Patent ID: 7182510
Filing Date: 2007-02-27
Classification: G01N

Abstract:
1. A method for measuring the thermal conductivity on micrometer length scales, the method comprising: depositing a transducer film onto a specimen; providing a mode-locked femtosecond pulsed laser, said laser has a wavelength in the range of about 740 to about 840 nanometers; providing a beam splitter, said beam splitter separates said pulsed laser beam into the pump beam and the probe beam; providing a modulator to modulate said pump beam to a frequency in the range of 10 kHz to 20 MHz; providing a variable delay mechanism for said pump beam, said variable delay mechanism can produce a delay time (t) from 100 to 10000 picoseconds; focusing said pump beam onto a spot on the surface of said transducer film on said specimen, said pump beam heats the near surface layer of said transducer film, the temperature at the surface of said transducer film decays as the heat is conducted through the transducer film to the specimen; providing a modulator to modulate the frequency of the aforementioned probe beam to the range of 10 to 1000 Hz; focusing said probe beam on the same spot on the transducer film as said pump beam, said probe beam is reflected from said transducer film and directed to a photodiode detector; providing a rf lock-in amplifier to detect the signal from the modulation frequencies of said pump beam, said rf lock-in amplifier produces in-phase output voltage Via (t) and out-of-phase voltage Vout (t) that are dependent on the delay time t; providing a mathematical thermal model to calculate the heat conduction in the transducer film, the interface between the transducer film and the specimen, and the specimen, said model takes into account the heat flow in a minimum of three layers: said transducer film, said interface, and said specimen, and said model relates the ratio of in-phase output and out-of-phase output, Vin (t)/ Vout (t), to the delay time t and the thermal conductivity; performing experiments with varying delay time t and collecting Vin (t)/ Vout (t) data, and fitting the thermal model equations with two free parameters: thermal conductivity and the interface conductance G between the transducer film and the unknown specimen under test, and obtaining both the thermal conductivity and the interface conductance.