Nano-Thermometry: Transmission Electron Microscopy of Femtosecond Laser Irradiated Co/Si Multilayer Thin Foils
- PDF / 1,371,110 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 161 Views
0899-N07-30.1
Nano-Thermometry: Transmission Electron Microscopy of Femtosecond Laser Irradiated Co/Si Multilayer Thin Foils Yoosuf N. Picard1,2 and Steven M. Yalisove1,2 1 Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2176, U.S.A. 2 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109-2099, U.S.A. ABSTRACT Pre-thinned foils composed of amorphous silicon and polycrystalline cobalt were irradiated using femtosecond pulse-length lasers at fluences sufficient for ablation (material removal). The resultant ablated hole and surrounding vicinity was studied using transmission electron microscopy to determine modifications to the structure. Evidence of cobalt silicide formation was observed within a 3 micron radius of the laser hole edge by use of selected area electron diffraction (SAED). In addition, elongated grains of crystalline silicon was observed within 500 nm of the laser hole edge, indicating melting of the amorphous silicon and heat dissipation slow enough to allow recyrstallization. This initial work demonstrates the use of predesigned nanostructured multilayer systems as a method for nanoscale profiling of heat dissipation following pulsed laser irradiation.
INTRODUCTION As femtosecond lasers continue to attract interests as an effective approach to nano-scale machining, measuring the heat dissipation into the surrounding target material is of great importance. Confined systems composed of ultrathin films can provide an avenue for direct temperature profile measurement under worst case scenarios (limited heat dissipation due to constricted conduction path). In this study, we use cobalt and silicon as two reactants that form various phases with specific formation temperatures. We seek to observe cobalt silicide formation within and outside the area of laser irradiation as an approach to nanoscale temperature profiling.
EXPERIMENTAL DETAILS Co and Si were deposited at room temperature using a molecular beam epitaxy (MBE) system at a base pressure of 5 x 10-11 Torr. The films were deposited on degreased Si (100) substrates that were prepared using a Shiraki cleaning method prior to loading in the MBE system. The sample was then raised to 900°C to blow off the Shiraki oxide and analyzed using low energy electron diffraction and auger electron spectroscopy to ensure the surface was atomically clean and free of contaminants prior to deposition. A 110 Å thick film of cobalt was deposited, followed immediately by deposition of 200 Å silicon. Auger electron spectroscopy
0899-N07-30.2
was performed after each layer was deposited to ensure purity of the films. Rutherford backscatter spectrometry was used for calibration of the film depositions. After film deposition, the samples were cut into 3 mm discs from the backside using an ultrasonic disc cutter. The discs were mechanically polished to 70 µm thickness and etched from the back side using a mixture of nitric, acetic, and hydrofluoric acid until perforation. After chemically etching, the sam
Data Loading...
