Metastable Materials Formation by ion Beam Assisted Deposition: Application to M Clusters in Ceramic Matrices
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ABSTRACT: The collision cascade, the fundamental event in ion-solid interactions, is responsible for the beneficial effects on thin films deposited by low energy ion beam assisted deposition (IBAD) or by energetic ion assisted deposition processes in general. However, the fundamental implications of the marriage of collision cascades and film growth processes have yet to be fully realized. The first half of this paper reviews the effects of ion bombardment on film growth and reaches some new conclusions. We propose that IBAD represents a different ion-solid interaction in a fundamental sense, and that as such, it should lead to new microstructures unattainable by other materials synthesis methods. The second part of this paper discusses the deposition of metal nanoclusters in a dielectric matrix by means of beam assisted phase separation (BAPS), a term coined here to describe deposition of phase-separated multicomponent materials. Examples discussed are gold nanoparticles in both niobium oxide and silica matrices. INTRODUCTION Ion beam assisted deposition (IBAD) has achieved significant penetration into the optical thin-film industry due primarily to the fact that IBAD films are denser than evaporated or sputtered films. The higher densities increase both optical performance
and production yield. The possibility for the production of unique metastable materials by IBAD has not been a focus of the research using the technique, with some exceptions (e.g., c-BN, MoN (BI phase), Cu504) [1,2,3]. In this paper we explore the fundamental aspects of ion-solid interactions and reach the following conclusions: IBAD processing drives material synthesis parameter space into new regimes in the timetemperature-flux continuum, and, this attribute of IBAD processing leads to microstructures far from equilibrium that are unattainable by other materials synthesis methods. Energetic deposition techniques have been studied for over 30 years [4] and intensively investigated for the last 15 years [5, 6]. The term "energetic deposition" is blanket term used to describe many different deposition techniques that possess one common feature - the application of energetic species to the surface of the growing film [7-9]. Ion beam assisted deposition is singled out in this paper, but the same principles will apply to other energetic deposition techniques as well. We will first discuss the basic mechanisms of ion-solid interactions and film growth. This follows with an example of a process that uses IBAD to control the kinetics of phase transformations that are thermodynamically favored but kinetically inhibited. We call this process beam assisted phase separation, or BAPS.
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Mat. Res. Soc. Symp. Proc. Vol. 504 01998 Materials Research Society
ION BEAM ASSISTED DEPOSITION (RELATIONSHIP TO ION-SOLID INTERACTIONS) Since the mid 1980's, ion beam assisted deposition (IBAD) has been heavily investigated for production of thin films [5, 6, 10]. The IBAD process, schematically represented at the top of Fig. 1, incorporates all of the ion-solid
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