Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Francois Lagugne-Labarthet

Abstract

Transition Metal Dichalcogenides (TMDs) are remarkable due to their distinct physical and chemical characteristics when the number of layers is changed. When interfaced with metal nanoparticles, these hybrid materials such as MoS2-Au nanoparticles exhibit enhanced properties that can be used for applications such as in sensing, catalysis, and photovoltaics devices by enhancing their signals and tuning their physical properties. Also, 2D MoS2 can be a useful platform as a SERS substrate for organic molecules detection, including Rhodamine 6G (R6G) as a photosensitizer in MoS2 devices.

In this thesis, MoS2 flakes were prepared using the chemical vapor deposition (CVD) technique on SiO2/Si substrates. Tip-Enhanced Raman Spectroscopy was used to investigate the effect of varying MoS2 thicknesses on Raman modes. Raspberry-like gold nanoparticles and R6G molecules were coated on MoS2 flakes to investigate the plasmon-exciton and dye effect respectively, on Raman and photoluminescence enhancements using tip-enhanced scattering and contact potential difference microscopy.

Summary for Lay Audience

The world is changing due to various nanomaterials. Computers and machines used to be large and bulky, but now they are small and light, with superior performance. This is owing to the rapid advancement of technology, which has allowed the development of smaller and faster equipment. Not only may the size of bulk devices be decreased by studying nanoparticles, but new material properties can also be discovered. As a result, modern societies have launched large-scale initiatives over the past 20 years to develop nanotechnologies to develop many applications ranging from sensing, displays, or wearables.

If common materials that we utilize every day are generally bulky and have a 3D organization, two-dimensional (2D) materials are of particular interest and present new properties due to this lower dimensionality. For instance, 2D materials are used to make automobile sensors, solar cells, semiconductors, batteries, and data storage. Graphene and transition metal dichalcogenides (TMDs) are examples of 2D materials with various uses. TMDs are utilized in solar cells, which is one of their most important applications. These materials are semiconductors in optoelectronic applications, and their optical and electrical characteristics result in efficiency improvement. In order to synthesize TMDs, new approaches and methodologies are now being studied. Furthermore, TMDs can be interfaced with other molecular or nanomaterials entities thus providing new properties. In this work, we describe the synthesis of TMDs, their interfacing with gold nanoparticles and organic molecules. Moreover, a series of experiments were conducted to characterize these materials at the nanoscale, thus ensuring that the properties are matching the desired outcome Atomic Force Microscopy (AFM) is a material characterization method that reveals the topography of the 2D nanoflakes and the presence of local nanoscale defects. Raman Spectroscopy and tip-enhanced Raman spectroscopy as spectroscopy methods that provide indications about the purity of the 2D materials as well as the presence of multiple layers. Combined together, these experiments are critical to characterizing these 2D materials ensuring that they exhibit tailored properties for specific applications.

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