bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain Effects in Heterogeneous Oxide Electrolyte Films
Authors: Shen Weida , Jiang Jun , Hertz Joshua L.
Published: February 2020

A number of opportunities exist to use thin film deposition methods to nanoengineer materials so that we can understand and improve their ion transport behavior and other electrochemical properties. Here, we describe experiments on sputter-deposited ceramic films with controlled, heterogeneous chemical composition. Films are created using a technique developed in our lab where pure, single-element targets are reactively co-sputtered to create ceria-zirconia films where both the host and dopant atom concentrations can be controlled at the nanometer scale through the film thickness. The ionic conductivity of all samples was determined using impedance spectroscopy in the temperature range 573 K to 1073 K and over a range of oxygen partial pressures.

Two sets of results using this system will be presented. First, we will discuss films made to have heterogeneous dopant content. By placing the dopants in 2-D atomic planes, defects are trapped in engineered space charge zones surrounding the interface, and vacancy-dopant associations can be studied. Specifically, by comparing samples using heterogeneous La, Gd, or Y dopants, the role of strain in the mobility and concentration of defects in the space charge region is examined, with larger dopant ion correlated to increased space charge conductivity. A second system to be presented will involve modulation of the Ce/Zr ratio through the thickness. Since the lattice parameter is a linear function of Ce/Zr ratio, these samples can be used to smoothly and systematically control lattice strain. Strain was determined by x-ray diffraction and microscopy, including selected area electron diffraction. Clear differences in interfacial structure are found as the lattice parameter differential between the layers is adjusted. The strained multilayers indicate both a strain-based change in vacancy mobility and a general reduction in conductivity as the interfacial density increases.
Spatial Fluctuation Fluorescence Spectroscopy: A New Method for Studying Single-Walled Carbon Nanotube Dispersions
Authors: Streit Jason K. , Bachilo Sergei M. , Weisman R. Bruce
Published: February 2020

We describe a novel spectroscopic method that has been applied to characterize liquid suspensions of single-walled carbon nanotubes (SWCNTs). When fluorescence spectra are sequentially measured from small volumes of very dilute samples, the intensities of emission features can fluctuate significantly because relatively few nanotubes of each type are present within the observation volume, and these concentrations vary statistically from observation to observation. By restricting acquisition times to ~200 ms and slowly flowing the sample so that a different region is sampled by each spectrum, we can observe such spatial concentration variations as spectral intensity fluctuations. Using observation volumes of only 10-7 mL and sample mass concentrations down to ~60 ng/mL, we acquire sequences of 3000 spectral snapshots and then analyze the set of data. At each emission wavelength, we compute the mean intensity and the variance (squared standard deviation) of intensity. The ratio of squared mean intensity to variance is then plotted as a function of wavelength to give an abundance spectrum, reflecting the number of nanoparticles contributing to emission at that wavelength.

Spatial fluctuation spectroscopy thus gives relatively direct access to the absolute (n,m) composition of SWCNT samples. Another benefit of this technique is that emission features from different (n,m) SWCNTs are better resolved in the variance spectrum than in the squared mean emission spectrum, allowing clearer detection of species with overlapping fluorescence spectra. In addition, the mean intensity spectrum can be divided by the abundance spectrum to obtain the relative fluorescence efficiency per nanotube for all of the (n,m) species represented in the data. These values can be used to validate the calibration factors that are central to conventional quantitative fluorimetric analysis of mixed SWCNT samples.

Furthermore, we have analyzed the spectral data sets to find correlations between signal fluctuations at different wavelengths. These are interpreted as reflecting the spatial correlations of nanotubes of different types, which implies the presence of aggregates. Studies will be reported showing how these cross-correlations depend on sample condition and processing. Spatial fluctuation spectroscopy appears to be a powerful new tool for analyzing and studying SWCNT suspensions.
Invited Presentation: Photoluminescence Imaging Probes of Contrasting 1-D and 0-D Exciton Behavior in Doped Carbon Nanotubes
Authors: Doorn Stephen K. , Yamaguchi Hisato , Yalcin Sibel , Ma Xuedan , Htoon Han
Published: February 2020

Introduction of new photoluminescent (PL) states upon low-level covalent doping of carbon nanotubes1,2 is gaining interest due to their chemical stability and potential for tube brightening. The nature of these optical states is not yet well-understood. We present PL imaging and spectroscopic studies of oxygen-doped tubes1 at the single-tube and single-dopant site levels. Dynamic and static emission behaviors will be presented as modulated by the relative dopant concentration. Results will be discussed as the interplay of 1-D bright exciton behaviors and 0-D trap states introduced at the dopant sites.

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

2. Y. Piao, et al., Nature Chem., 5, 840 (2013).
Invited Presentation: Optoelectronic and Thermal Transport Properties of Carbon Nanotubes and Related Materials
Authors: Cronin Stephen B.
Published: February 2020

I will report our latest results studying the optoelectronic properties and thermal transport characteristics of nanoscale materials and devices. In carbon nanotubes pn-junctions, we observe Zener tunneling behavior and photocurrent generation in quasi-metallic nanotubes1 and non-ideal diode behavior in semiconducting nanotube2. We observe enhanced photoluminescence and photocurrent in monolayer MoS2 under ionic liquid gating conditions due passivation of surface states. The Fabry-Perot resonance in GaAs nanowires can also be significantly enhanced through surface passivation and local field enhancement. Lastly, the thermal interface conductance across graphene/hexagonal boron nitride heterojunctions are measured using an electrical heating/optical measurement technique.

1. Amer, M.R., S.-W. Chang, R. Dhall, J. Qiu and S. Cronin, Zener Tunneling and Photocurrent Generation in Quasi-Metallic Carbon Nanotube pn-Devices. Nano Letters, DOI: 10.1021/nl402334e (2013).

2. Chang, S.-W., K. Bergemann, R. Dhall, J. Zimmerman, S. Forrest and S. Cronin, Non-ideal Diode Behavior and Band Gap Renormalization in Carbon Nanotube P-N Junctions. IEEE Transactions on Nanotechnology, DOI: 10.1109/TNANO.2013.2287124 (2013).
Invited Presentation: Optical Detection of Individual Carbon Nanotubes: Nanotube Spectroscopy and Bioimaging
Authors: Cognet Laurent
Published: February 2020

The optical microscopy of single molecules has recently been beneficial for many applications, in particular in biology. It allows a sub-wavelength localization of an isolated nano-object and a subtle probing of its spatio temporal nano-environment on cells as demonstrated on live neurons [1].

For many bio-applications, near infrared nanoprobes and/or more photostable nanoprobes than conventional fluorescent molecules or quantum dots are desirable. In this context, single walled carbon nanotube tubes are promising. A prerequisite is however to understand their optical properties in different environments including water/saline suspensions, to study their rheological/interaction behavior in crowded bio/cellular environments and further optimize their optical detection therein. Our current efforts toward these goals will be presented and comparisons with other near infrared probes will be performed [2].

References

[1] L. Groc, M. Lafourcade, M.Heine, M. Renner, V. Racine, J.-B. Sibarita, B. Lounis, D. Choquet & L. Cognet, J. Neuroscience, 27, 12433 (2007); M. Heine, L. Groc, R. Frischknecht, JC. Béïque, B. Lounis, G. Rumbaugh, RL. Huganir, L. Cognet, D. Choquet, Science, 320, 201 (2008).

[2] L. Cognet, D. Tsyboulski, J. Rocha, C. Doyle, J.M. Tour, R.B. Weisman, Science, 316 1465 (2007); N. Fakhri, FC. MacKintosh, B. Lounis, L. Cognet L, M. Pasquali, Science, 330 1804 (2010); S. Cambré, S.Santos, W. Wenseleers, R.T. Nugraha, R. Saito, L. Cognet and B. Lounis, ACS Nano
6, 2649 (2012); J.G. Duque, L. Oudjedi, J. J. Crochet, , S. Tretiak, B. Lounis, S.K Doorn and L. Cognet JACS 135 (2013) 3379. E. Genin, Z. Gao, J. A. Varela, J. Daniel, T. Bsaibess, I. Gosse, L. Groc, L. Cognet, M. Blanchard-Desce Adv. Mat (2013) in press
Invited Presentation: Direct Measurement of the Absolute Absorption Spectrum of Individual Carbon Nanotubes
Authors: Blancon Jean-Christophe , Paillet Matthieu , Tran Huy Nam , Than Xuan Tinh , Aberra Guebrou Samuel , Ayari Anthony , San Miguel Alfonso , Phan Ngoc-Minh , Zahab Ahmed-Azmi , Sauvajol Jean-Louis , Vallee Fabrice , Del Fatti Natalia
Published: February 2020

The unique optical properties of single-wall carbon nanotubes (SWNTs) are very promising for the development of novel opto-electronic components and sensors with applications in many fields. Despite numerous studies performed using photoluminescence or Raman and Rayleigh scattering, knowledge of their optical response is still partial, in particular direct and quantitative access to the intrinsic absorption characteristics of SWNT is still challenging. Their precise investigation is made difficult by the large heterogeneities of the carbon nanotube structural parameters in most synthesized ensembles, leading to measurement of mean properties. This can be avoided by performing optical investigations on individual nanotubes. We show here that the spatial modulation spectroscopy (SMS) technique, initially developed to quantitatively study the optical response of single metal nanoparticles1, can be applied to the investigation of individual SWNTs2,3. As compared to other optical techniques, SMS has the key advantage of being sensitive to the nano-object absorption and to directly measure its absolute absorption cross-section. Using this approach, we have determined, over a broad optical spectral range, the absorption spectrum of semiconducting individual SWNTs and the oscillator strength of their different excitonic resonances. A non-resonant background is also identified and its cross-section comparable to the ideal graphene optical absorbance. Furthermore, investigation of the same SWNT either free-standing or lying on a substrate shows large broadening of the excitonic resonances, as well as strong weakening of polarization-dependent antenna effects, due to SWNT-substrate interaction.

[1] A.Arbouet, D.Christofilos, N.Del Fatti and F.Vallée ; J-R.Huntzinger, L.Arnaud, P.Billaud and M. Broyer, Physical Review Letters 93, 127401 (2004).

[2] D.Christofilos , J-C.Blancon , J.Arvanitidis, A.San Miguel, A.Ayari, N.Del Fatti and F.Vallée, Journal of Physical Chemistry Letters 3, 1176 (2012).

[3] J.-C. Blancon, M. Paillet, H.N.Tran, X.T.Than, S. Aberra-Guebrou, A. Ayari, A. San Miguel, N-M. Phan, A-A. Zahab, J-L. Sauvajol, N. Del Fatti and F. Vallée, Nature Communications 4:2542 doi:10.1038/ncomms3542 (2013).
Invited Presentation: Single Molecule Bioelectronics with Carbon Nanotube Circuits
Authors: Collins Philip G.
Published: February 2020

Nanoscale electronic devices like field-effect transistors have long promised to provide sensitive, label-free detection of biomolecules. In particular, single-walled carbon nanotubes have the requisite sensitivity to detect single molecule events, and they have sufficient bandwidth to directly monitor single molecule dynamics in real time.

Recent measurements have demonstrated this premise by monitoring the dynamic, single-molecule processivity of three different enzymes: lysozyme [1,2], protein Kinase A [3], and the Klenow fragment of DNA polymerase I [4]. With all three enzymes, single molecules were electronically monitored for 10 or more minutes, allowing us to directly observe rare transitions to chemically inactive and hyperactive conformations. The high bandwidth of the nanotube transistors further allow every individual chemical event to be clearly resolved, providing excellent statistics from tens of thousands of turnovers by a single enzyme. Besides establishing values for processivity and turnover rates, the measurements revealed variability, dynamic disorder, and the existence of intermediate states. Initial success with three different enzymes indicates the generality and attractiveness of the nanotube devices as a new tool to complement other single molecule techniques. Furthermore, our focused research on transduction mechanisms provides the design rules necessary to further generalize this architecture [5]. This presentation will summarize these rules, and demonstrate how the purposeful incorporation of just one amino acid is sufficient to fabricate effective, single molecule nanocircuits from a wide range of enzymes or proteins.

[1] Y. Choi et. al., Science 335319 (2012). [2] Y. Choi et. al., JACS 1342032 (2012). [3] P. Sims et. al., JACS 1357861 (2013). [4] T. Olsen et. al., JACS 1357855 (2013). [5] Y. Choi et. al., Nano Lett. 13 625 (2013).
Invited Presentation: Cabon Nanotube Terahertz Detector
Authors: He Xiaowei , Erickson Kristopher , Talin Albert Alec , Mills Bernice , Fujimura Naoki , Kawano Yukio , Hauge Robert , Kono Junichiro , Leonard Francois
Published: February 2020

We present a macroscopic terahertz detector based on optically thick films of dense and aligned carbon nanotubes. This p-n junction detector responds to a broad range of frequencies, shows a response at zero bias, good linearity with THz power, and is intrinsically sensitive to polarization. A combination of electrical, thermal, opto-thermal, and thermoelectric experiments establishes the photothermoelectric mechanism of the response.
Investigating Exciton Dissociation Yields in Single-Walled Carbon Nanotube/Fullerene Blends
Authors: Mistry Kevin , Larson Bryon , Ferguson Andrew , Rumbles Garry , Blackburn Jeff
Published: February 2020

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have a number of remarkable optical and electrical properties including tunable band gaps and high charge mobilities that make them appealing for use in photovoltaic devices. Using narrow chiral distributions of large-diameter (d > 1.2 nm) s-SWCNTs can be beneficial to these devices through increased carrier mobility and reduced trapping due to energetic differences between different chiralities. Another benefit of using larger diameter SWCNTs is their lower exciton binding energies, which must be considered when designing a blend with sufficient driving force for charge separation. Additionally, much of the visible and near-infrared region of the solar spectrum can be covered by appropriately tuning the diameter range of these s-SWCNTs along with careful selection of the fullerene acceptor material. Time-resolved microwave conductivity (TRMC) was used to explore charge separation in such s-SWCNT:fullerene (donor:acceptor) blends. TRMC allows for sensitive monitoring of charge generation and decay in response to photoexcitation. We will report on dynamics of charge generation and changes to free carrier yield in blends using carefully tuned combinations of SWCNT diameters and fullerene acceptors. Furthermore, we will discuss how these results can be used to design enhanced s-SWCNT:fullerene active layers.
Surfactants' Key Role in Ionic Aqueous Two-Phase Separation of Carbon Nanotubes Towards Simple Chirality Isolation
Authors: Subbaiyan Navaneetha K , Cambré Sofie , Parra-Vasquez A. Nicholas , Haroz Erik , Doorn Stephen K. , Duque Juan G
Published: February 2020

SWCNTs are known to have wide distribution in diameter/chirality when produced; leading to variability in the starting material chirality distributions with respect to production batch and method. Therefore numerous separation methods that provide nearly single-chiralities have been reported. Most of these separation techniques involved numerous iterations to achieve high purity (gel chromatography, DGU) and long separation times, thereby preventing low-cost scalability of the method. Recently aqueous two-phase (ATP) separation has been explored as a new promising method to separate single-wall carbon nanotubes (SWCNTs) by diameter. In this work, we determined that the ATP separation mechanism is driven by the hydrophobicity of the surfactant, or combination of surfactants, covering the SWCNTs, which can be tuned by mixing different surfactants in well-defined ratios. Having a three-surfactant system, with very different diameter-dependent affinities for SWCNTs, and the combination of salt to adjust the specific surfactant structure surrounding the SWCNTs, has allowed us to develop a simple strategy for obtaining highly enriched single-chirality suspensions of (6,5) SWCNTs in only 1 or 2 steps, thereby obtaining a high separation yield and simplifying the separation technique. Single chirality solutions can now be obtained in an extremely fast, and easy-to-scale-up, cheap way.
Binding Configuration and Surface Coverage of Poly(9,9-dioctylfluorene-2,7-diyl) on Electronic Type-Sorted Carbon Nanotubes
Authors: Shea Matthew J , Brady Gerald J , Arnold Michael S
Published: February 2020

Several schemes have been demonstrated to successfully extract semiconducting (s-) single-walled carbon nanotubes (SWCNTs) from heterogeneous as-grown mixtures containing metallic (m-) SWCNTs. The polyfluorene family of conjugated polymers, specifically poly(9,9-dioctylfluorene-2,7-diyl) (PFO), have been shown to extract s-SWCNTs from mixtures of s- and m-SWCNTs with high selectivity (>99% s-SWCNT) by preferentially wrapping the s-SWCNT components. In addition to electronic type, the selectivity is heavily dependent on the nanotube diameter and chiral angle. To date, there is an inadequate understanding of the polymer-CNT interactions that lead to the high preference for s- over m-SWCNTs in the wrapping process. It is vital to understand these parameters to design separation schemes to reduce the proportion of m-SWCNT impurities to technologically relevant ppm and ppb levels.

In this work, we explore the chemistry of non-covalent nanotube-polymer wrapping processes and describe the effects of surface coverage and binding configuration on the separation efficiency. We disperse SWCNTs grown by the HiPCO process, which contain many chiral species of SWCNT with diameters near 1 nm, in toluene solutions of varying PFO concentration. The resulting dispersions are analyzed with optical absorption spectroscopy, excitation-emission photoluminescence spectroscopy, and photoluminescence anisotropy. First, we experimentally quantify the amount of PFO wrapping the SWCNTs by measuring exciton energy transfer from PFO to SWCNTs via photoluminescence spectroscopy. We characterize the dependence of the surface coverage on PFO concentration, finding that the surface coverage increases by a factor of 7 as PFO concentration increases from 0.2 to 2 mg/mL. Second, we demonstrate that the wrapping of nanotubes by PFO is described by a Langmuir adsorption isotherm, in which surface coverage of PFO on the nanotubes follows an S-shaped curve as a function of PFO concentration. The shape of the curve is related to the polymer-nanotube binding energy, which depends on the nanotube electronic type, diameter, chiral angle, solvent, and polymer molecular weight. Third, we determine the binding configuration of the PFO on the nanotube surface as a function of PFO concentration and demonstrate that the PFO becomes more ordered as the surface coverage decreases. In the highly-ordered PFO regime we estimate the wrapping angle of individual PFO strands around nanotubes in solution. Finally, we find that the metal-semiconductor separation efficiency is lowest when the concentration of PFO is high, surface coverage is high, and surface ordering is low.

Understanding the PFO wrapping process will be an important step toward attaining high-purity s-SWCNT from this and similar sorting procedures for a range of polymer-CNT systems. These advances will enable further development of technologically relevant high purity s-SWCNTs for next-generation electronic devices.
Invited Presentation: Nitrogen-Incorporated Single-Walled Carbon Nanotubes for Devices
Authors: Maruyama Shigeo , Thurakitseree Theerapol , Kim Sungjin , Kramberger Christian , Chiashi Shohei , Einarsson Erik
Published: February 2020

We synthesized single-walled carbon nanotubes (SWNTs) with small diameter and narrow diameter distribution using acetonitrile (AcN)-mixed ethanol (EtOH) feedstock. Due to the presence of nitrogen (N) during synthesis, the SWNT mean diameter was dramatically reduced from approximately 2.1 nm to less than 1 nm as AcN was added as carbon source [1, 2]. Surprisingly, the main nitrogen configuration was found to be encapsulated diatomic N2 molecules interior of SWNTs with the content of 1 at % [3, 4]. As the sequence of feedstock was switched during synthesis, SWNT diameter was changed along the vertically aligned array. A majority of nanotube junctions between two different diameter nanotubes were found to be discontinuous, while a minority of continuous junctions were revealed by high-resolution transmission electron microscope [5]. This diameter modulation was reversible upon the sequence of feedstock introduction. Additionally, the observed N2 molecules on the top of double-layered SWNT vertical array, where the top layer was EtOH-grown array, imply that encapsulated N2 molecules were migrating across nanotube junctions, indicating a viability of connected SWNTs with different diameters. We also address the role of nitrogen on influencing the SWNT diameter in which nitrogen affects only the surface of the catalyst particle, resulting in a change from the Octopus to the VLS growth mode, which results in a smaller diameter. Several devices using this nitrogen-incorporated SWNTs will be discussed.

References

[1] T. Thurakitseree, C. Kramberger, P. Zhao, S. Aikawa, S. Harish, S. Chiashi, E. Einarsson, S. Maruyama, Carbon
50 (2012) 2635.

[2] T. Thurakitseree, C. Kramberger, P. Zhao, S. Chiashi, E. Einarsson, S. Maruyama, Phys. Stat. Sol. B
249 (2012) 2404.

[3] C. Kramberger, T. Thurakitseree, H. Koh, Y. Izumi, T. Kinoshita, T. Muro, E. Einarsson, S. Maruyama, Carbon, 55 (2013) 196.

[4] C. Kramberger, T. Thurakitseree, E. Einarsson, A. Takashima, T. Kinoshita, T. Muro, S. Maruyama, Nanoscale, (2013), in press, (DOI: 10.1039/C3NR04729F).

[5] T. Thurakitseree, C. Kramberger, A. Kumamoto, S. Chiashi, E. Einarsson, S. Maruyama, ACS
Nano
7 (2013) 2205.
Towards High-Fidelity Single-Column Separation of Swcnts Using Agarose Gel
Authors: Clar Justin , Xu Jia , Silvera Batista Carlos , Yuan Tianyu , Bonzongo Jean-Claude J , Ziegler Kirk J
Published: February 2020

For their inclusion in novel electronic devices, the post synthesis separation of single walled carbon nanotubes (SWCNTs) is of great interest. While several methods have been utilized to achieve these separations with various levels in purity, one of the most promising techniques to produce large-scale separations is the selective adsorption of SWCNTs onto an agarose gel stationary phase. Recently, several researchers have reported successful modification to the process in order to achieve further separation of the semiconducting fractions by (n,m) type. While these changes are a significant step in SWCNT processing, they are difficult for development on an industrial scale due to the use of harsh chemical treatments (pH adjustments) and temperature gradients that may be difficult to control. In addition, many of these approaches require multiple (4 or more) columns in series, causing substantial dilution of the collected fractions, which increases the amount of surfactant required and may require the fractions to be concentrated before use. Here we report the mechanism of separation to the selective adsorption of semiconducting SWCNTs onto the agarose gels. The results indicate that the surfactant orientation on the SWCNT surface is an important parameter during separation and that the primary mode of attraction is ion-dipole interactions between SDS-SWCNTs and the agarose gel backbone. The selectivity of adsorption is then driven by the inherent differences in polarizability between the metallic and semiconducting species. Using our understanding of the mechanism behind selective adsorption of SWCNTs onto agarose, we have started to develop high-fidelity separations based on a single elution profile in a single column. The design of a simple, single-column technique to separate SWCNTs by (n,m) type is a major step in realizing their full potential.
Maximum Aromaticity As a Guiding Principle for the Most Suitable Hosting Cages in Endohedral Metallofullerenes
Authors: Garcia-Borràs Marc , Osuna Sílvia , Swart Marcel , Luis Josep Maria , Solà Miquel
Published: February 2020

Encapsulation of metal clusters in endohedral metallofullerenes takes place in cages that in most cases are far from being the most stable isomer in the corresponding hollow fullerenes. In large metal clusters and small fullerene cages, the election is mainly driven by the need to reduce strain. For the not so large metal clusters, it is usually said that the cage is chosen to minimize the electrostatic repulsion between charged five-membered rings.1 We have proved that maximizing the aromaticity is the main driving force that determines the most suitable hosting carbon cage for a given metallic cluster.2 This simple rule, the so-called Maximum ARomaticity Criterion (MARC), allow us to directly compare IPR (isolated pentagon rule) and non-IPR anionic isomers regardless the number of adjacent pentagon pairs (APP) they have. We have tested the MARC for the majority of endohedral metallofullerenes from C66 to C104 reported to date and the results show that MARC successfully predicts the most suitable C2n cage for hosting a given metal cluster among the manifold existing C2n isomers. In addition, using the Maximum ARomaticity Criterion, one can justify why the IPR rule is not always fulfilled when EMFs are considered.

[Figure 1 here]

Figure 1. Classification in terms of the ALA index of the anionic IPR and non-IPR fullerene isomers with 1-3 Adjacent Pentagon Pairs (APPs) for the most common C2
n (2n = 66–104) EMFs reported to date. Isomers experimentally observed are marked using black dots, and their corresponding isomer numbers are indicated. The ALA prediction ordering for the experimentally observed isomers are given in parentheses.

A. Rodríguez-Fortea, N. Alegret, A.L. Balch, J.M. Poblet, Nat. Chem.
2010, 2, 955.

M. Garcia-Borràs, S. Osuna, M. Swart, J.M. Luis, and M. Solà, Angew. Chem. Int. Ed.
2013, 52, 9275.
Fullerenes Encapsulating an Ytterbium Atom: Molecular Structures and Chemical Properties
Authors: Lu Xing
Published: February 2020

Endohedral metallofullerenes (EMFs) are novel hybrid molecules with metal atoms or metal clusters being encapsulated inside fullerene cages.[1] In spite that the EMFs encapsulating divalent metal ions are less produced than other species, a series of mono-ytterbium have been successfully synthesized and isolated in our recent experiments. Their cage structures were systematically investigated with 13C NMR spectroscopy in combination with computational works.[2] To seek insights into the metal location and metal-cage interactions in these Yb@C2n (2n = 80, 82) compounds, their cocrystals with NiII(octaethylporphyrin) have been investigated with X-ray diffraction (XRD) crystallography.[3]

More meaningfully, chemical properties of divalent EMFs were investigated for the first time with a carbene probe. The isolated derivatives were systematically characterized with a collection of theoretical and experimental techniques, including single crystal XRD crystallography. Unique interplays between the internal divalent metal ion and the addend have been observed.[4]

References:

[1] X. Lu, L. Feng, T. Akasaka, S. Nagase, Chem. Soc.
Rev.
2012, 41, 7723-7760.

[2] X. Lu, Z. Slanina, T. Akasaka, T. Tsuchiya, N. Mizorogi, S. Nagase, J. Am. Chem. Soc.
2010, 132, 5896-5905.

[3] (a) X. Lu, Y. Lian, C. M. Beavers, N. Mizorogi, Z. Slanina, S. Nagase, T. Akasaka, J. Am. Chem. Soc.
2011, 133, 10772-10775. (b) M. Suzuki, Z. Slanina, N. Mizorogi, X. Lu, S. Nagase, T. Akasaka, J. Am. Chem. Soc.
2012, 134, 18772–18778.

[4] (a)Y-P. Xie, M. Suzuki, W. Cai, N. Mizorogi, S. Nagase, T. Akasaka, X. Lu, Angew. Chem. Int. Ed.
2013, 52, 5142-5145. (b) W. Zhang, M. Suzuki, Y-P. Xie, L. P. Bao, W. T. Cai, Z. Slanina, S. Nagase, M. Xu, T. Akasaka, X. Lu, J. Am. Chem. Soc.
2013, 135, 12730-12735.
Studies of Top-Down Mechanistic Processes of Fullerene and Metallofullerene Formation for Cages Greater Than Ninety Carbons
Authors: Fuhrer Timothy , Zhang Jianyuan , Dorn Harry C
Published: February 2020

The elucidation of a mechanistic theory for fullerene formation in electric-arc plasmas, laser ablation, and interstellar space has been a subject of considerable interest over the past two decades. For many years, a “bottom-up” theory of fullerene formation from C2 units was dominant. However, in recent years evidence is emerging suggesting a “top-down mechanism” - that is, fullerenes are formed via shrinkage of giant fullerenes generated from graphene. Previously, we reported molecular structural evidence implying a top-down mechanism for the asymmetric non-IPR metal carbide metallofullerene, M2C2@C1
(51383)-C84 (M=Y,Gd) as a missing link in the mechanism for the formation of smaller, more symmetric metallofullerene cages. In this paper, we extend the study mechanism to include larger fullerenes, namely the C3v
(134)C94 and D3
(85)C92 cages.
Invited Presentation: Graphene Nanoelectromechanical Systems As Stochastic-Frequency Oscillators
Authors: Bockrath Marc , Miao Tengfei
Published: February 2020

We measure the quality factor Q of electrically-driven few-layer graphene drumhead resonators, providing an experimental demonstration that Q ~ 1/T , where T is the temperature. We develop a model that includes intermodal coupling and tensioned graphene resonators, yielding good quantitative agreement to experiment. Because the resonators are atomically thin, out-of-plane fluctuations are large. As a result Q is mainly determined by stochastic frequency broadening rather than frictional damping, in analogy to nuclear magnetic resonance. Additionally, at larger drives the resonator linewidth is enhanced by nonlinear damping, in qualitative agreement with a recent theory of damping by radiation of in-plane phonons[1]. Parametric amplification produced by periodic thermal expansion from the ac drive voltage yields an anomalously large linewidth at the largest drives. Our results contribute towards a general framework for understanding the mechanisms of dissipation and spectral line broadening in atomically thin membrane resonators.

1. Croy, A.; Midtvedt, D.; Isacsson, A.; Kinaret, J. M. Phys. Rev. B 2012, 86, 235435.
Field-Controlled Ion Doping of Graphene
Authors: Kinder Erich , Lu Hao , Hwang Wan Sik , Cho Byung Jin , Hong Seul-ki , Seabaugh Alan , Fullerton-Shirey Susan
Published: February 2020

Doping technologies are needed for the development of tunnel field-effect transistors based on graphene and other single-layer two-dimensional materials. Here we utilize Li+ and ClO4
− ions in polyethylene oxide (PEO) to enable dynamic and reconfigurable doping of graphene under electric field control. Ions are drifted across the PEO to the graphene where they induce electron or hole conductivity. Use of PEO:LiClO4 for ion-doping of carbon nanotubes [1], graphene [2, 3] and MoS2[4] have all incorporated the ion conductor and field plate above the transistor channel. This requires a dry process because the developers used in photolithography attack and contaminate PEO. This further restricts the field plate formation process to shadow evaporation or to macroscopic contacts formed by probes. Here we report on a new dry transfer process which allows the transistor to be placed on top of the PEO and the doping to be field-controlled by the substrate back gate. In this paper we show the transfer process and characteristics of the ion motion and conductivity modulation under field-control.

The dry transfer process is illustrated in Fig. 1. To create the top portion of the device, source and drain contacts are patterned onto wide area graphene formed by chemical vapor deposition. Polyisobutylene (PIB) and a PDMS stamp are then applied as handling layers (Fig. 1b). The Cu substrate is then etched in ammonium persulfate (APS) and the top portion is joined to the bottom (Fig. 1e). We have fabricated devices with both Au and graphene backgates, and initial tests were performed with an Au backgate, patterned into stripes to minimize leakage current through the electrolyte (Fig. 2).

Doping in the graphene channel is controlled by the backgate voltage (Vbg
). The conductivity, monitored by the drain current, (Id
), is varied by a factor of four by sweeping Vbg
at 0.5 V/s from −10 to 10 V (Fig. 3). The shift of the current minima (Dirac points) from zero are a direct measure of the ion doping of the graphene channel.

To characterize the retention of electrostatic doping, a 5 V backgate pulse is applied for 1 second and removed for 10 seconds while monitoring the drain current (Fig. 4). The current decreases by ~10% as the ions are polarized and then released.

Acknowledgements: This work was supported in part by the Center for Low Energy Systems Technology (LEAST), one of the six SRC STARnet Centers, sponsored by MARCO and DARPA.

[1] C. Lu et al. Nano Lett.
4, pp. 623–627 (2004)

[2] A. Das et al., Nat. Nanotech, 3, pp. 201-215 (2008)

[3] D. Efetov and P. Kim, Phys. Rev. Lett.,
105, pp. 256805 (2010)

[4] M. Lin, et al., J. Phys. D, 45, 345102 (2012).
Layer-Dependent Electrical Properties of Graphene: An Atomic Force Microscopy (AFM) Study
Authors: Yu Jing-jiang
Published: February 2020

Graphene has attracted much attention recently due to their exotic electronic properties. Potential applications of graphene sheets as ultrathin transistors, sensors and other nanoelectronic devices require them supported on an insulating substrate. Therefore, a quantitative understanding of charge exchange at the interface and spatial distribution of the charge carriers is critical for the device design. Here, we demonstrate that atomic force microscopy (AFM)-based technique Kelvin force microscopy (KFM) can be applied as an experimental means to quantitatively investigate the local electrical properties of both single-layer and few-layer graphene films on silicon dioxide. The effect of film thickness on the surface potential of few-layer graphene is observed. For example, a 66 mV increase in the surface potential is detected for a ten-layered film with respect to an eight-layered one. Furthermore, with the introduction of multiple lock-in amplifiers (LIAs) in the electronics for scanning probe microscopes, single-pass kelvin force microcopy and probing of the other electric property such as local dielectric permittivity via the capacitance gradient dC/dZ measurements are allowed by the simultaneous use of the probe flexural resonance frequency ωmech in the first LIA targeting the mechanical tip-sample interactions for surface profiling, and a much lower frequency ωelec (both in the second LIA and its second harmonic in the third LIA) for sample surface potential and dC/dZ measurements, respectively. In contrast to surface potentials, the dC/dZ measurements show that local dielectric permittivity of few-layer graphene films maintain at the same level regardless of the film thickness. Such simultaneous monitoring of multiple electronic properties that exhibit different behaviors in response to the graphene layers provides us a technique to achieve both a comprehensive characterization and a better understanding of graphene materials.
Electrochemical Synthesis of Graphene-Metal Oxide Heterostructure for Resistive Random Access Memory
Authors: Park MiSeok , Hong Kyung-Sik , Ahn SooHoon , Kwon HyukSang
Published: February 2020

Graphene has a lot of merits for many engineering applications due to its unique physical, electrical and chemical properties [1-2]. Recently, a soft chemical reduction process of graphene oxide has been reported as a very efficient and safe method to fabricate a pure graphene film [3]. Also, the graphene-metal hybrids are fabricated by electrochemical methods in aqueous solution [4]. However, in spite of aforementioned enormous interests and efforts, the reduction mechanisms of graphene oxide and graphene-metal hybrid during electro-deposition are still unclear and controversial.

In this study, the electrochemical characteristics of reduction phenomena of graphene oxide and graphen-metal oxide hybrids are investigated in detail. To investigate the exact reduction potential of graphene oxide and a variety of graphene-metal oxide hybrids in aqueous solution, the electrochemical analyses are accompanied by a cyclic voltammetry. The graphene-metal oxide hybrid film was electrochemically deposited on the conductive substrates using the cyclic co-electrodeposition method.

Furthermore, we have confirmed that the electrochemically formed hybrid film could be used for a Resistive Random Access Memory(RRAM) device through the test of resistive switching behavior of this hybrid films. This novel fabrication method of switching layer will provide several advantages for nonvolatile memory, such as low-power consumption, fast switching speed, and more simple and safe fabrication process.

References

[1] A. K. Geim, K. S. Novoselov, Nature Mater., 6, 183-191 (2007)

[2] H. Y. Jeong, and et al., Nano Lett., 10, 4381-4386 (2010).

[3] S. Stankovich, D. A. Dikin, R. S. Ruoff, et al., Carbon, 45, 1338-1565 (2007).

[4] R. S. Sundaram, C. G. Navarro, K. Kern, et al., Adv. Mater., 20, 3050-3053 (2008).
Structure-Dependent Photo-Induced Charge Separation in Type-II Semiconductor Heterostructures
Authors: Teranishi Toshiharu
Published: February 2020

Highly efficient photoenergy conversion in semiconductor nanoparticle heterostructures requires the formation of epitaxial heterointerfaces and band alignment engineering. This requirement has led to attention being given to recent advances and prospects in the charge separation properties of Type-II semiconductor heterostructures composed of chalcogenide–chalcogenide blends. Type-II semiconductor heterostructures with a staggered alignment of band edges at the heterointerface can be synthesized by seeded growth or ion exchange to promote the spatial charge separation between electrons and holes in different parts of the heterostructure. Special attention has been given to CdS–Cu2-x
S (0 ≤ x ≤ 0.0625) and CdS–CdTe combinations where CdS is a commonly used n-type semiconductor and both Cu2-x
S and CdTe are proper p-type semiconductors that are used as light absorbers in heterojunction solar cells.
Preparation, Characterization and Application of Noble-Metal Colloids Stabilized By Chiral Molecules
Authors: Takase Mai , Kimura Shunsuke , Ohtani Bunsho
Published: February 2020

Gold or platinum colloids stabilized with chiral compounds having a hydroxyl or amino group and multiple carboxylic acids (CHMCA) were prepared by a modified citric-acid method in which L-, D- or DL-tartaric acid, L-, D- or DL-malic acid were used instead of citric acid. Controlling the molar ratio to metal and concentration of CHMCAs and pH of the reaction mixture during the colloid preparation process, CHMCA-stabilized gold or platinum colloids, without giving precipitates even when stored for long time, was successfully prepared.

The CHMCA-stabilized gold colloids showed a photoabsorption peak at arou nd 520 nm, corresponding to the particle size of a few tens nanometer, and assigned to the surface plasmon resonance (SPR) and a peak in the circular dichromic spectra in the wavelength region of the SPR absorption though CHMCAs have no absorption there (Fig. 1). These results suggest that CHMCA-modified metal nanoparticles, i.e., "chiral surface plasmon resonance (cSPR)" depending on adsorption rotation direction of circularly polarized light. Application of the gold and platinum colloids loaded onto e.g., titania particles, to catalysis and photocatalysis using cSPR is discussed.
Single Crystalline CuO Nanowire for Resistive Random Access Memory Application
Authors: Hong Yi-Siang , Chan Jui-Yuan , Huang Chun-Wei , Wu Wen-Wei
Published: February 2020

For the development of high density memory arrays of resistive random access memory (RRAM), nanowires provide the potential to reduce the device size to overcome the limitation of conventional lithography. In this work, copper oxide nanowires were synthesized and served as the building block for 1-D RRAM nanodevice. The phase of Copper oxide was identified to be CuO by selected area electron diffraction (SAED) patterns and energy dispersive spectrometer (EDS). We fabricated the Au/CuO-nanowire/Au RRAM nanodevice by electron-beam lithography techniques. From I-V measurement, the forming voltage and RESET voltage were 0.64 V and 5.2 V, respectively. This low forming voltage and ultra-high reset voltage may result from stacking fault in the core of CuO nanowires. From scanning electron microscope (SEM) image ,the as-formed protrusion near the anode and reduction near the cathode after several electrical measurements indicated that the diffusion of oxygen vacancies generating the conducting filament from cathode, result in the change of nanowire morphology. The result will be beneficial to understand the switching properties of nonvolatile memory device at nanoscale.
Bis-Metal Coordination Chemistry of Doubly N-Confused Hexaphyrins
Authors: Furuta Hiroyuki
Published: February 2020

Expanded porphyrins have been received great interest due to the extended p-conjugation, multi-metal coordination, and multiple oxidation states, which consequently make them to be useful for optoelectronic applications, especially in the near-infrared (NIR) region. In contrast to the standard porphyrin with rigid planarity, expanded porphyrins are generally rather flexible and show the uncommon electronic and/or electromagnetic behaviors. However, the large flexibility of the molecules allows them to take various structures with many conformers and tautomers, which sometimes makes the metal coordination difficult and unpredictable. Thus, it has been awaited to synthesize the rigid-shaped expanded porphyrins possessing a large cavity that can accept bis-metals in the core without difficulty. Considering how enormous the achievement of porphyrin chemistry with a single metal is, the development of NIR dye chemistry with bis-metal expanded porphyrin ligands should be promising.

We have been working on N-confused porphyrinoids and exploring the unique features in view of their structures and electronic states.1 Replacing the regular pyrrole with N-confused pyrrole ring in the pyrrolic macrocycle, which we call “confusion approach”, is now recognized an effective strategy for controlling the electronic state and molecular shape (Figure 1).2 Recently, we have succeeded in synthesizing the singly, doubly, and triply N-confused [26]hexaphyrins and revealed the effects of confusion on the structures, optical properties, and metal coordination.3-7In this presentation, recent progress of the coordination chemistry of doubly N-confused hexaphyrins is overviewed.

References

1) Toganoh, M.; Furuta, H. Chem. Commun. 2012, 48, 937. 2) Srinivasan, A.; Furuta, H. Acc. Chem. Res.
2005, 38, 10. 3) Gokulnath, S.; Nishimura, K.; Toganoh, M.; Mori, S.; Furuta, H. Angew. Chem. Int. Ed.
2013
, 52, 6940. 4) Gokulnath, S.; Toganoh, M.: Yamaguchi, K.;

Mori, S.; Uno, H.; Furuta, H. Dalton Trans. 2012, 41, 6283. 5) Gokulnath, S.; Yamaguchi, K.; Toganoh, M.; Mori, S.; Uno, H.; Furuta, H. Angew. Chem. Int. Ed. 2011, 50, 2302. 6) Ikawa, Y.; Takeda, M.; Suzuki, M.; Osuka, A.; Furuta, H. Chem. Commun.
2010, 46, 5689. 7) Xie, Y.-S.; Yamaguchi, K.; Toganoh, M.; Uno, H.; Suzuki, M.; Mori, S.; Saito, S.; Osuka, A.; Furuta, H. Angew. Chem. Int. Ed.
2009, 48, 5496.
Electron-Deficient Porphyrin-Fullerene Cocrystallates: Effect of Fullerene on the Porphyrin Ring Conformation
Authors: P Bhyrappa , K Karunanithi
Published: February 2020

A new family of electron-deficient porphyrin-fullerene cocrystallates were examined by single crystal X-RD. Solvatedcocrystallates of 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrin, {[H2(TPP)(CN)4]3•C60, 1, [Cu(TPP)(CN)4]3•C60, 2 and [H2(TPP)(CN)4]•C70,
3} were examined to elucidate the influence of fullerene on the stereochemistry of the porphyrin macrocycle and the extent of intermolecular interactions in the solid-state. The C60 units are encapsulated into the triporphyrin capsule and intermolecular interactions are dominated by mainly porphyrin…C60 and porphyrin…porphyrin π…π type of interactions. Both the cocrystallates revealed the formation of hexagonal honeycomb layer-like structure with 10 Å cavity filled with lattice solvates. On changing the fullerene to C70, co-crystallate, 3
showed essentially one-dimensional chain structure. Cocrystallates, 1-3 showed considerable distortion of the porphyrin ring as evidenced from root-mean square (r.m.s.) deviation which is the deviation of the 24-atoms of the macrocycle from their least square plane (0.25 Å) relative to that observed in nearly planar (0.046 Å) parent free base porphyrin, H2(TPP)(CN)4 structure. Another less electron rich porphyrin-fullerene cocrystallate, H2(TPP)Br4•(C60)2•(TCE)2, 4 revealed corrugated layer-structure mediated by solvent and porphyrin…C60 interactions. The macrocycle in the cocrystallate, 4 shows slightly higher distortion than that observed in the reported structure, H2(TPP)Br4. In these cocrystallates, the intermolecular close contact distances between the porphyrin…fullerene was found to be (por)C…C(C60) = 3.185(16) Å and (C70)C…N(por) = 3.03 (3) Å. The normal coordinate structure decomposition analysis of the macrocycle for out-of-plane distortion in the cocrystallates, 1-3 revealed considerable saddling (69-71%) with very minimal ruffled (2-8%) and domed (10-15%) distortions. Cocrystallate, 4 shows enhanced of wave distortion than that observed in the parent porphyrin, H2(TPP)Br4. The nonplanar distortion of the porphyrin ring in the cocrystallates has been ascribed mainly to intermolecular interactions.
Photosynthetic Donor-Acceptor Mimicry Using Near-Infrared Photosensitizers
Authors: D'Souza Francis , Bandi Venugopal , Heine Brian , El-Khouly Mohamed , Nesterov Vlad , Ohkubo Kei , Zandler Mel , Fukuzumi S.
Published: February 2020

Supramolecular multi-modular donor-acceptor systems constructed using different photo- and redox-active species have been extensively investigated in the last three decades. With suitably designed and assembled modular systems, these supramolecules have found useful in solar-fuel and solar-electricity generation and in building optoelectronic devices. Traditionally, porphyrins and phthalocyanines have extensively been used as light-harvesting and electron-transfer units in these multi-modular systems performing photoinduced energy- and electron-transfer reactions. Recently, BF2-chelated dipyrromethene (BODIPY) dyes, and their structural analogs have emerged as efficient and tunable light-absorption and luminescent species. The present contribution summarizes our recent progress in the design, synthesis, electrochemistry, and photochemistry of donor-acceptor hybrids derived from BODIPY and azaBODIPY photosensitizers with emphasis on radical ion-pair formation.