studies also suggest that the first few layers of organic/polymeric semiconductors play key roles in determining the performances of FETs. [10][11][12][13][14][15] Moreover, downscaling the film thickness to a single molecular layer is of technological interest for the realization of bottomup electronic devices. [16][17][18] In particular, monolayer organic FETs (OFETs) are beneficial for sensing applications as the binding of the respective analytes with the semiconducting monolayer is expected to affect the charge transporting. [19][20][21][22][23] Consequently, such sensors with monolayer FETs can show high sensitivity and fast response.Various approaches have been explored to fabricate FETs with ultrathin semiconducting films. These include unconventional spin-coating and formation of self-assembly monolayer on surface. [24][25][26][27][28] Langmuir deposition method is known to enable the realization of monolayers at the air/liquid interface with precision control over the molecule lateral packing density. In fact, Langmuir technique was successfully utilized to transfer monolayer thin films of organic and polymeric semiconductors onto the substrates to fabricate FETs. [29][30][31][32][33][34][35] For instance, Yli-Lahti and co-workers first reported FETs with Langmuir-Blodgett (LB) films of poly(3-hexylthicphene)/ arachidic acid, but the resulting FETs exhibited rather low charge mobilities. [34] This is probably due to the fact that the LB films contain arachidic acid which is required for the formation of the polymer LB films at air-water interface. Facchetti and Pignataro and co-workers prepared n-type monolayer FET with naphthalene diimide based polymer (P (NDI2OD-T2)) by using Langmuir-Schaefer method. [35] These conjugated polymers are basically hydrophobic, but it is known that amphiphilic molecules with both hydrophobic and hydrophilic moieties can form more ordered monolayers at the air-water interface. [36][37][38] Leclerc and co-workers studied the formation of LB monolayers at air-water interface and the transfer of the monolayers onto the substrate for the conjugated polymer with both alkyl and oligo(ethylene glycol) side chains, but the semiconducting properties of the monolayers were not addressed. [38] Functional field-effect transistors (FETs) have received increasing attention in recent years. Herein, it is demonstrated that the incorporation of hydrophilic tetraethylene glycol (TEEG) chains into the diketopyrrolopyrrole (DPP)-based semiconducting polymer (PDPP3T1) can facilitate the formation of polymeric monolayer at the air-water interface, and the resulting field-effect transistors (FETs) show sensitive and selective response toward alcohol vapor. By using the Langmuir-Schaefer method, monolayer and ultrathin films from bilayer to five-layer can be successfully prepared. Interestingly, nanopores with sizes of 50-100 nm are formed within the monolayer film, as observed by using atomic force microscopy. The monolayer FET exhibits relatively high hole mobilities up to 0.014 cm 2 V −1 s −...

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