bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractLinear 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

AbstractPolydimethylsiloxane (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

AbstractExfoliated 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
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

AbstractWe 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

AbstractHigh‐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

AbstractThe 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

AbstractGrowth 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

AbstractAl0.4Ga0.6N 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

AbstractWe 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

AbstractThis 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

AbstractThis 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

AbstractWe 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

AbstractIn 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

AbstractWe 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

AbstractUnder 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

AbstractWe 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

AbstractWe 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

AbstractThe 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

AbstractIn 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

AbstractWe 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)