Laser induced patterning of Bi thin films
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Laser induced patterning of Bi thin films Carlos Acosta Zepeda1, Giovanni Mecalco1, J. L. Hernández-Pozos1, Marco Antonio Zepeda1, N. Batina2, E. Haro-Poniatowski1 1
Departamento de Física, Universidad Autónoma Metropolitana Iztapalapa, Av. San Rafael Atlixco No. 186 Col. Vicentina, C.P. 09340 México D.F., México; 2 Departamento de Química, Universidad Autónoma Metropolitana Iztapalapa, Av. San Rafael Atlixco No. 186 Col. Vicentina, C.P. 09340 México D.F., México. ABSTRACT Laser irradiation of Bismuth thin films through a diffractive mask was investigated. The thin films were composed of nano and microcrystals Bismuth with sizes ranging from 20 to 500 nm. Upon laser irradiation (λ=355 nm) the structured illumination field locally modified the material. In the high intensity regions the surface was transformed whilst low intensity areas were left intact. The modification mechanism was melting followed by coalescence of the nanocrystals giving rise to a more uniform structure. The laser irradiated area was characterized by scanning electron microscopy and atomic force microscopy. The patterns were computed by Fresnel diffraction theory and the agreement between the theory and the experiments was very good. INTRODUCTION Pulsed or continuous laser irradiation effects on metallic thin films deposited on various types of substrates have been studied extensively. One of the most important potential applications in the early eighties was the laser annealing of ion-implanted semiconductors [1]. Laser processing of materials is also a very active field of study [2]. Furthermore, several effects can be observed depending on the characteristics of the laser used, such as, wavelength, pulse duration, laser energy density etc…[3-4]. More recently, it has also been demonstrated that it is possible, by laser irradiation and the use of masks, to locally modify the size and morphology of nanostructured thin films [5]. This technique has been referred to as the diffraction-assisted method (DAM) [6]. We should also mention that, additional to nanopatterning created by the irradiation of films made up of nano or micro sized particles, it is also possible to obtain ordered micron-sized features on semiconductor surfaces by irradiating them near to the laser ablation regime with a diffractive element [7]. Furthermore, specific micro and nano patterns can be generated on the metal surface using one or a few laser pulses. In this work we present the results of bismuth patterning. Bi based thin-films have been intensively studied in particular because of their special thermoelectrical properties. Superconductivity and quantum-size phenomena have been also reported [8]. Nano and micro patterning of surfaces has several applications such as for memory devices, data encryption and sensors. A variety of different techniques have been employed to print patterns on material surfaces, such as nanolithography and bottom-up techniques. Recently, we have shown that it is possible to simultaneously change the morphology and atomic arrangement of quasi
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