K. Bharuth-Ram

Lattice sites of ion implanted Li in diamond

Radioactive Li ions were implanted into natural IIa diamonds at temperatures between 100 and 900 K. Emission channeling patterns of α‐particles emitted in the nuclear decay of 8Li(t1/2=838 ms) were measured and, from a comparison with calculated emission channeling and blocking effects from Monte Carlo simulations, the lattice sites taken up by the Li ions were quantitatively determined. A fraction of 40(5)% of the implanted Li ions were found to be located on tetrahedral interstitial lattice sites, and 17(5)% on substitutional sites. The fractions of implanted Li on the two lattice sites showed no change with temperature, indicating that Li diffusion does not take place within the time window of our measurements.

Europium doping of c-BN and ta-C thin films

Abstract We investigated the doping of thin films of tetrahedral amorphous carbon (ta-C) and cubic boron nitride (c-BN) with europium. The films were grown by mass selected ion beam deposition and doped with europium during growth. Analysis was performed in vacuo using photoelectron spectroscopy and ex vacuo with conversion electron Mossbauer, Fourier transform infrared and cathodoluminescence spectroscopy. Successful incorporation of europium into the c-BN films is achieved. These c-BN:Eu films show luminescence of the 5 D 0 – 7 F 2 intra-4f electron transition, measured at 12 and 300 K. The results are compared to Eu implanted poly crystalline c-BN. In case of the ta-C films doped with Eu during growth an accumulation of the deposited Eu atoms at the surface is observed.

Lattice sites of arsenic ions implanted in diamond

The lattice sites of As ions implanted in diamond and the annealing of implantation damage were investigated in emission channeling measurements. A dose of 1.0×1013 cm−2 73Se ions was implanted into IIa diamond at 300 K with an energy of 60 keV. 73Se (t12=7.1 h) decays to 73As (t1/2=80 d), which in turn decays to excited states in 73Ge. Channeling effects were measured on conversion electrons emitted in the 73Ge decay. Annealing studies in the range 873–1673 K showed an annealing stage of the implantation damage setting in at 1100 K. Comparison of the measured effects with simulations based on the dynamical theory of electron diffraction showed that after annealing at temperatures above 1100 K, 55(5)% of the implanted ions were located on substitutional lattice sites.

Spin–lattice relaxations of paramagnetic Fe3+ in ZnO

The spin–lattice relaxation rate of paramagnetic Fe3+ in single-crystalline ZnO has been determined following low-fluence (Φ<1012 cm−2) 60 keV implantation of 57Mn+ (T1/2=1.5 min) and emission Mossbauer spectroscopy on the 57Fe daughter nucleus in the temperature range from 300 to 664 K. The spin–lattice relaxation of Fe3+ is found to follow a T9 temperature dependence, in contrast to the T2 dependence expected for a two-phonon Raman process determined in both single-crystal MgO and α-Al2O3 using the same analysis method of the Mossbauer spectra measured without an applied external magnetic field. This is an unexpected result since ZnO has a lower Debye temperature than both MgO and α-Al2O3.

Alpha-emission channeling investigations of the lattice location of Li in Ge

The α-emission channeling and blocking technique is a direct method for lattice site determination of radioactive atoms in single crystals. Position-sensitive detection of emitted α particles provides an efficient means of carrying out such experiments at very low doses (10 10 -10 11 implanted probe atoms per spectrum). Comparison of the experimental data to Monte Carlo simulations of complete twodimensional channeling patterns (e.g. ±2ϒ around , and axes, which also includes all relevant planar directions) allows for straight-forward identification and rather accurate quantitative determination of occupied lattice sites, while at the same time the energy spectrum of emitted α particles gives information on the probe atom depth distribution. We illustrate this for the case of ion implanted 8 Li (t_=0.8 s) in Ge, where we identify mainly tetrahedral Li at room temperature, and bond-centered Li at slightly elevated temperature.

Lattice sites of Li in CdTe

Abstract The lattice site occupation of Li in CdTe at temperatures between 40 and 500 K was investigated with the emission channeling method. Radioactive 8Li ions were implanted at low doses into CdTe single crystals. Emission channeling patterns of α-particles emitted in the nuclear decay of 8 Li (t 1 2 = 838 ms ) were measured and compared to calculated emission channeling and blocking effects. At temperatures below 130 K the Li ions occupy mainly tetrahedral interstitial sites and about 10% substitutional sites. In the temperature range between 130 and 190 K, a site change from the tetrahedral interstitial sites to substitutional sites is observed. Between 190 and 470 K, in addition to the substitutional Li, all samples show Li at sites, which are displaced 0.7(1) A from the substitutional position, either along the 〈111〉 axis or 〈100〉 axis. Above 470 K out-diffusion of Li to the surface is observed.

Muonium studies of p-type semi-conducting diamond under conditions of UV-visible illumination

This work reports on the promptly forming fraction and the spin relaxation rate of the isotropic muonium (MuT) component in p-type semi-conducting diamond, measured under the condition of illumination. The data are the first such investigations for diamond. A broad band illumination with wavelengths ranging from 0.5 μm to 3 μm was obtained from a Xenon lamp. The energy of the photons was sufficient to excite electrons from the valence band to the 0.28 ppm boron impurity band (0.37 eV). The Transverse Field Muon Spin Rotation (TF-μSR) measurements were conducted as a function of temperature, ranging from 5 K to 300 K. An illumination effect at temperatures below 100 K is observed. It is not yet clear from these data whether the effect is due to Mut scattering off delocalized holes, which are removed by illumination or whether there is prompt trapping of Mut at boron impurities (passivation) which is affected by illumination.

A Search for Magnetic Effects in Ion Implanted ZnO and SiC

Mossbauer spectroscopy studies and magnetization measurements have been performed on ZnO and 3C‐SiC samples implanted with 57Fe ions with fluences of 0.5–2.0×1016 ions/cm‐2. For single energy implantations and annealing up to 1173 K, the Mossbauer spectra show the Fe3+ ions to remain fairly constant in the crystals, with little evidence of magnetic clustering at implantation fluencies below 2 at. % However, MOKE measurements on ZnO single crystals implanted with 1, 2 and 4 at. %56Fe in a box profile show ferromagnetic behaviour in the 4% implanted sample and weak paramagnetic or ferromagnetic behaviour at room temperature for the other samples. In a SiC sample implanted with 1×1016/cm2 57Fe and annealed at 973 K, magnetization measurements indicate a weak ferromagnetic effect.

Mössbauer study of 57 Fe in CVD diamond following 57 Mn implantation

57Fe Mossbauer spectroscopy, following the implantation of radioactive parent 57Mn+ ions, has been performed on two chemical vapour deposited diamond samples, one synthesized in 2003 (CVD03) and the other in 2005 (CVD05). The spectra of sample CVD05 were as observed previously in natural IIa diamonds: single lines corresponding to substitutional and interstitial Fe were superimposed on a broad quadrupole split doublet. The site fraction of Fei reached 30% at 90 K. The spectra of the CVD03 sample showed, in addition to the above features, a strong contribution (>30%) from a quadrupole doublet attributable to the presence of intrinsic amorphous inclusions in the crystallites. This observation has been confirmed by X-ray diffraction.

LOCATIONS OF IMPLANTED 19F* ATOMS IN SI, GE AND DIAMOND STUDIED THROUGH THEIR NUCLEAR QUADRUPOLE INTERACTIONS

The Hartree-Fock cluster procedure was used to obtain the associated electronic distributions for 19F* (I = 5/2, Ex = 197 KeV excited nuclear state of the 19F atom) at possible sites in crystalline Si, Ge and diamond and to calculate nuclear quadrupole coupling constants vQ and the asymmetry parameter η of the electric field gradient at the modelled sites. Lattice relaxation effects have been incorporated by employing a geometry optimization method to obtain minimum energy configurations for the clusters modelling each site. The intrabond (IB), antibonding (AB) and substitutional (S) sites in the bulk and the atop site on the surface were studied. From a comparison with vQ and η values observed in time differential perturbed angular distribution (TDPAD) measurements we were able to identify the high frequency component in Si and Ge with 19F* at the intrabond site. In diamond two high frequency components are observed. These are identified with 19F* at intrabond and substitutional sites. For the low frequency site in Si and Ge the assignment is made to 19F* implants at dangling bonds in the bulk resulting from implantation damage. In diamond none of the sites studied could provide lower frequency nuclear quadrupole parameters close to the observed ones.