Overview of the Method
Time-domain thermoreflectance (TDTR) is an optical pump-probe metrology for measuring the thermal conductivity of thin films, bulk materials, and the thermal conductance of interfaces. TDTR makes use of a high repetition-rate model-locked laser, variable time delay between pump and probe pulses, and a high modulation frequency of the pump. The pump beam is absorbed by a thin metal transducer layer on the sample surface, generating a periodic temperature oscillation. The time-delayed probe beam monitors the resulting change in reflectivity of the surface, which is proportional to the surface temperature excursions. By analyzing the ratio of the in-phase and out-of-phase components of the thermoreflectance signal as a function of pump-probe delay time, thermal transport properties of the sample can be extracted.
Technical Specifications
Applicable Materials
Polymers, dielectrics, 2D materials, semiconductors, and metals
Thermal Conductivity Range
Spans four orders of magnitude, from low thermal conductivity polymers (~0.1 W m⁻¹ K⁻¹) to single-crystal diamond (>2000 W m⁻¹ K⁻¹).
Layer Thickness Range
Thin films from ~10 nm to several micrometers, as well as bulk materials. Probing depth is the thermal penetration depth at the MHz modulation frequency.
Metrology Strengths
Highly sensitive probe of thin layers and individual interfaces and applicable to essentially any material with a smooth surface.
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