Markus Ahlskog

Femtosecond four-wave-mixing spectroscopy of suspended individual semiconducting single-walled carbon nanotubes.

Femtosecond four-wave-mixing (FWM) experiments of individual suspended semiconducting single-walled carbon nanotubes (SWCNTs) are presented. The chiral indices of the tubes were determined by electron diffraction as (28,14) and (24,14) having diameters of 2.90 and 2.61 nm, respectively. The diameter and semiconducting character of the tubes were additionally confirmed by resonance Raman measurements. The FWM signal showed electronic response from the SWCNTs. The results demonstrate that ultrafast dynamics of individual SWCNTs can be studied by FWM spectroscopies.

Bending of multiwalled carbon nanotubes over gold lines

We have investigated an experimentally moderate bending of multiwalled carbon nanotubes (MWNTs) in the perpendicular direction from flat substrates. The tubes were in the diameter range of 3–13nm and deposited over lithographically fabricated gold lines whose height determined the total bending. In our model for the bending profile we take into account the van der Waals attraction between the substrate and the MWNT and the opposing elastic bending force. With reasonable parameters for the competing forces we obtain an agreement between the model and the experimental data for the critical distance between two adjacent lines when the van der Waals attraction can no longer prevent elastic forces from straightening the tube to a suspended position between the lines. However, for the smallest nanotubes a simple classical model is clearly insufficient.

Measurement of optical second-harmonic generation from an individual single-walled carbon nanotube

We show that optical second-harmonic generation (SHG) can be observed from individual single-walled carbon nanotubes (SWCNTs) and, furthermore, allows imaging of individual tubes. Detailed analysis of our results suggests that the structural non-centrosymmetry, as required for SHG, arises from the non-zero chiral angle of the SWCNT. SHG thus has potential as a fast, non-destructive and simple method for imaging of individual nanomolecules and for probing their chiral properties.

Carbon nanotube radio-frequency single-electron transistor

AbstractWe discuss the theory of the radio-frequency single-electron transistor and the measurements that use multiwalled carbon nanotubes as active elements. Our devices made of plasma-enhanced chemical-vapor-deposition nanotubes yield charge sensitivities of 10-20 μe/

Carbon nanotube field-effect devices with asymmetric electrode configuration by contact geometry

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Conduction properties of thin films from a water soluble carbon nanotube/hemicellulose complex

. PACS numbers: 73.23.Hk, 73.63.Fg, 85.35.Gv, 85.35.Kt.

Multimodal nonlinear imaging of suspended carbon nanotubes using circular polarizations

We report an experimental noise study of intermediate sized quasi ballistic semiconducting multiwalled carbon nanotube (IS-MWCNT) devices. The noise is two orders of magnitude lower than in singlewalled nanotubes (SWCNTs) and has no length dependence within the studied range. In these channel limited devices with small or negligible Schottky barriers the noise is shown to originate from the intrinsic potential fluctuations of charge traps in the gate dielectric. The gate dependence of normalized noise can be explained better using ballistic the charge noise model rather than diffusive McWhorter’s model. The results indicate that the noise properties of IS-MWCNTs are closer to SWCNTs than thicker MWCNTs. These results can be utilized in future to analyze noise in other purely ballistic nanoscale devices.

Coiled carbon nanotubes as self-sensing mechanical resonators

We have studied experimentally the conductive properties of single walled carbon nanotube (SWNT) based field-effect type devices, with different contact geometries at the connecting electrode. The device designs are asymmetric with one end of the SWNT having the metal electrode deposited on top and immersing it, while at the other end, the SWNT is on top of the electrode. The devices were made with either gold or palladium as electrode materials, of which the latter resulted in different behavior of the different contact types. This is argued to be caused by the existence of a thin insulating layer of surface adsorbents on the palladium, possibly Pd5O4, the effect of which is enhanced by the 1D nature of the contact area in the configuration with SWNT on top of electrode.