The issue of topography artifacts has proven to play a very important role in interpreting images recorded in scanning near-field optical microscopy. We report on the fabrication and characterization of samples with essentially no topographic features while possessing very high optical contrast on the nanometric lateral scale. These samples open the door to routine and uncontroversial examinations of the resolution obtained in a scanning near-field optical microscope. (C) 2000 American Institute of Physics. [S0003-6951(00)04409-0].
Transmission of a microcavity structure in a two-dimensional photonic crystal based on macroporous silicon
A. Birner,
A.-P. Li,
F. Muller,
U. Gosele,
P. Kramper,
Vahid Sandoghdar,
Jürgen Mlynek,
K. Busch,
V. Lehmann
Materials Science in Semiconductor Processing
3
487-491
(2000)
| Journal
Photonic crystals consist of regularly arranged dielectric scatterers of dimensions on a wavelength scale, exhibiting band gaps for photons, analogous to the case of electrons in semiconductors. Using electrochemical pore formation in n-type silicon, we fabricated photonic crystals consisting of air cylinders in silicon. The starting positions of the pores were photolithographically pre-defined to form a hexagonal lattice of a = 1.58 mum. The photonic crystal was microstructured to make the photonic lattice accessible for optical characterization. Samples with different filling factors were fabricated to verify the gap map of electric and magnetic modes using Fourier-transform infrared (IR) spectroscopy. The complete band gap could be tuned from 3.3 to 4.3 mum wavelength. We were able to embed defects such as waveguide structures or microcavities by omitting certain pores. We carried out transmission measurements using a tunable mid-IR optical parametric oscillator. The resonance is compared with theoretical expectations. (C) 2001 Elsevier Science Ltd. All rights reserved.
We propose a new type of apertureless scanning near-field optical microscope based on detection of the second-harmonic signal induced by or generated at a probe tip. We discuss the image formation in this technique and present numerical studies for different experimental circumstances. In two extreme cases this method is shown to be the nonlinear analogue of apertureless scanning near-field optical microscopy based on local nanoscopic fluorescence or scattering. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Second-harmonic generation from individual surface defects under local excitation
Anantoly V. Zayats,
Thomas Kalkbrenner,
Vahid Sandoghdar,
Jürgen Mlynek
Enhancement of optical second-harmonic generation (SHG) at individual defects on metal surface has been studied. SHG has been excited locally at chosen defects using a near-field optical microscope with an uncoated fiber tip. SH intensity enhancement up to ten times has been observed at the apex of micron size defects on a gold surface while the average enhancement is of about 1.2 times. Observed SHG enhancement has been described by lightning rod effect. Specific features of SHG enhancement due to local excitation are briefly discussed.
Optical microscopy using a single-molecule light source
J. Michaelis,
C. Hettich,
Jürgen Mlynek,
Vahid Sandoghdar
Rapid progress in science on nanoscopic scales has promoted increasing interest in techniques of ultrahigh-resolution optical microscopy. The diffraction limit can be surpassed by illuminating an object in the near field through a sub-wavelength aperture at the end of a sharp metallic probe(1,2). Proposed modifications(3,4) of this technique involve replacing the physical aperture by a nanoscopic active light source. Advances in the spatial(5) and spectral(6) detection of individual fluorescent molecules, using near-field and far-field methods(7), suggest the possibility of using a single molecule(8,9) as the illumination source. Here we present optical images taken with a single molecule as a point-like source of illumination, by combining fluorescence excitation spectroscopy(10) with shear-force microscopy(11). Our single-molecule probe has potential for achieving molecular resolution in optical microscopy; it should also facilitate controlled studies of nanometre-scale phenomena (such as resonant energy transfer) with improved lateral and axial spatial resolution.
Multifunctional AFM/SNOM cantilever probes: Fabrication and measurements
M. Stopka,
D. Drews,
K. Mayr,
M. Lacher,
W. Ehrfeld,
T.. Kalkbrenner,
M Graf,
Vahid Sandoghdar,
Jürgen Mlynek
The microfabrication process for cantilever probes for combined atomic force (AFM) and scanning near-field optical microscopy (SNOM) is described. The probes feature an aperture tip with a Si3N4 core for SNOM operation as well as an integrated optical waveguide for illumination of the tip. First measurements have been performed using a home-made AFM/SNOM setup operating in tapping mode with optical beam deflection. A special test sample containing a pattern of gold nanostructures embedded in a transparent polymer matrix provides low topography but high optical contrast. An optical resolution of about 100 nm has been demonstrated by examining the contrast in transmitted intensity at the metal/polymer border.
Contact
Nano-Optics Division Prof. Vahid Sandoghdar
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
