Organic NO₂ Sensors Based On SAMs Modified Films

Nitrogen dioxide(NO2)plays an important role in air pollution,thus high performance NO2 sensor has grown an critical research issue.Most commercial NO2 sensors for now are based on inorganic semiconductors,with low selectivity and feasibility of room temperature(RT)detection.At the same time,organic semiconductors show good potential on gas sensing with low cost,RT detection and high selectivity.However,they don’t have enough performances on sensitivity and response/recovery time.An organic NO2 sensor based on TIPS-pentacene crystalline films has shown very good performance,which originating from the strong charge transport ability and low original conductivity.In this thesis,based on the above work,we hope to obtain better NO2 sensor through modulating the original conductivity by controlling the interface electronic structure of the TIPS-pentacene crystalline films with modification of self-assembled monolayers(SAMs).The purpose of this thesis is,1)to optimize the growth and modulate the interface electronic structure of the TIPS-pentacene films,and obtain high quality crystalline TIPS-pentacene films with different original conductivities;2)to study the responses to NO2 and NH3 of the series of TIPS-pentacene films and construct high performance NO2 and NH3 sensors.The main content of this thesis is,1.We selected a series of silane molecules with different terminal groups(OTS,APTS,4-PBTS,FPPTS;end group of methyl,amino,phenyl,five fluorinated phenyl,respectively)to modify the surface of SiO2,then grew TIPS-pentacene films on them,and studied the morphology and structures of the films.We obtained high performance films on OTS and APTS.2.We tested the performances of parallel diodes and transistors of the series of films to study the influences of different SAMs on interface electronic structure of the films.And we found APTS trapped holes in the TIPS-pentacene films and FPPTS provided extra holes while other SAMs showed weak charge transfer with the TIPS-pentacene films.3.We fabricated chemiresistor type gas sensors with the series of TIPS-pentacene films,to detect the responses to NO2 and NH3.And we obtained an ultrahigh performance NO2 sensors with a sensitivity more than 1600%/ppm and a response/recovery time within 1 minute.The relationship between sensor performance and interface electronic structure of the series of TIPS-pentacene films was also studied.4.Transistor type gas sensors based on the series of TIPS-pentacene films were also constructed to detect NO2 and NH3.The transistor type sensors showed different performance with the corresponding chemiresistors.A stable transistor sensor was obtained with the films on 4-PBTS.The above results would be helpful to study the organic gas sensors from different views.