Abstract
The paper proposes a new approach that enables the structure analysis and reconstruction of a rough surface where the height of inhomogeneities (from the depression to the upper point) varies within the spread about 20 nm. For the surface diagnostics, carbon nanoparticles are used, which serve as sensitive probes of the local surface height. A single nanoparticle can be positioned at a desirable point of the studied surface with the help of an optical tweezer employing the He-Ne laser radiation. Then the particle is illuminated by the strongly focused exciting beam of 405 nm wavelength, with the waist plane precisely fixed at a certain distance from the surface base plane. The particle’s luminescence response (in the yellow-green spectral range) strongly depends on the distance between the exciting beam waist and the particle, thus indicating the local height of the surface. After scanning the surface area and the consecutive interpolation, the surface “vertical” landscape can be reconstructed with a high accuracy: the numerical simulation shows that the RMS surface roughness is restored with an accuracy of 6.9% while the landscape itself is reconstructed with the mean error 7.7%.
Highlights
In the past years, a significant progress occurs in the development of a new branch of optical technology directed to the fabrication of thin, light and flexible electronic elements
Its implementation includes several steps: 1) digital modeling of the surface profile via the set of heights measured at a discrete set of points and formulation of the corresponding requirements to the probe particle localization with the sufficient lateral resolution; 2) the exciting beam localization with precise fixation of the horizontal position of its axis and vertical position of the waist; 3) calibration of the luminescence signal dependence on the particle-waist distance and 4) numerical reconstruction of the surface relief based on the measured luminescence data
It is reasonable to make the longitudinal position of the focused beam waist controllable: when the particle is fixed at a certain lateral location, the waist is adjusted beneath the surface
Summary
A significant progress occurs in the development of a new branch of optical technology directed to the fabrication of thin, light and flexible electronic elements. Its implementation includes several steps: 1) digital modeling of the surface profile via the set of heights measured at a discrete set of points and formulation of the corresponding requirements to the probe particle localization with the sufficient lateral resolution; 2) the exciting beam localization with precise fixation of the horizontal position of its axis and vertical position of the waist; 3) calibration of the luminescence signal dependence on the particle-waist distance and 4) numerical reconstruction of the surface relief based on the measured luminescence data All these steps are considered in detail in the subsequent sections. It is reasonable to make the longitudinal position of the focused beam waist controllable: when the particle is fixed at a certain lateral location, the waist is adjusted beneath the surface (cf Figure 4B) so that the energy gradient is directed towards the sample and “presses” the particle to it This action, in combination with the gravitational and adhesion forces, guarantees the particle’s contact with the surface, so that its vertical coordinate characterizes the local surface height. The modeling results enable to obtain the 3D map of the surface under consideration (Figure 8), and comparison with the input surface data of Figure 1 show that the mean relative deviation amounts to 7.74%
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