What is MRS?

The MicroScale Reflectance Spectrometer is an apparatus used to measure the spectral reflectivity of any small areas (i.e. thin films). The system consists of tungsten-halogen and dueterium light sources, a monochromator, a microscope with a photometry tube, a photomultiplier, a photodiode and fiber optics. The MRS is a unique system designed at the Thermal Analysis of Materials Processing Laboratory at Tufts University.

What does it do?

The MicroScale Reflectance Spectrometer measures the spectral reflectivity of microscopic areas. It is being used currently to measure the reflectivities of thin-film materials.

How does it work?

The MRS works by sending white light through a monochromator. A diffraction grating in the monochromator breaks up the light spectrum into various wavelengths. The monochromatic light is directed into a microscope through fiber optics. The light then travels through the microscope optics onto the specimen. Reflected light from the specimen bounces back through the objective of the microscope and travels up through the optics in the microscope to a photometry tube. Attached to the photometry tube is a detector which measures the amount of light being reflected off the sample. The detector can either be a photomultiplier or a photodiode. The signal is then fed into a computer for analysis and conversion into reflectivity. This system gives us the reflectivity as a function of wavelength.

Why do we want it?

We are currently studying heat transfer in thin films to further understand how we can improve the manufacturing process of silicon wafers used in the computer industry. Microelectronic thin-film structures vary on a very small scale, and the ability to measure reflectivities on a microscopic level will help determine the effect of changing film structures on the overall heat transfer of the wafer.

Biologically, we study the thin-film structures on butterfly wing scales. There is very little data on the radiative properties of these thin-film structures on butterfly wings.

A Beta-version of the Micro-RS is under development in the Comparative Biomechanics Laboratory. The new version features better wavelength resolution, larger wavelength range, and more sensitive detectors. It also uses better quality optics for the microscope to reduce the noise level and to control the sampling area.

For more information about this project, please contact: Prof. Peter Y. Wong

Thermal Analysis of Materials Processing Laboratory

College of Engineering, Tufts University, Medford, MA 02155