bluuebunny/crossref_metadata_2025 huggingface dataset:
An Effective Solution-Phase Dopant for Generating Thin Films of Single Walled Carbon Nanotubes with Varying P-Type Conductivity
Authors: Stanton Noah J. , Ihly Rachelle , Norton-Baker Brenna , Ferguson Andrew John , Blackburn Jeffrey L.
Published: February 2020

Single-walled carbon nanotubes (SWCNTs) have the potential to revolutionize many areas of opto-electronics, particularly thin-film photovoltaics and thermoelectrics due to their high carrier mobility and low-dimensional structure. Much effort has been devoted to increasing the thermoelectric power factor of SWCNTs by controlling the doping levels and doping types for enhanced thermoelectric conversion. Controlling the Fermi energy level within these unique 1D structures is often afforded by charge transfer interactions between host species (SWCNT) and electron or hole accepting species (dopant). Recent advancement of polymer-wrapped SWCNTs allows for thin-films of SWCNTs to be to cast using solution-based processing techniques. Conventional methods to dope SWCNTs rely upon intercalation of dopant molecules within solid-state networks of SWCNTs in a thin film. Here, we discuss methods to dope polymer-wrapped SWCNTs directly in solution by adding a p-type charge transfer dopant, F4-TCNQ, to SWCNT dispersions prior to thin-film deposition. This approach provides more control and reproducibility of the doping level and allows for SWCNTs inks to directly create doped thin films without the need for post-deposition treatments.

Interestingly, we show that introduction of the dopant at varying stages of polymer wrapping process of SWCNT dispersion impacts the polymer selectivity for semiconducting vs. metallic SWCNTs. By controlling the dopant concentration in solution, we show that the degree of doping is retained upon thin film formation, enabling creation of SWCNT thin films with controllable carrier concentrations for opto-electronic applications. We characterize the thermoelectric properties of the solution-phase doped films, and demonstrate large, tunable power factors that correlate well with the degree of doping in both the solution- and solid-state. Additionally, I will briefly discuss the implications of these results on the chemical interaction of F4-TCNQ with SWCNTs of various band gaps. This work has implications in the improvement of SWCNT-based thermoelectric devices and capability to create doped SWCNT thin films directly from solution for use in other opto-electronic applications such as thin-film photovoltaics.
(Invited) Deep Tissue Fluorescence Imaging in the Second Near-Infrared Window (NIR-II Window) Using Carbon Nanotubes
Authors: Hong Guosong , Diao Shuo , Dai Hongjie
Published: February 2020

In vivo fluorescence imaging in the visible and traditional near-infrared (NIR-I) windows with wavelengths of 400~900 nm has been limited with sub-optimal resolution at >500 µm depths, due to strong scattering and absorption of photons by the turbid biological tissue, as well as high autofluorescence interference from the tissue in these windows. By exploiting the unique second near-infrared (NIR-II, 1.0~1.7 µm) fluorescence of single-walled carbon nanotubes (SWNTs), in vivo fluorescence imaging can be significantly improved with crisper resolution at deeper tissue penetration. This talk will cover our recent research progress on NIR-II fluorescence imaging, from in vivo mouse hindlimb vascular imaging (Nature Medicine, 2012; Circ. Cardiovasc. Imag. 2014) to brain vascular imaging (Nature Photonics, 2014; Angew. Chem. 2015) using SWNTs as the NIR-II fluorophore. In the first work, we have demonstrated microvascular angiography with improved spatial resolution over X-ray based computed tomography (CT), and hemodynamic measurement with larger dynamic range than ultrasonography. Owing to the high resolution, deep tissue penetration and the ability to record fast dynamics, NIR-II fluorescence imaging has allowed us to detect ischemic blood hypoperfusion in an animal model of lower limb ischemia with high sensitivity. In the second work, we have achieved sub-10 µm resolution mouse cerebrovascular imaging at millimeter depth inside the mouse brain through intact scalp and skull, using chemically purified SWNTs with enriched fluorescence emission in two optimized NIR-II sub-regions, the NIR-IIa window (1.3~1.4 µm) and the NIR-IIb window (1.5~1.7 µm). The non-invasive NIR-II brain imaging has allowed us to visualize and quantify the severity of middle cerebral arterial occlusion in a mouse model of stroke. Finally I will discuss potential future directions of NIR-II fluorescence imaging, such as the development of novel NIR-II fluorophores with more favorable emission wavelength and higher quantum efficiency, and the use of NIR-II fluorescence imaging for understanding the brain functions with new technological advances of NIR-II imaging.

References:

1. “Multifunctional in vivo vascular imaging using near-infrared II fluorescence” Nature Medicine 2012, 18, 1841-1846

2. “Near-infrared II fluorescence for imaging hindlimb vessel regeneration with dynamic tissue perfusion measurement” Circulation: Cardiovascular Imaging 2014, 7, 517-525

3. “Through Skull Fluorescence Imaging of the Brain in a New Near-Infrared Window” Nature Photonics, 2014, 8, 723-730

4. “Fluorescence Imaging In Vivo at Wavelengths beyond 1500 nm” Angew. Chem. Int. Ed. 2015, 127, 14971-14975

5. “Carbon Nanomaterials for Biological Imaging and Nanomedicinal Therapy” Chemical Reviews 2015, 115, 10816-10906
(Invited) Multiphoton Imaging of Carbon-Based Nanomaterials
Authors: Corr Stuart J. , Curley Steven A. , Wilson Lon J.
Published: February 2020

Multiphoton Microscopy (MPM) has enabled an unprecedented level of dynamic exploration within living cells and organisms. The physical principle behind this imaging technique involves the use of near-infrared femtosecond lasers to excite optical processes in fluorescent molecules using two or more photons1. The use of long wavelengths (700 nm – 1000 nm) enables deep tissue penetration (up to 1000 μm) without inducing harmful biological effects. Previous studies include the examination of membrane potentials on the single-molecule scale2, the non-invasive observation of embryo development3, and the simultaneous multiplane imaging of calcium transportation in transgenic mice4. An excellent review of this field can be found in the literature5.

            Herein we demonstrate a novel multiphoton-based technique for imaging non-fluorescent
carbon-based nanomaterials such as C60 fullerenes, single-walled carbon nanotubes, and graphene. More specifically, we demonstrate optical and photoluminescent activity in water-soluble C60-serinol, highly enriched (95 %) metallic and semiconducting single-walled carbon nanotubes, and functionalized graphene nanoribbons. This multiphoton imaging technique was also applied to in vitro and in vivo animal model studies. Various concentrations of the above mentioned nanomaterials were given to human pancreatic ductal adenocarcinoma (Panc-1) and hepatocellular carcinoma (Heb3B) cancer cell lines, as well as normal, healthy pancreatic ductal epithelial cells (HPDE). In all cases, imaging of these nanomaterials was possible using the MP imaging technique even though the nanomaterials exhibit no inherent fluorescent properties. We also examined the ability to image these nanomaterials, real-time, in vivo, using mice with orthotopic 4T1 breast tumors.  Finally, we also include a range of spectroscopy data to examine the specific optical characteristics of the carbon nanomaterials.

References

1.         Denk, W.; Strickler, J.; Webb, W. Science
1990, 248, (4951), 73-76.

2.         Peleg, G.; Lewis, A.; Linial, M.; Loew, L. M. Proceedings of the National Academy of Sciences
1999, 96, (12), 6700-6704.

3.         Chu, S.-W.; Chen, S.-Y.; Tsai, T.-H.; Liu, T.-M.; Lin, C.-Y.; Tsai, H.-J.; Sun, C.-K. Opt. Express
2003, 11, (23), 3093-3099.

4.         Cheng, A.; Goncalves, J. T.; Golshani, P.; Arisaka, K.; Portera-Cailliau, C. Nat Meth
2011, 8, (2), 139-142.

5.         Hoover, E. E.; Squier, J. A. Nat Photon
2013, 7, (2), 93-101.
Probing DNA Conformational Changes in Real Time Using Single-Molecule Electronic Sensors Based on Carbon Nanotube Field-Effect Transistors
Authors: Bouilly Delphine , Hon Jason , Daly Nathan S. , Trocchia Scott , Vernick Sefi , Warren Steven , Shepard Kenneth L. , Gonzalez Ruben L. , Nuckolls Colin
Published: February 2020

In humans and other vertebrates, the ends of chromosomes are protected by a buffer region of single-stranded DNA (ssDNA) called the telomere. Telomeric ssDNA is made of multiple repeats of the nucleotide sequence GGGTTA and can form three-dimensional folded structures called G-quadruplexes, which are stabilized by monovalent cations like K+ or Na+.  The formation of G-quadruplexes has been shown to disrupt the activity of enzymes necessary for telomere maintenance, enzymes that are also upregulated in many types of cancer cells and play a significant role in regulating cellular senescence. As such, G-quadruplexes are considered a potential therapeutic target for inhibiting the proliferation of cancerous cells and for treating aging-associated diseases. In this work, we use single-molecule field-effect transistors (smFETs) made from carbon nanotube devices to characterize the folding and unfolding dynamics of short stretches of telomeric ssDNA, and investigate the stability of G-quadruplex structures. First, we demonstrate a method for reliably functionalizing a carbon nanotube device with an individual ssDNA, using a combination of nano-confined covalent chemistry and bioconjugation reactions. The resulting smFET devices are then used to detect changes in the conformation of the ssDNA, in real-time and over a broad range of time scales. In the presence of K+ or Na+, we observe quantized fluctuations between high and low states in the conductance, which we are able to assign to the unfolded and G-quadruplex conformations, respectively. We discuss the effect of the identity and concentration of these two cations on the folding dynamics of G-quadruplex-forming ssDNA. In particular, we find that the folded G-quadruplex structure is 10 times more stable in K+ than Na+. This approach paves the way for investigations of the folding dynamics of various biomolecules at the single-molecule scale.
(Invited) Chirality-Dependent Surfactant Interactions Unravelled By Systematic Ultracentrifugal and Aqueous Two-Phase Separations
Authors: Cambre Sofie , Defillet Joeri , Wenseleers Wim
Published: February 2020

The discovery that natural bile salt surfactants are extraordinarily efficient at solubilizing individual, intact single-wall carbon nanotubes (SWCNTs) in water[1], soon enabled the separation of different SWCNT structures for the first time by density gradient ultracentrifugation (DGU),[2] and more recently also by aqueous two-phase extraction (ATP).[3,4] Despite very nice results for a limited number of small diameter SWCNT chiralities that have been isolated as individual species by DGU and ATP, the underlying mechanisms are not fully understood and the number of variables to be explored and optimized is enormous, preventing a systematic extension to other chiralities.

Based on the unique capabilities of optical spectroscopy for characterizing SWCNTs, we present a systematic study of the structure sorting of DGU and ATP. We combine a direct in situ optical characterization of the centrifuge tubes after DGU[5] with systematic concentration-dependent ATP separations for different (mixed) surfactants and as such obtain a more detailed understanding of and control over both separation mechanisms. These systematic studies reveal that chirality-dependent surfactant interactions determine the separation order.

[1] W. Wenseleers et al.,
Adv. Fucnt. Mater.
2004, 14, 1105

[2]. M.S. Arnold et al., Nature Nanotechnol. 2006, 1, 60

[3]. C.Y. Khripin et al., J. Am. Chem. Soc.
2013, 135, 6822

[4]. N.K. Subbaiyan et al., ACS Nano
2014, 8, 1619

[5]. S. Cambré et al., Nanoscale
2015
, 7, 20015
(Invited) Formation of Thermodynamically-Stable Surfactant Structures Around Single Wall Carbon Nanotubes
Authors: Zhao Yang , Clar Justin , Xu Jia , Bonzongo Jean-Claude J , Ziegler Kirk J
Published: February 2020

Single-chirality single walled carbon nanotubes (SWCNTs) have unique optoelectronic properties that can be utilized in specific applications, such as photovoltaics and biosensors. However, due to the large variety of SWCNTs and the difficulty of separation, the application of chiral SWCNTs is still limited. The post-synthesis separation of SWCNTs has been studied with great interest in the past decade. The most promising techniques include the selective adsorption of SWCNTs onto hydrogel stationary phases and aqueous two-phase extraction. In the selective adsorption onto hydrogels, the surfactant structure surrounding the SWCNTs has been shown to play an important role in the separation. While several researchers have successfully achieved separation of the semiconducting fractions by (n,m) type by manipulating the selective adsorption of the nanotubes, these processes often require multiple columns or experimental conditions that are difficult to control. However, the high-fidelity desorption of SWCNTs would provide a simpler approach that minimizes dilution and provides higher yields. Here we report that the desorption of a single-chirality (6,5) fraction in a hydrogel-packed column only occurs once a specific ratio co-surfactant solution is used. High-purity fractions of (6,5) nanotubes are obtained at this ratio even with long elution times, different total co-surfactant concentrations, and moderate temperature changes. The elution of only one (n,m) type at a specific co-surfactant ratio while other types are exposed to more surfactant suggests that each (n,m) type forms a thermodynamically-stable surfactant structure in the co-surfactant solution. These thermodynamic equilibrium states result in entropy-driven desorption at specific co-surfactant ratios, enabling high-fidelity separations of a single (n,m) type in a single column.

Figure 1
Fullerene-Assisted Quenching of Single-Walled Carbon Nanotubes Photoluminescence through a Flavin-Helix
Authors: Papadimitrakopoulos Fotios , Mollahoseini Mehdi , Karunaratne Erandika , Gascon Jose
Published: February 2020

Maintaining single-walled carbon nanotubes in their pristine state (i.e. devoid of aggregation and inhomogeneous doping) within nanostructured photovoltaic devices is a major challenge.  In this contribution, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear aliphatic spacer.  Small amounts of FC60 (up to 3 molar %) were shown to co-assembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization.  Steady state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photo-induced charge transfer quenching of the encased SWNTs through the seamless helical encase.  This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix and the C60 cage, that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety.  Atomistic molecular simulations elucidate how the fullerene is brought in the vicinity of the isoalloxazine helix to quench the nanotube.  The narrow ES
ii
linewidth for the resulting ground state complex indicates a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices.
(Invited) Chiral, Semiconducting Polymer-Wrapped Single-Walled Carbon Nanotube Superstructures for Opto-Electronic Applications
Authors: Olivier Jean-Hubert , Park Jaehong , Deria Pravas , Glesner Mary , Bai Yusong , Bullad George , Therien Michael J.
Published: February 2020

We demonstrate that highly charged, chiral anionic semiconducting polymers helically wrap single-walled carbon nanontubes (SWNTs) at periodic and constant morphology.  These polymers can be used as tools to modulate SWNT electronic properties, provide expansive solubility, or engineer electron acceptor units (e.g., perylene diimide, PDI) at rigorously defined intervals along the nanotube backbone. Femtosecond pump-probe transient absorption spectroscopic experiments show that excitation into the SWNT E11 transition of a S-PBN(b)-Ph4PDI-[(6,5) SWNT] superstructure generates SWNT hole polaron [(6,5) SWNT(•+)n] and PDI radical anion (PDI−•) states.  These studies demonstrate for the first time a photoinduced electron transfer process involving a SWNT and a semiconducting polymer in which: (i) the charge-separated products, and (ii) photoinduced charge separation and thermal charge recombination dynamics, are fully characterized.  To fully exploit these and related polymer-SWNT hybrids in opto-electronic applications, we have developed solution-based processes to structure dense, highly aligned arrays of these nano-objects on solid substrates.  Polyanionic semiconducting polymers designed to wrap SWNTs with a fixed helical screw axis, used in combination with ionic self assembly approaches, enable for the first time the production of functionalized SWNTs that are fully soluble in organic solvents and capable of assembly into complex hierarchical structures that feature aligned nanotubes at high areal density (2.5 x1010 SWNTs cm-2) that maintain the opto-electronic properties characteristic of individualized SWNTs.  These porphyrin-polymer/SWNT superstructures can be engineered to undergo both photoinduced electron- and hole-transfer reactions, thereby defining unique energy conversion assemblies, compositions with which to interrogate mechanistic issues regarding photoinduced charge transfer reactions involving nanoscale objects, and utilized as building blocks for highly organized mesoscopic materials that make possible investigation of electron and hole polaron transport phenomena in the solid state, as well as new types of electro-optic materials.

Figure 1
Photoinduced Spontaneous Free-Carrier Generation of (7,5)-Chirality-Enriched Single-Walled Carbon Nanotubes in a Low Dielectric Solvent
Authors: Rumbles Garry , Park Jaehong , Reid Obadiah , Blackburn Jeffrey L.
Published: February 2020

We demonstrate photoinduced spontaneous free-carrier generation in highly individualized (7,5)- chirality-enriched SWCNT samples ((7,5)-SWCNTs) suspended in a non-polar organic solvent. Frequency-resolved solution-phase flash photolysis time-resolved microwave conductivity (fp- TRMC), provides a contactless and quantitative measurement of the real and imaginary photoconductance of these individually suspended nanotubes. We use substantially lower excitation fluences than have been possible in previous studies, corresponding to absorbed photon densities of ~0.05 photons per micron length of (7,5)-SWCNTs, allowing us to avoid complications from dielectric screening by nearby excitons or exciton-exciton collisions. Even under these mild conditions, we unambiguously measure a photoconductance due to free carriers that are generated following excitation of both the first and second exciton transitions (S11 and S22, respectively). The low-fluence carrier generation quantum yield (Φ) with S22 excitation appears c.a. 2.4 times higher than that with S11 excitation, suggesting that the autoionization of S22 excitons clearly enhances the carrier generation efficiency. In contrast, the transient decay dynamics are independent of excitation wavelength, suggesting that the mobile carriers generated from either S11 or S22 excitation undergo identical decay pathways (i.e. trapping, recombination, etc.).
(Invited) Photoluminescence Relaxation Dynamics of Covalently Doped Carbon Nanotubes
Authors: Doorn Stephen K. , Hartmann Nicolai F. , Velizhanin Kirill , Ma Xuedan , Htoon Han , Olivier Jean-Hubert , Therien Michael J. , Kim Mijin , Wang YuHuang
Published: February 2020

New red-shifted emitting states in carbon nanotubes, introduced by stable covalently-bound dopants,1,2 are gaining attention for their potential to boost photoluminescence quantum yields,1,2 add new functionality,3 and serve as single photon emitters.4  Critical to these possibilities is the demonstration of exciton localization or trapping at individual dopant sites.5  As a consequence of trapping, exciton dynamics are significantly altered, with photoluminescence (PL) lifetimes being extended significantly.4  We will present a detailed study of the emission dynamics associated with dopant states introduced by aryl diazonium functionalization of semiconducting carbon nanotubes.  Dopant-state PL lifetimes are found to increase by around a factor of 10 in comparison to E11 exciton lifetimes.  Dependence of lifetimes on nanotube chirality, specific dopant, and dielectric environment will be presented and shown to exhibit a strong dependence on emission energy.  Evidence for existence of an associated dark trap state will also be given.  The results indicate multiple mechanisms for radiative and nonradiative decay.  Of particular interest relevant to PL stability is the relation of PL decay to potential exciton detrapping.  Possible contributing factors to detrapping, including detrapping energy, will be discussed.

References

1.  Ghosh, S. et al., Science, 330, 1656 (2010).

2.  Piao, Y. et al., Nature Chem., 5, 840 (2013).

3.  Kwon, H. et al., J. Phys. Chem. C, 119, 3733.

4.  Ma, X. et al., Nature Nanotech., 10, 671 (2015).

5.  Hartmann, N.F. et al., Nanoscale, 7, 20521 (2015).
Functionalised Carbon Nanotubes As Components in Solid Acid Fuel Cell Electrodes
Authors: Naumov Olga , Lohmann Felix , Abel Bernd , Varga Aron
Published: February 2020

We report on the role of as-grown and plasma treated multi-walled carbon nanotubes (MWCNTs) as cathode components in solid acid fuel cells (SAFCs). SAFCs combine a true solid state, proton conducting electrolyte, CsH2PO4 with good conductivity at mild temperatures slightly above 228 °C, with fuel flexibility and a high resistance to catalyst poisoning.1,2 The widespread application of solid acid fuel cells has been partly hindered by the necessity of the precious metal catalyst platinum in the electrodes.3,4

A general new approach in electrode catalysis bearing immense potential for electrochemical technologies is the prospect of precious metal free electrodes based on carbon nanomaterials.5,6

MWCNTs were synthesised by chemical vapour deposition using Ni nanoparticles as the growth catalyst on carbon paper current collectors. Oxygen plasma treatment was applied on selected samples with the dual effect of removing remaining amorphous carbon and increasing the concentration of oxygen functional groups on the surface. Symmetric electrochemical cells (MWCNTs|CsH2PO4|MWCNTs) were fabricated by uniaxial cold-pressing for impedance spectroscopy in a humidified oxygen environment at 240 °C. A good long term stability over a 19 day period and electrode impedances as low as 22 Ω cm2were measured, Figure 1. The oxygen plasma treated samples showed significantly lower impedances compared to as-synthesized. However, the application of a 500 mV DC bias voltage caused a dramatic drop in the electrode impedance when using as-synthesised MWCNTs. The impedance data suggests the electrochemical activity towards oxygen reduction and water splitting reaction after an initial reversible activation step. However, carbon corrosion is shown to have a non-negligible but small contribution to the measured currents. Scanning electron microscopy, Raman and XPS spectroscopy before and after the electrochemical measurements show increased oxygen concentration, increased graphitisation and slight morphological changes in all electrodes.

Caption Figure 1: (a) Scanning electron micrograph of representative MWCNTs on carbon paper fiber. (b) Electrode impedance of symmetric electrochemical cells (MWCNTs|CsH2PO4|MWCNTs) measured in humidied oxygen at 240 °C as a function of oxygen concentration of MWCNTs.

References

[1] S. M. Haile, D. A. Boysen, C. R. I. Chisholm and R. B. Merle, Nature, 2001, 410, 910-913.

[2] D. A. Boysen, T. Uda, C. R. I. Chisholm and S. M. Haile, Science, 2004, 303, 68-70.

[3] A. B. Papandrew, C. R. I. Chisholm, R. A. Elgammal, M. M. Ozer and S. K. Zecevic, Chemistry of

Materials, 2011, 23, 1659-1667.

[4] M. W. Louie, A. Hightower and S. M. Haile, ACS Nano, 2010, 4, 2811-2821.

[5] S. Zhang, Y. Y. Shao, G. P. Yin and Y. H. Lin, Journal of Materials Chemistry A, 2013, 1, 4631-4641.

[6] K. N. Wood, R. O'Hayre and S. Pylypenko, Energy & Environmental Science, 2014, 7, 1212-1249

Figure 1
(Invited) Transport and Emission Properties of Polymer-Sorted Monochiral and Mixed Carbon Nanotube Networks
Authors: Zaumseil Jana
Published: February 2020

The selective dispersion of semiconducting carbon nanotubes (s-SWNT) by wrapping with conjugated polymers has enabled their application in electronic and optoelectronic devices such as field-effect transistors and light-emitting field-effect transistors. Here, we show that the dispersion process can be easily scaled-up while maintaining good photoluminescence yield (2%) and nanotube length (>1 µm) to obtain concentrated dispersions and ultimately thin (<10 nm) or thick films (>100 nm) of s-SWNT with excellent optical and electrical properties. We demonstrate ambipolar charge transport and near-infrared light-emission in field-effect transistors based on monochiral and mixed networks of s-SWNT and investigate the influence of the nanotube diameter distribution on charge transport within the network depending on the applied gate voltage and thus charge carrier density. Voltage-dependent photoluminescence and electroluminescence spectra provide insight into the charge distribution among the different nanotubes. For very high charge carrier densities (e.g. by electrolyte-gating) we observe red-shifted trion emission in addition to exciton emission. Furthermore, monochiral s-SWNT films are interesting materials for strong light-matter interaction due to their small Stokes shift and large exciton binding energy. Here, we demonstrate exciton-polariton formation in suitable cavities and emission enhancement in periodic feedback structures.
(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) Self-Assembly of Endohedral Metallofullerenes: A Decisive Role of Cooling Gas and Metal-Carbon Bonding
Authors: Popov Alexey A. , Deng Qingming , Irle Stephan
Published: February 2020

The endohedral metallofullerene (EMF) self-assembly process in Sc/carbon vapor in the presence and absence of an inert cooling gas (helium) is systematically investigated using quantum chemical molecular dynamics simulations. It is revealed that the presence of He atoms accelerates formation of pentagons and hexagons and reduces the size of the self-assembled carbon cages in comparison to analogous He-free simulations. As a result, the Sc/C/He system simulations produce a larger number of successful trajectories (i.e. leading to Sc-EMFs) with more realistic cage-size distribution than simulations of the Sc/C system. The main Sc encapsulation mechanism involves nucleation of several hexagons and pentagons with Sc atoms already at the early stages of the carbon vapor condensation. In such proto-cages, both Sc–C σ-bonds and coordination bonds between Sc atoms and the π-system of the carbon network are present. Sc atoms are thus rather labile and can move along the carbon network, but the overall bonding is sufficiently strong to prevent dissociation even at temperatures around 2000 Kelvin. Further growth of the fullerene cage results in encapsulation of one or two Sc atoms within the fullerene. In agreement with experimental studies, extension of the simulations to Fe and Ti as the metal component showed that Fe-EMFs are not formed at all, whereas Ti is prone to form Ti-EMFs with small cage sizes, including Ti@C28-Td
and Ti@C30-C
2v
(3).
(Invited) Butterfly inside Carbon Cage: Preparation, Structural Characterization and Chemical Properties of Novel Dimetallic Oxide Cluster Fullerenes
Authors: Chen Ning , Feng Lai
Published: February 2020

Fullerenes are spherical molecules composed of pentagons and hexagons. Endohedral fullerenes, which possess inner space capable of encapsulation of variable clusters and molecules, have generated considerable recent research interest. By introducing CO2 as the reactive gas source, the synthesis of extensive families of oxide clusterfullerenes was demonstrated in this study. Sc2O@C70, Sc2O@C2n (n=38-42) and mixed dimetaillic fullerenes ScGdO@C82, have been isolated and characterized by mass spectrometry, UV−Vis−NIR absorption spectroscopy, cyclic voltammetry, 45Sc NMR, DFT calculations and single crystal X-ray diffraction. Crystallographic studies unambiguously assigned the cage structures of these metallic oxide cluster fullerenes to Sc2O@C2(7892)-C70，Sc2O@T
d(19151)-C76, Sc2O@D
3h(5)C78, Sc2O@C
2v(3)C78, Sc2O@C
2v(5)-C80 and Sc2O@C
3v(8)-C82. Among them, Sc2O@C2(7892)-C70 presents the first detailed structural analysis of is a Non-IPR C70 endohedral fullerene and Sc2O@T
d(19151)-C76 is the first tetrahedral fullerene cage characterized by single crystal X-ray diffraction. The comparative crystallographic studies of these novel structures also demonstrate that Sc2O cluster is flexible inside the carbon cage and the Sc-O-Sc angle varies with the different cage size or symmetry. The discovery and characterization of these novel structures provide examples of stabilization of new endohedral fullerene structures resulting from the combined effect of electron transfer and the geometrical fit between Sc2O cluster and the cage.
(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
Hybrid Energy Harvester Using Piezoelectric and Pyroelectric Properties of PVDF Nanocomposite Films
Authors: Batra Ashok , Alomari Almuatasim , Brown David
Published: February 2020

This paper reports a novel hybrid piezoelectric-pyroelectric energy harvester using a copper cantilever beam with PVDF thick films. Polyvinylidene fluoride (PVDF) is used as the piezoelectric material, which also has pyroelectric characteristics. We will present an experimental study of electrical output parameters and the resonance frequencies of different thick piezoelectric films attached at the clamped end of copper beam. The experiments were carried out with different plate piezoelectric films such as; polyvinylidene fluoride (PVDF), PVDF/PZT, and PVDF/PZT with multi walled carbon nanotubes (MWCNT) with the thickness of 0.2 mm. The output power was measured with changing the load resistance and the optimum value was found around 1 MΩ. The maximum output power obtained at resonance frequency of the optimum resistance was 0.39, 0.84, and 1.3 nW for PVDF, PVDF/PZT, and PVDF/PZT MWCNT, respectively. By heating the film as well with infrared lamp, the output voltage shall be enhanced. The results of La2O3 nanoparticles embedded in PVDF matrix will also be presented
The Materials for Sodium Battery: Synthesis and Electrochemical Characterization
Authors: Nguyen Van Hoang , Man Tran Van , Huynh Nguyen Le Thanh , Phung LE My Loan
Published: February 2020

Sodium batteries are known as the vital power source for energy storage and conversion because of their high energy density, high voltage and long cycle and the abundance of sodium compoud. They can be found in a large number of applications in the fields of urban transportation, automotive, consumer goods, and industry. In this paper, we present our work focusing on the synthesis and electrochemical investigation of the novel cathode materials for sodium based on manganese and vanadium compounds. The effect of different types of carbon upon the performance of sodium energy storage will be presented too.
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