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LUCA BURSI

Ricercatore t.d. art. 24 c. 3 lett. A
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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Pubblicazioni

2024 - Initial stages of growth and electronic properties of epitaxial SrF2 thin films on Ag(1 1 1) [Articolo su rivista]
Borghi, M.; Mescola, A.; Paolicelli, G.; Montecchi, M.; D'Addato, S.; Vacondio, S.; Bursi, L.; Ruini, A.; Doyle, B. P.; Grasser, T.; Pasquali, L.
abstract

2023 - Chiral Plasmonic Pinwheels Exhibit Orientation-Independent Linear Differential Scattering under Asymmetric Illumination [Articolo su rivista]
Mccarthy, Lauren A.; Verma, Ojasvi; Narmada Naidu, Gopal; Bursi, Luca; Alabastri, Alessandro; Nordlander, Peter; Link, Stephan
abstract

Plasmonic nanoantennas have considerably stronger polar- ization-dependent optical properties than their molecular counterparts, inspiring photonic platforms for enhancing molecular dichroism and providing fundamental insight into light-matter interactions. One such insight is that even achiral nanoparticles can yield strong optical activity when they are asymmetrically illuminated from a single oblique angle instead of evenly illuminated. This effect, called extrinsic chirality, results from the overall chirality of the experimental geometry and strongly depends on the orientation of the incident light. Although extrinsic chirality has been well-characterized, an analogous effect involving linear polarization sensitivity has not yet been discussed. In this study, we investigate the differential scattering of rotationally symmetric chiral plasmonic pinwheels when asymmetrically irradiated with linearly polarized light. Despite their high rotational symmetry, we observe substantial linear differential scattering that is maintained over all pinwheel orientations. We demonstrate that this orientation-independent linear differential scattering arises from the broken mirror and rotational symmetries of our overall experimental geometry. Our results underscore the necessity of considering both the rotational symmetry of the nanoantenna and the experimental setup, including illumination direction and angle, when performing plasmon- enhanced chiroptical characterizations. Our results demonstrate spectroscopic signatures of an effect analogous to extrinsic chirality for linear polarizations.

2022 - Multifunctional Switch Based on Spin-Labeled Gold Nanoparticles [Articolo su rivista]
Lloveras, Vega; El('(i))as-Rodr('(i))guez, Pilar; Bursi, Luca; Shirdel, Ehsan; Go(~(n))i, Alejandro R.; Calzolari, Arrigo; Vidal-Gancedo, Jos('(e))
abstract

: The fabrication of multifunctional switches is a fundamental step in the development of nanometer-scale molecular spintronic devices. The anchoring of active organic radicals on gold nanoparticles (AuNPs) surface is little studied and the realization of AuNPs-based switches remains extremely challenging. We report the first demonstration of a surface molecular switch based on AuNPs decorated with persistent perchlorotriphenylmethyl (PTM) radicals. The redox properties of PTM are exploited to fabricate electrochemical switches with optical and magnetic responses, showing high stability and reversibility. Electronic interaction between the radicals and the gold surface is investigated by UV-vis, showing a very broad absorption band in the near-infrared (NIR) region, which becomes more intense when PTMs are reduced to anionic phase. By using multiple experimental techniques, we demonstrate that this interaction is likely favored by the preferentially flat orientation of PTM ligands on the metallic NP surface, as confirmed by first-principles simulations.

2022 - Oxygen Evolution and Reduction on Two-Dimensional Transition Metal Dichalcogenides [Articolo su rivista]
Karmodak, N.; Bursi, L.; Andreussi, O.
abstract

Motivated by the need to find good electrocatalysts for water oxidation and O2 reduction, composed of nontoxic and earth-abundant elements, a systematic screening of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is performed. To identify compounds that are intrinsically active and can fully take advantage of the high surface area of 2D catalysts, this study focuses on the properties of the ideal basal planes of 2D TMDCs, in the 2H, 1T, and 1T′ phases. Over two hundred materials proposed in computational databases are studied by means of first-principles-based simulations coupled with continuum embedding models to account for the presence of electrochemical environments. The best candidates with overpotentials for the oxygen evolution and reduction reactions (OER and ORR) lower than 0.5 V under acidic conditions and higher stability against degradation in electrochemical environments are selected. For OER, the designed workflow identifies one active and thermodynamically stable material, and seven materials that are metastable at the oxidative potentials and acidic pH. On the other hand, for ORR, we identify 20 materials with overpotentials less than 0.5 V. Among these compounds, six bifunctional materials have been experimentally reported, with 1T-NbTe2 and 1T′-MoTe2 being the best performing catalysts for OER and ORR, respectively.

2021 - Plasmon Energy Transfer in Hybrid Nanoantennas [Articolo su rivista]
Collins, S. S. E.; Searles, E. K.; Tauzin, L. J.; Lou, M.; Bursi, L.; Liu, Y.; Song, J.; Flatebo, C.; Baiyasi, R.; Cai, Y. -Y.; Foerster, B.; Lian, T.; Nordlander, P.; Link, S.; Landes, C. F.
abstract

Plasmonic metal nanoparticles exhibit large dipole moments upon photoexcitation and have the potential to induce electronic transitions in nearby materials, but fast internal relaxation has to date limited the spatial range and efficiency of plasmonic mediated processes. In this work, we use photo-electrochemistry to synthesize hybrid nanoantennas comprised of plasmonic nanoparticles with photoconductive polymer coatings. We demonstrate that the formation of the conductive polymer is selective to the nanoparticles and that polymerization is enhanced by photoexcitation. In situ spectroscopy and simulations support a mechanism in which up to 50% efficiency of nonradiative energy transfer is achieved. These hybrid nanoantennas combine the unmatched light-harvesting properties of a plasmonic antenna with the similarly unmatched device processability of a polymer shell.

2020 - Effects of Electronic Structure on Molecular Plasmon Dynamics [Articolo su rivista]
Chapkin, K. D.; Bursi, L.; Clark, B. D.; Wu, G.; Lauchner, A.; Tsai, A. -L.; Nordlander, P.; Halas, N. J.
abstract

Collective, coherent excitations in molecules, termed molecular plasmons, can be observed in neutral and charged polycyclic aromatic hydrocarbons (PAHs). Systems in this few-Atom limit show behavior strongly dependent on charge state, where the addition or removal of even a single electron dramatically alters electronic and optical properties. Here, we investigate the dynamics of PAHs by studying their excited-state lifetimes in four different charge states: cation, neutral, anion, and dianion. Those characterized by a closed-shell electronic structure-the neutral molecule and the dianion-exhibit long-lived, exponentially decaying lifetimes typical of radiative relaxation. In contrast, the open-shell cationic and anionic states exhibit far more rapid multiexponential decay dynamics. This can be attributed to the nonradiative de-excitation of multiple electron-hole pairs in the molecule through molecular plasmon "dephasing"and vibrational relaxation. This study gives insight into the nature of excited states of open-and closed-shell molecules and illuminates the role played by electronic structure in the collective electron dynamics of few-Atom plasmonic systems.

2020 - Polarized evanescent waves reveal trochoidal dichroism [Articolo su rivista]
Mccarthy, L. A.; Smith, K. W.; Lan, X.; Hosseini Jebeli, S. A.; Bursi, L.; Alabastri, A.; Chang, W. -S.; Nordlander, P.; Link, S.
abstract

Matter’s sensitivity to light polarization is characterized by linear and circular polarization effects, corresponding to the system’s anisotropy and handedness, respectively. Recent investigations into the near-field properties of evanescent waves have revealed polarization states with out-of-phase transverse and longitudinal oscillations, resulting in trochoidal, or cartwheeling, field motion. Here, we demonstrate matter’s inherent sensitivity to the direction of the trochoidal field and name this property trochoidal dichroism. We observe trochoidal dichroism in the differential excitation of bonding and antibonding plasmon modes for a system composed of two coupled dipole scatterers. Trochoidal dichroism constitutes the observation of a geometric basis for polarization sensitivity that fundamentally differs from linear and circular dichroism. It could also be used to characterize molecular systems, such as certain light-harvesting antennas, with cartwheeling charge motion upon excitation.

2019 - Aluminum Nanocubes Have Sharp Corners [Articolo su rivista]
Clark, B. D.; Jacobson, C. R.; Lou, M.; Renard, D.; Wu, G.; Bursi, L.; Ali, A. S.; Swearer, D. F.; Tsai, A. -L.; Nordlander, P.; Halas, N. J.
abstract

Of the many plasmonic nanoparticle geometries that have been synthesized, nanocubes have been of particular interest for creating nanocavities, facilitating plasmon coupling, and enhancing phenomena dependent upon local electromagnetic fields. Here we report the straightforward colloidal synthesis of single-crystalline {100} terminated Al nanocubes by decomposing AlH3 with Tebbe's reagent in tetrahydrofuran. The size and shape of the Al nanocubes is controlled by the reaction time and the ratio of AlH3 to Tebbe's reagent, which, together with reaction temperature, establish kinetic control over Al nanocube growth. Al nanocubes possess strong localized field enhancements at their sharp corners and resonances highly amenable to coupling with metallic substrates. Their native oxide surface renders them extremely air stable. Chemically synthesized Al nanocubes provide an earth-abundant alternative to noble metal nanocubes for plasmonics and nanophotonics applications.

2019 - Ligand-Dependent Colloidal Stability Controls the Growth of Aluminum Nanocrystals [Articolo su rivista]
Clark, B. D.; Desantis, C. J.; Wu, G.; Renard, D.; Mcclain, M. J.; Bursi, L.; Tsai, A. -L.; Nordlander, P.; Halas, N. J.
abstract

The precise size- and shape-controlled synthesis of monodisperse Al nanocrystals remains an open challenge, limiting their utility for numerous applications that would take advantage of their size and shape-dependent optical properties. Here we pursue a molecular-level understanding of the formation of Al nanocrystals by titanium(IV) isopropoxide-catalyzed decomposition of AlH 3 in Lewis base solvents. As determined by electron paramagnetic resonance spectroscopy of intermediates, the reaction begins with the formation of Ti 3+ -AlH 3 complexes. Proton nuclear magnetic resonance spectroscopy indicates isopropoxy ligands are removed from Ti by Al, producing aluminum(III) isopropoxide and low-valent Ti 3+ catalysts. These Ti 3+ species catalyze elimination of H 2 from AlH 3 inducing the polymerization of AlH 3 into colloidally unstable low-valent aluminum hydride clusters. These clusters coalesce and grow while expelling H 2 to form colloidally stable Al nanocrystals. The colloidal stability of the Al nanocrystals and their size is determined by the molecular structure and density of coordinating atoms in the reaction, which is controlled by choice of solvent composition.

2018 - Exploiting Evanescent Field Polarization for Giant Chiroptical Modulation from Achiral Gold Half-Rings [Articolo su rivista]
Smith, K. W.; Mccarthy, L. A.; Alabastri, A.; Bursi, L.; Chang, W. -S.; Nordlander, P.; Link, S.
abstract

For applications seeking to realize on-chip polarization-discriminating nanoantennas, efficient energy conversion from surface waves to far-field radiation is desirable. However, the response of individual nanoantennas to the particular polarization states achievable in surface waves, such as evanescent fields, has not yet been thoroughly investigated. Here, we report the giant modulation of visible light scattering from achiral gold half-rings when switching between evanescent surface wave excitation produced from the total internal reflection of left-handed and right-handed circularly polarized light. The effect is driven by a differing relative phase between the in-plane transverse and longitudinal field oscillations of the evanescent wave depending on the incident light handedness. Because longitudinal field oscillations are not found in free-space excitation, this presents a fundamentally different mechanism for chiroptical responses as traditional mechanisms for circular dichroism only account for purely transversal field oscillations. Although the half-ring scattering modulation is dependent on the wave-vector orientation, an orientation invariant response is also realized in planar chiral nanoantennas composed of 8 half-rings in a rotationally symmetric arrangement, with up to 50% scattering modulation observed at 725 nm. Although both structures are found to produce scattering modulation when switching the handedness of free-space light, the distinct polarization properties of evanescent fields are shown to be strictly required to observe giant scattering modulation. These results ultimately deepen our understanding of the range of possible chiroptical effects in light-matter interactions.

2018 - Lifetime dynamics of plasmons in the few-atom limit [Articolo su rivista]
Chapkin, K. D.; Bursi, L.; Stec, G. J.; Lauchner, A.; Hogan, N. J.; Cui, Y.; Nordlander, P.; Halas, N. J.
abstract

Polycyclic aromatic hydrocarbon (PAH) molecules are essentially graphene in the subnanometer limit, typically consisting of 50 or fewer atoms. With the addition or removal of a single electron, these molecules can support molecular plasmon (collective) resonances in the visible region of the spectrum. Here, we probe the plasmon dynamics in these quantum systems by measuring the excited-state lifetime of three negatively charged PAH molecules: anthanthrene, benzo[ghi]perylene, and perylene. In contrast to the molecules in their neutral state, these three systems exhibit far more rapid decay dynamics due to the deexcitation of multiple electron–hole pairs through molecular plasmon “dephasing” and vibrational relaxation. This study provides a look into the distinction between collective and single-electron excitation dynamics in the purely quantum limit and introduces a conceptual framework with which to visualize molecular plasmon decay.

2017 - How to Identify Plasmons from the Optical Response of Nanostructures [Articolo su rivista]
Zhang, Runmin; Bursi, Luca; Cox, Joel D.; Cui, Yao; Krauter, Caroline M.; Alabastri, Alessandro; Manjavacas, Alejandro; Calzolari, Arrigo; Corni, Stefano; Molinari, Elisa; Carter, Emily A.; García De Abajo, F. Javier; Zhang, Hui; Nordlander, Peter
abstract

A promising trend in plasmonics involves shrinking the size of plasmon-supporting structures down to a few nanometers, thus enabling control over light-matter interaction at extreme-subwavelength scales. In this limit, quantum mechanical effects, such as nonlocal screening and size quantization, strongly affect the plasmonic response, rendering it substantially different from classical predictions. For very small clusters and molecules, collective plasmonic modes are hard to distinguish from other excitations such as single-electron transitions. Using rigorous quantum mechanical computational techniques for a wide variety of physical systems, we describe how an optical resonance of a nanostructure can be classified as either plasmonic or nonplasmonic. More precisely, we define a universal metric for such classification, the generalized plasmonicity index (GPI), which can be straightforwardly implemented in any computational electronic-structure method or classical electromagnetic approach to discriminate plasmons from single-particle excitations and photonic modes. Using the GPI, we investigate the plasmonicity of optical resonances in a wide range of systems including: the emergence of plasmonic behavior in small jellium spheres as the size and the number of electrons increase; atomic-scale metallic clusters as a function of the number of atoms; and nanostructured graphene as a function of size and doping down to the molecular plasmons in polycyclic aromatic hydrocarbons. Our study provides a rigorous foundation for the further development of ultrasmall nanostructures based on molecular plasmonics.

2016 - Quantifying the Plasmonic Character of Optical Excitations in Nanostructures [Articolo su rivista]
Bursi, Luca; Calzolari, Arrigo; Corni, Stefano; Molinari, Elisa
abstract

The microscopic definition of plasmons in nanosystems is a tremendous challenge. Any sharp distinction of the excitation nature (nonplasmonic vs plasmonic) becomes blurred at the nanoscale, where quantum effects become important. Here we introduce the concept of plasmonicity index, i.e., a direct measure of the plasmonic character of the optical excitations in nanosystems. Its definition is based on a rigorous theoretical derivation, which leads to the physically sound result that the plasmonicity index is related to the capability of enhancing locally an applied electromagnetic radiation. The proposed expression is general and can be applied to any finite system. We show its usefulness in modeling metallic nanoparticles, prototypical C-based molecules, and paradigmatic hybrid systems, starting from first-principles calculations, based on (TD)DFT. Our results represent a step forward in the fundamental understanding of what a plasmon is in nanometer-sized particles and molecular systems.

2015 - Plasmonic and new plasmonic materials: General discussion [Articolo su rivista]
Garcia De Abajo, F. J.; Sapienza, R.; Noginov, M.; Benz, F.; Baumberg, J.; Maier, S.; Graham, D.; Aizpurua, J.; Ebbesen, T.; Pinchuk, A.; Khurgin, J.; Matczyszyn, K.; Hugall, J. T.; Van Hulst, N.; Dawson, P.; Roberts, C.; Nielsen, M.; Bursi, L.; Flatte, M.; Yi, J.; Hess, O.; Engheta, N.; Brongersma, M.; Podolskiy, V.; Shalaev, V.; Narimanov, E.; Zayats, A.
abstract

2014 - Light-Induced Field Enhancement in Nanoscale Systems from First-Principles: The Case of Polyacenes [Articolo su rivista]
Bursi, Luca; Calzolari, Arrigo; Corni, Stefano; Molinari, Elisa
abstract

Using first-principles calculations we studied the electric field enhancement in polyacene molecules upon illumination. These molecules can be seen as a specific class of C-based (i.e., graphene-derived) nanostructures, recently proposed as alternative materials for plasmonics. We demonstrate that optical transitions may generate oscillating dipolar response charge, giving rise to an induced electric field near the molecule, which thus acts as a plasmon-like nanoantenna. While the field amplification in the vicinity of single acenes is rather small and decreases when the size of the system is increased, it may be selectively enhanced in the case of acenes assemblies. This paves the way for the design of more complex C-based architectures explicitly conceived to improve the amplification factor.