[Show abstract][Hide abstract] ABSTRACT: β-active probe nuclei are implanted in nominally undoped ZnSe crystals. β-radiation detected nuclear magnetic resonance (β-NMR)
studies are described for two different probe nuclei, 8Li and 12B. This way, the implantation behavior of two “opposite”dopants, one acceptor (Li) and one donor (B) can be characterized
by the same microscopic technique. Such characterizations are attempted in terms of the structure of intermediate or final
lattice sites, defect charge states, or the kinetics of defect reactions and site changes.
[Show abstract][Hide abstract] ABSTRACT: Microscopic experimental data on the distribution of vacancies created in isolated implantation events are reported for the model system B in Cu. An interstitial-to-substitutional conversion process of the implanted 12B ions is utilized to detect lattice damage. We observe vacancy clouds with well-defined edges and a mean radius of 13.5(9) nm. The radial profile of the local vacancy concentration never exceeds 10-4 it is almost flat in the central region before it falls off rapidly, a behavior which cannot be explained by simple binary-collision computer models.
[Show abstract][Hide abstract] ABSTRACT: A density-matrix-based formalism is presented to extract activation parameters for the reorientational motion of an interstitial B defect in Si, a center created by ion implantation. β-radiation detected nuclear magnetic resonance (β-NMR) data show beginning mobility at . At the signal is lost even though the center is still present. The activation energy for its reorientation in p-type Si is determined to be .
Physica B Condensed Matter 12/2001; s 308–310:236–239. DOI:10.1016/S0921-4526(01)00680-9 · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Spin-polarized, radioactive 12B probe nuclei were implanted in microcrystalline Si with typical grain diameters of ~10nm. Using /beta-radiation detected nuclear magnetic resonance (/beta-NMR) we observed broad, unstructured spectra at room temperature. This broadening is shown to be due to structural disorder. It is not caused by hydrogen or other contaminations of the samples.
[Show abstract][Hide abstract] ABSTRACT: Using P-radiation detected nuclear magnetic resonance (beta-NMR), we investigated the microscopic behavior of implanted Li-8 in nominally undoped ZnSe crystals. From the temperature-dependent amplitudes of high-resolution NMR spectra we conclude a gradual interstitial-to-substitutional site change between 200 and 350 K. This is in accordance with earlier emission channeling results. We argue that this conversion proceeds via Li-i(+) + V-Zn(2-)--> Li-zn(-) and involves implantation related Zn vacancies.
[Show abstract][Hide abstract] ABSTRACT: Using β-radiation-detected nuclear magnetic resonance (β-NMR) in the special form of cross-relaxation spectroscopy we studied the diffusional behavior of implanted 12B nuclei in Cu single crystals at temperatures T=115–750K. An extended and completely revised dynamic theory of nuclear cross relaxation is developed to analyze the experimental data. Especially the incorporation of (hitherto neglected) spin-lattice relaxation effects turned out to be an important improvement. Applying this formalism we obtain activation energies of Ea=0.57(5)eV for the migration of interstitial B, the dominating fraction for T≲400K, and of Ea=1.15(10)eV for substitutional B formed at higher temperatures. The previously found direct-exchange mechanism for the diffusion of substitutional B in Cu is confirmed by our analysis.
[Show abstract][Hide abstract] ABSTRACT: Recently it was shown that substitutional B impurities in Cu metal diffuse via a direct-exchange mechanism. In this paper a model for this mechanism is proposed. From the temperature dependence of the electric field gradient produced by the B atom at its nearest Cu neighbors it is concluded that the local vibration of the B atom within its cage of Cu neighbors triggers the direct-exchange mechanism.
Physical Review B 11/2001; 64(22). DOI:10.1103/PhysRevB.64.224301 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lattice sites and annealing behavior of implanted 12N in
semi-insulating ZnSe are investigated by use of β radiation
detected nuclear magnetic resonance (β-NMR). For room-temperature
implantation only a small part of the N impurities is found at sites
with full Td symmetry; this fraction is attributed to
substitutional NSe. Above 500 K the population of this site
increases and saturates at a 10 times higher value for T>=950 K. This
increase is assigned to the change of initially interstitial N
(Ni), isolated or part of a complex, to unperturbed
NSe. An activation barrier Ea=0.47(5) eV is
determined for this process representing an upper limit for the
Ni migration energy. We do not observe configurations where
NSe is bound to a diamagnetic partner, like the
Physical Review B 06/2001; 63(24):241201-. DOI:10.1103/PhysRevB.63.241201 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Spin polarized radioactive 12B, 12N, and 8Li probe nuclei are implanted in nominally undoped ZnSe at stationary concentrations ≤ 1010 cm-3. These light dopants, one donor and two acceptors, are characterized by β-radiation detected nuclear magnetic resonance (β-NMR)
measurements. The donor 12B and the acceptor 12N show quite similar and rather simple implantation behaviour, the situation is markedly different for the second acceptor
8Li, however. This contrast indicates that in semi-insulating ZnSe the structure of dilute impurities is controlled by individual,
[Show abstract][Hide abstract] ABSTRACT: Spin-polarized radioactive 12B and 12N probe nuclei are produced in nuclear reactions and implanted into nominally undoped ZnSe at stationary concentrations ≲ 108 cm−3. The implanted impurities are characterized by β-radiation detected nuclear magnetic resonance (β-NMR) measurements within ∼20 ms after the implantation event. About 85% of the implanted B occupy substitutional Zn-sites after moderate annealing and are immobile there up to at least 950 K. Our first data on N implantation show a substantial fraction reaching cubic lattice sites, essentially without any annealing. We tentatively assign this fraction to unperturbed NSe−.
[Show abstract][Hide abstract] ABSTRACT: β-radiation detected nuclear magnetic resonance measurements are reported on the lattice site of 12N ions implanted into undoped ZnSe. At 800 K a Larmor resonance is observed indicating the existence of diamagnetic N with full Td symmetry. From the resonance intensity in ZnSe compared to the reference system 12N in Cu it is estimated that at 800 K about 40% of the implanted 12N end up in this highly symmetric site. An unambiguous experimental determination of the precise site is still lacking. Arguments are given, however, that the observed signal corresponds to NSe. Searches for quadrupolarly disturbed signals from some of the missing 60% of 12N in configurations of lower symmetry, e.g., complexes with intrinsic defects, were so far not successful.
Materials Science Forum 01/1997; 258-263(9993):1395-1400. DOI:10.4028/www.scientific.net/MSF.258-263.1395
[Show abstract][Hide abstract] ABSTRACT: The fraction of boron atoms that take up defect-free sites on ion implantation in diamond has been investigated in β-NMR measurements. Polarized 12B nuclei were produced in the reaction 11B(d,p)12B with 1.5 MeV deuterons and recoil implanted into a diamond Ib sample. Depolarization resonance spectra were measured in an external magnetic field of 1.0 kG at sample temperatures ranging from 300 K to 800 K, showing that the polarised B atoms retain their polarisation on implantation in diamond. The polarization asymmetry at the Larmor frequency yielded a fraction of boron atoms at defect-free tetrahedrally symmetric sites of 12(1)% at 300 K, increasing to 17(2) % at 800 K. The resonance spectra also showed evidence that some of the implanted boron atoms were at low symmetry sites. Measurements after pre-implantation of the diamond sample with 50 - 220 keV Li+ ions showed no significant change of the fraction of boron atoms that are implanted at defect-free symmetric sites in the diamond lattice.
Materials Science Forum 01/1997; 258-263:763-768. DOI:10.4028/www.scientific.net/MSF.258-263.763