scanning gate microscopy

The Scanning Gate Microscopy Laboratory at NEST

The new Scanning Gate Microscopy (SGM) laboratory at NEST (Fig. 1a) is aimed at combining our experience of the transport properties of nanostructures with the opportunity of investigation offered by scanning probe microscopy operating at ultra-low temperature (300mK), in a magnetic field tunable up to 9T.

sgmlab

Figure 1: (a) The new SGM lab at NEST. (b) The AFM head for SGM measurements.

The recently installed instrument allows to locally apply an electric potential by means of the conductive tip of an atomic force microscope (AFM) operating in non-contact mode. This has a number of important applications: for instance we were able to image the coherent flow of electrons across a quantum point contact by measuring the change in the conductance corresponding to the local depletion of the 2DEG underneath the tip. By scanning the sample at constant height above the sample, we obtained maps of the current signal such as the one shown in Fig. 2.

sgmlab

Figure 2: SGM visualization of coherent electron flow. Electrons are transmitted across a quantum point contact which is 4 um to the right of this area.

The fundamental element of our SGM system is the AFM head (Fig. 1b). The upper part contains the sample holder with the wires for transport measurements. This is placed on a stack of piezo actuators providing the coarse and fine positioning of the sample, which allow sample movements of several millimeters with a sub-micron resolution and reproducibility. The lower part of the AFM head contains the tuning fork with the conductive tip, which allows us to both measure the sample topography and to apply a local potential. Our setup is also equipped with a STM head, which is capable of obtaining topographic images of conductive samples with atomic resolution. Both the AFM and the STM heads are non-magnetic (all the metallic parts are in titanium) and are designed to suitably work either at ultra-low temperature or at room temperature. They are mounted to the cold finger of a 3He cryostat. The cryostat is inserted in a dewar suspended by means of springs in a soundproofed box in order to damp mechanical and acoustical noise. For low temperature operations a magnetic field up to 9 T is provided by a superconducting coil placed at the bottom of the dewar.

Contact

sample

Dr. Stefan Heun
Senior Scientist

NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore
Piazza San Silvestro 12
56127 Pisa, Italy

tel. office +39-050-509 472
SGM lab. +39-050-509 467
STM lab. +39-050-509 461
fax. +39-050-509 417

e-mail: stefan.heun@nano.cnr.it