Nanostructured Mn-Doped TiO2 Synthesized by Atomic Layer Deposition for Spintronics Applications

Tuesday, November 9, 2010: 3:35 PM
254 C Room (Salt Palace Convention Center)
Meredith C.K. Sellers and Edmund G. Seebauer, Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL

The progressive downscaling of integrated circuits and storage devices necessitates a better comprehension of how to electrically manipulate spin and magnetization in nanostructured ferromagnetic semiconductors. Devices leveraging the spin-dependent effects of these materials would allow for increased data processing speeds, decreased power consumption, and improved integration densities in comparison to standard charge-based electronics. In the past ten years, experimental and computational studies have demonstrated room temperature ferromagnetism (RTFM) for several TiO2-based dilute magnetic semiconductors (DMSs) namely TiO2 doped with Mn, Cr, Fe, and Co. It is proposed that room temperature ferromagnetism (RTFM) in transition metal (TM) doped TiO2 originates from native point defects, grain boundaries, and dislocations. There is a fundamental lack of understanding concerning how film preparation conditions, microstructure, and defect density affect the magnetic properties of DMSs. Standard DMS preparation methods such as sol-gel, pulsed laser deposition (PLD), and plasma-assisted molecular beam epitaxy (PAMBE) prohibit further decoupling of these factors. Additionally, these techniques are not well suited to the high throughput requirements of commercial manufacturing. On the other hands, atomic layer deposition (ALD), a pulsed-precursor vapor phase deposition method related to chemical vapor deposition (CVD), is an attractive technique for the fabrication of thin films with precise thickness and compositional control on large-area substrates. The present work involves the synthesis of Mn-doped anatase TiO2 (0 to 5 at% Mn) thin films on Si(100) via ALD at 200C and 400C. Ti(OCH(CH3)2)4 and H2O are utilized as ALD precursors and Mn(DPM)3 as a dopant source. X-ray photoelectron spectroscopy measurements indicate that Mn is successfully doped in the TiO2 matrix and reveal information about film composition and elemental chemical states. Microstructure, crystallinity, bulk density, and roughness were investigated with scanning electron microscopy, x-ray diffraction, and x-ray reflectivity. SQUID magnetometry was used as a probe of RTFM; the bulk density, microstructure, and magnetic moment of the TiO2 vary with the concentration of Mn. The results provide insight into the properties of nanostructured DMS TiO2 synthesized via ALD and address the coupling between TiO2 defect composition and RTFM.

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