Formation of Fe-Co-Si Structure in Fe and Co Implanted Si Substrate
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Formation of Fe-Co-Si Structure in Fe and Co Implanted Si Substrate Wickramaarachchige J. Lakshantha1, Satyabrata Singh1, Floyd D. McDaniel1, Bibhudutta Rout1 1
Ion Beam Modification And Analysis Laboratory, Department of Physics, University of North Texas, Denton, Texas 76203, USA.
ABSTRACT Ternary Fe-Co-Si B20 phase structure was formed by implanting Fe and Co ions consecutively into Si(100) substrate at 50 keV energy, each with a fluence of 1.0 × 1017 atoms/cm2 and post-thermal vacuum annealing at 500 oC for 60 minutes. An in-situ magnetic field was used to enhance the formation of the ternary phase in the Si substrate during the implantation process. The magnetic field of 0.05 T was applied perpendicular to the incoming ion beam direction and parallel to the substrate surface to form elongated clusters in the transverse direction of the sample. Prior to the implantation of ions, the implant ions depth profiles were simulated using a dynamic ion-solid interaction code (TRIDYN). The TRIDYN simulation predicted a saturation in the peak concentration of the Fe and Co ions at a fluence of 1.0 × 1017 atoms/cm2. XPS measurement at the peak concentration depth (40 nm) showed the presence of Fe (23 %) and Co (32 %) in the Si matrix. XRD characterization confirmed the presence of stable Fe-Co-Si B20 phase structure in the annealed samples implanted with the insitu magnetic field. INTRODUCTION Binary and ternary transition metal silicide thin films and nano-structures have been studied with great interest due to their unique structural, electrical and magnetic properties. The interests in these systems are triggered by their potential use in advanced silicon based optoelectronic devices. Most of the transition metal silicides show metallic behaviors in their stable phase configuration [1]. The well-known Fe-Si binary silicide phases show metallic, semiconducting, and half-metallic properties depending on the phase [2]. The ternary transition metal silicides, particularly Fe-Co-Si compounds have attracted considerable attention. The FeCo-Si alloy form several different phases including the Heusler phases, along with unique halfmetallic properties at higher Curie temperatures [3-6]. The binary iron silicide system synthesized via ion implantation have been studied by several groups [7]. However, the ternary silicides have been by far less studied than their binary counterparts due to the difficulties in the synthesis. The phase formation of ternary silicides is not well understood, because most often the ternary silicides are formed in metastable phases. Earlier, Dzsi et al. have reported the formation of metastable ternary phases by sequential Fe and Co ion implantation into Si [6]. Conventional ion implantation has the potential to be used to produce MxFe(1-x)Si2 (M=Co, Mn, Ni etc.) [6]. In this study, we have investigated the formation of Fe-Co-Si B20 phase ternary structures in Si substrates using low energy ion implantations and post-thermal annealing. EXPERIMENTAL The Fe and Co ions were implanted consecutively at an
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