M. C. Stemmet

Residence sites for19F ions implanted into diamond

Abstract19F has been used to probe the structure of the diamond lattice. The measurements were performed via the time differential perturbed angular distribution (TDPAD) technique applied to the 197 keV state (τ=128 ns,Q=0.10 b) of19F. The nuclei were excited and recoil implanted into an oriented diamond using a (p,p′γ) reaction initiated by a pulsed 4 MeV proton beam. Model functions simulating a variety of residence sites for the probe ions in a single crystal were developed for the analysis of the data. The data implies the formation of two molecular types, or sites within the lattice, with possibly a third radiation damage component.

Absolute sign of the Mu* hyperfine parameters in diamond

Standard μSR experiments in diamond have shown that the relative sign of the hyperfine parameters of the anisotropic Mu* state is negative (A‖/A⊥<0). We report an experimental determination of theabsolute sign of the Mu* hyperfine parameters by studying the transferred muon polarization during the thermally-activated transition from the isotropic Mu state to Mu*. The results demonstrate that the isotropic part of the Mu* hyperfine interaction is negative. In a nitrogen-poor diamond, both the Mu disappearance rate and the enhancement of the Mu* signals are well-described by a single Arrhenius law.

Hydrogen in and on natural and synthetic diamond

Abstract Diamond, both natural and metastable as well as stable growth synthetic, is a material of particularly attractive physical properties. In the characterization of diamond, light volatiles appear to play a significant role both in the determination of properties and in the control of the growth process itself. Historically nitrogen was perceived as the dominant impurity in natural diamond, but in the past decade both oxygen and hydrogen have been shown to be prolific to largely the same degree. This paper takes stock of the state of the art in the study of hydrogen in and on diamond of both natural and synthetic genesis. This includes the study of the surface and bulk hydrogen depth distribution as assayed by traditional nuclear reaction analysis, as well as recent high resolution resonant nuclear reaction analysis of hydrogen as it formally addresses the true surface of diamond. These analytical approaches are valuably complemented by the more subtle use of time dependent perturbed angular distribution studies which are shown to pick out a molecular hydrogen component in the bulk of diamond. Positively charged muons may combine with electrons to form the atom “muonium”, which for all practical purposes disports itself as a light isotope of hydrogen: muonium spin rotation studies are exploited in a radiation damage free manner to study the properties of hydrogen in diamond. Finally some specific work on hydrogen in CVD diamond (-like) materials is considered.

The fate of implanted 19F ions in diamond and their theoretical modelling

Abstract The ubiquitous use of ion implantation and the simultaneous interest in the emplacement of selected impurities in the matrix of choice bring added emphasis to the need for a quantitative understanding of the residence sites adopted by such imputities. The time-dependent perturbed angular distribution technique has been used to study the case of fluorine implanted in diamond. Careful examination is presented of the dependence of the perturbation parameters on the characteristics of the implant sites. These comprehensive investigations reveal the power of the technique in the richness of detail exposed and make possible the theoretical modelling of the data.

The electric field gradient at 19F in diamond

Abstract Time Differential Perturbed Angular Distribution (TDPAD) studies of fluorine isotopes implanted into diamond have revealed two distinct quadrupole interaction frequencies, 59 MHz and 23 MHz. These signals are consistent with cluster model molecular orbital calculations representing fluorine on substitutional and interstitial sites. At the substitutional site the electric field gradient is large but the fluorine ion experiences only a small deviation from tetrahedral symmetry resulting in the small TDPAD resonance. Conversely, at the interstitial site, where the electric field gradient is smaller, the distortion from tetrahedral symmetry is large and this gives the higher TDPAD frequency.

The lattice site of 10F implanted into diamond by TDPAD

Abstract Two distinct residence sites for 19F ions recoil-implanted into diamond have been identified, using the technique of time differential perturbed angular distributions (TDPAD) applied to the 197 keV state (t = 128 ns, Q = 0.10 b) of 19F. The electric field gradient parameters and their temperature dependence correlated well with the site assignments of recent cluster model calculations and strong host-impurity chemical effects are evident.

Temperature Dependence study of19F implants in diamond by TDPAD

We present results of Time Dependent Perturbed Angular Distribution (TDPAD) studies of the temperature dependence of the electric field gradient (efg) parameters for the two residence sites of the19F ion implanted in diamond. The fractional site population results correlate well with cluster model molecular orbital calculations and support the site identifications based on these calculations. The importance of chemical effects in the probe host interaction is emphasized. In addition, the dependence of the efg on temperature is consistent with the charge-carrier governed dependence observed in many semiconductors.

The transition from Mu to Mu* in diamond

Evidence is presented for a transition from the isotropic muonium state (Mu) to the [111] axially symmetric anomalous muonium state (Mu*) in diamond. Amplitude measurements for Mu* in a powder in zero field and with a single crystal oriented in a magnetic field indicate that such a transition occurs with a temperature-dependent rateΛ(T) and that the electron polarization is conserved during the transition. The possibility of determining the absolute sign of the Mu* hyperfine parameters is discussed.

Beam assisted molecular rearrangement observed by TDPAD for fluorine complexes in diamond

Abstract Time dependent perturbed angular distribution (TDPAD) measurements have consistently revealed two unique sites for recoil implanted 19F in different types of natural diamonds. These correspond to quadrupole coupling constants of 63(2) and 56(2) MHz. The first corresponds to the formation of a C-F bond at an intrabond site and the second is interpreted as a distorted substitutional site. A third resolved coupling constant of 33(3) MHz is associated with a broadly distributed site with random electric field gradient orientation which might be indicative of local amorphous conditions and is interpreted as arising from the formation of H-F molecular complexes. A strong dependence on the incident proton dose of this fraction has been observed for all types of natural diamonds. A model proposed for such an effect involves a beam-assisted mechanism which accounts for disruption of existing hydrogenic molecular complexes and rearrangement of ions under the influence of intense electronic excitation caused by the incident proton beam. Such results give new insights on 19F as a TDPAD probe. Its small size and chemical affinity render it particularly appropriate for studies of molecular complexes with TDPAD.

Temperature dependence of the electric field gradient parameters at 19F lattice sites in semiconducting and insulating diamonds

Abstract The electric field gradient parameters in insulating and semiconducting diamond, types IIa and IIb respectively, were measured as a function of temperature at residence sites of recoil implanted 19 F by using the time-dependent perturbed angular distribution nuclear solid state technique. An improved experimental arrangement enables three distinct residence sites to be resolved, where only two had been resolved before. These correspond to quadrupole coupling constants of 62(1), 56(2) and 31(3) MHz. A strong temperature dependence in the fractional population of the second site was observed and is different for each of the two types of diamond. These measurements provide additional evidence for the explanation of this temperature dependence, i.e. a charge transfer from the lattice to the 19 F occurs, which leads to the formation of the negative fluorine ion.