Selective fabrication of Si nanodots and nanowires
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Selective fabrication of Si nanodots and nanowires Anahita Haghizadeh1 and Haeyeon Yang1, 2* Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. 2 Center for Security Printing and Anti-Counterfeiting Technology, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. 1
ABSTRACT We report observation of narrow nanowires and high density nanodots on the Si(001) surfaces when they are exposed to a single application of interferential irradiation of laser pulses of 7 ns. These nanostructures form selectively depending on interference parameters so that their placements can be controlled by controlling the parameters. The morphologies of the nanostructures are studied by atomic force microscopy. The nanowire width increases with interference period. The narrowest nanowires observed have the width smaller than 26 nm, which is eight times smaller than the interference period while the nanodots have a very large density of 1.8 ± 0.45) × 1011/cm2. INTRODUCTION Fabrication of nanodots and nanowires on Si surface has been sought due to their wide applications such as in transistors[1] and solar cells[2]. Lithography has been successful in creating nanoscale features over a large area. Unlike lithography, direct laser patterning via interferential irradiation of laser pulses (IILP) is a simple and low-cost technique as it does not require processes involving photomasks, photoresist materials, and chemical etching.[3] It is desirable to fabricate Si based nanostructures directly on the surface by a single application of laser pulses. This is simple and economical as it does not require expensive equipment. This is a green technology because it does not require harmful chemicals. The laser based nanofabrication is straightforward as it takes a very short time. Furthermore, real time patterning is possible as well when the laser patterning is integrated into epitaxial growth process so that three dimensional features can be grown directly on top of laser patterned epitaxial surfaces or laser created nanostructures. For example, direct laser heating has been used to create and align selfassembled metallic nano dots on glass substrates.[4, 5] The dots are aligned along interference lines due to mass transport arising from selective heating in nanoscale. IILP has been used to selectively ablate surfaces. GaN nano lines[6] has been reported due to the ablation at interferential maxima lines when two beam interference is applied on the surface. Self-assembled nano dots created by applying IILP on semiconductor surfaces have been reported recently[7] and self-assembled metallic gallium nano dots were reported due to laser-dissociated desorption from GaAs(110).[8] In this paper, we present our recent results of direct laser fabrication of nanodots and nanowires from Si(001) surfaces. EXPERIMENT
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