Current-voltage characteristics of molecular conductors: two versus three terminal

Damle, Prashant S.; Rakshit, Titash; Paulsson, Magnus; Datta, Supriyo

doi:10.1109/tnano.2002.806825

Cited by 91 publications

(90 citation statements)

References 23 publications

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“…Au) contacts due to metal induced gap states resulted from metal-molecule interaction. 4 The relatively low density of states of SWNTs may circumvent this problem. Covalent contacts to molecules could also be made via C-C bonding to the nanotube ends.…”

Section: B Cmentioning

confidence: 99%

Miniature Organic Transistors with Carbon Nanotubes as Quasi-One-Dimensional Electrodes

et al. 2004

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With a cut metallic SWNT (gap L ~ 5-6 nm) bridged by a pentacene nano-crystallite (Fig.1b&c), we observed clear semiconducting FET characteristics in the current vs. gate (I ds -V gs ) curve (Fig. 2a). The device exhibited a current modulation of I max /I min ~ 10 5 under gating at a fixed bias voltage of V ds = -0.5V. The drastic switching clearly differed from the original metallic SWNT device (lack of gate dependence, Fig. 2a inset). This corresponds to the formation of a pentacene FET with channel length L ~ 5-6 nm and width of w ~ 2 nm (i.e., the diameter of the SWNT) as charge transport via hopping between pentacene molecules should be mainly confined in a width on the order of the tube diameter. Notably, the subthreshold swing of the device is S ~ 400 mV/decade (Fig. 2a).Small organic molecules and conjugated polymers can be easily processed to afford functional electronics such as field effect transistors (FETs), 1a and in principle, scaling 1b to singlemolecule long devices could circumvent the low carrier mobility problem for these materials to afford high performance ballistic FETs 2,3 . For highly scaled molecular transistors with short channels however, it is crucial to develop novel device geometries to optimize gate electrostatics needed for ON/OFF switching. 4,5 It is shown here that single-walled carbon nanotubes (SWNT) can be used as quasi one-dimensional (1D) electrodes to construct organic FETs with molecular scale width (~2 nm) and channel length (down to 1-3 nm). The favorable gate electrostatics associated with the sharp 1D electrode geometry allows for room temperature conductance modulation by orders of magnitude for organic transistors that are only several-molecules in length, with switching characteristics superior to devices with lithographically patterned metal electrodes. We suggest that carbon nanotubes may prove to be novel electrodes for a variety of molecular devices.We first developed a reproducible method of cutting metallic SWNTs to form small gaps within the tubes and with control over the gap size down to L~2 nm. The cutting relied on electrical break-down 6 of individual SWNTs between two metal electrodes (Fig. 1a), and the size of the cut was found to be controllable by varying the lengths of the SWNTs (see Ref.6b and Supp. Info). Organic materials were then deposited to bridge the gap in the vapor (for pentacene) or solution phase (for regio-regular ploy (3-hexylthiophene), P3HT), forming the smallest organic FETs with effective channel length down to L~1-3 nm and width ~2 nm. b cWe varied the channel lengths L of SWNT-contacted pentacene FETs (L ~ 1-3 nm, L ~5-6 nm and L ~10-15 nm respectively) and observed length dependent transport properties at various temperatures. At T=300K, the devices exhibited on-current I max scaling approximately with ~1/L (under V ds =-1 V). This suggests

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Section: B Cmentioning

confidence: 99%

Miniature Organic Transistors with Carbon Nanotubes as Quasi-One-Dimensional Electrodes

et al. 2004

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“…6 Another example of asymmetric I-V is when the electrostatics of the system is dominated by one contact, e.g., a gated molecule where the gate is electrically connected to the source electrode. 10,11 This gives rise to a spatially asymmetric electrostatic potential over the molecule which in turn generates a strong asymmetry in the I-V. In these, as well as most commonly studied examples of rectification, some kind of spatial asymmetry in the system seems essential, causing the energy levels, the electrostatic potential and the electron wave functions to be quite different for positive and negative voltages.…”

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confidence: 99%

Charging-induced asymmetry in molecular conductors

et al. 2004

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We investigate the origin of asymmetry in various measured current-voltage (I-V) characteristics of molecules with no inherent spatial asymmetry, with particular focus on a recent break junction measurement. We argue that such asymmetry arises due to unequal coupling with the contacts and a consequent difference in charging effects, which can only be captured in a self-consistent model for molecular conduction. The direction of the asymmetry depends on the sign of the majority carriers in the molecule. For conduction through highest occupied molecular orbitals (i.e. HOMO or p-type conduction), the current is smaller for positive voltage on the stronger contact, while for conduction through lowest unoccupied molecular orbitals (i.e. LUMO or n-type conduction), the sense of the asymmetry is reversed. Within an extended Hückel description of the molecular chemistry and the contact microstructure (with two adjustable parameters, the position of the Fermi energy and the sulphur-gold bond length), an appropriate description of Poisson's equation, and a self-consistently coupled non-equilibrium Green's function (NEGF) description of transport, we achieve good agreement between theoretical and experimental I-V characteristics, both in shape as well as overall magnitude.

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“…[11] This technologically challenging constraint is needed for efficient penetration of the gate-induced electric field through the molecular channel and enables the application of reliable and relatively low V G scans. [8,12] In this work we show, for the first time, a 1-nm-sized molecular transistor that fulfills these demanding requirements. We operate this device in two distinct modes: reversible voltage-controlled switching and gate-controlled hysteresis.…”

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confidence: 85%