LabAdviser/314/Microscopy 314-307/Technique/Holo/Off-axis ETEM: Difference between revisions
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# Align the biprism to the feature of interest. Usually the biprism should be at an angle to the feature, e.g. a straight line. When aligning the biprism, one has to consider where the object and reference wave are passed through. If the biprism is perpendicular to the feature, the reference and object wave both passes through that feature and would terminate each other. Therefore, the reference wave is usually passed through vacuum/substrate and the object wave over that feature. Rotate the biprism with the black knob on the SAD aperture (outermost knob). You may want to zoom out to not lose the biprism from the FOV | # Align the biprism to the feature of interest. Usually the biprism should be at an angle to the feature, e.g. a straight line. When aligning the biprism, one has to consider where the object and reference wave are passed through. If the biprism is perpendicular to the feature, the reference and object wave both passes through that feature and would terminate each other. Therefore, the reference wave is usually passed through vacuum/substrate and the object wave over that feature. Rotate the biprism with the black knob on the SAD aperture (outermost knob). You may want to zoom out to not lose the biprism from the FOV | ||
# Align the beam to the biprism. The beam should be elliptical and perpendicular to the biprism to achieve high spatial coherence. Aligning the beam is done by stigmating the beam through the condenser lens. For this: Press stigmator → Condenser Stigmation → Rotate MFx or MFy. Note, either MFx or MFy has to be at their maximum, e.g. MFx = +1 or -1. When that is fixed, rotate the other multifunction knob until the beam is perpendicular to the biprism. In order to see if the beam is aligned to the biprism, check for the “step” that is produced when condensing the beam (Intensity knob). The idea is illustrated in the figure below. | # Align the beam to the biprism. The beam should be elliptical and perpendicular to the biprism to achieve high spatial coherence. Aligning the beam is done by stigmating the beam through the condenser lens. For this: Press stigmator → Condenser Stigmation → Rotate MFx or MFy. Note, either MFx or MFy has to be at their maximum, e.g. MFx = +1 or -1. When that is fixed, rotate the other multifunction knob until the beam is perpendicular to the biprism. In order to see if the beam is aligned to the biprism, check for the “step” that is produced when condensing the beam (Intensity knob). The idea is illustrated in the figure below. | ||
#:[[file:Holo-beam-alignment.png|thumb|left|200px|Figure 6: Aligning the beam (schematic)]] <br clear=all | #:[[file:Holo-beam-alignment.png|thumb|left|200px|Figure 6: Aligning the beam (schematic)]] <br clear=all> | ||
# Recheck the alignments: Rotation Center, PPx/PPy, Beam shift and object astigmatism. Most crucial is rotation center and object astigmatism! | # Recheck the alignments: Rotation Center, PPx/PPy, Beam shift and object astigmatism. Most crucial is rotation center and object astigmatism! | ||
# Tune the biprism voltage: Usually around 150-180V is useful, but higher voltages can be used for better resolution. Note that the fringes should be separated enough to see the individual fringes + it is recommended that 4 pixels per fringe is the minimum of fringe width. | # Tune the biprism voltage: Usually around 150-180V is useful, but higher voltages can be used for better resolution. Note that the fringes should be separated enough to see the individual fringes + it is recommended that 4 pixels per fringe is the minimum of fringe width. | ||