Optical Microscopy at the Nanoscale

Optical Microscopy at the Nanoscale

Mine Memesa, Peter Schön, Davide D. Tranchida, InYee Phang, Jordi Djaz, Holger Schönherr

,

Julius G. Vancso

Materials Science and Technology of Polymers, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands

Introduction

In nanotechnology and bio-nanotechnology there is a strong need to access imaging techniques to visualize materials from mm down to nm length scales. Scanning force microscopy enabled visualization and study of soft matter across the length scales. Optical microscopy and its application in high resolution imaging is limited resolution to the half of the wavelength of the incident light. Nanometer scale optical properties are interesting in fields of resist layers, ultrathin coatings, nanocomposites, biological polymer platforms, sensors, and devices. Optical microscopy was extended to image below the diffraction limit in apertured and aperture-less scanning near-field optical microscopy (SNOM), and more recently stimulated-emission-depletion (STED) fluorescence microscopy.

In this project, an atomic force microscope (AFM) and an ellipsometer are combined to obtain near-field optical images. Our technique is non-destructive, economical and provide information about the lateral distribution of optical density heterogeneities. In addition to optical imaging of topological features, our approach would yield information about the optical properties (lateral distribution of refractive index) of materials down to the nm scale which holds promise to provide crucial, long-needed information for preparation and characterization of new optical (e.g. photonic) materials.

First measurements on Au nanoparticles in PMMA films, by Au coated Si tip

AFM height AFM phase Optical image Force curve

References

[1] Karageorgiev, P., Orendi, H., Stiller, B., Brehmer, L. Appl. Phys. Lett., 79, 1730, 2001 [2] Kelly, K.L., Coronado, E., Zhao, L.L., Schatz, G.C. J. Phys. Chem. B 107, 668, 2003 [3] Pitarke J.M., Silkin V.M., Chulkov E.V., Echenique P.M. Rep. Prog. Phys. 70, 1, 2007

P o l a r i s a t o r K o m p e n s a t o r y L a s e r P C x P r o b e A n a l y s a t o r A D e t e k t o r Tip holder

MFP-3D Head MFP-3D Scanner (XY)

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Ellipsometer - Null ellipsometry

The sample is aligned, and the Null Ellipsometry conditions are found.

AFM

The AFM head is placed on the sample. AFM laser is located on the tip.

Ellipsometer + AFM

Ellipsometer laser is located on the AFM tip. Elliptically polarized light is sent to the tip, exciting localized surface plasmons1 at themetal coated AFM tip. These cause a near-field interaction, and the corresponding light is detected in far field. The background, due to partial reflections of the incoming light, is cancelled through the analyzer

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An equivalent surface, containing both the topographical and the dielectric information, is imaged with this apertureless SNOM approach

[4] Gucciardi, P. G. et al. J. Appl. Phys. 101, 064303, 2007

[5] S. Schmatloch, M.A.R. Meier, U.S. Schubert, Macromal. Rapid Commun. 2003, 24, 33-46. [6] Flores, S.M., Toca-Herrera, J. Nanoscale, 1, 40, 2009.

Dr. Mine Memesa

E-mail: m.memesa@utwente.nl

Material Science and Technology of Polymers, University of Twente, MTP LA 1739, PO Box 217, 7500AE Enschede, The Netherlands phone: +31-53-489-2971, fax: +31-53-489-3823