Optical Response of CVD-Grown ML-WS2 Flakes on an Ultra-Dense Au NP Plasmonic Array

The combination of metallic nanostructures with two-dimensional transition metal dichalcogenides is an efficient way to make the optical properties of the latter more appealing for opto-electronic applications. In this work, we investigate the optical properties of monolayer WS2 flakes grown by chemical vapour deposition and transferred onto a densely-packed array of plasmonic Au nanoparticles (NPs). The optical response was measured as a function of the thickness of a dielectric spacer intercalated between the two materials and of the system temperature, in the 75–350 K range. We show that a weak interaction is established between WS2 and Au NPs, leading to temperature- and spacer-thickness-dependent coupling between the localized surface plasmon resonance of Au NPs and the WS2 exciton. We suggest that the closely-packed morphology of the plasmonic array promotes a high confinement of the electromagnetic field in regions inaccessible by the WS2 deposited on top. This allows the achievement of direct contact between WS2 and Au while preserving a strong connotation of the properties of the two materials also in the hybrid system

The additionally glycosylated variant of human sex hormone-binding globulin (SHBG) is linked to estrogen-dependence of breast cancer.

Summary Sex Hormone-Binding Globulin (SHBG), the plasma carrier for androgens and estradiol, inhibits the estradiolinduced proliferation of breast cancer cells through its membrane receptor, cAMP, and PKA. In addition, the SHBG membrane receptor is preferentially expressed in estrogen-dependent (ER+/PR+) breast cancers which are also characterized by a lower proliferative rate than tumors negative for the SHBG receptor. A variant SHBG with a point mutation in exon 8, causing an aminoacid substitution (Asp 327 → Asn) and thus, the introduction of an additional N-glycosylation site, has been reported. In this work, the distribution of the SHBG variant was studied in 255 breast cancer patients, 32 benign mammary disease patients, and 120 healthy women. The presence of the SHBG mutation was evaluated with PCR amplification of SHBG exon 8 and Hinf I restriction fragment length polymorphism (RFLP) procedure. This technique allowed us to identify 54 SHBG variants (53 W/v and 1 v/v) in breast cancer patients (21.2%), 5 variants (4 W/v and 1 v/v) in benign mammary disease patients (15.6%), and 14 variants (W/v) in the control group (11.6%). The results of PCR and RFLP were confirmed both by nucleotide sequence of SHBG exon 8 and western blot of the plasma SHBG. No differences in the mean plasma level of the protein were observed in the three populations. The frequency of the SHBG variant was significantly higher in ER+/PR+ tumors and in tumors diagnosed in patients over 50 years of age than in the control group. This observation suggests the existence of a close link between the estrogen-dependence of breast cancer and the additionally glycosylated SHBG, further supporting a critical role of the protein in the neoplasm

Local optical properties of 2D semiconductor/plasmonic heterostructures

The possibility to control the properties of low-dimensional semiconductors via the exploitation of properly engineered architectures shows promising implications for several potential applications in the fields of optoelectronic and quantum technologies. Among the plethora of semiconducting materials, two-dimensional group 6 transition metal dichalcogenides (TMDCs), when thinned down to the three-atoms-thick monolayer (ML), exhibit a transition of the electronic bandgap from indirect to direct, with the bandgap energy falling within the visible spectral range. This, together with other singular properties, makes TMDCs extremely appealing light-sensitive materials for optoelectronics and photonics applications. Among several strategies to enhance light-matter interaction in ultrathin TMDC films, the electromagnetic field confinement and amplification typical of nano-sized metallic objects supporting localized surface plasmon resonances, i.e. light-induced collective electronic oscillations, can significantly strengthen the interaction of atomically-thick TMDCs with light, with the opportunity to exploit hybrid systems to realize plasmon-enhanced devices. In addition, the structural, electronic and optical properties of 2D TMDCs can be properly manipulated via their integration with plasmonic materials. Moreover, strongly-coupled exciton-plasmon systems can be realized by combining few- and single-layer TMDCs with ad-hoc designed plasmonic nanostructures with promising implications both for fundamental research and quantum-based applications. In this context, the research activity reported in this thesis has dealt with the study of the optical properties of spatially-confined systems. Two main classes of nanomaterials were investigated, namely noble metal nanostructures, with specific interest on their plasmonic and thermoplasmonic properties, and 2D TMDCs, with a focus on their excitonic properties. This manuscript mainly deals with the local optical properties which arise when integrating ML-TMDCs with plasmonic nanosystems to form hybrid structures. The experimental investigations on the hybrid systems have in common the exploitation of laterally-resolved optical techniques with micrometric and even nanometric spatial resolution. In detail, I will show how the combination of imaging spectroscopic ellipsometry and imaging photoluminescence spectroscopy can provide a complete picture of the local excitonic properties of TMDC flakes (WS2 in this case) grown by chemical vapour deposition. Deep knowledge on the local excitonic properties of 2D TMDCs proved fundamental for studying how their properties can be tailored by coupling with plasmonic materials. In this thesis, hybrid systems with a double-layer architecture (i.e. ML-TMDC/plasmonic substrate) were realized for two main experimental investigations. The first study dealt with the role played by the morphology of the plasmonic substrate, an ultra-dense array of Au NPs (approximately 10^3 NPs/\ub5m^2), in affecting the plasmon-exciton interaction. In the second experiment, a 2D TMDC/plasmonic heterostructure was implemented as a system to probe the capabilities of tip-enhanced photoluminescence spectroscopy (TEPL) in mapping at the nanoscale the light-emission related properties of ML-TMDCs onto a plasmonic substrate. The last part of the thesis is dedicated to experimental investigations on the ultrafast temperature evolution of impulsively-excited plasmonic systems by means of pump-probe techniques. Two model-free approaches are presented for the direct assessment of the temporal evolution of the electron gas temperature after impulsive photoexcitation of metallic NPs. More in general, the results obtained from these last experimental studies pave the way for the assessment of the relaxation dynamics within physical systems and are inspiring towards further exploration on the phenomena which arise following photoexcitation of low-dimensional semiconductor/plasmonic heterostructures taking place on time scales of the fs-ps, such as the processes of charge and/or energy transfer and those related to hot electrons

Thermometric Calibration of the Ultrafast Relaxation Dynamics in Plasmonic Au Nanoparticles

The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ultrafast relaxation process involving the gradual re-equilibration of the system’s electron gas, lattice, and environment. One of the major hurdles in studying these processes is the lack of direct measurements of the dynamic temperature evolution of the system subcomponents. We measured the dynamic optical response of ensembles of plasmonic Au nanoparticles following ultra-short-pulse excitation, and we compared it with the corresponding static optical response as a function of the increasing temperature of the thermodynamic bath. Evaluating the two sets of data, the optical fingerprints of equilibrium or off-equilibrium responses could be clearly identified, allowing us to extract a dynamic thermometric calibration scale of the relaxation process, yielding the experimental ultrafast temperature evolution of the plasmonic particles as a function of time