FCC Superlattice Packing of Faceted Silver Nanocrystals

The ordering of size selected nanocrystaline particles into large, well ordered supercrystals has been under recent study. Here we describe the ordering of silver nanocrystals, of core diameter ca. 4.5nm, passivated with alkythiolate self-assembled monolayers. The faceted nanocrystals are found to size selectively condense into ordered supercrystals with edge lengths on the order of 0.1 to 0.5 microns. Further, evidence has been found in High Resolution TEM micrographs of packed monolayers of these same nanocrystals implying an orientational ordering of the silver nanocrystals’ atomic lattices within and co-aligning with the supercrystal’s “superlattice”. A three dimensional model using a truncated octahedron for the nanocrystal core morphology is constructed from this evidence into an FCC superlattice which fits the remaining experimental observations.Micrographs of the same region of a nanocrystal Ag supercrystal (NCASX) are shown in figure 1 under differing defocus conditions.

Download Full-text

Three-Dimensional Hexagonal Close-Packed Superlattices of Passivated Ag Nanocrystals

Microscopy and Microanalysis ◽

10.1017/s1431927600009041 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 431-432

Author(s):

S. A. Harfenist ◽

Z. L. Wang ◽

R. L. Whetten ◽

I. Vezmar ◽

M. M. Alvarez ◽

...

Keyword(s):

Carbon Film ◽

Three Dimensional ◽

Structure Characterization ◽

Self Assembled Monolayers ◽

Hexagonal Close Packed ◽

Self Assembling ◽

Transmission Electron ◽

Assembled Monolayers ◽

High Resolution Tem ◽

Nanocrystal Superlattices

Silver nanocrystals passivated by dodecanethiol self-assembled monolayers were produced using an aerosol technique described in detail elsewhere [1]. Self-assembling passivated nanocrystal-superlattices (NCS's) involve self-organization into monolayers, thin films, and superlattices of size-selected nanoclusters encapsulated in a protective compact coating [2,3,4,5,6,7]. We report the preparation and structure characterization of three-dimensional (3-D) hexagonal close-packed Ag nanocrystal supercrystals from Ag nanocrystals of ˜4.5 nm in diameters. The crystallography of the superlattice and atomic core lattices were determined using transmission electron microscopy (TEM) and high-resolution TEM.SEM was used to image the nanocrystal superlattices formed on an amorphous carbon film of an TEM specimen grid (fig. la). The superlattice films show well shaped, sharply faceted, triangular shaped sheets. Figure lb depicts numerous Ag nanocrystal aggregates uniformly distributed over the imaging region. Inset in this figure is an enlargement of the boxed region at the edge of a supercrystal typifying the ordered nanocrystal packing.

Download Full-text

Three-Dimensional Superlattice Packing of Faceted Silver Nanocrystals

MRS Proceedings ◽

10.1557/proc-457-137 ◽

1996 ◽

Vol 457 ◽

Author(s):

S. A. Harfenist ◽

Z. L. Wang ◽

M. M. Alvarez ◽

I. Vezmar ◽

R. L. Whetten

Keyword(s):

Electron Microscopy ◽

Three Dimensional ◽

Self Assembled Monolayers ◽

Microscopy Imaging ◽

Fundamental Properties ◽

Transmission Electron ◽

Assembled Monolayers ◽

Crystalline Films ◽

Orientational Ordering ◽

First Time

ABSTRACTOrientational ordering of faceted nanocrystals in nanocrystal arrays has been directly observed for the first time, by use of transmission electron microscopy imaging and diffraction to resolve the structure of thin molecular-crystalline films of silver nanocrystals passivated by alkylthiolate self-assembled monolayers. The type of ordering found is determined by the nanocrystals faceted morphology, as mediated by the interactions of surfactant groups tethered to the facets on neighboring nanocrystals. Orientational ordering is crucial for the understanding of the fundamental properties of quantum-dot arrays, as well as for their optimal utilization in optical and electronic applications.

Download Full-text