Chemoresponsive monolayer transistors

Abstract

This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules, their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane (TCNQ), forming the basis for new types of environmental and molecular sensors.chemistry ͉ electronic materials ͉ nanoscience ͉ self-assembly T his work details a method to make chemoresponsive transistors by making devices out of a monolayer of polycyclic aromatic hydrocarbons that are chemically attached to surfaces. The devices are formed through a self-assembly process of organic semiconductors on the oxide surface of a silicon wafer (Fig. 1A) (1, 2). Previous studies on organic field-effect transistors (OFETs) (3, 4) have shown that the path for electrical current is through at most the first few layers of molecules at the oxide interface (5-7). In general, when the semiconducting layers of typical OFETs are scaled down to a monolayer, their properties become poor, presumably due to discontinuities or defects in the films (8-11). The strategy used here circumvents this problem by a chemical functionalization of the molecular semiconductors ( Fig. 1B) so that they both assemble laterally and chemically attach themselves to the substrate (Fig. 1C). The important result is that when ultrasmall point contacts separated by molecular length-scales are used as the source and drain (S͞D) electrodes, transistors can be made that have high gate efficiency and large ON͞OFF ratios from only a monolayer of molecules. The electrical properties of these monolayers are responsive to electron acceptors such as tetracyanoquinodimethane (TCNQ). Results and DiscussionDevice Fabrication. We first describe the devices used to measure the properties of the monolayers and then the structural and electrical characterization of these monolayers. Fig. 2 shows a schematic and micrograph of the devices used. Au (50 nm) on Cr (5 nm) pads, which are separated by 20 m, form the contact to an individual single-walled carbon nanotube (SWNT). The nanotubes were grown by a chemical vapor deposition (CVD) process described elsewhere (12, 13). The nanotube is then oxidatively cut by using an ultrafine lithographic process that produces a very small gap between the nan...

Nanogap Electrodes

“…In this field, Nuckolls and Guo et al [140][141][142][143][144][145] have done many impressive works. They introduced precise oxidative cutting of single-walled carbon nanotubes through a lithographic mask ingeniously to produce ultra small point contacts separated by only a few nanometers.…”

“…They introduced precise oxidative cutting of single-walled carbon nanotubes through a lithographic mask ingeniously to produce ultra small point contacts separated by only a few nanometers. These point contacts were robust and could be utilized to fabricate devices with a variety of molecules, acting as pH sensors, [141] chemoresponsive transistors, [140] photogated switches, [142] scaffolding for the assembly of biological macromolecules, [143] and DNA hybridization sensors [144] (Fig. 14).…”

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

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Self assembled monolayer fi eld effect transistors (SAMFETs) have been demonstrated consisting of a single molecular layer of organic semiconductor, self assembled from solution. [8][9][10][11][12][13][14]16 ] The principal building blocks of these devices are molecules with a π-conjugated semiconducting core that is coupled to a surface anchoring group capable of covalently binding to a surface. These molecules create a self-limiting monolayer between source and drain contacts that functions as a two dimensional charge transport layer, comparable in thickness to the charge ambient, humid conditions relative to that of the analogous oligothiophenes.…”

“…[ 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.…”

Diketopyrrolopyrrole‐Based Semiconducting Polymer with Both Hydrophobic Alkyl and Hydrophilic Tetraethylene Glycol Chains for Monolayer Transistor and Sensing Application

“…[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.…”