Most effort in a spectroscopic ellipsometry and QCM-D measurement is done setting up the instruments and liquid flow assembly. To help make life a little easier, consider the following tips & tricks.
1. Use M3 nuts to secure the module thumbscrews when taking ellipsometry measurements of Q-Sensors.
For our older users of the ellipsometry module, you may have run into an issue where you need to take an ellipsometry measurement of the bare Q-Sensor surface. If you put the bottom half of the ellipsometry module into the Explorer chamber, the module is free to wobble. Then you would put the Q-Sensor on top of the wobbly module. Obviously, this is not an ideal situation for an optical measurement.
Until we release a solution for mounting the Q-Sensor without the module, an easy workaround is to use two M3 nuts to secure the thumbscrews, as shown here. However, be sure to use shorter M3 nuts than these so they don’t block your ellipsometry beam!
2. Check that your QCM-D sensor is properly mounted before filling the ellipsometry module with liquid.
Before pumping liquid through the ellipsometry module, try collecting QCM-D data in air ambient. If you find out you have to reseat the Q-Sensor after you’ve already filled the ellipsometry module with liquid, you will have to dry out the module before trying again. This takes time, and you may get a build-up of moisture on the module windows if the drying is not thorough enough. This moisture will affect the window calibration ellipsometry measurement.
3. After filling the ellipsometry module with liquid, use dental mirrors to see if bubbles are present. A pair of dental mirrors is invaluable for making sure that your ellipsometry beam channel is free of bubbles. First, use a shutter to block the ellipsometry light source. Always use suitable eye protection for your light source, especially for lasers. Place a mirror over the beam-inlet window, then place the second mirror over the beam-outlet window. Adjust the mirrors as needed to look through the beam channel. Remember not to move the ellipsometry module. If your light source does not have a shutter, you can place a piece of paper between the detector and the outlet window of the ellipsometry module so that you can observe the shape and coherence of the beam spot. If the spot is distorted, a bubble may be the cause.
4. Bubbles are trouble.
If you have bubbles in your beam channel, try the following steps:
- Avoid moving the ellipsometry module if possible, as this can nullify the window calibration ellipsometry measurement
- Flow liquid very quickly through the module to dislodge loose bubbles by connecting a syringe to the flow assembly or sharply increasing the flow speed
- Try filling the liquid cell with air and refilling slowly with your liquid
5. Avoid bubbles in the first place
- Degas your liquids and solutions for 20-30 minutes by bubbling nitrogen or argon through them before the measurement
- Use low flow rates (< 0.2 mL/min), especially when initially filling the ellipsometry module
- Consider adding bubble traps to your fluid handling system• Avoid bubbles in the first place
- Use Teflon tape with your tube fittings to ensure you have tight seals
If you want to learn more about combining QCM-D with spectroscopic ellipsometry? Check this webinar!