Logo

AG Scheer
Mesoscopic Systems

Login |
 
 

Transport Measurements of Atomic-Size Metallic Contacts under Laser Illumination

Conductance change
Top: The conductance G decreases, when the contact is stretched. The discrete steps can be explained by changes in the atomic configuration.
D. Benner, R. Waitz, in cooperation with P. Leiderer

The subject of this project is the influence of light on the electronic transport of atomic-size metal contacts, especially gold contacts. A combination of the mechanically controllable breakjunction technique and electromigration is used to form the nano contacts.

In order to reveal the possible mechanisms for light-induced conductance changes, we investigate the dependence on the initial conductance, the wavelength, the intensity, the polarization and the position of the laser spot with respect to the sample. Under most conditions, an enhancement of the conductance is observed.

Future investigations focus on

  1. the influence of optical antenna effects by variation of the electrode geometry
  2. the time dependence of the conduction change using pulsed lasers
  3. the use of different metals like platinum and silver

This experiment is going to provide fundamental insights for later measurement of molecules under light influence.

Öffnet externen Link im aktuellen FensterJ. of Microscopy 229, 407 (2008)

 

 

 

Influence of laser light onto the electronic transport properties of atomic-sized contacts

Matthias Bädicker, Golaleh Ghafoori

In this project we investigate the influence of laser light onto the electric conductance of an atomic-sized contact made of metal. These contacts are realized with the mechanically break junction technique. Recent works showed that upon illumination with laser light the electric conductance of such a contact increases and depends on the point of illumination. The maximum  increase in conductance is found at different points of illumination for different  wavelengths. For red light it was found that the maximum in change of conductance is observed while illuminating the metal leads which are pointing towards the atomic-sized contact (picture). These findings give rise to the idea that, aside from pure thermal effects, also surface plasmons might contribute to the conductance of an atomic-sized contact.

Currently we are working on performing the experiment inside a cryostat at about 1.5 K. Additionally the time resolution will be enhanced to be able to distinguish between thermal and non-thermal effects.

Simultaneously it is necessary to investigate the propagation of surface plasmons across a nano-contact or even gaps in the metal. For that purpose surface plasmons are excited by a focused laser beam hitting a grating structure in a microscope setup. Further gratings on both sides of a nano-contact allow tracking the propagation of the surface plasmons. The results of the measurements are compared to computer simulations made by FDTD.