arXiv subjects

Benjamin S. Flavel

Publications and source records attributed to Benjamin S. Flavel.

14 recordsLinked to original sources

arXiv2026

Direct Realization of Near-Ideal Carbyne in Ultrathin Boron Nitride Nanotubes

Carbyne, the sp-hybridized one-dimensional allotrope of carbon, is predicted to be the stiffest known material, with electronic and optical properties set by a single structural parameter, the bond length alternation. However, its intrinsic properties have never been measured: chains synthesized through molecular chemistry carry endgroup and finite-length perturbations that persist even in the longest molecules available, while chains grown inside carbon nanotubes strongly couple to the host, which renormalizes their vibrational frequency by up to 110 cm$^{-1}$ in a diameter-dependent manner. Here, we show that encapsulating and thermally converting hydrogen-capped polyynes inside ultrathin boron nitride nanotubes, structural analogues of carbon nanotubes but electrically insulating, yields carbyne chains in a near-ideal regime, where endgroup, finite length, and host-guest perturbations are reduced to secondary effects. Statistical Raman spectroscopy across 245 locations returns a vibrational frequency distribution an order of magnitude narrower than in carbon nanotubes, an anharmonicity consistent with the universal law for carbyne-like materials, and a bond length alternation matching correlated calculations for the free chain. No photoluminescence is detected, despite the transparent host, as expected for the dipole-forbidden emission of an unperturbed carbyne chain. Boron nitride nanotubes give experimental access to carbyne in its near-ideal form.

cond-mat.mes-hall↗

arXiv2026

Comparative Evaluation of Encapsulation Methods for Endohedral Doping of Single-Wall Carbon Nanotubes

Single wall carbon nanotubes (SWCNTs) are promising building blocks for nanoelectronic and optoelectronic devices, yet reliable and stable doping, particularly n type, remains challenging due to strong environmental sensitivity and competing extrinsic effects. Encapsulation of charge transfer molecules within the SWCNT cavity offers a promising route to stable doping while preserving the nanotubes outer surface for subsequent processing. Here, we systematically investigate the filling of arc discharge SWCNTs with the electron donor tetrathiafulvalene and electron acceptor tetracyanoquinodimethane, comparing different methods for filling, including melt filling, solution reflux, and vacuum phase sublimation. We follow the entire processing workflow from raw, unfilled powders to aqueous dispersions and employ density gradient ultracentrifugation to separate filled from empty nanotubes as well as metallic from semiconducting ones. Encapsulation efficiency and electronic modification are assessed using absorption spectroscopy, resonant Raman scattering, thermogravimetric analysis, and electron paramagnetic resonance. Finally, we introduce a complementary vacuum-phase method that removes externally adsorbed molecules without extensive solvent washing, enabling cleaner encapsulated systems.

cond-mat.mes-hall↗

arXiv2025

Ultrashort Carbon Nanotubes with Luminescent Color Centers are Bright NIR-II Nano-Emitters

In the fields of bioimaging, photonics, and quantum science, it is equally crucial to combine high brightness with nanoscale size in short-wave infrared (SWIR) emitters. However, such nano-emitters are currently lacking. Here, we report that when functionalized with luminescent color centers, ultrashort carbon nanotubes with length much shorter than 100 nm, are surprisingly bright in the near-infrared second-biological window (NIR-II) of the SWIR domain. We discuss the origin of this exceptional brightness based on the uncontrollable presence of quenching defects in dispersed carbon nanotubes. We further investigate the nonlinear photoluminescence behavior of color centers functionalized carbon nanotubes in response to varying excitation conditions, spanning from ensemble measurements to single-nanotube experiments. We discuss how this behavior influences the determination of their photoluminescence quantum yields, which can reach values as high as 20% for ultrashort ones detected at the single nanotube level. Notably, the corresponding NIR-II brightness exceeds that of well-known visible emitters, including quantum dots. After rendering them biocompatible, we demonstrate point-spread function engineering and high-resolution, 3-dimensional single-particle tracking using these bright ultrashort carbon nanotubes allowing nanoscale imaging in the NIR-II window within thick brain tissue.

cond-mat.mtrl-sci↗

arXiv2024

How to Recognize Clustering of Luminescent Defects in Single-Wall Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (SWCNTs) are a promising material platform for near-infrared in-vivo imaging, optical sensing, and single-photon emission at telecommunication wavelengths. The functionalization of SWCNTs with luminescent defects can lead to significantly enhanced photoluminescence (PL) properties due to efficient trapping of highly mobile excitons and red-shifted emission from these trap states. Among the most studied luminescent defect types are oxygen and aryl defects that have largely similar optical properties. So far, no direct comparison between SWCNTs functionalized with oxygen and aryl defects under identical conditions has been performed. Here, we employ a combination of spectroscopic techniques to quantify the number of defects, their distribution along the nanotubes and thus their exciton trapping efficiencies. The different slopes of Raman D/G+ ratios versus calculated defect densities from PL quantum yield measurements indicate substantial dissimilarities between oxygen and aryl defects. Supported by statistical analysis of single-nanotube PL spectra at cryogenic temperatures it reveals clustering of oxygen defects. The clustering of 2-3 oxygen defects, which act as a single exciton trap, occurs irrespective of the functionalization method and thus enables the use of simple equations to determine the density of oxygen defects and oxygen defect clusters in SWCNTs based on standard Raman spectroscopy. The presented analytical approach is a versatile and sensitive tool to study defect distribution and clustering in SWCNTs and can be applied to any new functionalization method.

cond-mat.mtrl-sci↗

arXiv2024

Easy Access to Bright Oxygen Defects in Biocompatible Single-Walled Carbon Nanotubes via a Fenton-Like Reaction

The covalent functionalization of single-walled carbon nanotubes (SWNTs) with luminescent oxygen defects increases their brightness and enables their application as optical biosensors or fluorescent probes for in-vivo imaging in the second-biological window (NIR-II). However, obtaining luminescent defects with high brightness is challenging with the current functionalization methods due to a restricted window of reaction conditions or the necessity for controlled irradiation with ultraviolet light. Here we report a method for introducing luminescent oxygen defects via a Fenton-like reaction that uses benign and inexpensive chemicals without light irradiation. (6,5) SWNTs in aqueous dispersion functionalized with this method show bright $E_{11}$* emission (1105 nm) with 3.2-times higher peak intensities than the pristine $E_{11}$ emission and a reproducible photoluminescence quantum yield of 3%. The functionalization can be performed within a wide range of reaction parameters and even with unsorted nanotube raw material at high concentrations (100 mg/L), giving access to large amounts of brightly luminescent SWNTs. We further find that the introduced oxygen defects rearrange under light irradiation, which gives additional insights into the structure and dynamics of oxygen defects. Finally, the functionalization of ultra-short SWNTs with oxygen defects also enables high photoluminescence quantum yields and their excellent emission properties are retained after surfactant exchange with biocompatible pegylated phospholipids or single-stranded DNA to make them suitable for in-vivo NIR-II imaging and dopamine sensing.

cond-mat.mtrl-sci↗

arXiv2024

Dielectric Screening Inside Carbon Nanotubes

Dielectric screening plays a vital role for the physical properties in the nanoscale and also alters our ability to detect and characterize nanomaterials by optical techniques. We study the dielectric screening inside of carbon nanotubes and how it changes electromagnetic fields and many-body effects for encapsulated nanostructures. First, we show that the local electric field inside a nanotube is altered by one-dimensional screening with dramatic effects on the effective Raman scattering efficiency of the encapsulated species for metallic walls. The scattering intensity of the inner tube is two orders of magnitude weaker than for the tube in air, which is nicely reproduced by local field calculations. Secondly, we find that the optical transition energies of the inner nanotubes shift to lower energies compared to a single-walled carbon nanotubes of the same chirality. The shift is higher if the outer tube is metallic than when it is semiconducting. The magnitude of the shift suggests that the excitons of small diameter inner metallic tubes are thermally dissociated at room temperate if the outer tube is also metallic and in essence we observe band-to-band transitions.

cond-mat.mes-hall↗

arXiv2024

Ratiometric fluorescent sensing of pyrophosphate with sp$^{3}$-functionalized single-walled carbon nanotubes

Inorganic pyrophosphate is a key molecule in many biological processes from DNA synthesis to cell metabolism. Here we introduce sp$^{3}$-functionalized (6,5) single-walled carbon nanotubes (SWNTs) with red-shifted defect emission as near-infrared luminescent probes for the optical detection and quantification of inorganic pyrophosphate. The sensing scheme is based on the immobilization of Cu$^{2+}$ ions on the SWNT surface promoted by coordination to covalently attached aryl alkyne groups and a triazole complex. The presence of Cu$^{2+}$ ions on the SWNT surface causes fluorescence quenching via photoinduced electron transfer, which is reversed by copper-complexing analytes such as pyrophosphate. The differences in the fluorescence response of sp$^{3}$-defect to pristine nanotube emission enables reproducible ratiometric measurements in a wide concentration window. Biocompatible, phospholipid-polyethylene glycol-coated SWNTs with such sp$^{3}$ defects are employed for the detection of pyrophosphate in cell lysate and for monitoring the progress of DNA synthesis in a polymerase chain reaction. This robust ratiometric and near-infrared luminescent probe for pyrophosphate may serve as a starting point for the rational design of nanotube-based biosensors.

physics.app-ph↗

arXiv2023

Near-Intrinsic Photo- and Electroluminescence from Single-Walled Carbon Nanotube Thin Films on BCB-Passivated Surfaces

Their outstanding electrical and optical properties make semiconducting single-walled carbon nanotubes (SWCNTs) highly suitable for charge transport and emissive layers in near-infrared optoelectronic devices. However, the luminescence spectra of SWCNT thin films on commonly used glass and Si/SiO2 substrates are often compromised by broadening of the main excitonic emission and unwanted low-energy sidebands. Surface passivation with a commercially available, low dielectric constant, cross-linked bis-benzocyclobutene-based polymer (BCB) enhances the emission properties of SWCNTs to the same level as hexagonal boron nitride (h-BN) flakes do. The presence of BCB suppresses sideband emission, especially from the Y1 band, which is attributed to defects introduced by the interaction of the nanotube lattice with oxygen-containing terminal groups of the substrate surface. The facile and reproducible deposition of homogeneous BCB films over large areas combined with their resistance against common solvents and chemicals employed during photolithography make them compatible with standard semiconductor device fabrication. Utilizing this approach, light-emitting (6,5) SWCNT network field-effect transistors are fabricated on BCB-treated glass substrates with excellent electrical characteristics and near-intrinsic electroluminescence. Hence, passivation with BCB is proposed as a standard treatment for substrates used for spectroscopic investigations of and optoelectronic devices with SWCNTs and other low-dimensional emitters.

physics.app-ph↗

arXiv2022

Absolute Quantification of sp$^{3}$ Defects in Semiconducting Single-Wall Carbon Nanotubes by Raman Spectroscopy

The functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) with luminescent sp$^{3}$ defects creates red-shifted emission features in the near-infrared and boosts their photoluminescence quantum yields (PLQYs). While multiple synthetic routes for the selective introduction of sp$^{3}$ defects have been developed, a convenient metric to precisely quantify the number of defects on a SWCNT lattice is not available. Here, we present a direct and simple quantification protocol based on a linear correlation of the integrated Raman D/G$^{+}$ signal ratios and defect densities as extracted from PLQY measurements. Corroborated by a statistical analysis of single-nanotube emission spectra at cryogenic temperature, this method enables the quantitative evaluation of sp$^{3}$ defect densities in (6,5) SWCNTs with an error of $\pm$ 3 defects per micrometer and the determination of oscillator strengths for different defect types. The developed protocol requires only standard Raman spectroscopy and is independent of the defect configuration, dispersion solvent and nanotube length.

cond-mat.mtrl-sci↗

arXiv2021

Charge Transfer from Photoexcited Semiconducting Single-Walled Carbon Nanotubes to Wide-Bandgap Wrapping Polymer

As narrow optical bandgap materials, semiconducting single-walled carbon nanotubes (SWCNTs) are rarely regarded as charge donors in photoinduced charge-transfer (PCT) reactions. However, the unique band structure and unusual exciton dynamics of SWCNTs add more possibilities to the classical PCT mechanism.In this work, we demonstrate PCT from photoexcited semiconducting (6,5) SWCNTs to a wide-bandgap wrapping poly-[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(6,6')-(2,2'-bipyridine)] (PFO-BPy) via femtosecond transient absorption spectroscopy. By monitoring the spectral dynamics of the SWCNT polaron, we show that charge transfer from photoexcited SWCNTs to PFO-BPy can be driven not only by the energetically favorable E33 transition but also by the energetically unfavorable E22 excitation under high pump fluence. This unusual PCT from narrow-bandgap SWCNTs toward a wide-bandgap polymer originates from the up-converted high-energy excitonic state (E33 or higher) that is promoted by the Auger recombination of excitons and charge carriers in SWCNTs. These insights provide new pathways for charge separation in SWCNT-based photodetectors and photovoltaic cells.

physics.app-ph↗

arXiv2019

Low-temperature electroluminescence excitation mapping of excitons and trions in short channel monochiral carbon nanotube device

Single walled carbon nanotubes as emerging quantum-light sources may fill a technological gap in silicon photonics due to their potential use as near infrared, electrically driven, classical or non-classical emitters. Unlike in photoluminescence, where nanotubes are excited with light, electrical excitation of single tubes is challenging and heavily influenced by device fabrication, architecture and biasing conditions. Here we present electroluminescence spectroscopy data of ultra short channel devices made from (9,8) carbon nanotubes emitting in the telecom band. Emissions are stable under current biasing and no quenching is observed down to 10 nm gap size. Low-temperature electroluminescence spectroscopy data also reported exhibits cold emission and linewidths down to 2 meV at 4 K. Electroluminescence excitation maps give evidence that carrier recombination is the mechanism for light generation in short channels. Excitonic and trionic emissions can be switched on and off by gate voltage and corresponding emission efficiency maps were compiled. Insights are gained into the influence of acoustic phonons on the linewidth, absence of intensity saturation and exciton exciton annihilation, environmental effects like dielectric screening and strain on the emission wavelength, and conditions to suppress hysteresis and establish optimum operation conditions.

physics.app-ph↗

arXiv2016

Light emission, light detection and strain sensing with nanocrystalline graphene

Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically light matter interaction in graphene is of a broadband type. However by integrating graphene into optical micro cavities also narrow band light emitters and detectors have been demonstrated. The devices benefit from the transparency, conductivity and processability of the atomically thin material. To this end we explore in this work the feasibility of replacing graphene by nanocrystalline graphene, a material which can be grown on dielectric surfaces without catalyst by graphitization of polymeric films. We have studied the formation of nanocrystalline graphene on various substrates and under different graphitization conditions. The samples were characterized by resistance, optical transmission, Raman, X-ray photoelectron spectroscopy, atomic force microscopy and electron microscopy measurements. The conducting and transparent wafer-scale material with nanometer grain size was also patterned and integrated into devices for studying light-matter interaction. The measurements show that nanocrystalline graphene can be exploited as an incandescent emitter and bolometric detector similar to crystalline graphene. Moreover the material exhibits piezoresistive behavior which makes nanocrystalline graphene interesting for transparent strain sensors.

cond-mat.mes-hall↗

arXiv2016

Chiral-Index Resolved Length Mapping of Carbon Nanotubes in Solution Using Electric-Field Induced Differential Absorption Spectroscopy

The length of single-walled carbon nanotubes (SWCNTs) is an important metric for the integration of SWCNTs into devices and for the performance of SWCNT-based electronic or optoelectronic applications. In this work we propose a rather simple method based on electric-field induced differential absorption spectroscopy (EFIDAS) to measure the chiral-index-resolved average length of SWCNTs in dispersions. The method takes advantage of the electric-field induced length-dependent dipole moment of nanotubes and has been verified and calibrated by atomic force microscopy. This method not only provides a low cost, in-situ approach for length measurements of SWCNTs in dispersion, but due to the sensitivity of the method to the SWCNT chiral index, the chiral index dependent average length of fractions obtained by chromatographic sorting can also be derived. Also, the determination of the chiral-index resolved length distribution seems to be possible using this method.

cond-mat.mes-hall↗

arXiv2013

Waveguide-integrated electroluminescent carbon nanotubes

Carbon based optoelectronic devices promise to revolutionize modern integrated circuits by combining outstanding electrical and optical properties into a unified technology. By coupling nanoelectronic devices to nanophotonic structures functional components such as nanoscale light emitting diodes, narrow-band thermal emitters, cavity controlled detectors and wideband electro optic modulators can be realized for chipscale information processing. These devices not only allow the light-matter interaction of low-dimensional systems to be studied, but also provide fundamental building blocks for high bandwidth on-chip communication. Here we demonstrate how light from an electrically-driven carbon-nanotube can be coupled directly into a photonic waveguide architecture. We realize wafer scale, broadband sources integrated with nanophotonic circuits allowing for propagation of light over centimeter distances. Moreover, we show that the spectral properties of the emitter can be controlled directly on chip with passive devices using Mach-Zehnder interferometers and grating structures. The direct, near-field coupling of electrically generated light into a waveguide, opposed to far-field fiber coupling of external light sources, opens new avenues for compact optoelectronic systems in a CMOS compatible framework.

cond-mat.mes-hall↗