Dipole-switch induced modification of the emissive response of carbonnanotubes

The interaction of carbon nanotubes with the molecular dipole switch spiropyran is expected to affect the optical response of the tubes. Until now, the need of anchor groups to immobilize the switches on the tubes has hindered the experimental observation of the effects of switching on the emission behavior of the tubes. Here we present spiropyran-carbon nanotube complexes obtained by micelle swelling. This method does not require any anchor nor sophisticated chemistry to warrant close tube-switch proximity. For the first time, we observe the shifts predicted theoretically and their effect on the tubes' excitation and emission energies

Carbon nanotubes for the optical far-field readout of processes that are mediated by plasmonic near-fields

As science progresses at the nanoscopic level, it becomes more and more important to comprehend the interactions taking place at the nanoscale, where optical near-fields play a key role. Their phenomenology differs significantly from the propagative light we experience at the macroscopic level. This is particularly important in applications such as surface-enhanced spectroscopies for single-molecule detection, where often the optimization of the plasmonic structures and surfaces relies on far-field characterizations. The processes dominating in the far-field picture, though, are not the same dominating in the near-field. To highlight this, we resort to very simple metallic systems: isolated gold nanorods in solution. We show how single-walled nanotubes can be exploited to read out processes occurring at the near-field level around metallic nanoparticles and make the information accessible in the far-field region. This is implemented by monitoring the spectral profile of the enhancement of the photoluminescence and Raman signal of the nanotubes for several excitation wavelengths. Through this excitation-resolved study, we show that the far-field optical readout detects the transversal and longitudinal dipolar plasmonic oscillations of gold nanorods, whereas the near-field readout through the nanotubes reveals other mechanisms to dominate. The spectral position of the maximum enhancement of the optical near-field mediated signals are located elsewhere than the far-field bands. This dichotomy between near-field and far-field response should be taken into account when optimizing plasmonic nanostructures for applications such as surface-enhanced spectroscopies

Carbon nanotubes for the optical far-field readout of processes that are mediated by plasmonic near-fields

As science progresses at the nanoscopic level, it becomes more and more important to comprehend the interactions taking place at the nanoscale, where optical near-fields play a key role. Their phenomenology differs significantly from the propagative light we experience at the macroscopic level. This is particularly important in applications such as surface-enhanced spectroscopies for single-molecule detection, where often the optimization of the plasmonic structures and surfaces relies on far-field characterizations. The processes dominating in the far-field picture, though, are not the same dominating in the near-field. To highlight this, we resort to very simple metallic systems: isolated gold nanorods in solution. We show how single-walled nanotubes can be exploited to read out processes occurring at the near-field level around metallic nanoparticles and make the information accessible in the far-field region. This is implemented by monitoring the spectral profile of the enhancement of the photoluminescence and Raman signal of the nanotubes for several excitation wavelengths. Through this excitation-resolved study, we show that the far-field optical readout detects the transversal and longitudinal dipolar plasmonic oscillations of gold nanorods, whereas the near-field readout through the nanotubes reveals other mechanisms to dominate. The spectral position of the maximum enhancement of the optical near-field mediated signals are located elsewhere than the far-field bands. This dichotomy between near-field and far-field response should be taken into account when optimizing plasmonic nanostructures for applications such as surface-enhanced spectroscopies

Controlled reversible debundling of single-walled carbon nanotubes by photo- switchable dendritic surfactants

Stimulus responsive surfactants based on dendritic glycerol azobenzene conjugates were used to solubilize and debundle single-walled carbon nanotubes in aqueous media. Their debundling property as well as their reaggregation behavior upon irradiation with light was examined and light triggered reversible bundling and precipitation are shown

Relaxation lifetimes of plasmonically enhanced hybrid gold-carbon nanotubes systems

Recently, we introduced a novel hybridization route for carbon nanotubes using gold nanoparticles, whose close proximity neatly enhances their radiative emission. Here we investigate the mechanisms behind the enhancement by monitoring the de-excitation dynamics of our π-hybrids through two-color pump- probe time-resolved spectroscopy. The de-excitation process reveals a fast component and a slow component. We find that the presence of gold prominently affects the fast processes, indicating a stronger influence of the gold nanoparticle on the intra-band non-radiative relaxation than on the inter-band recombination of the single-walled carbon nanotube. By evaluating the de- excitation times, we estimate the balance between near-field pumping and the faster metal-induced de-excitation contributions, proving the enhanced pumping to be the leading mechanism

Chiral selectivity of polyglycerol-based amphiphiles incorporating different aromatic cores

Customized polyglycerol-based surfactants incorporating different aromatic cores are used to isolate and suspend carbon nanotubes in water. Different cores yield suspension with distinct chiral species distribution. Increasing the number of the phenyl rings connecting head and tail, the dispersion of the semiconducting species becomes sharper toward the nanotubes with bigger family index

Preserving p-conjugation in covalently functionalized carbon nanotubes for optoelectronic applications

Covalent functionalization tailors carbon nanotubes for a wide range of applications in varying environments. Its strength and stability of attachment come at the price of degrading the carbon nanotubes sp 2 network and destroying the tubes electronic and optoelectronic features. Here we present a non-destructive, covalent, gram-scale functionalization of single-walled carbon nanotubes by a new 2+1] cycloaddition. The reaction rebuilds the extended p-network, thereby retaining the outstanding quantum optoelectronic properties of carbon nanotubes, including bright light emission at high degree of functionalization (1 group per 25 carbon atoms). The conjugation method described here opens the way for advanced tailoring nanotubes as demonstrated for light-triggered reversible doping through photochromic molecular switches and nanoplasmonic gold-nanotube hybrids with enhanced infrared light emission

nanograined anatase titania based optochemical gas detection

Optochemical sensing properties of thick films of titanium dioxide (titania) in anatase phase have been studied and compared with tin dioxide cassiterite. Anatase titania exhibits a large photoluminescence response to nitrogen dioxide, which acts as a luminescence enhancer. Intrinsic surface phenomena rather than bulk defectivity are proposed to account for the behaviour and the experimental results are fitted with the Langmuir model. Good operational performances working at room temperature are achieved

Classical Loop Actions of Gauge Theories

Since the first attempts to quantize Gauge Theories and Gravity in the loop representation, the problem of the determination of the corresponding classical actions has been raised. Here we propose a general procedure to determine these actions and we explicitly apply it in the case of electromagnetism. Going to the lattice we show that the electromagnetic action in terms of loops is equivalent to the Wilson action, allowing to do Montecarlo calculations in a gauge invariant way. In the continuum these actions need to be regularized and they are the natural candidates to describe the theory in a ``confining phase''.Comment: LaTeX 14 page