Shaped single crystal growth and scintillating application of Yb:(Gd,Lu)3(Ga,Al)5O12 solid solutions

Shaped single crystals of (Yb_0.05Lu_xGd_0.95−x)Ga₅O₁₂ (0.0x0.9) and Yb_0.15Gd_0.15Lu_2.7(Al_xGa_1−x)O₁₂ (0.0x1.0) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃(Ga,Al)₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect––host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.     

Growth reproducibility of the bubble properties of (YSmLuCa)3 (FeGe)5 O12 films

Reproducibility of CaGe garnet films grown by LPE is discussed in comparison with that of Ga garnet films. The influence of growth temperature deviation on the properties of CaGe garnet films is not compensated by the adjustment of the substrate rotation rate, although it is effective for Ga garnet film growth. On the other hand, the bubble collapse field of CaGe garnet films is less sensitive to the growth temperature than that of Ga garnet films. Therefore by determining the growth time accurately the bubble collapse field of as-grown films has been controlled within ±1%, even if the growth temperature deviates from the desired value by ±1°C.     

Growth and mobility measurements of (YLuCa)3(FeTiGe)5O12 films for magnetic bubble application

The liquid phase epitaxial growth conditions and properties of garnet films of nominal composition Y_1.8 Lu_0.2Ca_1.0Fe_4.0Ti_0.3Ge_0.7O₁₂ are described. Ca+Ge reduces the lattice parameter when substituted into yttrium-lutetium iron garnet. On the other hand, Ca+Ti increases it. Ca+Ti+Ge additions to the garnet make it easy to match the lattice parameter with the GGG substrate and to obtain stable bubbles. This material has low ferrimagnetic resonance damping loss and high mobility bubbles. The bubble mobility, estimated from the damping parameter and other static bubble properties, is 5626 cm/sec-Oe. This value approximately agrees with that measured by translational field gradient techniques. The bubble translation bias margin at 310 kHz and temperature coefficient of the static bubble properties are reported briefly.     

The effect of heat treatment on physical properties of nanograined (WO3)1-x-(Fe2O3)x thin films

Thin films of (WO₃)_1-x-(Fe₂O₃)_x composition were deposited by thermal evaporation on glass substrates and then all samples were annealed at 200-500 °C in air. Optical properties such as transmittance, reflectance, optical bangap energy, and the optical constants of the “as deposited” and the annealed films were studied using ultraviolet-visible spectrophotometry. It was shown that the annealing process changes the film optical properties which were related to Fe₂O₃ concentration. Moreover, using X-ray photoelectron spectroscopy, we have indicated that WO₃ is stoichiometric, while iron oxide was in both FeO and Fe₂O₃ compositions so that the FeO composition converted to Fe₂O₃ after the annealing process. Using atomic force microscopy, it was observed that surface of the “as deposited” films were smooth with a nanometric grain size. The film surface remained unchanged after annealing up to 300 °C. Surface roughness and the grain size of the films with x = 0, 0.05, and 0.75 highly increased at higher annealing temperatures (400 and 500 °C), but were nearly unchanged for medium x-values (0.3 and 0.4).     

Distribution coefficients in (YSmLuCa)3(FeGe)5O12 film growth

The composition of bubble garnet films has been analyzed by Inductively Coupled Plasma Emission Spectroscopy (ICP) to determine the distribution coefficients for different growth conditions. Under typical growth conditions, the distribution coefficients, k, of each element are as follows: k^Y = 2.15, k^Sm = 1.56, k^Lu = 1.32, k^Ca = 0.45, k^Fe = 0.98, k^Ge = 1.10. As the supercooling temperature (growth rate) increases, k^Ca, which is the smallest and deviates most from 1.0, changes in the direction approaching 1.0. For charge compensation, k^Ge also increases, consequently, k^Fe must decrease. Also k^Y, which is the largest, $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ change in the direction approaching 1.0. On the other hand, as the melt parameter R₁ (≡ $\text{Fe}{}_2\text{O}{}_3\text{Σ}\text{Ln}{}_2\text{O}{}_3$) increases, k^Fe decreases, and k^Y, k^Sm and k^Lu increase, whereas $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ remain constant at 0.73 and 0.61, respectively.     

The origin of the uniaxial anisotropy in thin films of (YLaPb)3 (FeGa)5O12 and its variation along the growth direction

The uniaxial anisotropy of La, Ga: YIG films grown by liquid phase epitaxy has been measured using spin-wave resonance techniques. The results show that in films produced at growth temperatures above 840°C on [111] Gd₃Ga₅O₁₂ substrates the uniaxial anisotropy is stress induced. At lower growth temperatures the Pb incorporation gives rise to a positive growth-induced anisotropy of 4×10⁴ erg/cm³ per Pb atom per formula unit. Around the growth temperature of 840°C, where the Pb and La effects cancel, homogeneous films can be grown. Variations of anisotropy within the filmsthickness will be shown to be due to variations of local growth rates which in turn cause composition changes.     

Control of properties during the growth of a large number of (Y,Sm)3(Ga,Fe)5O12 films from the same melt

For the growth of a large number of (Y, Sm)₃(Ga, Fe)₅O₁₂ films from the same melt, we describe the drift and methods to control the drift in film properties, so that the films are suitable for making magnetic bubble memory devices. The melt was based on PbO-B₂O₃ flux. The film thickness h and the characteristic length l were kept at around 5.4 μm and 0.54 μm respectively. The desired h was achieved by adjusting the growth time. The desired values for l were achieved by adjusting the growth temperature and by periodically adding small amounts of Ga₂O₃. The lattice constant was kept within the specified limits by periodic additions of Y₂O₃. Using these techniques we were able to grow more than a hundred films, out of which ～ 85% were acceptable for device fabrication. Based on the deduced values for the composition of our films, we have calculated the melt depletion resulting from the growth of a single film. We find that the experimentally determined additions of Ga₂O₃ and Y₂O₃ that gave us good control over film properties are almost equal to the calculated depletions for these two oxides.     

Growth of Ca3Fe2Ge3O12 and Ca3Fe(Al,Cr) Ge3O12 garnets in molten bismuth germanate glasses

Additions of Fe₂O₃ to CaO·Bi₂O₃·2 GeO₂ cause Ca₃Fe₂Ge₃O₁₂ garnets to precipitate from the resultant melt at 1250°C. Garnets with the composition Ca₃Fe(Al, Cr) Ge₃O₁₂ are also precipitated by adding either $\text{Al}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ or $\text{Cr}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ mixtures. The well-formed crystals range from several to 100 μm in size and are obtained in 50 to 70% yields at $\text{Fe}\text{Bi}\text{= 0.4}$. Additions of Fe₂O₃ (up to $\text{Fe}\text{Bi}\text{= 1.0}$) to compositions containing ZnO, CdO, SrO, and BaO yield only dark glasses. The physical properties of these glasses suggest that Fe(III), in contrast to AL(III) & Ga(III), prefers octahedral coordination.     

Stress-induced anisotropy in LPE grown Ni(Fe,Al)2O4 films

Preliminary results are reported about the growth of single crystal Ni(Fe,Al)₂O₄ films, grown by means of liquid phase epitaxy on (111)MgO and on (111)ZnGa₂O₄ substrates using a PbO-B₂O₃-Fe₂O₃ solvent. While films grown upon MgO show stress relief at the growth temperature, films grown upon ZnGa₂O₄ possess a tensile strain due to elastic deformation. Since λ₁₁₁ for NiFe₂O₄ is strongly negative a stress-induced uniaxial anisotropy is present in the films. Stripe domains can be observed with the Bitter technique and when a magnetic field is applied perpendicular to the plane of the film, magnetic bubbles with a diameter of ～2 μm appear. A bubble stability factor q exceeding unity is obtained. For the first time magnetic bubbles are found in LPE grown spinel ferrites.     

Gd3(Al,Ga)5O12:Ce闪烁晶体扭曲生长、组分偏析与性能研究

新型闪烁晶体Gd3(Al,Ga)5O12:Ce(简写为GAGG:Ce)在制备过程中易出现多晶扭曲生长、组分偏析等问题,严重影响晶体的性能.为了得到大尺寸高质量的GAGG:Ce晶体,采用X射线衍射(XRD)、电感耦合等离子体发射光谱(ICP-OES)和X射线激发发射谱(XEL)等手段,结合熔体特性分析了GAGG:Ce晶体...     

Magnetic and crystallographic properties of the mixed system (FeF3)1-x (KMnF3)x

The mixed system (FeF₃)_1-x (KMnF₃)_x with 0 ≤ x ≤ 1 has been prepared and investigated. The compounds with 0.19 ≤ x ≤ 0.22 are single phase hexagonal while the materials with 0.40 ≤ x ≤ 0.55 are single phase tetragonal. The powder samples are all light colored and at low temperatures become antiferromagnetic (with weak ferromagnetic moments.) The Néel temperatures are 111°K for the hexagonal compound with x = 0.20, and 160°K and 133°K for the tetragonal materials with x = 0.40 and 0.55, respectively. The reasons for the low ordering temperatures are examined using the generalized molecular field theory.     

Structural and optical analysis of nanocrystalline thin films of mixed rare earth oxides (Y1-xErx)2O3

Nanocrystalline thin films of mixed rare earth oxides (Y_1-xEr_x)₂O₃(0.1 ≤ x ≤ 1) were deposited by electron beam evaporation technique on polished fused silica glass at different substrate temperatures (200-500 °C). The effect of the substrate temperature as well as the mixing parameter (x) on the structural and optical properties of these films has been investigated by using X-ray diffraction (XRD), energy dispersive x-ray analysis and optical spectrophotometry. XRD investigation shows that mixed rare earth oxides film (Y_1-xEr_x)₂O₃ grown at lower substrate temperature (T_s ≤ 300 °C) are poorly crystalline, whereas films grown at higher substrate temperatures (T_s ≥ 400 °C) tend to have better crystallinity. Furthermore, the mixing parameter (x) was found to stabilize the cubic phase over the entire of 0.1 ≤ x ≤ 1. The crystallite size of the films was found to vary in the range from 25 to 39 nm. Optical band gap of the films was deterimined by analysis of the absoprtion coeffifcient. For films deposited at different substrate temperatures direct and indirect transitions occur with energies varied from 5.29 to 5.94 eV and from 4.23 to 4.51 eV, respectively. However, films of different composition x, give optical band gap varied from 6.14 to 5.86 eV for direct transition and from 5.23 to 4.22 eV for indirect transitions. Consequently, one may conclude that it is possible to tune the energy band gap by relative fraction of constituent oxides. It was found that optical constants increase with increasing the substrate temperature. Nevertheless, the values of n and k decrease with increasing the mixing parameter, x.     

Waveguiding properties of pulsed-laser deposition Ca4GdO(BO3)3 thin films

Waveguiding properties of stoichiometric Ca₄GdO(BO₃)₃ (GdCOB) thin films deposited on quartz substrates by the pulsed-laser deposition (PLD) technique are reported. The optical properties and the anisotropy of the obtained thin films are investigated using the prism-coupling technique. Refractive indices (n_x=1.666, n_y=1.673 and n_z=1.680 at 632.8 nm) were, respectively, determined from the transverse electric (TE) and the transverse magnetic (TM) mode excitations. These values are found to be 3% lower than those of the bulk material, which is likely due to the structural and morphological features of the deposited GdCOB films.     

Growth, thermal and optical properties of Yb:GdYAl3(BO3)4 crystal

Single crystal of Yb:GdYAl₃(BO₃)₄(Yb:GdYAB) has been grown by the flux method. The structure of Yb:GdYAB crystal has been determined by X-ray diffraction analysis. The experiment show that the crystal has the same structure as that of YAl₃(BO₃)₄ crystal and its unit cell constants have been measured to be a = 9.30146 Å, c = 7.24164 Å, Vol = 542.59 Å³. The absorption and fluorescence spectrum of Yb:GdYAl₃(BO₃)₄ crystal have also been measured at room temperature. In the absorption spectra, there are two absorption bands at 938 nm and 974 nm, respectively, which is suitable for InGaAs diode laser pumping. In the fluorescence spectra, there are two fluorescence peaks at 992 and 1040 nm. The thermal properties of Yb:GdYAl₃(BO₃)₄ crystal have been studied for the first time. The thermal expansion coefficient along c-axis is almost 5.4 times larger than that along a-axis. The specific heat of the crystal has been measured to be 0.77 J/g °C at room temperature. The calculated thermal conductivity is 5.26 Wm⁻¹ K⁻¹ along a-direction.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Texture and microstructure of Cr2O3 and (Cr,Al)2O3 thin films deposited by reactive inductively coupled plasma magnetron sputtering

Cr₂O₃ and (Cr,Al)₂O₃ films were grown using reactive dc and inductively coupled plasma magnetron sputtering at substrate temperatures of 300-450 °C. For pure chromia, α-Cr₂O₃ films with fiber texture were grown; the out-of-plane texture could be controlled from < 0001> to < 101?4>. The former texture was obtained as a consequence of competitive growth with no applied bias or inductively coupled plasma, while the latter was obtained at moderate bias (− 50 V), probably due to recrystallization driven by ion-bombardment-induced strain. By reactive codeposition of Cr and Al, a corundum-structured metastable solid solution α-(Cr,Al)₂O₃ with Cr/Al ratios of 2-10 was grown with a dense, fine-grained morphology. Hardness and reduced elastic modulus values were in the ranges 24-27 GPa and 190-230 GPa, respectively.     

Magnetic inhomogeneities in (YSmCa)3(GeFe)5O12 and their elimination by improved growth procedures

We have found that inhomogeneities in the growth direction are a very common occurrence in LPE films of (YSmCa)₃(GeFe)₅O₁₂. These inhomogeneities, which occur over a wide range of solution compositions and growth conditions, are not detected by the usual measurements of bubble parameters. However, they can be observed in the presence of an in-plane field using a technique which we describe. Experiments using this technique indicate that there is a thin (≤ 1 μm) layer at the film/substrate interface which has magnetic properties significantly different from the rest of the film. Special growth procedures which will avoid the formation of this “interface layer” are described in detail. Comparisons between films with and without this layer show, surprisingly, that there is no direct correlation between the coercivity and the presence of this layer. However, a correlation between coercivity and samarium concentration is observed when all other growth parameters are kept as constant as possible.     

Ferroelectric and dielectric properties of Bi4-xNdxTi3O12 thin films prepared by sol–gel method

Bi_4-xNd_xTi₃O₁₂ (BNT-x, x = 0, 0.25, 0.50, 0.75 and 1.0) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol–gel method. The microstructure, ferroelectric and dielectric properties of BNT-x thin films were investigated. The single-phase BNT-x thin films were obtained. With increasing Nd content, the preferred orientation changed from random to (117) and surface morphologies changed from the mixture of rod- and plate-like grains to rod-like grains. The Nd substitution improved the ferroelectric and dielectric properties of BTO films. BNT-x films showed better electrical properties at x = 0.50—1.0. BNT-0.75 film exhibited the best electrical properties with remanent polarization (2P _r) of 26.6 μC/cm², dielectric constant (ε _r) of 366 (at 1 MHz), dielectric loss (tanδ) of 0.034 (at 1 MHz), leakage current density (J) of ±3.0 × 10⁻⁶ A/cm² (at ± 5 V) and fatigue-free characteristics.     

Analysis of thin films arising from electron-, ion- and photon-beam-induced decomposition of Cr(CO)6 and Al(CH3)3

Thin films derived from ion and/or electron beam irradiation of condensed chromium hexacarbonyl (Cr(CO)₆) and trimethylaluminum (Al(CH₃)₃) and from laser-induced pyrolytic decomposition of Al(CH₃)₃ are analyzed using X-ray photoelectron spectroscopy. In all cases dissociation of the metal—carbon bonds may be achieved. Deposits of metallic aluminum overcoated with oxide were obtained from laser-induced pyrolysis, whereas oxides and carbides rather than metals usually result from the processing of the condensed molecular films by electron or ion beams. Modification to the sample composition as a function of electron, ion and photon beam dosage is discussed.     

Dielectric properties of sol-gel derived Ta2O5 thin films

The dielectric constant and the dielectric loss of tantalum pentoxide (Ta₂O₅) thin films, produced by sol-gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20-10⁵ Hz and the temperature range of 183-403 K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed.