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Spontaneous formation of nanospiked microstructures in germanium by femtosecond laser irradiation

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Barada K Nayak1, Mool C Gupta1,3 and Kurt W Kolasinski2

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We report a novel phenomenon of spontaneous formation of nearly regular arrays of nanospikes atop conical microstructures by exposing a germanium surface to femtosecond laser pulses in an environment of SF6. Silicon laser texturing has been reported, but no information has been published on laser microtexturing of Ge and in particular the observation of nanospikes atop conical microstructures. The nanospikes are around 2 µm high having a tip radius of 100 nm and are formed atop conical microstructures that are around 5 µm wide and 10 µm tall. The tip radius could be sharpened down to ~10 nm by brief chemical etching. A higher laser fluence and fewer shots favour the formation of nanospikes. By increasing the number of shots at higher fluence the surface morphology changes from conical microstructures to tall straight-walled pillar-like structures and the nanospikes disappear. The surface morphology of germanium has been compared with silicon. The germanium samples turn completely black after laser processing, i.e. they exhibit greatly reduced reflectivity throughout the visible spectrum.


PACS

81.16.Mk Laser-assisted deposition

68.35.B- Structure of clean surfaces (and surface reconstruction)

61.46.-w Structure of nanoscale materials

81.65.Cf Surface cleaning, etching, patterning

61.82.Fk Semiconductors

61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Subjects

Semiconductors

Surfaces, interfaces and thin films

Condensed matter: structural, mechanical & thermal

Nanoscale science and low-D systems

Dates

Issue 19 (16 May 2007)

Received 25 January 2007, in final form 12 March 2007

Published 17 April 2007



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