**5. Device fabrication and sensor setup**

Fabricated Si nanostructures were incorporated as the anode in gas ionization cell. The cathode is a piece of p-type Si cleaned with RCA method and coated with a 5 μm aluminum (Al) layer using thermal evaporation technique. The electrodes are separated, using an insulating thin film (double sided adhesive tape), by a narrow gap but wide enough to allow the flow of the gases through the cell. **Figure 7** shows the schematic illustration of the gas ionization cell.

The device was placed in the gas chamber and vacuumed to 10<sup>−</sup><sup>5</sup> Torr prior to introduce each gas to the chamber. The electrodes are connected to two source measure units (SMUs) of a HP4155 semiconductor parameter analyzer and I-V characteristics of the device was conducted by sweeping the voltage of the anode

#### **Figure 7.**

*Schematic of Si nanowires-based GITS. Fabricated sample is applied as the anode and it attached to SMU #1 of the parameter analyzer. An Al coated Si is applied as the cathode. Electrodes are separated by two pieces of double sided adhesive tape. The other sides are left open to facilitate the gas flow through the sensor.*

from 0 to 100 V, with steps of 1 V and 1 second sweep delay. The sensor was tested for oxygen (O2), argon (Ar), Nitrogen (N2) and helium (He) at low pressures.
