bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Conductive Carbon Nanofiber-Graphite Paper Electrodes with Ultrahigh Polysulfide-Loading for Advanced Lithium-Sulfur Batteries
Authors: Yan Jianhua , Li Bingyun , Liu Xingbo 
Published: February 2020

Lithium sulfur (Li-S) battery has attracted much attention due to its high energy density and the abundance of sulfur on the Earth, but some major problems including short cycle life, low sulfur loading, and inferior sulfur utilization have impeded its practical applications. Here, wereport a rational combination of conductive carbon nanofiber-graphite paper (CNGP) with dissolved polysulfides to the formation of advanced sulfur cathode structures that can take full advantage of each building block. The hierarchical CNGP electrode has an ultrahigh sulfur loading of 6.7 mg cm-2, and a high electrical conductivity of 328 S cm-1. In the CNGP electrode, the integrated carbon nanofiber paper (~100 μm) with extremely low density (2.1 mg cm-2) is used as current collector and carrier for the dissolved Li2S6 species, while the densely tapped graphite film (~5 μm) on the top of CNF acts as a protection layer to prevent migration of the dissolved polysulfides from the cathode to the anode. The use of CNGP electrodes and dissolved Li2S6 species enables the fabrication of remarkably improved Li-S batteries with a reversible capacity of 750 mAhg-1 over 300 cycles at 1 C, and 80% of capacity retention from 720 to 580 mAhg-1 over 500 cycles at 1.5 C with an average Coulombic efficiency of 99.5%. The results provide important progress towards the fabrication of Li-S batteries with long cycle life and high rate capabilities.
Carbon Wrapped Sulfur Cathode Materials for Rechargeable Batteries
Authors: Kumar Arun , Gallozzo moises-Miguel , Tomar Maharaj 
Published: February 2020

Introduction:

Currently available rechargeable Li-ion batteries based on spinal, layer and olivine crystal structures of Li (Mn, Ni, Co) Ox and related material systems, shows lower capacity and poor cycling characteristics. In addition, LiCoO2 is expensive and environmentally unfriendly. Due to high volume and gravimetric energy density, rechargeable lithium batteries have become the dominant power source for portable electronic devices including cell phones and laptops. However, the energy and power densities of rechargeable lithium batteries require significant improvement in order to power electric vehicles1. Lower specific capacities of cathode materials (~150mAh/g for layered oxides and ~170mAh/g for LiFePO4) compared to those of the anode (370mAh/g for graphite and 4200mAh/g for Si) have been a limiting factor to the energy density of batteries. It is highly desirable to develop and optimize high capacity cathode materials for rechargeable lithium batteries.
Sulfur is a promising cathode material with a theoretical specific capacity of 1672mAh/g,2 ~ 5 times higher than those of traditional cathode materials based on transition metal oxides or phosphates. Sulfur also possesses other advantages such as low cost and environmental friendly.

Experimental:

Here we present a rational design and synthesis of a novel carbon-sulfur composite material at low temperature. Sulfur particles are synthesized and wrapped by carbon black a simple assembly process. The phase formation behavior of the synthesized powder was investigated using X-ray diffraction, using Cu Kα radiation. The morphology of the synthesized powder was investigated using a scanning electron microscopy (SEM), and transmission electron microscopy (TEM, Carl Zeiss Leo Omega 922 at 200 KeV).

Result:

The XRD patterns (Fig1.) of all samples could be indexed to the orthorhombic space group based on the phase –pure ordered structure. Electrochemical properties will be study using cyclic Voltammetry, Charge-Discharge Curves, and Electrochemical Impedance spectroscopy (EIS). These measurements are still in progress.
Fig1. X ray diffraction patterns of Sulfur-carbon composite (insert morphology image).

References:

Bruce, P. G.; Scrosati, B.; Tarascon, J. Angew. Chem. Int. Ed. 2008, 47, 2930-2946

Ellis, B. L.; Lee, K. T.; Nazar, L. F. Chem. Mater. 2010, 22, 691-714

Figure 1
High Energy Density, Long-Life Li-S Batteries for Aerospace Applications
Authors: Bugga Ratnakumar V , Jones Simon C. , Pasalic Jasmina , Addison Dan , Thiallaiyan Ramanathan 
Published: February 2020

Lithium-ion batteries have been successfully employed in several Mars surface missions, e.g., Mars Exploration Rovers (Spirit and Opportunity), Mars Phoenix Lander, and more recently in the Mars Science Laboratory rover (Curiosity).1 With distinct benefits in gravimetric and volumetric densities combined with good low temperature performance relative to the aqueous battery systems, Li-ion batteries contribute to reduced launch costs, increased payload and science capabilities in the space missions. NASA’s upcoming missions however need energy storage systems with enhanced performance capability, especially higher specific energies and energy densities. One such application involves astronaut Extra Vehicular Activity (EVA), wherein the astronaut’s Portable Life Support System (PLSS) is expected to support 8 hours of EVA. The state of art batteries with ~200 Wh/kg at the cell level can support only four hours of EVA.
To address these needs, we are developing high-energy and long-life lithium-sulfur cells, with the following performance targets: cell specific energy of 400 Wh/kg ii) cycle life exceeding 200 cycles and iii) ability to operate safely over a wide temperature of -10 to +30 °C. We have been developing improved cell components for Li-S cells, e.g., protected Li anode, dense sulfur cathode and compatible electrolytes, mainly addressing the key technological hurdlesof poor utilization at high cathode loading (necessary for a practical high energy cell) and limited cycle life.2-5 We have developed new sulfur cathodes that show high specific capacities of ≥800 mAh/g at C/5 rate with practical material loadings, ii) Li anode protected with a polymer electrolyte that displays efficient Li cycling and durability in laboratory Li-S cells, and iii) Electrolytes and new proprietary coatings of polysulfide blocking layers which inhibit the deleterious effects of sulfur redistribution and contribute to a good cycle life. We have also developed suitable cell designs and fabricated pouch cells that displayed specific energies of ~300 Wh/kg, moderate cycle and safety towards thermal and electrical abuse. In this paper, we will describe some of these material developments and their performance in laboratory cells and later in prototype cells.

B. V. Ratnakumar, W. C. West, P. DeGrosse Jr., M. C. Smart, L. Jones and R.C. Ewell, NASA Battery Workshop, Huntsville, AL, November 6, (2012)

Y. Yin, S. Xin, Y. Guo and L. Wan, Angew. Chem. Int. Ed. 2013, 52, 13186 (2013).

S. Evers, L. F. Nazar, Acc. Chem. Res., 46, 1135 (2013);

X. Ji, K. T. Lee, L. F. Nazar, Nat. Mater. 8, 500 (2009).

A. Manthiram, S.-H. Chung, C. Zu, Adv. Mater. 27, 1980 (2015).

S. S. Zhang, Front. Energy Res. 1, 1 (2013).
(Invited) Vertical GaN p-i-n Diodes Formed by Mg Ion Implantation
Authors: Anderson Travis J , Greenlee Jordan D , Feigelson Boris , Hite Jennifer K , Hobart Karl D , Kub Francis J 
Published: February 2020

GaN is an ideal material for power applications due to its high breakdown field, high switching speed, and low switching losses. The ability to implant and activate dopants, particularly p-type dopants, in GaN still remains a challenge. Dopant implantation and activation is crucial for many devices since it is the most straightforward method of selective lateral doping in GaN. Devices such as the current aperture vertical electron transistor (CAVET), Schottky diodes with guard ring termination or grayscale junction termination extension, and vertical p-i-n diodes will be enhanced and enabled by the ability to selectively dope GaN without the need for etching or regrowth. Herein, we report on the first implanted p-i-n diode fabricated on a bulk GaN substrate.
A 8 μm thick unintentionally doped GaN layer was grown by metal organic chemical vapor deposition (MOCVD) on a n+ Ga-face c-oriented GaN substrate. The p-GaN anode and termination regions were formed by Mg implantation to a concentration of 2x1019 cm-3 following a box profile to a depth of 500nm. The implanted dopants were activated using the multicycle rapid thermal annealing (MRTA) technique described elsewhere [1]. After activation and removal of the protective cap structure [2], a 1 μm SiO2 field oxide layer was deposited by plasma enhanced chemical vapor deposition (PECVD). Contact windows were opened by reactive ion etching in a CHF3-based plasma. The anode metal was formed by lift-off of Pd/Au (20/100nm), followed by rapid thermal annealing in a N2atmosphere, and the cathode metal was a blanket film of e-beam deposited Al on the back side of the sample.
Rectifying behavior was observed, a first for a p-i-n structure formed by Mg ion implantation in GaN. The turn-on voltage is consistent with a p-n junction, and the ideality factor of 2.6 is consistent with a recombination/generation-based transport mechanism, confirmed by temperature-dependent I-V. Additional non-ideal behavior is associated with recombination in the drift layer due to crystalline defects. The devices suffer from high ON-resistance due to high contact resistance and recombination in the drift layer, which limited the forward current to 1 A/cm2. Capacitance-voltage measurements indicated the presence of a p-GaN layer, with a depletion layer thickness ~500nm and a doping density of 2x1018 cm-3, corresponding to an activation ratio of 10%.
1. B.N. Feigelson, et. al. J. Cryst. Growth. 350, 21-26 (2012)
2. J.D. Greenlee, et. al. Appl. Phys. Express 8 036501 (2015)
(Invited) Probing Metal-Graphene Interactions with Raman Spectroscopy
Authors: Cheng Guangjun , Calizo Irene , Hight Walker Angela R. 
Published: February 2020

Metal-graphene interactions play important roles in the fields of catalysis and electronics. In this talk, we demonstrate that Raman spectroscopy is a powerful tool to probe these interactions and will present two specific cases. First, we investigate the Fe-catalyzed etching of graphene layers in forming gas. Fe thin films are deposited by sputtering onto mechanically exfoliated graphene, few-layer graphene (FLG), and graphite flakes on a Si/SiO2 substrate. When the sample is rapidly annealed in forming gas, particles are produced due to the dewetting of the Fe thin film and those particles catalyze the etching of graphene layers. The microscopic and Raman spectroscopic evidence reveals that monolayer and FLG regions are severely damaged and that the particles catalytically etch channels in graphite. No etching is observed on graphite for the Fe thin film annealed in nitrogen. The critical role of hydrogen indicates that this graphite etching process is catalyzed by Fe particles through the carbon hydrogenation reaction. By comparing with the etched monolayer and FLG observed for the Fe film annealed in nitrogen, our Raman spectroscopy measurements identify that, in forming gas, the catalytic etching of monolayer and FLG is through carbon hydrogenation. During carbon hydrogenation, Fe particles are catalytically active in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon through hydrogen spillover. In the second case, we deposit a Ni thin film by thermal evaporation onto mechanically exfoliated graphene, FLG, and graphite, and probe the Ni-graphene interface using Raman spectroscopy. When the sample is annealed in forming gas, a Ni(111) thin film is produced on graphene, FLG, and graphite. We observe the disappearance of Raman signals from graphene underneath Ni(111) when using low laser power and the re-appearance of the Raman signals from the graphene with a higher power excitation laser. This work provides direct experimental evidence for the strong interaction between Ni(111) and graphene and confirms the result from the theoretical simulations that this strong interaction suppresses the Kohn anomaly in graphene.
(Invited) Electrochemical Nanowire Devices for Energy Storage
Authors: Mai Liqiang , Zhou Liang , Tian Xiaocong , Sun Ruimin , Yan Mengyu 
Published: February 2020

Nanowires have attracted increasing interests due to the one-dimensional nanomaterials can offer a range of unique advantages in many energy related fields. For previous lithium battery application, bulk materials made of nanowires were usually used as the electrodes. Although the electrochemical properties could be improved, the fast capacity fading is still one of the key issues and the intrinsic reasons are not clear until now. To understand intrinsic reason of capacity fading, we designed the single nanowire electrochemical devices for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode. Our results show that conductivity of the nanowire electrode decreased during the electrochemical reaction, which limits the cycle life of the devices. Based on this conclusion, a series of hierarchical structures nanowires have been obtained, including hierarchical MnMoO4/CoMoO4 heterostructured nanowires and hierarchical mesoporous La0.5Sr0.5CoO2.91 nanowires which show enhanced performance in Li-air batteries and supercapacitors.1 In our present work, a series of novel nanowire architecture have been designed and synthesized, including kinked hierarchical nanowires, hierarchical heterostructured nanowires and hierarchical scrolled nanowires which shows great electrochemical and biological probe performances.2-4 It is expected that our research may extend effective and helpful methods in directions that will solve the challenge of property degradation in energy storage and open new applications.5

References

[1] L. Mai, et al., Nat. Commun., 2011, 2: 381.
[2] L. Mai, et al., Nat. Commun., 2013, 4: 2923.
[3] Q. Qing, et al., Nat. Nanotechnol., 2014, 9, 142.
[4] Y. Zhao, et al., Nat. Commun., 2014, 2014, 5: 4565
[5] L. Mai, et al., Chem. Rev., 2014, 114, 11828.
Simulation of the pH Sensing Capability of an Open-Gate GaN-Based Transistor
Authors: Patrick Erin , Choudhury Mohua , Law Mark E 
Published: February 2020

Heterostructure transistors based on the AlGaN/GaN material structure are popular for chemical and biological sensors because of their nontoxicity and chemical inertness in biological or corrosive environments. They also offer very high sensitivity as a result of the very large gain and transconductance. Studies over the years show much research on this technology for sensing applications including pH sensing, prostate cancer detection, and breast cancer detection. However, the designs of these devices are not optimized because of nonexistent or rudimentary modeling and simulation support.
Commercial software packages adept at simulating III-V-based transistors do not have applications built-in for chemical sensing capability. Current research relies on analytical models and in-house numerical programs to do specific and limited simulations.
We build upon a TCAD simulation framework (FLOODS) specifically suited for III-V device simulation that is capable of self-consistent, fully-coupled simulation of reaction-dependent physics at the electrolyte/semiconductor interface. This paper outlines the simulation methodology for a pH sensor using an open-gate AlGaN/GaN High Electron Mobility Transistor (HEMT). The interfacial reactions are coupled to traditional device simulation equations, i.e. Poisson and carrier continuity. This enables surface charging reactions to be directly coupled to the device output terminal characteristics. We also solve for electrostatic field and ion transport in the electrolyte. This work will enable optimization of specific sensor technologies or exploration of the fundamental physics behind the sensing mechanism.
Investigation of the Dynamic Relaxation Behavior of Biomolecules Immobilized on Metal Electrode in Time Domain
Authors: Hsu Chen-Pin , Wang Yu-Lin 
Published: February 2020

Biomolecules such as DNA immobilized on metal electrodes and non-Faradaic current was measured in buffered solution. The metal-biomolecules-liquid-metal structure can be regarded as a liquid type of capacitor. The measurement of the capacitive current, which is affected by the ions, biomolecules, and liquid in the solutions. It is interesting to investigate the charging and discharging process in time domain, which brings important information of the dynamic behavior of the whole system. In this study, double-stranded DNA (dsDNA) was immobilized on gold electrodes and the capacitive current was measured in buffer solution with a pulse stimulus. Different relation time constants were revealed for various surface modifications. The transient current of the sensor was measured in de-ionized water and in 30 mM TE buffer before dsDNA immobilized metal electrode, and in 30 mM TE buffer after dsDNA immobilized on the metal electrode, followed by different concentrations of HIV-1 RT protein, ranging from 1 aM to 100fM. This technique shows ultra-high sensitivity of the protein detection (1 aM), indicating that this technique is promising for biosensor applications.
Figure 1 shows the schematic of device for capacitive current measurements.
Terahertz Spectroscopy: Studying Carrier Dynamics in Semiconductor Nanostructures
Authors: Titova Lyubov V. , Xu Sijia , Baribeau Jean-Marc , Lockwood David J , Hegmann Frank 
Published: February 2020

Understanding the ultrafast dynamics of photoexcited carriers in semiconductor nanostructures and their dependence on sample morphology is crucial for their incorporation into photonic devices. Time-resolved terahertz (THz) spectroscopy is an all-optical, contact free technique that allows directly measuring the transient mobile carrier dynamics and terahertz conductivity over picosecond time scales, and is uniquely suitable as a probe of conductivity in nanomaterials.
We have applied time-resolved THz spectroscopy to investigate ultrafast carrier dynamics to a variety of nanostructured semiconducting systems such as silicon nanocrystal films, nanogranular iron pyrate (FeS2) and vanadium dioxide (VO2). Furthermore, terahertz emission spectroscopy of nanomaterials, where the sample itself emits THz radiation in response to optical excitation, provides important insights into carrier dynamics. We have recently generated THz pulses from optically excited macroscopic arrays of aligned single-wall carbon nanotubes (SWCNTs). We propose that top-bottom asymmetry present in the SWCNT arrays produces a built-in electric field in semiconducting SWCNTs, which enables generation of polarized THz radiation by a photocurrent surge.
Measurement of Recombination Lifetimes in Gesn Alloys
Authors: Erdman Emily , Senaratne Charutha , Menendez Jose , Kouvetakis John , Mathews Jay 
Published: February 2020

Silicon photonics requires the development of Si-based lasers, modulators, waveguides, and detectors operating in the infrared beyond the band gap of silicon. A number of approaches to solving this problem have been pursued, including epitaxial growth of lower band gap materials on Si. The SiGe alloy system was explored for many years, but limitations in quality due the large lattice mismatch between Si and SiGe with high amounts of Ge, as well as the band gap (0.66 eV at its lowest for pure Ge) and its indirect nature, have prevented its widespread use. Integration of III-V materials such as InGaAs has also been tried extensively, but the problems of phase segregation and film quality have not been overcome.
The GeSn alloy system has been gaining attention in the photonics world due to its unique optical properties, and the growth of these alloys on Si platforms has jumpstarted efforts to employ this technology for the fabrication of CMOS-compatible infrared optoelectronics. These crystalline alloy films are grown directly on Si or Ge-buffered Si, have band gaps below that of Si or Ge, and are grown to thicknesses of up to 1 µm. Additionally, the band gap of GeSn should be direct for concentrations greater than about 10% Sn.
Much work has been done on the development of GeSn materials, and theoretical designs for lasers based on these alloys have been appearing in the literature frequently. However, the realization of complex optoelectronic devices like laser diodes requires materials with long recombination lifetimes to achieve population inversion. Thus, the study of recombination lifetimes in GeSn alloys is of paramount importance to the actualization of GeSn lasers. Unfortunately, the standard method of time-resolved photoluminescence (TRPL) is not well-suited to the study of GeSn alloys. For low Sn contents (<10% Sn), the band gap is indirect, so the intensity of optical emission is not high. Such a measurement would require single photon counting, but single photon detectors are not available at the emission wavelengths for the materials of interest. Conductivity-based methods should be more suitable, but the standard techniques of microwave photoconductive decay (µ-PCD) and RF-coupled photoconductive decay (RFPCD) suffer from low sensitivity in thin films or low temporal resolution.
In this work, we employ a new conductivity-based method for measurement of recombination lifetimes in thin film GeSn alloys. The method of transmission-modulated photoconductive decay (TMPCD) uses the transverse transmission of microwaves through a thin film, allowing for a very large interaction volume between the free carriers and the microwaves, thereby increasing the sensitivity for thin film materials. We will discuss this new method and show preliminary results on GeSn films with up to 7% Sn.
A Npg-Based Ultra-Thin Anode Catalyst Layer for Spewe
Authors: Zeng Yachao , Guo Xiaoqian , Wang Xunying , Wang Zhiqiang , Yu Hongmei , Shao Zhigang , Yi Baolian 
Published: February 2020

Nanoporous gold (NPG) has a long history of application. By electrochemical or chemical removal of Ag from AgAu alloy, the remaining gold undergoes a self-organization process forming a 3D bicontinuous network with interconnected ligaments. Due to its relatively high surface area, high conductivity, small size ligament and 3D bicontinuous porous structure, NPG has found its way in electrocatalysis, bio-sensors, and fuel cells. By extending dealloy time or thermal coarsening temperature; the structure of NPG can be easily tuned.
In this paper, a facile method was proposed for a novel MEA applied in solid polymer electrolyte water electrolysis (SPEWE). NPG with a thickness of 100 nm dealloyed from 12K gold foil was employed as substrate. IrO2 was deposited onto its surface via a conventional thermal decomposition method. A loading of IrO2 as low as 50 μg cm-2 was achieved in this experiment while keeping an acceptable performance. With a IrO2 loading of 0.2 mg cm-2，the performance was 1.686 V@ 1000 mA cm-2 at 80 ºC. Scanning electron microscopy measurement showed that IrO2 formed a uniform thin layer on the surface of NPG. The maximum thickness is 500 nm, which is only 1/20 to the conventional catalyst layer. The ultra-thin catalyst layer eased the transport of reactant and product, which reasonably explicated the remarkable performance. During the stability test, the cell voltage was constant over 200 h at 250 mA cm-2. The result here demonstrated that an ultra-thin catalyst layer with a low IrO2 loading could applied in real solid polymer electrolyte water electrolyzer.