The surfactant-assisted seeded growth method was adapted for growth of gold nanorods directly on mica surfaces. Spherical gold seed particles were first linked to the surface and then dipped in a cationic surfactant growth solution. Part of the grown particles were nanorods with a typical length of several hundred nanometers and diameter of 10-20 nm. The probability to grow elongated particles out of a seed on the surface was found to be larger than the comparable solution growth process. Successive dipping in the growth solution was found to increase the length and thickness of the gold nanorods without a significant increase in aspect ratio.

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Temperature-dependent fluctuations in the local current passing through close-packed magnetite nanocrystal ͑NC͒ films were probed by scanning tunneling microscopy. This phenomenon, which peaked near the blocking temperature ͑T b ͒, reflects spin-polarized tunneling fluctuations due to NC magnetization switching events. The current exhibited telegraph noise patterns, switching between low and high states. Above T b both states occurred with equal probability while below it the high current state dominated, which is consistent with a superferromagnetic ground state where the NC moments are aligned.

The dependence of tunnelling current fluctuations on temperature and magnetic field was studied in an organically capped magnetite (Fe3O4) nanocrystal (NC) array deposited between 30 nm spaced gold electrodes. Low-frequency Lorentzian (random telegraph) noise was observed around the magnetization freezing temperature due to magnetic moment switching of the NCs under zero magnetic fields, diminishing with a saturating magnetic field. The temperature dependence of current fluctuations followed the temperature dependence of magnetic susceptibility. This work offers a new tool for locally studying collective magnetization dynamics in strongly interacting magnetic NC arrays.

Scanning tunneling microscopy measurements were performed on close‐packed arrays of surfactant‐capped magnetite (Fe3O4) nanocrystals. Current noise measurements over individual nanoparticles (NPs) at 2–3‐particle‐thick positions displayed enhanced low‐frequency noise power around the magnetization blocking temperature of the array. This noise originated in a time‐varying spin filter effect due to slow magnetization switching of individual particles in the arrays, changing their magnetization orientation with respect to their neighbors. The magnetite nanocrystals, being half‐metallic, highly spin‐polarized conductors, enabled this new observation. Consequently, this type of experiment may provide new insight into the microscopic details of magnetization dynamics in strongly interacting arrays of dipoles, which resemble spin‐glasses.