bluuebunny/crossref_metadata_2025 huggingface dataset:
The Infinite Server Problem
Authors: Coester Christian , Koutsoupias Elias , Lazos Philip
Published: July 2021

We study a variant of the
k
-server problem, the infinite server problem, in which infinitely many servers reside initially at a particular point of the metric space and serve a sequence of requests. In the framework of competitive analysis, we show a surprisingly tight connection between this problem and the resource augmentation version of the
k
-server problem, also known as the
(h,k)
-server problem, in which an online algorithm with
k
servers competes against an offline algorithm with
h
servers. Specifically, we show that the infinite server problem has bounded competitive ratio if and only if the
(h,k)
-server problem has bounded competitive ratio for some
k
=
O
(
h
). We give a lower bound of 3.146 for the competitive ratio of the infinite server problem, which holds even for the line and some simple weighted stars. It implies the same lower bound for the
(h,k)
-server problem on the line, even when
k/h
→ ∞, improving on the previous known bounds of 2 for the line and 2.4 for general metrics. For weighted trees and layered graphs, we obtain upper bounds, although they depend on the depth. Of particular interest is the infinite server problem on the line, which we show to be equivalent to the seemingly easier case in which all requests are in a fixed bounded interval. This is a special case of a more general reduction from arbitrary metric spaces to bounded subspaces. Unfortunately, classical approaches (double coverage and generalizations, work function algorithm, balancing algorithms) fail even for this special case.
A Dataset and a Convolutional Model for Iconography Classification in Paintings
Authors: Milani Federico , Fraternali Piero
Published: July 2021

Iconography in art is the discipline that studies the visual content of artworks to determine their motifs and themes and to characterize the way these are represented. It is a subject of active research for a variety of purposes, including the interpretation of meaning, the investigation of the origin and diffusion in time and space of representations, and the study of influences across artists and artworks. With the proliferation of digital archives of art images, the possibility arises of applying Computer Vision techniques to the analysis of art images at an unprecedented scale, which may support iconography research and education. In this article, we introduce a novel paintings dataset for iconography classification and present the quantitative and qualitative results of applying a
Convolutional Neural Network
(
CNN
) classifier to the recognition of the iconography of artworks. The proposed classifier achieves good performances (71.17% Precision, 70.89% Recall, 70.25% F1-Score, and 72.73% Average Precision) in the task of identifying saints in Christian religious paintings, a task made difficult by the presence of classes with very similar visual features. Qualitative analysis of the results shows that the CNN focuses on the traditional iconic motifs that characterize the representation of each saint and exploits such hints to attain correct identification. The ultimate goal of our work is to enable the automatic extraction, decomposition, and comparison of iconography elements to support iconographic studies and automatic artwork annotation.
Report on supporting and understanding of conversational dialogues workshop (SUD 2021) at WSDM 2021
Authors: Ganguly Debasis , Jones Gareth J. F. , Sen Procheta , Verma Manisha , Pal Dipasree
Published: July 2021

This report describes the workshop on Supporting and Understanding of (multi-party) conversational Dialogues (SUD) organized as a part of the Web Search and Data Mining conference (WSDM) 2021. The aim of SUD workshop was to encourage researchers to investigate automated methods to analyze and understand conversations. We also discuss the release of a dataset that would be useful in IR research on conversations. The dataset was constructed to support the data challenge in SUD workshop and its precursor event - the Retrieval from Conversational Dialogues (RCD) track at the Forum of Information Retrieval and Evaluation (FIRE) 2020.
Report on the 2nd workshop on bridging the gap between information science, information retrieval and data science (BIRDS 2021)
Authors: Frommholz Ingo , Liu Haiming , Melucci Massimo
Published: July 2021

The aim of the BIRDS workshop (Bridging the Gap between Information Science, Information Retrieval and Data Science) is to bring together the Data Science, Information Retrieval, Information Science and HCI communities. BIRDS 2021 is the second in a series of workshops and was held in conjunction with CHIIR 2021, following a successful event at SIGIR 2020. It consisted of a selection of accepted papers and invited talks. This article reports on BIRDS 2021, provides a discussion of topics, tasks, approaches and data sets and an outline of future directions for interdisciplinary work.
Report on the 43rd european conference on information retrieval (ECIR 2021)
Authors: Perego Raffaele , Sebastiani Fabrizio
Published: July 2021

The 43rd European Conference on Information Retrieval (ECIR 2021), organized under the auspices of the Information Retrieval Specialist Group of the British Computer Society (BCS IRSG), took place between March 28 and April 1, 2021. As sadly customary in these dark times, the conference was held entirely online, due to the COVID-19 pandemic. According to the original plans, it should have instead taken place in Lucca, a small Italian town in Tuscany, Italy, which enjoys a beautiful, extremely well-preserved historic centre.
Report on the 11th bibliometric-enhanced information retrieval workshop (BIR 2021)
Authors: Frommholz Ingo , Cabanac Guillaume , Mayr Philipp , Verberne Suzan
Published: July 2021

The 11th Bibliometric-enhanced Information Retrieval Workshop (BIR 2021) was held online on April 1st, 2021, at ECIR 2021 as a virtual event. The interdisciplinary BIR workshop series aims to bring together researchers from different communities, especially Scientometrics/Bibliometrics and Information Retrieval. We report on the 11th BIR, its invited talks and accepted papers. Lessons learned from BIR 2021 are discussed and potential future research questions identified that position Bibliometric-enhanced IR as an exciting special yet important branch of IR research.
(Invited) Stereoselective Photoluminescent Properties of DNA-Carbon Nanotubes: A Primer for Molecular Perceptron
Authors: De los Santos Zeus , Zheng Ming
Published: July 2021

Single-walled carbon nanotubes (SWCNTs) have emerged to be useful tools in molecular recognition in recent years. Due to their well-defined optical properties, SWCNTs offer unique characteristics that most small-molecule sensors lack. For example, SWCNTs exhibit a near-IR (NIR) photoluminescence which makes them great candidates for sensing biomolecules. Typically, the synthesis of SWCNTs yields over 30 distinct tube chiralities, with two-thirds of the mixture comprising semiconducting and the remaining third consisting of quasi-metallic or true-metallic tubes. To add to the mixture’s structural complexity, each chirality that has the same helicity could also have different handedness – species that are enantiomeric in nature. In our lab at NIST, we have recently developed techniques based on aqueous two-phase extraction (ATPE) to separate enantiomers of SWCNTs wrapped with specific DNA sequences. Most of the sensors that have been developed in this field, whether they are coated and dispersed by surfactants or DNA, take advantage of mixtures of various SWCNT helicities to elicit an optical response from interactions of small molecules. However, the responses obtained from each enantiomeric species of SWCNT is largely ignored, or at best, assumed to be similar. In this presentation, we discuss the differences in photoluminescence responses observed when SWCNTs wrapped with various DNA sequences interact with enantiopure small molecules. With this study, we give proof that specific DNA sequences allow for specific optical responses between the mixtures of diastereomeric DNA-SWCNT nanohybrids and single-chirality enriched DNA-SWCNTs, and enantiomeric amino acids. This study is the first proof-of-concept that small chiral molecules interact with chirality enriched DNA-SWCNTs to different extents and give rise to specific optical signatures that could be exploited for future developments of sensing arrays for complex biological mixtures.
An Oligonucleotide Sensor with Parallel Electrical Pathways
Authors: Barnes Benjamin , Wang YuHuang
Published: July 2021

Point-of-care sensors can combat the spread of infectious diseases and inform timely treatments. But in order to be used in this capacity, point-of-care sensors need to combine rapid detection speed with high sensitivity. Detection speed has traditionally been reduced by increasing the sensing surface area of the device, but this can increase noise and reduce sensitivity. In this work we align multiple tube-in-a-tube (Tube^2) nanostructures across a trench between two electrodes. Each Tube^2 consists of a semiconducting carbon nanotube nested within an outer nanotube densely functionalized with oligonucleotide probes. This device design provides a high surface area, while forcing the electrical current through distinct electrical pathways, allowing the binding events to be sensitively detected. Using this device architecture, we demonstrate the selective detection of Lyme disease oligonucleotide biomarkers in physiological ionic strength conditions on the order of seconds.
(Invited) Near Infrared Imaging of Cellular Signaling
Authors: Kruss Sebastian
Published: July 2021

Cells use molecules to exchange information. A very prominent example is neurotransmitter signaling between neuronal cells or paracrine signaling between blood cells or bacteria. However, it is up to date difficult to visualize signaling processes between cells with high spatial, temporal and chemical resolution. We are interested in developing fluorescent sensors/probes that overcome these limitations and answer novel biological questions.

For that purpose we use near infrared (NIR) fluorescent single-walled carbon nanotubes (SWCNTs). SWCNTs fluoresce in the nIR tissue transparency window (900 nm -1700 nm) and do not bleach. They are chemically modified to render them selective for biological signaling molecules. In this context, we developed different chemical strategies that include screening for artificial binding motifs, aptamers and nanobodies. Using these strategies we created sensors for the neurotransmitters dopamine/serotonin, reactive oxygen species and bacterial signaling molecule. These sensors change their fluorescence in the presence of the target molecule and detect down to single molecules. Fast parallel imaging of many of those sensors provides a NIR image (>900 nm) of the neurotransmitter concentration around cells. This technique was used to image hot spots of dopamine release from primary dopaminergic under electrical stimulation and assess the heterogeneity of release sites. Neurotransmitters are not only relevant in the neuronal system but as well in the periphery e.g. in blood cells. In this context, we imaged for the first time how human blood platelets release serotonin after activation and resolved the location and the time scale of release. Finally, such sensors resolve signaling between bacteria and even detect them. These results illustrate that tailored SWCNTs are powerful tools for quantitative chemical imaging of biological processes.
(Invited) Glycopolymer-Wrapped Carbon Nanotubes for Profiling Carbohydrate-Protein Interactions
Authors: DiLillo Ana , Chan Ka Keung , Sun Xue-Long , Ao Geyou
Published: July 2021

Stable dispersions of single-wall carbon nanotubes (SWCNTs) by biopolymers in an aqueous environment facilitate their potential biological and biomedical applications. Synthetic glycopolymers – polymers with carbohydrate pendant groups – have been used extensively to mimic the functions of naturally occurring glycoconjugates. In this work, we created water soluble glycopolymer-wrapped SWCNTs (Glyco-SWCNTs) via noncovalent complexation utilizing lactose-containing polymers with various carbohydrate densities and chain lengths. Subsequently, Glyco-SWCNT complexes are utilized as near-infrared fluorescent probes to detect multivalent interactions between carbohydrates and carbohydrate-binding proteins. These SWCNT-based fluorescent probes can be potentially utilized for profiling targeted carbohydrate-protein interactions in complicated biological samples and in vivo analysis.
Development of Single-Walled Carbon Nanotube-Based Optical Sensors Via Data Analytics
Authors: Heller Daniel A. , Yaari Zvi A , Kim Mijin , Yang Yoona , Chen Chen , Antman-Passig Merav , Wang Peng , Wang YuHuang , Zheng Ming , Jagota Anand
Published: July 2021

The photoluminescence of single-walled carbon nanotubes (SWCNTs) offers unique advantages for the development of biological sensors, including the potential to sensitize emission to many classes of analytes. Methods to selectively transduce the local concentration of an analyte via an optical signal often involve the attachment of existing molecular recognition elements to the nanotube surface, or the development of selectivities by high-throughput screening or selection techniques. Due to the existence of several mechanisms of optical modulation of SWCNTs, as well as multiple carbon nanotube species with differing bandgaps, and the increasing number of excipients and polymers that can be used for colloidal suspension and non-covalent functionalization, data analytics can be used to facilitate selective recognition of bioanalytes to detect and process multi-parametric spectroscopic fingerprints. These strategies will be discussed for the detection of single and multiplexed analytes.
(Invited) Single Wall Carbon Nanotube Sensors Reveal the Brain’s Chemical Chatter
Authors: Beyene Abraham G.
Published: July 2021

In this work, we will present single wall carbon nanotube optical reporters that can measure spatially and temporally resolved dynamic behavior of neuromodulatory molecules on scales that elude conventional methods of inquiry. We will present work on the performance of such sensors on phenolic and catecholinergic neuromodulators, and introduce new concepts for tuning their performance and selectivity. We will additionally present new approaches for deploying such sensors in biological preparations of varying complexity that permit application of the sensors in ways that improve their overall performance in tissue.
Preclinical Imaging and Spectroscopy in the NIR-II Window with Indocyanine Green (ICG) and Single-Walled Carbon Nanotubes
Authors: Chung Wendy , Galassi Thomas , Harvey Jackson , Baker Hanan , Rioux David , Beaulieu Ouellet Émilie , Moreno Maria , Heller Daniel A.
Published: July 2021

We developed a near-infrared small animal imaging system, IR VIVO, that provides real-time images, videos and spectral imaging in the NIR-I and shortwave infrared (SWIR or NIR-II) regions. We found that SWIR wavelengths can give optimal resolution for in vivo optical imaging of deep organs in mice up to 3 cm due to the low tissue autofluorescence, scattering and absorption of light at these wavelengths. We also showed how this higher penetration depth can enable the detection of small wavelength changes in the emission of carbon nanotube-based sensors implanted in vivo using a continuously tunable filter.

First, we demonstrated superior image clarity and penetration depth at NIR-II wavelengths (1000-1700 nm) in vivo using an FDA approved dye, indocyanine green (ICG) in a mouse. We used 780 nm excitation, detection using a Zephir 1.7 InGaAs camera and 1250 nm long-pass emission filter. We found low tissue autofluorescence at 1250 nm. The ICG dye imaging resulted in superior visualization of microvasculature, perfusion, measurement of hearst rate, respiratory rate, hepatobiliary and intestinal contractions. Further anatomical and functional imaging was carried out by looking at the kinetics of ICG, resulting in the identification of different organs.

Second, In vivo near-infrared hyperspectral imaging of carbon nanotubes was conducted using a continuously-tunable filter in the imager. A diffraction volume Bragg grating (VBG), was used to provide narrow-band wavelength selection. Coupled with a homogeneous global illumination, spectrally-defined images were acquired in the entire field of view. The result was a dataset containing both 2D spatial information and the full spectrum for each point in the image. We conducted near-infrared hyperspectral imaging of single-walled carbon nanotubes to measure small wavelength changes of the nanotubes implanted into live mice. Hyperspectral measurements of carbon nanotube sensors for lipids in the liver as well as implantable sensors for doxorubicin were conducted, facilitating liver disease monitoring and drug pharmacokinetics measurements.

Finally, we believe wide-area NIR-II imaging and spectral/hyperspectral measurements have broad potential applications for the use of carbon nanotubes and other NIR-I/II materials in basic materials/biology, translational, and clinical work, including sensor arrays, point-of-care measurements, implants, whole small animal imaging and intraoperative/surgical imaging.
(Invited) Photostability of Core-Shell Structures at Low Temperature
Authors: Orcin-Chaix Lucile , Campidelli Stephane , Rondin Loic , Chassagneux Yannick , Voisin Christophe , Lauret Js
Published: July 2021

The use of carbon nanotubes as single emitters is currently developing. Being made only of surface

atoms carbon nanotubes are very sensitive to their environment. A fingerprint of this sensitivity is the

variation with time of their emission intensity (blinking) and energy (spectral jitter) in low temperature

experiments. To improve the stability of nanotubes, we have synthesized core-double shell structures

where two shells of polymers are rolled around the nanotube [1]. Here, we will show the influence of

these shells on the stability of both the emission intensity and energy [2].

[1] L. Orcin-Chaix et al, Journal of Material Chemistry C 6, 4786 (2018)

[2] L. Orcin-Chaix et al, ACS Appl. Nano Mater. 3, 7291-7296 (2020).
(Invited) Toward Spectral Homogeneity in Guanine Functionalized SWCNTs
Authors: Soltani Nima , Bachilo Sergei M. , Weisman R. Bruce
Published: July 2021

Different chiralities of single-walled carbon nanotubes (SWCNTs) have distinct electronic and optical properties, with a range of band gaps that make them appropriate for several opto-electronic applications. Due to the unusually high mobility of charge carriers in SWCNTs,1 semiconducting SWCNTs may find use as logic gates in future high-speed nano-electronic circuits. With this in mind, controlled modulation of the optical and electronic properties of individual carbon nanotubes may be valuable in optoelectronic and nano-bioelectronic applications.

It was recently discovered that when SWCNTs coated with single-stranded DNA are exposed to singlet oxygen, the guanine nucleobases in the DNA coatings form covalent bonds to the nanotube sidewalls.2 This alters the nanotube electronic and optical properties, allowing spatial and energetic control through selection of the DNA base sequence. However, the functionalized products display undesired spectral broadening interpreted as excess inhomogeneity compared to the pristine SWCNT reactants.

Here we will present the results of efforts to understand and reduce this inhomogeneity. Our study has used molecular dynamics simulations of ssDNA – SWCNT hybrid structures, as well as analysis of experimental data. We have explored the effects of varied reaction conditions, including temperature, ionic strength, and pH on product yields and spectra. An unexpected inverse dependence of functionalization density on reaction temperature was uncovered. We will also present photophysical results extracted from spectral data via statistical modeling, including the energy depth of localized exciton quantum wells created by functionalization. The analysis points to fluorescence red shifts that reflect the random number of functionalization sites felt by excitons.

Dürkop, T.; Getty, S. A.; Cobas, E.; Fuhrer, M. S. Extraordinary Mobility in Semiconducting Carbon Nanotubes. Nano Lett.
2004, 4, 35-39.

Zheng, Y.; Bachilo, S. M.; Weisman, R. B. Controlled Patterning of Carbon Nanotube Energy Levels by Covalent DNA Functionalization. ACS Nano
2019, 13, 8222-8228.
(Invited) The Moiré Structure of Double Walled Carbon Nanotubes Affects Their Electronic and Vibrational States
Authors: Gordeev Georgy , Wasserroth Soeren , Li Han , Flavel Benjamin S , Reich Stephanie
Published: July 2021

Double walled carbon nanotubes (DWCNT) are formed from two concentric single walled carbon nanotubes. They are a one-dimensional moiré system where the coupling strength between the two walls varies greatly depending on the atomic structure of the two tubes. In this talk we discuss the effect of moiré coupling on the electronic and vibrational states of DWCNTs. We focus on the regime of strong moiré coupling and the combination of semiconducting inner and semiconducting outer tube. For such DWCNTs moiré coupling leads to a red-shift of most optical transition energies. The coupling also affects the frequency of the radial breathing mode (RBM), which is an unexpected finding in connection with moiré interaction. We predict a linear correlation between the change in RBM frequency and in optical transition energy. To verify our predictions we will present resonant Raman experiments on DWCNTs sorted by metallic character. We show that the splitting of the RBM frequencies in DWCNT samples is a clear manifestation of the moiré coupling and construct a Kataura plot for the assignment of double walled tubes. Using resonance Raman profiles of the RBM we confirm the correlation between electronic and vibrational shifts. We also discuss the effect of dielectric screening on the Raman intensities. Our work shows how moiré coupling can strongly affect the vibrational in addition to the electronic and optical states of a one-dimensional system.
(Invited) Combining Absorption, Wavelength-Dependent Raman and Fluorescence-Excitation Spectroscopy with High-Resolution Transmission Electron Microscopy for Determining the Chiral Purity of Sorted SWCNT Samples
Authors: Cambré Sofie , Forel Salome , Castan Alice , Defillet Joeri , Levshov Dmitry , Fossard Frederic , Wenseleers Wim , Loiseau Annick
Published: July 2021

Single-wall carbon nanotubes (SWCNTs) possess unique electronic and optical properties that depend strongly on their exact chiral structure. Recent progress in the structure sorting of specific SWCNT chiralities, with increasing chiral purity[1], demands an effective characterization methodology to be developed to accurately determine the chiral composition of any SWCNT chirality. Very often, optical spectroscopy is used to assess the chiral composition of a sample, but absorption cross-sections, PL quantum efficiencies and Raman cross-sections are all depending on the exact chiral structure,[2] and can be strongly influenced by other factors such as the specific internal and external environment of the SWCNTs.[3] In this work, we systematically compare the chirality distribution obtained from 3 different optical spectroscopic techniques, i.e. absorption, wavelength-dependent Raman and fluorescence-excitation spectroscopy with the chirality distribution obtained from high-resolution transmission electron microscopy for both chirality-sorted and unsorted SWCNT samples. This combined approach demonstrates the importance of using a multi-technique characterization strategy for a reliable determination of SWCNT chirality distribution.[4]

[1] J.A. Fagan, Nanoscale Adv. 1, 3307 (2019) and references therein

[2] V.N. Popov, Nano Lett. 4, 1795 (2004)

[3] S. Cambré et al, Angew. Chem. – Int Ed. 50, 2764 (2011); ACS nano 6, 2649 (2012)

[4] A. Castan et al, Carbon 171, 968 (2021)
(Invited) Tuning the Properties of Luminescent Defects in Carbon Nanotubes for Applications
Authors: Zaumseil Jana
Published: July 2021

Luminescent sp3-defects (also called quantum defects or organic color centers) in single-walled carbon nanotubes (SWCNTs) with their characteristic red-shifted emission and long photoluminescence (PL) lifetimes enable higher PL quantum yields and single-photon emission at room temperature. They can be created in a controlled manner on polymer-wrapped semiconducting nanotubes via diazonium chemistry in organic solvents with a variety of functional substituents [ACS Nano
2019, 13, 9259]. Here we show, how attaching the stable and neutral perchlorotriphenylmethyl (PTM) radical to such sp3-defects impacts their emissive properties in dispersion at room temperature as well as under strong magnetic fields at cryogenic temperatures. Furthermore, the type of defect emission (E11* or E11*-) is governed by the precise binding configuration for chiral (6,5) SWCNTs. We introduce a simple synthetic protocol to obtain exclusively the more red-shifted E11*--defect emission with even longer PL lifetime and high single-photon purity. This new functionalization method relies on nucleophilic addition instead of radical-based reactions and can be transferred to other polymer-sorted nanotubes, e.g. (7,5) and (10,5) SWCNTs. The achieved tunability and control of sp3-defect emission facilitates applications in electroluminescent devices, radiative pumping of exciton-polaritons in metal-clad microcavities [ACS Photonics
2020, DOI: 10.1021/acsphotonics.0c01129] or in-vivo imaging in the 2nd biological window.
(Invited) Tailoring of Single-Walled Carbon Nanotube Luminescence as Photoswitchable Near-Infrared Emitters
Authors: Godin Antoine , Setaro Antonio , Gandil Morgane , Haag Rainer , Adeli Mohsen , Reich Stephanie , Cognet Laurent
Published: July 2021

Single-molecule localization microscopy (SMLM) has set a new paradigm in the field of optical imaging by delivering super-resolution images i.e. with resolution much better than the diffraction limit. We demonstrated over the last years that such approaches can be designed to understand basic excitonic processes in carbon nanotubes [1-2]. In the field of bioimaging, SMLM is currently limited to the visible or far-red range, missing the near-infrared region where biological tissues are however the most transparent. One reason for this is that single-molecule emitter optical properties still need to be tailored in the near-infrared, including photoswitching capabilities which is a basic ingredient to achieve single-molecule SMLM. To fill this gap, optical imaging of single-wall carbon nanotubes can first be greatly facilitated in brain tissues by covalent functionalization of luminescent defects, reducing the required excitation light intensity by one order of magnitude [3]. In addition, we have introduced a novel type of hybrid nanomaterials consisting of single-wall carbon nanotubes covalently functionalized with photo-switching molecules that are used to control the intrinsic luminescence of the single nanotubes in the near-infrared (beyond 1 µm) [4]. Through the control of photoswitching, we demonstrate super-localization imaging of nanotubes unresolved by diffraction limited microscopy opening the route toward SMLM in the near-infrared for biological applications. Photocontrol of individual near-infrared emitters will also be highly desirable for elementary optical molecular switches or information storage elements since most communication data transfer protocols are established in this spectral range.

References

[1] Cognet et al Nanoletters, 8 (2008) 749 - 753.

[2] Danné et al. ACS Nano, 12 (2018) 6059

[3] Mandal et al. Scientific Reports, 10 (2020) 5286

[4] Godin et al Science Advances, 5, (2019) eaax1166
Tailoring the Spectral Properties of Single-Wall Carbon Nanotube Samples through Structure-Selective Photochemistry
Authors: Zheng Yu , Espinoza Vanessa Briana , Bachilo Sergei M. , Weisman R. Bruce
Published: July 2021

The structural heterogeneity in mixed SWCNT samples results in extensive spectral complexity that can hamper a range of basic and applied research efforts. One approach to solving this problem is post-growth sorting, which unfortunately involves well known challenges. Here we report a photochemical strategy for spectral tailoring that uses monochromatic near-infrared (NIR) irradiation to selectively alter semiconducting (n,m) species based on their distinct and characteristic E11 optical transitions. This process does not physically isolate the targeted species, but it allows optical properties of the mixture to be modified without the need for physical separations. Our method achieves selective fluorescence quenching in aqueous dispersions of SWCNTs through irradiation of E11 transitions by NIR diode lasers in the presence of dissolved oxygen. Fluorescence emission from SWCNT species with transitions near the excitation wavelength is significantly and permanently suppressed, while the corresponding E11 absorptions are bleached and Raman D bands intensify. Results will be presented for several different oxygen headspace pressures and for wavelength-dependent irradiation data, which suggest a threshold consistent with the involvement of singlet O2. The method of near-IR photochemical tailoring may be useful for controlling SWCNT emission spectra in applications such as spectral bar-coding and strain sensing.
(Invited) Ab Initio Exciton and Phonon Dynamics in Transition Metal Dichalcogenides
Authors: Melo Pedro , Zanolli Zeila , Verstraete Matthieu
Published: July 2021

Interest in the properties of transition metal dichalcogenides (TMDs) has increased due to the discovery of the coupling between spin and valley degrees of freedom, which can be seen experimentally using a circularly polarised laser. After excitation the newly formed carrier populations must move towards the other valley until balance is reached. However, this relaxation process is not entirely understood in the literature, where the relative importance of the electron-electron (e-e) or electron-phonon (e-p) interactions is still a subject of debate. Previous works on WSe2 [A. Molina- Sánchez, et al - Nano letters, 2017] have shown that the e-p interaction is a good candidate to describe the relaxation process. Using a fully ab-initio framework based on the Baym-Kadanoff equations [P. M. M. C. de Melo and A. Marini, Phys. Rev. B 93, 155102 (2016)] we study the influence of the e-p interaction on MoSe2 after its excitation by a laser field. We show how phonons allow carrier relaxation and how the Kerr signal and total magnetisation are affected at different temperatures, with the latter exhibiting a non-monotonic behaviour as the temperature increases [M Ersfeld et al - Nano Letters 2019
19 (6), 4083-4090]. An important conclusion is that long lived spin states probably reside within defects. We calculate the spectral signatures of point defects in TMDs, finding two main classes based on the presence of in-gap states, and estimating the experimental resolution needed to provide quantification of the defect concentration [P de Melo et al. https://arxiv.org/abs/2010.10222]. The localization of excitonic states around the defect provides a benchmark for scanning probe characterization (figure shows a S vacancy exciton wave function, the green ball is the hole position).

Figure 1
(Invited) Light Emission Modulation from Individual Single-Walled Carbon Nanotubes By Chromophore Encapsulation
Authors: Chambard Romain , Izard Nicolas , Jousselme Bruno , Sato Yuta , Kazu Suenaga , Jean-Louis Bantignies , Patrick Hermet , Alvarez Laurent
Published: July 2021

The one-dimensional structure of single-walled carbon nanotubes (NT) display optical absorption and near-infrared emission (thanks to van Hove singularities). Chromophore encapsulation into host single-walled carbon nanotubes allows to create hybrid nano-systems with tunable opto-electronic properties. Up to now, we have been confining different kinds of chromophores,1-4 absorbing from the blue/ green (400/500 nm) range (tetracyanoquinodimethane (TNCQ), quaterthiophene derivatives (4T) and tetramethyl-paraphenylenediamine (TMPD)) to the red (700 nm) range (phthalocyanine (MPc)). In addition then can be either electron donor (4T, TMPD) or acceptor (TNCQ).

In this study, we investigate, at both the macroscopic and the individual scales, the electronic and the optical properties of our hybrid systems by means of Raman and photoluminescence spectroscopies.

Photoluminescence experiments clearly demonstrate changes on the emission properties after encapsulation. The intensities can be increased or reduced depending on the nature of the confined chromophores (electron donor or acceptor) and on the NT diameter.

From Raman measurements, a significant charge transfer from the confined dye to the nanotube is evidenced. The main relevant parameters that govern the charge transfer are the nanotube diameter and the nature of the chromophores (electron donor or acceptor).

Therefore, Raman and photoluminescence experiments strongly suggest charge transfer between the confined molecules and the nanotubes, leading to a Fermi level shift which governs the radiative de-excitation efficiency.

References

[1] L. Alvarez et al, J. Phys. Chem. C, 119, (2015), pp. 5203−5210

[2] Y. Almadori et al, J. Phys. Chem. C; 118, (2014), pp. 19462−19468

[3] A. Belhboub et al, J. Phys. Chem. C; 120, (2016), pp. 28802−28807

[4] Y. Almadori et al, Carbon 149, (2019), pp. 772-780
The Impact of Fiber Arrangement on Power Density and Electrodeposition in Porous Ag-Trab Electrodes
Authors: Cross Nicholas , Hall Derek M , Lvov Serguei , Logan Bruce , Rau Matthew
Published: July 2021

As the need for a sharp reduction in carbon emissions continues to grow, many researchers are looking to electrochemical technologies to provide sustainable power to the grid. One promising technology is the silver thermally regenerative ammonia battery (Ag-TRAB), which is a new approach for converting low-grade waste heat (<100 °C) to electrical power. These hybrid flow batteries are charged using energy derived from waste heat, rather than electrical power, and can be cycled hundreds of times without a decrease in performance. The Ag-TRAB uses silver as the active metal ion for deposition and dissolution on each half of the battery and porous carbon as the electrode material, driven by ammonia added into only one chamber. Following a discharge cycle, ammonia is removed using waste heat, and a new cycle is initiated using the ammonia added to the opposite electrolyte chamber. Design factors that impact operational conditions and performance are needed to improve reliability and electrode utilization. For example, the structure of the porous electrodes could alter silver deposition rates and porosities of the electrodes during operation, leading to preferential flow paths from clogging of pores that would impact cycle longevity and power.

A 2D numerical model was created using COMSOL Multiphysics to study the relationship between fluid flow, electrode structure, and electrodeposition in the porous electrodes using cylinders in cross-flow to represent the internal structure of a porous carbon fiber electrode. Lower void fractions resulted in 2.5% higher power density, but less uniform deposition and the pores clogging 3-5 times faster due to nonuniform deposition normal to the membrane boundary. It was found that the electric field resultant from the void fraction and fiber arrangement was critical to the performance of the electrode. The electrode microstructure can be modified to better distribute the deposition rate relative to the pore size to allow for higher power output for a longer discharge time before the pores begin to clog. An electrode with variable void fraction increased the peak power by 7.5% but the pores clogged 23% faster compared to homogenous void fraction.
Theoretical Study of Small-Sized Carbon Clusters and the Formation of Fullerene Cages
Authors: Gan Li-Hua
Published: July 2021

Systematical DFT study on small-sized carbon chains, rings, bowls and cages are performed. For carbon chains, the results show that the end bond will shorten compared with its nearest adjacent bond; the bond lengths are not alternated but symmetrically distributed based on the central atom (odd-number chains) and the middle point (even-number chains). Odd-number carbon chains are singlet and even-number chains are triplet. The diffidence in lengths of adjacent two bonds is slightly and much smaller than the length difference between triple and single bond in C2H2 and C2H6. All theoretical evidences here show that linear chains of carbon are polyene not polyalkyne. For carbon rings, their highest symmetrical (Dnh) isomers of Cn are not lowest energy ring isomers except for C25-Ring. For carbon cages, the interesting findings include (1) a new non-classical isomer of C24 is found to be more favored than the classical one which was reported to be most favored; (b) a new non-classical isomer of C26 is found to be more favored than the classical one which was reported to be the 2nd favored; (c) Small cages welcome strained square(s); and (d) The favored cages of them are structurally related to direct C2 insertion/extrusion. Comprehensive comparison show that carbon chains are more favored than rings and cages when n≤9,however, rings are more favored than chains when 10≤n≤20; Bowls/sheets are more favored than cages energetically for clusters of Cn with 18≤n≤24; The cages are increasing favorable and become dominant species when n≥26. These results clearly suggest the structural evolution from chains to rings or bowls and cages in turn.
(Invited) Porphyrinoid-Carbon Nanostructure Ensembles
Authors: Torres Tomas , López-Serrano Elisa , Martínez-García Miguel , Mateo Luis M. , Labella Jorge , Bottari Giovanni , Martinez-Diaz M.Victoria , Ince Mine
Published: July 2021

The development of new chromophoric receptors able to bind curved carbon nanostructures is at the epicenter of the quest for fullerene-based organic photovoltaics with improved performances. Herein, a subphthalocyanine-based multicomponent ensemble consisting of two electron-rich SubPc-monomers rigidly attached to the convex surface of a electron-poor SubPc-dimer has been synthesized and characterized. Such a unique conformation, especialy in terms of the two SubPc-monomers, together with the overall stiffness of the tether endows the multicomponent system with a well-defined tweezer-like topology to efficiently embrace a fullerene in its inner cavity. On the other hand, the selective on-surface synthesis of a porphyrin-graphene nanoribbon hybrid has been accomplished. The atomically precise structure of the hybrid has been unambiguously characterized by bond-resolved scanning tunneling microscopy and noncontact atomic force microscopy. Finally, a novel electron donor-acceptor hybrid consisting of a NIR absorbing azulenocyanine as electron donor and few-layer graphene as electron acceptor was prepared. The extended aromatic core of azulenocyanine assist in the exfoliation of graphite and allows formation of a very high-quality few-layer graphene azulenocyanine hybrid system.
Impedance Spectroscopy Study of Fiber-Based Supercapacitors for Wearable Electronics Applications
Authors: Kareri Tareq , Yadav Rohit L , Takshi Arash
Published: July 2021

Recently, the interest in wearable electronics technology has been increasing to replace conventional electronics in the near future, especially for body sensors, smart glasses, or smart watches applications. Therefore, major research efforts are needed to develop flexible energy storage devices with high electrochemical and mechanical performance. Herein, we have studied the effect of fiber structure on the impedance of the fiber-based supercapacitors. The fiber-based supercapacitors were fabricated in a two-electrode configuration combining two twisted conductive threads as electrodes and a gel electrolyte between them. Five different brands of commercially available conductive threads from Jameco, JL Fiber, BCP, 6K carbon (from easy composites), and Electronics123 Fiber were tested with different twisting structures based on the number of twists per length. The impedance of the devices was tested using the electrochemical impedance spectroscopy method to study the effect of twisting on the device's performance. The results exhibit that the Jameco thread with a capacitance of 2 mF/cm and series resistance of 1.8 Ω/cm has the highest capacitance compared to the other devices, with a lower internal resistance due to the large interface area between the electrodes and the electrolyte. The current results are inspiring the research for developing flexible and low-cost fiber-based supercapacitors to develop the emerging field of wearable electronics technology.
(Invited) From the Top or through the Edge: What Is the Most Scalable Contact to 2D Semiconductors?
Authors: Franklin Aaron D
Published: July 2021

The most common approach for establishing electrical contacts to 2D semiconductors, such as MoS2, is by fabricating metal contacts on top of the inert crystal surface. From an electron transport perspective, these top-contact interfaces can be awkward, with a van der Waals gap or some difficult-to-control form of interfacial bonding. Pure edge contacts (where the interface between the metal and 2D semiconductor occurs completely along the open bonds of the 2D crystal edge) provide a more natural bonding structure and potentially better carrier transport behavior; however, edge contacts have proven more difficult to realize. In this talk, recent success with establishing clean, pure edge contacts between metals and 2D semiconductors will be discussed, including an approach involving an in situ ion beam within a thin-film deposition system. Evaluation of these edge contacts compared to other approaches will be provided, along with demonstration of how edge-contact scaling affects the performance of 2D transistors compared to top-contact scaling. While there remains much to be learned about these interesting metal-2D edge interfaces, results thus far show significant promise for yielding a more scalable and potentially reproducible contact for 2D-based devices.
(Invited) Fluorescence Quenching Microscopy for Imaging 2D Materials: An Update
Authors: Huang Jiaxing
Published: July 2021

Fluorescence quenching microscopy (FQM) was initially developed for high throughput imaging of graphene based sheets on arbitrary substrates under a common fluorescence microscopy. It takes advantages of the long range, energy transfer-based fluorescence quenching effect of graphene-based materials, and can obtain images with high contrast and high layer resolution comparable to those of scanning electron microscopy (SEM) and atomic force microscopy (AFM). FQM was later applied to image other strongly quenching sheets such as transitional metal dichalcogenides.

The high-contrast optical imaging of nearly transparent 2D materials such as clays and some oxides sheets has been an outstanding challenge; yet it is a critical research capability needed in the synthesis and processing of these materials, which have shown promise in a number of applications including barrier coatings, membranes, and composites. Using delaminated silicate clay and titania sheets as model system, here we show that these weakly quenching, nearly transparent 2D sheets can also be readily imaged by FQM based on a new mechanism with SEM and AFM level of contrast and layer resolutions. When different 2D materials are co-deposited, FQM not only differentiates them readily based on their quenching capabilities, but also can resolve their vertical stacking sequence based on the contrast of their overlapped areas.
(Invited) Controlling Monolayer and Few-Layer MoS2 and WS2 Optoelectronic and Catalytic Properties
Authors: Miller-Link Elisa
Published: July 2021

By functionalizing, doping, and changing phases, we can control the optoelectronic and catalytic properties of 2D transition metal dichalcogenides (TMDCs), specifically MoS2 and WS2. These 2D layered nanomaterials can be made via a top-down (exfoliation) or bottom-up (chemical vapor deposition) approach. The optoelectronic properties of monolayer TMDCs are strongly influenced by their surroundings and can be used as a humidity sensor, which we demonstrate with photoluminescence and time-resolved microwave conductivity measurements. Furthermore, we quantify the stability of metallic, monolayer TMDCs when it is converted from the semiconducting to the metallic phase and functionalized, where comparisons are made to few-layer TMDCs. By controlling these optoelectronic properties, we can better understand the catalytic performance for hydrogen evolution and other other catalytic reactions.
(Invited) Scanning Photoelectrochemical Microscopy Reveals Doping Heterogeneity in Exfoliated MoS2 Nanosheets
Authors: Sambur Justin
Published: July 2021

Transition metal dichalcogenide (TMD) thin films are attractive for photoelectrochemical synthesis and energy conversion applications. One strategy to prepare large area films at low cost is to exfoliate nanoflakes from bulk samples such as MoS2 or WS2 powders or crystals. However, the exfoliated films often exhibit poor photoelectrochemical properties compared to single crystal photoelectrodes. Here we compare the photoelectrochemical performance of MoS2 nanoflakes prepared by mechanical exfoliation of bulk crystals from two commercial manufacturers. Ensemble-level photo electrochemical measurements show that, on average, both samples are n-type MoS2. However, scanning photocurrent microscopy measurements reveal that the low efficiency sample exhibits doping heterogeneity at the single nano flake-level. Interestingly, a single nanoflake exhibits highly efficient p-type domains within a dominantly n-type flake. Raman spectroscopy and laser reflection microscopy experiments are used to characterize the nature of the p-type domains.
(Invited) Fundamentals and Applications of Hexagonal Boron Nitride Ionogels
Authors: Hersam Mark C
Published: July 2021

Ionogel electrolytes based on ionic liquids (ILs) and a gelling solid matrix are an attractive alternative to conventional liquid electrolytes for electronic and energy storage applications. In particular, ILs offer several advantages as an electrolyte including nonflammability, nonvolatility, high electrochemical stability, and high ionic conductivity. Moreover, combining ILs with a gelling solid matrix leads to a solid-state electrolyte that is sufficiently mechanically robust to replace both the liquid electrolyte and separator in a single component, thus allowing easier packaging, streamlined manufacturing, and minimal risk of leakage [1]. For ionogel electrolytes, hexagonal boron nitride (hBN) is an especially desirable solid matrix due to its excellent chemical and thermal stability in addition to its mechanical robustness [2]. This talk will address recent efforts to realize high-performance hBN/IL ionogel electrolytes using hBN that has been solution-exfoliated into two-dimensional nanosheets using ethyl cellulose (EC) stabilizing polymers [3]. In addition to the intrinsic advantages of hBN, EC-exfoliated hBN nanosheets significantly enhance both ionic conductivity (> 1 mS/cm) and mechanical strength (storage modulus > 1 MPa) compared to conventional hBN microparticles, providing additional competitive advantages for energy storage applications [4]. The high thermal stability of hBN/IL ionogel electrolytes also enables safe, high-rate operation (up to 10C charge/discharge rate) at high temperatures up to 175 °C, which represents the highest operating temperature to date for solid-state lithium-ion batteries. Since hBN ionogels can also be formulated into printable inks [5], they are particularly promising for printed devices including electrolyte-gated thin-film transistors, supercapacitors, and batteries.

[1] A. C. M. de Moraes, et al., ACS Applied Materials & Interfaces, 12, 8107 (2020).

[2] W. J. Hyun, et al., Advanced Energy Materials, 10, 2002135 (2020).

[3] A. C. M. de Moraes, et al., Advanced Functional Materials, 29, 1902245 (2019).

[4] W. J. Hyun, et al., ACS Nano, 13, 9664 (2019).

[5] W. J. Hyun, et al., Faraday Discussions, DOI: 10.1039/C9FD00113A (2020).