Subwavelength-resolution near-field Raman spectroscopy
- PDF / 324,799 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 234 Views
LECULES, OPTICS
Subwavelength-Resolution Near-Field Raman Spectroscopy S. S. Kharintseva, b, *, G. G. Hoffmannb, c, J. Loosb, G. de Withb, P. S. Dorozhkind, and M. Kh. Salakhova a
Kazan State University, Kazan, 420008 Russia Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands c University of Duisburg-Essen, D-45117, Essen, Germany d Institute of Solid-State Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia *e-mail: [email protected] b
Received April 10, 2007
Abstract—The resolution capabilities of near-field Raman spectroscopy based on a giant enhancement of the electric field near a nanosized metal probe are studied. As a test sample, bundles of single-walled carbon nanotubes deposited on glass substrates are used. It is shown that this method ensures a subwavelength spatial resolution of about 50 nm and demonstrates a Raman scattering enhancement of the order of 104. PACS numbers: 42.62.Fi, 42.65.-k, 42.65.An DOI: 10.1134/S1063776107110052
1. INTRODUCTION Optical spectroscopy methods are of fundamental importance in studying the structure and properties of matter. However, due to the well-known Abbe diffraction limit, which is about λ/2n (λ is the wavelength of radiation and n is the refractive index), these methods cannot be applied to study objects with a subwavelength resolution. The existing methods for the improvement of the spatial resolution in the visible range (for example, frequency mixing, second-harmonic generation, etc.) do not suffice to study nanostructures. The occurrence of evanescent waves in the nearfield region (not farther than 100 nm from the interface between two media) makes it possible to overcome the diffraction limit and, therefore, to achieve ultrahigh resolution in optical spectroscopy [1–3]. It has become possible to practically implement this approach by combining two methods, optical spectroscopy and scanning probe microscopy [1–5]. A key role in this method is played by a nanosized probe placed near the surface (at ~3 nm) of a sample under investigation. Unlike traditional optical spectroscopy, the resolving power is determined by the geometry of a probe rather than by the aperture of optical elements. Therefore, for this very reason, this method is often referred to as apertureless near-field optical microscopy [1–5]. With respect to the principle of formation of the optical image, local scattering-based and local excitationbased methods are commonly used [4]. In the first case, the evanescent field near nanosized structures is scattered by a probe and is measured in the far-field region by “ordinary” optics. In the second case, a probe placed in a tightly focused laser beam locally enhances the electromagnetic field near its tip due to the resonance
excitation of localized surface plasmons. An additional contribution to the field enhancement is made by a geometric singularity of the tip apex and by the chemical effect of adsorbed molecules [4–7]. The enhanced field is scattered from nanosized structures and is detected
Data Loading...
