Generally it is known that SEM is based on the principle of interaction of electron beam with matter. Proton and ion beam can be used instead of electron beam? How their interaction will be different?
which type of emission source gives better imaging?
In general, proton and ion beams will also lead to secondary electron emission from a surface and therefore allow secondary electron imaging. The interaction of ions differs from electrons, for example, in the energy transferred to an electron in the sample. Due to the large mass ratio between ion and electron, the energy transferred to an electron is in general small. This means that only electrons scattered very close to the surface will be able to leave the sample and contribute to the SE image. Using ions as primary beam therefore allows to produce very sharp SE images provided the beam focus is sufficiently small. This is achieved in the helium ion microscope (HIM) where a field emission ion source is used and beam spot sizes below 1 nm are possible. The helium ion beam is also comparably gentle to biological samples compared to electrons. Furthermore, charging of insulating samples that significantly reduces image resolution can be avoided more easily in a HIM by providing electrons for charge compensation.
Other ions can be used for SE imaging too, for example in a typical Ga focused ion beam system. Here, however, SE imaging is not the primary purpose of the machine, but ion milling. SE imaging is used to find the right place on your sample before the milling is started. So, it is possible, but probably not the ideal choice if you are only interested in the SE image.
Hello,
It exists an Helium Ion Microscope (HIM).
I join an article on a biological sample from 2015. You will found answers to your questions in the introduction.
All modern FIBs provide ion imaging. Ga is the most common element, but there are Xe, Ar, N2 and even O2 systems.
As it was mentioned above, there are Focussed Ion Beam (FIB) machines with a variety of different ion species from different types of ion sources. E.g., we recently equipped a FIB with a source for highly charged ions. Most of the time, the image is formed by measuring the secondary electron emission from the sample, but other types of signals from different ion-sample interactions can be imaged as well. When you ask which system "gives better imaging", it depends on what you are looking for. Liquid metal ion sources (LMIS), typically used for gallium ions, have a very small virtual source size, therefore the small focus spot on the sample surface yields a high resolution image. Different ion species in combination with certain surfaces result in a higher secondary electron yield and thus improved contrast. And then there is the damage to the sample that might be worth considering.
Any charged particle can be focused into a small spot. Many particle accelerators have ion microbeams and ion nanobeams. The state of the art on high energy nanobeams is about 50nm resolution. With neutrons is much harder, you have to use a proton microbeam with a very specific energy to impinge on a target and generate a neutron microbeam. I
The resolution in this case is about tens of microns. Depending on the application, it may be better or worse than a SEM.
Nahuel Vega, helium ion microscope has beam diameter (and resolution) comparable to an SEM.
Agreed but that is not what we call high energy beam. It probably has few tens of keV
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