Nanostructure Fabrication Using Pulsed Lasers and Near-field Optical Properties of Sub-micron Particles
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Nanostructure Fabrication Using Pulsed Lasers and Near-field Optical Properties of Sub-micron Particles L. Zhang, Y. F. Lu1, W. D. Song, Y. W. Zheng and B. S. Luk’yanchuk Laser Microprocessing Laboratory, Department of Electrical and Computer Engineering and Data Storage Institute National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 ABSTRACT Recently, the field of nanoelectonics has evolved into a major area of investigation. In this paper, we present a novel method of nanofabrication using pulsed lasers and near-field optical properties of sub-micron particles. For this purpose, spherical silica particles were deposited on a silicon surface. After laser illumination, hillocks with size of about 150 nm were obtained at the original position of the particles. The mechanism can be explained as the enhancement of light intensity near the contact area. Since the characteristic distance between particles and substrate is smaller than the radiation wavelength and the particle size is of the order of a wavelength, particle does not simply play the role of microfocusing lens as in far-field, but possess optical resonance effect in near-field. In our work, the light intensity on the surface under the spherical particle was calculated by solving the electromagnetic boundary problem “particle on suface”.
INTRODUCTION Laser-induced processing of materials has become an attractive field for both science and engineering since the invention of laser. It has been intensively investigated, and has been found to be greatly useful in many areas, such as microelectronics and magnetics. Laser processing has been demonstrated to be a valuable technology for fabrication of structures in the dimension of micrometers and sub-micrometers. However, due to the limitation of diffraction of light, laser processing cannot be directly used for fabrication of nanostructures. To overcome the diffraction limit, a lot of research attention today has been put into methods of scanning probe microscope (SPM)-based nanolighography [1-3]. Gorbunov, et al. [4], wrote features of 10 to 40 nm in diameter on gold films in vacuum. Jersch, et al. [1], created nanostructures from creaters and ditches to hillocks on gold films in air. They are expected to be potential methods in the fabrication of present and future nanodevices. Unfortunately, due to their low efficiency and their vulnerability to substrate vibration, the application of these methods is presently confined to experimental stage. In this paper, we report a novel, low-cost, and simple optical lithography technique to overcome the diffraction limit in laser processing by using near-field optical properties of sub-micron particles.
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THEORETICAL CALCULATION To calculate the light intensity on the surface under the spherical particle, we first performed simplified preliminary examination according to the Mie theory. In a second calculation, the secondary scattering effects due to reflected radiation by substrate surface was
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