title: Gold nanoparticle functionalization and thin-film deposition of layered group VI transition metal dichalcogenides
creator: Grieger, Sebastian
subject: ddc-500
subject: 500 Natural sciences and mathematics
subject: ddc-540
subject: 540 Chemistry and allied sciences
description: Transition metal dichalcogenides (TMDs) are an intensively investigated class of layered materials and are regarded as promising candidates for various applications based on their exotic, layer-dependent optical and electronic properties. When applications are envisioned for a new material, control over the properties of the material is indispensable for efficient integration. Hence, the functionalization of layered nanomaterials is an ever-growing field with countless possibilities for tailoring these properties. However, literature focuses mostly on novel functionalization approaches and proof-of-principle applications, with fundamental questions of hetero­geneous reactions at the nanosheet-solution interface rarely being tackled. In the first part of this thesis, insights into the influence of the surface chemistry on heterogeneous function­alization reactions at surfactant stabilized transition metal dichalcogenide nanosheets will be presented. A significant dependence of the heterogeneous gold nanoparticle functionalization of group VI TMDs, namely WS2 and MoS2, will be presented and a simple model is developed to explain observed regioselectivities based on the choice of surfactant and material. Preferential adsorption of representatives of commonly employed surfactants to distinguishable sites on the nanosheets is demonstrated and linked to the chemical structure of the respective surfactant.    	Based on this demonstration, precise surfactant-mediated control of heterogeneous functionalization reactions can be envisioned and a generalization of the model for other material-surfactant systems is plausible.    	The layer dependence and sensitivity of optical properties of transition metal dichalocgenides towards their environment is one particularly fascinating characteristic of this class of materials. However, a major drawback of the same characteristic is, that reproducibility and comparability of experimental results cannot be guaranteed where perfect control over the environment is not maintained. Especially for film deposition, where individual nanosheets come in close proximity, film morphology has a severe impact on optical properties and can lead to uncertainties in data interpretation. In the second part of this thesis, a promising method for thin-film production from liquid dispersions of nanosheets is presented, capable of largely alleviating these problems, at least on the laboratory scale. A custom deposition setup was developed to enable reproducible formation and transfer of films after preassembly of the layered materials at the interface between two immiscible solvents. These films are extremely thin and smooth, both on the order of 10^0 to 10^1 nm, and nanosheets are aligned over a sizeable area. A proof-of-principle experiment is presented that demonstrates non-covalent solid-state functionalization of WS2 thin-films with organic dyes and indications for electronic interactions between films and dyes are discussed based on changes in photoluminescence of both dyes and films. This well-defined deposition method is further compared to a complementary deposition approach producing porous films with randomized nanosheet orientation and the influence of morphology on the electrocatalytic activity of WS2 thin-film electrodes towards the hydrogen evolution reaction is discussed.    	This deposition method should enable experimental designs previously inaccessible to layered nanomaterials produced from liquid phase exfoliation and improve reliability of both film production and data interpretation.
date: 2022
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/31321/1/PhD_Thesis_Sebastian_Grieger_PDF-A.pdf
identifier: DOI:10.11588/heidok.00031321
identifier: urn:nbn:de:bsz:16-heidok-313219
identifier:   Grieger, Sebastian  (2022) Gold nanoparticle functionalization and thin-film deposition of layered group VI transition metal dichalcogenides.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/31321/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng