A new approach, molecular layer epitaxy (MLE), is introduced for the vapor‐phase assembly of organic multilayers integrated in molecular electronic devices. The MLE approach uses carrier gas assisted epitaxial deposition, covalent bonding, and horizontal π stacking in a pulsed mode for layer‐by‐layer growth of 1,8:4,5‐naphthalenetetracarbodiimide with a hexamethylene spacer (shown schematically).

Solid solutions of VxCo1–x[TCNE]2 composition have been prepared from the reaction of V(CO)6 and Co2(CO)8 in dichloromethane. All magnetically order above 280 K for x > 0.05 and their coercivity increases with decreasing x, reaching a maximum of 270 Oe for x = 0.3 (see Figure). Hence, the magnetic properties of this magnet can be finely tuned via a synthetic organic chemistry methodology.

We have fabricated a variety of novel molecular diodes based on self-assembledmonolayers (SAM) of solid-state mixture (SSM) of molecular wires (1,4 benzenedimethane-thiol; Me-BDT), and molecular insulator spacers (1-pentanethiol; PT) with different concentration ratios r of wires/spacers, which were sandwiched between two gold (Au) electrodes. We introduce two new methods borrowed from Surface Science to (i) confirm the connectivity between the Me-BDT molecules with the upper Au electrode, and (ii) count the number of isolated molecular wires in the devices.The electrical transport properties of the SSM SAM diodes were studied at different temperatures via the conductance and differential conductance spectra. We found that a potential barrier caused by the spatial connectivity gap between the PT molecules and the upper Au electrode dominates the transport properties of the pure PT SAM diode (r = 0). The transport properties of SSM diodes with r-values in the range 10 -8 < r < 10 -4 are dominated by the conductance of the isolated Me-BDT molecules in the device. We found that the temperature dependence of the SSM diodes is much weaker than that of the pure PT device indicating the importance of the Me-BDT simultaneous bonding to the two Au electrodes that facilitate electrical transport. From the differential conductance spectra we also found that the energy difference, ∆ between the Au electrode Fermi-level and the Me-BDT HOMO (or LUMO) level is ~1.5 eV; whereas it is ~2.5 eV for the PT molecule. The weak temperature dependent transport that we obtained for the SSM diodes reflects the weak temperature dependence of ∆.

This paper reports analysis of direct (low bias regime that corresponds to Simmons model) and field emission, Fowler-Nordheim (FN) tunneling, and a crossover between these regimes in molecular nanojunction. We have fabricated molecular devices based on a heterogenius mixture of molecular wires of 2-[4-(2mercaptoethyl)-phenyl]ethanethiol (Me-PET) as self-assembled monolayer (SAM) molecules incorporated into the matrix of molecular insulator spacers [penthane 1-thiol (PT)] at a concentration ratio of r ) 10 -6 wires/spacers. The monolayer is sandwiched between two gold (Au) electrodes. A temperature-depended conductivity in this structure was analyzed at both low and elevated biases using models of direct tunneling (Simmons model) and field emission (FN) regime. A crossover voltage, V trans , between these two regimes was determined at different temperatures. Comparison of temperature-dependent Simmons and FN barriers, (Φ B Sim (T) and Φ B FN (T)), and transition bias (V trans (T)) reveals an anomaly in position of V trans (T) with respect to Φ B Sim (T) and Φ B FN (T) at low temperatures (15-100 K). The change in slopes of Φ B Sim (T), Φ B FN (T), andV trans (T) at different temperatures pointed to the switching of the transport mechanism in the system as well. Activated by temperature, the observed phenomenon can be attributed to the existence of an additional transport barrier, which operates in series with the molecular barrier. As candidate for this additional barrier, the injection barrier must be considered. In this context, the transport was controlled by the injection barrier or injection barrier regime (IBR) at low temperatures (15-100 K), and by molecular barrier or molecular barrier regime (MBR) at high temperatures (150-294 K). A molecular diode, with the same structure (Me-PET/PT r ) 10 -6 ), but with Al electrodes, was fabricated to check this assumption. While devices with Au electrodes have a low tunneling barrier (Φ B Sim ≈ 1.2 eV), devices with Al electrodes have a high tunneling barrier (Φ B Sim ≈ 3 eV). Only direct tunneling could be observed in measured bias range (V ) (2 V). Nevertheless the "crossover behavior" was observed in the device with Al electrodes at low temperatures (15-100 K). Therefore, observed "crossover" in the device with Al electrodes is related to the transport processes, which occurs at the electrode due to the injection barrier, rather than the transition from direct to FN tunneling in the molecule at low temperatures. In this case a transition point, V trans , characterizes the IBR at low temperatures, the MBR at high temperatures, and the BTR between these two regimes.