Ph.D Thesis

Ph.D StudentDirawi Rawi
SubjectChemically Sensitive Silicon Nanowire Field Effect
Transistors Linked with Microfluidic Channels
for Enhanced Detection
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor PROF. Hossam Haick
Full Thesis textFull thesis text - English Version


Volatile organic compounds (VOCs) play an important role in our daily life. Some VOCs are dangerous to both human health and the environment. Other VOCs can be used to diagnose human health. In the current work we design, fabricate, and explore the potential to detect and classify VOCs by means of molecule-terminated silicon nanowire based field effect transistors (Si NW FETs) that is integrated with complementary microfluidic host cells.

FETs with an array of Si NWs were designed and fabricated. A systematic scaling study shows that a small number of bridged Si NW channels (3≤ n<80) provide random electrical features in these devices. Devices that are based on this understanding were then integrated with Microfluidic channels (MFCs) (~5 μL total volume). The combined devices were then exposed to a set of polar and nonpolar VOCs at various flow and concentration conditions. As a reference, all the results obtained with the microfluidic device were compared with a stainless steel chamber (SSC) (~194 ml total volume). The results showed the advantage of using MFCs over the SSC system in terms of sensitivity, response time, cleaning time and response amplitude, upon exposure to both polar and nonpolar VOCs. The significant advantages of MFCs over the SSC in all mentioned aspects were attributed to the specific type of flow, high velocity and mass transport caused by the miniaturization of the system. The same miniaturization has also affected the detectability of the polar and nonpolar VOCs. In the polar case, significant differences in the signals of the MFCs and SSC systems were obtained. These differences could be attributed to one or to a combination of factors. The first factor is the condensation of the VOCs and changing the dielectric medium, which, also, common with the nonpolar VOCs. The second factor is the electrostatic effect caused by the high friction between the monolayer and the polar VOCs. The third factor is the dipole moment and change in the surface states on the SiO2 surface of the Si NW due to condensation.

The results reported in this thesis show the ability to introduce a new generation of portable devices for real time detection of different kind of VOCs. These MFCs could lead to low production and exploitation costs of sensing analysis and to the improvement of the Si NWs FET detection system (i.e. sensitivity, response time, S/N ratio), with special emphasis on the detection of nonpolar VOCs.