Thermal Diffusivity/Conductivity Meter  

LaserPIT

The principle of the measurement method is shown below. A portion of a rectangular film specimen is heated by a modulated laser beam, which is a line heat source, made by scanning the laser spot rapidly with constant speed in the width direction of the specimen. Temperature waves, which propagate one-dimensionally in the long direction of the specimen, are produced. A schematic view of the setup is shown in Fig.1. As the irradiated portion of the specimen x changes, the ac temperature response is measured by a small thermocouple attached at the opposite face of the specimen. By analyzing the amplitude decay and the phase shift of ac temperature as a function of the spatial distance between the irradiated portion and the temperature sensor, logarithmic decrement of the amplitude, ka (reciprocal of the diffusion length) and phase shift increment, k_p (wavelength) can be obtained. By using k_a, k_p and the frequency f, according to the equation (1) and (2), it is possible to determine the in-plane thermal diffusivity, D of the specimen. By selecting the appropriate frequency the thermal diffusivity of wide variety of film materials from CVD diamond to polymers with a thickness of 3¨ 500 µm can be obtained.

Thermal conductivity of a thin film deposited on a substrate, k₂ can be determined from the measurements of thermal diffusivities of the deposited region (thin film + substrate), D₀₁₂ and the non-deposited region (substrate), D₀₁ and the measurements of the thickness of both the substrate and the thin film by other means. When the thermal conductivity of a thin film, k₂ is much greater than that of the substrate, it can be determined with its specific heat capacity per unit volume unknown. On the other hand, sensitivity of the measurement of thermal conductivity depends on the thermal conductivity of the substrate, thickness ratio, d₁/d₂ and precision of the thermal diffusivity measurement of a free-standing specimen. when a borosilicate glass substrate with a thickness of 30 µm is chosen, sensitivity of the thermal conductance of a thin film is ±90 nWK^-1. When the thickness of the thin film is 3000 Å, uncertainty of the thermal conductivity measurement of thin film is ±0.3 Wm^-1K^-1.

Features

• The method can provide accurate values of thermal diffusivity and derived thermal conductivity for wide variety of thin film materials from CVD diamonds to polymers with a thickness of 3~500 µm.
• The method is applicable for broad range of materials in the form of free-standing thinsheet or film, wires including fiber bundles and some films on substrate.
• The method can measure with very small temperature rise of the specimen.
• The LaserPIT module can be used by simple and easy operation of the sample assembly.
• The measurement and analysis can be made by the LaserPIT for Windows95/98/NT on a personal computer connected to the LaserPIT module via RS232C interface.
• The LaserPIT module has included all optical, mechanical and electronics systems in its compact body.
• The LaserPIT module requires only small space and power.

Constitutions

• LaserPIT module and the software of LaserPIT for Windows 95/98/NT
• Turbo molecular pump evacuation system (option)
• Personal computer with Windows 95/98/NT (option)

Specifications

Typical Applications

• Thermal diffusivity measurement of high conductivity materials, such as CVD Diamond, aluminum nitride, Silicon carbide, graphite, etc. (< 500µm thick)
• Thermal diffusivity measurement of low conductivity materials, such as glasses, plexiglass, etc. (30 - 500 µm thick)
• Thermal diffusivity measurement of wide variety of metal films (5 - 200 µm thick)
• Thermal diffusivity measurement of a single carbon fiber (>5 µm diameter)
• Thermal conductivity measurement of thin film deposited on a substrate, such as an aluminum nitride film (1000Å~3000Å thick) on a borosilicate glass (30 µm thick), etc. by using differential method (license pending).
  
  *Contents of this catalog may be changed without notice for improving the instrument