5 research outputs found
Formation of Hybrid Electronic States in FePc Chains Mediated by the Au(110) Surface
Iron–phthalocyanine (FePc) molecules deposited
on the Au(110)
surface self-organize in ordered chains driven by the reconstructed
Au channels. The interaction process induces a rehybridization of
the electronic states localized on the central metal atom, breaking
the 4-fold symmetry of the molecular orbitals of the FePc molecules.
The molecular adsorption is controlled by a symmetry-determined mixing
between the electronic states of the Fe metal center and of the Au
substrate, as deduced by photoemission and absorption spectroscopy
exploiting light polarization. DFT calculations rationalize this mixing
of the Fe and Au states on the basis of symmetry arguments. The calculated
electronic structure reproduces the main experimental spectral features,
which are associated to a distorted molecular structure displaying
a trigonal bipyramidal geometry of the ligands around the metal center
A combined theoretical and experimental study of the ultrafast photophysics of Rhodamine B
<p>The ultrafast dynamics of zwitterionic and cationic Rhodamine B in ethanol have been investigated using TDDFT calculations and ultrafast transient absorption spectroscopy. The calculations show that the zwitterionic form exhibits an electronically excited dark state which could potentially quench the initially photoexcited state, while in the case of cationic form the lowest excited lying dark state is outside the energy region of interest and cannot explain its quenching. Due to similarities in the relaxation dynamics of the two molecules, it is suggested that the electronically excited dark state may not play such an important role in the quenching process of this dye as previously proposed. Experimental evidence presented suggests that a quenching mechanism is active on the picosecond timescale for both forms of Rhodamine B.</p
Bis(triisopropylsilylethynyl)pentacene/Au(111) Interface: Coupling, Molecular Orientation, and Thermal Stability
The
assembly and the orientation of functionalized pentacene at the interface
with inorganics strongly influence both the electric contact and the
charge transport in organic electronic devices. In this study electronic
spectroscopies and theoretical modeling are combined to investigate
the properties of the bisÂ(triisopropylsilylethynyl)Âpentacene (TIPS-Pc)/Au(111)
interface as a function of the molecular coverage to compare the molecular
state in the gas phase and in the adsorbed phase and to determine
the thermal stability of TIPS-Pc in contact with gold. Our results
show that in the free molecule only the acene atoms directly bonded
to the ligands are affected by the functionalization. Adsorption on
Au(111) leads to a weak coupling which causes only modest binding
energy shifts in the TIPS-Pc and substrate core level spectra. In
the first monolayer the acene plane form an angle of 33 ± 2°
with the Au(111) surface at variance with the vertical geometry reported
for thicker solution-processed or evaporated films, whereas the presence
of configurational disorder was observed in the multilayer. The thermal
annealing of the TIPS-Pc/Au(111) interface reveals the ligand desorption
at ∼470 K, which leaves the backbone of the decomposed molecule
flat-lying on the metal surface as in the case of the unmodified pentacene.
The weak interaction with the metal substrate causes the molecular
dissociation to occur 60 K below the thermal decomposition taking
place in thick drop-cast films
Adsorption and Dissociation of <i>R</i>‑Methyl <i>p</i>‑Tolyl Sulfoxide on Au(111)
Sulfur-based molecules producing self-assembled monolayers
on gold
surfaces have long since become relevant functional molecular materials
with many applications in biosensing, electronics, and nanotechnology.
Among the various sulfur-containing molecules, the possibility to
anchor a chiral sulfoxide to a metal surface has been scarcely investigated,
despite this class of molecules being of great importance as ligands
and catalysts. In this work, (R)-(+)-methyl p-tolyl sulfoxide was deposited on Au(111) and investigated
by means of photoelectron spectroscopy and density functional theory
calculations. The interaction with Au(111) leads to a partial dissociation
of the adsorbate due to S–CH3 bond cleavage. The
observed kinetics support the hypotheses that (R)-(+)-methyl p-tolyl sulfoxide adsorbs on Au(111) in two different adsorption
arrangements endowed with different adsorption and reaction activation
energies. The kinetic parameters related to the adsorption/desorption
and reaction of the molecule on the Au(111) surface have been estimated
Dynamics of the Bulk-to-Topological State Scattering of Photoexcited Carriers in Bi<sub>2</sub>Se<sub>3</sub> Thin Films
Carrier dynamics
in polycrystalline Bi2Se3 topological insulator
thin films were investigated by femtosecond
transient absorption spectroscopy (FTAS) at 77 K, by using an infrared
pump photon of 0.62 eV energy and a white supercontinuum probe ranging
from the near infrared to ultraviolet regions (0.9–3.5 eV).
The Bi2Se3 samples were grown by vapor solid
deposition, a quick, inexpensive, and easy-to-control growth technique
to obtain films of different thicknesses, endowed with topological
properties. FTAS spectra present several absorption bleaching signals,
which can be attributed to electronic transitions involving both bulk
and surface states present in the complex Bi2Se3 band structure. We observe clear differences in the rise times of
several bleaching signals, differences that can be attributed to different
band filling dynamics. Fast rise times are observed for transitions
only involving bulk states, while a delayed onset of the bleaching
signal has been observed for transitions involving surface topological
states, which are more efficiently populated by carrier–phonon
scattering of bulk electrons and holes, rather than by direct photoexcitation.
The observed features shed fresh insights into the properties that
allow these materials to be employed as innovative, low-cost, and
wide-range photodetectors