bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonia Electrochemical Synthesis Using Platinum Ruthenium Alloy at Ambient Pressure and Low Temperature
Authors: Schechter Alex , Manjunatha Revanasiddappa , Karajic Aleksandar
Published: February 2020

Large scale energy storage from renewable is a critical step for development of CO2 free modern society. Electrical energy conversion to chemical compound is one of the preferred alternatives for grid leveling, photovoltaic and windmills storage applications. Nitrogen (N2) reduction to ammonia (NH3) is being offered as an interesting approach of chemical energy storage solution, due to the properties of ammonia which includes high energy density, liquefaction at relative low pressures (10 bars at room temperature) and availability N2 from air. Nevertheless, the slow electrochemical reduction of N2 to NH3 and low coulombic efficiency are the main herders in promoting nitrogen to ammonia technology.

Ammonia was electrochemically produced from nitrogen and water using a ruthenium-platinum (RuPt) alloy catalyst cathode and a nickel anode under ambient pressure and room temperature. The rate of ammonia formation was 5.1×10-9 gNH3 s-1cm-2 with a 13.2% faradaic efficiency at an applied potential of 0.123 V vs. RHE and it reached 1.1×10-8 gNH3 s-1cm-2 at 0.023 V. Ammonia formation reaction was investigated under selected potentials and temperatures and analyzed. Real-time direct electrochemical mass spectrometry (DEMS) analysis of the evolved gases measured at various applied potentials detected only the mass signals of hydrogen and ammonia, which exhibit intensities increase with overpotentials, with no trace of a hydrazine signal at the full potential range. Compared to metallic ruthenium and platinum catalysts, RuPt showed a an improved kinetic indicating a synergistic effect in the reduction of N2, attributed to proximity of Pt-H and Ru-N sites acting in a co-catalysis mechanism (figure 1). An analysis of these processes and comparison to FeOx based stat of the art catalysts are discussed.

Figure 1. Proposed Cooperative Reaction Mechanism for N2 reduction to NH3 on RuPt

Figure 1
(Invited) Investigating the Photoelectrocatalytic Activity of Titania for Nitrogen Fixation Using Rotating Ring-Disk Electrode Voltammetry
Authors: Hatzell Marta C. , Liu Yu-Hsuan
Published: February 2020

Reports of photocatalytic nitrogen fixation on titania have surfaced for nearly eight decades [1]. Demonstrations have occurred in both the gas and aqueous phase, and with various environmental conditions (relative humidity, temperature, pressure). Nearly all experimental observations suggest that abiotic nitrogen photofixation may be possible at ambient temperature and pressure [2,3]. This is impactful as it promotes the possibility for nutrient based fertilizer production from environmentally abundant materials (minerals) using only the sun as a source of energy. However, the reaction pathway that results in ammonia production is not well understood. Furthermore, the wide band gap mineral coupled with the location of the band edges, suggest that nitrogen reduction not likely. Here, we aim to investigate photo-catalytic nitrogen fixation by titania in an aqueous environment through a series electrocatalytic rotating ring disk voltammetry experiments. We demonstrate that this experimental approach is effective at discerning the low-level ammonium concentration intrinsic to photocatalytic nitrogen fixation experiments through monitoring the ammonia oxidation peak at the ring electrode. Results show that that no ammonium is detected without illumination with both a rutile and mix-phased titania photocatalyst. With illumination ammonium was detected with the rutile phase titania, but not with the mixed phase photocatalyst. This suggest that mineral phase plays an important role in promoting nitrogen photofixation. Rotating ring disk electrode experiments may provide a new avenue to attain a higher degree of precision for detecting ammonia at low levels from both photo and electrocatalyst.

[1]N. Dhar, E. Seshacharyulu and N. Biswas, Proc. Natl. Acad. Sci., India, 1941,7, 115–131

[2]A. J. Medford and M. C. Hatzell, ACS Catal., 2017, 2624–2643.

[3]G. Schrauzer and T. Guth, J. Am. Chem. Soc. , 1977, 99, 7189–7193.
Improvement of High-Rate Performance of LiFePO4 Cathode with through-Holed LiFePO4/Activated Carbon Hybrid Electrode Structure Fabricated with a Pico-Second Pulsed Laser
Authors: Watanabe Tatsuya , Tsuda Takashi , Gunji Takao , Ando Nobuo , Tanabe Toyokazu , Nakamura Susumu , Soma Naohiko , Hayashi Narumi , Ohsaka Takeo , Matsumoto Futoshi
Published: February 2020

In order to improve high-rate performance of lithium iron phosphate (LiFePO4, LFP) cathodes, the LFP and activated carbon (AC) layers were coated on one side and the other side, respectively, of an aluminum (Al) current collector (producing the LFP/AC cathode), and then through-holes with the average diameter of 18-23 mm and opening rate of 0.44-0.64 % were formed in the LFP/AC cathode (producing the through-holed LFP/AC cathode). The cell fabricated with one through-holed LFP/AC cathode and two lithium (Li) metal anodes exhibited a significantly improved high-rate performance in the C-rate region of 50 to 100 C. The through-holed LFP/AC cathode was found to be superior in high-rate performance to a through-holed LFP/LFP cathode, where the LFP layers were coated on the both sides of an Al current collector, and a LFP/AC cathode having no through-holes. From the results obtained, it was found that, in a high-rate discharging process, AC layer is at first discharged because of its higher high-rate performance than the LFP layer and then energy (electrons) is (are) transferred by the difference in the electrode potential between the AC and LFP layers from the charged LFP layer to the discharged AC layer with the transfer of Li+ ions via through-holes from the AC layer to the LFP layer (i.e., the AC layer is charged again) and a series of such processes are repeated (Fig. 1). Forming through-holes in the LFP/AC cathode results in an improvement in its charging/discharging capacity and high-rate performance.

Fig. 1 Schematic drawing of charging/discharging processes of the through-holed LFP/AC cathode. (A) Fully discharged condition, (B) fully charged condition, (C) first discharging of AC at high rate, (D) first open-circuit condition and electron and lithium transfer to charge the AC, (E) second discharging of AC at high rate, (F) second open-circuit condition and electron and lithium transfer to charge the AC.

Figure 1
Nanostructured Nickel Hydroxide Cathodes for Energy Dense, Safe, Aqueous Rechargeable Nickel–Zinc Batteries
Authors: Kimmel Samuel W. , Ko Jesse S. , Long Jeffrey W. , Parker Joseph F. , Rolison Debra R. , Rhodes Christopher P.
Published: February 2020

Batteries that offer high gravimetric and volumetric densities coupled to improved safety and lower cost are needed for applications ranging from electric vehicles, portable electronic devices, and grid-level energy storage. Lithium-ion is presently the go-to high-energy battery technology of choice due to its high energy content, but suffers from inherent safety issues that can result in fires and explosions causing property damage to injury or death. The alkaline nickel–zinc (Ni–Zn) battery is an attractive alternative to Li-ion because it uses nonflammable aqueous electrolyte and benign electrode materials. Recent work at the U.S. Naval Research Laboratory has demonstrated that monolithic three-dimensional zinc “sponge” architectures solve long-standing performance limitations for zinc anodes and pave the way for next generation Ni–Zn batteries that approach the specific energy of Li-ion systems.1 To match these advancements at the zinc anode, Ni(OH)2 cathode structures with device-relevant capacity loading and rate capability are required. We use precipitation and microwave-assisted synthesis to explore the effects of varying Ni(OH)2 composition and nanostructure as a means to increase specific capacity beyond the performance of benchmark β-Ni(OH)2 cathodes. Our preliminary results show that isomorphic metallic substitution within Ni(OH)2 stabilizes typically unstable α-Ni(OH)2 under alkaline conditions and provides improved charge-storage capability at high rate compared with β-Ni(OH)2. Promising α-Ni(OH)2 nanomaterials are fabricated into high areal–capacity cathodes, paired with zinc sponge anodes, and evaluated in coin cells under challenging charge–discharge conditions.

References

Parker, J.; Chervin, C.N.; Pala, I.R.; Machler, M.; Burz, M.F.; Long, J.W.; Rolison, D.R., Rechargeable Nickel–3D Zinc Batteries: An Energy-Dense, Safer Alternative to Lithium-Ion. Science
2017, 356, 414–417.
Role of Additive Structure on Controlling Ceria/Substrate Interactions Relevant to Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP)
Authors: Wortman-Otto Katherine M , Saucedo Cynthia , Keleher Jason J.
Published: February 2020

Chemical Mechanical Polishing (CMP) has emerged as a critical process step for achieving global planarization in advanced integrated circuit manufacturing and has lead to the extension of Moore’s Law. Specifically, Shallow Trench Isolation (STI) CMP is used in the electrical isolation of the active components in an integrated circuit by actively removing TEOS and stopping on Si3N4 to achieve angstrom level uniformity and limit defectivity. Planarization of the overburden material is achieved through a balance of an applied mechanical force and the delivery of a colloidal dispersion (slurry) containing ceria (CeO2) nanoparticles, complexing additives, and rheology modifiers to the substrate surface. Currently, STI slurries contain chemical additives that selectively boost material removal rate (MRR) as well as enhance selectivity via non-covalent passivation films formed at the polishing substrate surface. A crucial factor in maintaining a high MRR is the presence of CeO2 surface oxygen vacancies, commonly associated with Ce3+surface oxidation state, which can be achieved either from pre-dispersion particle processing or though additive/nanoparticle surface reactions present in the slurry formulation. This study probed the impact of the slurry additive functionality, such as carboxylic acids, amines, and phenols, on the removal rate and post-CMP defectivity. Results suggest that the Ce3+ oxidation state is critical to performance but the Ce4+ oxidation state is also a viable reaction site as long as it remains uncomplexed and free of any site-blocking additives. The additive adsorption to the CeO2 surface will result in altering the dynamic interplay of the abrasive particle/chemistry at the substrate surface shifting CMP performance. Employing and correlating a suite of modified analytical methods, such as atomic force microscopy (AFM), electrochemical quartz crystal nanobalance (EQCN), dynamic contact angle measurements, fluorescence microscopy, pre/post characterization of particle properties (size and zeta potential), and dynamic contact angle, a strong correlation between surface energy and CMP performance metrics has been uncovered.
Directed Evolution of the Optoelectronic Properties of Synthetic Nanomaterials
Authors: Lambert Benjamin Paul , Gillen Alice Judith , Schuergers Nils , Wu Shang-Jung , Boghossian Ardemis Anoush
Published: February 2020

Directed evolution is a powerful approach for tailoring protein properties toward new or enhanced functions. This technique allows one to alter a protein in a directed manner even in the absence of a known relationship between protein structure and function. Several nanocomplexes, such as optical sensors based on DNA-wrapped single-walled carbon nanotubes (DNA-SWCNTs), similarly lack a known structure-function relationship. For example, DNA-SWCNT complexes exhibit variations in their fluorescence that depend on the sequence of the DNA wrapping. However, little is known about the relationship between the DNA sequence and its effects on the fluorescence properties of SWCNTs. In this study, we use directed evolution as a guided approach to tuning the optoelectronic properties of DNA-SWCNT complexes through DNA mutation. Applying this technique over two rounds of DNA mutagenesis and screening, we evolved a DNA-SWCNT sensor with a 57% enhancement in fluorescence intensity. Furthermore, this sensor shows retained selectivity and sensitivity towards the analyte of interest. Though we demonstrate this approach to improve sensor brightness, directed evolution offers far-reaching possibilities in the field that can also be applied to improve additional sensor properties such as sensitivity and selectivity.
(Invited) Learning to Predict Single-Wall Carbon Nanotube-Recognition DNA Sequences
Authors: Yang Yoona , Zheng Ming , Jagota Anand
Published: February 2020

In this work, we demonstrate the applicability of machine learning methods to discovery of special DNA sequences that recognize partner single-wall carbon nanotubes (SWCNT). DNA/SWCNT hybrids have enabled many applications because of their special ability to disperse and sort SWCNTs by their chirality and handedness. Much work has been done to discover recognition sequences which recognize specific chiralities of SWCNT, and significant progress has been made in understanding the underlying structure and thermodynamics of these hybrids. Nevertheless, de novo prediction of recognition sequences remains essentially impossible and the success rate for their discovery by search of the vast ssDNA library is very low. Here, we report an effective way of predicting recognition sequences based on machine learning analysis of existing experimental sequence data sets. Multiple input feature construction methods (position-specific, term-frequency, combined or segmented term frequency vector, and motif-based feature) were used and compared. The transformed features were used to train several classifier algorithms (logistic regression, support vector machine and artificial neural network). Trained models were used to predict new sets of recognition sequences, and consensus among a number of models was used successfully to counteract the limited size of the data set. Predictions were tested using aqueous two-phase separation. New data thus acquired was used to retrain the models by adding an experimentally tested new set of predicted sequences to the original set. The frequency of finding correct recognition sequences by the trained model increased to >50% from the ~10% success rate in the original training data set.
(Invited) Tailoring Optical and Chemical Properties of Nanotube-Based Nanohybrids
Authors: Martel Richard
Published: February 2020

Carbon and boron-nitride nanotubes are used as 1D templates to produce nanohybrid materials exhibiting tailored properties for optical imaging. On the one hand, the inner cavity of the nanotube is a confined space to encapsulate molecules and to assemble organic dyes into well-ordered aggregates having preferred alignments, such as head-to-tail structures. It has been shown that these assemblies exhibit enhanced optical effects in Raman and fluorescence spectroscopy and that they are stable in harsh chemical conditions and resistant against photobleaching. [1-3] The external wall of the nanotube can be used, on the other hand, to build stable chemical interfaces to the nanohybrids and control their chemical properties in different media (e.g. dispersion, selective bonding, enhance diffusion, etc.). Together, the inner and outer functions can be used to tailor the chemical and optical properties of the nanohybrids and prepare novel optical nanoprobes for bio-imaging applications.

Here we will review our recent work on the preparation of different nanotube-based nanohybrids made of either carbon or boron-nitride nanotubes for optical imaging. More particularly, we have adapted the functionalization of the carbon nanotubes to work more effectively in biological media and target more selectively cancer cells. We have also made advances towards the preparation of boron-nitride nanotube nanohybrids for fluorescence imaging with visible and near-infrared emissions. Finally, we will present recent results on the preparation and use of the nanotube nanohybrids to probe optically (remotely) the electrochemical transduction of pH in the vicinity of the nanoprobe.

[1] E. Gaufrès et al. Nature Photonics 8, 72–78 (2014)

[2] E. Gaufres et al. ACS Nano 10, 10220-10226 (2016)

[3] C. Allard et al. submitted.

This work is done in collaboration with E. Gaufrès, N. Tang, C. Allard, N. Shoghi, S. K. Mal, R. Nascimento, L. Duarte and L. Gaboury
(Invited) Facile Isolation of Semiconducting Single-Walled Carbon Nanotubes By Flavin-Based Supramolecular Chemistry
Authors: Hashimoto Wataru , Toshimitsu Fumiyuki , Nishida Jin , Staykov Aleksandar , Nakashima Naotoshi
Published: February 2020

The separation/purification of semiconducting single-walled carbon nanotubes (sem-SWNTs) with high quality is one of the most important issues in the science and technology of carbon nanotubes[1-4]. We have already reported that supramolecular coordination polymer [1] and hydrogen bonding systems [2] as well as use of a flavin molecule [3] are powerful methods for highly efficient adsorbent-free sem-SWNT separation.

Here, we designed and synthesized a flavin with thioalkyl substituent at 7- and 8 positions, then examined its selective sem-SWNT sorting behavior. We have found that the addition of a metal ion formed a complex with the flavin, which enhanced selective (8,6)SWNT sorting.

References

[1] F. Toshimitsu, N. Nakashima, Nature Communications, 2014, 5, art no. 5041.

[2] F. Toshimitsu, N. Nakashima, Sci. Rep., 2015, 5, art. no.18066.

[3] F. Toshimitsu, N. Nakashima, Chem. Eur. J., 2015, 21, 3359-3366.

[4] K. Akazaki, F. Toshimitsu, H. Ozawa, T. Fujigaya, N. Nakashima, J. Am. Chem. Soc.2012, 134, 12700-12707.
(Invited) Separation of Small Diameter Swcnts in 1 – 3 Steps with Aqueous Two-Phase Extraction
Authors: Li Han , Gordeev Georgy , Garrity Oisin , Reich Stephanie , Flavel Benjamin S.
Published: February 2020

An aqueous two-phase extraction (ATPE) technique capable of separating small diameter single walled carbon nanotubes in 1, 2 or at the most 3 steps will be presented. Separation is performed in the well-studied two-phase system containing polyethylene glycol (PEG) and dextran but it is achieved without changing the initial concentration or ratio of co-surfactants. Instead, the technique is reliant upon the unique surfactant shell around each nanotube diameter at a fixed surfactant concentration. The methodology to optimize the surfactant to a single set of conditions for the diameter range (0.69 - 0.91 nm) is provided and 11 different chiralities with a purity of 73 – 97% are isolated. These include semiconducting and both armchair and non-armchair metallic nanotube species. Titration of co-surfactant suspensions reveal separation to be driven by the pH of the suspension with each (n,m) species partitioning over a unique pH range. This allows for an (n,m) separation approach to be presented that is as simple as pipetting known volumes of acid into the ATPE system.
(Invited) Methylene Blue Helps to Reveal Selectivity of Carbon Nanotube Affinity to Dispersing Agents
Authors: Bachilo Sergei M. , Zheng Yu , Weisman R. Bruce
Published: February 2020

Methylene Blue (MB) is a water-soluble dye which can physically absorb on single-wall carbon nanotube (SWCNT) surface. We discovered the dye can quench SWCNT fluorescence when it is added to a SWCNT dispersions in water. At the same time its own fluorescence is quenched. Analyzing the parameters of both these quenching processes we observed that the attachment of the dye to a SWCNT depends strongly on the quality of the SWCNT coating. As a result the quenching of specific SWCNT species can be used as a specific indicator of the species “protection” and its affinity to a dispersing agent.

We have observed that the SWCNT quenching by MB is relatively weak in a case of good ionic surfactants, and such a quenching process does not indicate any specific or unexpected trends. Lowing stability of the protective layer due to lower surfactant concentration or unfavorable pH was causing an increasing quenching. More specific effects were detected with more selective process or SWCNT suspended with single-stranded DNA (ssDNA). Relative quenching of SWCNT species in this case was not constant, and could be used as a measure of adhesion strength or density of the SS-DNA on these species. The process of MB attachment was found to be dynamic, and it be described by an temporal attachment of MB molecules to a SWCNT. A quenching model was developed, resulting in a mathematical description with only two parameters. One of them is the adhesion strength (or binding energy), and another is the available volume (space) near a nanotube surface. The most obvious parameter, the available volume, was increasing in a case of a weaker (sparse or thin) coating of SWCNT surface by ssDNA, that was associated with a lower affinity of such ssDNA type to a SWCVNT species. The volume was becoming much smaller with a good ssDNA-SWCNT affinity, preventing in this way the interaction of the quencher with this SWCNT species.

The studied process has appeared to be a simple and reliable tool for quick comparison of the affinity between specific SWCNT and ssDNA in bulk SWCNT solutions. Physical and mathematical models can also help to understand and analyze a wider variety of interactions between SWCNT and suspending agents or wrappers. The attachment of external ionic molecules, such as MB, may also help in development of SWCNT separation methods.
(Invited) In Situ Study of Cobalt-Tungsten and Cobalt Nanocrystals Under Reactive Environment
Authors: Li Yan , Yang Feng
Published: February 2020

Revealing the catalyst structure in the working environment is crucial for understanding the controlled growth mechanism of single-walled carbon nanotubes (SWNTs). We used the aberration-corrected environmental transmission electron microscope (ETEM) combined with electron energy loss spectroscopy to detect the Co7W6 catalyst structure and composition in the reaction environment. With the quantitative analysis of high-resolution image, we showed that the Co7W6 catalyst structure keep stable with carbon feeding at 700-1100 ○C. Carbon caps were clearly observed to nucleate from the Co7W6 nanocrystals from ETEM. We also established in situ synchrotron X-ray absorption spectroscopy operated in the atmospheric-pressure CVD and demonstrated the stable local coordination structure of Co7W6. No carbides or carbon diffusion induced structural change was observed from these in situ characterization. It reveals that Co7W6 catalysts act as the stable structure template for the chirality controlled growth of SWNTs. Cobalt catalyzed SWNT growth is generally believed to carry out via a vapor–liquid–solid mechanism. We investigated the synergetic role of Co3C in Co catalyzed SWNT growth by ETEM. The carbon atoms disperse from surface into bulk of Co nanoparticle. The metallic Co is effective for catalyzing the formation of a cap, while Co3C, depending on the carbon feeding rate, is essential for subsequently elongating of the carbon cap. The growth of SWNTs is realized only by the cooperation of Co with Co3C in proper carbon feeding condition. These findings are helpful for the rational design of catalysts with high activity for SWNT growth.
(Invited) Distinct Coating Displacement Kinetics for Single-Wall Nanotube Enantiomers
Authors: Weisman R. Bruce , Zheng Yu , Bachilo Sergei M.
Published: February 2020

It is known that specific oligomers of single-stranded DNA (ssDNA) can show selectivity toward different (n,m) structural species of single-wall carbon nanotubes (SWCNTs). These selective interactions can also extend to the left- and right-handed helical forms of a single (n,m) species. An example of this is the ability of the (ATT)4 oligo to strongly distinguish between the two optical isomers of (7,5) SWCNTs. We show that this helicity-selective coating interaction causes a resolvable shift between the two enantiomers’ fluorescence spectra. Most strikingly, the room temperature rates of displacement of the (ATT)4 coating on exposure to sodium deoxycholate are found to differ by two orders of magnitude. This is shown from measurements of time dependent fluorescence spectra. During coating displacement, the enantiomer with high affinity for the ssDNA oligomer is deduced to form an intermediate hybrid that is not observed for the low affinity enantiomer. These results demonstrate the diverse and dramatic enantiomeric differences in properties of SWCNTs complexed with ssDNA.
(Invited) Ultra-Low Power Light Emission Via Avalanche and Sub-Avalanche Breakdown in Suspended Carbon Nanotubes
Authors: Cronin Stephen B.
Published: February 2020

We report near-infrared light emission in suspended carbon nanotube field effect transistors over a wide range of gate and bias voltages. An abrupt increase in both the electric current (90 μA/V) and electroluminescence intensity is observed at high bias voltages (∼3.5 V), when gated in the “off’ state (i.e., Vgate > 0 V). For bias voltages below the threshold for avalanche breakdown, we observe light emission due to the creation of exitons by impact ionization under these high electric fields. Here, we find that there is a relatively small region over which low power (∼nW) light emission is observed. By plotting the relative luminescence efficiency (i.e., light intensity/electrical power) as a function of the gate and bias voltages, we observe a very sharp feature corresponding to avalanche emission at which the electroluminescence efficiency is 2−3 orders of magnitude higher than that under all other conditions of gate and bias voltage. A steep increase in the current with bias voltage (i.e., large dI/dVb) is observed at the same gate and bias conditions of the highly efficient electroluminescence and signifies the onset of the avalanche process. We believe that these results demonstrate additional mechanistic evidence for achieving highly efficient light emission in carbon nanotubes via avalanche breakdown.

References:

Wang, B., F. Rezaeifar, J.H. Chen, S. Yang, R.S. Kapadia and S.B. Cronin, Avalanche Photoemission in Suspended Carbon Nanotubes: Light without Heat. ACS Photonics, 4, 2706-2710 (2017).

Wang, B., S. Yang, L. Shen and S.B. Cronin, Ultra-Low Power Light Emission via Avalanche and Sub-avalanche Breakdown in Suspended Carbon Nanotubes. ACS Photonics, DOI: 10.1021/acsphotonics.8b00896 (2018).
Highly Flexible Agnw-CNT Sponge
Authors: Kim JaeKeon , Lee Junyeop , Jung Daewoong
Published: February 2020

Carbon based-nano materials such as fullerene, carbon nanotubes (CNTs) and graphene are nanoscale structures with excellent mechanical and electronic properties. To this end, CNT-based have been considered as sensing materials for optical sensor, chemical sensor, physical sensor and environmental sensors. CNT is widely used as a conductive material for strain sensors that detect changes external forces through electrical signals due to low conductivity.

CNT-based Strain sensors were generally fabricated by transferring the individual or bundles of CNTs to the substrates using spin-coating, spraying, dip coating, and inkjet printing methods [1-2].

CNT-based Strain sensors are only weak bonding due to the van der Waals attraction force. resistance change with applied strain force because slipping of the among CNTs. so Linear changes in electrical properties at low strain, but saturation properties at high strain due to the tunneling resistance of the between CNTs [3].

In This paper, we used Silver nanowire CNT (AgNW-CNT) nanocomposite, has much improved mechanical and electrical properties of the saturation properties at high strain.

As one of the most important conductive materials, Ag nanowires (AgNWs) have recently attracted a lot of attention for potential applications as transparent and flexible electrodes [4].

The nanocomposite was prepared by mixing the Agnw(0.5wt%) and CNT(0.5wt%). Then, the Agnw-CNT Coated at the sponges. This Agnw-CNT Sponge can be deformed into any shapes elastically, sustain large-strain deformations, recover most of the material volume elastically, and resist structural fatigue under cyclic stress conditions.

In order to investigate the reliability and stability of Agnw-CNT Sponge sensor, repeatable tests were conducted using cyclic stretching and releasing. The sensitivity of the Agnw-CNT Sponge sensor was reliable and reproducible with fully returned to its original resistance value and improve the strain transfer, repeatability and linearity of the strain sensor.

[1] Jung et al, J. Vac. Sci. Technol. 32 (2014), 04E107.

[2] Han et al, Microelectron. Eng, 168 (2017), 50-54.

[3] Ning Hu et al, Acta Materialia, 56 (2008), 2029-2936.

[4] Feng Xu et al, Adv. Mater, (2012) , 24 , 5117-5122

Figure 1
Photoluminescence Intensity Fluctuations and Temperature-Dependent Decay Dynamics of Individual Carbon Nanotube Sp
3 Defects
Authors: Kim Younghee , Velizhanin Kirill , He Xiaowei , Sarpkaya Ibrahim , Yomogida Yohei , Tanaka Takeshi , Kataura Hiromichi , Doorn Stephen K. , Htoon Han
Published: February 2020

Recent demonstration of room temperature, telecommunication wavelength single photon generation by sp
3 defects of single wall carbon nanotubes established these defects as a new class of quantum materials1. However, their practical utilization in development of quantum light sources calls for a significant improvement in their imperfect QY (10-30%). Understanding the nature of the PL intensity fluctuations and decay dynamics is of critical importance to optimize the quantum light emission of SWCNT defects. Aiming toward attaining fundamental understanding necessary for addressing these critical issues, we investigate PL intensity fluctuation and PL decay dynamics of aryl sp
3 defects of (6,5), (7,5), and (10,3) single wall carbon nanotubes (SWCNTs) at temperatures ranging from 300 K to 4 K. In this work we identify the mechanisms responsible for the PL intensity fluctuations by analyzing the correlation between PL intensity fluctuations and PL lifetimes. This fluctuation of exciton occupancy could result from random opening of nonradiative quenching sites intercepting exciton population and/or existence of a fluctuating potential barrier around the defect. Furthermore, by analyzing the temperature dependence of PL intensity and decay dynamics of individual defects based on a kinetic model involving the trapping and de-trapping of excitons by optically allowed and forbidden defect states, we estimate the height of the potential barrier. Our analysis also provides further confirmation of recent DFT simulation results that the emissive sp
3 defect state is accompanied by an energetically higher-lying dark exciton state2.

References

[1] X. He et al., Nat. Photon., 2017, 11, 577

[2] M. Kim et al., J. Phys. Chem. C, 2016, 120, 11268
Polymorphic Structure of 1T´-Mo6Te6 Nanoplates and Few-atomic-layered 2H-MoTe2 for Efficient Pseudocapacitor
Authors: Pawar Sachin A. , Patil Dipali S. , Kim Donghwan , Lee Rochelle , Kim TaeWan , Shin Jae Cheol
Published: February 2020

Te-based transitional metal dichalcogenides (TMDs) as supercapacitors are gaining substantial attention with a few reports. The integration of 1T´-Mo6Te6 nanoplates (NPs) into few-atomic-layered two dimensional (2D) 2H-MoTe2 thin film has not been realized in supercapacitive studies. Herein, we demonstrate the growth of 1T´-Mo6Te6 NP/2H-MoTe2 thin film polymorphic structure through metal organic chemical vapor deposition (MOCVD) on Si/SiO2 and thereby, the successful transfer of these polymorphic structure on a flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitors. A layer by layer study of the Mo6Te6/MoTe2 polymorphic structure is carried out by varying the number of transfer layers on the Ni foam. The resultant supercapacitors demonstrate a three-fold enhancement in areal capacitance (1542 mFcm-2 at 10 mVs-1) compared to a single layer transferred electrode, together with remarkable electrochemical stability (96%) and high energy density (140.36 mWcm-2 at 4 mA). These supercapacitors outperform the TMD-based (Te-based) supercapacitors presented in the past, demonstrating the high potential for their application in energy conversion devices.

Keywords: 2D TMD, 1T´ phase, molybdenum ditelluride, 1D/2D polymorphic structure, supercapacitor
(Invited) Study of Ion Adsorption-Transfer Mechanisms in Nanoporous Carbon Electrodes: Application to Supercapacitors
Authors: Wu Yih-Chyng , Tsai Wan-Yu , Simon Patrice , Taberna Pierre-Louis
Published: February 2020

Research into the design of electrolytes of ionic liquids (ILs) for supercapacitor applications has grown in popularity in recent years. Unlike Li batteries where the composition of the electrolyte and the stability must meet several requirements (formation of SEI, electrochemical kinetics), the use of ionic liquids in supercapacitors opens interesting perspectives, in particular thanks to their high electrochemical stability. [1]. In this communication, it will be presented the results of an experimental study conducted using quartz crystal microbalance (eQCM) on nanoporous carbon based electrodes in contact with different electrolytes : neat IL and solvated IL as well as electrolyte mixture. EQCM turns out to be an effective analytic tool to bring new insights regarding the charge compensation mechanisms occurring while polarizing the carbon based electrode. In particular, it will be shown that charge compensation can involve different levels of desolvation of the counter-ions and that co-ions can also be used when the carbon electrode is polarized [2,3,4].

Références :

[1] P. Simon et Y. Gogotsi, Nature Materials, 7 (2008) 845-854.

[2] W.-Y. Tsai et al. JACS 8722−8728 (2014)

[3] J. Griffin et al., Nature Materials, 22 juin 2015 (doi: 10.1038 / nmat4318).

[4] Y.-C. Wu, P.-L. Taberna, P. Simon, Communications en électrochimie. 93, 119-122 (2018).
Effects of Hexamethylenetetramine Concentration on the Structure and Capacitance Characteristics of Ni(OH)2 Pseudocapacitors Produced By Electrodeposition.
Authors: Kim Dong Yeon , Jeong Young-Min , Son Injoon , Baek Seong-Ho
Published: February 2020

Compared with EDLCs, pseudocapacitors use a transition metal capable of forming a complex by charging and discharging electrons through a redox reaction. Ni(OH)2-based pseudocapacitors prepared by hydrothermal, sol-gel, and PVD methods exhibit high theoretical capacity and thermal stability. Electrodeposition is easy and fast, and the material can grow uniformly. In this study, we investigated the effect of Hexamethylenetetramine on the structure and capacitance characteristics of Ni(OH)2 pseudocapacitors. Ni(OH)2 formed on the nickel foam with a three dimensional structure and exhibited high electrical conductivity and porosity. In addition, the effects of HMT addition on the Ni(OH)2 structure and the electrochemical properties of the supercapacitors were investigated; HMT is the source of amine-based OH- in the Ni nitrate solution and causes the formation of the three-dimensional structure. Moreover, the effect of HMT on the growth behavior of Ni(OH)2 was analyzed from the resulting nanosheet structure. When electrodeposited at a constant voltage mode of -0.85 V vs Ag/AgCl, the addition of (up to 7.5mM) HMT reduced the cathodic current and accelerated the nucleation rate, resulting in a dense Ni(OH)2 structure on the nickel foam. Under these electrodeposition conditions, a capacitance was of 1174.392 F·g-1 , and the a maximum energy density was of 69.129 mWh·g-1 were achieved.

Figure 1
Investigation of Gainp Quantum Dots in the AlGaInP-Based Light Emitting Diodes
Authors: Oh Hwa Sub , Park Jong Min , Jung Sung Hoon , Lee Hyung Joo , Cho Young Dae , Jun Kyung Nam
Published: February 2020

Recently, AlGaInP-based light emitting diodes (LEDs) have experienced an impressive evolution in both device performance and market volume. However, development of new applications is required in order to realize their full potential in areas such as use as a light source for auto focusing in digital cameras, special illumination for particular functions in agriculture, and in full color displays. To enlarge their utility in these applications, it is necessary to fabricate and understand a new structure capable of emitting longer wavelengths of around 700 nm. In particular, AlGaInP heterostructure LEDs are lattice-matched with respect to the GaAs substrate, which limits the emitting spectrum to around 650 nm at the longer peak wavelength side. To fabricate an LED structure capable of emitting at a 700 nm peak wavelength, the composition (x) of GaxIn1-xP material in the active layer requires a compressive strain of larger than 1 %. This large lattice mismatch, however, causes significant problems in terms of both growth and device properties due to the formation of defects. To overcome these problems, it is necessary to relieve the well strain via the formation of islands, referred to as a Stranski-Krastanow (S-K) growth mode, in order to prevent the generation of dislocations [1,2]. However, in AlGaInP-based LEDs emitting at a 700 nm peak wavelength, the effects of well strain on the epitaxial growth and the realization of device performance has yet to be extensively studied. In this study, we investigate the behaviors of morphological and optical characteristics on the composition of Ga0.33In0.67P material and demonstrate the performance of a device emitting at around 700 nm using quantum dot (QD)-based LEDs.

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(Invited) Emission Origin of Lowly-Oxidized Graphene Quantum Dot Toward Light Emitting Devices
Authors: Jeon Seokwoo
Published: February 2020

Graphene quantum dots (GQDs), simply making graphene typically under 10 nm, and the change of emission behavior from known fluorescence on graphene draws huge interest for potential applications to display, lighting, and optoelectronic devices. GQD could be a new class of optical material with useful properties of tunable luminescence, low cost, and superior photo and chemical stability. Our group has developed unique exfoliation and dispersion methods of 2D materials by the intercalation of alkali metal/organics. With the advantage of the methods generally excluding, or controlling, the oxidation of 2D materials, we have studied the origin of intrinsic emission (~ 400 nm) of graphene in depth. With those samples, I will introduce the role of oxidation in GQDs which forms isolated small sp2 carbon hexagons within a GQD, known as subdomains. Experimental evidences supported with calculation of the formation energy of subdomains and bandgap will give a guideline to improve emission properties. With those understanding the first demonstration of GQD light-emitting diodes (GQD-LEDs) with 1,000 cd/m2, alternating current powder elctroluminescence (ACPEL) device, and GQD phosphorescence for security application promise the optical applications of 2D materials with further improvement.
(Invited) Selected Issues for SiC Mosfet Reliability
Authors: Green Ron , Habersat Daniel , Lelis Aivars
Published: February 2020

There remain a number of potential reliability issues associated with SiC power MOSFETs that interest the reliability standards community, of which this work will provide an overview of our understanding of three of those issues: (1) threshold-voltage stability; (2) body-diode robustness; and (3) short-circuit current robustness.

A recent survey of commercially-available devices shows a wide range of responses in threshold-voltage stability, which is affected primarily by active charge traps in the near-interfacial region of the insulating gate oxide. Their close proximity to the semiconductor interface leads to a strong time dependence in the direct-tunneling mechanism in response to changes in gate bias, necessitating the need for faster measurements and the maintenance of the stress bias before making post-stress measurements. The observation of the activation of additional traps during bias-temperature stress in older devices underlines the need for additional attention to high-temperature charging effects as well.

It is the case for at least one commercial vendor, that improvement in lower BPD density and enhanced device fabrication have led to significant improvements in body-diode robustness. Earlier vintage devices had showed varying levels of degradation in both the body diode and MOSFET on-state properties following current stress of the body diode, as well as degradation in the off-state drain leakage current.

Experimental results show that both commercially-available planar and trench SiC MOSFETs have suitable short-circuit (SC) withstand times, ranging from 6 to 13 μs at T = 25 °C, VGS = 20 V, and VDS = 600 V. Even when trench devices have an identical rating to planar devices, they likely will have a significantly smaller area and heat conducting volume, contributing to their lower robustness for the same SC test conditions. All the electrical results reported seem to be consistent with thermally-driven failure mechanisms. The official standard test method of a single, long pulse is found to not be as effective as a series of shorter, incremental gate pulses, which more accurately detect failure time, even in the case of latent or delayed failure.

All this work will be presented within the context of standards development within JEDEC, including a number of SiC-focused reliability task groups.
A Numerical Study of the V/III Ratio in the MOCVD Process with Pulsed Injection Method
Authors: Chen Jyh-Chen , Lin Wei-Jie , Hu Chieh
Published: February 2020

AlN layer grabs lots of attention as a great super lattice layer between Si or sapphire substrate and GaN-based material. V/III ratio in the AlN MOCVD process is regard as an important parameter which causes different AlN growth modes on the substrate surface. The growth mode changes from 3D nucleation to 2D growth while the V/III ratio decreases. On the other hand, the pulsed injection method is applied in the MOCVD process to depress parasitic reaction and improve the quality of the AlN film. However, the growth conditions at the wafer surface are strongly affected by the mass transport in the reactor chamber which depends on the flow pattern and gas phase reaction. The momentum, heat and mass transfers are complicated by the pulse action. Different types of pulse sequences and pulse times are reported for finding a better process condition. Until now, it still depends on the empirical data very much and induces enormous time consumption and financial cost in the chamber design process. A suitable numerical simulation is needed to be developed for overcoming this difficulty.

In this study, a time-dependent numerical model is developed to analysis the flow motion and the heat and mass transfer caused by different pulse conditions. For the case with the TMAl gas mixture maintained a constant and a pulsed NH3 gas mixture, the V/III ratio at the surface of substrate increases with the process time after the pulse of NH3 mixture ejected into the chamber. It approaches to a constant when the time is greater than a certain value. The V/III ratio decreases to zero after the pulse of NH3 mixture ends. The V/III changes quickly in a little time when the pulse of NH3 mixture is turned on or off. When the NH3 and TMAl are pulsed into the chamber alternatively, the V/III ratio at the surface of the substrate keeps increasing after the pulse of NH3 mixture turned on. The V/III ratio decreases to zero after the pulse of NH3 mixture turned off. The V/III ratio does not stay at a certain value like the cases which has the constant supply of TMAl mixture. Based on the variation of V/III ratio at the surface of the substrate, we can predict the history of the growth mode at the surface of the substrate during the process.
Analysis of Basal Plane Dislocation Dynamics in PVT-Grown 4H-SiC Crystals during High Temperature Treatment
Authors: Raghothamachar Balaji , Yang Yu , Guo Jianqiu , Dudley Michael
Published: February 2020

The deformation processes in 4H-SiC crystals are of particular interest because they generate mostly basal plane dislocations (BPDs) which are implicated in the degradation or premature breakdown of SiC power devices [1]. Fundamental understanding of the generation and multiplication of BPDs is critical for design of growth strategies to control the density of BPDs during PVT growth of 4H-SiC crystals. Recently, we reported on the direct observation of thermal gradient induced motion of BPDs through in-situ synchrotron X-ray topography imaging of PVT-grown 4H-SiC wafers subject to high temperature treatment [2]. The multiplication of BPDs by the operation and interactions of multiple Frank-Read sources leading to formation of complex configurations was reported. We have analyzed the series of images recorded during the in-situ experiment in detail to deduce the Burgers vectors and core structures of the moving dislocation segments and measure their individual velocities. Dislocations with Burgers vector along the off-cut 11-20 direction were found to be the only dislocations undergoing deformation during heat treatment. Sample was imaged after heat treatment and the segments of dislocations used for velocity measurements were found to be either pure screw or 60° dislocations comprised of Si cores. Using the kink-diffusion model, the activation energies for dislocation motion have been estimated from the velocity data for each of these dislocation types and found to be 2.21 eV for 60° and 3.28eV for pure screw segments respectively. These values are in good agreement with the macroscopic studies of yielding of semiconductor crystals during high temperature compression and indentation experiments [3,4]. Quantitative expression of the temperature dependent critical resolved shear stress required for dislocation motion has been derived from this analysis.

References:

[1] Lendenmann, F. Dahlquist, N. Johansson, R. Soderholm, P. A. Nilsson, J. P. Bergman, and P. Skytt, Mater. Sci. Forum 353-356, 727 (2001)

[2] Yu Yang, Jianqiu Guo, Balaji Raghothamachar, Michael Dudley, Swetlana Weit, Andreas N. Danilewsky, Patrick J. McNally, Brian K. Tanner, Mater. Sci. Forum, 924, 172-175 (2018)

[3] V. Samant, P. Pirouz, Int. J. Refractory Metals and Hard Materials 16.4-6 (1998).

[4] J-L. Demenet, M. H. Hong, P. Pirouz, Scr. Mater., 43, 865-870 (2000).
Radiation Effects in Diamond pHEMTs
Authors: Thapa Aayush , Shahin David , Christou Aris
Published: February 2020

Field effect transistors (FET) based on diamond have 2-dimensional hole gas (2DHG) as conduction channel. In terms of usability in harsh environment, an important aspect of diamond-based FETs is its promise of radiation hardness. Because of high binding energy of diamond, diamond transistors are predicted to be radiation hard. However, the way radiation affects the 2DHG conduction layer is unknown. This may be a problem as radiation may disrupt the 2D hole concentrations in the 2DHG channel. In this work, radiation effects in diamond with 2DHG layer is explored in two ways: (1) Using Hall effect measurements to monitor changes in transport properties, and (2) measuring current-voltage characteristics for the three-terminal devices to analyze changes in their device properties. Two different types of radiation were used. A cyclotron was used for proton irradiation on diamond substrates, and a high capacity dry cell, panoramic gamma irradiator with 60Co as source material was used for gamma irradiation on diamond-based FETs. Diamond substrates were irradiated with protons at 152 keV and fluence of 1012 particles/cm2. Likewise, diamond-based FETs were irradiated with gammas from a total dose of 100kRad up to 10 MRads and exhibited an annealing effect.

ACKNOWLEDGEMENTS

The authors thank the University of Maryland NanoCenter, the University of Maryland Radiation Facilities and Argonne National Laboratory for equipment and staff support. The effort depicted is sponsored by the Department of Defense, Defense Threat Reduction Agency under Grant No. HDTRA1-17-1-0007. The content of this information does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred. The authors acknowledge the assistance in material preparation from Jim Butler of EuclidTech Labs.