Lecture 2 Basic alignment & Electron
material interaction
Bo Zhao
2014 Fall semester
Quick review for last lecture
 FESEM gun source—how electrons are generated
 Electromagnetic lenses, apertures—define a fine beam
 Deflection coils—direct the beam onto different locations
 Sample stage—move your sample around and grounding
Are you still a treasure hunter?
Electron Gun
 Candle
Apertures
Condenser lens
 Hand
Deflection or Raster coils
Objective lens
 Map
Sample
 Eyes
Detectors
 Brain/memory Viewing screen/camera
3
How can we make the image better?
 Spot size
Users define the resolution---------spot size!
4
Two main goals
 Focus a small beam of electrons onto the sample
------- alignment
 Detect products of beam/sample interaction
-------- signal generation and collection
Components
e-
Basic assembly in Hitachi S4300
 Condenser lens
 Main role: Concentrate the
electron beam
 Affect the spot size
 Objective lens
 Main role: focusing the beam onto
the sample
 Has some influence over the
diameter of the spot size
Note: a focused beam produces a
smaller spot on the sample surface
than an under or over-focused
beam
Basic Alignment
 Alignment steps goes from top to bottom
Beam alignment
Aperture alignment
Stig X, Stig Y alignment
On the Instrument
 We have learned how to load the sample into the S.C.,
so let’s continue….
Basic info the instrument needs to know
 Sample size--- sets limits of sample stage movement in XY
direction
 Working distance
 Accelerating voltage--- depends on your sample and what
info needs to be obtained from the sample
 Gun brightness--- the flow of electrons emitted by the
filament
h
Properties of Electron beam
• Gun Brightness
defined as beam current density per
unit solid angle.
12
Vacc: 1 KV
Gun brightness:1
Vacc: 10 KV
Gun brightness:1
Vacc: 1 KV
Gun brightness:2
Understand the difference between Vacc
and Ie
 Accelerating Voltage ----how fast an electron travels---
--How much energy it carries---- knock out different
signals
 Emission Current----how many electrons travels per
second-----how many bombard your sample per
second----signal
Turn on the HV
SOP
2.2 Find an image
2.2.1 Setup the high voltage and click on.
2.2.2 Adjust the image magnification couterclockwise. Click
ABC to auto adjust brightness and contrast. Use the Trackball
to move the sample to the area of interest.
2.2.3 Sharpen image and adjust the brightness and contrast
using the Focus, Brightness, and Contrast rotary controls.
SOP
 2.3 Alignment
 2.3.1 Click on the aperture option and center the aperture by click the





reset button at the bottom right corner. Pull the objective aperture out
to “0”position.
2.3.2 Click on the beam. Center the beam position. Then insert the
objective aperture. If no beam is visible, crank up the contrast and
brightness until you can observe beam light, then center the beam.
2.3.2 Click on the aperture option again, adjust the two knobs on the
objective aperture on the column unit to stop the image fluctuation.
2.3.3 Click on the stigma X, adjust the X,Y knobs on the control panel
to stop the image shift in any direction.
2.3.4 Click on the stigma Y, adjust the X,Y knobs on the control panel to
stop the image shift in any direction.
2.3.5 Click on “off ” to stop the alignment procedure.
Reset
 Aperture is out, aperture settings are reset
Center the beam
Choose the beam option,
center the beam by using the X,Y knobs
for alignment on the control panel
Put in the objective aperture
 Position to the desired aperture number and then center the
beam by adjusting the two knobs on the aperture
e
-
e
-
e
-
Aperture Alignment
No aperture
Good aperture alignment
Bad aperture alignment
Mechanically align the aperture
Top view
Side view
Fine alignment of aperture
 You will see the image
shifting back and forth, stop
the movement by tuning
the aperture knobs (one at a
time!) until the image stop
moving
Wobbler
Stig X Stig Y
 Align stig X and Stig Y
 Stop the imaging shifting by
using the two alignment X Y
knobs on the control panel.
Stigmatic Aberration
This defect is the result of the demagnification of the
condenser lenses in one direction being greater than the
demagnification in another direction
Wobbler
Off
 Switch back to the image and then focus
Questions?
Sputter coating
 Reduced electron beam damage.
 Increased thermal conduction.
 Reduced sample charging (increased conductivity)
 Improved secondary electron emission
 Reduced beam penetration with improved edge resolution
 Protects beam sensitive specimens
Mechanism
When a target is bombarded with
fast heavy particles, erosion of the
target material occurs.
Control panel
Beam material interaction
 SEM techniques
 SE
 BSE
 EDX
 Cathodoluminescence
 STEM
Electron beam-sample interactions
 The incident electron beam is scattered in the sample, both elastically and
inelastically
 This gives rise to various signals that we can detect (more on that on next
slide)
 Interaction volume increases with increasing acceleration voltage and
decreases with increasing atomic number
Signals from the sample
Incoming electrons
Secondary electrons
Auger electrons
Backscattered
electrons
Cathodoluminescence (light)
X-rays
Sample
What information does scanning electron
microscope provide us? surface morphology
Phase distribution
Elemental composition
Defects, impurities
41
http://mee-inc.com/sem.html
Macroscopic view
 Electron beam shooting on your sample, no matter how
conductive your sample is, it will have resistance, so there
will be heat generated, and it is the major damage cause
Microscopic view
particle collision theory
Inelastic collision when it lost energy, in what form that
energy has changed into? heat? Other form?
Elastic collinsion
small or no energy loss, opposite direction
Remember Electron has particle wave
duality?
 Particle Collision
 Inelastic
Secondary electron, X-ray
 Elastic
backscattered electron
Secondary electrons (SE)
 Low energy electrons (~10-50 eV)
 Only SE generated close to surface escape (topographic
information is obtained)
High resolution
Uniformity
SEM images of 1500/110 nm “raspberry-like” templates and bimodal porous gold electrode
45
•Bo Zhao, Maryanne M. Collinson, Chemistry of Materials 2010, 22(14), 4312-4319.
Edge effects
46
Backscattered electrons (BSE)
 A fraction of the incident electrons is retarded by the electro-
magnetic field of the nucleus and if the scattering angle is
greater than 180 ° the electron can escape from the surface
SE
MENA3100
BSE
 How many electrons got returned determine the signal
 Nuleus is a “particle” too, if the positive charge on it is
strong, it has more influence on the electrons,
Note: what determine the charge? proton number, which is
also Z value, atomic number
 When the atomic number is high, the atomic size is small,
which means that they are more compact.
Distribution of reinforcement phase in matrix
and their bonding
(a)
(b)
(a) W80Al20/90Ni-5Fe-5Mo (b) back scattering image of (a)
49
•B. Zhao, C.J. Zhu, X.F. Ma, W. Zhao, H.G. Tang, S.G. Cai, Z.H.Qiao, Materials Science & Engineering A 456, 2007, 337-344.
EDX spectroscopy
Emission energy is
“characteristic”
of energy level
differences
Each element has a fingerprint X-ray signal
50
SEM electron (e.g. 20 keV)
“kicks out” electron from
“K-shell”
EDX-qualitative and quantitative analysis
Y: 79.4%
Yb: 19.3%
Er: 1.3%
Characteristic x-rays
Continuum,
Bremsstrahlung
3+,SEM
Top) Powder XRD
pattern :and
(bottom)
image of3+NaYF4:2%Er,
NaYF
3%Er
17%Yb
4
le from Lorad Chemical Co. The XRD pattern is compared to ICCD
for hexagonal Consideration
() phase NaYF4. The crystallites are phase-pure and
cron size range.
Dead time
51
For quantitative analysis,
standard is required
Statistics: Signal-to-noise ratio
Drift in electron beam with time
Build-up of a carbonaceous contamination film
after extended periods of electron probe irradiation
Elemental mapping
Mapping
Allows selection of elements to be mapped
Shows spatial distribution of elements in sample
Meteorite sample
Fe
Mo
Ni
Ca
Mg
52
http://microanalyst.mikroanalytik.de/info7.phtml