Biomedical subjects

M Burghard

Publications and source records attributed to M Burghard.

5 recordsLinked to original sources

PubMed2006

Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction.

The electronic and vibrational density of states of a semiconducting carbon nanotube in a crossed junction was investigated by elastic and inelastic scanning tunneling spectroscopy. The strong radial compression of the nanotube at the junction induces local metallization spatially confined to a few nanometers. The local electronic modifications are correlated with the observed changes in the radial breathing and G band phonon modes, which react very sensitively to local mechanical deformation. In addition, the experiments reveal the crucial contribution of the image charges to the contact potential at nanotube-metal interfaces.

Journal Article↗

PubMed2004

Phonon spectromicroscopy of carbon nanostructures with atomic resolution.

The vibrational properties of single-wall carbon nanotubes have been probed locally with atomic-scale resolution by inelastic electron tunneling spectroscopy with a low-temperature scanning tunneling microscope. The high spatial resolution has allowed the unraveling of changes in the local phonon spectrum related to topological defects. We demonstrated that the radial breathing mode is suppressed within tube segments of lengths below approximately 3 nm, and that in the cap region phonon modes characteristic of the fullerene hemisphere are emerging. Phonon spectromicroscopy should lead to a better understanding of the mechanisms that limit the transport of heat or electrical charge inside nanostructured carbon materials.

Journal Article↗

PubMed2004

Dispersions of individual single-walled carbon nanotubes of high length.

In summary, we have presented a suitable approach to obtain surfactant-stabilized suspensions of long, individually dispersed SWCNTs essentially free of bundles. The combination of mild tip and bath ultrasonication has proven effective in unbundling the SWCNT ropes and, at the same time, in minimizing tube shortening. This method is expected to be useful for applications that critically depend on the availability of bulk dispersions of long, individual tubes with minimized defect densities, such as for nanotube-based electronics and composite materials. Furthermore, the observed purification-induced changes in the electronic structure of HiPco SWCNTs indicate that care has to be taken when comparing their properties with those of the as-produced material.

Journal Article↗

PubMed2000

Polarized raman spectroscopy on isolated single-wall carbon nanotubes.

Polarized micro-Raman spectroscopy has been performed on spatially separated single-wall carbon nanotubes (SWNTs) in the form of individual nanotubes or thin ropes of only a few SWNTs. Different from bulk samples, the Raman spectra are composed of well-resolved peaks which allow a direct comparison of experimental data with theoretical calculations. Orientation-dependent measurements reveal maximum intensity of all Raman modes when the nanotubes are aligned parallel to the polarization of the incident laser light. The angular dependences clearly deviate from the selection rules predicted by theoretical studies. These differences are attributed to depolarization effects caused by the strongly anisotropic geometry of the nanotubes and to electronic resonance effects for excitation at 633 nm.

Microchemistry↗

PubMed1999

Supercurrents through single-walled carbon nanotubes

Proximity-induced superconductivity in single-walled carbon nanotubes below 1 kelvin, both in a single tube 1 nanometer in diameter and in crystalline ropes containing about 100 nanotubes, was observed. The samples were suspended between two superconducting electrodes, permitting structural study in a transmission electron microscope. When the resistance of the nanotube junction is sufficiently low, it becomes superconducting and can carry high supercurrents. The temperature and magnetic field dependence of the critical current of such junctions exhibits unusual features related to their strong one-dimensional character.

Journal Article↗