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D Natelson

Publications and source records attributed to D Natelson.

8 recordsLinked to original sources
PubMed2006

Controlling charge injection in organic field-effect transistors using self-assembled monolayers.

We have studied charge injection across the metal/organic semiconductor interface in bottom-contact poly(3-hexylthiophene) (P3HT) field-effect transistors, with Au source and drain electrodes modified by self-assembled monolayers (SAMs) prior to active polymer deposition. By using the SAM to engineer the effective Au work function, we markedly affect the charge injection process. We systematically examine the contact resistivity and intrinsic channel mobility and show that chemically increasing the injecting electrode work function significantly improves hole injection relative to untreated Au electrodes.

Crystallization↗
PubMed2006

Three-terminal devices to examine single-molecule conductance switching.

We report electronic transport measurements of single-molecule transistor devices incorporating bipyridyl-dinitro oligophenylene-ethynylene dithiol (BPDN-DT), a molecule known to exhibit conductance switching in other measurement configurations. We observe hysteretic conductance switching in 8% of devices with measurable currents and find that dependence of the switching properties on gate voltage is rare when compared to other single-molecule transistor devices. This suggests that polaron formation is unlikely to be responsible for switching in these devices. We discuss this and alternative switching mechanisms.

2,2'-Dipyridyl↗
PubMed2005

Quantum criticality in ferromagnetic single-electron transistors.

Considerable evidence exists for the failure of the traditional theory of quantum critical points, pointing to the need to incorporate novel excitations. The destruction of Kondo entanglement and the concomitant critical Kondo effect may underlie these emergent excitations in heavy fermion metals (a prototype system for quantum criticality), but the effect remains poorly understood. Here, we show how ferromagnetic single-electron transistors can be used to study this effect. We theoretically demonstrate a gate-voltage-induced quantum phase transition. The critical Kondo effect is manifested in a fractional-power-law dependence of the conductance on temperature (T). The AC conductance and thermal noise spectrum have related power-law dependences on frequency (omega) and, in addition, show an omega/T scaling. Our results imply that the ferromagnetic nanostructure constitutes a realistic model system to elucidate magnetic quantum criticality that is central to the heavy fermions and other bulk materials with non-Fermi liquid behavior.

Chemistry↗
PubMed2005

Kondo resonances and anomalous gate dependence in the electrical conductivity of single-molecule transistors.

We report Kondo resonances in the conduction of single-molecule transistors based on transition metal coordination complexes. We find Kondo temperatures in excess of 50 K, comparable to those in purely metallic systems. The observed gate dependence of the Kondo temperature is inconsistent with observations in semiconductor quantum dots and a simple single-dot-level model. We discuss possible explanations of this effect, in light of electronic structure calculations.

Journal Article↗
PubMed2004

Inelastic electron tunneling via molecular vibrations in single-molecule transistors.

In single-molecule transistors, we observe inelastic cotunneling features that correspond energetically to vibrational excitations of the molecule, as determined by Raman and infrared spectroscopy. This is a form of inelastic electron tunneling spectroscopy of single molecules, with the transistor geometry allowing in situ tuning of the electronic states via a gate electrode. The vibrational features shift and change shape as the electronic levels are tuned near resonance, indicating significant modification of the vibrational states. When the molecule contains an unpaired electron, we also observe vibrational satellite features around the Kondo resonance.

Journal Article↗
PubMed2001

Anisotropic disorder in high-mobility 2D heterostructures and its correlation to electron transport.

Surface morphology of high-mobility heterostructures is examined and correlated with dc transport. All samples examined show evidence of lines in the [11-0] direction with roughness ranging from small-amplitude features to severe anisotropic ridges. Transport in these samples is consistent with that in samples having artificially induced 1D charge modulations. The native surface properties reflect a prevalent, anisotropic disorder affecting 2D electron conduction. Importantly, the native lines are orthogonal to the stripes theoretically proposed to explain high Landau level transport anisotropies.

Journal Article↗
PubMed2001

Geometry-dependent dephasing in small metallic wires.

Temperature dependent weak localization is measured in metallic nanowires in a previously unexplored size regime down to width w = 5 nm. The dephasing time, tau(phi), shows a low temperature T dependence close to quasi-1D theoretical expectations (tau(phi) approximately T(-2/3)) in the narrowest wires, but exhibits a relative saturation as T-->0 for wide samples of the same material, as observed previously. As only sample geometry is varied to exhibit both suppression and divergence of tau(phi), this finding provides a new constraint on models of dephasing phenomena.

Journal Article↗