bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Modified Activated Carbons Prepared from Orange Peel Waste As Potential Electrodes for Li-Ion Capacitors
Authors: Arie Arenst Andreas , Lee Joong-Kee , Halim Martin , Kristianto Hans
Published: February 2020

In this work, orange peel waste was used as the precursor for activated carbon-based electrodes for Li-Ion Capacitors. Initially, activated carbons were  prepared by chemical activation process using ZnCl2.  The surface of the activated carbon was then modified  with the oxidative chemical agents (H2SO4,  HNO3,  H2O2 and KOH solutions). The morphology, surface chemical composition, and surface area of the surface modified carbon materials were studied by scanning electron microscope, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller measurement, respectively. Electrochemical characteristics of the as-prepared sample were investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements.  Experimental results showed that the surface modification had a very significant effect on the improvement of electrochemical characteristics of activated carbon as electrodes in supercapacitors. The good electrochemical performance of the activated carbon was attributed to well-developed micropores, high surface area, the presence of   oxygen functional groups, and larger pore volume.The results indicate that orange peel waste can potentially be applied as a raw material for the production of low cost activated carbon electrode materials for Li-Ion Capacitors.
Cobalt Nanoparticles Embedded in Porous Carbon Nanofibers As Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions
Authors: Singhal Richa , Kalra Vibha
Published: February 2020

Increasing demand for clean and sustainable energy has accelerated research on alternative energy production and storage systems with high efficiency, low cost, and environmental benignity. Various renewable energy technologies such as fuel cells, metal-air batteries, and water splitting require efficient catalysts for oxygen reduction and evolution reactions. In the past, various precious (expensive) and non-precious metal catalysts have been studied as efficient ORR or OER catalysts, while only a few studies have reported bifunctional catalysts for both ORR and OER. Hence, it is highly challenging and desirable to develop low cost and bifunctional catalyst with high ORR and OER activity.

In the present study, cobalt nanoparticles embedded in porous carbon nanofibers have been reported as an efficient bifunctional electrocatalyst for both ORR and OER in alkaline medium. The polymer solution consisting of polyacrylonitrile (as carbon precursor), Nafion (as sacrificial polymer) and cobalt carbonate (as cobalt precursor) in DMF was electrospun to form nanofibers. During pyrolysis to 1000 °C in inert atmosphere, Nafion decomposes out to form porous carbon nanofibers, while cobalt carbonate reduces to cobalt oxide. Cobalt oxide is further reduced to cobalt by reduction in hydrogen at 500 °C. Thus, a stable, synergistic catalyst combining the high ORR activity of porous carbon nanofibers and the excellent OER activity of cobalt nanoparticles is obtained. The electrochemical tests on the fabricated materials were carried out using a rotating disc electrode setup. It was found that the hybrid catalyst exhibits comparable ORR activity to a commercial carbon-supported precious Pt catalyst (20wt% on Vulcan carbon) and improved OER activity than 20wt%Ir/C and 20wt% Ru/C in alkaline solutions. Such a high activity is attributed to the uniform distribution of cobalt nanoparticles within the porous carbon nanofiber matrix providing high surface area and efficient charge transfer ability.

Fig. 1. Comparison of ORR and OER activities of cobalt-porous carbon nanofibers (Co-PCNFs) with that of commercial Pt/C.  

*Singhal, R. and Kalra, V. Electrospun porous carbon nanofibers embedded with cobalt nanoparticles as an excellent bifunctional electrocatalyst for oxygen reduction and evolution reactions, to be submitted.

Figure 1
A Spatially Resolved PEM Fuel Cell Catalyst Degradation Study Under Automotive Load Cycle for Durability Prediction
Authors: Mayur Manik , Quinaud Manuelle , Bessler Wolfgang G.
Published: February 2020

One of the limiting bottlenecks of polymer electrolyte membrane fuel cell (PEMFC) technology to create a breakthrough in cost-effectiveness and lifetime in automotive applications is the highly load-sensitive degradation of cell components. Most of the cell performance evaluation on the single cell or system level provides only an averaged insight into cell voltage and current values, and does not reveal the spatial behavior of the cell state variables. Since, the reported cell failure cases in the literature show highly localized cell component degradation, an averaged analysis will not be able to provide a thorough insight in the causes of the cell failure, nor to propose mitigation strategies. The spatial distribution of reactants concentration and pressure gradients in the flow field leads to a spatially varying cell operating behavior. This creates specific zones of variable performance in the membrane electrode assembly (MEA). Hence, one can observe the redistribution of the local current density, leading to uneven reactant utilization, reduced overall efficiency, and localized accelerated degradation [1,2].

In this study, with the help of a 2D multiphysics model [3] of a single cell, we can not only have a high spatio-temporal resolution of the fuel cell state variables, but also a detailed insight in the spatial degradation of cell component properties. In particular, we study the loss of electro-chemical active surface area (ECSA) based on an electrochemical degradation reaction mechanisms. The degradation is quantified spatially resolved along the flow length. Using an in-house system model of a car, we expose the fuel cell model to a highly transient loading cycle (New European Driving Cycle). Using a time-upscaling methodology, we present a predictive analysis of cell end-of-life under different operating conditions.

References:

1.    C. Robin, M. Gerard, A. A. Franco, and P. Schott, “Multi-scale coupling between two dynamical models for PEMFC aging prediction,” International Journal of Hydrogen Energy 38, 4675–4688 (2013).

2.    J. Dillet, D. Spernjak, A. Lamibrac, G. Maranzana, R. Mukundan, J. Fairweather, S. Didierjean, R. L. Borup, and O. Lottin, “Impact of flow rates and electrode specifications on degradations during repeated startups and shutdowns in polymer-electrolyte membrane fuel cells,” Journal of Power Sources 250, 68–79 (2014).

3.    C. Bao and W. G. Bessler, “Two-dimensional modeling of a polymer electrolyte membrane fuel cell with long flow channel. Part I. Model development,” Journal of Power Sources 275, 922–934 (2015).
Carbon-Supported Metal Oxide Nanoparticles As Electrocatalysts for the Oxygen Reduction Reaction in Li-O2 Batteries
Authors: Chen Jenn-Shing , Yang Hong-Kai , Chin Chih-Chun
Published: February 2020

Oxygen reduction reactions (ORR) at the O2 cathode in nonaqueous electrolytes are known to influence the performance of Li-O2 batteries. In this work, we created two ordered mesoporous MnOx/C and TiO2/C composites by a simple hydrothermal process. The composites were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, small angle X-ray scattering, BET measurements, galvanostatic charge-discharge methods. Their ORR kinetics and mechanism have been investigated in Li-O2 batteries by using the rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) measurements. The electrochemical tests indicate that the MnO2/C composites have excellent catalytic activity towards ORR due to the larger surface area of order mesoporous carbon and higher catalytic activity of MnO2.
Investigating Failure of Li-Ion Batteries Using in Operando Electrochemical-Acoustic Time-of-Flight Analysis
Authors: Hsieh Andrew , Bhadra Shoham , Gjeltema Peter J , Steingart Daniel A
Published: February 2020

Electrochemical-Acoustic Time-of-Flight (EAToF) analysis takes advantage of the fact that in all closed electrochemical energy storage systems, regardless of the reaction mechanism (intercalation, dissolution/reprecipitation, phase change, etc.) the density and elastic modulus of each electrode changes as a function of its state of charge (SOC). This, in turn, affects how sound waves behave as they travel through the cell. Additionally, as a battery is cycled, progressive formation/degradation of critical surface layers, mechanical degradation of electrodes, consumption of electrolyte, etc. also affect the behavior of acoustic waves passing through the cell. Thus, the distributions of density and modulus within the cell as well as the rates of change of these distributions (and the resulting effect on the acoustic echoing behavior) can act as a fingerprint for the state of health (SOH) of the cell. In a previous study, we have demonstrated this in operando EAToF analysis experimentally using ultrasonic pulses during normal cycling of a wide variety of battery chemistries and form factors.

Here, we focus on the effect of long-term cycling on the electrochemical-acoustic fingerprints, particularly for commercially-available Li-ion 18650 type cells. We examine how the EAToF patterns evolve as a function of depth of discharge and cycling rate, and also investigate the effect of “abusive” cycling conditions (e.g., elevated temperatures, over-charge/discharge, etc. as prescribed by UN 38.3 and IEC 62133 standards) on acoustic behavior. Two failure modes that we study in detail are electrolyte consumption and lithium plating in Li-ion batteries, and we verify failure modes with post-mortem analysis. Our results show that the fingerprints from EAToF analysis, perhaps in combination with various numerical analysis methods, can be correlated not only to SOC during normal cycling, but also to SOH during extended cycling and catastrophic failure events.
Side-Chain Conducting and Phase-Separated Polymeric Binders for High Performance Silicon Anodes in Lithium-Ion Batteries
Authors: Zhao Hui , Park Sang-Jae , Ai Guo , Yang Wanli , Wang Cheng , Liu Gao
Published: February 2020

Here we describe a class of electric-conducting polymers that conduct electrons via the side chain π–π stacking. These polymers can be designed and synthesized with different chemical moieties to perform different functions, extremely suitable as a conductive polymer binder for lithium battery electrodes. A class of methacrylate polymers based on a polycyclic aromatic hydrocarbon side moiety, pyrene, was synthesized and applied as an electrode binder to fabricate a silicon (Si) electrode. The electron mobilities for PPy and PPyE are characterized as 1.9 × 10–4 and 8.5 × 10–4 cm2 V–1 s–1, respectively. These electric conductive polymeric binders can maintain the electrode mechanical integrity and Si interface stability over a thousand cycles of charge and discharge. The as-assembled batteries exhibit a high capacity and excellent rate performance due to the self-assembled solid-state nanostructures of the conductive polymer binders. These pyrene-based methacrylate binders also enhance the stability of the solid electrolyte interphase (SEI) of a Si electrode over long-term cycling. The physical properties of this polymer are further tailored by incorporating ethylene oxide moieties at the side chains to enhance the adhesion and adjust swelling to improve the stability of the high loading Si electrode.

Figure 1
Inhibition Performance Study of Aqueous Vanadate Species on Mg Alloys
Authors: Li Jichao , Hurley Belinda , Buchheit R.
Published: February 2020

This work presents the corrosion inhibition performance of vanadate on Mg alloy AZ31 and its dependence on pH and immersion time. Aqueous vanadate speciation, which has been shown to have a strong effect on corrosion inhibition, is a function of solution pH.  The pH dependence of vanadate corrosion inhibition is, therefore, attributed to the pH dependence of vanadate speciation. Immersion in tetrahedrally coordinated vanadate species, present in neutral and alkaline solution, was shown to decrease corrosion rate and increase pitting potential, both of which were enhanced with longer immersion times. Alternatively, exposure to octahedrally coordinated vanadate, which predominates in acidic solution, only slightly decreased the corrosion rate. An acidic solution (octahedrally coordinated speciation) was adjusted to alkaline conditions and samples were then immersed in the adjusted alkaline solution.  Inhibition on these samples was weaker than that of samples immersed in alkaline solutions that had never been acidic.  Regardless of speciation, vanadate was shown to provide limited inhibition on cathodic reaction kinetics (hydrogen reduction reaction).  Anodic inhibition was observed on samples treated in solutions containing tetrahedral species.  Inhibition performance was also characterized by electrochemical impedance spectroscopy. Aqueous vanadate in 0.1 M NaCl increased the total impedance at all pH values (5, 7.7, 9.2), with enhanced results observed with increasing immersion time. The greatest increase in impedance for a given immersion time occurred at pH 9.2, which is consistent with the inhibition determined by corrosion rate. SEM showed that vanadate forms a film across both secondary particles and the Mg matrix, and it provided qualitative evidence that inhibition efficiency increased as the pH of the exposure solution increased.  XPS results indicate that vanadate film formation is associated with the reductive adsorption of vanadate by Mg. Exposure at a pH of 5 produced vanadate predominated by V4+.  Exposure at pH values of 7.7 and higher, however, produced vanadate containing predominantly V3+.
in-Situ Critical Pitting Temperature on Duplex Stainless Steels
Authors: Garfias-Mesias Luis Francisco
Published: February 2020

The Critical Pitting Temperature (CPT) of 25Cr Duplex Stainless Steel (DSS) in chloride containing environments was obtained by using a mini-autoclave. The work presented here shows, for the first time, simultaneous In-situ micro-visualization and electrochemical monitoring of DSS. A real time video of the surface of the sample was recorded while electrochemical measurements were taken as the temperature was slowly increased to obtain the CPT. This methodology allowed the observation of metastable pitting, pit initiation and pit propagation in DSS.
Role of Confinement in Localized Corrosion
Authors: Puranik Rohit , Quesnel David J
Published: February 2020

In context of localized corrosion, the dissolution of metallic species into a bulk electrolyte solution will produce negligible changes in the concentration of a bulk solution (Refer Fig. 1a).  However, if the immediate environment is confined and has limited electrolyte with respect to the metal surface area - as would be the case for a crevice, environmentally assisted cracking, or a deep pit - the limited amount of dissolved species produced as a result of anodic dissolution would be adequate to change the chemical composition (i.e. concentration) of the confined solution as shown in Fig. 1a.  Should the change in chemical environment be adequately adverse, these primary reaction products will lead to secondary reactions within the confined space, thus accelerating corrosion damage.  This research explores the quantitative effect of confinement on chemical reactivity of metals susceptible to pitting and stress corrosion cracking (SCC).

    To investigate the effects of confinement, a simulated crevice was created by maintaining a tight spacing between the polished surface of  a flat pH probe and the metal test specimen, as shown in Fig. 1b.  The pH probe and the solution are held against the sample by an inert polyethylene fixture.  Sensitized AA5083 was chosen as the test material because of its susceptibility to SCC as a result of intergranular precipitates of Al2Mg3 known as β-phase.  The electrolyte was pH neutral 0.1 M sodium chloride solution.

    Exposing AA5083 to neutral-pH NaCl solution under confinement in free corrosion conditions triggered a spontaneous localized alkaline corrosion, which resulted in a gradual evolution of the pH from 6.9 to roughly 9. At this higher pH value, the passivation film was damaged and hydrogen evolution that promotes the increase in pH was observed as the counter-reaction to aluminum oxidation.  This research presents the effect of different ratios of metal surface area to electrolyte volume on the reaction kinetics, as characterized by the evolution of the solution pH with time. Surface area to volume ratios ranged from 4 cm2/ml to 100 cm2/ml.  The results are supported with microscopic analysis and EIS studies.

Figure 1
High Resolution in Situ Studies of Localized and Crevice Corrosion with Multiple Beam Interferometry and Atomic Force Microscopy
Authors: Shrestha Buddha Ratna , Bashir Asif , Ankah Genesis Ngwa , Renner Frank , Valtiner Markus
Published: February 2020

Crevice corrosion (CC) and localized corrosion of metals remains a serious concern for structural materials. Yet both, a real-time and in-situ visualization of (1) initiation of localized corrosion, and (2) corrosion within confined geometries, remains very challenging. In this contribution, we will discuss how multiple-beam interferometry (MBI) can be utilized to directly visualize corrosion processes in real-time and with Ångstrom resolution within well-defined confinement geometries[1]. Also, we will discuss how electrochemical AFM can be utilized to study localized phenomena such as dealloying on patterned surfaces[2]. We will particularly aim to discuss and describe techniques and electrochemical cells, that we recently developed and will discuss how they may become useful in the field of corrosion and localized corrosion.

With MBI, we can detect and track active sites of aluminum corrosion in NaCl solution within confined geometries[3]. We find that CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20-300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO3, while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone.

With our newly developed electrochemical AFM cell we can accurately track localized initiation sites of corrosion in model de-alloying experiments on patterned surfaces with nm resolution in x/y and atomic resolution in vertical directions[4]. The time resolution of our EC-AFM is currently limited to about 10 seconds per frame. In both parts of this contribution we will discuss experiments with model systems and we aim to specifically focus on technical hurdles and pros/cons of our techniques, including an outlook into what may be achieved in the future.

References:

[1]   M. Valtiner, X. Banquy, K. Kristiansen, G. W. Greene, J. N. Israelachvili, Langmuir 2012, 28, 13080.

[2]   M. Valtiner, G. N. Ankah, A. Bashir, F. U. Renner, Review of Scientific Instruments 2011, 82, 023703.

[3]   B. R. Shrestha, Q. Hu, T. Baimpos, K. Kristiansen, J. N. Israelachvili, M. Valtiner, Journal of the Electrochemical Society 162(7), 2015, C327.

[4]   B. R. Shrestha, A. Bashir, M. Valtiner, F. U. Renner, Faraday Discussion - Corrosion 2015, in press.
Nanoporous Silicon-Based Platforms for Biological Applications Fabricated by UV Laser Techniques
Authors: Recio-Sanchez Gonzalo , Pelaez Ramon J , Afonso Carmen N. , Vega Fidel , Martin-Palma Raul J
Published: February 2020

Nanostructured porous silicon (nanoPS) can be regarded as a complex network of silicon nanocrystals embedded in a porous matrix. NanoPS is fabricated by the electrochemical etch of silicon wafers in HF-based solutions. When crystalline Si is transformed into nanoPS, its intrinsic properties are altered owing to quantum confinement effects. That makes nanoPS an excellent candidate for the development of several applications in a broad range of fields including optoelectronics, photonics, and biomedicine.

Surface micro- and nano-patterning is becoming an important way to enhance the performance of materials. In particular, nanoPS patterns have been proposed for the fabrication of photonic devices, high-sensitivity sensors, etc. Different techniques have been used for the fabrication of patterns on nanoPS including microstructuring the crystalline silicon substrate before the electrochemical etching process, dry soft lithography, stamp pressing, etc. However, none of these methods has the capability to offer flex-ibility in the pattern design in a time-efficient process, in large areas, and in a single step pro-cess.

The present work reports on the fabrication of one- and two-dimensional platforms on nanoPS by phase-mask UV laser interference. This technique is a single-step and flexible approach to produce a large variety of patterns formed by alternate regions of almost untransformed nanoPS and regions where its surface has melted and transformed into Si nanoparticles.

By changing the main experimental parameters such as nanoPS layer porosity, average pore size, laser fluence or pattern period, the properties of the resulting structures can be controlled. These patterns have been proved to be good candidates for such applications as sensing and for the development of biological platforms.
Response Simulation and Extraction of Gas Concentrations for Nanostructure Decorated Nano-/Microporous Silicon Interfaces
Authors: Laminack William , Baker Caitlin , Gole James L.
Published: February 2020

Sensor and microreactor technology plays a major role in the detection, monitoring, and transformation of materials at interfaces.  We study the dynamics of a matrix of reversible interactions of gas analytes with the majority charge carriers of nanostructure modified extrinsic semiconductor interfaces.  Nanostructures are deposited on highly sensitive surface layers, created by forming an array of nanopore-coated micropores on p- or n- type silicon semiconductors.  The balance of physisorption and chemisorption of the interacting gas analyte on the porous silicon interface is achieved by following the tenants of the developing inverse hard and soft acid/base (IHSAB) interaction model to select metal oxide nanostructures for deposition.  These electronically independent metal oxide catalyst sites are readily modified through in-situ nitridation and sulfidation to create a broad sensing matrix. The resulting relative sensor responses of the modified interfaces to gas analytes are explained by the IHSAB interaction model, rather than simply by a shift in system basicity.  This expanded matrix of observed sensitivities can then be used to predict the relative response of the interface to a variety of gas phase analytes, as well as direct the choice of porous silicon interface modification for enhanced reversible chemical sensing and electron transduction, in the absence of significant chemical bond formation.  The characterization of multiple gas detection, under the guiding model of the IHSAB concept, describes the synergism of two or more analytes simultaneously interacting with an extrinsic semiconductor interface.  We are now extending the application of the porous silicon sensors to the identification of organic solvents by measuring impedance.  Through the use of an equivalent circuit model, we can explore the physical changes of the porous silicon sensor after metal oxide nanostructure depositions and exposure to various organic solvents.
Silicon Nanowires Self-Purification By Metal-Assisted Chemical Etching of Metallurgical Silicon
Authors: Schweizer Stefan L. , Li Xiaopeng , Wang Junna , Sprafke Alexander , Wehrspohn Ralf B.
Published: February 2020

The purity of metallurgical-grade silicon can be increased to solar grade by metal-assisted chemical etching (MaCE). Metal impurities are removed during the forming of porous silicon nanowires. We present a chemical etching model to explain the different levels of chemical reduction for various metals with pore formation during etching. Our study not only highlights the importance of controlling the metal ion concentration and selecting metal types for engineering porous features in NW, but also explains the reason for the difficulty in removing noble metals such as Cu.
Critical BEOL Aspects of the Fabrication of a Thermally-Assisted MRAM Device
Authors: O'Sullivan E. J. , Edelstein Daniel , Marchack Nathan , Lofaro Michael , Gaidis Michael , Joseph Eric , Annunziata Anthony , Pfeiffer Dirk , Trouilloud P. L. , Zhu Yu , Holmes Steve , Galan Armand , Pyzna Adam M. , Gonsalves Jemima
Published: February 2020

Recent developments in new switching methods, such as spin transfer torque [1] and temperature-assisted switching (TAS) [2], have greatly increased interest in MRAM. MRAM fabrication is challenging, however, due to the lack of magnetic materials processing experience by semiconductor lines. 

In this talk, we will discuss key back-end-of-line (BEOL) fabrication aspects for a CMOS-integrated thermally-assisted (TAS) MRAM on 200 mm wafers with, e.g., opens/shorts yields of 100% and 99% for 1Mb and 16 Mb arrays, resp. The cell sizes were 33F^2 for the 16M cell, and 73F^2 for the 1M cell, where F = 90 nm. This was achieved in our Microelectronics Research Laboratory (MRL) facility through careful process optimization and adherence to good BEOL processing practice.  Factors influencing opens and shorts yields will be discussed.  

In the TAS-MRAM magnetic tunnel junction (MTJ) device, data retention is enhanced through synthetic antiferromagnetic exchange coupling; during writing; coupling is overcome through passage of a heating current through the MTJ, and a lower switching field suffices to switch the heated device [2]. 

Figure 1 contains TEMs of a TAS MRAM structure with two dual-Damascene Cu levels and an Al level after the MTJ. The 90 nm base FEOL/BEOL CMOS technology wafers were fabricated by a third party. Fabrication at IBM commenced at V3, and trilayer via and trench RIE masking schemes were used below the final Al level. The field line (M4) had ferromagnetic (FM) cladding of either PVD Ni-Fe alloy or Co. Cladding proved challenging for narrow field lines (≤ 0.5 µm);  e.g., in the initial stages of Cu plating, imperfect  corner seedlayer coverage led to solution attack of the Co.

A Damascene TaN layer (ca. 50 nm thick) served as the pedestal for the MTJ. The MTJ resist mask patterns were trimmed using RIE to afford, after MTJ methanol-based RIE etching, final device sizes of about 110 nm.  After MTJ encapsulation with SiN and dielectric deposition, V4 vias were RIE etched, stopping on SiN. During M5 dielectric RIE, the MTJ pillar tops were exposed, and the V4 vias’ SiN cleared. The final V5/M6 Cu level was followed by an Al level. 

Besides the FM liner, other processing challenges included clearing isolated vias, and developing a robust trench RIE process to contact the MTJs. 

[1] J. C. Slonczewski, J. Magn. Magn. Mater.,159, L1 (1996).

[2] For example, I. L. Prejbeanu et al., J. Phys: Condens. Matter, 19 (16), 165218 (2007).

Acknowledgements:  Back-end-of-line fabrication was carried out in the Microelectronics Research Laboratory (MRL) at the T. J. Watson Research Center. The MRAM stacks were deposited at Crocus Technology in Grenoble, France.

Figure 1
Flexible Ultra-Thin Silicon Solar-Cell Implemented with Energy-Down-Shift Via Cd0.5Zn0.5s/ZnS Core/Shell Quantum Dots
Authors: Park Jin-Seong , Shim Jae-Hyoung , Ko Yun-Hyuk , Park Joo-Hyeong , Lee Gon-Sub , Park Jea-Gun
Published: February 2020

For the past few decades, flexible or bendable silicon, dye-sensitized, organic, and hybrid solar-cells have been intensively researched to improve power-conversion-efficiency (PCE) and to minimize the fabrication cost because of their attractive applications such as building-integrated photovoltaic (BIPV), and portable electronics power. Although flexible or bendable dye-sensitized, organic, and hybrid solar-cells have demonstrated a relevant PCE and solar-cell fabrication cost for a real photovoltaic application, their PCE and solar-cell fabrication cost was still quite higher than that of solid silicon solar-cells. Recently, S. Jeong et al. reported ultra-thin silicon (~10-um in thickness) solar-cell showing a maximum PCE of 13.7 %. However, it was fabricated with typical high-cost semiconductor processes such as SOI wafer, photolithograph, and deep reactive-ion etching (RIE). In addition, it could not demonstrate flexible or bendable solar-cell characteristics.

We, therefore, developed a flexible ultra-thin silicon solar-cell implemented with energy-down-shift layer via Cd0.5Zn0.5S/ZnS core/shell quantum-dots (QDs). In particular, in order to achieve a low cost solar-cell fabrication, we introduced ultra-thinning process (~30-um in thickness) via KOH etching, back-surface-filed (BSF) formation via thin Al-film evaporation and rapid-thermal annealing (RTA), top electrode patterning via thin film Ag evaporation, and spin-coating of core/shell QDs. In addition, in order to enhance an external quantum efficiency (EQE) at ultra-violet (UV) wavelength region, we implemented energy-down-shift layer by coating Cd0.5Zn0.5S/ZnS core/shell QDs on flexible ultra-thin silicon solar-cells.

It was observed that flexible ultra-thin (~30-um in thickness) silicon solar-cells implemented with energy-down-shift layer showed stable flexible and twistable characteristics as shown in Fig. 1. In addition, Fig. 2 presents the EQE as function of wavelength and current density vs. voltage characteristics. It was confirmed that the Cd0.5Zn0.5S/ZnS core/shell QDs on the flexible ultra-thin solar-cells enhanced the EQE of about 17 %P at the UV light region (300 – 400 nm) as shown in Fig. 2(a). In particular, the QDs enhanced the PCE   to 0.77%P by the energy-down-shift effect that enhanced the EQE, which resulting in that the PCE of the ultra-thin silicon solar-cells was about 12.37 %.

In the conference, we will present in detail physical, optical electrical, and flexible properties of flexible ultra-thin silicon solar-cells implemented with energy-down-shift layer. In particular, we will report how their PCE can be sustained after the bending cycles of 5,000.

* This work was financially supported by the Brain Korea 21 Plus Program in 2015.

Reference

[1] DH Lee, JY Kwon, and S Maldonado Nano letters 14
(4), 1961-1967(2014)

[2] S Wang, BD Weil, and Y Li, Nano letters, 13 (9), 4393-4398 (2013)

Figure 1
PTB7:PC71BM Bulk Heterojunction Solar Cells with Multiple Additives
Authors: Ohzeki Masaya , Qiu Jiayu , Fujii Shunjiro , Kataura Hiromichi , Nishioka Yasushiro
Published: February 2020

Bulk-hetero junction organic solar cells with active layers based on [4,8-biz[Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b']dithiophene-2,6-diyl]　[3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] and phenyl-C71-butyric-acid-methyl-ester (PC71BM) with an additive of diiodooctane (DIO) has attracted a lot of attentions due to their high power conversion efficiencies over 9% [1]. The addition of DIO significantly improved the solar cell performance, which was considered due to the change of the nano-structure configulations by the introduction of DIO. On the other hand,  the introduction of dimethyl sulfoxide　(DMSO) into the dicholobenzen solution of PTB7:PC71BM used to deposit the active layers [2]. However, the influence of the DMSO introduction into the PTB7:PC71BM:DIO systems have not yet been reported to the best of our knowledge.

In this work, active layers were fabricated by spin coating 1,2-dichlorobenzene (500 μl) solutions of PTB7 (5 mg): PC71BM (7.5 mg) containing 0.369 mg (3wt%) of DIO and additional DMSO with different weight ratios to the total weight of PTB7:PC71BM (12.5 mg) from 0 to 30 wt% (0 to 3.69 mg).  It was found that the solar cells with 13wt% (1.60 mg) of DMSO additives exhibited the best solar cell performance of an open circuit voltage of 0.72 V, short circuit current density of 15.63 mA/cm2, fill factor of 0.49, and power conversion efficiency of 5.47%. The significant structural changes were found from the surface morphology observations of the active layers depending on the DMSO concentration as observed by atomic force microscope.

[1] Z. He et al., Nat Photonics 6, (2012) 591.

[2] Chu et al., Appl. Phys. Lett. 98, (2011) 253301.
(Invited) Fabrication of N-Polar (Al,Ga,In)N Heterostructures for Transistor Applications
Authors: Keller Stacia , Mishra Umesh K
Published: February 2020

This presentation will address the growth of N-polar (000-1) (Al,Ga,In)N/GaN heterostructures by metal-organic chemical vapor deposition (MOCVD) with emphasis on transistor applications. While the N-polar growth direction is in particular advantageous for highly scaled devices operating at frequencies of 30GHz and beyond, results for high power transistors working at lower frequencies will be discussed as well.  Differences in the MOCVD growth of N-polar in comparison to metal-polar heterostructures will be described. Prerequisites for the fabrication of high quality (Al,Ga,In)N were the use of misoriented substrates in combination with a careful process  optimization.
(Invited) Effects of Ge Substrate Annealing in H2 on Electron Mobility as well as on Junction Leakage in n-channel Ge MOSFETs
Authors: Toriumi Akira , Lee Choonghyun , Nishimura Tomonori
Published: February 2020

A significant enhancement of electron mobility and understanding of carrier transport physics in Ge MOSFETs have been made thanks to significant reduction of major extrinsic carrier scattering sources such as Dit
and surface roughness, in addition to EOT scaling in Ge gate stacks. Since the phonon scattering is the dominant mechanism in Ge bulk, Ge substrate considerations have been out of scope for improving the carrier mobility in Ge MOSFETs. In this talk, however, we report that the peak electron mobility is dependent on how Ge substrates are treated.

We found that H2 annealing was quite effective for achieving the atomically flat surface of Ge substrates. In parallel with this effort, we recently found that H2annealing of Ge substrates could improve the peak electron mobility significantly, even though the peak electron mobility on as-received Ge substrates was poor. This fact indicates that there is definitely another origin of electron mobility degradation inside Ge bulk, because the peak electron mobility is not significantly affected by the surface roughness scattering. This fact indicates that electron mobility is not simply understood by considering the scattering mechanisms reported for Si MOSFETs. Here, we report the relationship between electron mobility and oxygen atom concentration in Ge substrate.

 Furthermore, we discuss effects of oxygen atoms in Ge substrate on reverse-biased n+/p junction leakage current. The oxygen atoms in Ge substrates experimentally reduced the leakage current in n+/p junctions. This result is good news for Ge technology, but it is incompatible with high electron mobility in terms of achieving high performance MOSFETs. Then, we fabricated MOSFETs with selective areal profile of oxygen atoms along the channel and source/drain regions. This method has enabled us to achieve high electron mobility in n-channel Ge MOSFETs together with high Ion
/Ioff
ratio.

Although the junction leakage has been considered to be intrinsically poor in Ge due to a narrower energy band gap, this paper strongly suggests that Ge technology will be further improved for the best with the help of a rich heritage of Si technology.
The Improvement Magnet Plate on a Reticle Stage of Lithography Equipment through Analyzing Adhesive and Roughness of Plate
Authors: Yu Ik Hwan , Kim Gun Rae , Jung Hag Su , Bae Jae Sung
Published: February 2020

Semiconductor lithography scanners are extremely complex equipment which is used to manufacture IC(Intergrated Circuit). Moore's law, which states that the computing power per chip doubles every one and a half to two years, has consistently held for four decades. [1] The exposure system in semiconductor has been rapidly developed based on the Moore's law. Most semiconductor manufacturers have been using ASML scanner for exposure on wafers. The reticle stage of ASML scanner exists over magnet plates. The electric currents are supplied to the coil of the inside magnet，the reticle stage can move forward and backward by Fleming's left hand rule. [3] The reticle stage is synchronized with wafer stage of movement. At that time, scan speed is very fast, reticle stage scan velocity is about 2.4m/sec, in addition acceleration reaches to 9G. So the conditions are very harsh to stage. However, with current technology, we cannot manufacture the whole mass of magnet as long as long stroke of reticle stage. (approximately 2.4m) So they manufacture it on plate by attaching 600mm pieces of magnet. Over time, the magnet plates attached to the main frame are getting weak. At the end of magnet which is the weakest point can be easily cracked because it is changing of flux density in magnet plate. We analyze bonding method between magnet and plate. In addition, we tested it on a different roughness for the plate. Through the change of the material and roughness, we could improve prevent the plate from cracking. In this paper, we propose how to protect broken magnet by changing the material of adhesive and roughness of plate. As a result, we can expect to increase stability in the magnet plate on a reticle stage by more than 10%.

 

[1] G. E. Moore, “Cramming more components onto integrated circuits,” Electron. Mag., vol. 38, no. 8, pp. 4–7, 1965.

[2] Hans Butler, “Position control in lithographic equipment”, IEEE Control Systems Magazine, October 2011

[3] Kenjō, Takashi, and Shigenobu Nagamori. Permanent-magnet and brushless DC motors. Vol. 18. Oxford University Press, USA, 1985.

 

Figure 1
The Studies of Spontaneous Potential Oscillation in a Galvanostatic Copper Electrodeposition and the Crystallographic Textures Thereof
Authors: Chan Po-Fan , Dow Wei-Ping
Published: February 2020

This study reports the influence of the current density and the electrode rotating speed on spontaneous potential oscillation and crystallographic textures of the electrodeposited copper. The potential only spontaneously oscillated in the range of -0.44V ~ -0.49V with respect to saturated mercury-mercurous sulfate electrode (SMSE). This result implies that the electrochemical reduction of copper ions at the metal/solution interface is affected by those organic additives, and the electrochemical oscillation reaction depends on a specific potential range, which may relate with the adsorbed chemical species. In addition, the waveform of the potential oscillation is adjustable by the electrode rotating speed and the current density, and it affects the crystal structure and the surface microstructure of the deposited copper. The plated copper layers were characterized by FIB, FE-SEM, and HR-TEM, and we found a layered structure with a series of parallel twinned boundaries. Furthermore, the layered structure only formed with the specific waveform of the potential oscillation. The spontaneous potential oscillations observed in the copper deposition are explained according to the electrochemical studies and the corresponding microstructure analyses.
Electrografted P4VP as Dielectric in High Aspect Ratio TSV: Surface Preparation and Thermomechanical Consideration
Authors: Dequivre Thomas , Al Alam Elias , Plathier Julien , Ruediger Andreas , Brisard Gessie , Charlebois Serge
Published: February 2020

A key to most 3D integration approaches is the deposition of the Through-Silicon-Via (TSV) dielectric layer. A TSV is traditionally electrically insulated from the silicon substrate by a thin SiO2 film. As TSV aspect ratio is getting higher, conformal SiO2 dielectric deposition is getting harder. Alchimer has proposed a high conformal organic (poly-4-vinylpyridine, P4VP) as dielectric. This polymer is electrografted through electrochemical reduction of diazonium salts in aquous media. Although the electrografting process is well described in the literature [1, 2], electrical and thermomechanical properties of such material grafted onto silicon structure remain incomplete. This information is mandatory in order to optimize 3D integrated processor’s layout.

Since electrografting mechanism is initiated from the surface [2], P4VP material properties and kinetic growth can vary with the surface preparation of the TSV. Results obtained on TSVs, with various surface preparations, insulated by electrografted P4VP suggest that the polymer is not only a good dielectric, but could allow a reduction of the Keep Out Zone (KOZ) size for a higher integration density. Furthermore, as P4VP is a viscoelastic material, its Young’s modulus is temperature dependent and dramatically drops down above its glass transition temperature. Such a material is particularly interesting to reduce stress as it can act as a buffer stress layer.We will present the study of electrical and thermomechanical properties of the electrografted P4VP dielectric realized on high aspect ratio TSV. We will discuss the impact of TSV surface preparation on the electrografting process and on the material properties of the P4VP grafted layer. Results will be compared to more conventional approaches based on a silicon oxide insulator. Acknowledgement

Université de Sherbrooke, Natural Sciences and Engeeniring Research Council of Canada (NSERC), Institut National de la Recherche Scientifique (INRS), Teledyne Dalsa and Alchimer are gratefully acknowledged for their help and their financial support.

Figure 1
(Invited) Microstructural Modeling of Heterogeneous Nucleation and Growth of Lithium Electrodeposits
Authors: García R. Edwin
Published: February 2020

Through numerical modeling and simulation, we explore the charge/discharge conditions that lead to the formation of lithium dendrites in rechargeable lithium-ion batteries. Firstly, by using high resolution X-ray tomography, a three-dimensional representation of a lithiated graphite anode microstructure from a commercial battery was used as input to simulate the local electrochemical behavior that will favor heterogeneous lithium nucleation. The analysis demonstrates that spatial variation in porosity, particle roughness and morphology significantly alter the local intercalation kinetics, state of charge and mechanical stability, and dendrite formation. Secondly, by using the phase field approach, we demonstrate the conditions that will enable an overpotential-controlled critical lithium electrodeposit to become energetically favorable and identify the regimes of dendrite nucleation, growth, and suppresion behavior.

Figure 1
Evaluation of Relationship Between Dynamic Structural Deformation and Output Performance in Lithium-Ion Battery By Numerical Simulation
Authors: Inoue Gen
Published: February 2020

In order to improve the performance of Lithium ion secondary battery (LiB), it is very important to understanding the internal transport phenomena under high rate condition to increase power density. In my previous study, I focused on the actual porous electrode structure, and the Li ion and electron conductivity was evaluated by the effective conductive path with the actual reconstruction electrode structure [1], [2]. However, the effect of volume expansion of charge-discharge state is not been understood enough. In this study, I examined the new model with structure change based on the actual porous electrode structure, and the relationship between structural change and battery performance was considered. Actual Graphite anode and LiCoO2 cathode electrode structure were reconstructed by FIB-SEM, and the reaction and mass transfer in these reconstructed electrode structure and simulated separator structure were simulated by multi-block method [3] which is the method of coarse graining to keep the information of heterogeneous structure. Li concentration and potential distribution in active material (AM) and electrolyte (EL) were calculated with Butler-Volmer equation as the boundary condition of the interface between AM and EL. it was assumed that temperature is constant, the formation of SEI is ignored, binder phase inhibit ionic transfer. The discharge performance was calculated with 1M LiPF6－EC/DEC (1:1) and the condition reported previous research[4]. Figure 1 shows the cell structure, current density distribution and Li concentration distribution in AM. The current density near LCO collector became lower because of the lack of Li ion caused by binder migration. In addition, the simulation results were compared with experimental results which were obtained by coin cell with same electrode structure. These results were almost equal to each other. Furthermore, the effect of volume expansion was included in this previous model. Especially, the effect of electrolyte convection caused by the change of porosity was examined. Figure 2 shows the simulation results of the discharge-distribution with volume expansion. From this result, it was found that the effect of convention cannot be ignored in the case of high expansion volume ratio (more than e=2)

References

[1] G. Inoue et al., Proc. PRiME 2012, B6 #803 (2012)

[2] G. Inoue et al.,
J. Power Source
175, 145-158 (2008)

[3] G. Inoue et al., ECS Trans.,
25 (1) 1519-1527 (2009)

[4] G. Inoue et al., ECS 226th meeting, A5 #374 (2014)

Figure 1