Istituto Nanoscienze-CNR and Scuola Normale Superiore
Piazza San Silvestro 12, 56127 Pisa, Italy
phone office: +39-050-509 472, mobile: +39-338-6244853
FAX: +39-050-509 473
Present position: Senior Scientist
Language skills: German (native), English (fluent), Italian (fluent), Japanese (basic knowledge)
Research areas: My main research interest is the physics of low-dimensional systems. This includes three aspects: (i) the synthesis of nanostructures, (ii) the manipulation of samples on the nanometer-scale, and (iii) their characterization with spatially resolved spectroscopic techniques.
Publications: Over 115 publications in refereed international journals.
Communications: Over 60 communications at conferences (17 inviteds) and 50 invited seminars.
Citation Statistics My papers have been cited over 1450 times which corresponds on average to 12.23 citations per published paper. h- index: 21 (source: Web of Science).
10/2006 - today Senior Scientist at NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore in Pisa, Italy.
04/2004 - 10/2006 Senior Scientist at CNR - Istituto Nazionale per la Fisica della Materia at the Laboratorio Nazionale TASC, Trieste, Italy.
07/1997 - 03/2004 Beam line scientist at the Sincrotrone Trieste, Italy.
06/1995 - 07/1997 TMR Marie Curie research fellow of the Commission of the European Communities in the Materials Division of the Laboratorio TASC-INFM, Trieste, Italy. [link]
11/1993 - 05/1995 Post-doctoral Fellow at the Interdisciplinary Research Laboratories, NTT, Tokyo, Japan.
2008 - 2010 Italian coordinator of project MST Spectroscopic investigations of dip pen nanolithography patterns within the program of scientific and technological cooperation between the Italian Republic and the Republic of India (Indian partner: Prof. C. N. R. Rao), total 24 kEuro. [link1] [link2] [link3]
2008 - 2010 Italian coordinator of project MST4 Innovative catalytic patterns for nanowire growth within the program of scientific and technological cooperation between the Italian Republic and the Republic of India (Indian partner: Prof. G. U. Kulkarni), total 24 kEuro. [link1] [link2] [link3]
2005 - 2007 Italian coordinator of project MST1 within the program of scientific and technological cooperation between the Italian Republic and the Republic of India (Indian partner: Prof. C. N. R. Rao), total 24 kEuro. [link1] [link2]
2009 - 2012 Project FIRB Entanglement and Statistics in Quantum Interferometry, number RBID08B3FM, responsible Vittorio Giovannetti, duration: from 04/02/2009 to 04/02/2012.
2006 - 2010 Project FIRB One-dimensional semiconductor nanostructures and microfluidic devices, number RBIN045MNB, responsible Fabio Beltram, duration: from 03/10/2006 to 03/06/2010.
2006 Project PRIN Fisica di Nanocontatti Metallici e Molecolari: Conduttanza in Presenza di Magnetismo e altri Gradi di Liberta' Interni, number prot. 2006022847, responsible Erio Tosatti.
2003 - 2007 Project FIRB Micro-strutture e nano-strutture a base di carbonio , number RBNE019NKS, responsible Silvio Modesti, duration: from 10/01/2003 to 10/07/2007.
2002 - 2005 Responsible for the Nanospectroscopy beamline and the SPELEEM microscope at Elettra (from 01/02/2002 to 31/05/2005), which includes the responsability for the staff (1 researcher, 1 technician) and the operation and budget of the beamline (approximately 10 external user groups per semester). Annual budget: approx. 50 kEuro.
2010 - today External Reviewer for the Canadian Light Source.
2009 - today Member of the Proposal Review Committee at the Swiss Light Source.
2005 - today Member of the Board of Delegates of the European Materials Research Society (E-MRS). [link]
1997 - today Manuscript referee for the following international journals: Nano Letters, Crystal Growth & Design, Applied Physics Letters, Physical Review B, Journal of Applied Physics, Surface Science, Journal of Vacuum Science and Technology B, Journal of Electron Spectroscopy and Related Phenomena, Physica E, Superlattices and Microstructures, Nuclear Instruments and Methods in Physics Research B, Journal of Physical Chemistry, Micro & Nano Letters.
2011 Expert evaluator of FIRB Futuro in Ricerca proposals for the Italian MIUR.
2010 Expert evaluator of People Marie Curie Individual Actions for the FP7 programme of the European Union.
2010 Member of the CNR selection committee NANO AR 009/2010 PI.
2010 Member of the SNS selection committee 669.
2006 External examiner for the PhD thesis of K. S. Joseph Wilson, Madurai Kamaraj University, India.
2005 - 2006 Member of the following INFM selection committees: Bandi 500r, 588, 675, 860 (in 2005) and Bando 1004 (in 2006).
2002 - 2006 Research proposal referee for the Academy of Sciences of the Czech Republic.
2009 - today Member of the Editorial Board of the International Journal of Nanoscience. [link]
2008 - today Member of the Editorial Advisory Board of The Open Condensed Matter Physics Journal. [link]
2010 Guest editor of a special issue of Nuclear Instruments and Methods B: Vol. 268, February 2010. [link]
2008 Co-editor of the book Beam injection based nanocharacterization of advanced materials, Research Signpost, Trivandrum, Kerala, India, 2008, ISBN: 978-81-308-0226-8. [link]
2006 Guest editor of a special issue of Nuclear Instruments and Methods B: Vol. 246, May 2006. [link]
2003 Guest editor of a special issue of Nuclear Instruments and Methods B: Vol. 200, January 2003. [link]
2002 Co-editor of the book Nanoscale Spectroscopy and Its Applications to Semiconductor Research, Lecture Notes in Physics, Vol. 588, Springer Verlag, 2002, ISBN: 978-3-540-43312-5. [link]
2011 Member of the Scientific Committee of Symposium M of the E-MRS ICAM IUMRS Conference, 9 - 13 May 2011, in Nice, France. [link]
2010 Member of the International Advisory Committee of the 6th International Workshop on Nanoscale Spectroscopy and Nanotechnology, 25 - 29 October 2010, in Kobe, Japan. [link]
2009 Co-organizer of the symposium X-ray Techniques for Advanced Materials, Nanostructures and Thin Films: from Laboratory Sources to Synchrotron Radiation at the E-MRS Spring Meeting, 8 - 12 June 2009, in Strasbourg, France. [link]
2008 Member of the International Advisory Committee of the Fifth International Workshop on Nanoscale Spectroscopy and Nanotechnology, 15 - 19 July 2008, in Athens, Ohio, USA. [link]
2006 Member of the International Programme Committee of the Fourth International Workshop on Nanoscale Spectroscopy and Nanotechnology, 17 - 21 September 2006, in Rathen, Germany. [link]
2005 Co-organizer of the symposium Synchrotron Radiation and Materials Science at the E-MRS Spring Meeting, 31 May - 3 June 2005, in Strasbourg, France. [link]
2004 Member of the International Programme Committee of the Third International Workshop on Nanometer Scale Spectroscopy and Nanotechnology, 10 - 14 December 2004, at the University of Maryland, College Park, USA. [link]
2002 Co-organizer of the symposium Synchrotron Radiation and Materials Science at the E-MRS Spring Meeting, 18 - 21 June 2002, in Strasbourg, France. [link]
2002 Member of the Conference Committee of the Second International Workshop on Nano-scale Spectroscopy and Nanotechnology, 25 - 29 November 2002, in Tokyo, Japan. [link]
2000 Secretary of the Organizing Committee of the First International Workshop on Nano-scale Spectroscopy and its Applications to Semiconductor Research, 11 - 14 December 2000, in Trieste, Italy. [link]
1999 2 hours of lectures on Spectromicroscopy at Elettra at the University of Calabria, Cosenza, Italy (Prof. E. Colavita), 18 - 19 October 1999.
1990 - 1993 Tutor in the students’ laboratory at the Physics department of the University of Hannover, Germany.
2005 - 2006 Y. Pramudya: Alignment of InAs Quantum Dot on InGaAs Buffers, diploma thesis, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy (with Prof. L. Sorba). [thesis]
2004 - 2005 G. B. Golinelli: Morphology and composition of self-assembled InAs quantum dots grown on GaAs(001), diploma thesis, University of Modena and Reggio Emilia, Italy (with Prof. L. Sorba). [link] [thesis]
My main research interest is the physics of low-dimensional systems. This includes three aspects: (i) the synthesis of nanostructures, (ii) the manipulation of samples on the nanometer-scale, and (iii) their characterization with spatially resolved spectroscopic techniques.
Since 2007 my research is mainly focused on the study of interference phenomena as a fundamental manifestation of the quantum mechanical nature of electrons. Two- dimensional electron systems (2DES) in the quantum Hall (QH) regime are especially suited for this purpose given the large electronic coherence length characteristic of edge-channel chiral transport. In order to address these issues we are exploring the use of scanning gate microscopy (SGM) to control the trajectory and interaction of edge channels. The experiments are performed in a low temperature (300 mK) AFM/STM system operating in magnetic fields up to 9 T. In first experiments we could demonstrate a new method for the control of the trajectories of individual edge channels by the tip of the SGM. Our results can represent a crucial step for the implementation of multi-edge beam mixers and interferometers. We are now working on more refined device geometries to exploit this possibility for a control of the interaction of edge channels in QPC devices in the QH regime.
Besides, I also investigated the physics of semiconductor quantum dots and rings. The model systems are InAs/GaAs and Ge/Si. Samples were grown by molecular beam epitaxy. Composition, valence band alignment, and work function of individual quantum dots were investigated by synchrotron radiation x-ray photoemission electron microscopy (XPEEM). The measurements showed that during heteroepitaxy of InAs a reaction takes place with the substrate, giving rise to an alloying on the cation sublattice. With the same technique I also studied the formation mechanism of InAs/GaAs quantum rings. The controlled positioning of quantum dots was achieved on patterned substrates. Regular arrays of GeSi quantum dots were then used as a template to define the position of magnetic dots.
On the other hand, part of my time was dedicated to instrumental development. During my time at the TASC lab in Trieste (04/2004 – 10/2006) I was heavily involved in the construction of a low temperature (4 K) scanning tunneling microscope (STM) operating in ultra high vacuum, which is operational since mid-2006.
As a beam line scientist at Sincrotrone Trieste (07/1997 – 03/2004) I was involved in the development of techniques for laterally resolved synchrotron radiation photoelectron spectroscopy and photoelectron diffraction. Responsible for the operation of the spectromicroscope SPELEEM (imaging microscope). Additional experience with the ESCA-microscope (using Fresnel zone plates) and the Spectromicroscope (using Schwarzschild optics). Spectromicroscopic investigations of low-dimensional systems:
Investigation of the mechanisms that induce nanoscopic pattern formation (self-organization). The Au induced faceting of vicinal Si was studied with chemical resolution. Driving force for this morphological transformation is a phase separation between Au enriched terraces and Au depleted step bunches, as demonstrated by a measurement of the local Au coverage by SPELEEM.
In collaboration with the Japanese Telecom NTT I investigated the electronic structure of aligned carbon nanotubes by cross-sectional photoelectron spectromicroscopy. We found that the tips have a larger density of states near the Fermi level than the sidewalls, which has important implications for their application as field emitters.
The properties of nanopatterns created by local anodic oxidation with an atomic force microscope and by dip pen nanolithography were studied by spatially resolved photoelectron spectroscopy. The oxide lines showed a chemical uniformity better than the spatial resolution of the microscope (20 nm). The chemical composition of the structures was stoichiometric, without formation of substoichiometric compounds (SiOx, x<2). The observed charging effects are consistent with a dielectric strength better than 1 MV/cm. This qualifies the oxide lines for reproducible device nanofabrication.
The structural and magnetic phase transition in MnAs/GaAs epitaxial films was studied by LEEM and XMCD-PEEM. The combination of these techniques shows a clear relation between the two-phase structure of the layers and their magnetic domain structure.
As a TMR Marie Curie research fellow at Laboratorio TASC-INFM (06/1995 – 07/1997) I was working on interfacial engineering of heterostructure interfaces to improve the growth of II-VI semiconductors on III-V substrates. I have grown the films (ZnSe on (In)GaAs) in a RIBER MBE 32-P machine. The effect of a Zn predosing of GaAs prior to ZnSe growth was investigated by XPS. Employing an interface control layer, the stacking fault density in II-VI/III-V heterostructures could be reduced by three to four orders of magnitude. The dislocation density in ZnSe grown on GaAs wafers could be reduced to zero by inserting a tailored InGaAs layer. These results were obtained by TEM, AFM, PL, RHEED, Nomarski optical microscopy, and XPS.
Working at the NTT Interdisciplinary Research Laboratories (11/1993 – 05/1995) I have investigated the surface passivation of III-V semiconductors using synchrotron radiation photoelectron spectroscopy. The measurements were performed at the NTT beamline in the Photon Factory, Tsukuba, Japan. The morphology of thin films (SrF2/InP, Si/GaAs, SrF2/Si/GaAs) and their chemical bonding to the substrate was determined. The films were grown in a chamber directly connected to the beamline. Additional measurements with RHEED, SEM, AFM, XPS, XRD, and TEM were performed.
For my Ph.D. Thesis (01/1990 – 10/1993) I performed measurements of the electrical properties of thin metal films (Ni, Ag, Pb, Au) in UHV at low temperatures (LHe) in high magnetic fields (8 T). A rich variety of low-dimensional effects was investigated, including percolation, quantum size effect, weak localization, metal insulator transition. The scattering mechanisms in these films were deduced from magnetotransport measurements. The films were grown on Si(111) by MBE in the same UHV chamber. The structural properties of the films were determined by SPA-LEED, STM, SEM, and XRD, and correlated to the transport data.
During my diploma thesis (10/1988 – 10/1989) I investigated the structure and performed defect characterization of MBE grown thin films of silicon on Si(100) by means of spot profile analysis of LEED (SPA-LEED) in UHV; additional measurements with AES, SEM, and STM.
Dr. Stefan Heun
NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore
Piazza San Silvestro 12
56127 Pisa, Italy
tel. office +39-050-509 472
SGM lab. +39-050-509 467
STM lab. +39-050-509 461
fax. +39-050-509 417