Two-photon photoluminescence (2PL), polarization-resolved second-harmonic generation (P-SHG) and polarization-resolved third-harmonic generation (P-THG) imaging microscopy of non-linear materials.

The goal of the project is to employ 2PL imaging and precise polarization measurements of SHG, and THG signal and interpret the produced signals in order to gain further physical insight into nanomaterials (e.g. the graphene or the graphene related 2D materials).

 

Contact Person(s):
Dr. Emmanuel Stratakis

Dr. Sotiris Psilodimitrakopoulos

Research Topics
Non-linear optical properties of graphene and graphene related 2D materials

Abstract

Despite their similarities, 2PL, SHG and THG are based on fundamentally different phenomena. 2PL relies on nonlinear multiphoton absorption, followed by fluorescence emission while SHG relies on non-centrosymmetry and nonlinear scattering. Finally, THG originates from changes in the samples’ index of diffraction. The consequences of those basic differences are exploited and utilized in this project as new contrast mechanisms for characterizing nanomaterials of interest, e.g. the graphene and the graphene related 2D materials.

In particular, by varying the polarization angle of the excitation field and recording the second and third harmonic intensity, we are able to produce polar diagrams whose patterns are consequently connected with the crystal orientation, the relative orientation between different layers or even the way in which electrons are distributed among the available energy states of the system. Such a link is made possible through application of nonlinear optics and the derivation of equations for the SHG and THG intensity that are used to fit the experimental data and infer the values of interesting parameters such as the armchair orientation, the twist angle, the valley population imbalance etc.

The continuous interaction between theory and experiment within the Imaging subgroup offers an ideal means for enhancing our insight on the nonlinear phenomena occurring in organic and inorganic systems under intense laser light excitation and allows for both prognostics and diagnostics of 2D materials and biological samples.

 

Femtosecond laser raster-scanning microscopy imaging is used to study the nonlinear optical properties (second and third harmonic generation) of atomically thin materials.

 

Fully-motorized Polarization-Resolved Non-Linear Microscope

– Simultaneous, 2p and 3p Fluorescence/ PL, P-SHG and P-THG

– 5 simultaneous channels

– Polarization control in both excitation and detection

-Temperature dependent (78K-300K) measurements, using a cryostat at the sample plane

– Dual beam – Simultaneous dual raster-scanning

  

 

Experimental Setup

 

 

 

 

Mapping of the main crystallographic axis and crystal quality diagnostics in transition metal dichalcogenides

Polarization-resolved second harmonic generation (P-SHG) imaging is performed in monolayer transition metal dichalcogenides (TMDs), such as MoS₂, WS₂, MoSe₂ and WSe₂, to map the main cystallographic axis (armchair) , and evaluate the crystal quality.

 

• [“Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation,” G. M. Maragkakis, S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, A. Lemonis, G. Kioseoglou and E. Stratakis, Opto-Electronic Advances, 2, 190026 (2019).]

 

 

 

Ultra-high resolution Mapping of Armchair orientation

[“Ultrahigh-resolution non-linear optical imaging of the armchair orientation in 2D transition metal dichalcogenides,”S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, A. Lemonis, G. Kioseoglou and E. Stratakis, Light: Science & Applications, 7, 18005 (2018).]

 

 

 

Quantification of Crystal quality

[“Ultrahigh-resolution non-linear optical imaging of the armchair orientation in 2D transition metal dichalcogenides,”S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, A. Lemonis, G. Kioseoglou and E. Stratakis, Light: Science & Applications, 7, 18005 (2018).]

 

 

 

 

Twist angle mapping

The twist angle (the relative angle between stacked 2D monolayers) is a new degree of freedom in 2D materials, since its affects the physical properties of a multilayer structure. Here, we map the twist angle in TMD-based structures by performing P-SHG imaging and developing suitable SHG interference models.

 

Twist angle mapping in TMD homobilayers

[“Twist Angle mapping in layered WS₂ by Polarization-Resolved Second Harmonic Generation,” S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, G. Kourmoulakis, A. Lemonis, G. Kioseoglou and E. Stratakis, Scientific Reports, 9, 14285 (2019).]

 

 

 

Real-time twist angle imaging in TMD heterobilayers

[“Real-time spatially resolved determination of twist angle in transition metal dichalcogenide heterobilayers,” S. Psilodimitrakopoulos, L. Mouchliadis, G. M. Maragkakis, G. Kourmoulakis, A. Lemonis, G. Kioseoglou and E. Stratakis, 2D Materials 8, 015015, (2021).]

 

[“Real-time spatially resolved determination of twist angle in transition metal dichalcogenide heterobilayers,” S. Psilodimitrakopoulos, L. Mouchliadis, G. M. Maragkakis, G. Kourmoulakis, A. Lemonis, G. Kioseoglou and E. Stratakis, 2D Materials 8, 015015, (2021).]

 

 

 

Comparison between optical and electron diffraction imaging of twist-angle in 2D TMD bilayers

[“Optical versus electron diffraction imaging of twist-angle in 2D transition metal dichalcogenide bilayers” S. Psilodimitrakopoulos, A. Orekhov, L. Mouchliadis, D. Jannis, G. M. Maragkakis, G. Kourmoulakis, N. Gauquelin, G. Kioseoglou, J. Verbeeck and E. Stratakis, npj 2D Materials & Applications 5, 77, (2021).]

[“Optical versus electron diffraction imaging of twist-angle in 2D transition metal dichalcogenide bilayers” S. Psilodimitrakopoulos, A. Orekhov, L. Mouchliadis, D. Jannis, G. M. Maragkakis, G. Kourmoulakis, N. Gauquelin, G. Kioseoglou, J. Verbeeck and E. Stratakis, npj 2D Materials & Applications 5, 77, (2021).]

 

 

 

 

Probing valley population imbalance  in TMDs with temperature-dependent SHG imaging

 

Degenerate minima in the bandstructure of TMDs—valleys—provide an additional degree of freedom that can be used for information transport and storage. When these atomically thin crystals interact with intense laser light, the emerging SHG inherits special characteristics that reflect not only the broken inversion symmetry in real space but also the valley anisotropy in reciprocal space. The temperature-induced change of the SHG intensity dependence on the excitation field polarization is a fingerprint of valley population imbalance in TMDs.

[“Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging” L. Mouchliadis, S. Psilodimitrakopoulos, G. M. Maragkakis, I. Demeridou, G. Kourmoulakis, A. Lemonis, G. Kioseoglou & E. Stratakis, npj 2D Materials & Applications 5, 6, (2021).]

 

[“Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging” L. Mouchliadis, S. Psilodimitrakopoulos, G. M. Maragkakis, I. Demeridou, G. Kourmoulakis, A. Lemonis, G. Kioseoglou & E. Stratakis, npj 2D Materials & Applications 5, 6, (2021).]

 

 

[“Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging” L. Mouchliadis, S. Psilodimitrakopoulos, G. M. Maragkakis, I. Demeridou, G. Kourmoulakis, A. Lemonis, G. Kioseoglou & E. Stratakis, npj 2D Materials & Applications 5, 6, (2021).]

 

 

[“Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging” L. Mouchliadis, S. Psilodimitrakopoulos, G. M. Maragkakis, I. Demeridou, G. Kourmoulakis, A. Lemonis, G. Kioseoglou & E. Stratakis, npj 2D Materials & Applications 5, 6, (2021).]

 

 

 

Third harmonic generation in 2D materials

THG imaging is performed in TMD-based structures in order to obtain complementary to second harmonic generation information about the crystal orientation and homogeneity.

 

 

 

 

Collaborators

Prof. Johan Verbeeck

Prof. Panos Patsalas

Prof. Andrey Turchanin

Dr. Maria Sygletou

Dr. Ioannis Paradisanos

 

 

Publications

• “Optical versus electron diffraction imaging of twist-angle in 2D transition metal dichalcogenide bilayers” S. Psilodimitrakopoulos, A. Orekhov, L. Mouchliadis, D. Jannis, G. M. Maragkakis, G. Kourmoulakis, N. Gauquelin, G. Kioseoglou, J. Verbeeck and E. Stratakis, npj 2D Materials & Applications 5, 77, (2021).
• “Self-assembled dichroic plasmonic nitride nanostructures with broken centrosymmetry for second-harmonic Generation”, D. Babonneau, S. Camelio, G. Abadias, D. Christofilos, I. Arvanitidis, S. Psilodimitrakopoulos, G. M. Maragkakis, E. Stratakis, N. Kalfagiannis, and P. Patsalas,, ACS Applied Nano Materials 4, 9, (2021).
• “Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging” Mouchliadis, S. Psilodimitrakopoulos, G. M. Maragkakis, I. Demeridou, G. Kourmoulakis, A. Lemonis, G. Kioseoglou & E. Stratakis, npj 2D Materials & Applications 5, 6, (2021).
• “Real-time spatially resolved determination of twist angle in transition metal dichalcogenide heterobilayers,” S. Psilodimitrakopoulos, L. Mouchliadis, G. M. Maragkakis, G. Kourmoulakis, A. Lemonis, G. Kioseoglou and E. Stratakis, 2D Materials 8, 015015, (2021).
• “Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation,” G. M. Maragkakis, S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, A. Lemonis, G. Kioseoglou and E. Stratakis, Opto-Electronic Advances, 2, 190026 (2019).
• “Twist Angle mapping in layered WS₂ by Polarization-Resolved Second Harmonic Generation,” S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, G. Kourmoulakis, A. Lemonis, G. Kioseoglou and E. Stratakis, Scientific Reports, 9, 14285 (2019).
• “Ultrahigh-resolution non-linear optical imaging of the armchair orientation in 2D transition metal dichalcogenides,”S. Psilodimitrakopoulos, L. Mouchliadis, I. Paradisanos, A. Lemonis, G. Kioseoglou and E. Stratakis, Light: Science & Applications, 7, 18005 (2018).
• “Effect of composition and temperature on the second harmonic generation in silver phosphate glasses” I. Konidakis, S. Psilodimitrakopoulos, K. Kosma, A. Lemonis, and E. Stratakis Optical Materials, 75, 796-801, (2018).

 

 

Media Coverage

1. LaserLab Cover (Issue 31, August 2021)
2. CretaLive Article (September 2021)

https://www.cretalive.gr/kriti/otan-ena-nompel-empneei-ereynites-toy-ite-kanoyn-thaymata

 

3.CretaLive Article (January 2021)

https://www.cretalive.gr/kriti/nompel-grafenio-i-nanotehnologia-kai-oi-ereynites-toy-ite

 

 

Project members

Dr. Emmanuel Stratakis

Prof. George Kioseoglou

Dr. Sotiris Psilodimitrakopoulos

Dr. Leonidas Mouchliadis

Mr. George-Miltos Maragkakis

Ms. Anna Koliofoti

Dr. Ioanna Demeridou

Mr. George Kourmoulakis

Dr. Abdus Salam Sarkar

Mr. Andreas Lemonis

Mr. Christos Ntoulias