Quadrupole Split Components Research Articles

Mössbauer study of Fe in 3C-SiC following 57Mn implantation

Mossbauer measurements have been performed on a GaAs single crystal sample following the implantation of radioactive 57Mn + (\(T_{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} = 1.5\) min) ions. The Mn + ions were implanted with 60 keV energy into a GaAs sample held at temperatures of 300–700 K in an implantation chamber. Implantation fluences were <2 × 1012 ions/cm2 which assured single ion implantations. Mossbauer spectra were measured with a resonance detector equipped with 57Fe enriched stainless steel foils mounted on a conventional drive system outside the implantation chamber. The spectra at the lower temperatures are dominated by an asymmetrically broadened quadrupole split doublet (FeD), assigned to Fe in implantation induced damaged surroundings; at higher temperatures a single line dominates, due to Fe at undisturbed substitutional sites (FeS). The spectra also required small contributions (approx. 13–5%) of a quadrupole split component, FeX, which may be due to interstitial Fe and Fe in vacancy complexes. A prominent annealing stage is evident in the temperature range 300–550 K, leading to substantial increase in the FeS fraction, and attributed to mobile Ga vacancies.

197Au Mössbauer study of gold particles obtained by evaporation of metallic gold on Mylar

Gold particles embedded in a Mylar matrix were studied by 197Au Mössbauer spectroscopy. The cores of the particles have metallic properties for particles ⩾1.5 nm. For particle sizes less than 6 nm, additional quadrupole split components attributed to surface atoms appear in the Mössbauer spectra. These components become dominant for the smallest particles.

Hyperfine interaction study of the decoration of the internal wall of nanosized voids by impurity probes

We observe the trapping of implanted radioactive 57Co atoms at empty nano-cavities formed in {111} Si by the desorption of He from bubbles. The absorption of 14.4 keV γ-rays roughly monitors the displacement of the activity, while anodic stripping and counting the remaining 122 keV γ-ray intensity is employed to obtain an accurate depth profile and to isolate the wanted fraction of the sample. Mössbauer spectroscopy shows that only damage and/or CoSi 2-nuclei related sites are present in samples implanted at 300 and 400°C. In a sample implanted with Co at RT at the same side as the cavity-generating He atoms, the Mössbauer spectra reveal two new quadrupole split components after 30 min annealing at 700°C. We present arguments for the tentative identification of these to a cavity edge site (79%, strong bonding) and to a cavity plane site (21%, weak bonding).

A Mossbauer study on solid krypton precipitates in aluminium

Mossbauer spectroscopy on the 9.40 keV transition 83Kr is used to obtain information about solid Kr precipitates in Al. Three different 83RbI sources differing in water content were used, which, when measured against a solid Kr absorber, show a quadrupole component in addition to a dominating single line. An analytical deconvolution technique is presented which takes care of the source characteristics. The spectra of Kr bubbles in Al obtained by high-dose implantation show two components: a single line from Kr atoms inside the bubble and a quadrupole split component from Kr at the Kr-Al interface. Spectra were taken as a function of temperature. The total absorption area could be fitted very well assuming a simple Debye model, yielding a Debye temperature of Theta DT=101(2) K. A decomposition of the total area in the areas of quadrupole and single-line components yields Debye temperatures of Theta DQ=98(6) K and Theta DS=90(10) K respectively.

59Co NMR from Magnetic Domains in Y2Co14B and Gd2Co14B

NMR measurements have been made for Y 2 Co 14 B and Gd 2 Co 14 B by the steady-state and spin-echo methods in zero external field as a function of temperature. By the steady-state method, the 59 Co domain signals with quadrupole splittings which originate from six non-equivalent Co sites have been observed together with wall signals for the two compounds. It is found that the spin echo peaks generally correspond to wall signals but not to domain signals in these compounds. The hyperfine field at Co nuclei in domains and the spacing between the quadrupole-split component lines for the domain signals are derived. The effect of substitution of Gd for Y on the Co hyperfine field and the magnetic exchange interaction between Co magnetic moments in the compounds is discussed.

A Mössbauer Study on Solid Krypton Precipitates in Aluminium and Silicon

ABSTRACTMössbauer spectroscopy on the 9.4 keV transition in 83Kr is used to study inert gases in metals and semiconductors. An absorber was made by implanting 83Kr at 110 keV in Al foils to a total dose of 1.7· 1016 Kr cm−2, leading to the formation of small precipitates (bubbles). Spectra on the as-implanted sample were taken as a function of temperature for three 83RbI sources which differ in line shape due to a different water content. A model is presented to extract the absorber parameters from the spectra in a consistent way, in spite of the different sources used. The spectra of Kr bubbles in Al produced by high dose implantation show two components: a single line from Kr inside the bubble and a quadrupole split component from Kr at the Kr-Al interface. The total absorption area could be fitted very well assuming a simple Debye model, yielding a Debye temperature of ΘDT = 101(2) K. For the individual components we obtained Debye temperatures of ΘDQ = 98(6) K and ΘDS = 90(10) K. The isomer shift of the bulk fraction is significantly larger than that of a solid Kr layer at ambient pressure, reflecting the fact that the s-density increases under compression. The size of the precipitates can be estimated to be 1.5–1.8 nm. Thin KrSi films, produced by Kr plasma sputter deposition, were characterized using cross-sectional X-ray analysis. The results clearly show two different layers. Presumably, the film grows at first as c-Si with a low Kr concentration, but after having reached a certain critical thickness, further growth proceeds as a-Si with a high Kr concentration. For Mössbauer spectroscopy an absorber of 83KrSi was made by plasma deposition on an Al foil. The spectra can be fitted with a single line and a quadrupole component, both with isomer shifts much larger than found in the case of small Kr bubbles in Al. No change in the total absorbed area was observed from 4.2 to 200 K indicating a lower limit of 250 k for the Debye temperature. Both observations indicate that the Kr resides in very small clusters.

NMR and Specific Heat of YCo12B6and LaCo12B6

NMR measurements were made for YCo 12 B 6 and LaCo 12 B 6 mainly by the steady-state method in zero external field as a function of temperature. Two 59 Co domain signals with quadrupole splittings and two wall signals with single lines were observed. With decreasing temperature, a low-frequency domain signal in LaCo 12 B 6 vanished below about 25 K but another domain signal emerged below about 40 K, revealing a discontinuous change in frequency and in spacing between the quadrupole-split components. The specific heat of LaCo 12 B 6 did not show any anomaly in this temperature range. These suggest that the observed change in NMR in LaCo 12 B 6 around 35 K is not of first order but is presumably associated with a change in magnetic states. In YCo 12 B 6 there was no such a discontinuous change in the NMR spectrum.

Mössbauer spectroscopy study of iodine and tellurium atoms in solid argon

Mössbauer effect studies were performed on the nucleogenic 125Te and 129I monomers formed by the decay of their respective parents 125mTe and 129mTe embedded in solid argon at 4.2 K. Rare-gasmatrix-isolation (RGMI) and ion implantation techniques were combined to produce those extremely diluted Mössbauer emitters. The 125Te spectrum is composed of a quadrupole split component with splitting e 2qQ 2 = 9.2(4) mm s and isomer shift IS = + 0.35(5) mm s , and a single line component with IS = +0.15(5) mm s with respect to a ZnTe absorber. They are attributed to Te 0 and Te −1 species, respectively. The 129I spectrum is composed of a single quadrupole split component with e 2qQ = −685(20) MHz and IS = +0.75(4) mm s with respect to a ZnTe source. This species is attributed to I 0. Two novel single-line absorbers with high f values at RT were developed for the Te and I experiments, e.g. Mg 3TeO 6 and Na 5IO 6. Based on our results for Te 0 and Te −1 and on relativistic Dirac-Slater atomic calculations, a new IS calibration curve under the form of a nonlinear relationship of IS versus the number of p holes ( h p ) in the closed shell configuration of 5 s 25 p 6 is established for 125Te. The IS data of the I 0 monomer are used to refine the IS( h p) relationship for 129I. From these new calibration curves values are deduced for the change in mean-squared charge radius Δ〈 r 2〉 = 3.4(3) 10 −3 fm 2 for 125Te and Δ〈r 2〉 = 19.9(7) 10 −3 fm 2 for 129I, respectively. The origin of the quadrupole interaction and the experimental features of this RGMI-implantation-Mössbauer emission spectroscopy are fully discussed.

The effect of nuclear spin on the polarisation ratio of resonance fluorescence

The nuclear quadrupole interaction causes the rotational angular momentum of a molecule with nuclear spin to precess about the total angular momentum whose projection along a space fixed axis is conserved. This effects the degree of orientation in the excited state of molecules optically pumped with circularly polarised light and reduces the polarisation ratio of fluorescence from molecules with large nuclear spin. Calculations are presented for the circular polarisation ratio of the forward scattered fluorescence when the exciting radiation is sufficiently broad-banded that it excites the full manifold of quadrupole split components of a given J″ → J′ transition. Results are also presented for the variation of the polarisation ratio and intensity as a narrow excitation source is tuned across the absorption.