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. (2009). Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors. Nature Nanotechnology, 4(10), 674-680.
The semiconductor of an organic field‐effect transistor is stripped with adhesive tape, yielding an exposed gate dielectric, accessible for various characterization techniques. By using scanning Kelvin probe microscopy we reveal that trapped charges after gate bias stress are located at the gate dielectric and not in the semiconductor. Charging of the gate dielectric is confirmed by the fact that the threshold voltage shift remains, when a pristine organic semiconductor is deposited on the exposed gate dielectric of a stressed and delaminated field‐effect transistor.
Detection of nitrogen dioxide, NO2, is required to monitor the air‐quality for human health and safety. Commercial sensors are typically chemiresistors, however field‐effect transistors are being investigated. Although numerous investigations have been reported, the NO2 sensing mechanism is not clear. Here, the detection mechanism using ZnO field‐effect transistors is investigated. The current gradually decreases upon NO2 exposure and application of a positive gate bias. The current decrease originates from the trapping of electrons, yielding a shift of the threshold voltage towards the applied gate bias. The shift is observed for extremely low NO2 concentrations down to 10 ppb and can phenomenologically be described by a stretched‐exponential time relaxation. NO2 detection has been demonstrated with n‐type, p‐type, and ambipolar semiconductors. In all cases, the threshold voltage shifts due to gate bias induced electron trapping. The description of the NO2 detection with field‐effect transistors is generic for all semiconductors and can be used to improve future NO2 sensors.
Patterned organic light-emitting diodes are fabricated by using microcontact- printed self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a direct handle on charge injection and enabling local modification of the light emission.
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