Direct laser fabrication of nanostructures on Si(001)
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Direct laser fabrication of nanostructures on Si(001) Anahita Haghizadeh1 and Haeyeon Yang1 * 1
Department of Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. ABSTRACT We study how the period of transient thermal gradient impacts on morphologies of nanostructures on the Si(001) surface. Strain-free, self-assembled nanodots as well as periodic nanowires are fabricated directly on Si(001) surfaces by applying high power laser pulses on the surface interferentially. The morphologies of the nanostructures are studied by atomic force microscopy. Generally, the laser irradiated surfaces show nanowires but nanodots are also observed. The nanowire width increases with interference period. The narrowest nanowires observed have the width smaller than 50 nm, which is four times smaller than the interference period while the nanodots have a base width of 43 nm and height of 8 nm. INTRODUCTION The ability to pattern surfaces in nanoscale has numerous applications such as magnetic data storage, efficient energy storage, photovoltaic cells, and other electronic devices.[1] Lithography has been successful in patterning surfaces 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.[2] Furthermore, real time patterning is possible 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. For example, direct laser heating has been used to create and align self-assembled metallic nano dots on glass substrates.[3, 4] 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[5] has been reported due to the ablation at interferential maxima lines when two beam interference is applied on the surface. Selfassembled nano dots created by applying IILP on semiconductor surfaces have been reported recently[6] and self-assembled metallic gallium nano dots were reported due to laser-dissociated desorption from GaAs(110).[7] In this paper, we present our recent results of direct laser fabrication of nanowires from Si(001) surfaces. EXPERIMENT In order to fabricate nanostructures, transient thermal grating was created on the surfaces by irradiating interferentially with high power laser pulses. The experimental setup is similar to that used to produce nano trenches and nano hills from GaAs(001)[8] while quantum dots from InGaAs layers[6] on GaAs(001). The fabrication is done in air on n-type Si(001) wafers from Virginia Semiconductors. Although there are complications in interpreting the surface images due to interaction with ambient gas molecules during the heating and relaxation processes (albeit short due to the short pulse width (7 ns)), in-air patterning is ea
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