Radial Etch Rate Research Articles

Investigation of the radial pore-etching rate in a plastic track detector as a function of the local damage density around the ion path

An attempt is made to define the sensitivity of plastic track detectors on the basis of a new concept. The main feature of this (micro)concept is the relation between the radial etching rate of a heavy ion track and the local ion damage density by means of a continuous function. The energy dose depending on the radial distance from the ion path is taken as a measure of the local damage density. The corresponding etching rate has been measured by the conductometric method. The sharp rise of the radial etching rate with increasing dose explains the threshold character of the track registration and confirms the applicability of the existing threshold registration criteria for practical purposes. The dependence of the radial etching rate on the radial dose can be described by the multi-target model which explains the preferential etching by the collective activation of a given number of sensitive elements. The lower slope of the corresponding curve for gamma radiation demonstrates the substantial influence of the dose rate on this collective activation process.

Radial Etch Rate Nonuniformity in Reactive Ion Etching

A study was performed to determine some of the causes of the edge‐to‐center “bullseye” clearing pattern, in which the etch rate decreases monotonically from the wafer periphery to its center, observed when certain films are etched in a parallel‐plate reactive ion etching system. It was found that gradients in local reactant concentrations, with a higher number density present near the edge of the substrate than over the center, are largely responsible for the observed nonuniformity. The concentration gradients appear to come about as a consequence of two reactant generation phenomena and one loss mechanism. The reactant generation phenomena are: (i) the “hot spot,” which the edge of the wafer may represent to the plasma, causing enhanced reactant generation there, and (ii) differences in capacitive coupling from the RF generator to the plasma between the wafer's location on the cathode and the rest of the cathode. Stronger coupling surrounding the wafer leads to increased production of reactant around the wafer compared to the area directly above it. The reactant loss mechanism is controlled by the relative etch rates of the wafer vs. the cathode material, the using cathodes which etch at an appreciable rate in the plasma was found to promote improved uniformity. Ion bombardment was found to be uniform across the surface of the wafer, and, consequently, etch processes which are strongly bombardment dependent were found to be uniform.

New experimental data on track formation theories in plastic detectors

Using NaOH solution simultanously as etchant and as electrolyte radial track etching rates of heavy ions in the latent tracks are studied. This innermost track region of radii up to several hundreds of Å carries the primary and essential information on the transfer of the energy loss of the ion into a change of the molecular structure of the plastic. For radii smaller than 50 Å the radial etching rate drops down to the bulk etching rate by a factor of about 20.

On the use of polyethyleneterephthalate as solid state nuclear track detector: Mechanism and kinetics of bulk etching

The alkaline hydrolysis of polyethyleneterephthalate (or PETP) is restricted to the polymer/solution interface. The degradation of the polymer surface is characterized by preferred cleavage from the terminal monomer unit resulting in a molecular weight dependence of the surface etch rate. The amount of crystallinity and orientation of the polymer chains has a weak influence on the rate determining step forming an activated complex from a charged intermediate. The surface etch rate correlates well with the product of hydroxide and water activity in the etchant. Using the thermodynamic activity instead of the stoichiometric concentration the difference between the etching strengths of NaOH and KOH disappears. On the basis of available data of the etch kinetics of polycarbonate it can be shown that the thermodynamic concept is valid for the alkaline hydrolysis of polycarbonate as well. The effect of anionic surfactants on the etch rates in PETP can be explained in terms of a competitive absorption of surfactant molecules at the carbonyl carbon atom. The radial etch rate in fission fragment tracks is higher than the surface etch rate of PETP, which is caused by residual stress cracking.

Electrolytically controlled nuclear track plastic-filter production

ABSTRACT Nuclear track filters are a helpful tool in aerosol research. The filtration process is governed mainly by the pore radius (r) and the porosity (P). As the air flow rate is proportional to r 4 a reliable knowledge of the pore radius is necessary for filter applications. The radial track etch rate is constant for pore radii ≥ 120a. Thus, as-summing irradiation with a monoenergetic particle beam the strength of the electrolytical current through the pores, which is measured during the etch process, represents a measure of the in-situ porosity of the produced filter.

Growth of fine holes by the chemical etching of fission tracks in polyvinylidene fluoride

Growth of holes in polyvinylidene fluoride film exposed to fission fragments in oxygen and etched in sodium hydroxide solutions was followed by measuring gas flow through the film as well as by electron microscopy. The radial etching rate was exceedingly small and it took more than a few tens of hours to obtain holes several hundred Å in diameter. Electron micrographs showed the track width to be fairly constant along its length, this being consistent with quite a large ratio (the etching rate along the track)/(the redial etching rate) deduced from gas-flow data. Etched tracks viewed by an electron microscope showed a curvature. The reason for the appearance of the curvature is not clear. The chemical etching in potassium hydroxide solutions was also studied. The etching proceeded much faster than in sodium hydroxide solutions. But at high concentrations, the deposition of crystallites occurred and the etching rate decreased with increasing concentration.

Chemical etching op fission tracks in ethylene-tetrafluoroethylene copolymer

Abstract The chemical etching of fission tracks in ethylene-tetrafluoro-ethylene copolymer was studied. Etched holes 3000–4000 A in diameter was recognized by electron microscopy for a film bombarded by fission fragments in oxygen and etched in a 12N sodium hydroxide solution at 125°C. The radial etching rate at 125°C was 6–8 A/hr, which is less than 17 A/hr for polyvinylidene fluoride in the same sodium hydroxide concentration at 85°C. The smaller rate is a reflection of the larger chemical resistivity of ethylene-tetrafluoro-ethylene copolymer than polyvinylidene fluoride.

Growth of fine holes in polyethylenenaphthalate film irradiated by fission fragments

Growth of fine holes by chemical etching in polyethylenenaphthalate films exposed to fission fragments were examined by measuring gas flow through the films. The etching rate along tracks, the radial etching rate, and the bulk etching rate were determined at effective hole diameters of 100–1 000 Å and hole densities of approximately 108 cm−2. The effects of ethanol and surfactants on the etching rates were studied from the viewpoint of attaining less-tapered holes.

Growth of fine holes in polyethyleneterephthalate film irradiated by fission fragments

Growth of fine holes by chemical etching in polyethyleneterephthalate films exposed to fission fragments were followed by measuring gas flow through films. The etching rate along tracks and the radial etching rate were determined at hole diameters of 100–3000 Å and hole densities of 106–108/cm2.