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Thesis defence by Petros ABI YOUNES

Published on March 2, 2023
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PhD Defense March 24, 2023
2pm - Room 205 - Building A2 - ground floor
au niveau de l'accueil principal du CEA
17 avenue des Martyrs - Grenoble
Accès : TRAM B : arrêt Marie-Louise Paris - CEA
Free entrance - No registration

“Synthesis of lamellar chalcogenide ultra-thin films on thermal silicon oxide by a hybrid Atomic Layer Deposition/Molecular Layer Deposition route, developed by in situ X-ray synchrotron and advanced characterization studies”.

Petros ABI YOUNES

Petros ABI YOUNES




Keywords:


ultra-thin films, lamellar, ALD/MLD, EDT, low temperature, thiolate, TiS2, GaSx, SnSx




cliquer pour voir la liste des membres du jury/clic here for the jury members
 

Abstract

    
     Lamellar metal chalcogenides have come into the spotlight due to their semiconducting nature, which is distinct from the most studied 2D semi-metallic graphene. Over the past twenty years, researchers have focused on exploring the anisotropic physical properties of lamellar metal chalcogenides, unveiling new properties due to the thickness-dependent nature, which allows these materials to represent an ultimate level of miniaturization. The lack of scalable fabrication methods of continuous ultra-thin films on developed surfaces, at moderate temperatures, stems an obstacle for the deployment of these materials. In this context, the objective of this thesis was to obtain continuous ultra-thin film of lamellar metal sulfides on non-epitaxial substrates (thermal silicon oxide which is widely used in microelectronics) by performing a complete dissociation between growth and crystallization. For that purpose, we used an innovative two-step process approach comprising the growth of an amorphous thin film by Atomic Layer Deposition/Molecular Layer Deposition (ALD/MLD) and a subsequent thermal annealing for obtaining the crystallization. The replacement of the highly toxic H2S co-reactant often used for growing ALD sulfide thin films with a safer organic molecule, i.e. 1,2 ethandithiol (EDT), permits to generate an amorphous inorganic/organic hybrid thin film at low temperature.

     The process was applied for the synthesis of Titanium Disulfide (TiS2) ultrathin films. Amorphous thin films (Ti-thiolate) were obtained by ALD/MLD process at 50 °C then, converted into textured ultra-thin films of TiS2 upon the annealing under Ar/H2 gas. Thanks to the high brilliance of the synchrotron, the process was monitored by in situ X-ray techniques, which allows to evaluate the repetitive self-limiting behavior from the first ALD/MLD cycle during the growth of the amorphous Ti-thiolate, and to observe the local structure transition during the annealing step. In situ measurements coupled with ex situ characterizations (Raman, XPS, HAXPES, and TEM) evidenced the synthesis of ultra-thin film of 5.5 nm upon annealing at mild temperature (300 °C). Four-points and spectroscopic ellipsometry measurements confirmed a semi-conductor behavior with a direct band gap of 1.72 eV.

     Besides, promising preliminary results on the synthesis of Gallium Sulfide (GaSx) thin films were obtained. During this work, an ALD/MLD window has been explored with EDT and a homogeneous film has been obtained at 250 °C. By contrast, we targeted to the synthesis of Tin Sulfide (SnSx) with EDT. However, the growth was not successful. Nevertheless, mechanistic studies were performed on a high surface area substrate that contributed to explain the result.

Membres du jury/ Jury members :

Prof.

Maarit KARPPINEN

PROFESSEUR, Aalto university, Finaland

Rapporteur

Prof.

Jolien DENDOOVEN

PROFESSEUR ASSISTANT, Ghent University, Belgium

Rapporteur

Prof

Christophe VALLÉE

PROFESSEUR DES UNIVERSITES, Université Grenoble Alpes

Examinateur

Dr

Mikhael BECHELANY

DIRECTEUR DE RECHERCHE, CNRS, Université de Montpellier

Examinateur

Dr

Muriel BOUTTEMY

INGENIEUR DE RECHERCHE, CNRS, Université Paris Saclay

Examinateur

Prof

Elsje Alessandra QUADRELLI

DIRECTEUR DE RECHERCHE, Université de Lyon

Invité

Prof

Hubert RENEVIER

PROFESSEUR DES UNIVERSITES, Université Grenoble Alpes

Thesis Director

Dr

Denis ROUCHON

Ingénieur HDR CEA-E4, Université Grenoble Alpes

Thesis Co-director

Dr

Nicolas GAUTHIER

Ingénieur Chercheur, CEA,Université Grenoble Alpes

Thesis Supervisor


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Date of update March 2, 2023

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