Two-Dimensional Layers of Colloidal CdTe Quantum Dots: Assembly, Optical Properties, and Vibroelectronic Coupling

Manufacturing of silica platforms functionalized by CdTe quantum dots (QDs) of 3.4 nm diameter through (3-aminopropyl)triethoxysilane (APTES) aliphatic organosilanes is performed to preserve QD excitonic properties after their transfer from colloidal solutions to surfaces at ambient air. Under these conditions, the chemical stability and the structural homogeneity of the 2D monolayers are monitored and attested by probing their optical efficiency through UV–visible spectroscopy (light absorption), time-resolved fluorescence spectroscopy, and microscopy (light emission). Grafting of the aliphatic organosilanes on silicon is examined by XPS measurements, showing that a 0.9 nm-thick sublayer is electrostatically stabilized between the SiO 2 substrates and the QD layers. These latter are deposited by physisorption or chemisorption. Surprisingly, the optical absorption of the physisorbed QD layers does not vary beyond 10 days, while that of chemisorbed QD layers degrades in 1 day. As a result, the chemical activation of QDs by EDC-NHS (1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide and N -hydroxysuccinimide) is not mandatory, contrary to what the literature states. Eventually, sum-frequency generation spectroscopy evidences a vibroelectronic coupling between the QDs and APTES monolayers, thus demonstrating the optical functionality of such QD-based platforms.