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Technical Briefs

Re-examining Electron-Fermi Relaxation in Gold Films With a Nonlinear Thermoreflectance Model

[+] Author and Article Information
Patrick E. Hopkins

 Sandia National Laboratories, Albuquerque, NM 87185pehopki@sandia.gov

Leslie M. Phinney, Justin R. Serrano

 Sandia National Laboratories, Albuquerque, NM 87185

J. Heat Transfer 133(4), 044505 (Jan 14, 2011) (4 pages) doi:10.1115/1.4002778 History: Received March 26, 2010; Revised June 22, 2010; Published January 14, 2011; Online January 14, 2011

In this work, we examine Fermi relaxation in 20 nm Au films with pump-probe themoreflectance using a thin film, intraband thermoreflectance model. Our results indicate that the Fermi relaxation of a perturbed electron system occurs approximately 1.10±0.05ps after absorption of a 785 nm, 185 fs laser pulse. This is in agreement with reported values from electron emission experiments but is higher than the Fermi relaxation time determined from previous thermoreflectance measurements. This discrepancy arises due to thermoreflectance modeling and elucidates the importance of the use of a proper thermoreflectance model for thermophysical property determination in pump-probe experiments.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Transient thermoreflectance data taken on a 20 nm Au film evaporated on a glass substrate fit with the TTM using two different source terms: (dashed line) the traditional source term (Eq. 4) and (solid line) the source term that accounts for a delay in electron thermalization (Eq. 5). Accounting for a delay in electron thermalization gives a much better fit of the TTM to the experimental data and yields a best fit value for G that is in much better agreement with previous measurements of G on Au.

Grahic Jump Location
Figure 2

Fermi relaxation times as a function of incident fluence determined from the fits of the thermoreflectance data to the TTM with Eq. 4 using the traditionally used thermoreflectance model ((Eq. 1) and the thin film intraband thermoreflectance model (Eq. 11). The Fermi relaxation time determined through the use of Eq. 11 does not exhibit a strong fluence dependency, which is consistent with the Fermi liquid theory of hot electron relaxation, compared with tth determined through the use of Eq. 1.

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