Reflection-mode Near-field Optical Microscope Research Articles

Topographic cross talk in reflection mode near-field optical microscopy on patterned structures

In scanning near-field optical microscopy the sample topography may have a strong effect on the optical image signal. This cross talk has been investigated in subwavelength-periodically patterned thin-film structures using a reflection-mode near-field optical microscope. A comparison between measured and simulated line scans shows that far-field light waves emitted from the tip aperture play a major role in the imaging process.

Modulation imaging in reflection-mode near-field scanning optical microscopy

A simple implementation of modulation of the near-field optical signal of near-field probes based on the shear-force feedback system is demonstrated in a reflection-mode near-field optical microscope. The modulation exhibits a derivative type of dependence on the near-field signal and no sensitivity to topography. It is shown that the modulation image can be calculated directly from the derivative of the conventional near-field scattering image. This type of near-field modulation is an excellent way to reject far-field artifacts from the near-field signal.

Resolution enhancement in a reflection mode near-field optical microscope by second-harmonic modulation signals

The motion of the probe tip in a near-field scanning optical microscope, dithered by vibration of a tuning fork, can modulate the reflection signal from the sample surface not only at the fundamental dithering frequency but also at its second harmonic. By lock-in amplification of these modulated signals, enhanced optical images are obtained, even with an uncoated fiber probe. In particular, accurate optical images with higher resolution are obtained when the second-harmonic signal is detected, which results from the parametric modulation of the tip-sample separation at the double frequency of the horizontal dithering motion of the tip. Using a DVD ROM with a track pitch of 0.74 mum as a test sample, we observed that the sharp edges around the pits are clearly resolved with the second-harmonic signals and obtained enhanced resolution of ~70 nm full width at half-maximum.

Reflection-mode scanning near-field optical microscopy using an apertureless metallic tip

Recently, a reflection-mode near-field optical microscope with an apertureless tungsten tip has been introduced and 100-nm resolution has been achieved [R. Bachelot, P. Gleyzes, and A. C. Boccara, Microsc. Microanal. Microstruc. 5, 389-397 (1994)]. The optical signal is recorded in parallel with a tapping-mode atomic force microscope signal. By showing several images here, we confirm the capabilities of this device and clearly demonstrate a 20-nm (~lambda/35) resolution that has been achieved with smaller tips. A study of these images shows that both the topography and the near electromagnetic field of the sample can be independently probed by this device. Additionally, we discuss the principle of our approach, notably on the basis of interference phenomena between a Rayleigh scatterer and its image through the reflecting surface, and some of the setup's experimental characteristics are presented.

Reflection-mode near-field optical microscope with a metallic probe tip for observing fine structures in semiconductor materials

We have developed a near-field scanning optical microscope with a metallic probe tip without an aperture that can be operated in the reflection mode. This near-field microscope can also be easily operated simultaneously as a scanning tunneling microscope. To prevent the unwanted contribution of specular reflection from contaminating the observed signal, dark-field illumination of the sample surface is employed. The microscope is suitable for characterizing opaque samples such as metals and semiconductor materials. We evaluated its imaging performance by obtaining both the near-field optical and scanning tunneling images of a semiconductor grating with a pitch period finer than the light wavelength.