Probing nanotribological and electrical properties of organic molecular films with atomic force microscopy

Nanoscale resistive switching Schottky contacts on self-assembled Pt nanodots on SrTiO(3)

A nanoscale Schottky diode using Pt nanodisks on a Nb-doped SrTiO3 (Nb:STO) single crystal was fabricated, and resistive switching (RS) was demonstrated with conductive atomic force microscopy at ultrahigh vacuum. Pt disks with diameters on the order of 10 nm were formed using colloidal self-assembled patterns of silica nanospheres, followed by evaporation of the Pt layers on the Nb:STO single crystal. Here we show that the reproducible bipolar RS behavior of the nanoscale Pt/Nb:STO Schottky junction was achieved by utilizing local current-voltage spectroscopy. The conductance images, obtained simultaneously with topographic images, show the homogeneous current distribution of selected triangular-shaped Pt nanodisks during repetitive resistive switching between the high-resistance state (HRS) and low-resistance state (LRS). The endurance characteristics of the Pt/Nb:STO junction exhibit reliable switching behavior. These results suggest that the rectifying and resistive Pt/Nb:STO junction can be scaled down to the 10 nm range and their position can be controlled.

Tuning nanoscale friction on Pt nanoparticles with engineering of organic capping layer

Nanoscale friction and adhesion on Pt colloid nanoparticles coated with different organic capping layers were probed with atomic/friction force microscopy. Platinum colloid nanoparticles with four types of capping layers have been synthesized and used as model lubricant systems: TTAB (tetradecyltrimethylammonium bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). Two-dimensional arrays of colloid nanoparticles were prepared using the Langmuir-Blodgett method. We found that the friction and adhesion properties on colloid nanoparticles are lower than those on a silicon surface. The variation of friction when changing the capping layers is ∼30%, and it appears that the friction depends on the packing and ordering of the capping layers. Partial removal of the capping layers using ultraviolet light (UV)-ozone surface treatment resulted in increased friction. These results suggest a new method of tuning nanometer scale friction and adhesion by engineering organic capping layers on nanoparticles.