Carbon nanotube | EPFL Graph Search

A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometer range (nanoscale). They are one of the allotropes of carbon. Single-walled carbon nanotubes (SWCNTs) have diameters around 0.5–2.0 nanometers, about 100,000 times smaller than the width of a human hair. They can be idealized as cutouts from a two-dimensional graphene sheet rolled up to form a hollow cylinder. Multi-walled carbon nanotubes (MWCNTs) consist of nested single-wall carbon nanotubes in a nested, tube-in-tube structure. Double- and triple-walled carbon nanotubes are special cases of MWCNT. Carbon nanotubes can exhibit remarkable properties, such as exceptional tensile strength and thermal conductivity because of their nanostructure and strength of the bonds between carbon atoms. Some SWCNT structures exhibit high electrical conductivity

Carbon nanotube uptake in cyanobacteria for near-infrared imaging and enhanced bioelectricity generation in living photovoltaics

Alessandra Antonucci, Ardemis Anoush Boghossian, Alice Judith Gillen, Benjamin Paul Johanès Gabriel Lambert, Mohammed Mouhib, Melania Reggente, Charlotte Elisabeth Marie Roullier, Nils Schürgers, Vitalijs Zubkovs

Single-walled carbon nanotubes (SWCNTs) have unique optoelectronic properties that make them suitable for applications ranging from phototherapy to imaging and sensing, but their uptake has mainly been explored in eukaryotic cells. Here the authors explore the interaction of SWCNTs with cyanobacteria, showing that they are spontaneously taken up by cells only when coated with positive charges, opening the possibility of prokaryotic-based biotechnology applications. The distinctive properties of single-walled carbon nanotubes (SWCNTs) have inspired the development of many novel applications in the field of cell nanobiotechnology. However, studies thus far have not explored the effect of SWCNT functionalization on transport across the cell walls of prokaryotes. We explore the uptake of SWCNTs in Gram-negative cyanobacteria and demonstrate a passive length-dependent and selective internalization of SWCNTs decorated with positively charged biomolecules. We show that lysozyme-coated SWCNTs spontaneously penetrate the cell walls of a unicellular strain and a multicellular strain. A custom-built spinning-disc confocal microscope was used to image the distinct near-infrared SWCNT fluorescence within the autofluorescent cells, revealing a highly inhomogeneous distribution of SWCNTs. Real-time near-infrared monitoring of cell growth and division reveal that the SWCNTs are inherited by daughter cells. Moreover, these nanobionic living cells retained photosynthetic activity and showed an improved photo-exoelectrogenicity when incorporated into bioelectrochemical devices.

2022

Atomic force microscopy studies of nanotribology and nanomechanics

Ismaël Palaci

This thesis comes within the scope of tribology studies at the nanometer scale. The experimental techniques used in this work are essentially related to atomic force microscopy, which gives a direct access to the topography and forces of the studied systems. Two principal aspects of the nanotribology have kept our attention. They are the nanofriction and the nanomechanics. These two domains divide the thesis in two main parts that remain however intimately bound. The first experimental part of the thesis describes the friction of a nanoscopic tip sliding on hydrophilic surfaces. The dependence of the friction force on the sliding velocity is studied for various applied normal loads and surrounding relative humidity levels. We found a logarithmic dependence of the friction force on both the scanning velocity and the relative humidity. For the first time, a transition from a positive to a negative slope of the friction force versus the logarithm of the sliding velocity has been observed for the very same tip-surface contact, by varying the relative humidity. The role of the relative humidity on the friction force has then been studied more deeply, leading to a two-thirds power law dependence of the capillary force on the normal load. Finally, analytical expressions for the friction phenomenon and the capillary condensation between the asperities of the tip and the surface have been developed to explain the phenomenological behaviors. The second experimental part describes themechanics of carbon nanotubes and tobacco mosaic viruses. In order to stay in the linear elasticity regime, small indentation amplitudes have been applied in the radial direction of multiwalled carbon nanotubes adsorbed on a silicon oxide surface. Using a theory based on the Hertz model, the radial stiffness has been evaluated and compared to molecular dynamics simulations. We found a radial Young modulus strongly decreasing with increasing radius and reaching an asymptotic value of 30 ± 10 GPa. The tobacco mosaic viruses have been adsorbed on a polyimide porous membrane. Evidence for the softness of the viruses has been obtained by imaging the tubes with the atomic force microscope in non-contact mode. Viruses hanging like ropes over the pores of the surface served as basis to measure their bending Young modulus. Using a model of a clamped beam loaded by a discrete gradient of van der Waals forces, we found a bending Young modulus of 3.1 ± 0.1 MPa.

EPFL2007

Carbon nanotubes functionalized with dye molecules and metal nanoparticles

Tilman Assmus

Single-walled carbon nanotubes are highly interesting quasi one-dimensional nanostructures. They possess a multitude of fascinating optical, mechanical and electrical properties, which can be even further expanded through appropriate functionalization strategies. This thesis covers a number of functionalization strategies and their effects on the nanotube's optical and electrical properties. The first part deals with the functionalization of carbon nanotubes with dye molecules and the characterization of the functionalized system. Both covalent and noncovalent approaches were investigated with the goal of modifying the nanotubes' photoelectrical properties. Upon excitation with light of the appropriate wavelength, a clear electrical response could be observed on some functionalized individual nanotubes. Depending on the attached dye molecule, the conductivity change is either induced by a light-induced conformational change or by a charge transfer between the nanotube and the excited dye molecule. The perspectives of constructing an optoelectronic nanoswitch based on these effects are discussed. The second part of the thesis addresses carbon nanotubes functionalized by a low density of electrodeposited gold nanoparticles with sizes in the range between 10 and 100nm. In this case, the functionalization is targeted on amplifying the nanotube's Raman response (SERS effect). The novel sample preparation technique developed in this thesis allowed for an investigation of SERS on the level of individual molecule / nanoparticle hybrids. The optical emission spectra of the nanotube-nanoparticle hybrid structure disclosed Raman peaks associated with the nanotubes, which are superimposed on a broad luminescence background originating from the metal particles. Wavelength dependent experiments revealed maximum Raman intensity when both the nanotube and the metal particle are in optical resonance. In well-prepared samples the Raman signals collected over isolated particles exhibited an intensity enhancement by at least one order of magnitude, as compared to bare sections on the same tube, without appreciably interfering with polarization dependent Raman measurements.

EPFL2008