In Scanning Tunneling Microscopy (STM), a very sharp tip is moved close to the sample and a small voltage is applied across the tip and the sample. This causes electrons to tunnel through the vacuum between the two electrodes. The tunneling current depends exponentially upon the height of the tip above the sample giving the STM atomic resolution.
Low Energy Electron Diffraction (LEED) involves scattering electrons with energies ranging from 30 to 200 eV off a surface. In traditional LEED, electrons diffract off the surface, excite a phosphor screen, and produce a diffraction pattern. In spot profile analysis LEED (SPA-LEED), specially designed electron optics are used to minimize beam divergence and measure the shape of the diffracted spot with a wavevector resolution 0.2% Brillouin Zone (BZ) (which is 10 times higher than conventional LEED). The technique offers a statistical representation of the growth morphology and reveals long-range order on the surface.
Omicron Variable Temperature STM (VT-STM)
The ultra-high vacuum (UHV) system contains an Omicron Variable Temperature STM (VT-STM) for imaging epitaxially grown structures, including several sample preparation tools and deposition sources for molecular beam epitaxy (MBE). It is also equipped with an Ar sputtering gun and rear-view video LEED. Various metal sources are available: magnetic (rare earth Dy, Gd, Eu and transition metals Fe, Cr) and non-magnetic metals (Pb, Si, Au, Mg). High quality graphene samples can be prepared in situ by thermally annealing SiC crystal to ~1400 °C for graphitization.
Omicron Low Temperature STM (LT-STM)
An Omicron Low Temperature STM (LT-STM) capable of reaching 4 K was installed in 2014. Both the sample and tip are cooled to low temperatures, enhancing stability and reducing drift for higher resolution spectra in scanning tunneling spectroscopy (STS). It features an eddy-current-based dumping stage and minimal thermal drift at liquid helium operating temperature (<1 Å/hour).
SPA-LEED System
The UHV system with high resolution surface diffraction (SPA-LEED), is also equipped with a cylindrical mirror analyzer (CMA) for Auger electron spectroscopy (AES), an ultra-pure gas dosing manifold, a UTI mass spectrometer, and Knudsen cell-based deposition sources for molecular-beam epitaxy (MBE) of Pb and Dy.