High-resolution microscope for tip-enhanced optical processes in

ultrahigh vacuum

Jens SteidtnerFritz Haber Institute, Physical Chemistry Department

Outline

• Lateral resolution of aSNOM

• aSNOM - Optical configurations

• Focusing with a parabolic mirror

• Experimental setup

• Experimental results

• Outlook

2

Overcoming the diffraction limit

(a) SNOM with a metal-coated tapered fiber tip

(b) Apertureless SNOM with a metallic probe

Rayleigh`s criterion:

D

frx

22.1

3

Lateral resolution of aSNOM

3

00)(

R

dRgERE S

3

2

2

)(1

)0(

)()(

dR

r

I

rIrF

SNF

NFNF

2

122 ))(( rdRR S

6

2

2

)(1

)0(

)()(

dR

r

I

rIrF

STER

TERTER

4

TERS - Optical configurations

Bottom-illumination1 Side-illumination2 Top-illumination3

5

[1] R. Stöckle, Y. D. Suh, V. Deckert, R. Zenobi, Chem. Phys. Lett. 318, 131 (2000)

[2] B. Pettinger, G. Picardi, R. Schuster, G. Ertl, J. Electroanal. Chem. 554, 293 (2003)

[3] J. Steidtner, B. Pettinger, Rev. Sci. Instrum., in print

Focusing with a parabolic mirror

6

Linear polarization Radial polarization

Si phonon band at 520 cm-1

Schematic of the optical setup

7

Optical platform

8

Vacuum system

9

Raman imaging the focus

Linear polarization Radial polarization

10

TERS of BCB adsorbates

Brillant cresyl blue

BCB monolayer on Au(111)

• ~36000 molecules are in the focal spot• Only 90 molecules are in the tip-enhanced region• By approaching the tip the signal is raised by a factor of 3920• This equals a Raman enhancement factor of 1.6*106

11

Photobleaching in UHV / O2

12

TERS of BCB molecules

13

Lateral resolution

of ~15 nm

)()(

1)0()(

6

2

2

bgIdR

rIrI

S

14

Single molecule aSNOM

aSNOM of BCB adsorbates

15

Outlook

16

• Implementation of a combined AFM/STM scanner

• Application of silver tips

• Investigation of catalytic reactions on single crystals and oxide supported metal clusters

Acknowledgement

17

• Dr. Bruno Pettinger

• Workshops of the Fritz Haber Institute

• Danish Micro Engineering

• Fritz Haber Institute of the MPS