Ultrathin Y2O3:Eu3+nanodiscs: spectroscopic investigations and evidence for reduced concentration quenching.

Here, we report the synthesis and spectral properties of ultrathin nanodiscs (NDs) of Y2O3:Eu3+. It was found that the NDs of Y2O3:Eu3+ with a thickness of about 1 nm can be fabricated in a reproducible, facile and self-assembling process, which does not depend on the Eu3+ concentration. The thickness and morphology of these NDs were determined with small angle x-ray scattering and transmission electron microscopy. We found that the crystal field in these nanoparticles deviates from both the cubic and monoclinic characteristics, albeit the shape of the 5D0 â†’ 7F J (J = 0, 1, 2) transitions shows some similarity with the transitions in the monoclinic material. The Raman spectra of the non-annealed NDs manifest various vibration modes of the oleic acid molecules, which are used to stabilise the NDs. The annealed NDs show two very weak Raman lines, which may be assigned to vibrational modes of Y2O3 NDs. The concentration quenching of the Eu3+ luminescence of the NDs before annealing is largely suppressed and might be explained in terms of a reduction of the phonon density of states.

Toward dynamic control over TiO2 nanocrystal monolayer-by-monolayer film formation by electrophoretic deposition in nonpolar solvents.

The controlled electrophoretic deposition of monolayers and ultrathin films of 4.0 nm TiO(2) nanocrystals from stable, nonpolar solvent-based suspensions is reported. Stable suspensions were prepared in hexane, and the electrophoretic mobility of the nanocrystals was enhanced by a combination of a liquid-liquid extraction followed by mechanical surfactant removal by high-speed centrifugation. The controlled evolution of the density of TiO(2) nanocrystal monolayers was studied by transmission electron microscopy and optical transmittance spectroscopy. Ultrathin films were assembled while maintaining monolayer-by-monolayer growth and uniform density of the film. A time-dependent, equivalent circuit model has been proposed to characterize the electrophoretic current that was recorded during our experiments. Further, we demonstrate that the proposed model, coupled with the mobility, provides a means to estimate the deposition rate and, hence, the time necessary to fabricate a submonolayer, a monolayer, and multilayers of nanocrystals.

Field Dependence of the Spin Relaxation Within a Film of Iron Oxide Nanocrystals Formed via Electrophoretic Deposition.

The thermal relaxation of macrospins in a strongly interacting thin film of spinel-phase iron oxide nanocrystals (NCs) is probed by vibrating sample magnetometry (VSM). Thin films are fabricated by depositing FeO/Fe(3)O(4) core-shell NCs by electrophoretic deposition (EPD), followed by sintering at 400°C. Sintering transforms the core-shell structure to a uniform spinel phase, which effectively increases the magnetic moment per NC. Atomic force microscopy (AFM) confirms a large packing density and a reduced inter-particle separation in comparison with colloidal assemblies. At an applied field of 25 Oe, the superparamagnetic blocking temperature is T(B) (SP) ≈ 348 K, which is much larger than the Néel-Brown approximation of T(B) (SP) ≈ 210 K. The enhanced value of T(B) (SP) is attributed to strong dipole-dipole interactions and local exchange coupling between NCs. The field dependence of the blocking temperature, T(B) (SP)(H), is characterized by a monotonically decreasing function, which is in agreement with recent theoretical models of interacting macrospins.

Understanding the growth of Eu(2)O(3) nanocrystal films made via electrophoretic deposition.

Eu(2)O(3) nanocrystals, surface-functionalized with oleic acid, were assembled into transparent thin films via electrophoretic deposition (EPD). Suspended in a non-polar solvent (hexane), the nanocrystals were cast into stable films on both the cathode and the anode. We characterized the nanocrystal films using optical microscopy, energy dispersive spectroscopy and photoluminescence spectroscopy. Scanning electron microscopy and atomic force microscopy provided information regarding the morphology, topology and surface coverage of the films. These homogeneous, densely packed films were composed predominantly of agglomerates (approximately 15 nm) of the Eu(2)O(3) nanocrystals rather than of individual nanocrystals. Nonetheless, the films possessed low root mean square (RMS) roughness (approximately 1.4 nm). High transparency of the film in the visible region was facilitated by the dense packing and the small diameter of the agglomerates, which reduced transmission losses due to scattering. The effect of EPD process parameters (applied voltage and nanocrystal concentration) on the growth uniformity and the thickness of the films was examined via surface contact profilometry. We discovered a correlation among the said EPD process parameters, the overall quality and thickness of these transparent films, which provided insight into the mechanisms of the nanocrystal deposition process.

Carbon nanotube-nanocrystal heterostructures fabricated by electrophoretic deposition.

Alternating layer, carbon nanotubes-nanocrystal composite films, comprising multi-walled carbon nanotubes (MWCNTs) and iron oxide (Fe(3)O(4)) nanocrystals, have been fabricated via electrophoretic deposition (EPD) on stainless steel and gold substrates. Low field-high current and high field-low current EPD schemes were integrated to produce the composite films. The low field-high current EPD approach produced porous mats from an aqueous suspension of the MWCNTs, while the high field-low current EPD approach produced tightly packed nanocrystal films from a dispersion of the nanocrystals in hexane. Large electric fields applied during the nanocrystal EPD and strong van der Waals interactions among the nanocrystals facilitated the formation of tightly packed nanocrystal films atop the MWCNT mats to create CNT mat-nanocrystal film composites. The surface coverage and homogeneity of the nanocrystal films improved with repeated deposition of the nanocrystals on the same mat. The assembly of nanotube mats on top of the CNT mat-nanocrystal film composite confirmed the feasibility of multilayered CNT mat-nanocrystal film heterostructures suitable for a range of devices. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were employed to characterize the surface coverage, homogeneity, and topology of these composite films.