Nanophysics & Surfaces:
Exploring Low Dimensional Structures

Dr Fran Pedreschi

The group concentrates on the study of low dimensional structures (such as one-dimensional “wires” and zero-dimensional quantum “dots”). As the length scales of such systems shrink, unusual properties arise due to the quantum confinement (squeezing) of electrons on scales approaching the electron wavelength. These properties can have commercial potential in novel device production. Understanding exactly why such unusual properties arise can help us to engineer new properties that are desirable for modern technologies.

Based at DIT's FOCAS research building, part of the work uses ultra-high vacuum technology (UHV) to prepare and preserve ultra-clean crystalline Silicon surfaces. Materials deposited on these surfaces in layers averaging less than one atom thick can form highly regular and localised structures, in some cases forming idealised quantum wires. These nanostructures are of practical interest but are also ideal model systems for the study of physics at its most fundamental level. The optical analysis technique of Reflection Anisotropy Spectroscopy (RAS) is used to monitor the growth of such ultrathin overlayers as well as low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and other in-situ techniques.

Studies of metallic nanoclusters are also ongoing in collaboration with Kees Flipse at the the Technical University of Eindhoven (TUE) using optical and magneto-optical techniques. This also involves work on the formation of nanocontacts to connect molecular transistor candidate materials to the outside world for conductance profiling. The delicate task involves using an AFM to pick up and move metallic nanoclusters and arrange them to form a contact between macroscopic wires and the molecules.

Calculations of the electronic and optical properties of nanoscale structures are also carried out using molecular dynamics methods (FireBall) at DIT.

A variety of ambient and UHV sample preparation and analysis techniques are available within the group:

• UHV low energy electron diffraction (LEED)
• UHV CMA-based Auger electron spectroscopy
• UHV deposition and growth monitoring
• UHV scanning ion beam (He, Ar, O2)
• UHV secondary ion emission spectroscopy
• Magnetic sample transfer
• Reflection anisotropy spectroscopy

Some recent group publications include:

RAS calculation of metallic overlayers on silicon
B Haycock, F Pedreschi, J D O’Mahony
Proceedings Condensed Matter and Materials Physics CMMP 2007 [3 pages]

Optical reflectance anisotropy studies of Fe nanostructures grown on vicinal W(110)
L Carroll, F Pedreschi, J D O’Mahony, and J F McGilp
Physica Status Solidi (B) 242 13 (2005) 2650-2654 [5 pages]

Magnetic force microscopy and simulations of colloidal iron nanoparticles
F Pedreschi, J M Sturm, J D O'Mahony, C F J Flipse
Journal of Applied Physics 94 5 (2003) 3446-3450 [5 pages]

Characterization of metal point contacts: conductance quantization and electron-phonon coupling
J M Wulveryck, J Amir, J Jennette, O Kurnosikov, G Tãnasã, C F J Flipse
SPM Conference, Twente NL, Novermber 15, 2001

Evidence of Electron Confinement in the Single-Domain (4x1)-In Superstructure on Vicinal Si(111)
F Pedreschi, J D O'Mahony, J R Power, P Weightman
Applied Physics Letters 73 15 (1998) 2152-2154 [3 pages]

Strong Optical Anisotropy of the Single-Domain 5x2-Au Reconstruction on Vicinal Si(111)
J R Power, P Weightman, J D O'Mahony
Physical Review B 56 7 (1997) 3587 [4 pages]

Scanning tunneling microscopy (STM)
image of Indium quantum wire structures
on the surface of a silicon crystal
(F Pedreschi)

Manipulation of metallic nanoclusters for use in
the development of contact wires for
molecular transistor studies
(J Jennette)

UHV evaporation cluster at DIT