XPS Info - Technotes

An argon purity check should be done after the argon line has been disconnected or when one suspects the argon contains either water or oxygen or both.

The argon purity check basically is creating a depth profile of oxygen and aluminium (and perhaps nitrogen) in aluminium foil. Initially there would be some oxygen because of aluminium oxide but deeper into the foil the oxygen should disappear.

Don't just look at the depth profile but also at the oxygen scans, because in constructing the depth profile the software might still assign some peak area to oxygen while there is no peak left.

Using the autoheight function on transparent samples can be tricky because, while visually obtaining the initial height, one sees the sample holder.

If the approximate thickness of the sample is known then the initial height can be set by first getting the sample plate into focus and then moving down to account for the thickness.

If the thickness can be more than 1 mm higher or lower than some average value, then there are 2 options to still correctly use the autoheight function:

1. Set the height for the aforementiones average value and set the range for the autoheight function to 2 or 3 mm. Be aware that the stage can't move up to 38 mm and above and trying to reach that height stalls the experiment

2. Move to the edge of the sample and switch to the side camera. In many cases the edge of the sample can now be seen from the side.

controlled shutdown... T

A controlled shutdown may have to be applied for example when it is known in advance that the electrical power will be shut off or when the argon line needs the be flushed. The following steps describe how to perform a controlled shutdown:

• In Avantage shut down all guns: Ion, Flood and X-Ray.
• Shut down Avantage.
• Turn off the PC.
• On the K-Alpha remove the small panel with the LEDs in order to get access to the inside of machine.
• Close the red valve at the left on the panel at the rear of the K-Alpha. This is the air supply for switching the pneumatic valves. With the air supply closed the valves can't switch and no inadvertent vent can take place. The vacuum remains and a bake out won't be necessary.
• Turn off the K-Alpha with the yellow/red button at the backside.
• Now, if so required, the gaslines can be disconnected for flushing.

After a (controlled) shutdown follow the following procedure:

• Reconnect the gaslines if they had been disconnected.
• Open the red valve of the air supply.
• Turn the K-Alpha back on with the yellow/red button.
• Turn on the PC.

The K-Alpha automatically executes its start procedure. Amongst others the high vacuum pumps will start automatically.

If the gaslines were disconnected the (internal) argon line needs to be flushed using Avantage.

PS. If the power supply of the backing pump isn't connected to the K-Alpha be sure it is turned on before starting the K-Alpha.

When etching with the ion gun, then the etch rate, in nanometers per second, is given for Ta2O5 for any set of conditions of the gun. Tables do exist for other materials than Ta2O5 and if such a table also mentions Ta2O5 then an estimated etch rate can be calculated. Unfortunately this method isn't very reliable because:

• sometimes Ta2O5 isn't mentioned in the table
• different tables seem to give different etch rates for the same material
• most of the time none of the table have an entry for the material under test

Instead of using a tabulated etch rate it is possible to measure the total depth of the etched area.

There are essentially 2 ways to export data:

1. Export data to an Excel spreadsheet.

2. Export data with the Dataspace Batchdump utility.

This utility lets you select the folder of which you want to export the data. It also lets you select an alternative folder to which to save the data. But in doesn't let you create a folder, so do so in advance.

If the Vacuum Transfer Module (VTM) is used as sample holder, then further avoiding contact with oxygen can be accomplished by flushing the loadlock. This action cannot be done as 'Expert' but must be done as 'Engineer' and should only be performed by the technician. It is assumed that after loading the VTM the following is true:

• V5 is closed (between backing pump and loadlock turbo pump)
• V3 is closed (in the loadlock to analysis chamber line)
• V2 is closed (N₂ inlet)
• T2 is off (the loadlock turbo pump)
• the loadlock door is closed

From here the following procedure shows which steps to take:

• if logged in as 'Expert':
  • close Avantage and run ServerStopper
  • log off and log in as 'Engineer'
  • start Avantage
• close V4 (between backing pump and analysis chamber turbo pump)

Now repeat the following 3 times:

• open V5
• wait until P_loadlock < 1*10^-1 mbar
• close V5
• open V2, which will actually open and close the valve several times
• wait until P_loadlock > 5*10² mbar and V2 is actually open
• close V2

After this:

• open V5
• wait until P_backing < 5*10^-2 mbar
• start T2
• wait until P_backing < 5*10^-3 mbar and T2 is at speed
• open V4
• close Avantage
• run ServerStopper
• log off and log in as 'Expert'

The basic ThermoFisher K-Alpha XPS at ChemE doesn't have options to add custom equipment like other X-ray sources or other etching sources. Also there are no provisions to perform some kind of reactions and to do in situ XPS measurements, but there is a work around to do some reactions and then to do XPS measurements shortly after.

It is possible to let a sample react with a certain gas and then to analyze the sample. The trick is to let this gas in through the venting line of the loadlock. Of course there are limitations to what gasses can be used and there is no control of the temperature and barely no control of the pressure at which the reaction takes place.

The general procedure for (almost) in situ XPS would be as follows:

• enter the sample into the analysis chamber
• the first time
  
  • : maybe etch away a protective layer
  • : pre-flush the line to the loadlock with the selected gas
• do a measurement
• move the sample to the loadlock
• fill the loadlock with the selected gas (to approx 5*10² mbar)
• keep the sample in the gaseous environment for a desired time
• pump down the load lock and repeat the procedure as often as required

This method requires assistance from the technician (and must be performed as 'Engineer'). The actual steps are similar to those described in the 'flushing the loadlock' topic.

When the measured peak is barely larger than the noise, the most used method to recuce the noice is by running more scans. Typically the noise will be reduced by the square root of the number of 'samples' taken (NIKOLAI V. TKACHENKO, in Optical Spectroscopy, 2006). Obviously running more scans will increase the 'samplingtime' accordingly.

A completely different method is using a higher pass energy. This will increase the signal count without increasing the 'samplingtime', but it will decrease the binding energy resolution. For obtaining relative atomic percentages it should be noted that the same pass energy should be used for all scans involved.

If the noise contains some kind of pattern that seems to originate from the electronics, e.g. due to hysteresis, then yet another method can be used. By default scans are run with an increasing binding energy. It is possible to use a decreasing binding energy, just by swapping the start and end binding energy values for the scan. Alternating scans with increasing and decreasing binding energy and adding and averaging the result might reduce the noise from what is effectively a systematic error.

Repeatedly alternating from an increasing to a decreasing binding energy scan can be achieved using the iteration option.

When using the Snap Mode for measuring, e.g. in depth profiling and area scans, then the number of channels can be set to a lower value than the default 128. Selecting 64 channels will effectively double the counts being measured while not losing too much of the (binding energy) resolution. Selecting 32 channels will even quadruple the counts being measured and is still good for assessing atomic percentages.

The composition of carbon tape is similar to the following:

peak	atomic %
C1s	74.0
O1s	22.9
Si2p	3.1

Data taken on December 7, 2022 (download AVG file)

 

The composition of copper tape is similar to the following:

peak	atomic %
C1s	84.7
O1s	14.3
N1s	0.7
Ca2p	0.3
S2p	0.1

Data taken on December 7, 2022 (download AVG file)

 

The composition of the sample holder (if not etched) is similar to the following:

peak	atomic %
C1s	69.71
O1s	23.28
Fe2p	2.31
Si2p	1.76
Cr2p ???	1.40
Ca2p ???	0.96
Ar2p ???	0.58

The composition after etching (and leaving out argon) is similar to the following:

peak	atomic %
O1s	28.12
C1s	25.63
Fe2p	24.56
Cr2p	11.33
Ni2p3	6.88
Si2p	1.78
Ca2p	1.70

 

The composition of a sample plate (if not etched) is similar to the following:

peak	atomic %
C1s	53.77
O1s	35.59
Si2p	2.70
Fe2p3	2.46
N1s	2.22
Mn2p ???	1.15
S2p ???	0.92
Na1s ???	0.68
Te3d ???	0.49

The composition after etching (and leaving out argon) is similar to the following:

peak	atomic %
Fe2p	50.07
O1s	25.88
Cr2p	15.42
Ni2p3	5.87
N1s	2.76

 

The composition of a sample clip (if not etched) is similar to the following:

peak	atomic %
C1s	63.93
O1s	20.32
Al2p	11.27
Cu2p3	2.18
Cl2p3	1.37
S2p	0.71
Mn2p3	0.17
Cd3d	0.05

The composition after etching (and leaving out argon) is similar to the following:

peak	atomic %
O1s	37.51
C1s	32.48
Cu2p3	14.23
Ca2p	6.07
N1s	2.78
S2p	2.63
Si2p	2.50
Cl2p	1.10
Na1s ???	0.71

The reference gold sample in the ThermoFisher K-Alpha XPS is typically used for calibrating the XPS. The following scans show what kind of signal can be expected (without etching the sample). It has to be stated explicitly that the actual measurement on another machine can and probably will be quite different, with for example different count rates and resolution.

The reference silver sample in the ThermoFisher K-Alpha XPS is typically used for calibrating the XPS. The following scans show what kind of signal can be expected (without etching the sample). It has to be stated explicitly that the actual measurement on another machine can and probably will be quite different, with for example different count rates and resolution.

The reference copper sample in the ThermoFisher K-Alpha XPS is typically used for calibrating the XPS. The following scans show what kind of signal can be expected (without etching the sample). It has to be stated explicitly that the actual measurement on another machine can and probably will be quite different, with for example different count rates and resolution.

The composition of the reference phosphor sample is similar to the following:

peak	atomic %
Gd3d3	51
O1s	39
S2p	11

So the phosphor contains no phosphorus but rather a gadolinium compound, most likely Gd₂O₂S, that lights up when irradiated with an X-ray. The real purpose of the phosphor is to calibrate the Z position as shown in the next three pictures:

Z in focus of X-ray

Z too high

Z too low

There are essentially 2 methods to automatically start an experiment at some later point in time. Both these methods can or will keep the sampleholder in the loadlock until a given time after which the sampleholder will be moved into the analysis chamber after a given time.

These methods allow you to do an initial experiment overnight and to do more refined experiments the following day. Or using one of these methods you can do a really long experiment, for example for 16 hours.

The first method uses the 'Automatically Transfer Sample And Run Experiment After Waiting For nnn minutes' option. This option can be found on the sample page of the experiment panel. When you mark this option the 'Transfer to Analysis Room' action will be postponed for the given time.

Note: The mark in front of this option will be removed as soon as you click the 'Transfer to Analysis Room' button. So if you cancel this delay action, e.g. for setting a new delay time, be aware to set the mark again.

You can't enter a value for the time in minutes to postpone the actual start of the experiment. All you can do is increase or decrease the current value. In practice this doesn't have to take very long; it takes 7 seconds to go from the minimum value (1) to the maximum value (999).

You don't need additional 'objects' in your experiment to make this work.

The second method uses some additional objects in the experiment.

Add a 'Wait Object' as the first object of your experiment. In the 'Wait Object' properties window you should choose the 'Wait until date and time' option for entering the time when to start the actual experiment. Then add a 'Gun Shutdown' object as the second object of your experiment. In the 'Gun Shutdown Object' properties window select 'Transfer To Analysis' as the sample action. After that the experiment can be set up as normal.

Use these methods with caution:

• be sure the z value of the selected points are within the correct range; the base plate is appr. at 34 mm, a 1 mm thick sample is at appr. 33 mm
• use a wider than normal range for the autoheight function, e.g. ± 2.5 mm instead of 1 ± mm
• be sure that the z position doesn't reach to 38 mm (which stops the experiment!)
• be sure that the x,y position is well within the area of the sample; the loadlock camera can be 1 or 2 mm off in both directions
• restrict this to samples your are familiar with (either films or powders are fine)
• leave at least 5 hours for the loadlock to be evacuated (earlier similar experiments, with the same number of samples or more samples, should prove that this is valid)
• be sure you (or your representative) will be available to check the XPS the next morning

Calculate the time to wait or when to start:

now:
delay:
start at:
duration:	:
stop at:	: