Properties of Eu-Yb-Y magnetic garnet films grown by liquid phase epitaxy

Epitaxial films of Eu_yYb_zY_3?y?zFe_5?xGa_xO₁₂ have been deposited from PbO-B₂O₃ solution on (111) Gd₃Ga₅O₁₂ substrates. Saturation magnetization, characteristic length, coercivity, anisotropy and domain wall mobility are discussed in relation to film composition. The films exhibit reasonable mobilities, satisfactory quality factors and good temperature stability. The system appears to be a promising candidate for bubble device application.     

The transient layer in magnetic garnet films grown by liquid phase epitaxy

A thin (～ 0.1 μm) layer is formed initially during the so-called “transient” period preceding the establishment of the steady state diffusion boundary layer in the melt, when films are dipped in a horizontal plane while undergoing axial rotation. Further evidence is given for the existence of the transient as a separate and distinct growth mode as compared to steady state growth. The transient layer, which grows comparatively rapidly, nevertheless has properties virtually identical to those of the subsequently grown steady state layer, except for its higher Pb concentration.     

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.     

Yb:CaF2 grown by liquid phase epitaxy

Ytterbium doped CaF₂ crystalline layers have been grown for the first time from high temperature solutions at controlled atmosphere by using the liquid phase epitaxy technique. Doped layers having thicknesses between a few microns to a hundred of microns have been grown onto non-oriented and (1 1 1) oriented CaF₂ substrates. The Yb³⁺:CaF₂ layers show structural properties very close to the undoped substrate without any further thermal treatment. Registration of room temperature emission spectra and fluorescence lifetime measurements performed with epitaxial layers corresponding to different ytterbium concentrations show similar spectroscopic properties as in the bulk crystals.     

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.     

An optical investigation of transient layers in magnetic garnet films grown by liquid phase epitaxy

The growth of garnet films using Liquid Phase Epitaxy has led not only to materials with improved performance for bubble domain memories but to materials which exhibit improved microwave properties as well. We have investigated the optical properties of such films and found that there exist transient layers at the substrate/film interface and at the film/air interface. Our results and conclusions regarding the substrate/film interface do not agree with those of Davies et al⁽¹⁾. The discovery of a post growth lead rich layer has not been previously reported to our knowledge and has important implications for both bubble domain and optical applications of garnet films.     

Rib waveguides based on Zn-substituted LiNbO3 films grown by liquid phase epitaxy

The fabrication of epitaxially grown Zn-substituted LiNbO₃ (Zn:LiNbO₃) waveguide films and rib waveguides is reported and detailed investigations about microstructure, morphology and optical waveguide properties are provided. Zn:LiNbO₃ films were grown on congruent X-cut LiNbO₃ substrates by a modified liquid phase epitaxy in solid–liquid coexisting solutions. The homogeneously Zn-substituted films exhibit high crystalline perfection and extremely flat surfaces with averaged surface roughness of rms = 0.2–0.3 nm. At the film/substrate interface a Zn-containing transient layer has been observed, which allows the growth of elastically strained Zn:LiNbO₃ film lattices. X-ray diffraction reciprocal-space measurements prove the pseudomorphic film growth. The refractive index difference between substrate and film depends on the zinc substitution content, which increase with rising growth temperatures. For films with 5.3 mol% Zn (Δn_o ≈ +5 × 10⁻³) only ordinary ray propagation was observed, while for films with 7.5 mol% Zn (Δn_o ≈ +8 × 10⁻³, Δn_e ≈ +5 × 10⁻³) both modes, TM and TE propagate. Stress-induced refractive index changes are in the order of Δn ≈ 10⁻⁴. In rib waveguide microstructures singlemode propagation with nearly symmetrical field distribution has been observed. To demonstrate the potential of the proton exchange-assisted dry-etching technique interferometer microstructures were fabricated.     

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.     

Nd optical multisites in the Ca3(Nb,Ga)2Ga3O12 laser garnet crystal

Laser excited site-selective luminescence of Nd³⁺ ion in the Ca₃(Nb,Ga)₂Ga₃O₁₂ garnet crystal has been investigated for the and transitions. Six main non-equivalent crystal field sites were detected in the garnet. The crystal splitting scheme of the and manifolds was obtained for each Nd³⁺ site. Energy transfer between Nd³⁺ sites was observed by using time resolved spectroscopy.     

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.     

Characterization of ultra-thin TiO2 films grown on Mo(112)

Ultra-thin TiO₂ films were grown on a Mo(112) substrate by stepwise vapor depositing of Ti onto the sample surface followed by oxidation at 850 K. X-ray photoelectron spectroscopy showed that the Ti 2p peak position shifts from lower to higher binding energy with an increase in the Ti coverage from sub- to multilayer. The Ti 2p peak of a TiO₂ film with more than a monolayer coverage can be resolved into two peaks, one at 458.1 eV corresponding to the first layer, where Ti atoms bind to the substrate Mo atoms through Ti-O-Mo linkages, and a second feature at 458.8 eV corresponding to multilayer TiO₂ where the Ti atoms are connected via Ti-O-Ti linkages. Based on these assignments, the single Ti 2p_3/2 peak at 455.75 eV observed for the Mo(112)-(8 × 2)-TiO_x monolayer film can be assigned to Ti³⁺, consistent with our previous results obtained with high-resolution electron energy loss spectroscopy.     

The magnetic properties of Fe(OH)2

Ferrous hydroxide free from oxidation was prepared by precipitation from an aqueous solution in an inert gas atmosphere and measured for magnetic susceptibility and magnetization. The antiferromagnetic transition was observed at 34 K, where the susceptibility showed a sharp maximum. The magnetization at 4.2 K increased as the external field increased, and reached 3.6 $\text{μ}{}_{\mathrm{B}}$ per ion at 75 KOe, which is about 90 % of the saturation magnetization of Fe⁺⁺ ion. By analyzing the magnetization curve and the Mössbauer effect, the magnetic structure in an ordered state was deduced as follows: the moments within the layer are arrayed parallel, while those between the adjacent layers antiparallel. The spin easy axis lies in the c-plane. The quadrupole splitting was 3.00 mm/sec at 90 K and showed little temperature dependence between 4.2 K and room temperature. The energy state of Fe⁺⁺ ion in Fe(OH)₂ was specified by the orbital singlet 5A_1g derived from the sign and the magnitude of $\text{1}\text{2}\text{e}{}^2\text{qQ}$. The difference in the magnetic property between Fe(OH)₂ and FeCl₂ was discussed from the energy state of Fe⁺⁺ ion.     

Crystal Structure of (H3O)6[(UO2)5(SeO4)8(H2O)5](H2O)5

Crystals of (H₃O)₆[(UO₂)₅(SeO₄)₈(H₂O)₅](H₂O)₅ were prepared from aqueous solutions by evaporation. The crystal structure [monoclinic system, space group P2₁/m, a = 13.835(2), b = 13.4374(16), c = 14.310(3) Å, β = 108.004(14)°, V = 2530.1(7) Å ³] was solved by the direct method and refined to R ₁ = 0.090 for 4409 reflections with |F _hkl ≥ 4σ|F _hkl |. The structure is based on [(UO₂)₅(SeO₄)₈(H₂O)₅]⁶⁻ layers arranged parallel to the (101) plane; these layers have a unique topological structure. The U(1)O₆(H₂O) and U(3)O₆(H₂O) linked through selenate groups form chains running along [ [`1]\bar 1 01] direction. The chains are combined in layers by U(2)O₆(H₂O) bipyramids. The layers are linked with each other by hydrogen bonds through the H₂O and H₃O⁺ groups located between the layers.     

Orthorhombic phase formation in electrochemically grown vanadium oxide (V2O5) nanofibers

The inner structure of V₂O₅ nanofibers synthesized by electrochemical deposition has been investigated by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The experimental results demonstrate that the fibers are formed by 2D orthorhombic layers of V₂O₅. The layers are formed along the plane ab stacked in the crystallographic direction c. Additionally the diffraction results indicate that the fibers grow preferentially along the (100) crystallographic plane with surface dominated by the plane (001). The formation of fibers is discussed in terms of the preferential growth along specific orientations in order to minimize the surface energy of the nanostructures.     

Observation of phase separation in (Ge2)x(GaAs)1−x alloys grown by molecular beam epitaxy

(Ge₂)_x(GaAs)_1?x alloys with 0 < x < 1 have been grown by molecular beam epitaxy on various Ge and GaAs substrates. The structure of these alloys has been studied using transmission electron microscopy. We observe that in all cases studied, Ge tends to phase-separate from GaAs, with the Ge domain size ranging from 100 to 300 Å.     

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.     

Single-crystalline Si grown on single-crystalline Gd2O3 by modified solid-phase epitaxy

We investigate molecular beam epitaxial overgrowth of Si template layers produced by different approaches on single-crystalline oxide grown on Si(111). Three approaches based on modified solid-phase epitaxy were found to be suitable for the subsequent Si epitaxial overgrowth. The crystalline quality and interface properties of single-crystalline silicon on single-crystalline oxide grown on Si(111) make the obtained structures suitable for silicon-on-insulator applications. First measurements of electrical properties of p-type samples indicate good electrical properties of the top Si layer. Supplemental investigations demonstrate that Si layers with thickness in the range of 10 nm remain stable during thermal annealing up to 900 °C in an ultra-high vacuum.     

Growth and magnetooptical properties of thin garnets films in the system (Pr Gd Yb)3-xBix(Fe Al)5O12

Growth from liquid phase epitaxy and magnetooptical properties of single crystal garnet films in (Pr Gd Yb)_3-xBi_x(Fe Al)₅O₁₂ system are reported. The dependences of the distribution coefficient and the Bi content of the films on the growth temperature are analyzed. The influence of the growth condition on the magnetic and magneto-optical properties of the materials are described and discussed in order to obtain in planemagnetization films having large Faraday rotation (> 1 800 degr./cm) and figure of merit (50 – 80 degr./dB) suitable for integrated magnetooptics application.     

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.