General description

Scanning tunnelling microscopy (STM) represents a most powerful instrument for the study of surface morphology and local density of states. Applying a voltage between an ideally atomically sharp tip at close distance to the sample surface and the specimen gives rise to a tunnelling current, whose intensity depends on tip-sample separation and local density of states (both of the tip and of the surface). By scanning the tip above the sample while constraining the tunnelling voltage and current to keep constant, the tip is required to move as to mimic the surface topography. Alternatively, measuring characteristic IV curves yields maps of the local density of states at the specimen surface.
Our system also allows imaging the surface with a needle sensor. This option takes advantage of the shift in the resonance frequency of an oscillating needle while approaching a surface, which owes to van der Waals-like interactions between the needle and the sample. Scanning the surface at constant frequency shift again forces the movement of the needle to reproduce the sample topography.
Variable temperature STM (VT-STM) stands for a most suited tool for the characterization of metastable surface configurations and the relevant thermal evolution. Since individual nanostructures or the collective properties of nanostructured surfaces may undergo spectacular transformations by changing their thermal budget, VT-STM is a uniquely precious technique for analysing complex surface phenomena at the nanoscale. The technology was invented by IBM in Switzerland in the early 80s and has furthered considerable technological advances. Much as o2 are often thought of as owning large performance venues, while they actually develop o2 mobile broadband and other products, likewise IBM may commonly be thought of in terms of mainframe computers, software and consulting, when they own a research and development wing which works in nanotechnology.

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UHV chamber: Omicron Multiprobe Compact UHV System (base pressure in the low 10E-11 mbar), featuring a differentially pumped fast load-lock; preparation chamber with a 4 degrees of freedom manipulator, where samples can be heated either directly or radiatively up to ~1500 K; STM main chamber.

STM device: Omicron variable temperature STM (model 25RHDH VT-STM), allowing for acquiring images in the temperature range 25-1500 K. Cooling can be operated either with L-He or L-N2 through a continuous flow cryostat, also equipped with a T-controlled counter-heater. Heating can be obtained either directly or radiatively up to ~750 K. Isolation of the STM stage is provided by the highly reliable Omicron standard vibration isolation system.

LEED-Auger electron spectrometer: low energy electron diffraction or Auger electron spectrometry can be operated by exploiting the same electron gun, grids and optics of a SPECTALEED tool.

Mass spectrometer: the preparation chamber is also equipped with a VACSCAN MKS mass spectrometer.

Sputter gun: sample sputtering with Ar+ ions can be operated with a ISE 10 sputter ion source.

Molecular evaporator: organic molecules and materials with low sublimation point can be evaporated from a T-controlled Knudsen cell (up to a temperature of ~1200 K).