NAST Report
Scientific Report 2007
Atomic Force Microscope (AFM) & Scanning Tunnelling Microscopy (STM)
The Variable Temperature STM/AFM
Characteristics
Stainless steel UHV system (Standard pressure 6 10-11mbar).Turbo molecular pump for roughing: 240 l/sec - Ionic pump: 500 l/sec - Titanium sublimator.X-Y-Z manipulator with direct current or resistive heating. Tmax=1500 K.STM/AFM (piezoresistive).Heating at the STM position: up to 1500 K.Cooling at the STM position: down to 25 K.E-beam evaporators at the STM position: Ge and Si.Reverse view LEED-Auger with LaB6 filament.
Some Results
Ge/Si(111) - experiments performed were related to the visualization of the growth by Physical Vapour Deposition of Ge nanostructures on 7×7 Si(111) reconstructed surfaces. By evaporating Ge on Si(111) at T=500°C the formation ofwetting layers have been studied by Scanning Tunneling Microscopy in situ. The evolution of the Ge islands appearing after the wetting layer (completed at 3 ML). The 3D islands appear as truncated tetrahedrons (7×7 reconstructed on the top) and evolves into rounded shape, flat islands with a central hole. An erosion of the substrate around the islands has been also evidenced and measured. The island have lateral dimensions in the range 200 - 500 nm. The statistical distribution of the islands shapes and contact angles has been analysed. On Si step bunched surfaces (obtained by flashing at 1200°C in proper condition the Si substrate) the self aggregation and ordering of the islands has been evidenced. These results have been published in several papers and conference or school proceedings [1-6].
Fig 1. Ge islands grown on Si(111) observed by STM and AFM at various stages of evolution. Top left, a) an island after the nucleation (STM: 236×236x8 nm), top rigth, b) new facets (100 and 117) appear (STM: 230×230x38 nm); bottom left, c). First stage of ripening. (STM: 527×527x12 nm) bottom rigth, d) final stage of ripening (AFM image: 527×527x10 nm). Ge flux was 1 Å/min. The substrate temperature was 530 °C for a), 450 °C for b) and 500 °C for c) and d).
Fig 2. Organization of the Ge islands on a Si(111) step-bunched substrate a) STM image of 2.5 nm Ge deposition on Si(111) at T=450 °C 2.7×3.7 μm2. The total height of the image is 56 nm. b) STM image of 6 nm Ge deposition on Si(111) at T=450 °C 10×10 μm2. The total height of the image is 82 nm.InAs/GaAs quantum dotsThe InAs quantum dots on GaAs were prepared ex-situ by MBE as follows: the GaAs(001) wafer was initially deoxidized in As flux at 640 °C until a weak 2×4 RHEED pattern appeared. Afterwards, the substrate temperature was lowered to 590 °C and an epitaxial GaAs buffer layer of approximately 0.75 mm was grown at a rate of 1 μm/h. After 10 min of annealing, the temperature was further lowered to 500 °C for the InAs growth. The deposition rate was 0.028 ML/s with an In/As flux ratio of 1/15. The InAs coverage was 3 ML (the 2D-3D transition occurs at 1.6 ML). A 50 nm As capping layer is grown on top of the quantum dots, in order to protect the surface during the transfer to the AFM/STM chamber if atomic resolution and reconstruction have to be obtained by STM. The other samples are grown on intrinsic GaAs exhibiting a resistance too high to be imaged by STM, so the measurements are normally performed by AFM. Many samples, with different InAs coverages and growth modes have been prepared and measured. The size and distribution of the dots obtained in various growth conditions have been measured. Two main growth modes have been analysed: Continuous (the In flux was never interrupted) and Migration Enhanced (the In flux was interrupted at regular intervals, in order to increase the atomic movements ad aggregation on the surface). The island size increases in the Migration Enhanced mode. The onset of the quantum dot formation has been evidenced by also by STM, by imaging 2D islands after which act as precursors. The results have been published in two papers [7-8]
Fig 3. STM images at 1.3 ML of InAs on GaAs(001); a) 2D-islands of average height 0.4 nm (precursors); b) high resolution image of the wetting layer. The RHEED image has been acquired in the MBE system at the end of the growth.
Fig 4. Needle-Sensor AFM of self-assembled quantum dots of InAs on GaAs(001) imaged using the VT SPM; dimensions: 300×300 nm. Height: 10 nm. The typical dot size is around 25 nm, and the height is 7 nm.
References on Ge/Si
[1] F. Boscherini, G. Capellini, L. Di Gaspare, F. Rosei, N. Motta and S. Mobilio, “Ge-Si intermixing in Ge quantum dots on Si(001) and Si(111)”, Appl. Phys. Lett. 76, 682 (2000).[2] F. Rosei, N. Motta, A. Sgarlata, G. Capellini and F. Boscherini, “Formation of the Wetting Layer in Ge/Si(111) studied by STM and XAFS”, Thin Solid Films 369 p29 (2000).[3] F. Boscherini, G. Capellini, L. Di Gaspare, F. Rosei, N. Motta and S. Mobilio, “Atomic intermixing in Ge Quantum Dots”,“ESRF Highlights” 1999, Surfaces and Interfaces (may be visualized on the web site www.esrf.fr).[4] F. Boscherini, G. Capellini, L. Di Gaspare, M. De Seta, F. Rosei, N. Motta A. Sgarlata and S. Mobilio, “Ge-Si intermixing in Ge quantum dots on Si”, Thin Solid Films 380, 173 (2000).[5] A. Sgarlata, F. Rosei, M. Fanfoni, N. Motta and A. Balzarotti, “STM/AFM study of Ge Quantum Dots grown on Si(111)”, IEEE Proceedings of the 11th International Semiconducting and Insulating Materials Conference, February 2000.[6] F. Rosei, N. Motta, A. Sgarlata and A. Balzarotti, “Growth and characterization of Ge nanostructures on Si(111)”, submitted for publication to Lecture Notes in Physics. (February 2001).[7] Nunzio Motta Self-assembled Quantum Dots studied by scanning probes and other structural techniques. Proc. Workshop on Nanotubes and Nanostructures 2000, S.M.Pula (CA), Ed. S.Bellucci, (Editrice Compositori 2001)[8] N. Motta, F. Rosei, A. Sgarlata, G. Capellini, S. Mobilio, F. Boscherini, Evolution of the intermixing process in Ge/Si(111) Self-assembled islands, submitted to Materials Science B
References on InAs/GaAs
[1] F. Patella, M. Fanfoni, F. Arciprete, S. Nufris, E. Placidi, and A. Balzarotti; Kinetic aspects of the morphology of self-assembled InAs quantum dots on GaAs(001) Applied Physics Letters 76 (2001) 320.[2] Arciprete, A. Balzarotti, M. Fanfoni, N. Motta, F. Patella, A. Sgarlata; Morphology of self-assembled quantum dots of InAs on GaAs(001) and Ge on Si(111) in Recent Research developments in Vacuum Science & Technology. Publisher: Transworld Research Network (2001).
Molecular Beam Epitaxy & Electron Spectroscopy
Molecular Beam Epitaxy
Characteristics
(Mod.32; Riber)Stainless steel UHV system (Standard pressure 6 10-11 mbar). Turbo molecular pump for roughing: 240 l/sec - Ionic pump: 500 l/sec - Titanium sublimator. X-Y-Z manipulator with resistive heating.
Tmax=800 °C. Knudsen cells: Ga, As, In, Al, Si (as dopant). Rheed optics E= 10 KeV.
High Resolution Electron Energy Loss Spectroscopy
HREELS cross section
Characteristics
Stainless steel UHV system (Standard pressure 4×10-11mbar). Turbo molecular pump for roughing: 240 l/sec - Ionic pump: 200 l/sec - Titanium sublimator. X-Y-Z manipulator with resistive heating. T max=800 °C. Leed optics.
Prof. Carla Andreani
Contact details
Office: Physics Department
Tel: +39 06 72594441
Lab: +39 06 72594422
Fax: +39 06 2023507
CA is Professor of Condensed Matter at the Faculty of Science of the University of Rome Tor Vergata.
Research Activity
Study of structure and dynamics of simple and complex fluids using spectroscopic techniques, (mainly x-ray and neutron scattering) and the design and construction of instrumentation for neutron scattering. CA most recent studies are about the static and dynamical properties of molecular (hydrogen bonded) and quantum systems in bulk and confined geometry [1,2,3,4]. Examples includes diatomic fluids, hydrogen halides, H2O, H2, D2, 3He, 4He and 3He/4He mixtures. Neutron scattering represents an important tool for the study of the properties of matter at the nanoscale, the ideal reciprocal space probe of microscopic correlations in bulk sample. Its provides relevant information to nanoscience and application to nanotechnology, which add and complement real space visualization and manipulation of matter on the nanometer scale. CA has been directly involved in the design and development of novel instrumentation for neutron spectroscopy at the eV energy, in particular DINS (Deep Inelastic neutron Scattering) [4,5]. The latter is the unique technique to access microscopic information on the dynamics and the local environment of light atoms and molecules in a variety of environments. Much of her work has focussed on the study of the single particle momentum distribution, n(p), and mean kinetic energy, K>, in light atoms and molecules, physical quantities which can be directly measured using DINS. In this area CA most recent work has been addressed to the study of liquid 3He and 4He and 3He - 4He mixtures [6], where the interplay between Bose and Fermi statistics dominates the behaviour, and to the study of liquid water in bulk and confined in nanopores. A recent research with eV spectroscopy is in progress where neutrons with energies similar to chemical bonds are used to produce quantitative measures and even 3D images of the elemental composition and physical structure of artefacts. This idea, aiming to develop an analysis technique based on neutron absorption, is quite innovative in the field of archaeology, with a number of scientific and technical challenges. This is the objective of the ANCIENT CHARM project
Teaching Activities
Undergraduate: Physics I and II (Biotechnology Degree)
Graduate: Spectroscopy (Degree in Physics)
PhD Schools: Experimental Techniques in Material Science (School Nanostructure and Nanotechnology, and School in Physics).
Administrative Responsabilities
Member of the Neutron Committee of Consiglio Nazionale delle Ricerche (CNR).
Member of the Administrative Board of University of Rome Tor Vergata.
Member of the ISIS Spallation Neutron Source Facility Access Panel (FAP) (2005-2007).
Member of the International Advisory Board of the Hungarian-Spanish ESS Collaboration.
Member of the Teaching Supervising Committee of the International Ph.D. Programs in Nanostructure and Nanotechnology, (a Joint Ph.D. Program between The Universities of Rome Tor Vergata and Milano Bicocca), and Physics (University Roma Tor Vergata).
Membership of Professional Bodies
Member of Italian Physical Society and American Chemical Society.
Editorial Roles
Editor of Notiziario Neutroni e Luce di Sincrotrone a journal supported by Consiglio Nazionale delle Ricerche (CNR)
Recent Publications
[1] A. Pietropaolo, R. Senesi, and C. Andreani, A. Botti, M. A. Ricci, and F. Bruni, Phys. Rev. Letts., 100, 127802 (2008)
[2] C. Pantalei, A. Pietropaolo, R. Senesi, S. Imberti, C. Andreani, J. Mayers, C. Burnham, and G. Reiter, Phys. Rev. Letts., 100, 177801 (2008).
[3] C. Andreani, C. Pantalei and R. Senesi, Journal of Physics Condensed Matter, 18, 5587 (2006)
[4] C. Andreani, D. Colognesi, J. Mayers, G. Reiter, R. Senesi, Advances in Physics, 54, 377 (2005)
[5] C. Andreani et al., Appl. Physics Letters, 85, 5454, (2004)
[6] R. Senesi, C. Andreani, D. Colognesi, A. Cunsolo, M. Nardone, Phys. Rev. Letts. 86, 4584, (2001)
Notes. CA is author of about 130 papers on international journals and about 100 scientific oral contributions at international conferences, meetings and schools.
Late News 3
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Late News 2
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Joint Laboratory for Advanced Nanostructured Materials for Energy, Catalysis and Biomedical Applications
Sub-Femtoseconds proton dynamics in confined geometry and near proteins
Collaborative research among scientists from Italy - the Nast Centre for Nanoscience Nanotechnology and Innovative Instrumentation, UK - ISIS Spallation Neutron Source - and US, - University of Huston - have used Deep Inelastic Neutron Scattering (DINS) to shows how the proton momentum distribution in liquid water monitors the changing occurring …
New neutron facility for fast neutron irradiation tests of electronics
Collaborative research among Italian and British scientists and engineers from Nast Centre for Nanoscience Nanotechnology and Innovative Instrumentation, CNR (I), ISIS Spallation neutron Source (UK), Universities of Central Lancashire, Padova and Milano Bicocca, and from the avionics and aerospace industries have been using VESUVIO neutron flux…
Test Knowledge Transfer 1
Work in progress Read more »
The NAST Directory
To phone dial +39 06 7259 plus Extension
Name |
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Extension |
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| Prof. Patrizia Beatrice ALBERTANO |  |
4589 | |||
| Prof. Carla ANDREANI | |
4441 | |||
| Dr. Fabrizio ARCIPRETE | |
4435/4428 | |||
| Prof. Giuseppe ARCOVITO | |
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| Prof. Luciana AVIGLIANO | |
6472 | |||
| Prof. Giuseppe BALESTRINO | |
7221 | |||
| Prof. Adalberto BALZAROTTI | |
4437/4428 | |||
| Prof. Antonio BERGAMASCHI | |
2090 2201 | |||
| Prof. Enrico BERGAMASCHI | |
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| Dr. Alessandra BIANCO | |
4493 | |||
| Dr. Gianfranco BOCCHINFUSO | |
4465 | |||
| Dr. Beatrice BONANNI | |
4288/4427/4451 | |||
| Prof. Fabio BRUNI | |
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| Prof. Salvatore CANNISTRARO | |
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| Prof. Gian Carlo CARDARILLI | |
7324/7370 | |||
| Dr. Paola CASTRUCCI | |
4545/4532 | |||
| Dr. Luciano CATANI | |
4544/4535 | |||
| Prof. Piero CHIARADIA | |
4546/4427 | |||
| Prof. Giovanni CICCOTTI | |
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| Prof. Michele CINI | |
4596 | |||
| Prof. Massimo COLETTA | |
6365 | |||
| Dr. Antonio CRICENTI | |
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| Prof. Arnaldo D’AMICO | |
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| Dr. Sabato D’AURIA | |
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| Prof. Ivan DAVOLI | |
4523 | |||
| Prof. Maurizio DE CRESCENZI | |
4547/4532 | |||
| Prof. Maria Pia DE PASCALE | |
4289 | |||
| Prof. Marco DE SPIRITO | |
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| Prof. Rodolfo DEL SOLE | |
4597 | |||
| Prof. Alessandro DESIDERI | |
4376 | |||
| Dr. Elisabetta DI BARTOLOMEO | |
4495 | |||
| Prof. Paolo DI NARDO | |
4215 | |||
| Dr. Almerinda DI VENERE | |
6464 | |||
| Dr. Fulvio ERBA | |
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| Prof. Mattia FALCONI | |
4326 | |||
| Prof. Massimo FANFONI | |
4439 | |||
| Dott. Alessandra FILABOZZI | |
4440 | |||
| Dr. Dino FIORANI | |
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| Prof. Laura FIORUCCI | |
6478 | |||
| Dr. Lina GHIBELLI | |
4323 | |||
| Prof. Claudio GOLETTI | |
4288/4427 | |||
| Dr. Paola GORI | |
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| Prof. Giuseppe GORINI | |
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| Prof. Leonardo GUIDONI | |
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| Dr. Conor David HOGAN | |
4908 | |||
| Prof. Alexey KAVOKIN | |
4121/4122 | |||
| Prof. Silvia LICOCCIA | |
4386/4397 | |||
| Prof. Mauro MACCARRONE | |
6388 | |||
| Prof. Andrea MAGRINI | |
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| Dr. Daniele MALFITANA | |
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| Dr. Andrea MARINI | |
4894 | |||
| Prof. Stefano MARINI | |
6354 | |||
| Prof. Giampiero MEI | |
6460 | |||
| Dr. Simone MELCHIONNA | |
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| Dr. Marilena MINIERI | |
4246 | |||
| Prof. Roberto MONTANARI | |
7182 | |||
| Dr. Pietro MORALES | |
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| Prof. Silvia MORANTE | |
4554 | |||
| Prof. Maurizio PACI | |
4446/4328 | |||
| Prof. Antonio PALLESCHI | |
44660 | |||
| Prof. Giuseppe PALLESCHI | |
4423 | |||
| Dr. Maurizia PALUMMO | |
4548 | |||
| Prof. Gaio PARADOSSI | |
4464 | |||
| Prof. Fulvia PATELLA | |
4438/4428 | |||
| Prof. Piergiorgio PICOZZA | |
4576/4486 | |||
| Dr. Antonino PIETROPAOLO | |
4549 | |||
| Dr. Ernesto PLACIDI | |
4266 | |||
| Prof. Paolo PODIO GUIDUGLI | |
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| Dr. Riccardo POLINI | |
4414 | |||
| Dr. Olivia PULCI | |
4548 | |||
| Prof. Maria Antonietta RICCI | |
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| Prof. Wolfgang RICHTER | |
4501 | |||
| Prof. Nicola ROSATO | |
6471 | |||
| Prof. Antonello ROSSI | |
6466 | |||
| Dr. Valerio ROSSI | |
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| Prof. Adelio SALSANO | |
7340 | |||
| Prof. Roberto SANTUCCI | |
6364 | |||
| Dr. Isabella SAVINI | |
6380 | |||
| Dr. Manuela SCARSELLI | |
4436/4532 | |||
| Prof. Orazio SCHILLACI | |
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| Dr. Roberto SENESI | |
4549 | |||
| Dr. Anna SGARLATA | |
4436/4406 | |||
| Dr. Roberta SPARVOLI | |
4103 | |||
| Dr. Gianluca STEFANUCCI | |
4596 | |||
| Prof. Lorenzo STELLA | |
4463 | |||
| Prof. Enrico TRAVERSA | |
4492 | |||
| Dr. Andrei VARLAMOV | |
7220 | |||
| Prof. Mariano VENANZI | |
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