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and Freund, H.-J. (2007) Phys. Rev. B, 75,
205443.
23 Schoiswohl, J., Sock, M., Chen, Q.,
Thornton, G., Kresse, G., Ramsey, M.G.,
Surnev, S., and Netzer, F.P. (2007)
Top. Catal., 46, 137.
24 Jensen, J.A., Rider, K.B., Chen, Y., and
Salmeron, M. (1999) J. Vac. Sci. Technol. B,
17, 1080.
25 Lægsgaard, E., Österlund, L., Thostrup,
P., Rasmussen, P.B., Stensgaard, I., and
Besenbacher, F. (2001) Rev. Sci. Instrum.,
72, 3537.
26 Kolmakov, A. and Goodman, D.W. (2003)
Rev. Sci. Instrum., 74, 2444.
27 R
€
oßler, M., Geng, P., and Winterlin, J.
(2005) Rev. Sci. Instrum., 76, 023705.
28 Hendriksen, B.L.M., Bobaru, S.C., and
Frenken, J.W.M. (2005) Top. Catal., 36, 43.
29 Rost, M.J., Crama, L., Schakel, P., van Tol,
E., van Velzen-Williams, G.B.E.M.,
Overgauw, C.F., ter Horst, H., Dekker, H.,
Okhuijsen, B., Seynen, M., Vijftigschild,
A., Han, P., Katan, A.J., Schoots, K.,
Schumm, R., van Loo, W., Oosterkamp,
T.H., and Frenken, J.W.M. (2005) Rev. Sci.
Instrum., 76, 053710.
30 Chambers, S. (2000) Surf. Sci. Rep., 48,
105 and references therein.
31 Guimond, S., Sturm, J.M., G
€
obke, D.,
Romanyshyn, Y., Naschitzki, M.,
Kuhlenbeck, H., and Freund, H.J. (2008)
J. Phys. Chem. C, 112, 12363.
32 Guimond, S., Sturm, J.M., G
€
obke, D.,
Romanyshyn, Y., Naschitzki, M.,
Kuhlenbeck, H., and Freund, H.J. (2008)
J. Phys. Chem. C, 112, 11835.
33 Matsumoto, T., Batzill, M., Hsieh, S., and
Koel, B.E. (2004) Surf. Sci., 572, 127.
34 Matsumoto, T., Batzill, M., Hsieh, S., and
Koel, B.E. (2004) Surf. Sci., 572, 141.
35
Niehus, H., Blum, R.P., and Ahlbehrendt,
D. (2001) Phys. Stat. Sol. (a), 187, 151.
36 Niehus, H., Blum, R.P., and Ahlbehrendt,
D. (2003) Surf. Rev. Lett., 10, 353.
37 Middeke, J., Blum, R.P., Hafemeister, M.,
and Niehus, H. (2005) Surf. Sci., 587, 219.
38 Tersoff, J. and Hamann, D.R. (1985) Phys.
Rev. Lett., 50, 805.
39 B
€
aumer, M., Freund, H.-J., and
Henry, C.R. (1998) Surf. Sci. Rep., 31, 235.
40 Franchy, R. (2000) Surf. Sci. Rep., 38, 195.
41 Jaeger, R.M., Kuhlenbeck, H., Freund,
H.-J., Wuttig, M., Hoffmann, W.,
Franchy, R., and Ibach, H. (1991) Surf.
Sci., 259, 235.
42 Doychak, J., Smialek, J.L., and
Mitchell, T.E. (1989) Metall. Trans., A20,
499.
43 Isern, H. and Castro, G.R. (1989) Surf.
Sci., 211/212, 865.
44 Libuda, J., Winkelmann, F., B
€
aumer, M.,
Freund, H.-J., Bertrams, Th., Nedder-
meyer, H., and M
€
uller, K. (1994) Surf. Sci.,
318, 61.
45 Kulawik, M., Nilius, N., Rust, H.-P., and
Freund, H.-J. (2003) Phys. Rev. Lett., 91,
256101.
46 Stierle, A., Renner, F., Streitel, R.,
Dosch, H., Drube, W., and Cowie, B.C.
(2004) Science, 303, 1652.
47 Kresse, G., Schmid, M., Napetschnig, E.,
Shishkin, M., K
€
ohler, L., and Varga, P.
(2005) Science, 308
, 1440.
48 Schmid, M., Shishkin, M., Kresse, G.,
Napetschnig, E., Varga, P., Kulawik, M.,
Nilius, N., Rust, H.-P., and Freund, H.-J.
(2006) Phys. Rev. Lett., 97, 046101.
49 Bardi, U., Atrei, A., and Rovida, G. (1990)
Surf. Sci., 239, L511.
50 Bardi, U., Atrei, A., and Rovida, G. (1992)
Surf. Sci., 286, 87.
51 Becker, C., Kandler, J., Raaf, H., Linke, R.,
Pelster, T., Tanemura, M., and Wandelt, K.
(1998) J. Vac. Sci. Technol., A16, 1000.
52 Rosenhahn, A., Schneider, J., Becker, C.,
and Wandelt,K. (2000)J. Vac. Sci. Technol.,
A18, 1923.
53 Degen, S., Krupski, A., Kralj, M.,
Langner, A., Becker, C., Sokolowski, M.,
and Wandelt, K. (2005) Surf. Sci., 576, L57.
54 Gritschneder, S., Becker, C., Wandelt, K.,
and Reichling, M. (2007) J. Am. Chem.
Soc., 129, 4925.
55 Schmid, M., Kresse, G., Buchsbaum, A.,
Napetschnig, E., Gritschneder, S.,
Reichling, M., and Varga, P. (2007) Phys.
Rev. Lett., 99, 196104.
184
j
6 STM Imaging of Oxide Nanolayer Model Systems
56 Becker, C., Rosenhahn, A., Wiltner, A.,
von Bergmann, K., Schneider, J.,
Pervan, P., Milun, M., Kralj, M., and
Wandelt, K. (2002) New J. Phys., 4, 75.
57 Linsebigler, A.L., Lu, G., and Jates, J.T., Jr.
(1995) Chem. Rev., 95, 735.
58 Fox, M.A. and Dulay, M.T. (1993) Chem.
Rev., 93, 341.
59 Kamat, P.V. (1993) Chem. Rev., 93, 267.
60 Bosh, H. and Janssen, F. (1988) Catal.
Today, 2, 369.
61 Forzatti, P. (2000) Catal. Today, 62, 51.
62 Hoffman, M.R., Martin, S.T., Choi, W.,
and Wahneman, D.W. (1995) Chem. Rev.,
95, 69.
63 Maldoti, A., Molnari, A., and Amareni, R.
(2002) Chem. Rev., 102, 3811.
64 Kalyanasendavan, K. and Gratzel, M.
(1999) Optoelectronic Properties of
Inorganic Compounds (eds D.M. Round-
hill and J.P. Fackler), Plenum Press,
New York, pp. 169–194.
65 Sheveglieri, G. (ed.) (1992) Gas Sensors,
Kluwer, Dordrecht.
66 Johnson, R.W., Thieles, E.S., and
French, R.H. (1997) Tappi J., 80, 233.
67 Phillips, L.G. and Barbeno, D.M. (1997)
J. Dairy Sci., 80, 2726.
68 Selhofer, H. and M
€
uller, R. (1999) Thin
Solid Films, 351, 180.
69 Fujishima, A., Rao, T.N., and Tryk, D.A.
(2000) J. Photochem. Photobiol. C:
Photochem. Rev., 1,1.
70
Diebold, U. (2 003) Surf.Sci.Rep., 48,
53.
71 Boffa, A.B., Galloway, H.C., Jacobs, P.W.,
Ben
ıtez, J.J., Batteas, J.D., Salmeron, M.,
Bell, A.T., and Somorjai, G.A. (1995) Surf.
Sci., 326, 80.
72 Sedona, F., Rizzi, G.A., Agnoli, S.,
Llabr
es i Xamena, F.X., Papageorgiou, A.,
Ostermann, D., Sambi, M., Finetti, P.,
Schierbaum, K., and Granozzi, G. (2005)
J. Phys. Chem. B, 109, 24411.
73 Sedona, F., Agnoli, S., and Granozzi, G.
(2006) J. Phys. Chem. B, 110, 15359.
74 Barbaro, G., Sedona, F., Fortunelli, A.,
and Granozzi, G. (2007) J. Phys. Chem. C,
111, 6095.
75 Sedona, F., Granozzi, G., Barbaro, G., and
Fortunelli, A. (2008) Phys. Rev. B, 77,
115417.
76 Orzali, T., Casarin, M., Granozzi, G.,
Sambi, M., and Cittadini, A. (2006)
Phys. Rev. Lett., 97, 156101.
77 Herman, G.S., Gallagher, M.C., Joyce,
S.A., and Peden, C.H.F. (1996) J. Vac. Sci.
Technol. B, 14, 1126.
78 Oh, W.S., Xu, C., Kim, D.Y., and
Goodman, D.W. (1997) J. Vac. Sci. Technol.
A, 15, 1710.
79 Guo, Q., Oh, W.S., and Goodman, D.W.
(1999) Surf. Sci., 437, 49.
80 Lai, X., Guo, Q., Min, B.K., and
Goodman, D.W. (2001) Surf. Sci., 487,1.
81 Chen, M.S., Wallace, W.T., Kumar, D.,
Yan, Z., Gath, K.K., Cai, Y., Kuroda, Y.,
and Goodman, D.W. (2005) Surf. Sci., 581,
L115.
82 McCavish, N.D. and Bennett, R.A. (2003)
Surf. Sci., 546, 47.
83 Ashworth, T.V. and Thornton, G. (2001)
Thin Solid Films, 400, 43.
84 Ashworth, T.V., Muryn, C.A., and
Thornton, G. (2005) Nanotechnology, 16,
3041.
85 Papageorgiou, A.C., Cabailh, G.,
Chen, Q., Resta, A., Lundgren, E.,
Andersen, J.N., and Thornton, G. (2007)
J. Phys. Chem. C, 111, 7704.
86 Papageorgiou, A.C., Pang, C.L., Chen, Q.,
and Thornton, G. (2007) ACS Nano,
1, 409.
87 M
€
annig, A., Zhao, Z., Rosenthal, D.,
Christmann, K., Hoster, H., Rauscher,H.,
and Behm, R.J. (2005) Surf. Sci., 576, 29.
88 Surnev, S., Vitali, L., Ramsey, M.G.,
Netzer, F.P., Kresse, G., and Hafner, J.
(2000) Phys. Rev. B, 61, 13945.
89 Surnev, S., Kresse, G., Ramsey, M.G.,
and Netzer, F.P. (2001) Phys. Rev. Lett.,
87, 086102.
90 Schoiswohl, J., Sock, M., Eck, S.,
Surnev, S., Ramsey, M.G., and
Netzer, F.P. (2004) Phys. Rev. B, 69,
155403.
91 Ranke, W., Ritter, M., and Weiss, W.
(1999) Phys. Rev. B, 60, 1527.
References
j
185
92 Stone, P., Bennett, R.A., and Bowker, M.
(1999) New J. Phys., 1,8.
93 Bennett, R.A., Stone, P., Price, N., and
Bowker, M. (1999) Phys. Rev. Lett., 82,
3831.
94 Takakusagi, S., Fukui, K., Nariyuki, F.,
and Iwasawa, Y. (2003) Surf. Sci., 523, L41.
95 Bursil, L.A. and Hyde, B.G. (1972)
Prog. Solid State Chem., 7, 177.
96 Hermann, K. and Witko, M. (2001)
Chapter 4, in The Chemical Physics of
Solid Surfaces: Oxide Surfaces, vol. 9
(ed. D.P. Woodruff), Elsevier Science,
p. 136 and references therein.
97 Surnev, S., Ramsey, M.G., and Netzer,
F.P. (2003) Prog. Surf. Sci., 73, 117.
98 Kung, H.H. (1989) Transition Metal
Oxides, Surface Chemistry and Catalysis,
Elsevier, New York.
99 Weckhuysen, B.M. and Keller, D.E. (2003)
Catal. Today, 78, 25.
100 Stefanovich, G., Pergament, A., and
Stefanovich, D. (2000) J. Phys.: Condens.
Matter, 12, 8837.
101 Schoiswohl, J., Surnev, S., Sock, M.,
Ramsey, M.G., Kresse, G., and Netzer,
F.P. (2004) Angew. Chem. Int. Ed., 43,
5546.
102 Schoiswohl, J., Sock, M., Surnev, S.,
Ramsey, M.G., Netzer, F.P., Kresse, G.,
and Andersen, J.N. (2004) Surf. Sci.,
555, 101.
103 Kresse, G., Surnev, S., Schoiswohl, J., and
Netzer, F.P. (2004) Surf. Sci., 555, 118.
104 Schoiswohl, J., Surnev, S., and Netzer,
F.P. (2005) Top. Catal., 36, 91.
105 Schoiswohl, S., Eck, S., Ramsey, M.G.,
Andersen, J.N., Surnev, S., and Netzer,
F.P. (2005) Surf. Sci., 580, 122.
106 Weiss, W. and Ranke, W. (2002) Prog. Surf.
Sci., 70,1.
107 Ritter, M., Ranke, W., and Weiss, W.
(1998) Phys. Rev., B57, 7240.
108 Weiss, W., Barbieri, A., Van Hove, M.A.,
and Somorjai, G.A. (1993) Phys. Rev. Lett.,
71, 1848.
109 Barbieri, A., Weiss, W., Van Hove, M.A.,
and Somorjai, G.A. (1994) Surf. Sci.,
302, 259.
110 Galloway, H.C., Benitez, J.J., and
Salmeron, M. (1993) Surf. Sci., 298, 127;
(1994) J. Vac. Sci. Technol., A12, 2302.
111 Galloway, H.C., Sautet, P., and Salmeron,
M. (1996) Phys. Rev., B54, R11145.
112 Kim, Y.J., Westphal, C., Ynzunza, R.X.,
Galloway, H.C., Salmeron, M., Van Hove,
M.A., and Fadley, C.S. (1997) Phys. Rev.,
B55, R13448.
113 Ritter, M., Ranke, W., and Weiss, W.
(1998) Phys. Rev., B57, 7240.
114 Massalski, T.B., Murray, J.L., Bennett,
L.H., and Baker, H. (1986) Binary Alloy
Phase Diagrams, American Society for
Metals, Metals Park, OH, p. 1807.
115 Tasker, P.W. (1979) J. Phys., C12, 4977.
116 Choudhary, V.R., Rajput, A.M., and
Mamman, A.S. (1998) J. Catal., 178, 576.
117 Takeguchi, T., Furukawa, S., and
Inove, M. (2001) J. Catal., 202, 14.
118 Zaera, F., Gleason, N.R., Klingenberg, B.,
and Ali, A.H. (1999) J. Mol. Catal. A:
Chem., 146, 1323.
119 Christoskova, S.G., Stoyanova, M.,
Georgieva, M., and Mehandzhiev, D.
(2002) Appl. Catal. A
, 173, 95101.
120 Ruckenstein, E. and Hu, Y.H. (2002)
Appl. Catal. A, 183, 85.
121 Christoskova, S.G., Danova, N.,
Georgieva, M., Argirov, O.K., and
Mehandzhiev, D. (1995) Appl. Catal. A,
128, 219.
122 Duma, V., Poppa, K.E., Kung, M.C.,
Zhou, H., Nguyen, S., Ohyamac, S.,
Kung, H.H., and Marshall, C.L. (2004)
Chem. Eng. J., 99, 227–236.
123 Kordesh, K. and Simadar, G. (1996) Fuel
Cells and Their Applications, Wiley-VCH
Verlag, Weinheim.
124 Escudero, M.J., Rodrigo, T., and
Daza, L. (2005) Catal. Today, 107 –108,
377–387.
125 Hotovy, I., Huran, J., and Siciliano, P.
(2004) Sens. Actuators B, 103, 300.
126 Canalini, C., Post, M., Buso, D.,
Guglielmi, M., and Martucci, A. (2005)
Sens. Actuators B, 108, 184–192.
127 Hotovy, I., Rehacek, V., and Siciliano, P.
(2002) Thin Solid Films, 418,9.
186
j
6 STM Imaging of Oxide Nanolayer Model Systems
128 Dirksen, J., Duval, K., and Ring, T.A.
(2001) Sens. Actuators B, 80, 106.
129 Shim, H.S., Ahn, H.J., Seong, T.Y., and
Park, K.W. (2005) Electrochem. Solid-State
Lett., 8, A277.
130 Fereira, F.F. and Fantini, M.C.A. (2004)
Solid State Ionics, 175, 517–520.
131 Kikatsu, N., Maurice, V., and Markus, P.
(1998) Surf. Sci., 411, 215.
132 B
€
aumer, M., Cappus, D., Kuhlenbeck, H.,
Freund, H.-J., Wilhelmi, G., Brodde, A.,
and Neddermeyer, H. (1991) Surf. Sci.,
253, 116.
133 Kikatsu,N.,Maurice,V.,Hinnen,C.,
and Markus, P . (199 8) Surf. S ci., 407,
36.
134 Hildebrandt, S., Hagendorf, Ch.,
Doege, T., Jeckstiess, Ch., Kulla, R., and
Neddermeyer, H. (2000) J. Vac. Sci.
Technol., A18, 1010.
135 Ventrice, C.A., Jr., Bertrams, Th.,
Hannemann, H., Brodde, A., and
Neddermeyer, H. (1994) Phys. Rev., B49,
5773.
136 Hannemann, H., Ventrice, C.A., Jr.,
Bertrams, Th., Brodde, A., and
Neddermeyer, H. (1994) Phys. Rev. Stat.
Sol. A, 146, 289.
137 Marre, K. and Neddermeyer, H. (1993)
Surf. Sci., 287–288, 995.
138 Bertrams, Th. and Neddermeyer, H.
(1996) J. Vac. Sci. Technol., B14, 1141.
139 Wollschl
€
ager,J., Erdoes, D., Goldbach, H.,
Hopken, R., and Schr
€
oder, K.M. (2001)
Thin Solid Films, 400,1.
140
Lamberti, C., Gropo, E., Prestipino, C.,
Cassasa, S., Ferrari, A.M., and Pisani, C.
(2003) Phys. Rev. Lett., 91, 46101.
141 Caffio, M., Rovida, G., Atrei, A.,
Giovanardi, C., di Bona, A., and Valeri, S.
(2003) Surf. Sci., 531, 368.
142 Caffio, M., Cortigiani, B., Rovida, G.,
Atrei, A., and Giovanardi, C. (2004)
J. Phys. Chem. B, 108, 9919.
143 May, F., Tisher, M., Arvantis, D., Russo,
M., Hunter Dunn, J., Henneken, H.,
Wende, H., Clauvistr, R., Mårtensson, N.,
and Baberschke, K. (1996) Phys. Rev.,
B53, 1076.
144 Barbier, A., Stanescu, S., Boeglin, C., and
Deville, J.-P. (2003) Phys. Rev. B, 68,
245418.
145 Stanescu, S., Boeglin, C., Barbier, A., and
Deville, J.-P. (2004) Surf. Sci., 549, 172.
146 Agnoli, S., Orzali, T., Sambi, M.,
Granozzi, G., Schoiswohl, J., Surnev, S.,
and Netzer, F.P. (2005) J. Electron
Spectrosc. Relat. Phenom., 144–147, 465.
147 Agnoli, S., Sambi, M., Granozzi, G.,
Atrei, A., Caffio, M., and Rovida, G.
(2005) Surf. Sci., 576,1.
148 Schoiswohl, J., Agnoli, S., Xu, B.,
Surnev, S., Sambi, M., Ramsey, M.G.,
Granozzi, G., and Netzer, F.P. (2005)
Surf. Sci., 599,1.
149 Agnoli, S., Sambi, M., Granozzi, G.,
Schoiswohl, J., Surnev, S., Netzer, F.P.,
Ferraro, M., Ferrari, A.M., and Pisani, C.
(2005) J. Phys. Chem., B108, 17197.
150 Schoiswohl, J., Zheng, W., Surnev, S.,
Ramsey, M.G., Granozzi, G., Agnoli, S.,
and Netzer, F.P. (2006) Surf. Sci., 600,
1099.
151 Wolf, D. (1992) Phys. Rev. Lett., 68, 3315.
152
Barbier, A., Mocuta, C., Kuhlenbeck, H.,
Peters, K.F., Richter, B., and Renaud, G.
(2000) Phys. Rev. Lett., 84, 2897.
153 Schoiswohl, J., Mittendorfer, F., Surnev,
S., Ramsey, M.G., Andersen, J.N., and
Netzer, F.P. (2006) Phys. Rev. Lett., 97,
126102.
154 Parteder, G., Allegretti, F., Wagner, M.,
Ramsey, M.G.,Surnev,S., and Netzer, F.P.
(2008) J. Phys. Chem. C, 112, 19272.
155 Trovarelli,A. (ed.) (2002) Catalysis by Ceria
and Related Materials, Imperial College
Press, London.
156 Fukui, K., Takakusagi, S., Tero, R.,
Aizawa, M., Namai, Y., and Iwasawa, Y.
(2003) Phys. Chem. Chem. Phys., 5,1.
157 Conesa, J.C. (1995) Surf. Sci., 339, 337.
158 N
€
orenberg, H. and Briggs, G.A.D. (1997)
Phys. Rev. Lett., 79, 4222.
159 Esch, F., Fabris, S., Zhou, L., Montini, T.,
Africh, C., Fornasiero, P., Comelli, G.,
and Rosei, R. (2005) Science, 309, 752.
160 Fukui, K., Namai, Y., and Iwasawa, Y.
(2002) Appl. Surf. Sci., 188, 252.
References
j
187
161 Namai, Y., Fukui, K., and Iwasawa, Y.
(2003) J. Phys. Chem., B107, 11666.
162 Gritschneder, S., Namai, Y., Iwasawa, Y.,
and Reichling, M. (2005) Nanotechnology,
16, S41.
163 Mullins, D.R., Radulovic, P.V., and
Overbury, S.H. (1999) Surf. Sci., 429, 186.
164 Lu, J.-L., Gao,H.-J., Shaikhutdinov,S., and
Freund, H.-J. (2006) Surf. Sci., 600, 5004.
165 Schierbaum, K.-D. (1998) Surf. Sci.,
399, 29.
166 Berner, U. and Schierbaum, K. (2001)
Thin Solid Films, 400, 46.
167 Berner, U. and Schierbaum, K.-D. (2002)
Phys. Rev., B65, 235404.
168 Eck, S., Castellarin-Cudia, C., Surnev, S.,
Ramsey, M.G., and Netzer, F.P. (2002)
Surf. Sci., 520, 173.
169 Castellarin-Cudia, C., Surnev, S.,
Schneider, G., Podloucky, R., Ramsey,
M.G., and Netzer, F.P. (2004) Surf. Sci.,
554, L120.
170 Hla, S.-W., Bartels, L., Meyer, G., and
Rieder, K.H. (2000) Phys. Rev. Lett., 85,
2777.
171 Chen, P. and Somorjai, G.A (2002) In situ
catalysis and surface science methods,
In-Situ Spectroscopy in Heterogeneous
Catalysis (ed. J.F. Haw), Wiley-VCH
Verlag, Weinheim, pp. 15–52.
188
j
6 STM Imaging of Oxide Nanolayer Model Systems
7
Surface Mobility of Atoms and Molecules Studied with
High-Pressure Scanning Tunneling Microscopy
Gabor A. Somorjai, Feng Tao, and Derek Butcher
7.1
Introduction
Atomic and molecular studies of solid surfaces have been an intensive research area
over the past few decades. Most of these investigations were carried out in vacuum to
take advantage of electron, ion, and molecular beam scattering techniques that
provided surface sensitivity because of their high scattering cross sections. However,
most surface phenomena occur at solid–high-pressure gas and solid–liquid inter-
faces that we call buried interfaces, including heterogeneous catalysis, electro-
chemistry, and corrosion, to mention a few. The lack of techniques for studies of
buried interfaces was commonly called the pressure gap in surface science. There
has been a great deal of effort in our laboratory and elsewhere to develop surface
techniques that provide molecular information at buried interfaces. Our laboratory
has focused on developing three of these techniques: high-pressure scanning
tunneling microscopy (HPSTM), sum frequency generation (SFG) vibrational
spectroscopy, and ambient pressure X-ray photoelectric spectroscopy (APXPS). This
paper reviews the development of the HPSTM technique and our research results,
including the determination of surface mobility, surface structure on the atomic and
molecular scales, and reaction kinetics.
7.2
Characterization of Surface Mobility of Molecules and Atoms
Since the most active catalytic sites are usually steps, kinks, and surface defects,
atomically resolved structural information including atomic distribution and surface
structure at low pressure, possible surface restructuring, and the mobility of
adsorbate molecules and of the atoms of the catalyst surface at high temperature
and high pressure is crucial to understanding catalytic mechanisms on transition
metalsurfaces.Theimportanceofstudyingthestructuralevolutionofbothadsorbates
j
189
and catalyst surfaces at high pressure has driven the development of new surface
analytical techniques to determine surface structure and mobility of molecules
and atoms in the harsh conditions of industrial catalysis. Scanning tunneling
microscopy (STM) has the capability to examine molecules and atoms of adsorbate
and catalyst surface to address several crucial issues in heterogeneous catalysis,
including the rearrangement of surface atoms, restructuring of the catalyst surface,
and mass transfer.
Since the advent of STM in the 1980s [1], it has been one of the dominant tools to
study catalytic reactions with a vacuum surface science approach. This is because it
has the unique ability to investigate adsorption and surface structure with atomic
resolution and in some cases the electronic structure as well. This technique can be
applied to a pressure range from ultrahigh vacuum (UHV) to atmospheric or high
pressure since the tunneling process between the sample and tip occurs only in a very
close range of 5–50 Å. We first applied STM to study adsorbate and surface structure
at high pressure by filling reactant gases into an STM chamber and keeping them at
the high-pressure during STM scanning [2, 3]. After the first demonstration, it has
been applied to catalysis studies under a condition of a high pressure by a few
groups [4–11].
Recently, a new high-pressure high-temperature STM reactor/UHV system was
designed and homebuilt by our group in 2006 and 2007 [12]. In this design, the STM
body, sample, and tip are placed in a small high-pressure reactor (19 cm
3
) installed
in a UHV chamber. A sealable port on the wall of the reactor separates the high-
pressure environment of reactant gases in the reactor from the vacuum environment
of the UHV chamber and permits one to change sample and tip in UHV. The
combination of a sample transfer arm, wobble stick, and sample load-lock system
allows convenient transfer of samples and tips between the preparation chamber,
high-pressure reactor, and ambient environment. Experiments performed on inert
samples such as HOPG and reactive samples such as hex-Pt(1 0 0) both in vacuum
and in high-pressure conditions demonstrate the ability to perform in situ investiga-
tions of heterogeneous catalysis and surface chemistry at atomic resolution at a wide
pressure range from UHV to a pressure higher than that of atmosphere and a
temperature range from 300 to 700 K.
Other than the STM techniques for catalysis studies at high-pressure conditions
in our group, sum frequency generation vibrational spectroscopy and ambient
pressure X-ray photoelectron spectroscopy were also developed for catalysis studies
at high pressures. Early on we developed SFG vibrational spectroscopy to study
surface chemistry at high-pressure conditions with an emphasis on catalysis
[13, 14]. SFG is a surface-specific spectroscopy that can be used to measure
vibrational spectra under realistic catalytic conditions to allow us to identify the
reaction intermediates and products and therefore reveal the catalytic mechanism
[15–17]. Recently, a synchrotron-based ambient pressure XPS was developed
[18–20]. Since the XPS signal is measured through the collection of electrons
ejected from the sample, the instrument performance is highly susceptible to
scattering from gas molecules between the sample and the detector. The APXPS
was developed with the idea of bringing a sample close enough to a differentially
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pumped skimmer cone with a small aperture diameter of <0.3 mm to decrease the
electron collision rate. Taking advantage of the tunability of X-ray energy from a
synchrotron source, this technique is highly desirable for fundamental study of
catalysis in realistic conditions. It is particularly useful for in situ exploration of the
evolution of composition and restructuring, the catalyst surface, and the atomic
layers under the catalyst surface during catalysis.
7.3
High-Pressure STM Technique and Instrumentation
The application of STM to catalysis studies at high-pressure and high-temperature
condition has a great challenge in instrumentation. In general, a homebuilt STM
body combined into a high-pressure reactor or a flowing cell is needed; or at least a
major modification for a commercial STM system is required. To study catalysis at a
high pressure of reactant gases and a high-temperature catalyst surface, a specially
designed STM system should meet the following requirements: (1) a reactor is
needed for maintaining a high-pressure environment of reactant gases; (2) the
volume of the reactor or flowing cell should be as small as possible for several reasons
including maintaining a high concentration of reaction products, low gas consump-
tion, easily maintaining a constant pressure of reactants during an experiment,
quickly restoring a UHVenvironment in the reactor after each experiment; (3) in situ
heating of the sample must be available for studying catalysis at high temperature;
(4) it must be possible to isolate the high-pressure environment in a batch or flow
reactor from the vacuum environment of a UHV system to remain at high pressure
during the catalytic reaction; (5) the reactor must be accessible to the UHV system
for sample cleaning and tip treatment and analysis of the catalyst surface before and
after the catalytic reaction; (6) there must be a reliable gas introduction system; and
(7) the system must include product measurement.
A simple method to carry out high-pressure STM studies is to fill the STM
chamber with reactant gases while the reactant gases remain in the chamber.
However, this method has disadvantages such as a large volume of reactant
gases and limits in sample heating and reactant gas pressure. To overcome these
difficulties, we designed and homebuilt a novel high-pressure–high-temperature
STM reactor/UHV system [12]. The new system overcomes these limitations and
allows catalytic studies under a wide pressure range of reactant gases (10
10
–5000
Torr) and a wide temperature range (300–700 K). Figure7.1 shows photographs of the
STM reactor/UHV system and electronic control units. The system is schematically
presented in Figure 7.2.
The STM chamber is separated from the sample preparation chamber by an 8 in.
gate valve. A quadrupole mass spectrometer is installed in this chamber for
monitoring reactants and products during STM scanning. The STM chamber
contains the high-pressure reactor, a docking scaffold assembled on a custom-
designed sample manipulator, and a wobble stick for sample and STM tip transfer
between the transfer rod, high-pressure reactor, and docking disk.
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The high-pressure reactor (Figure 7.3) is a special vessel designed for assembling
the STM body and sample, and providing a high-pressure environment of reactant
gases. It houses a homebuilt STM body. It has a volume of approximately 19 cm
3
and
is placed inside the vacuum environment of a UHV chamber by a special docking
scaffold and mounting framework (2, 3, and 4 of Figure 7.2). It is vibrationally isolated
from the UHV chamber with three springs, offering the capability of imaging the
surface with atomic resolution. The reactor consists of a cell lid, cell neck, cell top
stage, and cell bottom stage. There are recesses on the cell neck, cell top stage, cell
bottom stage, and port of the reactor, which host Kalrez o-rings, forming gas-tight
seals. The sealing of the Kalrez o-rings allows pressurization of the reactor while
Figure 7.1 Pictures of the high-pressure high-temperature STM reactor/UHV system.
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maintaining a high vacuum in the surrounding chamber. All four sections of the
reactor are assembled together with four venting screws and sealed by these o-rings.
The reactor was plated with a layer of gold (5 mm thick) to avoid possible reactions
between the materials of the high-pressure reactor and reactant gases. The cell lid has
a set of holes precisely designed to glue a set of pin-socket contacts (set II in
Figure 7.3a) for assembling a set of male contacts (set I) from the docking scaffold
and another set of male contacts (set III in Figure 7.3c) for the wiring connections
from the shear piezoelectric plates and the scanning tube. These pin-socket contacts
provide convenient detachable wiring connections for the high-pressure reactor.
The contacts (set I) from the docking scaffold can be inserted into the vacuum side
of the interfacial contacts (set II) glued on the cell lid. Another set of contacts (set III)
is glued onto a set of holes on the STM body (Figure 7.3b) that have the exact same size
and arrangement as the holes on the cell lid (Figure 7.3a). This convenient pin-socket
wiring strategy (Figure 7.3c) makes dismantling and assembling the STM convenient
when maintenance is required on the high-pressure reactor and STM body.
The STM body (Figure 7.3b) is the key component of the high-pressure reactor.
It includes a coarse approach system, a scanning tube, a receiver for the tip holder,
Figure 7.2 Schematic diagram of the high-
pressure high-temperature STM reactor/UHV
system. (1) View window, (2) mounting
framework, (3) docking scaffold, (4) docking
disk, (5) high-pressure reactor (STM body
housed within), (6) bayonet seal, (7) guide rod
of docking scaffold, (8) sample/tip load-lock
system, (9) transfer rod, (10) gate valve,
(11) four-finger sample stage, and
(12) sputtering ion gun.
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