Showing papers in "Physica Status Solidi B-basic Solid State Physics in 2004"

Bound exciton and donor–acceptor pair recombinations in ZnO

Abstract: The optical properties of excitonic recombinations in bulk, n-type ZnO are investigated by photoluminescence (PL) and spatially resolved cathodoluminescence (CL) measurements. At liquid helium temperature in undoped crystals the neutral donor bound excitons dominate in the PL spectrum. Two electron satellite transitions (TES) of the donor bound excitons allow to determine the donor binding energies ranging from 46 to 73 meV. These results are in line with the temperature dependent Hall effect measurements. In the as-grown crystals a shallow donor with an activation energy of 30 meV controls the conductivity. Annealing annihilates this shallow donor which has a bound exciton recombination at 3.3628 eV. Correlated by magnetic resonance experiments we attribute this particular donor to hydrogen. The Al, Ga and In donor bound exciton recombinations are identified based on doping and diffusion experiments and using secondary ion mass spectroscopy. We give a special focus on the recombination around 3.333 eV, i.e. about 50 meV below the free exciton transition. From temperature dependent measurements one obtains a small thermal activation energy for the quenching of the luminescence of 10 ± 2 meV despite the large localization energy of 50 meV. Spatially resolved CL measurements show that the 3.333 eV lines are particularly strong at crystal irregularities and occur only at certain spots hence are not homogeneously distributed within the crystal contrary to the bound exciton recombinations. We attribute them to excitons bound to structural defects (Y-line defect) very common in II–VI semiconductors. For the bound exciton lines which seem to be correlated with Li and Na doping we offer a different interpretation. Li and Na do not introduce any shallow acceptor level in ZnO which otherwise should show up in donor–acceptor pair recombinations. Nitrogen creates a shallow acceptor level in ZnO. Donor–acceptor pair recombination with the 165 meV deep N-acceptor is found in nitrogen doped and implanted ZnO samples, respectively. In the best undoped samples excited rotational states of the donor bound excitons can be seen in low temperature PL measurements. At higher temperatures we also see the appearance of the excitons bound to the B-valence band, which are approximately 4.7 meV higher in energy. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

P‐type doping and devices based on ZnO

Abstract: Both n-type and p-type ZnO will be required for development of homojunction light-emitting diodes (LEDs) and laser diodes (LDs). It is easy to obtain strong n-type ZnO, but very difficult to create consistent, reliable, high-conductivity p-type material. The most natural choice of an acceptor dopant is N, substituting for O, and indeed several groups have been able to obtain p-type material by such doping. Surprisingly, however, other groups have also been successful with P and As, elements with much larger ionic radii than that of O. Although ZnO substrates are now available, most of the epitaxial p-type layers so far have been grown on sapphire, or other poorly-matched materials. The lowest p-type resistivity obtained up to now is about 0.5 Ω-cm, which should be sufficient for LED fabrication. In spite of the present availability of p-type ZnO, very few homojunction LEDs have been reported so far, to our knowledge; however, several good heterojunction LEDs have been demonstrated, fabricated with p-type layers composed of other materials. One such structure, with fairly strong 389-nm emission at 300 K, involves n-type ZnO and p-type AlGaN, grown on an SiC substrate. Also, an N + -ion implanted ZnO layer, deposited by chemical vapor deposition on Al 2 O 3 , exhibits 388-nm emission at 300 K and could be economical to produce.

CdZnTe and CdTe materials for X-ray and gamma ray radiation detector applications

Abstract: Good detection efficiency and high energy-resolution make Cadmium Zinc Telluride (CdZnTe) and Cadmium Telluride (CdTe) detectors attractive in many room temperature X-ray and gamma-ray detection applications such as medical and industrial imaging, industrial gauging and non-destructive testing, security and monitoring, nuclear safeguards and non-proliferation, and astrophysics. Advancement of the crystal growth and device fabrication technologies and the reduction of bulk, interface and surface defects in the devices are crucial for the widespread practical deployment of Cd 1-x Zn x Te-based detector technology. Here we review the effects of bulk, interface and surface defects on charge transport, charge transport uniformity and device performance and the progress in the crystal growth and device fabrication technologies aiming at reducing the concentration of harmful defects and improving Cd 1-x Zn x Te detector performance.

Crystallization in hafnia- and zirconia-based systems

Abstract: Crystallization of hafnia and zirconia and their alloys with silica and lanthana was studied in bulk and thin film samples by thermal analysis, X-ray diffraction and electron microscopy. Crystallization temperatures of hafnia and zirconia increase by more than 300 °C with increase of surface/interface area of the amorphous phase. Crystallization temperatures of zirconia and hafnia alloys with silica and lanthana increase with dopant content and exceed 900 °C for 50 mol% SiO2 and LaO1.5. Energies for tetragonal HfO2 and ZrO2 interfaces with amorphous silica were derived from their crystallization enthalpies from silicates as 0.25 ± 0.08 and 0.13 ± 0.07 J/m2, respectively. The crystallization pathways in bulk powders and films of zirconia and hafnia can be interpreted as resulting from thermodynamic stabilization by the surface energy term of tetragonal and amorphous phases over monoclinic. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

First‐principles elastic constants and electronic structure of BP, BAs, and BSb

Abstract: We have carried out a first-principles total-energy calculation of the structural and the elastic properties for the series of boron compounds BP, BAs, and BSb. We have applied the augmented plane-wave plus local-orbitals method with both the local-density approximation (LDA) and the generalized gradient approximation (GGA). Since there have been no previous theoretical or experimental determinations, our calculations provide the first available information on the elastic constants of these materials. The elastic constants have been derived by the stress-strain relation. We have calculated all of the equilibrium structural parameters for both phases: rock salt and zinc blende structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural properties, infrared reflectivity, and Raman modes of SnO at high pressure

Abstract: We have investigated the high-pressure behavior of the ‘lone-pair’ compound SnO using monochromatic synchrotron X-ray diffraction, synchrotron far- and mid-infrared reflection measurements, and Raman spectroscopy. The litharge-type ambient pressure structure is observed up to at least 20 GPa, though with indications for a small distortion above 15 GPa. Changes in interatomic distances are determined via full Rietveld refinements of diffraction patterns. SnO is found to undergo a semiconductor to metal transition near 5(1) GPa; the transition is attributed to the closure of the indirect fundamental gap. The mode Gruneisen parameters of zone-center Raman mode frequencies are reported. The results are discussed in light of related experimental and theoretical studies of structural, dynamical, and electronic properties of SnO.

Magnetic properties of Mn-doped Bi2Te3 and Sb2Te3

Abstract: We have fabricated Mn-doped Bi2Te3 and Sb2Te3 single crystals by the vertical gradient solidification method. The compositions and crystal structures of Bi2−xMnxTe3 and Sb2−xMnxTe3 were determined using Electron Probe Micro-Analyzer (EPMA) and powder X-ray diffraction (XRD) patterns, respectively. Both crystal structures were rhombohedral with smaller lattice constants because of the smaller atomic radius of Mn than those of Bi and Sb. Based on the magnetization measurements, Mn-doped Bi2Te3 and Sb2Te3 compounds have ferromagnetic ordering at TC = 10 and 17 K, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A study of magnetic and optical properties of Cu-doped ZnO

Abstract: The ferromagnetism of ZnO-based magnetic semiconductors has been investigated by theoretical calculation and many kinds of experiments. In the Cu-doped ZnO system, ferromagnetic ordering by Cu magnetic moments does not exist, but Cu-doped ZnO can have ferromagnetism due to the distortion of the ZnO-based structure by Cu doping. In this study, we investigated the magnetic properties of Cu-doped ZnO and discussed the possible origin of magnetism in this system. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic properties of γ-Fe2O3 nanoparticles made by coprecipitation method

Abstract: We have synthesized maghemite (γ-Fe2O3) nanoparticles using chemical coprecipitation technique through a typical pipette drop method (pipette diameter: 2000 μm) and a piezoelectric nozzle method (nozzle size: 50 μm). The size distribution of the maghemite nanoparticles prepared by the pipette drop method is from 5 nm to 8 nm. However, the nanoparticles made by the piezoelectric nozzle method show smaller size and very narrow size distribution from 3 nm to 5 nm. Zero-Field-Cooled (ZFC)/Field-Cooled (FC) magnetization and magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer from 5 K to 300 K to investigate the magnetic properties of nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles with the blocking temperature of 119.5 K and 94.3 K for the nanoparticles made by the pipette drop method and the piezoelectric nozzle method, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydrostatic pressure effects on the structural and electronic properties of carbon nanotubes

Abstract: We study the structural and electronic properties of isolated single-wall carbon nanotubes (SWNTs) under hydrostatic pressure using a combination of theoretical techniques: Continuum elasticity models, classical molecular dynamics simulations, tight-binding electronic structure methods, and first-principles total energy calculations within the density-functional and pseudopotential frameworks. For pressures below a certain critical pressure P c , the SWNTs' structure remains cylindrical and the Kohn-Sham energy gaps of semiconducting SWNTs have either positive or negative pressure coefficients depending on the value of (n, m), with a distinct family (of the same n - m) behavior. The diameter and chirality dependence of the pressure coefficients can be described by a simple analytical expression. At P c , molecular-dynamics simulations predict that isolated SWNTs undergo a pressure-induced symmetry-breaking transformation from a cylindrical shape to a collapsed geometry. This transition is described by a simple elastic model as arising from the competition between the bond-bending and PV terms in the enthalpy. The good agreement between calculated and experimental values of P provides a strong support to the collapse interpretation of the experimental transitions in bundles.

Optical properties and structural phase transitions of lead-halide based inorganic–organic 3D and 2D perovskite semiconductors under high pressure

Abstract: Optical absorption, photoluminescence and Raman scattering of lead-halide based inorganic-organic perovskite semiconductors were measured under quasi-hydrostatic pressure at room temperature. For the 3D perovskite semiconductor, (CH 3 NH 3 )PbBr 3 , the free exciton photoluminescence band exhibits red-shifts with pressure, and jumps to a higher energy by 0.07 eV at 0.8 GPa, which is associated with a phase transition from a cubic to an orthorhombic structure confirmed by Raman scattering. Above the phase transition pressure, the exciton band shows blue-shifts with further increasing pressure, and eventually disappears above 4.7 GPa. The results are compared with those for the 2D perovskite semiconductor, (C 4 H 9 NH 3 ) 2 PbI 4 . First principles pseudopotential calculations were performed to investigate changes in octahedral distortion and electronic band structures with pressure. The calculations have explained the origins of the intriguing changes in the electronic states with pressure in view of bonding characters between atomic orbitals in octahedra.

Luminescence and defects creation in Ce3+-doped Lu3Al5O12 crystals

Abstract: Luminescence, energy transfer and defects creation processes were studied at 4.2–300 K for Ce3+-doped Lu3Al5O12 crystals under excitation in the 2.5–11.5 eV energy range. The results obtained were compared with the characteristics of Y3Al5O12:Ce crystals. It was concluded that in both systems the efficiency of energy transfer from the host lattice to the impurity ion can be noticeably increased by the decrease of concentration of the defects responsible for their intrinsic luminescence. The origin of the optically created defects and possible mechanisms of their formation are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Gallium nitride nanowires with a metal initiated metal-organic chemical vapor deposition (MOCVD) approach

Abstract: We have studied structural and electrical properties of one dimensionally grown single crystalline gallium nitride (GaN) nanowires (NWs) for nanoscale devices using a metal-initiated metal-organic chemical vapor deposition (MOCVD). GaN nanowires were formed via the vapor-liquid-solid (VLS) mechanism with gold, iron, or nickel as growth initiators and were found to have triangular cross-sections with widths of 15 ∼ 200 nm and lengths of 5 ∼ 20 μm. TEM confirmed that the nanowires were single crystalline and were well oriented along the [210] or [110] direction on substrate depending on the metal initiators. For electrical transport properties of un-doped GaN nanowires, the back-gated field effect transistors (FET) were also fabricated by standard e-beam lithography. In our electrical measurement, the carrier concentration and mobility were 2 ∼ 4 × 10 18 cm -3 and 60 ∼ 70 cm2/V s, respectively.

Influence of YAB:Cr3+ nanocrystallite sizes on two-photon absorption of YAB:Cr3+

Abstract: An influence of nanocrystalline sizes of YAB:Cr particles incorporated within olygoetheracrylate polymer matrix on the two-photon absorption was investigated. Maximal values of the two-photon absorption diagonal tensor component was observed at low temperatures (about 4.2 K) and corresponded to concentration of the YAB:Cr NC about the 3% by weight and about 22 nm in sizes. The Cr3+ ions inside investigated NC play the crucial role in the observed nonlinear optical phenomena. The observed temperature dependence is explained within a model of anharmonic electron–phonon contribution in the nanocrystallites. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Valence and Conduction Band Offsets of a ZrO2/SiOxNy/n-Si CMOS Gate Stack: A Combined Photoemission and Inverse Photoemission Study

Abstract: The densities of states above and below the Fermi energy for the ZrO 2 /SiO x N y /n-Si system are examined by photoemission and inverse photoemission and compared with results from first principles calculations. The measured band gap of ZrO 2 is 5.68 eV and the valence and conduction band offsets relative to silicon are 3.40 and 1.16 eV respectively.

Magnetic resonant excitations in High-Tc superconductors

Abstract: The observation of an unusual spin resonant excitation in the superconducting state of various High-T c copper oxides by inelastic neutron scattering measurements is reviewed. This magnetic mode is discussed in light of a few theoretical models and likely corresponds to a spin-1 collective mode.

CBD‐Cd1−xZnxS thin films and their application in CdTe solar cells

Abstract: Composition, optical properties, structure properties, and surface morphology of thin films of Cd 1-x Zn x S (x ≤ 10%) prepared by chemical bath deposition (CBD) are reported. The best cell efficiency was 15.7%. It used a Cd 1-x Zn x S window layer, was confirmed by NREL (V oc = 840.1 mV, J sc = 24.81 mA/cm2, and FF = 75.55%), and had a CTO/ZTO/Cd 0.92 Zn 0.08 S/CdTe cell structure. The use of low zinc concentration in the Cd 1-x Zn x S layer and interdiffusion between Cd 1-x Zn x S and CdTe layers were assumed to be the reasons for maintaining high V oc and FF.

Saturated absorption and reverse saturated absorption of Cu:SiO2 at λ = 532 nm

Abstract: Nonlinear absorption in copper-doped silicate glasses was investigated by the Z-scan technique using second harmonic radiation of a Nd:YAG laser (λ = 532 nm, τ = 55 ps). The simultaneous influence of saturated and reverse saturated nonlinear absorption processes was analyzed. The nonlinear absorption coefficient and the saturation intensity of copper-doped glasses at laser intensity of 5.4 × 109 W cm−2 were measured to be 6 × 10−6 cm W−1 and 4.3 × 108 W cm−2, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ferroelectric relaxor behaviour of Na0.5Bi0.5TiO3–SrTiO3 ceramics

Abstract: Investigations of ferroelectric perovskite-type compounds with different distributions of the 6-fold or 12-fold coordination cations are more and more being increased as these materials are involved in the fabrication of many devices, e.g. capacitors, piezoelectric ultrasonic tranducers, electrostrictive actuators, SAW substrates, etc [1–3]. However, most of these materials are made from lead-bearing compounds, e.g. lead zirconate titanate (PZT), lead magnesium niobate (PMN), etc. So for environmental, health and social reasons, manufacturers are more and more constrained to reduce and ultimately eliminate the lead content from their materials. The search for alternative ferroelectric materials is now being focused on alkali niobates, modified bismuth titanates and systems in which a morphotropic phase boundary (MPB) will occur, that is bi- or multiphase systems in which one of the end phases is tetragonal and the other trigonal. Among them the perovskite-like sodium bismuth titanate Na

Current fluctuations of polymeric chains

Abstract: Coherent electron transport is investigated in a molecular device made of a polymeric chain sandwiched between two metallic electrodes. The molecular system is described by a simple Huckel model, while the coupling to the electrodes is treated in a broad energy band approach. Transport characteristics and noise power are calculated in two response regimes: linear and non-linear. A strong dependence is shown of the shot noise on (i) the length of the polymeric chain and (ii) the strength of the molecule-to-electrode coupling. In particular, a detailed discussion of Poissonian to sub-Poissonian crossover in the noise spectra is included. An algorithm is presented that allows one to calculate the lowest possible level of current fluctuations (due to the Pauli exclusion principle) in designing molecular devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Stimulated emission from GaN nanocolumns

Abstract: Stimulated emission with very low threshold excitation power density was observed for GaN nanocolumns grown on (0001) sapphire substrate by RF-plasma assisted molecular beam epitaxy. The photopump measurements were carried out under 355 nm Nd:YAG laser excitation with the surface emission configuration. The threshold excitation power density was 198 kW/cm 2 at room temperature. The peak wavelength shifted from 370.2 to 370.9 nm when increasing the excitation power from 130 to 440 kW/cm 2 . The peak intensity increased nonlinearly with excitation power. For the lower excitation condition using a 325 nm He-Cd laser, the spontaneous emission peak was observed at 363.2 nm and the intensity was 20-30 times stronger than for a 3.7 pm-thick MOCVD-grown GaN film with a dislocation density of 3-5 × 10 9 cm -2 . With this configuration the peak intensity was increased propotionally with excitation power. These results indicate that GaN nanocolumns have high potential to realize high performance optical devices.

Characterization of nonlinear optical parameters of copper- and silver-doped silica glasses at λ = 1064 nm

Abstract: Investigations of nonlinear optical characteristics (nonlinear refractive indices, nonlinear absorption coefficients and third-order nonlinear susceptibilities) of copper and silver nanoparticles implanted in glasses are presented using picosecond Nd:YAG laser radiation (λ = 1064 nm) and the Z-scan technique. The variations of the sign of the nonlinear refractive indices depending on matrix properties are analyzed. It is shown that the nonlinear absorption in copper-doped glasses is due to the two-photon effect. The optical limiting properties of these materials are discussed in the framework of two-photon absorption. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of the magnetocaloric effect from magnetization and heat capacity data

Abstract: Magnetic refrigeration is based on the magnetocaloric effect (MCE) – the ability of some materials to heat up when magnetized and cool down when removed from the magnetic field. The available techniques for studying the MCE are: (i) direct measurements by monitoring the change in material's temperature during the application or removal of the magnetic field; and (ii) indirect calculations from experimental data of magnetization and/or heat capacity as functions of temperature and magnetic field. In this paper the procedure to evaluate the MCE from magnetization and zero-field heat capacity data is described. The MCE – isothermal magnetic entropy change (ΔSM) and adiabatic temperature change (ΔTad) – of gadolinium (Gd) obtained by this procedure is presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-pressure stability and structural properties of CdS and CdSe

Abstract: The structural phase transformations of CdS and CdSe under high pressure are studied by using the local approximation to the density functional theory, and the one-electron equations are solved by means of the full-potential linear muffin-tin-orbital method FP-LMTO. CdS and CdSe are found to have nearly similar structural systematics under high pressure. In CdS, the Pmmn phase is predicted after the rocksalt structure, and in CdSe the Cmcm structure is thermodynamically stable after the rocksalt structure. We also find a thermodynamic stability range for the CsCl phase of CdSe. The structural properties of the zincblende, wurtzite, rocksalt, Pmmn, and Cmcm phases are presented. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-pressure X-ray structural study of BeO and ZnO to 200 GPa

Abstract: We have carried out high-pressure X-ray structural studies of BeO and ZnO up to 200 GPa to find the phase transition of BeO from the wurzite to the NaCl structure and that of ZnO from the NaCl to the CsCl structure, which are expected theoretically. The phase transition of BeO occurred at 137 GPa, which is in good agreement with the theoretical value of 139 GPa. The wurzite phase persisted up to 175 GPa. The bulk modulus of BeO at zero pressure is determined to be 223 GPa by the Birch's equation. As previously reported, the ZnO sample transformed from the wurzite structure to the NaCl structure at 9.1 GPa. Extending the pressure range up to 202 GPa no phase transition to the CsCl structure occurred. The bulk modulus of the NaCI structure was determined to be 194 GPa.

Growth and properties of In‐rich InGaN films grown on (0001) sapphire by RF‐MBE

Abstract: We have performed detailed investigations of the optical properties of strain-free In-rich In x Ga 1-x N (0.61 ≤ x ≤ 1.0) films that were grown directly on (0001) sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy. In-composition dependence of photoluminescence peak energy for the In x Ga 1-x N films, measured at room temperature, exhibited a monotonic and smooth decrease with the increase in the In-composition, approaching to 0.66 eV of a strain-free InN film that was also grown directly on the sapphire substrate. The energy bowing parameter, b was determined to be 1.8 eV using these strain-free In x Ga 1-x N films. Structural properties of these films are also investigated in detail.

Large magnetocaloric effect in La0.845Sr0.155Mn1−xMxO3 (M = Mn, Cu, Co) perovskites

Abstract: We present the results of an investigation on the magnetocaloric effect in the perovskites of La{sub 0.845}Sr{sub 0.155}Mn{sub 1-x}M{sub x}O{sub 3} (M = Mn, Cu, Co). It is found that there was a large magnetic entropy change, i.e. a large magneto-caloric effect, in all these samples. Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu-doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology. The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic-paramagnetic transition temperature (T{sub C}) - which is experimentally verified by electron paramagnetic resonance study. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Structural, electronic and optical calculations of Cu(In,Ga)Se2 ternary chalcopyrites

Abstract: In this work, we have investigated the structural, electronic and optical properties of the ternary I–III–VI2 chalcopyrite semiconductors ABX2 (A = Cu, B = In, Ga, X = Se) by means of a first-principles density-functional total-energy calculation with the local-density approximation (LDA), using the all-electron full-potential linear-augmented plane-wave method (FP-LAPW). The equilibrium lattice constants and the bulk moduli (a, c, c/a, u and B0) are compared with other theoretical calculations. The energy gap at ambient pressure is found to be direct and the nature of the gap crucially depends on the manner in which the d electrons of the A atoms are treated. We have also reported the optical properties of two chalcopyrite semiconductors CuInSe2 and CuGaSe2. Results on complex dielectric functions, refractive indices n, extinction coefficients k, and normal-incidence reflectivity R in the two crystals are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magneto‐optical properties of Bi‐YIG nanoparticle with polymethacrylate matrix materials

Abstract: New magneto-optical Bi1.8Y1.2Fe5O12 nanoparticle hybridized materials have been developed which are composed of the nanoparticles and methyl, ethyl and butyl methacrylate matrix with poly(methyl methacrylate). The Bi1.8Y1.2Fe5O12 nanoparticles were prepared with coprecipitation and heat-treatment processes. The hybridized systems were prepared by a mechanical milling process. The magneto-optical properties of the solidified clear materials were measured. The Faraday rotation angle θF was about 19°/cm and the figure of merit θF/α was about 1.3° at 520 nm for the Bi1.8Y1.2Fe5O12 nanoparticle and ethyl methaclyrate hybrid material. These hybrid material systems have the very attractive feature of an easy molding ability. This property is important for mass production processes of magneto-optical devices. The Bi-YIG nanoparticle dispersed fluid and its stiffened bulk material are new promising magneto-optical materials. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

On the non‐monotonic lateral size dependence of the height of GaAs nanowhiskers grown by molecular beam epitaxy at high temperature

Abstract: GaAs nanowhiskers were grown by molecular beam epitaxy on the GaAs(111)B surface activated by Au at the surface temperature of 585 °C. The dependence of nanowhisker height on the size of Au–GaAs alloy drops was investigated. It has been found that the height of GaAs nanowhiskers is zero at a certain minimum diameter of drop, then increases with size, has a pronounced maximum at a certain size, decreases for thicker whiskers and finally goes to a certain asymptotic value. The theoretical model for the growth kinetics of nanowhiskers was developed in order to explain the observed size dependence. The results of comparison of theoretical and experimental data for the height of GaAs nanowhiskers are presented and analyzed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)