Comment on “Effects of focused ion beam milling on the nanomechanical behavior of a molybdenum-alloy single crystal” Appl. Phys. Lett. 91, 111915 (2007)

While this article provides insight into differences in mechanics between Ga+-irradiated and “pure” surfaces of molybdenum, there are several statements that are either inaccurate or poorly stated. It is clear that when a surface is directly irradiated by orthogonal ion beam (0.07–0.21 mW), a focused ion beam (FIB) damage layer will likely form and affect the strength. However, this finding does not provide adequate foundation for raising the question of FIB-induced hardening in nanopillars, given the vast differences between these experiments and procedure used in pillar fabrication. These issues would cause considerable confusion and result in disservice to mechanical testing community if not clarified

Size effects in LiF micron-scale single crystals of low dislocation density

This study examines the deformation response of 20, 5, and 1μm diameter samples fabricated by FIB-milling from bulk ultrapure LiF single crystals. The bulk crystals have a very low initial dislocation density as revealed by an etch-pit technique. Two types of 〈001〉 microsamples were compressed preferentially by single slip inside a nanoindentation system. Similar to previously studied FCC-derivative metals, LiF microsamples demonstrate dramatic strengthening achieving the engineering flow stress o ≈ 650 MPa in 1-μm samples. The stress-diameter dependence obeys a power law, σ∼D -m, where m ≈ 0.8. Stochastic variation of flow stress, fast intermittent deformation events ( avalanches ) and highly localized slip bands after avalanches - all characteristic of size effects in metals, are also observed in LiF. Possible dislocation mechanisms of the observed size effects are discussed. © 2007 Materials Research Society

Laser guidance deposition technique for patterning microstructures made of nanoparticles with varying surface functionality

We present results on patterning microstructures using laser-guidance deposition of nanoparticles from particle-in-solvent suspensions. A laser beam axially confines and propels the particles inside a hollow optical fiber towards a substrate. Confining is provided by the gradient forces arising from light refraction or electrical forces on polarizable particles. The driving force results from the momentum conservation of photons scattered on particles. Polystyrene particles (100 and 400 nm in diameter) and gold particles (from 8 to 50 nm) with different surface organic functionality serve as a constructive material for fabrication of microstrips. In the experiments, the laser power varies from 0.1 to 1.6 W. The microstrips produced under different deposition conditions are studied using optical microscopy and atomic force microscopy. It was found that deposited polystyrene and gold particles form nanoclusters consisting of at least several particles. If deposited at an appropriate rate, such nanoclusters form multilayer microstrips of high particle density. The typical width of the microstrips ranges from less than 10 microns to 100 microns. This technique allows us to fabricate parallel arrays made of colloidal particles with different surface functionality, which seems to be an especially attractive approach for developing novel chemical and biological microsensors

Statistical heterogeneity of plastic deformation: An investigation based on surface profilometry

The present paper investigates the intrinsic spatial heterogeneity of plastic deformation of crystalline materials by analysing surface profiles recorded by atomic force microscopy and scanning white light interferometry. Profiles were recorded before and after compressive deformation of three types of alkali halide single crystals: as-grown (AG) KCl and LiF and irradiated (IR) LiF. The profiles were characterized in terms of their height-height correlation function and scale-dependent roughness. We also investigated the statistics of surface step heights and found scale-free distributions over about three orders of magnitude in step (nm to μm) in the AG crystals. A different picture was observed in IR LiF at low plastic strains, where we could identify well-defined characteristic step heights. We discuss these findings in terms of slip avalanches caused by collective motion of dislocations. © 2010 Acta Materialia Inc

Scale-free statistics of plasticity-induced surface steps on KCl single crystals

Experimental investigations of plastic flow have demonstrated temporal intermittency as deformation proceeds in a series of intermittent bursts with scale-free size distribution. In the present investigation, a corresponding spatial intermittency is demonstrated for plastic flow of KCl single crystals. Deformation bursts lead to large surface steps with a height distribution that is consistent with the distribution of strain increments in deformation of micron-size samples and the energy distribution of acoustic emission bursts observed in deformation of macroscopic single-crystal samples of a wide class of materials. © 2007 IOP Publishing Ltd and SISSA