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41.
Abhijit Biswas Chan-Ho Yang Ramamoorthy Ramesh Yoon H. Jeong 《Progress in Surface Science》2017,92(2):117-141
Scientific interest in atomically controlled layer-by-layer fabrication of transition metal oxide thin films and heterostructures has increased intensely in recent decades for basic physics reasons as well as for technological applications. This trend has to do, in part, with the coming post-Moore era, and functional oxide electronics could be regarded as a viable alternative for the current semiconductor electronics. Furthermore, the interface of transition metal oxides is exposing many new emergent phenomena and is increasingly becoming a playground for testing new ideas in condensed matter physics. To achieve high quality epitaxial thin films and heterostructures of transition metal oxides with atomically controlled interfaces, one critical requirement is the use of atomically flat single terminated oxide substrates since the atomic arrangements and the reaction chemistry of the topmost surface layer of substrates determine the growth and consequent properties of the overlying films. Achieving the atomically flat and chemically single terminated surface state of commercially available substrates, however, requires judicious efforts because the surface of as-received substrates is of chemically mixed nature and also often polar. In this review, we summarize the surface treatment procedures to accomplish atomically flat surfaces with single terminating layer for various metal oxide substrates. We particularly focus on the substrates with lattice constant ranging from 4.00 Å to 3.70 Å, as the lattice constant of most perovskite materials falls into this range. For materials outside the range, one can utilize the substrates to induce compressive or tensile strain on the films and explore new states not available in bulk. The substrates covered in this review, which have been chosen with commercial availability and, most importantly, experimental practicality as a criterion, are KTaO3, REScO3 (RE = Rare-earth elements), SrTiO3, La0.18Sr0.82Al0.59Ta0.41O3 (LSAT), NdGaO3, LaAlO3, SrLaAlO4, and YAlO3. Analyzing all the established procedures, we conclude that atomically flat surfaces with selective A- or B-site single termination would be obtained for most commercially available oxide substrates. We further note that this topmost surface layer selectivity would provide an additional degree of freedom in searching for unforeseen emergent phenomena and functional applications in epitaxial oxide thin films and heterostructures with atomically controlled interfaces. 相似文献
42.
Immobilization of silver nanoparticles into POEGMA polymer brushes as SERS‐active substrates
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Qian Zhang Jun‐Jiao Yin Feng Liu Xue‐Na Zou Li‐Qiang Chu 《Surface and interface analysis : SIA》2017,49(4):316-322
Surface‐enhanced Raman scattering (SERS) has attracted a great deal of interest during the past four decades and emerged as an ultrasensitive optical technique for chemical and biomedical analysis. It is widely accepted that the facile fabrication of SERS substrates with high activity and good reproducibility is of crucial importance for their applications. Herein, we report on a fast and robust method for the synthesis and immobilization of silver nanoparticles (AgNPs) into poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes under mild conditions without using any reducing agents. POEGMA brushes of different chain lengths were synthesized directly on silicon wafers by surface‐initiated atom transfer radical polymerization with various reaction time. X‐ray photoelectron spectroscopy and field emission scanning electron microscope measurements indicated that the AgNPs were firmly and homogeneously embedded into POEGMA brushes. The resulting POEGMA–AgNP hybrid films were employed as SERS substrates for the detection of 4‐aminothiophenol, giving rise to an enhancement factor of up to 1.9 × 106. The influence of the POEGMA's chain length on SERS performance was also investigated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
43.
F. Gonzlez G. Videen P. J. Valle J. M. Saiz J. L. de la Pea F. Moreno 《Journal of Quantitative Spectroscopy & Radiative Transfer》2001,70(4-6):383-393
Four theoretical and computational methods to describe the scattering from simple particles on substrates are presented and discussed. These methods are based on the extinction theorem, image theory, the double-interaction model, and geometrical optics (ray-tracing). We compare the four methods with measurements of scattered light from gold metallic cylinders resting on a gold metallic substrate. In particular, we analyze the co-polarized (s and p polarization) full-scan and back-scattering intensities in the far field within the plane of incidence. Advantages and disadvantages of each method as a computational and reliable tool are discussed. 相似文献
44.
Recent developments in microbial inulinases 总被引:15,自引:0,他引:15
Ashok Pandey Carlos R. Soccol Ponniah Selvakumar Vanete T. Soccol Nadia Krieger Jose D. Fontana 《Applied biochemistry and biotechnology》1999,81(1):35-52
Microbial inulinases are an important class of industrial enzymes that have gained much attention recently. Inulinases can
be produced by a host of microorganisms, including fungi, yeast, and bacteria. Among them, however, Aspergillus sp. (filamentous fungus) and Kluyveromyces sp. (diploid yeast) are apparently the preferred choices for commercial applications. Among various substrates (carbon source)
employed for their production, inulin-containing plant materials offer advantages in comparison to pure substrates. Although
submerged fermentation has been universally used as the technique of fermentation, attempts are being made to develop solidstate
fermentation technology also. Inulinases catalyze the hydrolysis of inulin to d-fructose (fructose syrup), which has gained an important place in human diets today. In addition, inulinases are finding
other newer applications. This article reviews more recent developments, especially those made in the past decade, on microbial
inulinases—its production using various microorganisms and substrates. It also describes the characteristics of various forms
of inulinases produced as well as their applications. 相似文献
45.
Masatoshi Hasegawa Daiki Hirano Mari Fujii Misako Haga Eiichiro Takezawa Shinya Yamaguchi Atsushi Ishikawa Takashi Kagayama 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):575-592
This work presents novel colorless polyimides (PIs) derived from 1R,2S,4S,5R‐cyclohexanetetracarboxylic dianhydride (H″‐PMDA). Isomer effects were also discussed by comparing with PI systems derived from conventional hydrogenated pyromellitic dianhydride, that is, 1S,2R,4S,5R‐cyclohexanetetracarboxylic dianhydride (H‐PMDA). H″‐PMDA was much more reactive with various diamines than H‐PMDA, and the former led to PI precursors with much higher molecular weights. The results can be explained from the quite different steric structures of these isomers. The thermally imidized H″‐PMDA‐based films were colorless regardless of diamines because of inhibited charge‐transfer interaction. In particular, the H″‐PMDA/4,4′‐oxydianiline system simultaneously achieved a very high Tg exceeding 300 °C, high toughness (elongation at break > 70%), and good solution processability. In contrast, the H‐PMDA‐based counterparts were essentially insoluble. The outstanding solubility of the former probably results from disturbed chain stacking by its nonplanar steric structure. An advantage of chemical imidization process is also proposed. In some cases, a copolymerization approach with an aromatic tetracarboxylic dianhydride was effective to improve the thermal expansion property. The results suggest that the H″‐PMDA‐based PI systems can be promising candidates for novel high‐temperature plastic substrate materials in electronic paper displays. A potential application as optical compensation film materials in liquid crystal displays (LCD) is also proposed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
46.
Egbert Woelk Holger Jürgensen Randy Rolph Tim Zielinski 《Journal of Electronic Materials》1995,24(11):1715-1718
We use low pressure MOVPE to grow indium antimonide films on groups of eight 3 inch GaAs wafers per run. The films are used
for the production of magnetoresistive position sensors for the car industry. To meet the narrow specifications for automotive
components, the standard deviation of the sheet resistivity, and the thickness of the films have been reduced below 1.5%.
This uniformity is the result of an optimization process encompassing the determination of the best susceptor temperature
and the optimum flow. The gas velocity was found to have a large impact on the uniformity of the layers. Rotation of the wafers
and the use of an optimum gas velocity results in extremely uniform layers. 相似文献
47.
48.
M. N. Charasse B. Bartenlian J. P. Hirtz A. Peugnet J. Chazelas G. Amendola 《Journal of Electronic Materials》1990,19(6):567-573
The growth of GaAs on patterned Si substrates is essential for the integration of GaAs and Si devices. Moreover this growth
may have to be done in wells to planarize the surfaces of the Si and GaAs devices for their interconnection. In this study,
GaAs is grown by MBE on such patterned Si substrates, with window width down to 3 μm, and a complete structural characterization
of the material is made by electron microscopy. In every case, SEM observations show a very good definition of the pattern
by the contrast of the flat surface of the monocrystalline GaAs compared to the very rough surface of the polycrystalline
GaAs. Cross-sectional observations by STEM or TEM on non-etched samples reveal that the quality of the monocrystalline GaAs
is at least as good in terms of defect density as that of the standard GaAs on Si. On samples etched with a plasma to produce
wells, grains often form against the Si sidewall. Chemical etching with lateral etching avoids contact of the growing GaAs
with the Si sidewall and subsequent grain formation. The crystalline quality obtained on etched samples is not as good as
on non etched samples. A way of preparing the wells to improve this crystalline quality is proposed. 相似文献
49.
Kokovi M. Lawson DakuRoger F. Newton Simon P. PearceJulia Vile Jonathan M.J. Williams 《Tetrahedron letters》2003,44(27):5095-5098
Reverse-phase glass beads have been employed in Suzuki reactions to provide, in aqueous media, a route to diverse polar substrates in good yield and with low levels of palladium leaching. 相似文献
50.
G. P. Watson M. O. Thompson D. G. Ast A. Fischer-Colbrie J. Miller 《Journal of Electronic Materials》1990,19(9):957-965
As shown previously, the misfit dislocation density of strained epitaxial III–V layers can be significantly reduced by isolating
sections (via patterned etching) of a GaAs substrate before epitaxial growth. A disadvantage of this technique is that the
wafer surface is no longer planar, which can complicate subsequent device fabrication. As an alternative, we have investigated
growth of 350 nm of In0.5Ga{0.95}As by molecular beam epitaxy at two temperatures on substrates which were patterned and selectively damaged by Xe
ion implantation (300 keV, 1015 cm2). Selectively etched substrates were prepared as reference samples as well. The propagation of the misfit dislocations was
stopped by the ion-implanted regions of the low growth temperature (400° C) material, but the damaged portions also acted
as copious nucleation sources. The resulting dislocation structure was highly anisotropic, with dislocation lines occurring
in virtually only one direction. At the higher growth temperature (500° C) the defect density fell, but the ion damaged sections
no longer blocked dislocation glide. Images from cathodoluminescence and transmission electron microscopy show thatthe low
growth temperature material has a dislocation density of 70,000 cm-1 in the 110 direction and less than 10,000 cm-1 in the 110 direction. Ion channeling and x-ray diffraction show that strain is relieved in only one direction. The strain
relief is consistent with the relief derived from TEM dislocation counts and Burgers vector determination. However, even this
high dislocation count is not sufficient to reach the expected equilibrium strain. Reasons for the anisotropy are discussed. 相似文献