bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Flexible GHz Frequency and Low-Power Nanoelectronics Based on 2D Nanomaterials
Authors: Akinwande Deji , Chang Hsiao-Yu , Lee Jongho 
Published: February 2020

2014 is the 10th year anniversary of the groundbreaking work on graphene by several pioneering workers. Since then, the field has expanded exponentially and now includes two-dimensional (2D) atomic sheets beyond graphene such as hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDs), and group IV elemental monolayers (e.g. silicene, germanene). While there are many opportunities for these 2D crystals to enable transformational impact, it is widely understood that their greatest prospects are for flexible nanoelectronics where their combined synergistic properties are unmatched by conventional organic or inorganic materials. The 2D atomic sheets have emerged as near ideal nanomaterials to overcome the long running challenge of achieving Si CMOS like performance on soft substrates at scales that can be suitable for large integration. For instance, the high mobility and velocity accessible in monolayer graphene affords GHz analog transistor devices while the large bandgap of graphene’s semiconducting analogues (MoS2 and similar dichalcogenides) naturally lead to near ideal digital transistors with high on/off current ratio and low subthreshold slope while sustaining mobilities much larger than organic semiconductors or amourphous bulk semiconductors. Together, these physically similar atomic layers with vastly different electronic properties can serve as the electronic platform for low-power digital, high-speed mixed-signal, and high-frequency analog transistor building blocks for flexible nanoelectronic systems.
In this work, we present the latest findings on the high frequency properties of graphene with record frequencies in the microwave regime. These high frequencies are suitable for realizing GHz wireless analog circuits on soft substrates. The current frequencies are limited by the poor thermal conductivity and reliability of the plastic substrates. In addition, we report on the coupled device mechanics and device physics of 2D semiconducting sheets. The device mechanics on plastic substrate as a function of tensile strain reveal that dielectric cracking is responsible for off-current degradation while buckling is largely responsible for on-current degradation. The buckling scales with the thickness of the dichalcogenide semiconductor and can be mitigated by reducing the driving force for delamination. Optimized dielectric patterning for strain relaxation was found to improve device reliability at low bending radius. Our results collectively indicate that graphene is the most suitable material for flexible radio-frequency transistors while TMDs are ideal for low-power flexible transistors.
Effect of Using Ethanol as the Oxygen Source on the Growth and Dielectric Behavior of Atomic Layer Deposited Hafnium Oxide
Authors: Selvaraj Sathees Kannan , Colon Albert , Rossero Jorge Iván , Shi Junxia , Takoudis Christos G 
Published: February 2020

Hafnium oxide (HfO2) is widely identified as a suitable high-k material to replace conventionally used low-k silicon oxide for gate dielectric layers in complementary metal-oxide semiconductor (CMOS) devices. High dielectric constant (~ 25) and compatibility with silicon substrate makes HfO2 an ideal candidate for future scaling of transistors.1

HfO2 has been deposited using various methods. Of all, atomic layer deposition (ALD) seems to be the suitable method to deposit ultra-thin conformal layers on deep trenches and future 3D transistor structures. ALD is a vapor phase deposition technique, in which sequential exposure and purging of a surface to reactive elements in vapor phase is used to grow thin films in layer-by-layer fashion with excellent control on film thickness and composition down to Å level.2

There were numerous studies on ALD of HfO2 using different precursor and oxygen source combinations.3 The property of the resultant HfO2films depends on the precursor combination, deposition conditions, post deposition treatment conditions etc.
ALD of HfO2 is traditionally performed using oxygen, ozone or water as the oxygen source. These oxidizers oxidize the underlying silicon substrates during the initial ALD cycles and form thick interfacial silicon oxide layer. This layer reduces the dielectric constant of the structure. To reduce the risk of forming such thick interfacial layer we used ethanol as the ALD oxygen source. Ethanol showed good reactivity towards the hafnium precursor, tetrakis(diethylamino)hafnium, and displayed clean ALD growth behavior with a wide ALD process temperature window of 200-280 °C (Fig. 1). In this paper, ALD growth behavior, ALD process temperature window and dielectric characterization of the ALD HfO2films will be discussed in detail along with film compositional analysis.
References
1. J. Robertson, The European Physical Journal - Applied Physics, 28, 265 (2004).
2. S. M. George, Chem. Rev., 110, 111 (2009).
3. L. P. Riikka, J. Appl. Phys., 97, 121301 (2005).
Performance of Sintered Iron Electrodes for Rechargeable Alkaline Batteries for Large Scale Energy Storage
Authors: Yang Chenguang , Manohar Aswin K , Malkhandi Souradip , Prakash G. K. Surya , Narayanan S. R. 
Published: February 2020

With increased concerns about fossil fuel depletion and carbon dioxide emissions, renewable power generation from solar and wind sources is a promising solution for meeting our increasing need of energy. However, with renewable power there is a principal issue of power availability to match the demands. Therefore, inexpensive, long life and high-rate- capable energy storage systems are needed.
Iron based alkaline batteries are a promising candidate for large scale energy storage due to its low cost and abundance of raw material, long cycle life and high theoretical energy density of iron electrodes. [1] Despite these advantages, historically, iron electrodes have had low charging efficiency due to the hydrogen evolution reaction, and low utilization rate and poor rate capability due to the non-conducting nature of the discharge product. [2] In this study, a sintered iron electrode with high charging efficiency, high utilization rate and long cycle life is presented.
The iron electrode in this study was prepared by loading carbonyl iron on to a degreased nickel mesh and sintering under inert atmosphere. The iron electrode was then tested in a three-electrode configuration with two sintered nickel-oxide counter electrodes and a mercuric oxide reference electrode was used for electrode potential measurements. Sodium sulfide was added into the electrolyte to prevent passivation.
After the initial formation cycles, the utilization rate of the sintered iron electrode stabilized at 0.23 Ah/g. About 80% of this value was realized at C rate (Figure 1). This type of performance is very promising for large-scale energy storage applications since the high rate capability is necessary for rapid load-leveling. Following initial characterization of capacity, the electrodes were subjected to charge/discharge cycles with C/2 rate over 500 cycles without any significant change in capacity. The average faradaic efficiency during this high rate cycling is above 96% (Figure 2).
The properties of long cycle life and high faradaic efficiency are expected to lower the cost of implementing and operating iron-based energy storage systems. The future work of this study is focused on understanding the role of electrode design parameters (porosity, thickness and pore utilization) and sulfide additives on the performance of the iron electrode.

Acknowledgement

The research reported here was supported by the U.S. Department of Energy ARPA-E (GRIDS program, DEAR0000136), the Loker Hydrocarbon Research Institute, and the University of Southern California.

References

1. S.R. Narayanan, G. K. Surya Prakash, A. Manohar, B. Yang, S. Malkhandi, A. Kindler, Solid State Ionics,
216, 105 (2012).
2. A. K. Manohar, S. Malkhandi, B. Yang, C. Yang, G. K. Surya Prakash, S. R. Narayanan, J. Electrochem.
Soc., 159 (8), A1209 (2012).
Study of Transient Behavior of Vanadium Redox Flow Battery at Varying Flow Rates and States of Charge
Authors: Poudyal Aditya , Denisov Evgeny , Bund Andreas 
Published: February 2020

The Vanadium Redox Flow Battery (VRB) is one promising candidate for grid type storage because of its long life time, modularity, active thermal management, and good cycle life. There are various parameters that affect the performance of VRB for example: temperature, flow rate, state of charge etc. Flow rate is an important parameter, since the electrolyte flow rate influences the reaction rate of the vanadium ions. It is also important because it has a substantial influence on the system efficiencies.
Ma et al. [1] investigated the effect of flow rate on the system capacity and the efficiency. Fetlawai [2] investigated the effect of flow rate on the charge-discharge characteristics and on the gas evolution. It was established that flow rate is one of the important parameters which should be controlled to obtain high efficiency of VRB. The effect of the flow rate on the transient behavior of the battery has not got much attention which motivated this study.
We will present experimental results on the transient behavior of a VRB at various flow rates up to ca. 1 L/min. The battery was at 80% state of charge during experiment. It was observed that flow rate has a strong effect on the transient behavior of the battery (a typical examples is shown in Fig. 1). The load of the battery was varied in a regime typical for applications of VRBs. The results showed clear trends of the transient behaviour of the battery with changes of flow rate. The implications of these findings for the development of control systems in grid energy storage system design with VRBs will be discussed.
[1] X. Ma, H. Zhang, C. Sun, Y. Zou, and T. Zhang, “An optimal strategy of electrolyte flow rate for vanadium redox flow battery,” J. Power Sources, vol. 203, pp. 153–158, Apr. 2012.
[2] H. A.-Z. A.-Y. Al-Fetlawi, “Modelling and simulation of all-vanadium redox flow batteries.” 14-Apr-2011.
[3]J. Chahwan, C. Abbey, and G. Joos, “VRB Modelling for the Study of Output Terminal Voltages, Internal Losses and Performance,” 2007 IEEE Canada Electr. Power Conf., pp. 387–392, Oct. 2007.
(Invited) Deep Ultraviolet Light Emitting Diodes: Physics, Performance, and Applications
Authors: Shur Michael , Gaska Remis , Dobrinsky Alex , Shatalov M. 
Published: February 2020

Materials quality is the one of the key factors determining the Deep UV LED performance. It could be dramatically improved by using novel MEMOCVD® technique [1] using overlapping precursor pulses, optimized precursor waveforms and lower growth temperatures compared to the conventional MOCVD growth. Another key factor is the Deep UV LED design. Using very narrow quantum wells (QWs), we achieved an improved overlap between electron and hole wave functions and increased the Internal Quantum Efficiency. We also used “the energy tub” [2] to increase the electron capture into the QWs and eliminate or reduce the “blocking layer.” These approaches and a novel transparent and reflecting top contact have led to a high internal quantum efficiency, high power output and high external quantum efficiency of our Deep UV LEDs. Research is now under way to use these devices for improving quality and extending storage time of fruits and vegetables.[3] Other applications include water and air purification, sterilization, biological threat identification, applications in medicine, biology, industrial processes, defense, and homeland security. Deep UV LEDs have a potential of replacing conventional ultraviolet Hg vapor, Xenon and Deuterium lamps that are bulky, contain mercury, produce ozone, require high voltages, slow to turn on, and have a limited set of available wavelengths. DUV LEDs will also enable new applications that were not even possible with conventional deep UV technology.

[1] R. Gaska, J. Zhang, and M. Shur “Nitride-based light emitting heterostructure”, US Patent 7,326,963, Feb. (2008)
[2] Q. Fareed, R. Gaska and M. S. Shur, Methods of Growing Nitride-Based Film Using Varying Pulses, US patent 7192849, March 20 (2007)
[3] M. Shur and S. Britz, Fluorescent-based ultraviolet illumination, United States Patent Application Publication, US 2011/0147617, June 23 (2011), US patent 8,384,047, Feb. 26 (2013)
Rare Earth-Doped Si-Based Thin Films
Authors: Gourbilleau Fabrice , Fafin Alexandre , Benzo Patrick , Dumont Lucile , Cardin Julien , Labbe Christophe , Dufour Christian 
Published: February 2020

Since the discovery of the efficient sensitization of rare earth ions (RE) by nanometer sized Si clusters (Si-ncls), intense efforts have been focused on the study of the coupling Si-ncls:RE because of the promising solutions to gather electrical and optical efficient components on the same wafer compatible with the CMOS technologies. Thus Si-ncls:Er3+ systems have concentrated the most important works during this last decade. Silica is the commonly used host matrix in which Si excess has been incorporated to provide Si-ncls upon a suitable annealing treatment. However, such a system does not show till now a relevant net optical gain allowing the possible transfer of the technology to the industry. This can partially be attributed to numerous losses processes (cross relaxation processes, confined career absorption, reabsorption process etc…, ) occurring in such optical devices. An interesting point concerns the fact that the sensitizing of RE ions can be achieved not only via Si-ncls, but also via other radiative channels that can open the development of new devices. Indeed, recently, Nd- and Tb- as well as Tb-Yb-doped layers have attracted attention because of their potential applications in laser, light source and solar cell, respectively.
The aim of this talk is to give an overview of our recent results achieved on rare earth doped Si-rich matrices produced by reactive magnetron sputtering for Si-based light emitting materials or solar cell layers. Different host matrices such as SiOx, SixOyNz, SiNx, HfxSiyOwNz, … have been investigated with the aim to enhance the quantum efficiency of the emission of the rare earth ion. Depending on the intended application, optimisations of the emission properties have been carried out by means of deposition parameters, specific annealing treatments (classical or rapid thermal annealing), structures (single- or multilayers). The achieved results have been interpreted using on the one hand the framework of Maxwell equations (solved by a Finite Difference Time Domain (FDTD) method) coupled to Auxiliary Differential Equations (ADE) describing guided modes propagation as well as the concentration of rare earth and Si-ncls in different states resulting in estimation of gain and on the other hand a light extraction model in layered media. Specific spectroscopic experiments have been performed to determine the excitation mechanism according to the host matrix used. Finally, typical devices produced and studied will be described.
This work is supported by French National Agency (ANR) through GENESE-ANR Blanc and INTERREG MEET (Materiel for Energy Efficiency in transport) projects.
(Invited) Photoluminescence Enhancement of a Silicon Nanocrystal Plane Positioned in the Near-Field of a Silicon Nanowire
Authors: Kallel Houssem , Wiecha Peter , Zhao Yu , Arbouet Arnaud , Carrada Marzia , Ben Assayag Gérard , Periwal Priyanka , Baron Thierry , Normand Pascal , Chehaidar Abdallah , Paillard Vincent 
Published: February 2020

Semiconductor nanowires (NW) are good candidates for new optoelectronic or photovoltaic devices due to their exceptional ability to guide, scatter or absorb light, from near-ultraviolet to near-infrared. The occurrence of morphology-dependent optical resonances in nanowires opens a route to overcome the intrinsic limitations of some materials (for instance the limited absorption of silicon in the visible spectrum due its indirect band gap) and optimize their interaction with light.
Most optical applications of nanowires were recently focused on photovoltaic devices, because of their enhanced light absorption efficiency, which is also tunable either by the NW diameter, structure or chemical composition. It could be interesting to use the near-field enhancement around the NW induced by the excited resonances, in order to increase the emission of quantum dots or molecules placed in the NW vicinity. Semiconductor NWs could thus be used as optical antennas instead of plasmonic nanostructures, despite a much weaker enhancement, but with the advantages of field enhancement in larger volumes and using a fully compatible CMOS technology.
We investigate the influence of Si -NWs on the photoluminescence of a single plane of Si nanocrystals embedded in a silica matrix. The presence of an individual Si-NW on top of the silica layer, at about 3 nm above the Si-NCs plane, leads to a strong photoluminescence enhancement, by up to a factor of three, depending on the excitation light wavelength and polarization, and the nanowire diameter. This opens a route for improving light emitting devices using Si-based nanowires.
Electrical Properties of La10Si6O27 Electrolytes Prepared By an Innovative Chemical Route
Authors: Macedo Daniel Araujo , Macedo Graziele Lopes , Rajesh S , Figueiredo Filipe M , Martinelli Antonio Eduardo , Marques Fernando , Nascimento Rubens Maribondo 
Published: February 2020

Apatite-type lanthanum silicates have been widely used as solid oxide fuel cell (SOFC) electrolytes due to their relatively high oxide ionic conductivity (around 2×10−3 Scm−1 at 800 °C) and low activation energy for conduction. In the present study, we have focused on the preparation of apatite powders of composition La10Si6O27, synthesized by a novel combination of sol-gel and co-precipitation methods, and the correlation between microstructure and electrical properties of sintered ceramics. The herein proposed synthetic approach is advantageous in reducing energy consumption and processing time, key elements to decrease the total manufacturing cost.
The as-prepared powder was calcined between 500 and 900 °C, with dwell time from 2 to 4h. Phase formation of powders was determined by X-ray diffraction. The pure apatite powder was further analyzed by scanning electron microscopy (SEM). The sintering behaviour was studied by dilatometry in the temperature range of 30-1500 °C. The effects of the sintering temperature, ranging from 1350 to 1550 °C, on the microstructure and electrical properties were investigated by SEM and impedance spectroscopy. Ionic conductivity properties were measured in the 200 – 800 °C temperature range in air atmosphere.
Structure of the calcined powders, characterized by X-ray diffraction (XRD) and Rietveld refinement, indicated the formation of single – phase crystalline lanthanum silicate at 900 °C. Fig. 1 shows a representative impedance spectrum for the La10Si6O27 pellet sintered at 1400 °C and measured at 600 ºC in air. The features in this plot can be attributed to contributions of grain boundary at intermediate frequency and electrode polarization at low frequency.Fig. 2 shows the calculated total electrical conductivities, for the pellets sintered at 1400 and 1450 °C, as a function of temperature following the Arrhenius law. The lanthanum silicate electrolyte sintered at 1450 °C exhibited electrical properties comparable with samples prepared by solid state reaction and sintered at 1600 °C [1].
The findings in this study are an indication for the potential of an innovative chemical route, based on a combination between sol-gel and co-precipitation methods, for the synthesis of lanthanum silicate powders with apatite-type structure. Nanoparticles were obtained even after calcination at temperatures as high as 900 °C. Densities above 90% of the theoretical one were achieved after sintering at 1450 °C. The total electrical conductivity at 600 °C was comparable with the best values reported in the literature. The lower activation energy of total conductivity was 80 kJ/mol.

Acknowledgements

The authors acknowledge CAPES and FCT (Portugal) for the financial support.

Reference

[1] E. Béchade et al. Journal of the European Ceramic Society 28, 2717 (2008).
The Effect of Van Der Waals Interactions on the Sexithiophene Adsorption on Ag(110)
Authors: Matos Jeronimo , Rojas Tomas , Kara Abdelkader 
Published: February 2020

We use density functional theory to study the adsorption of Sexithiophene (6T) on Ag(110). Special attention is given for exploring the effects of van der Waals interactions on the adsorption geometry and energy using vdW-DF family functionals. The 6T molecule is found to bind to the Ag(110) surface via two orientations, with the long molecular axis parallel to the [001] and [110] directions. Including van der Waals interactions resulted in a substantial increase in the binding energy (from 0.6 eV to 4 eV), while the binding height is slightly modified (from 3.1 Å to 2.75 Å). Both the binding energies and heights show significant variations depending on the vdW functional used: the opt-type functionals (optB86, optB88, optPBE) further enhance the adsorption energy when compared to those obtained using PBE, revPBE, or rPW86 functionals. Upon adsorption, there is a small, however, noticeable broadening and a shift (towards higher binding energy) in the position of the d-band center of the substrate surface atoms is observed. Note that, the absence of charge transfer, interfacial states, changes in the atomic structure of the molecule or the substrate suggests that the bonding characteristic of the 6T/Ag(110) system can be categorized as weak chemisorption or strong physisorption.
This work is funded by the U.S. Department of Energy Basic Energy Science under Contract No DE-FG02-11ER16243
Simultaneous Detection of Trace Heavy Metal Ions Using a Chemically Activated Graphene / Bi Nanocomposites Electrode By Differential Pulse Anodic Stripping Voltammetry
Authors: Lee Sohee , Piao Yuanzhe 
Published: February 2020

Activated graphene were dispersed in Nafion (AG-NA) solution and used in combination with in situ plated bismuth film electrode for fabricating the enhanced electrochemical sensing platform to determine trace zinc, cadmium and lead by differential pulse anodic stripping voltammetry (DPASV). We report the first example of a bismuth film electrode plated in situ using activated graphene (AG) prepared by KOH activation. The as-synthesized AG-NA/Bi nanocomposite was characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microsopy (TEM) and scanning electron microscopy (SEM). Results are presented regarding the effects of different operational variables such as pre-concentration potential, bismuth deposition time, bismuth concentration, and stirring speed during pre-concentration were optimized for the purpose of determining trace metals in 0.1 M acetate buffer solution (pH 4.5).
In this study, activated graphene – Nafion / Bi composite film were prepared and used for a sensitive and mercury-free electrochemical platform for the analysis of the zinc, cadmium and lead. Liner calibration curves ranged from 10 μg/L to 50 μg/L for zinc and 10 μg/L to 80 μg/L for cadmium and lead. The composite film integrating the advantages of activated graphene, Nafion and bismuth enhanced the sensitivity of trace metal ion, especially zinc. The limit of detection was 1.71 μg/L for lead, 0.71 μg/L for cadmium and 0.60 μg/L for zinc (S/N = 3). The AG-NA/Bi composite film electrodes were successfully applied to analysis of trace metals in real sample.