R. Siegele

ERDA with very heavy ion beams

Abstract The use of very heavy ion beams such as 127I or 197Au with 1–2 MeV/u makes ERDA (elastic recoil detection analysis) a quite universal technique for thin film analysis capable of analyzing simultaneously light and heavy elements including H with almost constant sensitivity. Due to the strong increase of the recoil cross section with the projectile atomic number typically less than 1012 ions are required to get sensitivities in the 100 ppm range. Detector systems with particle identification are advantageous for ERDA, which can be improved additionally regarding depth resolution and detection efficiency, if the kinematic energy spread is corrected. The characteristic features of heavy ion ERDA will be briefly outlined and illustrated by several examples using a position sensitive detector system. Some general problems and limitations, which are caused by heavy ion beams, will also be discussed.

Helium bubbles in silicon: Structure and optical properties

Silicon samples were implanted with 20 keV He at various temperatures. The damage and the size of the He bubbles created during the implantation were measured with Raman spectroscopy and transmission electron microscopy. Room temperature implantation with 2.5×1017 He atoms/ cm2 produced an amorphized layer with a high density of small voids (∼5 nm). After annealing at 923 K the amorphous layer was recrystallized, but still contained extended defects. The He bubbles coalesced forming large bubbles in the implanted region. Implantation at 723 K left the Si essentially crystalline, but with a large number of defects. The He bubbles created at this temperature were larger than after room temperature implantation. Light emitting properties of this porous material are briefly discussed.

FORWARD ELASTIC RECOIL MEASUREMENTS USING HEAVY IONS

The application of the elastic recoil detection technique utilizing heavy ions for the analysis of semiconductor samples is demonstrated. With this technique the depth profiles of the primary constituents as well as profiles of all impurities can be measured in one spectrum. Depending on the target material, a depth resolution down to 20 nm can be achieved. All elements except hydrogen can be detected with almost the same sensitivity, namely ∼1×1015 at/cm2 with 136 MeV I in a 30° recoil geometry. For hydrogen, the sensitivity is about four times better.

Elastic recoil detection (ERD) with extremely heavy ions

Abstract Extremely heavy-ion beams such as 209Bi in elastic recoil detection (ERD) make ERD a uniquely valuable technique for thin-film analysis of elements with mass ≤ 100. We report ERD measurements of compositional analysis of dinosaur eggshells and bones. We also show the capability of the ERD technique on studies of thin-film, high-temperature superconductors.

Quantitative calibration of intense (α, α) elastic scattering resonances for 12C at 5.50–5.80 MeV and for 16O at 7.30–7.65 MeV

Abstract Extremely strong (α, α) elastic scattering resonances — more than 100 times the Rutherford value — occur in 16O at 7.35–7.65 keV and in 12C at 5.50–5.80 MeV, thus allowing the normal RBS technique to be extended to low-Z components, such as oxygen and carbon. Both resonances have been calibrated over the appropriate 300 keV energy regime with an overall accuracy of ±4%. Some recent examples of their use in profiling oxygen and carbon in various substrates are given.

APPLICATION OF ION-BEAM-ANALYSIS TECHNIQUES TO THE STUDY OF IRRADIATION DAMAGE IN ZIRCONIUM ALLOYS

Abstract Ion-beam-analysis techniques are being used to provide an understanding of the nature of collision cascades, irradiation-induced phase changes, lattice location of solute atoms and defect-solute atom interactions in various zirconium alloys. In zirconium intermetallic compounds, such as Zr3Fe, Zr2Fe, ZrFe2, and Zr3(Fex,Ni1 − x), electron and ion irradiations have been used to obtain detailed information on the crystalline-to-amorphous transformation occurring during the irradiation. Transmission-electron-microscopy (TEM) observations have provided information on the nature of the damage produced in individual cascades, the critical dose required for amorphization, and the critical temperature for amorphization. In a study on the electron-energy dependence of amorphization in Zr3Fe, Zr2Fe and ZrCr2 in situ high-voltage-electron-microscope investigations were combined with high-energy forward-elastic-recoil measurements to yield information on the threshold displacement energies for Zr and Fe or Cr in these lattices, as well as the role of secondary displacements of lattice atoms by recoil impurities (C,O) at low electron energies. In Zr implanted with 56Fe ions and subsequently bombarded with 40Ar ions at 723 K, subsequent secondary-ion-mass-spectrometry (SIMS) analyses were used to monitor the effect of irradiation on the migration of Fe in the Zr lattice. In addition, ion-channeling investigations have been used to determine the lattice sites of solute atoms in Zr as well as the details of the interaction between the solute atoms and the irradiation-produced defects.

Forward elastic recoil measurements using heavy ions

Abstract The potential of the elastic recoil detection technique using heavy ions for the analysis of low Z-elements such as C, N, and O is shown. Heavy ions at high energies, such as 136 MeV 127I, allow the separation of neighbouring elements up to Si. Heavier elements can also be separated as long as they are not too close together in atomic number.

Simultaneous multielement ERDA using a simple detector system and extremely heavy ion beams

Abstract The use of very heavy ion beams such as Au or Bi in elastic recoil detection analysis (ERDA) is increasing rapidly. However, one of the experimental problems is the simultaneous detection of the full range of recoil atoms ejected by such extremely heavy ion beams, since all low-mass surface recoils have almost identical velocity and also exhibit a wide spread of ranges in the detector. This makes it difficult to design a simple detector suitable for the full range of recoils. Often two or more gas pressures are required to allow the detection of both low-mass and heavy recoil atoms. Simultaneous measurement of all elements, from H to mass 100 and even higher, is highly desirable, since in this case no other parameters, such as collected charge are needed for the analysis of the data. To solve this problem, we have developed a simple Δ E−Er detector. A combination of a gas detector (Δ E) and a solid state detector (Er) leads to a very compact design. The advantages of this type of detector are discussed and its wide elemental range is demonstrated.

Origin of carbon and its influence on photoluminescence in porous silicon

Abstract Samples of porous Si (PS) were prepared from p -type 10–35 Ω-cm Si under anodisation in aqueous HF (20%) for 10 min. The composition of the PS was measured by heavy-ion elastic recoil detection analysis (HIERDA). In all samples a considerable carbon content varying from 2–20% was measured, while the oxygen and hydrogen concentrations ranged from 2–25% and 10–25%, respectively. The sample wax removing procedure was identified as a source for the high carbon content. The concentration of carbon and its influence on the photoluminescence due to different treatments of PS was investigated.

VISIBLE PHOTOLUMINESCENCE FROM HELIUM-ION IMPLANTED CARBON IN SILICON

Silicon wafers implanted with 30 keV He ions at room temperature in a low pressure hydrocarbon atmosphere exhibited visible photoluminescence. The samples were characterized by Raman, infrared, transmission electron microscopy, and heavy ion elastic recoil detection analysis. Two different layers were distinguishable on top of the silicon, with the upper layer comprising mostly amorphous carbon, as confirmed on a similarly implanted Be sample. Green photoluminescence was found to arise from the thinner a‐Si1−xCx:H interface layer. Such a buried intermixed layer could be incorporated into a stable visible light emitting device based on crystalline silicon.