Trichlorosilanes as Anchoring Groups for Phenylene‐Thiophene Molecular Monolayer Field Effect Transistors

Abstract

accumulation layer in a device. Thanks to this two dimensional transport layer SAMFETs show great potential in the fi eld of chemical sensors where direct access to the charge transport layer by analytes will have a strong infl uence on the device properties.Early attempts to fabricate SAMFETs resulted in poor performance at channel lengths >1 µm, due to high contact resistance and poor long range order of the π-conjugated cores. [ 14,16 ] The breakthrough was achieved when Smits et al. reported a SAMFET molecule consisting of a monochlorosilane anchoring group separated from a quinquethiophene core by an alkyl spacer. [ 12 ] The molecule showed long range order when deposited onto a silicon dioxide surface and fi eld effect characteristics could be obtained over large areas for channel lengths up to 40 µm. SAMFETs have now been reported using phosphonic acid anchoring groups to covalently attach to aluminum oxide and alternative aromatic cores to create p-and n-type transistors over long channel lengths. [8][9][10][11]17,25,26 ] Herein, we report a novel p-type SAMFET molecule anchored through a trichlorosilane to give working fi eld effect transistors for devices with long channel lengths (100 µm). The use of a trichlorosilane allows an accelerated deposition of a continuous monolayer over large areas with minimal post processing. The fi lms were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and variable angle attenuated total refl ectance -Fourier transform infrared (VATR-FTIR) spectroscopy. Results and Discussion Molecular Design ConsiderationsThe choice of the semiconducting core of the SAM molecule is crucial to the realization of high-performance SAMFETs with a dense and ordered semiconducting monolayer. It has been recognized that conjugated mesogens can be self-organized into large area monodomains without defects caused by grain boundaries by processing in the mesophase. [ 18,19 ] Conjugated mesogens based on a phenylene-bithiophene core (PTTP) are promising semiconductors employed in OFETs due to the simple synthesis and favorable liquid crystalline phase behavior. [19][20][21] Further, the introduction of the phenylene units lowers the HOMO level leading to improved device stability in Trichlorosilanes as Anchoring Groups for PhenyleneThiophene Molecular Monolayer Field Effect TransistorsAdam V. S. Parry , Kexin Lu , Daniel J. Tate , Barbara Urasinska-Wojcik , Dolores CarasQuintero , Leszek A. Majewski , and Michael L. Turner * Self assembled monolayer fi eld effect transistors (SAMFETs) are reported using a phenylene-thiophene containing semiconducting mesogen attached through a trichlorosilane anchoring group. Monolayer fi lms, covalently attached to silicon dioxide substrates, form in less than 10 h from solution, thanks to the accelerated reaction of the trichlorosilane anchor. Devices exhibit mobilities as high as 1.7 × 10 −2 cm 2 V −1 s −1 , currents of up to 15 µA (on/off current ratio of 10 6 ) with device yields close to unity over large areas for cha...

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N-Heterocyclic Carbenes for the Self-Assembly of Thin and Highly Insulating Monolayers with High Quality and Stability

“…The final step in BIM/Au analysis was testing the conductivity of these NHC SAMs in the molecular junction. Generally, the formation of such a junction is the most basic and, at the same time, the most critical step in the construction of virtually all organic/molecular electronic devices based on SAMs applications, − as briefly mentioned in the introduction. Whereas formation of the bottom electrode contact for SAMs is rather simple considering their spontaneous chemisorption on the metal substrate, the formation of the top contact is much more problematic due to the possible diffusion of the metal atoms from the top electrode through the film, leading to short circuiting of the junction.…”

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