No abstract

No abstract

No abstract

The structure of self-assembled monolayers (SAMs) of undecylenic acid methyl ester (SAM-1) and undec-10-enoic acid 2-bromo-ethyl ester (SAM-2) grown on hydrogen-passivated Si(111) were studied by X-ray reflectivity (XRR), X-ray standing waves (XSW), X-ray fluorescence (XRF), atomic force microscopy, and X-ray photoelectron spectroscopy (XPS). The two different SAMs were grown by immersion of H-Si(111) substrates into the two different concentrated esters. UV irradiation during immersion was used to create Si dangling bond sites that act as initiators of the surface free-radical addition process that leads to film growth. The XRR structural analysis reveals that the molecules of SAM-1 and SAM-2 respectively have area densities corresponding to 50% and 57% of the density of Si(111) surface dangling bonds and produce films with less than 4 angstroms root-mean-square roughness that have layer thicknesses of 12.2 and 13.2 angstroms. Considering the molecular lengths, these thicknesses correspond to a 38 degrees and 23 degrees tilt angle for the respective molecules. For SAM-2/Si(111) samples, XRF analysis reveals a 0.58 monolayer (ML) Br total coverage. Single-crystal Bragg diffraction XSW analysis reveals (unexpectedly) that 0.48 ML of these Br atoms are at a Si(111) lattice position height that is identical to the T1 site that was previously found by XSW analysis for Br adsorbed onto Si(111) from a methanol solution and from ultrahigh vacuum. From the combined XPS, XRR, XRF, and XSW evidence, it is concluded that Br abstraction by reactive surface dangling bonds competes with olefin addition to the surface.

Plastic zone evolution in Al-2 wt% Si metal films on silicon and sapphire substrates was studied using nanoindentation and atomic force microscopy (AFM). AFM was used to measure the extent of plastic pileup, which is a measure of the plastic zone radius in the film. It was found that the plastic zone size develops in a self-similar fashion with increasing indenter penetration when normalized by the contact radius, regardless of film hardness or underlying substrate properties. This behavior was used to develop a hardness model that uses the extent of the plastic zone radius to calculate a core region within the indenter contact that is subject to an elevated contact pressure. AFM measurements also indicated that as film thickness decreases, constraint imposed by the indenter and substrate traps the film thereby reducing the pileup volume.