The design of an integrated XPS/Raman spectroscopy instrument for - PowerPoint PPT Presentation

The design of an integrated XPS/Raman spectroscopy instrument for co-incident analysis Tim Nunney The world leader in serving science

XPS Surface Analysis 2

XPS + ... • UV Photoelectron Spectroscopy UPS He(I) (21.2 eV) UPS He(II) (40.8 eV) XPS (1486.6 eV) As rec SnO Intensity 20 18 16 14 12 10 8 6 4 2 0 -2 -4 Binding Energy (eV) 3

XPS + ... • UV Photoelectron Spectroscopy • Ion Scattering Spectroscopy Detected Incident Ion Scattered Ion Mass = M 1 Mass = M 1 Key: KE = E 0 KE = E S Known Measured Calculated Scattering Angle θ 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 High spatial Chemical Chemical Elemental Structural chemical resolution bonding bonding composition information state imaging information information High Crystallinity Very Structural Rapid Molecular sensitivity and surface information image ‘fingerprint’ composition sensitive analysis 6

Other techniques XPS EDS Raman FTIR XRF XRD Quantitative High spatial Chemical Chemical Elemental Structural chemical resolution bonding bonding composition information state imaging information information High Crystallinity Very Structural Rapid Molecular sensitivity and surface information image ‘fingerprint’ composition sensitive analysis 7

Raman Spectroscopy Sample ~~~~~~~~~~~~~~~ V = virtual state Raman scattering Excitation frequency Rayleigh scattering LASER Optics V = 1 V = 0 Blocking Filter Rayleigh Raman scattering scattering (filtered out) (Stokes shift) 0 2000 1800 1600 1400 1200 1000 800 600 400 200 Raman shift (cm-1) 8

XPS-Raman 9

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...? Raman intensity (counts/s) XPS 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 Penetration Penetration Penetration depth in a Wavelength Depth in Si Depth in Ge transparent Polymer (nm) (nm) (nm) 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 Si band 2D G D 8 mW No graphene signal from damage zone 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 ) Oxygen • Material of great interest due to its application in heterogeneous catalysis, dye-sensitised solar cells, bone implants and self-cleaning Titanium windows, amongst others • 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 valence band Ti2p Scan • Core level XPS spectra show Data offset Anatase-TiO 2 slightly for identical elemental and Rutile-TiO 2 clarity chemical composition for pure anatase and pure rutile samples Counts / s • There is a slight variation in peak shape of valence band, however this is not conducive to easy quantification of the amount of polymorph. 474 472 470 468 466 464 462 460 458 456 454 452 450 448 20 10 0 Binding Energy (eV) 21

TiO 2 powders Raman spectroscopy of single polymorphs Raman TiO 2 spectra – Linear background subtracted • Raman spectra were acquired 637.7 515.3 396.7 445.8 610.6 from pure anatase-TiO 2 and E g rutile-TiO 2 powders A 1g Intensity (norm.) E g • Pure spectra can be used as B 1g A 1g reference for determining the composition of powders with different proportions of anatase and rutile Anatase-TiO 2 powder Rutile-TiO 2 powder 800 700 600 500 400 300 Raman Shift (cm -1 ) 22

TiO 2 powders Raman spectroscopy of mixed powders Pure Anatase reference Mixed powder spectrum Pure Rutile reference Fit of combined reference spectra Sample #2 Sample #3 Sample #1 Anatase:Rutile Anatase:Rutile Anatase:Rutile 9:91 49:51 71:29 Counts / s 800 700 600 500 400 300 800 700 600 500 400 300 800 700 600 500 400 300 Raman Shift (cm -1 ) 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