Two-dimensional (2D) materials are a class of materials with unique properties that have attracted significant attention in recent years. Unlike 3D materials, which have bulk properties that are governed by their crystal structure, 2D materials have properties that are strongly influenced by their size and shape. Graphene is perhaps the most well known 2D material due to its exceptional properties. Preparation of 2D materials based on organic molecules is a key-point to obtain devices with original photonics functionalities.
Herein, we focused on 2D materials based on perylene diimide derivatives. Our main goal was to prepare highly oriented 2D materials while also controlling molecular orientations and intermolecular electronic interactions. The consequences on photonics processes will be presented. Moreover, we report preliminary results on the combination of such materials with graphene. Such systems could constitute building blocks for future innovative metamaterials.
This Conference Presentation, “Rare-earth ions-doped ferroelectric nanocrystals for optical sensing of electric potential in biological systems,” was recorded at Photonics Europe 2022 held in Strasbourg, France.
We report the formation of hybrid states of self-assembled PTCDI-C7 organic molecule excitons and surface plasmon polaritons (SPP).
Ten self-assembled monolayers with no host matrix are directly evaporated onto a gold thin film forming a ultra-dense and organized, 30nm thick layer. The π- π stacking among molecules leads to the formation of H-aggregates with alignment of molecular dipole moments along the local electric field vector. This collective excitations are known to give rise to a sharp excitonic peak in absorption with large oscillator strength, which are favorable properties for the observation of strong coupling.
Experimental wavevector-resolved reflectance spectra display an anticrossing, attesting the strong coupling regime with a Rabi splitting energy ΩR=102 meV at room temperature. By contrast, no anticrossing has been observed for PTCDI-C7 molecules evaporated in a different experimental condition and with a reduced local order. We interpret the observed strong coupling regime as resulting from the high degree of organization and the controlled molecular dipole orientation.
Under optical pumping, we observe an enhancement of the coupling efficiency between the molecular emission and the SPP mode. This observation is consistent with the small oscillator strength of the lowest Frenkel state of exciton and to the large Stokes shift of PTCDI-C7 molecules induced by H-aggregate stacking.
The use of ultra-dense layers of self-assembled molecules opens interesting perspectives for the control of the molecular dipole orientation at the nanoscale to maximize interaction with the SPP field and therefore the strong coupling strength.
We propose an experimental demonstration of a THz modulator with a visible optical command. The device is a n-doped
GaAs grating with subwavelength dimensions. The principle of this modulator is the control of the THz resonant
absorption by surface waves supported by the grating. This absorption is modulated with low power visible light, leading
to a modulation of the reflected THz beam. From experimental polarized THz reflectivity measurement of the grating,
we show that a depletion layer at the surface of the doped GaAs has to be taken into account to correctly describe the
observed resonant absorption. From experimental observation and modeling we are able to ascribe this absorption to the
coupling of incident THz light with surface plasmon-phonon polariton mode propagating along each wall of the grating.
Thus, each wall acts as a nano-antenna that resonantly absorbs light. The grating can be viewed as a metamaterial
composed of individual resonators. The theoretical model indicates that the reflectivity dip linked to the surface wave is
sensible to the electronic density in the walls of the grating. We performed an experiment to measure the THz
reflectivity while illuminating the grating with visible photons having energy higher than the bandgap of GaAs. The
created photoelectrons change the effective mode index, leading to a shift of the resonant absorption frequency. This
demonstrates the modulation of THz radiation around 8.5 THz with a visible optical command at room temperature.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.