Showing papers by "Pulickel M. Ajayan published in 1991"
TL;DR: In this article, the authors used high-resolution electron microscopy and real-time video recording to study the liquid-like coalescence of small gold particles supported on silica and reported that particles that are few nanometers in size, and decoupled from substrate interactions, coalesce extremely fast, in fractions of a second.
Abstract: Here we present experimental results, using high‐resolution electron microscopy and real time video recording, on the liquid‐like coalescence of small gold particles supported on silica. We report that particles that are few nanometers in size, and decoupled from substrate interactions, coalesce extremely fast, in fractions of a second. When the particles are properly supported on a substrate, coalescence is orders of magnitude slower, depending on the particle size, and influenced by the diffusion of atoms on the substrate surface. Necks are seen to develop distinctly during coalescence only for particles above certain size.
36 citations
NEC1
TL;DR: Ajayan et al. as mentioned in this paper showed that small particles of most metals de-wet from nonconducting or semiconducting substrates, remain passive on conducting ones, and coalesce with particles of the same material.
7 citations
TL;DR: In this paper, the question of structural instability during charging under electron irradiation in small particles and amorphous phases is semi-quantitatively explained and the critical size scale for instability when the coulombic stresses set up inside a particle enhance the point defect concentration such that the flux of atoms inside the particle reaches some critical value is defined.
Abstract: The question of structural instability during charging under electron irradiation in small particles and amorphous phases is semi-quantitatively explained. Experimental observations in electron microscopes during irradiation have reported that when the particle radius is less than ∼ 10 A complete random diffusion of atoms is seen over the whole particle volume, whereas for larger sizes, only local areas fluctuate. In amorphous structures similar local fluctuations are seen during high flux electron irradiation. Using thermodynamic arguments an empirical criterion is used to define the critical size scale for instability when the coulombic stresses set up inside a particle enhance the point defect concentration such that the flux of atoms inside the particle reaches some critical value. Agreement is seen between the predicted size ranges and experimental results. Enhanced diffusion due to charging may also account for anisotropic growth in materials when irradiation is localized or formation of he...
3 citations
NEC1
TL;DR: In this paper, the authors used transmission electron microscopy (TEM) and real-time video recordings to study the structural instabilities in amorphous silica structures during intense electron beam irradiation.
Abstract: We present here experimental results using transmission electron microscopy (TEM) and real time video recordings, of the many dynamic structural instabilities in amorphous silica structures during intense electron beam irradiation. It is observed that while the silica layers on oxidized silicon particles sinter when irradiated uniformly, they undergo necking and extensive plastic deformation when the beam is focused in the neck regions. Extremely thin silica fibers (less than five nanometers in diameter and microns in length) can be produced by the deformation of such necks between particles. The thin fibers and the sharp tips developed from the failure of such structures are seen to spheroidize and blunt when exposed to the electron beam. The instabilities are thought to arise from irradiation induced charging of the insulator surface which expands to reduce the density of accumulated surface charges.