YungWoo Park

The role of external defects in chemical sensing of graphene field-effect transistors

A fundamental understanding of chemical sensing mechanisms in graphene-based chemical field-effect transistors (chemFETs) is essential for the development of next generation chemical sensors. Here we explore the hidden sensing modalities responsible for tailoring the gas detection ability of pristine graphene sensors by exposing graphene chemFETs to electron donor and acceptor trace gas vapors. We uncover that the sensitivity (in terms of modulation in electrical conductivity) of pristine graphene chemFETs is not necessarily intrinsic to graphene, but rather it is facilitated by external defects in the insulating substrate, which can modulate the electronic properties of graphene. We disclose a mixing effect caused by partial overlap of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of adsorbed gas molecules to explain graphenes ability to detect adsorbed molecules. Our results open a new design space, suggesting that control of external defects in supporting substrates can lead to tunable graphene chemical sensors, which could be developed without compromising the intrinsic electrical and structural properties of graphene.

Theoretical and experimental investigations of three-terminal carbon nanotube relays

We present theoretical and experimental investigations of three-terminal nanoelectromechanical relays based on suspended carbon nanotubes. A charge is induced in the nanotube by applying a voltage to an underlying gate electrode thus inducing the nanotube to bend and make contact with a drain electrode. Such devices have potential applications as fast switches, logic devices, memory elements and pulse generators. We describe two modes of operation: a contact mode where the nanotube makes physical contact with the drain electrode and a non-contact mode where electrical contact between the nanotube and the drain electrode is made via a field emission current.

A carbon nanotube gated carbon nanotube transistor with 5 ps gate delay

Semiconducting carbon nanotubes (CNTs) are attractive as channel material for field-effect transistors due to their high carrier mobility. In this paper we show that a local CNT gate can provide a significant improvement in the subthreshold slope of a CNT transistor compared to back gate switching and provide gate delays as low as 5xa0ps. The CNT gated CNT transistor devices are fabricated using a two-step chemical vapour deposition technique. The measured transfer characteristics are in very good agreement with theoretical modelling results that provide confirmation of the operating principle of the transistors. Gate delays below 2xa0ps should be readily achievable by reducing the thickness of the gate dielectric.

Random Telegraph Noise in Individual Single-walled Carbon Nanotubes

The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with electrons.

Random Telegraph Noise in Carbon Nanotube Peapod Transistors

Abstract We investigated the switching of resistance between two discrete values, known as random telegraph noise (RTN), observed in carbon nanotube peapod transistors [single‐walled carbon nanotubes (SWNTs), C60‐peapods, and Cs‐encapsulated SWNTs (so‐called Cs‐peapods)]. By analyzing the features of the RTN, we suggest that this noise for SWNTs is due to the random transition of defects between two metastable states, activated by inelastic scattering with ballistic electrons. The noise for C60‐peapods (Cs‐peapods) is attributed to the motion of C60s (Cs) in the nanotubes.