UCSB NanoFab Microscope Training

Overview

We have numerous optical microscopes in our lab, each of which is a different model or manufacturer.

However, almost all of these microscopes share common features, even if the knob to enable the feature is in a different location. This "training" is intended to give the user an overview of these features, which are very useful for general observations, measurements, inspections after etching/other processing steps, identifying residues vs. delamination, to name a few.

Focus

General Focusing

The focus knobs on all of our microscopes turn towards the user to increase separation between the sample stage and microscope objectives. Thus, when focusing on a sample, always start by turning the knob in this "safe" direction to prevent crashing the sample into an objective. If the image gets blurrier, then turn the knob the other way, and confirm that the sample is becoming less blurry.

A useful trick before focusing is to do the following:

1. Observe the microscope illumination spot on the stage (looking directly at the sample/stage, not through the eyepieces)
2. Center the illumination spot on the edge of the sample, so there is a large height difference between the sample edge and the stage.
3. Then, while looking through the eyepieces, turn the knob towards you and observe whether the image becomes more or less blurry. (You can also look at the sample/stage directly to make sure nothing is going to crash.) You should be able to see the straight edge of the sample even when it is very blurry, and focus on the top-surface using this edge.

Measurements using focus

Many microscopes have gradations marked on the fine-focus knob, indicating microns of movement of the sample stage. Using these marks, one can focus on different surfaces and use the gradations to estimate how many microns of vertical separation is present between the two surfaces.

Microscope Objectives

Changing objectives is the easiest way to crash into a sample, especially with motorized objective turrets. A few tips can easily prevent this from happening.

The microscope objectives on all our microscopes are designed such that the sample is still approximately in focus when an objective is changed. Thus, one should only ever change objectives when there is some feature that is in focus on the sample. If you don't see anything at all, either because there are no features or because the sample is out of focus, find something to focus on before changing objectives! Pieces of dirt and dust are particularly useful for this purpose.

Working Distance

Working Distance or WD of an objective is the distance (usually in millimeters) from the objective lens to the sample, for the sample to be in focus.

Generally, the lower the magnification, the longer the working distance.

For example, a 5x objective may have a long working distance (distance to sample) of 10mm, while the 100x may be very small at 0.2mm.

Thus it is very important that initial focus is found with a low magnification (and corresponding long working distance). Also the focal depth (range over which sample stays in focus) is wider for low mag, making finding the appropriate focus generally easier, so you should always switch to the lowest mag. before starting to image your sample. (And switch back to lowest mag. when done, out of courtesy for the next user.)

Some objectives may actually have "WD" printed on them. For example, "WD 1.0" means that the sample will be in focus when it is approx. 1.0mm away from the objective. This is very helpful when estimating, by eye, whether you need to move the sample stage up or down to get into focus. If the objective says "WD 0.2" that means it has to be so close that you really should just start at low mag. and work your way up, keeping the sample in focus at each successive magnification!

This page is in-progress - More to come!
• DIC/Nomarksi
• Bright/Dark Field
• Digital Cameras and measurements
• Epi/DIa illum.
• Filters: Green, ND