bluuebunny/crossref_metadata_2025 huggingface dataset:
High Energy Rechargeable Metal Free Na-Ion Seawater Batteries: Phosphorus/Carbon Composite As a Promising Anode Material
Authors: Kim Yongil , Hwang Soo Min , Yu Hyein , Kim Youngsik
Published: February 2020

A new energy conversion and storage system, named ‘seawater battery’, has recently been introduced in electrochemical academia. The recently introduced seawater battery concept is an eco-friendly energy storage system that offers appealing electrochemical performance. Its radically innovative design, compared to conventional lithium-ion batteries, makes use of seawater as an almost infinite sodium reservoir for the positive electrode (catholyte) and, thereby, avoids the use of expensive, scarce, and toxic elements like nickel and cobalt.

Herein, we report a phosphorus/carbon composite anode material which was successfully employed as the anode in seawater batteries, showing good cycling stability with high reversible capacities exceeding 920 mAh g-1
composite with coulombic efficiencies over 92% for 80 cycles and good rate capabilities. These results show that the seawater battery system would be a new way to overcome the limitations caused by the use of high-capacity alloying reaction-based anodes in existing batteries with a closed system. The full cell system configuration problem caused by low coulombic efficiencies using alloying reaction anode materials were solved through the seawater batteries by supplying unlimited Na-ions. Therefore, these results represent an important step toward practical application of the sodium-based seawater battery technology.
Cyberdesign Computational Algorithm: Selecting Anode and Cathode Materials through Simulation for Lithium-Ion Batteries Based on Diffusivity
Authors: Miller Zachery , Miske Ian , Hosseinzadeh Hamed
Published: February 2020

A cyber-enabled approach to lithium ion battery design was developed in this work where the user inputs a charging voltage (V), desired charging time (t) in seconds, and desired capacity of charge at time t in mAh/cm2 for their battery. This developed program utilizes both a database brain and computational brain. The computational brain has a computational algorithm for macro/mesoscale Fickian approach of ionic diffusion. This algorithm has been equipped with the Butler-Volmer equation, stochastic methods, Poisson equation solver and other related transport equations. The database brain is at early stage in this software and it has been developed by experimental and computational data. An additional algorithm connects the database and computational brain to the user interface. By submitting a request to the software, the program outputs a combination of anode and cathode materials from an established database or computational brain that could achieve the desired input parameters. At the current state, the program will output a combination of materials from the database that can achieve the desired input parameters if the capacity at time t solved for by the computational brain is equal to the desired capacity established by the user. Further steps are being taken to improve the size of the database, consider systems where the user's parameters are not achievable by materials in the database, and consider other variables in the system besides diffusivity of anode and cathode materials. As an example, the capacity of 200 mAh/cm2 when 5V are applied for 10 seconds was submitted to the software. The software utilized the database and computational brain and it found that a pan-based carbon fiber anode combined with a LixCoO2 cathode charges to 53.823 mAh/cm2 according to simulation when 5V are applied for 10 seconds, which is far from the submitted capacity. Then the software used the computational brain to change the anode material to graphite under the same charging conditions which outputs the same capacity. Then by changing the cathode material to have a diffusivity coefficient one order higher than that of LixCoO2 under the same charging conditions the program was able to output capacities of 221.091 mAh/cm2 or higher.
Coupled Electrochemistry and Mechanics in Mesoscale Simulation of NMC Cathodes
Authors: Ferraro Mark E. , Trembacki Bradley L. , Brunini Victor E. , Noble David R. , Roberts Scott A.
Published: February 2020

Analysis of lithium-ion battery performance and degradation presents many multi-physics challenges as we look to understand the plethora of coupled mechanisms occurring within a single electrode. Electrochemical reactions in the active material introduce mechanical stresses as cathode particles swell upon lithium intercalation. Over numerous charge-discharge cycles, this behavior can lead to mechanical degradation, and thus, capacity fade. The presence of a secondary conductive binder phase additionally complicates these mechanisms, altering ionic and electronic conduction pathways, masking available surface area for reaction, and buffering mechanical contacts. As these mechanisms are largely governed by effects at the mesoscale (structures of 100s of active material particles joined by binder), we focus our computational efforts on resolved cathode mesostructures.

In this talk, we will present a variety of different simulations which study half-cell performance at constant current discharge. The Conformal Decomposition Finite Element Method (CDFEM) algorithm is used to generate conformal mesoscale meshes of particle, conductive binder, and electrolyte phases, derived directly from 3D computed tomography data of NMC333 cathodes. This mesoscale approach for coupled electrochemical and mechanical simulations allows exploration of phenomena at the particle scale, while also providing insight on macroscale effective properties. Here, we will discuss the manifestation of local stresses from lithiation-induced swelling, as well as the impact of concentration gradients and local mesostructure on half-cell discharge curves and other macroscopic behavior. Additionally, we will investigate the influence of manufacturing processes on cell performance by studying a range of calendering pressures and binder loading fractions.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Facile Synthesis of Large Area Two Dimensional Layers of Transition Metal Nitride and Their Use As Insertion Electrodes
Authors: Joshi Siddharth , Wang Qi , Puntambekar Ajinkya , Chakrapani Vidhya
Published: February 2020

In recent years, two-dimensional layers of transition metal carbides, nitrides and carbonitrides, also referred to as “MXenes” have been studied for use in a variety of applications such as batteries, supercapacitors and thermoelectric devices. Transition metal nitrides are especially promising as they show a variety of interesting properties such as high conductivity, compositional and surface termination-dependent band gap, high catalytic activity, high melting point and exceptional hardness. They are also ideal for use as lithium ion battery anodes due to their high specific capacity and lower redox potential for Li+ insertion than their corresponding oxides. We report a new technique for synthesizing large area, vertically oriented two-dimensional (2D) layers of molybdenum nitride (MoN) involving synthesis of 2D nanosheets of MoO3 using hot-filament chemical vapor deposition and their subsequent nitridation to δ-MoN using ammonia. This two-step process of phase transforming 2D oxide layers potentially enables easy synthesis of a wide variety of MXenes of nitrides, sulfides, and carbides of tunable composition. Using X-ray diffraction, X-ray photoemission spectroscopy and differential capacitance measurements, we show that 2D layers of MoN operate as insertion electrodes as opposed to bulk MoN which operate as conversion electrodes. Unlike conversion electrodes, the crystal lattice in insertion electrodes does not undergo compositional changes and therefore undergo small extent of volumetric expansion. Hence, these electrodes tend to show stable capacity even after several hundred charge-discharge cycles. Our electrodes show a stable capacity of 320 mAh/g after 200 cycles and do not show any loss in their crystallinity.

Figure 1
The Mechanism of Transformation of Graphite Electrode Materials in Lithium-ion Batteries After Cycling
Authors: Liu Gao , Dai Kehua , Lin Na
Published: February 2020

To reveal how graphite electrodes change with cycling in lithium-ion batteries, electrochemical experiments involving charge-discharge cycling at different current density conditions are performed on commercial pouch cells and the graphite electrodes after cycling. This research shows that the polyvinylidene fluoride (PVDF) binder does not degrade, confirmed by the stable molecular weight after different cycling conditions. Particle size analysis results indicate that the diameter of graphite particles after cycling is ~10% larger than that of the graphite before cycling, which results in a ~30% volume expansion after cycling. For the cells cycled at the same current density, the graphite particle size increases with cycle time. For the cells with the same cycle numbers, the graphite particle size is larger in the cells cycled at lower current density. X-ray diffraction characterization shows that the d-spacings of the graphite particles in all the cells at different cycling conditions are identical. These results suggest that the graphite particle size increase associated with cycling may arise specifically when primary particles inflate the secondary particle size, leading to dramatic volume expansion of graphite secondary particles.
Manganese Dioxide Nanoflowers Decorated Reduced Graphene Oxide As High-Performance Air Cathode for Zinc-Air Batteries
Authors: Teabnamang Pemika , Lao-atiman Woranunt , Kheawhom Soorathep
Published: February 2020

Recently, zinc-air batteries have attracted increasing attention. These batteries exhibit high potential for many future energy applications because they offer high energy density at low cost. Besides, the batteries use zinc anode which is abundant, safe and non-toxic. However, their practical and extensive application is hindered by the sluggish oxygen reduction reaction (ORR). Thus, ORR electrocatalysts are employed to enhance the battery performance.

Noble metals such as platinum have played a dominating role as ORR electrocatalysts. Though they offer the advantages of high catalytic activity, electronic conductivity, and stability, their high costs are a serious concern. Therefore, much effort has been paid to metal oxides that are environmentally friendly and low cost. Among these, manganese dioxide (MnO2) is recognized as a potential alternative because of its abundance, low cost, low toxicity, and efficient electrocatalytic performance. The catalytic activity of MnO2 depended on the crystallographic structure and surface area. However, MnO2 has low intrinsic electrical conductivity. Traditionally, MnO2 coating on carbon supports is used to improve the electrocatalytic performance. Graphene, with its intriguing properties such as large surface area and high electrical conductivity, has recently received enormous attention as a possible candidate.

In this work, a cost-effective approach to synthesis MnO2 nanoflowers decorated reduced graphene oxide is proposed. The ORR electrochemical performance of the synthesized catalysts was examined. The optimal loading ratio of MnO2 is then determined. A zinc-air battery installed with the synthesized catalyst air cathode outperforms and exhibited a larger current density compared with the battery using a commercial Pt/C air cathode. Also, the results indicated that MnO2 nanoflowers decorated reduced graphene oxide offers a promising and cost-effective air cathode for zinc-air batteries as well as other metal-air batteries.

Figure 1
The Hybrid Membrane Based on Sulfonated Poly(Phenylene Oxide) (sPPO) and Silica With Low Permeability for Vanadium Redox Flow Battery
Authors: Jung Ho-Young , Jung Ji-Hyun , Lim Min-Hwa
Published: February 2020

For application of Vanadium Redox Flow Battery (VRFB), the proton conductivity and vanadium permeability of organic-inorganic (sulfonated poly (phenylene oxide) (sPPO)-nano sized sulfonated silica (sSiO2)) hybrid membrane were analysed. Fourier Transform Infrared Spectroscopy (FT-IR) results proved the attachment of sulfonic acid (-SO3H) functional group in PPO polymer and SiO2. Compared with a typical organic sPPO membrane, the hybrid composite membrane (sPPO-2% sSiO2) shows an increased Water Uptake (WU), Ion Exchange Capacity (IEC), proton conductivity (IC) and thermal stability. The IC of sPPO and hybrid membranes are 0.050 and 0.077 S/cm, respectively. Compared to sPPO alone, the higher amount of hydrophilic functional group (-SO3H) existed in the hybrid membrane which is main reason for enhance the IC and WU. During VRFB unit cell operation, The measured Vanadium ion crossover is 14.66, 1.955 and 0.173 mmol/L for Nafion 212, sPPO and hybrid membranes, respectively and VO2+ permeability is 2.22 x 10-7, 2.50 x 10-8 and 4.76 x 10-9 cm2/min for Nafion 212, sPPO and hybrid membrane, respectively. The VO2+ permeability in hybrid membrane is significantly lowered than Nafion 212 and sPPO membranes. Inorganic nano particles acted as a barrier for vanadium ion crossover in the hybrid polymer membrane. The low cost of hybrid membranes can be efficiently considered as an alternative membrane material for advanced VRFB systems.

Key Words : Vanadium Redox Flow Battery, Hybrid membrane, Poly(phenylene oxide), Sulfonated silica, Vanadium permeability.
Investigation of Waste Heat Accumulation and Internal Resistance of AA Nimh Cells
Authors: Donnelly Daniel J , Patrissi Charles J. , Arruda Thomas M
Published: February 2020

Nickel metal-hydride (NiMH) cells have been of considerable interest for the powering of unmanned underwater vehicles (UUV), primarily for the outstanding safety of their water-based electrolyte compared to the flammable organic solvents used in Li-ion cells. High energy and power densities, rechargeability, commercial availability, and low cost in the AA form further strengthen the NiMH case for integration into UUVs. While these factors are motivating, secondary cells generate heat during charge, which in excessive amounts is damaging to both the cell and nearby electronics. Our objective is to model the temperature (T) rise of NiMH cells caused by waste heat (Q) accumulation during battery charging according to the equation following this text.

Heat generation is a function of charge current (I), time (t), and the internal resistance of the cell (R). The galvanostatic intermittent titration technique (GITT)1 is being used to investigate resistance as a function of the current , temperature, and state of charge. Calorimetric measurements are ongoing to investigate specific heat of the cells (c). The change in cell temperature (dT) can then be modeled for various discharge currents and masses (m) of cells2. A Thermal model of NiMH cells configured at the battery level may be used to determine the safety limits for charge rate with respect to heat production during charging in UUVs.

1.Weppner, W. & Huggins, R. A. determination of the Kinetic Parameters of Mixed-Conducting Electrodes and Application to the System Li3Sb. Journal of the Electrochemical Society: Solid State Science and Technology,
124
(1997),1569-1578

2.Maleki, Hossein et al. (1999)Thermal Properties of Lithium-Ion Battery and Components. Journal of the Electrochemical Society, 146(3), 947-954

Figure 1
Understanding the Effects of Lateral Dimensions on the Electrochemical Performance of 2D Mxenes
Authors: Kayali Emre , Beidaghi Majid
Published: February 2020

Two-dimensional (2D) transition metal carbide/nitrides, also called MXenes, have emerged an important family of 2D materials. Characterization of the properties of MXenes in the past few years has revealed their high potential for various applications. MXenes have a general formula of Mn+1XnTx, where M stands for an early transition metal, X denotes carbon or nitrogen, and Tx symbolizes surface terminations. Various MXene compositions are demonstrated to have high electrical conductivities and are shown to be dispersible in water and a range of organic solvents. Ti3C2Tx, the first discovered MXene, has shown exceptional properties as an electrode material for energy storage applications. This is because of the high electrical conductivity of this 2D material and fast redox reactions that can take place at its surface. Although both of these properties are expected to be highly dependent on the dimensions of 2D Ti3C2TX sheets, the limited control over the size of Ti3C2Tx during its common synthesis method has prevented clear understanding of the size-dependent properties of this material. In this talk, we will first introduce a general method to accurately control the lateral dimension of Ti3C2Tx sheets and then, present our recent results on the effect of the lateral dimensions on the electrochemical performance of Ti3C2Tx electrodes. Our results indicate that the electrical and electrochemical properties of MXene electrodes can be controlled by changing the dimension of flakes. Applying our findings to the design of freestanding MXene electrodes makes it possible to achieve exceptional high electrochemical performances. For example, Ti3C2 electrode designed using sheets of various lateral dimensions can reach specific capacitances as high as 450 F/g, when tested as an electrode in electrochemical capacitors.
Synthesis of WS2xSe2(1-x) Nanowalls through a Rapid Thermal Annealing Process for Hydrogen Evolution Reaction and Sensor Application
Authors: Tang Shin-Yi , Medina Henry , Yen Wen-Chun , Chen Yu-Ze , Wang Yi-Chung , Su Teng-Yu , Chen Chia-Wei , Chueh Yu-Lun
Published: February 2020

Owing to the exceptional physical properties and potential in sensor application, transition metal dichalcogenides (TMDCs) have attracted much attention in recent years. When the thickness of TMDCs is reduced to only monolayer or few atomic layers, a bandgap enlargement and transition from indirect to direct happen. Recently, researchers focus on the creation of various interesting nanostructures by different synthesis processes. Here, we present a novel chemical vapor reaction (CVR) method for the one-step synthesis of TMDC nanowalls from the reduction of WOx into WSe2 and WS2 through the rapid diffusion and segregation of chalcogenides. By the rapid heating and rapid cooling procedure, we can achieve the formation of nanowalls standing perpendicularly on top of both SiO2/Si and cabin-fiber paper substrates. Compared to the conventional solid-vapor phase CVD process, our approach is able to provide TMDCs with vertical nanostructures and enhanced surface area. Furthermore, the stoichiometry of WS2xSe2(1-x) walls can be adjusted by controlling the concentration ratio of sulfur and selenium. We provide Raman spectrum and X-ray Photoelectron Spectroscopies results supported by SEM and TEM observations to confirm the successful synthesis of the nanowalls with atomic thickness and varied compositions. This approach can also be applied to the synthesis of other TMDC materials, giving a step forward on the 2D materials research development.

The atomically thin TMDC materials are known for their great potential in sensing, optoelectronic, energy harvesting and Li-ion battery applications. Here, we demonstrate the catalytic property enhancement by utilizing WS2xSe2(1-x) on carbon-fiber paper as the cathode of hydrogen evolution reaction. In addition, due to the exposed edge sites of the TMDC nanowall structure, the application of gas sensing and photodetector was also investigated.
(Invited) Integrated Crystal Growth of 2D Materials
Authors: Hofmann Stephan
Published: February 2020

In order to serve the industrial demand for “electronic-grade” 2D materials, we focus on chemical vapour deposition (CVD), and in this talk I will review our recent progress in scalable CVD [1] and device integration approaches of highly crystalline graphene and hexagonal boron nitride (h-BN) films. The systematic use of in-situ metrology, ranging from high-pressure XPS to environmental electron microscopy, allows us to reveal some of the key mechanisms that dictate crystal phase, structural, defect, interfacial and heterogeneous integration control at industrially relevant conditions [2,3]. We systematically also explored the parameter space of atomic layer deposition (ALD) of oxides on graphene to achieve ultrathin continuous AlOx films directly on graphene [4]. These results have model system character for rational 2D/non-2D material process integration [5]. We highlight how the interplay between the 2D material and the catalyst is not only important for growth [6] but also decisive for transfer processes and show how intercalation processes allow for instance local Cu oxidation at the interface followed by selective oxide dissolution, which gently releases the 2D material [7]. We developed direct and transfer 2D material integration approaches for a large number of diverse applications, ranging from spintronics [8], to nanopore sensing [9] and THz devices [10]. Crystal growth and processing of these 2D materials reached a level where detailed, adequate characterisation over large areas has become a key challenge. Hence we also study new non-contact characterisation methods for rapid in-line monitoring [11].

References

Hofmann et al., J. Phys. Chem. Lett. 6, 2714 (2015).

Weatherup et al., Nano Lett. 16, 6196 (2016).

Caneva et al. Nano Lett. 16, 1250 (2016).

Aria et al. ACS Appl. Mater. Interfaces 8, 30564 (2016).

Alexander-Webber et al., 2D Mater. 4, 011008 (2016).

Braeuninger-Weimar et al., Chem. Mater. 28, 8905 (2016).

Wang et al., ACS Appl. Mater. Interfaces 8, 33072 (2016).

Piquemal-Banci et al., Appl. Phys. Lett. 108, 102404 (2016).

Walker et al., ACS Nano 11, 1340 (2017).

Degl’Innocenti et al., ACS Photonics 3, 1747 (2016).

Lin et al. Sci. Rep. 7, 10625 (2017).
Phase Instability and Thermal Properties of Multilayered Vanadium Diselenide: DAC-Based High Pressure Studies
Authors: Mishra Karuna kara , Ravindran T.R , Pandey K.K. , Katiyar Ram
Published: February 2020

Two-dimensional layered trichalcogenides are of current research interest because of their robust opto-electronics, and thermal properties. Mechanical and phonon vibrational properties of these materials are of significant importance in the field of stress and thermal management. Here we report the pressure dependence of structural and phonon behaviors of high quality few-layers vanadium diselenide nano-sheets grown by hydrothermal method employing synchrotron x-rays and micro-Raman scattering techniques. The high crystalline nature of the nanosheets was examined using transmission electron microscopy. Synchrotron x-ray studies at high pressure (up to 22 GPa) using a diamond-anvil cell identify a displacive type phase transition to a low symmetry monoclinic phase (C2/m) around 7 GPa corroborated with the P-dependent Raman scattering results. Raman spectroscopic studies at high pressure (up to 34 GPa) identify two prominent Raman bands with symmetry Eg and A1g. Eg band at 207 cm-1 shows normal hardening and A1g band at 236 cm-1 softens. The first order pressure derivatives of these phonons at ambient phase (P-3m1) are found to be -3.547(2) and 0.388(6) cm-1/ GPa, respectively. Using the experimental mode Grüneisen parameter of Eg Raman mode, the in-plane thermal expansion coefficient of the titular compound at the ambient phase is estimated. The observed results are expected to be useful in calibration and performance of next generation nano-electronics and optical devices under extreme stress conditions. These experimental results corroborated with our ab-initio calculations will be presented in the ECS meeting.
Photovoltage Optimization of Si Devices with a Fluorinated Graphene Interfacial Layer
Authors: Thompson Annelise C. , Lewis Nathan S
Published: February 2020

The photovoltage produced by a semiconductor device can be optimized by controlling the interfacial energetics, including the surface dipole and electric field. When a positive surface dipole is introduced to a p-type semiconductor surface, the band edges shift to increase the resulting barrier height in contact with a metal, which in turn improves the photovoltage of the device. To generate a positive surface dipole, highly electronegative moieties must be attached to create a layer of negatively charged species close to the surface. While numerous methods have been developed to modify semiconductor surfaces for control over surface dipole and electric field at the interface, introducing highly electronegative moieties like fluorine atoms directly to the surface is very difficult due to the lack of appropriate synthetic methods. Most fluorinating agents that could introduce fluorine atoms directly to a silicon surface instead etch the silicon (i.e. hydrofluoric acid, xenon difluoride, fluorine plasmas). Indirect modifications are also difficult as fluorocarbon-based nucleophiles are transient and decompose quickly in solution. This work demonstrates that a positive C-F dipole can be introduced to tune the band edges of p-type silicon (p-Si) by placing a monolayer of fluorinated graphene (F–Gr) at the interface of a semiconductor and metal. The barrier heights of bare, hydride-terminated p-Si electrodes coated a layer of platinum (Pt, ~100 nm) were measured using solid-state current-voltage measurements and impedance spectroscopy. These electrodes demonstrated ohmic behavior as expected given the work function of Pt. In comparison, identical electrodes with an interstitial layer of F–Gr demonstrated rectifying behavior and improved barrier heights, controlled by the degree of fluorination of the Gr basal plane. X-ray photoelectron spectroscopy indicated that the formation of Pt silicide at the interface was attenuated by the presence of the monolayer of F–Gr even after stress testing at high temperature. Additionally, these electrodes were tested for hydrogen evolution activity to demonstrate their viability for use in a solar fuels device. F–Gr shows promise to maximize the efficiency of a solar fuels device by favorably tuning the band edges of semiconductor surfaces.
(Invited) Quasi-Two-Dimensional Thermoelectricity in Snse
Authors: Szkopek Thomas , Gervais Guillaume , Grueneis Alexander
Published: February 2020

Stannous selenide is a layered semiconductor with a puckered honeycomb lattice that constitutes a polar analogue of black phosphorus, and of great interest as a thermoelectric material [1-3]. Hole doped SnSe supports a large Seebeck coefficient at high conductivity. We combine experimental techniques in the form of angle resolved photo-emission spectroscopy, optical reflection spectroscopy and magnetotransport measurements to map out a multiple-valley valence band structure and a quasi two-dimensional dispersion. The quasi two-dimensional dispersion realizes the low-dimensional Hicks-Dresselhaus thermoelectric, which contributes to the high Seebeck coefficient reported at high carrier density [1-2]. We further demonstrate that the hole accumulation layer in exfoliated SnSe transistors exhibits a field effect mobility of up to 250 cm2/Vs at T=1.3 K. Unintentional hole doping and persistent photoconductivity has been observed, suggesting material quality can be further improved. SnSe is thus found to be a high quality, quasi two-dimensional semiconductor.

References:

[1] L.-D. Zhao et al., Nature 508, 373 (2014).

[2] L.-D. Zhao et al., Science 351, 141 (2016).

[3] C. W. Li et al., Nature Phys. 11, 1063 (2015).
Simulation and Analysis of Phosphorene Nanoribbon Field Effect Transistors Using Non-Equilibrium Green's Function Formalism
Authors: Sarvari Hojjatollah , Liu Chaoyuan , Chen Z. , Ghayour Rahim
Published: February 2020

Few-layer black phosphorus is a semiconductor material which was discovered in 2014. Phosphorus has both high mobility (1100-1140 cm2/V.s in armchair direction) and finite bandgap (~0.35 eV for bulk) compared to the other two-dimensional materials such as MoS2 and graphene. A single layer of black phosphorus is named as phosphorene. Multilayer (ML) phosphorene has an adjustable direct bandgap that can be controlled either by changing the width of the ribbon or the number of layers.

In this work, first we calculate the band structure of ML phosphorene nanoribbons (PNRs) using the tight-binding method. Then, we analyzed the performance characteristics of SL- and ML-PNR field effect transistors (PNRFETs) with abrupt doping between the Source/Drain (S/D) region and the channel region by employing the non-equilibrium Green’s function (NEGF) formalism in real space. This type of FET with abrupt doping near S/D and channel regions is known as conventional FET. We found that the bandgap of armchair PNRs with 16 atoms across the width of PNR for single-layer (SL) and bilayer (BL) structures is 1.899 and 1.224 eV, respectively. We showed that increasing the number of layers reduces both the bandgap of the material and the turn on voltage of device, however, it increases the ON-current of device. Simultaneously, the off-current also increases due to a higher probability of tunneling in low bandgap devices. In addition, increasing the number of atoms across the width of PNR leads to an increase in the Ids due to the decrease of the bandgap. Moreover, both on- and off-currents increase by decreasing the channel length in multilayer PNRFETs.

Next, we compared the performance characteristics of conventional and junction-less (JL) PNRFETs. Recently, JL-FET with high doping concentration in S/D and channel regions was proposed to replace the conventional FET. The JL silicon-on insulator FETs fabricated by Tyndall group show outstanding output characteristics with low Drain Induced Barrier Lowering (DIBL), ideal subthreshold swing, etc. There is no p-n junction between S/D and channel regions in a JL transistor. Instead, all regions are highly doped with the same amount of dopant to increase the conductivity of the channel material. In this case, the barrier in front of the electrons coming from source, is formed by applying suitable gate voltage. From experimental point of view, it should be much easier to dope all S/D and channel materials with the same doping concentration compared to the conventional FETs which needs abrupt doping. Thus, it should be a point of interest to have a performance comparison between conventional and JL phosphorene FETs. We investigated the performance of phosphorene FETs in terms of Id-Vgs, Id-Vds characteristics, energy levels, subthreshold swing, DIBL, and ION/IOFF.
(Invited) Autoperforation of 2D Materials for Generating Two Terminal Memresistive Janus Particles
Authors: Liu Pingwei , Liu Albert Tianxiang , Kozawa Daichi , Dong Juyao , Saccone Max , Koman Volodymyr , Wang Song , Son Youngwoo , Wong Min Hao , Strano Michael S
Published: February 2020

Graphene and other 2D materials possess desirable mechanical, electrical and chemical properties for incorporation into or onto novel colloidal particles, potentially granting them unique electronic functions. However, this application has not yet been realized because conventional top-down lithography scales poorly for the production of colloidal solutions. Due to its inherent stochasticity, brittle fracture is seldom used as a fabrication method for materials at the nanometer scale. However, Griffith theory allows for the imposition of a specific strain field that can guide fracture along a pre-set design. Herein, we show that this autoperforation provides a means of spontaneous assembly for surfaces comprised of 2D molecular surfaces. Chemical vapor deposited mono- and bi-layer graphene, molybdenum disulfide, or hexagonal boron nitride (hBN) can autoperforate into circular envelopes when sandwiching a microprinted polymer spot of nanoparticle ink, allowing lift-off and assembly into solution. The resulting colloidal microparticles have two independently addressable, external Janus faces that we show can function as an intraparticle array of parallel, two terminal electronic devices. As an example, we print a 0.9 wt% black phosphorous (BP) nanoflake-in-polystyrene (PS) ink into mono-layer graphene sandwich particles, resulting in micro-particles possessing non-volatile, 15 bit memory storage via a spatially addressable memristor array throughout the particle interior. Such particles form the basis of particulate electronic devices capable of collecting and storing digital information in their environment. The 2D envelopes demonstrate remarkable chemical and mechanical stability for longer than 4 months of operation in aqueous buffer or even the highly acidic Human gastrointestinal environment at pH 1.5. Such particulate devices also survive aerosolization and re-collection for electronic interrogation. Autoperforation of 2D materials into such envelope structures allows precise compositing of particulate devices, extending nanoelectronics into previously inaccessible environments.
(Invited) 2D Semiconductors in Large-Area Flexible Opto/Electronics
Authors: Anthopoulos Thomas D
Published: February 2020

Successful implementation of two-dimensional layered materials (2DLMs) in opto/electronic applications of the future would require not only the production of high quality materials in large volumes, but also the design of innovative, low power devices that can be implemented onto arbitrary substrate materials, ideally using high-throughput manufacturing paradigms. In this presentation I will discuss the development of low operating voltage 2DLMs-based opto/electronic devices using a combination of self-assembly and top-down manufacturing techniques. Particular emphasis will be placed on the use of adhesion lithography (a-Lith) for the patterning of arbitrary width sub-20 nm nanogaps formed between various dissimilar electrode materials and its combination with 2DLMs for the development of prototype large-area, nano-gap devices including co-planar Schottky diodes, photodetectors, and low-power field-effect transistors.
(Invited) 2D and 2D/3D hybrid Photodetectors
Authors: Lemme Max Christian
Published: February 2020

2-dimensional materials show efficient light-matter interaction. In this talk, 2D material based photodetectors will be discussed. First, graphene detectors and modulators co-integrated with silicon photonics will be covered. The second part will introduce highly sensitive 2D/3D heterostructures.
(Invited) Atomristor: Universal Non-Volatile Resistance Switching in Monolayer Atomic Sheets of Transition Metal Dichalcogenides
Authors: Ge Ruijing , Wu Xiaohan , Kim Myungsoo , Lee Jack , Akinwande Deji
Published: February 2020

Over the past decade, the significance of two-dimensional (2D) atomic sheets has been fully demonstrated by a series of fascinating performances in electronic, photonic, and phononic nanotechnology including topologically-protected charge transport, spatially-separated excitons, and strongly anisotropic heat transport, respectively. Among various 2D materials, transitional metal dichalcogenides (TMDs) stand out due to their unique band gap, high mobility, and quantum confinement. In this work, a novel non-volatile resistive switching (NVRS) phenomenon is presented in the typical (MX2, M=Mo, W; and X=S, Se) transitional metal dichalcogenides (TMDs) single-layer atomic sheets in vertical metal-insulator-metal (MIM) structure. The intriguing findings subvert the traditional thinking that resistance switching is not accessible down to sub-nanometer scale owing to excessive leakage currents. Stable forming-free unipolar and bipolar operations are demonstrated under ambient condition at room temperature, with desirable transition voltage, large on/off ratio and promising reliability. Emerging device concepts in non-volatile flexible memory fabrics, zero static power radio-frequency switches, and neuromorphic computing could be inspired substantially from the universal NVRS effect in atomristor (in essence, memristor in single atomic sheet) and the associated wide materials space and electrode co-engineering for particular applications.
Measurement of Two Dimensional Van Der Waals Materials' Bandgap Using Ambipolar Field Effect Transistor with Graphene Contact and hBN Passivation
Authors: Park Sam , Lim June Yeong , Ahn Jongtae , Im Seongil
Published: February 2020

Two dimensional (2D) semiconductor materials haven been extensively studied for the last decade, regarded as one kind of the most important breakthrough materials toward future device technologies. Band gap of monolayer and few layer in 2D semiconductors has been reported, measured by optical probing such as photoluminescence (PL). However, if their exfoliated thickness is as large as multilayer over 10 layers (10L), PL measurements become less effective and inaccurate because the optical transition of 2D semiconductor is changed from direct to indirect mode. At the moment, the energy band gap also becomes smaller with the semiconductir thickness. In fact, for thick multilayer 2D semiconductors, practical band gap measurement is very difficult due to lack of measurementment technique, so that density function theory (DFT)-based calculations might be only way to conjecture the bandgap. Here, we introduce another way to measure such bandgap of multilayer 2D semiconductors; that is using field effect transistor (FET) as a platform. We have thus fabricated FETs with multilayer 2D channel using graphene contact and top passivation for this study. Because graphene contact would secure ambipolar behavior and Schottky contact barrier tuning of FETs with the assitance of top passivation, bandgap measurement was successfully carried out. Our FETs with WSe2, MoTe2, BP channel, show ambipolar behavior and their maximum Schottky barrier height are measured by temperature-dependent transfer curve characteristics. Bandgap values from WSe2 FET1, WSe2 FET2, MoTe2 FET, and BP FET were 1.16,1.44, 0.92, 0.42 eV, respectively obtained by twice the maximum Schottky barrier height. The values from WSe2 FETs were compared with those of PL measurement, to be confirmed for their compatibilities and according to literature, our values seems reasonable.
(Invited) Controlling Carrier Dynamics in Mesoscale Quantum Dot Assemblies: From Efficient Solar Cells to Ultrafast Photodetectors
Authors: Robel Istvan
Published: February 2020

Successful integration of semiconductor quantum dots (QDs) into real-world optoelectronic devices depends primarily on controlling the QDs’ electronic and transport properties upon their assembly into mesoscale films. While our understanding of carrier recombination in electrically isolated QDs is extensive, little is known about the dynamics of relevant transport and recombination events occurring in thin films of strongly interacting QDs. The recent development of a new device-based technique, ultrafast photocurrent spectroscopy, now enables the study of carrier transport in these QD films with picosecond time resolution. Employing this novel technique has been instrumental in developing transport and recombination models in QD films, offering a rational pathway toward tailoring their electronic properties for the intended target application. Within this context, examples of controlling carrier recombination by manipulating inter-QD coupling via chemical treatments, doping, or atomic layer deposition infilling will be discussed for achieving optimum operation of QD-based optoelectronic devices such as efficient solar cells or ultrafast photodetectors.
(Invited) Quantum Confinement Controls Effective Band Gap, Photocatalytic H2 Evolution and Photovoltage in CdSe Nanocrystals
Authors: Osterloh Frank E. , Zhao Jing , Holmes Michael A. , Nail Benjamin A
Published: February 2020

Here, we provide the first quantitative analysis of quantum-size-controlled photocatalytic H2 evolution at the semiconductor–solution interface. We find that the hydrogen evolution rate from suspended mercaptoethanol-ligated CdSe quantum dots in aqueous sodium sulfite solution depends on nanocrystal size. Photoelectrochemical measurements on CdSe nanocrystal films reveal that the observed reactivity is controlled by the free energy change of the system, as determined by the proton reduction potential and the quasi-Fermi energy of the dots. The corresponding free energy change can be fitted to the photocatalytic activity using a modified Butler–Volmer equation for reaction kinetics. In parallel, Surface photovoltage spectroscopy (SPS) was used to photochemical charge transfer at the CdSe quantum dot -indium doped tin oxide (ITO) interface. Negative photovoltages are observed under super band gap illumination from majority carrier (electron) injection into the ITO substrate. The photovoltage onset energies track the optical band gaps of the samples and are assigned as effective band gaps of the films. The photovoltage values (−125 to −750 mV) vary with quantum dot sizes and are modulated by the built-in potential of the CdSe–ITO Schottky type contacts. Deviations from the ideal Schottky model are attributed to Fermi level pinning in states approximately 1.1 V negative of the ITO conduction band edge. Positive photovoltage signals of +80 to +125 mV in films of >4.0 nm nanocrystals and in thin (70 nm) nanocrystal films are attributed to electron–hole (polaron) pairs that are polarized by a space charge layer at the CdSe–ITO boundary. The space charge layer is 70–150 nm wide, based on thickness-dependent photovoltage measurements. These findings establish a quantitative experimental basis for quantum-confinement-controlled proton reduction and electron transfer with semiconductor nanocrystals.

Figure 1
(Invited) Circularly Polarized Luminescence from Planar Chiral Molecules Based on [2.2]Paracyclophane
Authors: Morisaki Yasuhiro
Published: February 2020

Planar chirality is one of the unique features of mono- and polysubstituted [2.2]paracyclophane compounds. The potential applications of the [2.2]paracyclophane derivatives in materials chemistry necessitate the further development of practical optical resolution methods for planar chiral [2.2]paracyclophanes. Recently, we achieved the optical resolutions of 4,12-disubstituted [2.2]paracyclophane [1] and 4,7,12,15-tetrasubstituted [2.2]paracyclophane compounds [2]. By using the optically pure 4,12-disubstituted and 4,7,12,15-tetrasubstituted [2.2]paracyclophanes, we have prepared various planar chiral [2.2]paracyclophane building blocks [3] for π-system figuration. Herein, their optical resolution methods as well as subsequent transformations to the enantiopure conjugated compounds will be shown. As a representative example of π-system figuration, cyclic compounds based on planar chiral [2.2]paracyclophane will be introduced. These compounds comprise optically active higher-ordered structures such as propeller-shaped structure [2], double helical structure [3], and so on. They exhibit excellent chiroptical properties, i.e., large molar ellipticity in the ground state and intense circularly polarized luminescence (CPL) with large dissymmetry factors (g
lum) in the exited state. The results suggest that planar chiral [2.2]paracyclophane-based optically active higher-ordered structures (propeller-shaped and double helical structures in this study) are promising scaffolds for efficient CPL, and appropriate modifications can enhance the CPL properties.

References

[1] (a) Morisaki, Y.; Hifumi, R.; Lin, L.; Inoshita, K.; Chujo Y. Chem. Lett.
2012, 41, 990. (b) Morisaki, Y.; Hifumi, R.; Lin, L.; Inoshita, K.; Chujo Y. Polym. Chem.
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[2] (a) Morisaki, Y.; Gon, M.; Sasamori, T.; Tokitoh, N.; Chujo Y. J. Am. Chem. Soc.
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[3] For example, Morisaki, Y.; Sawada, R.; Gon, M.; Chujo Y. Chem.–Asian J.
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(Invited) Effect of Substrate-Metal Interaction on the Oxygen Reduction Reactivity at Pt-Ni Nanoframe Deposited on N-Doped Carbon Supports
Authors: Yagi Ichizo , Ogura Kazuya , Tokuda Shoichi , Kato Masaru
Published: February 2020

Carbon-supported platinum group metals (PGMs) are used as oxygen reduction reaction (ORR) electrocatalysts at cathodes in polymer electrolyte fuel cells (PEFCs). Since platinum reserves are limited, Pt-Ni alloy electrocatalysts for the ORR have been intensively studied. One of the highly active Pt-Ni alloy electrocatalysts is a carbon-supported Pt-Ni alloy nanoframe[1]. This electrocatalyst exhibits much higher catalytic ORR activity than commercial Pt/C catalysts and almost no activity loss after 10,000 potential cycles. In the practical point of view, further improvement of the durability and reactivity is required. The use of nitrogen-doped carbon as the catalyst support might improve the catalytic activity as well as durability because it is expected that nitrogen doping in carbon supports may modulate the electronic structure of the catalyst and/or give strong chemical bonding between the support and the catalyst[2].

Herein, we report electrocatlytic activity and durability of Pt-Ni alloy nanoframes on nitrogen-doped carbon supports to understand effects of the nitrogen content on the catalytic activity and durability. We used carbon black (Vulcan), N-doped carbon and graphitic carbon nitride (g-C3N4) were used as catalyst supports. Pt-Ni alloy nanoframes [1] and N-doped carbon supports were prepared according to the literature[3]. For the preparation of g-C3N4, melamine was heated at 600 °C under air for 2 hours. Linear sweep voltammetry of Pt-Ni alloy nanoframes on supports was carried out in 0.1 M HClO4 using a three electrode setup under oxygen.

TEM observations of Pt-Ni alloy nanoframes on supports suggested that the density of Pt-Ni nanoframes in a unit volume clearly increased with increase in the nitrogen content in the supports. Although the ORR activity of Pt-Ni nanoframes on N-doped carbon supports also depended on the nitrogen content, the optimum value of nitrogen content was 9%. The electronic interaction between N-species and Pt-Ni nanoframes will be the key to understand the activation mechanism.

This work was supported by NEDO.

[1] C. Chen et al., Science
343, 1339-1343 (2014); N. Becknell et al., J. Am. Chem. Soc.
137, 15817-15824 (2015).

[2] Y. Zhou et al., Energy Environ. Sci.
3, 1437-1446 (2010).

[3] Y. Zhang et al.,
Sci. Rep.
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Electrochemical Reduction of Carbon Dioxide with Nitrogen-Doped Copper Nanoparticles
Authors: Chen Shutang , Chen Gugang
Published: February 2020

The applications of copper and copper-based nanoparticles as catalysts have generated a great deal of interest in recent years because copper is inexpensive and earth abundant. However, direct conversion of carbon dioxide to fuels and chemicals remains a grand challenge in electrochemical reduction of CO2. Here we report a simple synthetic strategy on nitrogen-doped copper nanoparticles, and investigate the effect of doping amount on the products of CO2 reduction reaction. When the alkylamine is bound to a copper surface, the scission of C-N bond on the particles surface appears to provide nitrogen source to further react with copper nanoparticles through Ostwald ripening process. Compared to pure copper nanoparticles, nitrogen doping not only improves oxidation resistance, but also facilitates multiple proton and electron transfers to synthesize multicarbon products during CO2 reduction reaction. Furthermore, we envision that such unique doping strategy could be extended to the design of other inorganic nanoparticles for various catalytic applications.