About 150 nm sized marks were recorded and readout was
performed using a reflection-mode near-field scanning optical
microscope (NSOM) in the 4-layered phase-change optical disk
structure. Full-width at half-maximum (FWHM) values of the linewidth
of the marks recorded at different writing speeds decreased with
increasing writing speed. The thermodynamic stability of the
submicron-sized marks and its implications are discussed on basis of
the surface energy and its effect on the temperature of phase
transformation, including crystallization and melting.
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.
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