Terthiophene dyes were synthesized having a carboxylate or a phosphonate moiety at the 2-position which serves as an anchoring group to zinc oxide nanocrystals (ZnO NCs). Electronic absorption and fluorescence measurements, combined with reduction potentials, provided estimates of −1.81 and −1.86 V vs. NHE for the excited state reduction potential of the carboxylate and phosphonate, respectively. Static quenching was observed when the dyes were bound to the surface of acetate-capped ZnO NCs having a diameter of 2.8 nm. Stern–Volmer studies conducted at several dye concentrations established that a minor fraction of the adsorbed dye remained unquenched even at 1 : 1 dye to NC ratios. Adsorption isotherm measurements established that the phosphonate binds more strongly than the carboxylate and that saturation coverage was ∼1.2 dyes per nm2 for both dyes. Ultrafast transient absorption spectroscopic experiments were used to probe excited state dynamics. In the presence of ZnO NCs, disappearance of the singlet excited state of the dye corresponded to appearance of the spectroscopic signature of the oxidized dye with a time constant of 1.5 ± 0.1 and 6.1 ± 0.2 ps, respectively, for the carboxylate and phosphonate dye. The difference in the electron transfer rates was attributed to a larger electronic coupling for the dye having the carboxylate anchoring group.

Poly(cyclohexylethylene)-block-poly(lactide) (PCHE–PLA) block polymers were synthesized through a combination of anionic polymerization, heterogeneous catalytic hydrogenation and controlled ring-opening polymerization. Ordered thin films of PCHE–PLA with ultrasmall hexagonally packed cylinders oriented perpendicularly to the substrate surface were prepared by spin-coating and subsequent solvent vapor annealing for use in two distinct templating strategies. In one approach, selective hydrolytic degradation of the PLA domains generated nanoporous PCHE templates with an average pore diameter of 5 ± 1 nm corroborated by atomic force microscopy and grazing incidence small-angle X-ray scattering. Alternatively, sequential infiltration synthesis (SIS) was employed to deposit Al2O3 selectively into the PLA domains of PCHE–PLA thin films. A combination of argon ion milling and O2 reactive ion etching (RIE) enabled the replication of the Al2O3 nanoarray from the PCHE–PLA template on diverse substrates including silicon and gold with feature diameters less than 10 nm.Keywords: atomic layer deposition; block polymer; nanolithography; nanopores; selective infiltration synthesis; self-assembly; solvent vapor annealing

A series of heteroleptic bipyridine ruthenium complexes were prepared using known synthetic methods. Each compound incorporated one electron withdrawing 4,4′-dicarboxylic acid-2,2′-bipyridine and two bipyridines each of which had electron donating dialkylamine substituents in the 4 and 4′ positions. The electronic absorption spectra exhibited absorptions that moved to lower energy as the donor ability of the amine substituent increased. Density functional calculations established that the HOMO was delocalized over the metal and two pyridine groups located trans to the pyridines of the dicarboxylic acid bipyridine. The LUMO was delocalized over the dicarboxylic acid bipyridine. Cyclic voltammetry of the deprotonated compounds exhibit one quasi-reversible oxidation and three reductions. Coupled with the emission data, the excited state reduction potentials were estimated to range from −0.93 to −1.03 V vs. NHE. Monodispersed 3.2 nm diameter nanocrystals (NCs) of zinc oxide were found to quench partially the excited state of the dyes via a static quenching electron transfer process involving the formation of a dyad of the complex and the NC. The magnitude of the partial quenching of complexed dyes was correlated to the distribution of band gaps for the NCs, which is an inverse function of diameter. Dyes attached to the NCs on the small end of the particle size distribution had electron transfer rates that were uncompetitive with radiative and nonradiative decay mechanisms.

Low-temperature atomic layer deposition of conformal ZnO on a self-assembled block polymer lithographic template comprising well-ordered, vertically aligned cylindrical pores within a poly(styrene) (PS) matrix was used to produce nanocrucible templates with pore diameters tunable via ZnO thickness. Starting from a PS template with a hexagonal array of 30 nm diameter pores on a 45 nm pitch, the ZnO thickness was progressively increased to narrow the pore diameter to as low as 14 nm. Upon removal of the PS by heat treatment in air at 500 °C to form an array of size-tunable ZnO nanocrucibles, permalloy (Ni80Fe20) was evaporated at normal incidence, filling the pores and creating an overlayer. Argon ion beam milling was then used to etch back the overlayer (a Damascene-type process), leaving a well-ordered array of isolated ZnO nanocrucibles filled with permalloy nanodots. Microscopy and temperature-dependent magnetometry verified the diameter reduction with increasing ZnO thickness. The largest diameter (30 nm) dots exhibit a ferromagnetic multidomain/vortex state at 300 K, with relatively weakly temperature-dependent coercivity. Reducing the diameter leads to a crossover to a single-domain state and eventually superparamagnetism at sufficiently high temperature, in quantitative agreement with expectations. We argue that this approach could render this form of block polymer lithography compatible with high-temperature processing (as required for technologically important high perpendicular anisotropy ordered alloys, for instance), in addition to enabling separation-dependent studies to probe interdot magnetostatic interactions.Keywords: atomic layer deposition; bit patterned media; block copolymer; magnetic nanodots; nanocrucible; nanolithography;

Al- and In-doped CdSe nanocrystals were synthesized using a three-part core-shell synthesis. CdSe core nanocrystals were first prepared, then allowed to react with dopant precursors in the presence of weakly binding ligands, and finally overcoated with an additional shell of CdSe. The addition of Al dopants quickened shell overgrowth and led to more monodisperse nanocrystals while the addition of In dopants produced more polydisperse particles, as seen by absorption spectroscopy. Elemental analysis combined with chemical etching revealed the dopants were inside the particles and solid state 27Al nuclear magnetic resonance (NMR) spectra indicated that the Al impurities were well dispersed. When the Al-doped nanocrystals were processed into thin-film transistors, enhanced n-type transport was observed with a rise in the Fermi level compared to undoped particles.

This perspective offers a brief summary of a series of publications that reveal insight into the nucleation of titanium oxide on different surfaces.

The synthesis of 3′,4′-dibutyl-2-phenyl-2,2′:5′,2′′-terthiophene-5′′-carboxylic acid and its behavior with monodispersed ZnO having diameters from 2.7 to 3.2 nm are reported. The excited state of the dye (E0* = −1.61 V vs NHE) was quenched upon binding to ZnO nanocrystals. Adsorption isotherms were measured for the terthiophene dye in ethanol and fit with a Langmuir model, which gave a size-independent Kads of 2.3 ± 1.0 × 105 M−1. The maximum number of attached dyes per nanocrystal depended on the diameter and was consistent with each dye occupying 0.5 ± 0.1 nm2 at maximum coverage. Deviation from the Langmuir model observed at low dye concentrations was attributed to a small amount of free zinc ion present in solution that binds the carboxylate ions more strongly than do ZnO nanocrystals. Incorporation of the equilibrium expression between zinc ion and free carboxylate into the model provided a satisfactory fit for both the adsorption isotherm experiments and the complex shape of the Stern−Volmer graphs. Treatment of the terthiophene dye−nanocrystal dyads with increasing concentrations of sodium acetate in ethanol resulted in gradual displacement of the dye.

We exchanged the oleate ligands on as-prepared PbSe/CdSe core/shell nanocrystals with octyldithiocarbamate to enable the removal of insulating ligands by gentle heating. The octyldithiocarbamate ligand could readily be stripped from the surface by heating briefly to temperatures from 140 to 205 °C, which is substantially lower than the temperature (330 °C) required to remove oleate from the nanocrystal surface. X-ray diffraction and transmission electron microscopy reveal that the nanocrystals sinter around 250 °C, resulting in a loss of quantum confinement. Heating for 1 min to 205 °C removed 92% of the organics from the surface. We could therefore prepare densely packed films of quantum-confined nanocrystals via dithiocarbamate treatment. Conductivity increased by up to 4 orders of magnitude after annealing. In addition to PbSe/CdSe core/shell nanocrystals, we also examined the applicability of our ligand removal procedure to CdSe nanocrystals.Keywords: CdSe; colloidal quantum dots; dithiocarbamates; PbSe; semiconductor nanocrystals; surface ligands

Nearly monodispersed, spherical ZnO nanocrystals were synthesized from the reaction of an amide precursor, [Zn(NiBu2)2]2, with hexylamine followed by reactions of the as-formed solution in a moist air flow. Extensive experiments were conducted to optimize the synthesis and to characterize the nanocrystals. The room temperature reactions led to 3.3−5.3 nm nanocrystals with the sizes increasing in direct proportion to the relative humidity. Purification afforded high yields of free-flowing nanocrystals that were dispersible in nonpolar solvents. The overall synthesis requires several days, but it results in multigram quantities of stable, redispersible nanocrystals. The nanocrystals were characterized using elemental analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), solution and solid-state NMR, IR, UV−vis absorption, and photoluminescence spectroscopies. In addition to providing H2O to serve as the source of oxygen in the ZnO, the air flow adds CO2 that converts the alkylamine into an alkylammonium alkylcarbamate, which serves as the surfactant. Elemental analysis, TGA, and XPS results established that the total number of N-hexyl fragments on a 3.7 nm nanocrystal was 200, where they exist as an equal number of anionic carbamates and cationic ammonium ions. The addition of pure hexylammonium hexylcarbamate to ZnO nanocrystals prepared by literature methods resulted in the formation of a product that was similar to the ZnO formed using [Zn(NiBu2)2]2. Larger nanocrystals up to 7.3 nm were also obtained by heating smaller nanocrystals in a mixture of hexylamine and toluene at 119 °C.

Al- and In-doped CdSe nanocrystals were synthesized using a three-part core-shell synthesis. CdSe core nanocrystals were first prepared, then allowed to react with dopant precursors in the presence of weakly binding ligands, and finally overcoated with an additional shell of CdSe. The addition of Al dopants quickened shell overgrowth and led to more monodisperse nanocrystals while the addition of In dopants produced more polydisperse particles, as seen by absorption spectroscopy. Elemental analysis combined with chemical etching revealed the dopants were inside the particles and solid state 27Al nuclear magnetic resonance (NMR) spectra indicated that the Al impurities were well dispersed. When the Al-doped nanocrystals were processed into thin-film transistors, enhanced n-type transport was observed with a rise in the Fermi level compared to undoped particles.

A series of heteroleptic bipyridine ruthenium complexes were prepared using known synthetic methods. Each compound incorporated one electron withdrawing 4,4′-dicarboxylic acid-2,2′-bipyridine and two bipyridines each of which had electron donating dialkylamine substituents in the 4 and 4′ positions. The electronic absorption spectra exhibited absorptions that moved to lower energy as the donor ability of the amine substituent increased. Density functional calculations established that the HOMO was delocalized over the metal and two pyridine groups located trans to the pyridines of the dicarboxylic acid bipyridine. The LUMO was delocalized over the dicarboxylic acid bipyridine. Cyclic voltammetry of the deprotonated compounds exhibit one quasi-reversible oxidation and three reductions. Coupled with the emission data, the excited state reduction potentials were estimated to range from −0.93 to −1.03 V vs. NHE. Monodispersed 3.2 nm diameter nanocrystals (NCs) of zinc oxide were found to quench partially the excited state of the dyes via a static quenching electron transfer process involving the formation of a dyad of the complex and the NC. The magnitude of the partial quenching of complexed dyes was correlated to the distribution of band gaps for the NCs, which is an inverse function of diameter. Dyes attached to the NCs on the small end of the particle size distribution had electron transfer rates that were uncompetitive with radiative and nonradiative decay mechanisms.