Characterization of the laser ablation plasma used for the

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Applied Surface Science 254(2007) 185–188 www.elsevier.com/locate/apsusc

Characterization of the laser ablation plasma used for the deposition of amorphous carbon
´ ´ ´ Enrique Camps a,b, L. Escobar-Alarcon a,b,*, V.H. Castrejon-Sanchez a,b, ´ M.A. Camacho-Lopez b, Stephen Muhl c
´ ´ ´ Departamento de Fısica, Instituto Nacional de Investigaciones Nucleares, Apartado Postal 18-1027, Mexico DF 11801, Mexico b ´ ´ ´ ´ ´Facultad de Quımica, Universidad Autonoma del Estado de Mexico, Paseo Colon y Tollocan, Toluca, 50110, Mexico c ´ ´ ´ ´ Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 364, Mexico DF 01000, Mexico Available online 10 July 2007
a

Abstract The plasma produced by laser ablation of a graphite target was studied by means of optical emissionspectroscopy and a Langmuir planar probe. Laser ablation was performed using a Nd:YAG laser with emission at the fundamental line with pulse length of 28 ns. In this work, we report the behavior of the mean kinetic energy of plasma ions and the plasma density, as a function of the laser fluence (J/cm2), and the target to probe (substrate) distance. The characterized regimes were employed to deposit amorphouscarbon at different values of kinetic energy of the ions and plasma density. The mean kinetic energy of the ions could be changed from 40 to 300 eV, and the plasma density could be varied from 1 Â 1012 to 7 Â 1013 cmÀ3. The main emitting species were C+ (283.66, 290.6, 299.2 and 426.65 nm) and C++ (406.89 and 418.66 nm) with the C+ (426.65 nm) being the most intense and that which persisted forthe longest times. Different combinations of the plasma parameters yield amorphous carbon with different structures. Low levels (about 40 eV) of ion energy produce graphitic materials, while medium levels (about 200 eV) required the highest plasma densities in order to increase the C–C sp3 bonding content and therefore the hardness of the films. The structure of the material was studied by means ofRaman spectroscopy, and the hardness and elastic modulus by depth sensitive nanoindentation. # 2007 Elsevier B.V. All rights reserved.
PACS : 78.40.Fy, 81.05.Hd, 81.15.Fg Keywords: Amorphous carbon; Laser ablation

1. Introduction Amorphous carbon (a-C) thin films with properties close to those of diamond (high C–C sp3 content) have been the subject of many studies due to their potentialapplications. However, films with properties close to those of a graphitic-like material (i.e. high C–C sp2 content) are also of interest for biological applications [1], or doped with nitrogen for the formation of hard and very elastic materials [2]. In summary, different values of the sp2/sp3 ratios yields materials that can have different applications; therefore, a good control of the depositionprocess is required for a given application. The most commonly used methods to create these types of films involve the use of plasmas and the properties of the deposited films are closely

related to the plasma parameters used during deposition. In the present work, pulsed laser deposition technique was used for the formation of amorphous carbon thin films. The plasma produced when the target is...