Gap: Oxidation of Cu, Ag and Au Surfaces at 1 mbar O2 ... Roy, C. Prabhakaran Vinod, and Chinnakonda Subramanian Gopinath J. Phys. Chem. C, ... (Lab-APPES) are presented. A double
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Design and Performance Aspects of a Custom Built AmbientPressure Photoelectron Spectrometer Towards Bridging the Pressure
Gap: Oxidation of Cu, Ag and Au Surfaces at 1 mbar O2
pressureKanak Roy, C. Prabhakaran Vinod, and Chinnakonda Subramanian Gopinath
J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp312706s • Publication Date (Web): 08 Feb 2013
Downloaded from http://pubs.acs.org on February 12, 2013
Just Accepted
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1
Design and Performance Aspects of a Custom Built Ambient Pressure
Photoelectron Spectrometer Towards Bridging the Pressure Gap:
Oxidation of Cu, Ag, and Au Surfaces at 1 mbar O2 Pressure
Kanak Roy,# C. P. Vinod,
#,§,* and Chinnakonda S Gopinath
#,§,*
#Catalysis Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road,
Pune 411 008, India §Center of Excellence on Surface Science, CSIR-National Chemical Laboratory,
Figure 2.(a) A double front cone pumping arrangement (shown in green and yellow) effectively improves the differential pumping to minimize inelastic scattering in electrostatic lens regime (ELR) as well as to decrease the data collection time under high pressure conditions. The electron energy analyzer region is shown in purple (b) A schematic of the aperture free ELR and the electron trajectory for faster data acquisition.
critical factor that minimizes the loss of electrons in the ELR is the utilization of the advanced
concept of electron converging in the ELR. In contrast to the conventional ELR,9 electrostatic
voltages in the R3000HP model analyzer are applied in such a way that they converge all the
electrons.14 Further, unlike other high pressure electron analyzers,9 R3000HP employs an
aperture free ELR (Fig. 2b). This design enables the study of angle resolved XPS and fast data
acquisition under 1 mbar conditions. Fundamentally, an electrostatic lens in the APPES unit
refocuses the electron trajectory in such a way that electrons are converged due to the applied
especially critical at high pressure, where the heat dissipation is expected to be more due to
convection as well as conduction.9
One of the critical aspects of any high pressure experiments is the accurate measurement
of the pressure near the reaction zone, which is the sample surface. This is achieved using a CTR
gauge connected to the analysis chamber through a CF35 flange and extending all the way close
to the sample surface (Figure 3). This arrangement makes sure that the pressure achieved and
Figure 3. A bird’s eye view of the main chamber viewed from the analysis chamber side and without the analyzer. The inset shows an expanded view of the analysis spot to illustrate the pressure measurement with a CTR gauge and the gas dosing arrangements.
High resolution Pd 3d core level spectra measured under different O2 partial pressures at
ambient temperature are shown in Figure 4a. The same spectra, recorded in fixed or fast data
acquisition mode in 1 s, are shown in Fig. 4b. Only a marginal change in intensity and count rate
is observed for high resolution spectra between UHV and 10-2 mbar. However, at 1 mbar the
count rate decreases to about 45% of that of UHV conditions. We attribute the above quality
results to effective differential pumping in the ELR regime, which minimizes the inelastic
scattering. Hardly any change in BE (335 eV for Pd 3d5/2) is observed, indicating that the Pd
Figure 4: Lab-APPES measurements recorded for Pd-foil at ambient temperature for Pd 3d core levels at (a) different O2 partial pressure, and (b) spectra acquired in 1 s at different O2 partial pressure. The dashed line is a guide to the eye. 1 s spectra acquired indicate the possibility of measuring transient kinetic aspects and reaction dynamics on catalysts under 1 mbar conditions.
Figure 5: Core level spectra measured while exposing 1 mbar of O2 on a polycrystalline Au foil at various temperatures. (a) O 1s, and (b) Au 4f7/2. O 1s features from gas phase molecular oxygen appear between 538 and 540 eV. Arrows are a guide to the eye.
UHV conditions at RT shows the Ag 3d5/2 peak at 368.0 eV (dashed arrow) which is in
agreement with the literature values.23 No feature due to common impurities like C, O, or Si was
observed, indicating the atomically clean surface nature. After the above measurements, O2 was
allowed in the analysis chamber, and the O2 partial pressure was increased gradually to 1 mbar.
Once the pressure stabilizes at 1 mbar, XPS measurements were carried out at RT and higher
temperatures. There are no significant changes observed, either in terms of shift in BE or FWHM
of the Ag 3d features at RT. In fact, no O 1s feature was observed as well. The above
observations underscore the inert nature of the Ag-surface, similar to gold, to O2 at ambient
temperatures. The Ag 3d5/2 spectrum obtained at various temperatures at 1 mbar O2 pressure
showed an increased broadening and asymmetry on the lower BE side. It is to be noted that the
Ag 3d5/2 peak maximum occurs at the same BE irrespective of 1 mbar oxygen treatment at
different temperatures up to 600 K. Broadening of the Ag 3d5/2 peak observed at low BE is due
Figure 6. Ag 3d5/2 spectra at 1 mbar O2 pressure collected at different temperatures. Intensity is normalized to the UHV-RT spectrum. Difference spectra obtained by subtracting UHV-RT from 1 mbar - 600 K is given at bottom in yellow color demonstrate the presence of Ag2O like feature. Inset shows the deconvolution of Ag 3d5/2 spectrum measured at 1 mbar O2 pressure and 600 K. Black and red color for experimental and sum of the fitted peaks, respectively. Green and grey color for metallic Ag and precursor to Ag2O peaks, respectively. Background subtraction trace is given in pink color.
to gradually increasing interaction between the Ag surface and O atoms. Indeed the difference
spectra obtained between 1 mbar -600 K and UHV-RT spectra shows the feature at 367.5 eV,
due to Ag2O like feature. The inset in Fig. 6 shows the deconvolution of the Ag 3d5/2 core level
recorded at 1 mbar O2 pressure and at 600 K. The feature at 367.5 eV is similar to that of Ag2O.
However, the predominant Ag-feature suggests that either the interaction with oxygen is weak or
there might be other processes, like migration of atomic oxygen to subsurface layers and/or bulk.
Figure 7 shows the O 1s spectrum measured at different temperatures and at 1 mbar O2
pressure on Ag surfaces. Unlike gold surfaces, silver interacts with oxygen, and it is evident from
Figure 9: Schematic energy level to show charge transfer (∆) in the ground state and energy reversal in the final state configuration (due to Q), corresponding to main line. Energy of satellite feature due to Cu 3d9 configuration is relatively unaffected due to photoelectron emission.
500 K, the Cu(I) oxide phase at 916.7 eV increases at the expense of metallic Cu. On further
increasing the temperature to 500 K, the fully developed Cu2O feature is observed at 916.8 eV at
the expense of the metallic Cu feature. This indicates the complete surface oxidation of Cu to
Cu2O at 500 K and 1mbar O2. In fact, the above complete oxidation to Cu2O was observed better
with Auger spectral changes than with Cu 2p core level changes. On increasing the temperature
to 600 K the spectrum becomes broad, indicating the formation of a third type of species, Cu2+,
on the surface. The Cu2+ LMM Auger peak at 918.1 eV (dotted arrow) obtained in the present
case is in agreement with several literature reports.36-40 The growth of Cu2+ is much more evident
in the 625 and 675 K spectra where the peak maximum is centered around 918 eV. Oxidation of
Cu2O to CuO is equally evident from Cu 2p core level and Auger spectral changes and they are
in agreement with each other. Indeed, different KEs observed for different oxidation states lead
to different Auger parameter values, and this reiterates the changes in oxidation state.40
O 1s spectra acquired at different temperatures and at 1 mbar pressure are shown in
Figure 10. An increase in temperature to 375 K at 1 mbar O2 pressure is accompanied by a broad
peak centered at 530.4 eV (dotted arrow). The feature at 530.4 eV in the O1s spectrum is
attributed to oxygen in Cu2O.41 Along with the predominant 530.4 eV feature, the presence of a
532 eV species is observed in both the 375 and the 425 K spectra. The O 1s feature at 532 eV has
been attributed to OH species in the past, but it could also be attributed to oxygen bound to
residual impurities on the Cu surface.42 The O 1s feature at 530.4 eV grows in intensity, and
other features disappear on increasing the temperature from 375 to 500 K. The O 1s spectrum at
500 K is mostly dominated by oxygen from Cu2O species with the emergence of a new feature at
529.6 eV (dashed arrow). This feature is characteristic of CuO surfaces. Nonetheless, the
spectrum measured at 600 K is dominated by 529.6 eV species, at the expense of Cu2O, and
demonstrates the oxidation of the Cu(I) to the Cu(II) state on the surface. Interestingly, we could
find the presence of another species at around 531.3 eV which is attributed to the suboxide
species.41,43 The suboxide species is only stable under oxygen pressure and decomposes once the
high pressure regime is reverted to UHV (data not shown). Oxygen from Cu2O at 530.4 eV
completely disappears >600 K indicating the complete oxidation of the surface layers to CuO.
Figure 10: O 1s core level spectra measured while exposing a Cu foil to 1 mbar O2 at various temperatures. O 1s spectra were deconvoluted to show the systematic changes from Cu metal to CuO through Cu2O.
Figure 11: High pressure valence band spectra recorded at 1 mbar O2 and at different temperatures. Systematic conversion of Cu metal at UHV-RT to Cu2O (at 500 K) and CuO above 500 K is observed in 1 mbar O2.
observed between 4 and 8 eV with the main VB peak at 3.5 eV (solid arrow) at 600 K and above.
The above broad feature is attributed to the strong hybridization of Cu and O in CuO, which is
typical for cuprates.3,45 In comparison to the energy gap (~3.5 eV) observed between O 2p and
Cu 3d derived spectral weights in the VB spectra recorded between 375 and 500 K, the
overlapping shoulder with the main VB at ≥600 K demonstrates the formation of CuO due to
We thank Dr. S. Sivaram (Ex-Director, NCL, Pune), and Dr. S. Pal (Director, NCL, Pune) for supporting the Lab-APPES unit, and for establishment of the Center of Excellence on Surface Science at CSIR-NCL, Pune. CSG gratefully acknowledges the helpful discussions with Prof. Jörg Libuda, Univ. Erlangen-Nürnberg, and Dr. Axel Knop Gericke, FHI-MPI, Berlin, during the Humboldt Kolleg at Goa on Nov. 2011. CSG thanks Dr. J. Michael Gottfried for some helpful discussion on design aspects of Lab-APPES during a visit to Univ. Erlangen-Nürnberg on June 2009. We thank Mr. P. M. Suryavanshi for many practical discussions on some design aspects. VG Scienta, Sweden and Prevac, Poland is acknowledged for supplying Figures 2 and 3, respectively, and providing details of the same. We also acknowledge Prevac, Poland for fabricating the Lab-APPES system with many safety features. KR thank CSIR, New Delhi for senior research fellowship. Funding for Lab-APPES from CSIR, New Delhi is gratefully acknowledged. Partial financial support from CSIR under 12th FYP (CSC0404) for the presented work in the manuscript is acknowledged.
1. Siegbahn, K.; Allan, C. J. Electron Spectroscopy for Chemical Analysis (together with C.J. Allan), MTP Int. Rev. Science, 1973, Vol. 12, Analytical Chemistry, Part 1, Butterworths.
2. Libuda, J.; Freünd, H. -J. Molecular Beam Experiments on Model Catalysts. Surf. Sci. Rep. 2005, 57, 157-298.
3. (a) Velu, S.; Suzuki, K.; Vijayaraj, M.; Barman, S.; Gopinath, C. S. In Situ XPS Investigations of Cu1−xNixZnAl-mixed Metal Oxide Catalysts Used in the Oxidative Steam Reforming of Bio-ethanol. Appl. Catal. B – Environ. 2005, 55, 287-299. (b) Velu, S.; Suzuki, K.; Gopinath, C. S. Photoemission and in Situ XRD Investigations on CuCoZnAl-mixed Metal Oxide Catalysts for the Oxidative Steam Reforming of Methanol. J. Phys. Chem. B. 2002, 106, 12737-12746. (c) Mathew, T.; Vijayaraj, M.; Pai, S.; Tope, B. B.; Hegde, S. G.; Rao, B. S.; Gopinath, C. S. A Mechanistic Approach to Phenol Methylation on Cu1-xCoxFe2O4: FTIR Study. J. Catal. 2004, 227, 175-185.
4. (a) Thirunavukkarasu, K., Gopinath, C. S. Fabrication of an Effusive Molecular Beam Instrument for Surface Reaction Kinetics – CO Oxidation and NO Reduction on Pd(111) Surfaces. Catal. Lett. 2007, 119, 50-58. (b) Thirunavukkarasu, K., Thirumoorthy, K.; Libuda, J.; Gopinath, C. S. Molecular Beam Study of NO + CO Reaction on Pd(111) Surfaces. J. Phys. Chem. B. 2005, 109, 13272-13282.
5. Hünger, M.; Weitkamp, J. In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis. Angew. Chem. Int. Ed. 2001, 40, 2954-2971.
6. Lee, A. F.; Vinod, C. P.; Wilson, K. Surface X-ray Studies of Catalytic Clean Technologies. Chem. Commun. 2010, 46, 3827–3842.
7. (a) Soeren, P; Jiang, P.; Borondics, F.; Wendt, S.; Liu, Z.; Bluhm, H.; Besenbacher, F.; Salmeron, M. Charge State of Gold Nanoparticles Supported on Titania under Oxygen Pressure. Angew. Chem. Int. Ed. 2011, 50, 2266 –2269. (b) Miller, D. J.; Öberg, H.; Kaya, S.; Casalongue, H. S.; Friebel, D.; Anniyev, T.; Ogasawara, H.; Bluhm, H.; Pettersson, L. G. M.; Nilsson, A. Oxidation of Pt(111) under Near-Ambient Conditions. Phys. Rev. Lett. 2011, 107, 195502. (c) Renzas, J. R.; Huang, W.; Zhang, Y.; Grass, M. E.; Hoang, D. T.; Alayoglu, S.; Butcher, D. R.; Tao, F.; Liu, Z.; Somorjai, G. A. Rh1−xPdx Nanoparticle Composition Dependence in CO Oxidation by Oxygen: Catalytic Activity Enhancement in Bimetallic Systems. Phys. Chem. Chem. Phys. 2011, 13, 2556–2562 (d) Hueso, J. L.; Martínez-Martínez, D.; Caballero, A.; González-Elipe, A. R. ; Mun, B. S.; Salmeron, M. Near-ambient X-ray Photoemission Spectroscopy and Kinetic Approach to the Mechanism of Carbon Monoxide Oxidation over Lanthanum Substituted Cobaltites. Catal. Commun. 2009, 10, 1898–1902.
8. Joyner, R. W.; Roberts, M. W.; Yates, K. A “High-pressure” Electron Spectrometer for Surface Studies. Surf. Sci. 1979, 87, 501-509.
9. Salmeron, M.; Schlögl, R. Ambient Pressure Photoelectron Spectroscopy: A New Tool for Surface Science and Nanotechnology. Surf. Sci. Rep. 2008, 63, 169-199; and references therein.
10. Pantförder, J.; Pöllmann, S.; Zhu, J. F.; Borgmann, D.; Denecke, R.; Steinrück, H. -P. New Setup for in Situ X-ray Photoelectron Spectroscopy from Ultrahigh Vacuum to 1 mbar. Rev. Sci. Instrum. 2005, 76, 014102.
11. Bukhtiyarov, V. I.; Kaichev, V. V.; Podgornov, E. A.; Prosvirin, I. P. XPS, UPS, TPD and TPR Studies of Oxygen Species Active in Silver-catalysed Ethylene Epoxidation. Catal. Lett. 1999, 57, 233-239.
12. Jürgensen, A.; Esser, N.; Hergenförder, R. Near Ambient Pressure XPS with a Conventional X-ray Source. Surf. Interface Anal. 2012, 44, 1100–1103.
13. Tao, F. Design of an In-house Ambient Pressure AP-XPS Using a Bench-Top X-ray Source and the Surface chemistry of Ceria under Reaction Conditions. Chem. Commun. 2012, 48, 3812–3814.
14. Mangolini, F.; Ahlund, J.; Wabiszewski, G. E.; Adiga, V. P.; Egberts, P.; Streller, F.; Backlund, K.; Karlsson, P. G.; Wannberg, B.; Carpick, R. W. Angle-Resolved Environmental X-ray Photoelectron Spectroscopy: A New Laboratory Setup for Photoemission Studies at Pressures up to 0.4 Torr. Rev. Sci. Instrum. 2012, 83, 093112.
15. Kolmakov, A.; Dikin, D. A.; Cote, L. J.; Huang, J.; Abyaneh, M. K.; Amati, M.; Gregoratti, L.; Günther, S.; Kiskinova, M. Graphene Oxide Windows for in Situ Environmental Cell Photoelectron Spectroscopy. Nature Nanotech. 2011, 6, 651-657.
16. Tao, F.; Dag, S.; Wang, L.W.; Liu, Z.; Butcher, D. R.; Bluhm, H.; Salmeron, M.; Somorjai, G. A. Break-Up of Stepped Platinum Catalyst Surfaces by High CO Coverage. Science 2010, 327, 850-856.
17. (a) Maity, N.; Rajamohanan, P. R.; Ganapathy, S.; Gopinath, C. S.; Bhaduri, S.; Lahiri, G. K. MCM–41 Supported Organometallic Derived Nanopalladium as a Selective Hydrogenation Catalyst. J. Phys. Chem. C. 2008, 112, 9428-9433. (b) Murali, C.; Shashidhar, M. S.; Gopinath, C. S. Hydroxyl Group De-protection Reactions with Pd(OH)2/C: A Convenient Alternative to Hydrogenolysis of Benzyl Ethers and Acid Hydrolysis of Ketals. Tetrahedron 2007, 63, 4149-4155.
18. (a) Ekerdt, J. G.; Sun, Y. M.; Szabo, A.; Szulczewski, G. J.; White, J. M. Role of Surface Chemistry in Semiconductor Thin Film Processing. Chem. Rev. 1996, 96, 1499–1518. (b) Sinfelt, J. H. Role of Surface Science in Catalysis. Surf. Sci. 2002, 500, 923–946. (c) Zaera, F.; Gopinath, C. S. Surface Intermediates during the Catalytic Reduction of NO on Rh Catalysts: A Kinetic Inference. J. Mol. Catal. A 2001, 167, 23-31.
19. (a) D’Orazio, P. Biosensors in Clinical Chemistry. Clin. Chim. Acta. 2003, 334, 41–69. (b) Bustos, V.; Gopinath, C. S., Unac, R.; Zaera, F.; Zgrablich, G. Evidence for the Formation of Nitrogen Islands on Rhodium Surfaces. J. Chem. Phys., 2001, 114, 10927-10931.
20. (a) Soares, J. M. C.; Morrall, P.; Crossley, A.; Harris, P.; Bowker, M. Catalytic and Noncatalytic CO oxidation on Au/TiO2 Catalysts. J. Catal. 2003, 219, 17-24. (b) Bowker, M.; Bennett, R. A.; Poulstone, S.; Stone, P. Insights into Surface Reactivity: Formic Acid Oxidation on Cu(110) Studied using STM and a Molecular Beam Reactor. Catal. Lett. 1998, 56, 77-83. (c) Waugh, K.C. Methanol Synthesis. Catal. Today 1992, 15, 51-75. (d) Bowker, M. Active Sites in Methanol Oxidation on Cu(110) Determined by STM and Molecular Beam Measurements.
Topics in Catal. 1996, 3, 461-468. (e) Klust, A.; Madix, R. J. Partial Oxidation of Higher Olefins on Ag(111): Conversion of Styrene to Styrene Oxide, Benzene, and Benzoic Acid. Surf. Sci. 2006, 600, 5025-5040. (f) Ruggiero, C.; Hollins, P. Adsorption of Carbon Monoxide on the Gold(332) Surface. J. Chem. Soc. Farad. Trans. 1996, 92, 4829-4834. (g) Thirunavukkarasu, K., Thirumoorthy, K.; Libuda, J.; Gopinath, C. S. Isothermal kinetic study of nitric oxide adsorption and decomposition on Pd(111) surfaces: A molecular beam study. J. Phys. Chem. B. 2005, 109, 13283-13290. (h) Mathew, T.; Sivaranjani, K.; Gnanakumar, E. S.; Yamada, Y.; Kobayashi, T.; Gopinath, C. S. γ-Al2−xMxO3±y (M = Ti4+ Through Ga3+): Potential Pseudo-3D Mesoporous Materials with Tunable Acidity and Electronic Structure. J. Mater. Chem. 2012, 22, 13484-13493.
21. Evans, S.; Evans, E. L.; Parry, D. E.; Tricker, M. J.; Walters, M. J.; Thomas, J. M. Ultra-violet and X-ray Photoelectron Spectroscopy Studies of Oxygen Chemisorption on Copper, Silver and Gold. Faraday Discuss. Chem. Soc. 1974, 58, 97-105.
22. (a) Rocha, T. C. R.; Oestereich, A.; Demidov, D. V.; Havecker, M.; Zafeiratos, S.; Weinberg, G.; Bukhtiyarov, V. I.; Knop-Gericke, A.; Schlögl, R. The Silver-Oxygen System in Catalysis: New Insights by Near Ambient Pressure X-ray Photoelectron Spectroscopy. Phys. Chem. Chem. Phys. 2012, 14, 4554–4564. (b) Nagarajan, S.; Gopinath, C. S. Diffusion of Chemisorbed Oxygen into Pd Sub-surfaces and its Influence in Catalysis. J. Indian Inst. Sci. 2010, 90, 245-260.
23. (a) Toyoshima, R.; Yoshida, M.; Monya, Y.; Kousa, Y.; Suzuki, K.; Abe, H.; Mun, B. S.; Mase, K.; Amemiya, K.; Kondoh, H. In Situ Ambient Pressure XPS Study of CO Oxidation Reaction on Pd(111) Surfaces. J. Phys. Chem. C 2012, 116, 18691−18697. (b) Nagarajan, S.; Thirunavukkarasu, K.; Gopinath, C. S., J. Phys. Chem. C 2009, 113, 7385-7397.
24. Canning,N. D. S.; Outka, D.;Madix, R. J. The Adsorption of Oxygen on Gold. Surf. Sci. 1984, 141, 240–254.
25. Vinod, C. P.; Niemantsverdriet, J. W.; Nieuwenhuys, B. E. Interaction of Small Molecules with Au(310): Decomposition of NO. Appl. Catal. A: General 2005, 291, 93–97.
26. (a) Haruta, M. Catalysis of Gold Nanoparticles Deposited on Metal Oxides. Cattech 2002, 6, 102–115. (b) Hashmi, A. S. K.; Hutchings, G. J. Gold Catalysis. Angew. Chem. Int. Ed. 2006,
45, 7896-7936.
27. Sunil Sekhar, A. C.; Sivaranjani, K.; Gopinath, C. S.; Vinod, C. P. A Simple One Pot Synthesis of Nano Gold–Mesoporous Silica and its Oxidation Catalysis. Catal. Today 2012, 198, 92-97.
28. Jiang, P.; Porsgaard, S.; Borondics, F.;Köber, M.; Caballero, A.; Bluhm, H.; Besenbacher, F.; Salmeron, M. Room-temperature Reaction of Oxygen with Gold: an in Situ Ambient-pressure X-ray Photoelectron Spectroscopy Investigation. J. Am. Chem. Soc. 2010, 132, 2858–2859.
29. (a) Koslowski, B.; Boyen, H. -G.; Wilderotter, C.; Kästle, G.; Ziemann, P.; Wahrenberg, R.; Oelhafen, P. Oxidation of Preferentially (111)-oriented Au Films in an Oxygen Plasma Investigated by Scanning Tunneling Microscopy and Photoelectron Spectroscopy. Surf. Sci., 2001, 475, 1–10. (b) Gopinath, C. S.; Muthukumaran, R.; Welling, L. L.; Bennett, M. A.;
Manoharan, P. T. XPS Studies of Dinuclear Gold Complexes. Chem. Phys. Lett. 1998, 296, 566-570.
30. Krozer, A.; Rodahl, M. X-ray Photoemission Spectroscopy Study of UV/ozone Oxidation of Au under Ultrahigh Vacuum Conditions. J. Vac. Sci. Technol. 1997, 15, 1704-1709.
31. Pireaux, J. J.; Liehr, M.; Thiry, P. A.; Delrue, J.P.; Caudano, R. Electron Spectroscopic Characterization of Oxygen Adsorption on Gold Surfaces: II. Production of Gold Oxide in Oxygen DC Reactive Sputtering. Surf. Sci. 1984, 141, 221-232.
32. Aita, C.R.; Tran, N. C. Core Level and Valence Band X‐ray Photoelectron Spectroscopy of Gold Oxide. J. Vac. Sci. Technol. A 1991, 9, 1498-1506.
33. Bao, X.; Muhler, M.; Schedel-Niedrig, T.; Schlögl, R. Interaction of Oxygen with Silver at High Temperature and Atmospheric Pressure:A Spectroscopic and Structural Analysis of a Strongly Bound Surface Species. Phys. Rev. B 1996, 54, 2249-2262.
34. Schedel-Niedrig, T.; Schlögl, R.; Bao, X.; Muhler, M. Surface-Embedded Oxygen: Electronic Structure of Ag(111) and Cu(poly) Oxidised at Atmospheric Pressure. Ber. Bunsen Ges. Phys. Chem. 1997, 101, 994−1006.
35. Tanuma, S.; Powell, C. J.; Penn, D. R. Calculations of Electron Inelastic Mean Free Paths (IMFPs) IV. Evaluation of Calculated IMFPs and of the Predictive IMFP Formula TPP-2 for Electron Energies between 50 and 2000 eV. Surf. Interface Anal. 1993, 20, 77-89
36. (a) Vijayaraj, M.; Gopinath, C. S. On the “Active Spacer and Stabilizer” Role of Zn in Cu1-xZnxFe2O4 Towards Selective N-methylaniline from Aniline: XPS and Catalysis Study. J. Catal., 2006, 241, 83-95. (b) Mathew, T.; Shiju, N. R.; Sreekumar, K.; Rao, B. S.; Gopinath, C. S. Cu-Co Synergism in Cu1-xCoxFe2O4– Catalysis and XPS Aspects. J. Catal., 2002, 210, 405-417.
37. (a) Gopinath, C.S. X-ray Photoelectron Spectrocopic Study of Cu3+ in NaK2CuF6. J. Chem. Soc. Faraday Trans., 1996, 92, 3605-3610. b) Mathew, T.; Rao, B. S.; Gopinath, C. S. Tertiary Butylation of Phenol on Cu1-xCoxFe2O4: Catalysis and Structure-Activity correlation, J. Catal. 2004, 222, 107-116. (c) Mathew, T.; Shylesh, S.; Devassy, B. M.; Satyanarayana, C. V. V.; Rao, B.S., Gopinath, C. S. Selective Production of Orthoalkyl Phenols on Cu0.5Co0.5Fe2O4: A Study on Catalysis and Characterization Aspects. Appl. Catal. A - General 2004, 273, 35-45.
38. (a) Ghijsen, J.; Tjeng, L. H.; Eskes, H.; Sawatzky, G. A. ; Johnson, R. L. Resonant Photoemission Study of the Electronic Structure of CuO and Cu2O. Phys. Rev. B 1990, 42, 2268-2274. (b) Ghijsen, J.; Tjeng, L. H.; van Elp, J.; Eskes, H.; Westerink, J.; Sawatzky, G. A.; Czyzyk, M. T. Electronic Structure of Cu2O and CuO. Phys. Rev. B 1988, 38, 11322-11329.
39. Poulston, S.; Parlett, P. M.; Stone, P.; Bowker, M. Surface Oxidation and Reduction of CuO and Cu2O Studied Using XPS and XAES. Surf. Inter. Anal. 1996, 24, 811-820.
40. (a) Rao, C. N. R.; Sarma, D. D.; Hegde, M. S. A Novel Approach to the Study of Surface Oxidation States and Oxidation of Transition Metals by Auger Electron Spectroscopy. Proc. Roy. Soc. Lond A 1980, 370, 269-280. (b) van Wijk, R.; GÖrts, P. C.; Mens, A. J. M.; Gijzeman, O. L. J.; Habraken, F. H. P. M.; Geus, J. W. XPS/NRA Investigations of Particle Size Effects During the Oxidation of Cu Particles Supported on Oxidised Si (100). Appl. Surf. Sci. 1995, 90, 261-269. (c) Tobin, J. P.; Hirschwald, W.; Cunningham, J. XPS and XAES Studies of Transient
Enhancement of Cu1 at CuO Surfaces During Vacuum Outgassing. Appl. Surf. Sci. 1983, 16, 441-452.
41. Bluhm, H.; Hävecker, M.; Knop-Gericke, A.; Kleimenov, E.; Schlögl, R.; Teschner, D.; Bukhtiyarov, V. I.; Ogletree, D. F.; Salmeron, M. Methanol Oxidation on a Copper Catalyst Investigated Using in Situ X-ray Photoelectron Spectroscopy. J. Phys. Chem. B 2004, 108, 14340-14347.
42. Chak-tong, A.; Breza, J.; Roberts, M. W. Hydroxylation and Dehydroxylation at Cu(III) Surfaces. Chem. Phys. Lett. 1979, 66, 340.
43. Bukhtiyarov, V. I.; Prosvirin, I. P.; Tikhomirov, E. P.; Kaichev, V. V.; Sorokin, A. M.; Evstigneev, V. V. In Situ Study of Selective Oxidation of Methanol to Formaldehyde over Copper. React. Kinet. Catal. Let. 2003, 79, 181-188.
44. Yeh, J. J.; Lindau, I. Atomic Subshell Photoionization Cross Sections and Asymmetry Parameters: 1 ⩽ Z ⩽ 103. Atomic Data Nucl. Data Tables 1985, 32, 1-155.
45. (a) Reddy, A. S.; Gopinath, C. S.; Chilukuri, S. V. Selective ortho-Methylation of Phenol with Methanol over Copper Manganese Mixed Oxide Spinel Catalysts. J. Catal., 2006, 243, 278-291; (b) Gopinath, C. S.; Subramanian, S.; Prabhu, P. S; Rao, M. S. R.; Subba Rao, G. V. Structure, Superconductivity and XPS Studies of the Bi2.1Sr1.93Ca0.97-xYxCu2O8+y System. Physica C 1993, 218,117-129. c) Velu, S.; Suzuki, K.; Gopinath, C. S.; Yoshida, H.; Hattori, T., XPS, XANES and EXAFS Investigations of CuO/ZnO/Al2O3/ZrO2 Mixed Oxide Catalysts. Phys. Chem. Chem. Phys., 2002, 4, 1990-1999.