Physics 095 Nanoscience and Nanotechnology

Lab 04                                   
Fall 2005
Scanning Probe Microscope                       
Randy Headrick

        

Procedure:  The procedure for this lab involves a number of steps.  Please remember that once you align the microscope you cannot bump anything, such as the secondary mirror or you may have to start over from the beginning.  Also, there is a chance of breaking the stylus if too much pressure is applied to it.  Please work slowly and patiently!  Don’t turn any of the knobs until you are sure that you know what they do, and which direction is which.



1. Room lights on: In this step, we will do the initial checkout of the microscope. 

(i)    Make sure that the laser diode lights up when you turn the switch on.  Don’t attempt to adjust the laser diode, since it has delicate parts inside. 

(ii)    Trace the path of the laser beam with a small piece of paper, and make sure that it is deflecting off of the small mirror glued to the stylus.

(iii)    Make sure that the stylus is not touching the sample.  There should be a tiny, but visible gap between them. 

(iv)    Carefully lower the z-stage by one full turn of the micrometer; the gap should get larger.  Then raise it back up to its original position.  Make sure that the stylus does not contact the sample during this operation.

(v)    Make sure that you understand how to read the micrometer settings.  The smallest division is 0.001”, which is 25.4 μm.

(vi)    Position the apparatus so that the stylus is 50cm from the screen, measured horizontally along the table.

(vii)    Move the secondary mirror into place so that it intercepts the laser beam. The secondary mirror is on its own separate stand so that you can move it around easily.

(viii)    Attach a piece of graph paper to the screen.  Check to make sure that the divisions on the graph paper are 5 mm.

(ix)    I will check your setup, and then once all of the groups have completed this step, we will turn the room lights off.




2. Room lights off: In this step, we will adjust the secondary mirror and get the height calibration data.

(i)    Position the secondary mirror so that the laser beam hits it near the bottom of the mirror, but without any light leaking past the mirror.

(ii)    Trace the path of the laser reflection from the secondary mirror, and make sure that it is hitting the screen.  The mirror has a pivot, so that its angle can be adjusted easily by hand. 

(iii)    Note the position of the “crosshair” in the laser spot, and mark a line on the screen. Label this line “0”.

(iv)    Carefully raise the z-stage until the laser spot is deflected by about 5mm.  The sample is just barely touching the stylus now.  This is the most critical step, so make sure that you don’t accidentally go too far.

(v)    Lower the z-stage again so that the crosshair returns to zero. Position it so that the sample is just barely not touching the stylus.

(vi)    Raise the z-stage by 0.001” at a time and record the z-stage position (in thousandths of an inch) and the crosshair position (in millimeters).  Keep going until the crosshair deflects by about 4.0 cm.

(vii)    Lower the stylus back to the position in step (v) and repeat step (vi) a second time.  You should now have two sets of data for z vs. crosshair position. 

(viii)    Lower the z-stage again back to the “no contact” position. Then back off by an additional one full turn (0.025”) of the micrometer (we’ll call this the “safe” position). 




3. Room lights on: In this step, we will determine the height calibration by two methods.

(i)    Plot the data from step 2 on a piece of graph paper; both data sets should be linear with the same slope.  Get the slope in mm per micron.

(ii)    Measure the vertical height difference between the zero on your screen and the stylus.  Use this information to determine the distance from the stylus to the position of the laser spot on the screen.  Calculate the deflection of the stylus that corresponds to a 4.0 cm deflection of the laser spot (you will need the length of the stylus for this, which I will provide).

(iii)    Compare the results of (i) and (ii).  If they don’t agree, think about why they don’t agree.  If the disagreement is serious, then we may decide to do some additional measurements.




4. Room lights off: In this step, we will perform the initial x-scan along the surface of the corrugated sample.

(i)    Make sure that the deflection is zero.  If it is not, then check to see if any of the components have been bumped, and that the sample is not in contact with the stylus. 

(ii)    Raise the z-stage until the deflection is about 2.0 cm.  Record the position of the z-stage.

(iii)    Record the position of the x-stage.  Move the x-stage by 0.001” at a time and record the deflection at each step.  If the deflection ever goes below 1.0 mm, then abort the scan, and go to step (iv), otherwise continue for one full turn of the x-stage micrometer (0.025”) plus another 0.015”, for a total of 0.040”.

(iv)    If the deflection drops below 1.0 mm, then drop the z-stage to the “no contact” position plus one extra turn of the micrometer knob (i.e. the “safe” position), and then return the x-stage to its starting position.  Repeat step (ii), except raise the z-stage to get a 3.0 cm deflection instead of 2.0 cm.  Then repeat step (iii) again. Note that you might have to raise the z-stage more if the results of step (iii) are still not acceptable.

(v)    Finish by dropping the z-stage to the “safe” position, and then return the x-stage to its starting position.
5. Room lights on: In this step, we will do an initial calculation of the corrugation wavelength and amplitude.

(i)    Find the x- and z-positions of the minima and maxima of your scan.  Calculate the corrugation wavelength and period using the maxima and minima.

(ii)    Plot the scan (40 points total) on a piece of graph paper to get a feel for the shape of the corrugation (sawtooth, sinusoidal, etc.).


6. Room lights off: In this step, we will collect the final data.

(i)    Repeat step 4. Now we have two data sets with 40 data points each.

(ii)    If the two sets of data don’t agree, think about what went wrong.  

 


Lab writeup

The lab report for Lab 04 is due on Wednesday, October 19th.  The report should include the following:

1.    A one-page description of the lab, including a simple diagram depicting the layout of the different components.  This does not need to be typewritten, and the diagram may be drawn by hand.

2.    Calculations of the calibration factor H/h, as defined in class, performed two ways: (i) from your height calibration data in step 2, and (ii) from measurements of the path length L and the stylus length l.

3.    Plots of all of the data from steps 2, 4, and 6.  Your data from steps 4 and 6 should be converted to microns (25.4 microns per 0.001”).