Whereas electron microscopes make use of thewave properties of electrons, ion microscopes make use of the wave propertiesof atomic ions, such as helium ions 1He+2, to image materials. A heliumion has a mass 7300 times that of an electron. In a typical helium-ionmicroscope, helium ions are accelerated by a high voltage of 10–50 kVand focused into a beam onto the sample to be imaged. At these energies,the ions don’t travel very far into the sample, so this type of microscopeis used primarily for the surface imaging of biological structures. The useof helium ions with much greater energies (in the MeV range) has beenproposed as a way to image the entire thickness of a sample, becausethese faster helium ions can pass all the way through biological samplessuch as cells. In this type of ion microscope, the energy lost as the ionbeam passes through different parts of a cell can be measured and relatedto the distribution of material in the cell, with thicker parts of the cellcausing greater energy loss. [Source: “Whole-Cell Imaging at NanometerResolutions Using Fast and Slow Focused Helium Ions,” by Xiao Chenet al., Biophysical Journal 101(7): 1788–1793, Oct. 5, 201 Why is it easier to use helium ions rather than neutral helium atoms in such a microscope? (a) Helium atoms are not electrically charged, and only electrically charged particles have wave properties. (b) Helium atoms form molecules, which are too large to have wave properties. (c) Neutral helium atoms are more difficult to focus with electric and magnetic fields. (d) Helium atoms have much larger mass than helium ions do and thus are more difficult to accelerate.
Whereas electron microscopes make use of the
wave properties of electrons, ion microscopes make use of the wave properties
of atomic ions, such as helium ions 1He+2, to image materials. A helium
ion has a mass 7300 times that of an electron. In a typical helium-ion
microscope, helium ions are accelerated by a high voltage of 10–50 kV
and focused into a beam onto the sample to be imaged. At these energies,
the ions don’t travel very far into the sample, so this type of microscope
is used primarily for the surface imaging of biological structures. The use
of helium ions with much greater energies (in the MeV range) has been
proposed as a way to image the entire thickness of a sample, because
these faster helium ions can pass all the way through biological samples
such as cells. In this type of ion microscope, the energy lost as the ion
beam passes through different parts of a cell can be measured and related
to the distribution of material in the cell, with thicker parts of the cell
causing greater energy loss. [Source: “Whole-Cell Imaging at Nanometer
Resolutions Using Fast and Slow Focused Helium Ions,” by Xiao Chen
et al., Biophysical Journal 101(7): 1788–1793, Oct. 5, 201 Why is it easier to use helium ions rather than neutral helium
atoms in such a microscope? (a) Helium atoms are not electrically
charged, and only electrically charged particles have wave properties.
(b) Helium atoms form molecules, which are too large to have wave
properties. (c) Neutral helium atoms are more difficult to focus with
electric and magnetic fields. (d) Helium atoms have much larger mass
than helium ions do and thus are more difficult to accelerate.
Step by step
Solved in 2 steps
