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排序方式: 共有6558条查询结果,搜索用时 15 毫秒
21.
测量了GaAs/AlGaAs多量子阱红外探测器在零偏压、小偏流和大偏压等条件下的光电流谱,并结合理论计算的光跃迁能量讨论了光电流谱的多峰结构和异常增强特性。 相似文献
22.
As压对LT-GaAs/AlGaAs多量子阱光学特性的影响 总被引:2,自引:0,他引:2
在衬底温度为 3 5 0°C的条件下 ,用分子束外延的方法 ,在不同的砷压条件下生长了 Ga As/Al0 .3Ga0 .7As多量子阱结构。 77K的荧光实验证明 ,砷压对样品的光学特性影响显著。认为砷压对低温多量子阱光学特性的影响是点缺陷随砷压的演化和能级间相互补偿的共同结果。通过优化砷压 ,样品的荧光峰的半峰宽减小到 3 me V,这是到目前为止所报道过的最窄的低温多量子阱的荧光峰。相应的垂直场光折变器件的电吸收为 60 0 0 cm 相似文献
23.
Structural changes in the Brill transitions of Nylon 10/10 and its model compounds have been investigated by carrying out the temperature-dependent measurements of X-ray diffraction and infrared spectra along with the DSC measurement. The crystal structure at room temperature was found to be the so-called α form with the all-trans zigzag methylene segments. When the samples were heated, the infrared progression bands of the methylene segments, which are sensitive to the length of all-trans segmental parts, were found to change their spectral patterns in the transition temperature region: the progression bands decreased in intensity and disappeared above the transition region. At the same time several new bands were observed to appear, which were found to correspond to the progression bands of (CH2)7-(CH2)5trans-zigzag segments. These spectral changes indicate that the methylene segments were conformationally disordered by an invasion of some gauche bonds and as a result the effective length of trans-zigzag segments became shorter. This conformational disordering was found to occur more remarkably in the methylene segment of NH-(CH2)10-NH part than the CO-(CH2)8-CO part. At the same time the infrared bands of amide groups, in particular the bands sensitive to the twisting angles about the CH2-amide bonds were found to show the remarkable change, indicating the local conformational change from planar-zigzag to twisted form in the CH2-amide moiety. The frequency shift of amide A band (NH stretching mode) indicated a weakening of intermolecular hydrogen bonds, which however, did not disappear up to the melting region. From these data combined with the X-ray diffraction data, the structural disordering in the Brill transition phenomena was deduced concretely. 相似文献
24.
Kazufumi Ogawa 《Polymer International》1992,28(1):25-33
Studies have been carried out on KrF excimer laser light (EX), X-ray or electron beam (EB) induced polymerization of 10,12-pentacosadiynoic acid (PDA) Langmuir-Blodgett (LB) films in relation to molecular density or molecular arrangement of the films using X-ray diffraction analysis, infrared (IR) spectroscopy and Raman spectroscopy. The molecular arrangement or density of the PDA LB films was controlled by subphase conditions when the films were built up, such as pH, temperature of a subphase or salt concentration in the subphase. Polymerization sensitivity of the PDA LB film was affected by the arrangement or molecular density. On low density (A type) films the polymerization occurred by irradiation with EX, X-ray or EB, but on high density (B type) films the polymerization occurred only when the irradiation was carried out by high energy beams such as X-ray or EB. Decomposition of polymerized films was observed further by excessive irradiation of EX or X-ray, but not on the B type films. It was revealed by X-ray diffraction analysis that in the A type film, the PDA molecules bent to a larger extent than those in the B type film and the polymerization proceeded topochemically, that is, the thickness decreased little after EB irradiation in a helium atmosphere. On the other hand, in the B type film, the thickness decreased by about 10% as a result of EB irradiation. By IR reflection-absorption (RA) and Raman measurements, it was confirmed that conjugated diacetylenic bonds disappeared and conjugated double and new conjugated triple bonds appeared after high energy beam irradiations. These results support the supposition that 1,4-polymerization, i.e. polydiacetylene type polymerization, occurs easily in the A type film and 1,2- or 3,4-polymerization, i.e. polyacetylene type polymerization, occurs in the B type film, and that the polymerized A type film was decomposed at the polydiacetylenic bond when the irradiation continued further. It was also shown that the polyacetylene type polymer was obtained only when the B type film was irradiated with the high energy beam. 相似文献
25.
26.
The optical emission characteristics of biaxially compressed InAs
x
P1−
x
/InP strained single quantum well (QW) structures, with nominal compositionx=0.67, have been investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. The highly
strained QWs exhibit intense and narrow PL in the 0.9–1.5 μm wavelength range, similar to the lattice-matched InGaAs(P)/InP
system. The 20 K PLE spectra exhibit well-resolved features attributed ton=1 heavy hole (E1H1) and light hole (E1L1) transitions in the 1.0–1.5 μm wavelength range. In addition, features attributed
to transitions betweenn=2 electrons and heavy holes (E2H2), and betweenn=1 electrons and unconfined holes (E1Hf), were observed. The energy splitting between the heavy-hole and light-hole bands
was found to be a sensitive measure of the band offsets in the system. The best prediction of this splitting was obtained
for a valence band offset of δE
V
∼0.25δE
G
. This value of band offset was in agreement with the energy position of the E1Hf transition. The observed transition energies
were also compared with the results of a finite square well model, taking into account the effects of strain, and the results
offer further support for the band offset assignment. This study indicates that the InAsP system may be advantageous for application
in strained-layer optoelectronic devices operating in the 1.3–1.6 μm wavelength range. 相似文献
27.
28.
29.
Kum‐Il Lee Yong‐Sik Yim Sang‐Wook Chung Jiaqiu Wei Jong Il Rhee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):1036-1045
A two‐dimensional (2D) spectrofluorometer was used to monitor various fermentation processes with recombinant E coli for the production of 5‐aminolevulinic acid (ALA). The whole fluorescence spectral data obtained during a process were analyzed using artificial neural networks, ie self‐organizing map (SOM) and feedforward backpropagation neural network (BPNN). The SOM‐based classification of the whole spectral data has made it possible to qualitatively associate some process parameters with the normalized weights and variances, and to select some useful combinations of excitation and emission wavelengths. Based on the classified fluorescence spectra a supervised BPNN algorithm was used to predict some of the process parameters. It was also shown that the BPNN models could elucidate some sections of the process's performance, eg forecasting the process's performance. Copyright © 2005 Society of Chemical Industry 相似文献
30.
Strength reduction factors (SRFs) continue to play a key role in obtaining design forces from elastic design spectra (via
response modification factors) in ductility-based earthquake-resistant design. Despite several years of sustained research
efforts, it has not been conclusively shown how SRF for a given singledegree-of-freedom structural system depends on various
source and site parameters. A parametric study is carried out here for the explicit dependence of SRF spectrum (describing
variation of SRF with system period for a given ductility demand) on strong motion duration, earthquake magnitude, geological
site conditions, and epicentral distance in case of (non-degrading) elasto-plastic oscillators. For this, scaled response
spectra are considered for different combinations of earthquake magnitude, site conditions and epicentral distance, and SRF
spectra are generated from 1274 accelerograms recorded in western USA after making those compatible with each of these spectra.
It is shown that there is no clear and significant dependence of SRF spectrum on strong motion duration. Further, the parametric
dependence on earthquake magnitude, site conditions, and epicentral distance broadly conforms to the trends reported by earlier
investigations. In particular, this study confirms that the dependence of SRF spectra on earthquake magnitude should not be
ignored.
This paper has been contributed in honour of Professor R N Iyengar, Indian Institute of Science, on the occasion of his formal
retirement. 相似文献