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U of U PHYS 5739 - Scanning Electron Microscopy

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Scanning Electron Microscopy Lab 2SEM BasicsMachine: Leo 440iSamples: Au/C, Ni balls, razor edge, hair, other neat stuffObjective: To understand optimization of operating parameters using the Leo Tungsten (W)-filament SEMTime allotted: Two weeksInvestigate the following modes of operation:1. Important operating parametersC1 lens current, C3 lens current, probe current, specimen current, working distanceSample: Au/CObjective: To understand the correlation among the current in the first condenser lens, the current in the final focusing lens, the probe current, the specimen current and the working distance.Procedure:For probe currents from 10 pA to 5 μA, observe the changes in other parameters, specifically including specimen current with the beam going into the Faraday cup,as the probe current is changed. Also compare the probe and specimen currents for filament currents of 2.65 A and 2.75 A as well as 20 and 50 m apertures.C1 and C3 are best monitored under the “Status” window.For working distances from 1 to 120 mm, observe changes in the other parameters.Why is this useful? C1 determines the probe current; C3 determines the working distance. Different manufacturers have different terminology for obscuring this information, which is important in determining how badly the microscope is outsmarting you!2. High resolution modeSample: Au/CObjective: To obtain the sharpest image possible at the highest possible magnificationParameters to vary:Accelerating potential: 5 kV - 40 kVProbe current: 10 pA - 10 nA (Monitor specimen current)Aperture size: 20, 50, 100 mWorking distance: 5-40 mm (requires mounting sample a few mm above the stage)Signal integration time: 5 sec - 4.2 minPrelab question: estimate at least the trend in each of the above parameters(i.e. 23 kV, 314.16 pA, largest aperture...); justify your choices, e.g. “Will resolution improve or degrade as you increase the beam energy from 1.0 keV to 40 keV? Why?3. High current modeSample: carbon tapeObjective: To obtain the sharpest possible image of carbon tape at 1000X, 10 kV, 7 mm working distance, 1 min integration 30 m apertureParameter to vary: probe currentPrelab question: calculate the threshold current based on the threshold equation and assuming minimum contrast ratios of 5% and 10%4. Depth of focus mode Sample: 0-80 screwObjective: To establish conditions to maximize depth of field. Ideally you want the entire length of the screw, viewed nearly vertically, in focus at the same timeParameters to vary:Accelerating potential: 5 kV - 40 kVProbe current: 10 pA - 1 nAAperture size: 30, 50, 100 mWorking distance: 5-40 mm (or more)Signal integration time: 5 sec - 4.2 minPrelab question: estimate at least the trend in each of the above parameters(i.e. 23 kV, 314.16 pA, largest aperture...); justify your choices5. Low voltage modeSample: Nickel balls or other with lots of surface textureObjective: To optimize the image of the texture of the surface of a sample as a function of operating parameters, mostly by decreasing the voltageParameter choices: 8 mm WD, 300 pA, about 1000 X6. Measure the probe current as a function of actual specimen current at 1 kV, 5 kV and 20 kV.Prelab question: How do you measure the probe current as a function of actual specimen current? Writeup: Full-blown writeup describing what you did and what you learned. Follow the instructions in the handout “Concise Lab Write-up Protocol”Caution: your report should not be a narrative that reads like “My Summerin the


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U of U PHYS 5739 - Scanning Electron Microscopy

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