Thin film bi-epitaxy and transition characteristics of TiO 2 /TiN buffered VO 2 on Si(100) substrates
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Thin film bi-epitaxy and transition characteristics of TiO2/TiN buffered VO2 on Si(100) substrates Adele Moatti1, Reza Bayati2, Srinivasa Rao Singamaneni1, Jagdish Narayan1 1. Department of Materials Science and Engineering, North Carolina State University, EB-1, Raleigh, NC 27695-7906, USA 2. Intel Corporation, RA3, Hillsboro, OR 97124, USA ABSTRACT Bi-epitaxial VO2 thin films with [011] out-of-plane orientation were integrated with Si(100) substrates through TiO2/TiN buffer layers. At the first step, TiN is grown epitaxially on Si(100), where a cube-on-cube epitaxy is achieved. Then, TiN was oxidized in-situ ending up having epitaxial r-TiO2. Finally, VO2 was deposited on top of TiO2. The alignment across the interfaces was stablished as VO2(011)║TiO2(110)║TiN(100)║Si(100) and VO2(110) /VO2(010)║TiO2(011)║TiN(112)║Si(112). The inter-planar spacing of VO2(010) and TiO2(011) equal to 2.26 and 2.50 Å, respectively. This results in a 9.78% tensile misfit strain in VO2(010) lattice which relaxes through 9/10 alteration domains with a frequency factor of 0.5, according to the domain matching epitaxy paradigm. Also, the inter-planar spacing of VO2(011) and TiO2(011) equals to 3.19 and 2.50 Å, respectively. This results in a 27.6% compressive misfit strain in VO2(011) lattice which relaxes through 3/4 alteration domains with a frequency factor of 0.57. We studied semiconductor to metal transition characteristics of VO2/TiO2/TiN/Si heterostructures and established a correlation between intrinsic defects and magnetic properties. INTRODUCTION Combination of semiconducting and magnetic properties has led to development of spintronic (spin based electronics). This achievement facilitates production of spin-based devices. Different materials have been investigated for this application and some semiconductors such as VO2, ZnO, TiO2, Y2O3, and In2O3 have shown promising results at room temperature [15]. Among those VO2 shows a strong correlated electron system with a small band gap (~0.7 eV at room temperature) but its magnetic properties have not been studied yet. VO2 can serve as a smart material which generally responds to temperature, pressure variations and electric or magnetic fields. It is worth mentioning that VO2 has semiconductor-to-metal transition (SMT) at about 340 K resulting from an ultrafast phase transformation from a high temperature tetragonal state to a low temperature monoclinic state [6-8]. Considering practical applications, there is a problem with the bulk VO2 that it cannot withstand the repeated thermal cycling, while thin films and nanoparticles are more inclined to tolerate these stresses. Also, the SMT for films and nanoparticles can be tuned to room temperature, which makes their application very unique, such as, thermally activated optical switching [9,10], thermal relays and energy management devices [11,12], infrared sensors and actuators [13], micro-bolometers [14,15], electrochromic and photochromic memory and optical devices [16,17]. Magnetic, electrical, and optical properties of semiconductor
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