Presentation Title

Doubly Resonant Sum Frequency Generation in Photosensitized Surfaces

Presenter Information

Abraham EstradaFollow

Faculty Mentor

Luis Velarde

Start Date

18-11-2017 2:15 PM

End Date

18-11-2017 3:15 PM

Location

BSC-Ursa Minor 42

Session

Poster 3

Type of Presentation

Poster

Subject Area

physical_mathematical_sciences

Abstract

Sum frequency generation (SFG) spectroscopy is a method of obtaining measurements of electronic and vibrational modes of surface molecules by overlapping broad band IR wavelengths and narrow band visible wavelengths. FTIR, Raman, UV-VIS are other methods used to obtain vibrational or electronic information; however, none of these methods can be used to selectively obtain information of interfacial species. SFG’s of two different photosensitizers, Rhodamine 6G and, CdSe quantum dots with TOPO ligands were obtained. Using SFG with fixed IR wavelengths and varying visible wavelengths, electronically resonant and non-resonant spectra were acquired. A UV-Vis spectrum was obtained for the quantum dots, and was used to estimate what visible beam to use for the SFG; in addition, it was used to obtain the size of the quantum dots. Rhodamine 6G was observed on quartz and gold surfaces, both spectra results were distinct, indicating different orientations of the molecule on the substrate. Rhodamine 6G and Quantum Dots are very important, because they can be tuned to absorb specific wavelengths, which is very useful for the application to solar cells.

Summary of research results to be presented

•Sum-Frequency generation is a non linear process that generates surface specific vibrational spectra. • SFG is obtained by spatially and temporally over lapping a broad band IR pulse and a narrow band visible pulse on a sample surface. •Vibrational Sum-Frequency generation occurs when the vibrational state is excited and the electronic state is not. • Doubly resonant Sum-Frequency Generation examines the electronic and vibrational transitions together, which gives information on the electron-vibration coupling of surface molecules. • DRSFG was obtained on CdSe quantum dots with TOPO ligands on quartz and on Rhodamine 6G on gold and on quartz. •Quantum dots are semiconducting nanocrystals with a tunable absorption spectrum based on their size which makes them useful for solar cells. •Rhodamine 6G is a photosensitizer that can be useful to absorb energy from the visible region and transfer energy and charge to adjacent molecules or nano crystals. •UV-Vis shows the maximum absorption for the CdSe quantum dot at 584 nm. •C-H Fermi resonance is present at maximum intensity for the and C-H bend. •Small CH2 contribution indicates presence of some gauge defects on the TOPO ligands. •Rhodamine 6G on quartz has maximum intensity and doubly resonance at 590 vis. •Rhodamine 6G on gold displayed maximum intensity and doubly resonance at 570 vis. •Rhodamine 6G on quartz has higher SSP intensity, on gold it displays higher PPP intensity and is shifted. •PPP on gold is substantially higher, which indicates perturbations due to surface plasma. •The peak for Rhodamine 6G is from the conjugated aromatic ring.

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Nov 18th, 2:15 PM Nov 18th, 3:15 PM

Doubly Resonant Sum Frequency Generation in Photosensitized Surfaces

BSC-Ursa Minor 42

Sum frequency generation (SFG) spectroscopy is a method of obtaining measurements of electronic and vibrational modes of surface molecules by overlapping broad band IR wavelengths and narrow band visible wavelengths. FTIR, Raman, UV-VIS are other methods used to obtain vibrational or electronic information; however, none of these methods can be used to selectively obtain information of interfacial species. SFG’s of two different photosensitizers, Rhodamine 6G and, CdSe quantum dots with TOPO ligands were obtained. Using SFG with fixed IR wavelengths and varying visible wavelengths, electronically resonant and non-resonant spectra were acquired. A UV-Vis spectrum was obtained for the quantum dots, and was used to estimate what visible beam to use for the SFG; in addition, it was used to obtain the size of the quantum dots. Rhodamine 6G was observed on quartz and gold surfaces, both spectra results were distinct, indicating different orientations of the molecule on the substrate. Rhodamine 6G and Quantum Dots are very important, because they can be tuned to absorb specific wavelengths, which is very useful for the application to solar cells.