Applications of XPSDetermine surface contamination ofwire bonding fingers of TBGAXPS Au 4f 7/2image of bond fingers with and without contaminationUncontaminated bond fingerContaminated bond finger0 2 4 6 8 10 12 14 16 18 20 Energy loss (eV)HAO-1HAO-2 HAO-3 HAO-4Energy Loss Spectra Intensity (a.u.)HAO-5XPS O 1s energy loss spectra to obtain Energy gap (Eg) Information from secondary features in XPS spectra120001400016000180002000022000770 780 790 800 810Counts / sBinding Ener gy( eV )Co2pSatellite02000400060008000770 780 790 800 810Counts / sBinding Ener gy( eV )Co2pPlasmonCo/Si at room temperatureCo/H-Si(111) after annealingNew challenges of XPS in nanostructuresThin layer Island-like Hemisphere SphereConventional XPSGeneral nanostructured surface patternsUniform surface layer:1. Chemical states: related to charge exchange between atoms2. Quantitative analysis can be carried by relative sensitive factors=jj ji iS I S ICNew ChallengesNon-uniform surface:1. Chemical states : Core level shift is not only related to charge exchange between atoms, but also to structural dimensions2. Quantitative analysis? (size effect)Growth mode study by XPS:intensity vs adsorbate coverage0exp( )nas ssndI I= The intensity of the adsorbate signal )] exp( 1 [aaanandI I =The decay of XPS signal from substrate 0 20 40 60 80 1000.00.10.20.30.40.50.60.70.80.91.0(a)Si 2sCo 2p3/2XPS intensity (normalized)Time(min)0 10 20 30 40 50 60 70 800.00.10.20.30.40.50.60.70.80.91.0(b)C 1sCo 2p3/2XPS Intensity (normalized)Time (mins)Co on SiCo on HOPGSurf. Sci. 600(2006)1308, 532(2003)639SmoothmorphologyIsland growthNanostructure (2D) from background signals Thin layer position can causes different photoelectron scattering (peak shape), as found by D.R.Penn 30 years ago, and confirmed by S.Tougaard, as showing in Figures. Tougaard et al have shown that the inelastic scattering background near the peak can be used to reliable obtain detailed information about the surface under investigation a b cd1.1A50A20A30A50A[D.R.Penn, Phys.Rev.Lett., 40(1978)568; S. Tougaard, Surf.Interf.Anal. 26(1996)249; J.Vac.Sci.Technol., A14(1996)1415; J.Vac.Sci.Technol., B13(1995)949]Determine the thickness of ultrathin SiO2layers on Si Tox = SiO2Sin ln[(ISi/ ISiO2)(ISiO2exp/ISiexp) + 1]SiO2is the attenuation length of the Si 2p photoelectron in SiO2 is take-off angleSi 2p spectraSurf. Interface Anal. 36(2004)1269This method is only suitable for an oxide on its own elemental substrate (e.g. SiO2on Si)Determination of the heterojunction band offsets by a combination of core level and valence band photoemissionSchematic flat-band diagramValence band offset: E = (ECLY- E Y) (ECLx- E x) (ECLY(i) ECLx(i))Conduction band offset: Ec= Egx- EgY- E Band alignments at ZrO2/Si, SiGe and Ge interfacesValence and Ge 2p spectra of Ge with and without ZrO2overlayerSchematic flat-band diagram at ZrO2/Si, SiGe and Ge interfacesAPL 98(2010)113510, 96(2010)072111, 95(2009)192109, 95(2009)162104, 94(2009)142903, 94(2009)062101, 93(2008)222907, 93(2008)052104, 92(2008)032107, 91(2007)042102, 89(2006)022105, 89(2006)202107, 88(2006)192103, 86(2005)112910, 85(2004)6166Determination of nanoparticle size from XPS signal intensity)] exp( 1 [0cC CdI I =) , () , (21r Ir IR= For a sphere particles{ } 2 / ] 1 ] 1 ) / ( 2 [( ) / (/ 2 2 30 + + = dc ce d d I I[G.K. Wertheim and S.B. DiCenzo, Phys.Rev. B 37(1988) 844] For a sphere particles with shell} 2 / ] 1 ) 1 / 2 [( ) / {() / () , , (/ 2 2 3 / + +++= r de r r edd rr d I[D.-Q. Yang, J.-N. Gillet, M. Meunier and E. Sacher, J. Appl. Phys. 97(2005)024303] For rectangle or square shape[F. Kerkhof and J.A. Moulijn, J. Phys. Chem. 83(1979)1612] dr0 5 10 15 20 25 30 35 4081216202428 RNominal Cu thickness (A)Peak intensity method: Modeling of XPS signals is required The ratio oftwo photoelectron emission intensities from a nanoparticle is used to obtain its size.The ratio of Cu2p3 to Cu3d as Cu mass thicknessCore-level binding energy shifts of nanoparticles [H.G.Boyen et al, Phys.Rev.Lett., 94(2005)016804]The BE shifts of Ni 2p3/2core-level (solid squares) and L3M4,5M4,5Auger transitions (solid circles) as a function of Ni coverage0 1 2 3 4 5 6 7 80.00.51.01.52.02.5 Energy shift (eV)Ni thickness (Monolayer)850 852 854 856Ni 2p3/27.5 ML5.0 ML2.5 ML2.0 ML1.5 ML1.0 ML0.5 ML Normalized intensity (a.u.)Binding energy (eV)835 840 845 850Ni Auger Kinetic energy (eV)-2 -1 0 1 2 3Valence band Binding energy (eV)The Ni 2p3/2core-level, Ni L3M4,5M4,5Auger transitions and valence band spectra as a function of Ni coverage on rutile TiO2(001) surfaceCore-level and velance binding energy shifts of Ni clusters AFM images of Ni clusters on TiO2[J. G. Tao et al. Surf. Sci. 602(2008)2769]Major explanation of NPs binding energy shifting in XPS1. Initial effects proposed by Mason, due to surface atomic coordination number reducing in NPs surface2. Charging effects (final-state effects) of residing positive charge on a NP, proposed by Wertheim et al, due to photoelectron emission from a NP and leaving a positive charge, causing core level shiftsto high binding energy side.3. Both theoretical models indicate the binding energy shifting is proportional to 1/d, d is NPs size4. Peak width of core level is increasing with NPs size decreasing, and it is difficult to understanding by charge residing modelPoor electrical contact hinders the electron flow to screen the holes (hole delocalization).eE~ e2/rCoulomb interaction+ he e e e e eSemiconductor/Insulator Changes in the valence shell configuration Changes in the valence electron density (atomic renormalization) Differences in extra-atomic screening energiesFinal state screening effectInitial state effectDependence of the binding energy on cluster sizeAuger parameters and Wagner plotsThe Auger parameter has been used as an empirical, or fingerprinting, tool to characterize the chemical states of the elements in cases where charging of the sample or small shifts in core binding energies present problems.The Wagner Auger parameterfor the ith core-level, (i), and its shifts, (i), are:(i) =BE(i) + KE(klm)(i) = BE(i) + KE(klm)where i, k, l, and m are core levels. With several approximations, the (i) can be related to (i, Initial) and R (i, final )By:R (finial) = (i)/2BE (BE shift) = -(initial) - R (finial)0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.180.00.10.20.30.40.50.61/d (A-1)Initial-state contribution to EB(Cu 2p3/2) (eV)-0.14-0.12-0.10-0.08-0.06-0.04-0.020.00Final-state contribution to EB(Cu 2p3/2) ) (eV)Cu NPs supported on HOPG after different surface treatmentHOPG CyclotenesurfaceuntreatedAr+-treateduntreateduntreatedAr+-treatedN2-treatedmetallizationevaporatedevaporatedsputteredevaporatedevaporatedevaporatedratio 1.8 1.8 1.8 0.02 0.09 0.25Table. Initial- and final-state ratios of B(Cu 2p3/2)for Cu Clusters on HOPG and CycloteneInitial- and final-state contributions to binding energy shift of NPS0 1 2 3 4 5 6 7 8-0.10.00.10.20.30.40.5 (eV)Ni thickness (Monolayer) (001) (110)(a)0 1 2 3 4 5 6 7 8-1.0-0.8-0.6-0.4-0.20.0 R (eV)Ni thickness (Monolayer)(b) (001) (110)The Auger Parameter analysisBE (BE shift) = - (initial state)- R (finial state)The initial (a) and final (b) state effects contributions to the total shifts as a function of Ni coverage obtained by A.P. analysis for both TiO2(001) and (110) surfaces. Charge transfer between clusters and substrateRDetermination of cluster size[J. G. Tao et al. Surf. Sci. 602(2008)2769]Determination of cluster size using R10 nm 10 nmTEM images show Ni cluster size0 1 2 3 4 5 6 7 8-1.0-0.8-0.6-0.4-0.20.0 R (eV)Ni thickness (Monolayer)(b) (001) (110) R - determination of cluster size (0.85 nm on (001) and 1.38 on (110)). It has good agreement with TEM results that the size distribution of particles is quite narrow, with majority ranged from 1.5 -1.9 nm.reR024= Comparing with TEM, XPS estimated dimension information of NPs has following advantages and disadvantages:Average size information, it is better for relative narrow size distributionof NPsIt can be used for very small size, such as less than 1nm