We report a Monte-Carlo simulation of nanostructures that self-organize on surfaces under oblique ion bombardment. We have developed a quantitative solid-on-solid (SOS) model that describes the surface morphology during ion bombardment and performed the first systematic investigation for Cu bombarded by 1000 eV Ar+ ions at 0°–80° incidence. When the angle of ion incidence exceeds ∼40°, we observe 2–5 nm wide ripples aligned parallel to the ion beam plane in agreement with existing analytic theory. We also detect ripples directed perpendicularly to the ion beam plane, but the conditions under which they arise disagree with the theory. We have investigated the effect of surface relaxation on the morphologies and found two different regimes of ripple evolution depending on the efficiency of relaxation. After ∼100 nm are removed, secondary 10–50 nm wide patterns are formed provided that relaxation is sufficiently high. We compare our simulations with those from other authors and with experiments.

Silicon nanocrystals formed by ion implantation and annealing of fused silica wafers show a strong, broad photoluminescence (PL) peak centered at a wavelength between 750 and 900 nm, depending on the processing conditions. This luminescence has been extensively investigated and trial device structures based on these materials have been built. However, relatively few studies also report the optical absorption spectra. In fact, the absorbance of these specimens is quite low (usually < 10%) at wavelengths greater than 450 nm (i.e., at the pump wavelengths typically used for PL studies). This suggests that in numerous studies of Si nanocrystals produced by ion implantation, only a small fraction of the nanocrystals is responsible for the observed PL at the typical pump wavelengths. In this study, we investigated how the PL spectrum and intensity depend on the power and wavelength of the pump laser. We find that the PL intensity approaches saturation at high pump fluences, and that the peak emission wavelength is sensitive to the excitation power. These observations can be attributed to the dynamics of the excitation/recombination processes at different energies, and indicate that considerable care must be taken when comparing the emission spectra of different specimens. Our data are uniformly consistent with a mechanism of light emission involving subgap states (i.e., radiative trap sites) and are not supportive of a “pure” quantum confinement model.

A linear instability theory proposed by Bradley and Harper accounts for many of the features of ripple formation on amorphous and semiconductor surfaces, but it is not consistent with measurements of sputtered metal surfaces. In the present work, we report observations of sputter ripples on Cu(001) surfaces which are similar to amorphous and semiconductor systems. By using higher ion flux and temperature than previously used, we have produced ripples in which the wavelength is independent of time and the amplitude increases exponentially during the early stages of growth. The ripple evolution was measured using in situ light scattering during sputtering.

Copper migration is observed in the SEM in amorphous GeSe2/Cu thin films when an electron beam is focused in pulsed or continuous operation on the surface of these thin films. The phenomenon can be explained using a simple model in which the population of D- centers is considered to increase upon electron irradiation. The increase in the D- center population is envisaged as due to the breaking of bonds by the electron radiation and by the constant presence of negative charge in irradiated regions. Changes in copper concentration of 20%-30% have been obtained. Additionally we have observed the local crystallization of amorphous GeSe2/Cu thin films in the TEM when the samples were subjected to intense electron bombardment. The crystalline product has been identified as Berzelianite (Cu2Se).

Predominantly amorphous nano powders of calcium phosphate were produced by radio frequency (RF) plasma and subsequently characterised by SEM, TEM and XRD. Quantitative phase analysis was carried out by the Rietveld method. The starting feedstock was comprised of hydroxyapatite (HA) powders spray dried from a suspension. The input parameters were varied to produce predominantly amorphous calcium phosphate powders. Results showed that as the plate power was increased and the flow rate of feedstock was decreased the as-sprayed powders produced were predominantly amorphous. The average particle size of the powders was about 20-40 nm, depending on process parameters, as confirmed by TEM observation. These powders are thought to have excellent bio-resorbability and are targetted for use in gene and drug delivery technologies. These nano-sized powders are also envisioned to enhance the mechanical properties of bulk products sintered by appropriate techniques.

We present a method of direct magnetic patterning of nonmagnetic CoC and CoTaC films by electron irradiation-induced nano-scale phase transition. CoxC1-x (0.4<X<0.8) films were prepared by co-sputtering. The as-deposited films with Co concentration less than 60% are amorphous and non-ferromagnetic. All films become ferromagnetic after annealing. Doping Ta into the CoC films can enhance the segregation of Co and C and therefore reduce the phase transition temperature. It is found that the magnetic properties of annealed (Co60C40)97Ta3 films are much better than that of annealed Co60C40 films at the same annealing condition. Magnetic nano-patterning (dot/line array) of the as-deposited CoC and Co(TaC) films was realized by subjecting them to electron irradiation using a focused 30keV electron beam with a current of 7.1 nA and dwell time per dot of 0.75 to 15.2 seconds. A 250nm magnetic dot/line array was produced by this method. It was also found that the time required to magnetically pattern non-magnetic (Co60C40)97Ta3 thin films (0.75 seconds) is much shorter than that required for Co60C40 films (3.8 seconds). The present method of magnetically patterning a nonmagnetic film has the potential application for nanoscale solid magnetic devices.

Low dimensional systems on the nanometer scale afford a wealth of interesting possibilities including highly anisotropic behavior and quantum effects. Nanocolumns permit electrical and mechanical contact, yet benefit from two confined dimensions. This confinement leads to new optical, mechanical, electrical, chemical, and magnetic properties. We construct nanocolumn arrays with precise definition and independent control of diameter, length, orientation, areal density and composition so that geometry can be directly correlated to the quantum physical property of interest. The precision and control are products of the fabrication technique that we use. The process starts with an ion of sufficient energy to “track” a dielectric such as a film applied uniformly onto a substrate. The energy loss of the ion alters chemical bonding in the dielectric along the ion's straight trajectory. A suitable etchant quickly dissolves the latent tracks leaving high aspect ratio holes of small diameter (∼10nm) penetrating a film as thick as several microns. These small holes are interesting and useful in their own right and can be made to any desired size by continuing the etching process. Moreover, they serve as molds for electrochemical filling. After this electrodeposition, the mold material can be removed leaving the columns firmly attached to the substrate at the desired orientation. A variety of structures can be envisioned with these techniques. As examples, we have created arrays of Ni and of Pt nanocolumns (∼ 60 nm diameter and ∼ 600 nm long) oriented perpendicular to the substrate. The high aspect ratio and small diameter of the columns enables easy observation of quantum behavior, namely efficient electron field emission and Fowler Nordheim behavior.