Doctor of Philosophy (PhD)
In the present work, an apertureless atomic force microscope (AFM) tip-enhanced laser ablation (TELA) system was developed and investigated. An AFM was coupled to an optical parametric oscillator (OPO) wavelength tunable laser for sample ablation with a submicron sampling size. The AFM was used to image the surface and hold the AFM tip 10 nm above the sample surface. The AFM tip is coated with a layer of gold with a thickness of 35 nm. The incident laser wavelength was tuned in the visible and near-infrared (IR) region and focused on the AFM tip. With the tip-enhancement effect, ablation craters on the surface with a submicron size were obtained. The mechanism of TELA was investigated using anthracene and three laser dyes: rhodamine B, methylene blue, and IR 797 chloride. All samples were prepared in thin films and the laser energy was set just below their far-field ablation threshold. The wavelength was tuned from 450 to 1100 nm to cover the visible and near-IR range. It was found that ablation is independent of the absorption of the compounds. The ablation crater volume was measured and found to have a maximum at 500 nm and an approximately linear drop to 800 nm. Craters could not be produced between 800 and 1200 nm and were slightly smaller at 450 nm compared to 500 nm. Apertureless TELA was then performed to sample plasmid DNA with 532 nm, which resulted in a sampling volume of 0.14 μm3 with 12% in variation. The captured DNA was amplified and the amount of sample transferred from each ablation crater was quantitated at 20 ag/spot.
Cao, Fan, "Atomic Force Microscopy Tip-enhanced Laser Ablation" (2019). LSU Doctoral Dissertations. 4793.