119Sn Mössbauer study of the implantation behaviour of119In,119Sn,119mSn,119Sb and119mTe ions in SiC

The implantation behaviour of stable¹¹⁹Sn⁺ ions and radioactive¹¹⁹In⁺,^119mSn⁺,¹¹⁹Sb⁺ and^119mTe⁺ ions in SiC has been investigated by, respectively, conversion-electron Mössbauer spectroscopy on the 24 keV transition of¹¹⁹Sn, and by Mössbauer emission spectroscopy on the 24 keV radiation emitted by the¹¹⁹Sn daughter after the decays of the radioactive isotopes. The Mössbauer spectra could be decomposed in most cases into two groups of lines, one originating from¹¹⁹Sn atoms on substitutional Si sites, the other from various Sn-vacancy complexes distinguished by their Mössbauer parameters. Annealing experiments reveal a strong dependence of the structure of the defects and the formation and annealing kinetics on the chemical nature of the impurities. Defects formed in 297 K implantations with^119mSn and¹¹⁹Sb anneal above 500 C, resulting in a preferential location of the impurities on substitutional Si sites, whereas^119mTe atoms are efficient defect-trapping centres and no stable, substitutional fraction is observed on either lattice site. Possible structures for the Sn-vacancy complexes are discussed and comparison is made to similar defect complexes in group IV and in III–V semiconductors.     

Mössbauer studies of heterobimetallic and heterotrimetallic compounds containing iron and tin

A series of ferrocene derivatives was prepared and studied by⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy, as well as by other techniques such as NMR and IR spectroscopies. These complexes can be divided into three types: mercurated, organotin derivatives of ferrocene, and bi- and trimetallic derivatives of 1,1-bis(diphenylphosphino)ferrocene. Iron did not show great variation in its Mössbauer parameters in the compounds, in spite of their diversity; tin, however, gave important Mössbauer data for the elucidation of bonding and structural features of the complexes.     

Defect structures of ion-implanted α-tin

Single crystalline and polycrystalline -tin has been implanted at room temperature with 80-keV ions of radioactive^119m Sn,¹¹⁹Sb, and^119m Te. The radioactive nuclei decay to the Mössbauer level of¹¹⁹Sn. Mössbauer spectra of the emitted 24-keV radiation have been measured for different source temperatures by resonance counting techniques. Five individual lines in the spectra are characterized mainly by their isomer shifts and Debye temperatures. From these parameters the radiogenic¹¹⁹Sn atoms are concluded to be located in regular substitutional and interstitial lattice sites and in defect complexes. Simple models for the defects are proposed: A Sn-vacancy pair consists of Sn atoms on (nearly) substitutional sites with a dangling bond into an adjacent vacancy. In a complex oxygen-containing defect the Sn atoms have approximately a 5s ² configuration withp-bonds to two nearest neighbour atoms. Sn atoms, having an atomic 5s ² 5p ² configuration and large vibrational amplitudes, are concluded to be in non-bonding regular interstitial sites. For special implantation conditions minor fractions of SnO₂ molecules are formed in the bulk. The interstitial¹¹⁹Sn and the¹¹⁹Sn-vacancy pairs are proposed to represent elementary point defects in -tin. Conclusions are also drawn concerning the lattice location and the defects created in the implantation process of the implanted parent isotopes.     

57Fe and119Sn Mössbauer investigations on some substituted barium hexaferrites

⁵⁷Fe and¹¹⁹Sn Mössbauer measurements have been carried out on powder samples of three differently substituted M-type barium hexaferrites. By⁵⁷Fe Mössbauer measurements in an external magnetic field applied parallel to the -ray direction, we found a canted spin structure for all samples. Furthermore, we detected a strong preference of the Sn⁴⁺ ions for the 4f₂ sites. From⁵⁷Fe Mössbauer measurements aboveT _N, we conclude that the substitution does not influence the 2b sites. The analysis of the magnetically split¹¹⁹Sn Mössbauer spectra at room temperature in the case of the Co-Sn and Zn-Sn substituted samples shows a strong difference between the two. The spectra were interpreted due to the different surroundings of the Sn⁴⁺ ions.     

Tin-molybdenum organoheterobimetallics—a Mössbauer investigation

A series of cyclopentadienyl (cp) organoheterobimetallics involving tin and molybdenum were prepared and studied by several physical methods, of which¹⁹⁹Sn Mössbauer spectroscopy played a major role. The complexes were derived from [cpMo(CO)₃]^–, which reacted with different stannylated species giving the final products containing a direct Sn-Mo bond. Mössbauer spectroscopy was essential in the study of the constitution of the complexes, as well as in the determination of parameters such as the electronegativity of the [cpMo(CO)₃] moiety.¹H NMR spectroscopy showed the complexes to have only one kind of Sn in solution. The¹¹⁹Sn Mössbauer spectra surprisingly displayed two inequivalent Sn centers in the solid state, suggesting some degree of intermolecular association. The Mössbauer data for both Sn sites, however, led to the same calculated electronegativity for the [cpMo(CO)₃] group bonded to Sn.     

Evidence for Sb associated with multi-hydrogen in n-type silicon

The formation of Sb-H complexes in n-type Si after the induction of H by low-energy implantation has been investigated using¹¹⁹Sb ¹¹⁹Sn source Mössbauer spectroscopy. We have studied the different Mössbauer fractions as a function of H- and Sb-dose and as a function of H-implantation temperature. We can explain our results by assuming thermal equilibrium between Sb-H complexes and clustered H ₂ ^* pairs, attributing the visible hydrogen associated fraction to SbH and the invisible fraction to SbH₂ complexes. The results show that the binding energy of hydrogen in these three forms differ only by about 0.1 eV, being the highest for H ₂ ^* and the lowest for SbH.     

Strong oxygen trapping by Sb impurities in silver

¹¹⁹Sb atoms introduced into a silver matrix by means of ion implantation form Sb-O complexes when the samples are annealed in a residual air atmosphere of 10^–2–10^–3 Pa. Mössbauer spectroscopy on the daughter¹¹⁹Sn was used to study the Sn oxidation state and the dynamics and stability of the complexes formed.The authors are indebted to F. ten Broek, J.J. Smit and B. Stenekes for their help during various stages of the experiment. This work is part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM) and was made possible through financial support from the Nederlandse Organisatie voor Zuiver Wetenschappelijk Onderzoek (ZWO).     

Study of hexagonal R-type BaFe4Sn2O11 by57Fe and119Sn Mössbauer spectroscopy

Mössbauer data have been obtained from both the⁵⁷Fe and¹¹⁹Sn isotopes for BaFe₄Sn₂O₁₁. Variable temperature studies show that magnetic ordering occurs at 77K and is probably complete at 4K. Average hyperfine fields of 504kG and 45kG were observed at the iron and tin nuclei respectively.     

Mössbauer study of119Sn defects in silicon from ion implantations of radioactive119In

Radioactive¹¹⁹In⁺ ions (T _1/2=2.1 min) obtained from the ISOLDE facility at CERN have been implanted into silicon single crystals at room temperature. Mössbauer emission spectra from the 24 keV -radiation of the daughter¹¹⁹Sn have been measured by fast resonance-counting technique. Five independent lines, characterized by their hyperfine parameters and Debye temperatures, have been found in the spectra. From the bonding configurations, deduced for the Sn impurity atoms, these are concluded to be located in four different defects in the silicon lattice. Simple models are proposed for the defects.     

The problem of the Mössbauer isomer shift calibration for the119Sn resonance from rare-gas matrix isolation experiments

Data of new rare-gas matrix isolation experiments are presented and discussed in connection with the problem of the Mössbauer isomer shift calibration for¹¹⁹Sn. These experiments are: (i) A Mössbauer source experiment with^119mSn in solid xenon yielding the isomer shift of Sn⁺ with the atomic configuration 4d¹⁰5s²5p; (ii) Mössbauer absorption studies of isolated Sn(II) halide molecules (SnX₂, X-F, Cl, Br, I) in argon matrices; and (iii) Mössbauer absorption experiments with isolated¹²⁵Te atoms and molecules in argon and krypton matrices.This work was supported in part by a grant from the National Science Foundation and from the Bundesministerium für Forschung und Technologie     

The DX center and other tin-related defects in AlGaAs semiconductors

Al _x Ga_1-xAs semiconductors doped with both natural and enriched¹¹⁹Sn have been studied by Mössbauer spectroscopy (MS) to help to determine the atomic-scale nature of a deleterious, deep-level defect known as the DX center. Spectra have been acquired in the dark at 76 K and under sub-bandgap illumination at 4 or 10 K to distinguish the DX center from the substitutional shallow donor defect. Although electrical differences are clearly detected in these two states, no difference in the Mössbauer spectra are observed. Unexpected high Sn contents, determined by quantitative MS, demonstrate a large non-electrically active Sn fraction in some samples and this may be obscuring the observation of the DX center by both X-ray absorption spectroscopy and MS. Grinding the single-crystal layers into fine powders leads to an Sn defect that is attributed to a surface-oxidized site.     

Experimental study of the amorphous phases of group-IV semiconductors by the119mSn Mössbauer probe

The amorphous phases of silicon, germanium, and -tin have been studied by Mössbauer emission spectroscopy on ion-implanted, radioactive^119mSn. Amorphous samples have been produced by ion implantations of various elements and by vacuumevaporation techniques. The same well-defined type of complex spectrum is observed for all investigated amorphous samples. These spectra are characterized by an increase in average isomer shift of (0.15±0.03) mm/s, a line broadening of 20±2%, and the same Debye temperature as compared with spectra of substitutional Sn in the respective crystalline host lattices. The spectra are proposed to originate from Sn atoms incorporated substitutionally in the amorphous host with distorted local surroundings. The recrystallization of the amorphous phase upon thermal and laser annealing has been monitored. After appropriate annealing, spectra characteristic of crystalline materials are observed for most samples. An exception are high-dose, inert-gas implanted samples where different complex defects seem to be formed in the annealing process.     

Structure and Mössbauer effect studies of Y2Sn2-xFexO7-δ pyrochlores

Y₂Sn_2-x Fe _x O_7- pyrochlores were studied by means of X-ray diffraction,¹¹⁹Sn and⁵⁷Fe Mössbauer spectroscopy. The single phase Y₂Sn_2-x Fe_xO_7- Y pyrochlores up tox=0.8 were produced by the chemical coprecipitation method. The quadrupole splittings of¹¹⁹Sn decrease linearly with increasing iron content. The⁵⁷Fe Mössbauer spectra forx=0.6 and 0.8 both are composed of a sextet and two doublets, indicating that some Fe³⁺ ion environments in the pyrochlores are magnetically ordered. The magnetic hyperfine splitting disappears in the sample withx= 1.0, which contains a second phase.This work was partially supported by the National Natural Science Foundation of PR China.     

Defect annealing in Sb/Sn implanted diamond investigated with Sn Mössbauer spectroscopy

The annealing of defects in Sb/Sn implanted diamond has been studied in ¹¹⁹Sn Mössbauer spectroscopy following the implantation of radioactive parent isotopes ¹¹⁹Xe and ^119mSn. Our results show that after annealing above 1300 K, 40% of the implanted ions are located at or near regular sites in the lattice. Significant implantation induced defects however remain.     

Interpretation of the isomer shift of interstitially implanted119Sn impurities in group IV semiconductors

Recent Mössbauer measurements of the isomer shift of interstitially implanted¹¹⁹Sn impurities in group IV semiconductors are interpreted in terms of the electron contact density of compressed Sn atoms and ions, respectively. The finite space allowed to the impurity atom in the host crystal is approximated by a Wigner-Seitz sphere. Using a calibration procedure, the dependence of the isomer shift on the Wigner-Seitz radiusR _A has been calculated for several electron configurations of the tin atom (ion). The isomer shift values for¹¹⁹Sn interstitials in diamond, silicon, germanium, and -tin are found to correspond to compressed, neutral tin atoms; furthermore, the relaxation of the host lattice about the impurity Sn atom is discussed.     

Internal oxidation of sp-Impurities in silver studied by119Sn Mössbauer spectroscopy

The internal oxidation of the ion-implanted radioactive precursors¹¹⁹Cd and¹¹⁹Sb to the Mössbauer isotope¹¹⁹Sn in silver has been investigated. The oxidation is monitored by the intensity of a line in the Mössbauer spectra, which is characteristic of SnO₂ (δ=(0–0.23)mm/s relative to CaSnO₃, ΔEQ ≈ 0.5 mm/s, ? ≈ 220 K). This line is attributed to an internal oxidation of the implanted impurities by interstitially diffusing oxygen pairs. The formation and annealing kinetics of the impurity-oxygen complexes are interpreted in terms of the diffusion coefficients of oxygen and the sp-impurities in silver, respectively, and the reactivity between them. Comparison is made to Mössbauer experiments on SnAg alloys and to PAC measurements on¹¹¹cd in silver.     

Determination of the change of nuclear charge radius of the119Sn Mössbauer transition by internal conversion

Radioactive¹¹⁹Sb was implanted into six host matrices (CaSnO₃, Pt, Y, Au,-Sn, Pb) and internal conversion electrons of the 23.87 keV transition in¹¹⁹Sn were measured with an iron-free magnetic spectrometer as well as Mössbauer spectra. In the analysis of the conversion spectra of outermost electrons, the overlapping K-LM Auger lines were subtracted using the Auger spectrum of tin measured with another source of^117mSn, and the shake-off effect accompanying the conversion process was considered. From the correlation between the Mössbauer isomer shifts and the intensity ratios of O-shell to N₁-shell conversion electrons, the change of the nuclear charge radius of the 23.87 keV transition of¹¹⁹Sn was deduced to be R/R=(0.87 ± 0.25) × 10^–4 for a uniform charge distribution ofR= 1.2 ×A ^1/3 fm or, equivalently, r²>—=(3.6 ± 1.0) ×10^–3 fm².     

Mössbauer spectroscopy in the characterisation of new materials

The use of Mössbauer spectroscopy for the characterisation of new materials is illustrated here by examples of its application in the study of different types of solids. Firstly, the incorporation of large metal ions within the channels of the compound NbTiP₃O₁₂ which has a three-dimensional channel-type structure similar to that of the fast ion conductor called nasicon and the examination of the products by⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy and X-ray powder diffraction is discussed. Secondly, the investigation by¹¹⁹Sn Mössbauer spectroscopy and X-ray photoelectron spectroscopy of new conducting tin dioxide pillared clays synthesised by microwave heating is described. Finally, the examination by¹²⁵Te Mössbauer spectroscopy and X-ray powder diffraction of conducting selenium-tellurium alloys prepared by precipitation techniques is discussed.     

Formation of gold nanoparticles in gold ruby glass: The influence of tin

A ¹¹⁹Sn Mössbauer study was carried out of tin(IV) complexes with 2-benzoylpyridine thiosemicarbazone (H2Bz4DH) and its N(4)-methyl (H2Bz4M) and N(4)-phenyl (H2Bz4Ph) derivatives: [Sn(2Bz4DH)Cl₃] (1), [Sn(2Bz4DH)PhCl₂] (2), [Sn(2Bz4M)Cl₃] (3), [H₂2Bz4M]₂[Ph₂SnCl₄] (4), [Sn(2Bz4Ph)PhCl₂] (5), [Sn(2Bz4Ph)Ph₂Cl] (6), in which H2Bz4R stands for the neutral ligand and 2Bz4R stands for the anionic thiosemicarbazone. In addition, ¹¹⁹Sn Mössbauer studies of the tin(IV) complexes [Sn(H4Bz4DH)₂Cl₄H₂O] (7), [Sn(H4BzPS)₂Cl₄H₂O] (8) with 4-benzoylpyridine thiosemicarbazone (H4Bz4DH) and the correspondent semicarbazone (H4BzPS) were performed. The isomer shifts decrease upon coordination due to the variation in the percentage of s character as tin changes from approximately sp³ hybridization in the tin salts to sp³d² in the octahedral or sp³d³ in the heptahedral complexes. The Mössbauer parameters of compound (4) showed the existence of two tin(IV) sites, which have been attributed to the presence of the cis and trans isomers.     

119Sn Mössbauer Study of as-Deposited Layers Prepared by Co-evaporation of TeO2 and Sn

The deposited layers on glass surface with thickness between 230 and 500 nm were prepared by the chemical reactions of TeO₂ and Sn during vacuum co-deposition, and were characterized as a function of the Sn/Te ratio between 0.5 and 2.8 by ¹¹⁹Sn conversion electron Mössbauer spectroscopy. The as-deposited samples showed amorphous character with very finely dispersed microstructure. The ¹¹⁹Sn Mössbauer spectra of as-deposited samples revealed the dominance of Sn(II) and Sn(IV) states although SnTe was also found when the Sn/Te ratio was high. A monotonous increase of the Sn(II)/Sn(IV) ratio was observed with increasing Sn/Te ratio.