bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and Characterization of Photodetectors Composed of Graphene/Silicon Schottky Junctions
Authors: An Yanbin , Behnam Ashkan , Bosman Gijs , Pop Eric , Ural Ant
Published: February 2020

Graphene, which shows good electrical conductivity, high optical transparency, and mechanical flexibility, is a promising candidate for transparent, conductive, and flexible electrodes in optoelectronic and photovoltaic devices. Unlike conventional metal electrodes, graphene has the added advantage that its Fermi level and hence workfunction can be tailored by chemical doping or electrostatic gating. As a result, graphene can be used in traditional as well as novel device structures. For that purpose, integration of graphene into conventional semiconductor technologies, in particular those based on silicon, is of utmost importance.

In this talk, we discuss the fabrication of metal-semiconductor (MS) photodetectors [Fig. 1(a)], where chemical vapor deposition (CVD)-grown monolayer graphene [Fig. 1(b)] plays the role of the metal and p-type silicon (p-Si) is the semiconductor. We characterized the photodetector devices and extract important parameters which give insights into their fundamental electronic and optoelectronic properties.

First, we investigate the electronic properties of graphene/silicon junctions as a function of temperature. We find that thermionic emission is the dominant electronic transport mechanism above 260 K with a zero-bias barrier height of 0.48 eV. Using temperature dependent I-Vmeasurements, we investigate the reverse-bias dependence of the Schottky barrier height and conclude that the Fermi level change in graphene due to charge transfer from Si dominates this dependence.

We also characterized the photoresponse of photodetectors based on graphene/silicon Schottky junctions [Fig. 2]. The good photoresponsivity (~0.133 A/W at 633 nm) and external quantum efficiency (>15%) shows the great potential of this type of device for photodetector applications. Furthermore, we performed photoresponse measurements at different chopper frequencies and extracted the bandwidth of the photodetector.

Low frequency electronic noise spectra of the graphene/silicon device are also studied at both forward and reverse bias. The scaling of noise with device current shows SI ~ Iβ
dependence, with β = 1 for forward bias and β = 2 for reverse bias. This β dependence is in agreement with empirical models reported previously. The noise spectra indicate that the electronic transport is dominated by thermionic emission, which is consistent with our temperature dependent I-Vanalysis. Finally, we extracted important device parameters, including normalized photocurrent-to-dark current ratio, noise equivalent power, and detectivity, which are found to be better than those previously obtained for similar detectors based on carbon nanotubes.

Our results provide crucial insights into the fundamental electronic and optoelectronic properties of photodetectors based on graphene/silicon Schottky junctions, which is important for the integration of graphene based materials into existing semiconductor technologies.
Electron Transfer Kinetics on Mono- and Multi-Layer Graphene
Authors: Velicky Matej , Toth Peter S , Valota Anna , Cooper Adam J , Kinloch Ian A , Hill Ernie W , Novoselov Kostya S , Dryfe Robert AW
Published: February 2020

Since the first isolation of graphene monolayer via mechanical exfoliation in 2004, many other production methods have emerged in the following years. These methods include chemical vapour deposition, liquid phase graphite exfoliation, graphite oxide reduction and epitaxial growth, each having its pros and cons. The unique properties of graphene, such as high electron mobility, large specific surface area, mechanical strength and high transparency, ignited an enormous research interest to explore the electrochemical properties of graphene sheets, with potential uses in many immediate applications such as energy storage, solar cell technology and corrosion protection. Understanding how the electron transfer kinetics of a redox reaction between the graphene surface and a molecule compares to graphite or other carbon based materials is crucial to future use of graphene as a ‘supreme’ electrode material.1

Herein, the electrochemical response of mono-layer and multi-layer graphene electrodes, prepared using both chemical vapour deposition and mechanical exfoliation, is presented. Experiments were carried out using a microinjector, micromanipulator and optical microscopy, enabling precise deposition of size-controlled droplets on the flake surface.1 The insulating substrates used for flake preparation include inorganic materials and organic polymers. Graphene/graphite flakes were characterised using optical microscopy, Raman spectroscopy and atomic force microscopy.

The electron transfer rate at the basal planes, edge planes and boundaries between graphene flakes was determined using voltammetric techniques. The redox couple, number of graphene layers, presence of defects and nature of the substrate are all shown to have a significant effect on the electrochemical activity.2-3 Furthermore, the stability of the droplets on the surface depends on various factors, such as the solvent choice, electrolyte content, number of graphene layers, underlying substrate and method of flake preparation.

1. Valota, A. T.; Toth, P. S.; Kim, Y. J.; Hong, B. H.; Kinloch, I. A.; Novoselov, K. S.; Hill, E. W.; Dryfe, R. A. W., Electrochimica Acta, 2013, 110, 9-15.

2. Valota, A. T.; Kinloch, I. A.; Novoselov, K. S.; Casiraghi, C.; Eckmann, A.; Hill, E. W.; Dryfe, R. A. W., ACS Nano, 2011, 5 (11), 8809-8815.

3. P. S. Toth; A. Valota; M. Velicky; I. Kinloch; K. Novoselov; E. W. Hill; R. A. W. Dryfe, Chemical Science,
2013, DOI:10.1039/C3SC52026A.
First Principles Study of the Role of Defects for Graphene Lithiation
Authors: Yildirim Handan , Zhao Zhijian , Chan Maria K. Y. , Greeley Jeff
Published: February 2020

Since the discovery of freestanding graphene, this 2D structure is considered as a potential alternative for graphite, because of its outstanding electronic and mechanical properties. It has attracted much attention as a promising electrode material for electrochemical energy storage devices such as Li-ion batteries due to high surface area and superior electronic conductivity. For Li-ion battery applications, graphene is used as a buffer layer to suppress the large volume expansion observed in high capacity anode materials and as a coating material to enhance conductivity. It was shown that graphene sheets prepared by reduction of graphite oxide (GO) deliver a reversible capacity and good cycling stability. Large variation in the capacity is reported by several studies for graphene, which is prepared with the exact similar techniques. Such discrepancy is suggested to result from the disordered and/or ordered structure of graphene sheets affecting lithium storage capacity, suggesting that the structural characteristics influence the resulting electrochemical performance.

Note that earlier experimental studies have identified the existence of defects such as Stone-Wales and double vacancy defects, as well as grain boundaries in graphene. Thus, for complete understanding of the electrochemical performance of graphene, the role of different types of defects on the electrochemical performance should be identified as well as the defect density influence should be evaluated. Such comparative study along with pristine graphene can provide vast amount of information not only for the electrochemical performance, but also, for the structural and electronic structure differences with the types of defects, defect densities, and Li concentration.

In this study, we use density functional theory to build atomistic level understanding of topological defects in graphene and their role on the electrochemical performance. Li configurations are generated combining an algorithm whose results are tested using a genetic algorithm method. We explore the effect of each defect type on Li adsorption and obtain an atomic level understanding of the interaction between defected graphene and Li. The electrochemical performance of these defective sheets under varying Li concentration is studied, and compared with those obtained for pristine graphene. Furthermore, the effect of defect density on the electrochemical performance is evaluated. Lithiation voltages as function of each defect type will be reported and compared with those of the pristine graphene. The results are expected to shed light on the role of each defect type on the electrochemical performance of graphene as an alternative anode material for Li ion batteries.
Effect of Sub 2-Nm Pt Nanoparticle on the Conduction Properties of Graphene Based Field Effect Transistor
Authors: Zheng Haisheng , Mukherjee Somik , Gangopadhyay Shubhra
Published: February 2020

Graphene-based transistors are attractive platforms due to graphene’s promising electrical properties. Currently, depositing and controlling the size distribution of metal nanoparticles (NPs) on a support surface, such as graphene, without damaging the support is an issue faced in applications involving metal (NPs) in new age electronics. To overcome this barrier, we have developed a low power tilted target sputtering process for achieving sub-2 nm metal (NPs) on graphene with controlled sizes, number densities, and narrow size distributions. In this report, we study the unique properties of platinum (Pt) NPs and their applications in graphene-based FETs by modifying the conduction channel with sub-nm Pt NPs. By using ultra-small size Pt NPs with quantized energy level, we influence the electrical properties of large area single layer graphene through both electron transfer and carrier scattering, resulting in large Dirac point shifting (0.15MV/m for 300nm of SiO2 as blocking oxide) in the I-V characteristics and change in conductivity, respectively; all of which could be helpful to better understand the metal NP-Graphene interaction. We also show that the plasma damage created on the graphene surface from the sputter deposition of metal nanoparticles can be removed by 250 oC annealing in hydrogen.
Oxygen Reduction Reaction on Graphene /TiO2 Composite Electrodes
Authors: Al-Kandari Halema Ali , Abdullah Aboubakr Moustafa , Al-Kandari Shikah Ali , Mohammed Ahmed meslam
Published: February 2020

Graphene oxide (GO) was prepared using modified Hummer`s method using graphite as starting material. Reduction of graphene oxide (RGO) was applied using either hydrogen gas at different temperatures or hydrazine hydrate in microwave. Characterization of reduced graphene samples were performed using Raman, IR, XPS techniques. In addition BET measurements of reduced samples were performed. For example, XPS spectrum of GO showed the presence of hydroxyl, epoxy, carbonyl and carboxylic acids groups. After hydrogen reduction of GO at 200 °C the amount of hydroxyl groups is increased in expense of other groups which confirmed the success of reduction process. The GO and RGO were loaded on commercial TiO2 P25 at different percentage. The Oxygen reduction reaction on pure TiO2, GO/TiO2 and RGO/TiO2 was measured. The catalytic behavior of these materials was measured toward oxygen reduction reaction.
XAFS Study on the Structures of Catalysts for Photoelectrochemical Hydrogen Evolution and CO2 Reduction Prepared By the Incorporation of Metal Complexes within Viologen Multi-Layers Formed on Si(111) Surfaces
Authors: Masuda Takuya , Sun Yu , Morita Yuki , Fukumitsu Hitoshi , Uehara Hiromitsu , Takakusagi Satoru , Chun Wang-Jae , Kondo Toshihiro , Asakura Kiyotaka , Uosaki Kohei
Published: February 2020

Multi-electron transfer reactions such as the hydrogen evolution reaction, oxygen evolution reaction and carbon dioxide reduction reaction at semiconductor electrodes have been extensively studied because of the interest in solar-to-chemical energy conversion. Multi-electron transfer reactions at semiconductors are generally slow and a catalyst is required to efficiently promote these reactions. Hence, many groups have examined the modification of the semiconductor surface by catalytic metals. It was, however, found that direct contact of a metal leads to the formation of a Schottky junction and recombination center, resulting in a reduced efficiency.

In this study, we constructed organic molecular layers with viologen moieties as electron transfer mediators and various metal complexes such as PtCl4
2-, PdCl4
2- and AuCl4
- as catalysts for multi-electron transfer reactions on hydrogen terminated Si(111) surfaces and the modified Si(111) electrodes were utilized for photoelectrochemical hydrogen evolution and CO2 reduction reactions. Precise structures of the metal catalysts incorporated with the molecular layers were determined by polarization-dependent total reflection fluorescence (PTRF)-XAFS.

High selectivity for CO2 reduction in preference to the hydrogen evolution reaction was achieved at the Si(111) electrodes modified by molecular layers with viologen moiety and Pd and Au complexes, which are reduced to metallic nanoparticle under operation, and, therefore, actual catalysts for CO2 reduction were Pd and Au metal nanoparticles, which are known to be good electrocatalysts for CO2 reduction. High selectivity for CO2 reduction was also achieved at the Si(111) electrode modified by viologen moiety and Pt complex despite the fact that hydrogen evolution reaction is dominant at Pt metal electrode even in CO2 saturated solution. Pt complex is not reduced to metallic nanoparticle under operation, and, therefore, Pt complex acts as a confined molecular catalyst for CO2 reduction with high selectivity.

References

T. Masuda, K. Uosaki, Chem. Lett.,
2004,
33, 788-789.

H. Fukumitsu, T. Masuda, D. Qu, Y. Waki, H. Noguchi, K. Shimazu, K. Uosaki, Chem. Lett.,
2010,
39, 768-770.

Y. Sun, T. Masuda, K. Uosaki, Chem. Lett.,
2012,
41, 328-330.

T. Masuda, K. Shimazu, K. Uosaki, J.Phys. Chem. C,
2008,
112, 10923-10930.

T. Masuda, H. Fukumitsu, S. Takakusagi, W. -J. Chun, T. Kondo, K. Asakura, K. Uosaki, Adv. Mater.,
2012,
24, 268-272.
Carbon Supported Metal Oxide Nanoparticles: Hierarchical Porous Structure and Electrochemical Properties
Authors: Zhao Chunxia , Yang Yunxia , Chiang Ken
Published: February 2020

Energy storage devices made from nanostructured electrodes are reported to be lightweight and possess promising performance. Interest is growing in new energy storage devices that are low cost, lightweight, and deliver high energy and power densities. Supercapacitors are important energy storage devices that can deliver high power during short periods of time, making them attractive for electric vehicle applications.

Porous carbon supported metal oxide materials have been successfully used as electrode in supercapacitors. The efficiency of the electrochemical properties can be improved by using novel electrode with controlled nanostructure, nanoparticle size and electrochemical performance. In this work, hierarchically porous carbon supported metal oxides, including cobalt oxide and molybdenum oxide nanoparticles are designed, aiming to improve metal loading and dispersion with uniform nanoparticles, which in-turn enhances eletrochemical performance.

The hierarchically porous carbon matrix synthesized has bimodal porous structure with 300-400 nm macropores and ~ 20 nm mesopores with a BET surface area of ~370 m2/g. Cobalt oxides and molybdenium oxides were loaded by a wet impregnation method. The electrochemical properties of the synthesized hybrid materials will be demonstrated.

Current results demonstrate that cobalt oxide particles in the synthesized composites can be tuned from < 5 nm to 10 nm and are dispersed uniformly across the carbon matrix with loading as high as 15 wt%. Molybdenum oxide particles also can be well dispersed in the carbon matrix with a high loading up to 40 wt% and the valence of molybdenum can be tuned. We also demonstrate the network of meso- and macro- pores and high surface area offered by this type of carbon materials is promising to achieve high metal loadings and dispersion for better activity and mass transport.
Enhanced Electrocatalytic Reduction of Oxygen at Electrodes Coated with a Multi-Metallic Co(II)/Pt(II) Porphyrin
Authors: Swavey Shawn
Published: February 2020

Edge plane pyrolytic graphite (EPG) electrodes coated with the Co(II)/Pt(II)2 analog of 5,15-bis-(4-pyridyl)-10,20-bis-(3-methoxy-4-hydroxyphenyl)porphyrin undergo an electrochemical-chemical-electrochemical (ECE) reaction when anodically scanned in 1.0 M sulfuric acid. The new redox couple formed from this anodic conditioning of the coated electrode is dependent on the pH of the solution. Roughened EPG electrodes coated with the Co(II)/Pt(II)2 trimetallic porphyrin show a catalytic shift of 400 mV for the reduction of O2 when compared to the reduction of O2 at a bare EPG electrode. An additional catalytic shift of ca. 150 mV is observed for O2 reduction at an EPG electrode coated with the Co(II)/Pt(II)2 porphyrin which has been oxidized in 1.0 M sulfuric acid. In addition to the added electrocatalysis a significant percentage of O2 reduced at the oxidized Co(II)/Pt(II)2 EPG electrode is converted to H2O as determined by rotating disk electrode measurements.
Strained Hgte 3D Topological Insulator
Authors: Ballet Philippe
Published: February 2020

First proposed as a new class of matter depicted as a bulk insulator with conducting surfaces, topological insulators have recently stimulated an intensive research activity due to their unique electronic and spin properties. In particular, surface conduction is expected to occur from mass-less Dirac fermions with spin orientation locked to momentum.

A general requirement for turning a conventional insulator into its topological counterpart is the realization of an inverted band structure. Such inversion can be achieved experimentally using confinement or band-offset effects in hetero-structures, but may also be intrinsically present in the band structure of low band-gap materials with very large spin-orbit interaction (SOI).

Since the SOI scales with Z4, the family of intrinsic topological insulator material thus shrinks to very heavy elements. In particular, the most widely investigated Bi1-xSbx and Bi2Se3/Bi2Te3 compounds have shown, from angle resolved photo-emission spectroscopy, to exhibit such surfaces states in the form of Dirac fermions, but usually suffer from parasitic bulk conduction which has so far prevented the demonstration of convincing surface transport experiments.

In this picture, HgTe appears to be a good candidate for topological insulator structures, and we will show that the epitaxial growth of intentionally strained HgTe can provide “insulator-like” band structure material of very high quality. In particular, we will present extensive material characterization of the bulk crystal quality of HgTe and the surfaces and interfaces of HgTe/HgCdTe/CdTe structures designed for electronic transport experiments.

Samples processed into top-gated Hall-bar structures are investigated using variable magnetic field, low-temperature, electronic transport set-up. Strong experimental signatures of surface transport of Dirac particles will be given for different epitaxial configurations. Finally, perspective work as well as potential applicative developments will be discussed.
(Invited) Sputtered Metal Oxide Broken Gap Junctions
Authors: Campbell Stephen , Johnson Forrest , Karthikeyan Sreejith , Song Sang-Ho , Liptak Richard , Benton Brian
Published: February 2020

Both photovoltaic and light emitting devices require the unimpeded flow of electrons, holes, and photons. Often this represents a problem in high performance devices. The problem is sometimes resolved through the use of a tunnel junction formed by epitaxially growing a stack consisting of degenerately doped p- and n-type layers. Because the Fermi level resides in the valence and conduction band, respectively, the conduction band minimum is at a lower energy than the valence band maximum (Fig 1a). Such heavily doped layers are not easily formed in amorphous or polycrystalline semiconductors however, especially for p-type films. Alternatively, one can use a broken gap junction (BGJ) which relies on the difference in affinity to achieve the same result as the tunnel junction (Fig. 1b). The n-type side must have an electron affinity equal to or greater than the sum of the affinity and band gap of the p-type side. Numerical simulations of a metal-oxide broken-gap heterojunction between p-Cu2O and n-In2O3suggest that low-resistance ohmic behavior can be achieved for even for only moderate doping concentrations.

N-type zinc-stannate (ZnSnO3) was deposited by RF magnetron sputtering using an AJA ATC 2000 sputtering system in a reactive oxygen environment using a ceramic target made of 50% ZnO and 50% SnO2 by atomic percent. The target-substrate distance, oxygen partial pressure, total pressure, rf power, substrate temperature, and post deposition anneal were optimized to get the desired optical and electronic properties. P-type Cu2O was chosen due to the band alignment with ZnSnO3. Films were sputtered with a variety of techniques. RF sputtering of a ceramic target gave the best results – the films were stable and film stacks using this method showed very little interdiffusion, even for a 500 oC anneal. Both films were characterized by UV-vis spectroscopy, 4 point measurements, Hall measurements, x-ray diffraction, AFM, EDS, and Auger depth profiling. The latter proved to be problematic for Cu2O due to knock-on effects.

The best films were then sputtered sequentially to make a BGJ. Contacts were applied and the devices were characterized with a three terminal measurement. As expected, ohmic behavior was observed with a resistance below 1 Ohm-cm2. The results were found to be temperature independent between 38 K and 300 K. When the stable Cu2O films were used, the performance of the BGJ did not change upon annealing up to 500 oC. This suggests that hopping mechanisms are not involved, and that a true broken gap alignment was achieved. Freeze out is not observed since the band alignment autodopes both materials. We will also discuss applications of the BGJ to photovoltaics and quantum dot light emitters.
(Invited) Terahertz CMOS Electronics for Future Mobile Applications
Authors: Fujishima Minoru
Published: February 2020

The highest operation frequency of RFCMOS circuits has risen exponentially over the years. This improved performance has culminated in new wireless and wireline communication standards with higher data rates. There has been a tenfold increase in the wireless data rate every four years, being much faster than the increasing speed of wireline communications. If this trend is to continue, 100 Gb/s will be realized around 2020. In order to realize a terahertz CMOS transceiver with 100 Gb/s, not only is device performance improvement through miniaturization important, but also circuit design techniques that move the circuit operation frequency close to fmax must be developed. Furthermore, one has to remind that stringent practical issue, power consumption, still remains for mobile applications even if the terahertz transceiver is technically feasible. Namely, one must consider how the power consumption maintains at the level of the current mobile applications even when ultrahigh data rate is acquired. This challenging issue implies that the near-fmax design technique is extremely useful because the fmax of a given MOSFET is a function of bias voltage, and reduced-fmax circuits can have superior power efficiency.

To utilize near-fmax technology, firstly, one has to know the optimum bias point giving maximum operation frequency under limited power consumption. To achieve low-power operation at a high operation frequency, it is important to choose an appropriate set of bias voltages. The FP (frequency-power) plot is a useful guide to choosing such a set, which shows the gate and drain bias dependences of fmax and power consumption per unit gate width of an NMOSFET. The power-efficient bias points can be found from the FP plot as the points on the power contours where fmax is maximized. The power-efficient bias points give the best fmax for the given power consumption. Since the highest possible fmax of a given MOSFET is realized away from the power-efficient bias points, it is best to avoid the bias point that maximizes the transconductance (gm) if power efficiency is an important design goal. By reducing the actual fmax to be used through tracing the power-efficient bias curve, power consumption can be reduced considerably. As can be observed in 65- and 40-nm CMOS processes, reducing fmax enables exponential power reduction, where the reduction rate is 1/10 every 75 GHz in both process technologies.

When trying to obtain the highest possible performance of a MOSFET, the MOSFET must be biased such that its highest fmax is realized. If, on the other hand, the power consumption is a great concern in a terahertz mobile application, one can opt for a reduced-fmax design. Power-efficient bias points can be found in the FP plot. Continued improvement of the device performance is thus essential for achieving the ultimate low-power high-speed wireless communication even in mobile application.
Low-Cost, Long-Cycle-Life Sodium-Ion Battery to Enable Grid Scale Energy Storage
Authors: Song Jie , Guo Bingkun , Wang Long , Goodenough John B.
Published: February 2020

Large-capacity, cost-effective energy storage is the transformational technology needed to enable large scale integration of renewable energy (e.g. wind, solar). The rechargeable battery offers efficient electrical energy storage (EES). The Li-ion battery has been the leading option based on its performance, but it is too expensive for large-scale EES. Unlike Li, Na is readily available worldwide and therefore much less costly than Li.

Sodium-ion batteries (SIBs) based on a hexacyanometallate (HCM) cathode are good options for the purpose of a low cost battery for EES. These materials correspond to the general chemical formula, AxM1[M2(CN)6]y·zH2O, consisting of a cubic framework with cyanide (C≡N)- ligands bridging metal-ions, M1 and M2, thus forming large lattice interstitial spaces to facilitate efficient alkali-ion, “A”, intercalation. Electronic configurations of M1 and M2 are strongly affected by the cyanide ligands. In particular, ligand field splitting energy is higher for M2-ions associated with carbon than for M1-ions associated with nitrogen, which results in a low spin (LS) electron configuration for M2, but a high spin (HS) electron configuration for M1.

We will present our study on HCM-based cathode materials, including their bulk and surface structures as well as their electrochemical performance. We will demonstrate that the HCM-based cathodes provide promising low-cost and long-cycle life SIBs of high specific energy density and efficient EES.

References:

1. Long Wang, Yuhao Lu, Jue Liu, Maowen Xu, Jinguang Cheng, Dawei Zhang, and John B. Goodenough. Angew. Chem. Int. Ed., 2013, 52, 1964 –1967.

2. Yuhao Lu, Long Wang, Jinguang Cheng and John B. Goodenough. Chem. Commun., 2012, 48, 6544–6546.
Tandem Measurement of Ion and Water Transport Properties for Vanadium Redox Flow Batteries
Authors: Lawton Jamie S. , Jones Amanda , Tang Zhijiang , Zawodzinski Thomas A.
Published: February 2020

The vanadium redox flow battery (VRFB) is a tool for energy storage that has been promising in applications of large grid storage. The battery is composed of positive and negative cells operating with VO2+/VO2
+ and V(II)/V(III) redox couples, respectively. The two cells are separated by an ion exchange membrane, which allows proton conduction to maintain electrical balance during the charge/discharge cycles1. The membrane also allows water, vanadium and acid to crossover from one cell to the other, this can lead to concentration imbalances and self-discharge, ultimately decreasing the efficiency of the battery.2
,
3

Nafion, a membrane commonly used to study this application, has been observed to allow vanadium ion crossover. This causes self-discharge of the battery and affects battery lifetime.3 By gaining a better understanding of the effects of the vanadium ions in membranes such as Nafion, methods can be extended to comparison of alternative membranes for uses in VRFBs, such as those with a hydrocarbon base. EPR has also previously been used to further understand the environment of absorbed species in the membrane4, including alternative hydrocarbon membranes.5,6

Here we report tandem UV/Vis and EPR measurements of vanadium ion transport across ion exchange membranes. A diagram of the experimental setup is shown in Figure 1. Previous studies have shown the VO2+ ion permeability to have a dependence on acid concentration in solution.7,8 This study is extended to observe the effects of additional vanadium ions diffusing with and against each other while mimicking varying states of charge. The transport of one species is assumed to be intrinsically linked to the transport of the other vanadium species. Ultimately, the effects of convection on ion transport during battery charge/discharge cycles can be monitored with this tendem UV/vis / EPR method.

Figure 1. Diagram of the tandem EPR/UV/Vis method for monitoring water and ion transport in VRFB systems

References

(1) M. Rychcik; Skyllas-Kazacos, M. J. Power Sources
1988, 22, 59.

(2) J. Xi; Z. Wu; X. Qiu ; Chen, L. J. Power Sources
2007, 166, 531.

(3) Weidmann, E.; Heintz, E.; Lichtenthaler, R. N. J. Mem. Sci
1998, 141, 207.

(4) Lawton, J.; Budil,D. J. Phys. Chem. B
2009, 113, 10679.

(5) Lawton, J.; Budil, D. J. Membrane Sci.
2010, 357, 47.

(6) Lawton, J.; Budil, D. Macromolecules
2010, 43, 652.

(7) Lawton, J.; Jones, A.; Zawodzinski, T. A. J. Electrochem. Soc.
2013, 160, A697.

(8) Lawton, J.; Aaron, D.; Tang, Z.; Zawodzinski, T. A.; J. Membrane Sci.
2013,428, 38.
A Novel Safe and Ultrahigh-Energy-Density Aqueous Redox Flow Battery System
Authors: Li Bin , Nie Zimin , Vijayakumar Murugesan , Wang Wei , Sprenkle Vincent , Liu Jun
Published: February 2020

Redox flow batteries (RFBs), as one of the most promising electrical energy storage systems, provide an alternative solution to the problems of balancing power generation and consumption. RFBs are designed to convert and store electrical energy into chemical energy and release it in a controlled fashion when required. Many redox couples, such as all-vanadium, iron/chromium, iron/vanadium, bromide/vanadium systems, have been used as active materials for various RFB designs. Of them, all vanadium system (VRBs), utilizing vanadium-containing chemicals as positive V(IV)/V(V) and negative V(II)/V(III) electrolytes, is one of the most promising redox systems due to its high efficiency.[1] Especially, recently invented mix-acid based all vanadium system by Li and co-workers[2]at PNNL largely improved the energy density and temperature stability window of vanadium electrolytes. However, the energy density is still too low as compared with other secondary batteries, such as Li ion battery, which is very important especially in the application of large-scale energy storage system.

Here we report a novel aqueous redox flow battery system, which is safe and exhibits high discharge energy density. As shown in Fig. 1, the discharge energy density is around 135 Wh/L, which is about 5 times of that in VRB system. In addition, the chemistry and transportation mechanism of this system are investigated in detail.

Acknowledgements

The authors would like to acknowledge financial support from the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery and Energy Reliability (OE) (under Contract No. 57558). We also are grateful for insightful discussions with Dr. Imre Gyuk of the DOE-OE Grid Storage Program. The S/TEM work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE's Office of Biological and Environmental Research and located at PNNL. Pacific Northwest National Laboratory is a multi-program national laboratory operated by Battelle for DOE under Contract DE-AC05-76RL01830.

References

[1] Wang, W., Luo, Q., Li, B., Wei, X., Li, L. and Yang, Z. (2013), Recent Progress in Redox Flow Battery Research and Development.
Adv. Funct. Mater
., 23: 970–986.

[2] Li, L., Kim, S., Wang, W., Vijayakumar, M., Nie, Z., Chen, B., Zhang, J., Xia, G., Hu, J., Graff, G., Liu, J. and Yang, Z. (2011), A Stable Vanadium Redox-Flow Battery with High Energy Density for Large-Scale Energy Storage.
Adv. Energy Mater
., 1: 394–400.
Understanding the Performance of Aqueous Organic Redox Flow Batteries
Authors: Yang Bo , Hoober-Burkhardt Lena
Published: February 2020

Organic redox flow batteries (ORFB) are considered to be one of the most promising technologies for large-scale energy storage needed for integrating renewable energyrom intermittent sources such as solar photovoltaic and wind-based generation systems [1]. ORFBs are attractive because the proposed materials are potentially low cost, eco-friendly, and sustainable. Organic compounds, such as quinones and their derivatives, can be used as both the positive and negative active material of ORFB, due to their electrochemical reversibility and relatively high charge capacity of 200-490 Ah/kg. The use of water as the solvent lowers the cost and makes the system safe, non-flammable, and highly eco-friendly. Heavy metals such as chromium, vanadium, zinc and lead are completely avoided. Thus, the material cost can be reduced substantially for achieving the DOE-specified target of $100/kWh for the entire battery system.

In the present study, we have constructed redox flow cells operating on 0.2 M benzoquinone disulfonic acid (DSQ) and 0.2 M anthraquinone sulfonic acid (AQS). We have measured the rechargeability and current-voltage characteristics. We find that the cells are rechargeable and no loss of capacity was observed in 12 cycles (Figure 1). This result suggests that the quinones are chemically stable under the conditions of cycling.

The current-voltage curves were measured as a function of state-of-charge. We found that the power density decreased significantly below the 50% state of charge. This decrease is attributed to the mass transport limitations that can be severe at low reactant concentrations of 0.2 M (Figure 2). Analysis of the current-voltage and impedance data indicate that the power density can be increased by enhancing the solubility of the quinones, increasing the temperature of operation and by modifying the electrode structure to allow for rapid mass transport. In this presentation, we will discuss the improvements in power density achieved by these various approaches.

Acknowledgement

The work presented here was funded by ARPA-E (Open FOA) and the Loker Hydrocarbon Institute of University of Southern California.

References

1. Inexpensive Flow Batteries Based on Organic. Redox Couples. BoYang
, Lena Hoober-Burkhardt, G. K. Surya. Prakash, and S. R. Narayanan, the 224th meeting of Electrochemical Society, San Francisco, 2013, Abstract 468.
The Chemistry behind Quinone Flow Batteries
Authors: Marshak Michael P. , Huskinson Brian , Gerhardt Michael R. , Gordon Roy G. , Aziz Michael J.
Published: February 2020

In order to make flow batteries cost-competitive for large-scale stationary storage, significant reductions must be made in the cost of the redox-active materials. We will show that organic molecules such as quinones offer dramatic cost reductions to the storage medium in comparison with metal-based electrolytes. Quinones also provide the ability to tune the redox and solubility properties of the molecules through the incorporation of various substituent groups onto the aromatic ring.

We will report the synthesis, chemical, and electrochemical properties of several substituted quinone molecules. These results indicate that bulk solutions of quinones may be easily prepared and used as electrolyte solutions without purification. The reaction can be modified to affect the reduction potential of the solution, while maintaining rapid and reversible electrochemical kinetics. Finally, the unique electronic structure of quinone molecules is described to explain the origin of the fast, un-catalyzed two-electron redox kinetics.
Very Large Scale Integrated (VLSI) Photonics: Issues, Challenges and Visions
Authors: Lee El-Hang
Published: February 2020

This presentation discourses on a newly emerging frontier technology called VLSI (very large scale integrated) photonics. It is a new field of optical circuit or optical network technology rapidly evolving in micro/nano-scale yet to complete the unfinished information revolution brought forth by the megascale optical fiber-based global network. It discusses the science and engineering of micro/nano-photonics and integration that can lead to VLSI photonic circuits and networks of generic and application-specific nature. The world in the 21st century is facing many new kinds of problems, including increasing demand for big data, higher information capacity, increasing population, increasing cost of energy, shortage of food and natural resources, environmental problems, global warming, increasing medical and health problems, and increasing demand for well living. Electron-based technology in the 20th century is beginning to show many limitations in the face of these and other rising problems. Photon-based technology, on the other hand, is showing many new promises that can lead to solutions to many of thes problems that electrons alone cannot. Compact, high-speed, light-weight, and low-powered optical and photonic micro/nano-systems using nano-wires, micro/nano-structures, plasmonics, and metamaterials, show possibilities of new properties and functions that can provide new solutions for the rising problems, that can address green and sustainable IT/BT/NT applications in the 21st century. The new optical systems consist of arrays of micro/nano-scale optical wires, circuits and devices on chips or on modular boards to perform the functions of sensing, switching, modulating, processing, transporting, routing, and distributing optical signals. The optical components include micro/nano-scale light sources, waveguides, detectors, switches, modulators, sensors, couplers, filters, resonators, photonic crystal devices, plasmonic devices, and quantum structures, made of polymer, silicon and other semiconductor micro/nano-materials. We discuss scientific and technological issues and challenges for the miniaturization and integration of micro/nano-scale photonic materials, devices, circuits, and networks for ultra-small and high-density integration and application. It includes new physics, theories, materials, designs, and structures. New perspectives and visions will be discussed along with the historical perspectives of the electrical technology. Recent progresses and examples will be presented.
Fano Resonance Photonic Crystal Membrane Lasers and Filters for Integrated Silicon Photonics
Authors: Zhou Weidong , Ma Zhenqiang
Published: February 2020

Fano resonance, known from atomic physics, has been employed for a wide variety of nanophotonic structures, such as quantum dots, photonic crystal, plasmonics, and metamaterials, and so on. With modal dispersion engineering, Fano filters and reflectors can all be realized in single layer dielectric photonic crystal structures. Based on Fano resonance principle in 2D air hole photonic crystal slabs, combined with crystalline semiconductor nanomembrane transfer printing techniques, we have demonstrated a range of ultra-compact high performacne photonic and electronic devices on silicon and on flexible substrates.

By sandwiching InGaAsP quantum well cavity in between two single –layer silicon Fano resonance photonic crystal membrane reflectors (MR), membrane reflector vertical-cavity surface- emitting lasers (MR-VCSELs) were proposed and demonstrated. We will report our recent progresses on this new type of membrane lasers, which can be built on silicon, and on flexible substrates.

Ultra-compact high quality factor optical filters have also been realized experimentally, based on Fano resonances in single or coupled bi-layer photonic crystal slabs, without or with lattice displacements. Theoretically, with the control of lattice displacement between two coupled photonic crystal slabs layers, optical filter Q factors can approach 211,000,000 or infinite. Experimentally optical filters with quality factors up to 80,000 have been demonstrated.

Finally, we will review other type of Fano resonance based optical structures, such as vertical to in-plane couplers, and beam routing structures, for integrated silicon photonics. The convergence of nanomembranes and Fano resonance photonic crystals offer unprecedented opportunities for unique electronic and photonic devices for 3D multi-functional Si CMOS photonics, flexible, bio-inspired/integrated photonic/electronic systems, and multi-spectral multi-color infrared imaging and sensing systems, etc.

The work was supported by US AFOSR, ARO and NSF.
Applications of Optoelectronics Sensor Technology in Environmental and Personal Health Monitoring
Authors: Fang Qiyin , Deen M. Jamal , Selvaganapathy Ravi
Published: February 2020

Integrated optoelectronics is originally developed based on microelectronics processing, fabrication, and integration. Over the past decade, its focus has been shifted from telecommunication devices towards biomedical and environmental applications. The most notable advances include nano/micro-optical-electrical-mechanical systems (N/MOEMS) and optofluidics. Current technology developments not only lead to novel devices, but application oriented, full systems integration dissimilar materials and modules at the system level.

These enabling technologies, in turn, facilitated the emerging growth of a number of new frontiers in biomedical, clinical, and environmental applications. Highly integrated micro-nano-systems (MNS) technology will lead to wireless sensing devices that can fit into small spaces with improved sensitivity and specificity. As a result, a number of such technologies have find application in the emerging field of environment pollutant monitoring, wearable physiological monitoring, activity sensing, and even clinical diagnostic devices.

Another important feature of microelectronics fabrication based micro-nano system technology is the potential for low cost, sensitive, and automated sample handling capability. These advantages have enabled large scale, distributed sensing and monitoring applications.
Sapphire Substrate Geometrical Effects on III-N Blue LED Material Properties
Authors: Armour Eric A , Hu MingShien , Byrnes Daniel P , Sun Kenny , Papasouliotis George D , Maiocco Lisa B , Brosnan Maureen A , Gasdaska Charles J
Published: February 2020

Solid-state lighting modules based upon III-N light-emitting diodes (LEDs) are now progressing towards widespread adoption in residential and commercial applications. LED manufacturers are driving die performance and yield upwards while reducing cost. However, color binning due to the sensitivity of the human eye response, which can resolve differences in dominant wavelength within a 2 nm range, remains one of the primary yield and cost limiters. As we continue to improve and understand growth process-related reproducibility, we have observed that some of the within-wafer and wafer-to-wafer characteristics cannot be explained through known physical phenomena from the epitaxy, and are more likely related to substrate properties.

In this presentation, we will analyze a set of experiments designed to understand the effect of (0001) sapphire c-plane substrate physical dimensions (thickness, diameter, bow/warp/TTV, edge beveling) and crystal properties (misorientation, surface roughness) on uniformity and reproducibility of constituent LED layers. Our initial studies have found that precisely controlled crystal misorientation (offcut) towards the m-plane is a significant factor influencing wafer-to-wafer peak wavelength variation, GaN surface roughness, and p-doping levels. Quantitative analysis of these results with respect to variation in typical substrate manufacturing capabilities will be presented; the trends are in agreement with the materials characteristics explored in our previous studies [1, 2]. Warp and bow are critical parameters for control over GaN material characteristics. Furthermore, tight control over the total thickness variation (TTV) is needed to obtain highly uniform, repeatable sub-micron dimensions used to create current patterned substrate (PSS) wafers.

[1] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, J.C. Ramer, A. Parekh, and E.A. Armour, “Sapphire substrate misorientation effects on GaN nucleation layer properties”, J. Crystal Growth
272:353, (2004).

[2] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, A. Parekh, J.C. Ramer, S.P. Guo, and E. Armour, “Advanced characterization studies of sapphire substrate misorientation effects on GaN-based LED device development”, Phys. Stat. Sol.(a)
200:71, (2003).
(Invited) Effects of Environmental Exposure on Stability and Conductance Poly-l-lysine Coated AlGaN/GaN High Electron Mobility Transistors
Authors: Rohrbaugh Nathaniel , Bryan Isaac , Bryan Zachary , Collazo Ramon , Ivanisevic Albena
Published: February 2020

A study of AlGaN/GaN high electron mobility transistors (HEMTs) was done to assess their implementation as functionalized in situbiosensors [1]. Gallium nitride presents itself as a viable option in sensors which require a high degree of stability in aqueous and biological settings while also being a suitable wide band gap semiconductor for HEMTs [2]. The functionalization of HEMT biosensors bestows high specificity binding groups to the surface enabling characterization of singular biological functions or environmental conditions [3][4]. However, peptide adherence and stability over a given operational cycle are unknown and thus the efficacy and usable lifetime are yet to be determined.

Here, GaN based biosensors were fabricated, functionalized, and then tested with simulated solutions in which the HEMT biosensors would be expected to function. AlGaN/GaN HEMTs were grown via MOCVD (Fig. 1) and functionalized via physisorption of recognition peptides. HEMTs were tested in physiologically relevant solutions as well as controlled solution. Analysis was done upon initial peptide binding via AFM, XPS, and IV measurements. This was repeated after environmental exposure was completed over variable periods of time. The results show the stability of the surface over extended cycles along with the benefits associated with the functionalization of the device. The detailed surface and electrical characterization is essential for quality control and integrity of future sensor development based on GaN devices.

References

[1] M.S. Makowski, and A. Ivanisevic, “Molecular analysis of blood with micro/nanoscale field-effect-transistor biosensors,” Small, 7(14)1863 (2011)

[2] S. Jewett, M.S. Makowski, B. Andrews, M. Manfra, A. Ivanisevic, “Gallium nitride is biocompatible and non-toxic before and after functionalization with peptides,” Acta Biomaterialia, 8(2)728 (2012)

[3] A. Ramesh, F. Ren and P. Berger, “Towards in vivo biosensors for low-cost protein sensing,” Electronics Letters, 49(7) 450 (2013)

[4] M.S. Makowski, I. Bryan, R. Collazo, Z. Sitar, A. Ivanisevic, J. Xie, and C. Arellano, “Kinase detection with gallium nitride based high electron mobility transistors,” Applied Physics Letters, 103(8) (2013)