Kratos Axis Ultra X-ray Photoelectron Spectroscopy (XPS) system

(1) The upper and lower layers of the sample bar should have different thicknesses.

(2)The overall height of the samples must not exceed 4mm.

(3) Insert the samples between two screws for proper placement.

(4) Mount the samples on glass to prevent charging discrepancies between the metallic stage and insulative samples. This will help avoid spectrum peak shifting.

Chambers:

(a) The system consists of three chambers: the load lock chamber, STC (Sample Transfer Chamber) chamber, and SAC (Sample Analysis Chamber) chamber. These chambers are separated by two valves.

(b) The pressure in the SAC chamber should be maintained at 3-5 E-9 Torr. Do not open the STC-SAC valve if the pressure in the STC chamber exceeds 5E-7 Torr.

(c) The STC chamber serves multiple purposes, including handling freshly cut samples, performing ion gun cleaning, and conducting UPS (Ultraviolet Photoelectron Spectroscopy) experiments.

(d) The SAC chamber is specifically designated for actual sample analysis measurements.

(1)  We utilize two software programs for XPS analysis: "Vision Instrument Manager" for creating charts and "Instrument Manual Control" for setting experimental conditions. The real-time display is accessed through the Window menu.

(2) Ensure that the load lock/STC valve is closed. The presence of a cross sign (X) indicates that the valve is closed.

(3) Unscrew the button.

(4) Prior to venting the system, confirm that the nitrogen tank is open to allow the system to vent to atmospheric pressure using nitrogen.

(5) Vent the system in the following sequence: 1 => 2 => 2 (listen for a sound).

(6) Load the sample bar, taking note of its position, and close the chamber.

(7) Begin pumping the system: 2 => full screen => down.

(8) After a few minutes, retighten the screw to reseal the system.

(9) The turbo pump must operate in conjunction with the backup pump. The turbo pump enhances the vacuum level to the next stage after the backup pump.

(10) Allow the system to vacuum overnight.

(11) Verify that the pressure in the load lock is sufficiently low, typically around 4-5E-8 Torr according to the wide-range gauge (WRG), after leaving it under vacuum overnight.

(12) If the pressure remains around 4-5E-7 Torr, it suggests that the samples may be outgassing (oily, hydrated salts, suspension). In such cases, reject the samples and return them to the owner.

(13) The backing pump should run for 3 minutes before the turbo pump engages.

(14) It is important not to activate the turbo pump standby mode, as this will prevent the turbo pump from running at full speed.

(1) The fork positions in the system are as follows in the figure.

(2) Ensure that the system is in "Safe Manual" mode. Open the two valves.

(3) Begin by loading the sample bar into the STC chamber and shift it using the fork towards the side closer to us.

(4) Set the parking position to the following values: X = 65, Y = -3, Z = 0, theta = 1.9 (Goto) to unload the old sample bar. Gently wiggle the rod during the process.

(5) Note that a negative value of Y indicates that the position is closer to us. Avoid going beyond the range of Y = [-4.0, +3.0], as this can result in calibration loss.

(6) Park the old sample bar in the STC chamber and swap it with the new sample bar in the SAC chamber.

(7) Once the swapping is complete, fully retract the fork until it touches the magnetic sensor, and close both valves (|X| |X|).

(1) Turn on the TV and spot light. There are two windows where the spot light is used to observe the surface of the sample.

(2) The positive sign (+) indicates the area on the sample surface being characterized. The spot size is limited to 1mm x 1mm.

(3) For irregular samples, try to find a relatively flat surface for characterization.

(4) If the sample is a transparent film, use 3D features such as dust particles and edges as reference points.

(5) When all three chambers are open, one should observe that the pressure is not equalized, as there is an ionic pump in the SAC chamber.

(6) Clear all rows of the table. Start from the end and choose specific locations on the sample surface to be characterized.

(7) Use the remote control to select a central position on the sample, assuming it is the most uniform area.

(8) Adjust the Z position of the sample using the remote control until the "horizontal focus beam" is centered on the TV screen. The top and bottom regions may be slightly out of focus.

(9) Press "update" once you have found the focused positions.

(10) Repeat the same process for all samples and save the table.

Calibration:

(1) If the y-direction shift during sample loading on the fork is too significant, the system will lose its calibration. The acceptable range for y is [-4.0, +3.0].

(2) Save the previous sample location if you have identified the loading position.

(3) Open valves (|X| |X|) and ensure that there are no samples in the SAC chamber (unload). Load the sample bar into the STC chamber first.

(4) Set the following values for calibration: X = 7.5, Y = 1.6, Z = 0, theta = 1.96. To initiate calibration, go to "Instrument Manual Control" >> "Stage" >> "Calibration".

(5) Press "Calibrate" and "Confirm". You will hear some noises, and wait for the system to complete the calibration process.

(6) After calibration, the system will park in the 000 position. This process may take a few minutes to complete.

(1) Open the prescan file in Vision Processing by going to the Processing Zone, selecting "Vision Processing," and then clicking on "File" followed by "Open Data Set File for Processing." Locate and select the prescan data file.

(2) In the Vision Processing software, hold the Ctrl key and click to select the desired spectra for display. Use the middle scroll button to overlay the selected spectra for comparison.

(3) Examine the table and identify the characteristic peaks for each element. Note down the element and the orbital, such as "C 1s" for the carbon peak.

(4) Determine the range for the narrow scan based on the characteristic peaks observed in the prescan data.

(5) When entering the binding energy (B.E) values into the system, ensure that they are set in decreasing energy order. The detector collects signals from high to low energy, so the scan ranges should not overlap. Otherwise, the detector would need to return to collect the high-energy signals.

(6) Set the width of the scan range. Typically, a width of 20eV is used for elements like carbon (C), sulfur (S), nitrogen (N), etc., for convenience. However, the width can be adjusted based on the spectrum and the desired level of resolution.

(7) For elements like cobalt (Co) and nickel (Ni), set the width to be 60eV to include any abnormalities, satellites, or Auger electrons. The wider range is chosen for high binding energy peaks because high-energy electrons tend to lose energy, resulting in higher binding energy.

(8) Pay attention to the specific case of zinc (Zn) 2p peaks, where the width should be around 40eV, rather than the default 20eV.

(9) Note that the presence of silicon (Si) peaks may be due to the carbon tape used in the sample preparation. Therefore, sometimes Si peaks are found, but they do not originate from the sample itself.

(10) If two peaks are close to each other, they can be selected together with the middle of the peak shifted to a higher energy position. For example, "Mo 3d + 2S" refers to the molybdenum (Mo) 3d peak combined with two sulfur (S) peaks.

(11) In the case of carbon compounds, it is possible to combine the carbon (C) peaks with potassium (K) peaks, as they are close in energy.

(12) Keep in mind that the silicon (Si) substrate may exhibit additional peaks that are not related to the sulfur peaks.

(1) Open “Vision instrument manager” to create chart. 

• Position:
  remember to save file by selecting dataset. Auto-Z. Status: Not required >> no increment 21 >> Increment size (mm) 0.05 >> ordinate choice: counts >> center (eV) 280.50 >> width (eV): 1.67 >> B.E

• Dummy1
  >> leave on >> spectrum >> Hybrid >> pass energy 160 eV >> X-ray >> Emission: 5mA >> Anode HT (KV): 15.0 kV >> Neutralizer: On for acquisition >>  Filament current: 1.98 >> charge balance (V):  3.6 >> Filament Bias (V): 1 >> Technique: XPS >> spectrum >> B.E >> Al (Mono) >> Region Name: Dummy1 >>Center: 797 >> Width: 250eV >> Step 1eV >> Dwell ns 100 >> Sweep: 1 

• Dummy 2
  >> leave on >> spectrum >> Hybrid >> pass energy 20 eV >> X-ray >> Emission: 10mA >> Anode HT (KV): 15.0 kV >> Neutralizer: On for acquisition >>  Filament current: 1.98 >> charge balance (V):  3.6 >> Filament Bias (V): 1 >> Technique: XPS >> spectrum >> B.E >> Al (Mono) >> Region Name: Dummy1 >>Center: 288.5 >> Width: 30eV >> Step 0.1eV >> Dwell ns 100 >> Sweep: 1

• Narrow
  Goto standby >> Spectrum >> Hybrid >> pass energy 20 eV>> X-ray gun >> Mono (Al) >> Emission 10 mA >> Anode HT (kV): 15.0 >> Neutralizer: On for acquisiton >> Filament current (A): 1.98 >> charge Balance (V): 3.6 >> Filament Bias (V): 1 >> Technique XPS >> Spectrum >> B.E >> Al (mono)

(2) Region Name: O 1s, N 1s,…etc [very specific, stored in system lib]; >> Center(binding energy): ** Data** >> width(experimentally determined): 20-30 eV >> Step: 0.1 eV >> Dwell ns 100 >> Sweeps 2. Next background: linear; >> Acquisition Region Name: C 1s. 

(1) Process (top bar) >> vision processing >> File >> open dataset for processing >> Update

(2) “Vision processing” should be open in PROCESSING zone.
        Even the vision processing is shown in the CONTROL zone, it is not for used. 

(3) To delete: click the head “2016-06-30 …” >> file >> close “2016-06-30”

(4) The survey + narrow can be shown at the same time.

(5) For MoS2, Mo3d + S2s peaks are overlaped.

(6) Create chart:

• Position 

• Dummy 1  (Dummy for survey, pass energy 160, emission 5mA)

• Survey

• Dummy 2 (Dummy for narrow, pass energy 20, emission 10mA)

• Narrow (Go Standby, sweep 20-40)

• Counter

(1) Select the files you want to convert in Vision Processing.

(2) Go to "Options" in the Vision Processing software.

(3) Click on "Browser Actions" and select "Describe".

(4) Choose "Vamas File" as the conversion format.

(5) Click on "Apply" and specify a name for the converted file.

(6) Select the destination folder where you want to save the converted file.

(7) Open CasaXPS, a software designed for XPS data analysis.

(8) Read the converted file in XPScasa to ensure it has been converted properly. 

(9)Compare it with the original Vision Processing profile.