bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Photocurrent Spectroscopy of Exciton and Free Particle Optical Transitions in Suspended Carbon Nanotube Pn-Junctions
Authors: Cronin Stephen B. 
Published: February 2020

We study photocurrent generation in individual, suspended carbon nanotube pn-junction diodes formed by electrostatic doping using two gate electrodes. Photocurrent spectra collected under various electrostatic doping concentrations reveal distinctive behaviors for free particle optical transitions and excitonic transitions. In semiconducting nanotubes, the photocurrent generated by excitonic transitions exhibits a strong gate doping dependence, while that of the free particle transitions is gate independent.1 Here, the built-in potential of the pn-junction is required to separate the strongly bound electron-hole pairs of the excitons, while free particle excitations do not require this field assisted charge separation. We observe a sharp, well defined E11 free particle interband transition in contrast with previous photocurrent studies. Several steps are taken to ensure that the active charge separating region of these pn-junctions is suspended off the substrate in a suspended region that is substantially longer than the exciton diffusion length and, therefore, the photocurrent does not originate from a Schottky junction. We present a detailed model of the built-in fields in these pn-junctions, which, together with phonon-assistant exciton dissociation, predicts photocurrents on the same order of those observed experimentally. In addition, we investigate the competing photocurrent mechanisms in quasi-metallic nanotubes over a wide range of bandgaps (30–180 meV).2 Here, we correlate homogenous pn-doping dependence ( Vg1 = – Vg2 ) of the photocurrent with the current–voltage ( I–Vg ) characteristics (Vg1 = Vg2 ) of each device. These I–Vg characteristics, in turn, are used to determine the bandgap of the nanotubes by fitting our data to a Landauer transport model. The mechanism underlying photocurrent generation is then established by correlating the photocurrent transport with the calculated thermoelectric power, the measured conductance, and the extracted bandgap for all devices.
1. Chang, S.W., J. Theiss, J. Hazra, M. Aykol, R. Kapadia and S.B. Cronin, Photocurrent spectroscopy of exciton and free particle optical transitions in suspended carbon nanotube pn-junctions. Applied Physics Letters, 107, 053107 (2015).
2. Amer, M.R., S.W. Chang and S.B. Cronin, Competing Photocurrent Mechanisms in Quasi-Metallic Carbon Nanotube pn Devices. Small, 11, 3119-3123 (2015).
(Invited) Interaction of Molecules with Single-Walled Carbon Nanotube Probed By Photoluminescence and Raman Spectroscopy
Authors: Homma Yoshikazu 
Published: February 2020

The interaction of molecules and material surfaces is one of the fundamental topics in surface science. Also, understanding the behavior of molecules in nano-space is increasingly important in nano- and biotechnologies. A single-walled carbon nanotube (SWNT) is a monolayered material composed of all surface atoms, which provide a simple van der Waals potential originated from a single layer both for the outer surface (quasi 2D) and inner nano-space (quasi 1D). Furthermore, the quasi 1D electronic structure of SWNT allows resonant optical transitions, which are sensitively affected by the surrounding environment of SWNT. SWNTs are thus an ideal material for examining the behaviors of molecules on the surface or in the nano-space by means of optical spectroscopy.
We use a singly suspended SWNT between mesa structures to minimize the interactions with the substrate and other nanotubes, and expose it directly to the ambient gas. Semiconducting SWNTs suspended in space exhibit resonant photoluminescence (PL) and Raman scattering, and their optical responses depend on the state of molecules adsorbed on the SWNT surface or encapsulated in the tube [1-3]. Therefore, gas molecule adsorption/desorption on the SWNT surface or inside of the tube can be probed by PL and Raman spectroscopy.
We have found that water molecules form an adsorption layer of two-monolayer thickness on the hydrophobic SWNT surface as a result of hydrogen-bonding network of water molecules [2]. The water adsorption layer has a sizable effect on the radial breathing mode frequency in Raman scattering [4]. The phase of water molecules can also affect those properties of SWNTs. The phase diagrams of the water both outside and inside of SWNT will be constructed based on the results of spectroscopy. Furthermore, PL peak energies from hybrids of single-stranded DNA and SWNT were found to depend on the DNA base type, namely thymine, adenine, cytosine, and guanine [5]. The base type dependence was attributed to the adsorption energy of the DNA bases on the SWNT surface.
[1] S. Chiashi, et al. Nano Lett. 8, 3097 (2008).
[2] Y. Homma, et al. Phys. Rev. Lett. 110, 157402 (2013).
[3] S. Chiashi, et al. J. Phys. Chem. Lett. 5, 408 (2014).
[4] S. Chiashi, et al. Phys. Rev. B 91, 155415 (2015).
[5] M. Ito, et al. J. Phys. Chem. C 119, 21141 (2015).
Actinide Metallic Endohedral Fullerenes: Synthesis of Th@C2n and U@C2n(n=36-50) and the Electrochemical Properties of Th@C82 and U@C82
Authors: Wang Yaofeng , Chen Ning 
Published: February 2020

A series of actinide metallic endohedral fullerenes, Th@C2n (n=36-50) and U@C2n (n=36-50), were synthesized by arc-discharging method with graphite rods packed with graphite powder and metal oxide (ThO2 , U3O8 , respectively) under an atmosphere of helium. Among these novel endohedral fullerenes, Th@C82 and U@C82 were found to be most abundant species and one isomer for each endohedral fullerene has been isolated and purified by multistage HPLC methods respectively. The purified Th@C82 and U@C82 were characterized by mass spectrometry, UV-Vis-NIR absorption spectroscopy and for the first time, their electrochemical properties were investigated by cyclic voltammetry (CV). The UV-Vis-NIR absorption and electrochemical properties of U@C82 show large resemblance to those of previously reported lanthanide monometallic fullerenes, such as La@C82 ,Y@C82 ,Gd@C82 etc., which suggests that the oxidation state of the uranium atom in U@C82 is likely to be +3. Th@C82 , compared to those of the U@C82 as well as the lanthanide monometallic fullerenes, however, demonstrated significant differences both in the retention time on the Buckyprep and Buckyprep-D columns and the absorption spectra. In particular, Th@C82 demonstrated unique electrochemical properties. In the cathodic range, Th@C82 shows four irreversible reductive steps in which the first reduction potential was found to be -1.04V, far more negative than those of all lanthanides monometallic fullerenes. In the anodic range, the oxidative behavior of Th@C82 is similar to that of U@C82 , displaying a reversible first oxidation step at 0.49 V, and irreversible second oxidation step at 0.90 V. Thus the electrochemical potential gap of Th@C82 was determined as 1.53V. This value is much higher than those of the M@C82 of trivalent lanthanides and is the largest for all the mono-metal endohedral fullerenes discovered to date. This work demonstrated unique physical and electrochemical properties of actinide metallic endohedral fullerenes and their potential of application in material sciences.
(Invited) Structural Studies of Metal-Fullerene Interactions from Ouside to Inside
Authors: Aghabali Amineh , Olmstead Marilyn M. , Balch Alan L. 
Published: February 2020

Recent results on single crystal X-ray diffraction studies of various endohedral fullerenes and chemically modified fullerenes capable of bonding to metal ions will be presented. Some synthetic and crystallographic work on the interactions of open cage fullerenes with metal complexes will be presented.
(Invited) Electronic and Structural Properties of New Endohedral Metallofullerenes
Authors: Poblet Josep M. , Morales Roser , Rodríguez-Fortea Antonio , Fortier Skie , Buck David , Echegoyen Luis 
Published: February 2020

Recently, endohedral species containing uranium ions have been detected by MALDI mass spectrometry. In this communication, we will describe the electronic and structural features for some new uranium endohedral fullerenes. In particular, we will discuss the potential different oxidation states of the uranium ions when they are encapsulated in fullerenes. Because of their complex electronic structure we will also show that some models can be used to determine the optimal structures for uranium endohedral metallofullerenes.
(Invited) Near Infrared Photoluminescence of Endohedral Metallofullerenes
Authors: Okazaki Toshiya 
Published: February 2020

Physical properties of endohedral metallofullerenes can be tuned by changing the fullerene size as well as the metal atom(s) inside the fullerene cage. One of the most interesting characteristic properties of the metallofullerenes encapsulating lanthanide metal atoms is the near-infrared photoluminescence (NIR-PL) due to the f-f transition of M3+ (or M2+) in fullerene cages. Previously, we reported that (Er2C2)@C82 (III) has exhibited the strongest PL in isomer-separated Er2@C82 (I, II, III) and (Er2C2)@C82 (I, II, III) in CS2 solution [1]. The encapsulated C2 molecule enhances the PL intensity by increasing the efficiency of the energy transfer from the C82 cage to the encapsulated Er3+. In this talk, we will report the NIR-PL from Tm atom(s) in Tm metallofullerenes for the first time. The PL spectra and their intensities strongly depend on the electronic states of Tm ions and the fullerene cages. The detailed mechanisms will be discussed.

[1] Y. Ito, T. Okazaki, S. Okubo, M. Akachi, Y. Ohno, T. Mizutani, T. Nakamura, R. Kitaura, T. Sugai and H. Shinohara, ACS Nano, 1, 456-462 (2007).
Evolution of Fe-Antisite Defects in Standard Hydrothermal LiFePO4 Synthesis and Their Accelerated Removal with Ca2+
Authors: Paolella Andrea , Demopoulos George P. , Zaghib Karim 
Published: February 2020

Based on neutron powder diffraction (NPD), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), Electron Energy Loss Spectroscopy (EELS), X-Ray Photoelectron Spectroscopy (XPS) we show that Fe-antisites defects are surface defects (see Figure 1) and slowly eliminated by Fe-Li cation exchange during standard hydrothermal synthesis1. Recently2 we demonstrated that the calcium ions help eliminate the Fe antisite defects by controlling the nucleation and evolution of the LiFePO4 particles during their hydrothermal synthesis. The final Ca:LFP particles present Fe-antsite defects confined in a thin surface layer compared to standard LFP.

Fig. 1.
Figure 1: Schematic representation of Fe-antisite defects elimination during standard hydrothermal synthesis of LFP

Reference

1. Paolella, A. et al. Cation exchange mediated elimination of the Fe-antisites in the hydrothermal synthesis of LiFePO 4. Nano Energy
16, 256–267 (2015).
2. Paolella, A. et al. Accelerated Removal of Fe-Antisite Defects while Nanosizing Hydrothermal LiFePO 4 with Ca 2+. Nano Lett. 2–7 (2016). doi:10.1021/acs.nanolett.6b00334

Figure 1
Honeycomb Ordering to Trigger Stable Oxygen Redox Chemistry in Layered Cathode
Authors: Okubo Masashi , Mortemard de Boisse Benoit , Liu Guandong , Ma Jiangtao , Nishimura Shinichi , Chung Sai-Cheong , Kiuchi Hisao , Harada Yoshihisa , Kikkawa Jun , Yamada Atsuo 
Published: February 2020

Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium but the low capacities of available cathode materials make them impractical. Among the various positive electrode materials that have been investigated, sodium-excess metal oxides Na2
MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. Therefore, to establish the general strategies for enhancing the capacity of Na2
MO3 are primarily important.
In this work, using two polymorphs of Na2RuO3, we demonstrate the decisive role of honeycomb-type cation ordering in Na2
MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g-1 (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g-1 (1.0-electron reaction) [1]. We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure [2]. The highly stabilized intermediate phase with honeycomb-type cation ordering in the [Na1/3M2/3]O2 slab induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2
MO3 cathodes.
[1] M. Tamaru, et al., M. Okubo & A. Yamada, Electrochem. Commun. (2013) 33, 23-26.
[2] B. Mortemard de Boisse, et al., M. Okubo & A. Yamada, Nat. Commun. (2016) 7, 11397.

Figure 1
Determination of Space-Charge-Layer Width in Li-Ion Solid Electrolyte Under the Application of Voltages
Authors: Sugiyama Issei , Saito Masahiro , Aoki Yasuhito , Otsuka Yuji , Shimizu Ryota , Hitosugi Taro 
Published: February 2020

Distribution of conducting ions in solid electrolytes is key information for revealing operation mechanisms of ionics-based devices, such as Li-ion batteries and fuel cells. The distributions of conducting ions in liquid electrolytes are well understood, especially near liquid-electrolyte/electrode interface; an electric double layer is formed in nano-meter scale. In contrast, as for solid electrolytes, although the quantitative study of physics in space charge layer is of crucial importance, few researches have addressed the depth profile of the density of conducting ions.
Here we report applied-voltage-dependent Li-ion distributions in a Li-ion solid electrolyte, measured by using Rutherford backward scattering (RBS) and nuclear reaction analysis (NRA). Combining RBS and NRA, we were able to obtain the depth profile of chemical compositions for both light and heavy elements, in a sample under the application of bias voltage. Thus, quantitative study of Li-density distribution is possible. For the RBS and NRA measurements, 200 nm-thick Ni thin films were deposited as blocking electrodes using DC magnetron sputtering method on both sides of a Li1.5Al0.5Ge1.5P3O12 (LAGP, Toshima Co. Ltd.) solid electrolyte substrate. The sputtering conditions of Ar pressure, substrate temperature and DC output power were 1 Pa, room temperature and 30 W, respectively. H+ beam accelerated at 1 MeV was used for both the RBS and NRA measurements. We developed an original sample holder that would enable us to apply voltages (V= 0 V, +5 V and -5V) during the measurements. AC impedance spectroscopy was also measured before and after the RBS and NRA measurements.
Surprisingly, the NRA measurements revealed that the space charge layer in Li-ion solid electrolyte is in the order of micro-meters. Depth profiles of Li composition obtained from the RBS and NRA measurements are summarized in the Figure. It should be stressed here that the Li composition is depressed more than 40% at V = +5 V compared to that at V= 0 V. The width of Li-depressed region exceeds 8 μm. This result is in striking contrast to the liquid electrolyte case; the electric double layer is in the order of nano-meters.
This study was supported by JST-CREST, JST-ALCA and Kakenhi.
Figure: Depth profiles of the Li composition at 0 V (blue line) and at +5 V (red line). Li composition is normalized by the bulk Li composition at 0 V. The inset shows an experimental layout of RBS, NRA and electrochemical (Ec) measurements.

Figure 1
Three-Dimensional Amorphous TiO2 Thin-Film Electrodes Deposited on Micro-Pillars By Spatial Atomic Layer Deposition for Li+-Ion Batteries
Authors: Moitzheim Sébastien , Balder Elisabeth , Poodt Paul , Unnikrishnan Sandeep , Vereecken Philippe M 
Published: February 2020

A promising route to improve Li+-ion batteries in terms of capacity and rate-performance, is the development of all solid-state three-dimensional (3D) thin-film Li+-ion batteries. For this, the use of amorphous TiO2 (am-TiO2) as a 3D thin-film electrode was investigated. Using spatial atomic layer deposition (s-ALD), ~100 nm thick am-TiO2 films were deposited on high aspect ratio silicon micro-pillars. Due to the self-limiting nature of atomic layer deposition, high quality, uniform and conformal films can be deposited even on 3D structures. Spatial ALD is a fast and upscaleable technique which can significantly lower the cost above conventional ALD. The role of the am-TiO2 s-ALD deposition parameters were investigated for optimal conformal coating. With the optimized process, the thickness variation was at most ~20% for layers deposited on an aspect ratio of 25. Furthermore, the am-TiO2 layers using our process are shown to have a very high capacity and rate-performance, far above that for traditional anatase TiO2 thin-films. At a rate of 1C, near theoretical lithium insertion/extraction (i.e. Li1TiO2) is achieved of ~1150 mAh /cm3. Increasing the rate to 20C (theoretical charging in 3 minutes), results in a capacity of ~890 mAh/cm3, which is still above the average capacity of anatase TiO2 of 769 mAh/cm3 (i.e. Li0.6TiO2), which can typically only be achieved for slow C-rates (C-rate << 1C). This report shows for the first time the use of s-ALD to deposit am-TiO2 thin-films on 3D structures with ultra-fast lithium-ion insertion/extraction capabilities.

Figure 1
HE3DA
Authors: Prochazka Jan 
Published: February 2020

The HE3DA®concept of several millimeters thick electrodes (3D) gives the battery incomparable safety and brings a number of new technical attributes, which are not achievable by the existing thin film technology (2D).

Recently patented internal cooling system radically shrinks the battery pack size and extends the battery life.

The safe and robust construction with multifunctional frames, easy degassing, low internal resistance and electrolyte regeneration make this new lithium accumulator technology ideal for high capacity batteries and large energy storage modules.

The HE3DA® battery is based on fast Li+ diffusion into nanomaterials, special inorganic separators and several millimeters thick electrodes.

This fully inorganic battery does not contain any organic melting parts, demonstrates a very low internal resistance, allows easy degassing and shows a number of other advantages that are not possible to utilize by the conventional 2D technologies. HE3DA® battery technology provides an inherited safety to the batteries, enabling construction of very large cells on MWh level and modules on hundreds of MWh scale.

The performance of a small module of HE3DA® battery with photovoltaic panels will be demonstrated.
Aqueous Electrolyte Polyionic Batteries for Scaled Stationary Energy Storage
Authors: Whitacre Jay 
Published: February 2020

This presentation will cover the scaling and implementation of large-scale energy storage electrochemical batteries that use largely unexplored electrode interactions that exploit muti-cation interactions simultaneously, and have a high electrode mass to electrolyte mass ratio. The core (anode-limited) electrochemical couple uses a configuration wherein the active anode material consists of a blend of NaTi2(PO4)3 and activated carbon and the cathode is Li-inserted cubic spinel l-MnO2, and the electrolyte is a blend of Li+ and Na+ and hydrogen cation species (at some states of charge) solvated in an aqueous electrolyte with SO4
- and OH-(at some states of charge) as the countering anions. The basic function of the battery will be discussed, and comparisons between small bench top cells and fully scaled product-level devices will be drawn. Data will be presented showing that large scale industrially packaged batteries with over 3000 Wh in capacity have be produced and qualified. Further data will show that packs of these batteries in the multi-kWh range have been effectively implemented in field-testing around the world. These applications include support for both smaller off-grid applications with bus voltages in the in the 20 to 100 V range, as well as, grid compatible systems with bus voltages in excess of 1000 V.
Key topics to be addressed include: (0) a description of the core electrochemical technology, including Na/Li displacement reactions in the anode, (1) a novel charge cutoff methodology that optimizes lifetime and function, (2) lifetime performance of this system through a range of temperatures, and (3) data from field tests in relevant applications showing the performance of our batteries under application specific load profiles.
Improved Performance of Ti/Mn Redox Flow Battery By Thermally Treated Carbon Paper Electrodes
Authors: Dong Yong-Rong , Kaku Hirokazu , Hanafusa Kei , Moriuchi Kiyoaki , Shigematsu Toshio 
Published: February 2020

Nowadays, with the fast growing of fluctuating renewable energy like wind and solar, the rechargeable battery technologies have attracted much attention. Redox Flow Batteries (RFBs) offer the independent design of power and energy, which can provide capacity ranging from a few milliseconds to hours. The unique design flexibility and scalability enable RFBs to meet multiple applications simultaneously, such as frequency regulation, peak cut, surplus energy storage and etc. RFBs consist of tanks of electrolyte that storage chemical energy and electrochemical cells that reversibly convert chemical energy to electricity. Various RFBs have been developed, and they can be classified into two types according to the electrolyte: aqueous and non-aqueous RFBs. Among various aqueous RFBs, all vanadium RFBs are the most mature technology and have been used in practical applications.
We reported a Ti(IV) and Mn(II) mixed aqueous electrolyte which is applied for a Ti/Mn RFB[1]. The aqueous Ti-Mn RFB shows a high energy density of 23.5kWh/m3, and provides a low-cost option. However, the current density (50mA/cm2) remained low and need to be improved. The low activity of carbon electrodes leads to the low power density. In order to improve the power density, this work investigates the effect of thermal treatment of carbon papers for both positive and negative electrodes. Through the heat treatment in the air atmosphere, the surface area of the electrode is greatly increased, and the performance is improved at a high current density of more than 100mA/cm2.

Acknowledgments

This work is financially supported by Ministry of Economy, Trade and Industry (METI). This work is technically supported by The National Institute of Advanced Industrial Science and Technology (AIST).

References

[1] Y.-R. Dong et al. ECS Trans., 69(18), 59 (2015).