**2.2 Organic grafting via chlorination/alkylation**

Among those methods developed for planar silicon, the chlorination/alkylation process is considered a promising method for molecular grafting. In this method, we cover the Si surface with Cl atoms and then convert them to R molecules. The conversion process should maintain an inert atmosphere such as reflux system or glove box (**Figure 2**).

### **2.3 X-ray photoelectron spectroscopy**

X-ray photoelectron spectroscopy (XPS) can be used to investigate the chemical and electronic surface properties of the Si NWs. The final output of XPS measurements is the function of kinetic energy (or binding energy) versus the intensity. A schematic layout of the XPS system is depicted in **Figure 3** which shows the main components. Ay monochromatic Al K radiation (1487 eV) is irradiated to the sample to extract the core-level and valence band photoelectron spectra (0–1000 eV). They are collected at a take-off angle of 35° by a hemispherical analyzer with an adjustable overall resolution between 0.8 and 1.2 eV. In our case, it is very important to get high resolution for the following individual spectra:


#### **Figure 3.**

*Schematic layout of an X-ray photoelectron spectroscopy (XPS) system including the analyzer, sample stage, X-ray anode, X-ray monochromator, and electron gun.*

The resulting XPS spectra were analyzed, and oxide levels were determined by spectral decomposition using the XPS peak software.
