THEMES PROPOSED FOR THE XXXII CICLE OF PhD in PHYSICS AND NANOSCIENCES (3 years starting from Nov. 2016)

EXPERIMENTAL PROPOSALS
  • Title: Design suitable fabrication strategies for electrical and optical properties tunability and thermal stability of Ti-oxide thin films
  • Tutor:Sergio Valeri
    co-tutor:Alessandro di Bona
    Abstract: Interfaces in multi-phase materials and their assemblies (e.g. hetero-interfaces, phase boundaries, grain boundaries and free surfaces) impose dimensional and microstructural constrains to the mobility of atoms, single defects, dislocations, electrons, phonons, hence are decisive for tuning the functional properties of technological components and devices.
    The proposed activity aims at a comprehensive experimental assessment and comparison of the phase stability, defect structure, chemical reactivity, transport and electronic properties of a scientifically and technologically relevant material, namely Ti-oxide thin films, prepared by different deposition methods (MBE, magnetron sputtering and thermal oxidation of pure metal), oriented to design suitable fabrication strategies for electrical and optical properties tunability, thermal stability and cyclability.

  • Title: Nano mechanics at surfaces and interfaces
  • Tutor:Sergio Valeri
    co-tutor:Diego Marchetto, Guido Paolicelli
    Abstract: Friction, wear and adhesion properties of materials are strictly related to their “bulk” mechanical and physical characteristics like hardness, shear strength, thermal conductivity and energy dissipation, …, and to a number of chemical and physical processes occurring at the “external” and “internal“ surfaces and interfaces. In this context the proposed activity is oriented to explore how and to what extent friction and wear are influenced by nano- microstructures on and beneath the surface. These structures can be both natural (crystalline grains, dislocations, roughness…) and artificial (surface nanostructures, nano- micro multilayers, …).
    For this study several experimental techniques must be used, including scanning probe friction force microscopy and micro tribometers for tribological analysis (respectively at the nano and micro scale), and electron microscopies and spectroscopies for structural and chemical investigation. Nano- micro fabrication processes are used for the structure production.

  • Title: Growth and functional properties of pre-formed metal/ metal oxides core-shell nanoparticles
  • Tutor:Sergio D’Addato
    Abstract: The interest in metal nanostructured films has grown in the last years because of their fascinating physical properties and their potentiality in various applications, like magnetic recording industry, catalysis and plasmonics. We propose a PhD thesis devoted to the investigation of metal and core-shell oxide-metal nanoparticles with a recently developed source which is able to produce and mass-select clusters. The study will be focused on the structure, chemical and magnetic properties of the individual particles and of the nanoparticle assembled films. Some of the techniques to be used in campus will be XPS, SEM, TEM and visible-UV Reflectivity. Part of the experimental activity will be also carried out in external facilities like synchrotrons (XAFS, PEEM and XMCD experiments), in collaboration with other groups.

  • Title: Electrically detected Magnetic Resonance with planar devices
  • Tutors:A. Ghirri (CNR) and Prof M. Affronte (marco.affronte@unimore.it)
    Abstract: One challenge of Quantum Technologies is the coherent manipulation and the read-out of quantum objects by photons. This proposal aims at the development of hybrid devices for (pulsed) electrically detected magnetic resonance experiments. The first objective of the thesis is the realization of the experimental set-up, which combines planar microwave resonators and nanofabricated magneto-transport contacts, for the study of low-dimensional spin systems like nanowires or 2D nanostructures. Transmission spectroscopy experiments will be initially carried out in continuous wave mode and subsequently extended to pulse sequences for the coherent manipulation of the spins. Reference: Applied Physics Letters 106, 184101 (2015). The experiments will be partially carried out at international high magnetic field facilities and in collaboration with leading international laboratories.

  • Title: Molecular spintronics based on graphene and other 2D materials
  • Tutors:Dr. Andrea Candini (CNR) and Prof. Marco Affronte (marco.affronte@unimore.it)
    Abstract: Molecular- and atom- scale devices will be the driving core of the next generation of electronic components and architectures. In particular, the possibility to address and exploit the spin state of individual molecules leads to several possible applications ranging from advanced opto-eletronics to quantum technologies. Graphene, with its outstanding electrical properties and the low dimensionality, is considered an ideal platform to embed molecular scale components into reliable and scalable device architectures. The thesis work comprises the preparation and characterization of hybrid devices based on graphene and other two-dimensional materials and molecular units, such as single-molecule magnets (SMM) and graphene nanoribbons (GNR), by using state-of-the-art fabrication techniques and low temperature magneto-transport and opto-electronic measurements. The final goal is the realization and study of novel nano-devices where individual molecular spins are detected and manipulated (see Nano Letters 11, 2634–2639, 2011). The experiments will be partially carried out in collaboration with leading international laboratories.

  • Title: Studying protein folding and misfolding at single molecule level using optical tweezers.
    Tutors: Prof. Ciro Cecconi (ciro.cecconi@unimore.it), A. Alessandrini
    Abstract: Protein folding can nowadays be studied at single molecule level using optical tweezers (1,2,3). In these experiments, individual proteins are mechanically manipulated and their response to force characterized in terms of different parameters, including:
    i) mechanical compliance of the native state (4)
    ii) magnitude of the forces holding together secondary and tertiary structures (1,3)
    iii) height and position along the reaction coordinate of the activation barriers (5)
    iv) intermediate states (6)
    v) thermodynamics and kinetics of the interconversion between different molecular conformations (7)
    vi) misfolding pathways (8)
    vii) protein’s energy landscape (5)
    These studies have uncovered information previously inaccessible to more traditional ensemble techniques, and provided an innovative perspective on the protein folding problem.

  • Title: Mechanical properties of living cells.
    Tutors: Andrea Alessandrini
    Abstract: The thesis project involves the exploitation of different experimental techniques (atomic force microscopy, micropipette aspiration and fluorescence microscopy) to investigate the mechanical properties of living cells in relation to their pathological conditions and to the different scaffolds and substrates on which they are growing. The effect of the substrate physical and chemical properties on the cell fate will be investigated. The effects of chemical treatments targeting mechanical components of the cell (cytoskeleton) will be studied. The activity is also framed within a large project with the involvement of groups working on the development of new advanced scaffolds for bone transplantation. The activity will also include the development of new set-ups. All the project will be performed within a highly interdisciplinary environment.
    The Project is framed within the Regional Project POR-FESR 2014-2020 NIPROGEN. collaborations: Dipartimento di Scienze della Vita, Universitą di Modena e Reggio Emilia CNR-ISTEC- Faenza.

  • Title: Molecular approaches to nanoscale magnets.
    Tutors: Prof. Andrea Cornia (acornia@unimore.it)
    Abstract: A current fundamental and technological goal is the design of nanosized magnetic molecules amenable to be used in memory devices and spintronic applications. As an important requisite, the memory effect needs to be maintained in a manageable temperature range, i.e. at least above liquid nitrogen temperature. The proposed research activity, to be carried out at the Department of Chemical and Geological Sciences, takes up this challenge and focuses on metal-metal bonds as a means to convey to magnetic molecules a well-isolated high-spin state and a giant magnetic moment even at room temperature. Techniques: organic/organometallic synthesis, handling of air- and water-sensitive compounds, mass spectrometries, XRD, magnetic measurements and EPR.
    Available fellowship: No

THEORETICAL PROPOSALS
  • Title: Time-dependent dynamics of quantum complexes
    Tutor:Guido Goldoni
    Abstract: Indirect excitons are optically-generated quasi-particles which undergo Bose-Einstein condensation. In this project we develop theoretical computational tools to simulate the time-dependent dynamics of single or gases of indirect excitons, in connection with undergoing experiments. The activity is of a theoretical/computational character. The candidate will acquire a working knowledge in advanced modelling of nano-materials and simulative methods in quantum physics, as well as in the development of high performance software for parallel architectures.
  • Space- and time-dependent quantum dynamics of spatially indirect excitons in semiconductor heterostructures, J. Chem. Phys. 142, 034701 (2015)
  • Exact two-body quantum dynamics of an electron-hole pair in semiconductor coupled quantum wells: a time-dependent approach Phys. Rev. B 93, 195310 (2016)

  • Title: Core-shell nanowires: nano-materials for the next generation nano-opto-electronics
    Tutor:Guido Goldoni
    Abstract: Core-shell nanowires are engineered nano-materials, similar to long nano-needles. Material modulation both along and radially to the axis allow to tailor their electronic properties to a high degree, opening a wide range of application in nano-opto-electronics. At the same time, the electronic system is confined to new topologies, which opens to new quantum phenomena. This thesis will focus on the fundamentals of the electronic states of these nano-materials, with an emphasis on their thermo-electric properties.
    The activity is of a theoretical/computational character. The candidate will acquire a working knowledge in advanced modelling of nano-materials and simulative methods in quantum nano-devices, as well as in the development of high performance software for parallel architectures. Collaboration with partner experimental groups will give the opportunity to develop interdisciplinary collaborative skills in advanced research.
    - Electron and hole gas in modulation doped GaAs/AlGaAs radial heterojunctions Phys. Rev. B 84, 205323 (2011)
    - High mobility one- and two- dimensional electron systems in nanowire-based quantum heterostructures, Nano Letters 13, 6189 (2013
    - Unintentional p-type doping of a GaAs/AlAs core-multi-shell nanowire revealed by resonant phonon coupling, Nano Letters 14, 2807-2814 (2014)

  • Title: Real-time description of plasmon enhanced spectroscopy of (bio)molecules
    Tutor:Stefano Corni
    Abstract: Nowadays, by cleverly harnessing the interaction of molecules with plasmons (collective electron excitations supported, e.g., by metal nanoparticles) it is becoming possible to focus optical spectroscopy investigations on specific nanoscopic regions, such as a portion of a catalytic surface or of a photosynthetic membrane. This coupling can also produce new quantum effects such as molecule-plasmon hybrid excitations. On the other hand, it makes the real-time molecular evolution and its perturbation by light more complex, and thus calls for new theoretical treatments. The PhD project consists in the development and the application of such a theoretical approach. The latter will be based on a first principle description of the molecule to directly simulate its real time evolution when interacting with plasmons and light. It involves national∫ernational collaborations.
    Financial support: Y (ERC Tame Plasmons as mentioned in the PhD call).

  • Title: Molecular and nanoplasmonics by an atomistic perspective
    Tutors:Stefano Corni, Arrigo Calzolari, Elisa Molinari
    Abstract: Plasmons at the nanoscale are useful in several applications such as photovoltaics and spectroscopy. Interestingly, how to identify a nanoconfined plasmon excitation by an atomistic quantum perspective is still an open issue. In turn, such perspective naturally provides the coupling between plasmons and the excitations of a nearby molecule, the key to enhance spectroscopy. The PhD project consists in developing/applying computational/ theoretical methods to understand and predict molecular and nanoplasmonics phenomena. It involves national∫ernational collaborations.

  • Title: Multiscale simulations of protein-surface and protein-nanoparticle interactions
    Tutor:Stefano Corni
    Abstract: Protein-surface & protein-nanoparticle interactions are central to several material science and bio-oriented systems, such as enzymatic biofuel cells (electric power by organics fuels), guiding self-assembling at the nanoscale with material-specific proteins, nanoparticle effects on protein aggregation. The PhD project consists in extending the computational tools developed by our group, and/or to apply them to problems of biotechnological/material science relevance. It involves national∫ernational collaborations.

  • Title: First-principle simulation of high harmonic generation orbital tomography
    Tutors:Stefano Corni, Massimo Rontani, Daniele Varsano
    Abstract: High Harmonic Generation (HHG), a strongly non-linear optical process, has been experimentally investigated as a tool to disclose the undisputed signature of the quantum nature of electrons in molecules, i.e., the molecular orbitals. Many-body effects, beyond the independent particle picture, are also contained in the experimental results. However, the interpretation of the HHG experiments and the reconstruction of the orbitals is currently hampered by several assumptions. First principle simulations are needed to overcome them. The PhD project consists in developing and applying the necessary first-principle approaches to model the HHG experiments and provide improved techniques to extract the orbital shapes. It involves national and international collaboration with experimental and theoretical groups.

  • Title: First-principle simulation of photoemission and absorption spectroscopy in experimental condition
    Tutors:Elisa Molinari, Andrea Ferretti, Daniele Varsano
    Abstract: Photoemission and absorption spectroscopy are ubiquitous experimental tools to investigate the electronic and optical properties of matter. Accurate thoretical calculations based on first principle are needed to provide interpretation of these experiments and Many Body Perturbation Theory (MBPT) is nowadays a very powerful theoretical framework that allows to takes into account electronic correlation and electron-hole interaction. However, due to the computational difficulties to treat a very large number of atoms, ususally calculations are performed on isolated systems, ie discarding environment effects (solvent, substrate) which can have a large impact on the final measure. The PhD project consists in developing and applying a theoretical framework permitting to take into account in an effective way the influence of environmental effects in photoemission and absorption spectra in order to make possible direct comparison with experiments. Collaboration with experimental groups are envisaged.

  • Title: Multiscale simulations of oxide-based nanomaterials for applications to catalysis and clean energy production
    Tutor:Rita Magri
    Abstract: The thesis tackles the problem of how the physical and chemical processes occurring at the surfaces of metal-oxide nanostructures can be properly described. The interaction between a metal-oxide nanoparticle surface and a simple molecule will be studied through ab-initio methods and multiscale techniques. The energy barriers of the different physical processes will be calculated to provide an understanding of the catalytic efficiency of the surface as a function of its structure and composition. The effects of the surface structure, its defects, and the adsorbed specie on the oxide reducible behavior will be analyzed also through thermodynamics and electronic structure concepts. The work will be conducted in strict collaboration with the experimental groups growing, characterizing, and studying these materials in the FIM and CNR-NANO laboratories.

  • Title: Quantum charge-transport in semiconductor nanostructures
    Tutor:Paolo Bordone
    Abstract: The general purpose of the research is to use numerical and analytical tools for studying quantum transport of charges in semiconductor nanostructures and, more in general, to study quantum effects which can affect the functioning of some modern semiconductor devices working at the nanoscale. The research group of the proponent recently approached the coherent transport inside edge channels, and developed some numerical codes (based upon the solution of the time-dependent Schrödinger equation) and analytical methods to characterize the transport of localized carriers in solid-state single-particle logic gates (such as Mach-Zehnder interferometers). Some interesting scenarios were raised by the study of energy-dependent effects and the use of time-dependent potentials. The aim of this research project is to extend the current studies to more complex structures, even resorting to different analytical and/or numerical approaches, such as the Non-equilibrium Green function formalism and/or some dedicated software packages (such as “Kwant” or “Nextnano”).
    Collaborations: Dr. A. Bertoni, Center-S3, CNR-Insitute of Nanosciences

  • Title: Many-body quantum walks and their applications to quantum information theory
    Tutor: Paolo Bordone
    Abstract: The aim of the research is the study of quantum walks continuous in time for the case of 2 (or more) interacting particles moving on a one(bi)-dimensional lattice, in the presence of noise. Both random telegraph and 1/f noise will be considered. The approach is mainly numerical, and the motion of the walkers on the lattice is described in terms of a Hubbard like Hamiltonian. The effects of long range hopping and interactions will also be analysed. The key point is to understand the reciprocal role played by interaction, noise and long range hopping in the dynamical evolution of the walkers. The strong interest on the topic derive, for example, from the possible, and quite promising, applications to the field of quantum information.
    Collaborations: Prof. M.G.A. Paris and Dr. C. Benedetti, Dipartimento di Fisica, Universitą degli studi di Milano

  • Title: Quantum correlations in decohering systems
    Tutor: Paolo Bordone
    Abstract: This thesis is focused on the analysis of quantum correlations in simple theoretical models of few particles subject to environmental noise. Some entanglement and quantum discord criteria, commonly adopted in the analysis of bipartite systems, will be extended, by means of analytical and numerical techniques, to the case of multipartite systems. Such estimators will permit to investigate the dynamics of entanglement and quantum discord in different physical scenarios, namely classical and quantum noisy environment, characterized by various noise spectra. These analyses will be used as guidelines in the investigation of multipartite electronic (or bosonic) entanglement in nanometric structures coupled to noisy environments.
    Collaborations: Prof. M.G.A. Paris and Dr. C. Benedetti, Dipartimento di Fisica, Universtą degli studi di Milano

  • Title: Theoretical and computational study of organic molecules in the nonlinear regime
    Tutor: Franca Manghi
    Proposer: Carlo Andrea Rozzi
    Abstract: The accurate understanding of elementary excitations in organic materials is a crucial step toward the realization of high efficiency and low cost solar cells, and other optical devices such as photo-protectors based on nonlinear optical absorption. In the first class of materials, after the absorption of a photon the excess potential energy is conveniently stored into electrical or chemical energy and electrons and holes are eventually separated far apart. In the second case the excited state cross section can be larger than the ground state one leading to an increased absorption when the impinging light intensity is high enough. The aim of this proposal is to study photo-induced excitations in these classes of organic compounds. Building upon previous work performed at CNR-NANO S3 on these topics [1-5] the PhD fellow will specifically study the nonlinear behavior of organic compounds both in the few 100 fs time scale and in the high field intensity regimes. Time dependent Density-Functional theory will be the main theory framework of choice. The work will include a balanced mixture of theory development, code development, and high performance computing, according to the specific research goals. The research will benefit from the existing long standing collaborations with international theoretical and experimental groups.

  • Title: Ab initio description of excitons in the optical spectra of carbon nanotubes in the presence of an Aharonov-Bohm flux and related excitonic instabilities
    Tutors: Massimo Rontani (tutor, CnrNano), Daniele Varsano (co-tutor, CnrNano), Elisa Molinari (co-tutor, UniMoRe)
    Abstract: Carbon Nanotubes (CNTs), one dimensional structures obtained by wrapping up graphene strips, have appealing mechanical, electronic and optical properties that strongly depend on the tube chirality and diameter. Due to CNT peculiar topology, an external magnetic field allows to tune in a continuous way the CNT electronic gap (Aharonov-Bohm effect). This PhD project consists in the study of the excitonic features that dominate the optical spectra in different classes of CNTs under the effect of a magnetic field using analytical and/or numerical approaches based on Many Body Perturbation Theory. Emergent many-body states induced by ultra-strong excitonic correlations might be explored as well. Collaborations with the experimental groups of Shahal Ilani (Weizmann Institute, Israel) and Ethan Minot (Oregon State Univ.) on the investigation of the observable signatures of many-body excitonic phases in CNTs are envisaged.
    External Collaborations: Shahal Ilani (Weizmann Institute of Science, Israel), Ethan Minot (Oregon State University, Oregon)

  • Title: Time evolution of electronic states in irradiated materials
    Tutor: Franca Manghi
    Abstract: Under the influence of time-dependent fields quantum systems may reach regimes inaccessible under equilibrium conditions and new phases may be engineered by a tunable control. When a t-periodic field is applied to electrons in a periodic lattice the Bloch theorem can be applied twice, both in space and in time. Bloch theorem in the time domain is the essence of the Floquet approach that provides an exact representation of the time dependent states as a superposition of Floquet modes. By solving the Floquet Hamiltonian we will study the time-evolution of electronic states in a materials driven out of equilibrium by an electromagnetic oscillating field in different regimes of intensity, polarization and frequency. Both model systems and real materials will be addressed, merging ab-initio description with Floquet scheme.

  • Title: Worldline formalism for tree-level processes
    Tutors: Olindo Corradini, M. Ferrario.
    Abstract: The Worldline Formalism (WLF) has proven to be an efficient tool in relatvistic Quantum Field Theory (QFT), to compute one-loop effective actions and one-loop scattering amplitudes, in particular in the presence of external fields. Recently applications of the WLF to tree-level processes have been considered. The main difficulty, in employing the WLF for computations at tree level, is that fermions in this case may require matrix-valued potentials, or the use of suitable spinning particles, on a worldline path integral with open boundary conditions. More care is thus needed to treat these models. A worldline description of tree-level processes is surely welcome for several reasons. It may provide a more systematic way of computing scattering amplitudes, that could be beneficial both at the perturbative and nonperturbative levels. In the present project, the PhD students will investigate suitable relativistic particle models coupled to different external fields (Abelian and non-Abelian vector fields, gravity), obtaining new master formulas for the computation of scattering amplitudes.

  • Title: Understanding excitations in molecular and hybrid systems from first principles
    Tutors: Elisa Molinari, Andrea Ferretti, Deborah Prezzi.
    Abstract: The thesis will focus on the understanding of exciton and few-body states in molecular systems by density functional and many body perturbation theory, with special emphasis on the role of intermolecular couplings and on the derivation of fundamental parameters controlling the ultrafast excitation dynamics. The goal is to elucidate the interplay between structure and properties, possibly enabling their ab-initio design. To this end, the research will involve close collaborations with experimental groups in Italy and in Europe, who are now able to obtain and control different geometrical arrangements and investigate their excitations and dynamics on the sub-ps time scale.

  • Title: Reactions at materials interfaces activated by mechanical stresses: fundamental understanding and applications in tribology
    Tutors: M. C. Righi, M. Ferrario.
    Abstract: During the course of a chemical reaction, reactants need to overcome a free energy barrier to transform into products. The energy for this process is typically provided by heat or light. A fundamentally different way of initiating or accelerating a reaction is the use of mechanical work. Understanding reaction kinetics in the presence mechanical forces is a fundamental problem with important applications in many fields, such as mechanochemistry and tribology.
    The present PhD project is based on a theoretical multiscale approach that allows to accurately simulate physical and chemical processes involving molecules confined at solid interfaces under load and shear.
    The project aims at providing both a microscopic understanding of the functionality of boundary/solid lubricants and a fundamental understanding of stress-assisted reactions. The systems under consideration include lubricant additives, diamond-like-carbon films, layered materials such as graphene and MoS2. The activity may involve collaboration with industries, in particular Total S.A. and Toyota R&D Labs.

  • Title: Towards a fundamental understanding of adhesion and applications to realistic systems
    Tutors: M. C. Righi, C. Calandra, F. Manghi
    Abstract: Recent theoretical work, based on first principles density functional calculations, has shown that graphene layers deposited on iron have passivating effects, causing a reduction of metal-metal adhesion forces¹. Following this indication, we plan to carry a systematic study of the effect of graphene overlayers by calculating the vacuum fluctuation forces between metal coated systems using Lifshitz’ theory², which allows to determine the change in the interaction force through the modifications of the surface plasmon modes of the system induced by the overlayers. In this way we should be able to select the systems where the passivating effect is more significant and to carry out first principles calculation for them in order to achieve a microscopic understanding of the adhesion reduction.
  • 1. P. Restuccia, M.C. Righi: Carbon 106 (2016) 118
  • 2. V.A. Parsegian : “Van der Waals forces” (2006) Cambridge Univ. Press