Analysis Methods Flashcards
What are the structural components of an SEM?
An electron gun, an anode, a condenser lens, scanning coils, and an objective lens. 3 detectors: x-ray detector, back scattered electron detector, and secondary electron detector
What does the condenser lens in an SEM do?
Controls the size of the beam
What do the scanning coils in an SEM do?
They ensure the beam moves in a raster fashion when imaging a sample
What is a secondary electron?
A secondary eletron comes from the sample itself due to inelastic scattering
What is a backscattered electron
A backscattered electron comes from the depth of the sample as a result of elastic scattering. This is more common in heavier atoms like metals
When would you use SE imaging vs BSE imaging?
BSE imaging would be used when you have a sample with a higher atomic number. SE would be used when you want to image the surface of your sample.
How does SEM EDX work?
The SEM electron beam causes the ejection of a core electron in an atom. A higher energy electron replaces that hole and releases a characteristic x-ray in that process. That x-ray is detected by the x-ray detector and tells us what elements are present as well as quantities.
What are the main components of a Transmission Electron Microscope (TEM) that an electron beam passes through before and after interacting with the sample?
In a TEM, the electron beam travels through the electron source, condenser lens, condenser aperture, and objective lens before reaching the sample. After interacting with the sample, the beam passes through another set of objective lenses, an objective aperture, an intermediate lens, and a projector lens before reaching the fluorescent screen.
How do absorbed, scattered, and transmitted electrons contribute to the image formation in a TEM?
Absorbed electrons occur in highly dense regions of the sample, leading to stronger contrast in the image. Transmitted electrons travel through less dense regions and hit the fluorescent screen, resulting in lighter regions of the image. Scattered electrons can be elastically or inelastically scattered, contributing to diffraction patterns used for studying the crystallinity of the sample.
How does confocal microscopy work
Confocal microscopy focuses on one plane of a sample to take an image, rejecting out-of-focus light to create a better-resolved image.87 Images at multiple planes can be taken individually before being superimposed to provide 3D spatial information
How does a spinning disk confocal microscope work
The spinning disk confocal microscope relies on a spinning disk with pinholes which allow in-focus light to pass and filter out-of-focus light.87 A sample is illuminated with a laser that corresponds to the sample’s absorbance wavelength. The sample then emits light that reaches the pinholes of the spinning disk. If the light is from the focal point, that is, it is in focus, then it passes through. Otherwise, the light is filtered out. The light that passes through reaches a detector, which is used to reconstruct an image.
How does a laser scanning confocal microscope work
In an LSCM, a white light laser that can be set to a specific wavelength is used to illuminate a sample. The laser beam will scan the sample in a raster pattern.87 Light that emits from the sample reaches a single pinhole, compared to multiple pinholes in an SDCM. The single pinhole acts as a spatial filter, eliminating out-of-focus light.87
What’s the difference between the advancing and receding WCAs?
The advancing contact angle ΘAdv describes how a liquid drop wets a solid. In detail, it provides information on how the liquid drop wets a dry solid surface area. The receding contact angle ΘRec characterizes how the liquid detaches from a wet solid surface area, i.e., dewets the solid.
What is the difference between the two contact angles?
The difference between the two dynamic contact angles is referred to as the contact angle hysteresis ΘH: ΘH = ΘAdv - ΘRec. If the contact angle hysteresis is low, even a small change in the volume leads to a change in the contact area. The greater the contact angle hysteresis, the greater the change in liquid volume required for the contact area to change. The contact angle hysteresis is, therefore, a measure of the adhesion of the drop of liquid to the surface, i.e., how well a drop of liquid sticks to the surface.
Low contact angle hysteriss: liquid does not stick strongly to the surface.
