Structural and Surface Characterization
Contact person: Rossi Francesca
Scanning tunneling microscopy and spectroscopy
   CONTACT: Letizia Savio (letizia.savio@imem.cnr.it, tel 010-3536292)

 

Setup 

STM Createc

Scanning Tunneling Microscope (CreaTec).

Low temperature operation: 77 K (LN2) or 6 K (LHe).
Besocke modified  scanner; scanning range 1µmx1µm; bias voltage -10  V <V< +10 V; low noise. 
Integrated lock-in for spectroscopic measurements.

Setup

 UHV setup equipped with the LT-STM.
The microscope is coupled to a supersonic molecular beam.  

Method

The STM technique is based on the quantum phenomenon of the tunnelling effect, whereby the current passing between a conductive or semiconductive sample and a metal tip placed at atomic distance from it is measured. By acquiring the reading of the «tunneling current» while the tip scans the surface, a map of the electronic density of the surface is obtained, which is correlated to its morphology. Depending on the operation conditions, the following information can be retrieved:

  • Surface topography with atomic resolution
  • Surface LDOS maps
  • Spatially localized spectra of the LDOS around the Fermi level
  • Manipulation of single atoms / molecules
STM method

 

Highlights

Determination of surface morphology

From the integrated LDOS map of the surface, the morphology of the surface is obtained, both in the case of metal / semiconductor surfaces and of supported ultra-thin layers (organic or inorganic). In the examples:

morfologia superficiale
1) Graphene nanoribbons on Ag(110), produced by surface assisted synthesis of 1,6-dibromopyrene precursor. Ref: Nanoscale 2016.
2) Self-assembly of glutamic acid on Ag(100). Refs: Langmuir 2010, Langmuir 2011, J. Phys. Chem C 2014. 
3) OH/O/Ag(110), obtained by exposing O/Ag(110) to H2O.  Ref: Phys. Rev. B 2006.

 

Scanning Tunneling Spectroscopy: LDOS measurement

spettroscopia STS
LDOS of a MgO/Ag(100) monolayer. The oxide gap and the Ag surface states at 1.8 eV are visible.  Ref. Phys. Rev. Lett. 2014.https://doi.org/10.1103/PhysRevLett.112.126102

 

From the measurement of the dI / dV signal as a function of the bias voltage V at a specific point on the surface, the density of the states around the Fermi level at that specific point is obtained.