The design of an integrated XPS/Raman spectroscopy instrument for co-incident analysis Tim Nunney The world leader in serving science
2 XPS Surface Analysis
XPS +... UV Photoelectron Spectroscopy UPS He(I) UPS He(II) XPS (21.2 ev) (40.8 ev) (1486.6 ev) As rec SnO Intensity 20 18 16 14 12 10 8 6 4 Binding Energy (ev) 2 0-2 -4 3
XPS +... UV Photoelectron Spectroscopy Ion Scattering Spectroscopy Incident Ion Mass = M 1 KE = E 0 Detected Scattered Ion Mass = M 1 KE = E S Key: Known Measured Calculated θ Scattering Angle Sample surface Scattering Atom Mass = M 2 4
XPS +... UV Photoelectron Spectroscopy Ion Scattering Spectroscopy REELS Coating 5
(Some) other analysis techniques XPS EDS Raman FTIR XRF XRD Quantitative chemical state Very surface sensitive High spatial resolution imaging Rapid image analysis Chemical bonding information Structural information Chemical bonding information Molecular fingerprint Elemental composition High sensitivity Structural information Crystallinity and composition 6
Other techniques XPS EDS Raman FTIR XRF XRD Quantitative chemical state Very surface sensitive High spatial resolution imaging Rapid image analysis Chemical bonding information Structural information Chemical bonding information Molecular fingerprint Elemental composition High sensitivity Structural information Crystallinity and composition 7
Raman Spectroscopy LASER Optics Sample Excitation frequency ~~~~~~~~~~~~~~~ V = virtual state Rayleigh scattering Raman scattering V = 1 V = 0 Rayleigh scattering (filtered out) Raman scattering (Stokes shift) Blocking Filter 2000 1800 1600 1400 1200 1000 800 Raman shift (cm-1) 600 400 200 0 8
9 XPS-Raman
XPS with ixr Raman Spectrometer Integration of small form factor Thermo Scientific ixr Raman spectrometer with Thermo Scientific Theta Probe and Thermo Scientific Nexsa XPS systems Allows simultaneous acquisition of Raman & XPS data Correlated analysis position No need to move the sample to acquire data Analysis area is matched Software control allows complex hybrid experiments 10
Co-alignment of analysis positions 600% Zoom Raman Beam X-Ray Beam 11
Lithium niobate Raman intensity (counts/s) 12
Lithium niobate...? XPS intensity (counts/s) Raman intensity (counts/s) 13
Bulk vs surface For strongly absorbing materials such as semiconductors, the Raman signal is acquired from a volume defined by the Raman penetration depth and the diameter of the laser beam A lower laser wavelength gives smaller penetration and provides chemical information closer to the samples surface Nominal XPS sampling depth is 10 nm Laser Wavelength (nm) Penetration Depth in Si (nm) Penetration Depth in Ge (nm) Penetration depth in a transparent Polymer Film (nm) 633 3000 30 >5000 514 760 19 >5000 488 570 18 >5000 457 310 18 >5000 325 10 9 >5000 244 6 7 >5000 14
Lithium niobate with yttrium oxide coating Raman intensity (counts/s) Bulk XPS intensity (counts/s) Surface 15
Applications Area: Carbon 16
Graphene on SiO 2 Raman imaging of damaged graphene layer deposited on a silicon wafer (Mapping controlled through Avantage software) 17
Graphene PCA analysis of map Graphene area Damaged area Si band 2D G D Si band No graphene signal from damage zone 8 mw 50 µm pinhole 15 x 10s acquisitions 18
Graphene - XPS Contamination Contamination Both areas are contaminated by the adhesive material in the container that the sample was face down on. Not visible in Raman, but easy to see in XPS. 19
TiO 2 powders Introduction Titanium dioxide (TiO 2 ) Material of great interest due to its application in heterogeneous catalysis, dye-sensitised solar cells, bone implants and self-cleaning windows, amongst others Oxygen Titanium Frontier material in the development of nanotechnology, nanoparticles, nanorods etc. fabricated to improve application properties Most abundant polymorphs are rutile and anatase Degree of mixing between two polymorphs influences material properties, such as catalytic activity Rutile-TiO 2 Anatase-TiO 2 20
TiO 2 powders XPS of single polymorph Core level XPS spectra show identical elemental and chemical composition for pure anatase and pure rutile samples Data offset slightly for clarity Ti2p Scan valence band Anatase-TiO 2 Rutile-TiO 2 There is a slight variation in peak shape of valence band, however this is not conducive to easy quantification of the amount of polymorph. Counts / s 474 472 470 468 466 464 462 460 458 456 454 452 450 448 Binding Energy (ev) 20 10 0 21
TiO 2 powders Raman spectra were acquired from pure anatase-tio 2 and rutile-tio 2 powders Raman spectroscopy of single polymorphs Raman TiO 2 spectra Linear background subtracted E g 637.7 515.3 396.7 610.6 445.8 A 1g Pure spectra can be used as reference for determining the composition of powders with different proportions of anatase and rutile Intensity (norm.) A 1g E g B 1g Anatase-TiO 2 powder Rutile-TiO 2 powder 800 700 600 500 Raman Shift (cm -1 ) 400 300 22
TiO 2 powders Raman spectroscopy of mixed powders Pure Anatase reference Pure Rutile reference Fit of combined reference spectra Mixed powder spectrum Sample #1 Anatase:Rutile 9:91 Sample #2 Anatase:Rutile 49:51 Sample #3 Anatase:Rutile 71:29 Counts / s 800 700 600 500 400 300 800 700 600 500 400 Raman Shift (cm -1 ) 300 800 700 600 500 400 300 23
Summary Adding extra analytical techniques increases the information that can be obtained. Matching the technique to the application is important Having co-incident analysis points ensures that the data is collected from the same point on the sample, but......consideration must be made of variations between analysis volumes. Offers opportunities for Bulk surface studies Carbon nanomaterials Coating analysis... 24