bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of human osteoblasts exposed to wear particles generated at the interface of total hip stems and bone cement
Authors: Lenz Robert , Mittelmeier Wolfram , Hansmann Doris , Brem Regina , Diehl Peter , Fritsche Andreas , Bader Rainer
Published: April 2008

Aseptic loosening of total hip replacement is mainly caused by wear particles. Abrasive wear occurs at articulating surfaces or as a consequence of micro‐motions at the interface between femoral stem and bone cement. Direct impact of wear particles on osteolysis, the remodeling of the bone stock and a directly affected function of osteoblasts was described. The present study examined the response of human osteoblasts exposed to different wear particles, which were generated in a test device providing oscillating micro‐motions at the interface between femoral stem and standard bone cement. Characterization of released particles was performed by quantifying the size distribution and the metal content of the wear debris. Human osteoblasts were incubated with particles obtained from hip stems with different material compositions (Ti‐6Al‐7Nb and Co‐28Cr‐6Mo) and rough and smooth surface finishings combined with standard bone cement (Palacos® R) containing zirconium oxide particles. Commercially pure titanium particles (cp‐Ti) and particulate zirconium oxide (ZrO2) were used for comparative analyses. The results revealed significant (p < 0.05) reduction of the cell viability after exposure to higher concentration of metallic particles, particularly from Co‐based alloys. In contrast, ZrO2 alone showed significantly less adverse effects on the cells. When increasing metallic particle concentrations massive inhibition was also observed in the release of cytokines including interleukine‐6 (IL‐6) and interleukine‐8 (IL‐8), but the expression of Procollagen I and the cell viability showed the highest reduction after exposure to Co‐based alloy particles from rough stems. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Bond strength of adhesively luted ceramic discs to different core materials
Authors: Bozogullari Nalan , Inan Ozgur , Usumez Aslihan
Published: April 2008

The purpose of this in vitro study was to compare the shear bond strengths of resin, glass‐ionomer, and ceramic‐based core materials to all ceramic discs. Five core materials (Core max, Sankin; Clearfil AP‐X, Kuraray; Empress Cosmo, Ivoclar‐Vivadent; Photocore, Kuraray; Dyract Extra, Dentsply) were prepared as discs 10 mm in diameter and 2 mm in height according to the manufacturer's instructions. Ten disc specimens per group were prepared, and dentin served as the control. All resin specimens were embedded in autopolymerizing acrylic resin, with one surface facing up. All ceramic discs (IPS Empress I, Ivoclar‐Vivadent) 3 mm in diameter and 2 mm in height were prepared and bonded to core specimens with a dual‐curing luting resin cement (Variolink II, Vivadent). Specimens were stored in distilled water at 37°C. Shear bond strength of each sample was measured after 24 h using a universal testing machine at a crosshead speed of 0.5 mm/min. The data were analyzed with one‐way analysis of variance and Tukey HSD tests (α = 0.05). Shear bond strength varied significantly depending on the core material used (p < 0.05). Clearfil AP‐X and Photocore showed the highest shear bond strength value while Empress Cosmo provided the lowest (p < 0.05). There were no statistically significant differences among Clearfil AP‐X, Photocore, and Core‐Max (p > 0.05). And also there were no statistically significant differences between Dyract Extra and the control group (p > 0.05). In vitro shear bond strengths of ceramic discs bonded to resin‐based core materials showed higher bond strength values than ceramic‐based core material. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Differential fine‐tuning of cochlear implant material–cell interactions by femtosecond laser microstructuring
Authors: Reich Uta , Mueller Peter P. , Fadeeva Elena , Chichkov Boris N. , Stoever Timo , Fabian Tilman , Lenarz Thomas , Reuter Guenter
Published: April 2008

Cochlear implants (CIs) can restore hearing in deaf patients by electrical stimulation of the auditory nerve. To optimize the electrical stimulation, the number of independent channels must be increased by reduction of connective tissue growth on the electrode surface and selective neuronal cell contact. The femtosecond laser microstructuring of the electrode surfaces was performed to investigate the effect of fibroblast growth on the implant material. A cell culture model system was established to evaluate cell–material interactions on these microstructured CI‐electrode materials. Fibroblasts were used as a cell culture model for connective tissue formation, and differentiating neuronal‐like cells were employed to represent neuronal cells. For nondestructive microscopic examination of living cells on the structured surfaces, the cells were genetically modified to express green fluorescent protein. To investigate the special interaction between the electrode material and the tissue we used electrode material which is originally used for manufacturing CI for human applications, namely platinum (contact material) and silicone carrier material (LSR 30, HCRP 50). Microstructures of various dimensions (groove width 1–10 μm) were generated by using femtosecond laser ablation. The highest fibroblast growth rate was observed on platinum, but cell growth rates on the silicone carrier material were lower. Microstructuring reduced fibroblast cell growth on platinum significantly. On the microstructured silicone, a trend to lower cell growth rates was observed. In addition, microgrooves on platinum surfaces can direct neurite outgrowth parallel to the grooves. The implications of the results are discussed with respect to the design of a microstructured CI surface. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008
Hierarchically mesoporous–macroporous bioactive glasses scaffolds for bone tissue regeneration
Authors: Yun Hui‐suk , Kim Seung‐eon , Hyun Yong‐taek , Heo Su‐jin , Shin Jung‐wook
Published: April 2008

Hierarchically 2D/3D mesoporous–macroporous bioactive glasses (MMBG) with good molding capabilities and compressive modulus were synthesized by sol–gel method and evaporation‐induced self‐assembly process in the presence of both nonionic triblock copolymers, EO70PO20EO70 (P123) or EO100PO65EO100 (F127), templates and methyl cellulose template. P123 or F127 acts as both a template, inducing the formation of mesopore, and an effective dispersant of MC, which produces macropores. In vitro bioactivity studies were carried out in simulated body fluid and showed superior bone‐forming bioactivities of hierarchical MMBG. Human osteoblastlike cells, MG63, were seeded on MMBG and were determined using MTT [3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5,‐diphenyl‐tetrazolium bromide] assay to confirm biocompatibilities of MMBG. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008
Infinite families of non‐embeddable quasi‐residual Menon designs
Authors: Alraqad Tariq , Shrikhande Mohan
Published: April 2008

A Menon design of order h2 is a symmetric (4h2,2h2‐h,h2‐h)‐design. Quasi‐residual and quasi‐derived designs of a Menon design have parameters 2‐(2h2 + h,h2,h2‐h) and 2‐(2h2‐h,h2‐h,h2‐h‐1), respectively. In this article, regular Hadamard matrices are used to construct non‐embeddable quasi‐residual and quasi‐derived Menon designs. As applications, we construct the first two new infinite families of non‐embeddable quasi‐residual and quasi‐derived Menon designs. © 2008 Wiley Periodicals, Inc. J Combin Designs 17: 53–62, 2009
Fermentative production of L(+)‐lactic acid from starch hydrolyzate and corn steep liquor as inexpensive nutrients by batch culture of Enterococcus faecalis RKY1
Authors: Wee Young‐Jung , Reddy L V A , Ryu Hwa‐Won
Published: April 2008

BACKGROUND: Attempts were made to determine the lactic acid production efficiency of novel isolate, Enterococcus faecalis RKY1 using four different starches (corn, tapioca, potato, and wheat starch) with different concentrations (50, 75, 100, and 125 g L−1) and corn steep liquor as an inexpensive nitrogen source.

RESULTS: The yield of lactic acid from each starch was higher than 95% based on initial starch concentrations. High lactic acid concentration (129.9 g L−1) and yield (1.04 g‐lactic acid g−1‐starch) were achieved faster (84 h) from 125 g L−1 of corn starch. Among the starches used, tapioca starch fermentation usually completed in a shorter incubation period. The final dry cell weight was highest (7.0 g L−1) for the medium containing 75 g L−1 of corn starch, which resulted in maximum volumetric productivity of lactic acid (3.6 g L−1 h−1). The addition of 30 g L−1 corn steep liquor supplemented with a minimal amount of yeast extract supported both cell growth and lactic acid fermentation.

CONCLUSION: Enterococcus faecalis RKY1 was found to be capable of growing well on inexpensive nutrients and producing maximum lactic acid from starches and corn steep liquor as lower‐cost raw materials than conventionally‐used refined sugars such as glucose, and yeast extract as an organic nitrogen source in laboratory‐scale studies. These fermentation characteristics are prerequisites for the industrial scale production of lactic acid. Copyright © 2008 Society of Chemical Industry
Hypospadias mimicking female genitalia on early second trimester sonographic examination
Authors: Odeh Marwan , Ophir Ella , Bornstein Jacob
Published: April 2008

Female fetal sex was assigned based on downward direction of the genital tubercle at 14 weeks' gestation. Subsequently, amniocentesis performed due to the finding of an echogenic focus in the left ventricle revealed a male karyotype. Sonographic examination at 22 weeks' gestation revealed a markedly curved penile shaft. Power Doppler at that time demonstrated a urine jet emanating from the penile base, verifying the diagnosis of penoscrotal hypospadias. We therefore suggest that female fetal sex assignment should be based on the demonstration of the 2 or 4 parallel lines representing the labial folds and not only upon the demonstration of the downward direction of the genital tubercle. © 2008 Wiley Periodicals, Inc. J Clin Ultrasound 36:581–583, 2008
On two questions about circular choosability
Authors: Norine Serguei
Published: April 2008

We answer two questions of Zhu on circular choosability of graphs. We show that the circular list chromatic number of an even cycle is equal to 2 and give an example of a graph for which the infimum in the definition of the circular list chromatic number is not attained. © 2008 Wiley Periodicals, Inc. J Graph Theory 58:261‐269, 2008
‘Green earths’: vibrational and elemental characterization of glauconites, celadonites and historical pigments
Authors: Ospitali Francesca , Bersani Danilo , Di Lonardo Gianfranco , Lottici Pier Paolo
Published: April 2008

‘Green earths’ are employed since antiquity as pigments in the creation of artworks. The minerals responsible for the colour belong to four groups: (1) the clayey micas celadonite and glauconite, undoubtedly the most common; (2) smectites; (3) chlorites; (4) serpentines. Whereas there have been several studies on clayey materials, mineralogical analyses in the field of cultural heritage are mainly limited to the identification of the green earth without specific characterization of the mineralogical species. This work shows a preliminary characterization by the multi‐techniques approach of some raw minerals (glauconite, celadonite and ferroceladonite).

Vibrational analyses have been correlated with elemental analyses, thanks to the hyphenated instrumentation of scanning electron microscopy with EDS and Raman structural and chemical analyser (SEM‐EDS‐SCA) probes, which permitted collection of EDS and Raman spectra on the same microscopic area. Micro‐Raman and Fourier transform infrared attenuated total reflectance (FTIR‐ATR) spectroscopies were able to distinguish between celadonite and glauconite. The use of different lasers revealed resonance effects in the Raman spectra. In addition to pure minerals, archaeological samples and commercial green earths were also analysed, thereby enabling a more precise classification of the green pigments in heterogeneous samples such as wall paintings. Some commercially available green earths were found to contain organic dyes. Copyright © 2008 John Wiley & Sons, Ltd.
Study on characterization and properties of nanosilica‐filled thermoplastic vulcanizates
Authors: Chatterjee K. , Naskar K.
Published: April 2008

Thermoplastic vulcanizates (TPVs) are a special class of thermoplastic elastomer, produced by simultaneously mixing and cross‐linking a rubber with a thermoplastic at elevated temperature. Dicumyl peroxide‐cured TPVs based on blends of maleated ethylene propylene rubber (m‐EPM) and polypropylene (PP) thermoplastic using maleated‐PP as a compatibilizer have been developed. To reinforce the properties of these TPVs, nanosilica was added at different levels. With the increase of nanosilica concentrations, significant improvement in tensile strength, modulus, and impact strength of TPVs have been achieved. Morphology study shows that nanosilica is uniformly dispersed in the polymer matrices. Dynamic mechanical analysis shows that tan δ value at low temperature decreases with increasing nanosilica concentration indicating less damping characteristics. Thermogravimetric study revealed that thermal stability of TPVs is improved in presence of nanosilica. Equilibrium swelling study confirms that solvent resistance of TPVs could be improved by nanofiller incorporation. Rubber process analyzer found a very useful tool to understand the melt rheology of nanosilica filled TPVs in terms of dynamic functions over a wide range of strain amplitude and frequency. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Prediction of processability at extrusion coating for low‐density polyethylene
Authors: Kouda Shingo
Published: April 2008

The neck‐in level and the maximum drawdown speed at extrusion coating for low‐density polyethylene are studied with the evaluation of the rheological properties in the molten state and the dilute solution properties. It is found that the viscous properties in the molten state and the dilute solution properties are not sensitive to the processability, whereas the elastic nature has a great impact. In particular, the elastic response in the nonlinear region, such as drawdown force and strain‐hardening behavior in elongational viscosity, can be employed for the prediction of the processability at extrusion coating. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Characterization of processing effects in HIPS‐CNF composites using thermogravimetric analysis
Authors: Kota Arun K. , Kerzner Rachel , Bigio David I. , Bruck Hugh A. , Powell Dan
Published: April 2008

To completely establish the processing–structure–property relationships of polymer composites such as Carbon Nanofibers (CNFs) in high‐impact polystyrene, it is necessary to understand the effects of different processes and processing conditions on the properties of the composites. In this work, using thermogravimetric analysis, the effects of solvent processing and twin‐screw extrusion on the weight loss rates and the corresponding temperatures were studied. While there were only marginal effects of the CNF concentration, the type of processing significantly affected the thermo‐oxidative behavior. Extrusion resulted in composites that had better thermal stability compared to the solvent processed ones. Furthermore, higher shear rates in extrusion also led to composites with higher thermal stability. This has important implications in choosing the appropriate process and processing conditions for producing polymer‐CNF composites. It was also demonstrated that thermogravimetric analysis can provide a means of characterizing the degree of dispersion resulting from the processing of the composites that complements conventional microscopy techniques. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Characterization and thermal degradation of polyimides derived from ODPA and several alicyclic‐containing diamines
Authors: Chen Chao‐Feng , Qin Wei‐Min , Huang Xiang‐An
Published: April 2008

Thermal properties of polyimides with main chain containingalicyclic units derived from 3,3′ 4,4′‐oxydiphthalic anhydride (ODPA) and several alicyclic‐ containing diamine monomers, including 1,4‐bis (4‐aminophenoxymethylene) cyclohexane (BAMC), 1,4‐bis (3‐aminophenoxymethylene) cyclohexane (mBAMC), 1,4‐bis (4‐aminobenzoyoloxymethyl) cyclohexane (BAZMC), and 1,4‐bis (3‐aminobenzoyoloxymethyl) cyclohexane (mBAZMC) were characterized in detail. The thermal stability, apparent activation energy, and evolved gas analysis of these polyimides were done using thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) spectroscopy. Experimental results indicated that the resulting polyimides showed fairly high thermal stability, no weight loss was detected before a temperature of 400°C in nitrogen, and the values of glass‐transition temperature of them were in the range of 134–181°C. Activation energy for the initial thermal degradation of polyimide derived from ODPA and mBAMC in nitrogen were 166 and 162 kJ/mol in two different methods. The TG‐IR results represented that the major evolved products from the nonoxidative thermal degradation were detected to be hydrocarbons, CO, CO2, H2O, and aromatic compounds. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.
Nanocomposites derived from in situ grafting of linear and hyperbranched poly(ether‐ketone)s containing flexible oxyethylene spacers onto the surface of multiwalled carbon nanotubes
Authors: Jeon In‐Yup , Tan Loon‐Seng , Baek Jong‐Beom
Published: April 2008

Linear and hyperbranched poly(ether‐ketone)s (PEKs) containing flexible oxyethylene spacers grafted multiwalled carbon nanotube (PEK‐g‐MWNT) nanocomposites were prepared by direct Friedel‐Crafts acylation as the polymer forming and grafting reaction. To achieve the composites, in situ polycondensations of AB monomers 3‐(2‐phenoxyethoxy)benzoic acid (3‐PEBA) and 4‐(2‐phenoxyethoxy)benzoic acid (4‐PEBA), and AB2 monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid (3,5‐BPEBA) were carried out in the presence of multiwalled carbon nanotubes (MWNTs). The reaction conditions, polyphosphoric acid (PPA) with additional phosphorous phentoxide (P2O5) in the temperature range of 110–120 °C, were previously optimized. The conditions were used as the polymerization and grafting medium that were indeed benign not to damage MWNTs but strong enough to promote the covalent attachment of PEKs onto the surface of the electron‐deficient MWNTs. From scanning electron microscopy (SEM) and transmission electron microscopy studies, the polymers were uniformly grafted onto the MWNTs. The resultant nanocomposites are soluble in most strong acids such as trifluoroacetic acid, methanesulfonic acid, and sulfuric acid. Both isothermal and dynamic TGA studies in air showed that nanocomposites displayed improved thermo‐oxidative stability when compared with those of corresponding PEK homopolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3471–3481, 2008
Photomediated crosslinking of cinnamated PDMS for in situ direct photopatterning
Authors: Chen Jianxin , Vaino Andrew R. , Smith Rosemary L. , Collins Scott C.
Published: April 2008

Polydimethylsiloxane (PDMS) polymers incorporating pendant cinnamate groups have been synthesized and evaluated for their ability to form patterned thin films via photo‐crosslinking. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3482–3487, 2008
Nonisothermal crystallization behavior of exfoliated poly(ethylene terephthalate)‐layered silicate nanocomposites in the presence and absence of organic modifier
Authors: Chung Jae Woo , Son Se‐Bum , Chun Sang‐Wook , Kang Tae Jin , Kwak Seung‐Yeop
Published: April 2008

Exfoliated poly(ethylene terephthalate) (PET)‐layered silicate nanocomposites (PetLSNs) excluding (PetLSNeom) and including (PetLSNiom) organic modifiers were obtained by solution methods with and without solvent‐nonsolvent system, respectively. From wide angle X‐ray diffraction and high resolution transmission electron microscopy, both PetLSNs were found to have exfoliated structure attributed to sufficient dispersion of silicate in prepared solvents, regardless of sample preparation method. However, organic modifier in PetLSNeom was confirmed to be well removed by elemental analysis, whereas organic modifier was still remained in PetLSNiom. Thus, the effect of the presence and absence of organic modifiers in PetLSNs on the nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) on the basis of a modified Avrami analysis and polarized optical microscopy (POM). From DSC results, it was found that both PetLSNs had higher degrees of crystallinity and shorter crystallization half‐times than neat PET, because of the dispersed silicate layers acted as nucleating agents in both PetLSNs. However, PetLSNiom exhibited a lower degree of crystallinity and longer half‐time of crystallization than PetLSNeom. Difference of crystallization behavior between PetLSNeom and PetLSNiom was ascribed to organic modifier in PetLSNiom, which may act as crystallization inhibitors. POM measurements also revealed the results which were in good agreement with crystallization behavior observed from DSC measurement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 989–999, 2008
Current approaches to the management of COPD
Authors: Ruse Charlotte
Published: April 2008

Our series Prescribing in older people gives practical advice for successful management of the special problems experienced by this group. Here, the author describes the current recommended management of COPD. Copyright © 2008 Wiley Interface Ltd
rf‐MBE growth and characterizations of AlGaN/GaN HEMTs on vicinal sapphire (0001) substrates
Authors: Shen X. Q. , Sazawa H. , Okumura H.
Published: April 2008

We report the rf‐MBE growth and characterizations of AlGaN/GaN heterostructures and their HEMTs on vicinal sapphire (0001) substrates. Vicinal angle dependences of the property (surface morphologies and 2DEG mobility) in AlGaN/GaN heterostructures are investigated. It is found that the surface morphology and the 2DEG mobility is greatly improved by using vicinal substrates. Furthermore, the gate‐leakage current in the AlGaN/GaN‐based HEMTs, which is important for the device operation, is suppressed due to the improvement of the surface morphology and the reduction of the dislocation density in the heterostrucutes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improved surface morphology of flow‐modulated MOVPE grown AlN on sapphire using thin medium‐temperature AlN buffer layer
Authors: Li Da‐Bing , Aoki Masakazu , Miyake Hideto , Hiramatsu Kazumasa
Published: April 2008

High‐temperature (HT) AlN films were grown on (0001) sapphire by low‐pressure flow‐modulated (FM) metal organic vapor phase epitaxy (MOVPE) with and without inserting a thin medium‐temperature (MT) AlN layer. To suppress parasitic reactions between the sources of trimethylaluminum (TMA) and ammonia (NH3), TMA and NH3 was introduced to the reactor of MOVPE by alternating supply way. Surface morphology and crystalline quality were characterized by a scanning electronic microscopy (SEM), atomic force microscopy (AFM) and X‐ray rocking curve (XRC) measurements of (0002) and (10‐12) diffractions. The AFM and SEM measurements indicated that the thin MT‐AlN layer had a strong influence on the surface morphology of the HT‐AlN films. The surface morphology became quite smooth by inserting the thin MT‐AlN layer and surface RMS roughness values were 0.84nm and 13.4nm for the HT‐AlN films with and without inserting the thin MT‐AlN buffer layer, respectively. By etching the samples in aqueous KOH solution, it was found that the polarity of AlN films was different, the HT‐AlN film with the thin MT‐AlN layer could not be etched, indicating that the film had an Al‐polar surface; however, the film without the MT‐AlN layer was etched, which was explained that that film had a N‐ or mixed polar surface. The mechanism for the origin of the different polarity of HT‐AlN with and without the thin MT‐AlN layer was proposed and discussed in detail. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InGaN/GaN light emitting diode with R‐plane polygonal facet deflectors
Authors: Kim Hyung Gu , Cuong Tran Viet , Kim Hyun Kyu , Kim Hee Yun , Ryu Jae Hyung , Na Min Gyu , Hong Chang‐Hee
Published: April 2008

The optical characteristics of periodic deflector embedded light emitting diode (PDE‐LED) with the artificial inverted polygonal pyramids (AIPPs) were studied in terms of focusing on the ratio between the flat active area and the AIPPs‐occupied area. Our result indicated that the AIPPs‐occupied area should be optimized equal to 25% for achieving the maximum of optical output efficiency from our PDE‐LED structure. Herein, the AIPPs were formed on SiO2 patterned by selective MOCVD growth technique. AIPPs including six {1‐102} R‐plane polygonal facets of 57° against {0001} c‐axis played an important role in promoting multiple chances to escape the photons and the redirected photons deflected through polygonal facets. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of periodic micropits InGaN‐based LED structure on wet‐etch patterned sapphire substrate
Authors: Kim H. Y. , Cuong T. V. , Kim H. G. , Cha O. H. , Park J. Y. , Lee Y. S. , Jeong H. , Hong C.‐H. , Suh E.‐K. , Jeong M. S. , Cheong H. S.
Published: April 2008

Growth of periodic micropits InGaN‐based light emitting diode (LED) structure on wet‐etch patterned sapphire substrate (WPSS) was introduced. Two‐step growth of GaN on the triangle shape of WPSS promotes the ability to control the density/size of honeycomb shape GaN template and resulting in the threading dislocation density of 8‐9×106 cm‐2. Moreover, this template also was acting as the seeds to conduct the periodic distribution of micropits InGaN/GaN multiple quantum wells (MQWs). Spatially and spectrally resolved luminescence from periodic micropits LED is obtained using near‐field scanning optical microscope (NSOM). The results revealed that the excited carrier has facilitated the confinement at the horizontal MQW region rather than in the inclined facet MQW. Consequently, intensity of the light emitting from the horizontal region is much higher than that of the inclined facets region. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improved optical properties of AlGaN using periodic structures
Authors: Miyake Hideto , Ishii Takeharu , Motogaito Atsushi , Hiramatsu Kazumasa
Published: April 2008

Al0.4Ga0.6N periodic structures were fabricated on Al0.4Ga0.6N epilayers grown on AlN/sapphire templates by electron‐beam (EB) lithography and by reactive ion etching (RIE) using chlorine plasma. The effects of etching depth, dot size and lattice constant on the emission intensity were investigated. It was found that for the AlGaN periodic structures with triangular lattice patterns, which have a lattice constant of 300 nm and a dot size of 150 nm, antireflection and enhanced transmission were obtained from the deep‐ultraviolet region to the visible region (240∼700 nm). The emission intensity of the periodic structure also increased to about 3 times that of the structure with a smooth surface. The excellent optical properties of the periodic structure are expected to improve the performance of photo‐detectors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct MOVPE‐ and MBE‐growth of a‐plane GaN on r‐plane sapphire
Authors: Aschenbrenner T. , Goepel K. , Kruse C. , Figge S. , Hommel D.
Published: April 2008

We report on the growth of pit‐free a‐plane GaN on (1$ \bar 1 $02) sapphire (r‐plane) substrates by metal organic vapor phase epitaxy (MOVPE) using a three step growth method without low temperature nucleation layer. X‐ray diffraction ω ‐scans of the symmetric GaN (11‐20) reflex revealed for 1.2 μm thick crack‐ and pit‐free GaN layers low FWHM of 885 arcsec and 2484 arcsec measured by inclination in c‐ and m‐direction, respectively. To analyze the evolution growth was stopped at different stages and the samples were measured with AFM, SEM, and XRD.

Furthermore, we discuss the overgrowth of MOVPE GaN layer with molecular beam epitaxy (MBE). For smooth MOVPE templates with closed surfaces the morphology was reproduced, whereas for not coalesced thinner layers a different growth mode and a smoothening of the layers occurred. We will discuss SEM‐ and AFMdata in detail to examine this overgrowth procedure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Distributed Bragg reflectors in comparison to RUGATE and nested super lattices – growth, reflectivity, and conductivity
Authors: Figge Stephan , Dartsch Heiko , Aschenbrenner Timo , Kruse Carsten , Hommel Detlef
Published: April 2008

This paper investigates the feasibility of conductive Al‐GaN reflectors with corRUGATEd (RUGATE) index profiles in comparison to standard distributed bragg reflectors (DBR) and nested super lattice (NSL) DBRs. The samples are analyzed by reflectometry, x‐ray diffraction, and electrical measurements.

The RUGATE implementation of the reflectors exhibited two times higher vertical conductivity in comparison to the DBRs and showed slightly lower reflectivity. The nested super lattice approach for DBRs turned out to be an alternative which is easy to manufacture and which shows high reflectivity values. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characteristics of InGaN designed for photovoltaic applications
Authors: Trybus E. , Jani O. , Burnham S. , Ferguson I. , Honsberg C. , Steiner M. , Doolittle W. A.
Published: April 2008

This work addresses the required properties and device structures for an InGaN solar cell. Homojunction InGaN solar cells with a bandgap greater than 2.0 eV are specifically targeted due to material limitations. These devices are attractive because over half the available power in the solar spectrum is above 2.0 eV. Using high growth rates, InGaN films with indium compositions ranging from 1 to 32% have been grown by Molecular Beam Epitaxy with negligible phase separation according to X‐ray diffraction analysis, and better than 190 arc‐sec ω‐2θ FWHM for ∼0.6 μm thick In0.32Ga0.68N film. Using measured transmission data, the adsorption coefficient of InGaN at 2.4 eV was calculated as α ≅ 2×105cm–1near the band edge. This results in the optimal solar cell thickness of less than a micron and may lead to high open circuit voltage while reducing the constraints on limited minority carrier lifetimes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarkable enhancement of 254‐280 nm deep ultraviolet emission from AlGaN quantum wells by using high‐quality AlN buffer on sapphire
Authors: Hirayama Hideki , Yatabe Tohru , Ohashi Tomoaki , Kamata Norihiko
Published: April 2008

We observed remarkable enhancement of 254‐280 nm deep ultraviolet (UV) emission from AlGaN multi quantum wells (MQWs) by using low threading dislocation density (TDD) AlN templates on sapphire substrates. High‐quality AlN templates were fabricated using ammonia pulse‐flow multi‐layer (ML) AlN growth technique by metal‐organic chemical vapor deposition (MOCVD). The photoluminescence (PL) intensity of AlGaN‐QW with emission wavelength of 280 nm was increased by approximately 30 times by reducing the full width at half‐maximum (FWHM) of X‐ray diffraction (102) ω‐scan rocking curve (XRC) of AlGaN buffer on ML‐AlN from 1214 to 488 arcsec. We obtained similar emission enhancement for AlGaN QWs with emission wavelengths of 254, 260 and 270 nm. We found that PL intensity of the QWs were rapidly increased when FWHM of XRC (102) is reduced as narrow as 800‐1000 arcsec. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
M‐plane III‐nitride materials for polarization sensitive devices grown by PAMBE with real time analysis by spectroscopic ellipsometry
Authors: Misra P. , Boney C. , Pillai R. , Starikov D. , Bensaoula A.
Published: April 2008

In this paper we present a study of the growth of M‐plane GaN epilayers on LiAlO2 substrates under Ga rich conditions and growth at Ga stable conditions by plasma assisted molecular beam epitaxy (PAMBE) coupled with in‐situ spectroscopic ellipsometry (SE). Previous studies on M‐plane materials have suggested that optimum growth conditions with respect to surface morphology are those giving rise to Ga trilayer coverage at low growth temperature. By studying Ga adsorption/desorption in vacuum and in the presence of active nitrogen, we find that the total coverage for M‐plane material is distinctly different for these two conditions. Under vacuum, the stable Ga coverage corresponded of 0.48 nm, while a thicker Ga stable coverage of 0.7 nm was determined N plasma. Using these GaN growth conditions, M‐plane InGaN layers were grown and fabricated into polarization‐sensitive photodetectors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MBE growth and characterization of Mg‐doped InGaN and InAlN
Authors: Matthews K. D. , Chen X. , Hao D. , Schaff W. J. , Eastman L. F.
Published: April 2008

We report on the growth of high quality Mg‐doped InGaN and InAlN alloys on (0001) sapphire substrates by molecular beam epitaxy. Phase separation does not occur in InxGa1‐xN films with Indium content up to 0.88. Hall measurement shows that a hole concentration of 7.7x1017cm–3is achieved on Mg‐doped In0.04Ga0.96N. When x > 0.11, the Hall samples exhibit strong n‐type polarity, whereas p‐type polarity is confirmed by hot probe measurement for all of Mg‐doped InGaN. Ni/Au film is deposited on Mg‐doped InxGa1‐xN as the p contact met al. A contact resistivity as high as 9.95 Ωcm2is obtained when x = 0.25 while it is only 6.81x10–5Ωcm2when x = 0.85. High quality crack‐free InAlN films are also grown on sapphire substrates with AlN/InN quantum‐well buffer layers. When Mg is incorporated near the solid solubility limit, donor defects form and In0.62Al0.38N films show n‐type polarity by Hall measurement, however lower Mg flux yields p‐type polarity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photon modulated electroluminescence of GaInN/GaN multiple quantum well light emitting diodes
Authors: Li Y. , Senawiratne J. , Xia Y. , Zhao W. , Zhu M. , Detchprohm T. , Wetzel C.
Published: April 2008

Under external laser excitation, we studied the electroluminescence (EL) of GaInN/GaN green light emitting diodes (LEDs) grown on sapphire by metal organic vapor phase epitaxy. The EL intensity was found to be greatly enhanced under the photon bias. This enhancement strongly supersedes the photoluminescence (PL) signal. The EL enhancement varied with injection carrier density. The relative EL enhancement under 325‐nm laser bias starts with a high ratio and decreases monotonically. This increase of the EL intensity is tentatively attributed to a balance between photocarrier screening and carrier drift within the active region. These findings elucidate the transition from highly efficient recombination at low current density to the region of efficiency droop at high current densities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time‐resolved photoluminescence studies of high‐brightness 340‐nm LEDs under current injection
Authors: Garrett G. A. , Reed M. L. , Shen H. , Wraback M. , Chua C. , Johnson N. M.
Published: April 2008

We present time‐resolved photoluminescence studies on high‐brightness, 340‐nm LEDs under current injection. Devices exhibiting >5 mW at 100 mA drive current from a 100 µm × 100 µm area have been fabricated. PL lifetime measurements of InAlGaN multiple quantum well active regions under current injection are correlated with device operating parameters by using a nonlinear downconversion, optical‐gating technique. In wafer level measurements, a decrease in PL lifetime by ∼17% from 410 to 340ps as the injection current is increased from turn‐on to the onset of roll‐over (∼150 mA) may be at tributed to enhanced nonradiative recombination associated with device heating. An increase in the low‐current PL lifetime relative to that measured in the unbiased device is representative of trap saturation and screening of the MQW electric field through current injection prior to device heating. In addition, the PL lifetime was found to vary little over an operating time of ∼1900 hours, despite the drop in EL power by ∼50 percent. This result suggests that the degradation of the active region is not the major cause of the decrease in device performance over time. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microcavity InGaN light emitting diodes with a single Fabry‐Pérot mode
Authors: Choi Yong‐Seok , Iza Michael , Koblmüller Gregor , Hurni Christophe , Speck James S. , Weisbuch Claude , Hu Evelyn L.
Published: April 2008

We report on InGaN microcavity light‐emitting diodes supporting a single Fabry‐Pérot mode with an effective thickness of 450 nm and a cavity order of 5 at the emission wavelength of 415 nm. The device is a simple asymmetric cavity structure bounded by a highly reflective mirror at the bottom and air at the top. The single Fabry‐Pérot mode alters the emission pattern, so that a larger fraction of the generated light can be coupled to the light extraction cone. The device is fabricated by utilizing flip‐chip bonding, laser lift‐off, dry‐etch thinning, mesa formation, and contact deposition processes. Of particular challenge in the processing is the high‐precision control of final microcavity thickness. The control of microcavity thickness afforded by our selective dry‐etch thinning method can be further complemented by photonic crystal patterning and roughening, leading to highest improvements in light extraction efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Selective growth of GaN nanocolumns on predeposited Al patterns by rf‐plasma‐assisted molecular‐beam epitaxy
Authors: Ishizawa Shunsuke , Kikuchi Akihiko , Kishino Katsumi
Published: April 2008

The selective area growth of GaN nanocolumns was performed on a Si (111) substrate using predeposited Al nanopatterns by rf‐plasma‐assisted molecular‐beam epitaxy. The nanopatterns consisted of Al dots with 20‐65 nm diameter and 9‐27 nm thickness that were arranged in a 300‐nm‐period triangular lattice array and prepared by electron‐beam lithography and a liftoff process. The shape of the Al pattern tended to change during the growth process before nanocolumn growth, but its significant deformation was suppressed by nitridation at temperatures below 860 °C. The configuration of the GaN nanocolumns grown on the nitrided Al patterns depended on the pattern configuration; a sufficient volume of nitrided Al was required for nanocolumns to grow perpendicular to the substrate surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quaternary InAlGaN quantum‐dot ultraviolet light‐emitting diode emitting at 335 nm fabricated by anti‐surfactant method
Authors: Hirayama Hideki , Fujikawa Sachie
Published: April 2008

In order to realize high‐efficiency ultraviolet (UV) light‐emitting diodes (LEDs) or low threshold current UV laser diodes (LDs), group‐III nitride quantum dots (QDs) are very attractive. We fabricated quaternary InAlGaN quantum dots (QDs) using an anti‐surfactant method. The InAlGaN‐QDs were grown by low‐pressure metal‐organic chemical‐vapor deposition (MOCVD) on an InAlGaN buffer surface treated by a silicon anti‐surfactant. The lateral size and height of the self‐assemble InAlGaN QDs were 8‐18 nm and 5‐8 nm respectively as observed by the atomic force microscope (AFM). We observed intense photoluminescence (PL) from the InAlGaN QDs at room temperature (RT). We also fabricated an InAlGaN‐QD UV‐LED on a high‐quality AlN/AlGaN buffer template grown on a sapphire substrate. We obtained current injection emission of the InAlGaN‐QD UV‐LED with the wavelength of 335nm under RT CW operation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimisation of AlInN/GaN HEMT structures
Authors: Rahimzadeh Khoshroo L. , Mauder C. , Zhang W. , Fieger M. , Eickelkamp M. , Dikme Y. , Woitok J. , Niyamakom P. , Vescan A. , Kalisch H. , Heuken M. , Jansen R. H.
Published: April 2008

We report on the growth and characterisation of 190 nm thick Al0.83In0.17N layers and Al0.83In0.17N/GaN high electron mobility transistor (HEMT) structures on GaN/sapphire. High‐resolution X‐ray diffraction rocking curve measurements (HRXRD) exhibit full width at half maximum (FWHM) values of 68 and 175 arcsec for the GaN (0002) and (10‐15) reflections, respectively. The corresponding Al0.83In0.17N reflections yield 321 and 582 arcsec on 190 nm thick layers. XRD simulations of HEMT structures match well with measured data and with the intended heterostructure stack. Layer thickness fringes up to the 3rd order indicate a good heterointerface and enable precise barrier thickness determination. Further, no spinodal decomposition is detected for AlInN in both symmetrical and asymmetrical reciprocal space map measurements. Electrical characterisations of the HEMT at room temperature yielded a charge carrier density of ns = 2 x 1013 cm–2 and a mobility of µ = 1460 cm2/Vs underlined by processed devices demonstrating maximum drain current densities of 1.2 A/mm at VGS = 2 V and extrinsic transconductances of 243 mS/mm (LG = 1 µm, WG = 50 µm, 5 µm source‐drain spacing). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Valence band engineering for remarkable enhancement of surface emission in AlGaN deep‐ultraviolet light emitting diodes
Authors: Atsushi Yamaguchi A.
Published: April 2008

Valence band engineering for remarkable enhancement of surface emission in AlGaN deep‐ultraviolet (UV) light emitting diodes (LEDs) has been theoretically investigated by the calculation using the 6×6 k·p Hamiltonian. It has already been pointed out that the topmost valence band in deep‐UV AlGaN material has a Z‐like character and this causes the c‐axis polarized emission unfavourable for light extraction from c‐plane based LEDs. We have found, in this study, that this unfavourable polarization can be switched into favourable in‐plane polarization by decreasing quantum well (QW) width and/or introducing in‐plane compressive strain, which cause band‐crossing and change the character of the topmost band. It is also shown that such polarization changes occur in the QWs on semipolar substrates although that does not take place in those on nonpolar substrates. Furthermore, we have derived the condition of the polarization switch as an approximate analytical expression which could be useful for device structural design. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Unpolarized intersubband photocurrent in Te doped GaInAsN/GaAlAs quantum well IR photodetector
Authors: Albo Asaf , Fekete Dan , Bahir Gad
Published: April 2008

We report observation of unpolarized intersubband photocurrent (PC) in quantum‐well infrared photodetector (QWIP) based on Te doped GaInAsN/AlGaAs multiple‐quantum well structures (MQWs). The unpolraized photocurrent spectrum is peaked at 2.4 μm in front and wedge waveguide configuration illumination. Clear PC signals are observed up to room temperature. Reference sample not containing nitrogen with the same MQW structure shows p polarized intersubband photoresponse as expected in the conduction band of III‐V semiconductors MQWs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Design issues for adaptive control charts
Authors: Jensen Willis A. , Bryce G. Rex , Reynolds Marion R.
Published: April 2008

Adaptive control charts allow the components of the quality‐monitoring scheme to vary in order to obtain improved performance over non‐adaptive control charts. Research has centered on components such as the sample size, time between samples, warning limits, and control limits and has recommended a variety of schemes, many of which are optimal in some sense. In practice, there are many other adaptive schemes that are near optimal, which will still yield considerable improvement over non‐adaptive control charts. In addition, the impact of parameter estimation on adaptive control chart performance must be taken into consideration. Based on the simulation results shown here, adaptive control charts should only be used for mature processes, where a sufficient amount of Phase I data have been obtained to ensure that the estimated control limits are accurate. When evaluating control chart performance, we consider initial state performance measures for simplicity and note that the conclusions obtained here apply to steady‐state performance measures. The evaluation of performance measures is easily handled by the Markov chain approach detailed in the Appendix. Copyright © 2008 John Wiley & Sons, Ltd.
Hydraulically related hydro‐morphological units: description based on a new conceptual mesohabitat evaluation model (MEM) using LiDAR data as geometric input
Authors: Hauer C. , Mandlburger G. , Habersack H.
Published: April 2008

A new conceptual mesohabitat evaluation model was developed and applied to the Kamp River, Austria. The model uses a functional linkage of three parameters (velocity, depth and bottom shear stress) to distinguish six different mesohabitat types (riffle, fast run, run, pool, backwater and shallow water) based on two‐dimensional depth‐averaged hydrodynamic‐numerical modelling. The results clearly revealed the variety and change of mesohabitat‐units under various flow conditions (3.6–89 m3s−1). In particular for low‐energy habitats, a shift from shallow‐ to backwater habitats was recognized at increasing discharges. Fast runs featured a larger percentage of the total wetted area (9–33%) as discharges increased, whereas pool habitats showed low variability (means of around 15%). A velocity‐depth‐bottom shear stress relationship (VDSR) was most suitable to differentiate between mesohabitat patterns; this relationship was compared with Froude numbers and with velocity‐depth ratios using ANOVA statistical analysis. This study also documented that the accuracy of river geometry plays a decisive role in habitat descriptions. Different height tolerances for the computation mesh (0.2 m, 0.5 m, 1 m accuracy) based on LiDAR significantly reduced important mesohabitats. Copyright © 2008 John Wiley & Sons, Ltd.
Chronology of rainbow trout reproduction in a warmwater tributary of the Chattahoochee River: using an invasive species as an indicator of watershed integrity
Authors: Long James M. , Tupy John A. , Scales Jennifer
Published: April 2008

The Chattahoochee River near Atlanta, Georgia, USA is a stocked tailwater trout (Salmonidae) fishery and rainbow trout (Oncorhynchus mykiss) have been found to spawn in selected warmwater tributary streams. Because these stocked fish enter non‐stocked waters and produce offspring that reside year‐round, they are technically invasive. One tributary in particular, Cabin Creek, has had documented spawning activity for three consecutive years since the stream was monitored. We chronicled the production of the 2006 year‐class of rainbow trout in this small, warmwater tributary to the Chattahoochee River. Based on electrofishing samples and otolith microstructure, the 2006 year‐class of trout were produced from spawning that occurred from 6 February 2006 to 10 March 2006. Fish from this year‐class grew from an average size of 34.28 mm total length (TL) on 26 April 2007 to 102.00 mm TL on 14 May 2007, which is an average increase in size of 67.72 mm over a 383‐day period or 0.18 mm/day. Water temperatures in the stream were near the lethal limits for rainbow trout, reaching a maximum of 24.57°C on 1 August 2006 and a maximum 7‐day average maximum (M7DAM) of 22.99°C on 7 August 2006. The watershed of Cabin Creek is one of the least urbanized in the area, protected from development within lands owned by the National Park Service, with high levels of forest cover, which facilitates rainbow trout young‐of‐year survival through the summer. Thus, the documented spawning and young‐of‐year survival of this invasive species appears to be indicative of high forested watershed integrity. Copyright © 2008 John Wiley & Sons, Ltd.