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1.
PAC experiments using181Hf as probe atom were performed in Ta samples containing 1.1 at% of N and loaded with 0.2 at% of H or of 1.6 at% of D. At
room temperature only the known frequency due to N is present. Below 100K or 140K, for H and D respectively, the amplitude
of this interaction decreases and two new interaction frequencies characterized by V0=240MHz, η=0.80 and V0=250 MHz, η=0.40 appear. These frequencies are attributed to H(D) trapped by N in the vicinity of the probe atom181Hf. The disappearance of these interactions at 100K and 140K is interpreted as a release of H (D) from Hf but not from N.
From the data the jump rates of H(D) around N in Ta are derived. 相似文献
2.
When bombarding preoxidized silver with α-particles111In-oxygen-vacancy complexes are formed. PAC measurements on the most stable complex 6 (νq=161 (2) MHz, η=1, δ/νq=6(1) %) were performed to determine the structure of this highly asymmetric complex. On the basis of PAC experiments on Ag
single crystals and the variation of the oxygen concentration and the measuring temperature a structure model of this complex
6 is proposed. 相似文献
3.
P. Wodniecki B. Wodniecka M. Marszalek Z. Mazgaj B. Kubica 《Hyperfine Interactions》1990,60(1-4):841-844
The PAC method was applied to study the intermetallic compound formation at Ag−In interfaces. The electrodeposited Ag−In layers
of different Ag: In atomic ratios were prepared and isochronal annealing program was performed. For the comparison the bulk
Ag75In25 and Ag66In34 specimens were examined. The Ag2In and AgIn2 compounds were detected and the quadrupole hyperfine interaction parameters for111In in Ag2In were measured as υQ107.9(3) MHz and η=0.48 (2). 相似文献
4.
M. S. Moreno J. Desimoni F. G. Requejo M. Rentería A. G. Bibiloni K. Freitag 《Hyperfine Interactions》1991,62(4):353-358
In connection with a general study of the evolution of tin-oxygen thin films, we report here on the hyperfine interactions
of181Ta substitutionally replacting tin in the isolated phases SnO and SnO2. For this purpose, pure SnO pressed powder and a thin SnO2 film were implanted with181Hf. In both cases, unique quadrupole frequencies were found after thermal annealing treatments. The results indicate that
the following hyperfine parameters: υ
Q
= 740.6(2.1) MHz, η=0.07(2) and υ
Q
= 971.5(1.9) MHz, η=0.72(1) characterize181Ta in SnO and SnO2, respectively. 相似文献
5.
The defect formation in the bcc metals W and Mo above annealing stage III and the influence of rare gases on this process
were investigated by means of the perturbed angular correlation technique using111In as radioactive probe. In both metals a relatively high electric field gradient (EFG) could be observed at the indium site,
characterized by the quadrupole interaction frequencies υQ=263 MHz, ν=0 and υQ=220 MHz, ν≈0.15 for W and Mo, respectively. The observations are assigned to the growth of threedimensional vacancy clusters
at the probe atoms with the indium atoms situated in the inner surface of this cavities, thus experiencing the corresponding
surface EFG. 相似文献
6.
The PAC probe44Sc was employed to study the magnitude and temperature dependence of the electric quadrupole interaction at the site of the
transition metal Sc in the hexagonal host lattices Zr and Hf. In Zr ∼ 100% of the probe atoms were situated on regular lattice
sites and a quadrupole interaction frequency of υQ=7.8(1)MHz was measured at room temperature. For Hf the fraction of the probe atoms on regular lattice sites was smaller and
a damping of the interaction pattern (υQ=9.3(5)MHz at 293 K) could not be excluded. The temperature dependence of the electric field gradient in both host lattices
was found to be weak. 相似文献
7.
The perturbed angular correlation technique (PAC) was used to study the creation and development of He-induced cavities. In
order to investigate the interaction of Indium atoms with cavities in Silicon the Bonn isotope separator was used to implant
overlapping profiles of He (10 keV) and radioactive 111In (160 keV) into undoped FZ-silicon. To get insight into the cavity formation mechanism samples were prepared with various
He-doses (0.6, 2 and 6× 1016 ions/cm2). The samples were measured directly after implantation and after different annealing steps (thold= 10 min, T = 500–1100oC). Further, different implantation and annealing sequences were used. At higher He doses (2 and 6×
1016 ions/cm2) we find a large fraction of 111In probe atoms subjected to an electric field gradient (EFG) corresponding to a quadrupole interaction frequency (QIF) of
νQ= 411(6) MHz with η= 0.25(4). The corresponding defect configuration is formed most effectively after He implantation into
annealed, 111In doped Si. This and the affinity of In to vacancies leads us to the assumption that, similarly to the situation in metals,
the Indium atoms act as nucleation centres for vacancy clusters (cavities) and are situated on the inner walls of the cavities.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
The interaction of a In-monovacancy complex in niobium with hydrogen was studied with the PAC-technique between 24 K and 293
K. At 293 K no significant influence of hydrogen on the monovacancy-induced electric field gradient at the In-site was observed.
However at a sample temperature ≤ 135 K a new interaction frequency υQ3=122(1) MHz, η=O, appears in the spectra, which is assumed to be due to the trapping of hydrogen in a well defined location
on the axis between probe nucleus and the monovacancy. 相似文献
9.
A. A. Sorokin G. K. Ryasny B. A. Komissarova L. N. Fomicheva A. V. Tsvyashchenko S. M. Nikitin 《Hyperfine Interactions》2006,171(1-3):269-275
The perturbed angular correlation (PAC) measurements with the 111In-111Cd nuclear probe embedded into the lattice of the cubic (C15) Laves compound ZrZn2 showed that 111Cd nuclei experienced an axially symmetric electric quadrupole interaction with a frequency ν
Q
= 132.4 MHz at room temperature. The samples were synthesized and doped with the probe at a pressure 8 GPa. The temperature
dependence of ν
Q
was shown to be linear: ν
Q
(T) = 147(1 − 0.033 T) MHz. Since the value of ν
Q
is very close to that known for 111Cd in the lattice of Zn, we have checked if it could be assigned to residual Zn metal in the sample. For the Zn sample melted
and doped with 111In at 8 GPa we have obtained ν
Q
= 117.3 MHz at 300 K and 127 MHz at 80 K – both values considerably lower than that for 111In doped Zn samples prepared at an ambient pressure. These data, and the fact that ν
Q
(T) in Zn is known to follow the T
3/2 law, allow to attribute the ν
Q
value quoted above to 111Cd nuclei at the substitutional sites with tetrahedral symmetry in the Zn sublattice of ZrZn2. 相似文献
10.
11.
Akselrod Z. Z. Filossofov D. V. Kochetov O. I. Korolev N. A. Lebedev N. A. Milanov M. Novgorodov A. F. Shirani E. N. Timkin V. V. Velichkov A. I. 《Hyperfine Interactions》2001,136(3-8):705-710
111Cd–PAC measurements have been made using the high specific activity of 111In in the methanol–water mixtures of various concentrations at the room temperature. These experiments revealed that the perturbation
factors 〈A
2
G
2〉 (integrated over two mean lives τN) do not follow the dependence of the macroscopic viscosity η. The observed dynamic character of the PAC spectra in ice is
explained by the mobility of orientational and ionic defects. The activation energy for the diffusion process was determined
to be E
a
=0.35(1) eV.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
12.
Fajardo M. Pérez Alcázar G. A. Moreira A. M. Speziali N. L. 《Hyperfine Interactions》2004,158(1-4):395-400
The local environment of implanted 111Ag (t
1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following
the 60 keV low dose (1 × 1013 cm−2) 111Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps,
at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free SZn sites (ν
Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive
lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore
measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30%
of the 111Ag atoms, 7% of which were located in regions of high defects concentration. 相似文献
13.
In ZrW2O8, a material with negative thermal expansion, two nuclear quadrupole interactions at 187W(β-) 187Re with equal populations were determined by time differential perturbed angular correlation to be (at 295 K): ν_{\mathrm{Q}
1} = 336(1) MHz, η1 = 0 and νQ2 = 1391(2) MHz, η2 = 0.053(4). The nuclear quadrupole interactions are assigned to two crystallographically distinct tungsten sites. These results
are the bases for further TDPAC studies of the negative thermal expansion on a microscopic scale.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
The technique of perturbed angular correlations of gamma rays (PAC) is applied for the first time to study the structure of small metal clusters. Metal clusters containing111In probe atoms with 50 nm radii were synthesized by dissolving InCl3 containing111In in hexane using a surfactant, thereby creating an inverse micellar solution. The salt was then reduced to metal form by addition of NaBH4. 100% conversion efficiency of In salt to metal clusters was achieved. PAC measurements at 293 K on the111Cd daughter nuclide exhibited a nuclear quadrupole interaction with coupling frequency 0=16.0(5) Mrad/s and a small asymmetry parameter, =0.20(4). The frequency is as observed for bulk In crystals, but a non-zero value of has not been previously reported. Lack of inhomogeneous signal broadening and the faceted shape of some nanoclusters suggest high crystal perfection. 相似文献
15.
H. Metzner R. Sielemann S. Klaumünzer R. Butt W. Semmler 《Zeitschrift für Physik B Condensed Matter》1985,61(3):267-281
Radiation-induced lattice defects in high-purity niobium have been investigated in the temperature range of 30K to 540 K by means of - perturbed angular correlation (PAC) measurements using the radioactive probes100Pd/100Rh and111In/111Cd. Both probes were produced within the niobium samples by means of heavy-ion nuclear reactions. At the Pd impurities trapping of defects occurred during heavy-ion irradiation at about 30 K in two defined configurations: defect 1(Pd) withv
Q1=e
2
qQ/h=42(±2) MHz, 1=0 and defect 2 (Pd) withv
Q2=(±2) MHz, 2=1. Two defects were observed at the In impurities in annealing stage III (around 250 K) after heavy-ion as well as electron irradiations: defect 1(In) withv
Q1=87(±1) MHz, 1=0 and defect 2(In) withv
Q2=105(±2) MHz, 2=0.65(±0.02). A third defect (defect 3(In):v
Q3=177(±2) MHz, 30.2) appeared above 260 K after heavy-ion irradiation only. The data are interpreted in terms of interstitial trapping at the Pd impurities and vacancy trapping at the In impurities. Information on the microscopic structure of defect 1(In) and 2(In) is obtained from a PAC-single-crystal experiment. For defect 1(In) axial 111-symmetry is found, which leads us to identify this defect with a monovacancy as nearest neighbor with respect to the In probe. Defect 2(In) is the trapped divacancy for which an orientation is found that is consistent with both vacancies being nearest neighbor to the probe but second nearest neighbors to each other. 相似文献
16.
We report a comparison of electric-field gradients (EFGs) measured at the group-III sites on epitaxially-grown surfaces of
2×2-reconstructed GaAs and InAs crystals. For this purpose, we used 111In→111Cd perturbed-angular-correlation (PAC) spectroscopy. Sharp spectral lines characterize the perturbation functions corresponding
to both surfaces. On GaAs surface, we observe only one well-defined nuclear electric-quadrupole interaction (NQI); and on
the InAs surface, we observe a primary and a secondary NQI. Very similar but experimentally-distinguishable values of the
EFG-parameters characterize the primary interactions corresponding to the GaAs and InAs surfaces. Specifically, for the GaAs
and InAs surfaces, ω
Q
=28.0±0.2 Mrad s−1 and η=0.43±0.02 and ω
Q
=28.8±0.2 Mrad s−1 and η=0.39±0.02, and the angles between EFG z-axis and the (111) direction are 65°±3° and β=53°±3°, respectively. These unexpected results indicate that the so-called
lattice contribution to the EFG is not significant. Moreover, for the primary NQIs on both surfaces, the similar parameter
values demonstrate that chemical differences between the 111In probe and the indigenous Ga surface atoms cause no large quantitative effects. This information indicates that impurity
probes and PAC spectroscopy can be used effectively to investigate III–V surfaces.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
17.
Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of181Ta in Hf-doped YBa2Cu3O7−x
are presented. The181Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies
are observed in the as-irradiated sample:v
Q1=161±10 MHz with intensityf
1=75%, asymmetry parameterη
1=0.32 and damping parameter Λ1=0.42, andv
Q2=1108±40 MHz withf
2=25%,η
2=0.62, and Λ2=0.60. On annealing the sample in air at various temperaturesT
a and quenching to room temperature,f
1 remained nearly constant forT
a<600°C andv
Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted
to be due to181Hf substitutingY sites. BeyondT
a=600°C,f
1 increased and reached a constant value of 90% forT
a=800°C. The value ofv
Q2 showed a slight variation between 1086 and 1160 MHz, whilef
2 remained nearly constant at 25% forT
a<600°C. This component is identified to be due to181Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv
Q2 decreased and reached a value of 808 MHz beyond 750°C. 相似文献
18.
Using 111In–111Cd perturbed angular correlations, we investigated the behaviour of In in heavily As-doped polycrystalline silicon. The nuclear
In tracers were either introduced by means of grain boundary (GB) diffusion or ion implantation. We find, that the in-diffused
In tracers exclusively probe GBs which give rise to a broad distribution of static quadrupole frequencies. The implanted tracers
exclusively probe Si bulk material, where they encounter As-dopants during thermal annealing and form the well-known In–As
complexes #1 and #2, and the previously unknown complex #4 (eQVzz=117 MHz, η=0) which involves three As atoms on nearest neighbor sites with respect to the probe. The implications of the
present experiment on acceptor doping and GB probing are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Using perturbed angular correlations of γ rays the behaviour of Frenkel defects in n-type germanium is studied.111In/111Cd probes either serve as primary knock-on atoms in the production of Frenkel defects by neutrino recoil or as trapping agents
for defects produced by electron irradiation. The neutrino recoil process leads to a defect which is characterized by vQ=e2qQ/h=42(2) MHz (η=0.6), while a defect with vQ=423(1) MHz (η=0) is observed after electron irradiation and thermal annealing. 相似文献
20.
The temperature dependence of the hyperfine field of substitutional111Cd in antiferromagnetic CoO has been measured by means of the perturbed angular correlation technique. The Larmor frequency
ωL is found to obey a power law ωL(t=ω0
t
β) up tot
max=0.4 wheret=1−T/T
N is the reduced temperature withT
N=291.2(3) K and β=0.393 (5) the critical exponent. The results are discussed and compared with PAC experiments on111Cd in NiO and Ni and with results obtained by other methods. 相似文献