Coaxial Metal-Silicide Ni 2 Si/C54-TiSi 2 Nanowires Chih-Yen Chen, † Yu-Kai Lin, † Chia-Wei Hsu, † Chiu-Yen Wang, † Yu-Lun Chueh, † Lih-Juann Chen, † Shen-Chuan Lo, ‡ and Li-Jen Chou* ,† † Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, ‡ Material and Chemical Research Laboratories, ITRI, Hsinchu, Taiwan * S Supporting Information ABSTRACT: One-dimensional metal silicide nanowires are excellent candidates for interconnect and contact materials in future integrated circuits devices. Novel core-shell Ni 2 Si/C54- TiSi 2 nanowires, 2 μm in length, were grown controllably via a solid-liquid-solid growth mechanism. Their interesting ferro- magnetic behaviors and excellent electrical properties have been studied in detail. The coercivities (Hcs) of the core-shell Ni 2 Si/ C54-TiSi 2 nanowires was determined to be 200 and 50 Oe at 4 and 300 K, respectively, and the resistivity was measured to be as low as 31 μΩ-cm. The shift of the hysteresis loop with the temperature in zero field cooled (ZFC) and field cooled (FC) studies was found. ZFC and FC curves converge near room temperature at 314 K. The favorable ferromagnetic and electrical properties indicate that the unique core-shell nanowires can be used in penetrative ferromagnetic devices at room temperature simultaneously as a future interconnection in integrated circuits. KEYWORDS: Core-shell, nanowire, Ni 2 Si, C54-TiSi 2 , silicide, interconnect A s the scaling trend of the microelectronics continues, one- dimensional nanowires are attractive materials for nano- electronics owing to their peculiar morphology as well as unique electronic, magnetic and piezotronic properties. 1-3 Nanostructured-metal-oxide-semiconductor field-effect transis- tors (MOSFET) devices have been made in integrated circuits comparable to the macroscale devices fabricated from the same materials. 4,5 Accordingly, there have been numerous studies in the literature dealing with the interface between semi- conductors and metallic electrodes, 6-8 in which metal silicides have attracted much attention for their low resistivity serving as device-to-device interconnects and nanocontacts in silicon complementary metal-oxide-semiconductor (CMOS) devi- ces. 6-10 Furthermore, nickel silicides 9-12 and titanium silicides are the two most extensively investigated group of silicides. 9,10,13 NiSi has the best lattice match to silicon, TiSi 2 also possessed low resistivity, and both silicides have been utilized often in the electronic devices. Ni 2 Si has been used as a gate material for 45 nm CMOS devices and p-MOS technology due to their low process temperature, higher conductivity, and more suitable work function compared to other nickel silicides. 14,15 Besides, Ni 2 Si has achieved great importance in recent years due to its ferromagnetic properties and significant catalytic activity. 16-18 On the other hand, C54-TiSi 2 is also a well-known semiconductor material, which has a lower electrical resistivity and is commonly used in small scale devices. 19,20 While considerable attention has been paid in the past to axial metal silicide nanowire heterostructures, 6,21-25 concerns about radial silicide nanowire heterostructures have only recently emerged. 20,26-28 It is worth mentioning that one dimensional (1D) core-shell Ge/Si nanowires have been used as high-performance coaxial FET devices 26 and core-shell Cr 5 Si 3 /Si nanopillars can improve the carrier transport between the metal and semiconductor layers. 28 As a result, core-shell metal silicide nanostructures should be explored as nanodevices due to their interesting and unique properties. Herein, we report the formation of core-shell Ni 2 Si/C54-TiSi 2 nanowire heterostructures as well as their magnetic and electrical properties. Results and Discussion. Core-shell Ni 2 Si/C54-TiSi 2 nanowires were fabricated by annealing NiSi 2 films on Si substrate at an ambient containing Ti vapor in an ultrahigh vacuum (UHV) chamber. Silicon (100) wafers (1-5 Ω-cm) were cleaned using a standard RCA cleaning process. Next, a 30 nm Ni thin film was deposited on the Si substrate using a UHV electron beam evaporator. The samples were then annealed at 600 °C for 30 min without breaking the vacuum to develop the NiSi 2 film into a nanodot sample. 29,30 The chamber pressure was below 10 -9 Torr during both processes. The annealed samples were quickly transferred into a heating chamber for annealing at 850 °C in a vacuum below 10 -7 Torr and heated with a Ti filament at 800 °C during the designated time Received: December 18, 2011 Revised: March 27, 2012 Published: March 27, 2012 Letter pubs.acs.org/NanoLett © 2012 American Chemical Society 2254 dx.doi.org/10.1021/nl204459z | Nano Lett. 2012, 12, 2254-2259