bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and analysis of interference in Listen‐Before‐Talk spectrum access schemes
Authors: Leu Alexe E. , McHenry Mark , Mark Brian L.
Published: March 2006

Spectrum measurement studies have shown that substantial portions of the allocated wireless spectrum are highly underutilized. Frequency‐agile radios (FARs) have the potential to make opportunistic use of such spectrum holes without causing harmful interference to users of the allocated spectrum. Toward this goal, we develop a framework for modeling the interference caused by FARs employing spectrum access mechanisms based on the simple Listen‐Before‐Talk (LBT) scheme. Two variations of LBT are considered: individual LBT, whereby the FARs act independently of each other; and collaborative LBT, whereby the FARs communicate with each other in order to more accurately identify the spectrum holes. Our analysis of the LBT scheme reveals the fundamental interdependencies among key system design metrics and provides a basis for analyzing more complex spectrum access methods. In particular, the analysis of LBT provides a lower bound on the capacity gain achievable by FARs employing spectrum‐sharing schemes. Our numerical results show that the individual LBT scheme can provide substantial capacity gains, while even more gain can be achieved using the collaborative LBT schemes. Our analysis suggests that much greater gains should be achievable via spectrum access schemes that incorporate location information and/or more sophisticated group behaviors. Copyright © 2006 John Wiley & Sons, Ltd.
A bidirected generalization of network matrices
Authors: Appa Gautam , Kotnyek Balázs
Published: February 2006

We define binet matrices, which furnish a direct generalization of totally unimodular network matrices and arise from the node‐edge incidence matrices of bidirected graphs in the same way as network matrices do from directed graphs. We develop the necessary theory, give binet representations for interesting sets of matrices, characterize totally unimodular binet matrices and discuss the recognition problem. We also prove that binet constraint matrices guarantee half‐integral optimal solutions to linear programs. © 2006 Wiley Periodicals, Inc. NETWORKS, Vol. 47(4), 185–198 2006
Prenatal diagnosis and molecular cytogenetic characterisation of a small de novo interstitial duplication 16q11.2‐q13
Authors: Trimborn Marc , Wegner Rolf‐Dieter , Tönnies Holger , Sarioglu Nanette , Albig Matthias , Neitzel Heidemarie
Published: February 2006

We describe the first prenatally detected case of a small de novo interstitial duplication of chromosome 16q. This chromosomal aberration is extremely rare. Amniocentesis was indicated by advanced maternal age only. Ultrasound examinations of the foetus showed no abnormalities. Conventional and molecular cytogenetic analyses on cultured amniocytes by comparative genomic hybridisation (CGH) and fluorescence in situ hybridisation (FISH) using partial chromosome paints and a locus‐specific YAC clone revealed a de novo direct duplication of the chromosomal region 16q11.2‐q13 leading to a partial trisomy 16q (46,XX,dup(16)(q11.2q13)). There are only five postnatal reports of comparable duplications involving this chromosomal region. These patients presented with little or no associated dysmorphic features but with significant neurodevelopmental delay and severe behavioural problems. After genetic counselling, the parents opted for termination of pregnancy. Post‐mortem examination showed slight facial dysmorphic signs, minor dysgenesis of the ovaries and an atypical outflow of the arteria thyroidea ima. Copyright © 2006 John Wiley & Sons, Ltd.
Prenatal findings and molecular cytogenetic analyses of partial trisomy 12q (12q24.32→qter) and partial monosomy 21q (21q22.2→qter)
Authors: Chen Chih‐Ping , Chern Schu‐Rern , Lin Chyi‐Chyang , Wang Tzu‐Hao , Li Yueh‐Chun , Hsieh Lie‐Jiau , Lee Chen‐Chi , Hua Hui‐Min , Wang Wayseen
Published: February 2006

Objectives

To present the prenatal findings and molecular cytogenetic analyses of partial trisomy 12q and partial monosomy 21q, and a review of the literature.

Methods

Amniocentesis was performed at 23 gestational weeks in a 33‐year‐old woman because of abnormal sonographic findings. Amniocentesis revealed a derivative chromosome 21, or der(21), with a deletion on the region of 21q22.2 and an addendum of a small chromosomal segment of unknown origin. The maternal karyotype was subsequently found to be 46,XX,t(12;21)(q24.32;q22.2). Level II ultrasound showed microcephaly, micrognathia, a ventricular septal defect, and rocker‐bottom feet. The pregnancy was terminated. A malformed infant was delivered without the phenotype of holoprosencephaly (HPE). Fluorescence in situ hybridization (FISH) and polymorphic DNA markers were used to investigate the involved chromosomal segments.

Results

FISH study showed the absence of the signal of 21q subtelomeric probe and the presence of the signal of 12q subtelomeric probe in the der(21).The fetal karyotype was 46,XY,der(21) t(12;21)(q24.32;q22.2)mat. Genetic marker analysis showed a deletion at 21q22.2 and a breakpoint between D21S156 (present) and D21S1245 (absent). The deleted segment was measured about 4.5 Mb encompassing the HPE critical region.

Conclusions

Molecular genetic analyses help in determining the prenatally detected unbalanced cryptic translocation as well as parental balanced subtle translocation. A duplication of 12q24.32→qter and a deletion of 21q22.2→qter may be associated with prenatal sonographic findings of microcephaly, borderline ventriculomegaly and cerebellar hypoplasia, micrognathia, a ventricular septal defect, and rocker‐bottom feet. Haploinsufficiency of the HPE critical region at 21q22.3 may not cause an HPE phenotype. Copyright © 2006 John Wiley & Sons, Ltd.
Isodicentric Yp: prenatal diagnosis and outcome in 12 cases
Authors: Bruyère H. , Speevak M. D. , Winsor E. J. T. , de Fréminville B. , Farrell S. A. , McGowan‐Jordan J. , McGillivray B. , Chitayat D. , McFadden D. , Adouard V. , Terespolsky D. , Prieur F. , Pantzar T. , Hrynchak M.
Published: March 2006

Objectives

To present the prenatal cytogenetic findings and postnatal outcome of 12 cases with an isodicentric chromosome composed of the short arm of the Y chromosome.

To review the literature and provide recommendations for cytogenetic analysis and counseling.

Methods

Prenatal and postnatal cytogenetic data and clinical findings of isodicentric Yp ascertained in six institutions were gathered and reviewed.

Results

Nine of the twelve cases were referred for advanced maternal age (AMA), one of which was a twin pregnancy with one twin having an increased nuchal translucency measurement. The remaining cases were referred owing to a family history of hemophilia and an abnormal maternal serum screen, respectively. Nine of these pregnancies resulted in the birth of a normal‐appearing male infant with subsequent normal growth and psychomotor development. Follow‐up ranged from birth to 7 years. In two cases, the pregnancy was terminated and the fetuses showed male external genitalia. In the case ascertained because of an increased nuchal translucency measurement, the prenatal diagnosis of 45,X was made. At birth, there were ambiguous genitalia, and postnatal cytogenetic studies found an isodicentric Yp. In 11 of the 12 cases, mosaicism was present.

Conclusion

Our cases show that the prenatal finding of an isodicentric Yp, with or without 45,X mosaicism, is compatible with normal male phenotype in most cases, particularly in the absence of other anomalies. To ensure accuracy in cytogenetic reporting and prenatal counseling, the identification of a structurally abnormal or small Y chromosome, either alone or in the presence of 45,X colonies, should be followed immediately by confirmatory molecular cytogenetic investigations as well as by ultrasound determination of the phenotypic sex of the fetus. Copyright © 2006 John Wiley & Sons, Ltd.
Benefit assessment of therapeutic products: the Centers for Education and Research on Therapeutics
Authors: Califf Robert M. ,   for the CERTs Benefit Assessment Workshop Participants
Published: February 2006

The ability to manage risk depends critically on an understanding of the degree to which a known risk is balanced by the probability of a clinical benefit. Despite the massive emphasis on risk and risk management in the past few years and the long‐term focus on defining benefit in the regulatory system, considerable uncertainty remains about the methods of defining benefit and how to operationalize this knowledge. In this ‘think tank,’ part of a larger series on risk management, issues were divided into those that can be identified before a study is initiated, those that commonly arise after a study is completed, biomarkers and surrogates, use of benefit findings in defining quality and performance indicators, implementation of findings into health systems and formularies, and methods of comparative trials. Key categories for the establishment of a research agenda to fill in gaps in our understanding of assessing benefit were developed by the group. Copyright © 2006 John Wiley & Sons, Ltd.
Thermal properties and non‐isothermal crystallization behavior of biodegradable poly(p‐dioxanone)/poly(vinyl alcohol) blends
Authors: Zhou Zhi‐Xuan , Wang Xiu‐Li , Wang Yu‐Zhong , Yang Ke‐Ke , Chen Si‐Chong , Wu Gang , Li Jun
Published: March 2006

Blends of two biodegradable semicrystalline polymers, poly(p‐dioxanone) (PPDO) and poly(vinyl alcohol) (PVA) were prepared with different compositions. The thermal stability, phase morphology and thermal behavior of the blends were studied by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). From the TGA data, it can be seen that the addition of PVA improves the thermal stability of PPDO. DSC analysis showed that the glass transition temperature (Tg) and the melting temperature (Tm) of PPDO in the blends were nearly constant and equal to the values for neat PPDO, thus suggesting that PPDO and PVA are immiscible. It was found from the SEM images that the blends were phase‐separated, which was consistent with the DSC results. Additionally, non‐isothermal crystallization under controlled cooling rates was explored, and the Ozawa theory was employed to describe the non‐isothermal crystallization kinetics. Copyright © 2006 Society of Chemical Industry
Study on spatial–temporal kinetics of photo‐initiated frontal polymerization in stacked reaction cells
Authors: Tao Youji , Yang Jianwen , Zeng Zhaohua , Cui Yanyan , Chen Yonglie
Published: March 2006

The spatial–temporal kinetics for photo‐initiated frontal polymerization(PFP) of isobornyl acrylate with 2,4,6‐trimethylbenzoyldiphenyl phosphine oxide (TPO) as photobleaching initiator was studied experimentally in stacked reaction cells. FTIR and NMR spectroscopy were employed to measure the polymerization conversion, which is dependent on the exposure time, sample depth, light intensity and photo‐initiator concentration. The experimental results are consistent with the theoretical model prediction and show that prolonged irradiation time, higher light intensity and lower photo‐initiator concentration are favorable in enhancing the advance of the polymerization front. The depth‐resolved GPC analysis shows that the average molecular weight of the PFP product dramatically increases with sample depth, while the molecular weight polydispersity reduces steadily with increase in sample depth. Copyright © 2006 Society of Chemical Industry
Synthesis of polyblends from polypropylene and poly(R,S)‐β‐hydroxybutyrate, and their characterization
Authors: Arcana I Made , Sulaeman Aminudin , Pandiangan Kamisah D , Handoko Arie , Ledyastuti Mia
Published: March 2006

Blends of modified polypropylene (PP) with poly(R,S)‐β‐hydroxybutyrate (PHB) were prepared by casting polymer solutions, followed by compression molding into thin films. The modified polypropylene was obtained by oxidation with hydrogen peroxide. Oxidation of polypropylene produced new functional groups such as carbonyl and hydroxyl groups on the polymer chain, and a decrease in molecular weight and crystallinity of the polymers. Maximum crystallinity and mechanical properties of the polyblends were found with a PP/PHB ratio of 90/10 (w/w), and then decreased with increasing PHB content in the polyblends. Biodegradability of the polyblends was lower than that of bacterial and synthetic PHBs. Furthermore, an increase of PHB proportion in the polyblends resulted in highly non‐compatible polyblends. Hence only PHB and small parts of the polyblends were decomposed by microorganisms. Copyright © 2006 Society of Chemical Industry
Stabilized dispersions of titania nanoparticles via a sol–gel process and applications in UV‐curable hybrid systems
Authors: Zhang Xiahong , Yang Jianwen , Zeng Zhaohua , Huang Liang , Chen Yonglie , Wang Haihua
Published: March 2006

Organic–inorganic hybrid UV‐curable coatings were synthesized through blending UV‐curable components and stabilized titania sol prepared via a sol–gel process of tetrabutyl titanate (TBT) with three different stabilizers, acetylacetone (Acac), isopropyl tri(dioctyl)pyrophosphato titanate coupling agent (TTPO) and a polymerizable organic phosphoric acid (MAP). The size and the dispersion of titania particle in the UV‐cured organic matrix were dominated by the properties of these stabilizers. A cured hybrid film with titania particle size around 20 nm was obtained when TTPO was utilized as protection agent for the sol. It is interesting that the hardness and flexibility of the photocured hybrid films were improved simultaneously, in contrast to results with neat organic UV‐curable formulations. Copyright © 2006 Society of Chemical Industry
Synthesis and evaluation of photoluminescent and electrochemical properties of new aromatic polyamides and polyimides with a kink 1,2‐phenylenediamine moiety
Authors: Liou Guey‐Sheng , Yang Yi‐Lung , Su Yuhlong Oliver
Published: March 2006

A series of novel triphenylamine‐containing aromatic polyamides and polyimides having a crank and twisted noncoplanar structures were synthesized in inherent viscosities of 0.14–0.64 dL/g and 0.11–0.67 dL/g, respectively. These polymers had useful levels of thermal stability associated with relatively high glass‐transition temperatures (174–311 °C). They exhibited strong UV–Vis absorption bands at around 300 nm in NMP solutions. The PL spectra of these polymers in NMP solutions (1 × 10−5 M) showed maximum peaks around 396–479 nm. The hole‐transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammetry (CV) of the polymer films cast onto an indium‐tin oxide (ITO)‐coated glass substrate exhibited two reversible oxidation redox couples at potentials of 0.70–1.01 V and 1.10–1.46 V, respectively, vs. Ag/AgCl in acetonitrile solution. The polymer films revealed electrochromic characteristics, with a color change from neutral pale yellowish to green and then to a blue oxidized form at applied potentials ranging from 0.00 to 1.75 V. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2587–2603, 2006
Acrylic acid level and adhesive performance and peel master‐curves of acrylic pressure‐sensitive adhesives
Authors: Gower M. D. , Shanks R. A.
Published: March 2006

Three series of pressure‐sensitive adhesives were prepared with constant glass‐transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate (EHA), methyl methacrylate (MMA), and acrylic acid (AA). Within each polymer series, the proportion of AA monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. Adhesion performance was assessed by measurement of loop tack, static shear resistance, and through the construction of peel master‐curves. Peel master‐curves were generated through peel tests conducted over a range of temperatures and peel rates and through application of the time–temperature superposition principle. Bulk effects dominated by polymer zero shear viscosity change as AA and EHA levels were varied were attributed to the observed effect on static shear resistance and the horizontal displacements of peel master‐curves. Static shear resistance was found to strongly correlate with log(aC), a parameter introduced to horizontally shift peel master‐curves to form a superposed, “super master‐curve”. An interfacial interaction was proposed to account for deviations observed when loop tack was correlated with log(aC). Surface rearrangements via hydrogen bonding with the test substrate were suggested as responsible for the interfacial interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1237–1252, 2006
Metallocene copolymers of propene and 1‐hexene: The influence of the comonomer content and thermal history on the structure and mechanical properties
Authors: López‐Majada J. M. , Palza H. , Guevara J. L. , Quijada R. , Martínez M. C. , Benavente R. , Pereña J. M. , Pérez E. , Cerrada M. L.
Published: March 2006

The relationships between the structure and properties have been established for copolymers of propylene and 1‐hexene synthesized with an isotactic metallocene catalyst system. The most important factor affecting the structure and properties of these copolymers is the comonomer content. The thermal treatment, that is, the rate of cooling from the melt, is also important. These factors affect the thermal properties, the degree of crystallinity, and therefore the structural parameters and the viscoelastic behavior. A slow cooling from the melt favors the formation of the γ phase instead of the α modification. Regarding the viscoelastic behavior, the β relaxation, associated with the glass‐transition temperature, is shifted to lower temperatures and its intensity is increased as the 1‐hexene content raises. The microhardness values are correlated with those of the storage modulus deduced from dynamic mechanical thermal analysis curves, and good linear relations have been obtained between these parameters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1253–1267, 2006
Correlated mutations: Advances and limitations. A study on fusion proteins and on the Cohesin‐Dockerin families
Authors: Halperin Inbal , Wolfson Haim , Nussinov Ruth
Published: February 2006

Correlated mutations have been repeatedly exploited for intramolecular contact map prediction. Over the last decade these efforts yielded several methods for measuring correlated mutations. Nevertheless, the application of correlated mutations for the prediction of intermolecular interactions has not yet been explored. This gap is due to several obstacles, such as 3D complexes availability, paralog discrimination, and the availability of sequence pairs that are required for inter‐ but not intramolecular analyses. Here we selected for analysis fusion protein families that bypass some of these obstacles. We find that several correlated mutation measurements yield reasonable accuracy for intramolecular contact map prediction on the fusion dataset. However, the accuracy level drops sharply in intermolecular contacts prediction. This drop in accuracy does not occur always. In the Cohesin‐Dockerin family, reasonable accuracy is achieved in the prediction of both intra‐ and intermolecular contacts. The Cohesin‐Dockerin family is well suited for correlated mutation analysis. Because, however, this family constitutes a special case (it has radical mutations, has domain repeats, within each species each Dockerin domain interacts with each Cohesin domain, see below), the successful prediction in this family does not point to a general potential in using correlated mutations for predicting intermolecular contacts. Overall, the results of our study indicate that current methodologies of correlated mutations analysis are not suitable for large‐scale intermolecular contact prediction, and thus cannot assist in docking. With current measurements, sequence availability, sequence annotations, and underdeveloped sequence pairing methods, correlated mutations can yield reasonable accuracy only for a handful of families. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Defect‐related emission in CdS films grown directly on hydrogen‐terminated Si(111) substrates
Authors: Seto S. , Kuroda T. , Suzuki K.
Published: March 2006

Defect‐related emission at 2.451 eV in epitaxial CdS films on Si(111) substrates was observed for the first time in low‐temperatures photoluminescence spectra. Temperature and excitation intensity dependence of the defect‐related emission were measured to examine its emission mechanism. It was shown that this defect‐related emission in CdS hetero‐epitaxial films exhibits similar behaviours to the so‐called “Y‐line” observed in other zincblende structure II‐VI semiconductor films such as ZnSe/GaAs or ZnTe/GaAs heteroepitaxial films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of the vapour grown CdTe crystals for high energy radiation detectors
Authors: Popovych V. D. , Virt I. S. , Tsutsura D. I. , Tsybrii (Ivasiv) Z. F. , Sizov F. F. , Parfenjuk O. A. , Ilashchuk M. I.
Published: March 2006

Growth steps and set‐up for the pure and chlorine doped cadmium telluride single crystals preparation by a vertical configuration of sublimation travelling heater method without seeding are described. The structural, electrical and transport properties of as‐grown material were investigated by different techniques: infrared transmission spectroscopy, double‐crystal X‐ray diffractometry, Hall effect, conductivity, photoelectric measurements and chemical etching. It was concluded that the most suitable material for fabrication of X‐ray and γ‐ray non‐cooling detectors are single crystals doped with Cl in the range of NCl = 1018–1019 cm–3. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of high efficient green LEDs of ZnSSe:Te‐ZnMgSSe DH structure on p‐GaAs and its degradation mechanism
Authors: Abe T. , Makimoto K. , Adachi M. , Tanikawa T. , Inoue N. , Nishinaga T. , Kasada H. , Ando K.
Published: March 2006

We present new green double‐hetero (DH) structure light‐emitting diodes (LEDs) of ZnSSe:Te (active layer)–ZnMgSSe (cladding layer) on p‐type GaAs substrates grown by molecular beam epitaxy (MBE).We have confirmed very efficient green emission in Te‐bias modulation doped ZnSSe:Te consists of ZnSSe:Te (Te: 2%, 50 Å)/ZnSSe:Te (Te: 5%, 50 Å) superlattice. A LED with this modulation doping also shows a strong durability for device degradation due to effective Te‐hardening effect. A new LED structure on ptype GaAs exhibits a high extraction efficiency of light emission, which is three times larger in magnitude than LEDs on n‐type GaAs. The new LED also reveals a long device lifetime (in bare chip) over 1300 hours under 3A/cm2 at room temperature. From a simple aging test on the green LEDs, gradual degradation is classified into “slow‐mode degradation”, which is caused by a generation of point defects (donor‐like centers) in p‐type ZnMgSSe cladding layer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrophysical and cathodoluminescent properties of low‐dimensional CdSSe/CdS structure
Authors: Kozlovsky V. I. , Kuznetsov P. I. , Litvinov V. G. , Sannikov D. A. , Yakushcheva G. G.
Published: March 2006

The CdSSe/CdS structure grown by metalorganic vapour phase epitaxy (MOVPE) and prepared for vertical cavity surface emitting laser (VCSEL) was investigated by the capacitance‐voltage characteristics (CV), thermostimulated capacity (TSC), current deep level transient spectroscopy (CDLTS) and cathodoluminescence (CL) methods. Deep levels (DLs) with an activation energies 0.279–1.145 eV were detected by CDLTS and TSC. Hole emission from the ground quantized level in the CdSSe quantum well (QW) was studied. The activation energy of hole emission was used for an estimation of the valence band offset in the type‐II CdSSe/CdS heterostructure. Luminescence and laser properties are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Complete magneto‐optical TE‐TM mode conversion in Cd1–xMnxTe waveguide for integrated optical isolator
Authors: Debnath M. C. , Zayets V. , Ando K.
Published: March 2006

Complete magneto‐optical mode conversion was obtained in a 500 nm‐thick graded‐refractive‐index Cd1–x MnxTe waveguide grown on GaAs substrate. For the annealed waveguide, significant improvement of the complete mode conversion ratio was achieved up to 35 nm operational wavelength range. The Cd1–x MnxTe waveguide also showed very low optical loss of 0.2 dB/cm, high magneto‐optical figure‐of‐merit of more than 1000 deg/dB/kG and isolation ratio of more than 20 dB. This result is an important step toward acheiving a practical integrated optical isolator. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐polarised carriers in CdS quasi‐spherical quantum dots
Authors: Sprinzl D. , Nahálková P. , Devreese J. T. , Gladilin V. N. , Malý P. , Němec P.
Published: March 2006

The properties of spin‐polarised carriers in quasi‐spherical CdS quantum dots in a strong confinement regime were investigated by photoluminescence and pump‐probe experiments. The obtained results were explained in terms of time‐dependent occupation probabilities for the lowest exciton states. The electron spin flip time of 3.5 ns was measured at room temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence properties of Zn0.77Cd0.23O/Mg0.04Zn0.96O heterostructures
Authors: Nakamura A. , Ishihara J. , Yamamoto K. , Aoki T. , Temmyo J.
Published: March 2006

Zn1–xCdxO/MgyZn1–yO heterostructures were successfully grown by RPE‐MOCVD and were investigated by photoluminescence (PL) spectroscopy in order to examine the effects on the barrier and active bandgap energy. Double‐heterostructures typically consisting of 15 nm‐thick MgyZn1–yO/z (z = 15, 30, 50, 100 nm)‐thick Zn1–xCdxO/200 nm‐thick MgyZn1–yO were grown on a‐plane sapphire substrate. PL measurements were carried out using a He‐Cd laser (325 nm) at room temperature. The relationship between the dependencies of luminescence intensity and the PL emission wavelength on the Zn1–xCdxO layers by changing the thickness were discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman spectra and phonon modes of MgxZn1–xO alloy films
Authors: Wei Z. P. , Lu Y. M. , Shen D. Z. , Zhang Z. Z. , Wu C. X. , Zhang J. Y. , Yao B. , Fan X. W.
Published: March 2006

Hexagonal MgxZn1–xO alloy layers with 0 ≤ x < 0.3 have been grown by plasma‐assisted molecular beam epitaxy on sapphire (006) and Si (111) substrates. Their crystal structures are characterized by x‐ray diffraction spectroscopy. The nonresonant and resonant Raman spectra were measured using 488 nm line from Ar+ laser, and 325 nm line from He‐Cd laser by backscattering geometry. Four Raman modes (E2high, LO, TO, multiphonon processes) were observed in the nonresonant Raman spectra of hexagonal MgxZn1–xO with different Mg contents. The optical phonon frequencies were found to display one‐mode behaviour for all the samples since no separate ZnO‐ and MgO‐like modes were observed. The long‐wavelength frequencies of ZnO‐like optical phonons measured in the resonant Raman spectra can be expressed as linear functions of x. These behaviours can be explained within a modified random‐element‐ isodisplacement model (MREI). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Negative U‐properties of the oxygen‐vacancy in ZnO
Authors: Pfisterer Daniel , Sann Joachim , Hofmann Detlev M. , Meyer Bruno , Frank Thomas , Pensl Gerhard , Tena‐Zaera R. , Zúñiga‐Pérez J. , Martinez‐Tomas C. , Muñoz‐Sanjosé V.
Published: March 2006

It is shown that the intensity of the oxygen vacancy (VO) related emission in ZnO at 2.45 eV correlates to the concentration of the donor level E4. E4 is located 530 meV below the conduction band and attributed to the VO0/++ recharging. Deep level transient spectroscopy (DLTS) experiments with optical excitation locate the VO2+/+ level position 140 meV below the conduction band and give evidence for the “negative‐ U” properties of the oxygen vacancies in ZnO. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spontaneous phase condensation of CdTe exciton‐polaritons
Authors: Kasprzak J. , Richard M. , André R. , Romestain† R. , Malpuech G. , Kavokin A. , Si Dang Le
Published: March 2006

We have studied CdTe/CdMgTe microcavity samples containing 4 quantum wells and characterized by a vacuum field Rabi‐splitting of 13.2 meV. Electron‐hole pairs were excited at 7.3K by linearly‐polarized light at 1.74 eV provided by a Ti:sapphire laser operating in the pulsed mode (at 80 MHz rate). Spectroscopic imaging in reciprocal space as well as near‐field spectroscopy show that, above a critical stimulation threshold, polaritons in our microcavity undergo a spontaneous transition to a condensed phase characterized by the massive occupation of the polariton ground state. The coherence of this quantum state is evidenced by the spectral and angular narrowing of its emission. We point out the conditions which should be fulfilled to achieve BEC of microcavity polaritons. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of Cd1–x–yBexZnySe mixed crystals via electromodulation spectroscopy
Authors: Liu Y. T. , Sitarek P. , Huang P. J. , Huang Y. S. , Firszt F. , Łęgowski S. , Męczyńska H. , Marasek A. , Paszkowicz W.
Published: March 2006

A detailed optical characterization of three wurtzite‐type Cd1–x–yBexZnySe mixed crystals has been carried out by using contactless electroreflectance (CER) and photoreflectance (PR) in the temperature range of 15 to 400 K. The samples were grown by the modified high pressure Bridgman method. The transition energies of the A, B and C features of Cd1–x–yBexZnySe are determined via a lineshape fit to the CER and PR spectra. The parameters that describe the temperature dependence of the interband transition energies of the features A and C are evaluated and discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of substrate temperature upon photoluminescence and electrical properties of ZnTe in atmospheric pressure MOVPE using tris‐dimethylaminophosphorus
Authors: Hayashida Kazuki , Tanaka Tooru , Nishio Mitsuhiro , Guo Qixin , Tanikawa Tuyoshi , Ogawa Hiroshi
Published: March 2006

The effect of substrate temperature upon the photoluminescence (PL) properties of phosphorus‐doped ZnTe layers grown by atmospheric pressure metalorganic vapor phase epitaxy using tris‐dimethylaminophosphorus as a dopant source has been investigated together with the growth rate behaviour. At a substrate temperature of 400 °C corresponding to the growth condition close to the mass transport to surface kinetic transition region, the PL spectrum at 4 K is characterized by a strong Ia and a weak free‐to‐bound transition emission, implying a P‐doped ZnTe layer of good crystalline quality. For the layers grown at the substrate temperatures away from this temperature, on the other hand, a donor‐acceptor pair recombination emission appears in the spectra. The P‐doped layers exhibit only the edge emission at ∼549 nm in the room temperature PL specrum, independent of substrate temperature. The relationship between the electrical properties of P‐doped layers and the substrate temperature has also clarified. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metastabilities in the electrical characteristics of Au‐CdMnTe Schottky contacts
Authors: Płaczek‐Popko E. , Sierański K. , Trzmiel J. , Szatkowski J. , Nowak A.
Published: March 2006

Schottky Au‐Cd0.99Mn0.01Te:Ga contacts were studied by the use of the capacitance – voltage measurements and thermally stimulated capacitance technique. Capacitance was recorded within 77 K–400 K temperature range. Persistent photocapacitance was observed at temperatures as high as 260 K. Obtained results can be explained assuming the presence of DX centers in the semiconductor and the interface states at the metal–semiconductor interfacial layer. The low temperature photocapacitance has been attributed to the presence of DX centers whereas that observed at higher temperatures has been linked with the interface states. The presence of the interface states has been confirmed by the thermally stimulated capacitance studies performed at various reverse biases. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Compensation and defect passivation processes in polycrystalline CdTe: Cl layers
Authors: Consonni V. , Baier N. , Renet S. , Brambilla A. , Feuillet G.
Published: March 2006

An extensive optical spectroscopy investigation of Polycrystalline Cl doped CdTe layers brings new insights into the compensation and passivation processes typical of such structurally imperfect materials. 10 K Photoluminescence shows that if some of the main Cl related compensation processes are similar in poly‐ and mono‐crystalline materials, specific mechanisms are evidenced in polycrystalline layers involving complexes between chlorine atoms and extrinsic point defects in the vicinity of structural defects (e.g. extended defects). Using low temperature Cathodoluminescence imaging, it is also demonstrated that structural defects can be efficiently passivated by chlorine atoms, leading to improved electro‐optical properties. Finally, using cross‐section photoluminescence on thick layers, we correlate the evolution of the defect levels to that of the structural properties along the growth axis. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phosphorus‐doped ZnMgTe bulk crystals grown by Vertical Bridgman Method
Authors: Saito Katsuhiko , Kinoshita Keisuke , Tanaka Tooru , Nishio Mitsuhiro , Guo Qixin , Ogawa Hiroshi
Published: March 2006

Phosphorus‐doped Zn1–x Mgx Te (0 ≤ x ≤ 0.31) bulk crystals with zinc‐blende structure were grown by vertical Bridgman technique. Single crystalline wafers cut from the ingots have been systematically characterized by energy dispersive X‐ray analysis, photoluminescence, optical reflection and transmission, and Hall measurements together with the evaluation of electroless Pd electrode to Zn0.9Mg0.1Te. The linear increase in the lattice constant and the band‐gap energy with x was confirmed. In photoluminescence spectra at 4.2 K, two distinct band‐edge luminescence peaks were observed, whereas there are no deep emission bands. These peaks were assigned to be bound exciton emission due to neutral P acceptor and a P acceptor related free‐to‐bound transition emission. Electroless Pd electrode shows the specific contact resistance lower than 5 × 10–3 Ω cm2 for the carrier concentration of ∼1017 cm–3. Conductive p ‐type Zn1–x Mgx Te crystals with the carrier concentration of ∼1017 cm–3 were obtained for Mg composition x from 0 to 0.19. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep electron states in indium‐doped Cd0.93Mn0.07Te DLTS study
Authors: Hajdusianek A. , Szatkowski J. , Płaczek‐Popko E. , Sierański K. , Becla P.
Published: March 2006

Electron traps in indium doped Cd0.93Mn0.07Te were studied with Deep Level Transient Spectroscopy. Five electron traps were found (labeled as E1 ‐ E5). Energy levels ET of related defects are equal to E T 1 = 0.09 eV, E T 2 = 0.12 eV, E T 3 = 0.18 eV, E T 4 = 0.56 eV and E T 5 = 0.65 eV. Three of them (E1, E2, E3 ) are related to the defects with thermally activated capture cross section. Electric field enhanced electron emission from the trap E4 was observed and described in the terms of the Poole‐Frenkel ‐ mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
(ZnSe/MgS)/ZnCdSe DBRs grown by molecular beam epitaxy using ZnS as a sulphur source
Authors: Sorokin S. V. , Solnyshkov D. D. , Sedova I. V. , Toropov A. A. , Ivanov S. V. , Kop'ev P. S.
Published: March 2006

MBE growth and study of optical and structural properties of (ZnSe/MgS)/ZnCdSe distributed Bragg reflectors with λ = 520 nm and Rmax = 97% are presented. The samples were grown pseudomorphically on GaAs (001) substrate using ZnS as a sulphur source. The details of MBE growth of such structures are discussed. Scanning electron microscopy, X‐ray diffraction and optical measurements demonstrate good optical and structural characteristics of the Bragg reflectors. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Predominant point defects in tellurium saturated CdTe
Authors: Fochuk P. , Panchuk O. , Korovyanko O. , Verzhak Ye. , Yuriychuk I. , Fatuyev A.
Published: March 2006

High temperature Hall effect measurements at 570–1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ∼870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 × 1016 to 1 × 1017 cm–3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n‐type one. A theoretical analysis of native point defects contents at different conditions in the framework of Krögers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect – the oxygen interstitial acceptor. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High efficiency blue‐violet optical modulators of ZnSe/ZnMgSSe asymmetric coupled quantum wells
Authors: Abe T. , Yoshida T. , Yamane N. , Nishiguchi T. , Kasada H. , Ando K.
Published: March 2006

We report a high efficiency blue‐violet optical modulator consisting of ZnSe/ZnMgSSe asymmetric‐coupled quantum wells (ACQWs). The modulator devices were designed based on the finite element method in the framework of the effective‐mass approximation and grown by molecular beam epitaxy (MBE) systematically. The new device with an electron‐resonant type ACQW of [ZnSe (6 ML)/ZnMgSSe (2 ML)/ZnSe (12 ML)] has revealed a large Stark shift of ΔE ∼ 34 meV at room temperature in low electric field condition of 480 kV/cm. The maximum modulation depth is 51% with transmission configuration, and the devices show very stable operation. Differential absorption coefficients Δα between reverse bias of 0 and 24V are –26000 cm–1 at the ground state exciton resonance (E e1–hh1), and +11500 cm–1 in transparent region below the ground state, which is promising for practical waveguide optical modulators for the short wavelength. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of self‐assembled CdSe quantum dots in MgS barriers
Authors: Gust Arne , Kruse Carsten , Sebald Kathrin , Lohmeyer Henning , Gutowski Jürgen , Hommel Detlef
Published: March 2006

Samples containing CdSe quantum dots (QDs) embedded in MgS barriers have been grown by molecular beam epitaxy. Photoluminescence (PL) investigations at room temperature show a QD ensemble shift between 240 meV and 280 meV due to the enhanced carrier confinement compared to a reference sample without MgS barriers. Temperature dependent micro‐PL measurements on single QDs indicate an activation energy of 70 meV for MgS barriers, which is a factor of 2.5 higher compared to ZnS0.06Se0.94 barriers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical spectroscopy of CdTe/ZnTe quantum dot multilayers
Authors: Onishchenko Evgeny E. , Bagaev Victor S. , Karczewski Grzegorz , Kozyrev Stanislav P. , Kucherenko Inna V. , Mel'nik Nikolai N. , Vinogradov Vladimir S. , Vodop'yanov† Lev K.
Published: March 2006

Electronic and vibrational states in CdTe/ZnTe quantum dot multilayers grown on a thick ZnTe buffer layer are studied using optical spectroscopy methods (photoluminescence in a wide temperature range, Raman scattering, and IR reflection). It has been established that a new band appears in the Raman spectra of sample with a small ZnTe spacer layer thickness, which can be ascribed to a vibrational mode of two closely‐spaced quantum dots. A comparison of results obtained under studies of structures grown on ZnTe and CdTe buffer layers shows that change of strain distribution pattern substantially modifies electron and optical spectra of QD structures. In particular, it can result in change of the band diagram type. A reason of anomalous peak position shift of quantum dot emission band is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient spin injection in self‐assembled CdSe quantum dots coupled with a diluted magnetic semiconductor quantum well
Authors: Asahina T. , Kayanuma K. , Nishibayashi K. , Souma I. , Hyomi K. , Murayama A. , Oka Y.
Published: March 2006

Electron‐spin injection has been studied from a diluted magnetic semiconductor quantum well (DMS‐QW) of Zn1–x–yCdxMnySe into self‐assembled quantum dots (QDs) of CdSe through a tunneling barrier of ZnSe. The spin injection is experimentally evidenced by time‐resolved circularly polarized photoluminescence (PL) in the QDs with the circular polarization degree up to 40%. The fast injection time of 20 ps can be attributed to the tunneling probability of the electron from the DMS‐QW side. In addition to this, circularly polarized PL with the lifetime of 3.5 ns is simultaneously observed, indicating type‐II transition between the electron in the QDs and the spin‐polarized heavy hole in the DMS‐QW. Those PL energies directly indicate that the electron tunneling is assisted by a LO phonon in the CdSe QD. The spin injection via LO‐phonon‐assisted resonant electron tunneling provides an efficient spin‐injection process into the self‐assembled QD exhibiting strong quantum confinement effects. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropic spatial correlation of CdSe/Zn(S)Se quantum dot stacks grown by MBE
Authors: Roventa E. , Alexe G. , Schowalter M. , Kröger R. , Hommel D. , Rosenauer A.
Published: March 2006

Spatial correlation of five‐ and ten‐fold stacks of CdSe quantum dots separated by Zn(S)Se spacers with different thicknesses has been investigated in plan‐view and cross‐section geometry using transmission electron microscopy and compared with grazing incidence x‐ray results. For different spacer layer thicknesses investigations revealed a strain induced ordering process which breaks down for spacer layers thicker than 8 nm. An anisotropy of the lateral alignment of the quantum dots was also found, connected with the anisotropic strain distribution around the quantum dots and surface diffusion. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular beam epitaxy and structural properties of ZnCrS
Authors: Ichino Kunio , Morimoto Yasuharu , Kobayashi Hiroshi
Published: March 2006

Zn1–x Crx S thin films were grown on GaP substrates by molecular beam epitaxy. Maximum Cr content of the films in this study was x = 0.04 which was limited by the maximum operating temperature of the Cr cell in our growth system. For the Cr content of x < 0.015, zinc blende (ZB) crystals of Zn1–x Crx S were epitaxially grown, while the phase separation was observed for the larger Cr content. For the ZB thin films, lattice constant seems to depend on the growth temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of photoluminescence from annealed bulk‐ZnO single crystals
Authors: Yoneta M. , Yoshino K. , Ohishi M. , Honda M. , Saito H.
Published: March 2006

We have investigated the influence of rapid thermal annealing on the photoluminescence of bulk‐ZnO single crystal. As‐grown ZnO wafer, illuminated by 325 nm ultraviolet light at 4.2 K, emitted the visible luminescence of pale green centered of 2.29 eV. The luminescence was observed by the anneal at the temperature range between 400 °C and 1000 °C, however, its intensity decreased with anneal temperature. The free‐exciton and the 2.18 eV emission line were obtaiend by the anneal at 1200 °C for 60 sec. From the X‐ray diffraction and the surface morphology measurments, the improvement of the crystallinity of bulk‐ZnO crystal were confirmed. We suggest that a rapid thermal annealing technique is convenience to improve the the quality of bul‐ZnO single crystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Free exciton luminescence of ZnO:Zn microcrystals under electron beam excitation
Authors: Ichimiya M. , Sawada Y. , Ashida M. , Itoh T.
Published: March 2006

Cathodoluminescence in a ZnO:Zn microparticle has been investigated at room temperature. The luminescence band in the ultraviolet region is attributed to the recombination of free exciton (FE) which is hardly observed under photoexcitation due to the band bending near the particle surface due to ionized oxygen vacancies. The intensity of FE luminescence becomes large in high accelerating voltage where the penetration depth of injected electrons exceeds the width of depletion layer. The band bending is found to be reduced by means of direct injection of electrons to the oxygen vacancies near the surface, and the intensity of FE luminescence increases nonlinearly with the beam current due to the improvement of recombination efficiency by the reduction of surface electric field. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiarities of defect formation processes in ZnSe crystals with isovalent Te impurity
Authors: Makhniy Victor P. , Tkachenko Irina V. , Gorley Petro M. , Horley Paul P. , Dugaev Vitalii K. , Barnaś Joseph , Vieira Maria Manuela , Dobrowolski Witold
Published: March 2006

Using quasi‐chemical reaction methods, we calculated concentrations of equilibrium defects for zinc selenide crystals doped with ZnSe〈Te〉 during the growth process and with ZnSe:Te from the vapour phase. It was found that the main irradiation peak at ħω m ≈1.7 eV for ZnSe〈Te〉 samples is defined with the associates formed by single‐charge intrinsic defects – positive interstitial zinc atoms $ {\rm Zn}^{\bullet}_i $and its negative vacancies $ V_{\rm Zn}^{\prime}$. These vacancies, reaching the concentrations of 1022 cm–3 in ZnSe:Te crystals, are also responsible for the luminescence and absorption peaks at the energies of 2.4 eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vapour growth of II‐VI single crystals doped by transition metals for mid‐infrared lasers
Authors: Akimov V. A. , Frolov M. P. , Korostelin Yu. V. , Kozlovsky V. I. , Landman A. I. , Podmar'kov Yu. P. , Voronov A. A.
Published: March 2006

A modified vapour phase contact‐free method to grow homogeneous single crystals of II‐VI compounds doped by transition metals is presented. Single crystals of ZnSe:Cr, ZnSe:Fe, ZnSe:Co, ZnSe:Ni, CdSe:Cr, ZnTe:Cr, ZnS:Fe and ZnS:Mn with doping level up to 1019 cm–3 have been grown. Efficient lasing at about 2.5 and 4 µm with ZnSe:Cr and ZnSe:Fe crystals respectively has been achieved. Dependence of Fe2+:ZnSe laser characteristics on temperature is presented in more detail. A possibility of using Cr2+:ZnSe laser in intracavity laser spectroscopy is demonstrated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conductivity switching effect in Cd1–xZnxTe films
Authors: Wojciechowski T. , Janik E. , Dynowska E. , Fronc K. , Karczewski G.
Published: March 2006

We report an experimental study of the conductivity switching effect in mono and polycrystalline layers of Cd1–xZnxTe grown by MBE on the Si(001)/Au and n+‐ GaAs(001) substrates. The current‐voltage (I‐V) characteristics of metal‐semiconductor junctions show that the conductivity of the Cd1–xZnxTe structures exhibit two states: high‐ and low‐resistive. Electrical pulses applied to the layers trigger the switching effect between these two states. The coefficient of resistivity switching is of the order of 104 while its reproducibility is repetitive about 100 switching cycles. The bistablity of the conductance in Cd1–xZnxTe layers supports the hypothesis of the ferroelectricity in this material. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)