co on mo(110) studied by scanning tunneling microscopy

Surface Science 557 (2004) 109–118

www.elsevier.com/locate/susc

Co on Mo(1 1 0) studied by scanning tunneling microscopy

A. Mikkelsen *, L. Ouattara, E. Lundgren

Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund, Sweden

Received 13 February 2004; accepted for publication 12 March 2004

Abstract

We have studied the interface formation of thin films of Co on a Mo(1 1 0) surface by the use of scanning tunneling

microscopy (STM), low energy electron diffraction (LEED) and auger electron spectroscopy (AES). Below a coverage

of about 0.4 monolayers (ML) we find that Co grows in small islands which are pesudomorphic with the Mo substrate.

At a Co coverage above 0.4 ML, the Co atoms condense into larger islands and forms a close-packed Co layer close to

that of the Co(0 0 0 1) plane resulting in a coincidence structure with the underlying Mo(1 1 0) substrate. Increasing the

Co coverage, we observe that the film grows in a layer-by-layer fashion up to 2 ML at room temperature, however by

annealing such a film to 670 K the Co forms 3D islands. STM images displaying atomic resolution, reveal the atomic

arrangement and corrugation of the close-packed Co film formed at Co coverages above 0.4 ML at room temperature.

In particular, the STM data directly demonstrate the appearance of the coincidence lattice between the Nishiyama–

Wasserman orientated Co film and the Mo(1 1 0) substrate. We show how this appearance may change due to subtle

changes of the registry between the Co film and the Mo(1 1 0) surface. This behavior can be explained by partial dis-

locations relaxing the strained close-packed Co layer by a small rigid translation.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Scanning tunneling microscopy; Low energy electron diffraction (LEED); Auger electron spectroscopy; Cobalt;

Molybdenum

1. Introduction

Ferromagnetic thin films have been studied for

a considerable time. A major reason for this largeand increasing interest is due to their unusual

magnetic properties [1–3], which are related to the

thickness of the film and the influence of the

interface with a paramagnetic material. There is

currently a strive towards understanding the de-

* Corresponding author. Tel.: +46-462229627; fax: +46-

462224221.

E-mail address: [email protected] (A. Mikkel-

sen).

0039-6028/$ - see front matter � 2004 Elsevier B.V. All rights reserv

doi:10.1016/j.susc.2004.03.020

tailed relationship between the structure on the

atomic scale and the magnetic properties of the

thin film, not only to design future magnetic nano-

structures but also for more fundamental physicsreasons [4]. Because of the ferromagnetic film

being very thin, and because of the presence of an

interface of a different material with a different

lattice, the structures formed at the interface be-

tween the film and the substrate are in many cases

rather complicated. If a deeper understanding of

the properties of these structures is to be achieved,

the geometrical arrangement on the atomic level isneeded. Therefore, atomic scale direct imaging by

the use of scanning tunneling microscopy (STM) is

highly attractive.

ed.

mail to: [email protected]

110 A. Mikkelsen et al. / Surface Science 557 (2004) 109–118

Because of their high specific surface free ener-

gies cs and dense packing, W(1 1 0) and Mo(1 1 0)

are favorable substrates for a smooth monolayer-

by-monolayer [5] growth of fcc metal layers with

(1 1 1) orientations. Consequently, a number of

studies of various metals deposited onto thesesubstrates have been performed previously [6–

8,13–15]. The formation of metallic hexagonal

superlattices on (1 1 0) substrates has been dis-

cussed in detail elsewhere [16,17]. When depositing

Co on either W(1 1 0) or Mo(1 1 0) at room tem-

perature (RT), the Co is known to grow pseudo-

morphic (ps) with the Mo(1 1 0) substrate if the Co

coverage is below approximately 0.5 monolayers(ML; 1 ML is defined as 1 ps Co layer or in other

words as the number of atoms in the Mo(1 1 0)

plane). However, at a Co coverage between 0.5

and 1.2 layers, the Co takes its own close-packed

(cp) hexagonal lattice instead of that of bcc

Mo(1 1 0). Previous investigations have [6,7,13],

based on low energy electron diffraction (LEED)

observations, proposed a Nishiyama–Wasserman(NW) oriented growth of the Co film, the ½110�Mo being parallel to ½1100� Co and the [0 0 1] Mo

being parallel to ½1120� Co (see below), in this

coverage region. Theoretical calculations has also

been performed using the embedded-atom method

on this type of system [9,10]. It was found that the

ps phase is energetically favorable up to 1 pseu-

domorphic ML at equilibrium. However in kinet-ically limited systems a ps to cp transition should

occur, through misfit dislocations. While no STM

studies have been published for the Co/Mo(1 1 0)

system, a recent STM study of the similar Co/

W(1 1 0) has been published [11,12]. Whereas these

studies also concerns the Co submonolayer regime,

they differ from the present study in that the Co

layers deposited at RT were post-annealed to 635K. This resulted in large islands of cp NW oriented

Co, with small patches of ps Co. The LEED pat-

tern found in this study was identical to the LEED

pattern observed for the same Co coverage in this

study. Atomically resolved images of the NW

oriented Co islands revealed deviations from a ri-

gid cp(1 1 1) Co layer in that small oscillatory

relaxations were induced.In the present report, we present LEED and

STM results from thin Co films with a thickness

ranging from 0.25 ML to approximately 2 ML.

We show that above a Co coverage of approxi-

mately 0.4 ML, the STM results demonstrate the

undulation of the Co film and directly illustrate the

morphology and appearance of the NW oriented

growth of the Co film. We argue on the basis ofour observations that a simple interpretation of

the STM image can be made general for the

interpretation of STM images of fcc(1 1 1) on

bcc(1 1 0) systems. Finally we discuss some details

of the atomic geometry and island defects that may

be directly observed from the STM images in the

Co/Mo(1 1 0) system.

2. Experiment

The STM measurements were performed in a

UHV chamber with a base pressure below

1 · 10�10 mbar. All STM images were obtained in

constant current mode, using a commercial Omi-

cron room temperature STM. The Mo(1 1 0)sample was prepared in a separate chamber with a

base pressure of approximately 2 · 10�10 mbar.

The Mo(1 1 0) crystal was cleaned by cycles of Arþ

sputtering, annealing and oxygen treatments

keeping the sample at 870 K in an oxygen pressure

of 2 · 10�8 mbar followed by flashes to 1570 K.

The cleanliness of the Mo(1 1 0) surface and of the

Co prepared surface was checked by auger elec-tron spectroscopy (AES) using a double pass

cylindrical mirror analyzer. No contaminants such

as C and O could be observed within the detection

limits of 0.05 ML. Co was deposited from a water-

cooled electron beam evaporator at room tem-

perature (RT). A retarding voltage was applied to

the end of the evaporator in order to suppress ions

from the Co evaporator. The repeatability in Cocoverage was estimated to be less than 10% from

repeated measurements as determined from the

ratio between the Co 773 eV and the Mo 186 eV

Auger peak-to-peak signals.

3. Results and discussion

In Fig. 1 we show STM images from the

Mo(1 1 0) surface with different Co coverages in

Fig. 1. (a) STM images (1000· 1000 �A2) of Co deposited on Mo(1 1 0) at coverages of (a) 0.25 ML (I ¼ 0:8 nA, U ¼ �0:7 V), (b) 0.5

ML (I ¼ 0:3 nA, U ¼ �1:0 V), (c) 0.75 ML (I ¼ 0:5 nA, U ¼ �0:5 V) and (d) 1.0 ML (I ¼ 0:5 nA, U ¼ �1:8 V).

A. Mikkelsen et al. / Surface Science 557 (2004) 109–118 111

order to illustrate the morphology of the Co layers

deposited on Mo at RT. At a Co coverage of 0.25

ML, small Co islands with an average diameter of56 �A with a standard deviation of 12 �A are ob-

served in the STM image Fig. 1a. At this coverage

LEED displays a (1 · 1) pattern. Since the size of

the Co islands are large enough to result in visible

changes in the LEED pattern if the atoms within

the islands would have a different arrangement as

compared to the underlying Mo(1 1 0) substrate,

this observation indicates that the Co growspseudomorphic at this coverage in agreement with

previous studies.

As the Co coverage is increased, some of the Co

atoms grows from the Mo step-edge, but on the

terraces the Co islands coalesce, resulting in larger

and more irregular islands, as may be seen in

Fig. 1b. At this coverage, the LEED displays a

4 0

1 2

� �reconstruction which indicate that the Co

has taken its own cp hexagonal in-plane latticeparameter. The interpretation of the LEED pat-

tern and the atomic arrangement giving rise to the

reconstruction will be discussed in detail below. In

the area in-between the islands in Fig. 1a and b,

dark spots may be seen in the Mo surface. We

attribute this to a small amount of alloying be-

tween the Mo and the Co at room temperature,

which has been reported previously [7]. At a cov-erage of approximately 0.75 ML, it can be seen

that while the size of the islands in Fig. 1c is

roughly the same as in Fig. 1b, the number of is-

lands has increased which results in some coales-

cence of the islands. As the Co coverage is close to

1 ML, the Co wets the Mo(1 1 0) surface almost

completely, as can be seen in Fig. 1d. At this


coverage, the LEED pattern shows no observable

differences as compared to the corresponding

LEED patterns originating from the surfaces in

Fig. 1b and c. Ignoring the fact that we are far

from equilibrium at RT, the reason for the almost

perfect wetting is due to the high specific surfacefree energy of the Mo(1 1 0) surface as compared

to that of the Co(0 0 0 1) surface. Since the total

specific surface free energy should be minimized, it

is favorable not to expose the Mo(1 1 0) surface. At

higher coverages the growth continues to be two

dimensional (2D) as can be seen in Fig. 2a.

While the growth is kinetically limited at RT,

the growth has been proposed to result in three-dimensional Co crystallites [7] at higher tempera-

tures closer to equilibrium. This can be explained

Fig. 2. (a) 2000· 2000 �A2 STM image of Co deposited on Mo(1 1 0

corresponding to the line drawn in (a) demonstrating that the height o

(2.2 �A). (c) STM image of Co deposited on Mo(1 1 0) at coverages of

Linescan corresponding to the line drawn in (c) demonstrating that th

step height (4.4 �A).

in that close to equilibrium it is more favorable to

minimize the areas with interfacial strain, which is

confirmed by the STM images in Fig. 2. Fig. 2a

show a STM image after 2.5 ML of Co have been

deposited on the Mo(1 1 0) surface at RT. The

appearance of the surface is flat or 2D. The linescan in Fig. 2b show that the height of the islands

are close to the expected height for a monoatomic

step of a Co(0 0 0 1) island (2.2 �A). As the sample is

post-annealed to 670 K, the morphology of the

surface changes, as shown in Fig. 2c, the islands

grow larger and thicker. The line scan in Fig. 2d

show that the height of the islands now corre-

sponds to the height of 2 times the expected heightof a monoatomic step of a Co(0 0 0 1) island. This

shows that the Co grows in 3D islands at elevated

) at coverages of 2.5 ML (I ¼ 0:6 nA, U ¼ 1 V). (b) Linescan

f the islands correspond to the height of a single Co step height

2.5 ML and post-annealed at 400 �C (I ¼ 0:8 nA, U ¼ 1 V). (d)

e height of the islands correspond to the height of a double Co


temperatures. The LEED pattern after annealing

is very similar to the pattern found prior to

annealing except for some very weak extra (2 · 2)spots attributed to alloying in the exposed Mo

surface.

Having described the general growth and mor-phology of the Co/Mo(1 1 0) system we now turn

to the details of the reconstruction formed above

approximately 0.4 ML of Co deposited at RT. In

Fig. 3a we present the resulting LEED pattern

after having deposited approximately 0.5 layers of

Co on the Mo(1 1 0) surface. The LEED pattern

has been observed previously [7,13] and has been

denoted (8 · 1) or (8 · 2), however in the presentreport we prefer to denote the pattern by the G-

matrix4 0

1 2

� �. Apart from the spots originating

from the Mo(1 1 0) substrate, additional spots may

be observed at a position away from the integral

order (1 0) Mo(1 1 0) spots in reciprocal space. A

straightforward interpretation would be that these

spots originate from the formation of a hexagonalCo layer on the surface. This interpretation is

substantiated by the sketch in correct scale of the

Co(0 0 0 1) and Mo(1 1 0) lattices shown in Fig. 3b.

If the orientation of the Co lattice is chosen so that

the ½1120� Co is parallel to the [0 0 1] Mo direction,

the lattice mismatch between the Co and the Mo

in the ½110� Mo isffiffiffi3

paCo=

ffiffiffi2

paMo ¼ 0:98 or very

close to 1 and thus explaining the (1 · 1) periodicityobserved in the LEED pattern in this direction. In

the [0 0 1] bcc direction, the lattice mismatch is

Fig. 3. (a) The LEED pattern observed from 0.5 ML of Co on Mo(1 1

lattice, respectively. Two of the integer order spots are indicated. (b)

cells illustrating the NW oriented growth of the Co film. The consta

neighbor ratio r ¼ b=a of 0.92, respectively, while a ¼ 54:736 and b ¼

aCo=aMo ¼ 0:8 or very close to the corresponding

ratio as measured directly from the LEED pattern.

From these observations, we now have a reason-

able good picture of the in-plane properties of the

film. Based on the LEED pattern we may propose

that the Co film at this coverage takes a latticeclosely resembling its bulk (0 0 0 1) lattice plane and

that the growth is NW oriented. This can be

quantified by the parameter r defined as the ratio

between the nearest neighbor distance b in Co and

the nearest neighbor distance a in Mo (see Fig. 3b).

For NW oriented growth of fcc(1 1 1) on bcc(1 1 0)

the optimum r is expected to be 0.943 [17], close to

the value of 0.92 in the present case. However, theLEED pattern displays additional satellites. Such

spots indicates a larger cell than the (1 · 1)Co(0 0 0 1) and in this case reflects the coincidence

between the Co lattice and the Mo lattice below

resulting in a undulating periodic structure in the

½110� Mo//½1100� Co direction. In this particular

case the positions of the satellite spots indicate that

the coincidence is commensurate with the sub-strate, which is not always the case, see for instance

Ref. [18]. The fact that the satellite spots appear to

be sharp and intense indicate a well ordered

structure and a detailed quantitative diffraction

based structural study should provide the out-of-

plane structure and the resulting out-of-plain

strain, an important quantity for the understand-

ing of the magnetic properties of the interface.Returning to the STM observations, and by

imaging a small area on one of the islands as

0). The full and the hatched lines represent the Mo and the Co

Real space representation of the Co(0 0 0 1) and Mo(1 1 0) unit

nts a for Co and Mo are 2.51 and 3.15 �A, yielding a nearest

60:0.

Fig. 4. STM image of 0.5 ML of Co on Mo(1 1 0): (a) 3000· 3000 �A2 (I ¼ 0:6 nA, U ¼ �0:8 V) and (b) 150· 150 �A2 (I ¼ 1:2 nA,

U ¼ �1:7 mV).


illustrated in Fig. 4a, the surface structure is re-

vealed, as shown in Fig. 4b. In this image, we are

able to resolve the individual Co atoms in the is-

land. A particular striking feature of the Co latticeis the periodic darker and brighter stripes from the

bottom left to the top-right in the image.

The appearance of the darker and brighter

stripes on the surface may most easily be explained

by superimposing the two lattices of a Co(0 0 0 1)

plane and a Mo(1 1 0) plane orienting the Co layer

in the NW orientation, as shown in Fig. 5a and b

for two different relative positions of the Co latticewith respect to the Mo substrate. Regardless of the

position of the Co lattice the resulting 1D Moir�epattern produces five Co atoms (bright) along Mo

[0 0 1] on top of four (dark) Mo atoms while it is

commensurate in the Mo ½110� direction. The Co

lattice has been stretched by )0.4% alongMo [0 0 1]

and 2.5% in the Mo ½110� direction to obtain the

exact match, resulting in a strain of the Co layer.Thus the orientation and strain of the Co lattice

can be established from the unit cell and orienta-

tion of the corrugation of the Co atoms, but further

information can also be obtained from the specific

corrugation pattern. The corrugation of the Co

lattice for various translations relative to the Mo

substrate can, in a simple approximation, be

modelled by assuming that the Co atoms follows ahard-sphere model of the Mo substrate. In Fig. 5c

and d the gray scale coloring of the Co layers re-

flects the calculated corrugation of the two lattice

positions shown in Fig. 5a and b, respectively. The

models has Co atoms in on-top–hollow sites (hol-

low site position perturbed towards a on-top po-

sition in the ½110� Mo direction) and bridge sites,

and in on-top and hollow sites, respectively. Thesetwo Co layer positions represents two extremes,

thus in Fig. 5a all Co atoms are in-between Mo

atoms, while in Fig. 5b some Co atoms are in high

symmetry hollow sites, however then some Co

atoms are also in on top sites. These two models

have been chosen as all other Co lattice positions

are essentially translative perturbations between

these two models yielding qualitatively similarcorrugation patterns. By comparison of Fig. 5c and

d with the STM image of Fig. 5e, it is seen that the

model of Fig. 5a (corresponding to the coloring of

Fig. 5c) is the model compatible with the observed

STM images. It should be noted that a translation

of only 0.3�A away from the position used to obtain

the coloring of Fig. 5c results in a model incom-

patible with the STM image. Therefore, we believethat the dark stripes in the STM image in Fig. 4b

and Fig. 5e are due to Co atoms in bridge sites

while the bright stripes are due to Co atoms in on-

top–hollow sites. In conclusion, since the model in

Fig. 5a results in an appearance (Fig. 5c) which

reproduce the STM image (Fig. 5e) we believe that

the model in Fig. 5a represents the combined Co/

Mo interface structure.This simple interpretation of the STM image

yields the basics of the structure and an explana-

tion for the observed LEED pattern. We are

therefore able to confirm previous observations [6]

Fig. 5. The stripes observed on the islands may be explained by superimposing the Co(0 0 0 1) lattice on the Mo(1 1 0) substrate. The

resulting surface unit cell is indicated. Two high symmetry positions of the Co lattice with respect to the Mo substrate are shown in (a)

and (b). In (a) the Co atoms are in on-top–hollow sites and in bridge sites. In (b) the Co atoms are in on-top and hollow site positions.

(c) and (d) show the corrugation of the Co lattice based on a simple hard-sphere model of Co layer and Mo substrate. The coloring

represent the relative Co atom distance to the Mo substrate (darker atoms are closer to the Mo substrate). The positions of the Co

atoms in (a) and (b) have been used to calculate the coloring in (c) and (d), respectively. (e) Close-up of the structure of Fig. 4b. The

unit cell of the coincidence lattice between the Co(0 0 0 1) and the Mo(1 1 0) lattices is indicated. Note that only the coloring in (c) match

the experimental corrugation seen in (e), indicating that the Co atoms reside in on-top–hollow and bridge sites as shown in (a).

Fig. 6. 100· 100 �A2 STM image of a Co island on Mo(1 1 0)

(I ¼ 2:9 nA, U ¼ �1:5 mV). Notice the missing striped pattern

at edge.


concerning the growth of Co on Mo(1 1 0), sup-

porting the validity of the theory for fcc on

bcc(1 1 0) growth [9,14,16]. The STM image in Fig.

4b also excludes all other surface unit cells except

for the one shown in Fig. 5. Therefore, a quanti-

tative study of this structure using LEED or sur-

face X-ray diffraction (SXRD) should be

straightforward.While the ideal structure of the islands have

now been established, several common defect

structures of the Co islands are also revealed by

the STM images. From Fig. 2b–d it is seen that the

edges of the close-packed Co layer are different in

texture than the rest of the islands. From the STM

image in Fig. 6 displaying atomic resolution of an

island one of these edges can be seen. While theatoms of this edge are also ordered they do not

display the dark and bright stripes of the center of

the island. This indicates that the edges of the is-

lands are most likely pseudomorphic, which would

be in agreement with Pratzer et al. [11], who also

found pseudomorphic patches on the close-packed

Co islands on W(1 1 0). The fact that larger pseu-domorphic domains were found in their study

could be attributed to their post-annealing to

635 K.


A detailed inspection of the island corrugation

in Fig. 4b reveals dislocations in the striped pat-

tern on the island perpendicular to the stripes, as

shown in Fig. 7a. The schematic drawing in Fig. 7c

shows such a line defect as compared to the ideal

pattern using the same coloring scheme as for Fig.5c and d. This type of defect line is rather com-

mon. For example, an island as visualized in Fig.

4b one finds a line dislocation in about every third

4 0

1 2

� �unit cell in the Mo [0 0 1] direction. The

defect lines can be explained as a simple disloca-

tion of part of the Co lattice used in Fig. 5a. As

seen in Fig. 7b, the line defect can come about by arigid relaxation of part of the Co lattice by 0.63 �A(1/5 of a Co lattice spacing in the Mo [0 0 1]

direction). By introducing this partial dislocation it

is possible for more Co atoms to be positioned in

bridge sites, which presumably are more favorable

than on-top–hollow sites. We also find that the

coloring of Fig. 7c can be obtained by using the

same scheme as for calculating Fig. 5c and d. InFig. 8a, we show a case of an island were the

corrugation pattern is influenced by several peri-

odically positioned partial dislocation lines acting

Fig. 7. (a) Zoom in on a partial dislocation (I ¼ 2:9 nA, V ¼ �1:5 mV

Calculated corrugation of a line defect as compared to the calculate

represent Co atoms relaxed towards the Mo substrate.

in both directions along the Mo [0 0 1] axis, as

shown in Fig. 8b. Thus one obtain a Co overlayer

in which a periodic compressive and tensile dis-

placement of the Co layer in the Mo [0 0 1] direc-

tion has occurred. Finally it should be noted that

the wave-like relaxation along the bcc ½110�direction found in the study of Pratzer et al. [11,12]

are not seen in this study. In fact no displacements

from the original lattice are observed along the bcc

½110� direction.The STM image in Fig. 5e supports the

assumption that a simple interpretation such as in

Fig. 5a will yield the basic appearance of the STM

image of a fcc metal on a bcc(1 1 0) substrate. Ourinterpretation is also supported by previous use of

superpositions of nets of discs representing atoms

in the bcc(1 1 0) planes and fcc(1 1 1) planes,

resulting in Moir�e fringes [19]. The only restric-

tions are the b=a relation, which determines the

directions of the growth and the amount of

alloying between the adatom and the substrate.

For instance, the Co/W(1 1 0) should yield a verysimilar result as in the present report since a

(W )¼ 3.16 �A as compared to the 3.15 �A for Mo

and as the LEED pattern displays the same dif-

). (b) Indication of the relaxation involved in the line defect. (c)

d corrugation (see Fig. 5) of the ideal structure. Darker atoms

Fig. 8. (a) 125· 125 �A2 STM image (I ¼ 4 nA, U ¼ �0:13 mV) of a Co island, in which periodic partial dislocations occur resulting in

an overall corrugation pattern different from what is observed in Fig. 4b. (b) Two partial dislocations acting in opposite directions. (c)

The resulting corrugation pattern from the dislocations of (b) calculated in a similar fashion as the corrugation patterns of Fig. 5c and

d. Unit corresponding unit cells are shown in (b) and (c).


fraction as in the present case [6,8,13,14]. Also in

the case of 1 ML Rh on Mo(1 1 0) a similar STM

appearance would be expected, except that in this

case the Rh forms a 7/6 coincidence lattice with the

rows in the Mo(1 1 0) [20]. However, at Rh cov-erages below 1 ML, the same investigation reports

on a distorted Rh layer resulting in a Kurdjumov–

Sachs relationship (KS). The structural transition

between the two orientations is clearly an inter-

esting candidate to study using STM. Another

interesting example would be the STM appearance

of submonolayer adsorption of Sm on Mo(1 1 0),

since the Sm is divalent a low coverages but tri-valent at higher coverages resulting in an large

contraction of the radius of the Sm atom [17]. This

should have interesting consequences for the

resulting STM images, since the preferred growth

direction could change, which then would directly

indicate areas with divalent and trivalent Sm

atoms, respectively. This behavior would however

depend on whether or not the valency of the Sm ishomogeneously or heterogeneously mixed within

the Sm layers. The previous LEED observations

from this system do not give a straightforward

interpretation [21]. The list of combinations can be

made long, the interested reader is referred to Ref.

[17].

4. Summary

In summary we have studied the growth of

Co on Mo(1 1 0) by the use of LEED, AES and

STM. The STM images reveals 2D island growthof the Co layers up to a Co coverage of 2.5 ML

at room temperature. If a 2.5 ML thick Co film

is annealed, our results demonstrate the onset of

3D growth of the Co films. The hexagonal Co

film grows in the NW orientation resulting in

a striped appearance, which is due to the coin-

cidence between the Co atoms and the Mo

atoms in the Mo(1 1 0) surface underneath thefilm. Our measurements confirm the prediction by

previous theoretical investigations [16,17] con-

cerning the orientation of the growth of Co on

Mo(1 1 0), and a simple Moir�e based interpretation

explains the STM image. Finally we show that a

common partial dislocation line relaxes the is-

lands.

Acknowledgements

This work was financially supported by the The

Swedish Science Council and the Crafoord foun-

dation.


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