bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of α-MnO2/Graphene Nanocomposites for Applications to in High Performance Super Capacitors
Authors: Singhal Rahul , Lemaire Peter , Omidwar Amir
Published: February 2020

In recent years, supercapacitors have attracted a lot of attention due to their applications in portable electronic devices such as mobile phones, laptops, digital camera and also for power applications in hybrid electric vehicles, engine start, and solar energy storage, etc. [1-3]. Transition metal oxides and carbon materials are widely being used in supercapacitors. Among transition metal oxides, MnO2 has been one of the most studied electrode materials because of its cost effectiveness, natural abundance and environmental compatibility. In spite of its various advantages, MnO2 in its pure state is not very useful for supercapacitor applications because of its poor electrical conductivity and electrochemical dissolution upon cycling. On the other hand, graphene has drawn considerable interest because of its ultrahigh surface area (up to 2630 m2/g), and excellent conductivity. Up to now, composites of graphene and MnO2 have been used to improve their capacitance.

We have synthesized hetero-structured - nanorods using the low temperature hydrothermal technique [4]. Finally -/graphene nanocomposite was synthesized by sonochemical co-precipitation method as reported earlier [5]. Graphene oxide power, suspended in sulfuric acid solution (1mg/ml), and manganese sulfate (dissolved in sulfuric acid) were mixed together and potassium permanganate solution was added to this solution drop by drop. After 2 hours -/graphene nanocomposite was filtered using centrifuge, washed with DI water and ethanol and dried. The phase structure of - nanorods and -/graphene nanocomposites were studied using powder X-ray diffraction (XRD). The results of physical, thermal and electrochemical characterization of -/graphene nanocomposite will be presented during 231st Electrochemical Society Meeting.

References:

Z. Yang, J. Zhang, M.C. Kintner-Meyer, X. Lu, D. Choi, J.P. Lemmon, J. Liu, Chem. Rev. 111 (2011) 3577.

H. Zhang, G. Cao, Y. Yang, Energ. Environ. Sci. 2 (2009) 932.

X.H. Lu, X. Huang, S.L. Xie, T. Zhai, C.S. Wang, P. Zhang, M.H. Yu, W. Li, C.L. Liang, Y.X. Tong, J. Mater. Chem. 22 (2012) 13357.

 Z.K. Ghouri, M.S. Akhtar, A. Zahoor, N. A. M. Barakat, W. Han, M. Park, B. Pant, P.S. Saud, C. H. Lee, H. Y. Kim, J. Alloy and Compounds
642 (2015) 210 .

B. Zhao, M. Lu, Z. Wang, Z. Jiao, P. Hu, Q. Gao, Y. Jiang, L. Cheng, J. Alloy and Compounds B 663 (2016) 180.
(Invited) Flexible Mxene/Graphene Films for Ultrafast Supercapacitors
Authors: Yan Jun , Ren Chang E. , Hatter Christine , Anasori Babak , Urbankowski Patrick , Kurra Narendra , Maleski Kathleen , Sarycheva Asya , Gogotsi Yury
Published: February 2020

Due to their unique properties and a great diversity, various two-dimensional nanomaterials have attracted interest from scientific community for energy storage applications in recent years. Herein, we present a facile strategy to prepare MXene/graphene films with excellent flexibility and electrical conductivity for supercapacitors by using layer-by-layer electrostatic self-assembly from solution between positively charged graphene and negatively charged MXene nanosheets. Graphene nanosheets are intercalated in-between MXene layers after electrostatic assembly. As a result, the face-to-face self-restacking of MXene nanosheets is effectively prevented, leading to the considerably increased interlayer spacing of MXene layers and more active sites accessible to electrolyte ions, which ensures high diffusion rate and transport of electrolyte ions during the charge/discharge process. The as-prepared freestanding MXene/graphene (5wt.%) film displays outstanding volumetric capacitance of 1040 F cm-3 at a scan rate of 2 mV s-1 and impressive rate capability with 61% capacitance retention at 1000 mV s-1. Meanwhile, the film electrode exhibits a long cycle life with almost no capacitance decay after 20,000 cycles. More importantly, our fabricated symmetric supercapacitor shows a maximum volumetric energy density of 34.6 Wh L-1 and an ultrahigh volumetric power density up to 74.4 kW L-1, which is among the highest values reported for carbon and MXene based materials in aqueous electrolytes so far. This work not only provides fundamental insights to the effect of interlayer spacing on the electrochemical performance of emerging MXene materials but also sheds light on future design of next-generation flexible, portable and highly integrated supercapacitors with high volumetric and rate performances.

Figure 1
(Invited) Space-Confined Assembly of All-Carbon Hybrid Fibers for Capacitive Energy Storage
Authors: Chen Yuan
Published: February 2020

Miniaturized portable and wearable electronics have diverse power requirements, ranging from one microwatt to several milliwatts. Fiber-based micro-supercapacitors are promising energy storage devices that can address these manifold power requirements. Here, we demonstrate a hydrothermal assembly method using space confinement fillers to control the formation of nitrogen doped reduced graphene oxide and multi-walled carbon nanotube hybrid fibers. Consequently, the all-carbon hybrid fibers have tunable geometries, while maintaining good electrical conductivity, high ion-accessible surface area and mechanical strength; this allows us to address two important issues in micro-supercapacitor research. First, we found a clear correlation between the geometry of the hybrid fibers and their capacitive energy storage properties. Thinner fibers (30 mm in diameter) have higher specific volumetric capacitance (281 F cm-
3), superior rate capability, and better length dependent performance. In contrast, larger-diameter hybrid fibers (236 mm in diameter) can achieve much higher specific length capacitance (42 mF cm-1). Second, we realized the first built-to-order concept for micro-supercapacitors by using all-carbon hybrid fibers with diversified geometry as electrodes. The device energy can cover two orders of magnitude, from <0.1 μW h to nearly 10 μW h, and the device power can be tuned in four orders of magnitude, from 0.2 μW to 2000 μW. Furthermore, multiple mechanically flexible fiber-based micro-supercapacitors can be integrated into complex energy storage units with wider operation voltage windows, demonstrating broad application potentials in flexible devices. 

Figure 1
Delignification Enhances Capacitance of Wood-Derived Electrodes
Authors: Zhao Yepin , Islam Mohammad F.
Published: February 2020

In recent years, diverse types of biomass materials have been pyrolyzed and activated to generate carbon materials that are subsequently utilized as electrodes in electrochemical cells because they are inexpensive, abundant, and sustainable. The principal components of most biomasses are cellulose, hemicellulose and lignin. When pyrolyzed and activated, cellulose makes leading contribution to charge storage while hemicellulose and lignin add minor contributions, disproportionately increasing the mass and cost of electrochemical cells. Further, biomass-derived electrodes frequently only have shapes of extraordinarily thin supported films, which require multiple layers of electrodes to generate appreciable electrochemical performance, increasing cost and complexity of electrochemical cells. We have developed an acid-based strategy to delignify Balsa wood that removes hemicellulose and lignin while retaining cellulose, and then pyrolyzed and activated this wood to create freestanding thick (0.5 mm) electrodes that possess exceptional power and energy densities. The delignified wood derived electrodes exhibit a specific capacitance of 266 F/g (310 F/g) at 0.1 A/g, gradually decreasing to 170 (90) F/g at 20 A/g in aqueous electrolyte 1M Na2SO4 (room temperature ionic liquid, RTIL; 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), which are more than 50% greater than that of electrodes fabricated using non-delignified wood. Furthermore, the electrodes are highly durable, retaining 92% (82%) of capacitance after 10,000 charge-discharge cycles in aqueous (RTIL) electrolyte. The electrodes demonstrate a high energy density of 5 (73) Wh/kg and a corresponding power density of 4060 (16500) W/kg in aqueous (RTIL) electrolyte. Our work provides guidance on the use of delignification to enhance electrochemical performance of biomass-derived electrodes. This work has been partially supported by the NSF through Grant CMMI 1335417.
Nanocarbon Current Collectors for Aqueous Batteries
Authors: Hayden John , Lin Chuan-Fu , Luo Wei , Rubloff Gary W , Hu Liangbing
Published: February 2020

Carbon materials are a promising alternative to metal current collectors that are currently used in aqueous batteries, because of their light weight, high electrical conductivity, and promising corrosion resistance. In this report, we investigate the corrosion resistance of multiple flexible and robust nanocarbon current collectors (NCCCs) for aqueous battery applications.

We have fabricated a number of polymer-nanocarbon composite materials to serve the purpose, including activated carbon cloth (ACC) with carbon nanotubes (CNTs) and cellulose nanofibers combined with CNTs (CNT/CNF), both of which exhibit high conductivity and mechanical strength.

We evaluated durability of these composites under potentiostatic stress in conditions mimicking those of lead-acid and nickel metal hydride (NiMH) batteries in an attempt to expose the carbon current collectors to the most severe conditions they would experience in an aqueous battery. Cyclic voltammetry and Fourier transform infrared spectroscopy (FTIR) were used to characterize the oxidation of the NCCCs after holding them at stressing potentials for long periods of time. Stress-strain and four-point probe measurements were also taken before and after holding potential to evaluate changes in mechanical strength and DC conductivity of the NCCCs.

The CNT/CNF show improved electrochemical stability in acidic conditions compared to ACC while maintaining reasonable mechanical and electrical properties, and thus they are promising as alternative current collectors in an acidic aqueous battery such as lead-acid. We are also exploring other variations of nanocarbon-based current collectors and the use of atomic layer deposition to further develop NCCC technology options.
DFT Simulation of the Oxygen Reduction Reaction on Graphene Catalyst Edges
Authors: Ly Quang , Goddard William A , Yu Ted H.
Published: February 2020

We utilized density functional theory (DFT), to calculate energy barriers for various reaction steps leading to the 4e- water formation and the 2e-formation on graphene catalysts. We examined the Eley-Rideal reactions for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells, determining the energy pathways for associative electrocatalytic mechanism generated by stepwise addition of hydrogen.

Our binding energy calculations show why ORR occurs only on the graphene edges because the O2 and OOH intermediates do not bind on the basal plane surface. We predict an onset potential for ORR to produce 2e- products on armchair graphene edges to be 0.65 V, which compares very well to the experimental onset potential of 0.68 eV1. We find that the onset potential for ORR to produce 4e- products on armchair graphene is also 0.65 V. In comparison, we find that the zigzag graphene edges formed bonds to the ORR intermediates that were too strong, requiring an onset potential of 0.14 V to produce 4e- ORR products. This result shows that the preferred site for ORR is the armchair edge.

These PBE calculations were carried out to determine energy barriers as a function of applied potential2 using the a new CANDLE method to simulate the effect of water solvation3. We found the rate determining step (RDS) to form the 2e- product is OO + H -> OOH, with an electronic energy barrier of 0.78 eV at a potential of 0.65 V. We found that the RDS to form the 4e-product is the reaction, O + H -> OH, with a barrier of 1.35 eV at a potential of 0.65 V. Figure 1 shows the compares the ORR mechanism for the 2e- and 4e- reaction. Figure 2 shows the calculated Tafel Plot of the preferred 2e- reaction using the Butler-Volmer equation using current densities calculated from potential dependent barriers.

References:

1. S. Malkhandi, P. Trinh, A. K. Manohar, K. C. Jayachandrababu, A. Kindler, G. K. Prakash and S. R. Narayanan, J Electrochem Soc 160(9), F943-F952 (2013).

2. H. Xiao, T. Cheng, W. A. Goddard and R. Sundararaman, J Am Chem Soc 138(2), 483-486 (2016).

3. R. Sundararaman and W. A. Goddard, J Chem Phys 142(6), 064107 (2015).

Figure 1
Electrochemical Properties of PDTT and PETDP As Cathode Materials for Rechargeable Lithium Battery
Authors: Shadike Zulipiya , Bak Seong-Min , Wang Xue-Long , Lee Hung-Sui , Yang Xiao-Qing
Published: February 2020

Recently, Organodisulfide compounds have attracted extensive research interests as cathode materials due to the advantages of higher theoretical capacity, environmental friendness, lightweight and abundant resources for high specific energy lithium secondary batteries. The key moiety of high specific capacity in organodisulfide compounds is the reversible two-electron redox reaction of the disulfide bond (S-S). However, the exiting problem of organodisulfide compounds as electrodes materials in LIBs is the large capacity fading caused by the high solubility of polysulfides in liquid electrolytes. An Important strategy to solve this problem is to polymerize the small molecules into insoluble polymeric chains in order to improve the cyclic stability of the electrodes.

Based on this strategy, the electrochemical performance and energy storage mechanism of Poly [1, 2-dithiole-3-thion-4(5)-thio] (PDTT) and Poly [2-(1, 2-ethylenediamino)-1, 6, 6a, Δ4-trithia-1, 6-diaza-pentalen-5-yl] (PETDP) were designed, synthesized, and investigated. As shown in figure 1, based on the two-electron reaction, PDTT can provide theoretical capacity of 326 mAh g-1, and the theoretical capacity of PETDP is calculated to be as high as 371 mAh g-1 based on the three-electron reaction. Electrochemical performances of PDTT and PETDP were evaluated by cyclic voltammogram and galvanostatic discharge/charge measurements. CV results indicated that PDTT electrode has two pairs of redox peaks at 2.09/2.38 and 2.29/2.63 V. PETDP cathode also presents two pairs of well-defined redox peaks at 2.11/2.26 and 2.37/2.42 V, respectively. Cyclic performance of PDTT and PETDP was compared using two type of electrolytes, the ether based (1M LiTFSI in DME/DOL) and carbonate based (1M LiPF6 in EC/DMC) electrolytes. Results show that both of them deliver best cyclic stability in ether based electrolyte. In addition, the discharge and charge profiles of PDTT electrode are consistent with its CV curves and having specific capacity of 321 mAh g-1 at a current density of 0.1 C (1C=33 mA g-1), this value is as high as 98.4% of the theoretical capacity. Even at 0.5C rate, high initial capacity of 318 mAh g-1 (97.5% of theoretical value) was obtained, confirming the almost fully utilization of active materials. When cycled over 50 cycles, PDTT electrodes can still deliver high capacities of 291 mAh g-1with capacity retentions of 90.6%, showing a high potential to be used as organodisulfide cathode materials for high capacity Li-S batteries.More details about the charge storage mechanism studies using synchrotron based X-ray absorption spectroscopy will also be presented at the meeting.

Acknowledgement

The work at Brookhaven National Lab. was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies (BMR and VTO Battery500 projects) under Contract Number DE-AC02-98CH10886.

Figure 1
Novel Obstructed Flow Field Designs for Improved Perfomance in Vanadium Redox Flow Batteries
Authors: Akuzum Bilen , Robinson Nick , Agar Ertan , Kumbur E. Caglan
Published: February 2020

One of the major challenges that limits the widespread commercialization of vanadium redox flow batteries (VRFBs) is their relatively low power density, which often results in higher cost [1]. In recent years, significant effort has been put on understanding the effect of flow field design on the power density performance of VRFBs [2-3]. Flow fields play a crucial role in effective delivery and removal of active species from the electrode surface and hence they can significantly alter the power output of the VRFBs. Due to inherent similarities between fuel cells and redox flow batteries, flow field designs for VRFBs have been limited to previously studied conventional flow designs such as parallel, serpentine, and interdigitated. Though significant effort has been placed on analyzing which design performs better and how certain parameters can result in higher performance; investigation of novel flow designs outside the fuel cell research has remained much unexplored.

Although conventionally utilized flow field designs have very different flow paths for delivery of the electrolyte in two dimensions; the channel depth seems to remain constant for the flow field studies reported so far. Considering the porous electrodes lie in parallel with the channel floors in most of the VRFB cell fixtures, it is believed that alterations of the channel depth throughout the length of the flow channels can help facilitate better transport of active species to the electrodes. Motivated by this, various forms of channel obstructions and ramped flow field designs have been investigated to understand the effect of channel depth and delivery of electrolytes on the power density of the VRFBs. Results have shown significant improvements in power density (up to 90%) with the addition of alterations to the channel depth with minor (10%) or no change in pumping losses. These findings suggests that engineering of the flow field designs in all three dimensions can help further improve the power density of VRFBs.

References

[1] Agar, E., Dennison, C.R, Knehr, K.W., Kumbur, E. C., J. Power Sources, 2013, 225, 89-94.

[2] Kumar, S., Jayanti, S., J. Power Sources, 2016, 307, 782-787.

[3] Dennison, C.R., Agar, E., Akuzum, B., Kumbur, E.C., 2016, J. Electrochem. Soc., 163, A5163-A5169.
Metaheuristics Computation-Assisted Multi-Element Doping Design in Electrode Materials for Rechargeable Batteries
Authors: Jung Young Hwa , Ahn Docheon , Park Woon Bae , Sohn Kee-Sun
Published: February 2020

Low-level doping of electrode materials is known to be a common and simple method that can be used to improve electrode performance. However, multi-element doping compositions have generally been confined to the empirical intuition of researchers via trial-and-error. Here we propose a more systematic approach to designing multi-element doping compositions for electrode materials via a non-dominated sorting genetic algorithm (NSGA-II)-based computation. LiMnPO4 was selected to demonstrate our strategy not only because of its promising features such as a high operating voltage, comparable capacity, and structural stability, but also because it is known for insufficient electrochemical performance with poor reversibility and rate capability. In this study, a NSGA-II was employed to determine the optimum multi-element doping composition at the Mn site of olivine-structured LiMnPO4 through six consecutive generations, each of which contained 25 dopant sets that finally led to the pinpointing of two potential candidates for a multi-element doped LiMnPO4. Both the doped LiMnPO4/C with selective compositions delivered a reversible capacity of about 150 mA h g˗1, and also exhibited a high rate capability at the 2C rate and a decent cyclability with 91% capacity retention during 30 cycles. This approach can be widely applied to explore local optimization of multi-element substitutions for high performance electrode materials, and further it would provide a broader view for investigating other functional materials with multiple compositions that could be locally optimized.
(Keynote) Organic Coatings for Corrosion Protection: Self-Healing at the Delaminated Interface
Authors: Rohwerder Michael
Published: February 2020

Recently significant progress has been made in developing self-healing coating systems capable of healing even macroscopic defect sites (see e.g. [1-3]). The corrosion triggered release and transport of sufficient amounts of inhibitors and/or self-healing agents to the defect site is enabled by the delamination of the coating. This allows fast spreading of the trigger signal, such as change of pH or potential, into the coating and also fast transport of the released active agents along the delaminated interface. However, when corrosion in the defect site is successfully inhibited it is important that also at the delaminated interface corrosion is inhibited and adhesion between metal and the organic coating is re-established again. Our knowledge of how to do this is still limited. Recent progress on this topic will be presented and discussed.

[1] D. Crespy, K. Landfester, J. Fickert, and M. Rohwerder, Self-Healing Materials 273 (2016) 219-245.

[2] T.H. Tran , A. Vimalanandan , G.Genchev , J. Fickert , K. Landfester , D. Crespy , M.Rohwerder, Advanced Materials 27(25) (2015) 3825-3830.

[3] A. Vimalanandan, L.P. Lv, T.H. Tran, K. Landfester, D. Crespy, M. Rohwerder, Advanced Materials 25(48) (2013) 6980-6984.
Corrosion Sensors to Monitor the Degradation of Hot-Dip Galvanised Steel and Painted Steel during Accelerated Corrosion Tests
Authors: Thierry Dominique , Ledan Frederic , Diler Erwan , Le Bozec Nathalie
Published: February 2020

Hot-dip galvanised steel and electrogalvanised steel are widely used in the automotive and construction industry. The corrosion testing of these metallic coatings includes exposure at natural weathering sites and exposure in cyclic corrosion tests in the laboratory. The corrosion rate is then evaluated using mass loss measurements and visual observations such as time to red rust. In this work we have developed a new sensor based on electrrical resistance measurements and applied it on galvanised steel. This new device allow in-situ and real time measurements of the corrosion rate of galvanised steel. Exemple of utilisation of the sensor in cyclic corrosion tests will be given. The new device offer the possibility to better undertand the different phases of cyclic corrosion testing with the ultimate goal to develop more relevant testing procedure. This provides new possibilities to study the atmospheric corrosion of metallic coated steel in various environments. Exemple of use in the case of painted steel will also be given.
Corrosion Behavior of Carbon Steel Under Environment Simulated inside of Concrete Containing Chloride Ion
Authors: Katayama Hideki , Doi Kotaro , Yamada Maya , Hoshi Yoshinao , Shitanda Isao , Itagaki Masayuki
Published: February 2020

Many infrastructures such as expressways and buildings were constructed in Japan between the 1950s and the 1970s. There is greatly influence of airborne sea salt on corrosion in Japan surrounded by the sea, and reinforcement corrosion is accelerated by rainfall, dew condensation and water absorption of airborne sea salt. Therefore, many of these infrastructures are in a condition requiring repair or renewal in the present. In this study, electrochemical measurements of carbon steel were conducted in an aqueous solution simulated the inside of concrete, in order to investigate corrosion behavior of reinforcing bars in concrete. In addition, the influence of surface condition of the reinforcing bars before corrosion on their corrosion resistance was examined by the corrosion monitoring using an electrochemical impedance method.

Carbon steel and 0.1% Ca(OH)2 solution were used as the sample for the reinforcing bar in concrete and as the test solution simulating the internal environment of the concrete, respectively. The corrosion resistance of passive film in concrete was investigated by anodic polarization measurement and electrochemical impedance measurement. The passive film region was observed regardless of concentration of chloride ion in the test solution. The current density in the test solution containing 0M and 0.01M of chloride ion did not abruptly increase in the passive state region and local corrosion such as pitting corrosion did not occur on the steel surface. A sharp rise in current density was observed in the test solution containing 0.1M or more of chloride ion.

The anodic polarization curves of carbon steel with passive film formed by immersion in the test solution was measured, in order to investigate the influence of the film formation period on the properties of passive film. A passive region was observed in the anodic polarization curves of all samples. The passive current density decreased with an increase of immersion time, indicating that the corrosion resistance of the passive film improved as the immersion time increased. Furthermore, the electrochemical impedance measurements of carbon steel passivated in the test solution were carried out. The impedance characteristic can be represented by a typical Randles type equivalent circuit, and the diameter of the semicircle corresponds to the film resistance. The film resistance increased in proportion to the immersion time in the test solution. This result is consistent with the result of the anodic polarization measurement.
Dielectric Property of Concrete Investigated By EIS
Authors: Hasegawa Chiaki , Okamoto Tatsuki , Tokieda Hiroyuki , Hoshi Yoshinao , Shitanda Isao , Itagaki Masayuki , Kato Yoshitaka
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is effective tool to investigate degradation of concrete and corrosion of reinforcing steel bar. The impedance spectrum of concrete reinforced by steel bar shows many capacitive loops on the Nyquist plane. McCarter et al. [1] reported that capacitive loop in the high frequency range originated form the dielectric property of concrete absorbing water. According to the paper by McCarter et al. [1], the EIS allows the information concerning the amount of water and pore structure in concrete. We measured impedance spectra of concrete sandwiched between two stainless steel electrodes, and found that the capacitance is very large when the concrete absorbed much water. We observed the variation of capacitance during the drying process of concrete, and proposed a complicated pore structure in concrete.

Reference:

[1] W. J. McCarter and S. Garvin, J. Phys. D: Appl. Phys., 22 (1989) 1773-1776.
Enhancement of Switching Property of Perpendicular- Magnetic Tunnel Junctions Using Single MgO Based Co2Fe6B2 Double Free Layer Structure
Authors: Kondo Kei , Lee Julie , Lee dong-Gi , Park Jea-Gun
Published: February 2020

Recently, perpendicular-spin-transfer torque magnetic random access memory (p-STT MRAM) has received considerable attention as the next-generation memory referred from its pre-eminent characteristics. It has high speed writing and reading property like dynamic random access memory (DRAM) with an additional property of non-volatility. Furthermore, it also has stable endurance (> 1014), less electric energy consumption to maintain its data (~1 pJ/bit) and high scalability. Because of these properties, p-STT MRAM has been considered to be the universal memory that can replace other memories in the market. However, it is difficult to be commercialized due to many critical issues of device parameters i.e., the tunneling magnetoresistance (TMR) ratio, thermal stability (Δ), and switching current density (JC). In particular, theses three device parameters should be achieved at 400oC temperature of the back-end of line (BEOL) to be manufactured into the market. To gain a reputation as a non-volatile memory at the market, p-STT MRAM needed low switching current density for low-power operating device.

In our research, we investigated new MTJ structure using single MgO based double Co2Fe6B2free layers separated by a W spacer layer (See Fig.1) for low current switching.

Samples were made by utilizing　12-inch multi-chamber magnetron sputtering system and magnetic vacuum oven. After sputtering process, samples were ex-situ annealed at 350 or 400oC under a perpendicular magnetic field of 3T for 30 minutes.

Figure 2 shows the switching voltage of anti-parallel state to parallel state (AP-P) and parallel state to anti-parallel state (P-AP) on I-V measurement. The switching voltage of AP-P and P-AP at newly double free layer decreased about 3.8 and 5.2% respectively, compared with the conventional free layer. This means that upper Co2Fe6B2 free layer had an influence for the lower Co2Fe6B2 free layer, therefor the lower Co2Fe6B2free-layer easily switched to perpendicular direction by in-plane magnetic anisotropy (IMA) magnetic resonance coupling.

In our presentation, we will present the switching property of Co2Fe6B2 double free layer for p-MTJs and review the switching mechanism for IMA magnetic resonance coupling by using IV measurement. In addition, we review the magnetic properties, atomic composition and TMR ratio, by using vibrating-sampling-magnetometer (VSM), Secondary-Ion-Mass-Spectrometry (SIMS), current-in–plane-tunneling (CIPT) measurement respectively.

* This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2014R1A2A1A01006474) and the Brain Korea 21 PLUS Program in 2014.

Figure 1
(Invited) Design and Challenging Issues of Core/Shell Quantum Dots for Enhancing Power-Conversion-Efficiency in Si Solar-Cells
Authors: Park Jea-Gun
Published: February 2020

For last several decade, although intensive researches has been conducted, the maximum power-conversion-efficiency (PCE) of Si solar cells has been economically limited to ~25%. Since Si solar cells absorbed mainly photons in visible wavelength, the silicon solar cells using energy-down-shift (EDS) mechanism has been recently proposed. Un-doped core/shell quantum dots such as CdSe/ZnS or Cd0.5Zn0.5S/ZnS have well demonstrated EDS by the Stokes shift of 52~127 nm and enhances ~1% of the PCE in the Si solar cells by implementing them on the Si solar-cell surface1. In addition, environment-safe InP/ZnS core/shell quantum dots well demonstrated the PCE enhancement of the Si solar cells. However, such small Stokes shift from core/shell quantum dots led the Si solar cell surface to resorb partially the emitting blue light so that the possible PCE enhancement would be limited to ~1%. Recently, the higher than ~200 nm of the Stokes shift from Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell quantum dots has been demonstrated and enhances ~0.5% of the PCE in Si solar cells. Since Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell quantum dots basically performs a lower quantum yield (~51%) so that their PCE enhancement would be limited to less than 1%2. Thus, another challenge such as energy-up-conversion through the core/shell quantum dots is necessary to overcome the limit of EDS in enhancing the PCE of Si solar cells. In this presentation, we will discuss these issues.

Reference

1. S.W.Baek, J.H.Shim, H.M.Seung, G.S.Lee, J.P.Hong, K.S.Lee, and J.G.Park, Nanoscale, 6, 12524 (2014).

2. M.Jalalah, Y.H.Ko, F.A.Harraz, M.S.Al-Assiri, and J.G.Park, Nano Energy, 33, 257 (2017)
Experimental Study of PVD Cu/CVD Co Bilayer Dissolution for BEOL Cu Interconnect Applications
Authors: Sun Xiaoxuan , Peethala Brown , Hopstaken Marinus , Hu Chao-kun , Mclaughlin Paul S , van der Straten O. , Demarest James , Motoyama K. , Nogami Takeshi , Lin Xuan , Zhang Xunyuan , Kelly James
Published: February 2020

CVD Co liners are of interest for back end of the line (BEOL) interconnects due to improved Cu interconnect gapfill, especially at narrow feature widths.1-4 The stability of Co liner during downstream BEOL processing is a concern that has been discussed with respect to chemical mechanical planarization (CMP),5-6but its behavior during Cu plating has received less attention. Since Co is less noble than Cu (and its oxide is unstable at low pH), an optimized BEOL metallization process is important to prevent Co liner loss during plated Cu fill. Insufficient Cu seed coverage could expose Co to oxidation and attack in the Cu electrolyte, compromising yield and reliability.

In this study, we characterize the anodic dissolution behavior of thin PVD Cu/CVD Co bilayer films using linear sweep amperometry. The thin blanket seed layers are intended to mimic the sparse Cu seed coverage that might be present over a Co liner in a narrow dual damascene geometry. An example of this type of analysis is shown in Figure 1. The top figure (1a) shows the anodic polarization behavior of two separate electrode samples (plotted together), one for thick Co, another for thick Cu. The expected potential difference in the stripping peaks is observed, with Co dissolving at less anodic potentials. The middle (1b) and bottom (1c) figures show the behavior of bilayer electrodes having Cu overlayers of varying thickness. The Cu thickness clearly affects the polarization behavior of the underlying Co, with a fairly thick overlayer required to completely suppress early Co dissolution. The impact of these effects and other Cu chemistry aspects on the interconnect yield and reliability will be discussed.

1. T. Nogami, J. Maniscalco, A. Madan, P. Flaitz, P. DeHaven, C. Parks, L. Tai et al., In Interconnect Technology Conference (IITC), 2010 International, pp. 1-3. IEEE, 2010.

2. H. Shimizu, K. Sakoda, T. Momose, Y. Shimogaki, Japanese Journal of Applied Physics, 51, 05EB02-1 (2012).

3. A. H. Simon, T. Bolom, C. Niu, F. H. Baumann, C-K. Hu, C. Parks, J. Nag et al., In Reliability Physics Symposium (IRPS), 2013 IEEE International, pp. 3F-4. IEEE, 2013.

4. M. He, X. Zhang, T. Nogami, X. Lin, J. Kelly, H. Kim, T. Spooner, D. Edelstein, and L. Zhao, J. Electrochem. Soc., 160, (12) (2013): D3040-D3044.

5. N. Heylen, L. Yunlong, K. Kellens, L. Carbonell, H. Volders, G. Santoro, V. Gravey et al. In Interconnect Technology Conference (IITC), 2010 International, pp. 1-3. IEEE, 2010.

6. K. Tanwar, D. Canaperi, M. Lofaro, W. Tseng, R. Patlolla, C. Penny, and C. Waskiewicz, J. Electrochem. Soc., 160, D3247 (2013).

This work was performed by the Research Alliance Teams at various IBM Research and Development facilities.

Figure 1
(Invited) Nanofabrication of Devices Using Scanning Force Microscopes
Authors: Bouchiat Vincent
Published: February 2020

Among the most promising nanometer-scale manufacturing methods are lithographies using scanning probe microscopes mainly because they operate in the near field, contrary to all the competing techniques that operate by emitting radiation (light, electrons) in a far-field regime.  The local probe microscopes encompasses a large family, the best known of which are the tunneling microscope (STM) and the atomic force microscope (AFM). They are based on a very local interaction between a tip and a given substrate. The scanning of the tip is carried out by piezoelectric ceramics whose movement is controlled to a fraction of angstrom. The measurement of the signal given by the tip/sample interation gives a topographical image of the surface, which can reach atomic resolution. The principles of these nanolithography techniques derived from these microscopes are based on a simple observation: since these techniques make it possible to carry out topographic imaging of a surface on a nanometric or even atomic scale, why not use them to modify surfaces at this same scale?

I will make a review of recent advances in the field of nanofabrication of fully operational quantum devices using Scanning Probe microscopes. In particular I will detail the techniques involving anodization techniques under the voltage biased tip of an Atomic Force Microscope and will conclude on the perspectives of using these techniques for large throuput at the industrial scale.
(Invited) Scalable Growth of Two-Dimensional Materials – a Prerequisite for Process Integration
Authors: Kataria Satender , Wagner Stefan , Lemme Max Christian
Published: February 2020

Materials have always been at the heart of new inventions and, semiconductor industry is not an exception in this case. Two-dimensional (2D) materials are further enriching the available atlas of such novel materials. After the discovery of graphene in 2004, hundreds of other 2D materials are being explored owing to their distinct structures which lead to exciting properties and applications, unseen in other dimensions. Graphene and transition metal dichalcogenides (TMDs) based on molybdenum and tungsten have shown great promises for future technological applications including Internet of Things. Moreover, intriguing desired properties can be obtained by making hybrids and heterostructures of suitable 2D materials. Chemical vapor deposition (CVD) is the technique with a potential for scaling up the production of good quality 2D materials.

In this talk, I will give a brief introduction to 2D materials like graphene and molybdenum disulphide (MoS2) with emphasis on their large-scale production using CVD method. The open challenges for integrating these materials, especially graphene, into process technology will be discussed.

References:

1. Butler SZ, Hollen SM, Cao L, Gupta JA, Gutierrez HR, Heinz TF et al. Progress, Challenges and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano 7 (2013) 2898.

2. Kataria S, Patsha A, Dhara S, Tyagi AK, Barshilia HC. Raman Imaging on High-Quality Graphene Grown by Hot-Filament Chemical Vapor Deposition. J Raman Spectrosc. 43 (2012) 1864.

3. Chang C-K, Kataria S, Kuo C-C, Ganguly A, Wang B-Y, Hwang J-Y, et al. Band Gap Engineering of Chemical Vapor Deposited Graphene by in Situ BN Doping. ACS Nano 7 (2013) 1333.

4. Kataria S, Wagner S, Ruhkopf J, Gahoi A, Pandey H, Bornemann R, et al. Chemical Vapor Deposited Graphene: From Synthesis to Applications. Phys Status Solidi A 211 (2014) 2439.

5. Lupina G, Kitzmann J, Costina I, Lukosius M, Wenger C, Wolff A, Kataria S et al. Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene. ACS Nano 9 (2015) 4776.

6. Bablich A, Kataria S, Lemme MC. Graphene and Two-Dimensional Materials for Optoelectronic Applications. Electronics. 5 (2016) 13.

7. Riazimehr S, Bablich A, Schneider D, Kataria S, Passi V, Yim C et al. Spectral Sensitivity of Graphene/Silicon Heterojunction Photodetectors. Solid-State Electron 115 (2016) 207.

8. Kataria S, Wagner S, Cusati T, Fortunelli A, Iannaccone G, Pandey H, Fiori G, Lemme MC. Growth-Induced Strain in Chemical Vapor Deposited Monolayer MoS2: Experimental and Theoretical Investigation. Adv Mat Inter (2017) DOI: 10.1002/admi.201700031.
(Invited) Peltier Supercooling with Isosceles Current Pulses: Cooling an Object with Internal Heat Generation
Authors: Piggott Alfred J , Allen Jeffrey S
Published: February 2020

Applying an electrical current pulse enables a transitory state in which the cold junction of a Peltier couple reaches temperatures below that obtained with a steady-state optimal current. This is known as supercooling. This supercooling is followed by a period of superheating. It has been shown for isosceles triangle shaped current pulses with the optimal combination of pulse-height and duration, the sum of supercooling and superheating can provide a net cooling advantage. In most cases, supercooling has been studied as a standalone couple and not as a system. The objective of this paper is to gain insight about the sensitivity of system performance metrics of COP, power consumption, cold junction cooling rate (Qc) and average mass temperatures during pulsed operation when used to cool a mass with internal heat generation. To accomplish this, a comprehensive parametric study was performed that includes pulse-height, pulse duration, thermal interface resistance, thermal effusivity of the cooled mass, heat spreader thermal conductivity, and internal heat generation of the cooled mass were varied. The temperature distribution inside the thermoelement during pulsing, and the effects of continuous pulsing at an optimized pulse-height and duration were also investigated. The study was accomplished with a system model that utilized electrical-thermal analogies in SPICE. It was demonstrated that Qc over an entire pulse event can be improved over Imax steady operation but not steady Iopt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced during pulse operation due to different time constants of Qc rate and power consumption. During part of the transient, lower performance interface materials can improve Qc and COP.
(Invited) 2D Materials for Solid State Thermionic Power Generation
Authors: Zebarjadi Mona
Published: February 2020

Solid-state thermionic power generators are an alternative to thermoelectric modules. In this presentation, we report an analytical model to investigate the performance of these generators in the non-linear regime. We identify dimensionless parameters determining their performance and provide measures to estimate acceptable range of thermal and electrical resistances of thermionic generators. We find the relation between the optimum load resistance and the internal resistance and suggest guide lines for the design of thermionic power generators. Finally, we discuss the possiblity of using layered 2D heterostructures to design nanoscale thermionic coolers capable of working at relatively low temperatures.
(Invited) Exploring Thermoelectric Materials Using Predictive Theoretical Modeling
Authors: Maassen Jesse , Askarpour Vahid
Published: February 2020

An important challenge facing society involves reducing our energy consumption and shifting away from fossil fuels and towards sustainable, abundant sources of power that do not harm the environment. Waste heat is a tremendous unutilized energy source, accounting for roughly 60% of the energy humans produce, that if we could only partially recover would have a major impact. Thermoelectrics (TE) provide a solution as materials than can convert heat into electrical power. A major goal is to enhance the TE conversion efficiency, characterized by the figure-of-merit ZT, which depends on the material TE properties: Seebeck coefficient, electrical conductivity and electronic/lattice thermal conductivities. Increasing ZT is critical for the advancement of TE technologies, but difficult since the TE properties are interrelated. To discover more high-ZT materials, it is important to explore and design new materials with unique properties tailored for TE conversion. In the past decade, there have been several breakthroughs in this direction, including nanostructured alloys, resonant impurity states, superlattice structures, all-scale defect engineering, and ultra-low thermal conductivity materials. These, like most advances, were experimentally led and based on trial-and-error, which can be expensive and time-consuming. To help guide experimental efforts and expedite discoveries, there is an opportunity to explore emerging materials using predictive theoretical modeling.

In this talk, I will present recent work focused on the development and application of a first principles approach for TE parameter predictions. I will describe our adopted framework, which combines density functional theory (DFT) and the Boltzmann transport equation (BTE). DFT is employed to extract the full electron and phonon dispersions, and to compute the detailed electron-phonon and phonon-phonon lifetimes, the dominant scattering mechanisms for electrons and phonons, respectively. These material properties serve as input for the BTE, which is solved for the TE transport coefficients. With this DFT-based approach, all TE parameters are obtained predictively, including Seebeck coefficient, electrical conductivity and electronic/lattice thermal conductivities, as a function of temperature and carrier concentration. Recent results on select materials, for example SnSe, will be presented to demonstrate the approach and to illustrate how we can gain physical insight. This work will help guide experimental breakthroughs by theoretically exploring and identifying new TE materials with enhanced properties.
(Invited) High Performance and Flexible Nanostructured Thermoelectric Devices By Additive Printing of Colloidal Nanocrystals
Authors: Zhang Yanliang
Published: February 2020

Thermoelectric generators (TEGs) produce electrical power using thermal energy from various sources, including the waste heat. Thermoelectric materials have undergone tremendous improvement of the figure of merit ZT in recent two decades largely attributed to nanostructuring. Despite these progresses in materials performances, the high cost of manufacturing the nanostructures into functional materials and devices is still a significant barrier to bring these materials into commercial domain.

Screen printing allows for direct conversion of thermoelectric nanocrystals into flexible energy harvesters and coolers. However, obtaining flexible thermoelectric materials with high figure of merit ZT through printing is an exacting challenge due to the difficulties to synthesize high-performance thermoelectric inks and the poor density and electrical conductivity of the printed films. Here, we demonstrate high-performance flexible films and devices by screen printing bismuth telluride based nanocrystal inks synthesized using a microwave-stimulated wet-chemical method. Thermoelectric films of several tens of microns thickness were screen printed onto a flexible polyimide substrate followed by cold compaction and sintering. The n-type and p-type films demonstrate peak ZTs of 0.43 and 0.8 along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. The printed nanostructured thermoelectric films present ultralow thermal conductivities due to the nanoscale grains and pores, which significantly scatter the phonon transport and reduce phonon mean free path.

A flexible thermoelectric device fabricated using the printed films produces a high power density of 4.1 mW/cm2 with 60 ºC temperature difference between the hot side and cold side. The highly scalable and low cost process to fabricate flexible thermoelectric materials and devices demonstrated here opens up many opportunities to transform thermoelectric energy harvesting and cooling applications.