bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) High Performance Deep Ultraviolet Nanowire Light Emitting Diodes and Lasers
Authors: Mi Zetian , Zhao Songrui , Liu Xianhe 
Published: February 2020

Deep ultraviolet light sources are important for a broad range of applications including water purification, disinfection, and medical diagnostics. The currently reported AlGaN planar light emitting diodes (LEDs) and lasers generally exhibit poor performance, due to the presence of large densities of defects and dislocations and the inefficient p-type doping. In this context, we have investigated the molecular beam epitaxial growth and characterization of nearly defect-free AlGaN nanowire heterostructures grown directly on Si substrate. We have demonstrated AlGaN nanowire LEDs that can operate in the UV-B (280-320nm) and UV-C (<280 nm) bands, which exhibit excellent current current-voltage characteristics. We have further demonstrated electrically injected AlGaN nanowire lasers on Si that can exhibit relatively low threshold current densities (~ 100 A/cm2).
In this work, catalyst-free AlGaN nanowires were grown directly on Si substrate by radio-frequency plasma-assisted molecular beam epitaxy. Due to the diffusion controlled growth process, such self-organized AlGaN nanowires exhibit unique core-shell structures, with the presence of Al-rich AlGaN shell. As a consequence, the nonradiative surface recombination can be greatly suppressed. By varying the Al/Ga flux ratio during the growth process, the emission wavelengths can be controllably varied from ~ 210 nm to >340 nm. The nanowire heterostructures exhibit relatively high internal quantum efficiency (~ 80%) at room-temperature in the UV-C band. We have further identified that Mg-dopant incorporation can be significantly enhanced in AlGaN nanowires, compared to their planar counterparts, due to the reduced formation energy for Al(Ga)-substitutional Mg-doping. The resulting AlN nanowire LEDs can exhibit excellent current-voltage characteristics, with a turn-on voltage of 6 V.
We have also demonstrated that self-organized AlGaN nanowire arrays can function as a high Q optical cavity, due to the Anderson localization of light. The AlGaN nanowire lasers consist of n-AlGaN cladding layer, i-AlGaN active region, and p-AlGaN cladding layer. The devices were fabricated using standard photolithography and metallization techniques. Under continuous wave biasing conditions, the devices can exhibit very low threshold current density. For devices operating in the UV-AII (~ 320-340 nm) band, the threshold current density is ~ 12 A/cm2 at 6 K. The threshold current density increases slightly to ~ 200 A/cm2 for operation wavelengths in the UV-C band. The measured threshold current densities are nearly two to three orders of magnitude lower, compared to conventional AlGaN quantum well lasers under either optical pumping or electrical injection.
(Invited) Band Gap Tunable Monolayer WSe2(1-x)S2x Synthesis, Characterization and Device Applications
Authors: Xiang Bin , Huang Jian , Yang Lei , Fu Qi 
Published: February 2020

“Band gap engineering” in two-dimensional (2D) materials plays an important role in tailoring their physical and chemical properties. The tuning of the band gap is typically achieved by controlling the composition of the semiconductor alloys.1-4 Here, we report the synthesis and electrical properties of monolayer WSe2(1-x)S2x. The photoluminescence (PL) spectroscopy results confirm the tunable band gap in WSe2(1-x)S2x, which is modulated by varying the S content. Atomic-scale analysis was performed and the chemical composition was characterized using high-resolution scanning transmission electron microscopy and X-ray photoemission spectroscopy. The mobility and carrier concentrations were measured in as-grown monolayer-based transistor devices. The emergency of these 2D materials provides grand possibilities for future semiconductor device applications.
References:
1. Q. Feng, Y. Zhu, J. Hong, M. Zhang, W. Duan, N. Mao, J. Wu, H. Xu, F. Dong, F. Lin, C. Jin, C. Wang, J. Zhang and L. Xie, Adv. Mater., 2014, 26, 2648–2653.
2. Y. Gong, Z. Liu, A. R. Lupini, G. Shi, J. Lin, S. Najmaei, Z. Lin, A. L. Elías, A. Berkdemir, G. You, H. Terrones, M. Terrones, R. Vajtai, S. T. Pantelides, S. J. Pennycook, J. Lou, W. Zhou and P. M. Ajayan, Nano Lett., 2014, 14, 442–449.
3. H.-P. Komsa and A. V. Krasheninnikov, J. Phys. Chem. Lett., 2012, 3, 3652–3656.
4. M. Zhang, J. Wu, Y. Zhu, D. O. Dumcenco, J. Hong, N. Mao, S. Deng, Y. Chen, Y. Yang, C. Jin, S. H. Chaki, Y.-S. Huang, J. Zhang and L. Xie, ACS Nano, 2014, 8, 7130–7137.
(Invited) Hybrid Two-Dimensional Nanosheet Materials for Energy Storage Devices
Authors: Peng Lele , Zhu Yue , Yu Guihua 
Published: February 2020

Two-dimensional (2-D) materials have emerged as a promising material platform for next-generation energy storage and conversion devices. Owing to their advantageous features such as high mechanical flexibility, large surface area and open ion transport pathway within 2D layers, graphene and other 2-D metal oxides and metal phosphates based nanosheets materials have shown great promise in flexible high-density energy storage devices. In this talk we will discuss recent progress on graphene/inorganic based hybrid 2-D materials for high-performance energy storage devices including high-rate-capable Li-ion batteries and ultraflexible solid-state supercapacitors.
(Invited) Microscopic Studies of Black Phosphorus and Its Field-Effect Transistors
Authors: Pan Minghu , Yuan Hui , Xu Ya-Qiong , Zhou Zhixian , Meunier Vincent 
Published: February 2020

An increasing number of alternative two-dimensional (2D) materials are being explored in the “post-graphene age”, such as transition metal dichalcogenides (TMDs), silicene, and germanene. These materials are studied with the hope of overcoming graphene’s deficiencies such as its zero bandgap. Among these 2D layered materials, layered black phosphorus (phosphorene) is expected to exhibit superior mechanical, electrical, and optical properties due to an intrinsic and tunable bandgap. It is, besides graphene, the only stable elemental 2D material that can be mechanically exfoliated. Its high hole mobility and direct semiconducting bandgap hold the hope for the development of new electronic devices in the postsilicon era. However, before phosphorene can be integrated in everyday electronics, many aspects of the material still remain to be elucidated. Here we report atomic scale studies of electronic variation related to strain-induced anisotropic deformation of the puckered honeycomb structure of freshly cleaved black phosphorus using a high-resolution scanning tunneling spectroscopy (STS) survey along the light (x) and heavy (y) effective mass directions. Through a combination of STS measurements and first-principles calculations, a model for edge reconstruction and the related edge states are also determined. Besides, we also investigate electrical transport and optoelectronic properties of field effect transistors (FETs) made from few-layer black phosphorus (BP) crystals down to a few nanometers. In particular, we explore the anisotropic nature and photocurrent generation mechanisms in BP FETs through spatial-, polarization-, gate-, and bias-dependent photocurrent measurements. Our results reveal that the photocurrent signals at BP-electrode junctions are mainly attributed to the photovoltaic effect in the off-state and photo-thermoelectric effect in the on-state, and their anisotropic feature primarily results from the directional-dependent absorption of BP crystals.
1. Liangbo Liang, Jun Wang, Bobby G. Sumpter, Vincent Meunier, and Minghu Pan, “Electronic Bandgap and Edge Reconstruction in Phosphorene Materials”, Nano Letters, 2014, 14 (11), 6400–6406

2. Tu Hong, Bhim Chamlagain, Wenzhi Lin, Hsun-Jen Chuang, Minghu Pan, Zhixian Zhou, and Ya-Qiong Xu, “Polarized Photocurrent Response in Black Phosphorus Field-Effect Transistors”, Nanoscale, 6, 8978-8983(2014).
(Invited) Ultrashort Channel Length Black Phosphorus Field-Effect Transistors
Authors: Miao Jinshui , Zhang Suoming , Cai Le , Wang Chuan 
Published: February 2020

Layered black phosphorus (BP) is an emerging two-dimensional (2D) semiconductor with a decent bandgap and great mobility that bridges the gap between graphene (extremely high mobility, no bandgap) and transition metal dichalcogenides (low mobility, large bandgap). As a result, 2D layered BP has attracted significant amount of research interest recently as a promising candidate for high-performance ultimately-scaled electronic and optoelectronic devices. To the best of our knowledge, the smallest BP field-effect transistor demonstrated so far has a channel length of approximately 100 nm fabricated by electron beam lithography (EBL). It gets significantly more challenging to further scale down the channel length to below 100 nm due to the limitations in ebeam resist and lift-off process used.
In this paper, we report a novel and facile process combining EBL and angle evaporation to fabricate high-performance top-gated BP transistors with channel length down to 20 nm (the smallest 2D material transistor to date). By controlling the evaporation angle, the channel length of the transistors can be effectively and reproducibly controlled to be anywhere between ~20 to ~70 nm. With the high quality few-layer BP obtained from mechanical exfoliation and ultrashort channel length, such devices exhibit respectable on-current and transconductance up to 174 μA/μm and 50 μS/μm, respectively, at a small drain-to-source voltage of 100 mV. Owing to the use of 2D BP as the channel material, the transistors exhibit no obvious short channel effects, preserving a decent on-off current ratio of 102 even at extremely small channel lengths. Additionally, unlike the unencapsulated BP devices, which are known to be chemically unstable in ambient conditions, the top-gated BP transistors passivated by the Al2O3 gate dielectric layer remain stable without noticeable degradation in device performance after being stored in ambient conditions for more than one week. This work demonstrates the great promise of atomically thin BP for applications in ultimately-scaled transistors.
Bioelectrocatalysis of Fructose Dehydrogenase at Polyanilline-Modified Electrodes
Authors: Sarauli David , Schulz Burkhard , Fattakhova-Rohlfing Dina , Lisdat Fred 
Published: February 2020

Polymers can provide a suitable chemical environment for the immobilization of biomolecules in an active form on surfaces. Furthermore they can be used to wire redox proteins and enzymes with electrodes. For this purpose mainly redox polymers with well-defined redox centres and conductive polymers with intrinsic electron conductivity are applied. Polyanillines are belonging the latter class of polymers. Their properties can be easily tuned by the substitution pattern on the monomeric units. Recently we have shown that sulfonated polyanillines are suitable partners in the interaction with the enzyme PQQ-dependent glucose dehydrogenase [1]. On the basis of efficient electron exchange different enzyme electrodes can be constructed [2-4].
In this study we have investigated whether it is possible to connect the multi-domain enzyme fructose dehydrogenase FDH with electrodes using the same group of polymers. The interaction of a sulfonated and methoxy-substituted polyanilline with FDH is studied in solution using UV/Vis spectroscopy. It can be demonstrated that electron transfer from the substrate reduced enzyme to the polymer is feasible, but also that this interaction is enhanced by the presence of calcium ions. Subsequently the reaction has been investigated by electrochemical means with all partners in solution verifying the spectroscopic results. In a next step of development the enzyme has been fixed on planar ITO electrodes by means of a polymer layer. Such an enzyme electrode exhibits effective, substrate-induced bioelectrocatalysis starting at rather low potential (~0mV vs Ag/AgCl). The efficiency can be significantly enhanced when macroporous ITO electrodes are used. They have pore size diameters of ~ 300nm and allow incorporation of higher amounts of polymer and enzyme. A current enhancement of ~ 35 is found compared to the flat ITO. The study demonstrates that sulfonated polyanillines can be considered as valuable matrices in connecting redox enzymes with electrodes.
[1] D. Sarauli; C.G. Xu; B. Dietzel; B. Schulz; F. Lisdat, Acta Biomater.
2013, 9, 8290
[2] I. Schubart; G. Göbel; F. Lisdat, Electrochimica Acta
2012, 82, 224
[3] D. Sarauli, C.G. Xu, B. Dietzel, B. Schulz, F. Lisdat, Journal of Materials Chemistry B 2 (21) 2014 3151-3404
[4] D. Sarauli, K. Peters, Xu, B. Schulz, D. Fattakhova-Rohlfing, F. Lisdat, ACS Appl. Mater. Interfaces
2014, 6, 17887
Electrochemical Synthesis of Magnetic Core-Shell Nanoparticles
Authors: Huang Yu-Fen 
Published: February 2020

Core-shell nanostructures have attracted considerable interest as a new class of nanomaterials due to the fascinating physical and chemical characteristics. Herein, a facial and low-cost approach was reported for the synthesis of gold@iron oxide core-shell nanoparticles. By using the citrate-stabilized gold nanoparticles as seeds, the gold@iron oxide nanoparticles were prepared via an electroxidation of iron nail at 1.0 V between the electrodes in aqueous solution. Modulating with the parameters such as pH values, buffers and reaction time make the iron shell thickness to be well controlled. Most importantly, gold@iron oxide nanoparticles turn superparamagnetic after annealing at 350℃ for six hours under nitrogen environment. The enhanced magnetic properties of the resulting core-shell nanoparticles show their future potential in magnetic resonance imaging as well as targeted delivery through magnetofection.
Simulating RF Performance of Proton Irradiated AlGaN/GaN High Electron Mobility Transistors (HEMT)s
Authors: Mukherjee Shrijit , Patrick Erin , Law Mark E 
Published: February 2020

Due to their relative radiation hardness, High Electron Mobility Transistors (HEMTs) with an AlGaN/GaN heterostructure are of high interest for space applications. Many studies have been performed to quantify the level of degradation due to proton radiation, with the majority being focused on the effects on the DC or steady-state performance. Fewer studies have evaluated degradation of the radio frequency (RF) performance due to proton radiation. Chen et al. caution that degradation due to proton irradiation has a more measurable impact on the RF performance in comparison to the DC performance [1]. In particular, gate lag and increases in both channel resistance and device capacitance due to fast bulk and surface traps contribute more notably to RF degradation than to DC degradation [1]. Understanding the dynamics of these traps is required for modeling and simulation of GaN HEMTs for RF applications.
In this paper, we aim to identify the necessary input parameters for future RF simulation of radiation effects on AlGaN/GaN HEMTs. In previous work, we have found that donor traps have a larger role than previously thought on the magnitude of DC performance degradation. We use experimental techniques to identify the donor trap lifetimes and energies, both of which are incorporated into a transient simulation of the HEMT and compared to results obtained experimentally. The experiments are long-term transient measurements of drain current after a step in gate voltage for various temperatures, resulting in the establishment of capture and release time constants associated with donor traps.
(1) J. Chen, E. X. Zhang, C. X. Zhang, M. W. McCurdy, D. M. Fleetwood, R. D. Schrimpf, S. W. Kaun, E. C. H. Kyle, and J. S. Speck, IEEE Trans. Nucl. Sci, 61 (6), 2959, (2014).
Effects of Cobalt Cation on Low Pt-loaded PEM Fuel Cell Performance
Authors: Cai Yun , Kongkanand Anusorn , Gu Wenbin , Moylan Thomas E 
Published: February 2020

PtCo and PtNi alloys are attractive as cathode catalysts in PEM fuel cell systems due to their high catalytic activities. However, dissolution of cobalt or nickel in a fuel cell causes not only oxygen reduction kinetic losses, but also ohmic losses, especially at high current densities, due to the migration of the cations into the ionomer. Several groups [1-3] have developed models to understand these effects on PEM fuel cell performance, mainly focusing on their macroscopic transport properties. To meet stringent cost requirements, the Pt loading in the electrode must be reduced significantly from the levels used in these previous studies. We have found that low Pt loaded cathodes showed larger high-current-density performance losses than higher loaded cathodes for a given cation doping concentration. This result is not readily explained using the current models. In this study, we performed controlled experiments where known amounts of Co or Ni cations were exchanged into the membranes in order to investigate the effect of cation concentration on the performance of cathodes with different Pt loadings, as shown in Figure 1. We used impedance spectroscopy and limiting current method to study the effect of cation contamination on membrane and electrode proton resistances, local oxygen transport resistance, properties not been quantified in previous studies. These newly acquired results will be used to improve our current model and provide direction for future fuel cell development.
This work was partially supported by the U.S. DOE-EERE under grant DE-EE0000458.
References
[1] B. Kienitz, H. Baskaran, T. Zawodzinski and B. Pivovar, ECS Trans.,
11, 777 (2007)
[2] T. A. Greszler, T. E. Moylan and H. A. Gasteiger, Chapter 49, Handbook of Fuel Cells – Fundamentals, Technology and Applications. Edited by Wolf Vielstich, Harumi Yokokawa, Hubert A. Gasteriger. Volume 6: Advances in Electrocatalysis, Materials, diagnostics and Durability. 2009 John Wiley & Sons, Ltd.

[3] T. Okada, H. Satou, M. Okuno and M. Yuasa, J. Phys. Chem. B, 106 1267 (2002)

Figure 1
Current State of the Art in Water Electrolysis Performance Based on Anion Exchange Membranes
Authors: Ayers Katherine E , Parrondo Javier , Capuano Chris , George Morgan , Ramani Vijay K , Fujimoto Cy 
Published: February 2020

Hydrogen represents a major chemical feedstock worldwide, and is currently manufactured primarily from fossil fuel-based sources. Obtaining hydrogen from non-fossil sources is thus an important part of the overall strategy to reduce greenhouse gas emissions, including the potential tie to transportation infrastructure. Large scale renewable hydrogen production is also a key part of the global energy storage strategy, to capture peak solar and wind and convert energy that would otherwise be stranded to a deployable source. Water electrolysis is the only technology currently mature enough to meet the scale requirements in the near term for renewable hydrogen. However, manufacturing and material cost need to be decreased to meet the economic requirements of these applications.
Commercial options for water electrolysis are currently limited to liquid KOH electrolyte based systems, and proton exchange membrane (PEM)-based systems. Both have advantages and disadvantages. Anion exchange membrane (AEM) technology represents a potential hybrid approach which leverages the advantages of both legacy systems. However, the key obstacle in the AEM systems is the robustness of the polymers, both in the ionomer and membrane form. The ionomer is subject to chemical degradation leading to loss of integrity of the electrocatalyst layer, while the membrane can lose mechanical strength due to both thermal damage during processing and chemical attack of the polymer backbone during operation, leading to pinhole failures. The membrane can also lose efficiency through loss of active sites, either through carbonation of the hydroxide conducting sites, or chemical degradation. These membrane and ionomer materials are much less mature than the PEM analogs, and fundamental understanding is still being developed around polymer design and degradation methods.
Proton OnSite has developed cell designs and manufacturing processes which improve the robustness of the existing AEM materials, and have also collaborated with several membrane partners to develop improved materials. Most recently, the Illinois Institute of Technology (IIT) performed mechanistic studies to determine potential membrane degradation pathways, while both IIT and Sandia provided materials for cell testing. In this talk, results of these studies will be discussed, as well as resulting performance in commercial stack hardware. Proton has currently achieved stable operation of the AEM cell for over 1700 hours, with over 1000 hours at 500 mA/cm2, and has scaled the technology to a 1 L/min prototype AEM generator. Comparison to state of the art in PEM technology and the ultimate outlook for each technology will also be discussed.
Proton and Metal Cage-Based Anion-Conductive Fluoropolymers for AMFCs
Authors: Xu Shaoyi , Jiang Rong , Gao Yong 
Published: February 2020

Alkaline membrane fuel cells (AMFCs) have attracted a great deal of attention due to its use of non-precious metal catalysts. However, the lack of chemically stable and highly ion-conductive anion-exchange polymer membrane has impeded the development and adoption of AMFCs by our society. Under strong alkaline conditions, hydroxide anions can be both a nucleophile and a strong base that degrade the hydrocarbon polymer backbones as well as the anion-exchange groups attached to the side chains of the polymer. Typically, positively charged quaternary amine or guanidinium groups are used for hydroxide transportation. Unfortunately, these functional groups are subjected to nucleophilic and elimination attacks by hydroxide anions.
In this presentation, we will disclose a new class of chemically stable anion-exchange fluoropolymers that can be casted into AMFC membranes. The structure of a proton trap-based fluoropolymer is shown in the attached figure. This polymer was chemically synthesized from a perfluorosulfonic acid (PFSA) via a novel C-C coupling reaction. The highly fluorinated polymer backbone and side chains were known to tolerate chemical degradation while its proton cage group is robust against caustic conditions. In our polymer, a proton is encapsulated inside a three-dimensional cage and it is protected from hydroxide attacks. Such a polymer demonstrated remarkable stability in strong alkali media with good ion conductivity. In our talk, we will also discuss several other types of anion-exchange fluoropolymers including zirconium-based membranes and lithium cage-based electrolytes.

Figure 1