bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective detection of 2‐nitrobenzenesulfenyl‐labeled peptides by matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry using a novel matrix
Authors: Matsuo Ei‐ichi , Toda Chikako , Watanabe Makoto , Ojima Noriyuki , Izumi Shunsuke , Tanaka Koichi , Tsunasawa Susumu , Nishimura Osamu
Published: March 2006

The 2‐nitrobenzenesulfenyl (NBS) method, which is useful for quantitative proteome analysis, is based on stable isotope labeling of tryptophan residues with NBS chloride (12C6‐NBSCl or 13C6‐NBSCl). We found that 3‐hydroxy‐4‐nitrobenzoic acid (3H4NBA) is a more suitable matrix than 2,5‐dihydroxybenzoic acid (DHB) for detecting NBS‐labeled peptides by MALDI‐quadrupole IT (QIT)‐TOF MS . Furthermore, NBS‐labeled peptides were selectively ionized and detected in a mixture of NBS‐labeled and unlabeled peptides. Labeled paired peaks were easily detected without enrichment, nonpaired labeled peaks were clearly distinguished from unlabeled contaminating peptides, and nitrotyrosine‐containing peptides were also selectively detected on the 3H4NBA matrix, while by‐product‐peaks arising from nitrobenzene moieties were suppressed. The use of 3H4NBA as a comatrix with CHCA improved the sensitivity of detection while substantially retaining the selectivity of 3H4NBA. The 3H4NBA matrix offers great advantages in terms of simplicity, sensitivity, and usability when used for the NBS method and for MALDI‐TOF MS analysis applied to compounds having a nitrobenzene ring.
Star polystyrenes by anionic star–star coupling reactions with divinylbenzene
Authors: Lee Hyung‐Jae , Lee Kwanyoung , Lee Soo No
Published: March 2006

The incremental addition of divinylbenzene was used to generate star polystyrenes in a nearly full conversion of a living polystyrenyl anion. The dramatic increase in the molecular weight of the star polystyrenes with a limited supply of the living polystyrene supported the formation of gradient‐star polystyrenes through star–star coupling. The stoichiometric analysis of the star polymers revealed that their connection polymer had a shorter length than their branch polymer. The measured solution viscosity of the gradient‐star polymers greatly deviated from a linear correlation with the molecular weight and was in parallel to a theoretical simulation based on a highly branched structure of the gradient‐star polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2579–2586, 2006
Nitro‐substituted iron(II) tridentate bis(imino)pyridine complexes as high‐temperature catalysts for the production of α‐olefins
Authors: Ionkin Alex S. , Marshall William J. , Adelman Douglas J. , Shoe Aaron L. , Spence Rupert E. , Xie Tuyu
Published: March 2006

A new series of nitro‐substituted bis(imino)pyridine ligands {2,6‐bis[1‐(2‐methyl‐4‐nitrophenylimino)ethyl]pyridine, 2,6‐bis[1‐(4‐nitrophenylimino)ethyl]pyridine, (1‐{6‐[1‐(4‐nitro‐phenylimino)‐ethyl]‐pyridin‐2‐yl}‐ethylidene)‐(2,4,6‐trimethyl‐phenyl)‐amine, and 2,6‐bis[1‐(2‐methyl‐3‐nitrophenylimino)ethyl]pyridine} and their corresponding Fe(II) complexes [{p‐NO2o‐MePhNC(Me)PyC(Me)NPho‐ Mep‐NO2}FeCl2 (10), L2FeCl2 (11), {m‐NO2o‐MePhNC(Me)PyC(Me)NPho‐Mem‐NO2}FeCl2 (12), and {p‐NO2PhNC(Me)PyC(Me)NMes}FeCl2 (14)] were synthesized. According to X‐ray analysis, there were shortenings of the axial FeN bond lengths (up to 0.014 Å) in para‐nitro‐substituted complex 10 and (up to 0.015 Å) in meta‐nitro‐substituted complex 12 versus the Fe(II) complex without nitro groups [{o‐MePhNC(Me)PyC(Me)NPho‐Me}FeCl2 (1)]. Complexes 10, 12, and 14 afforded very active catalysts for the production of α‐olefins and were more temperature‐stable and had longer lifetimes than parent non‐nitro‐substituted Fe(II) complex 1. The reaction between FeCl2 and a sterically less hindered ligand [p‐NO2PhNC(Me)PyC(Me)NPhp‐NO2] resulted in the formation of octahedral complex 11. A para‐dialkylamino‐substituted bis(imino)pyridine ligand [p‐NEt2o‐MePhNC(Me)PyC(Me)NPho‐Mep‐NEt2] and the corresponding Fe(II) complex [{p‐NEt2o‐MePhNC(Me)PyC(Me)NPho‐Mep‐NEt2}FeCl2 (16)] were synthesized to evaluate the effect of enhanced electron donation of the ligand on the catalytic performance. According to X‐ray analysis, there was a shortening (up to 0.043 Å) of the axial FeN bond lengths in para‐diethylamino‐substituted complex 16 in comparison with parent Fe(II) complex 1. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2615–2635, 2006
Synthesis and characterization of polyimides from bis(3‐aminophenyl)‐4‐(1‐adamantyl)phenoxyphenyl phosphine oxide
Authors: Kwak S. M. , Yeon J. H. , Yoon T. H.
Published: March 2006

A novel diamine, bis(3‐aminophenyl)‐4‐(1‐adamantyl)phenoxyphenyl phosphine oxide (mDAATPPO), was synthesized via the Williamson ether reaction of 4‐(1‐adamantyl)phenol and bis(3‐nitrophenyl)‐4‐fluorophenyl phosphine oxide, followed by reduction. The phenol group was prepared by the Friedel–Crafts reaction of 1‐bromoadamantane and phenol, whereas the phosphine oxide group was synthesized by the Grignard reaction of 1‐bromo‐4‐fluorobezene and diphenyl phosphinic chloride, followed by nitration. The monomer and its intermediate compounds were characterized with Fourier transform infrared, NMR, and melting‐point apparatus. The monomer was then used to prepare polyimides with 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride, 4,4′‐oxydiphthalic dianhydride, and pyromellitic dianhydride by the conventional two‐step synthesis: the preparation of poly(amic acid) followed by solution imidization. The molecular weights of the polyimides were controlled to 20,000 g/mol by off‐stoichiometry, and the synthesized polyimides were characterized with Fourier transform infrared, NMR, gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry. In addition, the solubility, intrinsic viscosity, dielectric constant, and birefringence of the polyimides were evaluated. Novel polyimides with mDAATPPO exhibited good solubility, high glass‐transition temperatures (290–330 °C), excellent thermal stability (>500 °C), low dielectric constants (2.77–3.01), low refractive indices, and low birefringence values (0.0019–0.0030). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2567–2578, 2006
Photocrosslinked poly(vinylbenzophenone)‐core micelles via mild Friedel–Crafts benzoylation of polystyrene amphiphiles
Authors: Chen Ying , Tavakley Anita E. , Mathiason Tate M. , Taton T. Andrew
Published: March 2006

Photocrosslinkable poly(vinylbenzophenone)‐containing polymers were synthesized via a one‐step, Friedel–Crafts benzoylation of polystyrene‐containing starting materials [including polystyrene, polystyrene‐block‐poly(tert‐butyl acrylate), polystyrene‐block‐poly(ethylene oxide), polystyrene‐block‐poly(methyl methacrylate), and polystyrene‐block‐poly(n‐butyl acrylate)] with benzoyl trifluoromethanesulfonate as a benzoylation reagent. The use of this mild reagent (which required no added Lewis acid) permitted polymers with well‐defined compositions and narrow molecular weight distributions to be synthesized. Micelles formed from one of these benzoylated polymers, [polystyrene0.25‐co‐poly(vinylbenzophenone)0.75]115‐block‐poly(acrylic acid)14, were then fixed by the irradiation of the micelle cores with UV light. As the irradiation time was increased, the pendent benzophenone groups crosslinked with other chains in the glassy micelle cores. Dynamic light scattering, spectrofluorimetry, and Fourier transform infrared spectroscopy were all used to verify the progress of the crosslinking reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2604–2614, 2006
Appraisal of the cancer experience by family members and survivors in long‐term survivorship
Authors: Bowman Karen F. , Rose Julia H. , Deimling Gary T.
Published: March 2006

This study assessed the appraisal of the stressfulness of the cancer experience and its correlates for family members and older survivors living in the long‐term survivorship phase of the disease. On average, family members appraised the cancer experience as more stressful than their surviving relatives. Beliefs about the effect of the diagnosis and treatment on family members were important correlates for both family members and survivors in the appraisal process. Cancer characteristics were not related to appraisal for survivors, but stage at diagnosis was associated with a more stressful appraisal for family members. Demographic characteristics were unrelated to appraisal for family members, but being African‐American was linked to a less stressful appraisal for survivors. These findings highlight the stressful impact of the cancer experience on family members and can help guide health care interventions which include family members from African‐American and White ethnicities. Copyright © 2006 John Wiley & Sons, Ltd.
ARTIST: An activated method in internal coordinate space for sampling protein energy landscapes
Authors: Yun Mi‐Ran , Lavery R. , Mousseau N. , Zakrzewska K. , Derreumaux P.
Published: March 2006

We present the first applications of an activated method in internal coordinate space for sampling all‐atom protein conformations, the activation–relaxation technique for internal coordinate space trajectories (ARTIST). This method differs from all previous internal coordinate‐based studies aimed at folding or refining protein structures in that conformational changes result from identifying and crossing well‐defined saddle points connecting energy minima. Our simulations of four model proteins containing between 4 and 47 amino acids indicate that this method is efficient for exploring conformational space in both sparsely and densely packed environments, and offers new perspectives for applications ranging from computer‐aided drug design to supramolecular assembly. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Optical quantum control using II–VI quantum dots
Authors: Henneberger F. , Akimov I. A.
Published: March 2006

II–VI quantum dots are used to control and to manipulate single charge and spin excitations in semiconductors. Two‐photon excitation enables us to generate an entangled state and to control the emission cascade of the exciton‐biexciton system. On charged quantum dots, we demonstrate direct optical manipulation of the resident electron spin. The spin life‐times are significantly larger than 10 µs in low magnetic field. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the number of Mn ions inside CdMnTe self assembled quantum dots
Authors: Wojnar P. , Suffczyński J. , Kowalik K. , Golnik A. , Karczewski G. , Kossut J.
Published: March 2006

We have grown self assembled CdMnTe/CdZnTe quantum dots with small amount of Mn ions by molecular beam epitaxy. Using atomic layer epitaxy growth mode for the deposition of the QDs layer, we were able to add the manganese ions only into the two central monolayers of six monolayers‐thick CdTe layers, thus, achieving great dilution of Mn ions. Micro‐photoluminescence measurements performed in an external magnetic field confirmed that the Mn ions are successfully incorporated in the CdTe QDs, which manifests itself by the strong circular polarization and the giant Zeeman splitting of PL‐lines coming from individual QDs. Studying the magnetic field dependencies of several QDs from our ensemble, we found that the energy shifts acquire, approximately, only few nearly discrete values. We attribute this effect to small number of Mn ions inside our QDs that contribute to the splitting of excitons and we use the saturation values of the shift it to determine this number precisely. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of sub‐gap irradiation on the time‐of‐flight current waveforms of high resistivity CdTe
Authors: Suzuki K. , Seto S. , Sawada T. , Imai K.
Published: March 2006

Effects of IR irradiation on TOF current waveforms of a CdTe:Cl crystal with Pt electrodes on its (111) faces have been investigated. An increase of TOF current and a change in the evolution of DC photocurrent versus applied voltage by IR irradiation are observed. By taking into account an effect of surface recombination, satisfactory fits to theory are obtained for the charge collection efficiency and the DC photocurrent versus applied voltage. These results show that the observed effects are mainly explained by a reduction of surface recombination velocity rather than by an increase of bulk carrier lifetime. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High p‐type doping level of MgZnCdSe on InP substrates by inserting ZnTe thin layers
Authors: Saitoh Takumi , Nomura Ichirou , Sueoka Kan , Kikuchi Akihiko , Kishino Katsumi
Published: March 2006

A novel p‐type doping method for MgZnCdSe on InP substrates was proposed. In this method, highly p‐type‐doped thin layers, such as N‐doped ZnTe, are inserted at proper intervals into MgZnCdSe layers. The inserted thin layer emits holes and the p‐type coduction was achieved. ZnCdSe/ZnTe superlattices (SLs), where thin p‐type‐doped ZnTe layers were periodically inserted, were grown on InP substrates by molecuar beam epitaxy. When the ratio of ZnTe layer thickness to one insertion period was 0.17, the net acceptor cocentration (NA‐ND) value reached 8.0 × 1017 cm–3. This value was more than one order of magnitude greater than that of a simple N‐doped ZnCdSe layer (3.5 × 1016 cm–3). To obtain wide bandgap p‐type materials, MgSe/ZnCdSe/ZnTe SLs were fabricated. NA‐ND values from 4.7 × 1017 to 8.0 × 1017 cm–3 were observed for samples with bandgap energies from 2.33 to 2.04 eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent control of polariton modes in pulse‐transmission and four‐wave‐mixing experiments
Authors: Kudyk I. , Wischmeier L. , Voss T. , Rückmann I. , Gutowski J.
Published: March 2006

We report coherent optical control of polariton modes in pulse‐transmission and four‐wave‐mixing experiments realized on a ZnSe/ZnSSe heterostructure containing a 25 nm thin active ZnSe layer. It is shown in linear pulse‐transmission at low excitation density that the modes can be separately controlled. The coherent control of nonlinear polaritonic FWM polarization is different for both directions of first‐order diffraction. The FWM signal observed in direction 2k1‐k2 shows that the polariton modes can be separately manipulated. Contrasting to that, in the direction 2k2‐k1 all polariton modes are simultaneously enhanced or diminished. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Far‐infrared spectroscopy of HgMnTe–MnSe mixture
Authors: Romčević N. , Romčević M. , Milutinović A. , Kostić R.
Published: March 2006

Far‐infrared reflectivity spectrum of Hg0.91Mn0.09Te‐MnSe mixture, grown by Bridgman method, was measured in the 80–500 cm–1 range at room temperature. The investigated mixture consists of MnSe clusters randomly distributed in Hg0.91Mn0.09Te matrix. The analysis of the far‐infrared spectrum was made by a fitting procedure. The Maxwell‐Garnett effective medium theory is used for modeling the effective dielectric function, and by that way calculating both the electron and phonon response. There is a good agreement between the experimental results and the applied model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence, Raman scattering and vertical transport of CdSe/CdMgSe superlattices
Authors: Reshina I. I. , Ivanov S. V. , Mirlin D. N. , Sedova I. V. , Sorokin S. V.
Published: March 2006

Photoluminescence and photoluminescence excitation spectra, vertical transport of photoexcited charge carriers and excitons and Raman scattering by optical phonons have been studied for the first time in low‐strained superlattices CdSe/CdMgSe grown by molecular‐beam epitaxy on InAs substrates. The vertical transport was studied by purely optical means involving an enlarged quantum well built into the superlattice. The enlarged quantum well served as a sink for the photoexcited carriers and excitons that have tunnelled through the superlattice. The measurements conducted in temperature range 2–150 K and also under in‐plane strong magnetic fields show that vertical transport occurs mainly by free heavy‐hole excitons but in superlattices with 5.9 nm and 7.3 nm periods it is not of the Bloch type. A comparison of the calculated energies of the interband transitions with the experimental data provides the valence‐band ofsett in the range 0.4–0.5. The Raman spectra indicate a two‐mode behavior of the optical phonons in CdMgSe barriers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shorter wavelength intersubband absorption down to λ = 1.55 µm in (CdS/ZnSe)/BeTe type‐II superlattices
Authors: Li B. S. , Akimoto R. , Akita K. , Hasama T.
Published: March 2006

We first present the dependence of intersubband transition (ISB‐T) on the electronic doping density in (CdS/ZnSe)/BeTe superlattices (SLs). The in situ RHEED and X‐ray diffraction measurements reveal these SLs with perfect structure. An ISB‐T energy as high as 0.787 eV is observed in this structure. The intensity of ISB absorption increases with increasing ZnCl2 flux until reaches a maximum and then decreases with further more ZnCl2 flux supplying. The ISB‐T energy slightly red shifts from 0.787 to 0.775 eV with ZnCl2 flux increasing and then blue shifts to 0.785 eV when the intensity of ISB decreases with more chlorine doping. Finially, The anneal effects on the properties in (CdS/ZnSe)/BeTe as well as CdS/ZnSe structures are studied. The explanations to result in the change in (CdS/ZnSe)/BeTe and CdS/ZnSe structures are given. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magneto‐optical Faraday effect in II–VI based semimagnetic semiconductor nanocrystals
Authors: Savchuk Andriy I. , Fediv Volodymyr I. , Stolyarchuk Ihor D. , Savchuk Tetyana A. , Perrone Alessio
Published: March 2006

Different physical and chemical methods were used to prepare II–VI based semimagnetic semiconductor nanocrystals. A study of magneto‐optical Faraday effect in the nanocrystals revealed its enhancement as compared with bulk crystals. It is explained in framework of increase in the oscillator strength of exciton transitions and to the difference between these strengths in an external magnetic field. It was observed almost linear dependence of the Faraday rotation as function of magnetic field strength for nanocrystals at liquid helium temperature in contrast to the dependence with saturation in bulk case and changes in process of a transition of the semimagnetic nanocrystals from the paramagnetic state to a spin glass state. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Colloidal nanocrystals integrated in epitaxial nanostructures: structural and optical properties
Authors: Arens Ch. , Roussau N. , Schikora D. , Lischka K. , Schöps O. , Herz E. , Woggon U. , Litvinov D. , Gerthsen D. , Artemyev M. V.
Published: March 2006

Using the well established MBE process, we introduced colloidal nanocrystals (NCs) into monocrystalline semiconductor layers. CdSe nanorods (NRs) and CdSe(ZnS) core‐shell nanodots (NDs) with radii R between 2 and 4 nm on a ZnSe surface are capped by thin (d ∼ 2R ) and thick (d > 2R ) MBE‐grown ZnSe layers of a thickness d . This new growth technique does not rely on strain like the Stranski‐Krastanow growth of CdSe/ZnSe quantum dot layers, and thus offers additional degrees of freedom for choosing the NC composition, shape and size. In‐ and ex‐ situ characterisations of the samples are showing a ZnSe cap layer of high crystalline quality. After the growth of the cap layer the dots preserve their shape and emission spectrum. High‐resolution transmission electron microscope images show the direct connection of the NCs crystal lattice to the crystal lattices of the ZnSe buffer and the epitaxially grown cap layer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of electric field on fine structure of exciton complexes in CdTe/ZnTe self‐assembled quantum dot
Authors: Kowalik K. , Kudelski A. , Golnik A. , Suffczyński J. , Krebs O. , Voisin P. , Karczewski G. , Kossut J. , Gaj J. A.
Published: March 2006

We report on micro‐photoluminescence (µ‐PL) measurements of CdTe/ZnTe self‐assembled quantum dots. Jumps in the line positions are observed and attributed to fluctuations of local electrostatic environment. We find that fine structures of exciton, biexciton and charged exciton originating from the same QD are correlated with line positions. We observe stronger influence of the field on the excitonic states of lower binding energy. The local field likely originates from charges localized at defects in the close vicinity of the QD, and correlations indicate that its direction is not completely random. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acceptor doping in ZnO with group‐I elements
Authors: Sann Joachim , Hofstaetter Albrecht , Pfisterer Daniel , Stehr Jan , Meyer Bruno K.
Published: March 2006

We study the interaction of hydrogen donors and Lithium acceptors in bulk ZnO by electron paramagnetic resonance and photoluminescence. With increasing diffusion temperature the number of hydrogen donors increases whereas the number of deep Li acceptors decreases. In the temperature range between 450 and 600 °C a shallow Li related acceptor is formed. The very same defect is found in Li diffused ZnO, and in epitaxial ZnO thin films by in‐situ doping with Li. We suggest a tentative model for the shallow Li acceptor whereby hydrogen would be an essential part of the defect core. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Majority‐carrier mobilities in undoped andn‐type doped ZnO epitaxial layers
Authors: Makino T. , Segawa Y. , Tsukazaki A. , Ohtomo A. , Kawasaki M.
Published: March 2006

Transparent and conductive ZnO:Ga thin films are prepared by laser molecular‐beam epitaxy. Their electron properties were investigated by the temperature‐dependent Hall‐effect technique. The 300‐K carrier concentration and mobility were aboutns∼ 1016cm–3and 440 cm2/V s, respectively. In the experimental ‘mobility vs concentration’ curve, unusual phenomenon was observed, i.e., mobilities atns∼ 5 × 1018cm–3are significantly smaller than those at higher densities above ∼1020cm–3. Several types of scattering centers including ionized donors and oxygen traps are considered to account for the observed dependence of the Hall mobility on carrier concentration. The scattering mechanism is explained in terms of inter‐grain potential barriers and charged impurities. A comparison between theoretical results and experimental data is made. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oxygen in sputter‐deposited ZnTe thin films
Authors: Merita S. , Krämer T. , Mogwitz B. , Franz B. , Polity A. , Meyer B. K.
Published: March 2006

Bandgap‐bowing has been observed in many of the zinc‐group‐VI compounds, when the anion is substituted with an isovalent element. Recently new results on the ZnO1–xSx and ZnO1–xSex system have been presented, but so far only one report on ZnO1–xTex is known. We examine the possibility of substituting tellurium by oxygen in sputter‐deposited polycrystalline ZnTe thin‐films and the effects on bandgap energy and crystal structure. A first approximation of the bowing curve with a lower limit of the bowing parameter of 2.7 eV is performed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of ZnO nanostructures by remote plasma‐enhanced metal‐organic chemical vapor deposition
Authors: Zhang G. , Nakamura A. , Nakagawa S. , Aoki T. , Temmyo J.
Published: March 2006

Remote plasma‐enhanced metal‐organic chemical vapor deposition was employed to grow ZnO nanostructure. The position of molecular O nozzle tip was optimized to improve the quality of the ZnO nanostructures based on photoluminescence measurement. The influence of the substrate orientation (a, c, and R‐plane sapphire) and growth temperature on the surface morphology for well‐assembled ZnO nanostructure was investigated. It is found that the surface morphologies appear as island and needle‐like crystals at low growth temperature (360 °C). With increasing temperature, faceted terraces are observed on c and R‐plane substrate and faceted needle‐like crystals were formed on a‐plane substrate. Regular terrace surface is achieved on R‐plane substrate and the step distance is increased with increasing growth temperature. The epitaxial relationship and optical property of the ZnO nanostructures were characterized by X‐ray diffraction and photoluminescence. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence and structural properties of defects in ion implanted ZnO
Authors: Monteiro T. , Soares M. J. , Neves A. J. , Carmo M. C. , Peres M. , Cruz A. , Alves E. , Wahl U. , Rita E. , Munoz‐SanJose V. , Zuniga‐Perez J.
Published: March 2006

ZnO substrates and films were intentionally implanted with rare earth and transition metal ions. The influence of the implantation and subsequent air thermal annealing treatments on the structural and optical properties of ZnO samples were studied by using Rutherford backscattering spectrometry and low temperature photoluminescence techniques. Intraionic Tm‐related emission was observed for bulk and ZnO films. Similarly, Eu and Tb‐doped ZnO films follow the same trend observed in bulk samples. No intraionic related emission was observed for Eu‐doped samples even being the ion in Zn sites and for the Tb‐doped samples ion segregation was observed for thermal annealing temperatures above 800 °C. For the Mn‐doped ZnO bulk samples the lattice recovery follows the same trend to that one observed for the Fe‐doped samples, starting near 800 °C being fully recovered at 1050 °C. Although Fe3+ was observed no intraionic Mn‐related emission was detected under the used conditions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ultraviolet electroluminescence of ZnO based heterojunction light emitting diode
Authors: Jiao S. J. , Lu Y. M. , Shen D. Z. , Zhang Z. Z. , Li B. H. , Zhang J. Y. , Yao B. , Liu Y. C. , Fan X. W.
Published: March 2006

ZnO/GaN p‐i‐n heterojunctions light emitting diodes were fabricated by plasma‐assisted molecular beam epitaxy. We make use of high resistivity of nitrogen doped ZnO to fabricate n‐ZnO/i‐ZnO/p‐GaN heterojunction light emitting diode. The emission of i‐ZnO was obtained due to the limitation effect of i‐ZnO on electrons and holes. Moreover, n‐ZnO/i‐MgO/p‐GaN heterojunction light emitting diode was also fabricated. The limitation effect on electrons is increased in this heterojunction. The bright ultraviolet electroluminescence at 382 nm originating from the ZnO layer was observed in the room temperature electroluminescence spectrum. We hope to realize the stimulated emission of ZnO using these heterojunctions by the improvement of crystal quality and the optimization of device structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependent band gap and homogeneous line broadening of the exciton emission in ZnO
Authors: Hauschild R. , Priller H. , Decker M. , Brückner J. , Kalt H. , Klingshirn C.
Published: March 2006

We report on an experimental study of the temperature dependent band gap shift and the homogeneous line broadening of the excitonic luminescence in ZnO. This data is derived from photoluminescence (PL) measurements at temperatures from T = 10–290 K and fitting the PL line shape with a theoretical model for the exciton line and its LO‐phonon replica. Additionally, transmission measurements are utilized to extend the data of the temperature dependent band gap into the temperature range from 290 K up to 800 K. The experimentally determined shift is compared with one that is obtained numerically from the phonon density of states, the pressure dependent band gap, the thermal expansion coefficient and the bulk modulus with only a single fit parameter. The interaction of excitons with phonons leads to a homogeneous broadening of the excitonic emission which reaches values of 40 meV at room temperature. This mechanism results in a substantially increased threshold for stimulated emission from every process involving excitons. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The exciton polariton model and the diffusion of excitons in ZnO analyzed by time‐dependent photoluminescence spectroscopy
Authors: Hauschild R. , Priller H. , Decker M. , Kalt H. , Klingshirn C.
Published: March 2006

We investigate the lineshape of the zero‐phonon luminescence of the A‐exciton polariton and of the LO‐phonon replicas in ZnO and their dynamics. The lineshape verifies details of the A‐exciton polariton model and confirms the inverted band structure (AΓ7, BΓ9, CΓ7). The dynamics give information on relaxation, diffusion and recombination processes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of MBE grown ZnO on GaAs(111) substrates
Authors: Matsumoto Takashi , Nishimura Kazuto , Nishii Akito , Ota Atsuya , Nabetani Yoichi , Kato Takamasa
Published: March 2006

ZnO epitaxial layers grown on GaAs(111)B substrates by plasma assisted MBE with different O/Zn flux ratios are characterized by photoluminescence (PL), X‐ray diffraction (XRD) θ –2θ scan, ω scan, and reciprocal lattice mapping. Low temperature PL spectra are dominated by bound exciton bands at 3.360 eV and 3.330 eV. The 3.360 eV band is strong in samples grown under Zn‐rich cindition and the 3.330 eV band is strong in samples grown under O‐rich condition. The epitaxial orientation relationship is ZnO(0001)//GaAs(111) and ZnO[11‐20]//GaAs [01‐1] irrespective of the O/Zn flux ratio. The ZnO c‐axis tilts by 0.2° ∼ 0.3° from the GaAs [111] axis toward 〈1‐10〉 or 〈2‐1‐1〉 direction. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
p‐type ZnO and ZnMnO by oxidation of Zn(Mn)Te films
Authors: Przeździecka E. , Kamińska E. , Dynowska E. , Dobrowolski W. , Jakieła R. , Kłopotowski Ł. , Sawicki M. , Kiecana M. , Kossut J.
Published: March 2006

ZnO and ZnMnO doped with N and/or As layers were fabricated by thermal oxidation of ZnTe and ZnMnTe grown by MBE on different substrates. The Hall measurements demonstrated p ‐type conductivity with the hole concentration of ∼5 · 1019 cm–3 for ZnO:As and ZnO:As:N on GaAs substrates and ∼ 6 · 1017 cm–3 for ZnTe:N on ZnTe substrates. Optical study showed meaningful differences between samples with different acceptor, grown on different substrates. Magnetoptical experiment demonstration Zeeman splitting in ZnMnO samples. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A study of ZnMnO as a material for magneto‐ and spin‐electronics
Authors: Mofor A. C. , Reuss F. , El‐Shaer A. , Ahlers H. , Siegner U. , Bakin A. , Limmer W. , Eisenmenger J. , Mueller Th. , Ziemann P. , Waag A.
Published: March 2006

Due to the large spin moment exhibited by the transition metal Mn, it is being extensively investigated as a candidate element for producing ferromagnetic ZnO for magnetoelectronic and spintronic applications. However, ferromagnetism in ZnMnO is being controversially discussed. We review our investigations on epitaxially grown ZnMnO layers and present findings on Mn‐implanted ZnO layers. The results of our investigations on the magnetic properties of the fabricated ZnMnO show that it is not trivial to confirm ferromagnetism in ZnMnO grown on sapphire because of ferromagnetic signal produced by the substrate. After a deduction of the substrate contribution to magnetisation data, both epitaxially doped ZnO layers and Mn‐implanted bulk and epitaxial layers show paramagnetic behaviour. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aqueous chemical growth and patterning of ZnO nanopillars on different substrate materials
Authors: Kreye M. , Postels B. , Wehmann H.‐H. , Fuhrmann D. , Hangleiter A. , Waag A.
Published: March 2006

Aqueous chemical growth (ACG) is a low‐temperature approach that is only weakly influenced by the substrate and allows for the growth of ZnO nanopillars on various substrates. ACG is an efficient way to generate wafer‐scale and densely packed arrays of ZnO nanopillars even on polymer materials. Photoluminescence (PL) characterisation clearly shows a comparatively strong band‐edge luminescence even at room temperature that is accompanied with a rather weak visible luminescence in the yellow / orange spectral range. We introduce a rather simple postgrowth lithographic technique. Patterning of ZnO nanopillars even on layered conducting and flexible substrate materials using ACG as a low‐temperature growth technique is demonstrated. The economical potential for future applications and devices using ZnO nanopillar arrays is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Epitaxial growth of nonpolar ZnO by MOVPE
Authors: Moriyama Takumi , Fujita Shizuo
Published: March 2006

Epitaxial growth characteristics of nonpolar (M‐ and A‐plane) ZnO on M‐ and R‐plane sapphire substrates were investigated. The growth of ZnO along the c‐axis direction, which aligns parallel to [2‐1‐10] and [01‐11] directions of M‐ and R‐plane sapphire, is achieved under lower growth temperature and/or VI/II ratio, and this growth direction is preferable for smooth lateral growth. Increasing the growth time, the surface becomes rough on M‐plane, while is significantly improved on R‐plane sapphire. The growth behaviour on R‐plane sapphire can be attributed to the small lattice mismatching along the ZnO c‐axis direction and enhanced lateral growth characteristics. From photoluminescence measurements, the appearance of peak at 3.383 eV, which is at higher energy compared to well‐known impurity‐ and/or defect‐related peaks, at 10 K suggests the residual strain in ZnO films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impurity segregation in CdZnTe by photoluminescence mapping
Authors: Horodyský P. , Franc J. , Grill R. , Hlídek P. , Höschl P.
Published: March 2006

Low temperature photoluminescence (PL) mapping is employed to retrospectively monitor the processes taking place during crystal growth. Time evolution of the solidification of the melt is derived from zinc concentration map, which is calculated from energy gap obtained from free‐exciton (FX) reabsorption in the PL spectra. Investigation of the distribution of PL intensities of specific defects shows that at least relative segregation coefficients can be calculated. This method has a potential application in preparation and characterization of pure and homogeneous CdZnTe wafers and also in identification of unknown defects. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of BexCd1–xSe alloys by contactless electroreflectance
Authors: Huang P. J. , Sitarek P. , Huang Y. S. , Maksimov O. , Tamargo M. C. , Firszt F. , Męczyńska H.
Published: March 2006

We present characterization of a Bridgman‐grown wurtzite‐type Be0.075Cd0.925Se mixed crystal and a zinc‐blende Be0.09Cd0.91Se epilayer grown by MBE on InP substrate using contactless electroreflectance in the temperature range of 15 to 400 K. Various interband transitions, originating from the band edge and spin‐orbit splitting critical points, of the samples have been observed. The parameters that describe the temperature dependence of the fundamental and spin split‐off band gaps are evaluated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and optical properties of graded band‐gap CdHgTe and CdMnHgTe structures
Authors: Zakharuk Z. I. , Rybak E. V. , Rarenko H. I. , Koval'chuk M. L. , Tal'yanski E. B. , Fochuk P. M.
Published: March 2006

The present paper deals with the technology of CdTe, Cd1–yMnyTe substrates and CdxHg1–xTe, CdxMnyHg1–x–yTe graded band‐gap structures (GBS). Investigation results of structural quality, IR‐radiation transmission and optical density of the GBS are represented. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the thermophysical parameters of Zn1–xBexSe mixed crystals by means of photothermal techniques
Authors: Zakrzewski J. , Maliński M. , Pawlak M. , Firszt F. , Łęgowski S. , Męczyńska H. , Strzałkowski K.
Published: March 2006

This paper presents the results of the studies of a thermal diffusivity of a series of mixed Zn1–xBexSe crystals by means of the piezoelectric technique. For determination of a thermal diffusivity of samples the method based on the measurement of the phase of the piezoelectric signal, in the rear configuration, as a function of a frequency of modulation was chosen. This method enabled analysis of the influence of Be concentration and the process of annealing of crystals on the values of their thermal diffusivities. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of growth temperature conditions on electric properties of CdTe:Ge crystals
Authors: Nikonyuk Ye. , Zakharuk Z. , Rarenko A. , Rybak Ye. , Kuchma M. , Shlyakhoviy Vya. , Fochuk P.
Published: March 2006

A model of Ge incorporation into CdTe lattice based on the analysis of temperature influence of post‐growth crystal annealing on CdTe:Ge electric properties is proposed. Ge impurity is mainly placed in Te sublattice in crystals fast cooled from high temperatures. GeTe defect is an acceptor defining the electric and photoelectric properties at T ≤ 290 K. GeCd donors and deep (GeCdVCd)/ acceptors are generated in lesser amount. Long‐term ingot thermal treatment at T < 1090 K causes germanium atom relocalization chiefly into cadmium sublattice. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth optimisation of CdTe epitaxial layers for p‐i ‐n diode X‐ray detector fabrication
Authors: Traversa M. , Marzo F. , Prete P. , Tapfer L. , Cappello A. , Lovergine N. , Mancini A. M.
Published: March 2006

We report on the atmospheric pressure metalorganic vapour phase epitaxy of both nominally undoped and iodine (I) donor doped CdTe layers on high resistivity (111)B CdTe substrates, as a preliminary step towards the fabrication of p‐i‐n diode X‐ray detectors. CdTe epilayers were grown at 330 °C after in‐situ H2 heat treatment of the substrate for surface oxide removal. We show that the homoepitaxy of CdTe critically depends on in‐situ heat treatment temperature (TA), best epilayer morphology and reduced surface roughness being obtained for TA = 350 °C. Secondary ion mass spectrometry analysis of I‐doped samples shows good dopant incorporation, which increases for Te:Cd precursor molar flow ratios in the vapour below unity. I‐doped samples grown under the latter conditions have room temperature resistivity three orders of magnitude lower than for undoped layers and electron concentrations ∼1016 cm–3. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
HgTe segregation process in HgCdTe studied by E1 reflectance peak positions
Authors: Pociask M. , Pukowska B. , Kisiel A. , Sheregii E. M. , Berchenko N. N.
Published: March 2006

Long term diffusion processes near the Cd1–xHgxTe surface influences the electronic structure as is shown in this paper. Measurements of reflectivity and surface characterisation by means of scanning electron microscopy (SEM) were performed for samples with x = 0.4 and x = 0.62. The optical results were compared with the reflectivity spectra obtained 22 years ago using the same samples. We discuss the observed dramatic changes in the optical changes upon the SEM and comparative analysis. E 1 + Δ reflectance peak position corresponds to binary HgTe in both recently investigated samples. That method reflection is sensitive to no more than 120 µm the upper depth of investigated samples. The measurements of the E 1 reflectance peak has proven to be a helpful and convenient tool for mercury telluride segregation near the HgCdTe surface and may be used to determine composition and age of HgCdTe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
CdTe native point defects under Cd saturation
Authors: Fochuk Petro , Panchuk Oleh
Published: March 2006

The high temperature point defect (PD) structure of undoped CdTe under well‐defined Cd vapour pressure was studied. The single crystals were grown by different techniques (vapor phase, THM, classical and high pressure Bridgman methods). By using in situ Hall effect measurements it was established that the native double charged PDs $ {\rm Cr}^{2+}_{\rm i} $ and $ {\rm V}^{2+}_{\rm Te} $ are the dominant donors at t > 500 °C. The formation enthalpies of these PDs were determined from [e–] temperature dependencies (Δ$ {\rm H}_{ {\rm V}^{2+}_{\rm Te} } $=1.3 eV; Δ$ {\rm H}_{ {\rm Cr}^{2+}_{\rm i} } $=2.5 eV). The PD structure modelling demonstrated satisfactory agreement with experimental results both for temperature and Cd vapor pressure dependencies. It showed that $ {\rm V}^{2+}_{\rm Te} $ dominates at low temperatures and $ {\rm Cr}^{2+}_{\rm i} $ begins to prevail at t > 930 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence characterization of cubic CdS epilayers
Authors: Yu Young‐Moon , Choi Yong Dae
Published: March 2006

Cubic CdS epilayers were grown on (100) GaAs substrates by hot‐wall epitaxy and their photoluminescence (PL) characteristics were studied. A heavy hole free exciton peak was observed even at room temperature and a light hole free exciton peak was observed at 30–100 K. The temperature dependence of the free excitonic emission intensity was demonstrated using a two‐step quenching mechanism. The excitation power dependence showed that the PL peak at 2.367 eV is due to the free‐to‐bound transition. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐linear thermal broadening of exciton lines in CdTe self‐organized quantum dots
Authors: Ikeda K. , Ogawa Y. , Minami F. , Kuroda S. , Takita K.
Published: March 2006

Micro‐photoluminescence is used to study the temperature dependence of CdTe self‐assembled quantum dots. The observation of the micro‐photoluminescence spectra with temperature shows that there are two different structures, namely the zero‐phonon line and the phonon sidebands. When the temperature increases, the sidebands become clearer and show substantial broadening. The experimental data are reproduced well by a theoretical model taking into account the carrier‐acoustic‐phonon coupling. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optically pumped ultraviolet lasing of BeMgZnSe based quantum well laser structures
Authors: Niiyama Yuuki , Murata Tomoyuki , Watanabe Masahiro
Published: March 2006

Ultraviolet lasing by optically pumping from BeMgZnSe quantum well laser structures on GaP(001) substrate was demonstrated using molecular beam epitaxy (MBE). The lasing wavelength was 373 nm at 13 K. The threshold power density at 13 K was 415 kW/cm2. In addition, the characteristic temperature from 13 to 90 K was 87 K. The lasing was confirmed up to 130 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth and study of ZnCdSe/ZnSSe MQW structures for green VCSELs
Authors: Kuznetsov P. I. , Yakushcheva G. G. , Jitov V. A. , Zakharov L. Yu. , Shchamkhalova B. S. , Kozlovsky V. I. , Sannikov D. A. , Skasyrsky Ya. K. , Tiberi M. D.
Published: March 2006

ZnCdSe/ZnSSe MQW structures for an electron beam pumped VCSEL with resonant periodic gain were grown by MOVPE at 425–470 °C. Strong contamination of the structure by Ga from a GaAs substrate was found and its effect on the growth rate and photoluminescence characteristics was studied. A protective thin ZnSSe layer deposited at lower temperature (350 °C) or thin layers of ZnS and ZnS/ZnSSe SL grown at temperature 425–470 °C prevent Ga penetration and allowed improving the quality and periodicity of the structure. Based on the grown MQW structure, green VCSEL was fabricated. Lasing at 542 nm with 3 W output power was achieved at RT and 40 keV. The threshold was as low as 8 A/cm2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Suppression of electron‐spin relaxation induced by magnetic fields in a Cd1–xMnxTe quantum well
Authors: Seo K. , Kayanuma K. , Aoshima I. , Nishibayashi K. , Souma I. , Murayama A. , Oka Y.
Published: March 2006

Carrier‐spin relaxation under a magnetic field has been studied in a diluted magnetic semiconductor quantum well (DMS‐QW) of Cd0.95Mn0.05Te, by means of pump‐probe absorption spectroscopy. With resonant excitation using a circularly polarized pump‐pulse, dynamical spin‐flip processes of an electron and heavy‐hole (hh) are clearly observed in time dependences of the circularly polarized differential absorbance. In 0 T, time constants of 17 ps and 0.4 ps for the electron‐ and hh‐spin relaxations in the Cd0.95Mn0.05Te QW are shorter than those of 46 ps and 1.0 ps in a non‐magnetic CdTe QW, due to s‐d exchange interactions between the carriers and Mn spins. The spin‐flip time of the electron due to the exchange mechanism is determined as 27 ps. In an intense magnetic field of 5 T, the electron‐spin relaxation due to the exchange mechanism is found to be strongly suppressed in the DMS‐QW by magnetic‐field‐induced pinning of the Mn spins, exhibiting a longer time constant of 29 ps than that of 17 ps in 0 T. The role of LO‐phonon is also discussed in the electron‐spin relaxation under magnetic fields. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence from Cd(Se,Te) quantum dots in a ZnSe matrix
Authors: Lyublinskaya O. G. , Sedova I. V. , Sorokin S. V. , Nekrutkina O. V. , Toropov A. A. , Ivanov S. V.
Published: March 2006

We report on the photoluminescence (PL) and PL excitation studies of CdSe/ZnSe quantum dots (QDs) grown by molecular beam epitaxy using super‐strained CdTe fractional monolayer deposition prior to the CdSe growth. We have shown that introduction of CdTe stressor initiates the formation of a dense array of Cd(Se,Te) QDs and demonstrated the co‐existence of type‐I and type‐II structures within the dot sheet. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of Cd(Zn)Se/ZnMgSSe heterostructures with fractional QD‐like CdSe insertions at high excitation levels
Authors: Lutsenko E. V. , Gurskii A. L. , Pavlovskii V. N. , Zubialevich V. Z. , Yablonskii G. P. , Sedova I. V. , Sorokin S. V. , Toropov A. A. , Ivanov S. V. , Kop'ev P. S.
Published: March 2006

It was found that in the Cd(Zn)Se/ZnMgSSe heterostructures with QD‐like CdSe insertions in the lasing regime the structure changes take place manifesting itself, first, in the irreversible blue shift of the laser radiation spectra. This process depends on excitation intensity and on the cavity length, correlating with the inherent radiation density in the cavity. At excitation densities above 250 kW/cm2, the reduction of the radiative efficiency was observed. The second process is the increase of radiation intensity during laser operation under certain excitation conditions caused by the self‐annealing of the laser structure induced by the inherent laser light and resulting in a decrease of the laser threshold by about 15–20%. Choosing the appropriate excitation regime, one may prolong the lifetime of this type of lasers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of annealing influence on electrical and morphological properties of ZnO:Ga thin films
Authors: Khranovskyy V. , Grossner U. , Lasorenko V. , Lashkarev G. , Svensson B. G. , Yakimova R.
Published: March 2006

In this study, the influence of thermal annealing in different ambients on the electrical and morphological properties of Ga‐doped ZnO films with 1wt.% gallium acetylacetonate in the precursor mix is investigated systematically. As‐grown samples were prepared on c‐plane Al2O3 by PEMOCVD with a substrate temperature of 300 °C and possess a resistivity of about 10–2 Ω cm. The annealing was realized in isochronal steps between 300 to 1000 °C for 1 hour in argon and air ambient, respectively. The resistivity of the films was found to be dependent on the annealing atmosphere. During annealing in air, the resisitivity increases monotically with an abrupt reduction at 800 °C, whereas the annealing in argon does not induce significant changes but results in two clear minima at 300 °C and 800 °C. These effects are explained with crystal improvement at low temperature (300 °C) and successive dopant activation at higher temperature (800 °C). Furthermore, an anomalous surface flattening at 800°C was observed. The obtained results suggest that the annealing procedure does allow to decrease the resistivity and roughness of as‐grown ZnO:Ga films, what would be beneficial for the application of PEMOCVD‐grown ZnO thin films for the formation of abrupt junctions in p–n device structures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)