Dynamic force microscopy study of the microstructural evolution of pulsed laser deposited ultrathin Ni and Ag films
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M. Ghanashyam Krishnaa) School of Physics, University of Hyderabad, Hyderabad-500046, India; and Department of Engineering Sciences, Oxford University, Oxford OX1 3PJ, United Kingdom
A.K. Bhatnagar School of Physics, University of Hyderabad, Hyderabad-500046, India
A.K. Bhattacharya Department of Engineering Sciences, Oxford University, Oxford OX1 3PJ, United Kingdom (Received 14 July 2007; accepted 27 November 2007)
Ultrathin films (6–10 nm) of silver and nickel were deposited by pulsed laser deposition (PLD) in high vacuum (1 × 10−6 mbar). Microstructural evolution of these films as function of incident laser energy, substrate temperature, substrate material [borosilicate glass, fused silica, MgO(100) and Si (311)] and target–substrate distance was studied in detail using dynamic force microscopy. It is shown that with increase in laser energy incident on the target, there is a substantial increase in particle size in the film. The effect of increased laser energy on microstructure is much more drastic than that for the increase of substrate temperature. In general, denser packing of nanoparticles and increased clustering have been observed at elevated substrate temperature. Increase in laser energy gives rise to higher average grain size, packing density, and clustering in comparison to substrate temperature. It is observed that the aspect ratio of grains is dependent on incident laser fluence and substrate temperature, but more drastically on the substrate material. Substrate coverage and aspect ratio of the grains are particularly dependent on the nature of crystallinity of the substrates. It is demonstrated that PLD provides a greater degree of microstructural manipulation than other physical vapor deposition techniques. I. INTRODUCTION
Pulsed laser deposition (PLD) was first conceived as a technique to aid in the synthesis of multicomponent and complex materials in thin film form.1–5 The basic process involves the ablation of the target material by a focused pulsed-laser beam. PLD is, for many reasons, a versatile technique. Because, in this method, the energy source is located outside the chamber, the use of ultrahigh vacuum (UHV) can be made to deposit ultrathin films with high purity and varying microstructures. In comparison with the more conventional vapor deposition techniques such as sputtering and evaporation, PLD provides additional parameters, i.e., laser energy, repetition rate, and angle of laser incidence, which should, in principle, afford greater flexibility to the process. Though these advantages have been recognized, literature on elemental metallic ultrathin films deposited by PLD is relatively scarce.6–10 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0228 1826
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 7, Jul 2008 Downloaded: 13 Mar 2015
There are no studies on initial stages of growth of metallic films by PLD on different substrates as a function of the ablation parameters and other process variables such as substr
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