XSTM

XSTM and low-temperature STM of nanostructures

research

The following research projects are in progress:

1) Cross-sectional scanning tunneling microscopy (XSTM) and spectroscopy (XSTS) of nanostructures in semiconductors
Cross-sectional STM images of nanostructures in GaAs are obtained by cleaving the samples in UHV and transferring the sample to the STM head. The tip is then placed within a few microns from the region of the nanostructures with the help of an optical microscope. In this way cross-sectional images of the nanostructures can be obtained within a few minutes from the sample cleavage. We have developed a method for measuring the local electrostatic potential in semiconductor nanostructures with a sensitivity of 10 mV and a spatial resolution of a few nm. We are investigating by XSTMS with atomic resolution the compensation mechanism in delta doped layers of Si and Mn in GaAs, and the transition from the delta doped layers to superlattices when the surface density of the dopant increases. We are also measuring the shape and the composition of InAs quantum dots in GaAs and AlGaAs. These studies are performed in collaboration with the Materials Division and the TEM Laboratory of TASC, Maria Peressi from the University of Trieste, Stefano Baroni (SISSA), and Giancarlo Salviati (IMEM-CNR).

2) Structure of functionalized carbon nanotubes
The organic functionalization of CNT's may allow the use of the nanotubes as a normal building block in nanostructures and composite materials. Cycloaddition reactions allow the insertion of any functional group in the system and the formation of useful compounds for many applications, such as donor-acceptor dyads for photoinduced electron transfer. We are investigating the structure of functionalized nanotubes in order to measure the distribution of the sizes of the CNT after the functionalization, the distribution of the inserted groups and their electronic structure. This study is performed in collaboration with Prato's group at the Dipartimento di Scienze Farmaceutiche dell' Università di Trieste and with The S3 Research and Development Center of INFM at Modena.

3) Metallic surfaces on semiconductors
We are using STM, high-resolution angle-resolved photoemission spectroscpy, and photoelectron diffraction to study the structure, the electronic properties, and the phase transitions of the metallic surface formed by 1/3 of a monolayer of tetravalent adatoms like Sn and Pb on the (111) surfaces of Ge and Si. Charge disproportionation, soft phonons, and possible electron correlation effects make these systems particularly attractive. This study is done in collaboration with Tosatti's group at SISSA.

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