STM Group - ISOF

The continuous need for faster and more powerful microprocessors, and the widespread interest for nanotechnology, demand for a better understanding and manipulation of surfaces at the atomic level. While several successes have been achieved in the creation of very small structures and devices, there are still obstacles for the connection and mass production of working devices. The main interest of our group is to study on atomic and microscopic scale (from 1 to 1000 nm) the transformation of semiconductors surface using chemical and physical treatments. The techniques used range from Scanning tunnelling Microscopy in ultra high vacuum to LEED and, in collaboration with other groups, AFM, XPS, DLTS and several others.
Since January 1st, 2002, we are part of ISOF (Istituto per la Sintesi Organica e la Fotoreattivita'), formerly ICOCEA (Istituto per i composti del carbonio contenenti eteroatomi).

With the help of STM, we can follow the interaction of small organic molecules with Si surfaces at an atomic level. Adsorption dynamics and site selectivity can be extracted from real time sequences of STM images taken on the same area.
Organic molecules can adsorb dissociatively on the highly reactive silicon surface, forming Si-C-R type chemical bonds. For some molecules the adsorption process is very regular and reproducible, yerlding uniform coverages of organics mojeties on the Si surface.
The interaction of each molecule with sites on the surface having different electronic structures can also give importan informations on the reaction energetics. Once the molecules have been chemically linked to the surface, I/V spectroscopy can be performed on each site with a lateral resolution below 1 Angstrom, and current resolution below few picoamperes.

We are interested in the complex dynamic and surface roughness deriving from the oxide desorption on crystalline Si[100] and Si[111] surfaces. The desorption is not uniform and creates in the oxide circular voids of diameter ranging from few tens to several hundreds of nanometers. While the oxide desorbs, silicon atoms diffuse on the crystal surface and, under particular conditions, create nanocrystals of silicon at the center of each void. The void nucleation is favoured by silicon carbide or metallic contaminants. Stopping the desorption and letting new contaminants adsorb on the surface, it is possible with a second thermal treatment to create complex self-assembled structures on the silicon surface.

The process of surface roughening and nanoislands growth can be successfully reproduced by simple, 1-dimensional models implemented using a Montecarlo algorythm. The simulation modeled on a silicon surface yelds a metastable system, where two energy minima correspond to a flat surface or to periodic mounds.
In the presence of a diffusion barrier the surface shows two different phases-flat areas in coexistence with tall mounds, in agreement with experimental results. Mound growth begins when the local slope reaches a critical value; this slope- controlled instability is a non-trivial effect of the diffusion barrier.

The cleaning of Silicon wafers prior to microdevice fabrication is one of the fundamental steps of IC industry. Several methods and reagents are used to clean the surface. We study the effect of different chemical treatments on the silicon surface, observing the resulting surface morphology with STM and trying to correlate it with the electrical behaviour of simple devices (diodes) built on the surface. Among the others, the cleaning and etching effect of fluorine-based solutions is studied. According to concentration, pH and etching time, the treatment with fluorurated solutions yelds several different morphologies, from very flat, atomically clean to extremely rough surfaces, covered with mesoscopic holes.

Slope-controlled surface instabilities
Palermo V., PHILOSOPHICAL MAGAZINE LETTERS, 2004, v.84, p.157

News story: Diffusion narrows contact gap by L. Kalaugher, NANOTECHWEB
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Lateral diffusion of titanium disilicide as a way to contacting hybrid Si-organic nanostructures
Palermo V., Buchanan M., Bezinger A., Wolkow R.A., APPLIED PHYSICS LETTERS, 2002 v.81, p. 3636
(this article has been selected for publication on the VIRTUAL JOURNAL OF NANOSCALE SCIENCE & TECHNOLOGY, 2002, v.6, issue 20)
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Surface modifications in Si after Rapid Thermal Annealing
Castaldini A., Cavalcoli D., Cavallini A., Jones D., Palermo V., Susi E., JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 2002 v. 149 , p.G633

Production of nanostructures of silicon on silicon by atomic self-organisation observed by scanning tunnelling microscopy
Jones, D. Palermo, V. APPLIED PHYSICS LETTERS, 2002 v. 80, p. 673
(this article has been selected for publication on the VIRTUAL JOURNAL OF NANOSCALE SCIENCE & TECHNOLOGY, 2002, v.5, issue 5)
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Nucleation of nanostructures from surface defects on silicon
Palermo, V. Jones, D. SOLID STATE PHENOMENA, 2002 v. 82-84, p. 687

Self-Organised Growth of Silicon Structures on Si(100) During Oxide Desorption
Jones, D. Palermo, MATERIALS SCIENCE AND ENGINEERING B, 2002, v.88 (2-3), p.220

Morphological changes of Si[100] surface after treatment with concentrated and dilute HF
Palermo, V. Jones, D. MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 2001, v. 4, p. 437

Electrical and structural properties of processed silicon surfaces
Susi, E. Cavallini, A. Castaldini, A. Cavalcoli, D. Jones, D. Palermo, V. “RECENT RESEARCH DEVELOPMENTS IN VACUUM SCIENCE & TECHNOLOGY”, 2001, v. 3, p.189

Numerical Solutions of the Stochastic Equations of Crystal Growth
Mazzone, A. M. Palermo, V. INTERNATIONAL JOURNAL OF MODERN PHYSICS C 2000 v. 11; Part 1, p.195-204

Advances in silicon surface characterisation using light beam injection techniques
Acciarri, M. Pizzini, S. Simone, G. Jones, D. Palermo, V. MATERIALS SCIENCE AND ENGINEERING B 2000 V.73 (1-3), p. 235 - 239

Transformation of small organic molecules in SiC nanoislands
Palermo V., Parisini A., Jones D., 2nd NATIONAL CONFERENCE ON NANOSCIENCE AND NANOTECHNOLOGY: THE MOLEUCLAR APPROACH, Bologna (Italy), February 2004

Formation on nanoclusters on silicon from carbon deposition
Palermo, V. Jones, D., E-MRS SPRING MEETING, Strasbourg (France), June 2003. (this work won the "YOUNG SCIENTIST AWARD" as best paper presented in his symposium)

The use of oxide desorption and surface diffusion for the creation of silicon on silicon nanostructures
Palermo, V. Jones, D., 1ST NATIONAL WORKSHOP ON CURRENT TRENDS IN NANOTECHNOLOGIES, Catania (Italy), Feb 2002

Self-Organised Growth of Silicon Structures on Si(100) During Oxide Desorption
Jones, D. Palermo, V. E-MRS Spring Meeting, Strasbourg (France), June 2001

STM study of surface transformations on silicon during UHV annealing
Palermo, V. Jones, D. 4TH MULTINATIONAL CONGRESS ON ELECTRON MICROSCOPY, Veszprem (Hungary), Sept 1999

Advances in silicon surface characterisation using light beam injection technique
Acciarri M., Pizzini S., Simone G., Jones D., Palermo V., E_MRS SPRING MEETING, June 1999

Spontaneous nano-wire growth on silicon
Palermo V., Jones D., SMARTON workshop, Leuven (Belgium), October 2002

Ordered circles of nano-islands on silicon from CO adsorption
Palermo V., Jones D., TRENDS IN NANOTECHNOLOGY 2002, Santiago de Compostela (Spain), September 2002

Production of nanostructures of silicon on silicon by atomic self-organisation
Palermo, V. Jones, D. EUROMAT, Rimini (Italy), June 2001

Etching holes and anisotropic corrosion on silicon [100]
Palermo, V., Jones, D., Susi, E., Asoli, B., SILICON WORKSHOP, Genova (Italy), February 2001

Morphological and electrical characteristics of damaged silicon surfaces
Susi, E., Castaldini, A., Cavalcoli, D., Cavallini, A., Jones, D., Palermo, V., SILICON WORKSHOP, Genova (Italy), February 2001

Effect of HF etching on the roughness of a silicon surface
Palermo, V. Jones, D. NATIONAL CONFERENCE ON PHYSICS OF MATTER, Genova (Italy) June 2000

Effect of Native Oxide Desorption upon the Surface Morphology of Si[100] by STM and LEED
Palermo, V. Jones, D. SILICON WORKSHOP, Genova (Italy), February 2000

Characterisation of silicon surfaces for microelectronics through STM measurements
Palermo, V. Jones, D. 4TH MULTINATIONAL CONGRESS ON ELECTRON MICROSCOPY, Veszprem (Hungary), Sept 1999