Surface Damage from Electrons -- Graphic and caption

Surface Damage from Electrons

A scoop of rainbow sherbet floating among mini icebergs? No, the graphic above is a snapshot of the damage that can be done to a biosensor film when it is exposed to an electron beam. Electron beams are commonly used to view topgraphy and to chemically analyze samples. Because electrons have much shorter wavelengths than visible light, they produce images of samples with much higher resolution than optical microscopes. Unlike light microscopes, however, electron microscopes can damage sample surfaces in the process of analyzing them. This is especially true for organic surfaces like those used in biological sensors or diagnostic devices, such as detectors for glucose in blood or E. Coli in food. NIST researchers recently quantified the damage done by an electron beam by combining scanning electron microscopy with secondary ion mass spectrometry or SIMS. The researchers exposed a biosensor film to an electron beam and then analyzed the film with SIMS. The SIMS instrument scans a beam of ions across the sample, knocking a row of molecules at a time off the surface. The dislodged molecules are collected and analyzed for their molecular weight by a mass spectrometer. The resulting composite graphic above shows that the electron beam removed some atoms from the biosensor film, changing the chemical composition of the surface. The heights of the raised areas in the graphic correspond to the extent of damage to those areas on the film. The NIST SEM/SIMS technique should help to better quantify the percentage of scattered electrons outside the focused area of an electron beam. This will be useful both for better understanding unintentional damage to SEM samples and for the study of electron beams as a way to deliberately etch patterns in microcircuits. Contact: Greg Gillen, (301) 975-2190.

Surface Damage from Electrons

graphic of damaged biosensor(2043160 bytes)

A scoop of rainbow sherbet floating among mini icebergs? No, the graphic above is a snapshot of the damage that can be done to a biosensor film when it is exposed to an electron beam. Electron beams are commonly used to view topgraphy and to chemically analyze samples. Because electrons have much shorter wavelengths than visible light, they produce images of samples with much higher resolution than optical microscopes. Unlike light microscopes, however, electron microscopes can damage sample surfaces in the process of analyzing them. This is especially true for organic surfaces like those used in biological sensors or diagnostic devices, such as detectors for glucose in blood or E. Coli in food.

NIST researchers recently quantified the damage done by an electron beam by combining scanning electron microscopy with secondary ion mass spectrometry or SIMS. The researchers exposed a biosensor film to an electron beam and then analyzed the film with SIMS. The SIMS instrument scans a beam of ions across the sample, knocking a row of molecules at a time off the surface. The dislodged molecules are collected and analyzed for their molecular weight by a mass spectrometer.

The resulting composite graphic above shows that the electron beam removed some atoms from the biosensor film, changing the chemical composition of the surface. The heights of the raised areas in the graphic correspond to the extent of damage to those areas on the film. The NIST SEM/SIMS technique should help to better quantify the percentage of scattered electrons outside the focused area of an electron beam. This will be useful both for better understanding unintentional damage to SEM samples and for the study of electron beams as a way to deliberately etch patterns in microcircuits.

Contact: Greg Gillen, (301) 975-2190.