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排序方式: 共有224条查询结果,搜索用时 31 毫秒
211.
S. Banerjee N. Halder S. Chakrabarti 《Applied Physics A: Materials Science & Processing》2010,99(4):791-795
We have described Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Ge substrate by MBE. The growth technique includes
deposition of a thin germanium buffer layer followed by migration-enhanced epitaxy (MEE) grown GaAs layer at 350°C. The MEE
layer was overgrown by a thin low-temperature (475°C) grown GaAs layer with a subsequent deposition of a thick GaAs layer
grown at 590°C. The sample was characterized by AFM, cross-sectional TEM and temperature-dependent PL measurements. The AFM
shows dense formation of QDs with no undulation in the wetting layer. The XTEM image confirms that the sample is free from
structural defects. The 8 K PL emission exhibits a 1051 nm peak, which is similar to the control sample consisting of In(Ga)As/GaAs
QDs grown on GaAs substrate, but the observed emission intensity is lower. The similar slopes of Arrhenius plot of the integrated
PL intensity for the as-grown QD sample grown on Ge substrate as well as for a reference QD sample grown on GaAs substrate
are found to be identical, indicating a similar carrier emission process for both the samples. This in turn indicates coherent
formation of QDs on Ge substrate. We presume due to the accumulated strain associated with the self-assembled growth of nanostructures
on Ge that nonradiative recombination centers are introduced in the GaAs barrier in between the QD layers, which in turn degrades
the overall optical quality of the sample. 相似文献
212.
N. Halder S. Adhikary S. Chakrabarti 《Applied Physics A: Materials Science & Processing》2012,107(4):977-983
We have investigated the effect of post growth rapid thermal annealing on self-assembled InAs/GaAs multilayer QDs (MQD) overgrown with a combination barrier of InAlGaAs and GaAs for their possible use in photovoltaic device application. The samples were characterized by transmission electron microscopy and photoluminescence measurements. We noticed a thermally induced material interdiffusion between the QDs and the wetting layer in the MQD sample up to a certain annealing temperature. The QD heterostructure exhibited a thermal stability in the emission peak wavelength on annealing up to 700 °C temperature. A phenomenological model has been proposed for this stability of the emission peak. The model considers the effect of the strain field, propagating from the underlying QD layer to the upper layers of the multilayer QD and the effect of indium atom gradient in the combination barrier layer due to the presence of a quaternary InAlGaAs layer. 相似文献
213.
We highlight the advantages of using simultaneously the Shannon and Fisher information measures in providing a useful form of the uncertainty relation for the position-momentum case. It does not require any Fourier transformation. The sensitivity is also noteworthy. 相似文献
214.
Halder M Chowdhury PK Das R Mukherjee P Atkins WM Petrich JW 《The journal of physical chemistry. B》2005,109(41):19484-19489
The photophysics of hypericin have been studied in its complex with two different isoforms, A1-1 and P1-1, of the protein glutathione S-transferase (GST). One molecule of hypericin binds to each of the two GST subunits. Comparisons are made with our previous results for the hypericin/human serum albumin complex (Photochem. Photobiol. 1999, 69, 633-645). Hypericin binds with high affinity to the GSTs: 0.65 microM for the A1-1 isoform and 0.51 microM for the P1-1 isoform (Biochemistry 2004, 43, 12761-12769). The photophysics and activity of hypericin are strongly modulated by the binding protein. Intramolecular hydrogen-atom transfer is suppressed in both cases. Most importantly, while there is significant singlet oxygen generation from hypericin bound to GST A1-1, binding to GST P1-1 suppresses singlet oxygen generation to almost negligible levels. The data are rationalized in terms of a simple model in which the hypericin photophysics depends entirely upon the decay of the triplet state by two competing processes, quenching by oxygen to yield singlet oxygen and ionization, the latter of these two are proposed to be modulated by A1-1 and P1-1. 相似文献
215.
Propagation of both low and high frequency waves in a plasma consisting of electrons, ions, positrons and charged dust particles
have been theoretically studied. The characteristics of dust acoustic wave propagating through the plasma has been analysed
and the dispersion relation deduced is a generalization of that obtained by previous authors. It is found that nonlinear localization
of high frequency electromagnetic field in such a plasma generates magnetic field. This magnetic field is seen to depend on
the temperatures of electrons and positrons and also on their equilibrium density ratio. It is suggested that the present
model would be applicable to find the magnetic field generation in space plasma. 相似文献
216.
Structural Chemistry - HIV-1 protease (HIV PR) is one of the most promising targets for anti-HIV drug discovery. Extensive anti-HIV drug discovery research was focused on HIV-1 subtype B protease... 相似文献
217.
Aslam Halder Sunandan Gangopadhyay 《International Journal of Theoretical Physics》2017,56(6):1831-1844
Landau system in noncommutative space has been considered. To take into account the issue of gauge invariance in noncommutative space, we incorporate the Seiberg-Witten map in our analysis. Generalised Bopp-shift transformation is then used to map the noncommutative system to its commutative equivalent system. In particular we have computed the partition function of the system and from this we obtained the susceptibility of the Landau system and found that the result gets modified by the spatial noncommutative parameter θ. We also investigate the de Hass–van Alphen effect in noncommutative space and observe that the oscillation of the magnetization and the susceptibility gets noncommutative corrections. Interestingly, the susceptibility in the noncommutative scenario is non-zero in the range of the magnetic field greater than the threshold value which is in contrast to its commutative counterpart. The results obtained are valid upto all orders in the noncommutative parameter θ. 相似文献
218.
We present the theory of border collision bifurcation for the special case where the state space is piecewise smooth, but two-dimensional in one side of the borderline, and one dimensional in the other side. This situation occurs in a class of switching circuits widely used in power electronic industry. We analyze this particular class of bifurcations in terms of the normal form, where the determinant of the Jacobian matrix at one side of the borderline is greater than unity in magnitude, and in the other side it is zero. (c) 2002 American Institute of Physics. 相似文献
219.
S. Halder P. Gerber T. Schneller R. Waser 《Applied Physics A: Materials Science & Processing》2006,83(2):285-288
Hafnium-substituted barium titanate thin films were deposited on platinized silicon substrates. Two different concentrations
of solutions (0.1 M and 0.3 M) were used to deposit films of various compositions Ba(Ti1-x,Hfx)O3 (x=0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4). The microstructure of the films depended on the concentration of the solution.
Lower concentration (0.1 M) solutions led to columnar films, but with higher hafnium percent compositions the columnar structure
was lost. The films which were derived from the 0.1 M concentration solutions had better dielectric and electrical properties
compared to the films derived from a higher concentration (0.3 M). All the films were found to be polycrystalline in nature.
The dielectric constant of the films was found to decrease with higher amounts of hafnium substitution. From the I–V characteristics
it is noticed that the leakage decreases by almost four orders of magnitude with a hafnium substitution of 40%. The d33 values of the films were between 23 and 5.6 pm/V for the different films.
PACS 68.55.-a; 81.20.Fw; 77.84.Dy; 77.55.+f 相似文献
220.
Heinz-Richard Halder 《Geometriae Dedicata》1973,2(1):101-109
Ohne Zusammenfassung 相似文献