Stepwise behaviour of magnetization temperature dependence in iron nanoparticle assembled films.

An unusual stepwise behaviour is reported in the temperature dependence of the zero field cooled magnetization in iron nanoparticle dense films produced by ultra-short pulsed laser deposition assisted by irradiation of nanoparticles with a nanosecond UV laser pulse, appropriately delayed, during their flight from the target to the substrate. This behaviour, induced by the particle system's morphology, characterized by clusters of tightly coupled nanoparticles as well as by some voids between them, is ascribed to the competition between Zeeman energy density, intracluster anisotropy energy density and intercluster exchange energy density. A phenomenological model and Monte Carlo simulations are reported, which support the proposed interpretation.

Calibration issues for nanoindentation experiments: direct atomic force microscopy measurements and indirect methods.

This article discusses calibration issues for shallow depth nanoindentation experiments with Berkovich tips with respect to the accurate measurement of the diamond area function (DAF). For this purpose, two different calibration procedures are compared: (i) the direct measurement of the DAF through atomic force microscopy (AFM) imaging of the Berkovich tip at shallow depth and (ii) a novel indirect calibration method based on an iterative robust and converging scheme in which both reduced modulus and indentation hardness are simultaneously used. These results are obtained by indentation measurements on a standard specimen of fused silica, performed in the 0.5-200 mN load range with a Berkovich indenter. Direct tip shape measurements were carried out through different AFM methods. Comparisons with the standard indirect calibration procedure are also reported. For both the indirect calibration procedures a sensitivity and convergence study is presented.

Detection of combustion formed nanoparticles.

UV-visible extinction and scattering and two extra situ sampling techniques: atomic force microscopy (AFM) and differential mobility analysis (DMA) are used to follow the evolution of the particles formed in flames. These particle sizing techniques were chosen because of their sensitivity to detect inception particles, which have diameters, d<5 nm, too small to be observed with typical particle measurement instrumentation. The size of the particles determined by AFM and DMA compares well with the size determined by in situ optical measurements, indicating that the interpretation of the UV-visible optical signal is quite good, and strongly showing the presence of d=2-4 nm particles. UV-visible extinction measurements are also used to determine the concentration of d=2-4 nm particles at the exhausts of practical combustion systems. A numerical model, able to reproduce the experimentally observed low coagulation rate of nanoparticles with respect to soot particles, is used to investigate the operating conditions in the combustion chamber and exhaust system for which 2-4 nm particles survive the exhaust or grow to larger sizes. Combustion generated nanoparticles are suspected to affect human and environmental health because of their affinity for water, small size, low rate of coagulation, and large surface area/weight ratio. The ability to isolate nanoparticles from soot particles in hydrosols collected from combustion may be useful for future analysis by a variety of techniques and toxicological assays.