The energy dependence and depth distribution of lattice disorder in ion-implanted silicon

Silicon single crystals were implanted at room temperature with Xe and I ions in the energy range 20 to 150 keV and with 20 to 50 keV P ions. The lattice disorder induced by these implants was measured by a combination of the channeling and Rutherford backscattering techniques. The disorder produced by implanting I and Xe ions exhibited a similar relationship with implantation energy to that previously established for bismuth implants. The P ion implants induced less lattice disorder per incident ion in the energy range studied. Integral depth distributions of the implanted ions and of the lattice disorder were obtained by combining a layer removal technique with radiotracer implants of 110 keV ¹³³Xe and 40 keV ³²P. The depth distributions showed that in both cases the ions penetrate deeper into the crystal than the damage they produce but that the separation is significantly greater for the P implant than for the Xe implant.     

High pressure studies of optical properties and crystal lattice stabilit of ZnFeSe

Abstract

The presence of iron ions in the ZnSe crystal lattice influences strongly the optical absorption properties of this semiconductor. We observed three different mechanisms of the absorption: the intra-ion transitions, photoionisation transition, and interband transition. The first two mechanisms originate from the presence of iron ions in the crystal. The pressure coefficients of intra-ion transitions were determined. The pressure red shift of ionisation spectrum was attributed to the transition of an electron from the valence band to the iron level. The influence of iron on the critical pressure for the phase transition from zincblende to rocksalt structure was also established.     

Multi-range high-frequency EPR spectroscopy of LiYF<Subscript>4</Subscript> and LiLuF<Subscript>4</Subscript> crystals doped by rare-earth ions

EPR spectra of isostructural LiYF₄ and LiLuF₄ crystals doped by Dy³⁺, Er³⁺, and Ho³⁺ ions are measured at 4.2 K in the frequency range 40–800 GHz. The effects caused by isotopic disorder in the lithium sublattice, the random crystal field, and the interaction between paramagnetic impurity ions are detected and studied. The results of the measurements are used to determine the spectral characteristics of the compounds and the crystal field parameters. It is demonstrated that the formation of the isotope structure of the EPR signal is dominated by local deformations of the crystal lattice induced by mass defects.     

Optical constants of yttrium–iron garnet single-crystal film structures

Light-attenuation spectra of yttrium–iron garnet single-crystal film structures grown on a gallium–gadolinium garnet substrate by liquid-phase epitaxy from the undercooled solution in the melt have been studied and compared with those of bulk yttrium–iron garnet samples. The calculated optical constants are discussed taking into account the influence of crystal field on the splitting of the energy states of iron ions in the film samples. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 218–224, March–April, 2009.     

Impurity effect on the Raman spectra of Sr0.6Ba0.4Nb2O6

Impurity effect on the rare earth ion doped Sr_0.6Ba_0.4Nb₂O₆(SBN40) was studied at room temperature. Doping the rare earth ions of Pr³⁺ or Nd³⁺ changed the Raman profile: spectral broadening, central frequency shifts and relative intensity decreasing. Two reasons are considered according to the ferroelectric and optical properties of the rare earth ion doped SBN40: impurity-induced crystal disorder and the crystal structure change. SBN40 is the general disorder crystal and the disorder which is enhanced by doping the rare earth ion is especially strong along the x?y plane of the material compared with that along the polar C-axis.     

Iron-related luminescence centers in ZnWO 4 :Fe

A systematic spectroscopic study of single ZnWO 4 :Fe crystals with different iron concentrations has been performed under excitation by ultraviolet light, by synchrotron radiation or under photostimulation by near-infrared light. The luminescence of Fe 3+ -related centres has been studied. It is shown that iron centres of different types efficiently promote the formation of crystal defects at low temperatures. Electrons and holes can be trapped near Fe 2+ or Fe 3+ ions, which is further revealed in phosphorescence, thermostimulated or photostimulated luminescence. At room temperature the main effect of iron impurity is to reduce the light yield of a ZnWO 4 scintillator.     

Structural deformations of the cubic lattice of the Zn1 ? x Fe x Se (x = 0.001) crystal

The structural state of a Zn_{1 ? x} Fe _x Se (x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.     

Ferromagnetic ordering of iron impurities in the valence-fluctuating semiconductor SmB6

The electron paramagnetic resonance (EPR) of the valence-fluctuating semiconductor SmB₆ doped by 1 at % Fe is studied. The EPR measurements are performed on a SmB₆ single crystal in a temperature range of 1.6–300.0 K. A number of resonance lines whose g factors indicate the presence of iron ions in the Fe⁰, Fe⁺, Fe²⁺, and Fe³⁺ states have been detected. The iron ions are ferromagnetically ordered below a Curie temperature T = 100 K, and this ordering can be caused by the exchange interaction of impurity ions due to matrix polarization (a similar mechanism is observed in PdFe alloys). This exchange interaction is estimated to be significantly higher than that in PdFe; this fact can result from a very high density of states in the narrow f band, which is characteristic of a valence-fluctuating material.     

Local states of iron ions in perovskite Bi0.815Y0.085La0.10FeO3

Bi_0.815Y_0.085La_0.10FeO₃ perovskite is studied by ⁵⁷Fe Mössbauer spectroscopy at 87, 295, and 670 K. The measured temperature of the magnetic phase transition (the Néel temperature) is T _N = 666 ± 5 K. It is found that substituting Y³⁺ ions for 0.085 at % Bi³⁺ in the Bi_0.9La_0.1FeO₃ perovskite destroys the spatially spin-modulated structure while the rhombohedral crystal structure is retained. Two structurally nonequivalent states of iron ions are found above the Neel temperature. Below the Neel temperature, there are four magnetically nonequivalent states of trivalent iron ions.     

Crystallization of mullite from kaolin according to optical spectroscopy of impurity ions

The luminescence spectra of Cr³⁺ and Eu³⁺ ions embedded in mullite ceramic samples are studied. The samples were annealed at temperatures from 600 to 1200°С. Beginning at a temperature of 890°С, the spectra demonstrated the presence of a newly formed crystal phase. At temperatures from 920 to 1200°С, the crystalline form manifested itself as a stable mullite phase. A temperature of 920°С corresponded to a sharp change in the symmetry of the crystal field around Eu³⁺ (phase transition). The parameters of the spectral lines of ions were used to estimate the mullite crystal-lattice disorder and the residual deformations in ceramic samples. The spread of the mullite crystal-lattice parameter is determined as |Δа/а| ≈ 0.028 and is independent of the annealing temperature.     

Structure dependence of magnetic properties in yttrium iron garnet by metal-organic decomposition method

The yttrium iron garnet(YIG) samples are prepared at different temperatures from 900?C to 1300?C by the metalorganic decomposition(MOD) method. The chemical composition and crystal structure of the samples are studied by scanning electron microscope(SEM), XRD, and M ¨ossbauer spectrometer. It is shown that the ratio of ferric ions on two types of sites, the octahedral and the tetrahedral, is increased with the sintering temperature. At 1300?C, the pure garnet phase has been obtained, in which the ferric ions ratio is 2:3 leading to the minimum magnetic coercivity and maximum saturation magnetization. These results provide a route to synthesize pure YIG materials as the basic materials used in various spintronics applications.     

Temperature dependence of linewidths in the Raman spectrum of pyrargyrite (Ag3SbS3)

The linewidths of bands in the Raman spectrum of pyrargyrite (Ag₃SbS₃) have been examined as a function of temperature. A band at 190 cm^-1 arising from stretching of Ag-S bonds has been studied in detail and is shown to broaden with increasing temperature much faster than other bands in the spectrum. The connection between this enhanced broadening and the possible disordering of the Ag ions is discussed. The linewidth behaviour is shown to be similar to the corresponding results for the isomorphous crystal proustite (Ag₃AsS₃) and it is concluded that the disorder or motion of the Ag ions that is responsible for the broadening is unrelated to the phase transitions that occur in proustite.     

Valence states of iron ions in nanostructured yttrium iron garnet Y3Fe5O12 studied by means of soft X-ray absorption spectroscopy

Nanostructured samples of yttrium iron garnet Y₃Fe₅O₁₂ obtained by plastic deformation method (high-pressure torsion) were studied with help of soft X-ray absorption spectroscopy using Fe 2p and O 1s spectra. Experimental spectra were compared with crystal field multiplet calculations for Fe ions. Some amount of Fe²⁺ ions in nanostructured Y₃Fe₅O₁₂ was found. The concentration of Fe²⁺ ions was found to be increased with the increase of the degree of plastic deformation.     

Spatial topology of local nano scale inhomogeneity of crystal structure Zn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> = 0.001)

The method of thermal neutron diffraction is used to study a structural state of crystal Zn_{1 − x} Fe _x Se (x = 0.001) obtained in the sphalerite modification. It was found that the diffractive pictures of a cubic crystal contain the regions of diffuse scattering in the vicinity of Bragg reflections of an initial crystal lattice. It was shown that the diffuse scattering effects were caused by the local transverse displacements of atoms in a crystal lattice induced by Fe²⁺ ions. It is concluded that a static tetragonal-type Jahn-Teller effect exists in a ZnSe alloy doped by magnetoactive iron ions.     

Oxygen and gold ion irradiation effects on hydroxyethylammonium (l) tartrate monohydrate single crystals

Hydroxyethylammonium (l) tartrate monohydrate (HEALT) single crystals were grown by slow evaporation solution growth method and irradiated at room temperature with 100 MeV oxygen and 200 MeV gold ions. The powder X-ray diffraction study shows that the title crystal has undergone lattice disorder after irradiation. UV–Visible study reveals that there is a decrease in band gap values on irradiation. The scanning electron and atomic force micrograph discloses the defects which was formed due to irradiation. The unirradiated as well as irradiated crystals were characterized by photoluminescence. Further dielectric and Vickers microhardness measurements were studied for oxygen and gold ions irradiated crystals and compared with pristine HEALT single crystals.     

CEMS measurements at low temperatures with Fe-Implanted sapphire

A single crystal of sapphire was implanted with 100-keV⁵⁷Fe to a dose of 3.4×10¹⁵ ions/cm². The charge states of iron ions were investigated with the CEMS technique at low temperatures. The formation of the observed charge states Fe²⁺(1) and Fe²⁺(2) were elucidated in terms of crystal structure.     

The influence of iron,fluorine and boron implantation on the magnetic properties of graphite

Iron, fluorine and boron ions were implanted into highly oriented pyrolytic graphite (HOPG). The samples were characterized before and after ion implantation as well as after heat treatments in vacuum by measurements of the magnetic moment and element analysis. Whereas the main magnetic contribution remains diamagnetic the paramagnetic one clearly increases with implantations and correlates with the amount of implanted ions. It is shown that a large part of the paramagnetic contribution is caused by the structural disorder created by particle bombardment using iron, fluorine or boron. All implanted HOPG samples show practically no change of the small ferromagnetic signal observed in their virgin state. No particular influence of iron on the ferromagnetic properties of HOPG is observed, up to ∼4000 μg/g Fe-concentration in the implanted region. For comparison, ferrous sulphates were added to ultra-clean graphite powder. This iron addition increases the number of paramagnetic spins proportional to the iron content in the untreated samples. In heat-treated samples however, a clear ferromagnetic behaviour is observed due to the formation of a ferromagnetic iron compound.     

The spectrum of the photoinduced change in the absorption coefficient of doped Y3Fe5O12 single crystals

For yttrium iron garnet single crystals with different types of majority impurities, the spectra of the photoinduced change in the absorption coefficient α are studied experimentally in the spectral range 0.7–1.9 μm. It is shown that the features of these spectra depend on both the impurity type in the crystal and the spectrum of the illuminating radiation. The experimental results can be explained in terms of the change in the Fe²⁺(Fe⁴⁺) absorption and the changed intensity of optical transitions in the Fe³⁺ ions in the vicinity of charged defects.     

Mössbauer spectroscopic studies of [Fe(H2O)6]3+ in amorphous frozen solutions at weak applied magnetic fields

The ferric hexaquo complex, [Fe(H₂O)₆]³⁺, has been studied by Mössbauer spectroscopy of amorphous aqueous frozen solutions at weak applied magnetic fields. Spectra of well resolved paramagnetic hyperfine structure have been interpreted in terms of a spin Hamiltonian model for the crystal field interaction proposed in a previous work. Reasonable fits could be obtained only by the addition of a random magnetic field of a few Gauss which is attributed partly to the dipolar interaction with neighbouring iron ions, and partly to the ligand hyperfine interaction.     

Effect of coimplantation of iron and chromium ions on the optical properties of aluminum oxide

The optical absorption of leucosapphire and polycrystalline corundum (polycor) upon coimplantation of iron and chromium ions and subsequent annealing in vacuum is studied. The structure of the states localized in the band gap induced by radiation defects exhibits a higher stability to annealing as compared to implantation of other types of ions into aluminum oxide and to separate irradiation with iron and chromium ions. The governing contribution to the exponential and interband absorption is made by substitutional defects of either type, their clusters, and impurity-vacancy complexes. The effect of incorporated iron ions on the population of levels of chromium-containing defect clusters, on their recharge, and on interaction with intrinsic radiation and biographical defects is revealed. Mixed clusters of substitutional defects are optically active in a spectral range of 2.0–4.0 eV after annealing at a temperature of 1300–1600 K.