bluuebunny/crossref_metadata_2025 huggingface dataset:
Intrinsic Conductivity in Magnesium-Oxygen Battery Discharge Products: MgO and MgO2
Authors: Smith Jeffrey Gordon , Naruse Junichi , Hiramatsu Hidehiko , Siegel Donald J
Published: February 2020

Non-aqueous magnesium-oxygen (or ‘Mg-air’) batteries are attractive next generation energy storage devices due to their high theoretical energy densities, low cost, and potential for rechargeability. Prior experiments identified magnesium oxide, MgO, and magnesium peroxide, MgO2, as the primary discharge products in a Mg/O2 cell. Charge transport within these nominally-insulating compounds is expected to limit battery performance, yet these transport mechanisms are either incompletely understood (MgO2) or remain a matter of debate (MgO). The present study characterizes the conductivity associated with intrinsic (point) defects within both compounds using first-principles calculations. For MgO, negative Mg vacancies and hole polarons localized on oxygen anions were identified as the dominant charge carriers. Nevertheless, the large formation energies associated with these carriers suggest that their equilibrium concentrations are low. Furthermore, a large asymmetry exists in the carrier mobility: Mg vacancies are essentially immobile at room temperature, while hole polarons are highly mobile. Importantly, the calculated formation and mobility data for MgO are in remarkable agreement with the three “Arrhenius branches” observed in conductivity experiments, and thus clarify the long-debated transport mechanisms within these regimes. In the case of MgO2, electronic charge carriers alone – electron and hole polarons – are the most prevalent. Similar to MgO, the concentration of carriers in MgO2 is low, and poor mobility further limits conductivity. We conclude that: (i.) sluggish charge transport in MgO or MgO2 will limit battery performance when these compounds cover the cathode support, and (ii.) what little conductivity exists is primarily electronic in nature (i.e., polaron hopping). Artificially increasing the carrier concentration is suggested as a strategy for improving battery performance.
Calculating Anisotropic Correlated Chemical Expansion of Oxygen and Lithium Vacancies in Li2MnO3 to Determine Vacancy Concentrations
Authors: James Christine , Nation Leah , Li Juchuan , Dudney Nancy J , Sheldon Brian W. , Qi Yue
Published: February 2020

Lithium-excess layered cathode materials for lithium-ion batteries of the form Li2MnO3-LiMO2 (M=transition metal(s)) show high capacities (>200 mAhg-1) due to the activation of the Li2MnO3 component.1 This activation process occurs during the first cycle at >4.4V, where it is widely accepted that oxygen is removed from the Li2MnO3 component. Thus, Li2-XMnO3-δ is formed upon cycling, creating a structure with both oxygen vacancies (VO) and lithium vacancies (VLi). It has been shown previously that the VLi and VO interact and that it is energetically favorable for VLi to form near VO.2 VO concentration in the Li2-XMnO3-δ is believed to be dilute, although the exact amount of VO(δ) is unclear.

To estimate the VO concentrations, calculations of the chemical expansion coefficient for vacancies in Li2MnO3 are combined with experimental stress measurements of a lithium-excess layered cathode material. The coupled VO and VLi have previously been shown to exhibit correlated anisotropic chemical expansion in Li2-XMnO3-δ at dilute concentrations.3 Thus, the chemical expansion coefficients for VO and VLi in the system are broken down into a dilute component for coupled VO and VLi and a component to capture the rest of the VLi which are far away from VO  and contribute to the high capacity of these materials. The computational results are used to interpret stress measurements from a multibeam optical stress sensor (MOSS) on Li1.2Mn0.55Ni0.125Co0.125O2.

1. Thackeray, M. M.; et al., Journal of Materials Chemistry
2007,
17(30), 3112-3125.

2. James, C.; et al., Solid State Ionics
2016,
289, 87-94.

3. James, C.; et al., MRS Advances
2016, 1(15), 1037-1042. doi:10.1557/adv.2016.48.
A Statistical Mechanical Model Incorporating Coupled Concentration-Strain Effects in Lithium Ion Battery Electrode
Authors: Chen Hongjiang , Huang Hsiao-Ying Shadow
Published: February 2020

Electrochemical storage system such as Lithium-ion batteries have been widely used from power tools and portable electronics to recent PHEV/EV. However, Li-ion batteries’ low power density and cycling capability have limited many potential applications. Many studies have shown that mechanical deformation plays a significant role in these drawbacks. To understand the influence of mechanical deformation on electrochemical reactions and phase transition in electrodes, studies have used the phase field method to model the mechanical stresses/strains or Li-ion concentration profiles. Yet few of them have considered “coupling effects” of these two factors, and resulting in inaccurate simulation results. In this study, we use statistical mechanics and transition state theory to develop constitutive equations of electrodes that include the concentration-strain coupling effects. Specifically, we relate the activation energy change of microscopic particles of electrode components with materials’ strain energy density. Further, we model microscopic processes of electrodes’ deformation by describing the behavior of activated particles and their probability relationship with all local particles in electrodes. By combining the phase field method, our generalized constitutive equations could provide much more accurate simulation results of the concentration field and/or phases distributions, which could be used to design better electrodes structure and improve batteries’ power/cycling performance.
NaVO3: A Surprising Cathode Material for Rechargeable Na-Ion Battery
Authors: Zhang Jiaolong , Yu Denis Yau Wai
Published: February 2020

In the past few years, Na-ion batteries (NIBs) have attracted much attention as an alternative energy storage device because Na is abundant and evenly-distributed in the world. However, commercialization of Na-ion batteries that have performances similar to existing lithium-ion batteries (LIBs) still requires the discovery and optimization of new high-capacity high-voltage electrode materials. NaVO3, which has been studied as anode for NIB based on the redox reaction of V5+/V4+
[1
,

2
], is evaluated as cathode material for NIB for the first time in this work.

Commercial NaVO3 shows no capacity at all when tested between 1.5 V and 4.5 V vs. Na/Na+, since the initial valence state of vanadium in NaVO3 is 5+ and the V5+/V4+ reaction occurs below 1.5 V. However, when the charging potential is increased to 4.9 V, capacities of 72.0 and 28.4 mAh g-1 are obtained from charge and discharge, respectively (see Figure 1(a)). Electrolyte decomposition alone during charging cannot account for the observed non-zero discharge capacity, so there has to be other mechanisms that can compensate for the charge transfer. We note that the second charging profile is different from that of the first charging profile. This result reassembles that of Li2MnO3 in LIB, which also shows electrochemical activity after a high-voltage activation process. We suspect NaVO3 undergoes a similar reaction mechanism as Li2MnO3, possibly a participation of oxygen redox-couple during the charge/discharge processes. Further work is being carried out to elaborate on the charge-discharge mechanism of NaVO3. When the commercial NaVO3 material is subjected to cycling, the capacity continues to increase, and eventually stabilizes at around 47 mAh g-1 after 50 cycles (see Figure 1(d)). This indicates that the charge-discharge process is reversible.

The theoretical capacity of NaVO3 is 220 mAh g-1 if one Na is removed from the lattice. Yet, the obtained capacity from commercial NaVO3 is only about 50 mAh g-1. The low capacity is partly attributed to the insulating nature of the material. We found that the available capacity from the material depends on particle size and electrical conductivity. Figures 1(b) shows the charge-discharge curves of ball-milled NaVO3 sample, which exhibits similar storage behavior to the pristine NaVO3, but delivers a higher capacity. Further ball-milling with carbon (acetylene black) increases the initial charge and discharge capacities to above 100 mAh g-1, but capacity degradation is severe. More results on the charge-discharge mechanism and stability of the material will be presented during the meeting.

Reference:

[1] G. Venkatesh, V. Pralong, O. I. Lebedev, V. Caignaert, P. Bazin and B. Raveau, Electrochemistry Communications, 40, 100 (2014).

[2] X. Liu, Y. Zhao, Y. Dong, Q. Kuang, Q. Fan, Z. Jing, S. Hou, J. Solid State Electroche
m,

20, 1803 (2016).

Figure 1
CoMn2O4 Anchored on N-Doped High-Dimensional Hierarchical Porous Carbon Derived from Biomass As a Bifunctional Oxygen Electrocatalyst
Authors: Digol James Lincuna , Divinagracia Maricor Fernandez , Labata Marc Francis Maligsa , Cervera Rinlee Butch , Ocon Joey Duran
Published: February 2020

There is an emerging interest in developing bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as they are key electrochemical reactions that govern the overall performance of emerging rechargeable metal-air batteries. However, such undertaking has been a huge challenge due to the high cost of noble metals (Pt, Ir, and Ru) and their stability when used as catalysts for both the oxygen reactions. Herein, we report CoMn2O4 embedded on three-dimensional (3D) hierarchical porous carbon (HPC) derived from waste biomass (corn cobs) as an efficient noble metal-free bifunctional electrocatalyst for both ORR and OER. The hybrid catalyst (CoMn2O4/N-3DHPC) is fabricated by solvothermal reaction of as-prepared nitrogen-doped 3D HPC and CoMn2O4. The three-step template-free approach in preparing N-3DHPC ensures ample nitrogen doping using melamine as source to improve electronic conductivity of the carbon and formation of three-dimensional interconnected pore network which is favorable to a well-dispersion of CoMn2O4 crystals. Thus, the N-3DHPC possesses a high specific surface area and good electrical conductivity as a result of N doping. The same hybrid material also presents high catalytic activity towards OER, rendering them high-performing inexpensive dual-function electrocatalyst. Our result opens up new alternative cathode materials based on earth-abundant, scalable, noble metal-free catalysts for future electrochemical energy storage systems.

Figure 1
Supercapacitor Stack Built from Monolithic Porous Glassy Carbon Electrodes
Authors: Braun Artur
Published: February 2020

The inherent high porosity of glassy carbon, a monolithic carbon form, can be opened by various oxidation processes. I present a gasphase thermal oxidation process which has been shown easy and successful for the opening and connecting of IUPAC micropores in the nanometer range. The precise control of this carbon "actication" process allows for the engineering of monlithic bipolar electrode assemblies with high porosity carbon films on top and bottom with an electroncilly conducting and ionically blocking layer inbetween. Stacks of several such electrodes have been built and tested for 100,000 cycles.

I will also show the detailed pore building and connection process which was assessed with small angle xray scattering and cyclic voltametry and impedance spectropscopy. The charge carrier dynamics follows consequently the evolution of the pore space. A mathematical model is presented which precisely reflects the evolution of porous film thickness, pore growth and double layer capacity.

[1] A. Braun, J. Ilavsky, S. Seifert, Highly porous activated glassy carbon film sandwich structure for electrochemical energy storage in ultracapacitor applications: Study of the porous film structure and gradient, J. Mater. Res. (2010) 25(8) 1532-1540.
Vertical Aligned Graphene/Metal Sulfides/N-Doped Carbon Ternary Sandwich Hierarchical Structure for Sodium Storage
Authors: Xie Dong , Xia Xinhui , Tu Jiangping
Published: February 2020

Nowadays, sodium ion batteries (SIBs), one of the realistic promising alternatives to the lithium ion batteries (LIBs), have drawn increasing attention because of the high availability, the low cost and the intercalation chemical similarity of sodium compared with lithium. However, many active materials in application of LIBs are invalid for SIBs as far as the different ionic radium (Na+ ,1.06 Å vs. Li+ ,0.76 Å). Thus, much effort has been taken to explore suitable host material to allow reversible and rapid sodium ion insertion or extraction, especially for advanced anode materials.

Fortunately, the transition metal dichalcogenides (TMDs) with the formula MoX2 (S or Se) and graphene-like structure are widely studied as anode materials for SIBs due to the unique two-dimensional layered structure and high specific capacity. Nevertheless, the practical application of the graphene-like TMDs is impeded by its inherent limitations. First, layered TMDs nanosheets are so easy to restack with the van der Waals interaction, resulting into the decrease of accessible active sites for sodium ions. Second, compared with carbon-based materials, especially, graphene or carbon nanotubes, the TMDs have lower electrical conductivity, which is not favor electrode reactions. Third, the volume change and structural variation during discharge-charge process cause the pulverization and loose contact of the active materials, resulting rapid capacity fading. Fourth, the TMDs-based anodes face the dissolution issue of polysulfides or polyselenides, resulting in fast capacity fading and low Coulombic efficiency during the discharger-charge process. To combat the aforementioned problems, in this present work, we have made double modifications on the MoX2 by introducing the vertical aligned graphene (VG) as support backbone and nitrogen-doped carbon (N-C) coating as outer protective layer via a simple two-step process. The curved MoX2 nanoflakes are controlled deposited on the VG skeleton, which the cloth fabric server as current collector, via a facile hydrothermal method; subsequently, the N-C layer uniformly coats on the MoX2 nanoflakes by self-polymerizing dopamine followed by a post carbonization process. These samples are directly assembled into SIBs without any binders or conductive materials, and exhibit excellent electrochemical performance for SIBs. For example, our synthesized VG/MoSe2/N-C ternary composite exhibits superior storage sodium performance, with high capacity (540 mAh g-1), enhanced high rate capability and long-term cycling stability (298 mAh g-1 at 2.0 A g-1 after 1000 cycles). These designed ternary sandwich VG/MoX2/N-C ternary sandwichhierarchical structures, which provide a flexible vertical aligned graphene to accommodate volume changes, introduces large efficient active areas, good conductivity, and omnibearing paths for sodium ion and electrons, contributes to their superior performances and enables its application in energy storage.
Theoretical Investigation of Oxygen- and Bromine-Functionalized Model Carbon Structures for Li-Redox Activity
Authors: Rawal Saurin Hiren , Dathar Gopi Krishna Phani , Shelton William A , Xu Ye
Published: February 2020

Carbon materials such as graphene, nanotubes and even aromatic compounds1-3 are being widely considered as active electrode materials in Li-ion batteries owing to their light weight and low cost. The functionalization of carbon appears to be the key to enabling faradaic electrochemical activity. We are investigating the possibility of bromine-functionalized carbon materials as redox active with Li ions. We have shown that carbon functionalized with oxygen groups can undergo redox reaction with Li at a range of potentials, including some that are sufficiently high for such structures to be appropriate for use at cathodes.4 Some such structures may also be able to catalyze the oxygen reduction reaction in Li (Li-ORR). Furthermore we are carrying out density functional theory calculations coupled with electrochemical modeling to investigate the redox properties of bromine-functionalized carbon moieties. We find that under-coordinated carbon atoms can form certain stable brominated structures that can undergo redox reaction with Li. Local chemical environments plays an important role in efficient electrochemical reactivity of the carbon structures.5, 6 Our results provides insights at the atomic scale on the functionalizations required for activating carbon for these important electrochemical reactions.

References

1. B. Z. Jang, C. Liu, D. Neff, Z. Yu, M. C. Wang, W. Xiong and A. Zhamu, Nano letters, 11, 3785 (2011).

2. S. W. Lee, N. Yabuuchi, B. M. Gallant, S. Chen, B.-S. Kim, P. T. Hammond and Y. Shao-Horn, Nature Nanotechnology, 5, 531 (2010).

3. H. Chen, M. Armand, G. Demailly, F. Dolhem, P. Poizot and J. M. Tarascon, ChemSusChem, 1, 348 (2008).

4. Y. Xu and W. A. Shelton, Journal of the Electrochemical Society, 158, A1177 (2011).

5. Y. Zhao, Y. Ding, J. Song, L. Peng, J. B. Goodenough and G. Yu, Energy & Environmental Science, 7, 1990 (2014).

6. P. Bai and M. Z. Bazant, Electrochimica Acta, 202, 216 (2016).
(Invited) Advanced Carbon Structures for PEMFC
Authors: Strmcnik Dusan , Li Dongguo , Lopes Pietro Papa , Coleman Eric , Lv Haifeng , Markovic Nenad M , Stamenkovic Vojislav
Published: February 2020

Interactions between advanced catalytic systems with ultra-low PGM (platinum group metal) loadings and various carbon supports have been investigated in order to harvest maximal catalytic performance without sacrifice in durability. Different classes of catalysts with controlled size, shape, surface morphology, composition and compositional gradients in the form of solid monometallic and multimetalic nanoparticles (NPSs), core-shell nanostructures and subsurface interlayers (CS), multimetallic nanowires (NWs), mesostructured thin film catalysts (MSTF) and multimetallic nanoframes (NFs) were evaluated at atomic level in conjunction with tailored carbon supports such as amorphous high surface area glassy carbon, carbon nanotubes (single and multiwall), carbon nanofoam, graphite, fullerenes and graphene. Activity and durability performance of the advanced classes of catalysts have been evaluated by rotating-disk electrode, membrane-electrode assemblies and various methods for structural characterization. Tailoring the properties of catalyst-support can lead to substantial increase of the electrode lifetime and superior fuel cell performance.
Freestanding Graphene-Coated Carbon Nanotube Aerogels Decorated with Metal Nanoparticles As High Performance Electrodes for Ethanol Oxidation
Authors: Xie Minghao , Islam Mohammad F.
Published: February 2020

There has been increasing demand to develop sustainable energy sources with high energy-conversion efficiency. Direct ethanol fuel cells (DEFCs) are one type of clean power source that is promising for a variety of applications. DEFCs typically consist of an anodic chamber that oxidizes ethanol and transfers electrons via an external circuit to a cathodic chamber that reduces oxygen. Nobel metals such as platinum (Pt) and palladium (Pd) are often used as electrocatalysts for the ethanol oxidation reaction (EOR) in the DEFC anode because of their intrinsic electrochemical properties. Unfortunately, cost and poor market supply require manipulating structural features of catalysts including shapes, sizes, and compositions to achieve optimal benefit from Pt and Pd. Further, to realize the utility of DEFCs in these applications, they must be cheap, lightweight, highly efficient, and stable over long operation lifetimes. We have developed DEFCs with enhanced electrochemical performance using three different electrocatalysts (Pt, Pd, and Pd-Pt core-shell nanoparticles) supported on graphene-coated carbon nanotube aerogels. These three-dimensional, porous aerogels are lightweight, and provide easy transport pathways for fuel and ions. The ultrahigh surface area of the aerogels allows deposition of small catalyst nanoparticles, while the graphene coating hinders coarsening of the nanoparticles during operation, improving the DEFC lifetime. The catalysts are spherical nanoparticles of diameter ≈ 5 nm (Pt), ≈ 8 nm (Pd), and ≈ 9 nm (Pd-Pt core-shell). The current densities of our DEFCs in alkaline media are ≈ 118 mA/cm2 with Pt, ≈ 150 mA/cm2 with Pd, and ≈ 283 mA/cm2 with Pd-Pt core-shell electrocatalysts, which are at least an order of magnitude larger than that of DEFCs that utilize commercially available electrodes, typically comprised of Pd nanoparticles supported on carbon black. Further, the performance of our DEFCs shows minimal degradation of 30–60% over 1,000 cycles. This work has been partially supported by the NSF through Grant CMMI 1335417 and US Army Research Office through grant W911NF-14-1-0651.
Enhanced Visible Light Photocatalytic Activity of Carbon Nanotube Aerogels Decorated with Titania By Phase Selective Interface Engineering
Authors: Xu Yao , Liu Siyuan , Salvador Paul A , Rohrer Gregory S. , Islam Mohammad F.
Published: February 2020

Composites of photocatalysts such as titania (TiO2) and various carbon allotropes such as carbon nanotubes (CNTs) are being extensively explored because of enhanced visible light response resulting from interfacial bonding between photocatalysts and carbon that extends light absorption bandwidth and reduces recombination of photogenerated carriers through efficient interfacial charger transfer. We have developed highly visible-light photoactive composites comprised of anatase-TiO2 nanoparticles decorated on single-wall CNT (SWCNT) aerogels (TiO2/SWCNT). SWCNT aerogels are three-dimensional, highly porous network of isotropically oriented SWCNTs. We used X-ray photoelectron spectroscopy to establish interfacial bonding between TiO2 and SWCNTs mediated through Ti–C and Ti–O–C bonds, narrowing the absorption edge to ≈ 2.4eV as confirmed by absorbance spectroscopy and greatly reducing the interfacial resistance as corroborated by electrochemical impedance spectroscopy, giving rise to visible-light photoactivity. The composites rapidly degrade methylene blue dyes at a rate of 56 μmol/h/g and exhibit a high photocurrent density of 80 μA/cm2 under visible-light. In contrast, composites prepared by mechanically mixing TiO2 and SWCNTs exhibit no photoactivity in the visible-light and only slight photoactivity in the white-light. Moreover, transformation of TiO2 from anatase to rutile phase lead to a reduction in the Ti–O–C bonds, likely during crystal structure reorganization associated with anatase-to-rutile phase transformation, markedly decreasing the dye degradation rate and photocurrent density in visible-light by ≈ 50%. Our work demonstrates the impact of interfacial bonds on emergent visible-light photocatalytic response of TiO2/SWCNT heterogeneous photocatalysts and provides guidance in designing new heterocatalysts based on SWCNT aerogels for efficient solar energy conversion. This work has been partially supported by the NSF through Grant CMMI 1335417.
Toward Single-Color Carbon Nanotube Fluorescence Microscopy
Authors: Langenbacher Rachel E , Budhathoki-Uprety Januka , Heller Daniel A , Jena Prakrit Vaibhav , Roxbury Daniel , Zheng Ming , Harvey Jackson Dean
Published: February 2020

The properties of single-walled carbon nanotubes make them well-suited for potential uses in imaging and sensing applications. Their environmentally-sensitive, photostable emission does not exhibit the blinking phenomenon observed with other nanostructures such as quantum dots, and they emit in the near-infrared where tissue autofluorescence is low, making them ideal for imaging in tissue or cells. Due to the large number of optically distinct emitters, nanotube-based probes could potentially be developed for extensive multiplexed imaging applications. Although single-walled carbon nanotubes are synthesized as a heterogeneous mixture of many different chiralities, aqueous two-phase extraction methods allow enrichment of single nanotube chiralities to the purities needed for imaging applications. We developed hyperspectral microscopy instrumentation and techniques to distinguish between 17 optically distinct nanotube chiralities, each with a narrow and distinguishable near-infrared emission band. We are also developing polymeric materials to facilitate probe development. Polycarbodiimides are helical polymers which allow for highly modular derivitization. Polycarbodiimides can non-covalently encapsulate carbon nanotubes to enable optical modulation and diverse surface functionalization. We will discuss how polycarbodiimide-nanotube complexes can be developed for near-infrared imaging applications.
Spectral Inhomogeneities in Swcnts Sorted By Nonlinear Dgu
Authors: Kadria-Vili Yara , Sanchez Stephen R. , Bachilo Sergei M. , Weisman R. Bruce
Published: February 2020

Single-walled nanotubes are widely studied nanomaterials because of their unusual properties and potential applications. Unfortunately all practical current growth methods produce nanotubes with a variety of (n,m) structures and therefore physical properties. This inhomogeneity hinders some studies and applications in which samples with a single structure or a narrow range of structures are needed. To date, a number of sorting methods have been introduced to separate single-walled from multi-walled nanotubes, individualized from aggregated, metallic from semiconducting, water-filled from empty, and even right-handed from left-handed forms of the same (n,m) SWCNT species. Nonlinear density gradient ultracentrifugation (nDGU) separation has been shown to be one of the most selective tools for preparing high purity SWCNT samples. However, there has been little study of whether nDGU fractions actually are highly homogeneous. We have analyzed such fractions and find that layers containing enantiomers of individual (n,m) species show unexpected spectral inhomogeneities.

Each enantiomeric layer of (6,5) SWCNTs was extracted into three or four 48 µL fractions using a custom-built high precision automated fractionator. These extracted fractions were analyzed for their fluorescence and absorption spectra. They were then diluted into sodium cholate solution to provide uniform coatings, and the spectral measurements were repeated along with determinations of their absolute fluorescence quantum yields and measurements of variance spectra. The undiluted fractions within a single layer showed significant differences in spectral peak position and line width. Dilution reduced these inhomogeneities and caused ca. 50 cm-1 blue shifts in E11 peak positions for the upper enantiomer band but only 5 cm-1 shifts for the lower one. Emission line widths were also decreased substantially and quantum yields increased by a factor of ca. 2. Nevertheless, the diluted fractions gave quantum yields of 0.8 ± 0.1% and varied by a factor of 1.5 within the lower layer. They reached a maximum of approximately 1%, which is similar to that for SWCNTs wrapped by PFO in toluene. Further insight was obtained from variance spectral data, which confirmed the differences in emission per nanotube within layers and revealed that the low frequency wing of the E11 emission band of each fraction results from inhomogeneous broadening. Our results show that even the use of a highly selective SWCNT sorting method may not ensure spectroscopic homogeneity within the separated samples.
Diameter Selective Chemical Doping of Semiconducting Single-Wall Carbon Nanotubes
Authors: Achsnich Melanie , Deutsch Marian , Muetzel Carina , Hertel Tobias
Published: February 2020

Doping of semiconductors, such as single-wall carbon nanotubes (SWNTs), by the introduction or removal of charges can be used for modification of their electronic and optical structure. This offers unique opportunities for the fabrication of versatile materials with new properties. However, despite a broad body of work,1−3 the control and spectroscopic assessment of the doping of SWNTs is still being developed4,5 in order to be able to reproducibly tailor semiconductor properties.

Here, we have studied the photophysical properties of chemically doped SWNTs by absorption and photoluminescence spectroscopy. Polychiral samples of purified HiPCO soot were charged by oxidation with gold chloride. Thanks to very well-resolved and narrow exciton bands in these samples, the trionic signatures induced by charges could be resolved for up to five distinct nanotube species. An investigation of spectral changes in absorption measurements as a function of gold chloride concentration reveals that tubes with smaller bandgaps are doped at lower gold chloride concentrations. The trion binding energy with respect to the dipole-allowed first sub-band exciton transition was also found to increase systematically with decreasing diameter in agreement with previous findings.1,2 In addition, we find that SWNT oxidation potentials decrease nearly linearly with increasing nanotube diameter. Lastly, a surprisingly abrupt change of exciton oscillator strengths at redox potentials near the nanotube band edge provides evidence for band gap renormalization.

References

1. R. Matsunaga, K. Matsuda, Y. Kanemitsu, Phys. Rev. Lett. 2011, 106, 037404.

2. J. S. Park, Y. Hirana, S. Mouri, Y. Miyauchi, N. Nakashima, K. Matsuda, JACS
2012,
134, 14461−14466.

3. S. M. Santos, B. Yuma, S. Berciaud, J. Shaver, M. Gallart, P. Gilliot, L. Cognet, B. Lounis, Phys. Rev. Lett. 2011, 107, 187401.

4. H. Hartleb, F. Späth, T. Hertel, ACS Nano
2015, 9, 10461−10470.

5. M. Yoshida, A. Popert, Y. K. Kato, Phys. Rev. B
2016, 93, 041402.
(Invited) Effects of Residual Wrapping Polymer on Charge and Exciton Transport in Semiconducting SWCNT Thin Films
Authors: Blackburn Jeffrey L. , Norton-Baker Brenna , Gould Isaac E. , MacLeod Bradley A. , Owczarczyk Zbyslaw R. , Stanton Noah J. , Ihly Rachelle , Doorn Stephen K. , Ferguson Andrew John
Published: February 2020

The optical and electrical properties of single-walled carbon nanotubes (SWCNTs) make them attractive for a number of energy conversion devices, including thin-film photovoltaics and thermoelectrics. Both fundamental studies and device efficiencies have benefited from the ability to selectively extract semiconducting SWCNTs (s-SWCNTs) with high yield, purity, and throughput with pi-congujated semiconducting polymers such as polyfluorenes. However, it has proven to be challenging to quantitatively remove these polymers after selective extraction of s-SWCNTs, so thin films prepared from polyfluorene-based dispersions typically have significant amounts of residual polymer. Since charge and exciton transport within s-SWCNT thin films can be sensitive to the degree of inter-nanotube electronic coupling, the ultimate effects of this residual polymer on transport are unclear although they are likely to be deleterious. A number of polymers have recently emerged that can be decomposed into monomers after selective extraction of s-SWCNTs, enabling thin s-SWCNT film fabrication in the complete absence of residual wrapping polymer. In this presentation, I will discuss our recent results demonstrating large improvements to transport for films that are prepared with a removable polymer. These improvements translate directly into improved performance for a variety of thin-film devices based on s-SWCNTs.
(Invited) Developments in Modulating Carbon Nanotube Photoluminescence
Authors: Heller Daniel A , Budhathoki-Uprety Januka , Galassi Thomas Vito , Harvey Jackson Dean , Horoszko Christopher Peter , Jena Prakrit Vaibhav , Langenbacher Rachel E , Roxbury Daniel , Williams Ryan M.
Published: February 2020

The photoluminescence of single-walled carbon nanotubes may facilitate quantification of analytes within complex environments. To design quantitative sensors using carbon nanotubes, greater understanding of the optical modulation of their photoluminescence is necessary. On exploring the modulation of nanotubes, we found new methods to enable unprecedented control over the shifting of emission wavelength towards both red and blue wavelengths, facilitated by adsorbed species including biomacromolecules and polymers that allow for switchable modification of surface coverage and charge on the nanotube surface.
(Invited) Probing Optical and Magneto-Optical Properties of Carbon Nanotubes Using Enriched Carbon Nanotube Materials
Authors: Haroz Erik H.
Published: February 2020

Enriched carbon nanotubes materials, whether purified in electronic type, diameter, filling or even specific chirality, have deepened researchers' understanding of the fundamental optical properties of single-wall carbon nanotubes (SWCNTS). In particular, density gradient ultracentrifugation and aqueous two-phase extraction techniques have enabled the production of sizable aqueous suspensions and aligned films, allowing the interrogation of chiral-specific absorption, emission and scattering properties. In this talk, I will discuss two particular aspects: the chiral-specific nature of the Raman M-mode in small-diameter semiconducting SWNCTs and the large orbital magnetic susceptibility anisotropy of large-diameter metallic SWCNTs.

In the first part of the talk, I examine the unusual frequency dependence and excitation profile shape of the M-mode (~1620-1800 cm-1) in small-diameter semiconducting species such as the (5,4), (6,4), (8,3), (9,1), (6,5), (7,6), (11,0), (9,4) & (8,6). In particular, semiconducting species exhibit a mod- and diameter-dependent "fanning-out" behavior for E22 excitation, reminescent of that observed for optical transition energies. Even more interesting is the strongly asymmetrical excitation profile of the M-mode for a specific (n,m) species, deviating from the standard symmetrical profile observed for the radial breathing mode and the non-Condon-violating profile observed for the G-band. At certain energies in the excitation profile, the M-mode exceeded the G-band in intensity and unlike the G-band, the most intense peaks in the M-mode profile do not correspond to either the incoming or outgoing resonances. The M-mode seems to exhibit a new type of excitation profile shape.

In the second part of the talk, I discuss the magneto-optical properties of metallic SWCNTs. Using the strongly anisotropic optical and magnetic properties arising from the one-dimensional nature of carbon nanotubes, we aligned SWCNTs in aqueous suspension in magnetic fields up to 22T. Specifically, the orbital magnetic susceptibility anisotropy (Δχ) was measured, via magnetic linear dichroism spectroscopy enabled by the unique Florida Split-Helix magnet system, of multiple large-diameter metallic and semiconducting SWCNT species. In particular for the metallic species, Δχ’s on the order of 10-4 emu/mol, an order of magnitude larger than any Δχ measured previously for SWCNTs, were observed. Additionally, broadening and the beginnings of peak splitting of metallic optical absorption features, due to the Aharanov-Bohm effect, were also seen. The emergence of such magneto-optical behavior at such relatively “low” magnetic fields, combined with new developments in carbon nanotube sample preparation science, opens the door to observing new many-body effects through magneto-optics.

Lastly, I will share a few memories of my time with my friend and mentor, Robert Hauge.
(Invited) Carbon-Based Nanomaterials for Bioelectronics
Authors: Xu Ya-Qiong
Published: February 2020

Carbon-based nanomaterials, such as carbon nanotubes (CNTs) and graphene, have gained significant interest as one of the most promising materials in biological applications due to their unique physical and chemical properties. Recently we have developed an optoelectronic probing system, combining CNT/graphene transistors with scanning photocurrent measurements, fluorescence microscopy, and optical trapping techniques to investigate the molecular interface between CNTs/graphene and biological systems. Here, optical tweezers have been used to manipulate individual DNA molecules with sub-piconewton force precision and to directly measure the binding force between a DNA molecule and a CNT. Three-dimensional scanning photocurrent microscopy has been utilized to monitor the morphology changes of CNTs, allowing for a comprehensive reconstruction of the CNT-DNA interaction dynamics. We have also integrated graphene-based scanning photocurrent microscopy with microfluidic platforms to study the electrical activity in neuronal networks. These fundamental studies not only provide a new platform for exploring mechanical and electrical coupling at nanobio-interfaces, but also shed light on new design rules for future nanobioelectronics.
(Invited) Massively Parallel, Aligned Arrays of Semiconducting Carbon Nanotubes for Realizing Field Effect Transistors with Current Density Exceeding Silicon and Gallium Arsenide
Authors: Arnold Michael S
Published: February 2020

Calculations have indicated that aligned arrays of semiconducting carbon nanotubes (CNTs) promise to outperform conventional semiconducting materials in short-channel, aggressively scaled field effect transistors (FETs) like those used in semiconductor logic and high frequency amplifier technologies. These calculations have been based on extrapolation of measurements of FETs based on one CNT, in which ballistic transport approaching the quantum conductance limit of 2Go
=4e2/h has been achieved. However, constraints in CNT sorting, processing, alignment, and contacts give rise to non-idealities when CNTs are implemented in densely-packed parallel arrays, which has resulted in a conductance per CNT far from 2Go
. The consequence has been that it has been very difficult to create high performance CNT array FETs, and CNT array FETs have not outperformed but rather underperformed channel materials such as Si by 6x or more.

Here, we report nearly ballistic CNT array FETs at a density of 50 CNTs um-1, created via CNT sorting, wafer-scale alignment and assembly, and treatment. The on-state conductance in the arrays is as high as 0.46 Go
per CNT, and the conductance of the arrays reaches 1.7 mS um-1, which is 7x higher than previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density reaches 900 uA um-1 and is similar to or exceeds that of Si FETs when compared at equivalent gate oxide thickness, off-state current density, and channel length. The on-state current density exceeds that of GaAs FETs, as well. This leap in CNT FET array performance is a significant advance towards the exploitation of CNTs in high-performance semiconductor electronics technologies.

*Brady GJ, Way AJ, Safron NS, Evensen HT, Gopalan P, Arnold MS, Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs, SCIENCE ADVANCES, 2 (9), e1601240 (2016)
Quantum Optical Studies on Diazonium Doped Carbon Nanotubes
Authors: He Xiaowei , Hartmann Nicolai F. , Ma Xuedan , Gao Weilu , Kono Junichiro , Blackburn Jeffrey L. , Htoon Han , Doorn Stephen K.
Published: February 2020

The intentional incorporation of impurities and defects can serve as a powerful tool for modification of the electronic and optical properties of host nanomaterials and enabling of new functionalities1. Introduction of Sp3 defects by covalent functionalization to single-walled carbon nanotubes (SWCNTs) generates new emission states with energies lower than the optical bandgap (E11) of SWCNTs by 100 to 300 meV2. With controllable emission wavelengths and high quantum yield, these defect states open up new opportunities for the applications of SWCNTs in photonics such as lasing, photon upconversion and single photon emission3.

Recently, it has been shown that such doping sites are capable of emitting single photons at room-T, which opens the possibility of building room-T electrically-driven single photon emitters based on doped-SWCNTs. The realization of these devices needs the fine control of doping densities, to the point of introduction of solitary dopants on individual SWCNTs. It also requires the high emission quality from doping states, such as sharp linewidth of the emission spectra and non-blinking of the emission intensity.

In this work, we showed a chemical approach capable of creating solitary dopants on SWCNTs of different diameters. Our method was based on the fine control of the doping of surfactant-suspended and poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) wrapped SWCNTs by different diazonium salts. Quantum optical studies were performed on the diazonium doped-SWCNTs. We first investigated the photoluminescence (PL) spectra of doped-SWCNTs at room temperature and low temperature (4K). Individual, bright and stable emission peaks were observed from doped SWCNTs at room-T. The linewidth of the PL peaks decreased to 200 mirco-eV at 4K. Next, Hanbury Brown-Twiss (HBT) experiment was performed to explore the single photon nature of the emissions. Strong photon ant-bunching behavior with purity above 99% were observed on the doping emission peaks in the range of 1100-1400 nm at RT(295k).

[1] Piao, Yanmei. et al. Nature Chem. 2013, 5, 840.

[2] Hartmann, Nicolai F. et al. Nanoscale. 2015, 7,20521.

[3] Kim, Mijin. et al. J. Phys. Chem. C . 2016, 120, 11268.

[4] Ma, Xuedan. et al. Nature Nanotech. 2015, 10, 671.
(Invited) Optical Bistability in Air-Suspended Carbon Nanotubes
Authors: Kato Yuichiro K.
Published: February 2020

Screening is limited in single-walled carbon nanotubes because of their one-dimensional nature, and the strong Coulomb interactions result in optical spectra dominated by excitons with binding energies lager than half an eV. Also because of the limited screening, a charged carrier can be bound to an exciton to form a trion that is stable at room temperature. In particular, air-suspended nanotubes exhibit pronounced effects because of reduced environmental screening [1,2], where adsorption and desorption of molecules on the surface of nanotubes can readily modulate such interactions.

Here we show that large screening effects on excitonic energies can cause laser-induced optical bistability [3]. Molecular desorption can occur with sufficient heating by laser, which in turn results in significant blueshift of exciton emission wavelength. When the excitation is detuned to a higher energy shoulder of the E22 absorption resonance, we observe abrupt transition and hysteretic behavior of emission wavelength in the excitation power dependence. We explain the bistability by simultaneous shifts of absorption and emission resonances, and perform time-resolved measurements to obtain relevant time scales.

Work supported by JSPS (KAKENHI JP26610080, JP16H05962), The Canon Foundation, and MEXT (Photon Frontier Network Program, Nanotechnology Platform).

[1] T. Uda, M. Yoshida, A. Ishii, Y. K. Kato, Nano Lett. 16, 2278 (2016).

[2] M. Yoshida, A. Popert, Y. K. Kato, Phys. Rev. B 93, 041402(R) (2016).

[3] T. Uda, A. Ishii, Y. K. Kato, in preparation.
(Invited) On the Theory of Nanotube-Graphene Crossiton: A New Class of Topological Solutions
Authors: Petrov Alexey G. , Rotkin Slava V.
Published: February 2020

aIoffe Institute, 26 Polytekhnicheskaya, St. Petersburg, 194021, Russia

bDepartment of Physics, Department of Material Science; the Center for Advanced Materials & Nanotechnology and the Center for Photonics & Nanoelectronics, Lehigh University, Bethlehem, Pennsylvania 18015, United States

A problem of strong (aka non-perturbative) coupling between quantum systems has been in the focus of physics research for many decades, having both fundamental interest and value for applications from quantum information to spintronics. Most recently it received attention due to technological capability to couple electronic systems of different dimensionality, for example, one-dimensional (1d) to 2d-systems. Cross-dimensional excitation were shown here to form a new class of solutions of strongly coupled Hamiltonians.

We use the formalism of coupled Dyson equations, and propose an efficient method of obtaining a distinct family of non-perturbative solutions. It reproduces known ``polariton''-family in the limit of the same symmetry of the coupled systems. On contrary, when the symmetry of one system makes a sub-group of the other, and the coupling interaction preserves a sub-set of quantum numbers, like a wavevector along 1d-axis, a special class of solutions - crossiton - is found.

Green's functions (GF) of crossiton sub-modes can be expressed via GFs of uncoupled systems and interaction vertexes. The general crossiton Hamiltonian can be mapped on a wide range of quantum-mechanical problems (like Fano-Anderson problem) that, otherwise, are not obviously related. Such a solution, to the best of our knowledge, was not demonstrated before. We emphasize on that the problem is solved non-perturbatively, presenting full solution, beyond weak coupling model.

This research is supported by the NSF ECCS-1509786 (SVR) and RFBR 14-02-01223А (AGP).

Fig. 1. Bare (dashed) and renormalized (solid) GF of the crossiton in the 1d-system.

Figure 1
A Novel Multi-Sine Excitation Procedure for Impedance Spectroscopy Supports Automatic Drift Correction and Online Error Determination
Authors: Feihl Sebastian , Sholin Mark , Schiller Carl-Albrecht , Fröba Steffen , Multerer Michael , Strunz Werner
Published: February 2020

The traditional way to measure impedance using single-sine (monochromatic) excitation is the most transparent and robust way to find reliable EIS data. Compared to the time saving polychromatic (i.e. multi-sine) excitation, the advantage of single-sine excitation is the unequivocal assignment of harmonic content in the response signal to unwanted interference. Systematic analysis of these harmonics allows for the determination of a reliable measurement variance for every single data sample immediately after raw data collection is complete. For decades, such a procedure named “Weighted Harmonics Autocorrelation” has proven its benefit for the EIS instruments of the authors group [1]. Another helpful feature is owed to the periodicity of the monochromatic excitation: unwanted time drift contributions can be calculated from succeeding periods of the response signal for the reconstruction of the drift-free response. This allows for an automatic drift correction [2].

These valuable features are hardly achievable using standard multi sine techniques. Here, even in the absence of interference, the response signals are neither periodic nor free of harmonics. In spite of the fact that monochromatic techniques have the better relationship between information density and time effort [3], it is sometimes preferable to use multi-sine whenever the total measurement time is crucial for practical reasons.

In this poster, a novel multi-sine excitation method will be presented that keeps the advantages of automatic drift correction and online error determination analogous to the monochromatic single-sine procedure.

Keywords: EIS, error determination, drift correction, multi-sine, single-sine

References:

[1] C.-A. Schiller, R. Kaus; Impedance Contributions Online 2008, 6, P4.1 - P4.13 http://accessimpedance.eu/images/stories/ICO6_P4.pdf

[2] C. A. Schiller, F. Richter, E. Gülzow, N. Wagner; J. Phys. Chem. Chem. Phys. 2001, 3, 374-378

[3] Ruben H. Milocco, Minimal measurement time in electrochemical impedance identification, Electrochim. Acta 1994, 39, 1433-1439