## 3 Results and Discussion
### Properties of Silicide-Si Interface  
To investigate the phase of the silicide and the quality of the silicide-Si interface, an exemplary NW was sectioned parallel to its length. Subsequently, HRTEM was performed. The resulting images are shown in Figure 9. Starting with Ni-rich phases near the Ni-reservoir, the Si fraction increases towards the silicide-Si interface.  
Figure 8: SEM micrograph of silicidation of oxidized nanowires. Annealing is performed at 450 \({}^{\circ}\)C for 80 s.  
Figure 7: SEM images of (**a**) single, (**b**) double, and (**c**,**d**) triple nanowires, showing uncontrolled silicidation. The outer nanowires in images (**c**,**d**) have Ni-rich silicide phase while the inner ones appear to have NiSi\({}_{2}\). Annealing is performed at 450 \({}^{\circ}\)C for 10 min.  
HRTEM images show the formation of an atomically sharp Schottky junction, which is required for size downscaling and enhanced performance of the devices. FFT studies confirmed the formation of the desired NiSi\({}_{2}\) near the silicide-Si interface. The interface orientation is [111] in accordance with [16].  
In order to better understand our experimental observations, we calculated interface energies using density functional theory (DFT) as implemented in Atomistix ToolKit 15.1 [57]. The Perdew-Burke-Ernzerhof exchange-correlation function from [58] was used and the reciprocal space was sampled with a spacing of around 0.25 nm\({}^{-1}\).  
A periodic structure consisting of alternating silicon and NiSi\({}_{2}\) was studied. The length of the resulting supercell perpendicular to the interface was at least 12 nm. Periodic boundary conditions were employed in the parallel directions. The atomic arrangements of the studied interfaces are described in [59]. In order to mimic our experimental setup of a nanowire lying on a substrate, the lattice constants in the silicon and NiSi\({}_{2}\) regions were both fixed to the silicon lattice constant of the undisturbed silicon crystal. The atomic coordinates of all atoms within a 10 nm neighborhood around the interface were relaxed.  
We defined the interface energy density as:  
\[e_{\text{interface}}=\Big{(}E_{\text{supercell}}-N_{\text{NiSi}_{2}}E_{\text{ NiSi}_{2}}-N_{\text{Si}}E_{\text{Si}}\Big{)}/2A. \tag{1}\]  
\(E_{\text{supercell}}\) is the total energy of the calculated supercell, \(E_{\text{NiSi}_{2}/\text{Si}}\) are the total energies of bulk unit cells, and \(N_{\text{NiSi}_{2}/\text{Si}}\) follows from the number of unit cells in the supercell. \(A\) is the cross-section of the system and the factor 2 arises because two interfaces are included in a single supercell.  
The calculation resulted in interface energy densities of around 2.2 eV/nm\({}^{2}\) for the [111] interface (an A-type interface was assumed, see [59] for details) and around 4.2 eV/nm\({}^{2}\) for the [110] interface. This effect is partially compensated by the higher area of a {111} interface in a <110> nanowire, because an angle of 35\({}^{\circ}\) between the normal vector of the interface and nanowire orientation occurs. For geometrical considerations, the interface area is increased by a factor of around 1.2 compared to a {110} interface. Hence, the total energy contribution of the interface is smaller for a tilted {111} interface, which makes such an interface energetically more favorable. The experimental observations of the {111} interface are; therefore, explained by the calculated interface energy densities.  
Figure 9: HRTEM images of silicide–Si Schottky junction: (**a**) NW sectioned along the NW length, (**b**) high magnification image of the interface showing an atomically-sharp Schottky junction, and (**c**) Fast fourier transform (FFT) studies confirm formation of NiSi\({}_{2}\) phase near the silicide–Si interface. Annealing is performed at 450 \({}^{\circ}\)C for 80 s.