Recoil implantation of alpha sources for thickness measurement of thin films

Abstract

A sequence of radioactive decays can be used to implant alpha-emitting sources in substrates for thickness measurements of films grown on them. Starting with 228Th, both direct recoil implantation of 224Ra and a two-stage recoil implantation of 212Pb were performed. The thickness of germanium layers grown on gallium arsenide was determined by measuring the energy loss of the alpha particles traversing them. The results were found to be consistent with those obtained by other methods. The special advantages of the present procedure are discussed.

HST Highlights: The Extragalactic Distance Scalea,b

“…Thirty Cepheids were discovered and a distance to this galaxy has recently been p~blished.~'~ In addition, a field in the outer regions of the face-on spiral galaxy MlOl was observed and 29 Cepheids discovered. 6 The field observed is one of two chosen to allow a test of the metallicity sensitivity of the Cepheid PL relation. Since the refurbishment mission in December of 1993, the pace of the program has begun to increase rapidly.…”

Feasibility and Safety of Diffusing Alpha-Emitter Radiation Therapy for Recurrent or Unresectable Skin Cancers

“…1,2 The mechanism of action has been previously described extensively in preclinical studies. 3,4 To this end, a previous report 5 summarized the results of a first in human pilot study using diffusing alpha-emitter radiation therapy (DaRT; AlphaTau Medical), a novel alphaparticle therapy delivered via interstitial intratumoral placement of radium-224 sources (3.7 days…”

Film thickness and composition monitoring during growth by molecular beam epitaxy using alpha particle energy loss

“…In this letter, we present the first real-time implementation of the ␣-particle energy loss method ͑AEL͒, a novel approach to in situ growth rate measurements in molecular beam epitaxy ͑MBE͒. [3][4][5] For epitaxial semiconductor films of known density, this method provides absolute thickness measurements and does not depend on optical properties or fitting of data to complex models. The AEL method has already been implemented, in situ and off-line, to measure the thickness of different materials 4,5 but the use of a weaker marking source prevented true real-time monitoring.…”

“…The AEL method is described in more detail in previous publications. [3][4][5] Prior to insertion into the MBE, radioactive nuclei are recoil implanted in GaAs and InP substrates by a number of hours of exposure to a 228 Th source. The implanted species are 224 Ra with 3.66 days half-life and the nuclei resulting from its decay chain.…”

“…As these emitted ␣ particles pass through a film of thickness X, they lose an average amount of energy Ē loss ϭX(dE/dX), where dE/dX is the characteristic energy loss per unit length at that energy for the material making up the film. 3 Since dE/dX is known for most elements, 6 and is relatively insensitive to chemical bonding configurations for MeV energy alpha particles, a measurement of Ē loss gives the thickness X directly for films of known atomic density. The statistical uncertainty in the mean thickness is given by ⌬Xϭ␦E/͓(dE/dX)ͱN͔,…”