Slow Positron Implantation Spectroscopy Research Articles

Hydrogen-induced defects in bulk niobium

Our aim in the present work was to investigate changes of the defect structure of bulk niobium induced by hydrogen loading. The evolution of the microstructure with increasing hydrogen concentration was studied by x-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with the measurement of Doppler broadening, in defect-free Nb $(99.9%)$ and Nb containing a remarkable number of dislocations. These samples were electrochemically loaded with hydrogen up to ${x}_{\mathrm{H}}=0.06\phantom{\rule{0.3em}{0ex}}[\mathrm{H}∕\text{Nb}]$, i.e., in the $\ensuremath{\alpha}$-phase region, and it was found that the defect density increases with hydrogen concentration in both Nb samples. This means that hydrogen-induced defects are created in the Nb samples. A comparison of PAS results with theoretical calculations revealed that vacancy-hydrogen complexes are introduced into the samples due to hydrogen loading. Most probably these are vacancies surrounded by 4 hydrogen atoms.

Hydrogen-Induced Defects in Niobium Studied by Positron Annihilation

Changes of the defect structure of niobium induced by hydrogen loading are presented in this work. It was found that annealing of virgin bulk Nb (99.9%) at 1000 °C for 1h leads to a complete recovery of defects. Subsequently, the defect-free samples were step-by-step electrochemically loaded with hydrogen up to xH = 0.06 (H/Nb atom ratio), i.e. in the �-phase region, where the Nb-H system represents a single- phase solid solution. The evolution of the microstructure with increasing hydrogen concentration was studied by X-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with measurement of Doppler broadening. It was found that new defects were created due to hydrogen loading. The concentration of these hydrogen-induced defects increases with increasing hydrogen concentration. A comparison of PAS results with theoretical calculations revealed that complexes consisting of a vacancy, surrounded likely by four hydrogen atoms, were introduced into the samples due to hydrogen loading.

Fluence dependence and thermal stability of defects in helium-implanted cubic zirconia

Slow positron implantation spectroscopy investigations of yttria-stabilized cubic zirconia implanted with 50 keV He ions detect, at 60% of the projected range ( R p), a concentration of defects maximum, which may constitute a barrier for the diffusion of helium towards the surface. The Doppler broadening lineshape ( S) dependence on the fluence suggests a change in the nature of defects above 4 × 10 16 ions/cm 2, with an enhancement of the trapping efficiency. These defects evolve into large bubbles by Ostwald ripening after annealing at temperatures higher than 573 K, as suggested by their distribution narrowing. Above 973 K, a breaking- up of the bubbles occurs, with helium release and diffusion towards the surface and eventual out-gassing.

Characterisation of defects in LiF implanted with Ar + using variable energy positron beam

Slow positron implantation spectroscopy has been used to determine the surface and near surface defect profile in LiF after implantation with 100 keV argon ions for a range of fluences from 10 13 to 10 16 cm −2. The measured S-parameter is used to characterise the radiation damage as a function of depth. The spatial extent of the defect distributions was estimated by employing the computer program VEPFIT. Maximum lattice damage is shown to occur at incident positron energy of 4.0 keV for low doses and 5.0 keV for the high dose. This energy corresponds to a sample depth of about 200 nm. The positron annihilation spectroscopy results are correlated with optical absorption measurements on the crystals.

The influence of substrate temperature on the evolution of ion implantation-induced defects in epitaxial 6H–SiC

An epitaxial n-type 6H–SiC layer has been four-fold implanted with Al + ions at temperatures ranging from room temperature (RT) to 1200 °C in order to create a buried p-doped layer from 200 to 600 nm below the surface. The defects induced by the ion implantation at different temperatures have been investigated by slow positron implantation spectroscopy (SPIS). Higher substrate temperatures were found to lead to a significant reduction in the depth of the damage. However, this is accompanied by the formation of vacancy clusters of sizes up to seven Si–C di-vacancies. Only at 1200 °C does the vacancy agglomeration disappear in the implanted region and larger agglomerates are formed immediately below the surface. Furnace annealing at 1650 °C was found to be insufficient to remove all damage.

Investigation of spatial distribution of defects in ultra-fine grained copper

Ultra-fine grained copper prepared by high pressure torsion has been studied by means of slow positron implantation spectroscopy with Doppler broadening measurement. In addition, conventional positron lifetime and Doppler broadening spectroscopy have been utilised. Defects present in the specimens were identified, their spatial distribution and depth profile have been determined. The results are discussed in correlation with those obtained by XRD and TEM.

Characterization of Sn Films on Silicon by Slow Positron Implantation Spectroscopy

Characterization of Sn Films on Silicon by Slow Positron Implantation Spectroscopy

Characterization of rf-sputtered platinum films by positron annihilation spectroscopy

Pt films on alumina substrates, both in their as-received and annealed states, have been extensively characterized by slow positron implantation spectroscopy (SPIS). Bulk Pt samples have been investigated by conventional positron annihilation spectroscopy (PAS) as well as by SPIS. A variety of state-of-the-art theoretical calculations have been performed to aid the interpretation of experimental findings. The research shows that a re-interpretation of earlier defect studies of bulk Pt by PAS is required in order to achieve a satisfactory agreement with the present experimental findings and theory.

Characterisation of defects in ion implanted SiC by slow positron implantation spectroscopy and Rutherford backscattering

(SiC) 1− x (AlN) x has been prepared by ion co-implantation of N + and Al + into a 6H-SiC n-type wafer. The substrate temperature during implantation was varied from 200°C to 800°C in order to reduce the damage created by ion implantation. The obtained structures have been investigated by Slow Positron Implantation Spectroscopy (SPIS) and Rutherford Backscattering and Ion Channeling (RBS/C). Both methods are sensitive to different kinds of defects and the results are complementary. The defect structures determined by SPIS and RBS/C are presented and the influence of the variation of the substrate temperature is discussed.

Positron annihilation spectroscopy of laser-irradiated 4H-SiC

Slow positron implantation spectroscopy has been applied to the study of samples of 4H-SiC irradiated by excimer lasers at different wavelengths and fluences. Measurements suggest that irradiation by light of wavelength 193 nm leads to amorphisation of the material, whereas irradiation by 308 nm wavelength light at fluences above 1300 mJ cm −2 creates subsurface damage consistent with the formation of vacancy agglomerates.

Characterization of vacancy-type defects in Al + and N + co-implanted SiC by slow positron implantation spectroscopy

6H–SiC n-type wafers were implanted with Al + and N + ions in two ways: first Al + followed by N + and vice versa. The implantation was carried out at four different substrate temperatures between 200 and 800°C. Depth profiles of the defects were evaluated from measured Doppler broadening profiles of the annihilation radiation as a function of incident positron energy for both co-implantation sequences. Differences in the defect distribution and in the defect size are shown and discussed.

Enhancement of depth sensitivity in slow positron implantation spectroscopy of Si

Information gained by non-destructive slow positron implantation spectroscopy on the depth distribution of open-volume defects created by ion implantation in Si is limited. In particular, determination of the shape of defect tails is hampered by the dominance of the positron response to defects in the peaked subsurface distribution and the unavoidable decrease in depth resolution as the incident positron energy increases and the positron implantation profile broadens. Enhanced depth resolution is achieved by combining standard positron-beam-based Doppler broadening spectroscopy with controlled removal of thin layers of the implanted sample by anodic oxidation and etching. The technique is described in detail and examples of its capabilities are shown using both simulated and experimental data.

Damage in silicon carbide induced by Rutherford backscattering analysis

Damage in silicon carbide generated by ion implantation or irradiation is usually analyzed by Rutherford backscattering spectroscopy in combination with channeling (RBS/C) of MeV He + ions, a technique which is considered to be largely non-destructive. In this paper we report on swelling of 6H–SiC induced by He + implantation at doses commensurate with, or lower than those commonly used for obtaining RBS/C spectra of desirable statistics. The swelling increases by about 40% if the He + ions are implanted in a non-channeling direction. The formation of high concentrations of deep-reaching (μm range) defects due to RBS/C is confirmed by slow positron implantation spectroscopy (SPIS) measurements. An optical damage depth-profile, with distinct optical properties corresponding to the regions of electronic and nuclear stopping, is obtained from a fit to polarized infrared reflection spectroscopy (PIRR) data and compared to TRIM calculation. Auger electron spectroscopy (AES) shows that the specific color of the implanted area is not due to the deposition of a thin surface film during He + implantation, and the swelling is not related to chemical reactions in the near-surface region. The formation of additional disorder from RBS/C may corrupt the respective data obtained subsequently by SPIS and PIRR. Therefore, RBS/C measurements should always be carried out last, i.e. following analytical techniques which are certainly non-destructive.

Defects in -implanted Si studied by slow positron implantation spectroscopy

Slow positron implantation spectroscopy has been applied to the investigation of point defects formed during the synthesis of buried SiGe alloy layers in Si by high-dose implantation and post-amorphization with . It is seen that omitting the post-amorphization stage prior to annealing leaves a damaged layer, containing open volume defects, extending beyond the -implanted overlayer. Provided that the Ge dose is low enough to allow planar crystal regrowth, post-amorphization appears to inhibit defect formation. Samples implanted with higher doses contain as-yet unidentified defects.

Slow positron implantation spectroscopy of high current ion nitrided austenitic stainless steel

Surface modification of austenitic stainless steel by high current ion nitriding at 400°C has been studied by Slow Positron Implantation Spectroscopy (SPIS). In addition, Nuclear Reaction Analysis (NRA) has been applied to obtain information about the nitrogen depth profile. The results obtained from both methods are compared and discussed with respect to the nature of defects produced by high current ion nitriding and their influence on the formation of a surface layer, called expanded austenite.

Characterization of Vacancy-Type Defects in Ion Implanted and Annealed SiC by Positron Annihilation Spectroscopy

ABSTRACTNew examples of characterization of vacancy-type defects in ion implanted and annealed SiC by the established technique of slow positron implantation spectroscopy are presented. In particular, the estimation of the depths of damaged regions and their change (a) after post-irradiation annealing, or (b) due to variation of substrate temperature during implantation, is addressed.

The effect of thermalisation length and work function on epithermal positron emission from solids

Measurements have been made of the yield of slow positrons from Ag(100), polycrystalline Au, Pb and Sn, and 8 Å, SiO 2 Si . The measured dependence of the total yields of re-emitted positrons upon incident positron energy indicates that only epithermal positron emission is observed from these samples. By fitting the data using a procedure more commonly applied to the evaluation of thermal diffusion lengths by slow-positron implantation spectroscopy the length L T, over which positrons are reduced in energy from ∼ 10 1 eV to below the positron work function, has been determined. L T is related to the positron thermalisation length. The largest value of L T of 24 ± 3 A ̊ is for the SiO 2 Si structure, attributed to the absence of a strong energy loss mechanism for positrons with energies below the SiO 2 Si bandgap(s). By assuming that the most significant effect on the positron yield at the lowest incident energies is the size of the positive surface potential step, work-function values have been deduced for the polycrystalline metallic samples of 0.9 ± 0.25 eV for Au and Pb, and 0.8 ± 0.25 eV for Sn.

A computer-controlled system for slow positron implantation spectroscopy

The design and construction of a computer-controlled beam transport system and its application to slow positron implantation spectroscopy is described. The control features include the facility to vary the positron beam energy, observe visually the associated spatial movement of the beam profile, and change the beam position so as to hit the sample centrally at all energies selected. This procedure allows the automatic collection of annihilation gamma ray energy spectra and calculation of lineshape parameters as a function of incident positron energy. Examples of such measurements for metallic and semiconductor samples are used to illustrate the performance of the system.

The study of sub-surface and interface characteristics of semiconductor heterostructures by slow positron implantation spectroscopy

Experiments are described in which the controlled implantation of mono-energetic positrons is used to gain information non-destructively on epilayer and interface defects in semiconductor heterostructures. The implantation, and hence annihilation, profile is changed by varying the incident positron energy from 1 to 35 keV. Characteristics of the positron state at the annihilation site are reflected in the width of the measured Doppler-broadened annihilation line. The fractions of positrons annihilating from each state are deduced by solving the steady-state diffusion equation. The technique is illustrated by application to a series of SiO2-Si samples.