A.F. Quenneville

A study of interstitial trapping configurations in fcc metals by ion channeling

Abstract Channeling measurements have shown that self-interstitial atoms in Al and Cu are trapped strongly by small solute atoms and weakly by large solute atoms. The strong trapping configuration is the 〈100〉 mixed dumbbell, in which the solute atom is displaced from its lattice site by 0.1–0.14 nm in a 〈100〉 direction. Mn, Cu, Fe, Zn and Ag solutes in Al, and Be solutes in Cu form strong traps which are stable up to stage III recovery. In the weak trapping configuration, the self-interstitial retains its identity and the solute atoms are displaced very little. Mg and Sn solutes in Al and Sb, Ag and Au solutes in Cu are weak traps, which release trapped interstitials during stage II recovery.

Detection of In‐P and In‐Sb atom pairs by perturbed angular correlation in silicon

We report the observation of In‐P and In‐Sb atom pairs in Si using the perturbed γγ angular correlation technique with 111In as radioactive probe atoms. The pairs are characterized by νQ=179(1) MHz and 271(1) MHz, respectively, and their electric field gradient tensors are axially symmetric about a 〈111〉 lattice direction. The results suggest a strong interaction between acceptor and donor atoms in elemental semiconductors like Si and Ge.

The combined effects of lattice vibrations and irradiation-produced defects on dechanneling

Abstract The combined effects of lattice vibrations and irradiation-produced defects on dechanneling have been studied in various crystals by measuring backscattering yields of He + and H + ions for 〈111〉 or 〈111〉 channels in the temperature range 40–300 K. For an Al-0.08 at% Ag crystal examined along 〈110〉 and a Si crystal examined along 〈111〉, the dechanneling contributions from thermal vibrations and from irradiation-produced defects were additive (i.e. the deviation Δ from additivity was essentially zero). However, for the remainder on the crystal systems(Cu-006 at% Au 〈110〉, Ge 〈111〉 and 〈110〉 and Si〈110〉) the contributions of the defects and thermal vibrations to dechanneling were not independent i.e. Δ was found to be appreciable. Also, in general, Δ varied linearly with the mean vibrational amplitude of the crystal atoms.

Backscattering measurements of the trapping of Zr Self-interstitial atoms by Au Atoms in irradiated Zr-Au Crystals

Abstract Backscattering of 2 MeV He + ions from Zr-0.2% Au and Zr-0.3% au crystals was measured for [0001], 〈1 120〉 and 〈1010〉 directions and the (0001) plane in order to determine the trapping characteristics of Au atoms for irradiated-induced defects. It was observed that Au atoms were displaced from substitutional lattice sites during post-irradiation annealing near 120K, indicating that the Au atoms formed strong traps for Zr self-interstitial atoms which became mobile at that temperature. The direction of Au atom displacements was between 〈4043〉 and 〈1010〉 axes. The displacement of the Au was reduced during annealing from 200–400K, and was reduced further from 550–700K. These recovery stages could be due to migration of a second type of self-interstitial and to migration of vacancies respectively.

Backscattering measurements of the temperature dependence of irradiation-induced displacement of as and sb atoms in Si crystals

Abstract The temperature dependence of the irradiation-induced displacement of As and Sb atoms into 〈100〉 channels in diffused crystals of Si-0.1% As, Si-0.4% As and Si-0.1% Sb has been studied by backscattering of 1–2 MeV He+ ions. The maximum displaced fraction and the initial displacement rate varied with irradiation temperature, reaching a maximum at approximately 420 K for the Si-0.1% As crystal. The displaced fractions of As and Sb atoms were reduced by irradiation at 30 K after initial irradiation at 293 K. The results indicate that the solute atom displacement was caused by the trapping of several vacancies at each solute atom.

A channeling investigation of the interaction between solute atoms and irradiation-produceddefects in magnesium

Abstract The trapping of irradiation-produced defects by solute atoms in Mg crystals was monitored by measuring the displacement of the solute atoms from lattice sites using the backscattering-channeling technique. In Mg-0.2 at.% Ag crystals, irradiation at 30 K with 1 MeV He+ ions resulted in a very large fraction of Ag atoms being displaced from their lattice sites. The Ag atom displacement appeared to be along (4043) directions and is attributed to the trapping of migrating Mg interstitial atoms by Ag atoms to form Mg-Ag mixed dumbbells. Recovery of the Ag atom displacements and the irradiation-induced dechanneling increment occurred principally in two stages, 80-160 K (stage III) and 200-280 K (Stage IV). Stage III is attributed mainly to some type of interstitial migration and stage IV is attributed to the migration of single vacancies. In contrast to the Mg-Ag results, a very small displaced fraction of Bi atoms occurred in an irradiated Mg-0.08 at% Bi crystal; hence Mg-Bi mixed dumbbells do not app...

Irradiation-induced displacement of Ag atoms from lattice sites in an Al-0.2% Mg-0.1% Ag crystal

In irradiated alloys of Al containing approximately 0.1 at.% Ag, Al-Ag (100) dumbbells are created by the trapping of Al interstitial atoms at Ag solute atoms. The results demonstrate that the addition of 0.2% at.% Mg retards not only the formation of Al-Ag dumbbells during annealing from 30 to 100K but also their annihilation during annealing from 180 to 240K. Al interstitials are released from Mg traps at 100-160K, causing further trapping at Ag atoms. Approximately 70% of the Ag atoms return to lattice sites at approximately 200K (stage III) and the remainder at approximately 260K. These results favour migration of Al-Ag dumbbells rather than vacancies during stage III annealing.

Lattice location of 15N in Fe

Abstract The lattice position of 15 N atoms in crystals of Fe was studied using measurements of backscattering yields of 0.8 MeV 1 H + and alpha particle yields from the nuclear reaction 15 N(p, α) 12 C. The 15 N atoms were introduced into the Fe by three methods: (1) implantation at 35 K or 293 K with 300 keV 15 N + 2 to an atomic fluence of 7.5×10 15 atoms cm −2 in a random crystallographic direction; (2) implantation under the same conditions, but in a 〈100〉 aligned direction; (3) diffusion at 770 K followed by quenching into water at 273 K. In all cases, the normalized yield of alpha particles in a channeling analysis showed a peak at 〈100〉 alignment, superimposed on a broad dip at the level χ N ≃ 0.7. The peak-to-valley ratio was P/V = 1.9 in case 2 and 2.5 in case 3. These results indicate an octahedral or near-octahedra site for the 15 N atoms. This conclusion was supported by angular scans through 〈110〉 axial and 〈100〉 planar channels. The 15 N atom position was quite stable with respect to irradiation by the 0.8 MeV 1 H + beam up to fluences of 10 17 ions cm −2 at 35 K. Subsequent annealing up to 300 K caused only small changes in χ 〈100〉 N , while reduction in dechanneling of the 1 H ions indicated that considerable point defect migration had taken place. During heating following implantation at 293 K, the 15 N was released or diffused away from the sub-surface region in two stages, centred at 520 K and 650 K. The first is likely due to bulk diffusion of 15 N, and the second is the result of release from defect traps.

Investigation of the interaction between irradiation-induced defects and solute atoms in dilute copper alloys by ion channeling

Abstract The backscattering-channeling method was used to investigate the interactions between irradiation-induced defects and solute atoms of Ag, Sb and Au in dilute copper alloys. Since the solute atoms were not displaced appreciably from lattice sites by irradiation with ∼1016 1.5 MeV He+ ions/cm2 at 40 or 70 K, it is concluded that the Cu self- interstitials created by the irradiation retained their identity when trapped by the solute atoms. During subsequent annealing between 180 and 270 K, the solute atoms were displaced from lattice sites. The irradiation-induced increase in dechanneling recovered only ∼30% in this temperature range. Further low temperature irradiations reduced the solute atom displacements. These results are consistent with multiple trapping of vacancies at the solute atoms.

Channeling studies of mixed dumbbells in metals

Abstract Measurements of ion channeling in irradiated metals have shown that small solute atoms trap self-interstitial atoms to form the mixed dumbbell configuration, in which a solute atom and a host atom straddle a lattice site. By monitoring the concentration of mixed dumbbells (which can be measured to an absolute accuracy of 10%) during an irradiation and annealing experiment, detailed information can be obtained about the properties of point defects. In the present channeling studies, the orientation of mixed dumbbells was determined for a series of dilute alloys. In addition, the efficiencies with which solute atoms trap self-interstitials to form mixed dumbbells, and the thermal stability of mixed dumbbells were measured for selected Al alloys. The channeling results are compared with data obtained from Mossbauer, diffuse X-ray scattering and electrical resistivity experiments.