Surface Science @ Universidad Autónoma de

Madrid

Roberto OteroRoberto OteroOn behalf of all the members of the Surface

Science Laboratory @ Universidad Autónoma de Madrid

Nanosciences & Surface Science

Optical devices based on organic thin films

Nanomechanical biosensors

Molecular electronic

devices

Functionalized surfaces for

implant applications

Intr

oduct

ion

Organic Optoelectronic Devices

Example: Pentacene thin filmsIn

tens

ity (

a.u.

)

2θ (º)

C. D. Dimitrakopoulos & P. L. Malefant, Advanced Materials 14, 99 (2002)

Intr

oduct

ion

Thin Film GrowthIn

troduct

ion

For organic adsorbates:

-3D molecular structure (degrees of freedom)

-Specificity in intermolecular interactions

Ultra-High Vacuum (UHV)

How long does it take for an atomically clean single-crystal surface to get dirty?

Tmk

P

B2Nº of incident molecules/time × area =

At RT, P = 1 Atm, m = 4 uma, about 7.71 × 1027 molecules per second and square meter hit the surface. For Cu (100) (square lattice with lattice parameter 2.56 Å) this number equals 5 × 109 molecules/second and unit cell

At P = 10-10 Torr, only 6 × 10-4 molecules per second and unit cell hit the surface, i.e. an average of 25 min are necessary to have all the unit cells hit by one molecule

Intr

oduct

ion

Ultra-High Vacuum (UHV)In

troduct

ion

Ultra-High Vacuum (UHV)In

troduct

ion

20 × 20 nm2

O/Cu(110)

PO = 10-8 Torr

tframe = 20 s

Experimental TechniquesIn

troduct

ion

• Structure:– Real Space (STM)– Reciprocal Space (SXRD, TEAS)

• Chemistry (XPS)

• Electronic Structure (UPS, STS)

• Other properties… magnetism? (SP-STM, SMOKE)

Scanning Tunneling Microscopy and Spectroscopy

Scanning Tunneling Microscopy (STM)

STM

Things to do in the lab when you have an STM…

STM

Atomic structure of solid surfaces with vertical pm resolution

Morphology of epitaxial systems

Subnanometer-resolution electronic

spectroscopy

Diffusion of atomic

adsorbates

Atom-by-atom

nanostructure fabrication

TIREMISU (TIme REsolved MIcroscopy of SUrfaces)

STM

José María Gallego

Me

David Écija

Christian Urban

Marta Trelka

SITTA (Sistema Integral de Túnel y Técnicas de Análisis)

STM

Fabián Calleja

Juan José Hinarejos

Amadeo L. Vázquez de Parga

STM/STS: Layer-Dependent Roughening Transition

F. Calleja, M. C. G. Passeggi, Jr., J. J. Hinarejos, A. L. Vázquez de Parga, and R. Miranda, Phys. Rev. Lett. 97, 186104 (2006)

STM

Diffraction and the Reciprocal Space

Elementary Diffraction Theory

n2 k'kR

Reciprocal space vector

Wavelength ≈ Lattice parameter

Diffr

act

ion

X-Rays: SXRDλ ≈ 1 Å, E ≈ 12.3 keV → X Rays

Large penetration depth!!!Large penetration depth!!!

Real Space Reciprocal Space

Diffr

act

ion

Baby Chambers at Synchrotrons

Diffr

act

ion

Jesús ÁlvarezMaría José Capitán

Me

Hamburg

Adenine Self-AssemblyD

iffr

act

ion

Molecule Diffraction from Surfaces

Diffr

act

ion

The Atomic and Molecular Beam Diffraction Apparatus at LASUAM

Diffr

act

ion

Guillaume Laurent

Daniel Farías

Daniel BarredoPablo Nieto

H2 Diffraction

40 50 60 70 80 90 100 1100

1

2

3

4

5

6

7

8

9

10

X2

X2

f = 0º

f = 8.7º

f = 17.7º

Diffr

act

ion

In

ten

sity

[a

.u.]

(1,1)

(0,1)

(1,0)

i+

f [degres]

[101]E

i = 77.5 meV

i = 37.6º

(0,0)

In-plane and out-of-plane H2 diffraction spectra from Pt(111) recorded along the two main azimuths:

P. Nieto, E. Pijper, D. Barredo, G. Laurent, R.A. Olsen, E.J. Baerends, G.J. Kroes and D. Farías, Science 312, 86 (2006)

Diffr

act

ion

Surface PhononsD

iffr

act

ion Phonons on Pd(110):

Chemical and Electronic Characterization

Electrons in SolidSpect

rosc

opy

XRPS

Cristina Navío

Jesús Álvarez

María José Capitán

Spect

rosc

opy

X-Ray and UV Photoelectron Spectroscopy (XPS)

Spect

rosc

opy

3000 Å x 3000 Å

N 1s

Fe 2p

Fe4N stoichiometry

Other Techniques

SMOKE (Surface Magneto-Optical Kerr Effect)

Dr. Julio Camarero

HeNe

laser

polarizer

lens

Wollastonprism

analyser

DSO

Field servo-loop-control

power supplyFREQFREQ

FIELDFIELD

fastphotodiodes

++––

Hall signal

lens

air gap ferrite

/2 plate

1 current sensor

Magneti

sm

Spin-Polarized STM

SampleTip

MsMT

Φ

EF

EF

High current

Amadeo L. Vázquez de Parga

Magneti

sm

Sample: Mn/Fe(001)Mn grown at 370 K (<4x10-

10mbar)

STM image after depositing 7 ML

140 x 150 nm2

Vs= - 0.5 V I=0.5 nA

6

78

9

9

98

8

0.16 nm

0.14 nmFe(001)-whisker

Mn(001)

film

4.5

2.5

0.5-1.0 -0.5 0.0 0.5 1.0 1.5

dI/d

V [n

A/V]

Sample voltage [V]

6789

6

789

99

8

8

dI/dV curves

dI/dV map at +0.2 V

STS measured with clean W tip

Spin-Polarized STMM

agneti

sm

89

10

100 x 100 nm2

Vs= - 0.5V, I=0.5nA

10

11

11

12

Sample voltage [V]-1.0 -0.5 0.0 0.5 1.0

dI/

dV

[n

A/V

]0.5

1.5

2.589

1011

dI/dV map at +0.2 V

89

1011

11

10

9

STM image

With the Fe-coated W tip alternating contrast with a clean W tip there is no contrast

Reversed contrast with different Fe-coated W tips due to different tip magnetization

9

12

dI/dV curves

STS measured at room temperature with Fe-coated W tip

100 x 100 nm2

Spin-Polarized STMM

agneti

sm

80 x 80 nm2

I map at V=0.10 V

6.5 ML of Mn/Fe(001)

Topography

Measured at room temperature

Spin-Polarized STMM

agneti

sm

Conclusion

• A multitechnique approach to address problems related with the growth and characterization of nanostructures