5-1 Conclusion
In this thesis, we investigated that the influence of SAM on the surface energy.
And propose the method to form the covalent bonding between APTES and BSA.
Then, we discuss the comparison of electrical characteristics between ODMS and APTES-OTFTs. Finally, research the interaction of different SAM-treated OTFTs to NH3 gas via the gated-4-probes OTFTs in a gas-sensing system.
First of all, we study the surface characteristics of SiO2 which are modified by ODMS and APTES. The ODMS and APTES transformed the SiO2 surface from hydrophilic to hydrophobic, and ODMS and APTES do not affect the surface roughness significantly but the surface of ODMS mixed with APTES is rough obviously. Because of the above reasons, we choose ODMS and APTES as our main SAM in our experiments. We also propose the manner which can cause BSA and anti-body to form covalent bonding with APTES. According to AFM analysis of BSA and SEM analysis of anti-body with APTES or ODMS, we see the surface of BSA with APTES is uniform and the Au atoms on anti-body can be seen, but BSA with ODMS is not easy to be detected by AFM. Therefore, we deduce that –NH2 on APTES will bond to BSA, but there are no functional groups on ODMS which can
bond to BSA.
Further, we compare ODMS with APTES-OTFTs electrical characteristics. The threshold voltage of APTES-OTFTs with functional group (-NH2) is obviously higher than ODMS-OTFTs and the field-effect mobility of APTES-OTFTs is smaller than ODMS-OTFTs because of –NH2 on APTES which can trap hole carriers to induce the low current and low mobility during on state.
Besides, in our observation, when ammonia (NH3)gas interacted with the OTFT, the threshold voltage is also shifted negatively to a larger value for both ODMS and APTES-OTFTs, and the field-effect mobility get lower with more NH3 .However, the subthreshold swing was almost unchanged. We also propose that the percentage (%) of Rcont and Rfilm versus injected NH3 and the percentage (%) of Rfilm is as high as about 90% during the NH3 gaseous experiment for ODMS and APTES-OTFTs.
Thus, we deduce the OTFT characteristics should be mainly dominated by the pentacene film properties rather than the contact properties.
We have proved that the functional groups,-NH2, on APTES affect electrical characteristics of OTFTs and electrical characteristics of OTFTs in ammonia. Through this thesis, we compare the sensitivity of ODMS and APTES-OTFTs in gas sensor.
Finally, we hope to research more functional groups like –COOH,-SH to enhance the diversity of OTFTs sensing gas in the future.
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