[en] We have measured the sensitivity of three highly conjugated organic compounds to electron irradiation. Using a 200 keV TEM, loss of crystallinity was determined from quantitative electron-diffraction measurements. Degradation of the molecular ring structure was monitored from fading of the 6 eV π-excitation peak in the energy-loss spectrum. Measurements at incident energies between 30 keV and 100 eV were made using a scanning electron microscope (SEM), by recording gradual decay of the cathodoluminescence (CL) signal. Expressed in Grays, the energy dose required for CL decay in coronene is a factor of 30 lower than for destruction of crystallinity and a factor of 300 lower than for destruction of the molecular structure. Below 1 keV, the CL-decay cross section shows no evidence of a threshold effect, indicating that the damage involved is caused by valence-electron (rather than K-shell) excitation. Therefore even relatively radiation-resistant organic materials may undergo some form of damage when examined in a low-energy electron microscope or a low-voltage SEM

[en] We discuss vibrational-mode energy-loss spectroscopy using an aloof beam of electrons positioned a small distance b from the edge of a specimen in a probe-forming TEM or STEM equipped with a high-resolution monochromator. Due to the delocalization of inelastic scattering, a strong vibrational-loss signal can be recorded without causing significant damage to a beam-sensitive specimen. Calculations for b=20 nm suggest that damage is reduced by typically a factor of 1000 (relative to electrons of the same energy transmitted through the specimen) for the same signal strength and spatial resolution. About 50% of the vibrational-loss signal comes from material lying within a distance b of the edge of the specimen and extending over a length 2.5b parallel to the edge. Although energy-filtered imaging appears impossible in aloof mode, an undersampling STEM technique is proposed, taking advantage of scattering delocalization to obtain a vibrational-loss image that leaves most of the imaged area undamaged. - Highlights: • Delocalization of inelastic scattering is discussed from three viewpoints. • Aloof-beam EELS is discussed as a way to minimize radiation damage to a specimen. • The dependence of aloof signal on impact parameter is logarithmic over most of the useful range. • Quantitative estimates are given for spatial resolution and damage in aloof-spectroscopy mode.

[en] An accelerating voltage of 100–300 kV remains a good choice for the majority of TEM or STEM specimens, avoiding the expense of high-voltage microscopy but providing the possibility of atomic resolution even in the absence of lens-aberration correction. For specimens thicker than a few tens of nm, the image intensity and scattering contrast are likely to be higher than at lower voltage, as is the visibility of ionization edges below 1000 eV (as required for EELS elemental analysis). In thick (>100 nm) specimens, higher voltage ensures less beam broadening and better spatial resolution for STEM imaging and EDX spectroscopy. Low-voltage (e.g. 30 kV) TEM or STEM is attractive for a very thin (e.g. 10 nm) specimen, as it provides higher scattering contrast and fewer problems for valence-excitation EELS. Specimens that are immune to radiolysis suffer knock-on damage at high current densities, and this form of radiation damage can be reduced or avoided by choosing a low accelerating voltage. Low-voltage STEM with an aberration-corrected objective lens (together with a high-angle dark-field detector and/or EELS) offers atomic resolution and elemental identification from very thin specimens. Conventional TEM can provide atomic resolution in low-voltage phase-contrast images but requires correction of chromatic aberration and preferably an electron-beam monochromator. Many non-conducting (e.g. organic) specimens damage easily by radiolysis and radiation damage then determines the TEM image resolution. For bright-field scattering contrast, low kV can provide slightly better dose-limited resolution if the specimen is very thin (a few nm) but considerably better resolution is possible from a thicker specimen, for which higher kV is required. Use of a phase plate in a conventional TEM offers the most dose-efficient way of achieving atomic resolution from beam-sensitive specimens. - Highlights: • 100–300 kV accelerating voltage is suitable for TEM specimens of typical thickness. • Lower voltage is preferable for thin specimens not damaged by radiolysis. • For very thin specimens, scattering contrast (but not phase contrast) is better at low voltage. • For thick specimens, higher voltage provides better resolution for STEM and EDX analysis. • For EELS elemental analysis, higher accelerating voltage is generally preferable

No abstract available

[en] An energy-selecting electron microscope was used to measure the loss spectra of thin samples of carbon and beryllium. Data in the region of K-shell excitation were corrected for plural scattering and valence-electron background. From the resulting spectra it is estimated that in these materials less than 5% of K-shell excitations are accompanied by simultaneous generation of a plasmon. (author)

[en] The ratio n of cross-sections for inelastic and elastic scattering of 80 keV electrons is measured for thin solid films of the elements Be, C, Al, As, and Sn. The values obtained are in reasonable agreement with theoretical predictions of Lenz and Burge and Smith. Measurements of n are also made for diphenyl anthracene as a function of electron exposure; the method is discussed as a means of monitoring ionization damage in organic compounds. (author)

[en] Electron-beam microanalysis is most commonly carried out by recording the spectrum of X-rays emitted from a sample. However, an alternative method is to analyse the energy spectrum of electrons transmitted through a thin specimen. For the detection and measurement of elements of low atomic number, this energy-loss method is capable of high sensitivity; detection of less than 10^-20 g has been reported, while the attainable spatial resolution is probably below 1 nm. After outlining the basic physics involved, the paper gives examples of energy-loss analysis of thin films, intercalation compounds, ceramics and biological samples, and its application to the measurement of radiation damage in organic materials. (author)

No abstract available

[en] A magnetic spectrometer is described which can be installed beneath the viewing screen of a 100 keV CTEM in order to provide electron energy-loss spectra and (if the microscope is fitted with a scanning attachment) energy-filtered images and diffraction patterns. Expensive electronics are not essential and the normal performance and ease of operation of the microscope remain unaltered. Procedures are described for adjusting and measuring the performance of the spectrcmeter. Fitted to a JEM 100B with thermionic gun, the system gives an energy resolution in the range 1.7 to 10 eV, depending on the operating conditions. (Auth.)

[en] A high-voltage electron microscope has been used to study displacement damage at 600⁰C in graphite. Small defect clusters were observed for incident electron energies above 150 keV, indicating a threshold energy of 34 +- 2 eV for atomic displacement along the c-axis. (author)