| Rational design and fabrication of nano-devices based on one-dimensionalnanostructures have flourished in the digital age, due to their broad application andhigh performance. Among the huge variety of1D nanostructures, nanofibersfabricated by electrospinning technology are attracting increasing research attention innano-device fabrication, due to their unique advantages, such as super-long andcontinuous1D structure, large and tunable surface area and porosity, varied andcontrolled components, low-cost and convenient assembly, and so on. However thereare still lots of problems hindering the practical application. By far, most of the formerresearch on electrospun nanofiber nano-devices is imitated from0D or other1Dnanostructures, and few research attention has been paid on structure design andmodulation for nanofibers toward devices. As a result, the performances of thenanofiber devices were often lower than conventional1D nanostructures in manyfields, and even worse than their bulk counterparts sometimes.In this thesis, we engage in structure design and modulation for nanofibers toimprove the performance of the corresponding devices, based on electrospinningtechnology. We will choose three kinds of typical and important electronic devices:chemical/electrochemical sensors, photoelectronic devices, and field-effect transistors(FETs). Firstly, inorganic p/n heterojunction, polymeric adsorbent/conducting polymer1D core-shell structure, and bimetalic oxide catalysts are designed and prepared toimprove the performance of chemical/electrochemcail sensors. Secondly,1Dweak-acceptor/donor core-shell polymeric heterojunction nanofibers are constructedfor high-performance photoelectronic devices. Thirdly, metal nanoparticelsimpregnated polymer semiconductor nanofibers and polyelectrodes/polymer semiconductors core-shell nanofibers are fabricated to improve the properties ofpolymer OFETs. The details are exhibited as follows:1. Electrospun nanofibers have been successfully applied for chemical sensors.In order to further improve the performance and do in-depth research, inorganic andpolymeric semiconductor devices have been investigated here.(i) For inorganicdevices, certain amount of Cr2O3has been in situ added into ZnO nanofibers duringthe electrospinning process and subsequent calcination to form p-Cr2O3/n-ZnOheterojunction (C/Z) nanofibers. The effect of the Cr2O3component in the C/Znanofibers on the gas sensing properties has been evaluated by the responses toethanol vapor. The results have showed that the C/Z nanofibers containing4.5wt%Cr2O3exhibit the best sensing properties to ethanol vapor. The response to1ppmethanol vapor is as high as3.6, and the response and recovery time are about1and5s,respectively. The as-prepared sensors also exhibit excellent selectivity and stability.(ii)For conducting polymers devices, we use polymeric adsorbents as sensitizers, insteadof inorgainc sensitizers (oxides or metals), and design a novel gas sensing structure:polymeric adsorbents/conducting polymers one-dimensional core-shell nanostructure,based on sulfonated poly(ether ether ketone)(SPEEK)/polypyrrole (PPy) core-shellnanofibers, via electrospinning and solution-phase polymerization. The SPEEK coresserve as sensitizers, which can not only provide excellent mechanical flexibility, butalso one-dimensional charge transport and collection. Most importantly, they canfacilitate more tested gases to pass through and react with the conducting polymershells, hence increasing the sensing response. Based on the SPEEK/PPy nanofibers,the sensors exhibit large gas responses, even when exposed to very low concentrationof NH3(20ppb) at room temperature. The work can be extended to other polymericsensitizers, and can develop a new platform to understand and designhigh-performance conducting polymer gas sensors2. Electrospun oxide semiconductors are used for electrochemical detectors, forthe first time in this part. Firstly, we fabricate NiO and CuO pure nanofibers and studytheir non-enzyme sensing properties towards glucose. Then a novel amperometricnon-enzymatic glucose sensor based on Pd/Cu bimetal oxide nanofibers (PCNFs) hasbeen successfully fabricated via electrospinning and calcination, and then employed toconstruct an amperometric non-enzymatic glucose sensor. The PCNFs glucose sensors display distinctly enhanced electrochemical sensing properties towards glucose,showing significantly lower overvoltage (～0.32V), ultrafast (0.5s) and ultrasensitivecurrent (1061.4μA mMï¼1cmï¼2) response, as well as good stability andanti-interference ability. Additionally, the effect of the1D nanostructure of nanofibers,and the inhomogeneous components on the electrochemical sensing properties arealso discussed.3. Promoted by the bulk heterojunction photoelectronic devices, a novelpolymeric heterojunction based on weak-acceptor-polyacrylonitrile/donor-polyanilinecore-shell nanofibers is designed for photoconductive devices through electrospinningfollowed by solution polymerization. The heterojunction provides phase-separatednano-interface for charges separation between the cores and shells, andquasi-one-dimensional charge collection and transport along the nanofiber structure,resulting in greatly enhanced optoelectronic performance. The short0.1secondresponse time upon irradiation is among the fastest values, as is the short0.1secondtime for return to the non-irradiated state. Extremely high on-off resistivity ratios(exceeding4×104) result for a drive voltage of only0.01V, which indicates the energyrequired for electrical input is small. Higher drive voltages (a modest10V) provide avery high responsivity of20AW–1driven by365nm UV irradiation. In addition, theas-prepared flexible photoconductive device maintains performance even afterbending fatigue tests for bending angles as large as180o.4. Polymeric field-effect transistors (FETs) have been widely investigated fortheir broad applications. They can increase the signal of chemical/electrochemicalsensors, photoelectronic devices, etc. In order to improve the generally low carriermobilities of polymeric FETs, we develop two effective approaches by structuredesign and modulation via electrospinning.(i) Au nanoparticles impregnatedpolyacrylonitrile (PAN)/conducting polymers (PANi, PPy, PTH) core–shell nanofibersare fabricated, which involves electrospinning of the cores and subsequent in-situgas-phase polymerization of the shells. These nanofibers provide very high mobilities(generally larger than1cm2/Vs), without crystallizing the molecular structures ofpolymers. These high mobilities owe to the nanofiber structure, which promotescharge transfer and reduces the grain-boundary effect; and the insertion of Au nanoparticles, which can be regarded as "nano-electrodes" to shorten the effectivechannel length and polymer semiconducting interconnections.(ii) Two effectiveroutes have been developed to improve the performance of FETs by researchers. Oneis the combination of semiconductors with electrolytes, the other is to useone-dimensional nanostructure as active channel. we herein introduce theelectrolytes-modulation route into one-dimensional core-shell nanostructure forOFETs for the first time, and fabricate sulfonated poly(arylene ether ketone)(SPAEK)/polyaniline (PANi) core-shell nanofibers via electrospinning combiningsolution-phase selective polymerization. Different from the reportedelectrolyte/semiconductor structures, the SPAEK core nanofibers do not serve as gatedielectric, but can provide an internal modulation. Based on the SPAEK/PANinanofibers, a high mobility of≈3cm2/Vs is obtained with the current on/off ratio ofexceeding104. Those figures of merits are both much better than previous PANi FETs. |
