North Seattle Community College
Nanotechnology 230
Lab 1
EDS Analysis of a Penny
Introduction
In class lectures we have discussed SEM analysis and energy dispersive spectroscopy (EDS) for
analyzing what materials are present in a sample. EDS works by measuring the energy of
emitted x-rays that are caused by electrons transitioning between the K, L, M and N quantum
energy levels. Each element has a unique set of energy peaks that identify it. In SEM analysis
the electrons do not bounce off of the surface but actually penetrate some distance into the
material being imaged. The penetration depth is a function of the energy of the incoming electron
beam above the 10 KeV energy level.
In this lab we will analyze the Cu film that was sputter deposited in a previous lab and change the
accelerating voltage to see how this affects amount of silicon and copper that is detected. The
previously deposited film was about 200 nm of Cu on a Si wafer. Equation 1 below gives an
estimate of the electron penetration depth as a function of accelerating voltage for voltages of 10
KV and above. Using this equation you will estimate the electron penetration depth when the
accelerating voltage is varied between 10, 15, 20, 25 and 30KV. We will then use the counts per
second (cps) of the Si Kα peak at 1.74 KeV and the Cu Lαβ peak at 0.933 KeV to determine the
relative amounts of Cu and Si in the sampled region.
R
4120

E (1.265 0.0954*ln E )
Equation 1
R  electron penetratio n depth ( m)
E  Accelerati ng voltage (MeV)
  Density (g/cm 3 )
R
Materials and Equipment
 Leica Stereo scan 420 with x-ray detector.
 Sample of silicon wafer with Cu thin film.
North Seattle Community College
Nanotechnology 230
Procedure
1. Place a piece of silicon wafer with Cu thin film in the SEM chamber and pump the
chamber to operating pressure.
2. Obtain an image on the SEM, move to the Cu film and set the following operating
parameters:
Beam current
= 400µA
Collector Bias
= 0V
Probe current (I Probe)
= 100nA
Accelerating voltage (EHT)
= 10KV
Optibeam
= On
Working distance
= 25mm
3. Check that there is liquid nitrogen cooling the x-ray detector by removing the plug from
the top of the detector LN2 dewar and looking for a frozen section at the end of the dip
stick.
4. Activate the Link ISIS software by accessing programs from the start bar and selecting
“Oxford Instruments”, “Link ISIS”. When the software starts select “Chris Sanders” and
click the lab notebook icon. Jobs should be set to HRGpaintchip”.
5. Select the icon of peaks to open the x-ray analysis window.
6. Click the button with a circle to start the acquiring x-rays. The button with a square will
stop the analysis.
7. Adjust the probe current on the SEM to obtain an optimum x-ray count rate around 1.5
Kcps.
8. Within the x-ray analysis window click on the magnifying glass icon to see an enlarged
view (zoom window) of the acquisition spectrum and zoom in near the 1.0 – 2.0 KeV
section that we are interested in.
9. From the main x-ray analysis window you can also click on the “?” icon to see select
elements from a library to see all of the emission peaks for a given element.
10. When the acquisition is finished bring up the zoom window as scale it using the left
mouse button and cursor so that the 0.933 peak touches the top of the window. The
count rate for that peak can then be read from the “Full Scale” chart in the upper left
corner and entered into the data table.
11. Scale the window so that the 1.74 KeV peak touches the top and enter the count rate in
the data table.
12. On the SEM adjust the accelerating voltage (EHT) to 15KV and repeat steps 6 – 11 to
take data accelerating voltage.
13. Repeat step 12 for accelerating voltages of 20, 25 and 30 KeV to complete the table.
14. Close all of the x-ray analysis windows in the Link ISIS software.
15. Return the SEM to the operating conditions in step 2.
16. Place the SEM at a low magnification and return the screen image to the grid structure.
17. Obtain a clear low magnification image of the grid structure and shut the SEM down by
selecting “SEM Shutdown” from the drop down menu obtained from the box in the upper
left hand corner of the screen.
18. A “SEM Shutdown” dialog box will appear. With the question “Save operating
conditions?” click “Yes”.
North Seattle Community College
Nanotechnology 230
Data
Name:__________________________
Beam accelerating
voltage (KV)
Counts per second
for
Si Kα at 1.74 KeV
Counts per second
for
Cu Lαβ at 0.933 KeV
Ratio of
Cu Lαβ / Si Kα
10
15
20
25
30
Analysis
1) Use equation 1 to estimate the electron beam penetration depth into a copper film at:
A) 10 KV accelerating potential.
B) 20 KV accelerating potential.
C) 30 KV accelerating potential.
2) Using the estimates from question 1, what percentage of the beam penetration depth will be
within the first 200nm of a Cu specimen for a:
A) 10 KV accelerating potential.
B) 20 KV accelerating potential.
C) 30 KV accelerating potential.
3) Based on question 2A and the assumption that the Cu film is 200nm thick, what value would
you expect for the Si Kα peak at 10 KV?
North Seattle Community College
Nanotechnology 230
4) Using equation 1 for a copper film at what accelerating voltage would half of the beam
penetration depth be within 200nm of the surface? A more direct way to ask this question would
be to find the accelerating potential for a 400 nm penetration depth. Hint: there are two ways to
approach this, you can manipulate and solve the equation or guess the answer until you get it
right.
5) For our sample with a 30KV accelerating voltage will the actual beam penetration be greater or
less than that estimated in question (1). Why? Hint: think about the situation that equation one is
estimating penetration depth for and what our sample actually is.
6) Draw a graph with accelerating voltage on the x-axis and ratio of Cu Lαβ / Si Kα on the y-axis
and include it with your lab write-up. Be sure to put a title on the graph and label the axes with
proper titles and units. Using Excel to plot the graph is recommended but not required.