STM under SEM observation with laser excitation of the specimen
A home made piezoscanner, designed for xy scanning of the sample, is hosted on the sample stage of a modified Cambridge S200 scanning electron microscope, while the STM tip is positioned on the desired feature under study by a ρ,θ,φ nanomanipulator. This configuration is the most suitable to minimize mechanical vibration of the STM; alternatively, a particularly low weight scanner is mounted on the nanomanipulator while the sample is fixed. Laser beams can be directed to the interaction zone through an optical port at the back of the SEM chamber, which also serves for microscopic observation of the laser beam alignment on the STM junction. Directing the Laser beam onto the tip allows tip enhanced localised laser nanostructuring (ablation or multiphoton deposition) and localised spectroscopy.
A scheme of the STM-SEM facility is reported below (left). The images on the right show an optical microscope view of the laser irradiated STM tip on the sample, and an SEM scan of the STM tip operating to deposit material on the tips of a couple of lithographic nanoelectrodes fabricated by A. Gerardino at the CNR-IFN electron beam facility. 
This facility is particularly useful for precise positioning of the tip on the specific features or devices to be analyzed or operated upon. It allows STM electronic spectroscopy to be effected on features previously easily located on the basis of the difference in secondary electron emission. It allows a prompt characterization of both tip and sample surface damage. It supplies a first easy characterization of surface modifications, like nanometric pit formation or inorganic material depositions, when the sample is irradiated by laser beams. Finally it gives us the possibility to effect much shorter, and as a consequence slower and less damaging, STM scans for a complete characterization of the sample.
Nanomanipulated Piezoelectric Dynamometers (AFM and Piezoresistive Cantilevers)
Within the general issue of nanofabrication in our laboratory we are interested in controlling the applied forces during sharp probe interaction with the samples. We have purchased commercial piezoresistive cantilever based dynomometer probes and are planning to build more sensitive ones. Attaching this kind of piezoresistive or mechanical probes to a piezoelectric inertial nanomanipulator allows measurement of the stiffness and compliance of a wide range of materials. If the interaction is made under electron microscopy observation, we can easily gain a practical experience on the interaction of sharp tips with materials. We show here how a commercial AFM probe can be stressed and used to dig pits on a gold surface (movie), how we can measure the sensitivity of insects’ tactile hair sensors (movie), how we can measure the compliance of carbon nanotubes wool (movie), and even how we can accomplish a micrometric electrical switch based on a carbon nanotubes helical spring (movie).
UHV STM with microscopic spectral analysis capabilities
This facility based at the ENEA laboratories is hosted in a 35 l ionically pumped ultra-high vacuum vessel endowed with a home made STM, a Z inertial piezo slider for sample approach and a remotely controlled ρ,θ,φ nanomanipulator for sample movement with submicron precision. The vessel has two load-lock chambers for tip and sample load and a hand actuated wobbling pincer for manual operations. It also has optical ports for access to the tip region by two different laser beams.
Above on the left is the scheme of the UHV STM system coupled to the available laser sources and to the spectroscopic analysis system devoted to “tip-enhanced” photoluminescence studies. On the right, a photograph of the UHV vacuum vessel with its lid lifted shows details of the optical microscope case and of the STM. Below, an optical microscope image of the STM tip over a layer of Rhodamine 6G fluorescent dye in white light (left) and excited by a green laser (540 nm) as recorded through a long wavelength pass filter with cutoff at 560 nm with the tip within tunnelling distance (center) and 5 μm away from the surface (right). Light from the tip-enhancement area is spatially selected by a moveable pinhole and analyzed by a monochromator producing the R6G emission spectrum reported below.
Bottom-up Nanofabrication by Lasers and Scanning Probes
The idea that bottom up nanofabrication can be achieved by the joint use of nanometrically controlled sharp tips and electromagnetic radiation. If we think of an irradiated STM tip as an electromagnetic antenna operating at optical rather than radio frequencies, we can understand how, in the vicinity of its highly curved apex,…
Prof. Giovanni Ciccotti
Contact Details
Professor in Structure of Matter
Department of Physics,
University of Rome La Sapienza,
Piazzale Aldo Moro 2, 00185 Rome ITALY
Tel: +39 06 49914378
Fax: +39 06 4957697
Research Outline
Molecular Dynamics and Monte Carlo of Statistical Mechanical Systems
The focus of my research activity is on developing algorithms fro Molecular Dynamics simulation of complex systems in condensed matter phases. From the from now ancient SHAKE algorithm (a procedure to introduce holonomic constraints in MD) or the Subtraction Technique (a noise reducing approach to compute the response to weak external fields in Nonequilibrium MD) to the introduction of the Blue Moon’s ensemble (to simulate in MD rare events) and techniques to simulate Brownian motion to the most recent, and still very active, field of rigorous algorithms to compute nonadiabatic quantum-classical dynamics, the attempt is to widen the domain of computer simulation in condensed matter with a particular emphasis on MD (as distinguished from the very close but different MC- Monte Carlo). Together with that, I have been, and still am, also interested in challenging applications od atomistic MD simulations ranging from surface/interface physics problems in Materials sciences to simulations of biological molecules to find atomistic level explanations of their behavior or functioning mechanisms. More generally, I am interested in considering a variety of developments/applications in the simulation of systems of Statistical Mechanics interest.
Curriculum Vitae et Studiorum
Full List of Publications
Most Recent Publications
[135] E.Vanden Eijnden, and G. Ciccotti, “Second-order integrators for Langevin equations with holonomic constraints”, Chem. Phys. Lett., 429, 310, (2006)
[134] M. S. Causo, G. Ciccotti, S.Bonella, and R. Vuilleumier, “An adiabatic linearized path integral approach for quantum time correlation functions II: A cumulant expansion method for improving convergence”, J. Phys. Chem. B, 110, 3638, (2006)
[135] V. Marry, and G. Ciccotti, “Trotter derived algorithms for molecular dynamics with constraints : Velocity Verlet revisited”, J. Comp. Phys., 222, 428, (2007)
[132] L. Maragliano, A. Fischer, E. Vanden Eijnden, and G. Ciccotti, “String method in collective variables: minimum free energy paths and isocommittor surfaces”, J. Chem. Phys., 125, 024106, (2006).
[131_B] R. Kapral, and G. Ciccotti, “Transport Coefficients of Quantum-Classical Systems”, in “Computer Simulations in Condensed Matter: From Materials to Chemical Biology (The Erice Lectures)”, M. Ferrario, G. Ciccotti, and K. Binder Eds, LNP, Springer Verlag, (2006).
[130_B] G. Ciccotti, D. Coker, and R. Kapral, “Quantum statistical dynamics with trajectories”, in Quantum Dynamics of Complex Molecular Systems, p. 275-294, I. Burghardt and D. Micha Eds, Springer Verlag, Berlin, (2007)
[129] G. Kalibaeva, R. Vuilleumier, S.Meloni, A. Alavi, G. Ciccotti, and R. Rosei, “Ab initio simulation of carbon clustering on Ni(111) surface: a model of the poisoning of nickel based catalysts”, J. Phys. Chem. B, 110, 3638, (2006)
[128] F. Pizzitutti, A. Giansanti, P. Ballario, P. Ornaghi, P. Torreri, G. Ciccotti, and P. Filetici, “Relevant role of loop ZA and Pro371 in the function of yeast Gcn5p bromodomain: evidences from Molecular Dynamics and experiments”, Journal of Molecular Recognition, 19, 1, (2006)
Books
B1) “Molecular Dynamics Simulation of Statistical Mechanical Systems.”, ‘E. Fermi’ 1985 Summer School. G.Ciccotti and W.G.Hoover, Eds., North Holland 1986.
B2) “Simulation of Liquids and Solids. Molecular Dynamics and MonteCarlo methods in Statistical Mechanics. A reprint book.”, G. Ciccotti, D. Frenkel and I. R. Mc Donald, Eds. North Holland, 1987.
B3) “MC and MD of condensed matter systems”, Euroconference 1995, K. Binder and G. Ciccotti, Eds., SIF 1996.
B4) “Simulation of classical and quantum dynamics in condensed phase”, Euroconference 1997, B. J. Berne, G. Ciccotti and D. F. Coker, Eds., World Scientific, 1998.
B5) “Bridging time scales: Molecular simulations for the next decade”, SIMU Conference, Konstanz 2001, P. Nielaba, M. Mareschal, and G. Ciccotti, Eds., Springer, Berlin, 2003
B6) “Computer Simulations in Condensed Matter: From Materials to Chemical Biology (The Erice Lectures)”, M. Ferrario, G. Ciccotti, and K. Binder, Eds, LNP, Springer Verlag, Berlin, (2006)
Laser assisted fabrication of biomolecular sensing microarrays
The Pulsed Laser Deposition technique is used in these experiments in conjunction with micro and nanopatterning techniques to produce very high density arrays of localized active biomolecular layers. Such patterned layers of homogeneous or heterogeneous biomolecules are particularly interesting for the accomplishment of high density biosensing arrays.