[4] E. Levi, M. D. Levi, O. Chasid, D. Aurbach, J Electroceram. 22 (2009) 13-19.

[5] M. Bouroushian, Electrochemistry of metal chalcogenides, Springer Science & Business Media, Heidelberg, Berlin, 2010.

[6] M. Mao, T. Gao, S. Hou, C. Wang, Chem. Soc. Rev. 47 (2018) 8804-8841.

[7] J.-M. Tarascon, M. Armand, in: V. Dusastre (Ed.), Materials for Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group, World Scientific, Singapore, 2011, pp. 171–179.

[8] Y. Sun, Q. Zou, Y. Lu, Adv. Energy Mater. 9 (2019) 1903002.

Acknowledgements
:

This work was supported by a grant from the Research Grants Council (RGC) of the Hong Kong Administrative Region, China, under an RGC project No. T23-601/17-R.
Oxygen Reduction Pathways in the Li-O2 Battery: Understanding Solvent-Water Interactions
Authors: McNulty Rory , Holc Conrad , Walsh Darren Anthony , Rogers David , Newton Graham N. , Bruce Peter G. , Johnson Lee R
Published: December 2020

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that exceeds the capacity of Li-ion batteries. We must explore alternatives to Li-ion if we are to have any hope of meeting the long-term requirements for energy storage. One such alternative technology is the Li-air (O2) battery; its theoretical specific energy exceeds that of Li-ion five-fold, but many obstacles face its realisation.1–4

It is assumed that H2O in the Li-O2 battery will result in irreversible formation of LiOH and thus gas streams must be dried before entering the battery. Projections have suggested that this would sacrifice one third of the pack weight to a gas filtration unit required to bring atmospheric H2O content to functional levels (<1 ppm).5–9 Understanding the specific solvent properties that are associated with H2O tolerance, or distinct lack of, can guide rational selection of solvents able to tolerate wet air streams and reduce the requirements of the gas filtration unit, increasing the practical energy density.

Here we consider competition between reversible 2e- O2 reduction and proton coupled irreversible 4e- O2 reduction. The predisposition to favour one of these O2 reduction pathways is largely solvent dependent. We have combined a range of methods including cyclic voltammetry, operando pressure analysis, NMR, FTIR, Raman, UV-vis spectroscopy and SEM to investigate the O2 reduction pathways in four common Li-air electrolytes containing H2O.10 H2O concentrations spanning 0–36% were employed to understand the onset and of the irreversible 4e- O2 reduction process across these solvents, with specific solvent properties being attributed to their performance. The results of these studies will be presented, along with their implications on rational future solvent development for rechargeable Li-O2 battery electrolytes.

Reference
s
:

[1] X. Gao, Y. Chen, L. Johnson and P. G. Bruce, Nat. Mater. 15 (2016) 882–888.

[2] N. Feng, P. He and H. Zhou, Adv. Energy Mater. 6 (2016) 1502303.

[3] L. Ma, T. Yu, E. Tzoganakis, K. Amine, T. Wu, Z. Chen and J. Lu, Adv. Energy Mater. 8 (2018) 1–13.

[4] D. Aurbach, B. D. McCloskey, L. F. Nazar and P. G. Bruce, Nat. Energy 1 (2016) 16128.

[5] K. G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu and V. Srinivasan, Energy Environ. Sci. 7 (2014) 1555-1563.

[6] P. Tan, W. Shyy, T. S. Zhao, R. H. Zhang and X. B. Zhu, Appl. Energy 182 (2016) 569–575.

[7] C. Shu, J. Wang, J. Long, H. K. Liu and S. X. Dou, Adv. Mater. 31 (2019) 1–43.

[8] A. Dai, Q. Li, T. Liu, K. Amine and J. Lu, Adv. Mater. 31 (2018) 1805602.

[9] D. G. Kwabi, T. P. Batcho, S. Feng, L. Giordano, C. V. Thompson and Y. Shao-Horn, Phys. Chem. Chem. Phys., 18 (2016) 24944–24953.

[10] H. Guo, W. Luo, J. Chen, S. Chou, H. Liu and J. Wang, Adv. Sustain. Syst. 2 (2018) 1700183.
(Invited) Fast Charging Anodes for Aqueous Sodium-Ion Batteries
Authors: Feng Zhenxing
Published: December 2020

Aqueous sodium-ion batteries are attractive battery alternatives for stationary energy storage due to their inherently low cost and high safety. The development of advanced electrode materials with excellent performance and low cost is crucial for the success of aqueous Na-ion batteries. Our group recently has studied several types of iron phosphate-based electrodes including NASICON and layered materials as promising anodes alternative for aqueous Na-ion batteries. We found these anodes can exhibit very fast ionic diffusion that enables the fast charging rate (up to 200C), long cycling life (6000 cycles), high capacity retention (~70%) and rate capability. In combination of electrochemical characterization and multimodal synchrotron X-ray scattering and spectroscopy methods, we further reveal the reaction mechanism associated with these high performance ionic conducting ceramics. Our work also underlines the importance of fabricating aqueous batteries on the basis of the Earth-abundant, cost- effective, and non-toxic elements.
How Safe Are Li-Metal Batteries?
Authors: Pol Vilas G. , Puthusseri Dhanya
Published: December 2020

For last three decades, Li-ion batteries are the energy storage device of choice; however, the limited theoretical capacity of anodes and cathodes hampers its wide adaption in many applications. Li metal batteries (LMBs) encompassing a lithium metal anodes with sulfur/layered oxide-based cathode material (Li-S and Li-NMC532) provide a sustainable possibility to improve energy/power density. However, thermal safety and overall stability issues continues to hinder its use in practical applications. In spite of the significant effort to alleviate the cycle life of LMBs, the thermal safety aspects of these systems remain unknown, therefore could lead to thermal runaway under extreme conditions. This talk will provide an understanding of the thermal stability of LMBs from materials level to cell level. The amount of exothermic heat generated for Li-NMC (2.9 KJ/g) and Li-S (188 J/g) from the coin cell DSC analysis shows amplified safety risk in Li-NMC532 batteries.
In-Situ Observation of Electrodeposition in a Microfluidic Device with through Silicon Via Model
Authors: Akita Takanori , Otsuka Yuki , Irita Masaru , Hayase Masanori
Published: December 2020

Nowadays, the high performance of integrated circuits is due to packaging technologies, and 3d-packaging using TSVs (Through Silicon Vias) have entered use in commercial products. Copper electroplating is used to form TSVs, since bottom-up filling is available using a combination of several additives, but the filling mechanism is not clear yet. Recently, we have observed the adsorption and deactivation behavior of typical suppressing additives by using a disk electrode with a diameter of 100 μm in a microchannel that allows precise control of mass transport [1]. In this study, in order to understand the details of the TSV filling behavior, we propose a microfluidic device that has TSV feature in the channel, and in-situ observation of the electrodeposition behavior is enabled.

The microfluidic device was fabricated using the silicon substrate. First, Au is sputtered on the silicon substrate and the Au film is patterned by photolithography and wet etching. Then, the micro channel is defined by a 19 μm thick photoresist pattern on the silicon substrate. In the micro channel, a rectangular area on Au film is exposed. The exposed Au film and the surrounding resist pattern model the TSV. The width, height, and depth of the via are 20 μm, 19 μm and 100 μm, respectively. Finally, a glass cover plate is put on the substrate, and the microchannel is mounted on a base. A mercury sulfate electrode (MSE) is connected to the resin base and works as a reference electrode. A copper wire is inserted into the outlet tube and works as a counter electrode.

An acid copper sulfate plating solution was prepared as a VMS (Virgin Makeup Solution). Initially, additive-free VMS was supplied, and the working electrode was pre-plated with copper. Then, the solution was switched to the VMS + Leveler and open circuit potential was maintained for 120 s. Finally, -600 mV vs. MSE was applied on the working electrode, and plating behavior was observed. Figure 1 shows the appearance of the working electrode along time. At 5 s, clear interface was observed at the depth around 20 μm from the opening of the via. Below the interface, the working electrode became dark because the deposition proceeded. While no obvious change was observed above the interface and it was found that the deposition was strongly suppressed by the leveler adsorption. The interface line inclined and it was assumed that the leveler penetrated deeper in downstream side because of the solution flow.

Reference

[1] T. Akita, M. Tomie, R. Ikuta, H. Egoshi, and M. Hayase, J. Electrochem. Soc., 166(1), D3058 (2019).

Figure 1
Deposition of Large-Grain Polycrystalline Aluminum Nitride at Low Temperature Via Bias-Enhanced Atomic Layer Annealing
Authors: Kummel Andrew C , McLeod Aaron , Ueda Scott T
Published: December 2020

Three-dimensional integration of microelectronic devices and high-power radio frequency devices requires the integration of electrically insulating heat spreaders. Aluminum nitride is one potential material, as it can be deposited within backend thermal budgets and conducts heat isotopically, as opposed to diamond which requires deposition temperatures in excess of 900 °C and hexagonal boron nitride which only conducts heat laterally. Growth of crystalline aluminum nitride on non-lattice matched substrates is possible using bias-enhanced atomic layer annealing, in which a plasma treatment step with controlled ion energy follows each cycle of traditional atomic layer deposition precursor dosing. Tris(dimehtylamido) aluminum was used as the aluminum precursor to minimize carbon contamination, and anhydrous hydrazine was used to prevent oxygen contamination. Plasma treatment with neon, krypton, and argon at substrate biases of -10V, -25V, and -40V were investigated. Varying the gas identity and substrate bias provides control over the momentum and kinetic energy of ions bombarding the surface, resulting in selective control over the crystalline orientation. Across all gas and bias combinations ion flux is held constant by adjusting the power applied to the plasma. In-situ x-ray photoelectron spectroscopy (XPS) is used to study the elemental composition of the samples. Films deposited with this technique routinely show carbon and oxygen content less than 3% by XPS. Ex-situ grazing-incidence X-ray diffraction (GI-XRD) and x-ray reflectivity (XRR) are used to analyze the crystallinity, thickness, and density of the deposited material. 40 nm thick films were deposited onto HF-etched Si(111) and SiC substrates. GI-XRD scans of each condition are shown in Figure 1. Atomic layer annealing on Si(111) substrates with neon plasma produced films with poor crystallinity and preferential (002) orientation. For these films, the AlN (002) peak position is shifted relative to the peak position in films treated with argon and krypton, indicating the deposition of strained films. This may be due to embedding of neon ions, causing relatively small crystallite sizes of 5 nm to 9 nm. Films deposited with krypton plasma treatment also showed preferential AlN (002) deposition, though crystallite sizes are large and range from 9 nm to 11 nm. Optimal crystallization occurred when using argon plasma treatment with a -25V substrate bias, producing a film with selective (200) orientation and an average crystallite size of 27 nm. This crystallinity resulting from this condition may be the result of enhancing the preferential (200) crystallinity afforded by the purely thermal atomic layer deposition of the same precursors. Accordingly, the impinging argon ions would have significant momentum to increase surface adatom mobility, but kinetic energy sufficiently low as to not change the preferential orientation.

Figure 1
Directly Visualized Mechanical Strain Distribution in Package Interconnect Using Digital Image Correlation
Authors: Lee Tae-Ik , Paik Kyung-Wook , Kim Taek-Soo
Published: December 2020

For advanced package interconnects, analyzing strain distribution within the complex three-dimensional structure is important in order to design a mechanically reliable system. Electronic packages frequently undergo various types of deformation including tension, compression, bending, and thermal treatments. Failures under these loading modes can be prevented with accurate information of distribution and degree of the mechanical strains. This information, however, is difficult to obtain using conventional methods due to the small-sized packages with complex internal structures. It is also uncertain to rely on predictive results from analytical solutions because it is hard to theoretically calculate the complex strain mechanics, especially for the heterogeneously integrated structures. Therefore, experimental methods have been recently demanded for direct evaluation of mechanical deformation in the package interconnects.

In this study, a novel method that visualizes and accurately measures the internal strain distribution in package interconnects is developed. This method is based on digital image correlation (DIC), which utilizes microscopic images of the internal structure. The DIC method is adopted by taking advantage of non-contact and full-field analysis capability. Images from both optical microscopy and scanning electron microscopy are utilized for the non-contact strain evaluation method for the micro-scale deformation analysis. In order to obtain clear image of the internal structure, mechanical polish is conducted to form cross-section. For image pattern tracking, micro/ nano sized particles are deposited onto the cross-section to serve as speckle pattern of the DIC analysis. After the specimen preparation, the digital images are obtained before and after a mechanical loading at a same position. The consecutive images are then compared to execute image tracking analysis to result in the microscopic deformation contour. The results can be fully adopted in prediction of failure site or failure modes by providing essential data such as weak spot or intensity of deformation. Using the quantitative strain information, predicting the failure cycle could be also possible based on mechanics of fatigue fracture.

We demonstrate that this method is effectively utilized for various package interconnects including printed circuit boards (PCBs), flexible chip packages, and through-hole stress analysis in a 3-D stacked structure. Bending strain analysis of flexible packages and composite substrates, thermal strain analysis of the PCB interconnects are shown as applications of the thermo-mechanical reliability evaluation method. We believe that this experimental method will enable to fully understand the internal stress-strain behavior of the advanced package interconnects and flexible devices that require high mechanical reliability for commercialization.
Study of Refining and Purification Processing of Gallium Metal As a Raw Materials for Compound Semiconductor
Authors: Yoon Jaesik , Yang Jaeyeol
Published: December 2020

Gallium is used in III-V compound semiconductors according to the development of the semiconductor industry, and increasingly requires high purity gallium metal, and the amount of use is also increasing. The rare earth metal, gallium, has low reserves, which makes it difficult to supply raw materials. Therefore, process waste containing gallium is used to secure raw materials.

In this study, high-purity gallium metal was fabricated from process wastes by electrolytic refining and Czochralski(CZ). The CZ device was operated in a clean room of 400 class or less for a high purity environment, and the source crucible was controlled with oxidation of metal using sodium hydroxide and mineral oil. Gallium has a low melting point of 303 K, so the seed portion was cooled to 260 K to make an ingot.

The impurity elements in the highly purified gallium metal of about 8N grade was quantitatively analyzed using a glow discharge mass spectrometer(GD-MS). In quantitative analysis using GD-MS, relative sensitivity factors(RSF) are used. For RSF of each element, a standard sample containing gallium as an impurity in an aluminum matrix was used. By analyzing the aluminum matrix CRM, quantitative analysis is possible for a total of 17 elements: Mg, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Ag, Cd, Sn, Pb, Bi, etc. Lastly, in the analysis of gallium crystallized using the CZ method, four of impurity elements were detected: Al, Si, Cr, and Fe, and all other elements were below the detection limit. In the quantitative analysis of impurities in the gallium metal, the total impurity element was 5.58 ppbw, and the final purity of gallium was about 99.9999994% (8N).
(Invited) Design Hybrid Nanocomposites As Electrode Materials for High Performance Na-Ion Batteries
Authors: Yu Yan
Published: December 2020

Sodium-ion batteries are of major importance, especially for large-scale energy storage devices, due to low cost and abundant source of sodium. As for the anode side, commercial graphite shows a limited capacity for sodium storage. Compared to graphite based intercalation, the electrode materials based on conversion and alloy have been identified as promising anode candidates for sodium storage due to high theoretical capacity. However, poor kinetics and large volume change result in a low reversible capacity and fast capacity decay.

In order to address the above problems, we have designed a series of carbon-based hybrid materials with hierarchical structures, such as carbon nanowire-encapsulated selenides, carbon nanosheet-supported sulfides, and mesoporous carbon-encapsulated phosphorus. These multi-scale and hierarchically organized structures construct a highly efficient and stable mixed conductive network around the nano-active components. At the same time, they can keep the electrode integrity on cycling. These lead to excellent electrochemical performance.
(Invited) Complex Phase Transitions in Layered Sodium Transition Metal Oxides
Authors: Kim Jae Chul , Kwon Deok-Hwang , Yang Julia , Ceder Gerbrand
Published: December 2020

As an alternative to Li-based technologies to develop stationary energy storage systems, Na-ion batteries have attracted substantial interest. Unlike the Li-ion, layered sodium transition metal oxide (NaTMO2) cathodes can diversify their redox centers from expensive Co to cheap Mn and Fe to achieve high energy density, offering a wide variety of chemistry selection to design low-cost, high-performance batteries.1 These cathode materials often undergo discontinuous, yet reversible, phase transitions upon Na intercalation due to complex interatomic interactions, which result in multiple plateau-like features in their voltage profiles. However, large desodiation of Fe-containing Na-ion cathodes often leads to an unclarified, irreversible phase transition at high voltage, hindering the full use of Fe redox.2

In this talk, we will discuss how transition metal selection affects the thermodynamic stability of desodiated structures of NaTMO2. First, we demonstrate this insight by comparing two prototypical compositions, NaNi0.5Co0.5O2 and NaNi0.5Fe0.5O2, with detailed experimental and computational investigation.3 The Na intercalation processes of the two compounds are carefully investigated by electrochemical methods and in situ X-ray diffraction. We confirm that although the two materials share the same Ni3+/Ni4+ redox, their structural changes are very different from each other. Na
x
Ni0.5Co0.5O2 goes through multiple phase transitions including three different O3-type and three different P3-type structures. In contrast, Na
x
Ni0.5Fe0.5O2 only undergoes a generic O3-P3 transition with no sign of monoclinicity, leading to a smoothly increasing voltage profile. Second, our recent findings on a quaternary transition metal system, NaTi0.25Fe0.25Co0.25Ni0.25O2,4 will be underlined. We will present structural evidence and characterization of the highly-desodiated, high-voltage phase that exhibits peculiar oxygen stacking. This phase consists of alternating octahedral and prismatic Na layers, namely OP2 stacking, in which formation is afforded by distortion-tolerant Ti and Jahn-Teller-active Fe. Moreover, we will demonstrate that this new phase participates in redox reaction reversibly, fundamentally distinct from inactive high-voltage phases in many Na-ion cathodes. Finally, a strategy to stabilize Fe-containing NaTMO2 materials to create layered cathodes with high reversible Na capacity will be briefly discussed. Our results demonstrate that we can manipulate the redox reaction and associated structure change by transition metal mixing.

References

Yabuuchi, K. Kubota, M. Dahbi, and S. Komaba, Chem. Rev., 2014, 114, 11636−11682

Jeong, H. Lee, J. Yoon, and W.-S. Yoon, J. Power Sources, 2019, 439, 227064

Vassilaras, D.-H. Kwon, S. T. Dacek, T. Shi, D. -H. Seo, G. Ceder, and J. C. Kim, J. Mater. Chem. A, 2017, 5, 4596–4606

Vassilaras, S. T. Dacek, H. Kim, T. T. Fister, S. Kim, G. Ceder, and J. C. Kim, J. Electrochem. Soc., 164, 2017, A3484–A3486
(Invited) Challenges of Today for Na Based Batteries of the Future
Authors: Casas-Cabanas Montserrat
Published: December 2020

The global rise of Li-ion battery (LIB) production is linked with a number of challenges. From one side, the growing risks of demand-supply mismatch and supply constraints of the raw materials. From the other, environmental and social challenges linked with the mass production of LIBs become increasingly important as the market expands. Indeed, LIBs contain a number of critical raw (and/or toxic) materials, such as cobalt and natural graphite, whose suppliers concentrate in a number of third countries, including conflict zones. Within this scenario, Na-based batteries are rising as potential alternative technology to Li-ion batteries, as the combination of attractive properties potentially NIBs offer (i.e., low cost, sustainable precursors and secure raw material supplies), fill a niche and could represent an important step forward towards beyond Li technologies in certain applications where energy density is less critical.

Na-ion chemistry suffers however from some intrinsic drawbacks compared to Li-ion (heavier and larger alkali ion, 0.33V larger standard potential) which tend to lower cell voltage and capacity. Nevertheless, with ongoing development, materials available for Na-ion cells should allow approaching the energy density of the present generation of Li-ion commercial cells.

In this talk, the potential of Na-ion batteries will be thoroughly analyzed and our recent research regarding positive and negative electrode materials will be reviewed. Results related to several phosphate-based families of cathode materials will be shown, together with the challenges of developing competitive anode materials. Finally, a high-throughput screening approach capable of quickly revealing the possible existence of good ionic conductor materials in the huge structural and compositional space of existing explored databases will be discussed.
(Invited) SiC and GaN High Aspect Ratio Nanostructures By Plasma-Free Photo-Assisted Inverse-Macetch
Authors: Michaels Julian , Chan Clarence , Li Xiuling
Published: December 2020

Etching wide bandgap semiconductors including SiC and GaN, has been challenging. Achieving damage-free device quality high aspect ratio nanostructures is even more difficult. Currently, to produce SiC or high aspect ratio structures, ICP-RIE is generally used, which often results in high energy ion induced damages.

Metal-assisted chemical etching (MacEtch) defies the isotropic nature of chemical etch by utilizing a patterned metal catalyst for spatially defined etching of semiconductors. MacEtch has been successfully demonstrated for various types of semiconductors, including Si, GaAs, InGaAs, AlGaAs, InP, InGaP, GaN, b-Ga2O3, SiC. The metal catalyst type that has been proven to be effective include Au, Pt, Ir, Ru, TiN, CNTs, and graphene. Aspect ratios produced using MacEtch can readily exceed 100:1 in some cases, while limited in other cases. The resulted tapering and porosity are strong function of the etch kinetics for the particular semiconductor material, metal catalyst type and pattern, and etchant condition. The loading effect is determined by the local carrier generation rate and mass transport rate. Depending on how the etching evolves relative to the catalyst pattern and additional assistance, we classify MacEtch into forward, inverse (i-MacEtch), magnetic-fielded guided (h-MacEtch), self-anchored-catalyst (SAC-MacEtch), vapor phase (VP-MacEtch), and UV assisted (UV-MacEtch).

In this work, we report the successful demonstration of SiC and GaN nanostructures with various sidewall morphologies using UV-assisted i-MacEtch. Produced structures are characterized as a function of etch conditions by SEM, 3D profilometer, AFM, reflection and Raman spectroscopy, as well as the interface properties using Schottky barrier diodes and MOSCAP structures. This work lays the foundation for producing 3D wide bandgap device structures with damage-free pristine surfaces and interfaces, as well as controlled defect engineering for quantum states.
Electrical Characterization of Gallium Nitride Thin Films Synthesized By Electrochemical Deposition
Authors: Ali Abdulraoof Idriss Ahmed , Nel Jacqueline , Meyer Walter
Published: December 2020

Group III-nitride semiconductor materials show promise in a variety of electronics applications, including diodes, transistors, LEDs and photovoltaic applications. The new generation of semiconductors rely heavily on nanotechnology and advances in nanomaterials. Group III-nitride semiconductor materials such as GaN, AlN and InN are promising materials since their properties are ideal for use in optoelectronic devices, high power and high temperature electronic devices. These materials have wide band gaps between 1.9 and 6.3 eV and, for electronic applications, these materials are usually synthesised by means of chemical vapour deposition or molecular beam epitaxy. These techniques are expensive, therefore we investigated room temperature electrochemical growth to synthesize GaN. The advantages of electrochemical deposition are the controllability of the thickness and surface morphology by varying the deposition parameters, cost-effectiveness, the minimum waste generation, long bath lifetime and easy set-up. In this study, room temperature electrochemical deposition has been used to synthesise GaN nitride on Si substrate.

Results:

The XRD spectrum of GaN thin films grown under the different conditions are shown in Figure 1. Sample a (1 mA/cm2 for 30 min) and b(3 mA/cm2 for 30 min) were prepared at room temperature. The XRD analysis showed the presence of hexagonal and cubic structure with crystallite sizes calculated from Scherer’s formula were 130 and 140 nm From SEM images, however, the results varied with growth condition. Good quality Schottky diodes were fabricated on the GaN thin films and DLTS measurements were performed. Electron traps with an activation energy of 0.48 and 0.47 eV, were observed in sample a and b, respectively.

Figure 1
Photo-Electrochemical Etch of Beta-Phase Gallium Oxide and Its Optoelectronic Applications
Authors: Choi Yong ha , Lee Suk Joong , Kim Jihyun
Published: December 2020

The chemical etch of a beta-phase gallium oxide semiconductor is difficult because it has high chemical robustness. Since a chemical etch has many merits over a dry etch, we will present the photoelectrochemical (PEC) etching of beta-phase gallium oxide when electrical potential and etch temperature are changed. In our experiments, the etch pit probably initiated at the intrinsic defect sites progressed along the [001] with a low activation energy. The PEC etching rate was estimated to be 0.7 μm/min in the [001] direction at a bias of 20 V. The facet exposed by PEC etching in phosphoric acid was considered to be (−201). The optoelectronic performances, including the responsivity and response/decay characteristics, were significantly improved. More results will be presented at the ECS meeting.
Characterization of Hazy Morphology on AlInP/GaAs Epitaxial Wafers Grown by Organometallic Vapor Phase Epitaxy
Authors: Peng Hongyu , Ailihumaer Tuerxun , Liu Yafei , Raghothamachar Balaji , Dudley Michael
Published: December 2020

6-inch AlInP/GaAs epitaxial wafers grown by organometallic vapor phase epitaxy (OMVPE) technique are being developed for light emitting diodes (LEDs) applications [1]. Recently, dislocation configurations in the GaAs substrates and AlInP epilayers have been characterized and conditions for relaxation and formation of misfit dislocations were analyzed [2,3]. Apart from defects such as dislocations, epilayer surface reveals a hazy morphology formed when the epitaxial growth pressure is increased. It is observed that the epilayer surface is rougher compared to regular clear regions as revealed by both optical microscopy and atomic force microscopy. Additionally, the size of the hazy regions increases with growth pressure but other growth parameters such as growth temperature, V/III ratio, likely influence the onset of hazy morphology. Previous research on the formation of hazy features reports that these can be caused by the deficiency of phosphorus [4], lowered V/III ratio [5] or stacking faults [6]. However, the hazy features in our case, are different from the ones reported. Synchrotron X-ray topographs of the hazy regions showed blurred contrast, indicating disordered lattice arrangement. Moreover, internal structure of the hazy regions was studied by reciprocal space mapping (RSM), where weakened and broadened peaks around the clear epilayer peak were observed using 004 reflection, indicating continuously varying strain and tilt between the hazy region and the clear region. The thickness of the hazy regions was also analyzed by employing the 002 RSM, where the X-ray penetration depth is lower. Comparison of the 002 and 004 RSMs reveals that at the beginning of epitaxial growth, the epilayers do not suffer from lattice distortion and the formation of the hazy morphology occurs when a critical thickness is exceeded.

Reference:

[1] C. H. Chen, S. A. Stockman, M. J. Peanasky, C. P. Kuo. Brightness Light Emitting Diodes Semiconductors and Semimetals, SEMICONDUCT SEMIMET, 48 (1997) pp. 97–144

[2] Hongyu Peng, Tuerxun Ailihumaer, Yafei Liu, Balaji Raghothamachar and Michael Dudley, J. Cryst. Growth, 533 (2020) 125458

[3] Hongyu Peng, Tuerxun Ailihumaer, Balaji Raghothamachar and Michael Dudley, J. Electron. Mater. 49, 3472–3480 (2020)

[4] H. H. Ryu, M. H. Jeon, J. Y. Leem, H. J. Song, L. P. Sadwick, G. B. Stringfellow, J Mater Sci (2006) 41:8265–8270

[5] D. S. Cao and G. B. Stringfellow, Journal of Electronic Materials, Vol. 20, No. 1, 1991

[6] Yoshihiro Hiraya, Fumiya Ishizaka, Katsuhiro Tomioka and Takashi Fukui, Applied Physics Express 9, 035502 (2016)

Figure 1
Rapid Annealing of Perovskite Solar Cells through Intense Pulsed Light
Authors: Druffel Thad
Published: December 2020

The perovskite solar technology has managed a fair amount of excitement since it was first introduced nearly ten years ago by Miyasaka’s group. The efficiency of small devices has increased rapidly from the 3.8% reported by Miyasaka to well over 20%. The efficiency now stands near that of the market dom,inated crystalline silicon solar cell, and the durability has been demonstrated for upwards of 1,000 hours. The organo-metal halide perovskite that is the core layer of the perovskite solar cell can be deposited using simple solution phase processes at low temperatures. The materials tend to have very high defect tolerances and hence have long excited charge carrier lifetimes. The excitement in the research and manufacturing communities’ centers around the simplicity of the device fabrication. Other layers within the stack also lead to simple solution phase deposition and low temperature processing.

The deposition of the perovskite material generally involves a precursor chemistry that undergoes evaporation and crystallization. The crystallization typically involves thermal energy often at temperatures less than 100 oC. The activation energy of the organo-metal halide perovskite crystallization is very low especially when compared to that of amorphous silicon. Thus annealing is typically accomplished using low temperatures conduction (hot plates); however, several studies using radiative processes inducing much higher temperatures have also been established.

These radiative processes include the intense pulsed light process (IPL). The IPL process involves the absorption of light energy into a thin film from an intense rapid pulse with a broad spectrum that can cover large areas. A thin film with absorptivity within the spectrum of light will absorb the energy, which is then rapidly transformed into thermal energy. The technology has been utilized in processing polymers, metals, metal oxides and semiconductors since the 1970’s and was recently reviewed specifically for materials in the photovoltaic technologies. The advantage of this technique for plastic substrates is that it can initiate very high temperatures within a thin film without damage to the underlying substrate.

In this work we will describe the intense pulsed light process as it relates to the annealing of perovskite solar cells on plastic substrates on a roll-to-roll manufacturing line. The work will include the description of careful control of the IPL process parameters and the impact on the crystallization of the perovskite layer. The talk will concentrate on the tuning the IPL parameters to fit into high speed roll-to-roll applications. The films are characterized using UV-Vis spectroscopy, x-ray diffraction and scanning electron microscopy. Finally, devices built on the roll-to-roll platform will be discussed.
(Invited) Fabrication and Analysis of Fully-Printable Multi-Porous-Electrode-Layered Perovskite Solar Cells
Authors: Itou Seigo
Published: December 2020

Lead-halide perovskite solar cells have received significant research interest; however, thermal stability issue still remains. Carbon-based triple-porous-layer perovskite solar cells without any hole transporting material were selected in order to investigate the internal degradation process by thermal stresses. The sealed perovskite solar cells at 100 °C showed stable performance in the power conversion efficiency up to 4500 h, but the degradation was accelerated after that. By analyzing the perovskite solar cells aged for 7000h at 100°C, the results of energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy suggest that, although Pb, I, and N were sealed inside of the devices, a plenty amount of CH3NH3
+ deactivated in the sealant UV-curable adhesive at 100 °C, which is the reason of the thermal degradation for the sealed perovskite solar cells.
Charge Transfer Kinetics in the Dark at Oxide Semiconductor/ electrolyte Interfaces
Authors: Firouzan Farinaz , Vali Abbas , Rajeshwar Krishnan
Published: December 2020

Among all the requisite properties of an inorganic semiconductor, the dynamics of interfacial charge transfer is an important common denominator for numerous technologically important applications such as PEC water splitting, photocatalytic pollutant degradation, or photovoltaic solar energy conversion.Most attention in this regard has been paid to the dynamics of minority carrier transfer; only sporadic studies have focused on majority carrier transfer across the solid/electrolyte interface. However, recent studies have underlined the growing realization that the charge transfer kinetics of both minority and majority carriers are often coupled. Performance optimization of the interfaces must address both these charge transfer pathways such that deleterious carrier recombination can be minimized. Therefore, this study addresses the fundamental and experimental understanding of interfacial charge transfer dynamics at semiconductor/electrolyte interfaces
in the dark
. A variety of interfaces were studied to gain a unified and self-consistent picture.

Firstly, binary n-type TiO2 and WO3 semiconductors were chosen because of their excellent chemical/photoelectrochemical (PEC) stability, high PEC activity, and overall robustness over a wide pH range. Secondly, binary and ternary p-type semiconductors such as copper bismuth oxide (CuBi2O4),silver vanadate (AgVO3),and copper (II) oxide (CuO) were selected to compare their charge transfer kinetics in the dark. Such comparative studies are conspicuously absent in the literature, and in particular, dark current-forward bias potential measurements are lacking for these compounds. Tafel analyses were used to evaluate the standard rate constant, k
0 and the exchange current density, jo

in all these cases.

Based on these kinetics data, a general conclusion could be made that p-type oxide semiconductors exhibited faster kinetics than their n-type counterparts. For comparison, Pt and fluorine doped tin oxide (FTO) electrodes were included as benchmarks in these experiments. The data also indicated that heterogeneous charge transfer at metal/electrolyte interfaces had faster kinetics compared to the semiconductor/electrolyte interfaces. This contrasting and self-consistent behavior stems from surface state density variations in the two sets of cases. The practical implications of these data are finally discussed.
Minimization of Optical Losses in Colorful Semitransparent Organic Solar Cells Using Antimony Oxide Cavity-Based Fabry-Pérot Etalon Electrodes
Authors: Yeom Hye Rim , Song Seyeong , Park Song Yi , Woo Han Young , Kim Jin Young
Published: December 2020

Semitransparent organic solar cells (STOSCs) are a technology that combines the benefits of visible light transparency and light-to-electrical energy conversion. One of the greatest opportunities for STOSCs is their integration into windows and skylights in energy-sustainable buildings. For this application, the aesthetic aspects of solar cells may be as important as their electrical performance. Here, our strategy enables to achieve high-quality and colorful STOSCs using Fabry-Pérot etalon-type electrodes. These electrodes are composed of an antimony oxide (Sb2O3) cavity layer and two thin Ag mirrors. These dichroic tri-layer structures perform two functions as top conducting electrodes and color filters. The electrodes are fabricated by thermal evaporation of smooth sheets of Ag and metal oxide thin films, with appropriate thicknesses calculated by the transfer matrix methodology. In this manner, dichroic electrodes with a high spectral purity were achieved with transmission wavelengths that could be accurately tuned throughout the visible spectrum by varying the Sb2O3 cavity thickness. These dual-function electrodes were applied to photovoltaic devices and displayed vivid colors, natural transparency, and good performance as compared to devices that use conventional metal electrodes. Furthermore, to achieve saturated colors and low photocurrent losses, active layer materials were selected such that their transmission peaks matched the transmission maxima of the electrodes. These strategies for colorful STOSCs resulted in power conversion efficiencies (PCEs) of up to 12.1% and maximum transmittances (T
MAX) of 22.5% in blue devices, PCEs of up to 9.71% and T
MAX of 35.4% in green devices, and PCEs of up to 7.63% and T
MAX of 34.7% in red devices.
Development of Transparent and High-Voltage Electrolyte Using Binary Redox Couples for Dye-Sensitized Solar Cells
Authors: Yoo Kicheon , Kang Hyeong Cheol , Nath Narayan Chandra Deb , Lee Jung Jae , Lee Jae-Joon
Published: December 2020

The conventional iodine-based electrolytes of DSSCs has several limitations such as ~30% absorption of visible light in the range of 300 to 500 nm wavelength by itself and large potential difference between the Fermi level of I−/I3− and the HOMO level of dye, which creates negative impact on both transparent and high-voltage DSSCs. In this work, a series of transparent electrolytes are prepared with the variation of additives of I2, LiI, GuSCN (guanidine thiocyanate)/GuNO3 and Br2 for high transparent and high voltage DSSCs. From the results of this study, it is found that the use of optimized electrolyte with binary redox couples (I, Br)/(I3,I2Br) (instead of single I/I3 couple), 0.003 M Br2, 0.01 M LiI, and 0.1 M GuNO3 contributes to increase the transmittance of ~25% compared with the conventional electrolyte as the content of I3 decreased significantly in binary redox system. Furthermore, the downward shifting in Fermi level of the binary redox system induces the enhancement of the open circuit voltage (Voc) of the cell by ca. 120 mV compared with the conventional electrolyte. The devices with the optimized binary redox system achieved a high efficiency of ~ 6.22 % with a least sacrifice compared with the conventional one. It indicates that the present study could play an essential role to fabricate high voltage and transparent DSSCs for the application of see-through photovoltaic windows.
A Plasmonic Platform for Upconversion Luminescence Enhancement
Authors: Shin Jae-Min , Ahn In-Hwan , Ko Doo-Hyun
Published: December 2020

The approach to adapt upconversion nanoparticles to plasmonic structures has been studied to improve their inherent low quantum efficiency. However, the metal-based plasmonic structures have limits in extending their applications since they are rigid and opaque. In this study, we demonstrate a plasmonic film composed of an array of microbeads, which provides transferability and flexibility as well as distinctive upconversion luminescence enhancement. Our proposed structure comprises plasmonic silver nanoparticle-decorated silica microbeads on the dielectric-metal substrate, thereby providing remarkable improvements in absorption efficiency of near-infrared (NIR) light, and emission of visible (Vis) light via resonance mode excitation. As a result, the observed upconversion luminescence intensity exhibited three-order enhancement compared to reference under low power excitation. In addition, transparency and wide viewing angle property of emitted light for our film further extend its applicability for various fields such as absorption enhancement of photovotaics through visible light conversion in NIR and attachable NIR detection film.
(Invited) Reliability of Ultra Nano-sheet InWO Thin Film Transistor for Back-end of Line Applications
Authors: Liu Po-Tsun , Li Zhen-Hao , Kuo Po-Yi , Lin Yi-Syuan , Tien Chung-Hao
Published: December 2020

The amorphous indium-tungsten oxide (a-IWO) ultra nano-sheet (UNS) thin-film transistor (TFT) has been developed successfully and exhibited high device performance. It is also suitable for the back end of line (BEOL) technologies due to its superior electrical characteristic and low operation voltage[1, 2]. In this work, we study the reliability of TFT with nano-sheet IWO as channel layer for BEOL applications. The backchannel passivation with an organic layer was proposed to effectively isolate the humidity in the atmosphere. Experimental results have shown that the a-IWO nano-sheet TFT can exhibit the great potential and excellent reliability for BEOL IC applications.

Experiment

The bottom gate structure was used. A Mo films was deposited by DC sputter as gate electrode. Then, a layer of HfO2 film was deposited through the atomic layer deposition (ALD). Next, the 4nm-thick nano-sheet a-IWO thin film was deposition as the channel layer by RF sputter. The Mo source/drain contacts were deposited by DC sputter. Finally, the organic passivation layer covered on the device with spin coating method. The conditions of thermal annealing process were studied for the optimization of the interface quality between IWO nano-sheet backchannel and organic passivation layer.

Result and discussion

The amorphous oxide semiconductor (AOS) channel layer is easily affected by the atmosphere from the environments, like oxygen and moisture causing the electrical degradation [3, 4]. Therefore, the passivation effectively avoids the degradation of device features under positive bias thermal stress (PBTS) measurement, as shown in Fig. 1. The passivation layer can effectively improve the TFT device reliability and reduce the positive shift of threshold voltage.

Reference

[1] P. Y. Kuo, C. M. Chang, and P. T. Liu, pp. 21-22.

[2] P. Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019.

[3] J. Yao, N. Xu, S. Deng, J. Chen, J. She, H. P. D. Shieh, P. T. Liu, and Y. P. Huang, IEEE Transactions on Electron Devices, vol. 58, no. 4, pp. 1121-1126, 2011.

[4] P. T. Liu, Y. T. Chou, and L. F. Teng, Applied Physics Letters, vol. 95, no. 23, pp. 233504, 2009.

Figure 1
Low-Temperature Processed Metal-Semiconductor Field-Effect Transistor with In–Ga–Zn–O Channel Deposited by Ar+O2+H2 Sputtering
Authors: Magari Yusaku , Furuta Mamoru
Published: December 2020

We developed low-temperature (150 °C) processed top-gate and coplanar metal-semiconductor field-effect transistors (MES-FETs) with a stacked In–Ga–Zn–O (IGZO) channel consisting of a hydrogenated IGZO (IGZO:H) on conventional IGZO (IGZO). The IGZO and IGZO:H films were prepared by Ar+O2 and Ar+O2+H2 sputtering, respectively. By applying an IGZO:H on IGZO (IGZO:H/IGZO) stacked channel, the on-current of the MES-FET significantly increased while maintaining a low off-current. An on-off current ratio of 4.2×108, a turn-on voltage of -5.9 V and a subthreshold swing of 155 mV/decade were achieved by the IGZO:H/IGZO = 25/25 nm stacked channel. The carrier concentration of the IGZO:H/IGZO stacked film dramatically increased to 1.4×1019 cm-3 by stacking the IGZO:H (4.4×1017 cm-3) film on the IGZO (7.6×1017 cm-3) film. It was suggested that diffused hydrogens from IGZO:H to IGZO enhanced carrier concentration in the IGZO near the IGZO:H/IGZO interface, which acts as a pseud two dimensional electron gas. Moreover, a potential barrier was formed at the IGZO:H/IGZO interface, which could have helped to maintain the low off-current of the MES-FETs. Therefore, the IGZO:H/IGZO stacked channel plays an important role in improving the performance of the MES-FETs.