In Situ Characterization of the Pulsed Laser Deposition of Magnetic Thin Films
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IN S/1/U CHARACTERIZATION OF THE PULSED LASER DEPOSITION OF MAGNETIC THIN FILMS
A.J. Paul, D.W. Bonnell, J.W. Hastie, P.K. Schenck, R.D. Shull, J.J. Ritter, National Institute of Standards and Technology. Gaithersburg, MD, 20899.
ABSTRACT Pulsed Laser Deposition (PLD) has been proven as an effective means of depositing films from refractory targets. In our earlier work, either Nd/YAG or excimer lasers, interacting directly with target surfaces, were used to deposit thin films of high Tc superconductors, high dielectric constant BaTiO 3 and ferroelectric PbZro. 53Tio.470 3 (PZT). Time-resolved molecular beam mass spectrometry and optical emission spectroscopic techniques have been developed to characterize the vapor plumes responsible for film formation. More recently, this work has been extended to the PLD of magnetic thin films of AgFe3O 4 nanocomposites using excimer (ArF*, 193 nm) laser excitation. Optical emission spectra of the excited vapor phase species, formed during the plume generation and material deposition process, indicate that physically compressed powdered metal targets have inadequate homogeneity for film production, compared to targets that are chemically produced. An in situ Laser-induced Vaporization Mass Spectrometry (LVMS) technique utilizing a Nd/YAG (1064 rnm) laser has been used to determine Timeof-Arrival (TOA) profiles of the atomic, molecular, and ionic species produced in the plumes of AgFe 3O4 . The neutral species TOA profiles indicate velocity distributions that are multimodal and not Maxwellian. These observations are in contrast to the TOA profiles observed from one-component targets (Ag or Fe 30 4 ), where a single Maxwellian velocity distribution is found. M6ssbauer effect measurements of the thin films have been made for correlation with the gas phase studies. INTRODUCTION The use of PLD in the manufacture of magnetic and electronic thin film devices is increasingly becoming a viable alternative to ion sputtering. However, there is considerable lack of understanding concerning the dynamics of the laser-induced ejection of material from a target and the subsequent chemical processes that lead to the controlled production of thin films. Depending on the laser wavelength and the energy density at the target surface, a number of different processes that yield fundamentally different modes of material transport can occur separately or simultaneously [1]. Laser desorption occurs when individual laser photons interact with adsorbed or weakly bound surface species, providing enough energy to liberate individual atoms or molecules. Laser vaporization occurs when the photon bombardment of the surface acts as a thermal source, vaporizing refractory and chemically bound materials under local equilibrium conditions. Laser ablation occurs at relatively high laser fluences and short wavelengths, where multiphoton processes and surface-plasma interactions predominate. Multiphoton interactions result in the indiscriminate destruction of chemical bonds and the production of excess excited neutr
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