bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of pseudo‐multilayer structures based on starch‐polycaprolactone extruded blends
Authors: Bélard Laurent , Dole Patrice , Avérous Luc
Published: March 2009

This article is focused on the analysis of the structure‐process relationships of biodegradable materials. It is mainly focused on the analysis of phase separation phenomenon occurring during the extrusion of plasticized starch/polycaprolactone blends, in a slit die. Rheological characterizations are carried out, in‐line in an instrumented slit die at the exit of the extruder and, out‐line with different rheometers. In certain conditions, a pseudo‐multilayer structure can be generated with a polyester rich skin. Then, Electron Spectroscopy for Chemical Analysis (ESCA) and Fourier Transformed Infrared Attenuated Total Reflectance (FTIR‐ATR) analyses are conducted to evaluate semi‐quantitatively the polyester surface enrichment. In the range of available shear rates, the phase separation is mainly driven by the molecular weight of polycaprolactone, linked to its molten state viscosity. Three zones of surface enrichment, dependent on the molecular weights, are identified. Above 60,000 g·mol−1, no surface enrichment could be detected; below 37,000 g·mol−1, the phase separation occurs with no dependence on the processing conditions; between these two limits, the phase separation depends on both, the formulation and the processing conditions. A correlation between the rheological measurements and the phase separation is given. A predictive criterion based on the viscous behavior of the blend is established. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Synthesis and characterization of styrene butadiene rubber—Bentonite clay nanocomposites
Authors: Chakraborty Sugata , Sengupta Rajatendu , Dasgupta Saikat , Mukhopadhyay Rabindra , Bandyopadhyay Samar , Joshi Mangala , Ameta Suresh C.
Published: March 2009

In the present study, naturally occurring unfractionated bentonite clay was used to prepare styrene butadiene rubber/bentonite clay nanocomposite by latex stage blending. The bentonite clay was organo‐modified by in situ resol formation by the reaction of resorcinol and formaldehyde. The latex clay mixture was co‐coagulated with acid. The resulting clay masterbatch was compounded and evaluated by Fourier Transform Infrared spectroscopy, X‐ray diffraction (XRD), Transmission Electron Microscopy (TEM), Energy Dispersive X‐ray spectroscopy (EDS), Scanning Electron Microscopy, Thermogravimetric analysis, and Differential Scanning Calorimetry. XRD showed that the interplanar distance of the in situ resol‐modified bentonite clay increased from 1.23 to 1.41 nm for the unmodified bentonite. TEM analysis indicated partial exfoliation and/or intercalation. EDS (Si and Al mapping) of the clay revealed the nature of the dispersion in the nanocomposites vis‐à‐vis the conventional styrene‐butadiene rubber (SBR)/bentonite clay composite. Thermogravimetric analysis was used to compare the decomposition trends of the SBR/clay nanocomposites with the SBR/clay composite. The glass transition temperature of SBR/clay nanocomposites increased as compared with that of neat SBR. Substantial improvement in most of the other mechanical properties was also observed in case of the nanocomposites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Anisotropic mechanical properties of hot‐pressed PVDF membranes with higher fiber alignments via electrospinning
Authors: Na Haining , Li Qunying , Sun Hua , Zhao Ci , Yuan Xiaoyan
Published: March 2009

By the use of a high‐speed collection drum, poly(vinylidene fluoride) (PVDF) was electrospun into aligned ultrafine fibrous membranes from its solutions in a mixture of N,N‐dimethylformamide and acetone (9:1, v/v), and a continuous hot‐press post‐treatment was performed on the membranes to improve their mechanical properties. Anisotropic tensile results and rupture behaviors of the hot‐pressed PVDF membranes with higher fiber alignments in both revolving direction (RD) and cross direction were obtained. It was found that, due to the true fracture of electrospun fibers and improvement of the interfiber compaction by hot‐press, the tensile strength and modulus of the hot‐pressed membranes in RD reached the highest values at 58.12 ± 4.46 MPa and 519.9 ± 34.1 MPa, respectively when the collection speed was 10.42 m/s. The decrease of porosity and liquid absorption also represented the compaction improvement of the electrospun fibrous membranes. The combination of fiber alignments and hot‐press could provide a novel method to fabricate high strength of electrospun membranes which have highly potential applications in filtration or battery separators. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
The effects of frequency on fatigue threshold and crack propagation rate in modified and unmodified polyvinyl chloride
Authors: Samat Noorasikin , Burford Robert , Whittle Alan , Hoffman Mark
Published: March 2009

The cyclic fatigue crack behavior of polyvinyl chloride (PVC), with (PVC‐M) and without (PVC‐U) chlorinated polyethylene (CPE) impact modifier, was studied. The effect of impact modifier upon fatigue crack growth rate and threshold was evaluated at frequencies of 1, 7, and 20 Hz. It was shown that the addition of CPE lowered the threshold stress intensity factor amplitude for crack growth (ΔKth) of PVC‐M compared to that of PVC‐U at lower frequencies, and that the effect became more pronounced at lower frequency. At lower stress intensity factor amplitudes (below ΔK = 1 MPa·m1/2), there was a slight difference between the crack growth rates of U‐ and M‐PVC. The crack advance mechanism is investigated by microscopic observation of the crack tip process zone. Although the zone is relatively large in PVC‐M, associated with higher toughness, it did not improve the fatigue crack growth resistance significantly. Fracture surface observations reveal a higher density of fibrils on the fatigued surface of PVC‐M with the density, relative to that observed in PVC‐U, reducing with frequency. It is therefore hypothesized that accelerated fibril failure is a mechanism of fatigue. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
The effect of copper(II) on the thermal and mechanical properties of poly(vinyl alcohol)/silica hybrid
Authors: Li Juan , Suo Jinping , Wang Shifang
Published: March 2009

A novel copper‐poly(vinyl alcohol) (PVA)/silica complex was prepared and its chemical structure, thermal, and mechanical properties were studied. The results showed that the crystallinity of PVA first increased and then decreased by the addition of copper chloride, whereas, the thermal decomposition temperature increased dramatically. For PVA/silica hybrid, the decomposition temperature associated with the removal of water molecules in PVA chains was 262°C. But the temperature increased to 361°C when the content of copper chloride was 2 wt%. The intelligent electronic tensile tester was used to investigate the mechanical properties of these complexes. The results suggested that the tensile strength of the complexes is improved with negligible decrease in the plasticity. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Dual‐type electrochromic device with single wall carbon nano tube employment in gel electrolyte
Authors: Kösemen Arif , San S. Eren , Yerli Yusuf , Okutan Mustafa , Uygun Melek , Yilmaz Faruk , Celik Asuman
Published: March 2009

A novel conducting polymer‐based electrochromic device is proposed with single walled carbon nanotube (SWCNT) employment in gel electrolyte. Electrochemical film deposition on indium tin oxide substrates were governed and monitored via cyclic‐voltametry. Construction details of the proposed device are presented with its optimized parameters and SWCNT doping caused a noteworthy enhancement in efficiency and stability of the device performance. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Experimental and theoretical study on 3,5‐(oxo/thioxo) derivatives of 2,7‐dimethyl‐1,2,4‐triazepines–iodine molecular complexes
Authors: Esseffar M'Hamed , El Messaoudi Malika , Bouab Widad
Published: March 2009

Intermolecular charge‐transfer (CT) spectra of 3‐thioxo‐5‐oxo‐, 5‐thioxo‐3‐oxo‐, and 3,5‐dithioxo‐ derivatives of 2,7‐dimethyl‐[1,2,4]‐triazepine 1:1 molecular complexes with molecular iodine were studied in the UV‐visible region. Equilibrium constants and free energy changes of the formed complexes were determined in solution. Ab initio calculations at HF/LANL2DZ* and MP2/LANL2DZ* were carried out to establish the nature of the complexation site, to determine the complex structures, and to examine the basicity of these compounds toward molecular iodine. The 3,5‐dithioxo‐2,7‐dimethyl‐[1,2,4]‐triazepine is the most basic one toward molecular iodine. In all cases, the complexation takes place at the heteroatom attached to position 3 of the triazepine. Hence, although in general, thiocarbonyls are stronger bases than carbonyls in the gas phase, 5‐thioxo‐2,7‐dimethyl‐[1,2,4]‐triazepin‐3‐one behaves as an oxygen base towards I2. Experimental free energies in solution and gas‐phase computational values are linearly correlated. Copyright © 2009 John Wiley & Sons, Ltd.
Self‐doping PPV oligomers – electrochemistry and structure of the self‐doped systems
Authors: Baeke Jan K. , De Borger Roeland , Lemière Filip , Van Alsenoy Christian , Blockhuys Frank
Published: March 2009

A novel class of self‐doping conjugated oligomers, E,E‐2‐(sulfoalkoxy)‐5‐alkoxy‐1,4‐bis[2‐(2,4,6‐trimethoxyphenyl) ethenyl]benzenes, is presented. The synthesis and spectroscopic characterisation of five such oligomers are described, and an electrochemical analysis using cyclic voltammetry is performed to determine the anodic peak potentials. A structural study is performed on six self‐doping oligomers in which the structures and energies of the possible mono‐molecular forms of the electrically conducting doped material are described and evaluated using Hirshfeld charges and the Quantum Theory of Atoms In Molecules. Copyright © 2009 John Wiley & Sons, Ltd.
Manifestations of string theory in astrophysical data and at the LHC
Authors: Nawata S.
Published: March 2009

With the advent of the LHC and the continuing influx of cosmological data, phenomenological aspects of string theory have received renewed attention in recent years and many problems have been properly incorporated in this framework. For instance, recent theoretical considerations in string theory have applied a statistical approach to the enormous landscape of metastable vacua. The large number of vacua may shed some light on the cosmological constant problem. In addition, in string theory, attempts have been made to address the hierarchy problem within the context of the existence of large or warped internal dimensions transverse to a braneworld where we are confined, which lowers the effective scale of gravity to the TeV region. If this were the case, unseen dimensions of the space‐time can be at the border of the energy domain within reach of the next generation of particle accelerators.

Although the picture of the landscape may be the key to the cosmological constant problem, it is well‐known that the compactification of a string background to a four dimensional solution undergoing accelerating expansion is difficult, which is described by the no‐go theorem of Maldacena‐Nuñez. In the first part of this paper, we investigate the cosmological content of the Salam‐Sezgin supergravity which circumvents one of the hypotheses of the no‐go theorem of Maldacena‐Nuñez and consequently can support a de Sitter phase when lifted to string theory. We find a solution to the field equations in qualitative agreement with the observed dark energy density. The carrier of the acceleration in the present de Sitter epoch is a quintessence field slowly rolling down its exponential potential. Intrinsic to this model, there is a second modulus, which is automatically stabilized and acts as a source of cold dark matter with a mass proportional to an exponential function of the quintessence field.

In the second part, we explore a “new physics” signal at LHC, in the processes pp →γ + jet and pp→γ γ. In D‐brane quivers, there are one or more additional U(1) gauge symmetries, beyond the U(1)Y of the standard model, which follows from the property that the gauge group for open strings terminating on a stack of N identical D‐branes is U(N) rather than SU(N) for N > 2. (For N = 2 the gauge group can be Sp(1) rather than U(2).) With this property, the photon will participate with the SU(N) gauge boson in string tree level scattering processes which in the standard model occur only at one‐loop level. In order to evaluate this stringy correction, we considered the processes gg → g γ and gg →γγ, and found that cross section measurements of the process pp →γ + jet at the LHC will attain 5 σ discovery reach on low scale string models for Mstring as large as 4 TeV.
Shared TP53 gene mutation in morphologically and phenotypically distinct concurrent primary small cell neuroendocrine carcinoma and adenocarcinoma of the prostate
Authors: Hansel Donna E. , Nakayama Masashi , Luo Jun , Abukhdeir Abde M. , Park Ben H. , Bieberich Charles J. , Hicks Jessica L. , Eisenberger Mario , Nelson William G. , Mostwin Jasek L. , De Marzo Angelo M.
Published: March 2009

BACKGROUND

Small cell carcinoma of the prostate is an uncommon neoplasm, the origin of which has been controversial. To address this, we performed transcriptome profiling and TP53 sequencing of concurrent small cell and prostatic adenocarcinoma to determine the relationship between these entities.

METHODS

We identified an unusual case of primary prostate cancer that contained adjacent acinar adenocarcinoma (Gleason score 4 + 3 = 7) and small cell carcinoma. We performed laser capture microdissection to isolate tumor components and performed gene expression and TP53 gene sequence analysis on each component, with results validated by immunohistochemistry for PSA, PSAP, PSMA, androgen receptor, NKX 3.1 and neuroendocrine markers.

RESULTS

Transcriptome profiling of the carcinoma components identified 99 genes with a greater than 10‐fold differential expression between prostatic adenocarcinoma and small cell carcinoma, many of which have not been previously reported in prostate cancer. The small cell carcinoma component demonstrated upregulation of proliferative and neuroendocrine markers and tyrosine kinase receptors, and downregulation of cell adhesion molecules, supporting the aggressive nature of this form of carcinoma. Sequencing of the TP53 gene suggested a common clonal origin for both components.

CONCLUSIONS

This is the first report of a primary small cell carcinoma of the prostate subjected to extensive molecular analysis and the first to show a clonal relation between two morphologically distinct prostate cancer types. The evidence of progression to small cell carcinoma may yield important insights into the pathogenesis of this entity and provide a novel spectrum of molecular markers to further dissect cellular pathways important in tumor progression. Prostate 69:603–609, 2009. © 2009 Wiley‐Liss, Inc.
Overexpression of 5α‐reductase type 1 increases sensitivity of prostate cancer cells to low concentrations of testosterone
Authors: Thomas Lynn N. , Douglas Robert C. , Rittmaster Roger S. , Too Catherine K.L.
Published: March 2009

INTRODUCTION

Conversion of testosterone to dihydrotestosterone (DHT) by the enzymes 5α‐reductase types 1 (5αR1) and 2 (5αR2) is important for normal and pathological growth of the prostate. The predominant isoenzyme in normal prostate is 5αR2. However, prostate cancer (PCa) development is accompanied by a decrease in 5αR2 and an increase in 5αR1. The biological significance of increased 5αR1 expression is not fully understood. Therefore, the aim of this study was to determine the effect of overexpression of 5αR1 on growth and prostate‐specific antigen (PSA) production in PCa cells.

MATERIALS AND METHODS

LNGK‐9 PCa cells, transiently transfected with pTRE‐5αR1 or pTRE alone, were cultured in the presence or absence of testosterone at varying concentrations. Cell growth and PSA secretion were measured after 4–6 days. Cyclin E1, Ki67, and PSA mRNA levels were evaluated using RT‐PCR after 24 hr of treatment.

RESULTS

10 pM testosterone increased growth of pTRE‐5αR1 transfectants by 54.1% over cells grown in the absence of testosterone, compared to 25.0% in pTRE transfectants (P < 0.01). Likewise, PSA secretion was increased by 56‐fold in pTRE‐5αR1 transfectants treated with 10 pM testosterone, compared to 26‐fold in pTRE transfectants (P < 0.01). At concentrations of testosterone above 10 pM, the stimulatory effect on growth and PSA secretion was not distinguishable between pTRE‐5αR1 and pTRE transfectants.

CONCLUSIONS

These results demonstrate that upregulation of 5αR1 enhances the cellular response to low, but not high, concentrations of testosterone. This explains one mechanism by which castration‐recurrent PCa can proliferate in the presence of castrate levels of circulating testosterone. Prostate 69:595–602, 2009. © 2009 Wiley‐Liss, Inc.
Effect of phase separation on optical and electrical properties of Sn–Sb–Se glassy films
Authors: Kumar Praveen , Thangaraj R. , Sathiaraj T. S.
Published: March 2009

This paper reports the effect of phase separation on the structural, optical and electrical properties of thermally evaporated Snx Sb20Se70–x (x = 10, 11, 12.5) films. The X‐ray diffraction studies of the devitrified films show the crystallization of SnSe2, Sn2Sb4Se8 and Sn4Sb4Se10 phases for x = 12.5 film, while Sb2Se3 is the other major phase in all the film samples. The optical constants are calculated by using Swanpole's standard envelop method. The dispersion of the refractive index is discussed in terms of the Cauchy's dispersion relation and the Wample–DiDomenico (WDD) single‐oscillator model in the weak absorption region. The optical gap and the tailing parameter were calculated in the fundamental absorption region, while the Urbach energy was calculated by using the value of extinction coefficients. The dc conductivity measurements with temperature have also been performed and electrical conduction has been discussed in conjunction with the Meyer–Neldel rule for the present system. These results have been discussed taking into consideration the structural modifications induced by the phase separation in the present system. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isochronal shear stress relaxation and recovery of bulk and ribbon glassy Pd40Cu30Ni10P20
Authors: Nguyen N. T. N. , Khonik S. V. , Khonik V. A.
Published: March 2009

Measurements of torque relaxation upon isochronal (= linear) heating of bulk and ribbon glassy Pd40Cu30Ni10P20 differing ∼104‐fold in the production quenching rates have been performed. It has been found that torque relaxation in bulk samples is notably faster than that in the ribbons despite the fact that the former are denser. Preannealing at a temperature Ta strongly decreases the relaxation rate at all temperatures T ≤ Ta and shifts the relaxation curves towards higher temperatures similarly in bulk and ribbon samples. The relaxation law has been determined. It has been revealed that rapid quenching of thermally aged samples from the supercooled liquid state recovers the ability to plastic flow. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ferroelectrics at the nanoscale
Authors: Gregg J. M.
Published: March 2009

There are several factors which make the investigation and understanding of nanoscale ferroelectrics particularly timely and important. Firstly, there is a market pressure, primarily from the electronics industry, to integrate ferroelectrics into devices with progressive decreases in size and increases in morphological complexity. This is perhaps best illustrated through the roadmaps for product development in FeRAM (Ferroelectric Random Access Memory) where the need for increases in bit density will require a move from 2D planar capacitor structures to 3D trenched capacitors in the next few years. Secondly, there is opportunity for novel exploration, as it is only relatively recently that developments in thin film growth of complex oxides, self‐assembly techniques and high‐resolution ‘top–down’ patterning have converged to allow the fabrication of isolated and well‐defined ferroelectric nanoshapes, the properties of which are not known. Thirdly, there is an expectation that the behaviour of small scale ferroelectrics will be different from bulk, as this group of functional materials is highly sensitive to boundary/surface conditions, which are expected to dominate the overall response when sizes are reduced into the nanoscale regime.

This feature article attempts to introduce some of the current areas of discovery and debate surrounding studies on ferroelectrics at the nanoscale. The focus is directed primarily at the search for novel size‐related properties and behaviour which are not necessarily observed in bulk. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron emission from amorphous carbon film on discontinuous Ag islands
Authors: Zhu Dan , Li Dejie , Wang Jian
Published: March 2009

Electron emission from amorphous carbon thin film on discontinuous Ag nanoislands is reported. The discontinuous Ag islands are formed by evaporating Ag film at a substrate temperature of 350 °C, introduce thickness ununiformity of carbon thin film on it and help forming a lap of μm width as the electron emission area. The electron emission has a threshold and performances as an exponential type emission to the anode voltage. Uniform and stable electron emission can be reproducibly obtained. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN HEMT and MMIC development at Fraunhofer IAF: performance and reliability
Authors: Waltereit P. , Bronner W. , Quay R. , Dammann M. , Kiefer R. , Müller S. , Musser M. , Kühn J. , Raay F. van , Seelmann M. , Mikulla M. , Ambacher O. , Rijs F. van , Rödle T. , Riepe K.
Published: March 2009

We present a systematic study of epitaxial growth, processing technology, device performance and reliability of our GaN HEMTs and MMICs manufactured on 3 inch SiC substrates. Epitaxy and processing are optimized for both performance and reliability. The deposition of the AlGaN/GaN HEMT epitaxial structures is designed for low background carrier concentration and a low trap density in order to simultaneously achieve a high buffer isolation and low DC to RF dispersion. Device fabrication is performed using standard processing techniques involving both electron‐beam and stepper lithography. Gate lengths of 250 nm and 500 nm are employed for 10 GHz and 2 GHz applications, respectively. The developed HEMTs demonstrate excellent high‐voltage stability, high power performance and large power added efficiencies. Devices exhibit two‐terminal gate–drain breakdown voltages in excess of 160 V (current criterion 1 mA/mm) across the entire 3 inch wafer with parasitic gate and drain currents well below 1 mA/mm when biased up to 80 V drain bias under pinch‐off conditions. Load‐Pull measurements at 2 GHz on 800 μm gate width devices return a well‐behaved relationship between bias‐voltage and output‐power as well as power‐added‐efficiencies beyond 60% up toUDS= 100 V. For a drain bias of 100 V an output‐power‐density around 22 W/mm with 26 dB linear gain is obtained. On large devices (32 mm gate width packaged in industry‐standard ceramic packages) an output power beyond 100 W is achieved with a PAE above 50% and a linear gain around 15 dB. Dual‐stage MMICs in microstrip transmission line technology yield a power added efficiency of 40% at 8.56 GHz for a power level of 11 W. A single‐stage MMIC yields a PAE of 46% with 7 W of output power atVDS= 28 V. Reliability is tested on HEMT devices having a gate periphery of 8 × 60 μm at an operating bias of 50 V under both DC and RF conditions. About 10% drain‐current change under DC‐stress (50 mA/mm) is observed after more than 1000 h of operation with an extrapolated drain‐current degradation below 20% after 200000 h (more than 20 years) of operation. Under RF stress (2 GHz, 1 dB compression) the observed change in output power density is below 0.2 dB after more than 1000 h. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of aluminum carbide buffer layer on growth and self‐separation of m ‐plane GaN by hydride vapor phase epitaxy
Authors: Sasaki Hitoshi , Sunakawa Haruo , Sumi Norihiko , Yamamoto Kazutomi , Usui Akira
Published: March 2009

An m ‐plane GaN layer with a thickness of approximately 500 μm was successfully obtained on a conventional m ‐plane sapphire substrate with a diameter of 2 inches. The GaN layer was grown by hydride vapor phase epitaxy (HVPE) on a buffer layer of low‐temperature (LT) GaN/Al4C3 structure deposited on the sapphire substrate by metalorganic chemical vapor deposition (MOCVD). The deposition temperature of the Al4C3 layer affected the appearance of the m ‐plane GaN layer. The c‐axes of the GaN layer is parallel to the a‐axis of the sapphire substrate. The thick GaN layer spontaneously separated from the sapphire substrate after its growth. Complete self‐separation of the m ‐plane GaN from the sapphire substrate was achieved with good reproducibility when the thickness of the Al4C3 layer was 70–100 nm. By lapping and polishing the self‐separated GaN crystal, a freestanding m ‐plane GaN wafer with a diameter of 45 mm was obtained. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of m ‐GaN layers by epitaxial lateral overgrowth from sapphire sidewalls
Authors: Okada Narihito , Kawashima Yuji , Tadatomo Kazuyuki
Published: March 2009

Nonpolar m ‐plane GaN layers were fabricated by epitaxial lateral overgrowth from etched sapphire sidewalls. The m ‐plane GaN layers with c ‐direction growth were grown from patterned c ‐plane and a ‐plane sapphire substrates with a ‐plane or c ‐plane sidewalls using a low‐temperature buffer layer. The growth of GaN from the surface was prevented by a SiO2 mask, and that from the bottom of grooves was also prevented by deep grooves. Thus, the growth orientation relative to the surface of the GaN layer was determined by the growth of the GaN layer from the sapphire sidewalls. Consequently, m ‐plane GaN layers were grown on c ‐plane sapphire with a ‐plane sidewalls or on a ‐plane sapphire with c ‐plane sidewalls with the terrace regions covered with a SiO2 mask and deep grooves. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
222–282 nm AlGaN and InAlGaN‐based deep‐UV LEDs fabricated on high‐quality AlN on sapphire
Authors: Hirayama Hideki , Fujikawa Sachie , Noguchi Norimichi , Norimatsu Jun , Takano Takayoshi , Tsubaki Kenji , Kamata Norihiko
Published: March 2009

We demonstrate 222–282 nm AlGaN and InAlGaN‐based deep ultraviolet (DUV) light‐emitting diodes (LEDs) fabricated on low threading dislocation density (TDD) AlN template. Low TDD AlN templates were realized by using ammonia (NH3) pulse‐flow multilayer (ML) growth technique. The edge‐ and screw‐type dislocation densities of AlN layer were reduced to 7.5 × 108 and 3.8 × 107, respectively. Single‐peaked electroluminescence (EL) were obtained for 222– 273 nm AlGaN multi quantum well (MQW) DUV‐LEDs. We obtained the maximum output power of 1.1 mW and 4.0 mW for the AlGaN‐QW LEDs with wavelengths of 241 nm, 256 nm, respectively, under room temperature (RT) CW operations. The maximum output power of 227 nm and 222 nm AlGaN‐QW were 0.15 mW and 0.014 mW, respectively, under RT pulsed operation. The maximum external quantum efficiency (EQE) of the 227 nm and 250 nm AlGaN LEDs were 0.2% and 0.43%, respectively. We also fabricated 280 nm band quaternary InAlGaN‐MQW DUV‐LEDs with n‐type and p‐type InAlGaN layers on ML‐AlN templates. We demonstrated extremely high internal quantum efficiency (IQE) of 284 nm InAlGaN‐QW emission, which was confirmed by the fact that the ratio of the integrated intensity of the RT‐PL against the 77 K‐PL was 86%. The maximum output power and EQE of the 282 nm InAlGaN LED were 10.6 mW and 1.2%, respectively, under RT CW operation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
N‐type doping of InGaN by high energy particle irradiation
Authors: Yu K. M.
Published: March 2009

This article reviews our extensive studies of the effects of native defects introduced by high energy particles on the electrical and optical properties of InGaN alloys. We show that the electronic properties of irradiated InGaN can be well described by the amphoteric defect model. Because of the extremely low position of the conduction band edge of InN the formation energy of native donor defects is very low in In‐rich InGaN alloys. High energy particle irradiation of InN and In‐rich InGaN, will therefore produce donor defects and result in more n‐type materials. As the irradiation dose increases, the electron concentration increases until the Fermi energy EF approaches the Fermi stabilization energy EFS. At this point both donor and acceptor‐type defects are formed at similar rates, and compensate each other, leading to stabilization of EF and a saturation of the electron concentration. Hence a large increase and then saturation in the Burstein–Moss shift of the optical absorption edge is also observed. Furthermore we also found that mobilities in the irradiated films can be well described by scattering from triply charged defects, providing strong evidence that native defects in InN are triple donors. The excellent agreement between the experimental results and predictions based on the ADM suggests that particle irradiation can be an effective and simple method to control the doping (electron concentration) in In‐rich Inx Ga1–x N via native point defects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐ and three‐dimensional composite photonic crystals of macroporous silicon and lead sulfide semiconductor nanostructures
Authors: Gutman Nadav , Armon Akiva , Osherov Anna , Golan Yuval , Sa'ar Amir
Published: March 2009

We describe a new method for direct deposition and growth of nanocyrstalline lead sulfide (PbS) thin films into two‐ and three‐dimensional arrays of macroporous silicon and the formation of composite silicon photonic crystals (PhCs). Infrared transmission measurements exhibit a substantial red‐shift of the photonic stop bands from the composite PhCs relative to the PhC substrates. Photoluminescence spectroscopy reveals the effect of slow‐light modes on the emission spectra from PbS thin films inside a two‐dimensional PhC. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reusable linking chemistry for His‐6 tagged proteins in an affinity‐based porous silicon biosensor
Authors: Bonanno Lisa , DeLouise Lisa
Published: March 2009

The inexpensive fabrication and intrinsic optical and filtering properties of porous silicon (PSi) make optical PSi biosensors ideally suited for diagnostic testing. Long term goals of a diagnostic sensor would benefit from reversible binding chemistry to allow retesting of patient samples and collection of captured target for analysis. This work illustrates a versatile method to immobilize hexahistidine (His‐6) tagged molecular probes and utilizes reversible competitive chelating chemistry to reuse the porous silicon sensor device. Reuse of this Ni–His‐6 chemistry in a PSi affinity‐based biosensor was demonstrated with two different His‐6 tagged proteins to give consistent probe loading values within mimimal error over 4 cycles of use. Advantages of utilizing any site‐directed immobilization method include the homogeneity of surface bound probe molecule orientation, which we also illustrate resulted in a 2‐fold increase in detection capability of a secondary target antibody. As the current sensitivity range of macroporous PSi sensors (diameters of 30–100 nm) pose limitations to their use in medical applications; this work identifies the ability to improve target capture through the development of an efficient and versatile linking chemistry. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of porous anodic alumina templates in selected micrometer‐sized areas on a Si substrate. Application for growing ordered Ti nanopillars
Authors: Gianneta V. , Huffman M. , Nassiopoulou A. G.
Published: March 2009

The local formation of porous anodic alumina (PAA) thin films on confined areas measuring few μm2 through an SiO2 masking layer on the silicon substrate has been developed. The locally grown porous anodic alumina thin films showed highly symmetric vertical cylindrical pores with a pore density that was much higher than that of films on non‐confined areas. Pore density as high as 6 × 1010 pores/cm2 was achieved, compared to ∼1010 pores/cm2 in corresponding large‐area samples. Pore diameter was as small as 30–50 nm. Alumina thin films on confined areas on a Si substrate are very interesting for use as masking layers for local Si nanopatterning or as templates for local growth of different nanostructures, e.g. nanowires of different materials, on wafer level. In this work, we used the PAA films as sacrificial templates to grow locally on a silicon wafer using sputtering, regular arrays of Ti nanopillars on pre‐selected areas on the Si wafer. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Location‐dependent controlled release kinetics of model hydrophobic compounds from mesoporous silicon/biopolymer composite fibers
Authors: Fan Dongmei , Loni Armando , Canham Leigh T. , Coffer Jeffery L.
Published: March 2009

In this study, biodegradable mesoporous Si (BioSiliconTM) was loaded with cis‐(2,2′‐bipyridine) dichlororuthenium (II) (Ru complex) as a model hydrophobic compound. This ruthenium complex‐loaded BioSiliconTM was either partially embedded on the surface of electrospun polycaprolactone (PCL) fibers or fully encapsulated within the fibers. To study release profiles in the above model delivery systems, porous Si/PCL constructs were soaked in DI water at 37 °C and the UV–Vis absorption spectrum of the supernatant was measured as a function of time. These results show that the Ru complex was released in a sustained manner over 7‐day period. In addition, it is shown that the controlled‐release of this complex depends on both the spatial location of the complex in the PCL fibrous scaffolds as well as the amount of Ru compound loaded in the mesoporous Si. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Subwavelength inhomogeneities in Cu(In,Ga)Se2 thin films revealed by near‐field scanning optical microscopy
Authors: Gütay Levent , Pomraenke Robert , Lienau Christoph , Bauer Gottfried Heinrich
Published: March 2009

We have analyzed Cu(InGa)Se2 thin films, fabricated by standard deposition technique for solar cells, by near‐field scanning optical microscopy (NSOM) which allows for simultaneous detection of photoluminescence (PL) and AFM‐like topography. In comparison with our former confocal microscopy studies this approach yields a lateral optical resolution of ≈200 nm which is substantially below the diffraction limit. The sample is investigated by a fiber probe which guides the laser excitation to the sample surface and collects the PL signal. The recorded scans show significant lateral variations of the PL yield on length scales of 0.2–1.5 μm. By applying Planck's generalized law we extract lateral variations of the splitting of quasi‐Fermi levels Δ(EFn–EFp) and optical threshold energies ΔEop,th (band gap) in the absorber. We find substantial lateral variations of these properties with ΔFWHM(EFn–EFp) ≈ 17 meV (FWHM: full width half maximum), ΔFWHM(Eop,th) ≈ 18 meV and ΔFWHM(thickness) ≈ 220 nm. While no significant correlation between local surface topography and PL yield or Δ(EFn–EFp) is observed, we find a clear anticorrelation between the optical threshold energies and the recorded height signal. Our results extend previous studies of inhomogeneity effects on solar cell absorbers towards the 100 nm regime. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impurity vibration modes in II–VI and III–V mixed semiconductors
Authors: Postnikov Andrei , Pagès Olivier , Souhabi Jihane , Nassour Ayoub , Hugel Joseph
Published: March 2009

The analysis of vibration frequencies in dilute semiconducting alloys is addressed, as part of a more vast paradigm for the description of lattice dynamics in semiconductor alloys within the “1 bond – 2 mode” concept. Specific cases considered are those of Be impurities in ZnSe (system with high elastic contrast; aspects of impurity clustering) and of (Ga,In)As alloys, exhibiting much smaller elastic contrast and almost vanishing value of the mode splitting parameter, Δ. First‐principles calculations of frequencies are done by Siesta method, using 64‐atom supercells. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Se activity and its effect on Cu(In,Ga)Se2photovoltaic thin films
Authors: Contreras Miguel A. , Repins Ingrid , Metzger Wyatt K. , Romero Manuel , Abou‐Ras Daniel
Published: March 2009

We study some physical properties of CuIn1–xGaxSe2thin‐films fabricated by evaporation from elemental sources under various Selenium environments. Specifically, thin‐films were fabricated under growth conditions such as Se deficiency, near stoichiometry and excess Se during coevaporation to investigate the impact of the Se environment on absorber film properties and ultimately the device performance. We determine the chemical activity of Se in the evaporation process has a strong influence on film macrostructure (prefered orientation) and microstructure, particularly at the grain and grain boundary level. It is shown that the optoelectronic properties at grain boundaries are affected by the Se environment used resulting in absorber thin‐films with distictive defect distribution and defect density. Consequently, the performance of the solar cells fabricated from those films is also affected by the Se environment. These effects on solar cell performance and absorber properties are reported in a (i) structural analysis of the CuIn1–xGaxSe2/Mo/glass samples by X‐ray and electron backscattering techniques; (ii) optolectronic radiative characteristics of the absorbers by cathode luminescence and photoluminescence studies and (iii) current–voltage, quantum efficiency and capacitance–voltage measurements for the solar cells made from the absorbers fabricated under the pre prescribed Se growth conditions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Use of contactless electroreflectance in the development of quantum cascade lasers from ZnCdSe/ZnCdMgSe
Authors: Muñoz Martin , Tamargo Maria C.
Published: March 2009

Electro‐modulation techniques have been used extensively to analyze interband transitions in materials and devices, however little has been done to use these techniques for the analysis of intersubband transitions in materials and devices. In this work, contactless electroreflectance has been used to determine the conduction band offset of ZnCdSe/ZnCdMgSe quantum well structures. Toward the development of quantum cascade lasers, multi‐quantum well structures with intersubband absorption at 178 meV were analyzed using contactless electro‐reflectance. Finally, quantum cascade laser structures were designed for emission at 4.8 μm. The multi‐quantum well structures presented an excellent agreement between the designed and measured absorption and emission, respectively. This work demonstrates that contactless electro‐reflectance can accurately determine the conduction band offset and is useful in the analysis of intersubband transitions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of polarization‐dependent photoreflectance studies for c ‐plane GaN films grown on a ‐plane sapphire
Authors: Röppischer Marcus , Goldhahn Rüdiger , Buchheim Carsten , Furtmayr Florian , Wassner Thomas , Eickhoff Martin , Cobet Christoph , Esser Norbert
Published: March 2009

The optical properties of c ‐plane GaN layers grown by molecular beam epitaxy on a ‐plane sapphire substrate are investigated. Polarization‐dependent photoreflectance spectroscopy was applied with the electric field vector of the probe beam being either parallel or perpendicular to the [10$ \bar 1 $0] direction of the GaN films. A pronounced in‐plane optical anisotropy under normal incidence of light is observed which is attributed to anisotropic in‐plane strain. It originates from the difference of the thermal expansion coefficients of the substrate parallel and perpendicular to its c‐axis. Temperature‐dependent studies and a comparison to photoluminescence and reflectance anisotropy studies indicate that the strain (anisotropy) increases with decreasing sample temperature. The dependence of transition energies and oscillator strengths of GaN as a function of strain values is calculated by k·p perturbation theory for comparison. The results emphasize the experimental data. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Piezoreflectance and photoreflectance study of annealing effects on GaAs0.916Sb0.084 and GaAs0.906Sb0.075N0.019 films on GaAs grown by gas‐source molecular beam epitaxy
Authors: Hsu H. P. , Huang Y. N. , Huang Y. S. , Lin Y. T. , Ma T. C. , Lin H. H. , Tiong K. K. , Sitarek P. , Misiewicz J.
Published: March 2009

Thermal annealing effects of GaAs0.916Sb0.084 and GaAs0.906Sb0.075N0.019 films grown on GaAs substrates by gas‐source molecular beam epitaxy have been characterized by piezoreflectance (PzR) and photoreflectance (PR). By a comparison of relative intensity of PzR and PR spectra, the identification of conduction to heavy‐hole (HH) band and conduction to light‐hole (LH) band transitions originated from the strained induced valence band splitting have been achieved. The near band edge transition energies are blue‐shifted, and the splitting of HH and LH bands is reduced after thermal annealing treatment. The annealing effects of GaAs0.906Sb0.075N0.019 are found to be more pronounced than that of GaAs0.916Sb0.084. The temperature dependences of near band edge transition energies are analyzed using Varshni and Bose–Einstein expressions in the temperature range from 15 K to 300 K. The parameters that describe the temperature variations of the near band edge transition energies are evaluated and discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of ultra‐high pressure sterilization on the structure of polymer films
Authors: Fairclough J. P. A. , Conti M.
Published: March 2009

The effect of ultra‐high‐pressure processing on the structure of polymer film pouches, commonly used in food packaging, has been studied. In particular, the effect of an air headspace on the polypropylene heat‐sealing inner layer is reported. With increasing pressure, both nitrogen and oxygen gases become increasingly soluble in the polymer layer. If the pressure is rapidly released, this causes voids and pits to form in the inner layer. An estimate of the increased solubility (70‐fold) is calculated from regular solution theory. Copyright © 2009 John Wiley & Sons, Ltd.
Theoretical studies on redox properties, protonation sites, and electronic spectrum of a new type of polyoxometalate [Ti12Nb6O44]10− by DFT
Authors: Si Yan‐Ling , Chen Wei‐Lin , Wang En‐Bo
Published: March 2009

The electronic structure of a new type of polyoxometalate [Ti12Nb6O44]10− has been investigated using density functional theory (DFT). The calculations represent that the LUMO in fully oxidized [Ti12Nb6O44]10− delocalizes among the titanium (Ti) and niobium (Nb). Therefore, both Ti and Nb have the probability to accept extra electron when [Ti12Nb6O44]10− as catalyst is reduced, which has been reinforced by the spin density for the monoreduced specie [Ti12Nb6O44]11−. Three kinds of possible protonated isomers [HTi12Nb6O44]9− are discussed. The results reveal that the preferred protonation sites correspond to bridging oxygens NbOTi. In addition, the calculation of electronic spectrum shows that there is an obvious intramolecular charge transfer from oxygen to metal. The solvent effects were also considered in the calculations by using a conductor‐like screening model (COSMO) of solvation with the solvent‐excluding surface. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Implementation and benchmark tests of the DFTB method and its application in the ONIOM method
Authors: Zheng Guishan , Lundberg Marcus , Jakowski Jacek , Vreven Thom , Frisch Michael J. , Morokuma Keiji
Published: March 2009

We present the theoretical and implementation details of the DFTB method with analytical gradients into the Gaussian package. SCF optimization performance with DIIS method is compared with modified Broyden method and Anderson methods, from which DIIS method is to be preferred. The number of geometry optimization steps can be significantly decreased with the Berny algorithm compared to the conjugated gradient method. From the comparison of geometry parameters as well as trends in the change of HOMO and LUMO energies, the results show clearly that DFTB can reproduce values obtained at the B3LYP/6‐31G(d) level well. We also investigated the DFTB method as the low level quantum mechanical (QM) method in an ONIOM (QM:QM′) description for an amino acid model system and found DFTB promising as a method to describe polarization and charge‐transfer effects in large systems. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Charge conducting properties of hydrated DNA duplex between Au electrodes obtained by molecular simulations and Green's function theory
Authors: Tsukamoto Takayuki , Wakabayashi Hajime , Sengoku Yasuo , Kurita Noriyuki
Published: March 2009

The dependence of charge conducting properties through DNA‐duplex + Au‐electrode systems on DNA base sequence, DNA conformation, structure of Au electrodes, and solvating water molecules was investigated by using molecular simulations and Green's function theory. The simulated results indicate that the conducting properties depend most strongly on the structure of Au electrodes. It is also clarified that the charge conductance through DNA duplex is largely affected by the conformational change of DNA and the structure of connection between DNA‐duplex and Au electrodes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
The chemiionization reactions Ce + O and Ce + O2: Assignment of the observed chemielectron bands
Authors: Todorova Tanya K. , Infante Ivan , Gagliardi Laura , Dyke John M.
Published: March 2009

Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemiionization reactions Ce + O → CeO+ + e− and Ce + O2 → CeO + e−. Selected spectroscopic constants for CeOn and CeO (n = 1, 2), as well as reaction enthalpies of the chemiionization reactions of interest, have been computed and compared with experimental values. In contrast to the lanthanum case, for both Ce + O2(X3Σ) and Ce + O2( a1Δg), the Ce + O2 → CeO + e− reaction is shown to be exothermic, and thus, contributes to the experimental chemielectron spectra. The apparent discrepancy between the computed reaction enthalpies and the high kinetic energy offset values measured in the chemielectron spectra is rationalized by arguing that chemielectrons are produced mainly via two sequential reactions (Ce + O2 → CeO + O, followed by Ce + O → CeO+ + e−) as in the case of lanthanum. For Ce + O2 (a1Δg), a chemielectron band with higher kinetic energy than that recorded for Ce + O2( X3Σ) is obtained. This is attributed to production of O( 1D) from the reaction Ce + O2( a1Δg) → CeO + O( 1D), followed by chemiionization via the reaction Ce + O( 1D) → CeO+ + e−. Accurate potential energy curves for the ground and a number of excited states of CeO and CeO+ have been computed, and a mechanism for the chemiionization reactions investigated experimentally was proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009