bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the dehydrogenative polymerization of monolignol β-glycosides. Part 6: Monitoring of horseradish peroxidase-catalyzed polymerization of monolignol glycosides by GPC-PDA
Authors: Tobimatsu Yuki , Takano Toshiyuki , Kamitakahara Hiroshi , Nakatsubo Fumiaki
Published: January 2010

Horseradish peroxidase (HRP)-catalyzed dehydrogenative polymerization of guaiacyl (G) and syringyl (S)-type monolignol γ-O-glucosides, isoconiferin (iso-G) and isosyringin (iso-S), which contain a hydrophilic glucosyl unit on γ-position of coniferyl alcohol and sinapyl alcohol, respectively, was monitored by gel permeation chromatography coupled with photodiode array detection (GPC-PDA). Contrary to the conventional dehydrogenative polymerization of monolignols, the polymerization of the glycosides produces water-soluble synthetic lignins (DHPs) in a homogeneous aqueous phase. Taking advantage of this unique reaction system, the method was developed to follow the changes of molecular weights in the course of DHP formations. Moreover, PDA detection permits determination of oligomeric S-type quinone methide intermediates (QMs) formed as stable transient compounds during polymerization of iso-S. A detailed comparison of the polymerization profiles revealed entirely different behaviors of G- and S-type monomers. The data strongly support the view that the low reactivity of oligomeric S-type QMs impedes the formation of DHPs from S-type monomers. In copolymerization of G- and S-type monomers, it is conceivable that G-type phenolic hydroxyl groups serve as good nucleophilic reactants to scavenge S-type QMs resulting in efficient production of DHPs. As a consequence, the present approach can be a powerful tool to study the in vitro dehydrogenative polymerization providing further mechanistic insights into lignin polymerization in vivo.
Determination of the change in appearance of lumber surfaces illuminated from various directions
Authors: Nakamura Masashi , Matsuo Miyuki , Nakano Takato
Published: January 2010

Optical appearance is an important aesthetic property of wood, and this unique visual characteristic needs to be described quantitatively for many industrial applications. The objective of this study is to demonstrate the change in appearance of lumber surfaces from the viewpoint of human observation. Ten different specimens of coated and uncoated fancy veneer overlaid plywood of four species and solid and print Sugi (Japanese cedar) boards were prepared. For observation purposes, a simple goniophotometric device was constructed. A series of digital images of each specimen was taken, whereas the surface was illuminated from various lighting azimuths. The images were evaluated by subtraction, correlation, and multiresolution contrast analyses. The first two methods detect reflection anisotropy on the specimen surface through comparison of two images. Subtraction analysis also distinguishes between the coated and uncoated surfaces. However, it is difficult to determine the difference between the solid and print Sugi specimens based on these techniques. By contrast, multiresolution contrast analysis renders possible evaluation of the size and degree of the change in the surface appearances by contrast values. By comparing the contrast values for every lighting azimuth and filter size, this analysis clearly determines the change in appearance peculiar to wood, such as reflection anisotropy, improvement in reflectiveness conferred by coating, and the difference between the solid and print Sugi specimens.
Thermal aging of 1-alkyl-3-methylimidazolium ionic liquids and its effect on dissolved cellulose
Authors: Liebner Falk , Patel Ilabahen , Ebner Gerald , Becker Ernst , Horix Michael , Potthast Antje , Rosenau Thomas
Published: January 2010

The thermal degradation products of 1-alkyl-3-methyl-imidazolium-type ionic liquids (e.g., BMIM, EMIM), which are commonly used in cellulose chemistry, were identified. Imidazole (5), N-methylimidazole (6), and N-alkylimidazoles (7, 8) are the main products. Moreover, dimeric substituted imidazoles (9–11) were found carrying a methylene bridge formed from the N-methyl structure. The former 1-alkyl group (butyl or ethyl) was not present in any of the dimeric compounds. The N-methylene intermediate (12) acts as a precursor for the substituted imidazoles linked by a methylene group. All thermal degradation products are bases and catalyze the previously described reaction between the reducing end of celluloses and 1-alkyl-3-imidazolium cations. To minimize this side reaction, ionic liquids have to be liberated from such basic compounds prior to application as cellulose solvents. In this regard, the usage of “recycled” (and unpurified) ionic liquids has to be treated with caution.
Extractives of the tropical wood wallaba (Eperua falcata Aubl.) as natural anti-swelling agents
Authors: Royer Mariana , Stien Didier , Beauchêne Jacques , Herbette Gaëtan , McLean J. Paul , Thibaut Anne , Thibaut Bernard
Published: January 2010

Wallaba (Eperua falcata) is a tropical wood that is known to have naturally high moisture related dimensional stability. Samples of wallaba heartwood were subjected to differential solvent extraction. Wood pieces that were extracted with methanol showed significantly greater swelling following rehydration from oven dry to 96% relative humidity than non-extracted samples and samples extracted with other solvents. Methanol soluble wallaba heartwood extract was purified by HPLC and the compounds present were characterized by NMR spectroscopy. The structure of 13 compounds in methanol extract was identified. The relative proportion of polar compounds in methanol extract was found to be high. The compounds identified are proposed to bind to the polymeric cell wall by means of multiple hydrogen bonds restricting the association of water and therefore act as natural anti-swelling agents.
Preparation of thermoplastic molding from steamed Japanese beech flour
Authors: Takahashi Isoko , Sugimoto Takanori , Takasu Yasuo , Yamasaki Mariko , Sasaki Yasutoshi , Kikata Youji
Published: January 2010

Thermoplastic molding has been prepared from beech wood flour steamed at 180°C or at higher temperatures without any additives. It exhibited a smooth and lustrous surface and had a high density of approximately 1.45 g cm-3. The internal structure of molding revealed that the flour particles were completely surrounded by black resin-like substance which was thermoplasticized by heat and pressure during the molding process. The chemical composition of the steamed flour and physical properties of molding were examined as a function of steaming temperature. Maximum bending strength and Young's modulus of molding reached 63 MPa and 11 GPa, respectively, at 180°C of steaming, which were much higher than those of a hardboard. The water absorption of the molding was 8% or less and decreased with the steaming temperature.
Taking Cognitive Dualism Seriously: Revisiting the Durkheim-Spencer Debate on the Rise of Individualism
Authors: Lizardo Omar
Published: January 2010

The question of the extent to which Durkheim's argument in Division of Labor in Society is continuous with or radically departs from the work of Herbert Spencer has been the subject of a long-standing debate. In this article, the author revisits this issue in light of recent scholarship that points to the pervasive role of the notions of “representation” and “dualism” in Durkheim's overall thought. The analysis shows that Durkheim's conception of the rise of individualism is significantly different from that of Spencer, precisely because it is based on idiosyncratic concepts with no analogue in Spencer's system. Because of this difference, Durkheim's critique of Spencer largely misses the mark and in fact requires an ambiguous projection of Durkheim's own theory-laden notion of individualism toward Spencer, in order to suggest that Spencer begs the question. The author concludes that Durkheim and Spencer had largely incommensurable ideas as to the primary consequence of the division of labor: The rise of “individualism.” This necessitates the analytical distinction between the two conceptions of “the individual,” which I label the “bio-psychological” and the “sociological.”
Absence of major fibrotic adverse events in hyperprolactinemic patients treated with cabergoline
Authors: Lafeber M , Stades A M E , Valk G D , Cramer M J , Teding van Berkhout F , Zelissen P M J
Published: January 2010

Background

Cabergoline, a dopamine agonist used to treat hyperprolactinemia, is associated with an increased risk of fibrotic adverse reactions, e.g. cardiac valvular fibrosis, pleuropulmonary, and retroperitoneal fibrosis.

Objective

This study evaluated the prevalence and risk of fibrotic adverse reactions during cabergoline therapy in hyperprolactinemic and acromegalic patients.

Design

A cross-sectional study was conducted in a University Hospital.

Patients

A total of 119 patients with hyperprolactinemia and acromegaly who were on cabergoline therapy participated in the study.

Methods

All patients were requested to undergo a cardiac assessment, pulmonary function test, chest X-ray, and blood tests as recommended by the European Medicine Agency. Matched controls were recruited to compare the prevalence of valvular regurgitation. Cardiac valvular fibrosis was evaluated by assessing valvular regurgitation and the mitral valve tenting area (MVTa). The risk of pleuropulmonary fibrosis was assessed by a pulmonary function test, a chest X-ray, and if indicated, by additional imaging studies.

Results

The prevalence of clinically relevant valvular regurgitation was not significantly different between cases (11.3%) and controls (6.1%; P=0.16). The mean MVTa was 1.27±0.17 and 1.24±0.21 cm2 respectively (P=0.54). Both valvular regurgitation and the MVTa were not related to the cumulative dose of cabergoline. A significantly decreased pulmonary function required additional imaging in seven patients. In one patient, possible early interstitial fibrotic changes were seen. Lung function impairment was not related to the cumulative cabergoline dose.

Conclusion

Cabergoline, typically dosed for the long-term treatment of hyperprolactinemia or acromegaly, appears not to be associated with an increased risk of fibrotic adverse events.
Protein-Losing Enteropathy Caused by Gastrointestinal Tract–Involved Langerhans Cell Histiocytosis
Authors: Shima Haruko , Takahashi Takao , Shimada Hiroyuki
Published: January 2010

Protein-losing enteropathy (PLE) is frequently complicated in patients with gastrointestinal tract–involved Langerhans cell histiocytosis (LCH); however, LCH per se is not generally included in the list of diseases that cause PLE. We report here a case of infantile PLE that presented with continuous diarrhea at the onset of LCH. She was initially diagnosed as having allergic gastroenteropathy and, thus, received intravenous prednisolone, which was thought to have induced immunodeficiency and consequently resulted in life-threatening cytomegalovirus-associated hemophagocytic syndrome and disseminated intravascular coagulation. Because chemotherapy for hemophagocytic syndrome was transiently effective for underlying LCH as well, the diagnosis of LCH was delayed until its recurrence. Gastrointestinal tract–involved LCH, a rare but highly fatal disease, should be considered for infants with refractory gastrointestinal symptoms, especially for those with PLE; endoscopic biopsy is strongly recommended for immediate diagnosis.
Fluorites: Superionics and Conduction Processes
Authors: Hull Stephen
Published: January 2010

The superionic conducting properties of fluorite structured compounds are discussed in this paper, starting with a brief historical overview of the topic. The current state of knowledge concerning the dynamic lattice disorder associated with the high values of ionic conductivity is summarized and illustrated using three examples taken from the author’s research program. These are chosen to highlight different aspects of the structure-property relationships within fluorite-structured superionics and, in particular, demonstrate the role of the neutron diffraction technique in investigations of compounds showing high levels of ionic conductivity. The paper concludes with an overview of some current developments within this research field.
Dissociation of H2O molecule adsorbed on Si (001) 2×1 surface: a theoretical study
Authors: Oh Hyun-Chul , Seo Hwa-Il , Kim Yeong-Cheol
Published: January 2010

The adsorption and dissociation behavior of water molecule below and above the critical dissociation temperatures were studied by first principles calculations. We found that water-molecule adsorption (surface coverage, θ=0.25) on the down Si atom of a Si dimer in two dimers surface model was 0.26 eV more favorable than that on the up Si atom. The activation energies of water molecule on the down Si atom for interdimer and intradimer dissociations were 0.17 eV and 0.20 eV, respectively. Due to the lower activation energy, the water molecule splits into H and OH immediately once it adsorbs on down Si atom of the Si (001) surface at room temperature. There were three different adsorption sites among four sites of the two dimers for the second water molecule (θ=0.5): one was preoccupied by OH of the first water molecule; up Si atom of the same-dimer with 76.3 % probability, up Si atom of the adjacent-dimer with 23.6 % probability, and down Si atom of the adjacent-dimer with 0.1 % probability. Thus, ½ monolayer of OH sites on the Si (001) surface are irregularly distributed when water molecules are adsorbed and dissociated at room temperature.
Nonvolatile Charge Storage Characteristics of a MOS Diode with Buried Silicon Nanocrystals and Interfacial Si Nano-pyramids
Authors: Lien Yu-Chung , Pai Yi-Hao , Lin Cheng-Tao , Lin Gong-Ru
Published: January 2010

The memory effect of MOS diodes made on Si substrate with Si nanocrystals (NC-Si) and interfacial Si nano-pyramids deposited by PECVD at different ICP powers is characterized. TEM analysis on the NC-Si reveals that the NC-Si average size are around 3.9±1.1 nm and 4.7±0.7 nmwhen grown at ICP power of 20 W and 30 W, respectively. The interfacial Si nano-pyramids can only be observed by growing at 30 W or larger. The density of NC-Si of 4.4 × 1018 and 5.6 × 1018 cm−3 are relatively in good agreement with the corresponding PL intensities of 45 and 73 count/nm, respectively, for 20 and 30-W grown SiOx samples.. The C–V curves of the NC-Si embedded MOSLEDs show flat-band voltage shift of 0.74 and 18.46 Vfor 20 and 30-W samples, respectively. The C-V hysteresis width also increases by enlarging the range of sweeping voltage. A strong correlation between the size/density of Si nanocrystals and the flatband voltage difference has been concluded. In the case of the C–t measurement, the charging and discharging behaviors were found to depend on charging conditions. Finally, the relationship of the electron/hole charge density with the retention time is analyzed. Our data shows the charge loss rate of 1.3 % for electron is better at 20-Wsample, but the charge loss rate of 0.23 % for hole is better at 30-Wsample with Si NCs embedded in MOSLED after 102 s.
A MHz Modulable Si-based LED Afforded by Engineering Light-emitting Defects in Si
Authors: Tana-ami Norishige , Igarashi Jun , Terada Yosuke , Yasutake Yuhsuke , Fukatsu Susumu
Published: January 2010

We demonstrate a Si-based light-emitting diode (LED) with MHz modulation capability containing a certain class of light-emitting defects in the active region. The emission spectra are characterized by a narrow peak centered at 900 meV (1377 nm), hereafter referred to as E-line, which is attributed to the {311} defects inherent to cubic crystals with the diamond sublattice. The luminescence intensity of the E-line was found to go through a maximum around 20K persisting above 150 K. In spite of the decay lifetimes even longer than 1μs, 31% amplitude modulation was achieved for 1-MHz rectangular pulses at 20 K while near 10-MHz bandwidth was obtained for dynamic operation with modulated pulse widths.
Metal Coated, fs-Laser Fabricated Silicon Spikes as Electron Emitters for Cold Cathode Applications
Authors: Spanakis Emmanuel , Barberoglou Marios , Tzanetakis Panagiotis , Fotakis Costas
Published: January 2010

We have studied the effect of thin metal coatings on the electron emission characteristics of self-assembled silicon microstructures with nearly identical sharp features. We have employed a common template of spikes produced by fs-laser self-driven structuring of Si on which several different metals have been deposited. We find that, in the pristine state and in vacuum conditions achievable in device applications, all metal coatings do not result in marked change of either the minimum electric field necessary for emission or the maximum obtainable current density. In contrast, the durability of the emitters depends strongly on the metal used and is always enhanced with respect to bare Si. Furthermore, no signs of degradation were found within the 3-day time scale of our experiments with gold and chromium. On the contrary, these two metal coatings resulted in emission characteristics improving with time in typical operation conditions.
GaN/ZnO and AlGaN/ZnO Heterostructure LEDs: Growth, Fabrication, Optical and Electrical Characterization
Authors: Benz Julian , Eisermann Sebastian , Klar Peter J. , Meyer Bruno , Detchprohm Theeradetch , Wetzel Christian M.
Published: January 2010

The wide bandgap polar semiconductors GaN and ZnO and their related alloys exhibit fascinating properties in terms of bandgap engineering, carrier confinement, internal polarisation fields, and surface terminations. With a small lattice mismatch of ∼1.8 % between GaN and ZnO and the possibility to grow MgZnO lattice-matched to GaN, the system AlGaN/MgZnO offers the opportunity to design novel optoelectronic devices circumventing the problem of p-type doping of ZnO. In such AlGaN/MgZnO heterostructures with either hetero- or isovalent interfaces, tuning of band offsets is possible in various ways by polarisation fields, surface termination, strain, and composition. These aspects need to be fully understood to be able to make full use of this class of heterostructures. We report on the growth of ZnO films by chemical vapor deposition on p-type GaN and AlGaN grown by metal-organic vapor deposition on sapphire templates and on the fabrication of corresponding light-emitting diode (LED) structures. Electrical and optical properties of the n ZnO/p-GaN and n-ZnO/p-AlGaN LEDs will be compared and the observed differences will be discussed in terms of the band alignment at the heterointerface.
Fabrication, Processing and Characterization of Thin Film ZnO for Integrated Optical Gas Sensors
Authors: Kamińska Eliana , Piotrowska Anna , Pasternak Iwona , Ekielski Marek , Gołaszewska Krystyna , Rzodkiewicz Witold , Wojciechowski Tomasz , Dynowska Elżbieta , Struk Przemysław , Pustelny Tadeusz
Published: January 2010

Zinc oxide layers deposited on quartz substrates by means of RF reactive magnetron sputtering with subsequent RTP annealing in a nitrogen flow at 400°C and in an oxygen flow at 500°C have been investigated in applications to waveguide structures. The ZnO films reveal a highly c-oriented columnar structure with a surface roughness of 4.3 nm. Annealing causes a significant increase of the lattice constant to the value of 5.210±0.001 Å suggesting the relaxation of the stress in the film. The annealing process causes a significant improvement of propagation properties of the fabricated waveguide structures in comparison to structures using as-deposited ZnO films. The minimal attenuation coefficient of the 630 nm thick films was found to be 2.8 and 3.0 dB/cm for TE0 and TM0 modes respectively.
Electrically Air-stable ZnO Thin Film Produced by Reactive RF Magnetron Sputtering for Thin Film Transistors Applications
Authors: Ngwashi Divine , Cross Richard B. M. , Paul Shashi
Published: January 2010

The influence of native point defects on the electrical and optical stability of zinc oxide (ZnO) layers in air produced by reactive RF magnetron sputtering is investigated. ZnO thin films are strongly affected by oxygen (O2) molecules in ambient atmosphere. For instance, surface defects such as oxygen vacancies act as adsorption sites of O2 molecules, and the chemisorption of O2 molecules depletes the surface electronic states and reduces channel conductivity. Thin films of ZnO produced have electrical resistivities between 8.6 × 103 and 8.3 × 108 Ω-cm, and were found to be electrically-stable in air. TFTs fabricated using these films exhibited effective mobilities of ∼3 cm2V-1s-1 and the threshold voltage shifts by < 5 V under gate bias stress of 1 MV/cm for up to 104 s.
An Inverse electrolysis method to Synthesize Surface Nano-roughened ZnO Contact Electrode
Authors: Liao Yu-Hao , Pai Yi-Hao , Lin Gong-Ru
Published: January 2010

The fabrication of surface nano-roughened zinc oxide (ZnO) is demonstrated by using a zinc/air fuel cell based chemical reactor. The chemical reaction creates the hydroxyl near the Zn and randomizes the pores with accumulated hydroxyls, which causes Zn to be oxidized to form thick and nano-roughened ZnO upon Zn anode or to be transformed into a soluble complex zincate ion in the excess electrolyte. Furthermore, controlling the quantity of (Zn(OH)2) and [Zn(OH)4]2− can significantly decrease the defect-related emission and blue-shift PL spectra to the UV range.
Al2O3 as a Transition Layer for GaN and InGaN Growth on ZnO by MOCVD
Authors: Li Nola , Wang Shen-Jie , Fenwick William E. , Melton Andrew , Huang Chung-Lung , Feng Zhe Chuan , Summers Christopher , Jamil Muhammad , Ferguson Ian
Published: January 2010

GaN and InGaN layers were grown on annealed 20 and 50nm Al2O3/ZnO substrates by metalorganic chemical vapor deposition (MOCVD). GaN was only observed by high resolution x-ray diffraction (HRXRD) on 20 nm Al2O3/ZnO substrates. Room temperature photoluminescence (RT-PL) showed the red shift of the GaN near band-edge emission, which might be from oxygen incorporation forming a shallow donor-related level in GaN. HRXRD measurements revealed that (0002) InGaN layers were also successfully grown on 20nm Al2O3/ZnO substrates. In addition, thick InGaN layers (∼200-300nm) were successfully grown on Al2O3/ZnO and bare ZnO substrates. These results are significant as previous studies showed decomposition of the layer at InGaN thicknesses of 100nm or less.
Crystal polarity control of ZnO films and nonlinear optical response
Authors: Park Jin Sub , Yamazaki Yoshiki , Takahshi Yoshihiro , Minegishi Tsutomu , Park Seunghwan , Hong Soonku , Chang Ji-Ho , Fujiwara Takumi , Yao Takafumi
Published: January 2010

We report that the nonlinear optical response of polarity controlled ZnO films grown by selective growth technique of Zn-polar and O-polar ZnO layers on sapphire substrate using Cr-compound buffer layers. ZnO layers grown on CrN/sapphire show Zn polar, while those grown on Cr2O3/sapphire result in O-polar ZnO films. In order to verify the origin of nonlinear optical response of ZnO, the polarity-controlled ZnO thin films grown on different buffer layers were investigated as nonlinear optical materials for second harmonic generation (SHG). The effective nonlinear optical coefficient (deff) of ZnO grown on Cr-compound buffer layers showed a higher value than that of ZnO grown on MgO buffer layers. Finally, by combining suggested in-situ polarity control technique with photolithography technique, we have fabricated 1D and 2D periodically-polarity-inverted (PPI) hetro-structures with periodicity ranging from 60 μm to 2 μm. The lateral polarity inversion is confirmed by piezo response microscopy. Such PPI ZnO heterostructures show the enhancement of SHG intensity comparing with the ZnO films.
Modification of structure and optical property of ZnO nanowires by Ga ion beam
Authors: Cheng Yao , Liang Yao , Lei Ming , Hark Siu Kong , Wang Ning
Published: January 2010

Based on the focused ion beam (FIB) technology, we have prepared ZnO nanowires containing periodic nano-sized structures by an ultra thin Ga ion beam. ZnO nanowires can keep a good crystal quality after Ga ion bombardment. The cathodoluminescence (CL) spectroscopy study of the Ga-doped ZnO nanowires at low temperatures shows that the Ga doping effect can largely suppress the green emission that may mainly originate from the defects on the surfaces of ZnO nanowires.
Influence of O2/Ar Ratio on the Properties of Transparent Conductive Titanium-Doped Indium Oxide Films by DC Radio-Frequency Sputtering
Authors: Li Lei , Li Li , Yu Xin , Yu Hai , Chen Chen , Song Zhenyu , Cong Menglong , Wang Yiding
Published: January 2010

Titanium doped indium oxide (TIO) thin films were deposited on glass substrate by DC sputtering with different O2/Ar gas ratios at 330 °C. The effects of sputtering on the structural, morphologic, optical and electrical characteristics of TIO thin films were investigated by XRD, Hall measurement and optical transmission spectroscopy. The deposited films exhibited polycrystalline in the preferred (222) orientation, with higher mean grain size and lower resistivity 3.37 ×10-4Ω·cm at O2/Ar ratio of 1/10. The average optical transmittance of the films is over 90%, and the transmittance has no evident change with changing O2/Ar ratio.
ZnO Thin Film Transistors Fabricated by Atomic Layer Deposition Method
Authors: Kawamura Yumi , Hattori Nozomu , Miyatake Naomasa , Murata Kazutoshi , Uraoka Yukiharu
Published: January 2010

In this study, we deposited zinc oxide (ZnO) thin film by atomic layer deposition (ALD) as an active channel layer in thin film transistor (TFT) using two different oxidizers, water (H2O-ALD) and oxygen radical (PA-ALD). The fabricated TFTs were annealed at various temperatures, in an oxygen ambient gas. The electrical properties of TFTs with PA-ALD ZnO film annealed at the temperature up to 400[oC] improved without any degradation of the subthreshold swing or any large shift of the threshold voltage. Through this study, we found that the high performance ZnO TFTs is possibly obtained using PA-ALD at low temperature, and the electrical properties are dependent on the annealing temperature.
Reaction Anisotropy and Size Resolved Oxidation Kinetics of Zinc Nanocrystals
Authors: Ma Xiaofei , Zachariah Michael R.
Published: January 2010

In this work, size-classified substrate-free Zn nanocrystals (NCs) are prepared and investigated for their oxidation kinetics using an in-flight tandem ion-mobility method. The first mobility characterization size selects the NCs, while the second mobility characterization measures changes in mass resulting from a controlled oxidation of the NCs. This method allows for a direct measurement of mass change of individual particles and thus enables us to explore the intrinsic reactivity of NCs while minimizing the sampling error introduced by mass and heat transfer. Two reaction regimes were observed for Zn NC oxidation. A shrinking core model is used to extract the size-dependent oxidation activation energies. We also observed a strong anisotropy effect in the oxidation process as imaged by electron microscopy. An oxidation mechanism is proposed that qualitatively explains the oxidation anisotropy and its relationship to the surface energy of the Zn NCs.
Selective Area Epitaxy of InGaN/GaN Stripes, Hexagonal Rings, and Triangular Rings for Achieving Green Emission
Authors: Feng Wen , Kuryatkov Vladimir , Rosenbladt Dana , Stojanovic Nenad , Pandikunta Mahesh , Nikishin Sergey A , Holtz Mark
Published: January 2010

We report selective area epitaxy of InGaN/GaN micron-scale stripes and rings on patterned (0001) AlN/sapphire. The objective is to elevate indium incorporation for achieving blue and green emission on semi-polar crystal facets. In each case, GaN structures were first produced, and the InGaN quantum wells (QWs) were subsequently grown. The pyramidal InGaN/GaN stripe along the <11-20> direction has uniform CL emission at 500 nm on the smooth {1-101} sidewall and at 550 nm on the narrow ridge. In InGaN/GaN triangular rings, the structures reveal smooth inner and outer sidewall facets falling into a single type of {1-101} planes. All these {1-101} sidewall facets demonstrate similar CL spectra which appear to be the superposition of two peaks at positions 500 nm and 460 nm. Spatially matched striations are observed in the CL intensity images and surface morphologies of the {1-101} sidewall facets. InGaN/GaN hexagonal rings are comprised of {11-22} and {21-33} facets on inner sidewalls, and {1-101} facets on outer sidewalls. Distinct CL spectra with peak wavelengths as long as 500 nm are observed for these diverse sidewall facets of the hexagonal rings.
On the Light Emission in GaN Based Heterostructures at High Injection
Authors: Ni Xianfeng , Li Xing , Liu Huiyong , Izyumskaya Natalia , Avrutin Vitaliy , Özgür Ümit , Morkoç Hadis , Paskova Tanya , Mullholland Greg , Evans Keith R.
Published: January 2010

For light emitting diodes (LEDs) to be used for general lighting, high efficiencies would need to be retained at high injection levels to meet the intensity and efficiency requirements. In this regard, it is imperative to overcome the observed drop in LED efficiency at high injection levels beyond that would be expected from junction temperature. The suggested genesis of efficiency degradation includes electron overflow or spillover, also suggested to be aided by polarization induced electric field, Auger recombination, current crowding, and elevated junction temperature. Setting the junction temperature aside, the degree to which or even whether each of these mechanisms plays a role is still under debate. We have undertaken a series of experiments to isolate, whenever possible, the aforementioned processes in an effort to determine the causes of efficiency loss at high injection levels. By using 1μs pulsed electrical injection with 0.1% duty cycle, we were able to minimize the effect of the junction temperature. By changing the design of the multiple quantum well region as well as by employing or not employing electron blocking layers, we demonstrated the important role that electron overflow plays on efficiency. Furthermore, by also exploring the same on non polar surfaces and observing any lack of dispersion in terms of the effect of the electron blocking layer we can conclude that the polarization induced field does not seem to play a major role. LEDs on non polar surface with no notable efficiency degradation, up to current densities of about 2250 Acm-2 used for measurements, have been obtained which seems to imply that Auger recombination up to these injection levels is not of major importance, at least in the structures investigated. The effect of current crowding on efficiency droop was investigated by comparing semitransparent Ni/Au p-contacts and transparent conducting oxide contacts (Ga-doped ZnO). Because the latter showed notably reduced efficiency degradation at high injection levels, we can conclude that current crowding plays a role as well.
Electronic Properties of III-Nitride Surfaces and Interfaces Studied by Scanning Photoelectron Microscopy and Spectroscopy
Authors: Kuo Cheng-Tai , Lee Hong-Mao , Wu Chung-Lin , Shiu Hung-Wei , Chen Chia-Hao , Gwo Shangjr
Published: January 2010

We report on a method based on cross-sectional scanning photoelectron microscopy and spectroscopy (XSPEM/S) for studying electronic structure of III-nitride surfaces and interfaces on a submicrometer scale. Cross-sectional III-nitride surfaces prepared by in situ cleavage were investigated to eliminate the polarization effects associated with the interface charges/dipoles normal to the cleaved surface. In contrast to the as-grown polar surfaces which show strong surface band bending, the cleaved nonpolar surfaces have been found to be under the flat-band conditions. Therefore, both doping and compositional junctions can be directly visualized at the cleaved nonpolar surfaces. Additionally, we show that the “intrinsic” valence band offsets at the cleaved III-nitride heterojunctions can be unambiguously determined.
Cubic AlGaN/GaN Hetero-Field Effect Transistors with Normally On and Normally Off Operation
Authors: As Donat J. , Tschumak Elena , Niebelschüetz Florentina , Jatal W. , Pezoldt Joerg , Granzner Ralf , Schwierz Frank , Lischka Klaus
Published: January 2010

Non-polar cubic AlGaN/GaN HFETs were grown by plasma assisted MBE on 3C-SiC substrates. Both normally-on and normally-off HFETs were fabricated using contact lithography. Our devices have a gate length of 2 μm, a gate width of 25 μm, and source-to-drain spacing of 8 μm. For the source and drain contacts the Al0.36Ga0.64N top layer was removed by reactive ion etching (RIE) with SiCl4 and Ti/Al/Ni/Au ohmic contacts were thermally evaporated. The gate metal was Pd/Ni/Au. At room temperature the DC-characteristics clearly demonstrate enhancement and depletion mode operation with threshold voltages of +0.7 V and −8.0 V, respectively. A transconductance of about 5 mS/mm was measured at a drain source voltage of 10 V for our cubic AlGaN/GaN HFETs, which is comparable to that observed in non-polar a-plane devices. From capacity voltage measurements a 2D carrier concentration of about 7×1012 cm-2 is estimated. The influence of source and drain contact resistance, leakage current through the gate contact and parallel conductivity in the underlaying GaN buffer are discussed.
Direct growth of carbon nanotubes atom by atom during field emission
Authors: Journet Catherine , Marchand Mickaël , Benoit Jean-Michel , Yakobson Boris I. , Purcell Stephen Thomas
Published: January 2010

We have designed a field emission microscope (FEM) coupled to a chemical vapor deposition (CVD) reactor in order to observe directly the growths of individual carbon nanotubes (CNTs) from the nucleation stage. Catalyst metals are first deposited in situ on a sharp metallic tip during direct FEM imaging and formed into nanoparticles by dewetting. CNTs are then grown directly on these nanoparticles by CVD in acetylene or other hydrocarbon gases at appropriate temperatures (600-900°C). The FEM patterns are formed by electrons emitted from individual CNT caps. The videos are analyzed to extract the growth rates and models. In situ field emission I/V measurements are also performed. The most interesting new discovery is that the CNTs often rotate axially during growth, thus strongly supporting a recently proposed model of ‘screw-dislocation-like’ (SDL) mechanism. The event is not rare as four rotating CNT growths versus six non-rotating growths were observed. In one case the CNT rotated quite uniformly ∼180 times during its 11 min growth. This observation should aid researchers to better understand and control the growth of SWNTs.
Post-Synthesis Crystallinity Tailoring of Water-Soluble Polymer Encapsulated CdTe Nanoparticles using Rapid Thermal Annealing
Authors: Rutledge Steven , Farah Abdiaziz A. , Dinglasan Jordan , Anderson Darren , Das Anjan , Goh Jane , Goh Cynthia , Helmy Amr S.
Published: January 2010

The crystallinity of colloidal CdTe nanoparticles has been enhanced post synthesis. This control over the nanoparticles’ properties has been achieved using non-adiabatic thermal processing. The technique preserves the polymer capping and hence introduces no adverse effects on the nanoparticles’ optical properties. The crystallinity is probed primarily through Raman spectroscopy in a hollow core photonic crystal fiber and x-ray diffraction powder studies.
Multiexcitons in a Single Core-Shell Colloidal Quantum dots
Authors: Cheskis Dima , Osovsky Ruth , Kloper Viki , Sashchiuk Aldona , Lifshitz Efrat
Published: January 2010

The micro-photoluminescence (μ-PL) spectra of a single CdTe/CdSe quasi- type II core-shell colloidal quantum dots (CQDs) unambiguously reveal an emission of a biexciton (2X), a triexciton (3X) and a quadraexciton (4X) under continuous-wave excitation. The CQDs were characterized by optical measurements and theoretical consideration of carrier's wavefunctions distribution of a quasi-type II core-shell structure.
Bonding of Cu wires by solid state sintering of Ag nanoparticles at low temperatures
Authors: Alarifi Hani , Hu Anming , Yavuz Mustafa , Zhou Y.
Published: January 2010

Solid state sintering of Ag nanoparticles was used to bond Cu wires to Cu foils at temperatures less than 250°C. The Ag nanoparticles are coated with an organic shell to prevent sintering at room temperature. After annealing the nanoparticles at 200°C, the decomposition of the organic shell was confirmed using TGA and Raman spectroscopy. The joint strength was measured by tensile shear tests, which shows that the joint strength increases as the bonding temperature increases. Metallic bond between Ag nanoparticles and Cu was achieved with no contamination. Bonds formed by our method, was confirmed to withstand temperatures higher than the bonding temperatures.
Synthesis of Organic Capped Colloidal Zinc Oxide Quantum Dots and Their UV Dominant Emission Property
Authors: Omata Takahisa , Takahashi Kazuyuki , Hashimoto Shinichi , Maeda Yasuhiro , Nose Katsuhiro , Otsuka-Yao-Matsuo Shinya
Published: January 2010

A novel synthesis route to organic-capped and colloidal ZnO quantum dots (QDs) has been developed. Specifically, zinc-di-butoxide was hydrolyzed with very dilute water (100˜600 mass ppm) dissolved in hydrophilic benzylamine and polymerized to ZnO by dehydration condensation. After formation of ZnO QDs with 2˜3 nm in diameter, growth of the QDs and exchange the surface capping ligand from hydroxyl groups and/or benzylamine to oleylamine were developed by heating the colloidal solution with oleylamine. The size of the ZnO QDs finally obtained was in the range 3˜5 nm in diameter. The QDs show high dispersibility in various organic solvents. Clear UV emission due to exciton recombination was observed; and its energy was varied according to the quantum size effect from 3.39 to 3.54 eV. By using lithium-free zinc-di-butoxide as a starting material, the defect-related VIS emission was successfully decreased and the UV emission becomes dominant. The influence of water concentration in benzylamine and oleylamine on UV emission intensity was also investigated.
Charge Storage and Optical Response of Hybrid Nanodots Floating Gate For Functional Memories
Authors: Miyazaki Seiichi , Morisama Naoya , Nakanishi Sho , Ikeda Mitsuhisa , Makihara Katsunori
Published: January 2010

We have proposed and fabricated a hybrid nanodots floating gate (FG), in which Si quantum dots (QDs) as charge injection/emission nodes and NiSi nanodots as charge storage nodes are stacked with an ultrathin SiO2 interlayer, to satisfy both large memory window and multivalued capability. In this study, Si-QDs with an areal density of ˜3×1011cm-2 were formed on ultrathin SiO2 layer by controlling SiH4 chemical vapor deposition (CVD) and NiSi nanodots were prepared by full-silicidation of Si-QDs promoted with remote H2-plasma exposure after Ni evaporation. From capacitance-voltage(C-V) characteristics of MOS capacitors with a NiSi nanodots/Si-QDs hybrid FG, stable storage of many charges in the deep potential well of each NiSi nanodot was confirmed. Also, by applying pulsed gate biases, stepwise charge injection to and emission from NiSi nanodots through discrete energy states in Si-QDs were demonstrated. In addition, by 1310nm (˜0.95eV) light irradiation, a distinct optical response in C-V characteristics was detected, which can be interpreted in terms of the shift of charge centroid in the hybrid FG stack due to transfer of photoexcited electrons from NiSi-nanodots to the Si-QDs.
Metal oxide rods and dots-based structures and devices: cost-effective fabrication and surface chemistry control
Authors: Vayssieres Lionel
Published: January 2010

The necessity of materials development which is not limited to materials that can achieve their theoretical limits, but makes it possible to raise theoretical limits by changing the fundamental underlying physics and chemistry while keep the fabrication cost to a minimum is crucial. Materials nanotechnologies based on chemical fabrication approaches is one of the immediate answer to the enormous need for cost-effective new materials for energy, environment, and health. R&D exploiting chemical nanoscience and nanotechnology has the greatest potential to efficiently contribute to such challenging goals. Indeed, the creation of new materials with higher performance and improved stability achieved by atomic, molecular and nanostructural design and control using unique nanoscale phenomena such as quantum confinements is the key. A synthesis involving the aqueous condensation of metal ions from solutions of metal salts for the low-cost fabrication of engineered arrays consisting of oriented nanorods of metal oxides orientations onto various substrates as well as the ability to control the surface acidity of quantum dots from acidic to neutral to basic by size effect are presented.
Porous ultrathin silicon membranes for purification of nanoscale materials
Authors: Striemer Christopher C , Gaborski Thomas R , Fang David Z , Snyder Jessica L , McGrath James L , Fauchet Philippe M
Published: January 2010

A new class of porous membrane has been fabricated that is unique in its combination of nanoscale thickness (<50 nm) with macroscopic, yet robust, millimeter-scale lateral dimensions and tunable pore size in the range of ˜5nm to ˜100nm. The membrane material is porous nanocrystalline Si (pnc-Si)1, and is being scaled-up to commercial volumes by a startup company, SiMPore, Inc. Standard commercial separation membranes with pores in this size regime are polymeric materials (poly ether sulphone, cellulose, etc.), microns in thickness, leading to pore morphologies that resemble long narrow tubes or tortuous-path 3-D matrices. As pnc-Si membrane thickness approaches the pore diameters, a simplified structure of holes in a thin sheet results, greatly enhancing both diffusive and forced flow transport through the membrane, as predicted by classical transport theories2. Pnc-Si has confirmed these theoretical predictions, demonstrating record-breaking transport rates, in addition to precise size-separation of nanoparticles, viruses, proteins, and nucleic acids.
Applications for this highly precise silicon-based membrane range from highly efficient separations and purification of biomolecules, complexes, and nanoparticles, to substrates for microscopy to cell culture and co-culture. SiMPore is focused on navigating this application space with the goal of quickly introducing products that will allow the company to become self-sustaining and profitable though direct sales or partnerships with market leaders. Key product development drivers include potential competitive performance advantages and perceived value to a particular market, the IP landscape, development costs of the membrane and the device package/interface, and alignment with existing in-house capabilities.
Large Scale Nanomaterial Production Using Microfluidizer High Shear Processing
Authors: Chomistek Kenneth John , Panagiotou Thomai
Published: January 2010

Large Scale Nanomaterial Production Using Microfluidizer High Shear Processing
Kenneth. J. Chomistek and Thomai Panagiotou, Ph.D.
Microfluidics Corporation, 30 Ossipee Rd., Newton, MA 02464, USA
Microfluidics has developed scalable and low cost award winning technologies, capable of producing nanomaterials with desirable properties for a wide variety of applications. The industries served are pharmaceuticals and biotech, energy, specialty chemicals, cosmetics and nutraceuticals. Microfluidics approach is based on an in-depth understanding of applications, unique design of high shear fluid processors, and development of processes tailored for each individual application.
The understanding of the requirements and ecosystem of specific applications includes the desired end properties of the material, the production environment requirements, time and cost restrictions. Pharmaceutical and biotech applications include the development and the production of FDA approved nanotechnology drugs such as vaccines, cancer drugs, anesthetics, controlled delivery systems that include polymers drugs and proteins, etc. Chemical applications include inkjet inks, fuel cell and battery electrodes, and carbon nanotube dispersion. Cosmetics include nanoencapsulation of oxygen carriers and nutrients, and collagen processing. Nutraceuticals include nanoencapsulation of fish oil for protection of omega-3 fatty acids and odor control, nanoemulsions that contain plant sterols and vitamins.
Two main methods are used for production of nanomaterials: (a) the “top down”, particle size reduction method, and (b) the “bottom up”, Microfluidics reaction Technology (MRT) for production of nanoparticles through chemical reactions and physical processes, such as crystallization. This technology received the Nano50 Award in 2007. Both technologies are continuous and can be used in line with upstream or downstream processes such as premixing, filtration, etc., and are consistent with process intensification principals.
The heart of the technology is the interaction chamber which consists of “fixed geometry” microchannels. Flow through the chamber is characterized by high fluid velocities (up to 500 m/s) and subsequent impingement of fluid jets to the chamber walls or to one another. The unique “fixed geometry” feature combined with the high shear rates ensure that varied formulations (emulsions, liposomes and dispersions) achieve the smallest particle size and the narrowest particle size distribution when compared to other particle reduction techniques.
The technology is fully scalable and has been used extensively from lab scale to production of market drugs, nutraceuticals and inks, among others. Microfluidizer® processors offer a variety of options, such as steam sterility, cleanability and data acquisition capabilities, so they are cGMP compliant, CE certified, ATEX and explosion proof, and therefore are suitable for a variety of manufacturing environments.
Performance Evaluation of an Oxygen Sensor as a Function of the Samaria Doped Ceria Film Thickness
Authors: Sanghavi Rahul Pankaj , Nandasiri Manjula , Kuchibhatla Satyanarayana , Nachimuthu Ponnusamy , Engelhard Mark H. , Shutthanandan Vaithiyalingam , Jiang Weilin , Thevuthasan Suntharampillai , Kayani Asghar , Prasad Shalini
Published: January 2010

The current demand in the automobile industry is in the control of air-fuel mixture in the combustion engine of automobiles. Oxygen partial pressure can be used as an input parameter for regulating or controlling systems in order to optimize the combustion process. Our goal is to identify and optimize the material system that would potentially function as the active sensing material for such a device that monitors oxygen partial pressure in these systems. We have used thin film samaria doped ceria (SDC) as the sensing material for the sensor operation, exploiting the fact that at high temperatures, oxygen vacancies generated due to samarium doping act as conducting medium for oxygen ions which hop through the vacancies from one side to the other contributing to an electrical signal. We have recently established that 6 atom % Sm doping in ceria films has optimum conductivity. Based on this observation, we have studied the variation in the overall conductivity of 6 atom % samaria doped ceria thin films as a function of thickness in the range of 50 nm to 300 nm at a fixed bias voltage of 2 volts. A direct proportionality in the increase in the overall conductivity is observed with the increase in sensing film thickness. For a range of oxygen pressure values from 0.001 Torr to 100 Torr, a tolerable hysteresis error, good dynamic response and a response time of less than 10 seconds was observed.