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1.
The possible presence of a large magnetic field due to spin polarization of a Cd nucleus (decay product of 111In) at an Al substitutional site in AlN is investigated with perturbed angular correlation (PAC) spectroscopy. The PAC spectra of 111In/111Cd in AlN show two probe environments: a weak quadrupole interaction (quadrupole interaction constant, $\nu _{\rm Q}^{\,\,\,\rm lattice} = 30$ MHz) due to 111In probes at a defect free Al substitutional site and an unknown large interaction ( $\nu _{\rm Q}^{\,\,\,\rm complex} = 300$ MHz) tentatively attributed to a nearest neighbour pair between 111In and a nitrogen vacancy (VN) aligned along the c-axis. Surprisingly, in density functional theory (DFT) calculations, such a large electric field gradient (EFG) could not be reproduced. However, an inclusion of spin polarization in the calculations indicates a strong magnetic field at ~50 % of the 111In/111Cd site. An attempt to verify the presence of the strong magnetic field and to explain the origin of the strong interaction is made. Orientation measurements show, the large interaction is not characterised by a magnetic interaction and is predominantly due to the EFG. However, in the presence of an external magnetic field, the strong interaction probe environment becomes more uniform and the EFG increases by ~10 %. This definitely hints towards some sort of magnetic interaction at the strong interaction probe site. 相似文献
2.
Burchard A. Deicher M. Fedoseyev V.N. Forkel-Wirth D. Magerle R. Mishin V.I. Steiner D. Stötzler A. Weissenborn R. Wichert Th. the ISOLDE-Collaboration 《Hyperfine Interactions》1999,120(1-8):389-395
The interaction between substitutional and interstitial donors and single or double acceptors in Si, GaAs, InP, and InAs has
been studied by perturbed angular correlation spectroscopy (PAC). For the case of Si, complex formation between substitutional
donors (As, P) and different radioactive acceptors (111In, 111Cd, 117Cd) has been observed. The formation of Cd–hydrogen pairs using either 111Cd or 117Cd is discussed for GaAs, InP, and InAs.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
A. W. Carbonari A. L. Lapolli R. N. Saxena J. Mestnik-Filho 《Hyperfine Interactions》2007,176(1-3):101-106
Perturbed gamma–gamma angular correlation (PAC) technique was used to measure the magnetic hyperfine field (mhf) in RNiIn (R = Gd, Dy, Tb, Ho) intermetallic compounds using the 111In→111Cd and 140La→140Ce probe nuclei. The PAC spectra for 111Cd measured above magnetic transition temperature show a major fraction with a well defined quadrupole interaction for all compounds except GdNiIn where a single frequency was observed. PAC measurements below T C showed a combined electric quadrupole plus magnetic dipole interaction for 111Cd probe at In sites, and a pure magnetic interaction for 140Ce at R sites. The temperature dependence of mhf measured with 140Ce at R sites shows that the values of fields drop to zero at temperatures around the expected T C for each compound. However, in the measurements with 111Cd at In sites, the mhf values become zero at temperatures which are smaller than T C . The difference between the temperatures at which mhf is zero for 140Ce and 111Cd probes correlates with T C . For each compound this difference decreases with T C . The results are discussed in terms of the RKKY model for magnetic interactions and the existence of two magnetic systems, with distinct exchange interaction energies due to different types of atomic layers in these compounds. 相似文献
4.
Ki‐Ha Hong Injun Hwang Hyuk Soon Choi Jaejoon Oh Jaikwang Shin U‐In Chung Jongseob Kim 《固体物理学:研究快报》2010,4(11):332-334
We investigate the role of fluorine (F) in GaN‐based high electron mobility transistors (HEMTs) with first principle calculations. Formation energy calculations of F in GaN and AlN reveal that energetically favored interstitial F (Fi) and substitutional F at N sites (FN) could play important roles in the performance of HEMTs. Fi is responsible for positive threshold voltage (Vth) shift by forming F– anion and depleting 2DEG carriers. The degradation of device performance at high temperature is ascribed to the defect energy state near conduction band edge of FN. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
A. L. Lapolli A. W. Carbonari J. Mestnik-Filho D. M. T. Leite R. N. Saxena 《Hyperfine Interactions》2007,176(1-3):75-79
Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the hyperfine interactions in the intermetallic compound GdPdIn using 111In→ 111Cd and 140La→ 140Ce probe nuclei at the In and Gd sites, respectively. The PAC results for 111Cd show two well-defined electric quadrupole frequencies above T C assigned to probes occupying Gd and In sites, with ~50% of site occupation each. The fraction corresponding to In sites increases with temperature reaching 95% around 500 K. Below T C the measurements for 111Cd probe showed combined electric quadrupole plus magnetic dipole interaction with sharp increase in the magnetic field below around 80 K. A pure magnetic interaction with lower hyperfine field values was observed at the Gd sites occupied by 140Ce below 100 K. 相似文献
6.
Ga2O3 is a promising material for use in “solar-blind” UV-detectors which can be produced efficiently by oxidation of GaN. In this study we focus on the evolution of the oxide layer when GaN is heated in air. The experimental method applied is the perturbed angular correlation (PAC) spectroscopy of γ-rays emitted by radioactive nuclides, here 111Cd and 181Ta, whose parent nuclei are ion implanted into films of GaN grown on sapphire. As the emission pattern for nuclei in GaN is clearly distinct from that of nuclei in Ga2O3, the fraction of probe nuclei in the oxide layer can be directly measured and allows to follow the time dependent growth of the oxide on a scale of less than 100 nm. Additional measurements were carried out with the oxidized sample held at fixed temperatures in the temperature range from 19 K to 973 K showing transitions between the hyperfine interactions of 111Cd in the oxide matrix both at high and low temperatures. A model for these transitions is proposed. 相似文献
7.
Dietrich M. Degering D. Kortus J. Unterricker S. Deicher M. Burchard A. Magerle R. the ISOLDE-collaboration 《Hyperfine Interactions》1999,120(1-8):359-364
Ternary semiconductors of type □AIIB
2
III
C
4
VI
with an ordered array of vacancies were investigated by PAC. Thereby the six probes 111Cd, 117Cd(117In), 111In(111Cd), 111Ag(111Cd), 77Br(77Se) and 77Kr(77Br) were applied. The positions of the different probes are determined and the corresponding electric field gradients by the
WIEN 95 code calculated. By 111Ag(111Cd)-probes the vacancies could be substituted. The electronic charge density distributions are discussed. At elevated temperatures
the substances show order–disorder transitions. As compared to the X-ray diffraction patterns the beginning of disorder is
observed by PAC at distinctly lower temperatures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
The time-differential perturbed angular correlation for 111Cd nuclei has been measured after 111In implantation into polycrystalline TiO2. The observed perturbation functions are characterized by a well-defined electric field gradient with the quadrupole coupling constant νQ = 105(1) MHz and the asymmetry parameter η = 0.18(1). We attribute these hyperfine parameters to 111Cd on the (distorted) substitutional cation site in rutile. The PAC results are compared with those in SnO2 rutile as well as with X-ray diffraction, RBS channeling experiments and point charge model calculations including relaxation of the probe atom surrounding. 相似文献
9.
F. Raether D. Wiarda K. P. Lieb J. Chevallier G. Weyer 《Zeitschrift für Physik B Condensed Matter》1989,73(4):467-478
The magnetic-dipole and electric-quadrupole hyperfine interactions of111Cd probes in fcc cobalt after implantation of radioactive111In+ ions have been investigated by PAC measurements with fast BaF2 detectors. Six different sites of the probe atoms could be distinguished and characterized by their hyperfine parameters and annealing behaviour. Besides the substitutional site, three sites are assigned to In-vacancy complexes which are formed athermally in the implantation process or by thermally-activated trapping of lattice defects in annealing stage III. The remaining two sites are attributed to In located in stacking faults or hcp regions of the host. Systematic trends of impurity hyperfine fields in defect sites become evident from a comparison with other impurity-host combinations. The temperature dependence of the magnetic hyperfine fields has been measured between 20 K and 390 K. Large differences found for the various sites are discussed. 相似文献
10.
Unterricker S. Samokhvalov V. Burlakov I. Degering D. Dietrich M. Deicher M. the ISOLDE Collaboration 《Hyperfine Interactions》2001,136(3-8):275-280
The ferromagnetic spinels CdCr2Se4 and CuCr2Se4 were investigated by PAC (perturbed angular correlations) after implantation of the probes 111In(111Cd), 111mCd, 111Ag(111Cd) and 77Br(77Se). The site occupation of different probes was determined by magnetic and electric hyperfine interactions. Theoretical calculations
of hyperfine parameters by the WIEN97 code gave satisfactory efg (electric field gradients) but the magnetic hyperfine fields
are inconsistent with the experiments.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
11.
12.
The perturbed angular correlation method (PAC) was applied to investigate the lattice location of implanted 111In probe ions in Hf2Ni and Zr2Ni intermetallic compounds. It is concluded that the 111In/111Cd probe nuclei experiencing the highly asymmetric electric field gradient (EFG) occupy the unique hafnium or zirconium 8(h) sites in the investigated phases. Above room temperature, the EFGs decrease linearly with temperature. The results are compared
with that of previous PAC measurements with 181Ta probes. 相似文献
13.
The electric and (antiferro-)magnetic hyperfine interaction of111Cd in α-Cr2O3 after111In implantation was studied via PAC. Two fractions with axially symmetric electric field gradients were observed having antishielding
factors of Vzz/Vzz
pc=79(12) and 106(16), respectively. From the line broadening of the Fourier components of the first fraction its supertransferred
magnetic field was estimated as Bloc (20 K)≤0.41 T, about two orders of magnitude smaller than for substitutional111Cd in NiO and CoO. 相似文献
14.
The hyperfine interaction (HFI) of 111Cd in different indium‐halides was studied by perturbed angular correlation (PAC). The 111Cd ion arises from a 111In by electron capture decay (EC) and joined Auger cascade. Coulomb fragmentation of the indium‐halide molecule produces the
free excited 111Cd ion. The nucleus decays via a γ–γ‐cascade which is perturbed by the HFI. Collisions of the 111Cd ion with indium‐halide molecules can strongly change the perturbation. The perturbation was measured by the attenuation
coefficient G22(∞) and G22(t). The molecular densities varied between 1014 and 1020 cm−3. The present article shows the temperature dependence of the indium(III)‐halides and a fit for an empirical basic approach.
The investigation of the InBr shows the independence of the attenuation coefficient from the temperature by indium(I)‐halides
in contrast to the dependence of the indium(III)‐halides.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Juliana Marques Ramos Thiago Martucci Artur Wilson Carbonari Messias de Souza Costa Rajendra Narain Saxena Reiner Vianden 《Hyperfine Interactions》2013,221(1-3):129-136
Electric quadrupole interactions were studied in pure and Mn-doped powder samples and thin films of SnO2 using perturbed γγ angular correlation spectroscopy (PAC). The powder samples were prepared by Sol gel method and the thin film were prepared on the Si (100) substrate by sputtering technique using Sn in the oxygen atmosphere. The samples were characterized by x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The thickness of the film was 100 nm. The average particle size of the SnO2 powder samples was determined to be smaller than 60 nm. The radioactive 111In and 181Hf tracers were introduced in the powder samples during the sol gel chemical process. Radioactive 111In was implanted on the SnO2 thin films using the University of Bonn ion implanter (BONIS). PAC measurements were carried out in a four BaF2 detector spectrometer in the temperature range of 77–973 K for samples annealed at different temperatures. The PAC results for both nuclear probes show the presence of two electric quadrupole interactions. The major fractions in both cases correspond to the substitutional sites in the rutile phase of SnO2. The results are compared with previous PAC measurements. 相似文献
16.
Renilson A. da Silva R. N. Saxena A. W. Carbonari G. A. Cabrera-Pasca 《Hyperfine Interactions》2010,197(1-3):53-58
Perturbed angular correlation (PAC) measurements have been carried out in the antiferromagnetic GdCrO3 perovskite oxide using 111In (111Cd) and 181Hf(181Ta) nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced in the compound through a chemical process during sample preparation. The PAC measurements were carried out in the temperature range 20–300 K. Measurements with the 181Ta indicated a unique quadrupole interaction above 170 K and a combined electric quadrupole and magnetic dipole interactions below this temperature. The observed interaction was assigned to the probe nuclei substituting Cr sites. Measurements with 111Cd showed two quadrupole interactions. Only one of the fractions however, showed a combined electric and magnetic interaction in the temperature rage 20–170 K which was assigned to 111Cd probe substituting Cr site. The other fraction was attributed to the Gd site. The present results are compared with those of LaCrO3 and NdCrO3. 相似文献
17.
Perturbed angular correlation (PAC) measurements using the In-111 probe were carried out on FeGa3 as part of a broader investigation of indium site occupation and cadmium diffusion in intermetallic compounds. One PAC signal was observed with hyperfine parameters ω 1= 513.8(1) Mrad/s and η= 0.939(2) at room temperature. By comparison with quadrupole frequencies observed in PAC measurements on isostructural RuIn3, it was determined that indium occupies only the 8j site in the FeGa3 structure, denoted Ga(2) below because two out of the three Ga sites have this point symmetry. PAC spectra at elevated temperature exhibited damping characteristic of electric field gradients (EFGs) that fluctuate as Cd probes jump among Ga(2) sites within the lifetime of the excited PAC level. A stochastic model for the EFG fluctuations based on four conceivable, single-step jump-pathways connecting one Ga(2) site to neighboring Ga(2) sites was developed and used to fit PAC spectra. The four pathways lead to two observable EFG reorientation rates, and these reorientation rates were found to be strongly dependent on EFG orientation. Calculations using density functional theory were used to reduce the number of unknowns in the model with respect to EFG orientation. This made it possible to determine with reasonable precision the total jump rate of Cd among Ga(2) sites that correspond to a change in mirror plane orientation of site-symmetry. This total jump rate was found to be thermally activated with an activation enthalpy of 1.8 ±0.1 eV. 相似文献
18.
Genene Tessema Mola 《Applied Physics A: Materials Science & Processing》2013,112(4):835-838
The temperature dependent nuclear hyperfine interaction of 111Cd-carbon complex in germanium has been studied using the perturbed γ–γ angular correlation (PAC) method. The parameters of the hyperfine interaction representing substitutional carbon–cadmium complex in germanium (ν Q1=207(1) MHz (η=0.16)) shows dependence on temperature. The formation and thermal stability of the complex has been reported by the same author earlier. It was found in this study that the quadrupole coupling constant of the interaction increases at sample temperature below 293 K. The results are encouraging toward better understanding of the complex in the host matrix. 相似文献
19.
GaN layers and Al1−xInxN/AlN/GaN heterostructures have been studied by scanning probe microscopy methods. Threading dislocations (TDs), originating from the GaN (0 0 0 1) layer grown on sapphire, have been investigated. Using Current-Atomic Force Microscopy (C-AFM) TDs have been found to be highly conductive in both GaN and AlInN, while using semi-contact AFM (phase-imaging mode) indium segregation has been traced at TDs in AlInN/AlN/GaN heterostructures. It has been assessed that In segregation is responsible for high conductivity at dislocations in the examined heterostructures. 相似文献
20.
The hyperfine interaction of111Cd probes in preoxidized and α-irradiated Ag0.94Cd0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were
distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen
and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature
and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of111Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very
similar to the ones observed after α-irradiation. 相似文献