bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.