Slow Positron Annihilation Spectroscopy Research Articles

Vacancy Defects in As-Polished and in High-Fluence H<sup>+</sup>-Implanted 6H-SiC Detected by Slow Positron Annihilation Spectroscopy

Vacancy Defects in As-Polished and in High-Fluence H<sup>+</sup>-Implanted 6H-SiC Detected by Slow Positron Annihilation Spectroscopy

The origin of optical absorption at 414 nm in the F2 region of ion-implanted LiF crystals

We report a comparative study of optical absorption in LiF crystals following implantation with Al+, Mg+ and Ar+ ions of 100 keV energy. These crystals have been examined by slow positron annihilation spectroscopy, the results we report separately. Here we focus on a band at 414 nm which is significantly enhanced in aluminium implanted samples. The dependence of the 414 nm band on ion species (Al+, Mg+, Ar+) is investigated at fluences of 1016 cm−2. Annealing studies are used to further clarify the nature of the band. These observations raise questions about the origin of the band at 414 nm. We suggest it may be linked to conditions associated with ion tracks in the crystal.

A comparative study of defects in LiF implanted with 100 KeV Al+, Mg+ and Ar+ by slow Positron Annihilation Spectroscopy

The fluence-dependent evolution of defects in LiF implanted at room temperature with Al+, Mg+, Ar+ ions is measured using the slow positron beam technique. Samples were implanted with 100 KeV ions to doses of 1015 and 1016 cm−2. Doppler broadened spectra of positron annihilation as a function of positron incident energy are measured and are analyzed by the computer program VEPFIT. The depth profiles of the defect distribution are presented and discussed as a function of dose and nature of the implanted ions. The Positron Annihilation Spectroscopy (PAS) results are correlated with optical absorption measurements on the crystals, and are shown to provide important information about the spatial extent of defects in ion-implanted samples.

Comparison between the different implantation orders in H+ and He+coimplantation

H+ and He+ were implanted into single crystals in differentorders (H+ first or He+ first). Subsequently, the samples were annealedat different temperatures from 200 °C to 450 °C for 1 h. Crosssectional transmission electron microscopy, Rutherford backscatteringspectrometry and channelling, elastic recoil detection were employed tocharacterize the defects and the distribution of H and He in the samples.Furthermore, the positron traps introduced by ion implantation and annealingwere characterized by slow positron annihilation spectroscopy. Both orders inthe coimplantation of H and He have the ability to decreases the totalimplantation dose after annealing. No bubbles or voids but cracks andplatelets, were observed by cross sectional transmission electron microscopy.The different implantation orders affect the density of interstitial atoms andpositron traps.

Investigation of defects and stresses in SiFe steel surfaces

SiFe specimens prepared from GO steel with different surface treatments were studied from the point of view of structure, stresses and defect density using the conversion electron Mössbauer spectroscopy (CEMS) and the slow positron annihilation spectroscopy (SPAS). Amounts of the high defect density (HDD) phase and defect depth profiles were obtained for specimens after mechanical and/or chemical surface polishing.

Formation of vacancy clusters and cavities in He-implanted silicon studied by slow-positron annihilation spectroscopy

The depth profile of open volume defects has been measured in Si implanted with He at an energy of 20 keV, by means of a slow-positron beam and the Doppler broadening technique. The evolution of defect distributions has been studied as a function of isochronal annealing in two series of samples implanted at the fluence of $5\ifmmode\times\else\texttimes\fi{}{10}^{15}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{He}\mathrm{}\mathrm{cm}}^{\ensuremath{-}2}.$ A fitting procedure has been applied to the experimental data to extract a positron parameter characterizing each open volume defect. The defects have been identified by comparing this parameter with recent theoretical calculations. In as-implanted samples the major part of vacancies and divacancies produced by implantation is passivated by the presence of He. The mean depth of defects as seen by the positron annihilation technique is about five times less than the helium projected range. During the successive isochronal annealing the number of positron traps decreases, then increases and finally, at the highest annealing temperatures, disappears only in the samples implanted at the lowest fluence. A minimum of open volume defects is reached at the annealing temperature of $250\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in both series. The increase of open volume defects at temperatures higher than $250\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ is due to the appearance of vacancy clusters of increasing size, with a mean depth distribution that moves towards the He projected range. The appearance of vacancy clusters is strictly related to the out diffusion of He. In the samples implanted at $5\ifmmode\times\else\texttimes\fi{}{10}^{15}{\mathrm{cm}}^{\ensuremath{-}2}$ the vacancy clusters are mainly four vacancy agglomerates stabilized by He related defects. They disappear starting from an annealing temperature of $700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ In the samples implanted at $2\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{cm}}^{\ensuremath{-}2}$ and annealed at $850--900\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ the vacancy clusters disappear and only a distribution of cavities centered around the He projected range remains. The role of vacancies in the formation of He clusters, which evolve in bubble and then in cavities, is discussed.

Vacancy Cluster Distributions in He Implanted Silicon Studied by Slow Positron Annihilation Spectroscopy

Doppler broadening measurements performed by a slow positron. beam on p-type Si samples implanted with He at 20 keV and at a fluence of 5 x 10 15 and 2.x 10 16 cm -2 are reviewed and dist:ussed. The evolution of the open volume defects distribution was studied as a function of isochronal and isothermal annealing of the samples. In the as implanted samples the majority of the open volume defects produced by implantation was passivated by He. The open volume defects density decreases, reaching a minimum at 250°C. In the 250-650°C temperature range there is an increase in defects due to the appearance of vacancy clusters. At the higher annealing temperatures (700-900°C) the vacancy clusters disappear only in the samples implanted at 5 x 10 15 cm -2 .

He-implantation induced defects in Si studied by slow positron annihilation spectroscopy

Open volume defect profiles have been obtained by performing Doppler broadening measurements with a slow positron beam on p-type Si samples implanted near liquid nitrogen temperature with He ions at 20 keV and at 5×1015 and 2×1016 cm−2 fluence. The evolution of the defect profiles was studied as a function of isothermal annealing at 250 °C. The fraction of released He was measured by thermal programmed desorption. The defects could be identified as a coexistence of monovacancies stabilized by He-related defects and divacancies. The number of defects decreases for annealing time of a few minutes, then increases at longer annealing times. The mean depth of the defect profiles in the as-implanted samples was found to be very near the surface. After annealing, the mean depth increases to less than one half of the projected He range. This complex dynamics has been interpreted as due to passivation of vacancies by He during the implantation process and the first annealing step when no appreciable He is lost, and to subsequent depassivation during He desorption.

Surface Properties of Polymers Studied by Slow Positron Annihilation Spectroscopy

Surface Properties of Polymers Studied by Slow Positron Annihilation Spectroscopy

Free-volume hole properties near the surface of polymers obtained from slow positron annihilation spectroscopy

We have measured the positron annihilation lifetime spectra in an epoxy polymer using the electrotechnical laboratory (ETL) slow-positron facility as a function of positron energy from 0.2 to 3.0 keV. The ortho-positronium lifetime from the bulk increases near the surface while the intensity decreases. The results are interpreted in terms of a Ps free-volume model. A larger hole size and fraction near the polymeric surface are observed. A reduction of glass transition temperature near the surface is estimated from the WLF theory.

Study of Defect Behavior in Ion-Implanted Si Wafers by Slow Positron Annihilation Spectroscopy

Study of Defect Behavior in Ion-Implanted Si Wafers by Slow Positron Annihilation Spectroscopy

Ion implantation induced defects in SiO2: The applicability of the positron probe

Boron ion implantation-induced defects in SiO2 were investigated using slow positron annihilation spectroscopy and electron spin resonance (ESR). The defects caused by ion implantation are manifest as a particularly low S parameter in the region of the SiO2 layer in which B implantation damage occurs. The annealing behavior of the defect responsible for positron trapping was studied. The defect to which the positron is sensitive is found to be unobservable in ESR measurements. The defect is suggested to be dissolved O2 or a charged Frenkel defect, such as the negative nonbridging-oxygen hole center (≡Si—O−).

Slow positron annihilation spectroscopy and electron microscopy of electron beam evaporated cobalt and nickel silicides

Metal silicide thin films on single-crystal silicon substrates are the subject of much research, due to their applications as electrical contacts and interconnects, diffusion barriers, low resistance gates, and field-assisted positron moderators, among others. Defects within the silicide layer and/or at the silicide/silicon interface are detrimental to device performance, since they can act as traps for charge carriers, as well as positrons. Pinholes penetrating the film are another detriment particularly for cobalt silicide films, since they allow electrons to permeate the film, rather than travel ballistically, in addition to greatly increasing surface area for recombination events. A series of epitaxial cobalt and nickel silicide thin films, deposited via electron-beam evaporation and annealed at various temperatures, have been grown on single-crystal silicon (111) substrates, in an effort to establish a relationship between deposition and processing parameters and film quality. The films have been analyzed by transmission and scanning electron microscopy, sputter depth profile Auger, and slow positron annihilation spectroscopy. The latter has been shown to both correlate and complement the traditional electron microscopy results.

Positron annihilation spectroscopy of the defect structure of sputter-deposited TiN

Doppler and slow positron annihilation spectroscopy (PAS) techniques were used to investigate defect structures, as a function of composition and deposition sputtering power, in TiNx (0.48 ⩽ x ⩽ 1.11) thin films fabricated by physical vapor deposition methods. The recovery of the defect structures during a 1 h anneal at 900 °C was also studied. The present data, together with previous positron lifetime data (for the same samples), indicate that PAS has the potential to become an extremely useful technique for the characterization of atomic-scale defects in these materials. The conventional bulk PAS techniques yield consistent data if the results are corrected for the substrate contribution to the measured S parameters and the films have thicknesses greater than a few microns. For films with thicknesses on the order of 1 – 2 μm the slow PAS technique must be used.

Slow positron annihilation spectroscopy of heterojunctions and homojunctions of GaAs-based semiconductor thin films

Slow positron annihilation spectroscopy of an AlGaAs/GaAs thin film heterostructure has been performed as a function of applied external bias. The defect density profile with zero bias indicates the presence of surface trap states and a high concentration of defects at the AlGaAs/GaAs interfaces. The defects are thought to be dislocations created by the lattice mismatch at the interface. Application of an external bias changes the observed Doppler parameter as a result of an apparent electical activity of a variety of trapping mechanisms within the film.