Light emissive nanostructures were prepared from boron nitride nanotubes (BNNTs) filled with inorganic lead halide perovskites. These one-dimensional nanocontainers provide a platform for facile synthesis of high aspect ratio perovskite quantum wires having color-tunable, highly polarized emission. BNNTs form a flexible and robust protective shell around individual nanowires, that mitigates degradation during post-processing for practical applications, while allowing to exploit the emission of the perovskite nanowires. The wire diameter can be tuned by choosing appropriate BNNT hosts, giving easy access to well-defined nanowires across the strongly quantum-confined diameter range. The individual encapsulated quantum wires can be used as building blocks for nanoscale photonic devices, and to create large-scale flexible assemblies.

Single-wall carbon nanotubes (SWCNTs) have extraordinary electronic and optical properties that depend strongly on their exact chiral structure and their interaction with their inner and outer environment. The fluorescence (PL) of semiconducting SWCNTs, for instance, will shift depending on the molecules with which the SWCNT's hollow core is filled. These interaction-induced shifts are challenging to resolve on the ensemble level in samples containing a mixture of different filling contents due to the relatively large inhomogeneous line width of the ensemble SWCNT PL compared to the size of these shifts. To circumvent this inhomogeneous broadening, single-tube spectroscopy and hyperspectral imaging are often applied, which until now required time-consuming statistical studies. Here, we present hyperspectral PL microscopy combined with automated SWCNT segmenting based on either principal component analysis or a convolutional neural network, capable of both spatially and spectrally resolving the PL along the length of many individual SWCNTs at the same time and automatically fitting peak positions and line widths of individual SWCNTs. The methodology is demonstrated by accurately determining the emission shifts and line widths of thousands of left- and right-handed empty and water-filled SWCNTs coated with a chiral surfactant, resulting in four statistical distributions which cannot be resolved in ensemble spectroscopy of unsorted samples. The results demonstrate a robust method to quickly probe ensemble properties with single-enantiomer spectral resolution. Moreover, it promises to be an absolute quantitative method to characterize the relative abundances of SWCNTs with different handedness or filling content in macroscopic samples, simply by counting individual species.

Graphene nanoribbons are prepared inside boron nitride nanotubes by liquid phase encapsulation and subsequent annealing of 1,2,4‐trichlorobenzene. The product is imaged with high‐resolution transmission electron microscopy, and characterized by optical absorption and Raman spectroscopy. Carbon‐containing material is detected inside the boron nitride nanotubes with energy‐dispersive X‐ray spectroscopy (EDS) and scanning transmission electron microscopy (STEM). The observed structures twist under the electron beam and the characteristic features of nanoribbons appear in the Raman spectra.

Growing graphene nanoribbons from small organic molecules encapsulated in carbon nanotubes can result in products with uniform width and chirality. We propose a method based on encapsulation of 1,2,4-trichlorobenzene from the liquid phase and subsequent annealing. This procedure results in graphene nanoribbons several tens of nanometers long. The presence of nanoribbons was proven by Raman spectra both on macroscopic samples and on the nanoscale by tip-enhanced Raman scattering and high-resolution transmission electron microscopic images.

Surface passivation is one of the commonly used approaches to reduce the density of defects on the surfaces and interfaces hindering the performance and stability of perovskite optoelectronic devices. Although surface passivation leads to performance improvement for the targeted devices, details of the complex intermolecular interactions occurring between the molecules and perovskites are not entirely known. Here, we investigated a variety of commonly used solvents in the post-processing of perovskites by using photoluminescence (PL) spectroscopy on single and mixed halide perovskites (MAPbI3, MAPbBr3 and MAPb(Br0.5I0.5)3). Our results show that solvents with medium and low Gutmann donor and acceptor numbers provide PL intensity increase for both single halide perovskites by passivating the surface defect sites. Among the single halide perovskites, MAPbBr3 is more attracted to hydrogen bonding solvents, in contrast to MAPbI3 that is preferred by Lewis bases. This halide selective attraction also has an influence on the mixed-halide composition. Identifying these interaction mechanisms provides new insights into passivating the surface of perovskites for future device design.

Potassium addition to mixed‐halide perovskites is found to be a promising way to overcome their major stability issue, the segregation of the mixed phase to iodide and bromide‐rich regions. To fully exploit the potential of potassium addition, it is essential to achieve a better understanding of its working mechanism, and understand the limitations of the stabilization it provides. Photoluminescence emission spectra of MAPb(Br0.6I0.4)3 films are studied upon addition of KBr and KI under nitrogen and air atmosphere. The halide exchange between the added potassium salts and the perovskite is demonstrated. It is shown that the potassium addition does not passivate the surface, and it is therefore prone to oxygen and water absorption. The significant contribution of the adsorbed water to the prevention of halide segregation is discussed, which should be taken into account when the stability of the mixed‐halide films is evaluated under ambient conditions.

Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest molecules with widely varying static dielectric constants. Filled through simple ingestion of the guest molecule, each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compounds, covering static dielectric constants from 1.8 to 109, are inserted in large diameter SWCNTs (d = 1.104-1.524 nm) and more than 10 compounds in small diameter SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielectric on the nanotube optical properties is a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude of the dielectric constant. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra additionally enables determination of the critical filling diameter for each molecule and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest molecule/SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is observed for low dielectric constants, with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examining higher-order effects, such as due to nonbulk-like molecule stacking, in host-guest interactions in well-controlled nanopore size materials.

Successful encapsulation of sexithiophene (6T) molecules by two different methods is presented: sublimation filling at 400 °C and nanoextraction from supercritical carbon dioxide (sc‐CO2) at 50 °C. Differences in the Raman spectra of the two samples indicate thermally induced polymerization during sublimation filling, increasing the electronic conjugation length of the chains inside the nanotubes. The thermal reaction is proven by heating the sc‐CO2‐filled nanotubes after encapsulation. Although the conjugation length in the thiophene chain is increasing upon heating, no Raman signatures of graphene nanoribbons are observed.

Hybrid materials based on carbon nanotubes continue to attract considerable interest due to the broad variety of both the cages outside and the encapsulated species inside. This review focuses on organic molecules as guests in single-walled carbon nanotube hosts. The majority of results presented here has been attained in recent years by various methods of optical spectroscopy, complemented by transmission electron microscopy. These spectroscopic methods yield information on electronic structure, as well as dynamic processes as structural transformations and chemical reactions.

The optical properties of single-wall carbon nanotubes (SWCNTs) are extremely sensitive to their external and internal environment. For example, filling the endohedral cavity with water molecules results in characteristic shifts and broadening of both the SWCNTs’ radial breathing mode vibrational frequency and their optical (electronic) transitions, as well as a quenching of their emission.[1] Although mostly ignored in literature, solvent ingestion effects are substantial, and can also be used to passivate the nanotube interior, by controlled manipulation of the endohedral environment prior to dispersion.[2] In this work, specific and tunable modification of the optical properties of SWCNTs is demonstrated through the direct encapsulation of guest molecules with widely varying dielectric constants. Over 30 different compounds with varying static dielectric constant have been encapsulated inside the SWCNTs and their spectroscopic analysis, in comparison to unfilled (empty) SWCNTs, demonstrates experimentally that the general effect of filler static dielectric constant on the SWCNTs’ optical properties corresponds to a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude for higher dielectric constants. In addition to these spectral shifts, the filling also reveals a general increase of fluorescence intensity with lower dielectric constants. Our investigation hence demonstrates a new degree of modulation of the SWCNTs’ optical properties by simple endohedral ingestion of various guest molecules. [1] S. Cambré et al. Phys. Rev. Lett. 104, 207401 (2010); W. Wenseleers et al. Adv. Mater. 19, 2274 (2007); S. Cambré et al. ACS Nano 6, 2649 (2012) [2] J. Campo et al Nanoscale Horizons 1, 317 (2016)

Adsorption of carboxymethyl cellulose (CMC) in aqueous solution onto a titania nanoparticle film has been studied using in situ attenuated total reflectance infrared spectroscopy (ATR-IR). CMC was adsorbed onto the positively charged titania surface in neutral, partially charged, and fully charged state. The response of the adsorbed polyelectrolyte layer was monitored upon changing the electrolyte pH and ionic strength. The degree of dissociation of the CMC increased upon adsorption onto the titania surface and changed with the surface coverage. Ionic strength change was observed to influence the degree of dissociation of the adsorbed CMC similar as when in solution. No significant peak shifts were observed in the spectrum of the adsorbed CMC during adsorption or in response to changing solution conditions; therefore, inner-sphere complexation between the carboxyl groups and the titania could not be confirmed. The effect of ion identity on the adsorption process was studied using soft and hard cations and mono-and divalent cations. The presence of a divalent counterion was observed to cause changes in the carboxymethyl vibrations, which can be related to formation of intra- or interchain linkages.

We report the development of a detection optics for the integration of Raman scattering and scanning probe microscopy at low temperature based on a parabolic mirror. In our set-up, half of the paraboloid mirror covers a solid angle of π corresponding to a numerical aperture of N.A. ≈ 0.85. The optical system can be used for far- and near-field spectroscopy. In the far field, the polarizations can be maintained to within 80%–90%. In combination with a scanning microscope (AFM/STM), tunneling or near-field experiments are possible with less than 10% loss of aperture. Our set-up provides ideal conditions for the future development of tip-enhanced Raman spectroscopy at low temperature.

Specific and tunable modification to the optical properties of single-wall carbon nanotubes is demonstrated through the direct encapsulation into the nanotube interior of guest molecules with measured static dielectric constants. Optical measurements on SWCNT populations containing over thirty distinct simple compounds of varying static dielectric from 1.8 to 109 in large diameter nanotubes, and 15 compounds in small diameter nanotubes demonstrate for the first time experimentally the general effect of filler static dielectric on the nanotube optical properties. Comparison to effective medium theory predictions is presented, and guest molecules are identified that lead to effects disobeying the general trend and theory. These results both demonstrate a new degree of exploitable modulation in the optical properties of SWCNTs, and provide a foundation for examining higher order effects in host-guest interactions in well controlled pore size materials.

By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures are prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via π-π interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor-phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes.

Coronene was encapsulated in single-walled carbon nanotubes (SWNT) by vapor-phase filling at high (450 degrees C) and low (385 degrees C) temperature and by nanoextraction from supercritical carbon dioxide. The presence of coronene inside the tubes was demonstrated indirectly via the formation of double-walled nanotubes (DWNT). To this end several subsequent annealing steps were applied and monitored by Raman spectroscopy. Our results show that the encapsulation is successful with all three methods. However, high-temperature vapor filling produces adsorbed dicoronylene, the dimerized form of coronene, as a side reaction. In order to avoid dicoronylene contamination, we suggest to use low-temperature methods for the production of coronene-filled carbon nanotubes. Coronene (top) and dicoronylene (bottom) molecules.

We report the preparation and characterization of hybrid materials from conducting polymers and single walled carbon nanotubes. Electrochemical polymerization yields nanotubes wrapped by conducting polymers – polyaniline, polycarbazole and melanin (i.e., polydopamine). The materials were characterized by ultraviolet–visible–near infrared, infrared, Raman and impedance spectroscopy. We found that wrapping the nanotubes with polymers can decrease the impedance of such composite electrode and increase the rate of electron transfer from the electrolyte to the electrode. From the attenuation of in-plane vibrations in the infrared spectra and the bathochromically shifted polaron band, we infer that the strongest interaction occurs between polyaniline and the nanotube surface.

Transparent conducting films are rapidly emerging as one of the most promising applications of carbon nanotubes. In these less-than-perfect materials, understanding the types of defects and their effect on the transport and optical properties plays a significant role. In this contribution, we present examples of these effects, both beneficial and adverse.