bluuebunny/crossref_metadata_2025 huggingface dataset:
New Fluorinated Pyrrolidine and Azetidine Amides as Dipeptidyl Peptidase IV Inhibitors.
Authors: Hulin Bernard , Cabral Shawn , Lopaze Michael G. , Van Volkenburg Maria A. , Andrews Kim M. , Parker Janice C.
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Avoiding Pyran Ring Opening During Palladium Acetate Catalyzed C‐Glycosidation of Peracetylated Glycals.
Authors: de la Figuera Natalia , Forns Pilar , Fernandez Joan‐Carles , Fiol Sandra , Fernandez‐Forner Dolors , Albericio Fernando
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Recent Developments in Physicochemical Characterization and Modelling of Ferroalloy Slag Systems
Authors: Jahanshahi S. , Sun S. , Zhang L.
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Modelling of Anisotropic Exchange Coupling in Rare‐Earth—Transition‐Metal Pairs: Applications to Yb3+—Mn2+ and Yb3+—Cr3+ Halide Clusters and Implications to the Light Up‐Conversion
Authors: Atanasov M. , Daul C. , Gudel H. U.
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
N‐Heteroatom‐Substituted Alkanamides
Authors: Blakemore P. R.
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Regioselectivity, Stereoselectivity and Catalysis in Intermolecular Pauson—Khand Reactions: Teaching an Old Dog New Tricks
Authors: Laschat Sabine , Becheanu Armand , Bell Thomas , Baro Angelika
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Single‐Reference ab initio Methods for the Calculation of Excited States of Large Molecules
Authors: Dreuw Andreas , Head‐Gordon Martin
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Theoretical Studies of Paracyclophanes and Related Molecules
Authors: Salcedo Roberto , Martinez Ana , Sansores L. Enrique , Mireles Norma
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
A Comparison of Stiff ODE Solvers for Astrochemical Kinetics Problems
Authors: Nejad Lida A. M.
Published: January 2006

For Abstract see ChemInform Abstract in Full Text.
Reproducibility of the diagnosis of atypical endometrial hyperplasia
Authors: Zaino Richard J. , Kauderer James , Trimble Cornelia Liu , Silverberg Steven G. , Curtin John P. , Lim Peter C. , Gallup Donald G.
Published: January 2006

BACKGROUND

Most gynecologists determine therapy based on current International Society of Gynecologic Pathologists (ISGP)/World Health Organization classification of endometrial hyperplasia, the reproducibility of which has been questioned. The Gynecologic Oncology Group (GOG) initiated a protocol to assess the efficacy of hormonal therapy of atypical endometrial hyperplasia (AEH). Primary goals of the first phase (Part A) were to prospectively determine reproducibility of referring institution's pathologist's diagnosis of AEH by a panel of 3 gynecologic pathologists and to determine reproducibility of diagnoses by panel members.

METHODS

Three hundred six women were entered on this protocol with a referring institution's pathologist diagnosis of AEH based on biopsy or curettage. Available slides were assessed independently and interpreted by each of a panel of 3 gynecologic pathologists who used International Society of Gynecologic Pathologists (ISGP)/World Health Organization criteria. The majority diagnosis was based on diagnostic concordance by at least 2 of the 3 panelists.

RESULTS

The referring institution's pathologist's diagnosis of AEH was supported by the majority of the panel in only 38% of cases. Overall kappa value for the panel diagnosis of AEH was 0.28. The majority diagnosis was adenocarcinoma in 29%, cycling endometrium in 7%, and nonatypical hyperplasia in 18% of cases. Unanimous agreement for any diagnosis was reached among all 3 of the panel in 40% of cases. For the panel, paired kappa values for any diagnosis ranged 0.34–0.43, with an overall kappa value of 0.40.

CONCLUSION

Reproducibility of referring institution's pathologists' diagnosis of AEH by a panel of gynecologic pathologists is poor. Both underestimation and overestimation of the severity of the lesion are very common. The level of reproducibility among subspecialist panel members for diagnosis of AEH in these specimens also is poor. Better criteria and better sampling are needed to improve reproducibility of this diagnosis, particularly if it is to be used for clinical decisions. Cancer 2006. © 2006 American Cancer Society.
Cover Picture: Silanediol Protease Inhibitors: From Conception to Validation (Eur. J. Org. Chem. 2/2006)
Authors: Sieburth Scott McN. , Chen Chien‐An
Published: January 2006

The cover picture shows the pathway of silicon from its natural source to an organosilane protease inhibitor. Nearly all silicon exists in the form of silica, commonly encountered as sand. Silica is reduced to silicon, some becoming computer chips and some converted to organosilanes using the Müller‐Rochow (Direct) Process, which transforms chloromethane and chlorobenzene to methyl‐ and phenyl‐substituted chlorosilanes, respectively. When the two small, commercially available reagents at the bottom of the picture are subjected to a sequence of chemical reactions, they are converted into the three silanediol‐based peptide mimics at the top, which are nanomolar inhibitors of the three enzymes angiotensin‐converting enzyme (ACE), HIV protease, and thermolysin (left to right). Details are presented in the Microreview by S. McN. Sieburth and C.‐A. Chen on page 311 ff.
The promise of nanotechnology for separation devices – from a top‐down approach to nature‐inspired separation devices
Authors: Eijkel Jan C. T. , van den Berg Albert
Published: January 2006

An overview is given of the possible applications of nanotechnology to optimise existing separation methods and to enable new methods. Attention is paid to nanotechnological contributions in the fields of HPLC, CEC, sieves, Brownian ratchets and preconcentration units. A brief description is also given of some selection/separation mechanisms that occur in biological (cell) structures and possible future applications of these mechanisms in separation devices are investigated. Especially the active transport in discrete events occurring in cells is mentioned as a potentially powerful separating mechanism.
Centrosome‐, chromosomal‐passenger‐ and cell‐cycle‐associated mRNAs are differentially regulated in the development of sporadic colorectal cancer
Authors: Gerlach Ulrike , Kayser Gian , Walch Axel , Hopt Ulrich , Schulte‐Mönting Jürgen , Werner Martin , Lassmann Silke
Published: January 2006

Dysregulation of the centrosome complex and chromosomal segregation has been associated with aneuploid cells and aggressive solid tumours, but the relevance of this mechanism to the adenoma–carcinoma sequence of sporadic colorectal cancer (sCRC), especially tumours showing chromosomal instability (CIN), is still unknown. In a series of matching normal epithelial cells (n = 41), dysplastic cells (n = 18), and invasive carcinoma cells (n = 41) from cases with sCRC, mRNA levels of the centrosomal kinase Aurora‐A/STK15 and the chromosomal passenger‐ and cell cycle‐associated molecules Incenp, Survivin, Mad‐2, and Cyclin‐D1 were therefore measured with specific reference to the type of genetic instability. Compared with normal epithelium, significant up‐regulation of mRNAs was already present for Aurora‐A/STK15 (p = 0.0313) in dysplastic cells and for all investigated markers in invasive carcinoma. Whereas Aurora‐A/STK15 mRNA levels were similarly up‐regulated in dysplastic and invasive carcinoma cells (p = 0.0797), Survivin (p = 0.0046) and Cyclin‐D1 (p = 0.0017) mRNA levels increased from dysplastic to invasive carcinoma cells. In carcinomas, Incenp mRNA correlated with T category (p = 0.0149), and Survivin (p = 0.0382) and Cyclin‐D1 (p = 0.0185) were associated with tumour differentiation. Importantly, a significantly higher (p = 0.0419) fold‐change of Aurora‐A/STK15 mRNA (p = 0.0419), but not Incenp, Survivin, Mad‐2 or Cyclin‐D1, was observed in sCRC cases with CIN (n = 29) when compared with tumours showing microsatellite instability (MIN, n = 10). The present data are the first to show an early increase of the centrosomal kinase Aurora‐A/STK15 in the adenoma–carcinoma sequence of sCRC. The regulation of this kinase differs in CIN‐ and MIN‐type sCRCs and the pattern of changes is different from those of the cell‐cycle‐associated markers Survivin, Mad‐2, and Cyclin‐D1. This reinforces the concept of preferential dysregulation of the centrosome complex in CIN‐type (aneuploid), compared with MIN‐type, sporadic colorectal cancers and may influence the response to and efficiency of novel therapeutics targeting Aurora kinases. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Potential biomarkers for ischemic heart damage identified in mitochondrial proteins by comparative proteomics
Authors: Kim Nari , Lee Youngsuk , Kim Hyungkyu , Joo Hyun , Youm Jae Boum , Park Won Sun , Warda Mohamad , Cuong Dang Van , Han Jin
Published: January 2006

We used proteomics to detect regional differences in protein expression levels from mitochondrial fractions of control, ischemia–reperfusion (IR), and ischemic preconditioned (IPC) rabbit hearts. Using 2‐DE, we identified 25 mitochondrial proteins that were differentially expressed in the IR heart compared with the control and IPC hearts. For three of the spots, the expression patterns were confirmed by Western blotting analysis. These proteins included 3‐hydroxybutyrate dehydrogenase, prohibitin, 2‐oxoglutarate dehydrogenase, adenosine triphosphate synthases, the reduced form of nicotinamide adenine dinucleotide (NADH) oxidoreductase, translation elongation factor, actin alpha, malate dehydrogenase, NADH dehydrogenase, pyruvate dehydrogenase and the voltage‐dependent anion channel. Interestingly, most of these proteins are associated with the mitochondrial respiratory chain and energy metabolism. The successful use of multiple techniques, including 2‐DE, MALDI‐TOF‐MS and Western blotting analysis demonstrates that proteomic analysis provides appropriate means for identifying cardiac markers for detection of ischemia‐induced cardiac injury.
Entropy capacity determines protein folding
Authors: Galzitskaya Oxana V. , Garbuzynskiy Sergiy O.
Published: January 2006

Search and study of the general principles that govern kinetics and thermodynamics of protein folding generate a new insight into the factors controlling this process. Here, based on the known experimental data and using theoretical modeling of protein folding, we demonstrate that there exists an optimal relationship between the average conformational entropy and the average energy of contacts per residue—that is, an entropy capacity—for fast protein folding. Statistical analysis of conformational entropy and number of contacts per residue for 5829 protein structures from four general structural classes (all‐α, all‐β, α/β, α+β) demonstrates that each class of proteins has its own class‐specific average number of contacts (class α/β has the largest number of contacts) and average conformational entropy per residue (class all‐α has the largest number of rotatable angles ϕ, ψ, and χ per residue). These class‐specific features determine the folding rates: α proteins are the fastest folding proteins, then follow β and α+β proteins, and finally α/β proteins are the slowest ones. Our result is in agreement with the experimental folding rates for 60 proteins. This suggests that structural and sequence properties are important determinants of protein folding rates. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Electron band structure and optical properties of InN and related alloys
Authors: Alexandrov D. , Butcher S. , Tansley T.
Published: January 2006

New metric system called electron metric system having basic metric constant is introduced. The connection between the electron metric system and the external metric system is defined. The symmetry relationships of the multinary semiconductor compound alloys are defined according to the electron metric system. The basic metric constant is found on the basis of diatomic tetrahedral cell. The electron wave vector in the new system is found and the electron energy states are determined. It is shown correlation between them in the multinary crystal. LCAO electron band structures of Inx Al1–x N and of Inx Ga1–x N are presented. The phenomenon tunnel optical absorption is investigated in Inx Al1–x N, in Inx Ga1–x N, in InN containing oxygen and in non‐stoichiometric InN. It is found the optical absorption edges begin in energies 0.2–1.62 eV that are lower than the energy band gaps due to this phenomenon. Existence of excitons of the structure is shown in these semiconductors and it is found that the peaks of the PL spectra correspond to annihilation energies of these excitons that change in interval 0.5–1.01 eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
RF plasma sources for III‐nitrides growth: influence of operating conditions and device geometry on active species production and InN film properties
Authors: Anderson P. A. , Reeves R. J. , Durbin S. M.
Published: January 2006

The optical emission from an RF inductively coupled plasma source has been monitored at various flow rates and RF powers in the spectral range of 500–900 nm. It was found that low powers and high flow rates resulted in emission from the 1st‐positive series of excited molecular nitrogen dominating the spectrum relative to atomic nitrogen. Growth of InN on GaN showed improved electrical properties when the molecular species dominated the spectrum. In contrast, growth of InN on (111) yttrium stabilised zirconia (YSZ) was found to yield films of similar electrical properties at different plasma operating conditions. Reflection high energy electron diffraction (RHEED) patterns were used to monitor the a ‐lattice constant during growth. Films grown on GaN with higher relative atomic flux were found to relax within the first several nm of growth, whereas films grown with higher molecular nitrogen species did not fully relax until approximately 50 nm of growth. These observations suggest that the active nitrogen species plays a significant role in determining how strain is accommodated during InN epitaxy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of crystallographic properties and defects via X‐ray microdiffraction in GaN (0001) layers
Authors: Barabash R. I. , Barabash O. M. , Ice G. E. , Roder C. , Figge S. , Einfeldt S. , Hommel D. , Katona T. M. , Speck J. S. , DenBaars S. P. , Davis R. F.
Published: January 2006

Intrinsic stresses due to lattice mismatch, high densities of threading dislocations, and extrinsic stresses resulting from the mismatch in the coefficients of thermal expansion, are present in almost all III‐Nitride heterostructures. Stress relaxation in the GaN layers occurs in conventional, cantilever (CE) and in pendeo‐epitaxial (PE) films via the formation of additional misfit dislocations, domain boundaries, elastic strain and wing tilt. Polychromatic X‐ray microdiffraction, high resolution monochromatic X‐ray diffraction and SEM analysis have been used to determine the crystallographic properties, misfit dislocations distribution and crystallographic tilts in uncoalesced GaN layers grown by PE and CE. The crystallographic tilt between the GaN(0001) and Si(111) planes was detected in the CE grown samples on Si(111). In contrast there was no tilt between GaN(0001) and SiC(0001) planes in PE grown samples. The wings are tilted upward for both the PE and CE grown uncoalesced GaN layers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stoichiometry effects and the Moss–Burstein effect for InN
Authors: Butcher K. S. A. , Hirshy H. , Perks R. M. , Wintrebert‐Fouquet M. , Chen P. P‐T.
Published: January 2006

We examine the Moss–Burstein effect for InN and demonstrate an independent method for determing its magnitude for high carrier concentration material. Consequently it is shown that the extent of the Moss–Burstein effect is less than 0.72 eV for a high carrier concentration sample with a 1.88 eV absorption edge. Early results are also provided for high band‐gap low carrier concentration InN films that can be grown reprodcibly, vindicating the work of early groups in the field. The role of stoichiometry is examined in relation to point defects that appear to be common to many forms of InN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface band bending at nominally undoped and Mg‐doped InN by Auger Electron Spectroscopy
Authors: Cimalla V. , Niebelschütz M. , Ecke G. , Lebedev V. , Ambacher O. , Himmerlich M. , Krischok S. , Schaefer J. A. , Lu H. , Schaff W. J.
Published: January 2006

Non intentionally doped and Mg‐doped InN layers were analyzed by sputter depth profiling in an Auger electron spectroscopy (AES) equipment and by Ultra‐violet photoelectron spectroscopy (UPS). On the surface of both types of layers a high concentration of oxygen and a strong accumulation of electrons was observed, however, in contrast to the undoped layers the conductivity profile of Mg doped InN shows a strong discontinuity close to the surface. The depth of this discontinuity strongly depends on the oxygen concentration. The energy shift of the InMNN peak was estimated during the depth profiling in order to obtain information about the position of the Fermi level. In the bulk of the Mg‐doped InN the InMNN peak shift of about 0.15 eV demonstrates the influence of the Mg on the Fermi level, while the surface is clearly n‐type. A strong shift of the Fermi level close to the surface was observed, which might be attributed to the formation of In2O3. By the combination of AES and UPS a model for the band bending is proposed, which demonstrates that Mg doping indeed can compensate the n‐type conductivity in the bulk and is therefore a prospective candidate to achieve p‐type doping in InN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Detailed analysis of the dielectric function for wurtzite InN and In‐rich InAlN alloys
Authors: Goldhahn R. , Schley P. , Winzer A. T. , Gobsch G. , Cimalla V. , Ambacher O. , Rakel M. , Cobet C. , Esser N. , Lu H. , Schaff W. J.
Published: January 2006

A detailed analysis of the dielectric function (DF) for wurtzite InN as well as for In‐rich InAlN alloys is presented. The experimental data, covering the energy range from 0.72 up to 9.5 eV, were obtained by ellipsometric studies of an (11&2macr;0) a‐plane InN film and low carrier density (0001) c‐plane films. Model calculations of the imaginary part of the DF around the band gap provide direct insight how to determine the energetic position of the Fermi energy from the experimental results. Then, taking into account both, band gap renormalization and Burstein–Moss shift, the values of the gaps at zero carrier density are calculated. The dependence of the InAlN band gap on the alloy composition is described by a bowing parameter of 4.0 eV. The a‐plane film exhibits a characteristic optical anisotropy below 1 eV which is attributed to the polarization dependence of transition probabilities from the three valence bands at the Γ point of the Brillouin zone into the conduction band. The splitting of 25 meV between the absorption edges for the two polarization directions can be well explained by a crystal field energy of 19 (24) meV if a calculated spin–orbit energy of 13 (5) meV is assumed. All results emphasize a band gap value of wurtzite InN of about 0.68 eV. By fitting the third derivatives of the dielectric function up to 9.5 eV we determine the compositional dependences of the transition energies for at least three critical points of the band structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wells
Authors: Haratizadeh Hamid , Monemar Bo , Amano Hiroshi
Published: January 2006

We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time‐resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self‐energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InGaN(0001) alloys grown in the entire composition range by plasma assisted molecular beam epitaxy
Authors: Iliopoulos E. , Georgakilas A. , Dimakis E. , Adikimenakis A. , Tsagaraki K. , Androulidaki M. , Pelekanos N. T.
Published: January 2006

Indium gallium nitride alloy (0001) films in the entire composition range were grown heteroepitaxially by radio‐frequency plasma assisted molecular beam epitaxy on Ga‐polarity GaN(0001)/Al2O3 substrates. A growth approach based on low substrate temperatures and near‐stoichiometric growth conditions was followed. Under these conditions incorporation efficiency of indium atoms was equal to one. X‐ray diffraction data reveal that phase separation phenomena were effectively suppressed. As the indium mole fraction increased, a tendency of the strain state of the films to change from compressive to tensile was observed. This was attributed to growth through nucleation and coalescence of three‐dimensional InGaN islands with high lattice mismatch on GaN(0001). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantitative electron microscopy of InN–GaN alloys
Authors: Bartel T. , Jinschek J. R. , Freitag B. , Specht P. , Kisielowski C.
Published: January 2006

Time series of high‐resolution lattice images are examined to probe for possible alterations of the indium distribution in GaN/InxGa1–xN/GaN quantum well structures during electron irradiation with energies of 150 kV and 800 kV. By comparison with theory it is reasoned that sample preparation, microscope stability, and chosen acceleration voltages are essential factors that determine the reliability of the results. If considered, it is shown that for relevant time scales of <2 minutes and current densities of 20–40 A/cm2 no measurable alteration of the initial element distribution occurs. A quantitative method is highlighted for the characterization of existing indium fluctuations that are concentration dependent. Consistency between measurements from lattice images, Z‐contrast images, and local band gap measurements support our conclusion. It is argued that the formation of such indium clusters is driven by strain‐dependent spinodal decomposition. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence of n‐InN with low electron concentrations
Authors: Klochikhin Albert , Davydov Valery , Emtsev Vadim , Sakharov Alexey , Kapitonov Vladimir , Andreev Boris , Lu Hai , Schaff William J.
Published: January 2006

Photoluminescence (PL) of n‐InN grown by molecular beam epitaxy with Hall concentrations from 3.6 × 1017 to 1.0 × 1018 cm–3 demonstrates new features as compared with that of the samples of previous generation which are characterized by a higher carrier concentration. The striking dependences of PL spectra on carrier concentration, temperature, and excitation density give evidences of a fast energy relaxation rate of photoholes and their equilibrium distribution over localized states. The well resolved structure consisting of three peaks was observed in the PL spectra of these samples in the energy interval from 0.50 to 0.67 eV at liquid helium and nitrogen temperatures. We attributed one of two low‐energy features of the spectra to the recombination of degenerate electrons with the holes trapped by deep acceptors with a binding energy of Eda = 0.050–0.055 eV and the other one is attributable to the LO‐phonon replica of this band. The higher‐energy PL peak is considered as a complex band formed by two mechanisms. The first one is related to the transitions of electrons to the states of shallow acceptors with a binding energy of Esh = 0.005–0.010 eV and/or to the states of Urbach tail populated by photoholes. The second mechanism contributing to this band is the band‐to‐band recombination of free holes and electrons. Relative intensities of two higher‐energy PL peaks were found to be strongly dependent on temperature and excitation power. At room temperature, the band‐to‐band recombination of free holes and electrons dominates in PL. Experimental results on PL and absorption are described by the model calculations under the assumptions of the band gap equal to 0.665–0.670 eV at zero temperature and zero carrier concentration and the non‐parabolic conduction band with the effective mass at Γ‐point equal to 0.07 of free electron mass. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mass flow and reaction analysis of the growth of GaN by HVPE
Authors: Kempisty P. , Grzegory I. , Boćkowski M. , Krukowski S. , Łucznik B. , Pastuszka B. , Porowski S.
Published: January 2006

HVPE growth in horizontal flow reactor has been analysed using finite element calculations and molecular estimates of the reaction rates. Finite element code FIDAP (commercially available from Fluent Inc.) has been used to calculate the flow pattern in the reactor. In the first approximation it was assumed that the flow pattern is weekly dependent on the temperature distribution in the reactor. It was also assumed that the volume reaction rates can be approximated by temperature independent reaction constants. The HCl + Ga(l) reaction rate has been estimated using ideal gas approximation for HCl vapour.

The degree of HCl to GaCl conversion was obtained in function of the pressure, flow velocity and geometry of the reactor. The conversion dependence on the sticking coefficient of HCl on liquid Ga surface was analysed. It is shown that for the typical design of the reactor, high conversion rates were observed, even for the sticking coefficient as low as 0.001. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Full‐potential study of d‐electrons effects on the electronic structure of wurtzite and zinc‐blende InN
Authors: Litimein F. , Bouhafs B. , Ruterana P.
Published: January 2006

In this paper, we focus on the role played by the relativistic and d‐electron effects on the electronic structure of both wurtzite (α‐InN), as well as the zinc‐blende (β‐InN) modifications of indium nitride. Here we perform all‐electron full‐potential linearized‐augmented plane‐wave calculations with spin–orbit interaction. The In 4d electrons are treated both as core and as valence electrons. We compare the performance of the local‐density approximation (LDA), the generalized gradient approximation (GGA) and the recently proposed non‐empirical meta‐generalized gradient approximation (Meta‐GGA) in calculations of the structural and electronic properties of InN. Band structures, densities of states, orbital‐resolved densities of states, charge densities and ionicity factors are analyzed in great detail. The calculated values of the energy gaps, bandwidths, spin–orbit and crystal‐field splittings and the correct band degeneracies are compared to experimental and/or ab‐initio results. The role played by relativistic effects and meta‐GGA functional on the band structure is discussed. For the structural properties meta‐GGA is more accurate and gives the best description of InN. We found that several features of α‐InN resemble those of β‐InN. Most of the calculated band parameters, of band gaps, total valence bandwidths for α‐InN are close to those of β‐InN to within 1%. The charges distributions have similar features meaning that this material has the same ionicity factor in both structures even when In 4d states were treated both as core and as valence electrons. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
III‐Nitrides semiconductor compounds for microwave devices
Authors: di Forte‐Poisson M. A. , Magis M. , Sarazin N. , Tordjman M. , di Persio J.
Published: January 2006

This paper reports on the LP‐MOCVD growth optimisation of GaAlN/GaN heterostructures grown on sapphire and silicon carbide substrates for HEMT applications, and on the device performances obtained with these structures. The devices performances related to the GaAlN/GaN HEMT structures grown on sapphire and silicon carbide have confirmed the high potentiality of GaN and related alloys for high power microwave transistors. Load–Pull measurements performed at 2 GHz on devices related to GaAlN/GaN/Al2O3 HEMT structures, have shown a remarkably high output power density (4.4 W/mm) and absolute power level (3.2 W for 1 mm devices). These power level results for devices on sapphire substrates measured on wafer, are well in agreement with the international state of the art.

Devices related to GaAlN/GaN/SiC HEMT structures have been measured at 10 GHz using a load pull system. They exhibited a CW output power in excess of 6.2 W/mm for a gate length of 0.25 µm and an absolute CW power level of 60 W (22 mm development). On the other hand, the GaAlN/InGaN/GaN double heterostructure, in which the channel layer is made of InGaN instead of GaN, is expected to significantly enhance device performance due to a stronger carrier confinement and a higher two‐dimensional electron gas (2DEG) density at the interface in comparison with an GaAlN/GaN single heterostructure. Simin et al. have demonstrated GaInN channel devices with RF output powers as high as 4.3 W/mm in CW mode [2]. Recently, HEMT devices based on InAlN/GaN lattice‐matched heterostructures exhibiting very promising RF performances have been reported (4.1 W/mm at 2 GHz) [3]. These different heterostructures used for HEMT devices are compared to the conventional GaAlN/GaN heterostructure in term of device results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of InN layers grown by MOCVD using analytical and high resolution TEM: The structure, band gap, role of the buffer layers
Authors: Ruterana P. , Abouzaid M. , Gloux F. , Maciej W. , Doualan J. L. , Drago M. , Schmidtling T. , Pohl U. W. , Richter W.
Published: January 2006

In this work we investigate the microstructure of InN layers grown by MOCVD on different buffer layers using TEM (InN, GaN). The large mismatch between the various lattices (InN, sapphire or GaN) leads to particular interface structures. Our local analysis allows to show that at atomic scale, the material has the InN lattice parameters and that no metallic In precipitates are present, meaning that the PL emission below 0.8 eV is a genuine property of the InN semiconductor. It is also shown that the N polar layers, which exhibit a 2D growth, have poorer PL emission than In polar layers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strain state analysis of InGaN/GaN – sources of error and optimized imaging conditions
Authors: Rosenauer A. , Gerthsen D. , Potin V.
Published: January 2006

Transmission electron microscopy investigation of the chemical composition of Inx Ga1–x N/GaN layers by strain state analysis can lead to substantial artefacts. We evaluated simulated images in dependence of specimen thickness, specimen orientation and objective lens defocus. We observed that the measurement is in agreement with the true strain profile for certain conditions only. An analysis of error sources revealed that artefacts are mainly caused by a combination of delocalization and the composition dependence of the phases of the beams contributing to the image formation. The delocalization effect is minimized for interference of the undiffracted beam with one of the 000 ± 2 beams. The least chemical shift of the phases is obtained using the 000 + 2 beam and a strong excitation of 000 + 4. Images simulated for these conditions taking into account lattice plane bending and strain using finite‐element calculations revealed a good agreement of evaluated and true strain profiles. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasmonic effects in InN‐based structures with nano‐clusters of metallic indium
Authors: Shubina T. V. , Ivanov S. V. , Jmerik V. N. , Toropov A. A. , Vasson A. , Leymarie J. , Kop'ev P. S.
Published: January 2006

InN is a unique material with a tendency for spontaneous formation of metallic indium particles during growth. To elucidate peculiarities related to plasmonic effects, the InN films have been grown either with or without such particles by molecular beam epitaxy using different growth regimes. Studies of the films have demonstrated that their optical properties are influenced by both absorption and electromagnetic enhancement related to the metallic clusters. Basic optical parameters of InN with the metallic inclusions are considered in relation to a cluster shape and orientation with respect to the electric field vector. The origin of infrared emission is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recombination processes with and without momentum conservation in degenerate InN
Authors: Valcheva E. , Alexandrova S. , Dimitrov S. , Lu H. , Schaff W. J.
Published: January 2006

We report on a theoretical approach in which the two cases of recombination with and without momentum conservation in optically excited high carrier concentration InN are considered. The calculations are used to analyze emission spectra of n‐type InN layers of electron concentrations from 7.7 × 1017to 1.4 × 1019cm–3studied in the temperature range between 9 and 100 K. The spectra peak near 0.7 eV and the applicability of the two approaches with increasing carrier concentration is estimated. Different transition mechanisms are considered in order to properly account for the observed features in the spectra. Recombination processes involving acceptor‐ and donor‐like localized states are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scanning tunnelling spectroscopy of quantized electron accumulation at InxGa1−xN surfaces
Authors: Veal T. D. , Piper L. F. J. , Phillips M. R. , Zareie M. H. , Lu Hai , Schaff W. J. , McConville C. F.
Published: January 2006

Electron tunnelling spectroscopy has been used to investigate quantized levels in electron accumulation layers at InGaN surfaces. The tunnelling spectra exhibit a plateau in the normalized conductance which widens with increasing Ga‐content, corresponding to the band gap of InGaN. The measured InxGa1–xN band gaps (between ∼0.65 eV for x = 1 and 1.8 eV for x = 0.43) are consistent with the band gaps determined by previous optical absorption and cathodoluminescence spectroscopy. Additional structures in the spectra reflect the two‐dimensional electronic subbands in the surface quantum well. The subband energies depend on Ga‐content, bulk doping level and the resultant shape of the surface potential well. The tunnelling spectra are compared with calculations of the potential well, the charge‐profile and the subband energies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inhomogeneities in MOVPE InN
Authors: Yamamoto Akio , Miwa Hiroshi , Wang Wen Jun , Hashimoto Akihiro
Published: January 2006

This paper reports the in‐depth and in‐plane inhomogeneities in InN films. Samples of InN are grown on sapphire substrates without or with a buffer using the atmospheric‐pressure MOVPE. For the in‐depth inhomogeneity analysis, the conventional PL measurement using an excitation source with a different wavelength is made from both the front surface and the film/substrate interface sides of samples. The measurement reveals that samples grown for a long time without buffer contain a deteriorated layer, which shows a higher PL peak energy, near the film/substrate interface. Such a layer is never found on the surface side. The deterioration is markedly enhanced when the sample is annealed in an NH3 flow. Since the coexistence of TMI and NH3 (growth environment) suppresses the deterioration and the InN samples used in this experiment have an In‐polarity, such a deterioration is hydrogen‐related degradation on the N‐face of InN film. In‐plane inhomogeneity of InN grown with a different buffer is studied by analyzing PL and absorption data. A wider PL spectrum and a larger discrepancy between PL peak energy and absorption edge, those are observed for films grown without buffer, are well explained by taking account of a large in‐plane inhomogeneity in the samples. The existence of the large in‐plane inhomogeneity is confirmed by the near‐field PL mapping obtained by the SNOM. The SNOM analysis also shows that, although the use of the buffer improves the apparent in‐plane uniformity, such a film has a fine inhomogeneity due to small grains of the buffer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of N‐polarity InN by ArF‐laser assisted MOVPE
Authors: Yamamoto A. , Kasashima K. , Miyanishi M. , Hashimoto A.
Published: January 2006

In this paper, the employment of the ArF excimer‐laser assisted nitridation of sapphire substrate is studied in the ArF‐laser assisted MOVPE (la‐MOVPE) of InN. An ArF excimer laser with an energy 50 mJ/pulse and a repetition rate 20 Hz is introduced parallel to the substrate surface. The surface morphology of InN film grown on α‐Al2O3 (0001) is found to be markedly dependent on the nitridation conditions for the sapphire substrate. When no nitridation is made, the surface of grown InN film is very rough and many In droplets are found on it. A film with a mixture of rough‐surface region with In droplets and smooth‐surface region is grown on the thermally‐nitrided substrate (1000 °C for 30 min). By employing the ArF‐laser irradiation to the NH3 flow during the substrate nitridation at 1000 °C for 30 min (la‐nitridation), a smooth surface region is expanded to the entire surface of film. The smooth surface is found to be stable at growth temperature higher than 700 °C. The KOH etching of grown films reveals that the smooth surface has 5–10 time higher etching rate than the rough one. From these facts, it is concluded that the film with the smooth surface has N‐polarity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fields of deformation anisotropy exploration in multilayered (In,Ga)As/GaAs structures by high‐resolution X‐ray scattering
Authors: Yefanov O. , Kladko V. , Gudymenko O. , Strelchuk V. , Mazur Yu. , Wang Zh. , Salamo G.
Published: January 2006

The results of investigation of In0.3Ga0.7As/GaAs superlattice by high‐resolution X‐ray scattering are presented. The influence of lattice distortion on diffraction curves (DC) were analyzed with dynamical diffraction theory. It allowed to explain azimuth dependence of experimental diffraction curves. Anisotropic changes in the shape of InGaAs lattice unit cell were shown and measured. The influence of smooth borders between hetero‐layers were analyzed. Comparative analysis of different gradient functions on the hetero‐border influence on diffraction curves was done. Parameters of heterojunction in investigated samples were determined with the help of DC modelling. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth of InN with ammonia on sapphire
Authors: Drago M. , Vogt P. , Richter W.
Published: January 2006

MOVPE growth of InN on sapphire substrate is reviewed focusing on the critical growth parameters. Based on our in situ spectroscopic ellipsometry results obtained during growth and the results found in the literature we suggest a strategy for successful growth of high quality InN layers. This includes nitridation of the substrate, growth parameters and suppression of layer peeling off. We find that the optimal temperature for the nitridation of the sapphire is around 1050 °C and the optimal growth temperature is always very close to the highest possible temperature which is determined by the thermal decomposition of the InN layer. The smallest accessible V/III ratio, before Indium droplets formation occurs, lies between 5000 and 10000 depending on the growth parameters. With the procedure we suggest here the growth temperature can be increased up to 580 °C with changes of the respective V/III ratio limits resulting in an improvement of the InN quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Half‐filled stripes in thet–t′–UHubbard model
Authors: Raczkowski Marcin , Oleś Andrzej M. , Frésard Raymond
Published: January 2006

Using a self‐consistent Hartree‐Fock approximation we investigate the relative stability of various stripe phases in the extendedt–t′–UHubbard model. One finds that a negative ratio of next‐ to nearest‐neighbor hoppingt′/t< 0 expells holes from antiferromagnetic domains and reinforces the stripe order. Therefore the half‐filled stripes not only accommodate holes but also redistribute them so that the kinetic energy is gained, and these stripes take over in the regime oft′/t≃ –0.3 appropriate for YBa2Cu3O6+δ. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiferroic bilayers of manganites and titanates
Authors: Dörr K. , Thiele C.
Published: January 2006

Isostructural ferromagnetic and ferroelectric perovskites like manganites (La,A)MnO3 and titanates Pb(Zr,Ti)O3 are favourable candidates for layered film structures with large magnetoelectric coupling phenomena. Manganites (La,A)MnO3 have already been intensively investigated: conduction electrons have a high degree of spin polarization and are strongly coupled to lattice degrees of freedom, making electric transport sensitive to lattice distortions. Epitaxial film systems of manganites and titanates have been prepared by off‐axis pulsed laser deposition (PLD). Field effect devices of La1–x Ax MnO3 (A = Sr; Ca; Ce) and PbZr0.52Ti0.48O3 (PZT) show channel resistance modulation from both, (i) the electric field effect at the PZT‐manganite interface and (ii) the biaxial strain induced by the inverse piezoeffect of PZT. Piezoelectric substrates have been employed to dynamically control the in‐plane strain state of manganite films, revealing strain‐dependent variation of the ferromagnetic Curie temperature and the resistance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fundamentals for magnetic patterning by ion bombardment of exchange bias layer systems
Authors: Ehresmann A. , Engel D. , Weis T. , Schindler A. , Junk D. , Schmalhorst J. , Höink V. , Sacher M. D. , Reiss G.
Published: January 2006

In the present paper we investigate whether the ion bombardment induced magnetic modifications in exchange biased bilayers are stable in time, whether the direction of the exchange bias can be set to any arbitrary (in‐plane) direction by the ion bombardment and whether the exchange bias field can be changed in successive bombardment steps. These three fundamental characteristics are prerequisites for ion bombardment used for an efficient, practical, and stable magnetic patterning of exchange biased layer systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic microstructure of NANOPERM‐type nanocrystalline alloys
Authors: Miglierini Marcel , Kaňuch Tomáš , Švec Peter , Krenický Tibor , Vůjtek Milan , Zbořil Radek
Published: January 2006

Controlled crystallization of amorphous NANOPERM‐type Fe76Mo8Cu1B15 alloy leads to the formation of crystalline grains of about 10 nm in size. The evolution of crystallization and its impact on the resulting magnetic properties is followed by nuclear and atomic based techniques of (subatomic) structural characterization comprising Mössbauer spectrometry, X‐ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, differential scanning calorimetry, and atomic force microscopy. The amount of nanocrystalline grains identified as bcc‐Fe rises with temperature of annealing and influences magnetic states of the original amorphous precursor. Results of structural characterization are correlated with magnetic data obtained from macroscopic measurements. In the samples with low contents of nanocrystallites, a deterioration of soft magnetic properties is observed. A very good soft magnetic behaviour is regained, however, towards the end of the primary crystallization process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New magnetostatic modes in small nonellipsoidal magnetic particles
Authors: Puszkarski H. , Krawczyk M. , Lévy J.‐C. S.
Published: January 2006

Magnetostatic normal modes are investigated here in elongated rods. The dipolar field resulting from the dipole–dipole interactions is calculated numerically in points of the axis connecting opposite rod face centers (central axis ) by collecting individual contributions to this field coming from each of the atomic planes perpendicular to the central axis. The applied magnetic field is assumed to be oriented along the central axis, and the magnetization to be uniform throughout the sample. The frequency spectrum of magnetostatic waves propagating in the direction of the applied field is found numerically by solving the Landau–Lifshitz equation of motion with the spatially nonhomogeneous dipolar field taken into account; the mode amplitude profiles are depicted as well. While energetically highest modes have bulk‐extended character, the modes forming the lower part of the spectrum are localized in the subsurface region (bulk‐dead modes ). Between these two mode types, magnetostatic modes of a new type (comb modes ) are found to occur, characterized by two clearly discernible regions: a zone of fast amplitude oscillations inside the rod, and narrow slow‐oscillation regions at the borders. Absorbing virtually no energy from an applied alternating field, comb modes will have no significant contribution to the magnetic noise. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Torque induced by spin‐polarized current in ferromagnetic single‐electron transistors
Authors: Kowalik M. , Wiśniewska J. , Barnaś J.
Published: January 2006

We present theoretical analysis of the current‐induced torque exerted on the magnetic moment of the central electrode (island) in a ferromagnetic single electron transistor with non‐collinear magnetic moments of the electrodes. The considerations are restricted to the sequential tunneling regime, and the charge and spin currents are calculated within the master equation approach. The torque is calculated from the net spin current absorbed by the island. The calculations are carried out in the limit of fast spin relaxation processes, when no nonequilibrium magnetic moment can build up on the island. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hall effect in the low charge‐carrier density ferromagnet UCo0.5Sb2
Authors: Tran V. H. , Paschen S. , Steglich F. , Troć R. , Bukowski Z.
Published: January 2006

The Hall coefficient R H of ferromagnetic UCo0.5Sb2 (T C = 64.5 K) has been measured on a single crystal in the temperature range 2–300 K and in magnetic fields up to 7 T. The values of the normal R 0 and anomalous R s) coefficients were estimated by comparing R H(B ) with magnetisation M (B ) data. The charge carrier concentration is found to decrease rapidly when the system undergoes a transition to the ferromagnetic ordered state. The charge mobility appears to fall down by as much as two orders of magnitude for temperatures from 20 K to 2 K. We ascribe this behaviour to an enormous decrease of the carrier collision time. The temperature dependencies of the Hall mean free path and mobility can be consistently interpreted within the 2D‐weak localization feature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)