Applications of Nanosecond Pulsed Lasers: Electronic Transitions of Atomic Si to Dewetting of Pt and Ag Metal Thin Films
Abstract
A nanosecond pulsed laser has been explored for spectroscopic and material processing applications. The electronic transitions of atomic Si were characterized using a high-voltage pulsed electric discharge (HV-PED) source coupled with resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry (TOF-MS). The species produced in the discharge were identified through mass mapping. Si, SiHn, SizCyHz, and CnHm were produced in the HV-PED source. The one-color (1+1) REMPI spectrum recorded in the one-photon energy range of 38466 – 46075 cm-1 showed 26 lines that were assigned to neutral atomic Si (Si I) transitions. Two new lines were observed at 43551.76 cm-1 and 44201.34 cm-1. Three Si I lines that were previously observed, but with no assignment, have been successfully assigned.
Pulsed laser-induced dewetting (PLiD) was used to form nanoparticles (NPs) from Pt and Ag thin films on a dimpled Ta (DT) substrate. The threshold laser fluence (LFth) required to dewet Pt films was determined to be 300 mJ/cm2. Short irradiation times (≤ 60 s) and high fluence favored the production of smaller NPs with narrower size distribution. The Pt NPs/DT were characterized electrochemically using cyclic voltammetry (CV). The charge densities obtained were generally small (< 210 µC/cm2). However, the roughness factor showed that as high as 57% – 82% of available geometric surface area of the NPs was accessible by the CV measurements.
The LFth to dewet Ag thin films was < 30 mJ/cm2. In comparison to the Pt NPs which were spherical in shape, Ag NPs showed both distorted spheres and non-spherical geometries. Distorted spheres were mostly produced at lower fluences of ≤ 240 mJ/cm2, while their non-spherical counterparts formed at relatively higher fluences of > 240 mJ/cm2. The Ag NPs/DT were explored as a substrate for surface enhanced Raman spectroscopy (SERS) application. A weak SERS enhancement factor of 2 was determined.
A quantitative evidence was obtained which showed that the characteristic length scale (Λ) has a quadratic power dependence on the metal film thickness (h). This was a confirmation that the mechanism of PLiD was spinodal dewetting. In a thickness-dependent temperature model for PLiD, a modified thickness (hT*) was introduced that included the thickness of the metal-Ta2O5-Ta system. The temperature rise (∆Th) predicted as a function of PLiD parameters for Ag, Au, Pd, Pt, and Ir films was in very good agreement with available literature.
Description
Keywords
Chemistry--Physical, Materials Science
Citation
Owusu-Ansah, E. (2017). Applications of Nanosecond Pulsed Lasers: Electronic Transitions of Atomic Si to Dewetting of Pt and Ag Metal Thin Films (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/24970