This page was developed by the Queen's University Applied Sustainability Research Group.

In the Material Physics Cleanroom (located in Stirling Hall atQueen's University), a Field Emission Scanning Electron Microscope is often used for imaging and characterization purposes. A scanning electron microscope^W uses an electron beam to obtain high levels of magnification and resolution for imaging. The specific type of FESEM found in the Materials Physics Cleanroom is the Leo/Zeiss 1530 Field Emission Scanning Electron Microscope^[1] with Gemini gun and Nordliest EBSD.

Application notes:

• SEM works best with electrically conductive samples.
• SEM machines detect secondary electrons released from the interaction of the sample with the electron column beam
• Some SEM machines have an optional auger-electron detector; this one does not
• An EBSD detector (present on this machine) is used to read crystal structures at high energy
• SEM is a very qualitative measurement technique
• SEM is very fast at doing a scan, compared to AFM (atomic force microscope), with little required sample preparation
• This model of SEM is a field emission microscope; this allows for lower electron energies in the column, and therefore a wider range of samples can be scanned
• The SEM has two pumps: turbo pump for high pressure, and roughing pump for lower pressures. It can achieve 1e-6 torr vacuum, 1e-5 is also typical
• The energy of the electrons in this machine can be varried from 25KeV to 2KeV, which affects resolution of the image - a higher voltage will have a higher resolution

Microscope Specifications

• Schottky field-emission electron source
• Operating voltage: 0.2 - 30 kV
• Rated resolution: 1.2 nm at 20 kV, 2.5 nm at 5 kV, and 3 nm at 1 kV^[2]

Protocol

• Working with the FESEM requires a trained lab researcher at all times.
• The lab researcher will assist in all of the imaging aspects and can offer helpful advice and guidance.
• The actual FESEM operation will be done by the researcher. A general outline of how the imaging program operates can be seen on this Georgia Tech College of Engineering page^[3]
• Samples should be clean, prepared and free of debris before imaging. Some samples may require conductive coatings in order for the electron beam to properly image the subject.
• If possible, clean sample with ethanol to remove dust and oils.
• Always clean all instruments that will touch the sample with ethanol (ie. tweezers)
• A clean sample will pressurize very quickly.
• Always wear gloves if you are touching your samples: fingerprints make the vacuum chamber pressurize very slowly.
• A freshly cleaved edge should be used to obtain a cross-sectional scan. To cleave a sample, first use a diamond cutter to nick the sample. Use special flat cleaving tweezers to grip a large area of the sample on both sides of the nick. Roll the tweezers away from each other to cleave the sample along it's crystal plane. Do not touch the cleaved plane with anything. This cleaved edge should be tangential to the mounting plate, on the outer edge when mounted.
• Some movement of the image may be seen while scanning. This can be either the electron beam bending due to the properties of the sample, or the sample physically slipping around in the machine. Silver glue is best to obtain a secure mount.

Tips

• Be familiar with the general cleanroom procedures before entering. The dress attire conists of a cleanroom lab coat and booties.
• Always work with a qualified lab researcher unless proper training has been covered.
• If a cross sectional view is desired, ensure a clean break can be found (use a diamond scribe) on the sample and mount the sample in such an orientation that one edge slightly hangs off of the round holder.
• Double check sample identifications, sample placements and sample orientations before placing the samples inside the FESEM chamber.

Basic Operation Instructions

These instructions should only be followed by a trained operator, in the presence of a lab research.

Other Equipment in the Materials Physics Cleanroom

• X-Ray diffraction: Philips X'Pert XRD
• Atomic force microscope^W: Digital Instruments Multimode Nanoscope AFM
• Variable angle Spectroscopic Ellipsometry^W

For all booking information, rates and schedules, please see the Materials Physics cleanroom page.

Sources and Citations