Scanning Electron Microscopy - Revision history

Rrahaman23: /* Sample Charging */ 'wil' -> 'while'

2025-07-24T18:54:14Z

Sample Charging: 'wil' -> 'while'

← Older revision		Revision as of 14:54, 24 July 2025
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	===Sample Charging===		===Sample Charging===
	Since SEMs blast a sample with electrons, samples will always charge ~~wil~~ imaging. The polarity of charge depends on the sample, but typically the sample emits more electrons than the number of incident primary electrons due to a SE yield of over 100%. Therefore, the sample becomes slightly positively charged. A charged sample results in several complications for SEM, whether positively or negatively charged. Charged samples will deflect both the primary e-beam at the surface and the emitted electrons. This disturbs focus, depth of field, and contrast, distorts and drifts the image, creates random dark and bright spots/streaks on the image, and in extreme cases, charging can even break parts of the specimen and damage the detector and source.		Since SEMs blast a sample with electrons, samples will always charge while imaging. The polarity of charge depends on the sample, but typically the sample emits more electrons than the number of incident primary electrons due to a SE yield of over 100%. Therefore, the sample becomes slightly positively charged. A charged sample results in several complications for SEM, whether positively or negatively charged. Charged samples will deflect both the primary e-beam at the surface and the emitted electrons. This disturbs focus, depth of field, and contrast, distorts and drifts the image, creates random dark and bright spots/streaks on the image, and in extreme cases, charging can even break parts of the specimen and damage the detector and source.

	To avoid this, several precautions can be taken during sample prep and during analysis. Firstly, either carbon or copper tape should be used to afix the sample to the sample stub or holder so that the sample is grounded. This allows electrons to freely travel to fill electron-holes in the sample to maintain a neutral charge. Non-conductive samples should be coated with gold nanoparticles (see [[Sputter Coater]]) to make the sample conductive—this allows topographical features to still be visible, although it will dampen contrast in BSD images and muddle EDS with gold peaks. If BSD or EDS are wanted, the sample should instead be imaged at a low accelerating voltage on the SEM (5kV) and rastering speed should be increased to avoid significant charging at any one spot. Conductive samples simply need to be grounded to the sample stub or holder. For samples mounted in a hot mounting press, use a conductive mounting compound (such as conductive phenolic powders) or afix carbon or copper tape directly onto the sample surface and ground point.		To avoid this, several precautions can be taken during sample prep and during analysis. Firstly, either carbon or copper tape should be used to afix the sample to the sample stub or holder so that the sample is grounded. This allows electrons to freely travel to fill electron-holes in the sample to maintain a neutral charge. Non-conductive samples should be coated with gold nanoparticles (see [[Sputter Coater]]) to make the sample conductive—this allows topographical features to still be visible, although it will dampen contrast in BSD images and muddle EDS with gold peaks. If BSD or EDS are wanted, the sample should instead be imaged at a low accelerating voltage on the SEM (5kV) and rastering speed should be increased to avoid significant charging at any one spot. Conductive samples simply need to be grounded to the sample stub or holder. For samples mounted in a hot mounting press, use a conductive mounting compound (such as conductive phenolic powders) or afix carbon or copper tape directly onto the sample surface and ground point.

Rrahaman23: typo 'caputured' -> 'captured'

2025-07-24T18:47:45Z

typo 'caputured' -> 'captured'

← Older revision		Revision as of 14:47, 24 July 2025
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	=== Software Features ===		=== Software Features ===
	'''Automated Image Mapping (AIM)''': SEMs will raster beam over a larger area of a sample at a given magnification and automatically stitch the ~~caputured~~ images together.		'''Automated Image Mapping (AIM)''': SEMs will raster beam over a larger area of a sample at a given magnification and automatically stitch the captured images together.
	<br>'''3D Roughness Reconstruction (3DRR)''': SEM will attempt to focus in a range of depths, then stitch together planes of features which are in focus to generate a 3D image representative of surface topology. This can be exported as an image or .stl file.		<br>'''3D Roughness Reconstruction (3DRR)''': SEM will attempt to focus in a range of depths, then stitch together planes of features which are in focus to generate a 3D image representative of surface topology. This can be exported as an image or .stl file.

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	*[[X-ray Notation]]		*[[X-ray Notation]]

	[[~~index~~.php?title=Category:Equipment\|char]]		[[Index.php?title=Category:Equipment\|char]]

Rrahaman23 at 18:30, 24 July 2025

2025-07-24T18:30:11Z

← Older revision		Revision as of 14:30, 24 July 2025
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	=== SED ===		=== SED ===
	Secondary electrons give an image which shows '''topographical''' features and a relatively large [[#Depth of Field\|depth of field]].		Secondary electrons give an image which shows '''topographical''' features and a relatively large [[Scanning Electron Microscopy#Depth of Field\|depth of field]].

	Since SEs have such low energies, they can only escape when present in the sample's surface (the top several nm). This also means SEs have low interaction volume, and have resolutions on the nm level. The most common type of SED is the Everhart-Thornley (ET) detector, which are placed off-center from the sample to provide better contrast between SEs coming from different areas on the sample surface in exchange for slightly worse signal-to-noise ratio. The reasoning for sacrificing signal is because SE yields (# of emitted SEs per PE) are over 100%—this is because high-energy PEs undergoing inelastic interactions can dislodge multiple SEs at a time.		Since SEs have such low energies, they can only escape when present in the sample's surface (the top several nm). This also means SEs have low interaction volume, and have resolutions on the nm level. The most common type of SED is the Everhart-Thornley (ET) detector, which are placed off-center from the sample to provide better contrast between SEs coming from different areas on the sample surface in exchange for slightly worse signal-to-noise ratio. The reasoning for sacrificing signal is because SE yields (# of emitted SEs per PE) are over 100%—this is because high-energy PEs undergoing inelastic interactions can dislodge multiple SEs at a time.
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	=== EDS ===		=== EDS ===
	Additionally, inelastic interactions which dislodge secondary electrons leave an electron vacancy which must be quenched, similar to '''[[X-ray Fluorescence Spectrometer (XRF) \| X-ray fluorescence spectroscopy (XRF)]]'''. The resulting vacancy is quenched, and the surplus energy is ejected as a secondary characteristic X-ray. Since energy drops between electrons levels in a given atom are discrete and distinct, a detector which can catch these secondary X-rays would be able to determine elemental composition. This is known as energy-dispersive X-ray spectroscopy (EDS/EDX), as is very common in SEM systems. Unlike XRF, secondary X-rays are only emitted from a small spot—more specifically, it is sensitive to interaction volume, which is typically 1-2 μm in diameter for characteristic X-rays, with a spot size of a few nm. For comparison XRF depth ranges from several μm to a few mm, and irradiates the entire sample at once. This makes EDS ''slightly'' more surface sensitive, while XRF is more bulk sensitive. In SEM, rastering the e-beam source across the sample generates an EDS map, which is useful to measue elemental composition of specific surface features such as pores and inclusions, as well as compositional differeneces across grain boundaries.		Additionally, inelastic interactions which dislodge secondary electrons leave an electron vacancy which must be quenched, similar to '''[[X-ray Fluorescence Spectrometer (XRF)\| X-ray fluorescence spectroscopy (XRF)]]'''. The resulting vacancy is quenched, and the surplus energy is ejected as a secondary characteristic X-ray. Since energy drops between electrons levels in a given atom are discrete and distinct, a detector which can catch these secondary X-rays would be able to determine elemental composition. This is known as energy-dispersive X-ray spectroscopy (EDS/EDX), as is very common in SEM systems. Unlike XRF, secondary X-rays are only emitted from a small spot—more specifically, it is sensitive to interaction volume, which is typically 1-2 μm in diameter for characteristic X-rays, with a spot size of a few nm. For comparison XRF depth ranges from several μm to a few mm, and irradiates the entire sample at once. This makes EDS ''slightly'' more surface sensitive, while XRF is more bulk sensitive. In SEM, rastering the e-beam source across the sample generates an EDS map, which is useful to measue elemental composition of specific surface features such as pores and inclusions, as well as compositional differeneces across grain boundaries.

	=== EBSD ===		=== EBSD ===
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	==Related Theory & Techniques==		==Related Theory & Techniques==
	*[[Sputter Coater]]		*[[Sputter Coater]]
			*[[Biological Sample Preparation]]
	*[[SEM Colorization]]		*[[SEM Colorization]]
	*[[Optical Microscopy]]		*[[Optical Microscopy]]
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	*[[X-ray Notation]]		*[[X-ray Notation]]

	[[Category:Equipment\|char]]		[[index.php?title=Category:Equipment\|char]]

Mjimenez47: fixed parse error

2025-06-14T18:25:56Z

fixed parse error

← Older revision		Revision as of 14:25, 14 June 2025
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	In optical microscopy, Abbe’s equation simplifies to <math>\delta=\frac{0.61\lambda}{nA}</math>, where the numerical aperture at high magnifications typically levels out at <math>nA \approx 1.35</math>. Plugging in the <math>\lambda</math> for green light gives:		In optical microscopy, Abbe’s equation simplifies to <math>\delta=\frac{0.61\lambda}{nA}</math>, where the numerical aperture at high magnifications typically levels out at <math>nA \approx 1.35</math>. Plugging in the <math>\lambda</math> for green light gives:

	:<math>\delta=\frac{0.61\cdot500\~~textrm~~{nm}}{1.35}=226\~~textnormal~~{nm}</math>		:<math>\delta=\frac{0.61\cdot500\text{nm}}{1.35}=226\text{nm}</math>

	In electron microscopy, the refractive index is typically 1, since the chamber is pumped down to near-vacuum conditions, and the aperture half-angle is typically very small. Using the [https://en.wikipedia.org/wiki/Small-angle_approximation small-angle approximation], we can simplify Abbe’s equation to		In electron microscopy, the refractive index is typically 1, since the chamber is pumped down to near-vacuum conditions, and the aperture half-angle is typically very small. Using the [https://en.wikipedia.org/wiki/Small-angle_approximation small-angle approximation], we can simplify Abbe’s equation to

Mjimenez47 at 19:47, 13 June 2025

2025-06-13T19:47:38Z

← Older revision		Revision as of 15:47, 13 June 2025
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	=== Proof ===		=== Proof ===
	Abbe’s equation defines the theoretical maximum resolution of a microscope, δ as:		Abbe’s equation defines the theoretical maximum resolution of a microscope, <math>\delta</math> as:
			:<math>\delta=\frac{k\lambda}{n\sin(\alpha)}</math>,
			where <math>k = 0.61</math> is an empirical constant, <math>n</math> is the refractive index, and <math>\alpha</math> is the aperture half-angle. The term in the denominator, <math>n\sin{\alpha)}</math>, is also known as the ''numerical aperture'', or nA.

	~~[[File:AbbeEquation.png\|90px]],~~		In optical microscopy, Abbe’s equation simplifies to <math>\delta=\frac{0.61\lambda}{nA}</math>, where the numerical aperture at high magnifications typically levels out at <math>nA \approx 1.35</math>. Plugging in the <math>\lambda</math> for green light gives:

	where k = 0.61 is an empirical constant, n is the refractive index, and α is the aperture half-angle. The term in the denominator, nsin(α), is also known as the ''numerical aperture'', or nA.

	In optical microscopy, Abbe’s equation simplifies to ~~[[File:simAbbeEq~~.~~png]]~~, where the numerical aperture at high magnifications typically levels out at nA ~ 1.35. Plugging in the λ for green light gives:

	:<math>\delta=\frac{0.61\cdot500\textrm{nm}}{1.35}=226\textnormal{nm}</math>		:<math>\delta=\frac{0.61\cdot500\textrm{nm}}{1.35}=226\textnormal{nm}</math>

Mjimenez47 at 17:41, 11 June 2025

2025-06-11T17:41:44Z

← Older revision		Revision as of 13:41, 11 June 2025
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	=== Proof ===		=== Proof ===
	Abbe’s equation defines the theoretical maximum resolution of a microscope, δ as:		Abbe’s equation defines the theoretical maximum resolution of a microscope, δ as:
	~~:<math>\delta=\frac{k\lambda}{n\sin(\alpha)}</math>,~~
	where <math>k = 0.61</math> is an empirical constant, <math>n</math> is the refractive index, and <math>\alpha</math> is the aperture half-angle. The term in the denominator, <math>n\sin{\alpha)}</math>, is also known as the ''numerical aperture'', or nA.

	In optical microscopy, Abbe’s equation simplifies to ~~<math>\delta=\frac{0~~.~~61\lambda}{nA}</math>~~, where the numerical aperture at high magnifications typically levels out at ~~<math>~~nA ~~\approx~~ 1.35~~</math>~~. Plugging in the ~~<math>\~~lambda~~</math>~~ for green light gives:		[[File:AbbeEquation.png\|90px]],

			where k = 0.61 is an empirical constant, n is the refractive index, and α is the aperture half-angle. The term in the denominator, nsin(α), is also known as the ''numerical aperture'', or nA.

			In optical microscopy, Abbe’s equation simplifies to [[File:simAbbeEq.png]], where the numerical aperture at high magnifications typically levels out at nA ~ 1.35. Plugging in the λ for green light gives:

	:<math>\delta=\frac{0.61\cdot500\textrm{nm}}{1.35}=226\textnormal{nm}</math>		:<math>\delta=\frac{0.61\cdot500\textrm{nm}}{1.35}=226\textnormal{nm}</math>

Mjimenez47 at 15:27, 10 June 2025

2025-06-10T15:27:11Z

← Older revision		Revision as of 11:27, 10 June 2025
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	=== Proof ===		=== Proof ===
	Abbe’s equation defines the theoretical maximum resolution of a microscope, ~~<math>\~~delta~~</math>~~ as:		Abbe’s equation defines the theoretical maximum resolution of a microscope, δ as:
	:<math>\delta=\frac{k\lambda}{n\sin(\alpha)}</math>,		:<math>\delta=\frac{k\lambda}{n\sin(\alpha)}</math>,
	where <math>k = 0.61</math> is an empirical constant, <math>n</math> is the refractive index, and <math>\alpha</math> is the aperture half-angle. The term in the denominator, <math>n\sin{\alpha)}</math>, is also known as the ''numerical aperture'', or nA.		where <math>k = 0.61</math> is an empirical constant, <math>n</math> is the refractive index, and <math>\alpha</math> is the aperture half-angle. The term in the denominator, <math>n\sin{\alpha)}</math>, is also known as the ''numerical aperture'', or nA.

Mjimenez47 at 14:46, 10 June 2025

2025-06-10T14:46:03Z

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Mjimenez47: Replaced content with "test"

2025-06-10T14:45:45Z

Replaced content with "test"

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MichaelJonesbey3: Added SEM Colorization to the notes

2024-12-13T22:11:39Z

Added SEM Colorization to the notes

← Older revision		Revision as of 18:11, 13 December 2024
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	==Related Theory & Techniques==		==Related Theory & Techniques==
	*[[Sputter Coater]]		*[[Sputter Coater]]
			*[[SEM Colorization]]
	*[[Optical Microscopy]]		*[[Optical Microscopy]]
	*[[Transmission Electron Microscopy (TEM)]]		*[[Transmission Electron Microscopy (TEM)]]