NAST Report
Scientific Report 2007 Read more »
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 Andrean
Contact details
Office: Physics Department
Tel: +39 06 72594441
Lab: +39 06 72594422
Fax: +39 06 72594089
Current Professional Positions
Full Professor in Condensed Matter at the Faculty of Science of the University of Rome Tor Vergata.
Research Experience
Following a Laurea in Physics at the Università degli Studi di Roma ‘La Sapienza’, Italy, (Final grade: 110/110 “Summa cum Laude”, dissertation Topic: “Missing Mass in the Universe and Black Holes”), I held a Post Docs positions at the AERE Harwell (UK) and visiting scientist positions at the ISIS Facility at the Rutherford Appleton Laboratory (UK), the ILL Reactor (F) and at the IPNS pulsed Neutron source, Argonne National Laboratory (USA).
I have a track record in studying and directing research on the study of microscopic structure and dynamics of disordered systems. In particular I have investigated the structure factor and single particle dynamics, i.e. momentum distribution – n(p) – and mean kinetic energy of light atoms – <EK> – of:
- quantum fluids and solids – liquid 4He, liquid and solid 3He, in bulk and confined geometry, and 3He-4He mixtures [1,2];
- molecular fluids and solid – [3,4,5,6,7]. Examples includes diatomic homonuclear fluids (Cl2, Br2, I2, H2, D2) hydrogen halides (HCl, HBr, HI), H2S and H2O (in bulk and confined geometry);
In my most recent n(p) experimental studies I have addressed the proton quantum dynamics in water – in normal and metastable phases – in bulk and confined geometry [5,6,7].
In most cases I have employed a combination of diffraction and spectroscopy techniques (most notably, neutron and x-ray diffraction, neutron spectroscopy, combined with Raman spectroscopy). Neutron scattering represents an important tool for the study of the properties of matter at the nanoscale, the ideal probe of microscopic correlations in bulk sample in reciprocal space. 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.
As experimental scientist I have contributed to the design and development of several instrumentation for neutron diffraction and scattering: the DBSS diffractometer, at PLUTO reactor (Harwell, UK), the 2 ASSI diffractometer at TRIGA reactor (ENEA Casaccia, I), the constant-Q spectrometer at HELIOS Linac (Harwell, UK), the TOSCA spectrometer at ISIS pulsed neutron source (UK). I have proposed a novel design a concepts for the VESUVIO and e.VERDI spectrometers at ISIS for Deep Inelastic Neutron Scattering (DINS) [3], and given a significant contribution to the development of gamma detector for epithermal neutron spectroscopy [8]. DINS is the unique technique to access microscopic information on the dynamics, n(p), and the local structure of light atoms and molecules in a variety of environments.
In eV spectroscopy I have proposed:
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the use neutrons at the eV energies to produce quantitative measures and even 3D images of the elemental composition and physical structure of artefacts. Within the ANCIENT CHARM project an analysis technique based on neutron absorption has been developed, quite innovative in the field of archaeology. This technique uses the “Neutron Resonant Capture Imaging” combined with “Neutron Resonance Transmission” (NRCI/NRT) as a non-invasive technique for producing quantitative measurements and even 3D images of the elemental composition and physical structure of artifacts.
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the use of neutrons at the MeV for accelerated irradiation test on electronic devices. Following benchmark experiments on VESUVIO a novel beamline (ChIPIR) for fast neutron irradiation tests of electronics is at present under construction at the ISIS spallation neutron source [9].
Teaching Activities
CA is member of the Graduate School in Physics – PhD Program at the University of Roma Tor Vergata – and the Graduate School Nanostructure and Nanotechnology – a joint PhD program between University of Tor Vergata and University of Milano-Bicocca. CA has a long-standing interest in teaching improvements in undergraduate and graduate physics also providing the students with a modern introduction to spectroscopic techniques. Much of this work has concentrated on the use of modern technology to improve the student’s conceptual understanding of basic experimental physical concepts.
Management and organizational experience
Member of the Neutron Committee of Consiglio Nazionale delle Ricerche (CNR) (1994-present)
Member of the Executive Board of University of Rome Tor Vergata (2005-2008).
Member of the International Advisory Board of the International Advisory Board ESS Bilbao Initiative (2008-present)
Member of the Novel Neutron Instrumentation Think Tank (2005-2009)
Member of the Science Advisory Board del Studsvik Neutron Research Laboratory (NFL) – Svezia (2000-2002 )
Member of the OECD MEGASCIENCE FORUM: NEUTRON SOURCES WORKING GROUP Panel B: International cooperation in the development of neutron instrumentation and data evaluation (1996-1999)
Member (scientific secretary) of the Scientific Advisory Board for Physical Sciences of the Italian national research Council CNR (1994-1998)
Member of the Round Table on Neutron Sources, http://neutron.neutron-eu.net/n nmi3/n (1994-present)
Peer Review
I served as:
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member of evaluation Area panel Physical Science, CIVR for Italian Ministry of Research (MIUR) (2003-2009)
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member of the ISIS Facility Access Panel (FAP 5), 2006-2008
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member of peer review panel for material science for Georgia National Science Fundation (2007-2008)
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Chairperson of the Area Panel for Physical Sciences, Italian Research Council, CNR Italy (2009)
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Chairperson of the Ministry of Research advisory board for the Italian Infrastructure roadmap prioritisation exercise (2010)
- member of review panel for research projects of Regione Lombardia (2010)
I currently serve as:
- member of SNS neutron scattering science proposal Review Panel (2008-present)
Since 1998 I serve as referee for:
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a number of National and international scientific journals (e.g. the Physical Review journals and Reviews of Modern Physics) and in a number of peer-review roles.
I am currently supervising 6 scientists. I have significant experience in recruiting and interviewing. I have served as project scientist and, more recently, project sponsor in a variety of instrument development projects at ISIS (UK) and SNS (US).
Membership of professional societies
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Italian Physical Society
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American Chemical Society
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School of Neutron Scattering “Francesco Paolo Ricci“
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Sociedad Española de Tecnicas Neutronicas
Editorial Roles
Editor of Notiziario Neutroni e Luce di Sincrotrone a journal supported by Consiglio Nazionale delle Ricerche (CNR)
Recent Publications
[1] C. Andreani, C. Pantalei and R. Senesi, Journal of Physics Condensed Matter, 18, 5587 (2006)
[2] R. Senesi, C. Andreani, D. Colognesi, A. Cunsolo, M. Nardone, Phys. Rev. Letts. 86, 4584, (2001)
[3] C. Andreani, D. Colognesi, J. Mayers, G. Reiter, R. Senesi, Advances in Physics, 54, 377 (2005)
[4] A. Pietropaolo, R. Senesi, and C. Andreani, A. Botti, M. A. Ricci, and F. Bruni, Phys. Rev. Letts., 100, 127802 (2008)
[5] C. Pantalei, A. Pietropaolo, R. Senesi, S. Imberti, C. Andreani, J. Mayers, C. Burnham, and G. Reiter, Phys. Rev. Letts., 100, 177801 (2008)
[6] A. Pietropaolo, R. Senesi, C. Andreani, A. Botti, M. A. Ricci and F. Bruni, Phys. Rev. Lett. 103, 069802 (2009)
[7] A. Pietropaolo, R. Senesi, C. Andreani, J. Mayers, Brazilian Journal of Physics, 39, 318, (2009)
[8] C. Andreani et al., Appl. Physics Letters, 85, 5454, (2004)
[9] C. Andreani, A. Pietropaolo, A. Salsano, G. Gorini, M. Tardocchi, A. Paccagnella,, S. C. D. Frost, S. Ansell, S. P. Platt, Applied Physics Letters, 92, 114101 (2008).
Notes. CA has authored about 150 publications 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 »