Ion beam assisted deposition of textured magnesium oxide templates on un-buffered glass and silicon substrates
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Biaxially textured magnesium oxide (MgO) templates of 10-nm thickness were successfully fabricated on glass and silicon substrates without any buffer layers using Ar+ ion beam assisted e-beam evaporation. With an additional layer of 100 nm homoepi MgO on top, the in-plane misorientation of ∼6.5° and out-of-plane misorientation of ∼2.0° have been obtained. Prior to growth, the substrates were bombarded with the same Ar+ ion beam for a certain period ranging from 5 to 35 min to provide initial substrate conditions for textured MgO formation. The ion beam induced modification of the substrate surface morphology was characterized using atomic force microscopy. Reduced surface roughness Ra from 2 to 3 nm on the original glass substrates to below 1.0 nm after 5 min ion beam bombardment was found to be an important condition for the textured MgO formation. The nearly unchanged Ra 艋 1 nm of the silicon substrate after the ion beam bombardment, however, suggests that additional surface modification is required for the textured MgO to form.
I. INTRODUCTION
Epitaxy is required in growth of thin films of many technologically important materials to realize the desired physical properties. To achieve epitaxy, a single crystal substrate is generally used to provide a textured template for the epitaxy to occur. The quality of epitaxy correlates directly to the lattice mismatch and chemical compatibility between the substrate and the film grown on top. In many practical applications, however, epitaxy is required on untextured substrates including amorphous and polycrystalline ones. Generating biaxially textured templates on non-textured substrates is therefore necessary to achieve epitaxy of thin films. One such example is in thin film ferroelectric infrared detectors.1–3 To improve the sensitivity, ferroelectric Pb–Zr–O (PZT) films are grown on Si substrates coated with a non-textured polymer sacrificial layer. Although promising results have been obtained in these polycrystalline ferroelectric devices, better performance is anticipated if epitaxy of PZT is achieved.4,5 Ion-beam-assisted deposition (IBAD) combines a traditional deposition technique and the simultaneous irradiation of the growing film with ions at a certain angle from the substrate normal. The simultaneous use of ion
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0039 194
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 1, Jan 2006 Downloaded: 14 Mar 2015
beam during deposition has been found to induce texture formation during thin film growth. Early studies have shown that ion beam assisted growth of Nb films develops in-plane crystallographic texture parallel to the ion beam direction while Nb films grown without ion assistance develop no in-plane texture.6 Recently, ion-beamassisted deposition has been adopted to generate biaxially textured templates. Among few others, popular template materials include yttria-stabilized zirconia (YSZ)7–10 and magnesium oxide (MgO),11–17 which have enabled hetero-epitaxy o
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