Dorte Nørgaard Madsen

Constructing, connecting and soldering nanostructures by environmental electron beam deposition

Highly conductive nanoscale deposits with solid gold cores can be made by electron beam deposition in an environmental scanning electron microscope (ESEM), suggesting the method to be used for constructing, connecting and soldering nanostructures. This paper presents a feasibility study for such applications. We identify several issues related to contamination and unwanted deposition, relevant for deposition in both vacuum (EBD) and environmental conditions (EEBD). We study relations between scan rate, deposition rate, angle and line width for three-dimensional structures. Furthermore, we measure the conductivity of deposits containing gold cores, and find these structures to be highly conductive, approaching the conductivity of solid gold and capable of carrying high current densities. Finally, we study the use of the technique for soldering nanostructures such as carbon nanotubes. Based on the presented results we are able to estimate limits for the applicability of the method for the various applications, but also demonstrate that it is a versatile and powerful tool for nanotechnology within these limits.

Nanoscale silicon structures by using carbon nanotubes as reactive ion etch masks

We demonstrate that multiwalled carbon nanotubes can be used as etch masks in a reactive ion etch, yielding silicon structures defined by the size and orientation of the carbon nanotube. The relationship between etch profile and reactive ion etch parameters is optimized to yield an anisotropic etch with vertical sidewalls, supporting carbon nanotubes of diameters down to 25 nm, without apparent damage to the nanotube. We demonstrate that the etched structures can be used as thermal nanoimprint stamps and that the carbon nanotube remains on the etched ridge after imprinting. The method is a route for creating nanoscale structures with a resolution defined by the smoothness and width of a macromolecular structure.

Nanoscale soldering of positioned carbon nanotubes using highly conductive electron beam induced gold deposition

We have developed an in-situ method for controlled positioning of carbon nanotubes followed by highly conductive contacting of the nanotubes, using electron beam assisted deposition of gold. The positioning and soldering process takes place inside an Environmental Scanning Electron Microscope (E-SEM) in the presence of a source of gold-organic precursor gas. Bridges deposited between suspended microelectrodes show resistivities down to 10/sup -4/ /spl Omega/cm and Transmission Electron Microscopy (TEM) of the deposits reveals a dense core of gold particles surrounded by a crust of small gold nanoparticles embedded in a carbon matrix. Nanoscale soldering of multi-walled carbon nanotubes (MWNT) onto microelectrodes was achieved by deposition of a conducting gold line across a contact point between nanotube and electrode. The solderings were found to be mechanically stronger than the carbon nanotubes. We have positioned MWNTs to bridge the gap between two electrodes, and formed soldering bonds between the tube and each of the electrodes. All nanotube bridges showed ohmic resistances in the range 10-30 k/spl Omega/. We observed no increase in resistance after exposing the MWNT bridge to air for days.

Effect of Temperature on the Transformation of Carbon Black into Nanotubes

In this paper, successful structural transformation of carbon black (CB) into nanotubes and nanoonion like structures at relatively low temperatures in the presence of transition metal catalyst is reported. This study focuses also on the influence of the temperature on the structural transformation of CB into nanostructures. The experiments were carried out at 700°C and 1000°C in a horizontal tube furnace under N2 atmosphere. The obtained samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). It was found that increase in the synthesis temperature from 700°C to 1000°C influences the morphology of the produced nanotubes significantly and the degree of crystallinity also increased with the temperature..