Aluminum incorporation into ZnO films during atomic layer deposition (ALD) is investigated using in situ quartz crystal microbalance and electrical conductance analysis. Chemical interactions between Zn and Al species during ZnO:Al ALD depend on the order of metal precursor exposure. Exposing the growing ZnO surface to trimethyl aluminum (TMA) impedes the subsequent ∼4 monolayers of ZnO growth. However, the extent of interaction can be reduced by performing the TMA exposure immediately following a diethyl zinc step, without an intermediate water exposure step, consistent with increased surface mixing of Zn and Al species. Infrared spectroscopy analysis of heavily aluminum doped ZnO shows features consistent with the presence of amorphous ZnAl 2 O 4 bonding units. For more lightly doped films, mass spectroscopic depth profiling confirms nonuniform aluminum distribution, even after annealing at 500 °C. Film conductance measured during growth shows complex trends that are highly repeatable over multiple doping cycles, and values for in situ conductance are consistent with postdeposition current vs. voltage characterization. Results are understood in terms of relative bonding energies of surface species, and expected reaction pathways for dopant atom incorporation.

Charge transport through alkane monolayers on gold is measured as a function of molecule length in a controlled ambient using a metal/molecule/nanoparticle bridge structure and compared for both thiol and amine molecular end groups. The current through molecules with an amine/gold junction is observed to be more than a factor of 10 larger than that measured in similar molecules with thiol/gold linkages. Conducting probe atomic force microscopy is also used to characterize the same monolayer systems, and the results are quantitatively consistent with those found in the nanoparticle bridge geometry. Scaling of the current with contact area is used to estimate that approximately 100 molecules are probed in the nanoparticle bridge geometry. For both molecular end groups, the room-temperature conductivity at low bias as a function of molecule length shows a reasonable fit to models of coherent nonresonant charge tunneling. The different conductivity is ascribed to differences in charge transfer and wave function mixing at the metal/molecule contact, including possible effects of amine group oxidation and molecular conformation. For the amine/Au contact, the nitrogen lone pair interaction with the gold results in a hybrid wave function directed along the molecule bond axis, whereas the thiol/Au contact leads to a more localized wave function.

In situ characterization of low temperature atomic layer deposition (ALD) of ZnO and aluminum-doped ZnO (ZnO:Al) establishes a relationship between species adsorption, mass uptake, and surface electrical conductance during deposition and dopant atom incorporation. Conductance measured in situ during ZnO ALD oscillates with species surface adsorption, consistent with surface potential modulation and charge transfer during surface reaction. Dopant introduction using trimethylaluminum impedes both surface potential modulation and film growth, and a reaction scheme involving surface proton exchange complexes is presented to understand the observed results. Electronically active doping is achieved only after Al species transition four to five monolayers into the film bulk, consistent with a nonuniform dopant atom distribution in the direction of film growth. Results have important implications in understanding relations between dopant incorporation, activation, and film growth mechanisms in atomic layer deposition and other vapor-phase chemical processes.

Three-dimensional nanoscale constructs are finding applications in many emerging fields, including energy generation and storage, advanced water and air purification, and filtration strategies, as well as photocatalytic and biochemical separation systems. Progress in these important technologies will benefit from improved understanding of fundamental principles underlying nanostructure integration and bottom-up growth processes. While previous work has identified hydrothermal synthesis conditions to produce nanoscale ZnO rods, sheets, and plates, strategies to systematically integrate these elements into more complex nano-architectures are not previously described. This article illustrates that amorphous nanoscale coatings formed by atomic layer deposition (ALD) are a viable means to modulate and screen the surface polarity of ZnO crystal faces and thereby regulate the growth morphology during successive hydrothermal nanocrystal synthesis. Using this new strategy, this work demonstrates direct integration and sequential assembly of nanocrystalline rods and sheets to produce complex three-dimensional geometric forms, where structure evolution is achieved by modifying the surface growth condition, keeping the hydrothermal growth chemistry unchanged. Therefore, rational planning of seed layer and feature spacing geometries may allow researchers to engineer, at the nanoscale, complex three-dimensional crystalline and semicrystalline constructs for a wide range of future applications.

Nanoparticle/molecule/nanoparticle dimer assemblies have been successfully trapped by dielectrophoresis across nanogap electrodes, enabling temperature dependent charge transport measurements through an oligomeric phenylene ethynylene molecule, and transition from direct tunnelling to Fowler-Nordheim tunnelling is observed at approximately 1.5 V. Samples formed by dielectrophoresis show better contact stability than those formed by receding meniscus. The junction shows stable operation over several weeks in a vacuum, but current increases with time upon exposure to air, possibly due to the adsorbed water molecules near the molecule/gold nanoparticle contacts.