Cao Z. (Ed.) Thin Film Growth: Physics, materials science and applications

Подождите немного. Документ загружается.

278 Thin ﬁlm growth

charged. Again, the formation of cationic gold is closely related to the polar

nature of the FeO lm. Only attachment of a positively charged species is

able to heal the oxide polarity, as this neutralizes locally the Fe

–O

d–

surface

dipole (Fig. 11.16a). Adsorption of Au

is therefore an efcient means to

lower the surface free energy of the polar system and fully comparable with

the common polarity healing mechanism via hydroxylation (H

attachment).

Energetically, the formation of cationic gold is supported by the unusually

high work function of the FeO/Pt(111) system that impedes charge transfer

out of the support (Giordano et al., 2007b, 2008).

It should be noted at this

point that Au

is an unusual charge state for the strongly electronegative

gold. In fact, Au becomes anionic on most non-polar oxide lms due to a

charge transfer into the adsorbate (Pacchioni et al., 2005; Nilius, 2009). The

positive charging in the present case can only be rationalized if the polar

character of the FeO lm is taken into account.

The charge state of Au atoms on the FeO/Pt(111) system has been veried

experimentally by probing the position of the Au 6s orbital with respect to

the Fermi level with STM conductance spectroscopy. The hcp-bound atoms

exhibit a pronounced dI/dV peak at +0.5 V that is readily assigned to the

unlled Au 6s orbital with help of the DFT results (Fig. 11.17a) (Nilius et al.,

2005; Giordano et al., 2008). Further evidence for the 6s character of this state

Conductance

AuCO

LDOS

0 0.2 0.4 0.6 0.8

Sample bias (V)

0 0.5 1.0

E-E

(eV)

(a) (b)

(c)

11.17 (a) Conductance spectra and (b) calculated state-density of Au

and AuCO species adsorbed on hcp-domains in the FeO/Pt(111) ﬁlm.

An STM image of the probed species is shown in the inset. The Au-

related peak at 0.5 V (exp.) and 0.3 eV (theory) corresponds to the

Au 6s orbital, while the AuCO state at 1.0 eV is of CO 2P* character

and not detected in STM. (c) Conductance maps of differently bound

Au atoms (13 ¥ 13 nm

). Whereas the upper atoms are attached to

hcp domains and appear bright in the conductance map taken at

the position of the Au 6s orbital (0.55 V), the lower species sits in

an adjacent domain and shows no 6s-related dI/dV intensity (lower

panel).

Below the resonance position, all adatoms are imaged with

the same dI/dV contrast (upper panel). Reprinted with permission

from Giordano et al. (2008), Copyright (2010) by the American

Physical Society.

ThinFilm-Zexian-11.indd 278 7/1/11 9:43:31 AM



279Electronic properties and adsorption behaviour of thin ﬁlms

comes from CO adsorption experiments. After CO exposure onto the Au–FeO

lm, the +0.5 V conductance peak vanishes, because the Au 6s level shifts

out of the accessible spectral range upon formation of the Au–CO bond (Fig.

11.17a). The origin of this up-shift is the Pauli repulsion that is exerted by

the CO orbitals onto the Au states (Persson, 2005). However, even bare Au

atoms do not display the +0.5 V dI/dV peak if they are not bound to an hcp

domain. As concluded from conductance spectra and images, Au atoms in

fcc and top regions of the coincidence cell do not possess an unoccupied 6s

orbital (Fig. 11.17c). Apparently, those adatoms have a deviating electronic

structure and are not charged, which explains their lower binding energy

with respect to the hcp-bound species. The self-assembly of Au therefore

results from an interplay between the spatially modulated oxide polarity and

the concomitant charging response of the gold, which leads to a binding

enhancement only for Au atoms on the FeO–hcp domains.

As the self-assembly of gold on the FeO/Pt(111) lm is partially induced

by a charge-mediated binding mechanism, it is not surprising that atoms

with a deviating electronic structure do not show the same ordering effect.

To a certain extent, palladium can be considered as the counterpart to gold,

because the Pd afnity levels are far away from the Fermi energy and hardly

involved in any charge transfer processes. More precisely, the Pd 5s orbital

is well above E

Fermi

and empty, while the 4d states are below and completely

lled. The inhibited electron transfer is expected to hamper the self-ordering

of Pd atoms on the FeO surface. Indeed, Pd deposition at 10 K results in

a random distribution of adatoms on the oxide lm, as evident in the STM

image shown in Fig. 11.18. Furthermore, the adsorbates tend to aggregate

Relative occurrence

0.0 2.0 4.0 6.0 8.0

Pair separation (nm)

(a) (b) (c)

11.18 STM images of (a) Au and (c) Pd atoms on FeO/Pt(111) (0.25 V,

50 ¥ 50 nm

). Arrows in (c) mark small Pd clusters. (b) Radial pair-

distribution function for the Au and Pd adatoms on the FeO surface,

calculated from hundreds of atom positions in different STM images.

In contrast to Au, no ordering effect is observed for Pd adatoms.

Reprinted with permission from Giordano et al. (2008), Copyright

(2010) by the American Physical Society.

ThinFilm-Zexian-11.indd 279 7/1/11 9:43:31 AM



280 Thin ﬁlm growth

even at small Pd exposure and low deposition temperature (see arrows in

Fig. 11.18c). The uncorrelated spatial arrangement becomes manifest in the

radial pair-distribution function calculated for Pd, which does not display any

maxima, in sharp contrast to the results obtained for Au (Fig. 11.18b).

The absence of self-ordering effects for Pd on the polar FeO lm has several

reasons, being elucidated in a DFT study (Giordano et al., 2008). In general,

Pd atoms experience a much higher binding energy than Au atoms (1.4 eV

versus 0.6 eV). The largest binding contribution comes from the formation

of covalent bonds with either a Fe or an O ion in the surface. Polarization

interactions in the spatially modulated FeO dipole eld, on the other hand,

are comparatively small. As a consequence, the adsorption landscape of

Pd adatoms is rather smooth on the FeO surface and local variations in

binding strength are only of the order of 5% (compared to 30% for the Au).

In particular, the different polarity of the top, fcc and hcp region does not

give rise to prominent changes in the adsorption strength. In addition, the

amplication of polar oxide properties due to charge transfer processes out

of the adatoms, as observed for Au, does not take place for Pd that remains

neutral on all binding sites of the FeO coincidence cell. It is the sum of

all these effects that prevents the ordered arrangement of Pd atoms on the

FeO lm and even facilitates their aggregation into small aggregates on the

surface (Giordano et al., 2008).

11.4.2 Adsorption of molecules on polar FeO ﬁlms

Charging is, however, not essential to induce the self-assembly of adsorbates

on polar oxide lms. Especially in the absence of strong chemical forces, the

modulated surface-dipole within the FeO coincidence cell might sufciently

perturb the adsorption landscape to trigger ordering effects. Self-assembly

phenomena that are exclusively driven by the spatially varying oxide polarity

are therefore expected for closed-shell, but highly polarizable electronic

systems that are unable to form strong covalent bonds with the support.

Ideal candidates in this respect are molecules with a conjugated p-electronic

system that couple to the inert oxide surface mainly via polarization

interactions (Witte and Wöll, 2004). Therefore, magnesium phthalocyanine

(MgPc) molecules have been chosen to study the adsorption behaviour of

a polarizable, but chemically inactive species on the FeO/Pt(111) lm (Lin

and Nilius, 2008).

Figure 11.19(a) shows an STM topographic image taken after MgPc

deposition onto the surface at 300 K. Close inspection of such images

reveals that also the MgPc preferentially adsorbs on the hcp domains of

the coincidence cell, which show up with bright contrast under the selected

experimental conditions. Particularly attractive binding sites for the molecules

are those hcp domains that are situated directly next to a rising step edge. A

ThinFilm-Zexian-11.indd 280 7/1/11 9:43:31 AM



281Electronic properties and adsorption behaviour of thin ﬁlms

statistical evaluation of dozens of STM images revealed that roughly 84%

of the MgPc bind to hcp domains, while only 14% and 2% attach to top and

fcc regions, respectively (Fig. 11.19b) (Lin and Nilius, 2008). Assuming a

Boltzmann distribution according to the MgPc binding energy, adsorption

to the FeO hcp domain is preferred with 90 meV over the fcc and with 46

meV over the top region. This result demonstrates the crucial importance

of polarization interactions between MgPc molecules and the dipole eld

of the polar oxide. It should be noted that an electrostatic coupling to the

vertical FeO dipole requires the induction of a dipole moment in the initially

planar MgPc molecule, for instance via a small vertical displacement of the

central Mg

ion against the Pc-cage (Ruan et al., 1999; Janczak and Kubiak,

2001).

The binding preference to the FeO hcp domain is almost one order of

magnitude larger for MgPc molecules than for Au adatoms (90 meV versus

10 meV) (Lin and Nilius, 2008; Nilius et al., 2005). This nding reects the

superior polarizability of the highly exible, organic molecule with respect

to a single atom. Furthermore, while polarization in the spatially modulated

hcp

fcc

top

(a)

(b)

(c)

0.3

0.2

0.1

0.0

Occurrence

fcc

~2%

hcp

~84%

top ~ 14%

10 40 70

Angle a (°)

11.19 (a) Topographic image of MgPc molecules on FeO/Pt(111)

adsorbed at 300 K (35 ¥ 35 nm

). The coincidence cell is indicated

by a rhomboid, the arrows mark the three rotational orientations of

the molecules. (b) Relative occurrence of MgPc in different domains

of the FeO coincidence cell. (c) Angular orientation of the MgPc

symmetry axes with respect to a horizontal line. More than 100

molecules have been included in the statistics shown in (b) and (c).

Reprinted with permission from Lin and Nilius (2008), Copyright

(2010) by the American Chemical Society.

ThinFilm-Zexian-11.indd 281 7/1/11 9:43:32 AM



282 Thin ﬁlm growth

dipole eld is the decisive interaction mechanism for MgPc, this contribution

competes with true chemical bonding in the case of Au. Because the latter

effect is less site-specic, the spatial modulations in the Au binding energy

are weaker, and well-dened Au super-lattices only develop at cryogenic

temperature. A self-assembly of the MgPc, on the other hand, is observed

even at 300 K.

The ordering of MgPc on the FeO lm affects not only the spatial

distribution, but also the rotational alignment of the organic molecule

(Lin and Nilius, 2008). The molecules always bind with one of their two

equivalent axes oriented parallel to a close-packed FeO direction. Reecting

the hexagonal symmetry of the oxide support, three molecular orientations

are distinguishable on the surface, separated by angles of 30° and 60°

(Fig. 11.19c). A rotation by 90°, on the other hand, reproduces the initial

binding situation of the fourfold symmetric adsorbate. The self assembly

of MgPc on the FeO/Pt(111) system therefore has two aspects: while the

spatial distribution is governed by the modulated surface potential within

the coincidence cell, the angular alignment is xed by the interaction of the

molecule with the atomic FeO lattice. In general, the adsorption of MgPc

to the polar FeO lm is a rare example, where self-assembly is not induced

by inter-molecular coupling (see, for instance, Dmitriev et al., 2003; Barth

et al., 2005), but by a template effect of the oxide support.

11.5 Conclusion and future trends

The adsorption properties of polar oxide surfaces have been discussed for

atomic and molecular adsorbates on the FeO/Pt(111) lm. In both examples,

the uncompensated surface dipole of the oxide lm inuences considerably the

binding behaviour, predominantly by inducing polarization and electrostatic

interactions between the ad-species and the oxide support. The binding

occurs preferentially in regions with large dipole strength, triggering the

formation of long-range ordered adsorbate structures on the oxide surface.

Similar behaviour has been reported for comparable systems, e.g. for Cr

and Fe aggregates on Fe

/Pt(111) and RhO

/Rh(111) lms (Berdunov et

al., 2006; Gustafson et al., 2004). For many other polar oxides, elucidation

of their adsorption behaviour including potential self-assembly effects is

still lacking.

In conclusion, polar materials have a number of interesting morphological,

electronic and chemical properties that arise from the electrostatic energy

stored in those systems. As demonstrated in this chapter, the adsorption

behaviour of polar oxides strongly deviates from that of non-polar systems,

as the ad-species are partly involved in quenching the energetically

unfavourable surface dipole. The resulting adsorption characteristics can

be exploited in various technologically relevant applications. The strong

ThinFilm-Zexian-11.indd 282 7/1/11 9:43:32 AM



283Electronic properties and adsorption behaviour of thin ﬁlms

adhesion between polar supports and metal adsorbates might be used, for

example, to produce ultrathin, homogeneous metal coatings for optical and

electronic devices. The observed self-assembly effects on polar surfaces

are an interesting starting point to produce ordered arrangements of single

atoms, molecules and metal particles. The fabrication of regular arrays of

dened entities is highly desirable for applications in molecular electronics,

heterogeneous catalysis and chemical sensing. However, the role of the

oxide polarity in triggering such ordering phenomena needs to be explored

in more detail. Another potential interest in polar systems arises from their

unusual chemical properties, which originate from the high surface free

energy of such structures. This energy contribution might be temporally

released by restructuring the surface during a chemical reaction and can

be transferred to the reactants. In a recent study, the polar FeO lm was

found to be 50 times more reactive than the widely-used Pt catalyst in CO

oxidation reactions (Sun et al., 2009). The understanding of the interplay

between polarity and chemical properties is, however, just at the beginning

and more work is required in the future. However, thin lms with polar

character will certainly remain in the focus of research in the next few

years.

11.6 Sources of further information and advice

For more detailed information on the topic, the reader is referred to the

books and review articles listed below:

Noguera C (1996), Physics and Chemistry at Oxide Surfaces, Cambridge

University Press.

Noguera C (2000), ‘Polar oxide surfaces’, Journal of Physics – Condensed

Matter 31, R367.

Goniakowski J, Finocchi F and Noguera C (2008), ‘Polarity of oxide surfaces

and nanostructures’, Reports on Progress in Physics 71, 016501.

Dillmann B, Rohr F, Seiferth O, Klivenyi G, Bender M, Homann K,

Yakovkin IN, Ehrlich D, Bäumer M, Kuhlenbeck H and Freund H-J

(1996), ‘Adsorption on a polar oxide surface: Cr

(0001)/Cr(110)’,

Faraday Discussion 105, 295.

11.7 Acknowledgements

My special thanks go to Hans-Joachim Freund for his constant support and to

the members of my group that have contributed to this work: Emile Rienks,

Xiao Lin and Philipp Myrach. I am grateful to Gianfranco Pacchioni, Livia

Giordano and Jacek Goniakowski for their theoretical insights into polar

materials.

ThinFilm-Zexian-11.indd 283 7/1/11 9:43:32 AM



284 Thin ﬁlm growth

11.8 References

Arita R, Tanida Y, Entani S, Kiguchi M, Saiki K and Aoki H (2004), ‘Polar surface

engineering in ultrathin MgO(111)/Ag(111): possibility of a metal-insulator transition

and magnetism’, Phys Rev B, 69, 235423.

Barbier A and Renaud G (1997), ‘Structural investigation of the NiO(111) single crystal

surface’, Surf Sci, 392, L15–L20.

Barbier A, Renaud G, Mocuta C and Stierle A (1999), ‘Structural investigation of the

dynamics of the NiO(111) surface by GIXS’, Surf Sci 433, 761.

Barbier A, Mocuta C, Kuhlenbeck H, Peters KF, Richter B and Renaud G (2000), ‘Atomic

structure of the polar NiO(111)-p(2 ¥ 2) surface’, Phys Rev Lett, 84, 2897–2900.

Barth JV, Costantini G and Kern K (2005), ‘Engineering atomic and molecular nanostructures

at surfaces’, Nature, 437, 671–679.

Bäumer M and Freund HJ (1999), ‘Metal deposits on well-ordered oxide lms’, Prog.

Surf Sci 61, 127–198.

Becker RS, Golovchenko JA and Swartzentruber BS (1985), ‘Electron interferometry at

crystal-surfaces’, Phys Rev Lett, 55, 987–990.

Berdunov N, Mariotto G, Balakrishnan K, Murphy S and Shvets IV (2006), ‘Oxide templates

for self-assembling arrays of metal nanoclusters’, Surf Sci, 600, L287–L290.

Binnig G, Rohrer H, Gerber C and Weibel E (1982), ‘Tunneling through a controllable

vacuum gap’, Appl Phys Lett, 40, 178–180.

Bottin F, Finocchi F and Noguera C (2003), ‘Stability and electronic structure of the

(1 ¥ 1) SrTiO

(110) polar surfaces by rst-principles calculations’, Phys Rev B, 68,

035418.

Chen JC (1993), Introduction Into Scanning Tunneling Microscopy, New York, Oxford

University Press.

Dmitriev A, Spillmann H, Lin N, Barth JV and Kern K (2003), ‘Modular assembly of

two-dimensional metal-organic coordination networks at a metal surface’, Angew

Chem Int Ed, 42, 2670–2673.

Dulub O, Diebold U and Kresse G (2003), ‘Novel stabilization mechanism on polar

surfaces: ZnO(0001)-Zn’, Phys Rev Lett, 90, 016102.

Dulub O, Batzill M and Diebold U (2005), ‘Growth of copper on single crystalline ZnO:

Surface study of a model catalyst’, Top Catal, 36, 65–76.

Finocchi F, Barbier A, Jupille J and Noguera C (2004), ‘Stability of rocksalt (111) polar

surfaces: beyond the octopole’, Phys Rev Lett, 92, 136101.

Galloway HC, Sautet P and Salmeron M (1996), ‘Structure and contrast in scanning

tunneling microscopy of oxides: FeO monolayer on Pt(111)’, Phys Rev B, 54,

11145–11148.

Giordano L, Martinez U, Sicolo S and Pacchioni G (2007a), ‘Observable consequences

of formation of Au anions from deposition of Au atoms on ultrathin oxide lms’, J

Chem Phys, 127, 144713.

Giordano L, Pacchioni G, Goniakowski J, Nilius N, Rienks EDL and Freund HJ (2007b),

‘Interplay between structural, magnetic, and electronic properties in a FeO/Pt(111)

ultrathin lm’, Phys Rev B, 76, 075416.

Giordano L, Pacchioni G, Goniakowski J, Nilius N, Rienks EDL and Freund HJ (2008),

‘Charging of metal adatoms on ultrathin oxide lms: Au and Pd on FeO/Pt(111)’,

Phys Rev Lett, 101, 026102.

Giovanardi C, Hammer L and Heinz K (2006), ‘Ultrathin cobalt oxide lms on Ir(100)-(1

¥ 1)’, Phys Rev B, 74, 125429.

ThinFilm-Zexian-11.indd 284 7/1/11 9:43:32 AM



285Electronic properties and adsorption behaviour of thin ﬁlms

Goniakowski J and Noguera C (2002), ‘Microscopic mechanisms of stabilization of

polar oxide surfaces: transition metals on the MgO(111) surface’, Phys Rev B, 66,

085417.

Goniakowski J and Noguera C (2009), ‘Polarization and rumpling in oxide monolayers

deposited on metallic substrates’, Phys Rev B, 79, 155433.

Goniakowski J, Noguera C and Giordano L (2007), ‘Prediction of uncompensated polarity

in ultrathin lms’, Phys Rev Lett, 98, 205701.

Goniakowski J, Finocchi F and Noguera C (2008), ‘Polarity of oxide surfaces and

nanostructures’, Rep Progr Phys, 71, 016501.

Goniakowski J, Noguera C, Giordano L and Pacchioni G (2009), ‘Adsorption of metal

adatoms on FeO(111) and MgO(111) monolayers: effects of charge state of adsorbate

on rumpling of supported oxide lm’, Phys Rev B, 80, 125403.

Gustafson J, Mikkelsen A, Borg M, Lundgren E, Kohler L, Kresse G, Schmid M, Varga

P, Yuhara J, Torrelles X, Quiros C and Andersen JN (2004), ‘Self-limited growth of

a thin oxide layer on Rh(111)’, Phys Rev Lett, 92, 126102.

Hacquart R and Jupille J (2007), ‘Hydrated MgO smoke crystals from cubes to octahedra’,

Chem Phys Lett, 439, 91–94.

Janczak J and Kubiak R (2001), ‘X-ray single crystal investigations of magnesium

phthalocyanine. The 4+1 coordination of the Mg ion and its consequence’, Polyhedron,

20, 2901–2909.

Kiguchi M, Entani S, Saiki K, Goto T and Koma A (2003), ‘Atomic and electronic

structure of an unreconstructed polar MgO(111) thin lm on Ag(111)’, Phys Rev B,

68, 115402.

Kim YJ, Westphal C, Ynzunza RX, Galloway HC, Salmeron M, van Hove MA and

Fadley CS (1997), ‘Interlayer interactions in epitaxial oxide growth: FeO on Pt(111)’,

Phys Rev B, 55, 13448–13451.

Kitakatsu N, Maurice V and Marcus P (1998), ‘Local decomposition of NiO ultra-thin

lms formed on Ni(111)’, Surf Sci, 411, 215–230.

Kittel C (1996), Introduction to Solid State Physics, New York, Wiley.

Knudsen J, Merte LR, Grabow LC, Eichhorn FM, Porsgaard S, Zeuthen H, Vang RT,

Lægsgaard E, Mavrikakis M and Besenbacher F (2010), ‘Reduction of FeO/Pt(111)

thin lms by exposure to atomic hydrogen’, Surf Sci 604, 11–20.

Kolesnychenko OY, Kolesnichenko YA, Shklyarevskii O and van Kempen H (2000),

‘Field-emission resonance measurements with mechanically controlled break junctions’,

Physica B, 291, 246–255.

Koplitz LV, Dulub O and Diebold U (2003), ‘STM study of copper growth on ZnO(0001)-

Zn and ZnO(0001)-O surfaces’, J Phys Chem B, 107, 10583–10590.

Kresse G, Dulub O and Diebold U (2003), ‘Competing stabilization mechanism for the

polar ZnO(0001)-Zn surface’, Phys Rev B, 68, 245409.

Kroll M and Köhler U (2007), ‘Small Cu-clusters on ZnO(0001)-Zn: nucleation and

annealing behavior’, Surf Sci 601, 2182.

Kulawik M, Rust HP, Heyde M, Nilius N, Mantooth BA, Weiss PS and Freund HJ

(2005), ‘Interaction of CO molecules with surface state electrons on Ag(111)’, Surf

Sci, 590, L253–L258.

Lin X and Nilius N (2008), ‘Self-assembly of MgPc molecules on polar FeO thin lms’,

J Phys Chem C, 112, 15325–15328.

Mantilla M, Jedrecy N, Lazzari R and Jupille J (2008), ‘Oxidation of Mg/Ag(111)

investigated using scanning tunneling microscopy: towards atomically smooth MgO

nanostructures’, Surf Sci, 602, 3089–3094.

ThinFilm-Zexian-11.indd 285 7/1/11 9:43:32 AM



286 Thin ﬁlm growth

Maurice V, Cadot S and Marcus P (2001), ‘Hydroxylation of ultra-thin lms of alpha-

(0001) formed on Cr(110)’, Surf Sci, 471, 43–58.

Merte LR, Knudsen J, Grabow LC, Vang RT, Laegsgaard E, Mavrikakis M and Besenbacher

F (2009), ‘Correlating STM contrast and atomic-scale structure by chemical modication:

vacancy dislocation loops on FeO/Pt(111)’, Surf Sci, 603, L15–L18.

Meyer B and Marx D (2004), ‘Density-functional study of Cu atoms, monolayers, lms,

and coadsorbates on polar ZnO surfaces’, Phys Rev B, 69, 235420.

Myrach P, Benedetti S, Valeri S, Nilius N and Freund HJ (2011), ‘Investigating polarity

healing mechanisms at the atomic scale: MgO on Au(111)’, forthcoming.

Nilius N (2009), ‘Properties of oxide thin lms and their adsorption behavior studied

by scanning tunneling microscopy and conductance spectroscopy’, Surf Sci Rep, 64,

595–659.

Nilius N, Rienks EDL, Rust HP and Freund HJ (2005), ‘Self-organization of gold atoms

on a polar FeO(111) surface’, Phys Rev Lett, 95, 066101.

Noguera C (1996), Physics and Chemistry at Oxide Surfaces, Cambridge, Cambridge

University Press.

Olesen L, Brandbyge M, Sorensen MR, Jacobsen KW, Laegsgaard E, Stensgaard I and

Besenbacher F (1996), ‘Apparent barrier height in scanning tunneling microscopy

revisited’, Phys Rev Lett, 76, 1485–1488.

Ostendorf F, Torbrugge S and Reichling M (2008), ‘Atomic scale evidence for faceting

stabilization of a polar oxide surface’, Phys Rev B, 77, R041405.

Pacchioni G, Giordano L and Baistrocchi M (2005), ‘Charging of metal atoms on ultrathin

MgO/Mo(100) lms’, Phys Rev Lett, 94, 226104.

Parker TM, Condon NG, Lindsay R, Leibsle FM and Thornton G (1998), ‘Imaging

the polar (0001) and non-polar (1010) surfaces of ZnO with STM’, Surf Sci, 415,

L1046–L1050.

Parteder G, Allegretti F, Surnev S and Netzer FP (2008), ‘Growth of cobalt on a VO(111)

surface: template, surfactant or encapsulant role of the oxide nanolayer?’, Surf Sci,

602, 2666–2674.

Persson M (2005), ‘Adsorption-induced constraint on delocalization of electron states in

an Au chain on NiAl(110)’, Phys Rev B, 72, R081404.

Pojani A, Finocchi F, Goniakowski J and Noguera C (1997), ‘A theoretical study of

the stability and electronic structure of the polar {111} face of MgO’, Surf Sci, 387,

354–370.

Poon HC, Hu XF, Chamberlin SE, Saldin DK and Hirschmugl CJ (2006), ‘Structure of

the hydrogen stabilized MgO(111)-(1 ¥ 1) surface from low energy electron diffraction

(LEED)’, Surf Sci, 600, 2505–2509.

Rienks EDL, Nilius N, Rust HP and Freund HJ (2005), ‘Surface potential of a polar

oxide lm: FeO on Pt(111)’, Phys Rev B, 71, 241404.

Rienks EDL, Nilius N, Giordano L, Goniakowski J, Pacchioni G, Felicissimo MP, Risse

T, Rust HP and Freund HJ (2007), ‘Local zero-bias anomaly in tunneling spectra of

a transition-metal oxide thin lm’, Phys Rev B, 75, 205443.

Ritter M, Ranke W and Weiss W (1998), ‘Growth and structure of ultrathin FeO lms

on Pt(111) studied by STM and LEED’, Phys Rev B, 57, 7240–7251.

Rohr F, Wirth K, Libuda J, Cappus D, Baumer M and Freund HJ (1994), ‘Hydroxyl

driven reconstruction of the polar NiO(111) surface’, Surf Sci, 315, L977–L982.

Ruan CY, Mastryukov V and Fink M (1999), ‘Electron diffraction studies of metal

phthalocyanines, MPc, where M=Sn, Mg, and Zn (reinvestigation)’, J Chem Phys,

111, 3035–3041.

ThinFilm-Zexian-11.indd 286 7/1/11 9:43:32 AM



287Electronic properties and adsorption behaviour of thin ﬁlms

Schoiswohl J, Surnev S, Sock M, Eck S, Ramsey MG, Netzer FP and Kresse G (2005),

‘Reduction of vanadium-oxide monolayer structures’, Phys Rev B, 71, 165437.

Sedona F, Rizzi GA, Agnoli S, Xamena F, Papageorgiou A, Ostermann D, Sambi M,

Finetti P, Schierbaum K and Granozzi G (2005), ‘Ultrathin TiOx lms on Pt(111): a

LEED, XPS, and STM investigation’, J Phys Chem B, 109, 24411–24426.

Silly F, Pivetta M, Ternes M, Patthey F, Pelz JP and Schneider WD (2004), ‘Creation of

an atomic superlattice by immersing metallic adatoms in a two-dimensional electron

sea’, Phys Rev Lett, 92, 016101.

Sun YN, Qin ZH, Lewandowski M, Carrasco E, Sterrer M, Shaikhutdinov S and Freund

HJ (2009), ‘Monolayer iron oxide lm on platinum promotes low temperature CO

oxidation’, J Catal, 266, 359–368.

Tasker PW (1979), ‘Stability of ionic-crystal surfaces’, J Phys C, 12, 4977–4984.

Tusche C, Meyerheim HL and Kirschner J (2007), ‘Observation of depolarized

ZnO(0001) monolayers: formation of unreconstructed planar sheets’, Phys Rev Lett,

99, 026102.

Vurens GH, Salmeron M and Somorjai GA (1988), ‘Structure, composition and

chemisorption studies of thin ordered iron-oxide lms on platinum(111)’, Surf Sci,

201, 129–144.

Wang XG, Chaka A and Schefer M (2000), ‘Effect of the environment on alpha-Al

(0001) surface structures’, Phys Rev Lett, 84, 3650–3653.

Wang Y (2008), ‘High resolution electron energy loss spectroscopy on perfect and

defective oxide surfaces’, Z Phys Chem, 222, 927–964.

Wang Y, Meyer B, Yin X, Kunat M, Langenberg D, Träger F, Birkner A and Wöll C

(2005), ‘Hydrogen induced metallicity on the ZnO(1010) surface’, Phys Rev Lett,

95, 266104.

Witte G and Wöll C (2004), ‘Growth of aromatic molecules on solid substrates for

applications in organic electronics’, J Mater Res, 19, 1889–1916.

Wolf D (1992), ‘Reconstruction of NaCl surfaces from a dipolar solution to the madelung

problem’, Phys Rev Lett, 68, 3315–3318.

Yin XL, Birkner A, Hanel K, Lober T, Kohler U and Wöll C (2006), ‘Adsorption of atomic

hydrogen on ZnO(1010): STM study’, Phys Chem Chem Phys, 8, 1477–1481.

ThinFilm-Zexian-11.indd 287 7/1/11 9:43:32 AM

