In situ Control of Atomic-Scale Si Layer with Huge Strain in the Nanoheterostructure NiSi/Si/NiSi through Point Contact Reaction

Abstract

Nanoheterostructures of NiSi/Si/NiSi in which the length of the Si region can be controlled down to 2 nm have been produced using in situ point contact reaction between Si and Ni nanowires in an ultrahigh vacuum transmission electron microscope. The Si region was found to be highly strained (more than 12%). The strain increases with the decreasing Si layer thickness and can be controlled by varying the heating temperature. It was observed that the Si nanowire is transformed into a bamboo-type grain of single-crystal NiSi from both ends following the path with low-activation energy. We propose the reaction is assisted by interstitial diffusion of Ni atoms within the Si nanowire and is limited by the rate of dissolution of Ni into Si at the point contact interface. The rate of incorporation of Ni atoms to support the growth of NiSi has been measured to be 7 x 10(-4) s per Ni atom. The nanoscale epitaxial growth rate of single-crystal NiSi has been measured using high-resolution lattice-imaging videos. On the basis of the rate, we can control the consumption of Si and, in turn, the dimensions of the nanoheterostructure down to less than 2 nm, thereby far exceeding the limit of conventional patterning process. The controlled huge strain in the controlled atomic scale Si region, potential gate of Si nanowire-based transistors, is expected to significantly impact the performance of electronic devices.

In-situ TEM Observation of Repeating Events of Nucleation in Epitaxial Growth of Nano CoSi2 in Nanowires of Si

“…Therefore, the interface between NiSi and Si is atomically sharp. 9 In addition, no misfit dislocations were found across the NiSi/ Si interface. Figure 1a,b shows that a Co particle (indicated by a blue arrow) disappeared within 0.07 s and the CoSi grew promptly within the same time period.…”

“…Since the Co source comes from both Co nanoparticles beside SiO 2 and point contact with Co nanowire, CoSi 2 tend to nucleate at high Co concentration region of the Si nanowire. 9 The selected area diffraction pattern (see inset) shows that the CoSi 2 is single crystalline with a CaF 2 structure.…”

“…As a result, the interface is rough. Comparing with NiSi formation within Si nanowire, NiSi was found to grow epitaxially on (111) Si with the following epitaxial relation; Si [1][2][3][4][5][6][7][8][9][10]//NiSi [1][2][3][4][5][6][7][8][9][10][11][12] and Si(111)//NiSi(31-1). Therefore, the interface between NiSi and Si is atomically sharp.…”

“…7,9 The movement of the NiSi/ Si interface producing 2 nm Si region was observed in situ. 9 In the present study, not only the stepwise axial growth but also lateral growth of atomic step at the CoSi 2 /Si interface was observed. In addition, the nucleation and growth stages of each layer of the epitaxial growth were well resolved in video images.…”

Nanoelectronic Devices from Nanowire Heterostructures

“…17,18 The formation of nanoscale metal silicide contact to silicon nanowires represents an interesting approach to address the above problems as the silicon/silicide interface is one with fewer crystal defects. 19,20 Nickel silicide has been reported and is being used as a contact material for silicon nanowire transistors to achieve both Ohmic and Schottky contacts by modulating the doping concentration in silicon nanowires. 21 In addition, some metal silicide nanowires are also reported to have ferromagnetic properties and can be used as the spin injector and detector for spintronics.…”