Cheat-Sheet Check List (Do List)

Producing & Publishing XPS Data from Simple Materials

This list assumes that you are allowed to operate the XPS instrument, the Argon Ion (Ar+) etching gun, and know how to exchange sample mounts safely.

X-ray Type:  Monochromatic Aluminum X-rays 

1. Check “Instrument Status” before trying to use the XPS instrument
   • Is a sample still inside the analysis chamber?
     • If true, then remove sample
     • If there are no samples inside, then continue
   • Is the sample-viewing camera or microscope working?
     • If true, then continue
   • Is vacuum in analysis chamber <1 x 10 (-7) mTorr?
     • If true, then you are ready to check instrument Calibration BEs, flood gun alignment, and X-ray beam position
     • Cut each Calibration Metal to ~5 x 10 mm size. Trap metals using screws or clips.  Do NOT use double-sided conductive tape.
     • Using a clean single edged razor blade, scrape a 4×4 mm area on the Copper (Cu) sample used to check the Calibration BEs
     • Cut a piece of polypropylene to be ~5 x 5 mm size.  Scrape the surface with a clean single edged razor blade or a knife. Use double sided tape (3×3 mm) to hold polypropylene.
     • Load sample mount that has all 3 Calibration Metals (Cu, Ag, Au), polypropylene (or Teflon), and X-ray Phosphor (P-31, ZnS) into Prep-Lock (Load-lock)
     • Wait until pressure is <1 x 10 (-7) mTorr
     • Pressure should be <5 x 10 (-8) if you want to collect data to be published
     • If pressure is >1 x 10 (-6) mTorr, absolutely do NOT turn on any filaments.  Immediately Contact Service.
     • NOTE:  If vacuum pressure is >1 x 10 (-6) mTorr, then all collected data will be bad and filaments oxidized or broken.
   • Is cooling water used to cool Aluminum X-ray source running?
     • Is water flow rate high enough?  (>3 L/min).  If true, then continue
     • Is water line cool, not cold, to touch?  (If too cold, then condensation can cause corrosion.)
2. Record “Calibration BEs” and check X-ray Beam position using ZnS phosphor
   • If X-rays are ON, then turn X-rays OFF
   • If Flood Gun (FG) is ON, then turn FG OFF
   • Transfer “Calibration Metals” (Cu, Ag, Au), polymer (polypropylene or Teflon) and X-ray Phosphor (P-31) from Load-Lock into “Analysis Chamber”
   • Was Copper (Cu) Calibration Metal sample scraped?  If not, then you will need longer ion etching to remove oxide.
   • Move “X-ray Phosphor” (ZnS, type P-31) to standard “Sample Analysis Position”
   • When pressure is <1 x 10 (-7) mTorr, continue
   • Turn ON X-rays
     • Maximum power settings
     • Largest spot size
   • Turn ON Argon Ion (Ar+) Gun to standby condition
     • Make sure that ion gun has Argon gas – Do not flood the ion gun with too much Argon (if too much Argon, then filament may break)
     • Select maximum acceleration voltage conditions (2-5 keV)
     • Select maximum current
     • Select 4 x 2 mm (or 4 x 4 mm) raster area
     • (We assume that Argon ion gun is already optimized for routine use.)
   • Adjust stage height to bring ZnS phosphor into good optical focus (Can you see grains?)
   • NOTE:  Good Optical Focus can be different from Good Electronic Focus by as much as 200 microns up or down
     • When sample is not at good electronic focus, then count-rate drops by 10-15% of maximum countrate
     • When sample is not at good electronic focus, then the BEs can shift by 0.1-0.2 eV from true value
   • Verify that X-ray Beam center is nearly same as Green X-ray Spot on ZnS phosphor  (Never ion etch ZnS)
   • If not, then adjust optical microscope (or camera) to match
   • Record Z-Height, and save as “Home Position” (record XYZ position)
   • Move Copper (Cu) to “Home Position”
     • Set analysis conditions to measure Cu (2p3) BE at 932.6 eV (KE = 554 eV) using a 10 eV narrow scan mode, or a SnapShot mode (~20 eV window)
     • Using fast scan conditions with a large Pass Energy, adjust Z-Height until you find Z-Height position that gives maximum count-rate for Cu (2p3) signal
     • Record XYZ position
     • Change argon ion gun from standby to operate (unblank) for a minimum of 60 seconds to remove carbon or oxygen from the freshly scraped Copper surface
     • Using fast scan conditions, adjust Z-Height to find Z-Height position that gives maximum count-rate for Cu (2p3) signal
     • If best count-rate position has changed, then record new XYZ position, and teach new position as new HOME position
     • Change fast scan conditions to measure Oxygen (1s) signal at 530 eV
     • Measure Oxygen (1s) signal for 1-2 scans or use SnapShot mode (10 sec or continuous).
       • If the Oxygen (1s) signal is very noisy, then the Copper surface is clean
       • If the Oxygen (1s) signal is large, then ion etch Copper again, for 2-3 minutes
       • NOTE:  If ion gun is not properly aligned to overlap X-ray Spot, then argon ion etch rate is very small.  Stop and adjust ion gun.
     • Now we are ready to record the Calibration BE of Cu (2p3), Cu (3p) and Valence Band region
       • Select Pass Energy that you normally use to measure high energy resolution (chemical state) spectra
       • Use a 10 eV window to record Cu (2p3)  (2 scans)  [928 – 938 eV]
       • Use a 30 eV window to record Cu (3p)   (2-3 scans)  [60-90 eV]
       • Use a 30 eV window to record Cu Valence Band and Fermi Edge (3-4 scans)  [ -10 to + 20 eV]
     • To check for cleanliness, and to check the “Transmission Function” of the instrument, collect two survey spectra from the copper sample
       • Energy range:  -10 to 1100 eV
       • Pass Energies:  Largest pass energy and pass energy used to measure high energy resolution (chemical state) spectra
       • Number of Scans: one (1) scan
       • Step Size:  0.7-1.0 eV/step
   • Move Gold (Au) to “Home Position”
     • Set analysis conditions to measure Au (4f) BE at 85 eV (KE = 1401 eV) using a 10 eV narrow scan mode, or a SnapShot mode (~20 eV window)
     • Using fast scan conditions with a large Pass Energy, adjust Z-Height until you find Z-Height position that gives maximum count-rate for Au (4f) signal
     • Record XYZ position
     • Change argon ion gun from standby to operate (unblank) for a minimum of 60 seconds to remove carbon from the Gold (Au) surface
     • Now record the Calibration BE of Au (4f) signal
       • Select Pass Energy that you normally use to measure high energy resolution (chemical state) spectra
       • Use a 10 eV window to record Au (4f)  (2 scans)  [79-89 eV]
   • Thank You.  You have completed the essential recording of Calibration BEs from freshly cleaned Calibration Metals (Cu and Au)
     • If you prefer to include Ag (3d) signal, then repeat the Gold cleaning and analysis procedure using Ag (3d) BE at 368.2 eV
3. For Insulating Sample – check if Electron Flood Gun is properly aligned
   • Turn ON the electron Flood Gun (charge neutralizer)
     • Set FG voltage = ~4 eV (10 mA) for older instruments, or
     • For very modern instruments, set FG voltage = 0.1 eV
   • Move the polypropylene or Teflon sample to “Home Position”
     • Move sample 2-3 mm in X and Y to spray electrons over the entire surface which produces a uniform electrical charge over the sample
     • Move to the center of the polypropylene (or Teflon) sample
     • Set analysis conditions to measure C (1s) BE at 284 eV for polypropylene (or 292 eV for Teflon) using a 20 eV narrow scan mode, or a SnapShot mode (~20 eV window)
     • Using fast scan conditions with a large Pass Energy, adjust Z-Height until you find Z-Height position that gives maximum count-rate for C (1s) signal
     • Record XYZ position
   • If the electron Flood Gun is properly aligned, then the C (1s) signal will be symmetrical and have a FWHM <1.4 eV after peak-fitting
   • If you see a small shoulder or a slope on the low BE side, then the Flood Gun needs to be aligned (the shoulder is due to differential charging)
   • If you look at this webpage (https://xpslibrary.com/charge-compensation) then you will see examples of differential charging and FWHM for polypropylene and Teflon
   • Place a transparent ruler or straight edge on your computer screen.  Line the edge to the center of the C (1s) peak maximum
   • Adjust the X and Y voltage settings (or the physical position) of the flood gun
   • The C (1s) peak will shift to the right to lower BE if you are improving charge control
   • The C (1s) peak will shift to the left to higher BE if you are making the charge control worse
   • Adjust X and Y several times until the C (1s) BE for polypropylene is below 285.0 eV.  For Teflon, the C (1s) BE is ~292 eV.
   • If the X and Y voltage positions are optimized, then the FWHM will be <1.3 eV.
   • If the C (1s) BE and FWHM are not improving enough, then increase the current and the voltage of the electron flood gun by 10%
   • NOTE:  electrons from the flood gun can and do cause degradation of a few materials.  Avoid very high voltage and high current settings
   • NOTE:  if you place a 90% transparent metal mesh-screen ~1 mm above the surface of the sample, then the electric field will decrease and you will get better results (https://xpslibrary.com/charge-compensation)
   • Now, you are ready to collect useful and reliable BEs from both conductors and non-conductors (insulators)
   • Remove the Calibration Metals samples and load your samples.
   • If you have a large sample mount (e.g. >50 x 50 mm, then you should load your samples, the Calibration Metals, the polypropylene, and X-ray phosphor, all together to save time)
4. Prepare Sample
   • NOTES:
     • Do NOT wear latex gloves (cheap latex gloves have Silicone Oil on outside that contaminate your UHV chamber)
     • Do NOT rinse or wipe surface with acetone or IPA, unless you know that someone has touched the surface to be analyzed.
     • We use Scotch-brand double-sided adhesive tape – very small pieces
     • Smaller sample size minimizes waiting time for sample to finish outgassing, especially porous materials (paper, powder, soft plastic…)
     • Smaller sample size gives better charge control – near edge usually
     • Decide if sample will degrade by exposure to monochromatic X-rays
     • If you suspect that the sample will definitely degrade, then after collecting each spectrum, move sample by 2 mm before collecting next spectrum, and also collect fast 1 scan survey spectrum at start, and also at finish – compare – look for changes in peak heights
   • Solid sample – non-conductive  (ceramic, plastic, glass, non-porous, insulator)
     • Avoid screws, masks, and clips to hold samples – they can cause differential charging near the metal piece
     • Place a 10 x 10 mm piece of Scotch brand non-conductive double sided tape on sample stage/mount (must be slightly bigger than sample size)
     • Use fine sandpaper to clean both edges of a single-edged razor blade or knife, then wipe edge with IPA or acetone
     • Cut or break sample until it is slightly smaller than ~9 x 9 mm (or ~9 x 20 mm).  (This style stops outgas from still exposed tape.)
     • Scribe a line down the middle of the sample, or use Sharpie marker to make a line (Sharpie pens have silicone, but very little)
     • On one side of the scribe line, scrape a 3×3 mm region of surface at 90 deg angle with the freshly cleaned razor blade or knife
     • Use 2 pairs of tweezers – press corners of sample onto double-sided tape
     • Or, place clean Aluminum foil (kitchen) on top of sample, press to make flat, and discard Al foil
     • (Fresh exposed bulk of sample can also give useful results)
   • Small grain or powder sample  (normal laboratory air)
     • NOTES: 
       • Old powders collect moisture from air or CO2 and may change surface chemistry over time.  Drying in a vacuum oven may help.
       • Brand new bottles of powders from chemical maker may be dirty with adventitious carbon, stabilizers, or contaminants
       • Brand new bottles of powders from cheap manufacturing companies will very likely be dirty, have water of hydration – not reported, and have contaminants
     • Clean mortar, pestle, and spatula with acetone and IPA 5 minutes before using. Blow dry with clean air or nitrogen.  Do not use canned gases.
     • Using a clean mortar and pestle, grind grains or powder gently for ~5 minutes
     • Use freshly cleaned spatula to transfer and press powder onto non-conductive double sided tape (tape size: 5 x 5 mm)
     • Use swab or Q-tip to gently brush off excess powder – trap excess powder in empty glove.  Tie glove closed. Dispose safely.
   • Solid sample – conductive  (pure element, film, steel, alloy, wire, fiber, ball-bearing)
     • Use electrical ohm-meter to measure conductivity at surface.  Metals often have thick insulating oxides or machine oils due to production
     • Clean edges of metal cutting shears with acetone and sandpaper before cutting sample
     • Cut sample to be 10 x 10 mm or 20 mm x 20 mm.
     • Scrape a small region where you put the screw or clip that traps sample
     • Scribe a line down the middle of the sample (or use Sharpie pen)
     • Scrape a 4 x 4 mm region with a clean single edged razor blade or knife
   • Solid wafer – semiconductor
     • Cleave wafer to be 10 x 10 mm. Gently scribe a line down the middle or use a Sharpie pen
     • Use a clip or a screw to trap the sample onto the sample mount, or use graphite paint to trap the sample
     • If you need true bulk information, then cleave the wafer in a glove box or cleave the wafer in air and very quickly load it into the load-lock
     • NOTE:  Do NOT use the electron flood gun on semiconductors.  BE sure the FG is turned OFF unless you truly need it to control charging.
5. Choose Instrument Settings for Data Collection
   • X-ray Power:  Maximum power
   • X-ray Beam Size:  Maximum beam size
   • Flood Gun Setting:  ~4 eV with 10 mA current, or 0.1 eV for dual beam source (Ar+/e-) for truly insulating samples (NOT semiconductors)
   • Usual electron take-off-angle
6. Choose Data Collection Variables and Collection Settings for Each Position (Sample)
   • Always analyze as received first – before any ion etching
   • Survey Spectrum #1:  -10 eV to 1,100 eV, 1 eV/step (1 eV/channel), 50 msec/step, 3-5 scans
   • C (1s) spectrum:  275 – 305 eV, PE =50 eV, 0.1 eV/step, 50 msec/step, 5-10 scans
   • O (1s) spectrum:  515 – 575 eV, PE =50 eV, 0.1 eV/step, 50 msec/step, 5-10 scans
   • Element signal #1 spectrum:  xxx-xxx eV (60 eV window), PE =50 eV, 0.1 eV/step, 50 msec/step, 5-10 scans
   • Element signal #2 spectrum:  xxx-xxx eV (60 eV window), PE =50 eV, 0.1 eV/step, 50 msec/step, 5-10 scans
   • Valence Band spectrum:  -10 – 40 eV, PE =100 eV, 0.2 eV/step, 50 msec/step, 10-20 scans
   • Auger Signal Spectrum: xxx-xxx eV (100 eV window), PE =100 eV, 0.2 eV/step, 50 msec/step, 5-10 scans
   • Survey Spectrum #2:  -10 eV to 1,100 eV, 1 eV/step (1 eV/channel), 50 msec/step, 3-5 scans
     • NOTE:  The repeat 2nd survey spectrum checks for sample degradation due to analysis
   • Collect the second survey spectrum after very soft ion etching that removes only 1-2 nm of adventitious carbon
7. Define and Record each position to be analyzed.  Take photo of sample inside instrument if possible.
   • Move stage to locate center of each sample position to be analyzed
   • Select O (1s) signal at 530 eV (NOTE:  Oxygen and carbon exist on all as-received samples)
   • Select “snapshot” or “fast scan conditions” to measure the O (1s) signal intensity
   • Adjust Z-Height to get the strongest intensity for the O (1s) signal
   • Define/Record each sample position to be analyzed
   • NOTE:  Optical focus is often wrong by 100-200 microns.  Better to use electronic focus
8. Collect Data
   • Define sample analysis position #1 using Snapshot mode or fast scan mode to find maximum (best) count rate from O (1s) or C (1s) signals
   • Continue collecting data from each sample or sample position
   • If degradation is suspected, then move to fresh position ~2 mm away, to define a new fresh position to collect the next spectrum
   • Do not use slits or apertures
   • Do not tilt sample
9. Process Data – Peak-fitting
10. Process Data – Atom% Quantification
11. Interpret Data – Peak-fits
12. Interpret Data – Atom% Values
13. Publish XPS results
14. Publish Instrument Description
15. Publish Data Collection Settings
16. Publish Calibration Values