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Transmission Measurement Procedure:MOST

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In this method, the goal is to measure the percentage of light which passes through a material(deposited on a glass slide specifically).

Introduction[edit]

Transmittance of a material is in effect how well it allows radiant energy(electromagnetic power) to be be transmitted(pass through). This is helpful to learn because it gives insight into material properties and usefulness of some materials and their applications. For example, higher quality glass would typically have a higher percentage transmittance. Or certain materials may be purposefully fabricated to reduce the amount of light which goes through them.

While normal transmittance is light going through an object, internal transmittance refers to an energy loss due to absorption of the light passing through a material by the material itself. Several other aspects may effect the amount of light transmitted, such as scattering or reflection, the combination of all of these potential effects is the total transmittance. It is the goal of the method to reduce as many of these effects in order to gather reliable data.

  1. Wikipedia Link
  2. SpectraSuite Manual for machine operation and set up

Safety[edit]

Proper sample handling is essential for good research. Whatever the material is which needs to be measured, ensure you are wearing proper gloves in order to protect both yourself from the sample, but sometimes equally as important, the sample from your body oils, or other contaminants.

Since light sources are in use for this method, it is important to not look directly into the light source, or any fiber optic cable connected to a light source. Additionally remember to unplug the light source after use so that it does not burn out and potentially cause problems in the lab.

Equipment or Bill of Materials[edit]

Equipment (everything is pictured)
  1. Computer with the Ocean Optics SpectraSuite Software
  2. Light source(we use an Ocean Optics DH-2000 UV-VIS-NIR)
  3. Two fiber optic cables
  4. USB Spectrophotometer(we use an Ocean Optics USB2000+ VIS-NIR)
  5. A device to hold the sample steady and isolate the sample/optic cables from ambient light(this example uses a printed part-design to be uploaded)
Fig 1: Example intensity spectrum  
Fig 2: Ocean Optics Spectrometer  
Fig 3: Glass slide sample holder device  
Fig 4: Ocean Optics UV-VIS-NIR Light source  
Bill of Materials
  1. A sample to measure - an example would be ultrathin-semiconductor layers deposited upon glass slides

Calibration & Tolerances[edit]

Calibration
  1. Having a clean sample is essential to getting good measurements
  2. Connect a fiber optic cable to the light source and to the sample holder
  3. Connect another fiber optic cable to the sample holder and the spectrometer.
  4. Place the sample holder in the wooden box with a black blanket(to keep light out) to isolate the sample/holder from ambient light.
  5. Connect the spectrometer to the computer via USB
  6. Turn on the light source and let it warm up for at least 10-15 minutes to reach nominal operating temperature -this is for consistent output
  7. Start the SpectraSuite software and follow this path to connect the spectrometer to the program: Spectrometer:Aquisition:Aquisition Console - Then click on the USB spectrometer
  8. An intensity value will be displayed on the data collection area of the screen, a stable connection between all physical devices in the set up is necessary for this value to be consistant - A variable intensity may mean a loose connection somewhere along the photopath
  9. Using the buttons on the screen(a light bulb) above the data collection area take a light reference sample and a dark reference sample following the guidelines in the SpectraSuite Manuel.
  10. Determine the mode for testing - in this example we are doing transmittance measurements, follow this path: Processing:Processing Mode:Transmission
  11. The data collection screen will change to show transmittance
  12. Change the Integration time to 1 second and the scans to average to be 10 - This is to reduce noise and improve reliability
  13. The system is now ready for sample testing
Tolerances
  1. The sample holder for slides is built to hold up to four glass slides 1mm thick each
  2. A wavelength range of 300-1000 is reliable for this experimental set up

Operation & Procedure[edit]

  1. Ensure proper calibration has been carried out and that the integration time/scans to average is the same as the calibration
  2. Set the wavelength of light to be measured by clicking on the screen, a green bar should appear at that wavelength
  3. Insert the reference sample into the holder and after three measurements(automatically done by the computer) record the red value at the bottom of the screen
  4. Remove the reference sample and replace it with a sample of your own. After three measurements record the value.
  5. Save the graph as it will give perspective over all wavelengths measured
  6. Repeat the reference measurement and sample measurement two more times, then finish off the run with another reference measurement. This process of reference - sample - reference is to ensure that the light source or fiber optic cables maintain their stability throughout the testing period.
  7. The values for a given sample should be averaged and then compared to the averaged reference values for that sample run, then normalized to 100% transmittance for the reference sample
  8. Repeat this process for all testing samples

Shutdown[edit]

  1. Close out of the SpectraSuite software
  2. Carefully remove and disconnect all cables
  3. Turn off the light source and log off of the computer

References[edit]